ABSTRACT

The lower Dornick Hills Group (Lower Pennsylvanian, Morrowan and Atokan Series) occurs in the Ardmore structural basin in south-central Oklahoma. It comprises over 2,000 feet of limestones, sandstones, conglomerates, and shales. The terrigenous clastics portion of this sedimentary sequence were derived from the adjacent Criner Hills anticlorium and were deposited to the northeast in a shallow, normal marine environment.

The thesis treats the lower Dornick Hills Group on the eastern limb of the axially faulted, overturned Overbrook anticline. The Overbrook anticline was developed and overturned against the Criner Hills (that is, to the southwest) during the Arbuckle orogeny (Virgilian). The strata strike northwest-southeast and dip to the northeast generally 65° to 90° with some overturning to the southwest.

The lower Dornick Hills Group, as used here, includes several mappable members. The oldest is the Primrose Member (Morrowan). It is thick-bedded, relatively unfossiliferous, calcareous siltstone up to 15 feet thick. It is overlain unconformably by the Jolliff Member (Morrowan) which includes a basal limestone and chert conglomerate, and some upper pebbly limestones and shales. Above the Jolliff is an Unnamed Unit (1) which comprises almost 800 feet of shales and sandy limestones that are gradational southwestward into conglomerates. The overlying Otterville Member (Morrowan) also becomes conglomeratic toward the southeast: Pebbly, oolitic grainstones become closely-packed, clastic packstones and conglomerates. The Otterville is overlain by an Unnamed Unit (2) which consists of shale and interbedded sandy, fossiliferous limestones. The Bostwick Member (Atokan) unconformably overlies the Unnamed Unit (2). The Bostwick is 600 feet of thick-bedded, lenticular limestone and chert conglomerates that are inter-bedded with sandy-pebbly limestone, sandstones, and shales. From the north to the south the basal Bostwick lithofacies changes from cherty and sandy conglomerates to limestone, chert and calcareous conglomerates.

The environment of deposition of the lower Dornick Hills Group was a shallow, normal marine shelf that sloped basin-ward (northeast and east) from the adjacent source area. The provenance was the Criner Hills anticlorium that was periodically tectonically affected by the Wichita orogeny that commenced in the Early Morrowan and continued into the Desmoinesian.

Index map of thesis area.

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