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GOODMAN, DAVID K., ARCO Oil & Gas Company, Midland, TX, and HENRY W. POSAMENTIER, ARCO Exploration and Production Technology, Plano, TX

ABSTRACT: Interpretation of Biostratigraphic Data at a Sequence Stratigraphic Scale

Recent advances in sequence stratigraphic concepts provide a framework within which biostratigraphic data can be utilized in conjunction with other stratigraphic tools in an integrated approach to stratigraphic analysis. Sequence stratigraphic concepts suggest that lithologic sections are composed of a succession of unconformity-bounded units or sequences. These sequences can, in turn, be subdivided into systems tracts bounded by flooding surfaces or maximum flooding surfaces. Three systems tracts comprise a sequence: the lowstand or shelf margin systems tract at the base, followed by the transgressive systems tract, and then the highstand systems tract. On continental margins characterized by a discrete shelf/slope break, deep-sea submarine fans, shelf-margin deltas, and incised-vall y fills characterize the lowstand systems tract. On ramp-like continental margin, the lowstand systems tract is characterized by basinally-isolated lowstand shorelines with or without preserved incised-valley feeder systems. The transgressive systems tract is characterized by backstepping shorelines and estuarine fill of incised valley systems. The highstand systems tract is characterized by forestepping depositional systems and widespread floodplain development.

Refinement of the empirical relationship between biofacies and sequence architecture provides an expanded role for biostratigraphy in sequence stratigraphic applications. A considerable amount of the structure in the stratigraphic distribution of fossils can be attributed to sequence architecture. This structure can be statistically delineated in terms of a hierarchy that is independent of both fossil group and geological age. The resultant definition of "biological analogs" of systems tracts reduces the complexity of paleontological census data to a set of (1) internal characteristics within genetic units and (2) boundary conditions at stratal discontinuities. Different taxon groups should ideally display unique and repeatable patterns within different systems tracts and at stratal d scontinuities within a basin, thus providing a new perspective of paleontological data across a spectrum of applications in sequence characterization and correlation.

AAPG Search and Discovery Article #90988©1993 AAPG/SVG International Congress and Exhibition, Caracas, Venezuela, March 14-17, 1993.