Abstract: Plate Tectonics, Organic Matter, and Basin Evaluation for Petroleum Potential

Colin Barker

The concepts of plate tectonics have been used to classify sedimentary basins in terms of physical characteristics, such as location on the plate and geothermal gradient. A complete classification must include the amount, type, and distribution of organic matter because this is the material that generates petroleum. Organic matter can be divided into that which grows on the land surface ("terrestrial") and that which grows in water ("aquatic"). This is an economically important distinction because aquatic material gives normal crude oils whereas terrestrially derived materials produce gas and waxy oil. Transport of terrestrial organic matter to areas of deposition depends on surface relief because this controls drainage patterns. The association of transported terrestrial organic matter with clastic sediments makes deltas the most gas-prone depositional environment. Organic materials are not distributed uniformly in deltas because terrestrial organic matter has its highest concentration nearshore, whereas aquatic material also is produced in large amounts offshore. The separation and distribution lead to gas fields near paleoshorelines and oil farther offshore. As the delta progrades, terrestrial organic matter is deposited over the previously deposited aquatic organic matter producing a vertical sequence from gas to oil in the delta. Sediments on subducting plates should show the same vertical sequence of terrestrial over aquatic because the sediments are transported slowly toward the source of terrestrial organic matter and its concentration increases a the subduction zone is approached. The opposite trend (i.e., aquatic over terrestrial) is found on pull-apart margins where the oldest sediments were formed in a continental rift rich in terrestrial organic matter and were overlaid by sediments containing increasing amounts of aquatic organic matter.

AAPG Search and Discovery Article #90961©1978 AAPG Annual Convention and Exhibition, Oklahoma City, Oklahoma