Strontium isotope diagenesis of biogenic aragonite and low-Mg calcite

Journal Article · Tue Jan 01 00:00:00 EST 1991 · Geochimica et Cosmochimica Acta; (United States)

DOI:https://doi.org/10.1016/0016-7037(91)90008-S· OSTI ID:5456975

Brand, U ^[1]

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1. Brock Univ., St. Catharines, Ontario (Canada) McMaster Univ., Hamilton, Ontario (Canada)

Using petrographic and geochemical criteria, it is possible to identify marine Sr isotopic compositions and diagenetic overprints in carbonate samples. The {sup 87}Sr/{sup 86}Sr ratio of originally low-Mg calcite brachiopods and aragonite molluscs from the Boggy, Magoffin, and Brush Creek Formation/Members increases with progressive post-depositional alteration in the presence of diagenetic meteoric waters. In contrast, brachiopods from the Codroy Formation exhibit an increase in non-radiogenic Sr with diagenetic alteration. Based on the seawater {sup 87}Sr/{sup 86}Sr curve, this alteration probably occurred in the presence of marine water during the mid-Permian, Triassic, or late-Cretaceous-early-Tertiary. The degree of change in radiogenic Sr probably reflects the physicochemical nature of the diagenetic microsystem. Diffusion-controlled altered material shows the smallest degree of change in Sr isotopic ratios as well as microstructural and other geochemical modifications. In contrast, fluid-controlled altered material shows the greatest shift in isotopic ratios with concomitant microstructural and geochemical changes. Data of diagenetically well-defined biogenic carbonates show that Mississippian seawater {sup 87}Sr/{sup 86}Sr was constant with a mean of about 0.70733 and a range of 0.7076-0.7078. The revised high-resolution curve shows significantly higher variations for Pennsylvanian seawater {sup 87}Sr/{sup 86}Sr (0.7076-0.7093). A low perturbation marks the mid-Virgilian (0.7076-0.7078), and high perturbations are observed for the early Missourian (0.70846) and latest Morrowan (0.70913). The mean value determined for the latest Morrowan is similar to {sup 87}Sr/{sup 86}Sr ratios measured for modern carbonate and seawater. It is further suggested that seawater {sup 87}Sr/{sup 86}Sr varies by as much as 0.000154 at any given time.

• OSTI ID: 5456975
• Journal Information: Geochimica et Cosmochimica Acta; (United States), Vol. 55:2; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
ARAGONITE
CHEMICAL COMPOSITION
ISOTOPE RATIO
CALCITE
CARBONATE ROCKS
DIAGENESIS
GEOCHEMISTRY
PETROGRAPHY
BRANCHIOPODS
CONCENTRATION RATIO
FOSSILS
GEOLOGIC FORMATIONS
GEOLOGIC HISTORY
MOLLUSCS
SEAWATER
STRONTIUM 86
STRONTIUM 87
ALKALINE EARTH ISOTOPES
ALKALINE EARTH METAL COMPOUNDS
ANIMALS
AQUATIC ORGANISMS
ARTHROPODS
BETA DECAY RADIOISOTOPES
CALCIUM CARBONATES
CALCIUM COMPOUNDS
CARBON COMPOUNDS
CARBONATE MINERALS
CARBONATES
CHEMISTRY
CRUSTACEANS
ELECTRON CAPTURE RADIOISOTOPES
EVEN-EVEN NUCLEI
EVEN-ODD NUCLEI
HOURS LIVING RADIOISOTOPES
HYDROGEN COMPOUNDS
INTERMEDIATE MASS NUCLEI
INVERTEBRATES
ISOMERIC TRANSITION ISOTOPES
ISOTOPES
MINERALS
NUCLEI
OXYGEN COMPOUNDS
RADIOISOTOPES
ROCKS
SEDIMENTARY ROCKS
STABLE ISOTOPES
STRONTIUM ISOTOPES
WATER
580000* - Geosciences