Tracing clastic delivery to the Permian Delaware BASIN, U.S.A.: Implications for paleogeography and circulation in westernmost equatorial Pangea

摘要

The Guadalupe Mountains of the southwestern U.S. (New Mexico-West Texas) expose the shelf edge of the Permian Delaware Basin, which formed near the western edge of the Central Pangean suture in equatorial Pangea. Voluminous siliciclastic strata filled this basin in mid-Permian time, and compose the Delaware Mountain Group (Brushy Canyon, Cherry Canyon, and Bell Canyon formations). These units have long been recognized to record ultimate deepwater deposition of siliciclastic sediments that were pre-sorted via eolian transport as they progressed toward the shelf edge of the Delaware Basin in Permian time. The generally arkosic mineralogy led most previous researchers to identify crystalline basement uplifts of the Ancestral Rocky Mountains (ARM) of the western U.S. as the primary source for the large volumes of Permian siliciclastic material that fill this basin. New provenance data combining modal mineralogy with detrital-zircon geochronology, however, refute this interpretation. Rather than an ARM basement source, indicated by Paleoproterozoic ages, the predominant age populations, comprising 70-80% of the grains, reflect contributions from Paleozoic, Neoproterozoic, and Mesoproterozoic (Grenvillian) age basement. The combined (arkosic-subarkosic) mineralogy and provenance spectra of the siliciclastic strata from the Delaware Mountain Group, together with comparisons with coeval strata and available paleocurrent data indicate sources in the Ouachita system, including recycled Appalachian detritus, and terranes accreted and uplifted south of the Ouachita suture, now in Mexico and Central America. Dispersal pathways likely involved a component of fluvial transport draining the piedmont region of the Ouachita orogenic belt, and ultimate eolian deflation of these fluvial systems within an easterly to southeasterly and seasonal westerly to northwesterly atmospheric circulation. Monsoonal transport, especially northern excursions of the ITCZ during northern hemisphere summers, would have facilitated transport from terranes south of the Ouachita-Marathon suture in present-day Mexico and Central America. Source locations predominantly south-southeast of the study region potentially obviate the need to call upon transcontinental fluvial transport directly from the Appalachian orogen to the southwestern edge of Pangea, at least for this time period. Furthermore, these results place new constrains on the final docking, major uplift, and consequent erosion of the Yucatan-Maya terrane south of the Ouachita orogenic belt, which provided significant siliciclastic detritus to depocenters in the western U.S. during middle Permian time. In contrast, the uplifts of the ARM were either covered, or greatly diminished as sources by this time.