GEOCHEMISTRY OF LATE ORDOVICIAN VIOLA LIMESTONE, OKLAHOMA - IMPLICATIONS FOR MARINE CARBONATE MINERALOGY AND ISOTOPIC COMPOSITIONS

Late Ordovician (Caradocian) age Viola limestones from the Arbuckle Mo untains, Oklahoma, have Sr concentrations from 216 ppm to 3720 ppm (av erage 1600 ppm), delta(18)O values from -5.1 parts per thousand to -3. 1 parts per thousand (PDB), and Sr-87/Sr-86 ratios from 0.70775 to 0.7 0793. Although textural and chemical evidence indicates that these lim estones suffered diagenetic alteration, the elemental and isotopic com positions still reveal important information about the primary marine mineralogy and seawater composition during Late Ordovician time. First , the high Sr concentrations suggest that original Viola sediments wer e composed mainly of aragonite. Second, the highest delta(18)O value ( -3.1 parts per thousand) of the limestones, which is interpreted to be the least altered, constrains the delta(18)O values of seawater to > -1 parts per thousand (SMOW), assuming that ocean temperatures were 27 degrees +/- 5 degrees C. Third, the Sr-87/Sr-86 ratios of Viola limes tones probably better represent the Sr-87/Sr-86 ratios of coeval seawa ter because the ratios from these Sr-rich limestones show less scatter than those of similar-aged samples previously published.