MULTI-MINERAL AND ELEMENTAL ANALYSIS OF WESTERN U.S. MIDCONTINENT MODERN RIVER SEDIMENT: IMPLICATIONS FOR GULF OF MEXICO CONTINENTAL MARGIN PROVENANCE ANALYSIS

The U.S. Gulf Coast sedimentary strata contain a record of changing North American climate and tectonic regimes, and sediment provenance analysis is critical to its interpretation. Although recent detrital zircon U/Pb (DZUPb) geochronology has resolved some source-sink pathways, limitations to the spatial resolution of this technique have become apparent. For example, detrital zircon age spectra in updip Cenozoic strata from central Texas to central Arkansas show only subtle spatiotemporal changes despite being interpreted as the sediment sink for a >1000 km wide swath of the Laramide province. In this context, we expanded our provenance tool-kit by performing mineralogical, elemental, and geo-/thermo-chronological analyses on sediment samples collected from eight western U.S. mid-continent rivers (Missouri, Platte, Arkansas, Red, Brazos, Colorado, Pecos, and Rio Grande). These rivers drain the entire U.S. Laramide province, over a distance of nearly 2000 km, and their headwater regions likely represent the major long-term sediment sources to the western Gulf Coast, at least for much of the Cenozoic Era. We measured bulk and heavy mineralogy; fine fraction major/trace and rare-earth element composition; and detrital apatite U/Pb (DAUPb) data for each sample.

From north to south, pre-Mesozoic DZUPb populations consist of Paleoproterozoic (Missouri), Paleoproterozoic–Mesoproterozoic (Platte, Arkansas, Red), Mesoproterozoic–Paleozoic (Brazos, Pecos), Mesoproterozoic-only (Colorado) and absent (Rio Grande). We show that DAUPb data record overprinting by mid-crustal thermal events in the Mesoproterozoic (Red) and the Paleozoic (Brazos, Pecos). Furthermore, refractory heavy minerals (e.g., zircon, tourmaline, rutile) are enriched in rivers that originate in Paleozoic sedimentary basin provinces of the southwestern midcontinent. Both of these findings could distinguish southern vs. central Laramide source regions that are otherwise un- differentiated. Finally, we show that river sediments are variably enriched with mafic minerals (e.g., augite) and elements (e.g., vanadium) hundreds of kilometers downstream from volcanic sources, resolving source elements in the Laramide province that are not well captured by zircon.