An aborted Triassic Ocean in west Siberia

Abstract

A small buried oceanic basin named the Obsky paleo‐ocean has been found in West Siberia. It developed from 235 to 218 m.y. during the Triassic by rift propagation and seafloor spreading inside the west Siberian region of the continent. During the postspreading period the Obsky paleo‐ocean did not collapse but instead was covered intact by a layer of sediments with a thickness of up to 15 km. This conclusion is based on detailed interpretation of geophysical and geological data. Striped magnetic anomalies marking the paleo‐ocean spreading have been separated from the total magnetic field. They have been dated and interpreted within the framework of the Vine‐Matthews concept. Seismic and gravitational data have permitted delineation of the Obsky paleo‐ocean depression and contouring of the basement relief within its bounds. Investigation of the Obsky paleo‐ocean basalts by means of deep boreholes has indicated that they are chemically similar to oceanic tholeiites and has also confirmed the presence of strong residual magnetism in them. Spreading of the Obsky paleo‐ocean was a stage in the initial disintegration of Pangea at the Paleozoic‐Mesozoic boundary. The presence of a north trending buried spreading center along the axial zone of West Siberia accounts for many features of the Mesozoic‐Cenozoic history of the region and its present‐day structure.