DELTAIC DISTRIBUTARY CHANNELS AND LOBES IN THE PERMO-TRIASSIC QUARTERMASTER FORMATION, WEST TEXAS; PALEOCURRENT ANALYSIS AND DEPOSITIONAL EVIDENCE

Sedimentological and paleogeographic studies indicate that the upper Permian of the Southern High Plains (TX/NM) were deposited by SW directed paleocurrents in fluvial deltaic or marginal marine meandering systems. However, Late Triassic paleocurrent analysis from the unconformably overlying Dockum group show a NW directed paleocurrent. The change in paleo flow is thought to reflect changes in paleogeography from infilling of the Permian Basin from the NE (directing flows SW) to uplift in the SE directing flows NW into the Dockum basin, linked to the initiation of Pangean rifting. The timing and nature of this change has not been previously studied. Recently published U/Pb ages from ashes in the lower part of the Quartermaster Fm (thought to be late Permian Ochoan age), yield ages of 252.1 ± 0.30 to 251.7 ± 0.28 Ma, indicating that the Quartermaster Fm is instead early Triassic.

This study investigates newly accessible canyonlands in the Southern High Plains, along the Caprock Escarpment in Pole Canyon, Quitaque, TX. The area offers continuous exposure of the upper Quartermaster Fm, which has not been previously mapped or studied here. Ongoing research aims to test two main hypotheses: 1) paleocurrent directions shifted from SW to NW during the deposition of the Permo-Triassic Quartermaster, and 2) the stratigraphy, lithology, architectural elements, and sedimentary features of the upper Quartermaster, represents marine deltaic distributary channels and mouth bar depositional system.

Ongoing mapping, measured stratigraphic sections, and field observations yield results of a coarsening upward sequence in grainsize and bed thickness. Fine to coarse-grained sandstone beds exhibit trough cross-bedding, climbing ripples, sand/mud lenses, planar laminations, and debris/gravity flows. Silt/mud beds display planar to wavy laminations, deformed bedding, loading structures, and tidal couplets. Paleocurrent data so far indicates SW-directed flows with no apparent NW shift. Large sets of clinoforms are observed and typical of delta lobe progradation. Evidence of distributary channel fill includes amalgamated channels with erosional bases, truncation and lenticular geometry, lateral accretion, and overbank deposits. These characteristics suggest a prograding deltaic system increasing in sediment supply, shifting from a deeper to shallower depositional setting.