U-Pb Detrital Zircon Geochronology of the Late Paleocene Early Eocene Wilcox Group, East-Central Texas

Abstract

Sediment delivery to Texas and the northwestern Gulf of Mexico during the Early Paleogene represents an initial cycle of tectonic-influenced deposition that corresponds with the timing of late Laramide uplift. Sediments shed from Laramide uplifts to east-central Texas and the northwestern Gulf of Mexico during this time are preserved in strata of the Wilcox Group and lower Claiborne Group. U-Pb dating of detrital zircons from closely spaced stratigraphic units within these groups and the underlying Midway Group by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) reveals the relative arrival time of late Laramide-age detrital zircons to east-central Texas and distinct detrital zircon age assemblages. Comparison of zircon age assemblages from this study with data from potential source regions and additional Wilcox and Claiborne Group samples along the Texas and Louisiana Gulf Coastal Plain provides insight into paleodrainage during the Early Paleogene.

The relative arrival time of late Laramide-age detrital zircons to east-central Texas corresponds with deposition of the Hooper Formation of the Wilcox Group, although the presence of these detrital zircons fluctuates within younger samples. Comparison of composite detrital zircon age spectra from sediment source regions and from locations along the Texas and Louisiana Gulf Coastal Plain shows that source regions contain unique distributions of ages, with age components that are similar to Gulf Coastal Plain data. Detrital zircon age data may support relatively similar sediment sources or a similar paleodrainage area for the majority of observed ages within the Midway Group, Wilcox Group, and Carrizo Formation in east-central Texas. Louisiana Wilcox Group and east-central Texas (Tehuacana Member through Carrizo Formation) data are similar and contrast with data of the south Texas Wilcox Group. This may support similar paleodrainage for Louisiana and east-central Texas and a different paleodrainage to the south Texas area. Data may also support the introduction of a new sediment source or a greater contribution of detrital zircons from an already existing source by the time of Queen City Formation (lower Claiborne Group) deposition in east-central Texas. Comparison of Louisiana Claiborne Group data with east-central Texas Queen City Formation data indicates that this source was also available during deposition of younger Claiborne Group strata in Louisiana.