Analyzing Sequence Architecture and Reservoir Quality of Isolated Carbonate Platforms with Forward Stratigraphic Modeling
Published:January 01, 2008
Phil Bassant, Paul M.(Mitch) Harris, 2008. "Analyzing Sequence Architecture and Reservoir Quality of Isolated Carbonate Platforms with Forward Stratigraphic Modeling", Controls on Carbonate Platform and Reef Development, Jeff Lukasik, J.A. (Toni) Simo
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Dionisos is a forward stratigraphic modeling package that can be used to analyze the facies distributions in an isolated carbonate platform. Two grainstone distributions are considered and used as “inspiration” for an unconditioned case study: grainstones around the platform margin and grainstones in the platform center. In one experiment a linear rate of sea-level rise is used and the rate is varied to generate a series of models. In a second experiment a cyclic sea-level curve is added, and the amplitude of the cycles is varied to generate a second series of models.
Platform-margin grainstone facies patterns develop during times of very shallow water depth on the platform top, and slow changes in bathymetry. Platform-center grainstone facies patterns develop during times of slightly deeper water depth and increasing bathymetry (flooding). Different facies patterns can occur at the same bathymetry, depending on whether water depth is increasing or decreasing. The difference is attributed to the persistence of local depocenters that depended on previous environments (stratigraphic inertia) and the roundness of the platform. In these experiments a platform will be flatter during deepening than during shallowing because of its previous history. Neither of these two factors is reflected in the average bathymetry value but is captured in the rate and sense of flooding.
The timing of interpreted sequence boundaries and maximum flooding surfaces is investigated. In some models these surfaces are clearly diachronous, and their timing relative to the accommodation cycle varies depending on the amplitude of the accommodation change. During “greenhouse” times the subtle environmental shifts created by changes in accommodation are more significant than the actual resulting bathymetry change, and the timing of sequences is poorly related to the highs and lows on the accommodation cycle. Conversely, during “icehouse” times bathymetry change is directly driven by the accommodation cycle and the resulting sedimentary cycle is in phase with accommodation.
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Controls on Carbonate Platform and Reef Development
Carbonate platforms and reefs emerge, grow and die in response to intrinsic and extrinsic mechanisms forced primarily by tectonics, oceanography, climate, ecology and eustasy. These mechanisms, or controls, create the physical, biological and chemical signals accountable for the myriad of carbonate depositional responses that, together, form the complex depositional systems present in the modern and ancient settings. If we are to fully comprehend these systems, it is critical to ascertain which controls ultimately govern the “life cycle” of carbonate platforms and reefs and understand how these signals are recorded and preserved. Deciphering which signals produce a dominant sedimentological response from the plethora of physical and biological information generated from superimposed regional to global-scale controls is critical to achieving this goal. With this understanding, it may be possible to extract common time- and space-independent depositional responses to specific mechanisms that may, ultimately, be used in a productive sense. Extensive research on a wide variety of carbonate platform and reefal systems in the past few decades has provided the foundation and understanding necessary to take carbonate research to a new level. With assistance from rapidly advancing computer software and an increasing use of cross-disciplinary integration, carbonate research is shifting from description and morphological analysis towards a science that is more focused on the assessment of process and genetic relationships. The aim of this special publication is to present a cross section of recent research that shows this evolution from a variety of perspectives and scales using examples distributed throughout the Phanerozoic.