PULHAM, ANDREW J., JULIE A. D'ABLAING, DAVID S. EPPS, and ROBERT K. KASTEN, BP Exploration, Houston, TX

ABSTRACT: Condensed Zones in the Deepwater Gulf of Mexico: Their Recognition and Stratigraphic Significance

Stratigraphic analysis in deepwater marine clastic systems is built upon the foundation of condensed zone recognition and age determination. In the offshore Gulf of Mexico, the interaction of shallow buried salt and sedimentation produces a depositional architecture that is a unique challenge to the stratigrapher wishing to identify systems tracts and other correlatable depositional units. Application of relatively recent concepts of Sequence Stratigraphy relies particularly upon accurate recognition of condensed zones in this complex depositional setting.

Hot shale has become the classic indicator of condensed zones in the deepwater Gulf of Mexico. Simple correlation of floral abundance to hot shales zones is widely accepted to be the key technique in building a Sequence Stratigraphic picture. We believe hot shales represent only a small part of condensed zone recognition, other lithologies are much more important for complete stratigraphic analysis. In contrast to the model ofthin hot shales, we recognize relatively thick (10's to 100's of feet) carbonate-rich intervals to be the most important condensed zones in Gulf of Mexico deepwater settings. These lithologies have distinctive well log and biostratigraphic signatures. Divided into a hierarchy, they represent a spectrum of stratigraphic events from major switches of the Mississipp Delta, through third and fourth order highstands, to temporary abandonments of active slope systems. Such condensed zones form excellent correlative markers and provide the means to better understand the depositional architecture of the complex Gulf of Mexico slope.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.