Abstract

In the Permian of West Texas signficant faunal changes took place across the hiatuses associated with sixteen sea level low-stands. Within the Early Permian Wolfcampian Epoch four of these changes took place in the lower (Nealian) part of the Zone of Pseudoschwagerina. The low-stand between the Nealian and overlying Lenoxian shows a major faunal change within the Wolfcampian. A low-stand marked the close of the Lenoxian.

The succeeding Leonardian Stage is divided into the Hessian (lower) and Cathedralian (upper) stages. The three depositional sequences of the Hessian mark changes from a zone of advanced species of Schwagerina into two zones of small, primitive species of Parafusulina. The Cathedralian Stage is bounded at its base and top by low-stands. It has a distinctive fauna of species of Parafusulina that are intermediate between the Hessian and Roadian species. On the shelves a major unconformity resulting from a low-stand marks the change from the Leonardian to Guadalupian faunas. This unconformity diminishes in magnitude into the adjacent basins, where sedimentation was more complete. The Guadalupian Series is formed by the Roadian (at the base), Wordian and Capitanian stages. The Roadian, composed of one depositional sequence, contains the first of a series of advanced species of large Parafusulina. This is followed in the Wordian by two depositional sequences containing two additional zones of large, advanced Parafusulina. The lower part of the Capitanian, the Goat Seep Dolostone, is separated from an upper part, the Capitan Limestone by a sequence boundary and hiatus. The limited faunas from the dolomitized Goat Seep and equivalent beds are large advanced Parafusulina, whereas those of the Capitan Limestone are Polydiexodina. Near the end of Capitanian deposition a specialized fusulinacean and conodont fauna with possible Tethyan earliest Dzhulfian affinities briefly appeared before a major sea level low-stand. This implies that the overlying Ochoan evaporites and red beds are Dzhulfian or younger, but the lack of diagnostic fossils does not permit internal age determinations or zonal subdivisions.

Comparisons with the Lower Permian in the Ural region and Russian Platform suggest that similar types of faunal changes occur at the same stratigraphic positions as those within the Wolfcampian-Leonardian interval. Post-Kungurian strata lack readily correlatable marine faunas.

Similar types of changes in fusulinacean zonations occur between depositional sequences in the Tethys, where changes in endemic Tethyan fusulinacean lineages, such as verbeekinids are particularly marked. This is possibly best documented in the Akiyoshi Limestone in southwestern Japan. There carbonate depositional sequences on a former oceanic plateau also have breaks in deposition that correlate closely in number and in types of faunal changes to those in the Wolfcampian, Leonardian and Guadalupian. For these patterns of evolution associated with depositional sequences in the fossil record we introduce the terms ‘sequence evolution’ and ‘sequence extinction’.