PETROLOGY AND PETROGRAPHY OF THE CURZON LIMESTONE MEMBER, TOPEKA FORMATION (SHAWNEE GROUP, VIRGILIAN STAGE, PENNSYLVANIAN) AT BARRETT HOLLOW, HOLT COUNTY, MISSOURI

The Curzon Limestone in Barrett Hollow shows a unique sequence of shallow water facies, not seen in other nearby outcrops in northwest Missouri, southwest Iowa and northeast Kansas. Here the Curzon consists of a 1.5 m thick lower limestone separated from a 72 cm thick upper limestone by a 15 cm mudstone. Above the upper Iowa Point Shale the basal Curzon is a series of weakly-laminated, bioturbated lime mudstones and interbedded shales. This is overlain by 30 cm of barren, micro-laminated lime mudstone with quartz silt and mica exhibiting soft-sediment deformation features and some bioturbation that disrupts laminae, interpreted as a tidal flat. Next higher is an 18 cm thick unit consisting of lime wackestone to packstone, interpreted as shallow lagoonal deposits. Above this is about 15 cm of carbonate with interbedded zones of micro-laminated, bioturbated lime mudstone and intraclast-bearing lime grainstone. The laminated lime mudstones are interpreted as fair-weather deposits with plant rootings and the grainstones are interpreted as storm deposits, on a tidal flat. This is overlain by a massive 76 cm thick bed of barren, very weakly laminated, bioturbated lime mudstone. The lower limestone is separated from the upper limestone by 15 cm of light gray, unfossiliferous clay mudstone, interpreted as being deposited by rapid clastic influx. The base of the upper limestone is a limestone-clast conglomerate that grades upward to algal-coated fossil grains in a lime packstone, probably deposited in a shallow lagoon with storm debris at the base. The top of the unit is an intraclastic, brecciated lime packstone with green shale-filled tubes, representing micro-karst development on the limestone during soil formation that is associated with the overlying Jones Point Shale.