Late Devonian greenhouse-icehouse climate transition: New evidence from conodont δ18O thermometry in the eastern Palaeotethys (Lali section, South China)

Abstract The Late Devonian is considered as a crucial climatic transition from the Devonian greenhouse to Carboniferous icehouse. Published Late Devonian marine palaeotemperature records are mainly based on conodont δ18Oapatite data from the Rheic Ocean. In order to reconstruct palaeotemperature variations in the eastern Palaeotethys, oxygen isotopes were measured on the latest Givetian to latest Famennian conodonts from the Lali section (South China). Assuming constant seawater δ18O, the early to middle Frasnian is marked by a warming trend (−1.5‰ shift in δ18Oapatite), with warmest temperatures reconstructed in FZ 11 (FZ = Frasnian Zonation). Late Devonian cooling during the middle to late Famennian (velifer to ultimus Zone) is documented by a long-term positive δ18Oapatite shift of +2‰. This increase corresponds to a similar δ18Oapatite increase in the Rheic Ocean and can be explained by cooling as well as the formation of ice masses as evidenced by the occurrence of glacial sediments in Gondwana and Euramerica during the late Famennian. The Late Devonian δ18Oapatite record largely matches 2nd-order T-R cycles. The δ18Oapatite record from the Lali section shows several short-term positive excursions coinciding with Late Devonian bio-events as the Middlesex (+0.5‰ δ18Oapatite), Lower Kellwasser (+1‰ δ18Oapatite) and Upper annulata (+0.8‰ δ18Oapatite) events. However, due to the lower sampling resolution of the F-F (Frasnian-Famennian) boundary interval, we did not recognize a positive shift in δ18Oapatite for the Upper Kellwasser event as reported from other sections.