Delineation of Late Quaternary Depositional Sequences by High-Resolution Seismic Stratigraphy, Louisiana Continental Shelf

John R. Suter, Henry L. Berryhill, Jr., Shea Penland

Interpretations of over 20,000 line km of single-channel, high-resolution seismic reflection profiles, coupled with nearshore vibracores and logs of industrial platform borings, provide the data base for determining the history and stratigraphy of late Quaternary sea level fluctuations on the Louisiana continental shelf. Regional unconformities, formed by subaerial exposure of the shelf during glacio-eustatic sea level withdrawals and modified by shoreface erosion during ensuing transgression, serve as markers to identify the boundaries of depositional sequences. Unconformities are recognizable on seismic profiles by high-amplitude reflectors as well as discordant relationships between reflectors.

Within the upper Quaternary section, six depositional sequences have been recognized. Five of these are related to glacio-eustatic sea level fluctuations, involving sea level fall close to, or beyond, the margin of the continental shelf. Three of these fluctuations culminated in the deposition of shelf margin delta sequences. Extensive fluvial channeling characterizes the regressive phase of these sequences. Transgressive phases are marked by infilling of fluvial channels, flood-plain aggradation, truncation, or deposition of sand sheets, depending upon sediment supply and rate of sea level rise. Sequences 4 and 5 are correlated with the late Wisconsinan glacial stage and Holocene transgression. The upper portion of sequence 5 consists of an early Holocene Mississippi delta complex. A andonment and transgression of this delta are responsible for the formation of sequence 6. Although these deposits cover a smaller area, this demonstrates that deltaic processes can produce sequences similar to those driven by glacially controlled sea level changes.

AAPG Search and Discovery Article #91038©1987 AAPG Annual Convention, Los Angeles, California, June 7-10, 1987.