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Tertiary
The older major
subdivision (period) of the Cenozoic Era, extending from the Cretaceous (top of
the Mesozoic Era) to the beginning of the Quaternary (younger Cenozoic Period).
The term Tertiary corresponds to all the rocks and fossils formed during this
period. Although the International Commission on Stratigraphy uses the terms
Paleogene and Neogene (pre-Quaternary part) instead, Tertiary is still widely
used in the geologic literature. Typical sedimentary rocks include widespread
limestones, sandstones, mudstones, marls, and conglomerates deposited in both
marine and terrestrial environments; igneous rocks include extrusive and
intrusive volcanics as well as rocks formed deep in the Earth's crust
(plutonic). See also: Cretaceous;
Fossil; Rock
The Tertiary
Period is characterized by a rapid expansion and diversification of marine and
terrestrial life. In the marine realm, a major radiation of oceanic
microplankton occurred following the terminal Cretaceous extinction events. This
had its counterpart on land in the rapid diversification of multituberculates,
marsupials, and insectivores—holdovers from the Mesozoic—and primates, rodents,
and carnivores, among others, in the ecologic space vacated by the demise of the
dinosaurs and other terrestrial forms. Shrubs and grasses and other flowering
plants diversified in the middle Tertiary, as did marine mammals such as
cetaceans (whales), which returned to the sea in the Eocene Epoch. The pinnipeds
(walruses, sea lions, and seals) are derived from land carnivores, or fissipeds,
and originated in the Neogene temperate waters of the
Fig. 1 Baluchitherium, the largest land mammal
known, from the Tertiary (Oligocene Epoch) of
Geography
The modern
configuration of continents and oceans developed during the Cenozoic Era as a
result of the continuing process known as plate tectonics. Mountain-building
events (orogenies) and uplifts of large segments of the Earth's crust
(epeirogenies) alternated with fluctuating transgressions and regressions of the
seas over land. This resulted in a complex alternation of marine and terrestrial
sediments and their contained records of the passage of life (fossils). Some
modern inland seas (for example,
The middle to
late Tertiary Alpine-Himalayan orogeny and the late Tertiary Cascadian orogeny
led to the east-west and north-south mountain ranges, respectively, which are
located in Eurasia and western
Rocks
Tertiary
sedimentary rocks occur as a relatively thin veneer of marine rocks on the
margins of continents around the world. In the petroliferous province of the
Gulf of Mexico, Tertiary rocks attain thicknesses in excess of 30,000–40,000
(9000–12,000 m); whereas in the more tectonically active borderlands around the
Pacific Ocean, such as the Santa Barbara–Ventura Basin of California, and the
flanks of the uplifted Himalayan-Alpine chain of Eurasia, thicknesses in excess
of 50,000 ft (15,000 m) have been recorded. Terrestrial (nonmarine) strata are
generally thinner, are more patchy in distribution, and occur predominantly in
the internal basins of the continents (for example, the Basin and Range Province
of North America and the Tarim Depression of
Stratigraphy and
history
Although the
ancient Greeks recognized the shells of mollusks far inland from the Aegean Sea
as fossil marine organisms, as did Leonardo da Vinci some 2000 years later, it
was not until the era of enlightenment in the eighteenth century that the first
attempt was made to place the Earth's rock record into a historical context. The
term Tertiary is derived from Giovanni Arduino, who in 1759 formulated a
threefold subdivision of the Earth's rock record in Primary, Secondary, and
Tertiary. While the first two terms have long since disappeared from geologic
hagiography, the term Tertiary persists in modern scientific literature. In its
more modern sense the term Tertiary is defined by its usage in 1810 by the
French Scientists Alexandre Brogniart and Georges Cuvier for all the rock
formations in the Paris Basin that lay above the Cretaceous chalk sequence.
Although many subdivisions of the Tertiary exist that developed in the
succeeding two centuries, only five major time-rock units generally are
recognized. In 1833, Charles Lyell made the first systematic hierarchical
subdivision of the Tertiary Period based upon the observations of his Parisian
colleague M. Deshayes and other contemporary European conchologists that the
percentages of living species in the fossil record increased as the Tertiary
stratigraphic record ascended (Fig. 2). Lyell's Tertiary subdivisions include,
in ascending order, the Eocene, Miocene, Older Pliocene, and Newer Pliocene. The
last term was subsequently (1839) changed to Pleistocene. Heinrich Ernst von
Beyrich later defined the term Oligocene for rocks exposed in the North German
Basin and the Rhine Basin that had been previously allocated to a part of either
the Eocene or Miocene by Lyell. The paleobotanist W. P. Schimper added the term
Paleocene in 1874 based on the oldest Tertiary terrestrial strata exposed in the
east
W. A. Berggren
Fig. 2 Mollusk fossils used by Lyell to zone
the Tertiary. (a) Miocene. (b) Eocene. (After C. Lyell, Principles of Geology,
1833)
Bibliography
-
R. H. Dott, Jr., and D. R. Prothero, Evolution of the Earth, 7th ed., 2003
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B. M. Funnell and W. R. Riedel, The Micropaleontology of Oceans, 1971
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S. J. Gould, Time's Arrow, Time's Cycle, 1987
-
H. L. Levin, The Earth Through Time, 7th ed., 2003
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