Abstract

The Plattin Limestone, a peritidal carbonate complex, crops out along an easterly trend in northern Arkansas. At five stratigraphic sections, 13 lithofacies comprise five informal rock-stratigraphic units in an overall transgressive sequence.

Unit 1, deposited in the initial phase of "Plattin" sedimentation, is composed, near the base, of predominately intertidal lithofacies; the upper portion is a mosaic of randomly stacked tidal flat and lagoonal lithofacies that accumulated during local oscillations of relative sea level. Unit II was deposited under more stable conditions when algal mats augmented shoaling and progradation of tidal flat lithotopes. Arid climate and restricted water circulation created a sabkha environment in which evaporitic minerals precipitated. In Unit III, subtidal lithofacies, particularly oolite, were deposited as subsidence exceeded sedimentation. With continued subsidence, depositional environments became normal marine, and coral-algal wave baffles formed Unit IV. Bioturbation and diverse fossil fragments characterize the lithofacies of Unit V, deposited in openly circulating marine water. Sedimentary structures indicative of subaerial exposure suggest the terminal event recorded by the Plattin Limestone was sudden local marine regression.

The lower contact is locally disconformable, dependent largely upon the paleotopograhpy of the underlying formation. An abrupt upper contact truncates features of the Plattin Limestone, suggesting that, subaerially or subaqueously, the material was at least partially lithified and then eroded prior to deposition of the overlying formation. Various erosional surfaces occurring locally within the formation attest to a history of discontinuous deposition that is natural for a sequence of peritidal strata.