Much has been written in recent years about the important role biostratigraphy has to play in sequence stratigraphic studies. Whilst it would be wrong to diminish the key role of biostratigraphy, it is important to realise that many of the supposed responses of palaeontological communities (biofacies) to relative sea-level change are based on theory rather than empirical observations and case studies. If biostratigraphy is to truly make a full contribution to sequence stratigraphic studies, then it is vital the biofacies response to relative sea-level change is tested in settings where that change can be documented from independent evidence such as stratal geometries and sedimentary facies changes.

Similarly, it is also important to realise that biofacies response to sea-level change will vary with depositional setting. In elastic delta-dominated successions, such as the Gulf of Mexico, biofacies show reductions of abundance and diversity during highstands because of effective elastic pollution. However, in carbonate platform settings, the converse can often be the case - abundance and diversity can increase during highstands as the platform is increasingly within the active photic zone.

Cretaceous carbonate platforms provide the ideal situation in which to investigate the biofacies response to relative sea-level change in a carbonate setting. Outcrops in the Mediterranean region, the southern United States and the Middle East display stratal geometries and sedimentary facies changes at a scale suitable to define relative sea-level changes and the products of that sea-level change - key bounding surfaces and systems tracts. Empirical observations can then be made on the biofacies changes without recourse to a priori expectations.

Biostratigraphy has a clear role to play in sequence stratigraphic studies because it supplies information on time, depositional environment and reworking - key aspects of any sequence stratigraphic interpretation. However, it should not be forgotten that high resolution biostratigraphy requires a sound taxonomic basis. Furthermore, palaeobathymetric resolution is often poor based solely on palaeontological data. In short, there is much fundamental palaeontological work to be undertaken before the biostratigraphic contribution to sequence stratigraphy can be fully realised. Coupled with this is a need to embrace quantitative analysis and statistical methods of investigating diversity and abundance.

AAPG Search and Discovery Article #90937©1998 AAPG Annual Convention and Exhibition, Salt Lake City, Utah