Depositional Environments of the Pitkin Formation, Northern Arkansas

Abstract

ABSTRACT Paleoenvironmental analysis of the Pitkin Formation of northern Arkansas indicates deposition in intertidal and subtidal zones associated with a bioherm. The major environments of deposition are lagoon, bioherm, and oolite bank. Rocks deposited in these environments can in turn be subdivided into associated lithofacies and biofacies. Rocks of the lagoonal environment are carbonaceous marls and wackestones, siliceous spiculites, brachiopod wackestones, pelletal packstones and skeletal grainstones. Rocks of the bioherm are coral-crinoid-bryozoan-algal boundstones and intraclastic grainstones in tidal channels. The oolite bank contains cross-bedded oolitic grainstones and skeletal oolitic grainstones. A typical sequence of facies going seaward from the shore would be: carbonaceous marls and wackestones interbedded with quartzarenites and siltstones; siliceous spiculites and black calcite mudstones; brachiopod wackestones; pelletal packstones; skeletal grainstones; bryozoan-coral-crinoid-algal boundstones; and skeletal oolitic grainstones. Environmental reconstruction of the Pitkin Formation indicates a near constant shoreline with major changes in the depositional environments controlled by growth of the bioherm, and by clastic influx into the lagoon. During deposition of upper Pitkin sediments, the bioherm died and the lagoon was filled with terrigenous clay and with oolitic grainstone from the oolitic bank.