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Carbonate Sequence Stratigraphy – An Historical Perspective


Utilizing discontinuities as a basis for packaging sediments, carbonate platforms can be divided into nested depositional sequences of various scales that contain repeated patterns of lithofacies, unique to this depositional system. During the last 40 years, carbonate sequence stratigraphy has seen enthusiastic testing and an evolution in ideas and applications. The advent of 3D seismic and application to classic carbonate outcrop areas have resulted in greater insight into platform growth and the effects of tectonics, climate (ice-house vs. greenhouse), and sea level on stacking patterns and growth history, and diagenetic alteration. Advances in carbonate sequence analysis fall into four areas. First, recognition that accommodation combines with biologic controls to exert a defining control on platform development and geometry has advanced our understanding of carbonate sequences. Paleo-oceanographic conditions determine growth rates and depositional patterns, thus influencing thickness and distribution of carbonate platforms (i.e., effective accommodation). All space may not be filled and this can have a profound effect on sequence development (e.g., lowstand deposition to fill unfilled space with little if any subaerial exposure). Second, changing oceanographic conditions (e.g., temperature, nutrients, salinity) during relative changes in sea level can result in biotic changes within different systems tracts (e.g., nutrient-rich, depressed growth in TST's vs. well circulated conditions and robust growth during HST's) resulting in distinctively different lithofacies. Third, slope declivity significantly influences sequence architecture (e.g., rapid S.L. falls associated with a steep rimmed platform may shut down the carbonate system). Fourth, carbonate platforms at sea level are sensitive indicators of sea level changes and have provided test locations to document global sea level changes during the Neogene. The Bahamas drilling legs have allowed dating of Neogene sea level fluctuations and accompanying platform responses. Consideration of diagenetic alterations under varying climate conditions within a sequence framework has enhanced reservoir characterization. Humid climate during sea level lowstands can result in significant karst formation. Dry climate settings diminish early meteoric changes and preserve greater volume of primary porosity. Integrated sequence and diagenetic analyses have resulted in better reservoir models for hydrocarbon recovery.