Tectono-climatic signatures during Late Quaternary in the Yunam basin, Baralacha Pass (upper Lahaul valley, India), derived from multi-proxy records
Introduction
The landscape evolution in the Indian Himalaya is highly influenced by both the tectonics and climate (Kotlia et al., 2000, Kotlia et al., 2010, Barnard et al., 2001, Prasad and Enzel, 2006). In this region, the nature of climate depends on the pressure gradient between ocean and land and seasonal migration of the Intertropical Convergence Zone (ITCZ) (Colin et al., 1998, McGregor and Nieuwolt, 1998). The east–west alignment of the Himalayan mountain chain forms a formidable physical barrier between the tropical and polar air masses and thus controls the northward extension of the ISM. During summer, the high mountains do not allow the equatorial maritime air masses from the Indian Ocean to cross Himalaya and thus force them to curve round to north-west. During winters, the mountains obstruct the penetration of cold polar air masses from Siberia into the Indian subcontinent. However, until now, it remains unclear to what extent monsoonal moisture has affected the interior of the Himalaya during the Last Glacial and Holocene intervals (e.g., Prell and Kutzbach, 1992).
The Himalaya has experienced three major tectonic activities at ca. 35, 21 and 10 ka BP resulting in blockage of rivers and formation of lakes (Kotlia et al., 2008, Kotlia et al., 2010) or intensified river discharges with huge sediment load (Bookhagen et al., 2005). These ancient lakes contain important information of past climatic change on centennial to millennial timescales. Several studies have been carried out to reconstruct the past climatic and environmental changes using palaeo-lacustrine deposits from the Indian Himalaya (e.g., Bagati et al., 1996, Kotlia et al., 1997a, Kotlia et al., 1997b, Kotlia et al., 1998a, Kotlia et al., 2000, Kotlia et al., 2008, Kotlia et al., 2010, Phadtare, 2000, Shukla et al., 2002, Phartiyal et al., 2003, Phartiyal et al., 2005, Rühland et al., 2006, Sangode and Mazari, 2007). However, only a few records cover the Late Glacial and Holocene intervals, representing the palaeoclimatic history of areas adjacent to Ladakh (Fort et al., 1989, Gasse et al., 1991; Kotlia et al., 1998b, Chakraborty et al., 2006, Wünnemann et al., 2008, Wünnemann et al., 2010, Demske et al., 2009, Leipe et al., 2014a, Leipe et al., 2014b) and the western part of Tibetan Plateau (Van Campo and Gasse, 1993, Van Campo et al., 1996, Fontes et al., 1996 and therein). The Late Quaternary tectonic activity has also played a considerable role in formation of palaeo-lacustrine deposits in the Lahaul and Spiti and surrounding areas (Bhargava, 1990, Bagati and Thakur, 1993, Phartiyal et al., 2005, Phartiyal et al., 2009a, Phartiyal et al., 2009b, Singh and Jain, 2007, Anoop et al., 2013, Bohra et al., 2014).
In this study, we present a 25 ka record from the lake sequence, exposed at Kilang Sarai along the Yunam River (32° 49′N: 77° 27′E, altitude 4,573 m asl), north of Baralacha Pass (Fig. 1). The laminated sequence was studied with respect to precipitation variability by using multi-proxy analyses such as mineral magnetism, clay mineralogy, geochemistry and carbon isotopes. The study area is climatically important because of its proximity to the glaciated mountain ranges and/or rain shadow zone, and is influenced by the westerly air flow (Bohra et al., 2014). The present work is thus aimed to evaluate various environmental proxies and to compare the results with other regional climatic data during the Late Quaternary.
Section snippets
Geological background
The study site is located above the tree line, comprising of two SE–NW trending mountain ranges, the Pir Panjal and the Great Himalaya, which are separated by the major valley of the Chandra River (Fig. 1). A number of geomorphological features such as development of gorges (Fig. 2a) and canyons, sinuosity of Yunam River (Fig. 2b), formation of river terraces, triangular fault facets, lineaments and entrenched meanders indicate that the terrain is tectonically active. The Yunam River, which
Materials and methods
The 8 m thick laminated lacustrine sequence (Fig. 4A–C) was sampled at an interval of 10 cm and sub-divided for various analyses. A total of 72 samples were subjected to mineral magnetism, carbon isotopes (δ13C), clay mineralogy and major elemental studies. Three levels of soft sediment structures have earlier been reported from the succession (Bohra et al., 2014).
Three organic-rich layers were subjected to radiocarbon dating (see Bohra et al., 2014). The ages were calibrated using INTCAL09 of
Response of proxies
C3 and C4 plants have average δ13C values in the range of −26 to −28‰ and −11 to −13‰, respectively (Smith and Epstein, 1971, Selvaraj et al., 2010), with C3 plants dominating in areas of higher soil moisture (Tieszen et al., 1979, Selvaraj et al., 2012), indicating warm/wet conditions possibly due to increased precipitation. At Baralacha, lower temperatures and drier climates facilitate occurrence of C4 vegetation. An increased TOC indicates wetter conditions (Talbot and Livingstone, 1989,
Chronology
The chronology of the Kilang Sarai profile was established using 14C dates on bulk sediment samples. The age depth model (adopted from Bohra et al., 2014) suggests a mean sedimentation rate of 31 cm/1000 y and each 10 cm sample gives an age of ∼350 years. The lowermost part of the profile has an age of 25.3 ka BP (Fig. 4A).
Lithology
The Yunam River is fed by the Baralacha glacier, and is the main source of sediment discharge, especially during the rainy season. The study site receives its sediment input
Discussion
During the time span of 25 ka, the study area experienced fluctuations of warming and cooling phases. It is interesting that the area has also preserved geomorphological features, such as, river terraces, deep gorge, fault facets, and river sinuosity, which generally occur in substantially humid climates. The precipitation records are in good agreement with other regions from Ladakh, Lahaul and Trans Himalayan region and present day arid Tibet (Fort et al., 1989, Bagati and Thakur, 1993, Gasse
Conclusions
A 8 m thick palaeolake sequence from Kilang Sarai (Lahaul Himalaya), has been studied for multi-proxy analyses, viz., δ13C, TOC, LOI, mineral magnetism, clay minerals and major elements. Based on the lithological texture and a number of analyses, we conclude:
- 1.
The ancient lake was tectonically formed around 25 ka BP by activity along the fault that dammed the Yunam River. The geomorphologic characters such as tilted terraces, fluvio-lacustrine sediments, fault facets, deep gorge and abrupt
Acknowledgements
The authors are thankful to the Director, Wadia Institute of Himalayan Geology, Dehradun and Dr. N.K. Saini for the support during clay mineralogy and geochemical analysis and to Dr N. Basaviah, Institute of Geomagnetism, Mumbai for providing facility for measuring magnetic susceptibility. Drs. Sushma Prasad and Brigit Pleesen, from GFZ, Potsdam, Germany are acknowledged for carbon isotopic data. AB is grateful to Drs. D.P. Dobhal, R. Islam, P. Srivastava, R. Bhambri, M. Mehta, N.K. Meena from
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