DETRITAL ZIRCON PROVENANCE OF THE HARTSELLE SANDSTONE, SOUTHEASTERN USA: INSIGHTS INTO SEDIMENT SOURCE, PALEOGEOGRAPHY, AND DEPOSITIONAL SETTING

The Hartselle Sandstone is a light-colored, thick-bedded to massive quartzose sandstone, that is widespread across an area from Georgia to Mississippi, and Alabama to Kentucky. Formation thickness reaches >150 feet, and the unit is Mississippian in age. The most commonly accepted hypothesis for Hartselle deposition suggests that the unit represents barrier islands located in the ocean between Gondwana and Laurentia. According to this interpretation, waves and currents along the shore carried sand and concentrated it into a set of NW to SE trending barrier islands. However, paleocurrent studies are inconsistent with the geographic position of the Hartselle Sandstone because the sand body is not parallel to the ancient shoreline. This research will clarify sediment sources and depositional environment of the unit via 5 samples that were collected across the geographic extent of the Hartselle Sandstone in Mississippi and Alabama. Thin sections were made from each sample for point counting. In addition, heavy mineral separations allowed extraction of zircons for U-Pb analyses.

Thin sections reveal variation in porosity and grain-to-grain contacts, indicating nonuniform diagenetic histories. The dominant material in the samples is quartz, with the exception of two carbonate-rich samples. One of these carbonate samples is the first example found from the Hartselle Sandstone with ooids which are mostly cored by quartz grains. Based on point-counting data and U-Pb zircon ages, we believe that sediment was sourced from the continental interior as well as from recycled orogenic material. Detrital zircon ages also reveal that the drainage basin contributing sediment to the Hartselle Sandstone is much larger than previously estimated as ages range from north-eastern Appalachian sediment to far western Wyoming province sediments. This represents a drastic difference in the interpretation of the drainage pattern of Laurentia in the Mississippian. The age spectra differ between samples, suggesting that the more western deposits are possibly sourced from a fluvial system with some isolation from the eastern sources. This would imply that barrier island sediment was reworked from a multi-deltaic system with a limited degree of sediment mixing.