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detrital zircon geochronology, Mississippi embayment, lithofacies analysis, sedimentology, ichnology


We provide new detrital zircon evidence to support a Maastrichtian age for the establishment of the present-day Mississippi River drainage system. Fieldwork conducted in Pontotoc County, Mississippi, targeted two sites containing montmorillonitic sand in the Maastrichtian Ripley Formation. U-Pb detrital zircon (DZ) ages from these sands (n = 649) ranged from Mesoarchean (~2870 Ma) to Pennsylvanian (~305 Ma) and contained ~91% Appalachian-derived grains, including Appalachian–Ouachita, Gondwanan Terranes, and Grenville source terranes. Other minor source regions include the Mid-Continent Granite–Rhyolite Province, Yavapai–Mazatzal, Trans-Hudson/Penokean, and Superior. This indicates that sediment sourced from the Appalachian Foreland Basin (with very minor input from a northern or northwestern source) was being routed through the Mississippi Embayment (MSE) in the Maastrichtian. We recognize six lithofacies in the field areas interpreted as barrier island to shelf environments. Statistically significant differences between DZ populations and clay mineralogy from both sites indicate that two distinct fluvial systems emptied into a shared back-barrier setting, which experienced volcanic ash input. The stratigraphic positions of the montmorillonitic sands suggest that these deposits represent some of the youngest Late Cretaceous volcanism in the MSE.

Funding Source

This research was funded by the University of Mississippi Department of Geology and Geological Engineering, the Geological Society of America Graduate Student Research Grants, and the Gulf Coast Association of Geological Societies Student Grants.



This work was first published in Geosciences 2020, 10(2), 80;

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Supplementary Table 1_U-Pb Data.xlsx (1908 kB)
Supplementary Table 1

Supplementary Table 2_K-S Statistics.xlsx (14 kB)
Supplementary Table 2

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