A PETROGRAPHIC STUDY OF THE METER-SCALE CYCLES WITHIN THE ORDOVICIAN MOUNTAIN LAKE MEMBER OF THE BROMIDE FORMATION, SOUTH-CENTRAL OKLAHOMA

Meter-scale cycles within the Upper Ordovician clastic-carbonate Bromide Formation have been previously described as both parasequences (shallowing upward cycles) and high-frequency sequences (shallowing and deepening, symmetric T-R cycles). Proper identification of T (transgressive) and R (regressive) components on one high-resolution meter-scale cycle was determined by sampling at an extremely fine scale of 12 cm intervals over a 3 meter section. Data from a point counting analysis of 400 points per thin section suggests an association between allochem type, mineralogy, and sequence stratigraphic motif. For example, the data suggest a generalized increase in authigenic pyrite and phosphate between the transgressive surface (TS) and maximum flooding surface (MFS), and an increase in carbonate intraclasts and hematite near the transgressive surface. Detrital siliciclastics increase in abundance during the regressive portions of the cycle, with overall changes more punctuated across bounding surfaces as would be expected in a high-frequency sequence, and not as gradual as would be expected if they were parasequences. Further, ordination (NMDS) and cluster analysis techniques suggest the most similar samples group together based on whether they are within the T or R part of the cycle, rather than across the cycles.