Current Science

A. B. Roy ¹, M. S. Sethumadhav ²

Affiliations
1 Department of Geology, Presidency University, Kolkata 700 073, IN
2 Department of Earth Science, University of Mysore, Mysore 570 006, IN

Abstract

Low-lying sediment mound, known as Talakad sand dunes, on the left bank of the meandering Kaveri River at Talakad, Mysore district, Karnataka, is an enigmatic geomorphic feature. Archaeological excavations in the area revealed the presence of a cluster of ancient temples, mostly in dilapidated condition, which were presumably built during the time-period dating back between 6th and 17th century AD. It is generally believed that the temples were entombed under a pile of riverine sand dunes during the 'ecodisaster' that lashed the region in the 17th century. Our field studies coupled with archaeological reports on excavations indicate that the mound is not entirely made of dune sands. Virtual absence of sand deposits over some severely damaged temples occurring near the top suggests that destruction could not have taken place only because of the load of the overlying sands. On the other hand, the scale of destruction witnessed in some of the affected temples can only be explained by the incidence of earthquakes of high magnitude. Additional proof of earthquake-related destruction comes from the occurrence of sedimentary layers (beds) containing fragmented pieces of building materials like bricks and stones in silt and clay-bearing flood plain deposits at the sites of the destructed temples and other buildings. Historical records of repeated renovation or rebuilding of temples at the same place provide further proof of recurrent incidence of earthquake-related destruction. Geomorphic changes manifested in the form of shifting of river courses consequent with the rise of the sediment mound also indicate uplift-related earth movements which must have ensued repeated earthquakes in the region.

Keywords

Ancient Temples, Disaster Archaeology, Neotectonic Landform Changes, Palaeoseimicity, Sand Dunes.

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A. B. Roy ¹, Alokesh Chatterjee ²

Affiliations
1 Department of Geology, Presidency University, Kolkata 700 073, IN
2 Hoogli Moshin College, Hoogli 712 101, IN

Abstract

The Bengal Basin evolved as a rift-controlled extensional basin along the NNE-SSW trending Basin Margin Fault coevally with the 85° East Ridge in the Bay of Bengal during the short-lived hotspot activity south of Bhubaneswar. The basin opening post-dated the Kereguelen Plume magmatism (at ~116 Ma), but predated the phase of continental collision that triggered the rise of the Himalaya in the north. Supply of sediments in the initial stages of basin opening was from the west, mainly through the denudation and erosion of the uplifted Precambrian Shield. Following virtually similar tectonic and depositional pattern in the entire basin, an abrupt change in depositional pattern was recorded during the Oligocene with the emergence of easterly source of sediments derived from the uplifting of Indo-Myanmarese Ranges. Between the Oligocene and Late Pleistocene different parts of the Sylhet Trough (the best-studied region in the deeper part of the Bengal Basin) received huge volumes of sediments, which resulted in deposition measuring between 10 km and over 17 km in thickness. This was followed by an equally sudden drop in the sediment supply from the east due to the basin inversion concurrently with the westward advance of the Indo-Burmese mountain front during early and mid-Pleistocene. Followed by a short hiatus, the depositional scenario changed completely with the arrival of thick volumes of sediment during the late Pleistocene-Holocene, which covered the entire Bengal basin with the sediments brought by the Ganga and Brahmaputra from the Himalayan sources.

Keywords

Basin Evolution Tectonics, Extensional Rift Basin, Depositional Pattern, Palaeogeographic Setting, Sediment Supply.

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A. B. Roy ¹, N. K. Chauhan ², Alokesh Chatterjee ¹

Affiliations
1 Department of Geology, Presidency University, Kolkata 700 073, IN
2 Department of Geology, ML Sukhadia University, Udaipur 313 001, IN

Abstract

Kachchh domes are recognized by the oval to elliptical- shaped outcrop patterns marked by outlines of bedding surfaces which invariably dip in the outward directions. The occurrence of domes in rows without having corresponding basin-like features implies that these are not superposed folds resulting due to constriction- type tectonic forces. Further, in spite of the close time-space relationship, the occurrence of domes is exclusively in the Mesozoic rocks on the uplifted block of the fault. The absence of any such rock formation on the other side of the fault rules out the possibility that these are 'drape folds' developed during the adjustment of the sedimentary blanket over the faulted-up edges of the basement blocks. Hinging on the evidence of intrusive plutonic (mafic) masses in the core of some of the domes, we suggest that the structures evolved through diapiric rise of magma bodies causing dome-shaped up-warping (bending) of the pre-existing (Mesozoic) flat-lying sedimentary formations. Linear disposition of domes is explained as due to channellization of magma along the fractures that developed around large-scale crustal doming during the early phase of the Reunion Plume impingement under the Indian Lithosphere.

Keywords

Diapiric Folds, Domes, Evolutionary History, Magma Bodies.

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A. B. Roy ¹, Krishan Dutt ², Sanjeeb Rathore ³

Affiliations
1 Department of Geology, Presidency University, Kolkata 700 073, IN
2 H. No. 20/75, Mansarovar, Jaipur 302 020, IN
3 No. 301, A.R. Complex, I-Block, Sector-14, Hiran Magri, Udaipur 313 001, IN

Abstract

The present communication discusses two separate instances where features commonly observed in DSZ are noted, one along the margin of the Kisengarh nepheline syenite and the other in the granulite bodies the Sandmata Complex in Rajasthan, India. The foliations in the nepheline syenite pluton show features similar to the mylonite gneisses that characterize DSZs in orogenic belts. Apart from simulating LS tectonite- type fabric the continuity of similar structures in adjacent cover rocks provides evidence of heterogeneous deformation during upward ascent of nepheline syenite. Based on tectono-metamorphic studies on granulites suggestion is made about the uplift of deepseated granulites accompanied by ductile shearing on along the margins. The development of DSZ along margins helped in reducing the frictional resistance during upward ascent and emplacement into Archaean gneissic terrane. The process is comparable to buoyancy- induced diapiric uplift of hot plutonic bodies through cooler upper crust.

Keywords

Ductile Shear Zone, Diapiric Magmatism, Exhumation of Granulites, Emplacement of Plutonic Bodies.

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A. B. Roy ¹, Harsh Bhu ², Pankaj Sharma ², Kishan Vaishnav ²

Affiliations
1 Niloy Apartment, Flat 3/2G, 46A, R.N. Das Road, Kolkata 700 031, IN
2 Department of Geology, Mohanlal Sukhadia University, Udaipur 313 001, IN

Abstract

Seismicity or seismic susceptibility implies proneness to earthquake incidence in a region. For this we cannot depend entirely on instrumental records, because this facility was almost unknown about 70-odd years ago, whereas the 'period of quiescence' between two successive major earthquakes in a region may be hundreds of years and sometimes more. This places a severe constraint on the understanding of the regional variability of seismic susceptibility or the proneness of any particular region to the occurrence of an earthquake. In such cases, the necessity is to look for evidence of palaeoseismicity in historic/pre-historic and archaeological records, and for much older events the different fault features preserved in geomorphic features. Here we cite an incidence of seismic event based on the examination of a large number of deserted early nineteenth century houses scattered around Jaisalmer region in western Rajasthan, India. Lying unoccupied for about 190 years or more, evidence of destruction is observed in each and every house, which is not generally witnessed in disused old houses standing for hundred years or more. Looking into the nature of collapse-related flattening features such as collapsed roofs, fallen joists, lintels and pillars in all these houses, we suggest that these are manifestations of earthquake-related destruction. Such an assumption finds strong support from the observed evidence of recent tectonic activities and from the observed ground movements along several major faults in the region covering Jaisalmer and the adjoining areas.

Keywords

Deserted Paliwal Villages, Evidence of Recent Tectonics, Earthquake Related Destruction, Historical Evidence of Earthquake, Palaeoseismicity.

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A. B. Roy ¹, Alokesh Chatterjee ², N. K. Chauhan ³

Affiliations
1 Niloy Apartment, Flat 3/2G, 46A, R.N. Das Road, Kolkata 700 031, IN
2 Geology Department, Hooghly Mohsin College, Chinsura 712 101, IN
3 1014 Hiran Magri, Sector 4, Udaipur 310 002, IN

Abstract

Kachchh geological province is conventionally referred to as 'Kachchh basin' or 'Kachchh rift basin' or even 'Kachchh aulacogen'. The geological records, however, recount a different history of the diverse depositional environment under diverse tectonic situations. The earliest Phanerozoic event was the deposition of Palaeozoic sediments during upper Permian and lower Triassic. Next event was a major marine incursion along rift zones coinciding with the Gondwana break-up and the initiation of northward drifting of the 'Indian land mass'. This was followed by the Reunion Plume related magmatism centring on the K- T boundary. Overlying this occur lignite deposits in the Naredi Formation correlatable with the global Eocene excursion. The Cenozoic basin closure corresponds to the major uplift in the Himalayas during the early Quaternary. Finally, the evidence of recurrent youngest block-movement-type active tectonics transformed the terrain into a zone of high seismicity.

Keywords

Cenozoic Depositories, Kachchh, Palaeocene–Eocene Thermal Maximum, Phanerozoic Events, Quaternary.

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A. B. Roy ¹, Harsh Bhu ¹, Pankaj Sharma ¹, Kishan Vaishnav ¹

Affiliations
1 Niloy Apartment, Flat 3/2G, 46A, R.N. Das Road, Kolkata 700 031, IN

Abstract

We must thank Bahadur et al. for mentioning the date of what they consider as the ‘Great migration’. Our suggestion about earthquake-related devastation was based on the field examination of different villages where the Paliwal Brahmins lived. We presented some telltale evidence of destruction of houses made of blocks of rocks without using any cementing materials. The earthquake-related destruction features in the poorly constructed stone-block houses of Kuldhar and other Paliwal villages were similar to those destroyed during the Latur earthquake in the recent past, and at about 4000 years ago site at the historical Mohenjodaro.

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