delta. sup 18 O values, sup 87 Sr/ sup 86 Sr and Sr/Mg ratios of Late Devonian abiotic marine calcite: Implications for the composition of ancient seawater

Journal Article · Mon Jul 01 00:00:00 EDT 1991 · Geochimica et Cosmochimica Acta; (United States)

DOI:https://doi.org/10.1016/0016-7037(91)90038-7· OSTI ID:5750889

Carpenter, S J; Lohmann, K C; Walter, L M; Huston, J G; Halliday, A N ^[1]; Holden, P ^[2]

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1. Univ. of Michigan, Ann Arbor (United States)
2. Univ. of California, Los Angeles (United States)

Late Devonian (Frasnian) abiotic marine calcite has been microsampled and analyzed for {sup 87}Sr/{sup 86}Sr ratios, {delta}{sup 18}O and {delta}{sup 13}C values, and minor element concentrations. Portions of marine cement crystals from the Alberta and Canning Basins have escaped diagenetic alteration and preserve original marine {delta}{sup 18}O values ({minus}4.8{per thousand} {plus minus} 0.5, PDB), {delta}{sup 13}C values (+2.0 to +3.0{per thousand}, PDB), {sup 87}Sr/{sup 86}Sr ratios (0.70805 {plus minus} 3), and Sr/Mg weight ratios (0.04 to 0.05). Marine {sup 87}Sr/{sup 86}Sr ratios are globally consistent and can be correlated within the Alberta Basin, and among the Alberta, Canning, and Williston Basins. Correlation of isotopic and chemical data strengthen the conclusion that marine cements from the Leduc Formation preserve original marine {delta}{sup 18}O values which are 3 to 4{per thousand} lower than those of modern marine cements. These low {delta}{sup 18}O values are best explained by precipitation from {sup 18}O-depleted seawater and not be elevated seawater temperature or diagenetic alteration. For comparison with Devonian data, analogous data were collected from Holocene Mg-calcite and aragonite marine cements from Enewetak Atoll, Marshall Islands. Mg-calcite and aragonite marine cements are in isotopic equilibrium with ambient seawater, and Mg-calcite cements are homogeneous with respect to Sr and Mg contents. Comparison of Sr and Mg contents of analogous Devonian and Holocene marine cements suggests that the Mg/Ca ratio of Late Devonian seawater was significantly lower and that the Sr/Ca ratio was significantly higher than that of modern seawater.

• OSTI ID: 5750889
• Journal Information: Geochimica et Cosmochimica Acta; (United States), Journal Name: Geochimica et Cosmochimica Acta; (United States) Vol. 55:7; ISSN GCACA; ISSN 0016-7037
• Country of Publication: United States
• Language: English

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58 GEOSCIENCES
580000* -- Geosciences
ALBERTA
ALKALINE EARTH ISOTOPES
ALKALINE EARTH METALS
BETA DECAY RADIOISOTOPES
BUILDING MATERIALS
CALCITE
CANADA
CARBONATE MINERALS
CARBONATE ROCKS
CEMENTS
CHEMICAL COMPOSITION
CHEMISTRY
COMPARATIVE EVALUATIONS
DEVELOPED COUNTRIES
DEVONIAN PERIOD
DIAGENESIS
ELECTRON CAPTURE RADIOISOTOPES
ELEMENTS
EVALUATION
EVEN-EVEN NUCLEI
EVEN-ODD NUCLEI
GEOCHEMISTRY
GEOLOGIC AGES
GEOLOGIC FORMATIONS
GEOLOGIC HISTORY
GEOLOGIC STRUCTURES
HOURS LIVING RADIOISOTOPES
HYDROGEN COMPOUNDS
INTERMEDIATE MASS NUCLEI
ISOMERIC TRANSITION ISOTOPES
ISOTOPE RATIO
ISOTOPES
LIMESTONE
MAGNESIUM
MATERIALS
METALS
MINERALS
NORTH AMERICA
NUCLEI
OXYGEN COMPOUNDS
PALEOZOIC ERA
PRECIPITATION
RADIOISOTOPES
ROCKS
SEAWATER
SEDIMENTARY BASINS
SEDIMENTARY ROCKS
SEPARATION PROCESSES
STABLE ISOTOPES
STRONTIUM
STRONTIUM 86
STRONTIUM 87
STRONTIUM ISOTOPES
WATER