SEDIMENTARY PROVENANCE OF A REGIONAL MIOCENE-PLIOCENE AEOLIAN AND FLUVIAL DEPOSIT ON THE HIGH PLAINS: EVIDENCE FOR UNROOFING OF THE SANGRE DE CRISTO MOUNTAINS?

A regional deposit of Neogene aeolian and fluvial sediments, the Ogallala Formation, from southern South Dakota to western Texas supplying a majority of the water necessary for agriculture and drinking water in the central United States. Previous clast provenance analyses from the lower fluvial strata of the Ogallala Formation from the Southern High Plains indicates sourcing from an array of lithologies including, basalt, granite, dacite, gneiss, and limestone. The variety of lithologies implicates the Sangre de Cristo Mountains in northern New Mexico and south-central Colorado as the predominant source area. We present kernel density estimates from four new detrital zircon U-Pb samples and paleocurrents to augment this dataset. From north to south, the samples are located in southeast Colorado, the Oklahoma panhandle, and west Texas. Youngest U-Pb ages from the four samples range from 36-11 Ma indicating input from the Cenozoic ignimbrite flare up. Together, detrital zircon U-Pb ages indicate the most sourcing from Appalachian-Ouachita, Cordilleran, and Grenville sources, with additional contributions from the Yavapai-Mazatzal orogenic belt and igneous intrusions in the southwest and central U.S. Paleocurrent datasets from southeastern Colorado indicate southeasterly flow, which may instead implicate sourcing from front range sedimentary strata versus sourcing from Appalachian-Ouachita or recycling from sedimentary underlying the Ogallala Formation. Clasts from southeastern Colorado contain similar lithologies to that found south of the Oklahoma panhandle including granite, sandstone, basalt, quartzite, and schist. Paleocurrent and clast data from southeast Colorado pair well with previous clast provenance analysis from West Texas and New Mexico. We speculate that the majority of sediment in the southern portion of the Ogallala Formation was shed from the Sangre de Cristo Mountains, implying a large-scale drainage network during Miocene-Pliocene time. Unroofing in the Sangre de Cristo Mountains may have been driven by extension of the Rio Grande Rift and associated lithospheric heating, ultimately leading to deposition of the Ogallala Formation.