LAUSR

ABSTRACT Collision of Gondwana and Laurentia in the late Palaeozoic created new topography, drainages, and foreland basin systems that controlled sediment dispersal patterns on southern Laurentia. We utilize sedimentological and detrital zircon data from early Permian (Cisuralian/Leonardian) submarine-fan deposits in the Midland Basin of west Texas to reconstruct sediment dispersal pathways and palaeogeography. New sedimentological data and wire-line log correlation suggest a portion of the early Permian deposits have a southern entry point. A total of 3259 detrital zircon U-Pb and 357 εHf data from 12 samples show prominent groups of zircon grains derived from the Appalachian (500–270 Ma) and Grenville (1250–950 Ma) provinces in eastern Laurentia and the peri-Gondwana terranes (800–500 Ma) incorporated in the Alleghanian-Ouachita-Marathon orogen. Other common zircon groups of Mesoproterozoic-Archaean age are also present in the samples. The detrital zircon data suggest throughout the early Permian, Appalachia and Gondwana detritus was delivered by a longitudinal river system that flowed along the Appalachian-Ouachita-Marathon foreland into the Midland Basin. Tributary channels draining the uplifted Ouachita-Marathon hinterland brought Gondwana detritus into the longitudinal river with headwaters in the Appalachians or farther northeast. This drainage extended downstream westward and delivered sediments into the Permian Basin near the west terminus of the Laurentia-Gondwana suture. Estimated rates of deposition and proportions of zircons from more local (Grenville) versus more distal (Pan-African) sources indicate that river strength decreased throughout early Permian time. Primary sediment delivery pathway was augmented by minor input from the Ancestral Rocky Mountains and wind deflation of fluvial sediments north and east of the basin. Slope failure associated with early Permian deposition in the southeastern margin of the Midland Basin triggered gravity flows leading to submarine fan deposition.