PICHA, FRANK J., Chevron Overseas Petroleum, Inc., San Ramon, CA
Abstract: Sedimentary Basins and Petroleum Systems in Terms of Global Tectonic Cycles
Worldwide exploration for the remaining undiscovered hydrocarbons requires a good understanding of geology and petroleum systems of many diverse provinces of the world. In order to see the critical aspects of any hydrocarbon habitat and predict potential new plays, various concepts must be integrated into a unifying interpretative system. Obviously, the sedimentary basins, their tectonic and depositional history and classification, represent such a principal category to which all other aspects, including elements of the petroleum system, such as source rock, generation, migration, and entrapment of hydrocarbons, are related.
The modern definition and classification of sedimentary basins and associated petroleum systems is principally based on concepts of plate tectonics. The plate-tectonic cycle, in its initial divergent setting, begins typically with intracratonic rifting, followed by opening of oceans and development of passive continental margins. Subduction, continental collision, and orogenesis mark the second, convergent part of the cycle. During the course of the plate-tectonic cycle, various sedimentary basins and related petroleum systems evolve in this dynamic global system. The hydrocarbon potential of each principal basin is determined by its tectonic and depositional history, which relates to succession of critical stages of the plate tectonic cycle: rifting, sagging, drifting, subduction, and collision. Among many types of basins, the rift and intracratonic rift-sag basins, and passive continental margins of the divergent settings, the foreland basins and fold and thrust belts of the convergent settings, and some borderland basins of the transform margins represent the most petroliferous provinces of the world. The petroleum systems, including all processes from source-rocks deposition to final entrapment of hydrocarbons, evolved in a single stage of a plate tectonic cycle; e.g., in simple rift basins or during two or more stages of a cycle, e.g., on passive continental margins with stages of rifting, sagging, and drifting. In some cases, the formation of a petroleum system even extends over several stages of two different plate tectonic cycles. An example of the latter is the petroleum system of the Trias basin in North Africa, in which the source rocks deposited in the Paleozoic-Hercynian cycle matured and generated hydrocarbons only during the Mesozoic to Cenozoic Tethyan/Alpine cycle.
Various types of sedimentary basins and related petroleum systems are demonstrated on examples from North and South America, Africa, Europe, and Asia. Also presented are maps of sedimentary basins of the whole continents of Africa and South America as examples of application of the plate-tectonic classification of sedimentary basins on a global scale.
Definition of sedimentary basins and petroleum systems in terms of plate tectonics not only enables better categorization and integration of data, but also serves as a predictive tool in evaluation of various properties and in search for new potential hydrocarbon plays. Well-defined hydrocarbon habitats of certain plate-tectonic settings will serve as potential models for other, less known basins and exploration plays. However, it is not the categorization and classification of sedimentary provinces and petroleum systems itself but the process of analyzing data within a universal concept of global tectonics that enhances creative thinking and consequently improves the chances for successful exploration.
AAPG Search and Discovery Article #90922©1998-1999 AAPG International Distinguished Lectures