PETROLOGY AND PETROGRAPHY OF THE OZAWKIE LIMESTONE MEMBER OF THE DEER CREEK FORMATION (PENNSYLVANIAN, VIRGILIAN) OF MIDCONTINENT NORTH AMERICA; NORTHWEST MISSOURI, AND NORTHEAST KANSAS

In the northern part of the Midcontinent outcrop belt of northeast Kansas and northwest Missouri the Ozawkie Limestone Member (Deer Creek Formation, Shawnee Group, Virgilian) represents the relatively nearshore expression of a minor transgressive/regressive event.

At an exposure near I-29/US Highway 59 in northwest Missouri, the Ozawkie Limestone is about 2.5 m (8.2 ft) thick. The lower unit is 62 cm (24 in) of dolomitic, clayey, ostracodes-rich lime mudstone with iron oxide lined vertical to subvertical tubes, inferred to have been deposited in a tidal flat environment, with the shale filled tubes representing root molds. This is overlain by 23 cm (9 in) of calcareous, sparsely fossiliferous shale, probably deposited during a clastic influx event. Overlying the shale is a second carbonate unit that is 51 cm (20 in) thick, grading from a skeletal lime mudstone at its base to a coated-grain packstone in the middle, to a coated-grain, oolitic grainstone at the top. The upper grainstone also has zones containing intraclasts of lime mudstones (including flat- pebbles) and packstones. This second limestone unit is inferred to represent shallowing from shallow lagoonal to shoal environments, with the intraclasts being ripped up and redeposited during storm events. The third limestone is nearly identical to the lower carbonate unit, but some of the tubes are filled with ostracodes bearing clays. This unit is also inferred to have been deposited in a tidal flat environment similar to the lower limestone unit. The upper lime mudstone unit is overlain by 7.5 cm (3 in) of shale with abundant foraminifers, ostracodes, and charophytes, representing deposition of terrestrial clastics into a nearshore marginal marine environment. The upper limestone unit is a 7.5 cm (3 in) very clay-rich, dolomitic, lime mudstone, with clay ‘clasts' isolated from the matrix by large cracks. This unit is inferred to have been deposited in a storm event with subsequent drying and cracking of the clay-rich carbonate, producing a conglomeritic appearance. At an outcrop south of Oskaloosa, Kansas, the Ozawkie is much thinner, 92 cm (3 ft) thick, and does not display the shale units. The limestone units are very similar to the lower and second limestone units of the Missouri section. Here some carbonate clasts in the grainstone facies exceed 13 cm (5 in) in diameter.