Summary Report for the 2004-2005 StateMap Project: Geologic Mapping to Support Improved Database Development and Understanding of Urban Corridors, Critical Aquifers and Special Areas of Environmental Concern in Texas

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2005

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Abstract

A geologic map of the Del Rio, Texas, area, scale 1:100,000, has been constructed through digital compilation of nine 1:24,000-scale open-file geologic maps. The map is intended to be used by professionals and laypersons as a source of general geologic information that relates to land and resource use and management. Geology of the study area consists of Cretaceous Salmon Peak limestone, Del Rio clay and minor calcareous siltstone, Buda limestone, Eagle Ford shale, siltstone and flaggy limestone, and Austin Group chalk, limestone, and lesser marl. These rocks were folded during Laramide deformation (Late Cretaceous to early Eocene), and they were faulted during development of the Miocene Balcones Fault Zone. Fractures and karst within the Edwards Group Salmon Peak limestone contribute to the porosity of the prolific Edwards aquifer, a source of groundwater for the study area. Cretaceous rocks are overlain by broad Tertiary to Quaternary alluvial deposits and younger Quaternary alluvium associated with the Rio Grande and its tributaries. Tertiary to Quaternary alluvial deposits, which contain older alluvium classified as part of the Uvalde aquifer, provide another source of shallow groundwater locally. Cretaceous limestone is an aggregate resource. The older alluvial deposits are a local resource for sand, gravel, and caliche.

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