Ashok Kumar Singhvi

Luminescence sensitivity is increasingly being used as a fingerprinting tool in sediment provenance and transport studies owing to its dependence on a variety of factors that operate during sediment transport. This study documented basin‐scale variability in quartz thermoluminescence sensitivity across the semi‐arid Sabarmati River basin, western India, by integrating basin‐scale sampling, laboratory luminescence sensitisation experiments, and single‐grain OSL analyses. Quartz TLS ranged from 1.6 to 6.2 Units in bedrock and 66–325 Units in river sediments. Spatial variability in TLS along the river course was random, and it could only be explained through allochthonous aeolian inputs (55–404 Units) from adjacent dunes rather than progressive in‐channel sensitisation as has been reported in other river basins. Laboratory sensitisation studies on bedrock‐derived quartz TLS show up to a two‐fold increase, with diminishing enhancement over successive cycles. Extrapolation of the initial trend suggests that >500 cycles would be required to match the sediment TLS values, and this implies sub‐million to million‐year timescales of repeated sediment reworking. Further, Sabarmati River sediment TLS suggest low ¹⁰ Be‐derived denudation rates (−1 ). Single‐grain OSL analyses suggest that fewer than 0.5% of exceptionally bright grains dominate the bedrock TLS signal, while non‐luminescent grains constitute up to 99% in bedrock and 60–80% in river sediments. These results suggest that aeolian contributions influence the distribution of single‐grain OSL and thereby determine the bulk TLS and therefore call for caution in the use of TLS as a sediment provenance proxy in dryland river basins that experience aeolian sediment transport. The results also suggest that the abundance of non‐luminescent grains could serve as a provenance indicator.

A brief narrative on early development of Quaternary Sciences in India and its association with International Quaternary Union is presented. A discussion on expectations that accrue from increasing demands on the use of geoscience as services is presented along with some thoughts on recalibration of scientific objectives, resource augmentation through enhanced inclusivity of other disciplines and capacity building in Global South, are outlined, both for the Indian and the international context.

We report the use of Luminescence sensitivity as a proxy to understand sediment dynamics in the Ganga River and its major tributaries, viz., the Yamuna, the Chambal and the Ramganga rivers in India. The Ganga River is one of the world’s largest dispersal systems that originates in the Himalaya and travels across central India to meet the Bay of Bengal. The basin size, catchment lithology, climatic conditions and geomorphic processes of these large rivers are diverse. The rivers are classified into reaches based on varied morphometric characteristics. Sampling strategies focussed on point bars and mid-channel bars mostly from the low-gradient reaches of the rivers, and intervals such that the influences of local dimensions such as hillslope processes and smaller tributary confluences get integrated. Luminescence sensitivity (photon counts/unit dose/unit mass) of quartz grains of 90-150 µm size are examined after check on their purity.The results suggest the following:A gradual change in luminescence sensitivity in the downstream direction. Change is slower at the beginning, then it increases to nearly twice the initial rates after the confluence with R. Ramganga suggestive of change in sediment flux and sediment transportation rates. In the upstream reaches of the river, influences of a landslide zone and the dun (intermontane valley) rivers are discernible. Rates of sensitivity change is nearly four times higher in the case of Yamuna River suggestive of longer transport times. Samples after the confluence of the Ganga and the Yamuna suggest variable contribution from the two rivers through time. Sensitivity of quartz suggests influence of tributary confluences on the change in luminescence sensitivity along the trunk rivers and offer prospect of developing it as an additional parameter to quantify river processes through time. This project is supported through DST SERB-YoSCP grant.

For the last 77 years, many science policy figures in the US have adhered to the principle that staying out of politics is the best way to ensure growth in science funding, and that doing so in the name of doing more science would eventually lead to wholesome uses of scientific information. Although the evidence of the failures of this philosophy have been apparent for several decades, the inability of scientists to communicate about the COVID-19 pandemic has exposed the flaws, effectively.

Thermoluminescence (TL) of feldspar is investigated for its potential to extract temperature histories experienced by rocks exposed at Earth's surface. TL signals from feldspar observed in the laboratory arise from the release of trapped electrons from a continuous distribution of trapping energies that have a range of thermal stabilities. The distribution of trapping energies, or thermal stabilities, is such that the lifetime of trapped electrons at room temperature ranges from less than a year to several billion years. Shorter lifetimes are associated with low-temperature TL signals, or peaks, and longer lifetimes are associated with high temperature TL signals. Here we show that trapping energies associated with shorter lifetimes, or lower-temperature TL signals (i.e. between 200 and 250 ^∘C), are sensitive to temperature fluctuations occurring at Earth's surface over geological timescales. Furthermore, we show that it is possible to reconstruct past surface temperature histories in terrestrial settings by exploiting the continuous distribution of trapping energies. The potential of this method is first tested through theoretical experiments, in which a periodic temperature history is applied to a kinetic model that encapsulates the kinetic characteristics of TL thermometry. We then use a Bayesian approach to invert TL measurements into temperature histories of rocks, assuming that past temperature variations follow climate variations observed in the δ¹⁸O records. Finally, we test the approach on two samples collected at the Mer de Glace (Mont Blanc massif, European Alps) and find similar temperature histories for both samples. Our results show that the TL of feldspar may be used as a paleothermometer.