Nilesh Bhatt

Geomorphic expression of late Quaternary sea level changes along the southern Saurashtra coast, western India

Geomorphic expression of land-sea interaction is preserved in the form of abandoned cliffs, marine terraces, shore platforms and marine notches along the southern Saurashtra coast. These features have been used to ascertain the magnitude of sea level changes during late Quaternary. Notch morphology and associated biological encrustation have been used to estimate the magnitude and duration of palaeo-sea strands. Marine notches and other erosive features occurring between 12 and 15 m above the present Biological Mean Sea Level (BMSL) are attributed to the last interglacial corresponding to the Marine Isotopic Stage 5 (MIS-5). However, 6 to 9 m upliftment of the coastal fringe is attributed to this sea level. The second major high sea strand was identified during the mid-Holocene when the sea rose 2 m above the present level. Notches corresponding to this high sea level are recorded 4 to 5 m above the present BMSL.

Provenance discrimination and Source-to-Sink studies from a dryland fluvial regime： An example from Kachchh, western India

Abstract Tracing the sediment delivery from its source terrain to its ultimate sink envisage multiple factors that play a vital role in understanding present day erosional engine. To accomplish this, it is significant to distinguish the variable end-members contributing to the basin. The findings from the study of dryland coastal fluvial regime in Kachchh (Western India), which is one of the end members contributing to the Gulf of Kachchh coast (partial sink) and finally to the Arabian Sea (ultimate sink) have been presented here. Multi-proxy sediment provenance proxies such as grain-size, clay minerals, geochemistry and magnetic minerals have been employed to evaluate the provenance discriminating characteristics of the Kachchh dryland fluvial system and factors influencing them. The results of different proxies indicate that the provenance signatures of uplands are quite characteristic with magnetic susceptibility (χ) values of −7 m 3 kg −1 and smectite (S)/kaolinite (K) ratio between 0.26 and 0.49. The middle reaches show marked increase in magnetic mineral concentration with χ values (14010 −7 m 3 kg −1 ) and S/K ratio (4.92), while the estuarine tract shows χ values (8010 −7 m 3 kg −1 ), S/K ratio (1.90) and, characteristic heavy minerals (i.e. mica minerals), probably reflect the interplay between land and sea oscillations. Major sources of sediments within catchment scale were identified, viz., upland sedimentary rocks (Juran and Bhuj Formation sandstone-shale) and middle reaches volcanic (Deccan Trap Formation basalt) rocks. The present study draw cautions in provenance of sediment discrimination in areas influenced by Deccan basalt that has the overwhelming sediment delivery and a comparatively subdued effects of other provenance signatures. The studied proxies of mineralogy of clays, magnetic minerals and geochemistry of heavy and major elements serve as the potential for fingerprint of sediment source regions and hence behold a strong position in source to sink studies globally.

Coastal boulders as evidences of high-energy marine events from Diu Island, west coast of India: storm or palaeotsunami?

Abstract The coastal segment of Diu Island from west coast of India has been studied for its boulder deposits. The dimensions, morphology and characteristics of these boulders were studied to elucidate the type of wave responsible for their detachment from jointed shore platform and transport them to their present final position. The generated data were compared with wave height decay curves of strongest storm that has hit the Gujarat coastline (May 2001 storm). It was concluded that even the strongest storm ever recorded in Arabian Sea (Gonu 2007) cannot detach and initiate the transport of these boulders to their final position. However, a tsunami wave of 3.5-m wave height can easily detach and mobilize these boulders to their final position. On the basis of imbrication direction, we postulate that the direction of source of tsunami wave is southwesterly. Owing to the strike-slip nature of Owen Fracture Zone and earlier documented large landslides along the Southern Owen Ridge, we postulate the most likely source of this tsunami wave could be a mega submarine landslide along the Southern Owen Ridge.

Distribution of Indus born Mica along Gulf of Kachchh Coast: Implications in Understanding Current Dynamics

Indus is one of the major sources of sediments to the Gulf of Kachchh. Yet only its <63 micron fraction is studied in detail with regards to the offshore current dynamics. Hence here we present our study on characteristic signature of the Indus sediment load (i.e. mica minerals) in >63 micron size fraction along the coast of Gulf of Kachchh. The spatial distribution of mica minerals along the Gulf of Kachchh coast was studied which showed in general decreasing trend as we move along the northern and southern coast of the Gulf of Kachchh but, an increase in amount near the southern mouth at Okha. The study shows that the earlier proposed tidal barrier is ineffective in restricting movement of mica across the mouth of the gulf due to its characteristic transport mechanism. Also the presence of mudflats along the gulf of Kachchh coast plays a vital role as sediment receptors in the active sediment transport processes and mica minerals prove to be a promising simple tracer in studying the Indus born sediments in the region.

Spatial variations in tectonic activity along the Kachchh Mainland Fault, Kachchh, western India: implications in seismic hazard assessment

Abstract The landscape of Kachchh is a unique example of active intraplate region in the world. Various structural features such as domes, faults, folds and associated intrusive suggest early tertiary tectonic history, while youthful topography like youthful nature of the fault scarps and gorges suggests Quaternary tectonic history. Kachchh Mainland Fault (KMF) is a 170-km-long E–W-oriented south-dipping reverse fault situated in pericratonic Mesozoic rift basin in western India. The KMF is a neotectonically active fault substantiated by distinct tectonic geomorphology and seismotectonic history. As Kachchh region experiences an arid climate, it lacks vegetation and provides favorable conditions for assessing the morphology of mountain fronts and gradient of channels using remote sensing to evaluate the relative tectonic activity. We employed the means of quantitative geomorphic analysis extracted from a DEM to access the spatial variation in tectonic activity. The assessment of geomorphic indicators of active tectonics was carried out using tectono-geomorphic parameters such as stream length-gradient index (SL index), mountain front sinuosity (Smf) and valley floor width–height ratio (Vf). These parameters were combined to generate the relative index of active tectonics (RIAT) which was further divided into four classes as per degree of tectonic activity. The RIAT classes show segmented nature of KMF, with four segments having decrease in degree of tectonic activity from east toward west. The central and the eastern segments of KMF fall in class 1 and class 2 of RIAT, indicating a relatively higher degree of recent tectonic activity undergone by them. The results of geomorphic analysis are consistent with the landforms present, geological setup and seismicity in the study area. The study would be helpful in accessing the regional seismic hazard from KMF for the entire western India.

Internal Sedimentary Architecture and Coastal Dynamics as Revealed by Ground Penetrating Radar, Kachchh coast, Western India

The coastline constitutes a very sensitive geomorphic domain which is constantly subjected to dynamic coastal processes and stores vital information regarding past sea level fluctuations. A ground-penetrating radar (GPR) survey was carried out along the northern coast of the Gulf of Kachchh which is one of the largest macrotidal inlets of the Arabian Sea, Western India. Our studies have delineated several radar surfaces and radar facies which reflect the internal architecture and sediment body geometry, which can be related to the processes acting along this coastline. Various radar facies, namely, beach ridge (Br), washover (Wo), coastal dune (Cd), swale (Sw), berm plain (Bp), and sandsheet facies (Ss) have been identified. The GPR studies successfully documented the subsurface presence of ancient beach ridge system towards the sea, and the coastal dunes towards the land side. The results are suggestive of signatures of changes in sea level and the coastline being prone to high energy events in the recent past. The GPR has been found to be an important non-invasive geophysical tool in the study of past coastal dynamics.

Understanding the sediment routing system along the Gulf of Kachchh coast, western India: Significance of small ephemeral rivers

The present study is an attempt towards understanding the sediment routing system in the semi-arid margin of the Gulf of Kachchh, which is one of the largest macrotidal regimes in the northern Arabian Sea. Investigations based on heavy minerals, clay minerals, mineral magnetic properties and sediment geochemistry indicated that there are three major sources of sediments contributing to the Gulf of Kachchh basin: (1) Indus River, (2) Kachchh mainland coastal rivers and (3) the Saurashtra peninsular coastal rivers. The flanks of northern and southern coast of western Gulf of Kachchh show dominant signatures of Kachchh mainland/Saurashtra peninsular provenance. In contrast, the eastern Gulf of Kachchh coast bearing fine grained sediments shows dominant Indus River Provenance. Although ephemeral in nature, the small coastal rivers of Saurashtra and Kachchh contribute significant amount of sediments to the Gulf of Kachchh coastline because of their ‘dryland’ nature and thus they control the coarse grained sedimentation processes.