EGU22-465, updated on 26 Mar 2022
EGU General Assembly 2022
© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

Evidence of high rainfall in India during Deccan eruptions based on triple oxygen isotope composition of petrified woods

Sangbaran Ghoshmaulik1, Sourendra Kumar Bhattacharya1, Manoshi Hazra2, Pallab Roy3, Mahasin Ali Khan2, Mao-Chang Liang3, and Anindya Sarkar1
Sangbaran Ghoshmaulik et al.
  • 1Department of Geology and Geophysics, Indian Institute of Technology Kharagpur, 721302, India
  • 2Department of Botany, Sidho-Kanho-Birsha University, Purulia, 723104, India
  • 3Institute of Earth Sciences, Academia Sinica, Taipei, 11529, Taiwan

The intertrappean sediments and the bole beds of the Deccan volcanic province hold clues to the climatic condition in India during the Cretaceous/Paleocene transition. Earlier isotopic studies of the bulk clays from the ‘bole beds’ showed that the rainwater composition was lighter (δ18O  -8‰) relative to the present-day (δ18O ~ -5‰). This was ascribed to an increase in the rainfall (amount effect). However, later reconstruction of the mean annual precipitation (MAP) from the intertrappean paleosol carbonates suggested that the amount was no different than the modern-day precipitation. One possible reason for this disagreement can be due to the low preservation potential of proxies used in these studies. The present study was carried out by analysing authigenic silica which is resistant to post-depositional modifications. Such silica deposits are abundant throughout the Deccan intertrappean sediments occurring as cherts, chertified limestone and silicified fossils. They form during the interaction of silica-rich water with the existing sediments or fossils, the silica being derived by leaching of the volcanic ash by surface run-off and/or from siliceous hydrothermal waters. Silicified woods were analyzed for their triple oxygen isotope ratios (expressed as δ17O and δ18O) to determine the silicification temperature and the isotopic composition of the silicifying fluid. The distribution of the obtained silicification temperature and water composition of diverse samples indicates a widely variable silicification environment. The silicification took place at temperatures from 25°C  (near surface temperature)  to 90°C (at relatively shallower levels of 50-100 m). In addition, the δ18O (VSMOW) values of silicification fluid varied from -14‰ to near 0‰. The geological, floral and faunal evidence suggest deposition of these woods in a continental fluvio-lacustrine environment. Isotope modelling of the data suggest a two-component fluid mixing between hydrothermal water and a lake water. Assuming this fluid to be derived from a mixture of meteoric water and volcanic hydrothermal water, the δ18O value of the local meteoric water is estimated to be -14‰ to -12‰. These values are lower by about 9‰ to 7‰ compared to today (mean annual δ18O over central India being ~-5‰). We ascribe this to an increase in the mean annual rainfall by about 400 mm. It is possible that the late cretaceous precipitation increased due to the warming caused by a high CO2 environment.

How to cite: Ghoshmaulik, S., Bhattacharya, S. K., Hazra, M., Roy, P., Khan, M. A., Liang, M.-C., and Sarkar, A.: Evidence of high rainfall in India during Deccan eruptions based on triple oxygen isotope composition of petrified woods, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-465,, 2022.


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