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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 North Atlantic and North Pacific. Indeed, the great diversification on land and in the sea of birds and, particularly, mammals has led to the informal designation of the Tertiary as the Age of Mammals (Fig. 1) in textbooks on historical geology. Fig. 1 Baluchitherium, the largest land mammal known, from the Tertiary (Oligocene Epoch) of Asia. It was 18 ft (5.4 m) high at the shoulders. (After R. A. Stirton, Time, Life and Man, Wiley, 1959) 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, Lake Baikal and the Caspian Sea) are remnants of once more extensive widespread epeiric (shallow) seaways of the early Tertiary. 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 North America. See also: Cordilleran belt; Mountain systems; Orogeny; Plate tectonics 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 Asia). Major Tertiary volcanic provinces include those of the Deccan region of India, the basaltic plateaus of Greenland and Iceland, and the Columbia Plateau of the northwest United States. 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 Paris Basin. See also: Cenozoic; Eocene; Holocene; Miocene; Oligocene; Paleobotany; Paleocene; Paleontology; Pleistocene; Pliocene; Stratigraphy 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 B. M. Funnell and W. R. Riedel, The Micropaleontology of Oceans, 1971 S. J. Gould, Time's Arrow, Time's Cycle, 1987 H. L. Levin, The Earth Through Time, 7th ed., 2003