DETRITAL ZIRCON AND MUSCOVITE AGE SPECTRA, ACROSS THE MISSISSIPPIAN-PENNSYLVANIAN BOUNDARY, OUACHITA BASIN, OKLAHOMA

In the Ouachita Mountains of Oklahoma and Arkansas, a major regional unconformity separates the Mississippian Stanley Group from the Pennsylvanian Jackfork Group and likely corresponds to the Mid-Carboniferous Eustatic Event (MCEE), a major global sea level drop in response to the onset of continental glaciation. The MCEE influenced drainage patterns, sediment provenance and distribution patterns, and the interconnectedness between the southern Appalachian, Black Warrior, and Ouachita basins. Rapid flexural deepening of the Ouachita trough resulted in a Late Mississippian starved basin until the onset of major early Pennsylvanian sediment thickening that was contemporaneous with the MCEE. We dated both detrital zircon and muscovite from the same samples of the uppermost Stanley and the lowermost Jackfork to evaluate the response of sediment provenance changes to the changes in continent-scale sediment transport patterns.

The uppermost Stanley Group sample yielded detrital muscovite ages mostly between 400-525 Ma, dominated by Taconian ages, with only 8 grains between 325 and 380 Ma and two grains at about 620 Ma. Detrital zircons show a similar Paleozoic spectrum with a prominent Mesoproterozoic peak and grains between 1.5-2.5 Ga. Detrital muscovite in the lowermost Jackfork sample show no grains younger than 375 Ma and a more prominent 375-400 Ma peak with a subdued 400-475 Ma peak compared to the Stanley sample. The Jackfork detrital zircon spectrum is dominated by Mesoproterozoic ages, with rare grains as young as 337 Ma and a Paleozoic peak at around 375-400 Ma.

Detrital mineral ages from the same samples are consistent with the idea that the zircon record is influenced by older, and more likely reworked, sedimentary components while the muscovite record better reflects the youngest, least reworked or even first-cycle, constituents. As shown in prior studies, detrital minerals from the Appalachian tectonic episode (i.e., Alleghanian) most closely preceding deposition are rare or absent. The change in detrital zircon ages across the MCEE is consistent with previous work that infers a change from more proximal sediment sources into nearby depositional basins during times of elevated sea level, to more distal sediment sources distributed by major axial river systems at times of lower sea level.