Triple oxygen isotopes in intertrappean fossil woods: Evidence of higher tropical rainfall during Deccan volcanism

• Published in: Chemical geology Vol. 634; p. 121599
• Main Authors: Ghoshmaulik, Sangbaran, Bhattacharya, Sourendra Kumar, Hazra, Manoshi, Roy, Pallab, Khan, Mahasin Ali, Liang, Mao-Chang, Iizuka, Yoshiyuki, Hsiao, Sung-Yun, Lee, Der-Chuen, Sarkar, Anindya
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 20-09-2023
• Subjects: Deccan volcanism; High rainfall; Intertrappean sediments; Late Cretaceous India; Silicified wood; Triple oxygen isotope; Silicified wood; Late Cretaceous India; Intertrappean sediments; High rainfall; Triple oxygen isotope; Deccan volcanism
• ISSN: 0009-2541; 1872-6836
• DOI: 10.1016/j.chemgeo.2023.121599

Despite several attempts, the effects of volcanism and greenhouse gas emission on climate (e.g., rainfall) over India across the Cretaceous/Palaeogene Boundary (66.1 ± 0.01 Ma) remain a contentious issue. Inferences from conventional isotopic, palaeosol, floral analysis, and palaeoclimate models are contradictory ranging from much lower- to higher-than-today rainfall during this high CO2 atmosphere. To resolve this, robust tracer of triple oxygen isotopic ratios (ẟ18O-∆′17O) of silicified fossil woods from Deccan intertrappean lacustrine sediments, central India were analysed for retrieving the silicification temperature and ambient fluid (water) isotopic composition. Under certain assumptions and uncertainty, triple oxygen isotope data indicate that the fluids were derived from a mixture of meteoric and hydrothermal water. The meteoric water end member possibly had a low ẟ18OVSMOW value (∼− 12 ± 2‰) compared to the modern mean monsoon rainwater (∼− 5‰) which implies a substantially higher rainfall than today (∼1760 ± 200 to 1860 ± 200 mm/year) in the terminal Cretaceous India. This result supports the prediction of elevated precipitation by the recent new generation of global coupled models that consider various feedbacks and ocean dynamics, at a high CO2 atmosphere. It is also consistent with the paleo-botanical evidence but far exceeds the amount predicted by the older paleoclimate models pertaining to the Cretaceous period.
•The ẟ18O-∆′17O values of silicified woods from Deccan intertrappeans were measured to estimate fluid composition.•Depleted δ18Ofluid (∼ -12 ± 2‰) values suggest a higher tropical rainfall (1760 − 1860 mm/y) in terminal Cretaceous period.•The change in rainfall during Cretaceous-Palaeogene transition closely follows the change in atmospheric CO2 concentration.•The inferred rainfall increase is consistent with palaeobotanical evidence and recent coupled climate models.