Genetic Stratigraphic Sequences in Basin Analysis I: Architecture and Genesis of Flooding-Surface Bounded Depositional Units

Abstract

Marine basin margins are characterized by repetitive episodes of progradation punctuated by periods of transgression and flooding of the depositional platform. The resultant stratigraphic units consist of genetically related (1) depositional systems and their component facies sequences; (2) bypass, nondepositional, and erosional surfaces; and (3) in thick sequences affected by gravity tectonics and crustal response to loading, syndepositional structural discontinuities. Units are bounded by hiatal surfaces preserved as submarine unconformities or condensed sedimentary veneers and that record maximum marine flooding of the basin margin. The repetitive stratigraphic architecture is the product of the ongoing interplay among sediment supply, basin subsidence (and uplift), an eustatic sea level change. Each of these three variables may dominate depositional evolution; furthermore, stratigraphic architecture is very similar regardless of the dominant control. A genetic stratigraphic sequence is the sedimentary product of a depositional episode. The sequence incorporates and reconciles depositional systems, bedding geometries, and bounding surfaces within the framework of cycles of basin-margin offlap and flooding. Each sequence consists of the progradational, aggradational, and retrogradational or transgressive facies deposited during a period of regional paleogeographic stability. The defining genetic stratigraphic sequence boundary is a sedimentary veneer or surface that records the depositional hiatus that occurs over much of the transgressed shelf and adjacent slope during maximum marine flooding. The genetic sequence paradigm emphasizes preserving the stratigraphic integrity of three-dimensional depositional systems and does not rely n widespread development of subaerial erosion surfaces caused by eustatic falls of sea level to define sequence boundaries. The physical stratigraphic record of transgression and flooding--distinctive thin but widespread facies sequences, prominent erosional surfaces, and superjacent marine condensed intervals or sedimentary veneers--provides readily recognized, regionally correlative, easily and accurately datable, and robust sequence boundaries that commonly define times of major basin-margin paleogeographic reorganization in terrigenous clastic basins.