Stable isotope systematics in ground water from the Edwards aquifer, south-central Texas

Conference · Wed Jan 01 00:00:00 EST 1992 · Geological Society of America, Abstracts with Programs; (United States)

OSTI ID:5819357

Blake, R E ^[1]

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1. Univ. of Texas, San Antonio, TX (United States). Div. of Earth and Physical Sciences

The Cretaceous Edwards aquifer in the Balcones fault zone of south-central Texas consists of a fresh-water zone to the north and a saline-water zone to the south. Isotopic analyses of water and rock samples collected from the fresh and saline zones, combined with additional chemical data, were used to examine regional variations in isotopic and chemical signatures. The fresh-water zone contains Ca-HCO[sub 3] water under oxidizing conditions. Water in the saline zone varies from Ca-SO[sub 4] to Na-Cl water under generally reducing conditions. The [delta] O-18 and [delta] D values of water from both zones have a meteoric signature. Mineral saturation indices suggest that water compositions are buffered by the predominant aquifer minerals; calcite (dedolomite) in the fresh-water zone and dolomite in the saline-water zone. Covariant linear trends in major element data indicate conservative mixing of a dilute end member with Na-rich and Ca-rich saline end members. Variation of delta C-13 of dissolved inorganic carbon (DIC) with conservative element and TDS concentrations does not suggest simple mixing, but rather that equilibrium processes are controlling the [delta] C-13 signature of DIC. Isotopic equilibrium is observed between DIC and late, pore-lining calcite cements in the fresh-water zone. Carbon isotopic equilibrium between saline-zone dolomite and DIC would imply a dolomite-HCO[sub 3] fractionation of up to 7[per thousand].

• OSTI ID: 5819357
• Report Number(s): CONF-921058-; CODEN: GAAPBC
• Journal Information: Geological Society of America, Abstracts with Programs; (United States), Vol. 24:7; Conference: 1992 annual meeting of the Geological Society of America (GSA), Cincinnati, OH (United States), 26-29 Oct 1992; ISSN 0016-7592
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
58 GEOSCIENCES
AQUIFERS
GEOCHEMISTRY
GROUND WATER
ISOTOPE RATIO
TEXAS
CALCITE
CALCIUM CARBONATES
CALCIUM SULFATES
CARBON 13
DEUTERIUM
DOLOMITE
OXYGEN 18
SODIUM CHLORIDES
ALKALI METAL COMPOUNDS
ALKALINE EARTH METAL COMPOUNDS
CALCIUM COMPOUNDS
CARBON COMPOUNDS
CARBON ISOTOPES
CARBONATE MINERALS
CARBONATES
CHEMISTRY
CHLORIDES
CHLORINE COMPOUNDS
DEVELOPED COUNTRIES
EVEN-EVEN NUCLEI
EVEN-ODD NUCLEI
HALIDES
HALOGEN COMPOUNDS
HYDROGEN COMPOUNDS
HYDROGEN ISOTOPES
ISOTOPES
LIGHT NUCLEI
MINERALS
NORTH AMERICA
NUCLEI
ODD-ODD NUCLEI
OXYGEN COMPOUNDS
OXYGEN ISOTOPES
SODIUM COMPOUNDS
STABLE ISOTOPES
SULFATES
SULFUR COMPOUNDS
USA
WATER
540210* - Environment
Terrestrial- Basic Studies- (1990-)
580000 - Geosciences