21-EPN-FT1-019: Isotopic composition of single detrital carbonate grains in the source-to-sink study of the Bengal Fan record
Visit by Mara Limonta, University of Milano-Bicocca (Italy), to TA2.9 Ion Probe Facility (IPF), CRPG (France).
Dates of visit: 25 July – 05 August 2022
The Bengal Fan forms the largest deep-sea turbidite system on Earth and hosts a unique sedimentary record of the evolution of the Himalayan orogenic belt.
This study aims to develop a new protocol to analyse single-grain isotopic signatures of detrital carbonates with primary application in source-to-sink studies and to foster the application of oxygen and carbon isotopes on single detrital grains of carbonates as a provenance tracer. δ18O and δ13C fingerprint of single detrital carbonate grains in Bengal Fan turbidites (IODP Expedition 354) will allow to detect and quantify the signature of different carbonate rocks from the Tethys Himalaya and High Himalaya and to better reconstruct the evolution of erosion processes in the Himalayan belt. This work will allow also testing the feasibility of the new single-grain approach. δ18O and δ13C fingerprint of detrital carbonate grains of selected Bengal Fan turbidites could not be measured due to their fine sand to silt grain-size.
We establish the grain-size feasibility limit at 200 microns in grain diameter. Otherwise, oxygen and carbon isotopic signature of single carbonate grains from Marsyandi and Kali Gandaki modern sand-sized river sediments were analysed to characterize isotopic fingerprint of carbonatic source rocks of Tethys Himalaya unit exposed along their drainage basin. Detrital carbonates of Marsyandi and Kali Gandaki rivers show similar low δ18O values, indicating depletion by metamorphic reactions. δ13C values range from +2‰ and -2‰ and mostly positive δ13C values characterise Kali Gandaki, whereas mostly negative δ13C values characterise Marsyandi carbonate grains.