THE PROVENANCE AND PALEOGEOGRAPHY OF THE LATE JURASSIC NORPHLET FORMATION, EASTERN GULF OF MEXICO

The late Jurassic Norphlet Fm. provides a record of rifted margin, siliciclastic sedimentation. Previous studies of Norphlet Fm. provenance in onshore Alabama and Florida suggest the Blue Ridge and Piedmont as primary sediment sources. However, considering the proximity of the Pan-African Suwannee Terrane to the eastern Gulf of Mexico (EGOM), the sedimentary provenance may have varied and the depositional character may be more complicated than previously thought. Little knowledge exists about the sedimentary sources and facies distribution of the Norphlet Formation in the EGOM due to sparse lithologic data. This study provides a paleogeographic model of the Norphlet Fm.- based on provenance and facies analyses projected from the onshore to the offshore EGOM in order to predict sedimentary transport pathways. Data are from wells drilled in onshore and state waters of Alabama, as well as offshore federal waters. These analyses use detrital zircon U-Pb geochronology, thin-section petrography and petrology, and core and well log analysis.

U-Pb analyses of detrital zircons from Norphlet Fm. cores indicate age populations between 350-500, 500-650, and 1000-1300 Ma. These coincide with Piedmont and Blue Ridge sources. 540-580 Ma zircons may support the potential of Pan-African Suwannee terrane sources. Norphlet Fm. compositional data plot in continental block, magmatic arc, and recycled orogen provenance fields in QFL and QmFLt diagrams. Core descriptions show facies interpretations: clast-supported conglomeratic facies indicate alluvial fan and fluvial depositional environments. Fine-medium grained, cross-bedded facies, and wavy laminated facies indicate an eolian depositional environment.

The synthesis of U-Pb ages and compositional data suggest the Appalachian orogen and Pan-African Suwannee Terrane are sources for the Norphlet Fm. Previous studies demonstrate that Norphlet Fm. sediment was carried south via fluvial, alluvial, and eolian systems. Sediment derived from the Suwannee Terrane implies alternate sediment transport pathways from the east. The resultant Norphlet Fm. paleogeographic model in progress provides interpretations of this scenario, illustrating sediment transport into the EGOM from the Pan-African Suwannee Terrane to the east and the Appalachian Mountains to the north.