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In many regions, Oligocene was a time of beginning of the neotectonic epoch, i.e. acceleation of vertical movements, resulted in recent mountain topography. This is manifested in Central Asia which is the region of collision of the Indian and Eurasian plates. The Oligocene molassa is exposed in lateral parts of recent foredeeps and intermountain basins of Central Tien Shan. The molassa is composed by sandstones, gravels and small-pebble conglomerates which consist of material eroded on the adjacent recent ridges and are replaced in the central parts of the basins by finer grained deposits. The previous Paleogene platform sedimentation was controlled by other tectonic zonation. It means that recent orogenic structures (ridges and basins) were originated in Oligocene as a system of relatively low-contrast uplifts and depressions. The Oligocene origin of recent orogenic structures is proved also for the Himalayas, Pamirs, Altai and other mountains of Central Asia. Their Neogene tectonic evolution was different. In the Tien Shan, Oligocene uplifts were to some degree eroded and they were transformed and rebuilt by large lateral movements in the Pamirs and Himalayas, but everythere quick acceleration of vertical movements took place in Pliocene-Quaternary and the younger structures inherited the Oligocene features in general. The same tendency is found in the Ural intraplate mountains. In the Alps and Carpathians, the main features of future orogenic structures were formed also in Oligocene. In the Caucasus - Near East region of the Arabian-Eurasian collision, Oligocene was characterized by development of the Aden-Red Sea graben (future rift) system. But to the north of the Arabian plate, Oligocene sections demonstrate the regression stage of the Paleogene sedimentary cycle which preceded the Neogene orogeny in the region. In the west of North America, the Oligocene geodynamic processes preceded origination in the Miocene of the San Andreas Fault system controlling the orogenic structures of the region. So, Oligocene was the turning point when the recent features of mountain systems were originated or their ground was formed. Oligocene was the beginning of neotectonic epoch which is characterized by acceleration of vertical movements and increase of relief contrasts. Their manifestations depended only partly or did not depend on local plate tectonic interaction. Such epochs continued for several ten million years and repeated regularly in the Phanerozoic history.
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