COMPARATIVE STUDY OF THE SEDIMENTOLOGY AND PROVENANCE OF THE ATOKA FORMATION IN THE OUACHITA FRONTAL THRUST BELT OF OKLAHOMA

The Pennsylvanian Atoka Formation in the Ouachita Mountains of Oklahoma is generally thought to be derived from the southeast extension of the Ouachita Mountains, the southern Appalachian Mountains, and the Illinois Basin. However, it is difficult to reconcile sediment transport from these sources with the northeast-directed paleocurrent indicators that dominate the Atoka Formation in the Choctaw thrust sheet south of Wilburton, Oklahoma. The provenance of the northeastward-deposited Atoka sandstones is not known. Detrital zircon U-Pb dates were determined for Atoka samples collected from five locations having northeast-directed paleocurrent indicators, from four locations having west-directed paleocurrent indicators, and from one location having south-directed paleocurrent indicators. Zircons of Grenville age (~1.1 Ga) dominate all samples. 350-500 Ma zircons were found in all samples. Northeastward-deposited samples contained many 600-850 Ma zircons. Only one zircon of this age was found in the westward deposited samples. The 350-500 Ma and 600-850 Ma zircons are probably from the Yucatan-Sabine Block, which collided with Texas in early Mississippian and with Mississippi in late Mississippian. The relative abundance of 600-850 Ma zircons in the northeast-deposited sediments could be due to deeper unroofing of the Yucatan-Sabine block in the Texas collision. In addition to radiometric age, several other zircon characteristics are used in this analysis including grain elongation, Th/U ratio, and presence/absence of zoning on cathodoluminescence images. These additional characteristics provide a way for distinguishing between zircons from different terranes that have similar radiometric ages.