--> --> Paleozoic Sediment Dispersal Patterns in the Fort Worth Basin, U.S.A.

AAPG Southwest Section Annual Convention

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Paleozoic Sediment Dispersal Patterns in the Fort Worth Basin, U.S.A.

Abstract

The Fort Worth basin in north-central Texas is a major shale-gas producer, yet its Paleozoic sediments dispersal patterns and their influences on hydrocarbon enrichment in the basin remain under debate. Here we apply detrital zircon U-Pb ages, sandstone petrography, rare-earth element (REE), and Nd isotope compositions to determine provenance of the Paleozoic sedimentary rocks in the Fort Worth basin and understand the sediment dispersal patterns on the southern margin of Laurentia before and during the Laurentia-Gondwana collision. The detrital zircon U-Pb ages of the Cambrian strata suggest that sediments were dispersed by local rivers from the Texas arch. Zircons of the Pennsylvanian strata suggest that sediments were derived from local sources including the basin-bounding Ouachita orogen and Muenster uplift, and distal source of the Appalachians. The sandstone composition changes from the Cambrian (Q91F6L3) to the Pennsylvanian and early Permian (Q87F2L11), suggesting more continental input from Laurentian craton during the Cambrian, but more recycled orogen input during the late Paleozoic. The Paleozoic mudstone samples show enrichment of LREE, flat distributions of HREE, and negative Eu anomalies (0.41 to 0.68) after normalized to Chondrite, consistent with the REE pattern of average upper crust. The Middle and Upper Pennsylvanian samples are progressively depleted in REE, suggesting more influence of source with depleted mantle input, such as the Appalachians. This change confirms the interpretation of Appalachian-derived sediments based on detrital zircon geochronology, and further suggests that the Appalachians became an important sediment source during the Pennsylvanian. Furthermore, mudstone εNd data will be used to test the interpretations.