Evidence for Additional Type 1 Sequences in the Lower Miocene of the Gulf of Mexico
Taylor E. Blood, Dennis W. Cratsley
The Minerals Management Service, United States Department of the Interior, has conducted regional stratigraphic studies of lower Miocene, Burdigalian and Aquitainian Stages. The lower Miocene boundaries occur just above the sequence boundaries at 25.5 and 16.5 million years. Previously, Vail, Haq, and others had subdivided the Lower Miocene into four third-order sequences. Regional stratigraphic, sedimentologic, and paleontologic data are integrated to establish a new subdivision of the lower Miocene into eight third-order, type 1 cycles. This study identifies four previously unrecognized type 1 sequence boundaries in the Aquitainian portion of the lower Miocene, and provides a chart of depositional cycles. Lacking planktonic information, sequence boundaries and condensed sections are identified primarily on the basis of benthonic paleontologic data.
The range of sea-level fluctuation creating these sequences is interpreted from paleobathymetry data from marine shales, depositional models for sands, and seismic facies analysis. These data are integrated into geologic cross sections at both the regional and field level. Examples are shown from Mustang Island, Matagorada Island, High Island, West Cameron, and East Cameron Areas.
In the lower Miocene sequences of the Gulf of Mexico Basin, the sands of the lowstand system tracts occur downthrown to contemporaneous growth faults, while highstand systems tracts are upthrown. The cycle chart provides a tool for prediction and identification of sequences.
AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995