Gastropoda - گاستروپودها

Gastropoda

 

The largest and most varied class in the phylum Mollusca, possibly numbering over 74,000 species and commonly known as snails.  See also: Mollusca

Functional Morphology

The shell is in one piece that, in the majority of forms, grows along a turbinate (equiangular) spiral (Fig. 1) but is modified into an open cone in various limpets or is secondarily lost in various slugs.

 

Fig. 1  Typical turbinate shell of gastropods. (a) Longitudinal section ground through the shell of a specimen of Conus purius to reveal the central columella and spiral of whorls expanding to the aperture. (b) Diagram of the shell to show the relationship of the whorls sectioned. (c) Stylized representation of the conchospiral line, as viewed with the shell apex tilted toward the observer. This logarithmic or equiangular line is the center line of a steadily expanding conic tube secreted by the mantle edge (at the shell aperture) during growth. (After W. D. Russell-Hunter, A Life of Invertebrates, Macmillan, 1979)

 

 

 

 

Effects of torsion

 All gastropods, at some time in their phylogeny and at some stage in their development, have undergone torsion. The process does not occur in any other mollusks. It implies that the visceral mass and the mantle shell covering it have become twisted through 180° in relation to the head and foot. As a result of torsion, all internal organs are twisted into a loop. Similarly in gastropods, the mantle cavity (the semi-internal space enclosed by the pallium or mantle) containing the characteristic molluscan gills (ctenidia) has become anterior and placed immediately above and behind the head. The most primitive gastropods, like stem stocks in the other molluscan groups, retain a pair of aspidobranch (bipectinate or featherlike) gills, each with alternating ctenidial leaflets on either side of a ctenidial axis in which run afferent and efferent blood vessels (Fig. 2). Lateral cilia on the faces of the leaflets create a respiratory water current (toward the midline and anteriorly) in the direction opposite to the flow of blood through the gills, to create the physiological efficiency of a countercurrent exchange system.  See also: Countercurrent exchange (biology)

As also occurs in other mollusks, the ctenidia form a gill curtain which functionally divides the mantle cavity into an inhalant part (lateral and below) with characteristic osphradia as water-testing sense organs, and an exhalant part into which the anus and renogenital ducts discharge. In zygobranch (two-gilled) gastropods, various shell slits or complex openings have been developed (Fig. 2c and d) to deal with the problems of sanitation created by the mantle cavity being brought anteriorly above the head. In various ways, these accommodate the exhalant stream of deoxygenated water and the feces and genital and kidney products which accompany it, so that this exhalant discharge is not directly over the head. In the majority of gastropods this problem is resolved by the reduction of the gill pair to a single ctenidium (Fig. 3) or to a pectinibranch ctenidium (a one-sided, comb-shaped “half-gill”).

 

Fig. 2  Mantle cavity and associated organs in a primitive zygobranch gastropod, with a symmetrical pattern of two aspidobranch gills (a) in dorsal view and (b) in cross section. This arrangement of mantle cavity is found in (c) abalones and (d) keyhole limpets. (After W. D. Russell-Hunter, A Life of Invertebrates, Macmillan, 1979)

 

مشاهده تصویر در ابعاد واقعی

http://aalliiffaazzeellii2.googlepages.com/gast2.gif

 

Fig. 3  Further evolution of the mantle cavity in gastropods. The mantle cavity and pallial complex is shown (a) in dorsal view and (b) in cross section for an asymmetric snail with a single aspidobranch gill, and (c, d) for an asymmetric snail with a “half-gill” or pectinibranch ctenidium. (e) The mantle cavity of a pulmonate land snail in dorsal view shows that there is now no gill and the mantle has become vascularized as a lung wall. (After W. D. Russell-Hunter, A Life of Invertebrates, Macmillan, 1979)

 

 

Shell coiling and asymmetry

 In a typical snail the shell is turbinate or helicoid, growing as a steadily expanding conic tube along the “screw spiral” of a logarithmic or equiangular line on the surface of a hypothetical cone (Fig. 1). Only a minority of gastropods have planospiral shells or the open limpet form. The majority with turbinate shells cannot have similar left and right halves, and almost all snails are anatomically asymmetric. Even in those gastropods in which the shell is lost and there has been a secondary return to a bilateral symmetry of external features, there remain marked asymmetries of internal anatomy. The majority of turbinate-shelled gastropods have dextral coiling, with a consequent reduction of the pallial organs of the right side, so that the left ctenidium persists. Internal organs are similarly reduced, so that “higher” gastropods have only the left auricle of the heart (the monotocardiac condition), and the left kidney and a single gonad opening to the exterior by the originally right-hand renogenital coelomoduct.

 

Mantle cavity evolution

 From the most primitive forms which retain most clearly the basic effects of torsion (Fig. 2), the further evolution of the gastropods has involved increasing asymmetry of the mantle cavity organs. Relatively few living gastropods are zygobranch with two ctenidia (and the diotocardiac condition, Fig. 2a). These include keyhole limpets such as Fissurella and abalones (Haliotis).

In most gastropods the right ctenidium is completely lost, and the pallial water flow has become inhalant from the left side of the snail, with the anus and renogenital openings moved over to the right (now exhalant) side (Fig. 3a and b). A minority of these single-gilled snails retain an aspidobranch gill, with some danger of particulate material clogging the dorsal part of the mantle cavity. Such snails include the limpet genus, Tectura (=Acmaea), common on both Atlantic and Pacific coasts, the big worldwide group of top shells (Trochus and its allies), and the tropical littoral genus Nerita. All these forms are ecologically limited to relatively clean water over hard substrata and are unable to invade areas of the sea bottom or seashore covered with mud or silt.

By far the most successful marine gastropods (without such ecological limitation) are those in which the pallial structures are further reduced (Fig. 3c and d), with a pectinibranch ctenidium whose axis is fused to the mantle wall, resulting in greater hydrodynamic efficiency. Note that this “half-gill” pattern still presents the same functional relationships of ciliary water currents and blood vessels in a countercurrent system. Most familiar snails of the seashore, including such genera as Busycon (whelks), Nassarius (mud snails), Littorina (periwinkles), Euspira (=Polinices) [moon snails], and very many others, have pectinibranch gills and this highly asymmetric arrangement of the mantle cavity.

A final reduction of pallial structures is found in the pulmonate snails and slugs (Fig. 3e), in which the mantle cavity is an air-breathing lung and there are no ctenidia. The other more specialized subclass, the Opisthobranchia, shows detorsion after loss of the shell and a variety of secondary (neomorphic) gills, especially in the extremely beautiful sea slugs or nudibranchs.  See also: Nudibranchia; Pulmonata

 Diversity and Classification

 More than half of all molluscan species are gastropods, and they encompass a range from the marine limpets, which can be numbered among the most primitive of all living mollusks, to the highly evolved terrestrial air-breathing slugs and snails. Pulmonates and certain mesogastropod families are the only successful molluscan colonizers of land and freshwaters. The anterior mantle cavity (resulting from torsion), as opposed to the posterior mantle cavity of all other major molluscan stocks, remains diagnostic of the class despite a diversity of functional morphology unequaled by any comparable group in the entire animal kingdom.

Presently classification of gastropods is rather unsettled, even though the phylogeny of this group is being examined vigorously. Consequently, an older arrangement of gastropod taxa, in practice prior to the onset of phylogenetic systematics, is presented here. While most of these taxa are now considered to be artificial, they are useful to consider in that each one demonstrates parallel morphologies and habitats.

The older systematic arrangement of the class Gastropoda involves three somewhat unequal subclasses: Prosobranchia, Opisthobranchia, and Pulmonata.

Prosobranchia

The largest and most diverse subclass is Prosobranchia, which is made up largely of marine snails, all retaining internal evidence of torsion. The prosobranchs have traditionally been divided into three orders: Archaeogastropoda, Mesogastropoda, and Neogastropoda. The primitive Archaeogastropoda are characterized by the presence of one or two aspidobranch (bipectinate) ctenidia, auricles, metanephridia (kidneys), and osphradia (Figs. 2, 3a and b). Members of the polyphyletic Mesogastropoda, which comprises almost 100 families, have only one pectinobranch (monopectinate) ctenidium (left), auricle, and nephridium (Fig. 3c and d). Members of the Neogastropoda, which appears to be monophyletic, also exhibit these characters, but their shell has a canal or notch that holds a tubular extension of the mantle (siphon).

In some current classifications, most families of the Mesogastropoda and Neogastropoda (and some Archaeogastropoda) constitute a taxon known as the Caenogastropoda, whereas most of the archaeogastropods are placed within the Patellogastropoda (true limpets) and Vetigastropoda (abalones, top and turban snails, keyhole limpets).  See also: Mesogastropoda; Neogastropoda; Prosobranchia

 Ali Fazeli = egeology.blogfa.com

 

Opisthobranchia and Pulmonata

 The other two subclasses (Opisthobranchia and Pulmonata) are each considerably more uniform than the subclass Prosobranchia and, in both, the effects of torsion are reduced or obscured by secondary processes of development and growth. Even so, in newer classifications they are often combined into a single group (Heterobranchia) along with a few groups (sundials, pyramidellids) formerly classified as prosobranchs.

The marine subclass Opisthobranchia consists largely of sea slugs, in which the shell and mantle cavity are reduced or lost and there is a bilaterally symmetrical adult with a variety of secondary gill conditions.  See also: Opisthobranchia

The final subclass, Pulmonata, consists of gastropods with the mantle cavity modified into an air-breathing lung and with no ctenidia (Fig. 3e). There are a few littoral marine forms, but the order Basommatophora is mainly made up of the freshwater lung-snails, and the order Stylommatophora consists of the successful land snails such as Helix plus a few shell-less families of land slugs.  See also: Pulmonata; Basommatophora; Stylommatophora

 

Bibliography

 V. Fretter and A. Graham, British Prosobranch Molluscs, 2d ed., 1994

F. W. Harrison and A. J. Kohn (eds.), Microscopic Anatomy of Invertebrates, vol. 5, 1994, vol. 6B, 1997

R. N. Hughes, A Functional Biology of Marine Gastropods, 1986

 Ali Fazeli = egeology.blogfa.com

R. M. Linsley, Shell form and the evolution of gastropods, Amer. Sci., 66:432–441, 1978

W. D. Russell-Hunter, A Life of Invertebrates, 1979

 Ali Fazeli = egeology.blogfa.com

J. Taylor (ed.), Origin and Evolutionary Radiation of the Mollusca, 1996

E. R. Trueman and M. R. Clarke, The Mollusca, vol. 10, 1985

 Ali Fazeli = egeology.blogfa.com

 

Additional Readings

 R. Bieler, Gastropod phylogeny and systematics, Annu. Rev. Ecol. Syst., 23:318–338, 1992

J. T. Pennington and F. Chia, Gastropod torsion: A test of Garstang's hypothesis, Biol. Bull., 169:391–396, 1985

 Ali Fazeli = egeology.blogfa.com

W. F. Ponder and D. R. Lindberg, Towards a phylogeny of gastropod mollusks: An analysis using morphological characters, Zool. J. Linn. Soc., 119:83–265, 1997

S. M. Stanley, Gastropod torsion: Predation and the opercular imperative, Neues Jahrb. Geol. Palaeontol. Abh., 164:95–107, 1982

 Ali Fazeli = egeology.blogfa.com

E. E. Strong, Refining molluscan characters: Morphology, character coding and a phylogeny of the Caenogastropoda, Zool. J. Linn. Soc., 137:447–554, 2003

P. J. Wagner, Gastropod phylogenetics: Progress, problems, and implications, J. Paleontol., 75:1128–1140, 2001

Gastropod Classification

 Ali Fazeli = egeology.blogfa.com

Tree of Life: Gastropoda

Marine Gastropods

Freshwater Molluscan Snails

Animal Diversity Web

 Ali Fazeli = egeology.blogfa.com

 Ali Fazeli = egeology.blogfa.com

 

تحرکات آزاد کربناتها در طبیعت

CARBONATE PLAYS

SUMMARY
There are several simplistic models that can be used to summarize the observed variation in carbonate play types.

Carbonate reservoirs that form stratigraphic traps may have lens-like, sheet-like or ribbon geometry. Carbonate bodies with lens-like geometries include biohermal or reef buildups that form during and after rapid relative sea level rises as well as down-slope debris fans. In contrast the sheet-like geometries may include muddy or grain-dominated progradational carbonate sheets that are terminated by exposure or flooding or prolonged stillstands. Trapping of hydrocarbons in reservoirs with sheet-like geometry requires some structuring before migration. Finally, plays with ribbon geometry are formed by carbonates that accumulate at the platform margin. These are commonly reefs or shoals but may be sand-filled tidal channels or beaches.

Lens Geometry

Bioherms may occur updip behind the major shelf-edge trend (left figure) or at the base of the break in slope or deeper portions of a ramp (figure below). The best reservoir facies commonly occurs along the margin of the buildup where original interparticle porosity occurs in mud-free carbonate sands or organically-bound rubble. The interiors of the buildups are usually muddy deposits which have little or no reservoir potential unless fenestral porosity remains or dolomitization occurs. The common seal is shale which covers and fills in around the buildups when they fail to keep pace with relative rise insea level and drown.

The deeper-water buildups usually begin as a mud mound with a pioneer faunal community. With establishment of the community, the rate of sedimentation accelerates over the mounds as the organisms trap and precipitate more carbonate. The development of the buildups is interrupted if the basin is isolated and becomes evaporitic. Silurian reefs in the Michigan Basin show evidence of several interruptions in development caused by basin isolation. The best reservoir quality in these very thick buildups is developed near the top of the reef where mud-free carbonate sands, fresh-water leaching and dolomitization are common. The source beds for these buildups are the laterally adjacent basinal carbonates and shales and in some cases the underlying limestones.

Sheet Geometry

Progradational carbonate sand sheets form as shoreline deposits, marine bars or tidal deltas on the seaward portions of carbonate platforms and mark the upper portions of shoaling upward sequences. The most porous fades form where bottom agitation is at maximum and interstitial lime mud is winnowed. Sedimentation may be terminated by exposure, which in turn causes the development of secondary leached porosity (figure above).

If deposition of carbonate sands is terminated by burial beneath deeper water sediments, their primary porosity is likely to be preserved (left figure). Similarly primary porosity will likely be preserved in carbonate sands terminated by the deposition of evaporites (figure below). The evaporites form a seal that prevents the movement of fresh water through the overlying strata and shields these sands from diagenesis. A reservoir example of this model is the Jurassic Arab "D" of Saudi Arabia. On the other hand, if a regional fresh groundwater system is confined beneath the seal, significant diagenesis including dolomitization may occur. Reservoir examples of this type occur in the Jurassic Smackover Formation of the U. S. Gulf Coast. Possible source rocks in each case are the underlying carbonate muds or shales. The seal could be updip progradational shales, evaporites or offshore marine shales deposited during a subsequent sea level rise.

Progradational sheets of muddy subtidal carbonate, usually associated with interior basins, may form plays if the muds are dolomitized (left figure). These fine carbonates are deposited in a shoaling cycle that is terminated by the deposition of supratidal evaporites. Source rocks are most probably the underlying muddy carbonates and shales. Reservoir porosity, which is a result of the dolomitizatlon, is characteristically patchy. Examples of this model include the Ordovician and Silurian of the Williston Basin.

Ribbon Geometry

The final play type, ribbon geometry reefs or shoals, which mark the margin of relatively steep-sided platforms, usually generates the most interest from explorationists (right figure). The potential reservoirs form as part of a package of prograding marginal sediments. Updip muddy carbonates or evaporites as well as overlying shales provide seals, and basinal deeper-water limestones or shales may serve as sources. If localized structuring does not occur before migration, the porous platform margin deposits will not become reservoirs. Instead, they will act as a pathway for the migrating oil that becomes trapped updip within the platform sequence. Downdip debris that forms an apron to a relatively dense carbonate margin is productive in the Lower Cretaceous of southeastern Mexico.

چینه شناسی کربناتها

Carbonate system tract boundaries, hierarchies & stacking patterns

Differences between carbonates and clastics
Carbonates have some similarities to clastics but major differences in the sequence stratigraphy of the two sediments exist. While both respond to changes in base level and both can be subdivided by similar surfaces, the difference in the sequence stratigraphy of these sediment types is related to carbonate accumulation tending to be "in situ production" while clastics are transported to their depositional resting place. Rates of carbonate production are linked to photosynthesis and so are depth dependent and greatest close to the air/sea interface. This favors carbonate facies and their fabrics as clear indicators of sea level position. Additionally carbonate sediments often have a biochemical origin and are influenced by the chemistry of the water from which they are precipitated. Thus the character of a carbonate sediment can change as the plate tectonic configuration of the depositional setting of the basin responds to pale-climate change, and/or changes in paleogeography related to isolation or access to the open sea. This means that carbonates can be used as indicators of depositional setting that, when combined with sequence stratigraphy, make carbonate facies analysis a powerful tool for the interpretation of the geological section and lithofacies prediction away from data rich areas.

Subdividing Surfaces
As with clastic rocks carbonates can be subdivided on the basis of bounding and internal surfaces into sequences, parasequences and/or truncated carbonate cycles. These can include

• Erosion surfaces (SB) or eroded parasequence boundaries
• Flooding surfaces including
  • Transgressive surfaces and/or
  • maximum flooding surfaces.

It should be emphasized that, as has been shown by Fischer (1964), Pomar & Ward (1999), Goldhammer,et al, (1990), and D'Argenio et al (1997), that though shallow cycles of carbonate are composed of a relatively conformable succession of genetically related beds or bedsets these cycles are often truncated and incomplete so that maximum flooding and trangressive surfaces can be missing. This means that these cycles are not, in the strictest sense, a match for the clastic models of parasequences described by Van Wagoner et al, (1999). However as one analyzes the cycles we argue that they can be used like parasequences to propose and build process/product oriented depositional models. However should they exhibit truncated cycles and miss the sediments of an initial transgression or maximum flooding event one should consider them as high frequency carbonates cycles, not parasequences.

 

Carbonate Response to Relative Sea Level Change - Links to Movies, Exercises & .pdf files.

Carbonate system tracts & enveloping surfaces; responses to sea level change.	Sea level rise & fall induce onlapping ramp, and forced regression of offlapping system tract (OST)	Lower rates of carbonate accumulation of interior shelf produce lagoon which gives up in response to sea level rise.
Bahamian Neogene carbonate margin responds to relative sea level change .	Early Cretaceous Shaybah Formation, UAE, carbonate margin responds to sea level change (Kendall et al, 2000) (below).	Carbonate sigmoids of Miocene of Mallorca capture sea level history (
Upper Devonian Judy Creek carbonate build up responds and "Gives up" with sea level change	Late Jurassic of Nequen Basin mixed carbonate & clastic system tracts with enveloping surfaces; responding to sea level change	Sedpak simulation of evolving carbonate and clastic geometries and cross section responding to changing base level

 

The Carbonate cycle of a Sigmoid verus Parasequence explained
The basic reefal accretional unit of the Miocene reef complex of Mallorca is the "sigmoid". This is bounded by clear erosion surfaces (the product of sea level lowering and erosion with a matching correlative surface downdip) but has no obvious marine flooding surfaces. Updip and landward the sigmoid is represented by a horizontal lagoonal bed that basinward passes in sigmoidal bedded reef-core lithofacies belt and seaward into clinoform bedded forereef slope beds and sub-horizontal basinal lithofacies. The boundary over the lagoonal and reef-core lithofacies of the sigmoid is formed by an erosional surface that basinward becomes a correlative conformable surface in the reef slope and basin lithofacies. Notably, the coral-morphology zonation within the reef-core facies of the sigmoid migrates seaward, aggrades vertically, or moves landward over the bounding erosional surfaces. This enables the sigmoid (like system's tracts) to be tied to specific segments of the sea-level curve. Consequently the sigmoid can be considered "genetically" as a depositional sequence, though not exactly fitting the original definition of a parasequence. This is because the sigmoid, like the parasequence, is composed of a relatively conformable succession of genetically related beds or bedsets. Also the geometric patterns shown by stacked sigmoids can be used, along with their position within a sequence, like the patterns of stacked parasequence sets, to define systems tracts, while within lower order depositional sequences there are sigmoid sets, sigmoid cosets and megasets.

In the interests of keeping the sequence stratigraphic literature from becoming over complex it is argued here that during the time interval between the development of the erosional surface on the underlying sigmoid and the deposition of sediment marking the boundary of the overlying sigmoid, sea level dropped to be followed by a trangressive flooding event and the development of a maximum flooding surface. However since no sedimentary fill has been recognized that records these events, the sigmoid cannot be inferred to be equivalent to the parasequence, or vice versa! Similarly this "simplification" should not be applied to a shoaling upward carbonate cycle missing transgressive or maximum flooding sediments. In this case the Transgression surfaces (TS) and maximum flooding surfaces (mfs) are not equivalent to erosion surfaces initially produced by a sea level fall, since the missing sediments mean that one cannot establish how the erosion surface was modified on the following transgression. Clearly the truncated high frequency carbonate cycle may have different genetic elements to a parasequence and should not be considered to be one! It should be noted that because "modern" type of reefal systems are able to build rigid frameworks, resistant to wave energy, this depositional system has the capacity to record even the highest-frequency sea-level cycles. Thus some sigmoids appear to record 7th order sea-level cycles that represent a periodicity of few-thousand years! Other depositional systems that have not produced this "rigid framework" to the sea level are not able to record such high-frequency cycles of sea level and parasequences may form.

Pomar (personal communication, 2004) proposes that parasequences form in response to sea-level para-cycles (rise and stillstand of sea level), commonly as a response of sea-level cyclicity when subsidence equals or exceeds the amount of sea-level fall, OR when the sedimentary systems are dominated by loose grains. In this latter case, lowering of base level (related to the fall in sea level) would increase basinward shedding of sediment and these erosional processes onto a granular seabed would not be recorded as an erosion surface. This could be the reason that higher-frequency sequences (simple sequences in Vail's definition) at the most commonly record up to 5th-order cycles of sea level. These high frequency carbonate cycles that have the genetic elements of the parasequence are "of course" carbonate parasequences.

Carbonate Parasequence Geometries - Tools of the Interpretation of Depositional Setting
The sequence stratigraphy of the carbonate sections is commonly determined from a combination of 2 and 3 D Seismic data (providing a comparatively low frequency resolution), well logs (providing a comparatively high frequency resolution), cores (providing very high frequency resolution) and outcrops (with best access to a combination of high frequency resolution and low frequency resolution).

Click thumbnail to access the large images

The analysis of the sequence stratigraphy of carbonates is improved by applying the recent realizations of Larue et al (1995); Sprague et al, (2002); Sprague et al, (2003); and Sprague et al, (2004) for depositional systems and integrating:

• The bounding surfaces to their system tracts
• The component lithofacies
• The hierarchies in the resulting geometries of the strata
• Their stacking patterns

Thus, as with clastic sediments (Sprague et al, 2002), at a general level the physical stratigraphy of the carbonate strata can be broken down into a hierarchical framework. This framework ties together genetically related architectural elements and their associated bounding surfaces. The hierarchy of these elements is independent of the thickness and the time invovled in their accumulation. A top down breakdown of the architectural elements shows a progressive decrease in scale from the complex facies geometries of the basin margin to single tidal flat cycles or beds that accumulated on shallow shelves or in shallow lagoons. As Sprague et al, (2002) showed for clastics, these carbonate hierarchical elements are directly relatable to stratal units defined on the basis of sequence stratigraphy. Biostratigraphic data tied to the stratal units enable the direct comparison between shallow-marine and deeper marine carbonate sequences and their related units with the potential of correlation of the carbonate cycles to base level rise and fall.

All are the combined products of base level change. This is particularly true of shallow water carbonate accumulations which are depth dependent, a response to the paleo-oceanography, and processes of the depositional setting. The result of such an analysis creates a "powerful" framework of parasequence and high frequency cycle geometries that can be used to explain, assess and predict reservoir and aquifer quality better independent of thickness and time.

This approach even applies in deepwater settings. For instance, using the Tamabra Formation of the Poza Rica Field Area of Mexico as an example, Loucks, et al (2006) have demonstrated that deeperwater mass-transport carbonate deposits are carried by gravity flow and suspension processes into deepwater basinal settings downslope from margins tied to shallow-water carbonate platforms. So while reefal and grain-rich debris accumulate on the shallow platform carbonate debris wedges extend into the deeperwater basin.

The architecture of this debris wedge is related to the availability of source material during changes in relative sea-level (Loucks, et al., 2006). During sea-level lowstands and transgressions or during early highstands when the platform rapidly aggrades, debris and mud flows composed of platform and slope carbonate mud, sand, and clasts generally accumulate. In contrast during highstands of sea level when the platform is flooded and shedding, density-flow and turbidite deposits composed of carbonate sand and lesser amounts of lime mud collect.

Click thumbnail to access the large images and click on the larger image to see them full size!

Over Simple Dip Section	Falling Stage & Lowstand System Tracts	Transgressive System Tract	High Stand System Tract
Normal Marine Setting - Stacking Patterns

Geometries of Carbonate Strata
The geometries of carbonate strata are products of the shape of the depositional surface, changing base level and sediment accumulation. They are defined by the underlying and overlying surfaces. These surfaces may be the products of deposition and/or erosion and can coincide with the depositional event or proceed or follow this. Physical erosion, burrowing, boring, dissolution (Clari et al, 1995; Lukasik & James, 2003), and/or cementation may have modified them. Whatever their origin, these surfaces provide a convenient means to subdivide the carbonate section. From the perspective of sequence stratigraphy these surfaces are used to determine the order in which strata are laid down and define the geometries that they enclose.

Over Simple Dip Section	Carbonate fill, a response to base level change - Murray Basin	Carbonate fill, a response to base level change - Murray Basin
Normal Marine Setting - Stacking Patterns

As with the products of other sedimentary depositional systems carbonate strata exhibit a hierarchy of scales that include at the small-scale end (beds, bed sets and bed cosets) and at the larger spatial scales reef complexes, basin margin and slope complexes etc. These strata can be expressed as unconfined sheets, unconfined but localized build ups (reefs, banks and islands), unconfined but localized sigmoids (reef cores, Pomar 1991), bank margins etc.,) and confined incised channels (tidal channels and the products of flood events). What ever the final geometry this is the product of both accumulation (aggradation ) and erosion.

Carbonate Sequence Stratigraphy Exercises
Click on the highlighted title above to access the exercises that are available on this site to examine the hierarchy of scales expressed by carbonate strata. These may be the lower frequency subdivisions that can be interpreted from seismic, or higher frequency subdivisions outcrop and well logs. These consider facies or more complex lithofacies assemblages from the perspective of sequence-stratigraphic concepts (systems tracts, parasequences, sequences and their response to seal level rise (TST), still stand (HST) fall (FSST) and lowstand (LST) and their response to the paleo-oceanography and processes of the depositional setting. The exercises are intended to develop skills that can be used to establish direct relationships between the nature of the carbonate bodies, the sequence stratigraphic architecture, reservoir connectivity, reservoir characterization and prediction. This would involve the use of systematic hierarchical relationships, integration of seismic, well, and core data with outcrop and subsurface analogs. From this you will gain a better understanding of how to predict accurate net-to-gross, continuity, architecture, and reservoir extent. If you are able to integrate biostratigraphy with your studies this will provide an independent time framework correlation made to cycles of base level rise and fall.

To conclude, carbonate depositional facies hierarchy provides a framework for the systematic description and comparison of carbonate deposits that is based on the physical relationships of strata and their bounding surfaces. The recognition of genetically related stratigraphic elements, is independent of the lithofacies assemblage of carbonate, and is applicable at all scales.

Carbonate Response to Sea Level - Papers

Link to a page that lists some of the literature on the carbonate sedimentary record and how its sequence stratigraphic character varies in response to base level change, usually eustasy and gain access to .pdf files of these papers.

Bosence, D.W.J., Pomar, L., Waltham, D.A. Lankaster, T., 1994. Computer modeling a Miocene carbonate platform, Mallorca, Spain. Arnerican Association of Petroleurn Geologists Bulletin, 78:247-266.
Kendall, Christopher G. St. C., Abdulrahman. S. Alsharhan, Kurt Johnston and Sean R. Ryan; 2000; "Can The Sedimentary Record Be Dated From A Sea-Level Chart? Examples from the Aptian of the UAE and Alaska". In A. S. Alsharhan and R. W. Scott, Eds, Society of Economic Petrologists and Mineralogists (SEPM) Special Publication 69 on the Jurassic/Cretaceous Platform-Basin Systems; Middle East Models; p 65-76 (Reference for the simulation of Shaybah formation above)
Loucks, R. G., Charles Kerans, and Alfredo Marhx, 2006, "Origin and Organization of Mass-Transported Carbonate Debris in the Lower Cretaceous (Albian) Tamabra Formation, Poza Rica Field Area, Mexico", SEPM Research Symposium: The Significance of Mass Transport Deposits in Deepwater Environments II, AAPG Annual Convention, April 9-12, 2006 Technical Program
Pomar, L. and Ward, W.C. 1994. Response of a Miocene carbonate platform to high-frequency eustasy. Geology, 22:131-134.
Pomar, L. and Ward, W.C, 1995. Sea level change, carbonate production and platform architecture, in B. Haq ed., Sequence stratigraphy and depositional response to eustatic, tectonic and climatic forcing, Kluwer Academic Press. p. 87-112.
Pomar, L. 2001, Ecological control of sedimentary accommodation: evolution from a carbonate ramp to rimmed shelf, Upper Miocene, Balearic Islands. Palaeogeography, Palaeoclimatology, Palaeoecology, 175:249-272.

References on a Hierarchical Approach to Sequence stratigraphy

D. K. Larue, A. R. Sprague, P. E. Patterson , J. C. Van Wagoner (1995): Multi-Storey Sandstone Bodies, Sequence Stratigraphy, and Fluvial Reservoir Connectivity, Bulletin AAPG, (Abstract) AAPG Annual Meeting, 79, 13, 54  Ali Fazeli = egeology.blogfa.com

Sprague,A. R., P. E. Patterson, R.E. Hill, C.R. Jones, K. M. Campion, J.C. Van Wagoner, M. D. Sullivan, D.K. Larue, H.R. Feldman, T.M. Demko, R.W. Wellner, J.K. Geslin1 (2002), The Physical Stratigraphy of Fluvial Strata: A Hierarchical Approach to the Analysis of Genetically Related Stratigraphic Elements for Improved Reservoir Prediction, (Abstract) AAPG Annual Meeting Ali Fazeli = egeology.blogfa.com

Sprague, A. R., M. D. Sullivan, K. M. Campion, G. N. Jensen, F. J. Goulding, T. R. Garfield, D. K. Sickafoose, C. Rossen, D. C. Jennette, R. T. Beaubouef, V. Abreu, J. Ardill, M. L. Porter, and F. B. Zelt, (2003), The Physical Stratigraphy of Deep-Water Strata: A Hierarchical Approach to the Analysis of Genetically Related Stratigraphic Elements for Improved Reservoir Prediction, AAPG Bulletin, (Abstract) AAPG Annual Meeting,.87, 10 p Ali Fazeli = egeology.blogfa.com

Sprague, A. R., P.E. Patterson, M.D. Sullivan, K.M. Campion, C.R. Jones, T.R. Garfield, D.K. Sickafoose, D.C. Jennette, G.N. Jensen, R.T. Beaubouef, F.J. Goulding, J.C. Van Wagoner, R.W. Wellner, D.K. Larue, C. Rossen, R.E. Hill, J.K. Geslin, H.R. Feldman, T.M. Demko, V. Abreu, F.B. Zelt, J. Ardill, and M.L. Porter (2004), Physical Stratigraphy of Clastic Strata: A Hierarchical Approach to the Analysis of Genetically Related Stratigraphic Elements for Improved Reservoir Prediction, ABSTRACT, AAPG 2003-04 Distinguished lecturer Tour Information. Ali Fazeli = egeology.blogfa.com

فرضیه تکامل سکانس های کربناته

EVOLUTION OF CARBONATE SEQUENCES

SUMMARY
Variations in carbonate depositional settings through time produce corresponding changes in their lateral and vertical facies geometry. High frequency changes in facies are induced by sea level, and climate, whereas long-term low frequency changes are commonly related to paleo-geography and plate configurations or the evolutionary changes in the carbonate producing organisms. The sections below provide a general and classical introduction to the eclectic responses of carbonates to changes in their setting.

CONTROLS ON CARBONATE DEPOSITION

The geometry and facies relationships of carbonate accumulations are closely tied to the paleogeographic setting and changes in that setting through time, particularly water depth variation. Paleolatitude and clastic influx are major influences on the distribution of the carbonates, with facies largely controlled by the proximity of the depositional basin to open marine circulation and the position of the depositional setting within the basin. Carbonate sediments and their associated buildups are largely the by products of organisms whose evolution has a significant influence on carbonate deposition. Wilson (1975) reviews in detail some of the similarities and differences that occur in carbonates of different ages.

As outlined in an earlier section, the position of the depositional setting controls the geometry and continuity of deposits. For instance, deep-water basinal deposits are commonly widespread, thin beds of fine-grained carbonate formed by a combination of pelagic fauna and suspended shelf muds. At the edges of the basin, contributions from the shallow platform are greater. These basin-edge deposits range from turbidite fans and debris flows to reef talus. Porosities may be higher in these deposits than in basinal muds, but continuity may vary greatly. In contrast the margins of the carbonate platform or shelf may consist of linear to mound-like reef or shoal buildups that may have local porosity. To the lee of the margin the "back-reef" lagoon sediments occur in widespread beds of even thickness with discontinuous and mounded patch reefs scattered within their more seaward portions. Toward the updip limit of the platform, the lateral continuity of platform carbonate sands decreases, and supratidal carbonates associated with evaporites and elastics are common.

An example of water depth changes in the Cretaceous.

Changing water depth primarily causes changes in the depositional setting. Worldwide changes in relative sea level have occurred repeatedly and cyclically through geologic time. The rate of relative sea level rise has an obvious effect on the sediment type and nature of deposition, whereas the rate and extent of relative sea level fall has a marked effect on the diagenesis and erosion of carbonate sequences. As indicated elsewhere in this site eustatic sea level changes are believed to have dual origins: either they are glacially induced and have a high frequency or there is a change in the shape of the oceans due to tectonics and low frequencies occur. Despite their small size, the rapidity of high frequency eustatic events makes them the driving mechanism behind much of the cyclic nature of sediments. These sea level changes may be sinusoidal but the corresponding relative changes and movements of the coastline, whether over a narrow or wide shelf, are asymmetric (figure below).

Relative sea level changes may be the products of eustatic fluctuations, but may also be a response to subsidence or uplift of the depositional setting. These later effects may be related to faulting, thermal regime, salt diapirism, or isostacy (See figure below). Local differences occur where the underlying sediment compacts at different rates. Other relative changes are initiated when basins become isolated by the development of sedimentary or tectonic sills in conjunction with eustatic drops in sea level. When this isolation occurs at low latitudes, evaporative drawdown often produces a corresponding drop in sea leve

RESPONSES TO RELATIVE SEA LEVEL CHANGES

The response of the carbonate depositional surface to relative sea level changes include drowning of the surface, catching up with sea level rise, keeping up with the rise, or build up to exposure. Drowning of a reef or platform is caused by the failure of carbonate production to keep pace with a relative rise of sea level so that as the water deepens carbonate accumulation slows and is outpaced by clastic deposition.

The sediment surface leaves the realm of shallow-water carbonate sedimentation altogether and becomes submerged below the euphotic zone (right figure). The onset of drowning is expressed by a change from shallow-water faunas to deeper-water communities in reefs and on lagoonal floors. Buildups truly abandoned by a rising sea are commonly capped by a submarine hardground and enveloped by a shale cap or deepwater limestone. An example of a drowned ramp reservoir is the Devonian Onadaga of New York.

Reservoirs in drowned buildups on rimmed margins include the Devonian Swan Hills, Leduc and Rainbow reefs of Western Canada.The Middle to Upper Triassic of Ragusa Field in Sicily is an example of a drowned isolated platform

The survival of the rim of the platform but not its interior is a complex, but common, response intermediate between complete failure and complete success of a platform's ability to survive. The rate of relative sea level rise is such that only sedimentation on the platform rim (normally a reef) and/or isolated patch reefs on the platform interior keeps pace while the remainder of the platform is drowned, becoming a deep lagoon or shelf sea (right & figures below).

This response, which probably occurs when the rising sea flooded the platforms tops after a period of exposure, is probably the result of small but rapid eustatic rises. The pattern tends to develop in stages: initially the rate of rise exceeds the growth rate of both rim and interior, and the depositional setting shifts to deeper and more open-marine conditions. Carbonate accumulation slows and widespread submarine hardgrounds develop.

The lag phase is followed by catch-up. During the catch-up phase the reef rim and newly established patch reefs in the interior accumulate faster and build to sea level.

A third phase may follow when the interior lagoon fills up and a flat platform top is re-established. Reservoir examples of such rimmed margins are the Lower Cretaceous Sligo and Stuart City trends of the U. S. Gulf Coast. Pennsylvanian production in Aneth Field in the Paradox Basin is from a catch-up ramp. Examples of an interior shelf that has caught up and kept up are the Jurassic Arab "D" and Cretaceous Natih Formations of the Middle East and the Permian Grayburg Formation of the Midland Basin.

In the keep-up response, growth potential of rim and interior matches or exceeds the rate of relative rise (figure right). The platform interior fills to sea level, and in most cases the platform rim progrades seaward, building on excess sediment dumped on the flanks. These rims may consist of reefs or stacked carbonate sand shoals that show little apparent change in water depth during deposition.

The depositional environment over the platform interior varies from supratidal to very-shallow subtidal. During sea level rises, shelf width usually increases and elastics are confined to the landward side of the shelf.

Shoaling upward carbonate sequences usually represent sedimentation, particularly toward the seaward margin of the shelf. Occasionally, during rises, isolated depressions land-ward of the shelf margins produced by wind deflation during a sea level low or during growth of a rimmed margin become evaporative lagoons. Individual shoaling cycles tend to be widespread and where clastic supply is low, are frequently terminated by supratidal evaporite sequences. On narrow shelves with low clastic supply, carbonates may dominate the seaward margin of a clastic-dominated shelf. Where clastic supply is high, carbonates and elastics interfinger rhythmically. When a relative sea level rise slows a carbonate shelf system can be expected to fill up to the supratidal with the excess sediment causing the coast to prograde seaward. Examples of producing shelf margins where carbonate production has kept up with sea level rise are the Permian reservoirs in the Delaware and Midland Basins.

Shoaling upward cycles in carbonates are common in stable platform and shelves ( figure below).

The supratidal evaporites associated with these shoaling upward carbonates are formed only during sea level rises and should not mistakenly be interpreted as forming during sea level falls. The shelf interior has few complete shoaling upward cycles because hiatuses are common and not all sea level rises extend all the way across the shelf interior. In contrast, the shelf margin and basin centers may lack shallow water sediments because the subsidence is so rapid that evidence of the progradation cycles is obscured.

Thus, where subsidence is extremely fast, as on a basin margin immediately following continental breakup, the effects of rapid subsidence may hide cycles. Instead of the asymmetric shoaling upward cycles common to stable shelves, symmetrical shoaling and deepening cycles might be predicted.

While carbonate platforms and reefs have the potential to keep pace with all but the fastest rises in relative sea level, they are very poorly equipped to shift the loci of carbonate production and deposition when there is a relative drop in sea level. The flanks of platforms are usually so steep that reefs or other carbonate fades belts are unable to gradually migrate down slope following the retreating sea. Beach erosion and subsequent terrestrial weathering, quickly remove what little sediment is deposited during this retreat. Consequently, the most common record of sea level drops on carbonate platforms is a subaerial hiatus associated with karst development, cliff erosion, leaching and possibly dolomitization.

During stillstands in the retreat of the sea, the connections of the basin to the open sea may be closed by fringing reefs or structural highs. This tendency toward isolation of the basin and the lack of clastic influx makes carbonate basins particularly prone to evaporite deposition when sea level drops (figure right). Typically a sea level drop terminates carbonate deposition; the exposed shelf is cemented so little detritus is shed and erosion of the elastics trapped on the shelf is minimal.

However, some basins at sea level lows are dominated by shelf derived elastics because their access to the open sea makes them non-evaporative (figure above). Reservoir examples of clastic offlap and smothering of downramp buildups are the Permian Scurry and Jameson Formations of the Midland Basin.

USEFUL REFERENCES

Asquith, G. B., 1979, Subsurface Carbonate Depositional Models — A Concise Review: Petroleum Publishing Co., Tulsa, 121 p. Ali Fazeli = egeology.blogfa.com

Kendall, G. C. St. C. and Schlager, W., 1981, Carbonates and Relative Changes in Sea Level: Mar. Geol, V. 44, p. 181-212. Ali Fazeli = egeology.blogfa.com

Vail, P. R.,et al, 1977, Seismic Stratigraphy and Global Changes of Sea Level: p. 49-212 in C. E. Payton (ed.), Seismic Stratigraphy —Applications to Hydrocarbon Exploration, AAPG Memoir 26, Tulsa. Ali Fazeli = egeology.blogfa.com

Wilson, J. L., 1975, Carbonate Facies in Geologic History: Springer-Verlag, New York, p. 96-347. Ali Fazeli = egeology.blogfa.com

پتروگرافی سنگهای کربناته 2

	Dolomites Most dolomites are diagenetic replacements of limestone. Sedimentary dolomite may have been more important in the past but the best known Holocene examples come from the evaporative coastal lagoons of the Coorong, of South Australia. Currently sedimentary dolomite is thought to have been rare in the sedimentary record and most is thought to be a product of diagenesis.     In contrast diagenetic dolomitization is the more important but the understanding of the process is still evolving. This encompasses an ever-increasing number of settings and geochemical models. Whatever the model proposed high magnesium to calcium ratios occur in the waters responsible for this diagenesis. This is particularly true of mixing zone brines with different compositions where dolomitization can become locally important. Although the deep burial diagenetic realm is not as well understood as near-surface conditions, it is apparent that dolomitization, pressure solution compaction, and cementation are associated with the deeper parts of the section. The subsurface fluids responsible for the diagenesis are thought to be derived from a variety of sources (figure above), and most likely from down-dip basinal shales and fine carbonates that expel fluids as they are compacted during burial. The term dolomite may be used as both a mineral name and a name for a carbonate rock containing more than 50% dolomite. Where good evidence exists that the rock was once limestone, the adjective dolomitized may be used. Although staining is the best method to distinguish dolomite from calcite, development of good rhombohedral structure is typical of dolomites and uncommon in calcites. This criterion should be employed with caution, however. Much mud-sized carbonate material can often be dolomite. A subsurface setting for the diagenesis associated with dolomitization is important but this process can occur in the following listed settings: Arid supratidal salt flats Capillary crusts in the up slope portions of tidal and supratidal flats Near surface submarine sediments of the margins of carbonate banks Flanks and interior of carbonate banks with circulating marine waters Near surface mixing zone with magnesium remobilization Late diagenesis by late movement of subsurface waters Arid Supratidal Salt Flats The association of dolomite and ancient tidal flat deposits is common. The exact mechanism for magnesium enrichment and subsequent dolomitization is not known, but several theories have been proposed (right figure). Freshwater mixing with marine waters that are washed onto tidal flats and evaporated are likely mechanisms in the tidal flat environment. Mineralogical changes are common in Holocene supratidal flats of arid areas including those of the United Arab Emirates (Butler et al 1982; Swart et al, 1987; and Kendall & Warren 1988). Here aragonitic sediments can be dolomitized and evaporites emplaced in these carbonate sediments (figure below). Landward, gypsum followed by anhydrite and halite may be precipitated. The gypsum may form individual displacive crystal laths or layers of mush, whereas anhydrite occurs in contorted layers or as nodules. The origins of the brines associated with this dolomitization is thought to be both marine groundwater influxing from the adjacent Arabian Gulf (Patterson and Kinsman 1977; and Butler et al 1982) and subsurface brines coming from the adjacent Oman Mountains (Wood et al 2001). Where the sulphates precipitate in standing bodies of water, for instance isolated coastal lagoons or playas, they form horizontal layers that parallel the sediment-water interface. The occurrence of evaporites at the updip side of a carbonate shelf or platform is important to the hydrocarbon industry since the evaporites often form the updip seals to reservoirs developed in dolomitized shelf carbonates. Capillary Crusts of Tidal and Supratidal Flats Evaporation of near surface waters in the capillary zone of tidal and supratidal flats in tropical and subtropical areas like the Bahamas (Whittle et al, 1992; Shinn et al, 1976) Shark Bay (Logan et al, 1970) and the coast of Abu Dhabi (Kendall et al, 1995) can lead to the precipitation of a carbonate that cements this surface. An increase in magnesium to calcium ratios in the capillary waters is believed to be responsible for the dolomitization of this cemented crust. Near Surface Submarine Sediments of the Margins of Carbonate Banks This setting for dolomitization has been recorded in the Upper Tertiary section of the Bahamas (Vahrenkamp & Swart 1994; and Swart & Melim 2000) and occurs beneath non-depositional surfaces, with the concentration and extent of the dolomitization being controlled by the length of time involved with non-deposition. These dolomites are recognized by their association with the non-depositional surfaces, and are thought to form from cold bottom waters, and in the presence of diffusive temperatures. Flanks and Interior of Carbonate Banks Penetrated by Circulating Marine Waters Two kinds of dolomitization occur in this setting. One is caused by in pore fluids in which the cation and anion profiles are governed by diffusive processes. The dolomite forming here is termed as background dolomite (Vahrenkamp & Swart 1994; and Swart & Melim 2000). These authors record the occurrence of microsucrosic dolomite and explain that this forms both by recrystallization of the existing sediment and precipitation directly into void space. They suggest that dolomitization of this kind has a local source for Mg2+, so that the dolomite never constitutes more than between 5 and 10% of the sediment. The second form of dolomitization associated with this setting occurs in coarse-grained reefal sediments (Swart and Melim 2000). It is suggested that the circulation of normal marine water in a relatively open system explains the pervasive character of the dolomitization and the relatively normal Sr concentrations. Near Surface Mixing Zone Remobilization of Magnesium Humphrey et (2001) have shown that in the low-flow freshwater lenses and meteoric vadose zones of Holocene and Pleistocene sediments in the Caribbean, some skeletal calcites including red calcareous algae have as much as 40 mol% MgCO3. They propose the additional magnesium as coming from the cannibalization magnesium from the algae. They found no dolomite in these samples but suggest that the very high magnesium calcite is a probable dolomite precursor. They note that Pleistocene red algae from Barbados mixing zones has preferentially partially dolomitized the hypothallus regions of the red algae where there is an increase in porosity. They believe that dissolution-reprecipitation of the high magnesian calcite of the less dense hypothallus in red algae is the start of early dolomitization. This process may explain the occurrence of discreet euhedral dolomite rhombs that often dispersed throughout ancient carbonates that show no sign of regional dolomitization related to ground water movements. Late Dolomitization Associated with the Late Movement of Subsurface Waters The genesis of dolomites that replace limestone in the deeper subsurface is currently explained by two models of fluid-flow that invoke the movement of waters with higher magnesium to calcium ratios in the subsurface. One is related to regional subsurface flow models, or burial-flow models which assume high temperatures for the subsurface fluids (Mountjoy and Amthor, 1994; Nadjiwon et al 2000); and the other less fashionable model assumes the evaporation of seawater in restricted lagoons and salt flats that produce dense near surface brines that move down into porous and permeable limestones and produce coarsely crystalline "early" seepage reflux dolomites (Shields and Brady 1995). Both models require magnesium and fluid to move this but differ in the character of the geochemical setting and timing. The first model requires a longer time period and higher temperatures than the second reflux model. However it is formed, the dolomite has the potential for creating reservoir quality porosity and permeability in originally tight limestones (left figure). Early dolomitization may preserve porosity by creating a rigid framework that inhibits compaction. In still other cases dolomitization in lime muds may enhance porosity, because dolomites are denser and so consequently take up less volume than the original calcite. Intercrystalline porosity in dolomites is responsible for many Paleozoic reservoirs, a good example is the Mississippian Little Knife field carbonates. Dolomitization may reduce, redistribute, preserve or create porosity. In a few carbonate reservoirs, as in the Jurassic Arab limestones of Ghawar field in Saudi Arabia, replacement dolomite crystals extend into adjacent pores thereby reducing the primary porosity. In many dolomitized reservoirs such as the Jurassic Smackover Formation of Alabama and the Leduc reef carbonates in Alberta, porosity and permeability have beeb redistributed during dolomitization and associated leaching and enhance reservoir character. Porosity that was formed during dolomitization is common in the Mission Canyon and Red River Formations of the Williston Basin. References l982 Butler, G.P., C.G.St.C.Kendall, and P.M.Harris, Abu Dhabi Coastal Flats: in Handford, C.R., Loucks, R.E. and Davies, G.R. eds. Depositional and Diagenetic spectra of Evaporites, a core workshop; Soc. Economic Paleont. Mineral Core Workshop No. 3, Calgary, Canada, p. 33-64. Humphrey, John D., Katz, David A., and Canter, K. Lyn, 2001 Quaternary diagenesis and dolomitization of calcareous red algae; GSA Annual Meeting Boston, Massachusetts, November 5-8, 2001 Kendall, Christopher G. St. C., Alsharhan, Abdulrahman. S., and Whittle, Gregory, 1995; Field Guidebook to Examine the Holocene Carbonates/Evaporites of Abu Dhabi, United Arab Emirates: for the International Geological Correlation Program (IGPCP-349), U.A.E. University Publication Dept., Dec. 5-7, pp46. 1988 Kendall, Christopher.G.St.C., and John Warren, Peritidal evaporites and their sedimentary assemblages, in C. Schrieber (ed.), Evaporites and Hydrocarbons, Columbia University Press p 66-138. Ali Fazeli = egeology.blogfa.com Logan, Brian W., Read, James F., Davies, Graham R., 1970, History of carbonate sedimentation, Quaternary epoch, Shark bay, Western Australia, Carbonate sedimentation and environments, Shark bay, Western Australia, Memoir - American Association of Petroleum Geologists, 13, p. 38-84. Ali Fazeli = egeology.blogfa.com Mountjoy, E. W. and Amthor, J. E., 1994, Has burial dolomitization come of age? Some answers from the Western Canada sedimentary basin, Purser, Bruce, Tucker, Maurice (, and Zenger, Donald (editors), Dolomites; a volume in honour of Dolomieu, Special Publication of the International Association of Sedimentologists, 21, p. 203-229. Nadjiwon, Lisa M., Morrow, David W., and Coniglio, Mario, 2000, Dolomitization of the Devonian Dunedin, Keg River and Slave Point formations of Northeast British Columbia, 2000 AAPG Eastern Section meeting London, ON, Canada, Sept. 24-26; abstracts, AAPG Bulletin, 84 (9), p. 1390. Ali Fazeli = egeology.blogfa.com Patterson, R. J., and Kinsman, D. J. J., 1977 Marine and continental groundwater sources in a Persian Gulf coastal sabkha, Studies in Geology (Tulsa) (4), p. 381-397. Shields Gordon and Brady 1999 Ali Fazeli = egeology.blogfa.com Shinn, E. A., Lloyd, R. M., Ginsburg, R. N., 1976, Anatomy of a modern carbonate tidal-flat, Andros Island, Bahamas; Klein, G. deV. (editor), Holocene tidal sedimentation, Benchmark papers in geology, 30, p. 352-378. Swart, Peter K. and, Melim, Leslie A., 2000; The origin of dolomites in Tertiary sediments from the margin of Great Bahama Bank; Journal of Sedimentary Research, 70 (3), p. 738-748. Swart, P. K., Shinn, Eugene A., McKenzie, J. A., Kendall, Christopher G. St. C., Hajari, S. E., 1987, Spontaneous precipitation of dolomite in brines from Umm Said Sabkha, Qatar; Dickinson, William R. (chairperson), Geological Society of America, 1987 annual meeting and exposition, Abstracts with Programs - Geological Society of America, 19 (7), p. 862, 1987. Annual Meeting of Geological Society of America, Phoenix, AZ, United States, Oct. 26-29.Ali Fazeli = egeology.blogfa.com 1993 Whittle, Gregory, Kendall, Christopher G. St. C., Dill, R. F., and Rouch, Linda; Carbonate cement fabrics displayed: a traverse across the margin of the Bahamas Platform near Lee Stocking Island in the Exuma Cays, Marine Geology, v. 110, p. 213-243 Ali Fazeli = egeology.blogfa.com Vahrenkamp, V. C., Swart, P. K., 1994, Late Cenozoic dolomites of the Bahamas; metastable analogues for the genesis of ancient platform dolomites; Purser, Bruce, Tucker, Maurice, and Zenger, Donald (editors), Dolomites; a volume in honour of Dolomieu, Special Publication of the International Association of Sedimentologists, 21, p. 133-153. Ali Fazeli = egeology.blogfa.com Wood. W. W, Sandford W. E. Abdul Rahman S. Al Habshi, 2002; Source of Solutes to the coastal sabkha of Abu Dhabi; G.S.A, Bulletin 114, 259-268. Ali Fazeli = egeology.blogfa.com Wood. W.W, and Sandford W. E, 2002; Hydrogeology and solute chemistry of the coastal-sabkhas acquifer in the Emirate of Abu Dhabi, Barth & Boer (eds) Sabkaha Ecosystems, Kluwer Academic Publishers, Printed in the Netherlands p 173-185. Ali Fazeli = egeology.blogfa.com Chertification Chertification is a diagenetic process that converts carbonate sediments into chert. These cherts are composed of microcrystalline quartz that contains abundant water that is dispersed interstitially between the crystals. In addition to replacing limestones, cherts can replace opal and/or dolomites. They may fill fractures and are derived from groundwaters rich in silica. Cherts can form nodules, breccias, beds, dikes, and spheroids. The setting of their formation is variable, as is their rate and timing of formation. They can be form contemporaneously with sediment deposition close to the sediment water/ or air interface form ground waters occur which are related to volcanism and so are rich in silica. They can also be late diagenetic features created during the migration of deepwater brines rich in silica. Thus chertification is a product of diagenesis that can be response to low temperature silica rich waters or the product of metasomatism related to volcanic extrusion and dyke intrusions. They form siliceous rocks that can arguably be chemical sediments or the products of replacement of pre-existing sediments (chertification) and the development of concretions. Chert nodules in limestones have been linked interstitial anoxia, soft-sediment deformation, when the secondary replacement of carbonate by silica can occur. They are also often associated with evaporites. In deeper waters opaline silica is commonly deposited as the tests of marine organisms that include Radiolarian and/or sponge spicules.to form an important component of marine sediments. After deposition, these oceanic sediments can undergo diagenesis and form cherts that replace pelagic limestones. Thus deep-sea cherts are found both in the central Atlantic and the Pacific Oceans. Post deposition erosion and transportation can lead to the development of siliceous turbidites that represent by bedded cherts derived from the vicinity of ocean ridges. Chemical Sediments Evaporites emplaced in carbonate sediments (figure below) through supratidal evaporation and from standing bodies of water. Supratidal flats of the Holocene arid areas of the United Arab Emirates (Butler et al 1982; and Kendall & Warren 1988) is a well know example of this.         Traverses of these flats traced landward show the precipitation of gypsum in the near surface sediments with anhydrite occurring upslope on these falts. A halite crust caps the surface. The gypsum may form individual displacive crystal laths or layers of mush, whereas anhydrite occurs in contorted layers or as nodules. The origins of the brines associated with these minerals and the associated dolomitization of the aragonitic marine carbonates is thought to be both marine groundwater influxing from the adjacent Arabian Gulf (Patterson and Kinsman 1977; and Butler et al 1982) and subsurface brines coming from the adjacent Oman Mountains (Wood et al 2001). Where the sulphates precipitate in standing bodies of water, for instance isolated coastal lagoons or playas, they form horizontal layers that parallel the sediment-water interface. The occurrence of evaporites at the updip side of a carbonate shelf or platform is important to the hydrocarbon industry since the evaporites often form the updip seals to reservoirs developed in dolomitized shelf carbonates (Kendall & Warren 1988). Pisolites, Oncoids, and Oncolites Pisolites, oncoids, and oncolites are enveloped by irregular layers. All these grains are frequently larger than ooids and commonly are over a centimeter in diameter. Pisolites form by the precipitation of calcium carbonate around nuclei trapped in sediment within the vadose zone of soils or marine tidal flats (Figure 24). Oncoids form on the surface of intertidal and supratidal flats where carbonate precipitates from salt water spray and marine flood waters (left figure).   Though these grains are termed oncoids, in limestones they probably cannot be distinguished from pisolites. Finally, other grains resembling pisolites but termed oncolites are formed by accretions of blue-green algae and trapped sediment around a nucleus in moderately protected marine environments (figure below). Variations of this type of grain occur when the coatings are formed by algae and foraminifera or by red algae to form rhodolites. Neomorphism - Recrystallization or Inversion To quote from Folk: Neomorphism is a broad "term of Ignorance" denoting merely the change from one aspect of calcium carbonate into another, by whatever mechanism. If it is possible to determine the specific mechanism, then that more exact term should be used rather than the broad "neomorphism". Chief processes are: Inversion, whereby aragonite changes to calcite, the two minerals remaining in essential contact (in sediments nearly always with a thin water-film allowing ion-transport between host and replacer). True "recrystallization" where calcite of a particular crystal size, shape, or orientation, may be either aggrading or degrading. Strain-recrystallization wherein a strained calcite lattice transforms to a mosaic of new unstrained calcite crystals. For details see Folk '65 SEPM SpP#13. Unfortunately, the term "recrystallization" has been used in the past for almost any method which explains the formation of sparry calcite in carbonates--even for simple cementation. Solution-cavity fill, where a large gap in time of in space separates the solution of one type of carbonate and precipitation of another type, is not considered neomorphism; it is no different than simple cementation. Of the processes grouped under neomorphism, inversion of aragonite to calcite is probably the most important and easiest to identify. True calcite to calcite recrystallization is probably rare, although it is certainly important in some localities. Neomorphism of carbonate mud to microspar, etc., is very common-- neomorphism is the proper word here because one does not know if the original mud was aragonite (most likely) of or calcite. Is a very slovenly and all-to-common tendency to ascribe everything one can't immediately understand either to "algae" or vaguely to "recrystallization". You should be able to show proof if recrystalization is your preferred model to explain a particular carbonate fabric.

 

صفحه اول

پتروگرافی سنگهای کربناته 1

SKELETAL GRAINS
The skeletal parts of organisms are commonly composed of calcite, magnesian calcite, aragonite or opaline silica. This mineralogy determines the susceptibility of the skeletal fragment to diagenetic change and so its current composition and fabric in a limestone or dolomite. Calcite skeletal grains, which contain less than 4 mole % magnesium in the calcite, include some foraminifera, brachiopods, bryozoans, trilobites, ostracodes, calcareous nannoplankton, and tintinnids. Skeletal grains of magnesian calcite, that is with 4-20 mole % magnesium in the calcite, include those produced by echinoderms, most foraminifera, and red algae. Aragonite skeletal grains are formed from corals, stromatoporoids, most molluscs, green algae, and blue-green algae. Skeletal grains of biogenic opaline silica include sponge spicules and radiolarians

 

Foraminifera
Foraminifera are one-celled animals that are free-floating (planktonic) or live on the sea floor (benthonic) and secrete a calcareous or agglutinated test that is commonly preserved unbroken. Foraminifera tests preserved in the sedimentary record are commonly used as indicators of water paleo-depth, paleotem perature, oceanic circulation, turbidity and age of the deposit. Planktonic foraminifera tests form reservoirs in the Cretaceous and Tertiary of the North Sea (the chalk reservoirs of Ekofisk Field are an example), and benthic foraminifera tests are responsible for hydrocarbon reservoirs in some porous carbonate sand deposits within the Permian Basin (Late Paleozoic fusilinids) and offshore Tunisia (Tertiary Nummulites).

Foraminifera tests display a wide variety of shapes and sizes, but most are less than 1mm in diameter (figure above). Most are multichambered and these chambers are arranged serially (uniserial, biserial or triserial) or are coiled (planispiral or conically spired). Recognition of wall structure is critical for the identification of foraminifera because random sections of specimens do not reveal all the chambers or their true shape. Unfortunately, the wall structure, especially in Paleozoic species, is often obscured or destroyed by diagenesis.

Brachiopods
Brachiopods are especially important contributors to the fossil record of Paleozoic shallow seas. The shells, which consist of two unequal valves or curved plates, are usually from 1 to 10 cm. in diameter.

They are either inarticulate and composed of calcium phospate, or articulate and made of a chitinous periostracum covering thin outer prismatic and thick inner lammelar calcite layers. As shown to left, the shells may be (1) impunctate, (2) pseudopunctate with the inner shell layer embedded with rod-like plugs, or (3) punctate in which small rounded to elongate pores penetrate the shell. Some brachiopods, like the late Paleozoic productids, grew spines which, when broken, contribute separately to the sediment.

Bryozoans

Bryozoans are colonial benthic organisms with calcareous skeletons that are encrusting, branching or fenestrate (resembling a window screen).

Their binding ability makes them especially important as contributors to the building framework in reef settings of all ages. Their recognition and subdivision into classes is based primarily on wall structure and the arrangement of internal round or polygonal elongate tubes (zooecia) (left figure). Laminated wall structure is a distinctive feature of bryozoan debris in thin section. Most bryozoans are calcitic, but some are partially or totally composed of aragonite.

Trilobites
Trilobite shells are especially common as skeletal debris in Cambrian and Ordovician limestones.

In cross section trilobite shells are long, sinuous and frequently have a recurved shepherds crook shape (left figure). Trilobite shells are generally less than 1mm thick. The shell may be a few centimeters long but they are formed of individual pieces that are millimeters or less in length. Their shell is composed of calcite crystals that are oriented perpendicular to the wall. However, when examined with a light microscope, the fabric appears to be homogeneous because the crystals are too small to be easily distinguished. The fabric exhibits undulose extinction under cross-polarized light.

Ostracodes
Ostracodes have two valves, usually less than 1 mm in diameter, that may be smooth or ornamented. The valves are joined along a hinge and overlap slightly, so that in section the shell is asymmetric (above figure). Some smooth-shelled forms have calcified projections on the shell that point inward. Although quite variable in microstructure, the shells usually have fine prismatic structure.

Coccolithophorids are planktonic calcareous yellow-green algae that are a major contributor to Mesozoic and younger deep-sea sediments. Individuals consist of round coccospheres covered by coccoliths. Coccoliths are a valuable biostratigraphic marker of age and oceanic circulation in rocks that are Jurassic and younger in age and are the major component of chalk reservoirs. Commonly the coccoliths form elliptical discs that consist of an intricate arrangement of calcite crystals (above figure). A coccolith is usually less than .02mm in diameter, therefore under a light microscope little detail can be seen. Fossil nannoplankton also include the star-shaped discoasters.

Tintinnids

Tintinnids are pelagic protozoan that have a microscopic cup-shaped calcite test commonly .1 to .2 mm across (left figure). In thin section the tests have U-shaped longitudinal cross-sections and circular or elliptical transverse sections. Usually, the longitudinal sections have characteristic flanges at the opening of the test that create a horseshoe shape. Tintinnids are very common in Upper Jurassic and Lower Cretaceous deep-water limestones of the Mediterranean region.

Echinoderms
Echinoderms today are composed of many individual magnesium calcite plates.

 

The plate fragments and spines are scattered through the marine sediments of reefs, shallow shelves and deep-sea basins. Individual plates and spines from echinoid tests are easy to identify in thin section because the entire fragment extinguishes with cross-polarized light. The spines exhibit characteristic internal radial patterns (right figure). Holothurian spicules (ossicles) are also single crystals. They are small, .07 to .1mm, and occur in a variety of shapes.

Ophiuroids and asteroids also contribute plates, spines and ossicles. In ancient limestones crinoid plates are easily distinguished in thin section by their reticulate pattern. Although these plates now have calcite mineralogy, they still behave as large single crystals. The plates usually appear dusty because the reticulate network of pores may be filled with micrite or inclusion-bearing cements. Pore filling or rims of cement on echinoderm plates are usually added in optical continuity.

Red Algae
Red algae are calcified benthonic plants that occur as crusts, nodules and branches. Coralline red algae occur in a variety of growth forms. Some have articulated branches of cylindrical or flattened leaf-like segments and usually grow in sheltered environments.

Others, which are encrusting or massive forms, grow on a variety of substrates within varied energy conditions. They form nodules on unstable sea bottoms and are important encrusters and cementers in modern coral reefs, particularly in the Pacific where algal ridges form a rim or lip to the reef. Red algae are important binders in reefs of all ages. They play an especially important role in Mesozoic buildups. Corallines can also be important in colder or deeper-water sediments.

Depending on the orientation of the section with respect to the growth surface, the calcified thallus of the alga has either a characteristic rectangular or rounded cellular pattern (above figure). Smaller fragments, only a few millimeters in diameter, may be distinguished by the structure, type of conceptacles (cavities where spore-bearing cells collect) and detail of the calcified tissue. These magnesium calcite algal fragments can be micritized to form a dark brown opaque mass.

Corals
Reef-building corals thrive in shallow warm waters of normal marine salinity, but tolerate a wide range of temperature and salinity.

Corals can be important contributors to the growth of carbonate platform margins because of their rapid growth rates in reef settings and their ability to produce large amounts of sediment. Stony solitary or colonial corals have similar calcareous skeletons with basic skeletal elements of aragonite or calcite fibers.

The fibers are grouped in sclerodermites that are aligned into trabeculae. The fibers are arranged somewhat differently in different parts of the coral, and some variation of fiber orientation exists between orders. The skeleton is characterized by an outer wall and by a series of internal vertical plates (septa), horizontal plates (tabula) and curved plates (dissepiments) (above figure). The patterns of internal plates and growth forms are used to identify the large variety of coral types. Alcyonarian corals, actually hydrozoans, are an exception in that they do not have massive skeletons but instead produce spicules. The spicules are varyingly shaped and range from 0.1 mm to 5 mm in length.

Stromatoporoids
Stromatoporoids are important reef formers in the Paleozoic and Mesozoic.

They are possibly ancient equivalents of sclerosponges that coat ledges in the deeper parts of modern coral reefs. Apart from siliceous sponges the fossil skeleton is normally calcite, but their preservation in limestones suggests that they were originally aragonite. The skeleton consists either of overlapping dome-shaped, convex-outward plates or of a trelliswork of concentric laminae with various supports or pillars (right figure). In sections parallel to growth direction, the stromatoporoid skeleton has a rectangular grid pattern.

 

Molluscs
Pelecypods and gastropods are the commonest mollusks. Rudists are probably the most important of the pelecypods to the exploration ist. Rudists formed carbonate banks (reefs) during the Cretaceous. These contain significant reservoirs in bank and associated rudist sand debris aprons.

Pelecypods have two shells that are hinged along one margin, while gastropods are coiled tubes that can form a number of shapes (left figure). Three or more layers form typical shells: an outermost layer of chitinous periostracum and two inner calcareous layers. Layers commonly have a nacreous or cross-laminated microstructure, but up to six types of microstructures are possible. The appearance of each structure varies according to its orientation. Molluscs can be recognized by shell shape and their multilayered wall structures. Broken pieces of fine mollusk debris may not be recognized as such because the fragments are commonly leached and infilled or replaced by calcite spar.

Mollusks inhabit nearly every marine environment. Shell growth is environmentally controlled; thin shells typify quiet-water or cold environments whereas thick shells occur in higher-energy environments. The shells are primarily aragonite or they may be a mixture of aragonite and calcite; thus, their manner of preservation is variable. In shells with mixed mineralogies, the outer layers are commonly calcitic and the inner layers are commonly aragonitic. Rudists represent a special case in that they underwent major changes in shell mineralogy and structure during the Cretaceous, involving an increase in the relative proportion of aragonite to calcite (and thus an increase in the likelihood of development of secondary porosity) and an increase in porosity and complexity of the shell. In contrast, oysters are shallow-marine benthic pelecypods having a three-layered calcite shell. Other pelecypods have similar mineralogy; an example is Inoceramus that is common to shelf and deep-shelf deposits of the Cretaceous.

Green Algae
Green algae are important contributors to mud-and sand-size carbonate sediment.

For instance, the phylloid or plate-like dasyclad algae Ivanovia contributed extensively to carbonate mound build-ups in the Mississippian and Pennsylvanian. Green algae are plants that precipitate carbonate in their flesh parts. They may be crustose, nodular growths or erect plants commonly formed of segmented, flattened or cylindrical branches (right figure). Green algae are distributed worldwide, principally in warm shallow seas. They are common in quiet lagoons, but are also found in less turbulent parts of open shelves and reefs.

Calcispheres are small hollow spheres that may be fruiting bodies of certain green algae. The spheres apparently were extremely buoyant and tended to accumulate in quiet settings like intraplatform basins.

Cyanobacteria
Cyanobacteria or blue-green algae are most important as binders in tidal flat, lagoon and reef settings.

Stromatolites are layered structures formed by cyanobacterai and carbonate sediment. They are commonly, but not exclusively, recognized in ancient carbonates that were deposited in tidal flat settings. Other blue-green structures include Girvanella, resembling an intestine-like mass of tubes (left figure), and Renalcis, a branching tree-like form. These forms are common in reefal cavities and some slope sediments of the lower Paleozoic.

In Recent environments, the blue-greens form slimy mats composed of filaments and carbonate. The carbonate may be precipitated through photosynthesis or trapped as grains washed onto the mat. The cyanobacteria form colonies that may be recognized by their external form (above figure). They may be stacked hemispheroids or saucers, etc. The crinkly banding of an ancient algal colony is difficult to distinguish from soil concretions or caliche in section because all of these deposits exhibit horizontal banding, spherical growths and heads. Occasionally algae infest the surface of grains and form an envelope of micrite. This envelope represents an alteration or addition to the perimeter of the grain. The alteration replaces the organized grain fabric with disorganized micrite in two steps: (1) the boring activity of the algae with dissolution of the grain followed by (2) reprecipitation or trapping of calcium carbonate in the void.

Sponges
Sponges were extremely important as reef builders in the Permian and the Mesozoic.

Other forms produce abundant sediment during bioerosion of reefs and other hard substrates. Most sponges live in water less than l00m deep on hard bottoms where there is some water circulation. Sponge spicules are commonly all that is preserved. These are composed of silica, but they may be calcite or spongin (right figure). Spicules vary in size and shape depending on their position within the sponge and their function as structural framework or as protection. Sponge spicules have smooth and simple geometrical shapes and a hollow central axis; in contrast, spicules of other organisms usually have a more complex shape.

Sclerosponges are calcareous sponges that precipitate a massive aragonite skeleton and have siliceous spicules. These sponges are important contributors to the formation of deepwater reefs, living mainly in crevices and caves. Another important group of sponges are the boring varieties, such as Cliona, which produce large quantities of silt-size carbonate sediment that collects near reefs and on hard bottoms. The excavating cells of the sponge form characteristic hemispherical-shaped chips (above figure).

Radiolarians
Radiolarians are microscopic pelagic organisms that construct a test of opaline silica (figure below).

Their mineralogy ensures that the varieties of Radiolarian tests seen in left figure are preserved below depths at which carbonate grains dissolve.

They can form thick widespread deposits over deep ocean bottoms or occur in silica-rich water associated with submarine volcanism. Radiolarians are an important biostratigraphic tool where they occur in deposits that commonly lack calcareous fossils. The radiolarian skeleton may be 2mm in diameter but is usually smaller. Skeletons vary greatly in shape and ornamentation. Often the shell is a hollow perforate sphere or vase. Most shells show low birefringence and fine-grained fibrous structure comparable with cherts or chalcedony. The porosity that characterizes the shells is usually occluded during this alteration.

Micrite

A large volume of any limestone is usually composed of carbonate mud or micrite. Because of the small size of the grains or crystals in the micrite, identification of their origin is difficult to impossible. The grain size boundary between sand and mud that is used by geologists for carbonates varies: for instance, Dunham (1962) puts it at .02 mm and Folk (1962) .004 mm.

 

Micrite may be precipitated chemically or biochemically from seawater, derived from the abrasion of pre-existing calcium grains, or form during disintegration of calcareous green algae (figure above). Micrite accumulates in a variety of settings: in the still water of protected lagoons, below wave base in deeper water, and even in agitated settings within and beneath the protection of algal mats. Should the presence of micrite be used to interpret depositional settings, then its vertical association with other lithologies and its faunal content should also be considered. Any interpretation is complicated by the existence of micrite-size cements, which may have a different distribution to that of fine sediments. The micritization of broken skeletal and non-skeletal grains, that is the recystalization of a preexisting crystal fabric to a micritic one, also adds to the confusion. This is because these micritized grains may be mistaken for fragments of sedimentary micrite. Micrite cement is discussed in the section on cementation and diagenesis.

NON-SKELETAL GRAINS
Nonskeletal carbonate grains are quite variable in origin and appearance. Their value as
indicators of the environment of formation is among authors, so care must be taken to define the name that one uses. Our terminology includes lithoclasts, intraclasts, pellets and peloids, and coated grains.

 

Lithoclasts
Lithoclasts (see illustration above) are irregular fragments of limestones that were eroded and transported within or from outside of the basin of deposition. They are sometimes called extraclasts or detrital grains (right figure). The clast boundary cuts across cement and particles in the fragment, reflecting its well-indurated nature. Lithoclasts are indicative of processes that rip-up, abrade, and transport pieces of previously lithified carbonates.

Intraclasts

Intraclasts are irregularly-shaped grains that form by syndepositional erosion of partially lithified sediment. Examples include mudlumps that are torn up from the bottoms of lagoons during storms, hardened desiccated mud flakes produced in intertidal and supratidal environments and fragments broken from cemented deep-sea crusts (above figure). Other intraclasts are aggregates of carbonate particles (figure below). These include grapestones and botryoidal grains. Grapestones are composite grains with an irregular shape that resembles a bunch of grapes, whereas botryoidal grains are similar but with oolitic coats enveloping the aggregate grain. These types of intraclasts from in shoal water environments with intermediate wave and current activity, where grains that are cemented on the sea floor are broken into aggregate fragments and lumps during storms.

 

Pellets and Peloids
Pellets are the excreta of various marine organisms (figure below).

 

These grains collect in protected lagoons and shallow intertidal ponds, environments of somewhat lower energy than those where grapestone and botryoidal grains form. Pellets commonly are not preserved but disaggregate into micrite during the dewatering and compaction of shallow burial. Where hardened by marine cements, the pellet may be preserved intact. This commonly occurs on open platforms where pellets are winnowed and washed by currents.

 

Peloids are grains of indeterminate origin. They are sand or silt-size and usually subangular in shape, though often they are rounded and resemble fecal pellets. Peloids retain no internal structures to identify their origins, which are probably diverse and include micritization of grains by boring algae and fungi (right figure).

Ooids
Coated grains include oolites, pisolites, oncoids, and oncolites. Oolites (figure below) are formed by a series of concentric layers surrounding a nucleus.

 

 

They generally form in agitated marine environments including tidal sand bars or tidal deltas between barrier islands. Qolite sands form important reservoirs, of which the Upper Jurassic Smackover Formation of the U. S. Gulf Coast is one of the best known.

Most recent ooids from modern marine settings like the Bahama Banks exhibit concentric coatings that have an organized microstructure of tangentially arranged aragonite needles. However, some recent ooids from the Great Salt Lake of Utah and the Persian Gulf in the vicinity of Qatar have a radial fabric of needles. A similar fabric is common to most ancient ooids. The size of ooids is controlled by rate of precipitation and abrasion. Oolites generally range between .5 and 1mm in diameter. Ooids with asymmetric coatings and superficial oolites form in quiet water. Occasionally broken radial ooids may act as the nuclei for other ooids suggesting that the radial fabric is developed during deposition. Breakage is common in oolites that collect on salt flats where halite precipitation has weakened the radial fabric.

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DEPOSITIONAL SETTING AND GEOMETRY OF
CARBONATE FACIES

 

SUMMARY
Carbonates accumulate in a variety of depositional settings that have become better known largely through the exploration for more hydrocarbon reserves and their exploitation in the last 35 years. Though reefs and grainstone shoals have been cited as common hydrocarbon exploration targets and so have been more intensively examined, other carbonate facies from both basin and/or platform interior settings have also been recognized to be important and have been studied too.

Collectively these studies have shown that carbonate facies are commonly the product of processes that are active in their depositional setting. Water depth, winds, waves, currents, temperature, water chemistry, and biologic action all affect the character of the carbonate formed. Diagenesis, which also plays a major role in forming and modifying the facies that are found in the subsurface, are dealt with separately in another section of this web site. Below we show that it is possible to group carbonate facies on the basis of their depositional settings (table below and figure above) and their response to changes in base level (often sea level).

These depositional settings can occur along continental margins, within epeiric seas, or on isolated platforms in oceanic basins (figure above).

High and low frequency changes in base level are believed to produce the vertical cyclic character exhibited by the sedimentary facies associated with of these carbonate settings and their common interface with terrigenous systems. It has been recognized that sediment layering and the surfaces that bound these layers have predictable continuity. This layering has been related to particular base level positions and has enabled a better understanding of the lateral and vertical relationships of carbonate sedimentary facies. This has been used to build better hydrocarbon exploration and production models for the petroleum industry and is the reason that we have the understanding of sediment facies and their geometries that is summarized below.

BASIN AND SLOPE

Pelagic Sediments

Pelagic calcareous sediments are open marine deposits that often form close to the water surface in the photic zone but collect below depths affected by wave action. They usually found at the seaward margins of shelves and platforms and extend basinward into areas below the photic zone. The percentage of pelagic carbonates in deep-sea sediments varies as a function of depth, because with increasing water depth there is increasing dissolution of aragonite and calcite skeletal particles. In modern oceans aragonite tends to dissolve at depths between 500 m and 1500 m, while calcite tends to dissolve at depths that are substantially deeper and between 750 m and 4300 m. The end result is that at great depths or in cold-water areas calcite skeletal components completely dominate calcareous oozes. In modern oceans at depths below about 4300 m, all carbonate particles dissolve and only fine terrigenous sediment is observed. Terminology used to describe these effects include the Lysocline is the depth at which dissolution of Calcium Carbonate is manifest and is shallower than Calcium Carbonate Compensation Depth (CCD) which is the depth at which ocean floor sediments have less than 10% Calcium Carbonate. Both tend to be in shallower water in the higher latitudes and become deeper towards the equator.

Bedding in open marine deposits is usually thin (5-10mm., rarely much thicker than 100 m). The characteristically thin beds are the result of the dominant mechanism of deposition, gravitational settling. Bed surfaces are planar to nodular (left figure) and sets of beds may be continuous over wide areas. Uneven nodular fabric, typical of many deep-sea carbonates, may originate in a number of ways. The nodules may be the result of burrowing or may also be produced by some initial marine cementation followed by pressure solution during burial. Because these sediments are deposited very slowly, they may be cemented by calcium carbonate, are commonly mineralized and may be encased by crusts of hematite, glauconite, pyrite and manganese.

Changes in base level lead to cyclic variations in the vertical character and composition of basinal sediments. In deeper water away from the platform, during high stands the sediment tends to be a mixture of pelagic tests, lime mud which may be interbedded with lowstand carbonates, and/or often silciclastic sediments, usually marl or shale but sometimes thin sands or siltstones. Toward the basin margin the highstand sediment becomes a mixture of pelagic and benthonic skeletal hash in a matrix of lime mud which are in turn interbedded with lowstand sediments often silciclastic sediments, commonly marls or shale, but including thin sands or siltstones. In both deep and basin margin settings the carbonate mud sized fraction predominantly consists of calcareous nannoplankton, broken pieces of planktonic foraminiferal tests, and fine sediment that is winnowed from adjacent shallow platforms and has settled through the water column. Pre-Jurassic deep-sea limestones are the most difficult to interpret because of the apparent worldwide absence of calcareous nannoplankton and planktonic foraminifera. The source of this carbonate is not fully understood. These deposits are usually interbedded with shales and marls and are dark in color. This shale and/or marl is commonly interpreted to be a response to lowstand deposition.

Source and Reservoir Potential

Although basinal sediments are dark colored and give off a fetid odor upon fracture and so are generally regarded as potential source rocks, they frequently contain little organic carbon. Thus, most deep-sea carbonates are not significant hydrocarbon sources for shallow shelf carbonate traps. However high organic matter production and euxinic conditions are more likely to prevail in shallower basins that have become isolated within the cratonic interiors or margins, or during the initial pull apart of continents. It is within these basins that source rock potential can be high. This was particularly true of the Arabian Gulf area where local intercratonic basins contain the basinal source rocks from the Middle Jurassic (Hanifa Formation) and the Lower Cretaceous (Lafan Formation) and supplied for many of the giant fields of the area.

Deep-sea micritic limestones generally have very low porosities and permeabilities, but are susceptible to fracturing and so form significant reservoirs at a number of localities. Primary porosity in pelagic chalks may be extremely high (e. g., 650/0 in Miocene chalks of the Caribbean), but this porosity is largely due to open chambers of pelagic foraminiferal tests and a loosely packed nannofossil matrix, thus their permeability is low. Chalks are significant reservoirs in the upper Cretaceous and Tertiary of the North Sea and the Upper Cretaceous of the U. S. Gulf Coast (the Austin Chalk Trend). North Sea chalks produce from a combination of preserved primary porosity, moldic porosity and fracture porosity; whereas the Austin Chalk produces where fractured.

Turbidites and Debris Flows

Basinal sediments shed from shelf margins include turbidites and debris flows. Turbidites are sediments transported and redeposited by turbidity currents. These deposits exhibit similar sedimentary structures whether they are carbonate or siliciclastic turbidites (figure below). Sediment type within carbonate turbidites is variable and controlled by source. Turbidites are among the few carbonates that have been transported significant distances. Close to the basin-platform margin carbonate turbidite deposits form irregular ribbons of channel-fill that are perpendicular to depositional strike. Farther from the margin, the turbidites form fan-shaped wedges which in cross-section are composed of evenly-bedded sheets. Bedding varies from thin to almost massive. These sediments, transported from shallow platform and upper slope, may include reef debris, oolites, lime mud or broken limestone blocks. Earthquakes, sea level changes or slope failure may initiate transportation.

Proximal carbonate turbidites are characterized by the lower part of the Bouma graded bed sequence and massive wackestones in which a lime mud matrix supports the grains. The basal layers of turbidites may be unsorted and may include ripups from the substrate. Bedding is irregular and discontinuous because the sediment is deposited as channel fills and levees on submarine fans. Bases of beds fill over match the contours over the scoured upper surfaces of previously deposited turbidites. Sediment composition and grain size are extremely variable and may include a wide range of shallow water biota mixed with pelagic skeletons. Distal turbidites are characterized by the upper part of the Bouma graded bed sequence. Bedding is regular, planar, and commonly the turbidites are interbedded with marls. These turbidite sediments are deposited at the margins of submarine fans some distance from their source. The biota is much the same as that of proximal turbidites except that there is a greater percentage and diversity of pelagic skeletal debris.

Carbonate debris flow deposits are characterized by a mixture of a wide variety of lithologic types and sizes of angular fragments that have anomalously oriented stratification. They include megabreccias of blocks, up to 25 x 30 m. in cross-section or larger, floating in an enclosing matrix of lime or terrigenous muds. Debris flows vary from lens-like or ribbon channel-fills to irregular beds that are locally adjacent to carbonate platform-basin margins. Some megabreccias are associated with high relief, active tectonism or steep slopes; but others may be the result of pervasive bio-erosion or submarine dissolution of fore-reef carbonates by fresh water springs.

Debris flows have often been misinterpreted as shallow water conglomerates, in situ bioherms, organic mounds and reef talus. Consequently debris flows are probably much more widespread than previously thought. Faunas contained in these deposits include mixed transported shallow-water and in situ deep-water forms.

Changes in base level are probably responsible for many of the above unstable slope deposits. This is because drops in base level will often expose a carbonate basin margin leading to an increase in instability and to slope failure, generating turbidites and megabreccias. Some unstable carbonate slopes and their failure can also result from over production in the shallow-water of the carbonate margin.

Turbidites could have significant source potential because of their origin in shallow water areas of high organic productivity. In addition, their porous facies may act as reservoirs or as conduits for migrating oil. The prolific Cretaceous reservoirs of the Golden Lane field of Mexico are interpreted by some geologists to be a gigantic carbonate breccia deposited by debris flows.

PLATFORM MARGIN

Introduction to Reefs and Organic Buildups

Reefs and organic buildups can form both in shallow normal marine waters where there is a break in slope on the sea floor (figure below), or they may also form landward of this break in slope within the slightly deeper water of platform interiors and epeiric settings. Reefs and buildups have two major forms: either continuous elongate bodies parallel
to the depositional strike of the shelf edge or as a series of isolated buildups which may occur on either side of the shelf break.

Changes in base level affect the geometries of these buildups. During high stands of sea level the geometries can be both progradational and aggradational, with the general accommodation being driven by the regional subsidence of the depositional setting. During falls in sea level the geometries will generally down step across the previously deposited slope, with the gentler wider slopes forming a substrate to forced regressive wedges of carbonate that step seaward. At the same time updip erosion of the earlier margin can occur, often cutting down to the new sea level. Transgressions can lead to the nucleation of local buildups on local high spots on the downslope portions of the basin margin and the erosion of the updip portions of the earlier margin as it becomes exposed to increasing wave energy.

Barrier Reefs and Mud-Skeletal Banks

Reefs and mud-skeletal buildups are best developed where open marine waters shoal against the basin margin. The slope of the seafloor on which the buildup grows is controlled by antecedent topography, by faulting or by the juxtaposition of active shallow-water accumulation and deeper water basin starvation. Barrier reefs tend to be massive but have associated discontinuous thin beds of sediment. Reef geometry is expressed as thick sheets or ribbons which parallel depositional strike and whose thickness may be related to a particular change in base level. The major sub-environments are the reef frame (the reef crest and reef wall), reef apron, back reef and barrier islands (sand cays). Reefs act as a sediment source to areas both landward and seaward. Major reef contributors through geologic time have included corals, stromatoporoids, calcareous sponges, algae, and rudists. Associated fauna is very diverse. The reef frame is characterized by in situ growth of calcareous organisms interbedded with calcareous sands, silts and muds that form as the result of bio-erosion and episodic storms. The frame is usually massive and cavernous, with void space filled by bladed and fibrous marine cements and by internal sediment that is often perched on or within these cements. Within the reef crest, the skeletal framework may vary from as little as 200/0 of the rock volume to as much as 80%, with a reciprocal distribution of sediment-cement infill.

The reef apron is composed of silt to boulder-sized debris derived from the reef frame and mixed with in situ fore-reef biota. It characteristically has a chaotic texture but may locally exhibit cross-bedding. Many cited examples of Holocene fore-reef and upper basin slope deposits contain huge blocks of reef rock that have slumped from the cliff-like fore-reef face. Most precipitous fore-reef slopes are characteristic of Quaternary and Holocene reefs which owe most of their major topographic features to pre-Holocene antecedent topography. Similar fore-reef cliffs occur in the Upper Devonian of the Canning Basin in Australia and portions of the Mesozoic margin of the U. S. East Coast. In general, most pre-Holocene coral reef buildups lack this steep fore-reef cliff, and therefore the associated reef apron sediments have correspondingly less reef core rock rubble. Reef apron sediments may typically be stabilized or encrusted by foraminifera, sponges, or algae. A typical fore-reef toe facies of late Mesozoic and Cenozoic reef buildups is composed of a gravel of irregular red algal nodules. The character to the sediments of the reef apron and foreslope will often have a cyclic variability that is the product of high frequency changes in base level.

Back reef sediment is formed by both localized patch reef framework that grew as carpets or patch reefs and by skeletal debris transported from the reef crest. The patch reefs tend to be massive and lens-like, while the adjacent back reef sediments are frequently burrowed, widespread, and sheet-like. The sediment varies in grain size from sand to mud. Barrier islands or beaches occur just behind the reef crest and show many of the characteristics of clastic barrier islands. A complex of linear carbonate sand bodies forms them parallel to depositional strike. The seaward margin tends to be smooth but storm wash-over fans and flood-tidal deltas serrate the leeside. Sedimentary structures associated with the islands include cross-laminated carbonate sands from the beach face, lamellar birdseye limestone, algal stromatolites, and storm wash-over layers. Diagenetic changes and cementation may produce beach rock and tepees. As with the reefs described above the character to the sediments of the back reef build ups and sheets will often have a cyclic variability that is the product of high frequency changes in base level.

Mud-skeletal banks are elongate massive bodies that form both parallel and perpendicular to the seaward edge of the platform margin (left figure). They range from knoll-like mounds of a few square meters to massive linear belts trending for hundreds of kilometers along depositional strike. The thickness of the banks varies from a meter to 100 meters or more. Beds may be thick to massive and range from horizontal to clinoform. Modern carbonate mud banks form in conjunction with sea grasses and green calcareous algae that bind and trap fine sediments derived from breakage in more turbulent water. Sediment in ancient banks of this kind varies from lime mud to
fossiliferous sand. The sediment is commonly neomorphosed and may contain cavities filled by internal sediment and cement. The irregular form of the cavities varies according to the position in the bank and the form of roof support. For instance, cavities in the Carboniferous Ivanovia banks that are exposed in the Sacramento Mountains of New Mexico are supported by algal plates and filled by mud and fibrous marine cements. Other Paleozoic mud banks contain similar mud-supported cavities known as Stromatactis. These cavities are filled by mud and cement. Again as with settings described above the character to the sediments of the mud banks will often have a cyclic variability that is the product of high frequency changes in base level

Pinnacles, Patch Reefs and Mounds

Pinnacles form during relatively rapid sea level rises when carbonate production only locally keeps pace (figure below). Bottom agitation is not as great over pinnacles, patch reefs, and sediment mounds as it is on shelf-edge reefs, so organisms tend to be different and winnowing and frame building are less important. These structures also differ from shelf-edge reefs in that they are more symmetrical and relatively less oriented with respect to wave and wind directions. The pinnacles and patch reefs are formed by frame builders whereas the mounds are accumulations of lime silt and mud that is trapped
by sponges, octocorals, algae, and crinoids.

Pinnacles reefs and sediment buildups are localized landward or seaward of the crest of the basin margin. They may be localized on highs, formed by previous kharst topography or some other local irregularity, that cause waves to shoal and break, or focus swift tidal currents. Core facies of these bodies are generally massive to thick bedded, while the flank beds have thin, irregular beds. Changes in texture tend to radiate outward from the buildup core. Seaward buildups commonly contain more porous grain carbonates than the more shelfward mounds, but pore-filling marine cementation occurs more readily in a seaward direction.

As with barrier reef buildups, the pinnacle reefs are characterized by in situ boundstones of calcareous organisms and sediments. The reef frame is massive and cavernous and the voids are filled with sediment and marine cement. These sedimentary features are exquisitely displayed in Silurian pinnacles from the Michigan Basin. Major facies variation is found in buildups that were initiated in deep water and grew upward into shallow water. The basal sediments of these buildups are usually finer grained than the crest. The fauna at the base is usually a pioneer community of low diversity while the fauna of the crest may be a more diverse climax community. Lower contacts are gradational with the platform sediments below the bodies. The pinnacles are commonly overlain sharply by basinal marls and shales similar to those deposited on the deeper parts of the platform and associated with transgressive rises in sea level. Rarely the bodies coalesce upward and are sharply overlain by tidal flat sediments.

Potential Reservoir and Source Rocks

The belt of reef and mud buildups at the depositional surface tends to be a narrow, ribbon-like feature usually less than about l00 m wide. The apron of skeletal sand shed back of the reef may be even narrower, while lagoonal sediments may stretch for tens of miles back of these buildups. In the subsurface all the facies may be quite extensive due to basinward pro-gradation. The reservoir potential of reefs and buildups is widely assumed to be high. However, studies indicate that both primary and secondary cements and internal sediments more often than not plug the porosity of reef bound-stones. Proximal back reef sand deposits can retain significant amounts of primary porosity, especially in reef-tracts where accumulation of skeletal rubble was rapid. Quiet-water carbonates of deeper lagoons tend to end up as muddy sediments (i.e., wackestones and packstones) with relatively low porosities and permeabilities. Fore-reef deposits and the aprons of mud buildups may have somewhat greater reservoir potential; especially if the reef itself is plugged by carbonate cements and acts as the updip seal in a stratigraphic trap. Some barrier reef deposits have proved to be major hydrocarbon reservoirs, although this facies commonly lacks an immediate updip trap. An excellent example of a giant field in a barrier reef is that of the Oligocene reef complex at Kirkuk, Iraq. Another producing barrier reef of Oligocene age occurs in SE Louisiana and SW Mississippi. A portion of the Devonian Leduc reservoir trend of Western Canada has both the characteristics of a linear mud skeletal margin and barrier reef complex.

Reef tract and linear mud skeletal sediments typically have relatively low source potential. This is in part due to the shallow, turbulent environment but also to the efficient recycling of organic detritus within the reef community trophic structure. Thus little organic debris leaks from the crest community into the apron or into the back margin lagoon.

In contrast to barrier facies, major hydrocarbon discoveries are common in ancient pinnacle reef and mud buildups. Reservoir volumes for pinnacles are likely to be more sharply limited than shelf-edge reservoirs. This is because the porous core facies is typically bounded on all sides by relatively impermeable flank and margin deposits, basinal shales or basinal evaporites related respectively to sea level transgressions or falls. These deposits form the seal but make recharge of reservoir hydrocarbons unlikely. Examples of oil fields in pinnacle buildups are the Silurian of the Michigan Basin and the Devonian of Western Canada. Pinnacles may be associated with fairly rich source rocks at their flanks and within the basinal sediments enclosing them. Organic productivity and preservation in the sedimentary column tends to be high for pinnacles situated on the lower basinal slope but declines updip.

Sand Shoals

Carbonate sand accumulations of reservoir size commonly occur near the seaward edge of banks, platforms, and shelves. Less commonly, they are formed within platform interiors and over topographically high areas within a regionally deep-water setting. Bank-margin sand accumulations may grade over short distances landward or seaward into other carbonate facies.

The development of these bodies requires sand-sized sediment and a means of removing sediment smaller or larger than sand-sized material. These requirements are often met where a change in shelf slope coincides with wave action or strong tidal currents in a zone of high carbonate production. Sand bodies in modern carbonate settings occur in many different forms, nearly all of which have ancient counterparts (left figure). Back-reef sheets, belts and lobes of skeletal sand form along open platform margins where sediment transport is toward the bank. Where small islands exist, the gaps between them may be the site of tidal deltas. Commonly the flood tidal delta is enlarged as a result of storm-created currents. If re-entrants or embayments occur along a margin, tidal and storm-generated currents can generate wide belts of tidal bars. Along windward margins, which are dominated by large islands, skeletal sands generated within the fore-reef environment may be carried seaward to the marginal escarpment. There they may accumulate behind rocky barriers or be carried further seaward into deep water. In contrast to the variety of sand bodies that form along windward margins, leeward open margins are dominated by off-bank sand transport. Here, wide belts or sheets of non-skeletal sands form at the bank edge.

The vertical sequence of deposits found in modern sand shoals often records progressively shallower water deposition because these shallow-water sites provide optimum conditions for carbonate production. As a consequence, platform carbonate sediments usually accumulate at greater rates than the rate of relative subsidence and repeatedly build-up to sea level or above, and thereby form cyclical packages that are each a few meters in thickness. Similar shoaling sequences are recognized in thick ancient carbonate sand deposits. The cyclic character of these shoaling sequences is a response to constant cyclic changes in base level.

Source and Reservoir Potential

Sand shoals do not have good source potential because the environment is oxygenated and highly agitated. Lateral facies equivalents must, therefore, be called upon to act as the source of hydrocarbons trapped in sand shoal reservoirs. In terms of reservoir quality, the carbonate sands have high initial porosities that may be preserved in the subsurface. In addition, because these sand shoals are commonly localized on paleohighs and generally build up to and above sea level, secondary porosity usually develops shortly after deposition. The best documented example of production from sand shoal reservoirs occurs in the Jurassic Smackover Formation of the U. S. Gulf Coast, but other well known grainstones that contain hydrocarbon reservoirs are the San Andres Formation in the Permian Basin and the Arab D Formation which forms the reservoir facies of the worlds largest field, Ghawar! The evaporative seals associated with many of these grain carbonate reservoirs probably owe their existence to a drop in sea level that initiates local isolation and the precipitation of evaporites that then onlap over the reservoirs.

PLATFORM INTERIOR

Epeiric Sea, Lagoon or Bay

This depositional setting, protected by a wide shallow sea, reefs, or mobile carbonate sand barriers, is characterized by continuous wide sheets of poorly-sorted sediments which are commonly extensively burrowed. The sediments either formed in situ or were transported from a seaward barrier by the winnowing action of waves and currents. In the normal marine setting the faunal remains are abundant but not diverse. However, when the setting is some tens of kilometers from the open sea, as in epeiric seas, faunas steadily decrease in species diversity as a response to elevated salinity. At the landward margins of epeiric seas, where salinities are frequently at their highest, the only evidence of life may be subtidal blue-green algal stromatolite heads and mats.

The principal facies in shallow water are clean carbonate sands, muddy skeletal sands, and lime muds, whereas in deeper water marls and shales are common. The sands in shallow water form on stable flats where current energy is sufficient to winnow lime mud but not grains. Grains may be oolitic but are more commonly pellets, grapestones or oncolites. Lime muds form in areas with restricted circulation. Along the land-ward margins of epeiric seas, the muddy sediment is usually dolomitic and stromatolitic. These sediments are well bedded and have wide lateral distribution. In subtidal areas, faunal abundance is low but diversity is high. In contrast, in intertidal areas faunal abundance may be high but diversity is low. Again the cyclic character of these shoaling sequences is a response to constant cyclic changes in base level

Tidal Flats

Tidal flat sediments include those forming in the intertidal zone (flooded by daily tides) and the supratidal zone (flooded by wind and spring tides) (figure below). Sediments range from carbonate sands to muds and commonly contain algal stromatolites. Tidal flat sediments occur as widespread sheets that are often dissected by channels. Bedding is thin and even and contacts are sharp; but evaporites show irregular bedding and may be nodular. Collapse breccias of angular fragments tend to parallel depositional strike and are local.

Traced landward the principal fades belts are: sandy tidal flats, muddy tidal flats, mangrove/algal flats and supratidal flats. The sandy flats, commonly cross-bedded and winnowed, reflect storm wave and current movement. The muddy tidal flats are burrowed and homogenized; bedding planes may be irregular, in part a result of the burrowing. Mangroves, algae and other plants bind and trap transported lime mud and may also aid its precipitation. Algae produce a variety of structures in response to desiccation and erosion; lamellar birdseye fabrics and dome heads are the most significant. Tidal creeks rework the tidal flat sediments, developing sandy or muddy point bars. The channel margins may be marked by levees. If the levees are made of lime mud, they generally exhibit a variety of laminations, mud cracks and intraclasts. The levees may pond water in the over-bank areas, where sediments are highly burrowed.

Supratidal flat sediments vary according to their climatic setting. For instance, with high salinities and magnesium concentrations dolomite replaces calcium carbonate and forms a cement. In arid regions gypsum and anhydrite may precipitate directly within the sediment. Simultaneously halite may precipitate locally on the sediment surface, but wind or marine flooding usually removes it.

Reservoir and Source Potential

Tidal flat muds and pelleted sands have low porosities due to dewatering and compaction. However, dolomitization of these deposits forms reservoirs by creating higher porosity and permeability. Tidal flat carbonates commonly are associated with evaporites that act as seals to the reservoirs. Examples of production from tidal flat sequences include the Ordovician Ellen-burger Formation, the Ordovician Red River of the Williston Basin, Permian Basin carbonates of Texas and the Cretaceous offshore of West Africa. The cyclic character of these tidal flat sequences is again a response to constant cyclic changes in base level

Tidal flat carbonates have abundant algal organic matter mixed into them. Although there may be ample opportunity for the organic matter to be oxidized and come in contact with fresh waters, there is evidence that some tidal flat sequences were deposited quickly enough to maintain a relatively high percentage of organic matter. In addition, there is a growing belief that evaporites may have a sufficiently high organic content to serve as a hydrocarbon source.

TERRESTRIAL

Dunes, Lakes, Cave Deposits, Soils, Fanglomerates

Carbonate dunes form where there is a source of loose sand, usually landward of a marine setting or on sand cays (figure below). These fine, well-sorted dune sands exhibit large-scale cross beds that are several meters heigh. The dunes commonly have irregular lower contacts and immediately overlie beach deposits with sharp, upper contacts. Root casts and soil horizons may occur. Dunes form long, linear localized deposits. They have not been recognized very often in subsurface studies, probably because they have been eroded by winds during sea level lows or in a few cases have been misinterpreted.
Lakes may be present in fault-block intermontane basins or on delta plains. Here if terrigenous influx is low, carbonates may accumulate in the lakes. Algal heads, pisolites and beach deposits composed of rock rubble or cross-bedded oolite sand typify shoreline sediments of lakes. Lake floor deposits consist of alternating light carbonate laminae and dark organic laminae, although terrigenous clays may replace the carbonate muds. The deposits vary from localized thin sheets of individual lake origin to widespread and complex sequences of beds related to stacked lakes. They can be distinguished from
marine deposits by the lack of marine fauna, presence of tufa, and association with other non-marine sediments. Modern examples include the Dead Sea and Great Salt Lake, and ancient examples include the Eocene Green River Formation of the Uinta Basin and Pennsylvanian-Permian Coal Measures of the Illinois and Appalachian Basins.

Cave deposits include travertines, stalagmites, and stalactites, cave pearls and carbonate sands. These carbonates are precipitated during exposure above sea level as waters supersaturated with respect to calcium carbonate are evaporated and carbon dioxide is released. Other deposits that form during breaks in deposition due to exposure are calcareous soils known as caliches. These soils represent a stage of substrate alteration during exposure in semi-arid Mediterranean climates. They are also termed calcrete or nan. Commonly the soil profile is characterized by thin, irregular to continuous layers and pisolites. Laminated soil zones are difficult to distinguish from algal stromatolites. Soil zones are important to recognize in ancient sequences because they indicate breaks in deposition during which surrounding carbonates may have been exposed to fresh waters and leached.

Fanglomerates are recycled limestone fragments (lithoclasts) usually found on the down-thrown side of faults in arid regions. The deposits are fan-shaped wedges formed of braided stream and sheet-flow deposits. Braided stream deposits exhibit large-scale festoon cross-beds and low-angle coarse planar beds that may show fining-upward grading. Channel-fill deposits within the fan are graded beds that fine upwards and show low-angle cross-beds. The sheet-flow sediments are alternating coarse and fine units with faint grading and some debris-flow boulder layers. Ancient fanglomerates include the Triassic in the Newark Basin and the Tertiary Overton Formation of southern Nevada.

USEFUL REFERENCES

Depositional Environments
Bathurst, RGC, 1975, Carbonate Sediments and their Diagenesis (2nd edn.): Amster dam, Elsevier, 658 p.   Ali Fazeli = egeology.blogfa.com
Milliman, JD, 1974. Marine carbonates. Recent sedimentary carbonates ; pt. 1. Springer, Berlin, Heidelberg, New York, xiv, 375 pp. Ali Fazeli = egeology.blogfa.com
Reading, H. G., 1978, Sedimentary Environments and Facies: Elsevier, 557 p.
Scholle, P. A. and Ulmer-Scholle, D. S, 2003, A Color Guide to the Petrography of Carbonate Rocks: AAPG Memoir 77, 474 p  Ali Fazeli = egeology.blogfa.com
Tucker, ME and Wright, VP, 1990. Carbonate Sedimentology. Blackwell, 482p.
Wilson, J. L., 1975, Carbonate Facies in Geologic Time: New York,Springer-Verlag, 471p.

طبقه بندی کربناتها

CARBONATE CLASSIFICATIONS

 

CLASSIFICATION OF CARBONATES
Rocks are classified in order to communicate information about them. All classifications of limestones are arbitrary and they frequently overlap or do not fit ones particular needs. Since binocular microscopes or hand lenses are the tools that are commonly available to the explorationist, a practical classification should be based on descriptions using them. When these instruments are used, it is usually possible to identify the individual grains forming the rock. Thus most classifications require that the most significant sedimentary particle in the rock be described. For instance, if a rock is composed of ooids, it is termed and oolitic limestone. If the limestone also contains a minor element such as skeletal fragments, then it is called a skeletaloolitic limestone.

Two of the most widely used classifications are those of Folk (1959,1962) and Dunham (1962). Both classifications subdivide limestones primarily on the basis of matrix content.

Most limestones are classified by Folk allochemical rocks if they contain over l0% allochems (transported carbonate grains). Based on the percentage of interstitial material, the rocks may be further subdivided into two groups: sparry allochemical limestones (containing a sparry calcite cement of clear coarsely crystalline mosaic calcite crystals) and microcrystalline allochemical limestone(containing microcrystalline calcite mud, micrite, which is subtranslucent grayish or brownish particles less than about 5 microns in size). Further subdivision is based on the allochem ratios of Folk (1962) are shown in Scholle & Ulmer-Scholle (2003).

Thus Folk's classification (figures above) is most suited for thin section study. Remember that he terms rocks with appreciable matrix as micrites while matrix-free rocks that contain sparry calcite cement are termed sparites. As you can see sparites and micrites are further subdivided by means of their most common grains.

 

In contrast, Dunham's classification (figures above) and its modification by Embry and Klovan (1971) and James (1984) deals with depositional texture. For this reason, his scheme may be better suited for rock descriptions that employ a hand lens or binocular microscope. For example, if the grains of a limestone are touching one another and the sediment contains no mud, then the sediment is called a grainstone. If the carbonate is grain supported but contains a small percentage of mud, then it is known as a packstone. If the sediment is mud supported but contains more than 10 percent grains, then it is known as a wackestone, and if it contains less than 10 percent grains and is mud supported, it is known as a mudstone.

If one compares the two classifications, a rock rich in carbonate mud is termed a micrite by Folk and a mudstone or wackestone by Dunham. Moreover, a rock containing little matrix is termed a sparite by Folk and a grainstone or packstone by Dunham. The wide range of percentage of mud matrix that a carbonate may have and still be termed a packstone by Dunham sometimes reduces the utility of this classification. Embry has modified Dunham's classification and Klovan (1971) to include coarse grained carbonates (above figure). In their revised scheme, a wackestone in which the grains are greater than 2mm in size is termed a floatstone and a coarse grainstone is called a rudstone.

Both terms are extremely useful in description of limestones. Embry and Klovan to more graphically reflect the role that the organisms performed during deposition also modified the boundstone classification of Dunham. Terms such as bafflestone, bindstone, and framestone are useful in concept but are extremely difficult to apply to ancient limestones where diagenesis and sample size limit ones ability to assess an organisms function.

References
Dunham, R. J., 1962, Classification of carbonate rocks according to depositional texture. In: Ham, W. E. (ed.), Classification of carbonate rocks: American Association of Petroleum Geologists Memoir, p. 108-121.  ali fazeli = egeology.blogfa.com
Embry, AF, and Klovan, JE, 1971, A Late Devonian reef tract on Northeastern Banks Island, NWT: Canadian Petroleum Geology Bulletin, v. 19, p. 730-781.
Folk, R.L., 1959, Practical petrographic classification of limestones: American Association of Petroleum Geologists Bulletin, v. 43, p. 1-38.
Folk, R.L., 1962, Spectral subdivision of limestone types, in Ham, W.E., ed., Classification of Carbonate Rocks-A Symposium: American Association of Petroleum Geologists Memoir 1, p. 62-84.  ali fazeli = egeology.blogfa.com
James, N.P., 1984, Shallowing-upward sequences in carbonates, in Walker, R.G., ed., Facies Models: Geological Association of Canada, Geoscience Canada, Reprint Series 1, p. 213–228.
Scholle, P. A. and Ulmer-Scholle, D. S, 2003, A Color Guide to the Petrography of Carbonate Rocks: AAPG Memoir 77, 474 p  ali fazeli = egeology.blogfa.com

مقالات مربوط به سطح آب دریاها

مقالات مربوط به سطح آب دریاها

 

Burton, R., C.G.St.C.Kendall, and I. Lerche, (1987), Out of Our Depth: On the Impossibility of Fathoming Eustasy from the Stratigraphic Record, Earth Science Review, v. 24, p. 237- 277
Cathro, Donna L., James A. Austin Jr., and Graham D. Moss, (2003), Progradation along a deeply submerged Oligocene–Miocene heterozoan carbonate shelf:How sensitive are clinoforms to sea level variations? AAPG Bulletin, v. 87, no. 10, pp. 1547–1574
Guidish, T.M., C.G.St.C.Kendall, I. Lerche and J.J. O'Brien, (l984), Relationship between eustatic level changes and basement subsidence: Am. Assoc. Petroleum Geol. Bull., v. 68, p. l64- l77.
Kendall,C. G.St.C., Moore, P., Whittle, G., and Cannon R.; (1992 ), A challenge : is it possible to determine eustasy and does it matter?, in Dott, R. H., Jr., ed., Eustasy: The Historical Ups and Downs of a Major Geological Concept: Geological Society of America Memoir 180 p93-107.
Kominz, Michelle A., and Stephen F. Pekar, (2001), "Oligocene eustasy from two-dimensional sequence stratigraphic backstripping", Geological Society of America Bulletin, v. 113; no. 3; p. 291–304.
Van Hinte, J. E., (1978), Geohistory analysis-application of micropaleontology in exploration geology: AAPG Bulletin, v. 62, p. 201-222.

چینه شناسی و ایکنولوژی

چینه شناسی و ایکنولوژی

 

Arnott, R. W. C., F. J. Hein and S. G. Pemberton, (1995), Influence of the Ancestral Sweetgrass Arch on Sedimentation of the Lower Cretaceous Bootlegger Member, North-Central Montana, Journal of Sedimentary Research, Section B: Stratigraphy and Global Studies, Vol. 65B, No. 2, Pages 222-234. [Recognition of the structural control on depositional setting recorded by burrowers.]
Bromley, Richard G., Alfred Uchman, Murray R. Gregory and Anthony J. Martin, (2003), Hillichnus lobosensis igen. et isp. nov., a complex trace fossil produced by tellinacean bivalves, Paleocene, Monterey, California, USA, Palaeogeography, Palaeoclimatology, Palaeoecology, Volume 192, Issues 1-4, Pages 157-186. [Details burrowing organisms and their response to the chemical and bacterialogical setting in a deeperwater canyon]
Bromley, Richard G., and Nils-Martin Hanken (2003), Structure and function of large, lobed Zoophycos, Pliocene of Rhodes, Greece; Palaeogeography, Palaeoclimatology, Palaeoecology, Volume 192, Issues 1-4, Pages 79-100. [Suggests importance of oxygen in the sediment and character burrrows.]
Droser, Mary L., Soren Jensen, and James G. Gehling (2002), Trace fossils and substrates of the terminal Proterozoic–Cambrian transition: Implications for the record of early bilaterians and sediment mixing; Proc. Natl. Acad. Sci. vol. 99, no. 20, p12575. [Substrate firmness shown important to preservation of bioturbation in the sediments]
Ekdale, A. A., and Richard G. Bromley (2003), Paleoethologic interpretation of complex Thalassinoides in shallow-marine limestones, Lower Ordovician, southern Sweden, Palaeogeography, Palaeoclimatology, Palaeoecology, Volume 192, Issues 1-4, Pages 221-227. [Subtleties of sedimentary responses to burrowing organisms in limestones!]
Frey, Robert W., and S. George Pemberton (1985), Biogenic Structures in Outcrops and Cores. I. Approaches to Ichnology, Bulletin of Canadian Petroleum Geology, Vol. 33 No. 1, Pages 72-115. [Classic really well illustrated heirarchical atlas of ichnology for the novice & experts!]
Frey, Robert W., and S. George Pemberton, (1987), The Psilonichnus Ichnocoenose, and Its Relationship to Adjacent Marine and Nonmarine Ichnocoenoses along the Georgia Coast, Bulletin of Canadian Petroleum Geology, Vol. 35 No. 3., Pages 333-357. [Use of more detailed ichnology better linked to coastal depositional settings].
Gingras, Murray K., S., Pemberton, G., and Saunders, T., (2001), Bathymetry, sediment texture, and substrate cohesiveness; their impact on modern Glossifungites trace assemblages at Willapa Bay, Washington. Palaeogeography, Palaeoclimatology, Palaeoecology, 169(1-2): 1-21. [Better numbers on constraints on using ichnology to determine depositional setting].
Gingras, Murray K., and S. George Pemberton, (2000), A Field Method for Determining the Firmness of Colonized Sediment Substrates, Journal of Sedimentary Research, Section B: Stratigraphy and Global Studies, Vol. 70, No. 6, Pages 1341-1344.. [Size of indent of hard sphere dropped from fixed height found inversely proportional to media firmness and the colonization of the surface by a variety of burrowers].
Gingras, Murray K., Bryce MacMillan, Bruce J. Balcom, Tom Saunders, and S. George Pemberton, (2002), Using Magnetic Resonance Imaging and Petrographic Techniques to Understand the Textural Attributes and Porosity Distribution in Macaronichnus-Burrowed Sandstone, Journal of Sedimentary Research, Vol. 72, No. 4, Pages 552-558. [Magnetic resonance images used to determine how subtle variations in grain size and porosity effect character and distribution of burrows].
Gingras, Murray K., James A. MacEachern, and S. George Pemberton, (1998), A Comparative Analysis of the Ichnology of Wave- and River-dominated Allomembers of the Upper Cretaceous Dunvegan Formation, Bulletin of Canadian Petroleum Geology, Vol. 46, No. 1, Pages 51-73. [Differentiation of wave versus fluvial depositional setting determined from Ichnology].
Gingras, Murray K., Matti E. Rasanen, S. George Pemberton, and Lidia P. Romero (2002), Ichnology and Sedimentology Reveal Depositional Characteristics of Bay-Margin Parasequences in the Miocene Amazonian Foreland Basin, Journal of Sedimentary Research Vol. 72 Journal of Sedimentary Research Vol. 72, No. 6, Pages 871-883. [The subtleties of depositional setting in stratigraphic sequences determined from Ichnology.]
Gingras, Murray K., S. George Pemberton, and Tom Saunders, (2000), Firmness Profiles Associated with Tidal-Creek Deposits: The Temporal Significance of Glossifungites Assemblages, Journal of Sedimentary Research, Section A: Sedimentary Petrology and Processes, Vol. 70, No. 5, Pages 1017-1025. [The firmness of Pleistocene versus Holocene sediment, setting & the role of grain size in compaction is considered important to the erosion & colonization of surfaces].
Gunatilaka, Ananda, (1976), Thallophytic Boring and Micritization Within Skeletal Sands from Connemara, Western Ireland, Journal of Sedimentary Petrology, Vol. 46 No. 3, Pages 548-554. [Enegmatic surface burrowed & altered by cyanano bacteria during a transgression?].
Hiscott, Richard N., Noel P. James, and S. George Pemberton, (1984), Sedimentology and Ichnology of the Lower Cambrian Bradore Formation, Coastal Labrador: Fluvial to Shallow-Marine Transgressive Sequence, Bulletin of Canadian Petroleum Geology, Vol. 32, No1, Pages 11-26. [Beautiful sedimentologic interpretation of burrowed geologicial section!].
Hubbard, S.M., M.K. Gingras, and S. G. Pemberton, M.B. Thomas, (2002), Variability in Wave-Dominated Estuary Sandstones: Implications on Subsurface Reservoir Development, Bulletin of Canadian Petroleum Geology, Vol. 50 No. 1, Pages 118-137. [Classic sedimentologic interpretation of barrier & estuarine setting in rock record].
Hubbard, S.M., S.G. Pemberton, E.A. Howard, (1999), Regional Geology and Sedimentology of the Basal Cretaceous Peace River Oil Sands Deposit, North-Central Alberta, Bulletin of Canadian Petroleum Geology, Vol. 47 No. 3, Pages 270-297. [This paper illustrates how ichnology is used to determine depositional setting and correlate lithofacies and chronostratigraphic surfaces. Neat stuff if you like rocks!].
Kobluk, David R., S. George Pemberton, Marika Karolyi and Michael J. Risk (1977), The Silurian-Devonian Disconformity in Southern Ontario, Bulletin of Canadian Petroleum Geology Vol. 25, No. 6, Pages 1157-1186. [Ichnology used to decipher character of boundary between the Silurian & Devonian.]
Leszczynski, Stanislaw, Alfred Uchman and Richard G. Bromley (1996), Trace fossils indicating bottom aeration changes: Folusz Limestone, Oligocene, Outer Carpathians, Poland Palaeogeography, Palaeoclimatology, Palaeoecology, Volume 121, Issues 1-2, Pages 79-87. [Ichnology used to determine the evolving character of the depositional setting.]
MacEachern, James A., Brian A. Zaitlin, and S. George Pemberton (3) (1999), A Sharp-Based Sandstone of the Viking Formation, Joffre Field, Alberta, Canada: Criteria for Recognition of Transgressively Incised Shoreface Complexes, Journal of Sedimentary Research, Section B: Stratigraphy and Global Studies, Vol. 69, No. 4, Pages 876-892. [Use of ichnology to identify, interpret & correlate stratigraphic surfaces including a transgressed sequence boundary. Paper shows why ichnostratigraphy is important].
Pemberton, S.G. and MacEachern, J.A. 1995. The sequence stratigraphic significance of trace fossils in examples from the Cretaceous of Alberta. In: Van Wagoner, J.A., and Bertram, G.T. (eds.). Sequence Stratigraphy of Foreland Basin Deposits - Outcrop and Subsurface Examples from the Cretaceous of North America. American Association of Petroleum Geologists Memoir, 64: 429-475. [In this landmark paper the fathers of ichnostratigraphy place their footprints all over the interepretion of sequence stratigraphic surfaces. Beautiful summary diagrams].

مقالات مربوط به چینه شناسی از روی رد پا

مقالات مربوط به چینه شناسی از روی رد پا

Arnott, R. W. C., F. J. Hein and S. G. Pemberton, (1995), Influence of the Ancestral Sweetgrass Arch on Sedimentation of the Lower Cretaceous Bootlegger Member, North-Central Montana, Journal of Sedimentary Research, Section B: Stratigraphy and Global Studies, Vol. 65B, No. 2, Pages 222-234. [Recognition of the structural control on depositional setting recorded by burrowers.]
Bromley, Richard G., Alfred Uchman, Murray R. Gregory and Anthony J. Martin, (2003), Hillichnus lobosensis igen. et isp. nov., a complex trace fossil produced by tellinacean bivalves, Paleocene, Monterey, California, USA, Palaeogeography, Palaeoclimatology, Palaeoecology, Volume 192, Issues 1-4, Pages 157-186. [Details burrowing organisms and their response to the chemical and bacterialogical setting in a deeperwater canyon]
Bromley, Richard G., and Nils-Martin Hanken (2003), Structure and function of large, lobed Zoophycos, Pliocene of Rhodes, Greece; Palaeogeography, Palaeoclimatology, Palaeoecology, Volume 192, Issues 1-4, Pages 79-100. [Suggests importance of oxygen in the sediment and character burrrows.]
Droser, Mary L., Soren Jensen, and James G. Gehling (2002), Trace fossils and substrates of the terminal Proterozoic–Cambrian transition: Implications for the record of early bilaterians and sediment mixing; Proc. Natl. Acad. Sci. vol. 99, no. 20, p12575. [Substrate firmness shown important to preservation of bioturbation in the sediments]
Ekdale, A. A., and Richard G. Bromley (2003), Paleoethologic interpretation of complex Thalassinoides in shallow-marine limestones, Lower Ordovician, southern Sweden, Palaeogeography, Palaeoclimatology, Palaeoecology, Volume 192, Issues 1-4, Pages 221-227. [Subtleties of sedimentary responses to burrowing organisms in limestones!]
Frey, Robert W., and S. George Pemberton (1985), Biogenic Structures in Outcrops and Cores. I. Approaches to Ichnology, Bulletin of Canadian Petroleum Geology, Vol. 33 No. 1, Pages 72-115. [Classic really well illustrated heirarchical atlas of ichnology for the novice & experts!]
Frey, Robert W., and S. George Pemberton, (1987), The Psilonichnus Ichnocoenose, and Its Relationship to Adjacent Marine and Nonmarine Ichnocoenoses along the Georgia Coast, Bulletin of Canadian Petroleum Geology, Vol. 35 No. 3., Pages 333-357. [Use of more detailed ichnology better linked to coastal depositional settings].
Gingras, Murray K., S., Pemberton, G., and Saunders, T., (2001), Bathymetry, sediment texture, and substrate cohesiveness; their impact on modern Glossifungites trace assemblages at Willapa Bay, Washington. Palaeogeography, Palaeoclimatology, Palaeoecology, 169(1-2): 1-21. [Better numbers on constraints on using ichnology to determine depositional setting].
Gingras, Murray K., and S. George Pemberton, (2000), A Field Method for Determining the Firmness of Colonized Sediment Substrates, Journal of Sedimentary Research, Section B: Stratigraphy and Global Studies, Vol. 70, No. 6, Pages 1341-1344.. [Size of indent of hard sphere dropped from fixed height found inversely proportional to media firmness and the colonization of the surface by a variety of burrowers].
Gingras, Murray K., Bryce MacMillan, Bruce J. Balcom, Tom Saunders, and S. George Pemberton, (2002), Using Magnetic Resonance Imaging and Petrographic Techniques to Understand the Textural Attributes and Porosity Distribution in Macaronichnus-Burrowed Sandstone, Journal of Sedimentary Research, Vol. 72, No. 4, Pages 552-558. [Magnetic resonance images used to determine how subtle variations in grain size and porosity effect character and distribution of burrows].
Gingras, Murray K., James A. MacEachern, and S. George Pemberton, (1998), A Comparative Analysis of the Ichnology of Wave- and River-dominated Allomembers of the Upper Cretaceous Dunvegan Formation, Bulletin of Canadian Petroleum Geology, Vol. 46, No. 1, Pages 51-73. [Differentiation of wave versus fluvial depositional setting determined from Ichnology].
Gingras, Murray K., Matti E. Rasanen, S. George Pemberton, and Lidia P. Romero (2002), Ichnology and Sedimentology Reveal Depositional Characteristics of Bay-Margin Parasequences in the Miocene Amazonian Foreland Basin, Journal of Sedimentary Research Vol. 72 Journal of Sedimentary Research Vol. 72, No. 6, Pages 871-883. [The subtleties of depositional setting in stratigraphic sequences determined from Ichnology.]
Gingras, Murray K., S. George Pemberton, and Tom Saunders, (2000), Firmness Profiles Associated with Tidal-Creek Deposits: The Temporal Significance of Glossifungites Assemblages, Journal of Sedimentary Research, Section A: Sedimentary Petrology and Processes, Vol. 70, No. 5, Pages 1017-1025. [The firmness of Pleistocene versus Holocene sediment, setting & the role of grain size in compaction is considered important to the erosion & colonization of surfaces].
Gunatilaka, Ananda, (1976), Thallophytic Boring and Micritization Within Skeletal Sands from Connemara, Western Ireland, Journal of Sedimentary Petrology, Vol. 46 No. 3, Pages 548-554. [Enegmatic surface burrowed & altered by cyanano bacteria during a transgression?].
Hiscott, Richard N., Noel P. James, and S. George Pemberton, (1984), Sedimentology and Ichnology of the Lower Cambrian Bradore Formation, Coastal Labrador: Fluvial to Shallow-Marine Transgressive Sequence, Bulletin of Canadian Petroleum Geology, Vol. 32, No1, Pages 11-26. [Beautiful sedimentologic interpretation of burrowed geologicial section!].
Hubbard, S.M., M.K. Gingras, and S. G. Pemberton, M.B. Thomas, (2002), Variability in Wave-Dominated Estuary Sandstones: Implications on Subsurface Reservoir Development, Bulletin of Canadian Petroleum Geology, Vol. 50 No. 1, Pages 118-137. [Classic sedimentologic interpretation of barrier & estuarine setting in rock record].
Hubbard, S.M., S.G. Pemberton, E.A. Howard, (1999), Regional Geology and Sedimentology of the Basal Cretaceous Peace River Oil Sands Deposit, North-Central Alberta, Bulletin of Canadian Petroleum Geology, Vol. 47 No. 3, Pages 270-297. [This paper illustrates how ichnology is used to determine depositional setting and correlate lithofacies and chronostratigraphic surfaces. Neat stuff if you like rocks!].
Kobluk, David R., S. George Pemberton, Marika Karolyi and Michael J. Risk (1977), The Silurian-Devonian Disconformity in Southern Ontario, Bulletin of Canadian Petroleum Geology Vol. 25, No. 6, Pages 1157-1186. [Ichnology used to decipher character of boundary between the Silurian & Devonian.]
Leszczynski, Stanislaw, Alfred Uchman and Richard G. Bromley (1996), Trace fossils indicating bottom aeration changes: Folusz Limestone, Oligocene, Outer Carpathians, Poland Palaeogeography, Palaeoclimatology, Palaeoecology, Volume 121, Issues 1-2, Pages 79-87. [Ichnology used to determine the evolving character of the depositional setting.]
MacEachern, James A., Brian A. Zaitlin, and S. George Pemberton (3) (1999), A Sharp-Based Sandstone of the Viking Formation, Joffre Field, Alberta, Canada: Criteria for Recognition of Transgressively Incised Shoreface Complexes, Journal of Sedimentary Research, Section B: Stratigraphy and Global Studies, Vol. 69, No. 4, Pages 876-892. [Use of ichnology to identify, interpret & correlate stratigraphic surfaces including a transgressed sequence boundary. Paper shows why ichnostratigraphy is important].
Pemberton, S.G. and MacEachern, J.A. 1995. The sequence stratigraphic significance of trace fossils in examples from the Cretaceous of Alberta. In: Van Wagoner, J.A., and Bertram, G.T. (eds.). Sequence Stratigraphy of Foreland Basin Deposits - Outcrop and Subsurface Examples from the Cretaceous of North America. American Association of Petroleum Geologists Memoir, 64: 429-475. [In this landmark paper the fathers of ichnostratigraphy place their footprints all over the interepretion of sequence stratigraphic surfaces. Beautiful summary diagrams].
Zonnevelda, J. -P., M.K. Gingras, and S.G. Pemberton, (2001), Trace fossil assemblages in a Middle Triassic mixed siliciclasticcarbonate marginal marine depositional system, British Columbia, Palaeogeography, Palaeoclimatology, Palaeoecology, 166, 249–276. [Match of ichnofacies to shoreline and nearby aeolian belt like modern UAE.]

مقالات مربوط به سیستم های عمیق دریایی

مقالات مربوط به سیستم های عمیق دریایی L. Droz, T. Marsset, H. Ondréas, M. Lopez, B. Savoye, and F.-L. Spy-Anderson, (2003), Architecture of an active mud-rich turbidite system: The Zaire Fan (Congo–Angola margin southeast Atlantic): Results from Zai¨Ango 1 and 2 cruises, AAPG Bulletin, v. 87, no. 7, pp. 1145–1168
Henry W. Posamentier & Venkatarathnan Kolla, (2003), Seismic Geomorphology and Stratigraphy of Depositional Elements in Deep-Water Settings, Journal Of Sedimentary Research, vol. 73, no. 3, p. 367–388
Shanmugam, G., 2006, The Tsunamite Problem, Journal of Sedimentary Research, 2006, V. 76, 718–730

مقالات مربوط به چینه شناسی و رسوب شناسی صخره ای

Dubiel, Russell F., Summary of Geology and Coal Resources of the Blackhawk Formation in the Southern Wasatch Plateau, Central Utah U.S. Geological Survey Professional Paper 1625–B, Assessment, Chapter K of Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah Edited by M.A.
Gary J., Hampson, John A. Howell, and Stephen S. Flint, (1999), A Sedimentological and Sequence Stratigraphic Re-Interpretation of the Upper Cretaceous Prairie Canyon Member ("Mancos B") and Associated Strata, Book Cliffs Area, Utah, U.S.A, Journal of Sedimentary Research, Section B: Stratigraphy and Global Studies, Vol. 69, No. 2, Pages 414-433
Johnson, Ronald C., Northwest to Southeast Cross Section of Cretaceous and Lower Tertiary Rocks Across the Eastern Part of the Uinta Basin, Utah, Chapter 11 of Petroleum Systems and Geologic Assessment of Oil and Gas in the Uinta-Piceance Province, Utah and Colorado, By USGS Uinta-Piceance Assessment Team, U.S. Geological Survey Digital Data Series DDS–69–B Paper
Kirschbaum, Mark A. and Robert D. Hettinger, (2002), "Variations in System Tract Architecture and Accomodation Space in Upper Campanian Strata, Eastern Book Cliffs, CO and UT", U.S. Geological Survey, Denver CO, 80225, USGS Poster.
Johnson, Ronald C., Northwest to Southeast Cross Section of Cretaceous and Lower Tertiary Rocks Across the Eastern Part of the Uinta Basin, Utah, Chapter 11 of Petroleum Systems and Geologic Assessment of Oil and Gas in the Uinta-Piceance Province, Utah and Colorado, By USGS Uinta-Piceance Assessment Team, U.S. Geological Survey Digital Data Series DDS–69–B, "PLATE of Cross Section"
Mellere, Donatella, (1994), Sequential Development of an Valley Fill: the Two wells Tongue of the Dakota Sandstone, Acoma Basin, New Mexico, Journal of Sedimentary Research , V 64, n,4 500-515
Miall, Andrew D., and Mohamud Arush, (2001), The Castlegate Sandstone of the Book Cliffs, Utah: Sequence Stratigraphy, Paleogeography, and Tectonic Controls, Journal of Sedimentary Research, Section B: Stratigraphy and Global Studies, Vol. 71, No. 4, Pages 537-548
Pattison, S.A.J., (1995), Sequence stratigraphic significance of sharp-based lowstand shoreface deposits, Kenilworth Member, Book Cliffs, Utah. American Association Petroleum Geologists Bulletin, v.79, p.444-462.
Van Wagoner, J.C., and G.T. Bertram, (1995), Sequence Stratigraphy and Marine to Nonmarine Facies Architecture of Foreland Basin Strata, Book Cliffs, Utah, U.S.A. American Association Petroleum Geologists Memoir 64: Sequence Stratigraphy of Foreland Basin Deposits; Pages 137 - 223
Yoshida,S., (2000), Sequence and facies architecture of the upper Blackhawk Formation and the Lower Castlegate Sandstone (Upper Cretaceous), Book Cliffs, Utah, USA Sedimentary Geology 136 239–276

مقالات مربوط به تفسیر چینه شناسی حوضه های رسوبی

 

مقالات مربوط به تفسیر چینه شناسی حوضه های رسوبی

Busch, Daniel A., (1974), Channel Sandstones; Stratigraphic Traps in Sandstones--Exploration Techniques, Memoir 21, Pages 72 - 107 [Clear expostion of the potential of channel sandstones as hydrocarbon traps.]
Busch, Daniel A., (1974), Ancient Examples of Beach Sandstones; Stratigraphic Traps in Sandstones--Exploration Techniques, Memoir 21, Pages: 48 - 71 [Clear expostion of the potential of channel sandstones as hydrocarbon traps.]
Cheong, Dae-Kyo, Kendall,C. G.St.C., Stoudt, David L., & Bowen, Bruce E.; (1992), Analysis of Jurassic Marine sedimentary sequence and hydrocarbon occurence in the U.S.Gulf Coast Basin; Ocean Research, v.14, n.2 , p.89-109. [An example of the sequence strtatigraphy and the evaluation of the potential for the Jurassic section to produce hydrocarbons.]
Collister, James, Robert Ehrlich, Frank Mango, and Glenn Johnson (2004), Modification of the petroleum system concept: Origins of alkanes and isoprenoids in crude oils AAPG Bulletin, v. 88, no. 5 pp. 587–611 [Establish that the source of petroleum was once dispersed through mcuh of the sedimentary sections and not neccessarily from classic organic rich source rocks.]
Guidish, T. M., C.G.St.C.Kendall, I. Lerche, D.J. Toth and R.F. Yarzab, (l985), Basin evaluation from burial history calculations: an overview: Am. Assoc. Petroleum Geol. Bull., v. 69 p. 92- l05. [Using burial history to determine the thermal history of a basin using subsidence behaviour.]
Kingston DR, Dishroon CP and Williams PA (1983) - Global Basin Classification System. American Association of Petroleum Geologists Bulletin, 67, 2175-2193 [Classic but dated way to classify a sedimentary basin. However in conjucntion with base level change this serves as a useful template for basin desciprition and history.]
Langhorne B. Smith, Gregor P. Eberli,Jose Luis Masaferro, and Salah Al-Dhahab, (2003), Discrimination of effective from ineffective porosity in heterogeneous Cretaceous carbonates, Al Ghubar field, Oman, Am. Assoc. Petroleum Geol. Bull., v. 87, no.9, pp. 1509–1529 [Determining carbonate porosity from their acoustic properties using logs and seismic].
Lerche, I., R.F. Yarzab and C.G.St.C.Kendall, (l984), Determination of paleoheatflux from vitrinite reflectance data: Am. Assoc. Petroleum Geol. Bull., v. 68, p. l704-l7l7. [Using vitrinite reflectance to determine the thermal history of a basin.]
Peters, K. E. , J. W. Snedden, A. Sulaeman, J. F. Sarg, and R. J. Enrico (2000), A New Geochemical-Sequence Stratigraphic Model for the Mahakam Delta and Makassar Slope,Kalimantan, Indonesia, AAPG Bulletin, V. 84, No.1, P. 12–44.
Rafavich, F., C.G.St.C.Kendall, and T.P. Todd, (l984), The relationship between acoustic properties and the petrographic character of carbonate rocks: Geophysics, v. 49, p. l622-l636. [Using the acoustic properties to determine carbonate porosity and lithology from logs and seismic].
Sclater, J.G., and Christie, P.A.F., 1980, Contintal stretching: an explanation of the post-mid Cretaceous subsidence of the Central North Sea Basin: JGR, v. 85, p. 3711-3739 [Appendix A, p. 3730-3735 [ The classic backstripping approach to thermal history....a landmark paper].
Suppe, J., 1985, Principles of Structural Geology: Prentice-Hall, Inc. Chapter 1 (p. 17-24). [A great isostasy exercise for a class].
Van Hinte, J. E., (1976a), A Jurassic time scale: AAPG Bulletin, v. 60, p. 489-497. [Simple but effective methodology outlined to put numerical ages on your sediments].
Van Hinte, J. E., (1976b), A Cretaceous time scale: AAPG Bulletin, v. 60, p. 498-516. [The same effective methodology outlined to put numerical ages on your sediments].
Van Hinte, J. E., (1978), Geohistory analysis-application of micropaleontology in exploration geology: AAPG Bulletin, v. 62, p. 201-222. [Methodology outlined to establish the numerical ages of your sediments].