CYCLICITY AND DEPOSITIONAL SEQUENCES IN A MIXED SILICICLASTIC-CARBONATE UNIT: IMPLICATIONS FOR INTRABASINAL CORRELATION AND SUBAQUEOUS EROSION IN THE ORDOVICIAN OF OKLAHOMA

The late Whiterockian to Mohawkian Bromide Formation succession in south-central Oklahoma was deposited along a mixed siliciclastic-carbonate ramp that distally steepened into the Southern Oklahoma Aulocogen (SOA). The depositional history and environmental context of the unit are reconsidered using lithofacies analysis and the characterization of sequence stratigraphic patterns at a variety of hierarchical scales. Ramp stratigraphy, facies associations and bounding surfaces suggest that three 3rd order depositional sequences are present in the Bromide. They demonstrate the transition from a primarily clastic ramp in the late Whiterockian to a carbonate-dominated ramp in the Mohawkian. These sequences show that the deposition of the Bromide was considerably more complex than the simple transgressive-regressive cycle traditionally used to describe accommodation dynamics in the basin. Meter and decameter-scale cycles are common within the depositional sequences, and the Corbin Ranch Submember records an important peritidal sequence prior to a major sequence boundary with the younger Viola Formation. New correlations based on measured sections, outcrop gamma ray profiles, and subsurface well logs suggest that the middle Bromide depositional sequence expanded down-ramp, while the carbonate-dominated upper sequence is progressively removed downramp, particularly in areas south of the basin axis. New facies evidence also suggests that localities that were previously considered the deepest portion of the basin are actually beyond the basin axis, and show slight shallowing out of the Southern Oklahoma Aulacogen.