SEDIMENT GENERATION, TRANSPORT, AND RECYCLING ALONG A LONG-LIVED CONTINENTAL MARGIN: BIG BEND NATIONAL PARK REGION, WEST TEXAS

The Big Bend region of west Texas represents a long-lived continental margin that has undergone several convergent-divergent tectonic cycles from Late Mississippian time to the present. This area has been deformed by Marathon/Ouachita and Laramide shortening as well as Late Triassic-Late Cretaceous rifting associated with the opening of the Gulf of Mexico and Cenozoic Basin and Range extension. Using U-Pb detrital zircon geochronology we are able to track sediment generation, dispersal, and recycling throughout the margin’s long history. We compare detrital zircon age probability curves, peak ages (and interpreted sources), along with spatial and temporal changes in sources to understand the various stages of development of this continental margin. Several Paleozoic, Mesozoic, and Cenozoic formations were analyzed that are exposed in and near Big Bend National Park. From oldest to youngest these include the Tesnus, Dimple, Haymond, Aguja, Javelina, Black Peak, Hannold Hill, and Canoe Formations as well as the modern Rio Grande River sediment. Major changes in detrital zircon populations occur between Paleozoic strata and Mesozoic strata which we interpret as reflecting a change from dominantly Ouachita-Marathon Orogen derived sediment to Cordilleran-Nazas arc derived sediment. Our data also show a second major change in detrital zircon populations between Mesozoic and Cenozoic strata that we interpret as recording the transition from sediment derived from Laramide uplifts and Cordilleran arc sources to more local Basin and Range sediment sources. The detrital zircon data also provide new information on the maximum depositional ages of the formations in this region and the timing of deformation along this continental margin.