Print this page
Charles A. Ross1,
June R. P. Ross1
(1) Western Washington University, Bellingham, WA
Abstract: Sequence Evolution and Sequence Extinction; species level recognition of individual sequences and parasequence sets, Lower Permian, West Texas
Depositional sequences, subsequences, parasequence sets and parasequences are well developed in Lower Permian Wolfcampian and Leonardian strata in the Glass Mountains, West Texas. The depositional sequences and some parasequence sets were of sufficient duration that many species of shallow-water carbonate foraminiferans evolved rapidly and were succeeded in the next higher depositional sequence by derived younger species. The stratigraphic ranges of many of these species are bounded by hiatuses of non-deposition and are classic examples of the phenomena of evolution within a sequence and extinction at the hiatus at the top of the sequence. The species identify individual depositional sequences.
The lower Nealian (Lower Wolfcampian) includes five major depositional sequences that record significant (±20m) sea-level fluctuations. They are defind by species ranges of Leptotriticites, Triticites, Paraschwagerina, Pseudoschwagerina, and Schwagerina. The upper Nealian has fifteen to twenty thinner cycles that represent smaller sea-level fluctuations (±5m) and ranges of species define five or six parasequence sets. The Lenoxian (Upper Wolfcampian) includes five depositional sequences; each characterized by a species assemblage.
In the Hessian Stage (Lower Leonardian), seven depositional sequences each have distinctive species of fusulinaceans. The higher depositional sequences have a progression of increasingly advanced species of primitive Parafusulina.
The Cathedralian Stage (Upper Leonardian) includes at least three depositional sequences. A single fusulinacean species, Parafusulina durhami, characterizes the lower two. The top of the upper depositional sequence is discontinuously preserved beneath the Mid-Permian event,
AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana