Columnar and clear blocky calcite cement from a Middle Ordovician carbonate succession in east Tennessee is interpreted as meteoric in origin. Columnar and clear blocky calcite from this succession does not show extremely large 13C depletions reported from meteoric phases of younger rocks. Meteoric fluid ??18O values calculated from clear blocky calcite are ??? 2 to 3??? more negative than approximately coeval sea water; a relationship typical of modern, low-latitude, coastal meteoric water. Comparison with meteoric ??18O values from Ordovician units elsewhere suggests that the geographic distribution of these values may be broadly similar to that observed today. Therefore, we tentatively suggest that geographic distribution of meteoric ??18O values during both icehouse and greenhouse eras are similar.
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Ordovician meteoric carbon and oxygen isotopic values: Implications for the latitudinal variations of ancient stable isotopic values