SIGNIFICANCE AND VARIATION IN d13C AND d18O ACROSS SURFACES OF SUBAERIAL EXPOSURE IN ORDOVICIAN LIMESTONES OF THE NASHVILLE DOME, TN
Variation between vertical transects suggests that dissolution of aragonite is not laterally uniform and implies that lateral multiples must be taken in order to define the isotopic composition of a horizon. Confidence limits determined for the mean d13C of each stratigraphic horizon indicate that negative excursions in d13C are statistically significant below sequence-stratigraphically defined subaerial exposure surfaces. These data also interpret the presence of two additional exposure surfaces previously undefined by sequence stratigraphy.
Oxygen isotopes are commonly variable in their usefulness for identifying exposure surfaces. Confidence limits on the mean of the horizon indicate that d18O in this diagenetic system increases upward toward each exposure surface due to calcite precipitation from isotopically heavy meteoric waters.