Changes in thermoluminescence sensitivity of 110°C glow peak of quartz grains from sediments of River Ganga: Observation and implications

Abstract

The luminescence sensitivity of minerals is being increasingly used to extract information related to geological and geomorphic phenomena experienced by rocks and sediments. Luminescence sensitivity of quartz depends on the source rock, and subsequent changes in it by exposure to ionizing radiation, heating (e.g. forest fires) and daylight exposures during cycles of sedimentation, burial and remobilisation. In the case of sediments, the travel distance has often been implicated for changes in luminescence sensitivity (LS; TLS for thermoluminescence sensitivity and OSLS for optically stimulated luminescence sensitivity).

This study documents changes in TLS of quartz grains from active bar sediments from four transects totalling to ∼4000 km in the Ganga River system (the Ganga, Yamuna, Ramganga and Chambal rivers), and examines its possible use for sediment provenance and in the estimation of sediment fluxes at confluences. This study enables following observations:

1. In a given reach between two major tributary confluences, TLS in UV and blue emissions for both bleached and unbleached samples showed similar behaviour. However, OSLS showed large variability, due possibly to changes caused by bleaching (Singhvi et al., 2011). This suggest that the often used OSLS on bleached samples should be avoided for such provenance studies.

2. No clear dependence of TLS on transport distance was seen, due possibly to the fact that these rivers transport sediments under turbid flow conditions and therefore, most grains do not receive the requisite daylight exposure.

3. TLS of quartz grains from rocks, regolith and fluvial sediments from the Chambal and Ramganga basins suggest that duration of sediment generation processes is key to sensitisation of quartz TLS. This observation leads to a plausible suggestion that TLS can serve as a surrogate of denudation rates, currently being estimated using cosmogenic isotopes.

4. Large variations in TLS in the areas of sand mining, offer a potential to use it in estimating the volumes of sands extracted, a factor critical for sustainability of river systems and economics. This needs to be explored further.

5. Single-grain OSLS suggests that grains with signal-to-background ratio (S/B) 5–50 contribute significantly towards OSLS and changes in the population of grains with S/B 5–50 and > 50 could also serve as tracer for sediment provenance.