PALEOMAGNETISM AND BIOSTRATIGRAHY OF UPPER CRETACEOUS MARINE DEPOSITS IN THE MISSISSIPPI EMBAYMENT

We correlate Upper Cretaceous marine deposits in Arkansas, Texas, Alabama, and Mississippi by paleomagnetism and biostratigraphy using the polarity time scale for Gubbio, Italy, (Lowrie and Alvarez, 1977) and of Gradstein et al. (2004). The combined data suggest that the Nacatoch Sand (Navarroan) and Brownstown Marl (Austinian) of southwestern Arkansas correlate with Gubbio Reversed Polarity Zones E- and A- (Polarity chrons C31 and C33 of Gradstein et al., 2004), respectively. Other Austinian, Tayloran, and Navarroan deposits (Tokio Fm, Ozan Fm, Annona Chalk, Marlbrook Fm, Saratoga Chalk, Arkadelphia Fm, Gober Chalk, Sprinkle Fm) possess a weak remanent magnetization of normal polarity. On the basis of alternating field demagnetization measurements, we believe that the normal polarity represents a primary magnetization, and interpret deposition of the Tokio Fm to have occurred during the Gubbio Long Normal Zone (Santonian and older; Gradstein et al., 2004, Chron C34), and that of the other units in Gubbio Normal Polarity Zone B+ (Gradstein et al., 2004, chrons C32 and C31)(Campanian to early Maestrichtian). The boundary between the Austinian and Tayloran Provincial Stages approximates the boundary between Gubbio Reversed Polarity Zone A- and Gubbio Normal Polarity Zone B+, and the Tayloran-Navarroan boundary is probably within the upper part of Zone B+, all within Chron C33 of Gradstein et al. (2004). The paleomagnetic record can be further examined using three exposures of the Cretaceous/Paleogene boundary along a 1600-km transect in south and east-central Texas. The exposures and thicknesses are at Walkers Creek, Milam County (4 m); Brazos River, Falls County (10 m); and Littig quarry, Travis County (15 m). Along that transect, the Navarroan (Cotton Creek), Austinian (Little Walnut Creek), and Tayloran (Bushy Creek) provincial stages in Texas warrant paleomagnetic study to correlate them more accurately with the invertebrate fossils in the northwestern Mississippi Embayment described above.