EARLY PENNSYLVANIAN SEDIMENT ROUTING TO THE OUACHITA BASIN BASED ON DETRITAL ZIRCON U-PB ANALYSIS

Previous detrital-zircon U-Pb (DZ U-Pb) studies of Paleozoic sediments of the western US Laurentian margin document the widespread arrival of Appalachian-Grenville age populations (ca. 500-275 Ma and 1250-950 Ma, respectively) during the Carboniferous. However, pathways for continental-scale east-to-west sediment transfer remain unclear. This study presents ~3540 new DZ U-Pb ages from 12 samples from the Lower Pennsylvanian Jackfork Group and Johns Valley Shale of the Ouachita deepwater basin in Arkansas to delineate sediment provenance and paleodrainage systems that sourced these deposits, and how these results bear on the issue of large-scale sediment transfer from the Appalachians to the western Laurentian margin.

U-Pb age spectra indicate that sediment for the Jackfork and Johns Valley were derived from the Laurentian Appalachians to the east, and the midcontinent to the north. All samples display prominent Laurentian Appalachian-Grenville peaks, but also Midcontinent (ca. 1550-1300 Ma), and Yavapai-Mazatzal (ca. 1800-1600 Ma) age peaks, as well as lower-abundance peaks associated with Peri-Gondwanan (ca. 700-500 Ma) and Superior (ca. >2500 Ma) source terrains. However, samples from the most northern, updip site, Big Rock Quarry in Little Rock, AK, exhibit relatively modest Appalachian peaks and elevated Yavapai-Mazatzal peaks when compared with samples collected farther to the south and west. These differences are interpreted to indicate that at least two sediment-routing corridors, from the Appalachian foreland-Black Warrior syntaxis and the US midcontinent, fed the Ouachita basin in Arkansas and Oklahoma. We conclude that Early Pennsylvanian sea-level fall, a contemporaneous shift to a humid climate, and collisional tectonics forced Laurentian sediment routing through at least two paleovalley systems, which sourced the Ouachita basin deepwater deposits.

The approx. north-to-south oriented paleodrainage systems of the US midcontinent, each at least 10⁵ km² in area, physically barred fluvial sediment transport directly from the Central Appalachian orogen to the Western US, as did the Ouachita deepwater basin, which represents a terminal sink. Hence the Appalachian-like DZ U-Pb signal that has been recognized in the Western US likely did not come directly from the US Appalachians.