DATING THE ARRIVAL OF LARAMIDE UPLIFT SEDIMENTS TO EAST-CENTRAL TEXAS AND THE NORTHWESTERN GULF OF MEXICO USING DETRITAL ZIRCON GEOCHRONOLOGY

New U-Pb dating of detrital zircons by LA-ICP-MS for samples obtained from central and eastern Texas documents the arrival time of Laramide uplift sediments to the northwest corner of the Gulf of Mexico coastal plain. Definitive Laramide sediment is identified by a dominance of 62-54 Ma age zircons that appear in Late Paleocene Calvert Bluff and basal Eocene Carrizo Formations (Hutto et al., 2009). Detrital zircon dating of the Early Paleocene (planktic zone P1c) Tehuacana Member (top of Kincaid Fm.) and Seguin Formation (top of Wills Point sequence) reveals a dominance of Yavapai-Mazatzal (1800-1600 Ma) zircons and moderate amounts of mid-continent Granite-Rhyolite Province (1500-1300 Ma) zircons, with minimal to no Laramide presence. Recent work (Blum and Pecha, 2014) shows that Laramide zircons are present in the fluvial-dominated upper Simsboro Formation of the middle Wilcox Group in Texas. This constrains the arrival of Laramide zircons to northeast Texas to the lower Wilcox Group (Hooper to lower Simsboro Formations). The arrival of Laramide (62-54 Ma) zircons to the Gulf of Mexico is potentially a late indicator of Laramide sediment delivery to fluvial systems, as arc-derived Yavapai-Mazatzal and mid-continent Granite-Rhyolite Province dominated zircon assemblages in lower Wilcox strata are consistent with erosion of sedimentary cover on Laramide uplifts.

Upper Wilcox Group sediments dominated by Laramide zircons in NE Texas are limited to a structural low bound on the southwest and northeast by the San Marcos Arch and the Amarillo-Wichita-Ouachita high, respectively. Several sandstones (Nacatoch, Tehuacana, Seguin, and Simsboro) are limited to or have one margin confined by these highs. This low contains the Houston Embayment of NE Texas, which is inferred to contain the trunk drainage of rivers flowing from central Laramide uplifts to the Gulf of Mexico during the Paleocene.