EARLY PENNSYLVANIAN SEDIMENT ROUTING FROM DISTINCT FLUVIAL SYSTEMS WITHIN THE APPALACHIAN FORELAND BASIN SYSTEM TO DEEP-SEA FANS

The Early Pennsylvanian Ouachita basin was a likely terminal sink for Alleghanian silicilastics, especially for paleovalleys to the east and northeast, but the paleodrainage area boundaries and relative contributions of feeder fluvial systems are unclear. This study presents new detrital zircon (DZ) U-Pb ages and Hf isotopic data values from the Lower Pennsylvanian Pottsville Formation of Alabama and Caseyville Formation of Illinois, as well as petrographic data from the Pottsville, Caseyville, and Jackfork (Arkansas) sandstones, to document provenance and delineate the likely sediment-routing systems within the Appalachian foreland basin system.

Four DZ U-Pb age spectra from the Pottsville and Caseyville Formations generally display prominent Grenville (ca. 1250-950 Ma) age populations, minor Appalachian (ca. 500-290 Ma), Midcontinent granite-rhyolite (ca. 1550-1300 Ma), Yavapai-Mazatzal (ca. 1800-1600 Ma), and Superior (ca. >2500 Ma) age populations, as well as small contributions from peri-Gondwanan (ca. 800-500 Ma), and Penokean/Trans-Hudson (ca. 2000-1800 Ma) source terranes. The Pottsville samples demonstrate a greater percentage of Appalachian and Grenville ages relative to the Caseyville samples, whereas the Caseyville samples have elevated Yavapai-Mazatzal and Superior percentages relative to the Pottsville. We interpret these differences to indicate parallel longitudinal fluvial systems in the foredeep and back-bulge depozones of the Appalachian foreland basin system.

Multidimensional scaling (MDS) analysis demonstrates that DZ samples from the Pottsville and Caseyville cluster with Jackfork samples and we infer a source-to-sink relationship from these two distinct sources. During Early Pennsylvanian icehouse lowstand conditions, contemporaneous rivers transected across shelves near the Appalachian-Ouachita syntaxis and Midcontinent regions. While there are questions regarding precise pathways from source-to-sink and the interpreted depositional environments for the Pottsville Formation, we suggest that sediment was routed from distinct feeder fluvial systems within the Appalachian foreland basin system to Ouachita deep-sea fans in Arkansas and Oklahoma.