Oil and Gas Prospects of Paleozoic Deposits of the Eastern Flank of the North Barents Depression
Sergey Pavlov, Valentina Shlykova, and B. Grigorieva
JSC Arctic Marine Geological Expedition (MAGE), Murmanks, Russia.
Analysis of new geological and geophysical information acquired by MAGE in 2006-2008 allows supposing that Late Devonian to Middle Permian sedimentation conditions within the Prednovozemelskaya structural area (except for Admiralty megaswell) and West Fobos trough were essentially different from those of the North Barents Basin. In Prednovozemelskaya structural area, the Upper Devonian to Middle Permian deposits form two thick fans filling up Sedov trough (total thickness 4.5 km) in the south and West Fobos trough (total thickness up to 8 km) in the north. Growth of the fans reflects development of a progradational shelf margin and postdates formation of a regional seismic unconformity III2 suggested to be of Pre-Frasnian age. Another prominent seismic unconformity identified in the top of the fans is considered to represent a Late Permian heterochronous surface. In the North Barents Basin coeval sediments can be represented by deep-water facies of outer continental margin.
In the area of Admiralty megaswell which wasn't affected by avalanche sedimentation, the seismic facies vary from Late Devonian - Early Permian shallow carbonate to Middle-Upper Permian deep-water clastics.
Five sedimentation cycles were identified within these thick sedimentary prisms reflecting main stages of the progradation: Upper Devonian, Lower Carboniferous, Middle Carboniferous, Carboniferous to Lower Permian, Middle-Upper Permian. The shelf progradation was sourced from the north and north-east where a high standing intensively eroded land was existed.
In Late Devonian to Early Carboniferous the rapidly subsiding Sedov and Fobos troughs were non-compensated by clastic sedimentation. In the Middle Carboniferous the rate of tectonically driven subsidence dropped down resulting in sediment overcompensation of the troughs. Zhelaniya Cape High remained rather stable in Early Carboniferous, and a carbonate platform was probably developed at present northern part of the Admiralty megaswell.
In Late Carboniferous and Early Permian time the transgressive cycle of sedimentation was apparently replaced by the regressive one. It is confirmed by the eastward shift of limit of the Upper Carboniferous to Lower Permian sediments showing the decrease of sea basin. The Middle-Upper Permian sedimentation cycle is characterized by the decrease of clastic sediment supply from the paleoland and termination of progradational sedimentation processes in the shelf zone.
Based on expected facial composition of the Paleozoic deposits the northern Prednovozemelsky area could be considered as more favorable in terms of it oil-and-gas potential as compared to Admiralty megaswell. Oil-and-gas prospects of Paleozoic Sedov and West Fobos trough fans are defined by structural factors as well as by their facial architecture caused by progradational sedimentation mode. In the seismic field wave anomalies of the «bright spot» and «flat spot» types are the direct indications of the Paleozoic deposit productivity of the ancient shelf continental margin.
AAPG Search and Discover Article #90096©2009 AAPG 3-P Arctic Conference and Exhibition, Moscow, Russia