Paleoclimate and ecology of Cretaceous continental ecosystems of Japan inferred from the stable oxygen and carbon isotope compositions of vertebrate bioapatite

Abstract

Abstract We investigated the environmental conditions that prevailed in continental ecosystems recorded in sedimentary deposits of Japan during the Cretaceous through the analysis of oxygen and carbon isotope compositions of phosphate (δ18Op) and apatite-bound carbonate (δ18Oc and δ13Cc) of vertebrate teeth and bones. Local surface water δ18Ow values were calculated using known phosphate-water isotope fractionation equations. Anomalously low δ18Ow values of local waters strongly suggest a significant contribution of high-altitude precipitation from nearby mountains to local surface waters. Mean air temperatures were estimated using a global meteoric water δ18Omw value – Mean Annual Air Temperature relationship, and compared to surface water temperatures estimated from fish apatite δ18Op values. Local mean annual precipitations (MAP) were estimated using the known relationship existing between MAP and C3 plant δ13Cp value, the latter being calculated using apatite-diet 13C-enrichment applied to plant-eating sauropod and ornithopod dinosaur δ13Cc values. Reconstructed environmental conditions suggest that climate changed from cool temperate to warm temperate, being relatively cold and dry during the Late Hauterivian and Barremian to warmer and seasonally more humid during the Aptian and Albian, and even warmer during the Cenomanian-Coniacian. Proposed thermal evolution during the Early Cretaceous is compatible with the absence of thermophilic taxa such as crocodylomorphs before the Aptian in the fossil record of Japan.