ORGANIC GEOCHEMISTRY AND SOURCE POTENTIAL OF THE LACUSTRINE SHALES OF THE UPPER TRIASSIC LOWER JURASSIC KAP STEWART FORMATION, EAST GREENLAND

The Upper Triassic - Lower Jurassic Kap Stewart Formation (Jameson Land, East Greenland) has been studied by a combination of sedimentological and organic geochemical methods (LECO/Rock Eval, sulphur, gas chromatography) in order to assess the hydrocarbon source potential of the abundant and extensive lacustrine shale intervals present in the formation. The organic matter in the shales is a mixture of algal and higher plant remains (type I and III kerogen). An organic assemblage dominated by algal material, having a rich oil potential, occurs in an interval approximately 10-15 m thick in the uppermost part of the formation. This interval has an organic carbon content up to 10% and Hydrogen Index values up to 700. The interval is consistently traceable along the exposed margins and the central part of the basin. The deposition of the uppermost shale interval coincided with the largest expansion of the lake, during a period with a stratified water column and anoxic bottom-water conditions. Locally the rocks exposed are thermally postmature due to the thermal influence of dolerite sills which intruded the Kap Stewart Formation in Tertiary time. However, the organic-rich shale interval is beyond the influence of the sills and indicates a maturity prior to or in the early stages of oil generation. Calculations of the generative potential of the lacustrine source rocks suggest that significant amounts of petroleum may have been generated in those sediments which have undergone sufficient burial in the southern and central part of the basin. Here, the contemporaneously deposited delta front and barrier island sandstones can thus be considered as potential targets for future hydrocarbon exploration. This type of play may also be of importance in other North Atlantic basins with a similar basin history. © 1990.