Sequence Stratigraphic Analysis of an Unstable Shelf Margin: An Example from Miocene Section of Offshore Western Louisiana, Gulf of Mexico

YANG, SU Y., and JOEL S. WATKINS, Texas A&M University, College Station, TX

Sequence stratigraphic analysis using seismic baselap terminations is not usually applicable to the Miocene section of offshore western Louisiana, Gulf of Mexico, because of the lack of identifiable baselap and expansion at growth faults. Identification of condensed sections, which usually occur at the top of the transgressive systems tracts and are easily identifiable marker beds in nannofossil, well log, and seismic data, is an alternative approach to sequence stratigraphic analysis. Integrated interpretation of high-resolution calcareous nannofossil abundance data from nine wells, 91 paleontological reports

(foraminifera), well log data from 73 wells, and more than 2400 mi of seismic data defines seven genetic stratigraphic sequences and corresponding systems tracts from the late Early Miocene through the early Pliocene.

The highstand systems tracts are dominant on the shelf and slope in the study area. The transgressive systems tracts are rather thin. The lowstand systems tracts are usually limited on the downthrown sides of major growth faults except for a thick lowstand prograding wedge of the Amphistegina B-Discorbis B sequence deposited on the shelf and slope. The seismic amplitudes of highstand systems tracts are moderate to variable in the updip area and low in the downdip area. The seismic attributes of transgressive systems tracts are moderate amplitude, high frequency, and moderate to high continuity. The condensed section exhibits a strong reflection. Seismic attributes of lowstand systems tracts are low amplitude and low continuity, and sometimes a hummocky pattern.

AAPG Search and Discovery Article #91007© 1991 AAPG International Conference, London, England, September 29-October 2, 1991 (2009)