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Abstract

The spectrum of carbonate-platform types, their heterogeneities, and their architecture is complex. Each platform succession has a distinctive and unique character that is a response to the particular geotectonic context and the physical, chemical, and biological conditions to that specific Phanerozoic window. Each succession has a distinct depositional profile, facies-belt distribution, and platform architecture, and it is expressed by the order of the basic accretional units and their stacking patterns. Critical differences between platform types are often the result of differences in their ecological accommodation. End members include (A) low-relief carbonate ramps that match a shelf equilibrium profile and are composed of either loose, fine-grained sediments produced in shallow, well-illuminated areas but shed downdip, or sediment produced and accumulated (sometimes as a distal bulge) in the deeper part of the depositional profile (poor-light or no-light zones), (B) open-shelf platforms involving large-skeleton metazoans with a marked to moderate capacity to build a platform margin above the shelf equilibrium profile, (C) rigid rimmed platforms with biotic components capable of accumulating to sea level with a maximum ecological accommodation, and (D) platforms with steep, massive and thick marginal slopes characteristic of many Paleozoic and some Mesozoic settings.

Interpretation of carbonate platforms and prediction of their facies heterogeneities involves analyzing and integrating geometrically related data. Analysis involves iterative and successive backstripping of sediment accumulation from youngest to oldest. This is reassembled to determine the genetic character of the carbonate sequences, cycles, parasequences, and/or beds as products of changes in physical and ecological accommodation. This reassembly considers the evolution of the biota involved, and the resulting changes in ecological requirements, the hydrodynamic setting, the physical accommodation, and the ecological accommodation (capacity of building up above a certain hydrodynamic energy level). The limits to this analytical strategy are tied to the knowledge of the ecology of ancient biota, while its advantage is that it formulates new questions that lead to more realistic interpretations and enhanced predictions of lithofacies heterogeneities.

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