Sedimentology and Regional Correlation of a Basinally Restricted Deep-Water Siliciclastic Wedge: Brushy Canyon Formation-Cherry Canyon Tongue (Lower Guadalupian), Delaware Basin

Christine Rossen, J. F. (Rick) Sarg

Sedimentologic data and a new regional correlation based on seismic and field data constrain depositional models for basinally restricted siliciclastics of the Brushy Canyon Formation and sandstones of the immediately overlying Cherry Canyon Tongue. In the Guadalupe Mountains, the Brushy Canyon thins at the basin margin, from 300 m to pinch-out, by onlap onto a basinward-sloping submarine unconformity. The onlapping wedge contains numerous basinward-trending channels (up to 50 m deep and 1 km wide). Laminated siltstones comprise interchannel areas and occur in channels as draping units of constant thickness. Sandstones (rippled, parallel laminated, and massive beds) are restricted to channels and onlap channel walls. Density-driven currents flowing into a density-stratifi d basin as interflows and underflows best explain these geometries.

Concentration of sandstones in vertically stacked, 20 to 50-m deep channels suggests sands were point-sourced into the basin. Increasing proportions of high-energy deposits in successive sandstone channel fills indicate progradation of the Brushy Canyon wedge.

Correlation of the Brushy Canyon unconformity shelfward to an interpreted disconformity within the San Andres Formation suggests that the shelf was subaerially exposed. Allochthonous fossils in Brushy Canyon sandstones indicate existing submerged shallow, upper slope areas were normal marine. Updip portions of the lower Cherry Canyon Sandstone Tongue are confined within paleocanyons and are deltaic in origin, suggesting fluvial delivery of sand across the shelf. These regional constraints suggest that density-driven currents were turbidity currents rather than saline density currents sourced by hypersaline shelf waters.

AAPG Search and Discovery Article #91038©1987 AAPG Annual Convention, Los Angeles, California, June 7-10, 1987.