SEQUENCE STRATIGRAPHY AND FACIES ARCHITECTURE OF THE BROMIDE FORMATION (UPPER ORDOVICIAN; SANDBIAN) OF OKLAHOMA

The Bromide Formation is an Upper Ordovician (Sandbian; Turinian), mostly carbonate succession that is divided into the Mountain Lake and overlying Pooleville members. The formation is well-known for its diverse echinoderm and trilobite faunas. Detailed facies and sequence stratigraphic analyses yield data on localized subsidence, third to fifth order relative sea level changes, and cyclicity in a carbonate ramp setting. In the Oklahoma aulacogen, much of the Mountain Lake Member comprises meter-scale, deep ramp cycles that overlie a lowstand systems tract of sandstones and sandy crinoidal grainstones. Cycle tops are starved surfaces with irregular, mineralized hardgrounds. In exposures along Interstate 35 in the Arbuckle Mountains, the upper part of the Mountain Lake, Member includes a thin transgressive package of rippled crinoidal grainstone that is overlain by a well-defined flooding surface. Higher in the succession, the Pooleville Member consists of an early highstand interval of shallow subtidal carbonates and late highstand peritidal carbonates (Corbin Ranch Submember). Down-ramp, the Pooleville is represented largely by cm-thick shales and interbedded lime mudstones. The latter include obrution deposits that preserve assemblages of articulated isoteline trilobites. The base of the overlying Viola Formation (late Sandbian-Katian) records deepening above a probable sequence boundary. The Bromide-Viola contact is generally abrupt, but a thin, condensed, back-stepping succession with irregular hardgrounds is developed locally. The systems tracts and sequence architecture of the carbonate ramp to basin transition recorded by the Bromide will provide the framework for analysis of biotic responses to relative sea level changes at a variety of scales.