Research Projects

Climate models predict that future climates would closely resemble early Pliocene climates by 2040 CE under RCP 4.5; however, the scenario could be reached by 2030 CE itself under RCP 8.5. It is also predicted that the future climate would be similar to Eocene climates by 2150 CE under RCP 8.5 (Burke et al., 2018). Past records of such high temperature scenarios in the Earth’s history offers an opportunity to study large-scale changes in fundamental Earth surface processes. Chemical weathering of silicate rocks is a fundamental process that not only acts as a natural thermostat by sequestering CO₂, but also releases various biologically significant cations to the oceans. It becomes significant to know how silicate weathering responded to elevated temperatures in the past. In comparison to the present-day base level, estimates show higher temperatures in the range of 8-13 ⁰C in the early Eocene, ~5 ⁰C in the Oligocene and Miocene, and about 2-3 ⁰C in early Pliocene. These time intervals offer the closest analogues to predicted future temperature scenarios. In India, Cenozoic sedimentary successions of Kutch and Jaisalmer basins provide the best options to study this period. The primary objective of the project is to study the variation in the intensity and rate of silicate weathering globally by studying the Cenozoic carbonate rocks of Kutch and Jaisalmer basins using lithium isotopes. Lithium has two isotope ⁶Li and ⁷Li and the isotopic composition is represented as δ⁷Li with respect to international standard L-SVEC. Silicate rocks of continental crust has abundant Li whereas the carbonate rocks are poor in Li making it an ideal proxy to study the variations in global silicate weathering (Misra and Froelich, 2012; Pogge von Strandmann et al., 2021). Incongruent chemical weathering of silicates causes fractionation of lithium isotopes causing ⁶Li to preferentially stay with clay minerals and thereby enriching the δ⁷Li of the dissolved phases. For example, modern river water has average δ⁷Li value of +31 per mil whereas δ⁷Li of upper continental crust is only 0±2 per mil (Pogge von Strandmann et al., 2020). Dissolved phases eventually end up in the ocean and in the marine carbonate record. Therefore, marine carbonates and calcareous fossils like foraminifera are studied to understand the past δ⁷Li variations which in turn tells us about the intensity of chemical weathering of silicates (Pogge von Strandmann et al., 2019). Along with silicate weathering, the project also aims at understanding variations in different carbon reservoirs, productivity, and long-term carbon cycle during early Cenozoic. Further, Sr isotope stratigraphy would be used to provide chronological constraints to the studied sections and redox sensitive trace element geochemistry will be used to decipher information on local depositional environments.

Chemostratigraphy, Silicate weathering, Cenozoic, Climate change, Lithium isotope