Abstract: Evolving Sequence-Stratigraphic Concepts: Emphasis on Siliciclastic Systems Tracts

L. F. Brown, Jr.

During the past five years, rapidly evolving new sequence-stratigraphic concepts have begun to impose significant changes in the application of stratigraphy in petroleum exploration and reservoir development. The growing number and variety of oral and published papers on sequence stratigraphy clearly document this stratigraphic revolution. Not since depositional systems concepts evolved in the 1960s to give rise to seismic stratigraphy in the 1970s has the field of stratigraphy changed so rapidly and so fundamentally. Within the next few years, sequence stratigraphy is destined to play an increasingly important role in the way basins are analyzed, hydrocarbon-play potential is assessed, and prospect and production strategies are devised. Geoscientists worldwide are struggling to keep p with the significance of all of these new ideas and techniques.

A thorough review of the current status of sequence stratigraphy, with emphasis on siliciclastic depositional systems, focuses on the direct and immediate applications of evolving ideas, as well as on some specific, documented results of their recent use in petroleum geology. Issues such as sequence boundaries (unconformities vs. flooding surfaces), systems tracts, tectonics and sediment supply vs. eustasy, and evidence for relative sea level and tectonic cycles are addressed but certainly not settled! Real-world examples are presented to show the importance of analyzing stacking patterns and stratal geometries of sequence and parasequence sets of various orders (frequencies) during both exploration and reservoir characterization. Of critical importance is the recognition of the varia ions in reservoir character, seal, source, and trap potential displayed by marine or lacustrine/continental depositional sequences and component systems tracts that were deposited under different climatic regimes and basin tectonic styles. Also emphasized is the role being played by high-resolution micropaleontology and geochemistry and how they contribute to the sequence interpretation of wireline logs and seismic profiles during the construction of sequence and chronostratigraphic frameworks and play delineation.

The principles and concepts of sequence stratigraphy, which may simultaneously excite, confuse, and perhaps even irritate those trying to apply them in the real world, are carefully reviewed and updated. The current applications, controversies, new ideas, and immediate potential in petroleum geology are evaluated. Above all, polarized viewpoints may be brought a little closer together for a more realistic perspective of sequence stratigraphy and its exceptional potential for contributing to the growing international search for and production of hydrocarbons.

AAPG Search and Discovery Article #90985©1994-1995 AAPG Distinguished Lecture