Abstract

Early Pennsylvanian sediment dispersal across the Laurentian supercontinent reflects the growth of the Appalachian–Ouachita Orogen that was formed by its collision with Gondwana. Occupying a key position within the Laurentian foreland of the Appalachian–Ouachita Orogen, the middle Bloyd sandstone member of the Bloyd Formation (Early Pennsylvanian) preserves evidence of Morrowan-age fluvio-deltaic depocenters in the southern Laurentian continental margin. The middle Bloyd sandstone provides direct constraints on provenance and dispersal paths of detritus shed from the Appalachian–Ouachita Orogen and other sediment sources on the North American craton during the Early Pennsylvanian. Eight outcrop samples of the middle Bloyd sandstone were collected and analyzed by U-Pb laser ablation ICP-MS detrital-zircon geochronology, producing a total of 850 concordant individual detrital-zircon ages with age ranging from 3.15 Ga to 374 Ma. Detrital-zircon age spectra of the eight middle Bloyd sandstone samples are characterized by a prominent Grenvillian age group (∼ 1350–900 Ma) with two discrete age peaks at ∼ 1070 and ∼ 1169 Ma. The remaining zircon fractions are interpreted as being sourced from the Archean Superior Province (> ∼ 2500 Ma), the Penokean and Trans-Hudson Proterozoic terranes (∼ 1900–1800 Ma), the Yavapai–Mazatzal terrane (∼ 1800–1600 Ma), the Granite–Rhyolite Province (∼ 1600–1350 Ma), and a minor Paleozoic age population (∼ 500–350 Ma) that likely reflects mixed Appalachian and Gondwanan sources. Overall, detrital-zircon age populations of the middle Bloyd sandstone share great similarity with Lower Pennsylvanian sandstones from the Michigan Basin and the central and southern Appalachian foreland, except that the Bloyd sandstone shows greater enrichment in the Yavapai–Mazatzal age population. These new age data provide additional constraints on multiple dispersal paths for fundamentally Laurentian-derived sediment that are ultimately directed southward toward the Ouachita foreland shelf during the Early Pennsylvanian. The Early Pennsylvanian (Morrowan) sediment dispersal in this part of Laurentia was accomplished by a regional-scale drainage system that integrated intracratonic and Appalachian–Ouachita foreland basin depocenters, all recording a recycled orogenic provenance. The new detrital-zircon data indicate that the middle Bloyd sandstone also incorporated significant contributions from Precambrian-age basement uplifts, possibly Ancestral Rocky Mountain uplifts to the west, indicating a complex geography of the Laurentian supercontinent at this time.