Abstract
ABSTRACT Conodont apatite δ18OV-SMOW values from Middle though Upper Pennsylvanian (Desmoinesian–Missourian) laminated, marine black shale units within cyclic deposits of intercalated terrestrial and marine strata (cyclothems) from the Illinois Basin (United States) were measured in order to evaluate their utility as a proxy for changes in the oxygen isotopic composition of the epicontinental Late Pennsylvanian Midcontinent Sea (LPMS). The average δ18OV-SMOW values of well-preserved monogeneric (Idiognathodus) separates of conodont apatite from 12 lithologic units representing nine cyclothems range from 17.0‰ to 20.1‰ and average 19.0‰ ± 0.4‰ (1σ). Within the limits of analytical uncertainty of stable isotope measurements, the stratigraphic distribution of conodont apatite δ18O values is nontrending; particularly, there is no significant shift in δ18O values across the Desmoinesian–Missourian boundary, a period that has been interpreted to preserve a shift toward a warmer climate, increased seasonality, a...
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