Abstract: Ochoan (Upper Permian) Stratigraphy and Age Determinations, Southeastern New Mexico and West Texas

S. G. Lucas, O. R. Anderson

Upper Permian strata, which are the stratotype of the Ochoan Stage (Series), have an extensive subsurface distribution and limited outcrop area in southeastern New Mexico and west Texas. The oldest strata are alternating laminae of anhydrite and calcite of the Castile Formation and are as much as 600 m thick. The closely related and overlying Salado Formation is as much as 600 m thick and is mostly halite and argillaceous halite with minor anhydrite. The overlying Rustler Formation is as much as 150 m thick and consists of anhydrite, red silty shale and magnesian limestone. Overlying red beds are the Quartermaster Formation (Dewey Lake Formation is a synonym, as is the term Pierce Canyon red beds), which is as much as 106 m thick and consists of fine sandstones, siltstones, and minor ypsum.

The Castile rests disconformably on the Capitanian (middle Permian) Lamar Limestone Member of the Bell Canyon Formation and its equivalent, the Tansill Formation of the Artesia Group. Counting of Castile-Salado laminae and their posited relationship to astronomical cycles suggests that Castile-Salado deposition took only 200,000-300,000 yr. Limited assemblages of brachiopods and conodonts from the Rustler Formation indicate a Late Permian age, but are no more precise age indicators. A small assemblage of bivalves, K-Ar ages and magnetostratigraphy indicate a Late Permian age for the Quartermaster Formation. There is no evidence to support a Triassic age assignment for the Quartermaster; it is disconformably overlain by the Upper Triassic (Carnian) Chinle group. Most workers use the Oc oan as a Late Permian Stage-Age, although its typical strata generally lack good age indicators and may represent relatively short and sporadic intervals of the Late Permian. We prefer recognition of the Ochoan as a lithostratigraphic unit (group) without regional or global geochronological significance.

AAPG Search and Discovery Article #90980©1994 AAPG Southwest Section Meeting, Ruidoso, New Mexico, April 24-26, 1994