Age and provenance of the Middle Jurassic Norphlet Formation of south Texas: Stratigraphic relationship to the Louann Salt and regional significance

Abstract: The age and provenance of the Norphlet Formation in south Texas and its stratigraphic relationship with the Louann Salt is documented for the first time using new detrital zircon U-Pb geochronological data. Nine samples from the Hockley salt diapir and four deep wells (three in south Texas, one offshore México) yielded 1001 zircon ages and eight age populations; most important are: Neoproterozoic (900–541 Ma), Cambrian-Middle Mississippian, and arc-related Middle to Late Mississippian-Permian-Triassic and Triassic-Jurassic, the latter two representing the first evidence of Nazas and Guerrero arc extrusive volcanism reaching south Texas. Statistical analyses of these data and published zircon ages support the interpretation that these age populations reflect the dominance of peri-Gondwanan sources, especially the Yucatán/Maya Block and Coahuila terrane, though Laurentian sources likely contribute to specific populations. The maximum depositional age of upper Norphlet Formation sandstones is 165.5  ± 1.5 Ma (Callovian). These upper sandstones are separated from lower Norphlet sandstones by an unconformity spanning 1.5 – 5 Myr; the lower sandstones are interbedded with halite of the Louann Salt, and may be as old as Bathonian. These new data may be of regional significance when applied to future models of the Jurassic evolution of the Gulf of Mexico.