Global significance of oxygen and carbon isotope compositions of pedogenic carbonates since the Cretaceous

Abstract

Few global syntheses of oxygen and carbon isotope composition of pedogenic carbonates have been attempted, unlike marine carbonates. Pedogenic carbonates represent in-situ indicators of the climate conditions prevailing on land. The δ18O and δ13C values of pedogenic carbonates are controlled by local and global factors, many of them not affecting the marine carbonates largely used to probe global climate changes. We compile pedogenic oxygen and carbon isotopic data (N= 12,167) from Cretaceous to Quaternary-aged paleosols to identify potential trends through time and tie them to possible controlling factors. While discrete events such as the Paleocene-Eocene Thermal Maximum are clearly evidenced, our analysis reveals an increasing complexity in the distribution of the δ18O vs δ13C values through the Cenozoic. As could be expected, the rise of C4 plants induces a shift towards higher δ13C values during the Neogene and Quaternary. We also show that the increase in global hypsometry during the Neogene plays a major role in controlling the δ18O and δ13C values of pedogenic carbonates by increasing aridity downwind of orographic barriers. Finally, during the Quaternary, an increase of 3‰ in δ18O values is recorded both by the pedogenic carbonates and the marine foraminifera suggesting that both indicators may be used to track global climate signal.