Abstract

Two units of the type Four Mile Dam Limestone provide petrographic evidence of extreme variations in environmental energy over several tens of feet horizontally. Various facies of biomicrite and biosparite display great variations in the grain/micrite ratio and are thereby interpreted to represent deposition in low-energy lagoon and higher-energy bank environments respectively. Slight variations in elevation of the sedimentary interface were sufficient to determine the degree of winnowing and sorting of the lenticular biosparite unit from the center to the flanks of the crinoidal bank lens. The biosparite phase of deposition was terminated by a phase of locally intense erosional scouring at the center of the lens with contemporaneous deposition at the flanks a short distance away.

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