Variable intensity of diagenesis is the factor primarily responsible for contrasting regional reservoir quality of Tertiary sandstones from the upper and lower Texas coast. Detailed comparison of Frio sandstone from the Chocolate Bayou/Danbury Dome area, Brazoria County, and Vicksburg sandstones from the McAllen Ranch Field area, Hidalgo County, reveals that extent of diagenetic modification is most strongly influenced by (1) detrital mineralogy and (2) regional geothermal gradients.

The publication comprises 24 structural dip cross sections, spaced 15 to 20 mi apart along the Texas coast, and 4 structural strike cross sections. Dip sections extend from near the Wilcox outcrop to the coastline. Tops of formations were chosen by correlations with Wilcox, Vicksburg, and Frio stratigraphic cross sections constructed in previous geothermal investigations. Formations include upper Oligocene to Pleistocene (undifferentiated); Frio; Vicksburg-Jackson (undifferentiated); upper and lower Claiborne (upper Claiborne being the Yegua Formation); and upper, middle, and lower Wilcox.

This report describes preliminary results of an ongoing study of the volcanic stratigraphy, caldera activity, and known and potential mineralization of the Chinati Mountains area of Trans-Pecos Texas. Many ore deposits are spatially associated with calderas and other volcanic centers. A genetic relationship between calderas and base and precious metal mineralization has been proposed by some (Albers and Kleinhampl, 1970) and denied by others (McKee, 1976, 1979).

The Salado-Tansill and Alibates Formations are the youngest evaporite and carbonate facies within a thick Permian sequence of evaporites, carbonates, and red beds in the Texas Panhandle. They accumulated during the final stages of a regional regression that began in Early Permian time, and they record the last minor incursion and subsequent regression of Permian seas in the Texas Panhandle.