EARLY MISSISSIPPIAN CALCIUM ISOTOPE STRATIGRAPHY AND IMPLICATIONS FOR CONDITIONS OF CARBONATE DEPOSITION

A +5.5 ‰ to +7.0 ‰ magnitude δ¹³C excursion, known as the Kinderhookian Osagean Boundary Excursion or KOBE, is preserved in lower Mississippian strata (during the Tournasian age, ca. 353 Ma) in North America, Europe, and East Asia. This has been linked to an interval of cooling as part of a long-term shift from greenhouse to icehouse conditions. One proposed cause of the cooling is the rise of vascular land plants which increased silicate weathering, CO₂ consumption, and phosphorus delivery to the oceans, which enhanced primary production and burial of organic matter to produce the δ¹³C excursion. However, the link between burial of organic matter and δ¹³C remains unclear because potential local controls on δ¹³C, which include diagenetic or mineralogic controls in shallow platform carbonates, can potentially decouple the shallow platform δ¹³C signal from the primary global DIC. This study pairs δ⁴⁴Ca data with Sr/Ca and δ¹³C to examine the possible diagenetic and mineralogic (calcite or aragonite) controls on the magnitude of the δ¹³C excursion. We present a bulk carbonate δ^44/40Ca record across this lower Mississippian stratigraphic interval from the Confusion Range, Utah. The beginning and end of the δ¹³C excursion have identical values of δ^44/40Ca (relative to the SRM915a standard) around 0.80 ‰ and similar Sr/Ca while δ¹³C values shift from 2.64 to –0.02 ‰, suggesting there is not covariation associated with diagenetic or mineralogic controls. Future work will provide higher resolution δ⁴⁴Ca data across this interval, along with Sr/Ca to pair with previously measured δ¹³C.