Late Guadalupian Biostratigraphy and Fusulinid Faunas, Altuda Formation, Brewster County, Texas

Occurrences of late Guadalupian (Zone PG-6, Wilde, 1990) fusulinid faunas in the Altuda Formation of the western Glass Mountains, Texas, confirm a biostratigraphic correlation with the upper Bell Canyon Formation (Lamar Limestone Member and post-Lamar siltstones) and the Tansill Formation of the Guadalupe Mountains. Codonofusiella (Lantschichites) altudaensis, new species, Paraboultonia splendens Skinner and Wilde, Reichelina lamarensis Skinner and Wilde, and Rauserella bengeensis, new species, all occur in the upper part of the Altuda Formation and above the zone of Polydiexodina (Zone PG-5, Wilde, 1990). The Altuda beds are overlain unconformably by strata referred to the Tessey Formation (originally King's upper massive member, Capitan Limestone). At least three important fusulinid subzones (in the sense of Wilde, 1990, but referred to herein as zones) have been identified in the Altuda, and another is suspected. Paraboultonia and Lantschichites mark a zone in the upper part of the Altuda covering a maximum thickness of about 20 m (65 ft.); Reichelina lamarensis marks the next older zone covering a maximum of approximately 12 m (40 feet); Paradoxiella marks a zone below this of unknown thickness. Although not identified as yet from collections, a lower zone of Yabeina texana should be expected below Paradoxiella because of its presence in this identical zonal configuration in the Guadalupe Mountains. Paraboultonia and Lantschichites are both recognized on the basis of their coiling habit, and Lantschichites is returned to Codonofusiella as a subgenus. Lateral thickness changes of strata in each of the fusulinid zones and the nature of the sediments therein are suggestive of a northeastward transgression accompanied by a gradual steepening of the shelf margin and a southwestward deepening in the Del Norte Mountains area.