Abstract: Late Jurassic Paleogeography and Tectonics of the Scythian Plate

ILINA V.V

The analysis of Late Jurassic evolution of the Scythian Platform on the base of junction and comparison of more than 200 wells was made in 1994-1996. The lithologic-paleogeographic maps were compiled for Early-Middle Callovian, Late Callovian-Early Kimmeridgian and Late Kimmeridgian-Tithonian stages. The modeling of subsidence history and sedimentation was made for all 200 boreholes.

The subsidence curves and lithologic-paleogeographic maps shows the substantial reconstructions of regional structures, landscape and climatic environment in Late Callovian and Middle Kimmeridgian. They provided deposition of reservoir carbonate formations and overlapping screening sequences.

Southern margin of the Scythian Plate was involved in subsidence in Early-Middle Callovian after pre-Callovian orogeny. Terrigenous sedimentation took place in humid climate. Late Callovian-Early Kimmeridgian was the time of increasing subsidence, transgression to the North. Carbonate sedimentation changed the terrigenous one in conditions of aridization and formation of barrier reefs along the southern Platform margin. Being overlapped by the younger sequences, on the depth of 5 - 6 km, reef massifs became good hydrocarbon traps.

In Late Kimmeridgian the most active subsidence concentrated in the inner part of the Platform, where the evaporitic basins originated. They were bordered from open part of marine basin by a morphological barrier in the zone of Oxford-Kimmeridgian reefs, some of which followed inherited reef construction. The evaporitic formations in following stages became the regional volatile-screening horizon and promoted origination of excess pressure zones.

AAPG Search and Discovery Article #90942©1997 AAPG International Conference and Exhibition, Vienna, Austria