ABSTRACT: Recognition and Significance of Sequences and Their Boundaries, Deep Gulf of Mexico

BUFFLER, RICHARD T., and FENG JIANHUA, University of Texas at Austin, Austin, TX

A detailed seismic stratigraphic analysis of the deep Gulf of Mexico basin has resulted in the definition of 18 post mid-Cretaceous seismic sequences. The definition of seismic sequences is mainly based on a pronounced depositional cyclicity. Each depositional cycle is characterized by a low-amplitude, variable continuity seismic facies (rapid deposition) capped by regionally extensive, continuous, high-amplitude reflections (sediment starvation). Each corresponding seismic sequence is interpreted to consist of distal lowstand systems tracts deposits overlain by a regional condensed section. Each condensed section is the basinal equivalent of transgressive and highstand systems tracts deposits present on the adjacent shelf margins.

The true sequence boundaries, therefore, are interpreted to be mainly correlative conformities directly overlying the condensed sections. They are inferred to be the basinal equivalent of sequence boundaries observed on the slope and shelf. In most places they are indistinguishable seismically from the condensed sections. In some places, however, the sequence boundaries are manifested by erosional truncation of the underlying condensed section and lowstand deposits, probably resulting from turbidity current and/or contour current scouring associated with sea level falls or lowstands. For example, prominent erosion occurs in the deep northeastern Gulf at the 94 Ma (MCSB), 30 Ma, and 5.5 Ma boundaries. These sequences and sequence boundaries are correlated with major depositional episod s and sea level changes observed on the adjacent shelf and slope, which can be used to establish a chronostratigraphic framework and develop a depositional history for the deep Gulf of Mexico basin.

The recognition of condensed sections and sequence boundaries in this deep sedimentary basin is important in the exploration for frontier reservoir sands. Favorable exploration targets include basin floor fans, fan channel complexes, and distal prograding wedges. Isopach mapping of these sequences has identified depositional lobes in the deep basin, which, in turn, can be used to infer major sediment sand fairways on the adjacent slope.

AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)