SEDIMENTARY FACIES IN AN INCISED VALLEY IN THE PENNSYLVANIAN OF BEAVER COUNTY, OKLAHOMA

The fill of an incised valley in the subsurface beneath Beaver County, Oklahoma, preserves the sedimentary response to a major cycle of chan ge in relative sea level that took place in the Anadarko basin at the end of the Mississippian and the beginning of the Pennsylvanian (Morro wan), The valley-fill sequence includes heterolithic elastic sediments of the lowstand systems tract (LST) and estuarine and marine sediment s of the transgressive system tract (TST), Deltaic sediments within th e TST record a minor cycle of base-level change and a small drop in re lative sea level within the major cycle of sea-level change that marks the Mississippian-Pennsylvanian boundary in the Anadarko basin. Congl omerates above the heterolithic facies of the LST formed as a transgre ssive lag on the ravinement surface at the base of the TST, Siliciclas tic tidal sediments overlie the conglomerates and in turn are overlain by crinoidal limestones that record relative deepening of the water a nd establishment of open marine conditions within the estuary, Above t he limestones are deltaic deposits indicating a minor drop in relative sea level during which fluvial conditions were established within the estuary, The sediments of the LST and the initial stages of the TST a re confined to the axis of the paleovalley and do not extend high onto its walls, The LST does not extend upstream into the higher reaches o f the paleovalley, In most places, shales deposited as shelf muds over lie the unconformity between the Mississippian and Pennsylvanian. The shales represent the later stages of the TST when sea-level rise resum ed following the episode of deltaic sedimentation, and marine waters f looded and drowned the preexisting topography.