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Abstract

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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