REEF TO BASIN SEDIMENTOLOGICAL PROCESSES IN THE LAMAR LIMESTONE (BELL CANYON FORMATION), GUADALUPE MOUNTAINS NATIONAL PARK, WEST TEXAS

The upper Guadalupian (Middle Permian) Lamar Limestone of the Bell Canyon Formation is the basinal equivalent of the Tansill Formation on the shelf and the Capitan Formation on the shelf crest and foreslope in the Delaware Basin. Sediment in this system was delivered to the slope and basin by sediment-gravity flows, but little is known about how the sediment type or frequency of flows differs at various places along the reef escarpment. This information is important for understanding environmental heterogeneity on the slope as well as the timing and distribution of sediment delivery to the basin. Four sections were measured through the Lamar Limestone in Guadalupe Mountains National Park, West Texas. Three sections are located on the western side of the park and the fourth is located on the southeastern side of the park in McKittrick Canyon. Initial results from fieldwork indicate that the Lamar can be divided into three packages: a lower limestone unit interbedded with siltstone or sandstone, a middle massive limestone unit, and an upper unit of interbedded conglomerates, normally graded wackestones, and thin-bedded to laminated limestones. Each unit is bounded by sharp contacts, and the contact between lower and middle units of the Lamar also is wavy. Bioturbation occurs in the middle and upper units, but bioturbation in the upper unit is more abundant in the McKittrick Canyon section. Chert nodules and layers are common throughout the Lamar. Fossils become more abundant upsection, and occur as whole, disarticulated, and fragmented specimens. Conglomerates contain bioclastic material (bryozoans, brachiopods, crinoid columnals, echinoid debris), lithoclasts, and/or reef rock in a carbonate matrix. The bioclastic material is transported to the slope and toe-of-slope by debris flows and turbidites. Debris flows thicken and thin along outcrop, and occur as single-event or amalgamated flows. Interbedded with conglomerates are normally graded beds of wackestone, thin-bedded limestone, and laminated limestone at the centimeter to sub-millimeter scale. The Lamar is overlain by the Reef Trail Member, which is siltier and also contains carbonate debris flows before deeper-water deposits become dominant in this succession.