TACONIC WEATHERING AND ORDOVICIAN COOLING: TESTING THE LINK USING PAIRED SR AND ND ISOTOPES, ANTELOPE VALLEY, CENTRAL NV

The Taconic Orogeny has been cited as a potential driver of the Ordovician greenhouse-icehouse transition, but evidence from paleoenvironmental proxies remains inconclusive. A long term decrease in marine ⁸⁷Sr/⁸⁶Sr and increase in δ¹⁸O values occurs roughly contemporary with enhanced continental weathering associated with the Taconic Orogeny, suggesting a causal relationship between weathering of volcanic rocks and Ordovician cooling. Nd isotope data compiled by Swanson-Hysell and Macdonald (2017, Geology, v. 45) seem to covary with the seawater Sr isotope curve, and have been interpreted by many as a change in the average composition of weathering sources following the collision of Taconic arcs. Certain intervals of the δ¹⁸O paleotemperature curve, however, appear inconsistent with inferred patterns of continental weathering. Observation of a lag in signal response times of marine Sr and Nd following the onset of Taconic weathering due to the difference in their oceanic residence times (~2.4 Myr and ~500 yrs, respectively) would support the Taconic as a primary driver of both isotopic trends. We present new Nd isotope data from Mid-Late Ordovician shallow-water carbonate strata of the Antelope Range, NV that preserve the initiation of the shift in Sr isotope values (Saltzman et al., 2014, GSABull, v. 126). If the expected lag in response time of 2-2.5 Myr is observed between isotopic signals, this suggests that the shift in both systems is tied to a singular driver, inferred to be the Taconic Orogeny. The realization of this hypothesis would further support Taconic weathering as a key driver of Mid-Late Ordovician climate, and suggest that increased temporal resolution of the δ¹⁸O paleotemperature curve may reconcile the inconsistencies with weathering proxy data.