U-PB DETRITAL ZIRCON GEOCHRONOLOGY OF THE LATE PALEOCENE EARLY EOCENE WILCOX GROUP, EAST-CENTRAL TEXAS

Arrival of Laramide uplift sediments to the Texas Gulf Coastal Plain and northwestern Gulf of Mexico during the Early Paleogene is recorded in strata of the Wilcox Group as a significant increase in sediment accumulation and in the appearance of detrital zircons with late Laramide ages (ca. 52-65 Ma). New U-Pb dating of detrital zircons by LA-ICP-MS for samples obtained from east-central Texas documents the arrival of late Laramide uplift sediments, distinguished by the presence of ca. 52-65 Ma detrital zircons. Dating of Early Paleocene Tehuacana Member through Early Eocene Queen City Formation sediments identifies the arrival of late Laramide-age detrital zircons to east-central Texas within the Hooper Formation of the Wilcox Group. These ages are not present in all Wilcox Group samples, are most pronounced in the basal Simsboro, Calvert Bluff, and Carrizo Formations, and are absent in the Queen City Formation. Late arrival of these young detrital zircons contrasts with timing of the initial flood of Laramide sediments recorded in the upper Wills Point Formation. Appearance of ca. 52-65 Ma detrital zircons is correlated with exposure of volcanics or igneous rock produced during uplift, while older Laramide-derived sediments are inferred to contain reworked detrital zircons and be derived from sedimentary cover on Laramide uplift blocks.

Age components of potential source regions within the southern Rocky Mountains, Arizona, and northern Mexico correspond with Gulf Coastal Plain data, while northern Rocky Mountain data are most dissimilar. Late Laramide-age detrital zircons are relatively absent in south Texas Wilcox Group data; these detrital zircon age spectra contrast with east-central Texas data. Wilcox Group data in northern Louisiana correspond with east-central Texas data and contain these young ages. This supports an overall sediment source and paleodrainage area for the south Texas Wilcox Group that differed from east-central Texas and northern Louisiana. Additionally, data indicate the introduction of a new sediment source and/or a greater contribution of detrital zircons from an already existing source by the time of Queen City Formation deposition in east-central Texas, which also appears to have been available during deposition of younger Claiborne Group sediments in northern Louisiana.