Oleg V. Pinous¹, Mikhail A. Levchuk², Dork L. Sahagian³
(1) University of New Hampshire, Durham, NH
(2) Institute of Oil and Gas Geology, Novosibirsk, Russia
(3) Univ. of New Hampshire, Durham, NH

Abstract: Neocomian sequence stratigraphy of West Siberia: regional framework

The Neocomian complex is the largest oil-producing unit of West Siberia that remains a major target for exploration. A first regional sequence stratigraphic framework for this interval was constructed for the central West Siberia. The Neocomian marine complex in the study area consists of the west-dipping clinoforms that are overlain by the topset package. Nineteen depositional sequences have been identified to comprise the section. A revision of 10 regional seismic lines has made it possible to map a large-scale spatial distribution of sequences and depositional systems on the area over 125,000 km2. Analysis of more than 400 well logs led to construction of 5 dip-oriented transects that revealed detailed features of the stratigraphic architecture and depositional history of the Neocomian section. A reliable chronostratigraphic framework for our sequence interpretation was developed through a revision of ammonite and bivalve biostratigraphy.

The main factors controlling deposition of the West Siberian Neocomian include: high sediment supply rates, slow subsidence, and frequent base-level oscillations. Progradation of the clinoforms occurred through lateral shelf outbuilding during lowstand periods when sandstone units accumulated in shallow marine systems and shelf-edge deltas at the shelf-break zone and in submarine fans in basinal parts. Periods of progradation were frequently interrupted by regional transgressions with significant retreat of depocenters landward over the shelf (up to 200 km). The topset package consists of a thick stack of various shallow marine to continental strata. Lowstand systems tracts on the shelf often contain channel sandstone units that are incised into underlying highstand deposits.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana