TRACING PALEOZOIC SILICICLASTIC SEDIMENT DISPERSAL TO THE FORT WORTH AND MIDLAND BASINS: IMPLICATIONS FOR PALEOGEOGRAPHY AND ORGANIC MATTER ACCUMULATION

Abstract

The Fort Worth and Midland Basins in central and West Texas are major petroleum-producing systems in North America. The provenances of the thick Paleozoic sedimentary rocks in both basins are poorly constrained, although they are important to the understanding of these petroleum systems. The siliciclastic grains of the upper Paleozoic in the two basins were proposed to be derived from local sources, including the basin-bounding Ouachita-Marathon orogen and crystalline basement-cored Ancestral Rocky Mountains, or distal source of the Appalachian highland. The distal source requires a transcontinental river system routing along the Appalachian-Ouachita forelands. Here I applied several provenance-tracking methods, including detrital zircon U-Pb geochronology and Lu-Hf isotope composition, sandstone petrography, and mudstone rare-earth element compositions, to the Paleozoic strata in the Fort Worth and Midland Basins in order to reconstruct sediment dispersal patterns in the southern margin of Laurentia, and test the sediment routing hypotheses. The data show that during the Cambrian, sediments were transported by local rivers from basement rocks exposed on the Texas Arch to the northwest of the basins. During the Pennsylvanian-early Permian, sediments were transported by a transcontinental river from the Appalachians in the front of the Appalachian-Ouachita orogen and by local rivers draining the peri-Gondwana terranes incorporated in the Ouachita-Marathon orogen. The late Paleozoic sediment dispersal may be assisted by another transcontinental river linking the Midland Basin and Appalachians through the midcontinent area. These rivers may have brought abundant nutrients into the two basins, promoted algal bloom and contributed organic matter enrichment in the basins.