Navin Juyal

Luminescence chronology of river adjustment and incision of Quaternary sediments in the alluvial plain of the Sabarmati River, north Gujarat, India

River adjustment and incision in the Sabarmati basin, Gujarat, India have been examined at a site near Mahudi. Towards this, the morphostratigraphy and depositional chronometry of the middle alluvial plains were investigated. The upper fluvial sequence, along with the overlying aeolian sand and riverbed scroll plains, provide clues to the evolution of the present Sabarmati River. Sedimentological analyses of the upper fluvial sequence indicate its deposition by a meandering river system during what is believed to be a persistent wetter phase. Luminescence chronology bracketed this sequence to between 54 and 30 ka, which corresponds to Oxygen Isotope Stage-3, during which the SW monsoon was enhanced. The overlying aeolian sand has been dated to 12 ka, indicating that dune accretion occurred simultaneously with the strengthening of the SW monsoon during the Early Holocene. Adjustment of the Sabarmati along a N-S transect is placed around 12 ka and the incision is bracketed between 12 and 4.5 ka. River adjustment could have been tectonic; however, the incision was facilitated by the availability of continuous flow in the river caused by the SW monsoon. The basin experienced two tectonic events at about 3 and 0.3 ka, as demonstrated by the morphology of the scroll plains.

Chronology of Late Pleistocene environmental changes in the lower Mahi basin, western India

Sediments exposed in the lower Mahi basin at the southern fringe of the Thar Desert, Rajasthan, India, provide evidence of three distinct depositional environments, namely marine, aeolian and fluvial. These have been used to reconstruct Late Pleistocene environmental and tectonic history of the region. Infrared stimulated luminescence (IRSL) chronology of the fluvial and aeolian litho-units provides evidence of two major fluvial aggradation phases in the region corresponding to Oxygen Isotopic Stages 5 and 3. The basal marine clay is inferred to represent the last interglacial stage and its present elevation at +20 m a.s.l. is attributed to post-depositional tectonism. Comparison of fluvial records from other regions indicates interhemispherically documented wetter phases during Oxygen Isotope Stages 5 and 3. Copyright

Reconstruction of the late Quaternary environment of the lower Luni Plains, Thar Desert, India

Geomorphological processes in the Thar Desert of India are largely climate driven. In the lower reaches of the River Luni (the only major drainage system in the Thar Desert) a fluvio-aeolian sequence was located at a site called Khudala. Sediments of this sequence represented a variety of depositional environments, namely aeolian, fluvially reworked aeolian, overbank deposits, gravels, and occasional evidence of pedogenesis. This provided a good opportunity to study aeolian–fluvial interaction in the region and for deducing climatic records. From the luminescence dating standpoint these sequences offered a good opportunity for a comparative study of thermoluminescence (TL), blue-green light stimulated luminescence (BGSL) and infrared light stimulated luminescence (IRSL) on different mineral separates of identical provenance but deposited under different environments. Broadly, within experimental errors, the TL ages agreed with BGSL and IRSL ages on aeolian sands, but differed substantially in the case of fluvially reworked and proximally deposited sands and silts. The sequence provided a record spanning more than 100 ka, with an aeolian phase at > 100 ka, a channel activation phase between 70 and 30 ka and a phase of climate instability between 13 and 8 ka. This appears consistent with the records of monsoon performance during this period, which includes the Younger Dryas. It is also inferred that during the Last Glacial epoch, geomorphological processes in the Thar (both aeolian and fluvial) were dormant largely on account of their relationship with the southwest monsoon. Copyright

Luminescence chronology of aeolian deposition during the Late Quaternary on the southern margin of Thar Desert, India

Abstract Aeolian deposits constitute the uppermost lithostratigraphic unit in the southern margin of the Thar desert. They occur as poorly organized dunes resting on the upper part of a major fluvial sequence. Considerable evidence exists to show that the southern margin witnessed fluvial aggradation before the onset of dune accretion. Transition from a dominantly fluvial phase to aeolian deposition was gradational. Blue-green light stimulated luminescence chronometry of six fossil dunes indicates that the dune building activity started around 26 ka and continued episodically until around 5 ka . Evidence of a phase of landscape stability is seen corresponding to the interval 11– 9 ka . This is also reflected by the presence of Stone Age artifacts (microliths) and fluvially reworked aeolian sand, and corresponds to the strengthening of the southwest monsoon in the region. A progressive northward shift through time in the parameters controlling dune building activity is seen. Aeolian accretion in the southern part (Mahi basin) ended around 10 ka , whereas in the northern Sabarmati it continued until around 5 ka and in the case of core regions of Thar, it continued until 0.6 ka . The southern margins of the Thar Desert thus have not experienced any major aeolian deposition since 5 ka .

Oxygen isotope in archaeological bioapatites from India: Implications to climate change and decline of Bronze Age Harappan civilization

The antiquity and decline of the Bronze Age Harappan civilization in the Indus-Ghaggar-Hakra river valleys is an enigma in archaeology. Weakening of the monsoon after ~5 ka BP (and droughts throughout the Asia) is a strong contender for the Harappan collapse, although controversy exists about the synchroneity of climate change and collapse of civilization. One reason for this controversy is lack of a continuous record of cultural levels and palaeomonsoon change in close proximity. We report a high resolution oxygen isotope (δ18O) record of animal teeth-bone phosphates from an archaeological trench itself at Bhirrana, NW India, preserving all cultural levels of this civilization. Bhirrana was part of a high concentration of settlements along the dried up mythical Vedic river valley ‘Saraswati’, an extension of Ghaggar river in the Thar desert. Isotope and archaeological data suggest that the pre-Harappans started inhabiting this area along the mighty Ghaggar-Hakra rivers fed by intensified monsoon from 9 to 7 ka BP. The monsoon monotonically declined after 7 ka yet the settlements continued to survive from early to mature Harappan time. Our study suggests that other cause like change in subsistence strategy by shifting crop patterns rather than climate change was responsible for Harappan collapse.

Chronology of late quaternary glaciations in Indian Himalaya: A critical review

The timing of glaciation is an important parameter that helps in the understanding of past climate change and provides valuable information for developing the predictive futuristic models. There are evidences to suggest that during the late Quaternary, Himalayan glaciers fluctuated considerably thus implying their sensitivity to changes in past climatic conditions. Although the Himalayan region is fed by two major weather systems viz. the southwest summer monsoon and the mid-latitude westerlies, however, the existing chronology (mostly exposure ages) indicates that irrespective of the geographical position, glaciers seem to grow during increased insolation and enhanced southwest summer monsoon including the mid-latitude westerly dominated north-western Himalayan glaciers (Ladakh and Karakoram). Considering the limited geographical coverage and the dating uncertainty, the above inferences should be treated as tentative.

Ladakh: The High-Altitude Indian Cold Desert

The arid landscape of Ladakh provides a rare opportunity to peep into the history of Earth surface processes. Because of the scanty rainfall, Quaternary landforms are better preserved in this part of the Himalaya. Glaciation, which is considered as the main driver of climate change, has undoubtedly played a key role in shaping the landforms. The alluvial fan dominated mountain slopes and valleys owe their genesis to the fluvial sculpturing and re-sedimentation of the glaciogenic sediments following the periods of glacier recessions. Lacustrine deposits, although important in terms of their climatic significance, constitute a minor component of the Quaternary landforms but provide important climatic data towards improving our understanding of temporal changes in moisture variability. In spite of the fact that the terrain is a cold-arid desert, sand dunes are scanty and limited to the river beds or the mountain flanks suggesting a precarious balance between the wind intensity and sediment supply. It can be suggested that the Ladakh Himalaya is a fascinating laboratory for Quaternary geomorphologists to unravel the history of landforms in a high, tectonically active and arid terrain.

Interpreting the geomorphometric indices for neotectonic implications: An example of Alaknanda valley, Garhwal Himalaya, India

Tectonic process can influence the erosion and exert the first order impression on hydrographic network of an area. Geomorphometry, a mathematical analysis of the configuration of the landforms, allows quantifying the degree of landform evolution and is widely used as a measure of tectonic deformation/uplift. Alaknanda valley lies in the tectonically active Garhwal Himalaya which has experienced two disastrous large earthquakes in the last two decades. Morphometric analyses of the valley were carried out in a fluvial erosion dominated regime and the morphometric indices were derived from the ASTER (30 m × 30 m pixel) Digital Elevation Model (DEM) using Arc GIS. The results of the analyses reveal two zones of high deformation/uplift in the valley, viz., the zone of high deformation proximal to the Main Central Thrust (MCT) in the Inner Lesser Himalaya (ILH) and the second zone of moderate deformation/uplift in the Outer Lesser Himalaya (OLH), south of the Tons Thrust (TT). The high deformation in the ILH is ascribed to the focussed convergence and high precipitation; however, the causes for the moderate deformation in the OLH are yet to be established.

Reconstructing the pattern of the Bara Shigri Glacier fluctuation since the end of the Little Ice Age, Chandra valley, north-western Himalaya

The pattern of glacial records since the end of the Little Ice Age (LIA) are essential for evaluating glacier fluctuations and their link to post-LIA climate change. Although recession of the Himalayan glaciers is well-documented in this period, debate continues as to the magnitude and accuracy of estimated recession rates. This study presents a reconstruction of the pattern of fluctuations at the Bara Shigri Glacier in the Himachal Himalaya during the termination of the LIA (∼1850). A multi-data integrative analysis (MDIA) technique consisting of repeat terrestrial photographs, historical archives and reports, geomorphological evidence and maps, and high to medium spatial resolution satellite images (Corona, Hexagon, Landsat and WorldView-2) was used with supplemented by extensive field validation. The results indicate that during the early part of the 19th century the terminus of Bara Shigri Glacier was at ∼3900 m asl. Following this, there was a continuous recession with a total retreat of 2898 ± 50 m, which corresponds to a frontal areal loss of 4 ± 1 km2 in the last 151 years (1863–2014). Compared to this, during the last half century (1965–2014), the glacierised area was reduced by 1.1 ± 0.02 km2 with a concomitant terminus retreat of 1100 ± 32 m. The early 19th century advance is ascribed to a combination of cooling during this period, glacier topographical characteristics and contributions from steep-fronted avalanching tributaries. The late 19th century recession can be attributed to an overall increase in the temperature with a corresponding decrease in precipitation in the north-western Himalaya. Results are at variance with earlier, larger estimates of the frontal area loss for the Bara Shigri Glacier using either Survey of India (SoI) topographic maps or coarse spatial resolution satellite images (e.g. Landsat MSS) as historical datasets, and demonstrate the utility of mixed method approaches including higher-resolution satellite imagery for accurate estimation of glacier behaviour in this region.

The Great Rann of Kachchh: The Largest Saline Marshland in India

The Great Rann of Kachchh in western India is a unique landscape in the Indian subcontinent. Barely rising above the sea level, it is a vast expanse of salt encrusted terrain which can neither be called a land or sea. Apparently looks topographically monotonous however, a close scrutiny indicates significant geomorphic variability. This is ascribed to a combination of earth surface processes and tectonics. In the absence of longer sedimentary records, the evolutionary history of the Great Rann is limited to the surface exposures of the deposits whose ages go back to about six thousand years. Landforms have a strong finger printing of marine process with subordinate fluvial contribution in landform evolution. The terrain witnessed two major earthquakes, one between 2.2 and 1.4 ka and another in 1819 CE. These earthquakes appear to have significantly influenced the terrain morphology and landform evolution. Although speculative, it seems that frequent earthquakes could have been one of the major reasons for the desertion of human occupation.