Clumped isotope records of terrestrial temperatures during the Middle Jurassic (180-150 Ma) in East China

The Jurassic is a crucial greenhouse period that witnessed a transition from the relatively colder Triassic to the relatively warmer Cretaceous. However, previous studies based on marine sections suggest different long-term paleotemperature trends throughout the Jurassic. Oxygen isotope (delta O-18) values of temperate belemnite and bivalve fossils suggest a general cooling followed by a general warming trend during the Jurassic, whereas TEX86H and clumped isotope sea surface temperature records available for parts of this period appear consistent with a relatively warm and stable climate. The paucity of Middle Jurassic paleotemperature estimates limits efforts to investigate the above disagreement. Here, we apply clumped isotope (Delta(47)) thermometry to paleosol carbonates from the central part of East China to reconstruct terrestrial paleotemperatures and paleoatmospheric CO2 (pCO(2)) in the Middle Jurassic. After evaluating potential burial diagenesis and seasonality of soil carbonate accumulation, we suggest that terrestrial mean annual temperatures ranged from 30 +/- 4 degrees C to 34 +/- 4 degrees C and the estimated mean pCO(2) was 1219 +/- 519 ppmv in mid-latitude East China during the Middle Jurassic. Based on the compiled marine temperatures and our results, we conclude that the paleoclimate was relatively warm and stable from the Middle Jurassic to at least the Earliest Cretaceous (ca. 180-135 Ma). Our estimated Middle Jurassic pCO(2) aligns with previous records, revealing minimal variations compared to the pCO(2) observed during the Early Cretaceous. These findings imply a link between the consistent temperatures and the relatively stable pCO(2) levels from the Middle Jurassic through the Early Cretaceous.