Linkage of Paraglacial Processes from Last Glacial to Recent Inferred from Spituk Sequence, Leh Valley, Ladakh Himalaya
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JOURNAL GEOLOGICAL SOCIETY OF INDIA Vol.78, August 2011, pp.147-156 Linkage of Paraglacial Processes from Last Glacial to Recent Inferred from Spituk Sequence, Leh Valley, Ladakh Himalaya 1 2 3 4 DHANANJAY A. SANT , SUDESH K. WADHAWAN , RAJINDER K. GANJOO , NATHANI BASAVAIAH , 1 5 PRABHIN SUKUMARAN and SOURABH BHATTACHARYA 1Department of Geology, Faculty of Science, Maharaja Sayajirao University of Baroda, Vadodara - 390 002 2Geological Survey of India, Desert and Environmental Geology Division, Jaipur - 302 004 3Department of Geology, University of Jammu, Jammu - 180 006 4Indian Institute of Geomagnetism, Plot 5, Sector 18, Kalamboli, New Panvel (W), Navi Mumbai - 410 218 5Department of Geology and Geophysics, IIT Kharagpur - 721 302 Email: [email protected]; [email protected] Abstract: The paraglacial sequence in the Leh valley, Ladakh Himalaya preserves imprints of various processes active during deglaciation in the late phase of Last Glacial. In present work, a high resolution sedimentological record generated for Spituk is presented identifying aeolian episodes, mudflow events from Ladakh Range and debris flows extending from Zanskar Range across present Indus River. Two temporal phases of water ponding within Spituk Sequence are also identified. The seismites recorded at various stratigraphic depths and their association with the sediment facies signifies gravity induced process besides possible seismic activity as an added phenomena. Linkage between paraglacial processes since Last Glacial to Recent is tracked and evaluated. Keywords: Paraglacial, Soft-sediment deformation structures, Leh, Spituk, Ladakh Himalaya. INTRODUCTION (Burgisser et al. 1982; Fort et al. 1989; Bagati and Thakur, The sedimentary sequences in the Leh valley, Ladakh 1993; Sangode and Bagati 1995; Bagati et al. 1996; Kotlia Himalaya provide a window to study the paraglacial et al. 1998; Shukla et al. 2002; Phartiyal et al. 2005; Phartiyal processes that were active during deglaciation ever since and Sharma, 2009) and on chronology using magnetic Last Glacial. The term ‘Paraglacial’, coined by Ryder method (Fort et al. 1989), radiocarbon method (Bagati et (1971a, b), and later, Church and Ryder (1972) describes al. 1996; Phartiyal et al. 2005) and surface dating of moraines non-glacial processes (mass movement and fluvial) that are using 10Be isotope (Brown et al. 2002; Owen et al. 2006). directly conditioned under glacial environment. The term is The present paper focuses on the detailed study of the also extended to cluster of non-glacial landforms that capture known sedimentary sequence exposed at Spituk (34°07' the response of high altitude mountains to changing 50.25" N; 77° 31' 28.30" E; 3213 m). The radiocarbon dates environmental conditions in terms of denudational history along the sequence (~40 ka: Phartiyal et al. 2005) places (Ballantyne, 2002a, b). In the present paper, we discuss the sequence in a time frame of Late phase of Last Glacial aggradation of Spituk sequence under the influence of three (LLG). The study records sedimentary facies, nature of paraglacial processes namely, mass movement (mudflows, transition, and sedimentary structures at high resolution so debris flow and sheet wash); fluvio-glacial (glacial wash); as to resolve paraglacial processes that operated during the aeolian (dunes and sand sheets) and local isolated lakes aggradation of Spituk sequence. The present findings are within the Leh valley. The Leh valley has been investigated significant for they establish the linkage of paraglacial by various workers on several aspects namely, moraines processes operative during LLG to Recent time. Further the (Drew, 1873; Dainelli, 1922; Fort, 1978, 1983; Burbank paper brings out a comprehensive understanding on and Fort, 1985; Fort et al. 1989; Osmaston, 1994); glacial recent catastrophe that occurred in Leh (Juyal, 2010) influence over transverse valleys (Jamieson et al. 2004); where a cloud burst triggered mud flows swept over the influence of glacial and fluvial processes over high mountain Leh town destroying civil infrastructure and buried several landscape (Hobley et al. 2010); lacustrine deposits persons within the flow. 0016-7622/2011-78-2-147/$ 1.00 © GEOL. SOC. INDIA 148 DHANANJAY A. SANT AND OTHERS Nimu valley; southeastern extremes: gorge SE of Karu). The GEOLOGY uplift in Ladakh Himalaya (Clift et al. 2004), studies on The Leh valley is bounded by Ladakh hill range plate movement (between Leh and Bayi, 17.8±1 mm/yr, Jade (undeformed Ladakh batholith and Khardung volcanics, an et al. 2004) and records of liquefaction structures / seismites igneous rock complex) to its north east and Zanskar hill from sedimentary sequence (Shyok valley, Upadhyay, 2001 Range (meta-sedimentaries: Paleozoic to Palaeocene age – and 2003; Spituk and Shyok, Phartiyal and Sharma, 2009) Zanskar Formation and latest Palaeocene to early Miocene have emphasized on neotectonics. However, earlier – Indus Formation) to its southwest (Brookfield and observation by Sinclair and Jaffey (Sinclair and Jaffey, Andrews-Speed, 1984; Garzanti and Van Haver, 1988; 2001, Fig.10, p.158) and our present investigations, across Searle et al. 1990; Searle et al. 1997; Sinclair and Jaffey, a variety of landforms, highlight primary trends of 2001; Jamieson et al. 2004; Wu et al. 2007; Bhutani et al. Quaternary sediments in Leh valley are not disrupted/ 2009). The contact between Indus Formation and Zanskar deformed. Formation is manifested by Choksti thrust along the northeastern fringe of the Zanskar hill Range. The upliftment GEOMORPHOLOGY of Zanskar hill Range occurred along Choksti thrust during Miocene, when Himalaya underwent a major upliftment Geomorphologically the Leh valley is divided into three attaining the present height (Thakur, 1981; Coleman and broad geomorphic units namely, the high elevated terrain of Hodges, 1995; Sinclair and Jaffey, 2001). Choksti thrust Shri Pather Sahib Gurudwara (Unit-1), the deglaciated has a substantial role in the development of gorges amphitheater valley (Unit-2) and low lying terminal alluvial (northwestern portion: gorge connecting Leh valley and fans (Unit-3) (Fig.1). The divisions of the units are based Fig.1. Location and Geomorphology of the Leh valley, Ladakh Himalayas (after Sant et al. 2011). 1 - Moraines, 2 - Glacial wash, 3 - Alluvial fans, 4 - Paraglacial sequences at Gumpuk, Leh and She, 5 - Indus flood plain; The encircled numbers from 1 to 13 represent names of amphitheater valleys namely, Umlah, Taru, Pyang, Gupugas, Leh, Choklamsur, She, Thekse, Rabinpura, Kildyrmala, Karu, Changa, Upshi respectively; The encircled letters from A to L identify various alluvial fans Ni – Nimu hill; Na – Shri Nanak moraine; Go – Gumpuk; Sp – Spituk; Sh – She. JOUR.GEOL.SOC.INDIA, VOL.78, AUGUST 2011 LINKAGE OF PARAGLACIAL PROCESSES FROM LAST GLACIAL TO RECENT, LEH VALLEY, LADAKH HIMALAYA 149 on assemblage of geomorphic features and sediment gravel facies. The intercalated clay facies and sand facies characteristics (Sant et al. 2011). in the lower part of Sputik sequence is capped by gravel Unit-1 forms a high ground, to the northwest of the Leh facies, which is also identified as uppermost lobe of alluvial valley sloping southeast, between the rivers Umlah Fu and fans emerged from Zanskar valley in the Leh valley. The Phyang Fu. The surface is mainly composed of moraine lobes of fan with gravel facies are laterally mappable across ridges (~100 m high) and glacial wash sediments (~10 m present day Indus channel into the Spituk sequence, abutting thick) derived from granites exposed along Ladakh Range. against the Ladakh hill Range. Unit-2 comprises thirteen triangular shaped and deglaciated valleys developed transverse to Ladakh hill SEDIMENTARY FACIES range (Fig.1; 1 to 13). The valleys show head ward erosion towards cirques, whereas downstream the valley forms a A systematic study was carried out in the cut-open wide sloping floor merging with the transverse floor of trenches over 12 benches across the 2796 cm vertical profile Leh valley. The upper reaches of these valleys have well of Spituk sequence. The younger unconsolidated sandy preserved repository of lateral and terminal moraines. The sequence (1050 cm) accreted over the upper slope of Ladakh glaciers melt/rain water drains the lower reaches, gently hills was also logged. sloping valleys show moderate incision exposing ~1 m Three sedimentary facies and five sub facies have been thick sediments. Presence of rounded to sub-rounded identified based on grain size and primary sedimentary gravels with intervening sand lenses manifest role of glacial structures along the 2796 cm sedimentary sequence exposed and paraglacial processes. at Spituk (Fig.2; Table 1). The most dominant lithofacies is Unit-3 constitutes a geomorphic depression between that of fine grained (clay, 68.36%) followed by sand Unit-2 and Zanskar Range filled up by thick sediments (26.26%) and gravel (5.38%). The sediment facies, their brought by mass movement. The most significant association and geometry of the litho-unit together are used geomorphic feature of the Unit-3 is alluvial fans. The alluvial to identify processes responsible in aggradation of the Spituk fans are composed of three independent sediment facies sequence. The intercalated fine and sand facies endorse that namely angular cobble-boulder facies, pebble facies and sediments were deposited by aeolian, mass flow, lacustrine Fig.2. Litholog of Spituk sequence: 1 - clay, 2 - clayey silt, 3 - silt, 4 - silty fine