Geochemical and radiogenic Sr-Nd isotope composition of sandy Thar surface sediments from southwest Rajasthan

Description

Sandy sediment supplies to the Thar Desert and its importance in downwind dust emissions toward the Himalayas are underexplored. We provide a new dataset of geochemical and radiogenic Sr-Nd isotope composition of 51 sandy surface sediments collected from a large hyper-arid area in Southwest Rajasthan. These data show compositionally immature but recycled sediments of the Himalayan orgen. The major sediment delivery to the Thar Desert was routed through the eolian transport of Indus shelf sediments exposed during the LGM and afterward deglaciation times. Significant sediment contributions from upwind Ghaggar-Hakra Paleochannels were also found. Further, the dust delivery to the Himalayan frontal glaicers from a proximal dust souce region (Indo-Gangetic Plain, IGP) was found as significant as remotely contributed from the Thar Desert.

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The bulk sediment was digested in 7 mL PFA vials using HF-HNO3-HCl acid-cocktails in a clean lab at IISER Bhopal. Acid digested materials were dried and redissolved 2 % N HNO3. The elemental concentrations in the In-doped sample solutions were analyzed using Q-ICPMS (i-Cap Q) at IISER Bhopal. For isotope works, Sr and REEs were purified from acid digested samples by column-chemistry using AG 50 W-X8 resin. Nd was purified from REEs by column-chemistry using LN-B50-S resin. Sr and Nd isotope compositions in the purified sample aliquots were determined using MC-ICPMS (Neptune Plus) at IISER Bhopal. Different geochemical phases of salts (milli-q leachate), carbonate (0.6 N HCl leachate), and silicate (0.6 N HCl residue) were also sequentially extracted from 8 samples selected from different dune types and underlying lithologies. Sr isotope composition in these materials were measured following the same method as done for the bulk sediment, while CaCO3 fraction was calculated from the Sr isotope mass balance between silicate and carbonate fractions.

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