THE SYNOROGENIC PROVENANCE RECORD OF THE LATE PALEOZOIC MARFA BASIN IN WEST TEXAS – A MICROCOSM OF THE ANCESTRAL ROCKY MOUNTAIN AND MARATHON-OUACHITA INTERPLAY

The Marfa Basin in West Texas is a late Paleozoic synorogenic depocenter characterized by syntectonic turbidite deposition that temporally overlapped with regional deformation linked to both Ancestral Rocky Mountain (ARM) uplift and Ouachita-Marathon (OM) shortening. The Marfa Basin occupies a key paleogeographic position at the intersection of ARM and OM structural trends and thus offers a unique opportunity to study potential provenance shifts governed by the temporal and kinematic interaction of these two deformation belts. In this work, we present new sandstone petrography and detrital zircon (DZ) U-Pb geochronology from the Pennsylvanian-Permian Alta Formation of the Marfa Basin to constrain the timing and interactions of the ARM and OM belts in late Paleozoic SW Laurentia. These new provenance constraints reveal three separate tectonically driven source stages: 1) syntectonic ARM deposition, 2) orogenic transition, and 3) progressive OM foredeep deposition. During Late Pennsylvanian-earliest Permian Alta Fm. deposition, sediment was sourced from Mesoproterozoic Laurentian basement, likely from the adjacent Diablo Platform, an ARM uplift, as evidenced by DZ signatures and quartzo-feldspathic sandstone composition. Middle Alta Fm. (lower Wolfcampian) turbidites archive a transition from ARM-related basement to Gondwanan-type sources. This transition is not characterized by source mixing, but rather by interfingering of turbidite lobes alternately sourced from the Diablo Platform and the advancing OM thrust belt, which contributed Gondwanan DZ signatures. In contrast, the upper Alta Fm. (middle to upper Wolfcampian) is dominated by detritus from the OM hinterland as evidenced by Gondwanan DZ signatures and sandstone containing abundant metamorphic lithics. By late Wolfcampian time, ARM basement uplifts were tectonically inactive and subsiding, and the advancing OM frontal thrust belt dominated the sediment supply to the Marfa Basin. Our new data illustrate a distinct switch from ARM- to OM-related syntectonic deposition in West Texas and thus provide critical new insights into temporal interactions between ARM and OM deformation in southern Laurentia during the late Paleozoic, leading up to final Pangea assembly.