An event of neotectonic activity on an NE-SW trending subsidiary fault in the zone of E-W running... more An event of neotectonic activity on an NE-SW trending subsidiary fault in the zone of E-W running intracrustal boundary thrust (South Almora Thrust) in the Champawat district of eastern Kumaun Himalaya resulted in creation of a lake at ca. 21.5 BP. The lake was drained out in the late Holocene leaving behind a 5.0 m thick sedimentary sequence of mostly black and carbonaceous mud indicating at the base a minor magnetic reversal between 20.5-19.7 ka BP. The profile, studied by using multi-proxies (e.g., carbon isotopes, pollen
Abstract Representing the southerly extension of the desertic Rajasthan plain, the Sabarmati plai... more Abstract Representing the southerly extension of the desertic Rajasthan plain, the Sabarmati plain in Gujarat conceals a N–S-trending, 50-km-wide graben defined by down-to-basin faults. Listric faults and ENE–WSW-oriented wrench faults have appreciably affected this hidden graben, which is in the line of similar grabens in westen Rajasthan. The 2000- to 3000-m-thick succession of Cenozoic sediments of this graben hosts petroleum and gas deposits. Repeated reactivation, including during the Later Holocene era, of the faults of the graben domain is evident from the southwestward tilting of the floodplain, the deflection and deep incision of the stream channels, the occurrence of palaeoseismites in the proximity of the graben-boundary faults, and a continuing seismicity. Belonging to the stable continental region of Peninsular India, the Saurashtra region exhibits microseismicity in a few geographically limited areas. Radically different in every respect and bearing a strong resemblance to the Himalayan mobile domain, the Kachchh (Cutch/Kutch) terrane is cut by a number of E–W-trending deep faults, giving rise to hill ranges in the southern part and a sunken tract known as Rann in the northern and eastern parts, which were under seawater until early historical times. The youthful geomorphology of horst-like hill ranges, drainage deviation, deep incision of subrecent colluvial–alluvial fans by perennial streams in the desertic terrain, palaeoseismites, and a continuing strong seismicity indicate that Kachchh (Cutch/Kutch) is tectonically the most resurgent part of Peninsular India.
Abstract The Ganga–Brahmaputra Plains represent a sediment-filled foreland basin in front of the ... more Abstract The Ganga–Brahmaputra Plains represent a sediment-filled foreland basin in front of the Himalaya. Characterized by disparate physigraphic units and occurring as large terraces at different elevation levels belonging to different chronological times of the Late Quaternary epoch, the Plains conceal under the thick pile of fluvial and alluvial sediments a number of very high NE–SW-trending basement ridges delimited by long, deep faults. Continual and episodic differential movements on these faults with an attendant rise and subsidence of ground caused the persistent shifting of the rivers of the Yamuna and Ganga systems eastwards and of the Gandak–Kosi and Brahmaputra systems westwards. The neotectonic movements also brought about drainage obstruction, culminating in the development of swamps, marshes, lakes, and waterlogging in the much-faulted Kosi–Gandak domain as well as in northern Bangladesh. The abandonment by the Brahmaputra River of its former course and joining with Ganga River in Bangladesh was a result of tremendous neotectonic resurgence in the Bengal Basin. Palaeoseismites in the foothill belt all along the length of the Ganga–Brahmaputra plains point to the havoc wreaked by many seismogenic faults that riddle the northern periphery of the Ganga–Brahmaputra Plains.
Monsoon in the Indian sub-continent remains a seasonal phenomenon which is awaited by all of the ... more Monsoon in the Indian sub-continent remains a seasonal phenomenon which is awaited by all of the humans of the subcontinent. It has long drawn the reverence of monks, travellers, poets, traders and researchers. All mortals from the sub-continent have looked to it from their own perspective and it continues to be the subject of intense multi-dimensional engagement. The monsoon has provided the means of survival to many civilizations, besides sculpting the drainages and the palaeogeography of the subcontinent. The evolution of Himalayas has played a critical role in the evolution of the summer monsoon, which gave life to rivers, crops and human settlements. The present synthesis of the Monsoon illustrates how it is linked to the history of human cultures and their evolution. Furthermore, we have attempted to place the monsoon in a historical perspective using ancient literature, besides considering the present monsoon variability and forecasting systems available.
A number of contributions to the understanding of geology of Himalaya prior to the 20th C. are de... more A number of contributions to the understanding of geology of Himalaya prior to the 20th C. are described. These include observations made by the Chinese about marine fossils found in high mountains; records from 1720s of the Jesuit Priest, Ippolito Desideri, along the course of the Yarlung-Tsangpo-Brahmaputra River; the work of Cautley and Falconer on vertebrate fossils from Miocene of the Siwaliks; and the first geological traverse of the mountain chain. This latter was undertaken by Lieutenant Richard Strachey in 1848 and his detailed cross sections were published in 1851. It is this transect that represents the ‘journey’ described in this paper where Strachey’s observations on the geology of the Himalaya are given. The work of some other notable geologists in the second half of the 19th C is recorded. This leads to a discussion of isostasy and theories about the structure of this and other mountain chains, including the geosynclinal theory that prevailed up until the end of the 1...
Abstract The early Precambrian Bastar and Singhbhum cratons, with their intimately associated Pro... more Abstract The early Precambrian Bastar and Singhbhum cratons, with their intimately associated Proterozoic mobile belts, are subdivided into disparate terranes by a number of long, deep, and curvilinear shear zones of Precambrian antiquity. Although the orthogonal Gondwanic Godavari Graben defines the western limit of the Bastar, the Mahanadi Graben separates the Bastar from the Singhbhum domain. Despite a multiplicity of terrane-defining curvilinear seismogenic shear zones, no work on neotectonism has been done in this part of the Indian subcontinent. A notable feature is that the laterite-mantled terrain characterized by many planation surfaces and delimited by escarpments has become rugged in some belts. Down these scarp faces descend rivers and streams as waterfalls. All these features collectively indicate the Late Quaternary uplift. In a sector of the E–W-trending, much-faulted Damodar Graben in the Singhbhum domain, palaeochannels are associated with archaeological remnants, implying tectonic disturbance in historical time in the graben zone.
Abstract Close to the Arabian Sea coast, the peaks of the 1600-km-long chain of the Sahyadri Rang... more Abstract Close to the Arabian Sea coast, the peaks of the 1600-km-long chain of the Sahyadri Ranges rise to an elevation of 1646 m in northern sector, 1646 m in the central sector, and 2695 m in the southern sector. It is cut by the E–W-trending, continent-wide Precambrian shear zones in the Palghat Gap which is no more than 75–300 m above sea level. Rising high against the 40–120 m of undulating terrain of the coast of emergence, the 900- to 2695-m high Sahyadri is remarkable for its spectacular western flank that is characterized by high escarpments alternating with narrow, irregularly tilted terraces forming a ‘landing stair’ (ghat) geomorphic architecture known as the Western Ghat. The Sahyadri terrane is split into a number of linear blocks by NW–SE, NNW–SSE, and N–S-trending faults and fractures. It is a product of the differential–intermittent uplift on these faults, predominantly in the Quaternary era. These rupture planes extend northwestwards through the coastal belt on to the offshore to form underwater basins (rifts) and ridges (horsts). Raised beaches, drowned forests, anomalous stream deflections, palaeolake deposits, and a continuing blockage of rivers at their fault crossing, geothermal springs, high emission of radon gas, and high seismicity in the much faulted areas in the coastal belt and Sahyadri domain eloquently testify to tectonic resurgence the two belts have witnessed and continue to undergo.
Abstract The geological layouts of Pakistan, Nepal, Bhutan, Bangladesh, and Sri Lanka are insepar... more Abstract The geological layouts of Pakistan, Nepal, Bhutan, Bangladesh, and Sri Lanka are inseparably linked with that of India. The Indian subcontinent encompasses as many as nine geological terranes, each having its own distinctive lithological-petrochemical characteristics, structural architecture, and different evolutionary history. There are Archaean cratons embodying composite, consolidated, and rigid blocks; Proterozoic mobile belts of high-grade metamorphic rocks; continent-interior basins comprising slightly deformed to practically undeformed Proterozoic sediments; Permian-age elongate Gondwanic grabens and half-grabens cutting across the cratons; a Cretaceous Volcanic Province covering vast swathes of land in western and central India; Mesozoic–Cenozoic sediments piled up on gradually sinking continental margins; a Cenozoic Himalayan Mobile Belt representing a youthful orogen formed due to the docking of India with Asia; flysch-dominated obduction complexes forming the much-faulted arcuate mountain ranges along the India–Myanmar border; and an oceanic trench-defined island-arc complex in the Bay of Bengal.
Abstract The laterite-capped Mysore Plateau is bordered both on the east and west sides by rugged... more Abstract The laterite-capped Mysore Plateau is bordered both on the east and west sides by ruggedly high and linear mountain ranges rising 500–1000 m above its 700- to 900-m-high planation surface of the plateau. Characterized by planar scarps with sparse gullies and a few planation surfaces, the high laterite-topped mountain ranges are dissected by N–S- and NNW–SSE-trending fractures and faults, whereas the main part of the plateau is broken into blocks by long, deep curvilinear shear zones of Precambrian antiquity. The mature old River Kaveri that consistently flows eastwards abruptly swerves left or right along the N–S fault planes and then drops into a canyon that is characterized by channel-in-channel geomorphology before leaving the mountain domain. Like the Kaveri (Cauvery), most of the rivers cross hills and ridges as antecedent rivers. Ponding of the Kaveri and its tributaries gave rise to a huge lake that stretched as much as 45 km upstream. The lake is now represented by a thick pile of black clay deposits of Late Quaternary age, forming the granary of Karnataka state. Demarcated by E–W-trending, two continent-wide shear zones of Precambrian age, the laterite-capped, 2670 m-high, Nilgiri massif is characterized by many planation surfaces, steep to nearly vertical scarps on all sides, and meandering streams descending through canyons as water falls. These features imply fast uplift and attendant exhumation of the Precambrian terrane that rose up like a horst.
Abstract Made up of high-grade metamorphic rocks that evolved under ultra-high temperatures, the ... more Abstract Made up of high-grade metamorphic rocks that evolved under ultra-high temperatures, the highly dissected Precambrian Eastern Ghat Mobile Belt is demarcated against the Dharwar–Bastar cratons by west-vergent shear zones dotted with plutons of alkaline and ultrabasic rocks, as well as against the Proterozoic Cuddapah sedimentary basin by a fold-and-thrust zone. A few NW–SE-oriented grabens that cut across the terrane served as floodplains of rivers like the Krishna and Godavari. In the coast of emergence that is the East Coast, lakes representing drowned embayments, sunken karstic topography with its pinnacles and domes, submerged V-shaped canyons offshore of the Krishna–Godavari domain, and archaeological remains of a seaport 30 m below the surface in the Kaveri delta, point to the sinking that continued into historical time. On the other hand, raised beaches, high strand lines, and progressive river migration in their deltas indicate uplift in some parts that are fault ridden. Seismicity in the southeastern part of the Godavari Graben and in east central Tamil Nadu indicates that some faults are very active.
Abstract The Indian subcontinent is a part of a very dynamic crustal plate that is converging nor... more Abstract The Indian subcontinent is a part of a very dynamic crustal plate that is converging northwards towards mainland Asia at a rate which varies in time and space. Within its fragmented framework, a large number of faults and shear zones developed thousands and even millions of years ago. Reactivated time and again due to the buildup of stresses resulting from the northwards movement of the Indian continental plate, these faults and fractures have played a primary role in the shaping of the landforms and landscapes that we see today. The movements on rupture planes also constrained the establishment of drainage patterns and the aberrations in river behaviour. It is the rupture-related dislocation of landforms and the sinking and rising of the fault-affected ground that brought about discernible physiographic changes, particularly where there were continued and ongoing movements, such as in the Himalayan province pressed hard between the northwards-pushing Peninsular India and the Asian landmass. Recurrent seismicity provides eloquent testimony to the neotectonic resurgence of the faulted terrains and the terrane-defining faults.
Abstract Between the 1000-km-long ENE–WSW-trending Narmada Graben in the north and much smaller b... more Abstract Between the 1000-km-long ENE–WSW-trending Narmada Graben in the north and much smaller but parallel Tapi Graben in the southwest, the Proterozoic Satpura Mobile Belt forms a prominent horst that rose up rapidly in the Later Quaternary time. Delimited by faults that are responsible for 500–800 m of cumulative throw, the Narmada Graben is a narrow zone of high heat flow, hot springs, parallel dyke swarms, and moderate seismicity. In the domain of this rift valley, the main river follows a remarkably straight course all along the reach, but its tributaries swerve abruptly before joining the Narmada across the Pleistocene terraces. Strong movements on the Tapi graben faults, which were accompanied by great earthquakes, resulted in an unusual continental-scale drainage pattern that created a large westwards-flowing catchment in the region where all other rivers flow either northeastwards or southeastwards. Shear zones of a large dimension south of the Satpura horst are seismogenic.
We reviewed the available climate records for the past 2 millennia based on the analyzed sediment... more We reviewed the available climate records for the past 2 millennia based on the analyzed sediment and speleothem archives from different regions of South Asia. Speleothem records from the core-monsoon regions of the Indian sub-continent have revealed the Little Ice Age (LIA) as a climatically dry phase, whereas the same from the western and central Himalaya recorded LIA as wet. Moreover, the sediment-derived vegetation proxy records [pollen-spores and stable organic carbon isotope (δ13Corg)] from the western Himalaya also reported LIA as a dry phase. Heterogeneous results by different proxies during LIA enhanced our interest to understand the response of the proxies toward the primary precipitation sources, Indian summer monsoon (ISM) and winter westerly disturbances (WDs), over the Himalaya. We emphasize that in the Himalayan region, the vegetation predominantly responds to the ISM dynamics, whereas speleothem also captures the WD effect.
In comparison to the east coast, the tsunami hazard for the west coast of India remains under-rec... more In comparison to the east coast, the tsunami hazard for the west coast of India remains under-recognized, despite the impact in 1945 following a M w 8.1 earthquake in the Makran subduction zone in the northern Arabian Sea. The previous occurrences of tsunamis in the Arabian Sea that would have a bearing on the west coast of India are being debated, including the question whether the Makran region has the potential to generate greater-magnitude earthquakes. With this in the backdrop, we present here the historical and geological evidence of a tsunami impact zone from a site on the Konkan Coast of western India. Located in the village of Kelshi, the impact zone is preserved within a coastal dune complex that also reveals occupation layers. This laterally extending 30-40-cm-thick zone, coinciding with a habitation level, displays varied sedimentary structures including scour-fill features, and is inter-layered with shells, at a height of * 3 m from the high-tide level. We attribute these sedimentary features to a tsunami flooding event that was contemporaneous with the transportation of shells, dated at 1508-1681 CE. The geological inference matches with the description by the Portuguese fleets of a sea disturbance in 1524 CE, reported from Dabhol, not far from Kelshi, and also from the Gulf of Cambay, located about 500 km to the north. Precluding submarine landslide scenarios, the modeling results suggest that the high impact in Kelshi could have been generated by a M w C 9 earthquake sourced in the Makran subduction zone. It is, however, intriguing how a M w C 9 earthquake in the Makran region finds no mention in the historical documentation. We underscore the need for fresh efforts along the Makran coast to reconstruct the tsunami recurrence history that would generate required validating constraints on the 1524 event, if it was indeed generated by a massive earthquake among other mechanisms.
Abstract The Aravali terrane is a highly deformed Proterozoic mobile belt entangled with an Archa... more Abstract The Aravali terrane is a highly deformed Proterozoic mobile belt entangled with an Archaean craton. It is split along its length by a number of crustal-scale shear zones, and dislocation zones developed in it during Precambrian time. Reactivation in the Late Quaternary of the shear zones is manifest in some areas, such as in the sinking of ground with a resultant formation of saline lakes, the bulging up of other areas with attendant watershed migration, the stream capture, the entrenched meander loops, and the persistent moderate to low seismicity in the fault-ridden northeastern part of the Aravali terrane. Separated from this consolidated complex by the Great Boundary Fault, which registers a cumulative throw of 500–1300 m, the vast Vindhyan Basin of Proterozoic sediments is largely undeformed, except for around its tectonic boundary with the Aravali in the west and the Satpura in the south. However, the Vindhyan basement is segmented by wrench faults as well as strike faults, some of which register a strike-slip motion. The pronounced development of badlands close to the northern faulted border against the Ganga Plain indicates a very slow uplift of the northern part.
Abstract The N–S trending array of mountain ranges along the border of India and Myanmar represen... more Abstract The N–S trending array of mountain ranges along the border of India and Myanmar represents the eastern arm of the Himalayan Mobile Belt. A linkage of three disparate mountain belts forming the Siang Syntaxis in the north separates this arcuate arm from the main Himalayan arc. Characterized by a schuppen structure (i.e., packs of imbricated thrust sheets that are folded and faulted), this orogenic unit of Late Mesozoic–Cenozoic flysch with its ophiolite implants is strongly affected by stresses generated due to the oblique convergence and attendant underthrusting of the Indian plate under the Burmese (Myanmar) microplate. The rate of slipping varies not only from sector to sector, but also from time to time. Very high seismicity and GPS measurements demonstrate continuing strong movements on faults of this fault-ridden palaeo-obduction complex. The epicentral distribution defines a distinct Benioff Zone dipping eastwards under Myanmar.
Abstract The early Precambrian Bastar and Singhbhum cratons, with their intimately associated Pro... more Abstract The early Precambrian Bastar and Singhbhum cratons, with their intimately associated Proterozoic mobile belts, are subdivided into disparate terranes by a number of long, deep, and curvilinear shear zones of Precambrian antiquity. Although the orthogonal Gondwanic Godavari Graben defines the western limit of the Bastar, the Mahanadi Graben separates the Bastar from the Singhbhum domain. Despite a multiplicity of terrane-defining curvilinear seismogenic shear zones, no work on neotectonism has been done in this part of the Indian subcontinent. A notable feature is that the laterite-mantled terrain characterized by many planation surfaces and delimited by escarpments has become rugged in some belts. Down these scarp faces descend rivers and streams as waterfalls. All these features collectively indicate the Late Quaternary uplift. In a sector of the E–W-trending, much-faulted Damodar Graben in the Singhbhum domain, palaeochannels are associated with archaeological remnants, implying tectonic disturbance in historical time in the graben zone.
Abstract Underneath the floodplains of the Sindhu and Ghagghar river systems, a number of subsurf... more Abstract Underneath the floodplains of the Sindhu and Ghagghar river systems, a number of subsurface basement ridges are related to the NW–SE-trending Aravali Mobile Belt. A multiplicity of long and deep faults also occurs. Seismicity in parts of the belts over these hidden ridges indicates the reactivation of faults across which flow the rivers of the two systems. Although the Sindhu River migrated 160 km westwards in the Holocene time, even as great subsurface depressions formed in front of the Sulaiman and Kirthar Ranges, the Ghagghar basin in the eastern part witnessed a strong tectonic upheaval. This manifested itself in subsidence, uplift and dislocation of ground. This resulted in drainage reorganization, channel segmentation, and, in one case, river piracy. This spectacular event happened at a time when a drastic decline in rainfall occurred, which caused not only a mass exodus of the people of the Harappan civilization in the mid-Holocene time, but also the development of the Thar Desert in western India and adjoining Pakistan.
An event of neotectonic activity on an NE-SW trending subsidiary fault in the zone of E-W running... more An event of neotectonic activity on an NE-SW trending subsidiary fault in the zone of E-W running intracrustal boundary thrust (South Almora Thrust) in the Champawat district of eastern Kumaun Himalaya resulted in creation of a lake at ca. 21.5 BP. The lake was drained out in the late Holocene leaving behind a 5.0 m thick sedimentary sequence of mostly black and carbonaceous mud indicating at the base a minor magnetic reversal between 20.5-19.7 ka BP. The profile, studied by using multi-proxies (e.g., carbon isotopes, pollen
Abstract Representing the southerly extension of the desertic Rajasthan plain, the Sabarmati plai... more Abstract Representing the southerly extension of the desertic Rajasthan plain, the Sabarmati plain in Gujarat conceals a N–S-trending, 50-km-wide graben defined by down-to-basin faults. Listric faults and ENE–WSW-oriented wrench faults have appreciably affected this hidden graben, which is in the line of similar grabens in westen Rajasthan. The 2000- to 3000-m-thick succession of Cenozoic sediments of this graben hosts petroleum and gas deposits. Repeated reactivation, including during the Later Holocene era, of the faults of the graben domain is evident from the southwestward tilting of the floodplain, the deflection and deep incision of the stream channels, the occurrence of palaeoseismites in the proximity of the graben-boundary faults, and a continuing seismicity. Belonging to the stable continental region of Peninsular India, the Saurashtra region exhibits microseismicity in a few geographically limited areas. Radically different in every respect and bearing a strong resemblance to the Himalayan mobile domain, the Kachchh (Cutch/Kutch) terrane is cut by a number of E–W-trending deep faults, giving rise to hill ranges in the southern part and a sunken tract known as Rann in the northern and eastern parts, which were under seawater until early historical times. The youthful geomorphology of horst-like hill ranges, drainage deviation, deep incision of subrecent colluvial–alluvial fans by perennial streams in the desertic terrain, palaeoseismites, and a continuing strong seismicity indicate that Kachchh (Cutch/Kutch) is tectonically the most resurgent part of Peninsular India.
Abstract The Ganga–Brahmaputra Plains represent a sediment-filled foreland basin in front of the ... more Abstract The Ganga–Brahmaputra Plains represent a sediment-filled foreland basin in front of the Himalaya. Characterized by disparate physigraphic units and occurring as large terraces at different elevation levels belonging to different chronological times of the Late Quaternary epoch, the Plains conceal under the thick pile of fluvial and alluvial sediments a number of very high NE–SW-trending basement ridges delimited by long, deep faults. Continual and episodic differential movements on these faults with an attendant rise and subsidence of ground caused the persistent shifting of the rivers of the Yamuna and Ganga systems eastwards and of the Gandak–Kosi and Brahmaputra systems westwards. The neotectonic movements also brought about drainage obstruction, culminating in the development of swamps, marshes, lakes, and waterlogging in the much-faulted Kosi–Gandak domain as well as in northern Bangladesh. The abandonment by the Brahmaputra River of its former course and joining with Ganga River in Bangladesh was a result of tremendous neotectonic resurgence in the Bengal Basin. Palaeoseismites in the foothill belt all along the length of the Ganga–Brahmaputra plains point to the havoc wreaked by many seismogenic faults that riddle the northern periphery of the Ganga–Brahmaputra Plains.
Monsoon in the Indian sub-continent remains a seasonal phenomenon which is awaited by all of the ... more Monsoon in the Indian sub-continent remains a seasonal phenomenon which is awaited by all of the humans of the subcontinent. It has long drawn the reverence of monks, travellers, poets, traders and researchers. All mortals from the sub-continent have looked to it from their own perspective and it continues to be the subject of intense multi-dimensional engagement. The monsoon has provided the means of survival to many civilizations, besides sculpting the drainages and the palaeogeography of the subcontinent. The evolution of Himalayas has played a critical role in the evolution of the summer monsoon, which gave life to rivers, crops and human settlements. The present synthesis of the Monsoon illustrates how it is linked to the history of human cultures and their evolution. Furthermore, we have attempted to place the monsoon in a historical perspective using ancient literature, besides considering the present monsoon variability and forecasting systems available.
A number of contributions to the understanding of geology of Himalaya prior to the 20th C. are de... more A number of contributions to the understanding of geology of Himalaya prior to the 20th C. are described. These include observations made by the Chinese about marine fossils found in high mountains; records from 1720s of the Jesuit Priest, Ippolito Desideri, along the course of the Yarlung-Tsangpo-Brahmaputra River; the work of Cautley and Falconer on vertebrate fossils from Miocene of the Siwaliks; and the first geological traverse of the mountain chain. This latter was undertaken by Lieutenant Richard Strachey in 1848 and his detailed cross sections were published in 1851. It is this transect that represents the ‘journey’ described in this paper where Strachey’s observations on the geology of the Himalaya are given. The work of some other notable geologists in the second half of the 19th C is recorded. This leads to a discussion of isostasy and theories about the structure of this and other mountain chains, including the geosynclinal theory that prevailed up until the end of the 1...
Abstract The early Precambrian Bastar and Singhbhum cratons, with their intimately associated Pro... more Abstract The early Precambrian Bastar and Singhbhum cratons, with their intimately associated Proterozoic mobile belts, are subdivided into disparate terranes by a number of long, deep, and curvilinear shear zones of Precambrian antiquity. Although the orthogonal Gondwanic Godavari Graben defines the western limit of the Bastar, the Mahanadi Graben separates the Bastar from the Singhbhum domain. Despite a multiplicity of terrane-defining curvilinear seismogenic shear zones, no work on neotectonism has been done in this part of the Indian subcontinent. A notable feature is that the laterite-mantled terrain characterized by many planation surfaces and delimited by escarpments has become rugged in some belts. Down these scarp faces descend rivers and streams as waterfalls. All these features collectively indicate the Late Quaternary uplift. In a sector of the E–W-trending, much-faulted Damodar Graben in the Singhbhum domain, palaeochannels are associated with archaeological remnants, implying tectonic disturbance in historical time in the graben zone.
Abstract Close to the Arabian Sea coast, the peaks of the 1600-km-long chain of the Sahyadri Rang... more Abstract Close to the Arabian Sea coast, the peaks of the 1600-km-long chain of the Sahyadri Ranges rise to an elevation of 1646 m in northern sector, 1646 m in the central sector, and 2695 m in the southern sector. It is cut by the E–W-trending, continent-wide Precambrian shear zones in the Palghat Gap which is no more than 75–300 m above sea level. Rising high against the 40–120 m of undulating terrain of the coast of emergence, the 900- to 2695-m high Sahyadri is remarkable for its spectacular western flank that is characterized by high escarpments alternating with narrow, irregularly tilted terraces forming a ‘landing stair’ (ghat) geomorphic architecture known as the Western Ghat. The Sahyadri terrane is split into a number of linear blocks by NW–SE, NNW–SSE, and N–S-trending faults and fractures. It is a product of the differential–intermittent uplift on these faults, predominantly in the Quaternary era. These rupture planes extend northwestwards through the coastal belt on to the offshore to form underwater basins (rifts) and ridges (horsts). Raised beaches, drowned forests, anomalous stream deflections, palaeolake deposits, and a continuing blockage of rivers at their fault crossing, geothermal springs, high emission of radon gas, and high seismicity in the much faulted areas in the coastal belt and Sahyadri domain eloquently testify to tectonic resurgence the two belts have witnessed and continue to undergo.
Abstract The geological layouts of Pakistan, Nepal, Bhutan, Bangladesh, and Sri Lanka are insepar... more Abstract The geological layouts of Pakistan, Nepal, Bhutan, Bangladesh, and Sri Lanka are inseparably linked with that of India. The Indian subcontinent encompasses as many as nine geological terranes, each having its own distinctive lithological-petrochemical characteristics, structural architecture, and different evolutionary history. There are Archaean cratons embodying composite, consolidated, and rigid blocks; Proterozoic mobile belts of high-grade metamorphic rocks; continent-interior basins comprising slightly deformed to practically undeformed Proterozoic sediments; Permian-age elongate Gondwanic grabens and half-grabens cutting across the cratons; a Cretaceous Volcanic Province covering vast swathes of land in western and central India; Mesozoic–Cenozoic sediments piled up on gradually sinking continental margins; a Cenozoic Himalayan Mobile Belt representing a youthful orogen formed due to the docking of India with Asia; flysch-dominated obduction complexes forming the much-faulted arcuate mountain ranges along the India–Myanmar border; and an oceanic trench-defined island-arc complex in the Bay of Bengal.
Abstract The laterite-capped Mysore Plateau is bordered both on the east and west sides by rugged... more Abstract The laterite-capped Mysore Plateau is bordered both on the east and west sides by ruggedly high and linear mountain ranges rising 500–1000 m above its 700- to 900-m-high planation surface of the plateau. Characterized by planar scarps with sparse gullies and a few planation surfaces, the high laterite-topped mountain ranges are dissected by N–S- and NNW–SSE-trending fractures and faults, whereas the main part of the plateau is broken into blocks by long, deep curvilinear shear zones of Precambrian antiquity. The mature old River Kaveri that consistently flows eastwards abruptly swerves left or right along the N–S fault planes and then drops into a canyon that is characterized by channel-in-channel geomorphology before leaving the mountain domain. Like the Kaveri (Cauvery), most of the rivers cross hills and ridges as antecedent rivers. Ponding of the Kaveri and its tributaries gave rise to a huge lake that stretched as much as 45 km upstream. The lake is now represented by a thick pile of black clay deposits of Late Quaternary age, forming the granary of Karnataka state. Demarcated by E–W-trending, two continent-wide shear zones of Precambrian age, the laterite-capped, 2670 m-high, Nilgiri massif is characterized by many planation surfaces, steep to nearly vertical scarps on all sides, and meandering streams descending through canyons as water falls. These features imply fast uplift and attendant exhumation of the Precambrian terrane that rose up like a horst.
Abstract Made up of high-grade metamorphic rocks that evolved under ultra-high temperatures, the ... more Abstract Made up of high-grade metamorphic rocks that evolved under ultra-high temperatures, the highly dissected Precambrian Eastern Ghat Mobile Belt is demarcated against the Dharwar–Bastar cratons by west-vergent shear zones dotted with plutons of alkaline and ultrabasic rocks, as well as against the Proterozoic Cuddapah sedimentary basin by a fold-and-thrust zone. A few NW–SE-oriented grabens that cut across the terrane served as floodplains of rivers like the Krishna and Godavari. In the coast of emergence that is the East Coast, lakes representing drowned embayments, sunken karstic topography with its pinnacles and domes, submerged V-shaped canyons offshore of the Krishna–Godavari domain, and archaeological remains of a seaport 30 m below the surface in the Kaveri delta, point to the sinking that continued into historical time. On the other hand, raised beaches, high strand lines, and progressive river migration in their deltas indicate uplift in some parts that are fault ridden. Seismicity in the southeastern part of the Godavari Graben and in east central Tamil Nadu indicates that some faults are very active.
Abstract The Indian subcontinent is a part of a very dynamic crustal plate that is converging nor... more Abstract The Indian subcontinent is a part of a very dynamic crustal plate that is converging northwards towards mainland Asia at a rate which varies in time and space. Within its fragmented framework, a large number of faults and shear zones developed thousands and even millions of years ago. Reactivated time and again due to the buildup of stresses resulting from the northwards movement of the Indian continental plate, these faults and fractures have played a primary role in the shaping of the landforms and landscapes that we see today. The movements on rupture planes also constrained the establishment of drainage patterns and the aberrations in river behaviour. It is the rupture-related dislocation of landforms and the sinking and rising of the fault-affected ground that brought about discernible physiographic changes, particularly where there were continued and ongoing movements, such as in the Himalayan province pressed hard between the northwards-pushing Peninsular India and the Asian landmass. Recurrent seismicity provides eloquent testimony to the neotectonic resurgence of the faulted terrains and the terrane-defining faults.
Abstract Between the 1000-km-long ENE–WSW-trending Narmada Graben in the north and much smaller b... more Abstract Between the 1000-km-long ENE–WSW-trending Narmada Graben in the north and much smaller but parallel Tapi Graben in the southwest, the Proterozoic Satpura Mobile Belt forms a prominent horst that rose up rapidly in the Later Quaternary time. Delimited by faults that are responsible for 500–800 m of cumulative throw, the Narmada Graben is a narrow zone of high heat flow, hot springs, parallel dyke swarms, and moderate seismicity. In the domain of this rift valley, the main river follows a remarkably straight course all along the reach, but its tributaries swerve abruptly before joining the Narmada across the Pleistocene terraces. Strong movements on the Tapi graben faults, which were accompanied by great earthquakes, resulted in an unusual continental-scale drainage pattern that created a large westwards-flowing catchment in the region where all other rivers flow either northeastwards or southeastwards. Shear zones of a large dimension south of the Satpura horst are seismogenic.
We reviewed the available climate records for the past 2 millennia based on the analyzed sediment... more We reviewed the available climate records for the past 2 millennia based on the analyzed sediment and speleothem archives from different regions of South Asia. Speleothem records from the core-monsoon regions of the Indian sub-continent have revealed the Little Ice Age (LIA) as a climatically dry phase, whereas the same from the western and central Himalaya recorded LIA as wet. Moreover, the sediment-derived vegetation proxy records [pollen-spores and stable organic carbon isotope (δ13Corg)] from the western Himalaya also reported LIA as a dry phase. Heterogeneous results by different proxies during LIA enhanced our interest to understand the response of the proxies toward the primary precipitation sources, Indian summer monsoon (ISM) and winter westerly disturbances (WDs), over the Himalaya. We emphasize that in the Himalayan region, the vegetation predominantly responds to the ISM dynamics, whereas speleothem also captures the WD effect.
In comparison to the east coast, the tsunami hazard for the west coast of India remains under-rec... more In comparison to the east coast, the tsunami hazard for the west coast of India remains under-recognized, despite the impact in 1945 following a M w 8.1 earthquake in the Makran subduction zone in the northern Arabian Sea. The previous occurrences of tsunamis in the Arabian Sea that would have a bearing on the west coast of India are being debated, including the question whether the Makran region has the potential to generate greater-magnitude earthquakes. With this in the backdrop, we present here the historical and geological evidence of a tsunami impact zone from a site on the Konkan Coast of western India. Located in the village of Kelshi, the impact zone is preserved within a coastal dune complex that also reveals occupation layers. This laterally extending 30-40-cm-thick zone, coinciding with a habitation level, displays varied sedimentary structures including scour-fill features, and is inter-layered with shells, at a height of * 3 m from the high-tide level. We attribute these sedimentary features to a tsunami flooding event that was contemporaneous with the transportation of shells, dated at 1508-1681 CE. The geological inference matches with the description by the Portuguese fleets of a sea disturbance in 1524 CE, reported from Dabhol, not far from Kelshi, and also from the Gulf of Cambay, located about 500 km to the north. Precluding submarine landslide scenarios, the modeling results suggest that the high impact in Kelshi could have been generated by a M w C 9 earthquake sourced in the Makran subduction zone. It is, however, intriguing how a M w C 9 earthquake in the Makran region finds no mention in the historical documentation. We underscore the need for fresh efforts along the Makran coast to reconstruct the tsunami recurrence history that would generate required validating constraints on the 1524 event, if it was indeed generated by a massive earthquake among other mechanisms.
Abstract The Aravali terrane is a highly deformed Proterozoic mobile belt entangled with an Archa... more Abstract The Aravali terrane is a highly deformed Proterozoic mobile belt entangled with an Archaean craton. It is split along its length by a number of crustal-scale shear zones, and dislocation zones developed in it during Precambrian time. Reactivation in the Late Quaternary of the shear zones is manifest in some areas, such as in the sinking of ground with a resultant formation of saline lakes, the bulging up of other areas with attendant watershed migration, the stream capture, the entrenched meander loops, and the persistent moderate to low seismicity in the fault-ridden northeastern part of the Aravali terrane. Separated from this consolidated complex by the Great Boundary Fault, which registers a cumulative throw of 500–1300 m, the vast Vindhyan Basin of Proterozoic sediments is largely undeformed, except for around its tectonic boundary with the Aravali in the west and the Satpura in the south. However, the Vindhyan basement is segmented by wrench faults as well as strike faults, some of which register a strike-slip motion. The pronounced development of badlands close to the northern faulted border against the Ganga Plain indicates a very slow uplift of the northern part.
Abstract The N–S trending array of mountain ranges along the border of India and Myanmar represen... more Abstract The N–S trending array of mountain ranges along the border of India and Myanmar represents the eastern arm of the Himalayan Mobile Belt. A linkage of three disparate mountain belts forming the Siang Syntaxis in the north separates this arcuate arm from the main Himalayan arc. Characterized by a schuppen structure (i.e., packs of imbricated thrust sheets that are folded and faulted), this orogenic unit of Late Mesozoic–Cenozoic flysch with its ophiolite implants is strongly affected by stresses generated due to the oblique convergence and attendant underthrusting of the Indian plate under the Burmese (Myanmar) microplate. The rate of slipping varies not only from sector to sector, but also from time to time. Very high seismicity and GPS measurements demonstrate continuing strong movements on faults of this fault-ridden palaeo-obduction complex. The epicentral distribution defines a distinct Benioff Zone dipping eastwards under Myanmar.
Abstract The early Precambrian Bastar and Singhbhum cratons, with their intimately associated Pro... more Abstract The early Precambrian Bastar and Singhbhum cratons, with their intimately associated Proterozoic mobile belts, are subdivided into disparate terranes by a number of long, deep, and curvilinear shear zones of Precambrian antiquity. Although the orthogonal Gondwanic Godavari Graben defines the western limit of the Bastar, the Mahanadi Graben separates the Bastar from the Singhbhum domain. Despite a multiplicity of terrane-defining curvilinear seismogenic shear zones, no work on neotectonism has been done in this part of the Indian subcontinent. A notable feature is that the laterite-mantled terrain characterized by many planation surfaces and delimited by escarpments has become rugged in some belts. Down these scarp faces descend rivers and streams as waterfalls. All these features collectively indicate the Late Quaternary uplift. In a sector of the E–W-trending, much-faulted Damodar Graben in the Singhbhum domain, palaeochannels are associated with archaeological remnants, implying tectonic disturbance in historical time in the graben zone.
Abstract Underneath the floodplains of the Sindhu and Ghagghar river systems, a number of subsurf... more Abstract Underneath the floodplains of the Sindhu and Ghagghar river systems, a number of subsurface basement ridges are related to the NW–SE-trending Aravali Mobile Belt. A multiplicity of long and deep faults also occurs. Seismicity in parts of the belts over these hidden ridges indicates the reactivation of faults across which flow the rivers of the two systems. Although the Sindhu River migrated 160 km westwards in the Holocene time, even as great subsurface depressions formed in front of the Sulaiman and Kirthar Ranges, the Ghagghar basin in the eastern part witnessed a strong tectonic upheaval. This manifested itself in subsidence, uplift and dislocation of ground. This resulted in drainage reorganization, channel segmentation, and, in one case, river piracy. This spectacular event happened at a time when a drastic decline in rainfall occurred, which caused not only a mass exodus of the people of the Harappan civilization in the mid-Holocene time, but also the development of the Thar Desert in western India and adjoining Pakistan.
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