Литосфера (Jun 2015)
Features of the black shale Bazhenovo Formation on the transition from Jurassic to Cretaceous in the central part of the Western Siberia
Abstract
A detailed study of the lithological sections of the Upper Jurassic-Lower Cretaceous black shale Bazhenovo Formation was made in the central part of the West Siberian geosyneclise (Salym and surrounding regions). In the most of the studied sections it is observed the following upward sequence of rocks: siliceous-clayey rocks-radiolarian cherts-microcrystalline cherts-mixtites (calcite, quartz, clay with organic matter about 15-20% each)-argillites. Clastic input shows the regular pattern up the section following the sea level evolution (high stand systems tracts). The most favorable period for the accumulation of organic matter (OM) was the late stage of high sea level stand (LHST1). In the present study, in the Western Siberia during transition from Jurassic to Cretaceous stages it is observed: a. abnormally high uranium content (the maximum for the section of the Formation); b. change of biogenic siliceous sedimentation to the siliceous-carbonate one. This change in sedimentation during this period was also recorded in the Tethyan belt, and is associated with the global restructuring of the geochemical conditions in the oceanic waters of the northern hemisphere in the J/K boundary.
