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Abstract: Tectonic and Sedimentary Evolution During the Compressive Phases in Southern Ural (Devonian to Tertiary)

Jean Paul Richert, Herbert Eichenseer, Pierre Gruneisen

The main compressive tectonic phases and their sedimentary response have been studied by Elf Aquitaine in cooperation with ZAPKAZGEOLOGIA (Aktyubinsk-Kazakhstan).

The main results of this field study indicate a progressive westward migration of the main depocenters in relation to "in sequence" thrusting for the period from the Late Devonian to the Permian.

The closure of the Uralian ocean begins during the Early Devonian with a change from basic to acid volcanism. This evolution suggests a period of subduction followed by the obduction of the Kazakh Plate over the Russian Plate during the Late Devonian.This major episode of plate convergence produces folds and cleavages of a northeastern orientation (Emba Trend) and leads to the deposition of volcanoclastic megabreccias and tectonic melanges.

The Early to Mid Carboniferous corresponds to a period of tectonic quiescence. The margins of the West Uralian basin are covered by shallow marine carbonate platforms. The basin contains mainly moderately deep water radiolarites and siliceous marls.

From the Late Carboniferous to Mid Permian, successive phases of thin-skinned thrusting create a major north-south orientated foreland basin. The rising mountain range sheds alluvial clastics and turbidites towards westwards into this sedimentary trough.

The main thrusts are sealed by the "Kungurian" salt deposits of the Mid Permian linked to the opening of the Precaspian basin.

Post salt deformations are represented by blind thrusts which increasingly affect the foreland area.

Weak post Cretaceous reactivation of the Uralian suture (Main Uralian Fault) consists of right lateral wrenching.

AAPG Search and Discovery Article #90956©1995 AAPG International Convention and Exposition Meeting, Nice, France