Provenance and paleotectonic setting of conglomerates in the Virgilian Holder Formation, northern Sacramento Mountains, New Mexico
Dunning, Charles Preston
Wilson, James Lee
Master of Arts
The Late Pennsylvanian (Virgilian) Holder Formation of the Sacramento Mountains, south central New Mexico, is composed of clastic and carbonate rocks cyclically deposited on the narrow Sacramento Shelf. Coarse channel fill conglomerates are often found in the lower terrigenous member of the cycles. The cycle thicknesses, coarse terrigenous clastic thicknesses and the trend of the conglomerate channels respond to both the pre-cycle topography and the growth of topographic structures during deposition of the cycle. The prominence of the tectonic structures appear to have increased during the early Virgilian to a maximum during cycle 6. The relatively thin and uniform thicknesses during cycle 7 indicates that growth of shelf structures was at a minimum. Growth was renewed during cycles 8 and 9, documented by the rejuvenation of the La Luz Anticline and the Dry Canyon Syncline. Paleotransport directions from the lower 9 cycles generally indicate southwesterly transport, away from the Pedernal Uplift and into the Orogrande Basin. Where channels are recognized, there is good correlation between channel trends and transport directions. During the height of the transgressive phase of the cycle, the Paleozoic detritus derived from the Pedernal Uplift was involved in high energy coastal processes at the base of the escarpment. It was in this environment that Paleozoic chert and Cambro-Ordovician Bliss Formation quartzite clasts were rounded, and whatever feldspars and Pre-Pennsylvanian limestones that has not been reduced insitu on the uplift or in transport, were destroyed. High energy runoff from the uplift spread the cherts, quartzites and quartz sand across the shelf as clastic flows. These flows cut the channels, incorporating shelf linestones of Virgilian age into the Virgilian conglomerate deposits.