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

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