Sedimentology and stratigraphy of microbialite facies in the roubidoux and Jefferson City formations of central and southwest Missouri and central Kansas
Outcrop studies of sedimentary and stratigraphic features of microbial buildups are important in developing conceptual models for exploration of potential microbialite reservoirs. This study examines the occurrence and distribution of Lower Ordovician microbial fabrics in central Missouri and Kansas. The units studied include the Roubidoux and Jefferson City-Cotter Formations of the Arbuckle Group. To determine the depositional environments suitable for microbialite development, micro, meso, and macro-scale features were examined and their stratigraphic relationships established to the surrounding lithofacies. Microscopic-scale analysis reveals heavy dolomitization of strata, however remnant syndepositional features provide vital clues about the microbialite development. The occurrence of microbial structures is placed within a T-R cycle stratigraphic framework. The microbialites occurred within cyclical shallow marine deposits and are grouped into three cycle types. Type 1 deposits include subtidal mudstones to packstones that graded into intertidal stromatolites. Type 2 deposits include subtidal mudstones and packstones with thrombolite fabrics that graded into supratidal facies. Type 3 deposits include intertidal or supratidal facies that graded into supratidal facies. Thrombolites were more prevalent during the Jefferson City-Cotter and less during the Roubidoux times when sedimentation was high. They mostly grew at the top of the TST and bottom of the HST sequences. The stromatolites occurred right before the thrombolites during a TST sequence and after the thrombolites during an HST sequence.