SIMMONS, MIKE, BP exploration, Stockley Park, Uxbridge, Middlesex, UK

ABSTRACT: Biofacies Characterisation of Systems Tracts in Cretaceous Carbonate Platforms

Biostratigraphy has an important role to play in sequence stratigraphic studies, beyond simply providing a chronostratigraphic framework. Recognition of systems tracts is a powerful predictive tool for the exploration geoscientist -- an application of biostratigraphy to sequence stratigraphy is the characterization of systems tracts in terms of their biofacies.

Systems tracts prograde, retrograde or aggrade, depending on their position during sea-level rise and fall. From the detailed study of biofacies, shallowing-up or deepening-up trends can be established, which indicate likely systems tract. Furthermore, it seems possible that for given environmental settings at given geological times, systems tracts could be characterised by particular assemblages (i.e. the composition, diversity and density of assemblages and the morphology and size of individuals) that are themselves the response to relative sea-level change. Opportunistic taxa may characterize a transgressive system tract, whilst species diversification may take place during the highstand systems tract.

This study considers the biological response to system tracts development in Cretaceous carbonate platforms, using the early-mid-Cretaceous platforms of the Middle East as an example. In addition, the Cretaceous platform carbonates of Central Asia and the Mediterranean region are reviewed and their responses compared to those of the Middle East platforms.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.