DETRITAL ZIRCONS FROM TERTIARY STRATA ON THE MISSISSIPPI AND ALABAMA COASTAL PLAIN INDICATE SEDIMENT SOURCING FROM APPALACHIAN-OUACHITA HINTERLAND AND/OR FORELAND

Understanding the provenance of Cenozoic sandstones from the U.S. Gulf Coastal Plain has the potential to illuminate the erosion of the North American continental interior and to inform petroleum system analysis by better delineating/predicting the spatial distribution and dimensions of various elements of the petroleum system, including elements in prospective down dip portions of the basin. We present a provenance analysis for ten sandstone samples collected from the Mississippi and Alabama coastal plain, based on ~120-140 new U-Pb detrital zircon ages from each sample. Depositional age control comes from biostratigraphy and lithostratigraphic correlation, and depositional ages range from Paleocene to Pliocene. The results reported herein are for a subset of samples from paired transects through delta plain and shallow marine strata that crop out across the southern portion of the two states.

All samples are dominated by age probability peaks at 1200-1100 Ma, 1100-1000 Ma, and several peaks between 500-300 Ma. A few samples with Paleocene-Eocene depositional ages have minor age probability peaks at 1800-1600 Ma. About half of the samples have a small number of single grain ages that are <250 Ma, but we do not detect any robust age probability peaks (defined by ≥3 overlapping single grain ages) that are <250 Ma. Although the dominant age distributions in these samples are commonly found in potential sediment source regions around interior North America, the age distributions have a paucity of zircons (~0 - 10% of overall distribution in each sample) known to be exclusive to sediment sources in the North American Cordillera. Thus, our findings suggest that crystalline or sedimentary rocks in the Appalachian-Ouachita hinterland and/or foreland, in the eastern portion of the continent, were the primary source of sediment to the Alabama and Mississippi coastal plain during the Cenozoic. Detrital zircon age spectra presented here contrast with those from correlative Tertiary strata in Louisiana, which generally contain high proportions of zircons that must have been derived from sources in the North American Cordillera. Therefore, our findings reinforce the notion that there was a depositional divide between sediment dispersal systems in Louisiana and the eastern Gulf of Mexico during much of the Cenozoic.