Nd isotopic evidence for enhanced mafic weathering leading to Ordovician cooling

It remains unclear whether waning of the volcanic degassing CO2 source or enhancement of the mafic (Ca, Mg-silicate) weathering CO2 sink, or both, caused global cooling leading to the Ordovician greenhouse-icehouse transition. We present a uniquely age-constrained and integrated Middle-Late Ordovician (470-450 Ma) continental weathering isotopic proxy data set (Sr-87/Sr-86 and epsilon(Nd(t))) from carbonate rocks of the Antelope Range of central Nevada, USA, paired with published paleotemperature proxy measurements (delta O-18) of conodont apatite from the same locality. This suite of proxy records signals an increase in mafic weathering of the Taconic mountains (eastern United States) at ca. 463 Ma, which forced a period of global cooling. We adapt a Sr-87/Sr-86 and pCO(2) mass balance approach to model CO2 draw-down during the Ordovician, and show that a combined decrease in volcanic degassing and increase in mafic weathering approximately halves pCO(2) in agreement with delta O-18 trends and paleotemperature reconstructions.

Automated summary

This study presents an integrated analysis of continental weathering isotopic proxy data and paleotemperature proxy measurements from carbonate rocks in the Antelope Range of central Nevada, USA. The findings suggest that an increase in mafic weathering in the Taconic mountains at approximately 463 Ma led to global cooling. The modeling of CO2 draw-down during the Ordovician indicates a decrease in volcanic degassing and an increase in mafic weathering, which halved the pCO2 levels and align with the reconstructed paleotemperatures.