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.