Abstract

A surface geologic map is constructed for an area of approximately eight square miles both east and west of Texas FM 2185, 35 miles northeast of Van Horn, West Texas in the northwestern part of the Apache Mountains. Middle Permian Guadalupian-Late Permian Ochoan age strata containing Capitan Reef debris and shelf to basinal beds are exposed and can be correlated to similar age strata of the Guadalupe Mountains to the north and northwest of the map area. Three formations of the uppermost Middle and Upper Permian, Bell Canyon, Castile, and Rustler, expose strata that can be seen in a series of road cuts along Texas FM 2185. The Bell Canyon Formation, a sequence of approximately two hundred meters of strata consisting of limestone, silt-stone and debris flows, is the oldest unit exposed in the map area. The strata of the Castile and Rustler Formations successively overlie the strata of the Bell Canyon Formation. The Castile Formation is an evaporite with alternating dark and light gray laminations at the base and is brecciated towards the top. The Rustler Formation is also an evaporite, primarily brecciated, with rare exposures of red sandstone at the base. The strata exposed in this area are structurally complex due to the intersection of the Stocks fault, the Border fault zone, and the Seven Heart graben complex. The main goals of this study are: 1) to construct a geologic map of the area, 2) to use microfossil data from conodonts, fusulinaceans, and small foraminifers to correlate the Bell Canyon succession in the map area to similar age strata in the Guadalupe Mountains located about 50 miles to the north, 3) present a discussion of the carbonate facies and depositional processes that resulted in several extensive debris flows exposed in the latest Middle Permian, upper part of the Bell Canyon Formation strata.