Articles written in Journal of Earth System Science

    • Chronology of desert margin in western India using improved luminescence dating protocols

      Naveen Chauhan P Morthekai

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      The present study provides improved chronology for the desert margin fluvial sediments of semi-arid region located in the Mahi river basin, western India. The sequence has preserved a near-continuous record of climate change since the Last Interglacial. An earlier attempt of dating based on feldspar IRSL chronology shows a combined effect of anomalous fading and unbleached components resulting in age inversions. The present work tries to explore the possibility of using blue light stimulated luminescence (BLSL) of quartz, infra-red stimulated luminescence (IRSL) of feldspar and the newly developed methodologies, like natural correction factor based single aliquot regeneration (NCF-SAR) protocol and decision making schemes based on distribution of doses and beta heterogeneity concept for luminescence dating of sediments. Observations suggest that quartz suffered from significant sensitivity changes during natural signal measurement and partial bleaching. A combination of NCF-SAR protocol and sample specific equivalent dose computation helped in arriving at better age estimate for present samples. The study also compares the criteria for the selection of different age models that are used at present. The age of the alluvial sequence is now bracketed between 10 ka (upper aeolian unit) and 75 ka (lowermost fluvial unit).

    • Bleaching of blue light stimulated luminescence of quartz by moonlight


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      Moonlight is sunlight reflected from the moon’s surface. It is additionally modulated by the Earth’s atmosphere, dust and pollutants on its way to the surface of the Earth. This contribution reports the bleaching rates of blue light stimulated luminescence (BLSL) signal of Quartz under full moonlight exposure at the Earth’s surface. Quartz BLSL reduced to 70% by an exposure of 5 hrs moonlight, is in contrast to $\sim$90% reduction in < 3 s with daylight. This was anticipated due to (a) reduced moonlight flux by about a factor of half a million (Agrawal in Lat. Am. J. Phys. Educ. 4(2):325–328, 2010; J. Phys. Astron. 5(1):1–15, 2017); (b) inverse power law dependence of bleaching efficiency on wavelength (Spooner in The validity of optical dating based on feldspar, Ph.D. Thesis, Oxford University, Oxford, 1993; Chen and McKeever in Theory of Thermoluminescence and related phenomena, World Scientific Publications, London, 1997, Chen and Pagonis in Thermally and optically stimulated luminescence: A simulation approach, Wiley and Sons, Chichester, 2011); and (c) moonlight and daylight have spectral peaks around 650 and 550 nm, respectively. Deconvolution of OSL components suggests that moonlight affects the fast component of OSL signal the most. This has ramification for the application in polar regions, where the availability of daylight is at a premium during the winter months. Within a given context, it is conjectured that this could be used to infer the seasonality of sediment transport.


      $\bullet$ Up to 40% reduction of quartz luminescence signal observed over long moonlight exposure.

      $\bullet$ Moonlight can bleach up to 70% of the fast component of blue light stimulated luminescence signal.

      $\bullet$ Moonlight bleaching may hamper the accuracy of ages of sediments which are only transported during night.

      $\bullet$ Seasonality of sediment deposition can be studied using the bleaching effect of moonlight on quartz.

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