A contribution to the evolving stratigraphic framework of middle Permian strata of the Delaware Basin, Texas and New Mexico

Abstract

We propose a new scheme for correlation of upper Leonardian through Guadalupian units of the Permian Basin and focus on two key correlations within the older, San Andres equivalent, portion of this succession. The lower San Andres Formation of the Algerita Escarpment is here considered equivalent to the uppermost Victorio Peak Formation of the western Escarpment and not the Cutoff Formation as proposed by earlier workers. This revised correlation is derived from extensive measured section data from the Algerita Escarpment, Brokeoff Mountains, Cutoff Mountain and the Western Escarpment, and conodont biostratigraphic data from Lawyer Canyon on the Algerita Escarpment. Conodont data, when reconciled with existing fusulinid biostratigraphic data from Lawyer Canyon, establish the position of the Leonardian-Guadalupian boundary well within the San Andres and support the lower San Andres to upper Victorio Peak correlation that was originally derived from lithostratigraphic correlation. A second key correlation involves the position within the San Andres Formation platform carbonates of bypass surfaces coeval with basinal Brushy Canyon and Cherry Canyon siliciclastics. We assert that the shelf equivalent of the voluminous Brushy Canyon sandstone succession is reflected by a single bypass surface recorded on the Algerita Escarpment as the first widespread karstic surface within the San Andres. A basinward shift in the rampcrest facies tract of at least 5 mi also occurs across this karst-modified sequence boundary, emphasizing the significance of this surface in the platform stratigraphy. The Brushy Canyon bypass surface is 100 ft below the Lovington sandstones, which are in turn tied to the lower Cherry Canyon Formation or Cherry Canyon Tongue. Thus, two key bypass surfaces occur in the upper San Andres depositional sequence, one at the base, which is equivalent to the Brushy Canyon Formation and one in the middle, equivalent to the Cherry Canyon Tongue.