Geologic framework, hydrostratigraphy, and ichnology of the Blanco, Payton, and Rough Hollow 7.5-minute quadrangles, Blanco, Comal, Hays, and Kendall Counties, Texas by Allan K. Clark, James A. Golab, and Robert R. Morris 2016 Scientific Investigations Map 3363 Version 1.1 ABSTRACT: This report presents the geologic framework, hydrostratigraphy, and ichnology of the Trinity and Edwards Groups in the Blanco, Payton, and Rough Hollow 7.5-minute quadrangles in Blanco, Comal, Hays, and Kendall Counties, Texas. Rocks exposed in the study area are of the Lower Cretaceous Trinity Group and lower part of the Fort Terrett Formation of the Lower Cretaceous Edwards Group. The mapped units in the study area are the Pearsall Formation and Glen Rose Limestone of the Trinity Group and the lower portion of the Fort Terrett Formation of the Edwards Group. The Pearsall Formation consists of, in ascending order the Hammett Shale, Cow Creek Limestone, and Hensell Sand Members. The Glen Rose Limestone is composed of the lower and upper members. These Trinity Group rocks contain the upper and middle Trinity aquifers. The only remaining outcrops of the Edwards Group are the basal nodular of the Fort Terrett Formation within the study area, which caps several hills in the northern portion of the study area. These rocks were deposited in an open marine to supratidal flats environment. The faulting and fracturing in the study area are part of the Balcones fault zone, an extensional system of faults that generally trends southwest to northeast in south-central Texas. The hydrostratigraphic units of the Edwards and Trinity aquifers were mapped and described using a classification system based on fabric or not-fabric-selective porosity types. The only hydrostratigraphic unit of the Edwards aquifer present in the study area is hydrostratigraphic unit VIII. The mapped hydrostratigraphic units of the upper Trinity aquifer are (from top to bottom) the Camp Bullis, upper evaporite, fossiliferous, and lower evaporite which are interval equivalent to the upper member of the Glen Rose Limestone. The middle Trinity aquifer encompasses (from top to bottom) the lower member of the Glen Rose Limestone and the Hensell Sand Member and the Cow Creek Limestone Member of the Pearsall Formation. The lower member of the Glen Rose Limestone was subdivided into six informal hydrostratigraphic units (from top to bottom): the Bulverde, Little Blanco, Twin sisters, Doeppenschmidt, Rust, and Honey Creek hydrostratigraphic units. This study used the ichnofabric index scale to interpret the amount of bioturbation in the field. Most of the geologic units in the study area are assigned to the Cruziana and Thalassinoides ichnofacies consistent with interpretations of a tidal-dominated open marine environment (sublittoral zone). Ichnofossil assemblages are and are dominated by Thalassinoides networks, but also contain Cruziana, Ophiomorpha, Paleophycus, Planolites, and Serpulid traces. DISCLAIMERS: This database, identified as SIM3363, has been approved for release and publication by the Director of the USGS. Although this database has been subjected to rigorous review and is substantially complete, the USGS reserves the right to revise the data pursuant to further analysis and review. Furthermore, it is released on condition that neither the USGS nor the United States Government may be held liable for any damages resulting from its authorized or unauthorized use. Although these data have been processed successfully on a computer system at the U.S. Geological Survey, no warranty, expressed or implied is made regarding the display or utility of the data on any other system, or for general or scientific purposes, nor shall the act of distribution constitute such warranty. The U.S. Geological Survey shall not be held liable for improper or incorrect use of the data described and/or contained herein. Any use of trade, product or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Geological Survey. Although this information product, for the most part, is in the public domain, it also contains copyrighted material as noted in the text. Permission to reproduce copyrighted items for other than personal use must be secured from the copyright owner. DATA FILES: The database can be downloaded via the Web from http://dx.doi.org/10.3133/sim3363/ ArcInfo export files, ArcView shapefiles, and an ArcGIS geodatabase may be extracted from a zip-compressed file (SIM3363_GIS.zip). In addition, an Adobe Portable Document Format (PDF) file (SIM3363 _map.pdf) can be downloaded, from which paper copies may be printed. The database contact is: Diana E. Pedraza 210-691-9237 dpedraza@usgs.gov U.S. Geological Survey 5563 Dezavala Road San Antonio, TX 78249 The data were compiled from field mapping of the hydrostratigraphic units was accomplished on an Apple iPad2 containing geospatially- registered 7.5-minute USGS topographic maps and utilizing integrated global positioning system (GPS). The field data were transferred to Esri ArcMap (Esri, 2014), quality checked, and then used to produce the study area’s hydrostratigraphic map. Lithologic and hydrostratigraphic descriptions are from field observations and previous investigations. This geospatial database consists of ArcView shapefiles and ArcGIS geodatabase files contained in a zip archive. See the list below. Please refer to the file SIM3363.met for detailed metadata documentation for this geospatial database. List of files: 00ReadMe.txt SIM3363_map.pdf SIM3363.met (.xml) bprhbasr_1983.tif bprhbasr_1983.tfw bprhbasr_1983.prj SIM3363_GIS.zip: shapefiles directory: Geo_Polys.shp (.dbf/.prj/.sbn/.sbx/.shx.xml/.shx) polygon Geo_Lines.shp (.dbf/.prj/.sbn/.sbx/.shx.xml/.shx) line SIM3363_GIS.gdb directory (contains GIS data as geodatabase feature classes) ********************************* Revision History ----------------------------------------------------- Posted online September 13, 2016 ----------------------------------------------------- Revised and reposted September 20, 2016, version 1.1 Replaced the bar scales with the correct 1:25,000-scale bars. The first version had erroneously used scale bars for 1:250,000-scale map. ********************************* HOW TO OBTAIN THE DIGITAL FILES: The digital files constituting the geologic map database of this report can be obtained via the Internet from the U.S. Geological Survey publications website. Go to the web page at http://dx.doi.org/10.3133/sim3363/ and follow the directions to download the files. The main product is a Portable Document Format (.pdf) map, which requires Adobe Acrobat for viewing. Acrobat software runs on a variety of systems, and is available for download free of charge from Adobe at http://www.adobe.com.