Strontium, boron, oxygen, and hydrogen isotope geochemistry of brines from basal strata of the Gulf Coast sedimentary basin, USA
- Amoco Production Co., Houston, TX (United States)
- Univ. of Michigan, Ann Arbor (United States)
- Univ. of Texas, Austin (United States)
Significant spatial heterogeneities exist in the stable isotopic composition of saline formation waters from reservoirs of the Smackover Formation (Upper Jurassic). The authors focused on the southwest Arkansas shelf, a structurally simple portion of one of the interior basins of the northern Gulf Coast sedimentary basin. Brines from this area have exceptionally high Br and alkali element concentrations and have spatially heterogeneous hydrogen sulfide concentrations. Strontium, boron, oxygen, and hydrogen isotope composition exhibit coherent relations with other aspects of brine geochemistry. Sr isotope compositions range from those expected for carbonates and evaporites deposited from Jurassic seawater (0.7071) to radiogenic ratios as high as 0.7107. Generally, most radiogenic Sr isotope values are associated with H[sub 2]S-rich waters which also have elevated alkali element (Li, B, K, Rb) concentrations. These alkali element-rich waters are associated with portions of the South Arkansas fault system which reach basement. Boron isotope compositions are similarly heterogeneous, ranging from values of +26 to +50[per thousand]. Brines with highest B contents are most depleted in [sup 11]B. Normalizing B contents to Br in the brines reveals a reasonable mixing trend between a Dead Sea-type composition and Texas Gulf Coast-type shale/sand reservoir waters. Oxygen and hydrogen isotope data exhibit regional variations which are controlled by meteoric water invasion along the northern limb of the southwest Arkansas Fault. Although oxygen isotope compositions are often near equilibrium with respect to reservoir carbonate, it is more difficult to ascribe trends in [delta]D values to local water-rock interaction. Spatial heterogeneity in isotopic composition of formation waters from this study area suggests that assumptions of a homogeneous Sr reservoir in dating regional mineralization events require careful assessment in ancient systems. 99 refs., 16 figs., 1 tab.
- OSTI ID:
- 7368981
- Journal Information:
- Geochimica et Cosmochimica Acta; (United States), Vol. 57:9; ISSN 0016-7037
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
58 GEOSCIENCES
BORON ISOTOPES
ECOLOGICAL CONCENTRATION
BRINES
GEOCHEMISTRY
HYDROGEN ISOTOPES
OXYGEN ISOTOPES
STRONTIUM ISOTOPES
US GULF COAST
AGE ESTIMATION
ARKANSAS
BORON
HYDROGEN
OXYGEN
RUBIDIUM
STRONTIUM
ALKALI METALS
ALKALINE EARTH ISOTOPES
ALKALINE EARTH METALS
CHEMISTRY
DEVELOPED COUNTRIES
ELEMENTS
ISOTOPES
METALS
NONMETALS
NORTH AMERICA
SEMIMETALS
USA
540210* - Environment
Terrestrial- Basic Studies- (1990-)
580000 - Geosciences