Biostratigraphic Calibration in Sequence Stratigraphic Analysis: Pliocene-Pleistocene Case Study from Gulf of Mexico

Walter W. Wornardt, Jr., John M. Armentrout, J. L. Clement

Biostratigraphic analysis provides chronostratigraphic data for correlating depositional sequences and paleoecologic data helpful in identifying depositional facies. These data sets are essential for correct analysis of sequence stratigraphy in areas of complex depositional architecture and structural style.

The most useful sequence stratigraphic element for correlation is the condensed section. The condensed section is a facies consisting of thin marine beds of hemipelagic or pelagic sediments deposited at very slow rates. They are most extensive during the time of regional transgression of the shoreline. Condensed sections are excellent correlation data because they contain abundant hemipelagic and pelagic fossil materials and form regionally continuous high-amplitude seismic reflectors. In well samples condensed sections are recognized by peaks in marine fossil abundance and diversity and by high carbonate content; on electric logs they are recognized as high-resistivity clays.

Three types of condensed sections are recognized in the Galveston area-South Addition A-158 No. 1 well. Condensed sections deposited in paleowater depths of less than 600 ft occur within the third-order depositional sequences, indicating relatively thick lowstand and highstand sediments. Condensed sections deposited in paleowater depths of 600-3,000 ft occur at or just below the third-order depositional sequence boundaries, indicating relatively thin or absent sediments of the highstand systems tract. Condensed sections deposited at paleowater depths deeper than 3,000 ft extend through most of the third-order sequence, suggesting essentially no eustatic influence on sediment accumulation.

AAPG Search and Discovery Article #91022©1989 AAPG Annual Convention, April 23-26, 1989, San Antonio, Texas.