Key subsurface data help to refine Trinity aquifer hydrostratigraphic units, south-central Texas

Abstract

Finer grained micritic limestone; orange wisps and dark flecks of dolomitic limestone; no areas with porosity observed 281.0 White biomicritic limestone; corals at this level 299.0 Biomicritic limestone, some areas with grain support; moldic porosity; gastropods abundant; white limestone; some molds filled with spar; some shell fragments; areas with sporadic grainstone; some grains appear to be fossils or ooids(?) 302.1-324.8 White, biomicritic limestone; heavy moldic porosity; large vugs; well-developed molds; abundant gastropods; areas of grain support 324.8-325.0 Biomicritic limestone; moldic porosity not connected; white, finely disseminated shell fragments; spar-filled shell fragments 325.0 Lower Glen Rose Limestone and Bexar Shale Member of the Pearsall Formation contact; micritic limestone; rip-up clasts; vugs filled with spar; shell molds filled with spar; minor moldic porosity; vug-filled with clay; probably an erosional surface; vug-filling highly calcareous 325.0-326.5 Light-gray microspar matrix with large grains of spar; some vug-filled spar; oyster fragments increasing in size downhole; minor intercrystalline porosity 327.9 Light-gray micritic matrix; large spar grains touching in areas; minor intercrystalline porosity; spar in-filling; some fractures; shell fragments 329.0 Gray micritic limestone with areas of microspar; very abundant spar grains in many areas appear to be grain supported; minor moldic porosity not connected; no intercrystalline porosity; shell fragments; light-gray to white mottled 330.0 Gray to light-gray, micritic limestone with interspersed microspar; shell fragments replaced with spar; abundant rip-up clasts; small amount of nonconnected moldic porosity 330.3 Gray, microspar-rich limestone; oyster and other shell fragments; most fragments replaced with spar; some rip-up clasts of micrite; most molds filled with spar; some open molds; clast size and abundance increase upward; clasts mostly spar grains 331.0 Gray-mottled, microspar-rich limestone; areas of spotty dolomitic limestone; grading into limestone at 330.3 feet; shell fragment abundance increases from 331-330.3 feet; particle size increases between 330.3 to 331.0 feet; intercrystalline porosity 332.0 Gray mottled microspar-dolomite; small shell fragments; intercrystalline porosity; isolated larger spar grains; some moldic and small-vug porosity 332.8 Gray mottled dolomitic clasts; microspar dolomitic limestone; soft-sediment deformation; intercrystalline porosity; particle size increases with larger grains of spar; shell fragments increase to whole shells uphole at 332.

Geologic framework, hydrostratigraphy, and ichnology of the Blanco, Payton, and Rough Hollow 7.5-minute quadrangles, Blanco, Comal, Hays, and Kendall Counties, Texas

“…The Hensell Sand commonly forms slopes, often with thicker soils and lush grasses. Whitney (1952), Lozo and Stricklin (1956), Stricklin and others (1971), Rose (1972), Stricklin and Smith (1973), Amsbury (1974), Inden (1974), Perkins (1974), Clark and others (2010), Blome and Clark (2014), Clark and others (2014), and the U.S. Geological Survey National Geologic Map Database, GEOLEX (http://ngmdb.usgs.gov); aquifers from Maclay and Small (1976), Ashworth (1983); thickness from outcrop, Clark and others (2009) (2015); Porosity types modified from Choquette and Pray (1970). Fabric selective, I = Interparticle porosity, SH = Shelter porosity, MO = Moldic porosity, BU = Burrowed porosity, BP = Bedding plane porosity.…”

“…In the northern Bexar County area, the Upper Member of the Glen Rose Limestone was subdivided into five informal HSUs (named A through E from top to bottom) to better describe the unit's hydrologic properties (Clark, 2003(Clark, , 2004. These HSUs were mapped in northern Bexar County and renamed as (top to bottom) cavernous, Camp Bullis, upper evaporite, fossiliferous, and lower evaporite, respectively others, 2009, 2011;Blome and Clark, 2014). The cavernous HSU is absent from the current study area because of differences in depositional environments and a disconformity.…”

“…The informal HSUs of the upper and middle Trinity aquifer have been mapped (sheet 1) using porosity types and lithologic characteristics identified in the field during mapping in conjunction with data from previous studies (Wierman and others, 2010;Blome and Clark, 2014;Clark and others, 2014;Pantea and others, 2014). Blome and Clark (2014) is the primary publication used in defining the hydrostratigraphic units.…”

“…Blome and Clark (2014) is the primary publication used in defining the hydrostratigraphic units. Blome and Clark (2014) described borehole cores and took plugs from those cores for both thin-section and permeability analysis.…”

“…Blome and Clark (2014) is the primary publication used in defining the hydrostratigraphic units. Blome and Clark (2014) described borehole cores and took plugs from those cores for both thin-section and permeability analysis. In addition, geophysical data were obtained from wells in Blanco, Comal, and Hays Counties to identify specific HSU contacts based on contacts identified in the gamma logs ( fig.…”