Depositional System Evolution within Paleogene Supply-Dominated Genetic Stratigraphic Sequences, Northwest Gulf of Mexico Basin

GALLOWAY, WILLIAM E., University of Texas at Austin, Austin, TX

The Paleogene fill of the northwest Gulf Coast basin consists of eight genetic stratigraphic sequences that record a succession of major and minor depositional episodes. The major sequences were characterized by very high rates of deposition during their periods of maximum continental-margin outbuilding; in contrast, periods of retrogressive deposition and continental-margin flooding were times of decreasing and minimal sediment input and accumulation. Each sequence consists of a unique paleogeographic array of six generic depositional systems: fluvial, streamplain, delta, shore-zone, shelf, and slope. Paleogeographic reorganization of the array of depositional systems composing each sequence occurs during the periods of

transgressive flooding. During each episode, the depositional systems evolved in response to the changing balance among sediment supply, marine energy flux, potential for gravity redistribution, and patterns of subsidence.

Calculation of sediment accumulation rates along profiles through each of four subbasins shows that regionally correlative 5- to 10-fold changes of average rate occurred at time spans of 1 to 3 Ma. The component depositional systems within sequences, such as the Oligocene Frio, reflect this recurrent motif of accelerating supply and outbuilding, followed by waning sediment input and retrogradation. Progradational shelf and shelf-edge deltas as well as retrogradational deltas each display distinctive patterns of depositional geometry and facies development. Shorezone and shelf systems evolve from progradational to retrogressive/transgressive types. Fluvial systems respond to changing coastal-plain width, base-level change, and load-induced tectonic subsidence patterns.

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)