VOICES FROM THE DEEP: THE SEDIMENTOLOGY AND DETRITAL MINERAL GEOCHRONOLOGY OF THE BLACK WARRIOR BASIN DEPOCENTER

The Alleghanian foreland depocenter formed at the syntaxis of the Appalachian and Ouachita orogens and is represented by ca. 6500’ of sediment in the Black Warrior basin. There is an abundance of core material drilled in the Greater Black Warrior basin for coal and methane exploration, and we are utilizing those cores to provide a relatively continuous stratigraphic sampling of the basin. The most central and deepest core material available from the depocenter was retrieved in the ‘Hendrix core,’ which affords samples from a depth of ca. 500’ to 4300’ (another 2500’ of the Pottsville Formation is between the bottom of the Hendrix core and its contact with the underlying Parkwood Formation). Lithologies in the Hendrix core comprise interbedded sandstone, mudstone, and coal units of the Pottsville Formation from the Brookwood to the Black Creek coal zones, including the Cobb, Pratt, and Mary Lee coal units. Major sandstone units in the core include the Razburg, Camp Branch, Lick Creek, and Bremen Sandstones. At this location and through these stratigraphic levels, the Pottsville Formation is texturally immature, containing a variety of lithic fragments and mineral assemblages. Laser single crystal 40Ar/39Ar ages for muscovite (more than 100 per sample) were determined for six major sandstones in the Hendrix core. In contrast to other muscovite age data we have reported for the Greater Black Warrior basin, the results for these samples seem relatively consistent over the ca. 3800’ interval sampled. Overall, the ages for all samples range from ca. 450 to 280 Ma, though Ordovician ages are less than 5% of any sample. Modes of ca. 320 Ma and 370 Ma are prominent in all samples; though the relative proportion of these varies, the 320 Ma mode tends to dominate the age distributions. The data can be interpreted to indicate that sediment from various sources was thoroughly mixed by the time it reached the depocenter, and thus there is little stratigraphic variation in age over a wide range of section. The relative lack of a Taconian age signal in these samples may indicate it is only prominent in the earliest (deeper) sections of the Pottsville Formation. We are testing this hypothesis and evaluating other parts of the basin through the study of additional samples from other cores and surface exposures.