• P Morthekai

      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).

    • RedeBning the timing of Tongul glacial stage in the Suru valley, NW Himalaya, India: New insights from luminescence dating

      S NAWAZ ALI P MORTHEKAI SHACHI BAJPAI BINITA PHARTIYAL ANUPAM SHARMA M FIROZE QUAMAR SIDDHARTH PRIZOMWALA

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      The present study investigates latero-frontal moraines to reconstruct the pattern of glacier advances and associated climate variability in the Suru valley, southwestern Zanskar Himalaya. Impressive sets of latero-frontal moraines and discontinuous morainic ridges (recessional) represent the records of the past glacier advance and retreat. The northerly trending latero-frontal moraines that descend down the tributary valleys and terminate at the trunk Suru valley are the geomorphic expression of one of the oldest preserved record of glacier advance and is named as Tongul glacial stage. Previous studies (based on $^{10}\rm{Be}$ and $^{14}\rm{C}$ ages) deBning the chronology of Tongul glacial stage are either limited in number ($^{14}\rm{C}$ ages) or have a large spread ($^{10}\rm{Be}$ ages) and hence demand further investigation. Optically stimulated luminescence (OSL) dating suggests that the Tongul glacial stage responded to the global last glacial maximum (gLGM) dated between $\sim$ 20 and 24 ka. We suggest that the Tongul glacial stage was driven by enhanced mid-latitude westerlies and reduced temperature (viz., continental cooling) during MIS 2 andfacilitated by corresponding long winters.

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