SANDSTONE PETROGRAPHY, REE AND NEODYMIUM ISOTOPE CONSTRAINTS ON PALEOZOIC SEDIMENT DISPERSAL TO THE FORT WORTH BASIN

The Fort Worth basin in east-central Texas is a late Paleozoic foreland basin of the Ouachita orogen. Sediment provenance and routing of the basin fill are important to the reconstructions of basin evolution and tectonic setting. Detrital zircon U-Pb ages of the Upper Pennsylvanian strata in the basin suggest that the clastic grains were from both local sources including the basin-bounding Ouachita orogen and Muenster uplift of the Ancestral Rocky Mountains and distal source of the Appalachians. However, the lack of coarse-grained material in the lower and middle Paleozoic strata limits our understanding of the timing of initial arrival of the Appalachian grains, and the interpretation of Appalachian source based on abundant Grenvillian zircons needs to be verified because of their high fertility in sediment recycling. Here we determine sediment provenance of the Paleozoic sedimentary rocks in the Fort Worth basin using sandstone petrography analysis, and mudstone rare-earth element (REE) and Nd isotope compositions. The sandstone composition changes from the Cambrian (Q₉₁F₆L₃) to the Pennsylvanian (Q₉₁F₄L₅), suggesting more continental input from Laurentian craton during the Cambrian, but more recycled orogen input during the Pennsylvanian. 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. Mudstone εNd data will be used to confirm the interpretations.