Abstract

The productive complex of the Priobskoe field formed during the Hauterivian in the central part of the West Siberian basin as part of the Neocomian (Early Cretaceous) progradational complex. Its depositional setting was a shelf-break margin with well-developed clinoform units and a 1-2 degrees slope gradient. Two depositional sequences have been identified and consist of distinct systems tracts. The lowstand systems tract of the lower sequence (AC12.2-4) formed as a result of rapid high-amplitude relative sea level fall, and is clearly differentiated into lowstand fan and lowstand prograding wedge deposits. Sea level fall of lower amplitude (and rate) led to deposition of a lowstand systems tract in the upper sequence (AC10.1-2) in which no lowstand fan unit was deposited. A thin transgressive systems tract of the lower sequence (AC11.0) formed during a short-term sea level rise. In contrast, prolonged high-amplitude sea level rise led to deposition of a thick transgressive deposit in the upper sequence (AC10.0-AC8). Deposition of the sandiest units is related to shelf (shoal-water) deltas and shelf-edge deltas on the shelf, and to submarine fans in basinal portions. Deposition of shelf-edge deltas was accompanied by abundant gravity-driven processes and formation of shingled turbidites, during which the basin margin significantly prograded and infilled accommodation space. In many cases, sediment supply into the deep-marine systems of Priobskoe was provided from multiple feeder entry points that led to coalescence of individual submarine fans into thick submarine ramps. Because it is based on copious drilling and seismic data, the sequence stratigraphic framework developed for the Priobskoe field may serve as a useful analog model for exploration and prospect generation in Hauterivian clinoforms, as well as in the entire West Siberian Neocomian. There is good correspondence between the relative sea level change interpreted for Priobskoe to the quantified eustatic curve (QEC) generated from Russian platform stratigraphy. This implies that eustasy played an important role in controlling sedimentation in the Priobskoe field. In addition, it supports the validity for the Hauterivian interval of the QEC.

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