Provenance of the Upper Jurassic Norphlet and Surrounding Formations from U-Pb Detrital Zircon Geochronology

Abstract

U-Pb detrital zircon geochronology supplemented by thin-section petrography, dense mineral analysis of samples, and well log analysis from onshore Florida (western panhandle and western peninsula) as well as from the offshore federal lease blocks, Mobile Bay, Pensacola, Destin Dome, St. Petersburg, and Florida Middle Ground are used to constrain the provenance of the Upper Jurassic Norphlet and surrounding formations. Using LA-ICPMS, 867 U-Pb ages from 10 samples, core and cuttings, were determined. Results show an influence of both Laurentian and Gondwanan (Suwannee Terrane) derived sediments. Four major U-Pb age populations exist in the samples which include 250-500 Ma, 500-700 Ma, 900-1400 Ma, and 1950-2250 Ma. These age populations are coeval with several known tectonic events in the source terranes: Laurentian Appalachian mountain building (Alleghanian, 280-325 Ma, Acadian, 384-425 Ma, Taconic, 430-480 Ma) and Grenville orogenies (900-1300 Ma) and the Gondwanan, Pan-African (500-680 Ma) and Trans-Amazonian/Eburnean (1900-2250 Ma) events. To understand sediment distribution in the study area, four geochronologic source areas, based on suites of U-Pb age distributions, were identified: Appalachian hinterland, Appalachian foreland basin, Mesozoic rift basin, and the Suwannee Terranne. Only the Mobile Bay sample showed an almost entirely Laurentian suite of U-Pb ages. The three samples from the Florida Panhandle showed some mixing of Laurentian and Gondwanan sediments. While the U-Pb age distribution of the Florida Panhandle samples showed a more abundant Laurentian population (250-500 Ma and 900-1300 Ma), a Gondwanan population is also present (500-700 Ma and 1900-2250 Ma). The two samples within the Apalachicola Embayment (i.e., Destin Dome and Pensacola federal lease blocks) have a stronger Gondwanan influence but the Laurentian-aged zircon are still present. The samples from southeastern Gulf of Mexico are past the updip limit of the Norphlet Formation and consist of Paleozoic Basement, the Haynesville Formation, and the Cotton Valley Group. Their U-Pb age distribution shows an entirely Gondwanan source with most ages between 500-700 Ma (Pan-African). The U-Pb detrital zircon data along with thin-section petrography and dense mineral analysis support previous paleogeographic models that consist of a proximal paleo-high source in which alluvial and wadi facies carry sediment into the eolian system. Point-counting of five samples showed the Norphlet to increase in compositional maturity away from the paleo-high source areas. The Norphlet consists of subarkose in the Florida Panhandle with an average modal abundance of Q64F33L3 and arkose in the Apalachicola Embayment with an average modal abundance of Q79F15L6. Dense mineral analysis showed that detrital samples closer to the paleo-high source area have more of the less resistant phyllosilicate material (Florida Panhandle and Mobile Bay) than those more distal (Apalachicola Embayment). The provenance data also supports the hypothesis of two major…