Table 1.  Summary of the lithologic and hydrogeologic properties of the hydrogeologic subdivisions of the Glen Rose Limestone and associated units that crop out, Camp Stanley Storage Activity and immediately adjacent area, Bexar County, Texas. 

[Groups, formations, and members modified from Forgotson (1956), Rose (1972), Ashworth (1983); hydrogeologic subdivisions (aquifers, zones, intervals) from Maclay (1995), Barker and Ardis (1996); Clark (2003); lithologic terminology modified from Dunham (1962); and porosity type modified from Choquette and Pray (1970). AQ, aquifer; CU, confining unit; *, not exposed in the study area] 

Group,
formation,
member
Hydro-
geologic
subdivision
Hydro-
logic
function
Thickness
(feet)
Lithology
Field
identification
Karst
features
Porosity type/
permeability
Edwards Group Kainer Formation Basal Nodular
member
Edwards aquifer VIII1 

AQ karst; 

CU not Karst,

50–60

Shaly, nodular limestone, mudstone, and miliolid grainstone

Massive, nodular, and mottled; abundant gastropods and Exogyra texana

Large lateral caves at surface

Fabric; stratigraphically controlled/large conduit flow at surface

Glen Rose Limestone Upper member Trinity aquifer Upper Zone Interval A

AQ associated with fractures and karst;

CU if not

230–120

Alternating and interfingering medium-bedded mudstone, wackestone, and packstone with solution zones locally

Near contact with Edwards Group; stair-step topography; devoid of fossils; evaporite beds locally

Some caves below contact with Edwards Group. Caves associated with fractures and bedding planes

At surface, not-fabric selective fracture and cavern porosity; probably very permeable near contact with Edwards Group, which decreases with depth, breccia porosity associated with collapse resulting from dissolution of evaporite beds

Interval B

CU;

AQ associated with fractures and karst

120–150

Alternating and interfingering mudstones, clays, wackestone, and packstones

Devoid of fossils; stair-step topography; evaporite bed at top of zone

Few caves

Fabric selective interparticle porosity and not-fabric selective fracture and some cavernous porosity; generally low permeability away from caves and solutionally enlarged fractures.

Interval C AQ 10–20

Yellow to white calcareous mud and vuggy mudstone

Yellow calcareous mud, with springs and seeps; topography tends to be flat; few fossils

No known caves

Fabric selective, breccia and moldic (boxwork) porosity

Interval D

AQ associated with bioherms;

CU above and below bioherms

135–180

Alternating beds of wackestone, packstone, and marl; thin-bedded “platy” mudstone; thick-bedded biostromes locally

Profuse Orbitolina texana; “platy” mudstone bed; generally low relief; stair-step topography not well defined

Relative abundance of caves related to fractures and bedding planes 

Both fabric and not-fabric selective porosity; vug, fracture, cavern, and moldic porosity within biostrome; in lower 90 feet very low porosity, primarily fracture related 

Interval E AQ 7–10

Yellow-to-white calcareous mud and vuggy mudstone

Yellow-to-white calcareous mud, with springs and seeps; topography tends to be flat; Corbula bed at base separating upper and lower Glen Rose Limestone; numerous fossils 

No known caves

Fabric selective, breccia and moldic (boxwork) porosity

Lower member Middle Zone

AQ in bioherms and evaporite bed; also associated with karst and fractures;

CU elsewhere

320–340

Thick-bedded mudstone; thin-to-medium-bedded mudstone, wackestone, packstone, and grainstone

Massive mudstone 

Relatively more caves than in other subdivisions except interval D

Both fabric and not-fabric selective porosity; large fracture, cavern, and moldic porosity within bioherms; mudstones and marls primarily fracture porosity; low permeability in mudstones and marls; good permeability in bioherms

Pearsall Formation Bexar Shale member CU 60–70

Dark mudstone, clay, and shale

* * *

1 Referred to as “hydrostgratiraphic zone” VIII by Maclay (1995).

2 30–40 feet thick at Camp Stanley Storage Activity. 

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