Sequence Biostratigraphy

LOUTIT, T. S., J. HARDENBOL, and R. C. WRIGHT, Exxon Production Research Company, Houston, TX

Sequence biostratigraphy is a relatively new discipline that has rapidly expanded in parallel with the development of sequence stratigraphy. Sequence biostratigraphic concepts result in significant improvements in our ability to determine ages, correlate stratigraphic units, and to estimate environments of deposition. Significant advances in the development of integrated biostratigraphic methods and knowledge during the past 20 years are now being rapidly integrated into the physical framework provided by depositional sequences. Sequence stratigraphy provides a physical framework consisting of a predictable hierarchy of correlation surfaces, ranging from sequence boundaries to parasequence boundaries, within which biostratigraphic observations may be placed. These physical correlation surfaces define true chronostratigraphic units that can be used to assess, using time-distance grids, the relative position of biozone "tops" or "bases." These surfaces also provide a physical link between sedimentary basins and the open-ocean planktonic microfossil chronozones established by the Deep Sea Drilling and Ocean Drilling Programs. Another important role for sequence biostratigraphy is the calibration of nonmarine biozones with open ocean microfossil zones via physical correlation surfaces.

Sequence stratigraphic concepts have also played an important role in the estimation of depositional environments, particularly water depths and distance from shoreline. The recognition of large, apparently sudden (but actually gradual), water depth changes within condensed sections results in more accurate and precise paleobathymetric estimation in exploration wells. The design of biostratigraphic sampling strategies is also influenced by sequence-stratigraphic concepts. Biostratigraphic sample quality (high) is inversely proportional to sedimentation rate (low). Sequence stratigraphy provides a consistent, predictable method of recognizing low sedimentation rate units in the subsurface using a variety of tools, ranging from seismic to well-log facies analysis.

Sequence biostratigraphers now utilize a wider range of tools to accomplish the traditional tasks of age determination and paleoenvironmental analysis and produce results more efficiently and effectively.

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)