Hydrothermal-metasomatic processes in Santonian (Upper Cretaceous) argillaceous opoka in Western Siberia north
In the Jurassic-Paleogene section of Western Siberia, along with the predominant intervals of terrigenous sedimentary rocks (allochtonous; Middle Jurassic, Neocomian deposits, etc.), there are thin horizons of biogenic-chemogenic type of sedimentation (autochthonous; Bazhen, Slavgorodsky, Lyulinvorsky horizons) are identified. The results of integrated analysis of huge amount of geological and geophysical materials (seismic, well logging, and core data) made possible more detailed representation of the Upper Cretaceous depositional environments and settings; at the same time, four seismic sequences (from bottom to top) were identified in the Upper Cretaceous part of the section, they are: Kuznetsovsky (Turonian - Lower Coniacian), Nizhneberezovsky (Middle Coniacian - Santonian), Verkhneberezovsky (Campanian), and Gan’kinsky (Upper Campanian - Maastrichtian). More sub-divisions (packages, horizons or stratigraphic units) are identified and characterised in sufficient detail within the seismic sequences on the basis of core data and logging materials. The authors present a brief characteristic of argillaceous opoka of НБ1 package that occurs at the Nizhneberezovsky member Top; they describe certain features of relatively intensive hydrothermal-metasomatic processes (micaceous quartzite with cone-in-cone structure), which locally altered the primary sedimentary chemogenic rocks