Detrital zircon U-Pb age constraints on the provenance of the late Jurassic Norphlet Formation, eastern Gulf of Mexico: implications for paleogeography
Detrital zircon U-Pb geochronology and thin-section petrology of core samples taken from onshore Alabama and offshore federal lease blocks, including Destin Dome, Pensacola, and Mobile, constrain sediment provenance for the Upper Jurassic Norphlet Formation in the eastern Gulf of Mexico. Previous research of the Norphlet Fm. in onshore Alabama suggests that sediments near onshore areas of Alabama originated from metamorphic rocks of the Talladega slate belt and Piedmont. This study provides evidence that the Gondwanan Suwannee terrane is another potential source for the Norphlet Fm. in the EGOM. This study determined U-Pb ages for 1111 detrital zircons from 13 Norphlet Fm. core and cutting samples were determined using LA-ICPMS. The Norphlet Fm. yields four major U-Pb age ranges: 197.9 - 350 Ma, 350 - 770 Ma, 800 - 1650 Ma, and 1650 - 3390 Ma. These ages correspond with known U-Pb ages of source terranes common to Laurentia, including the Grenville (950 - 1300 Ma), (Granite-Rhyolite (1350 - 1550 Ma), Yavapai-Matzatzal (1650 - 1750 Ma), Penokean (1800 - 1900 Ma), and Superior Provinces (>2500 Ma). U-Pb ages also reveal sourcing from the Gondwanan Suwannee Terrane (540 - 580 Ma and 2000 - 2200 Ma). This study establishes four geochronologic source terranes: the ancient Appalachian Mountains, the Appalachian foreland basin, Mesozoic rift basins, and the Suwannee Terrane. Ten samples from onshore Alabama yield detrital zircon U-Pb ages characteristic of Laurentian sources (Appalachian mountains and Appalachian foreland basin), whereas two offshore samples yield characteristic Gondwanan (Suwannee Terrane) ages. Four samples located adjacent to the Mesozoic rift basin reveal ages characteristic of both Laurentia and Gondwana - indicating an area of sediment mixing during the late Jurassic. Twelve thin-sections taken from 9 cores in the onshore and state waters areas were point counted for 400 grains each for compositional analysis. Petrolographic analyses reveal plagioclase and potassium feldspars, polycrystalline quartz, metamorphic and volcanic lithic fragments as dominant grain types. Petrologic data corroborate that onshore Alabama samples were sourced by recycled orogenic and cratonic rocks of Laurentia and southern samples were sourced by less mature sources characteristic of a rift basin (Mesozoic rift basins). A paleogeographic reconstruction illustrates sediment being distributed from Laurentian and Gondwanan sources via alluvial, fluvial, eolian, and marine depositional environments.