Neogene Period

Neogene Period, younger of two geological periods comprising the Cenozoic Era (formerly Cainozoic), the last of the three eras making up the Phanerozoic Eon of the geological timescale. It is preceded by the Palaeogene Period. The Neogene Period extends from about 23 million years ago to the present day and is divided into four epochs: Miocene (23 to 5.3 million years ago), Pliocene (5.3 to 1.8 million years ago), Pleistocene (1.8 million to 11,500 years ago), and Holocene (11,500 to the present day). Sedimentary deposits of Neogene age are widely distributed around the globe. Marine deposits are found on the passive margins of all continents, in Europe, the Middle East, North Africa, eastern United States, the Atlantic coasts of Central America and northern and southern South America, and southern Australia, often occupying the same basins as underlying Palaeogene rocks. A continued fall in global sea levels over the past 100 million years has, however, resulted in generally smaller onshore depositional basins than those of the preceding Palaeogene.

Throughout the Neogene Antarctica remained stationary over the South Pole but all other continents continued their northward movements, resulting in increasing fragmentation of land masses, division of oceans, and increased latitudinal temperature differences. As a result, many organisms, both marine and terrestrial, developed steadily more provincial distributions, for example, many angiosperms (flowering plants) became latitudinally segregated into the distinct floral provinces seen today and the latitudinal ranges of marine molluscs became narrower.

The youngest of today’s major mountain chains include the Rocky Mountains of western United States, which were initiated during the Late Miocene to Pliocene by uplift of the whole region, and the Andes chain that was rapidly uplifted during the Neogene following subduction of the Pacific Plate beneath the South American Plate (see Orogeny; Plate Tectonics). Thick non-marine deposits were laid down at the foot of the Andes, including massive freshwater deposits in the region of the Amazon. Uplift of the Himalaya and the Tibetan Plateau accelerated through the Neogene following its initiation in the Eocene Epoch. Extensive volcanism continued through the Neogene, in the circum-Pacific “Ring of Fire”, Central America, and north-western United States and Canada.

The collision of Africa and Eurasia in the region of Iran in the Early Miocene finally divided and closed the Tethyan seaway and only sporadic connections between the Indian Ocean and the western arm occurred through the Mid Miocene. The western portion of Tethys evolved into the present-day Mediterranean Sea. Following closure of its western portal in the Late Miocene, a rapid (0.5 million years duration) dessication (drying up) of this basin occurred (the Messinian Salinity Crisis), with consequent deposition of evaporites up to 3 km (1• mi)in thickness. This arid interval ended when the Straits of Gibraltar opened and the Mediterranean became flooded with seawater during the Early Pliocene. The present-day Mediterranean is geologically younger (Pleistocene) and formed when the Gibraltar sill was uplifted and so prevented ingress of deep Atlantic bottom waters. From Mid Miocene onwards the north-eastern margin of the Mediterranean became more or less isolated and formed a vast inland sea (the Paratethys) stretching 4,500 km (2,800 mi) across central Eurasia. This gradually became freshwater and is today represented by the Aral, Black, and Caspian Seas in the former Soviet Union.