Sedimentary basins of the Tethys and Arctic Ocean: the analysis of their deep structure

Abstract

The deep structure of the South Caspian Basin and South Kara Basin with different geodynamic regimes was studied.

The South Caspian Basin consists of a thick sequence of sediments reaching 30 km. Thickness of the Pliocene - Quaternary sediments is about 10 km. Below there are clay rocks of Miocene and Oligocene, which are associated with the roots of mud volcanoes. The thickness of the crust is 10-20 km. The intensive subsidence of the South Caspian basin began in the Oligocene with the accumulation of sand and clay sediments over 10 km thick. In the Late Miocene, because of the “Messinian Salinity Crisis” (when the Mediterranean Sea had lost touch with the ocean) the level of the Caspian Sea has dropped dramatically. The Caspian Sea again was formed during the Pliocene, when the Strait of Gibraltar finally reopened. At that time the process of subsidence increased steeply, and as a result, over 5 million years more than 10 km of sediments were accumulated in some areas of the sea. The boundary Moho under the basin is at a depth of about 35 - 40 km. Asthenospheric diapir is located under the South Caspian Basin at a depth of 40-60 km. The South Caspian Basin is probably a flow of mantle material traced on the surface - a hot spot, where under the influence of asthenospheric fluids the continental crust of the South Caspian Basin was transformed into oceanic crust.

The South Kara Basin is located on the continental shelf of the Arctic Ocean. Its formation is associated with the development of the West Siberian Plain, as well as with the formation of the Arctic Ocean in the Mesozoic era. The boundary Moho is located at a depth of 43 km. The maximum thickness of the sedimentary layer reaches 12 -15km. The South Kara Basin represents a continuation of the West Siberian Plain, at the base of which the rift system of Late Permian-Early Triassic age is located. The eruption of basaltic magma in the South Kara Basin was expected to be in the early stages of rifting as in the West Siberian Plain, where basalts of trap formation associated with asthenospheric diapirs were drilled. The basement of South Kara basin composed of Paleozoic rocks. The Triassic sediments are composed of coastal marine rocks. In the Kara Sea sedimentation in the Early-Middle Jurassic time occurred in a shallow marine basin. The transgression of sea tends to peaks in the end of the Jurassic. At this time, the South Kara Basin was isolated due to the formation of the Amerasia and Eurasia Basins of the Arctic Ocean. In the Cretaceous the accumulation of interbedded sandstones, siltstones and shales was continued.

South Caspian Basin and the South Kara Basin formed at different geodynamic regimes. However, the formation of rifts and eruption of basalts is common for the initial stage of development of these basins.

AAPG Datapages/Search and Discovery Article #90226 © 2015 European Regional Conference and Exhibition, Lisbon, Portugal, May 18-19, 2015