EFFECTS OF EARLY DIAGENESIS ON δ44/40CA RECORDS OF UPPER ORDOVICIAN DOLOSTONES
We analyzed δ44/40Ca in subtidal to peritidal dolostones from three stratigraphic sections that transect a shallow carbonate shelf in the eastern Great Basin. Two of the sections, from Pancake Range and Silver Island Range, contain a Hirnantian record, identified by stratigraphic correlation and the presence of the Hirnantian δ13C excursion; the Hirnantian is missing in Barn Hills due to non-deposition or erosion during glacioeustatic sea level fall. This shallowing is represented at Pancake Range by karstic features indicating meteoric exposure and at Silver Island Range by a thin interval with aeolian sand grains. We combine these field observations with δ44/40Ca, δ13C, and trace element data to quantify the impact of early diagenetic processes in uppermost Ordovician strata across the carbonate platform. These data, supplemented by a hand-sample scale study of δ13C variability, should also aid in explaining minor variations in carbon isotope ratios observed across stratigraphically correlated units. These results demonstrate the utility of δ44/40Ca records in ancient dolomitized carbonates and help to constrain the diagenetic history of these strata.