Geochemistry of Cambro-Ordovician Arbuckle limestone, Oklahoma: Implications for diagenetic. delta. sup 18 O alteration and secular. delta. sup 13 C and sup 87 Sr/ sup 86 Sr variation

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

DOI:https://doi.org/10.1016/0016-7037(91)90456-F· OSTI ID:7302560

Gao, Guoqiu; Land, L S ^[1]

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1. Univ. of Texas, Austin (United States)

Isotopic analyses of 227 limestone samples from the Cambro-Ordovician Arbuckle Group, Oklahoma, document slow secular changes in the chemistry of the limestones. From late Cambrian to early Ordovician, the {delta}{sup 18}O values of the limestones increase from {minus}10{per thousand} to {minus}7{per thousand} (PDB); {delta}{sup 13}C values decrease from 0{per thousand} to {minus}2{per thousand} (PDB); and {sup 87}Sr/{sup 86}Sr ratios decrease from 0.7091 to 0.7088. The light {delta}{sup 18}O values suggest that all Arbuckle limestones underwent diagenetic alteration, probably caused by meteoric water recharged during the development of the overlying, pre-middle Ordovician unconformity. The gradual {delta}{sup 18}O increase from late Cambrian to early Ordovician reflects reduced {sup 18}O depletion with decreasing burial temperature during alteration, although the presence of additional primary secular {delta}{sup 18}O variation cannot be ruled out. The {delta}{sup 13}C and {sup 87}Sr/{sup 86}Sr variations, in accord with {delta}{sup 13}C and {sup 87}Sr/{sup 86}Sr variations in the literature, represent primary secular variations. The variations indicate that the {delta}{sup 13}C value and {sup 87}Sr/{sup 86}Sr ratio of early Paleozoic surface seawater decreased from late Cambrian to early Ordovician. The {delta}{sup 13}C variation during this time period seems to correlate with sea-level variation. Specifically, during sea-level fall, an increase in the rate of oxidation of organic matter caused {sup 13}C depletion of inorganic bicarbonate in seawater. As a result, early Ordovician carbonates, probably deposited during the regression stage of the latest Precambrian to latest early Ordovician cycle, became {sup 13}C depleted, relative to late Cambrian carbonates. The decrease of seawater {sup 87}Sr/{sup 86}Sr ratio from late Cambrian to early Ordovician may have resulted from decreased riverine Sr input caused by decreased rate of continental weathering.

• OSTI ID: 7302560
• Journal Information: Geochimica et Cosmochimica Acta; (United States), Vol. 55:10; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
LIMESTONE
DIAGENESIS
GEOCHEMISTRY
ISOTOPE RATIO
OKLAHOMA
GEOLOGIC DEPOSITS
CAMBRIAN PERIOD
CARBON 13
GEOLOGIC FORMATIONS
ORDOVICIAN PERIOD
OXYGEN 18
SEAWATER
STRONTIUM 86
STRONTIUM 87
ALKALINE EARTH ISOTOPES
BETA DECAY RADIOISOTOPES
CARBON ISOTOPES
CARBONATE ROCKS
CHEMISTRY
DEVELOPED COUNTRIES
ELECTRON CAPTURE RADIOISOTOPES
EVEN-EVEN NUCLEI
EVEN-ODD NUCLEI
FEDERAL REGION VI
GEOLOGIC AGES
HOURS LIVING RADIOISOTOPES
HYDROGEN COMPOUNDS
INTERMEDIATE MASS NUCLEI
ISOMERIC TRANSITION ISOTOPES
ISOTOPES
LIGHT NUCLEI
NORTH AMERICA
NUCLEI
OXYGEN COMPOUNDS
OXYGEN ISOTOPES
PALEOZOIC ERA
RADIOISOTOPES
ROCKS
SEDIMENTARY ROCKS
STABLE ISOTOPES
STRONTIUM ISOTOPES
USA
WATER
580000* - Geosciences