ON FIVE ORDOVICIAN CARBONATE FACIES - DEPOSITIONAL SETTING AND DIAGENESIS OF LIMESTONES IN THE TOPMOST POOLEVILLE MEMBER (SIMPSON GROUP) AND BASAL VIOLA SPRINGS ((VIOLA GROUP): I-35 ROAD CUTS, ARBUCKLE MOUNTAINS, SOUTHERN OKLAHOMA

Five distinctive carbonate lithologies are juxtaposed on the I-35 road cuts on the south flank of the Arbuckle anticline. The lowest unit, a dense, sparsely fossiliferous micritic limestone with bioturbation, is interpreted as a low energy peritidal facies. The succeeding sequence of bioclastic and micritic limestones is punctuated by numerous erosional hardgrounds with relief of up to 15 cm. Bioclastic accumulations of current - and wave-sorted shell hash, dominated by brachiopods, and bryozoans, fill the relief. The micrite layers display both burrowing and boring. This facies is interpreted as an intertidal facies, responding to short term fluctuations in sea level. The third unit, a dense bioturbated micritic limestone that is locally highly fossiliferous, is interpreted as a peritidal deposit. The lower three units are placed in the Pooleville member, Bromide Formation, Simpson Group. Patchy ferroan dolosparite precipitation in all three units was controlled by burrows, brings and some bed boundaries. Contact with the overlying Viola is sharp but not erosional at outcrop scale. It appears that the Pooleville was completely lithified prior to Viola basin development. The lowermost Viola Springs unit is a cross laminated alternation of lime mud and ostracod-bearing non-ferroan sparry limestone that contains chert nodules and graptolites. The top of this unit is a hiatus marked by pyrite and an impersistent bed of granule sized phosphatic and carbonate grains, overlying which is the fifth facies, a black carbonate-rich shale containing abundant graptolites and cut by bedded radiolarian cherts. The basal Viola is traditionally interpreted as deep water deposits; the distinctive nature of the lowermost unit suggest the the definition of the Viola depocenter was a two step process.