Sandstone petrographic and mudstone REE and Nd-isotopic evidence for Middle Pennsylvanian arrival of Gondwana sediments in the Fort Worth Basin

Abstract

The Fort Worth Basin in north-central Texas is a foreland basin of the Ouachita Orogen that was formed during the late Paleozoic Laurentia-Gondwana collision, and its Paleozoic strata contain key information about the tectonic processes on the southern margin of Laurentia. Here we study sandstone petrography, mudstone rare-earth element (REE) and Nd isotope geochemistry of the Paleozoic clastic rocks in this basin. These data were integrated with previously published detrital zircon UPb data to determine Paleozoic sediment provenance in the Fort Worth Basin and response of the sedimentary system to the Laurentia-Gondwana collision. Sandstone composition changed from the Cambrian (Q90F6L4)–Middle Pennsylvanian (Q89F4L7) to the Late Pennsylvanian-earliest Permian (Q84F2L14), suggesting an increase of input from a recycled orogen after the Middle Pennsylvanian. The mudstones have REE patterns of average upper crust. Compared to the Cambrian-Lower Pennsylvanian mudstones, the Middle Pennsylvanian-lowermost Permian mudstones have more depleted light REE, larger Eu anomalies, and lower εNd values, suggesting a change of sediment provenance after the Early Pennsylvanian. This change is best explained by the arrival of clastic grains from Gondwana, most likely the Sabine Peri-Gondwana terrane, during the Middle Pennsylvanian. Our new provenance data support the previous interpretation that Gondwanan detritus contributed sediment to the Fort Worth Basin during the Middle Pennsylvanian-early Permian, most likely through erosion by transverse rivers linking the high Ouachita hinterland and foreland as the collision of Laurentia and Gondwana advanced to the east of the Fort Worth Basin.