Within the Mississippian (Valmeyeran) strata of Indiana, the uppermost Harrodsburg and lowermost Salem limestones contain a variety of grainstone facies that were deposited within a tide- and wave-dominated, shallowing-upward sequence. Compositions of autochthonous fossil assemblages in each facies are interpreted to have been constrained primarily by sediment stability. For example, echinoderm-bryozoan-brachiopod assemblages apparently thrived on stable substrates. Conversely, gastropod-dominated assemblages lived on frequently reworked, tidally influenced substrates. Low-diversity assemblages lived on substrates that were almost continually reworked. Faunal diversity decreased with increasing sediment mobility because of the increased (biological) energy required to mai tain a life position at the sediment-water interface. Within modern analogs, a decrease in faunal diversity commonly correlates with increased sediment mobility.

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