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Tectonophysics 501 (2011) 41–51

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Tectonophysics

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Remote sensing revealed drainage anomalies and related tectonics of

SM. Ramasamy a,⁎, C.J. Kumanan b,c, R. Selvakumar b,c, J. Saravanavel b a Gandhigram Rural University, Gandhigram, Dindigul, , 624302, India b Centre for Remote Sensing, School of Geosciences, Bharathidasan University, , Tamil Nadu, 620 023, India c School of Civil Engineering, SASTRA University, , Tamil Nadu, 613401, India article info abstract

Article history: Drainages have characteristic pattern and life histories with youthful stage in hilly areas, mature stage in Received 25 December 2008 plains and old stage in the coastal zones. The deviations from their normal life histories, especially aberrations Received in revised form 4 May 2010 in their flow pattern in the form of various drainage anomalies have been inferred to be the indications of Accepted 7 January 2011 dominantly the Eustatic and Isostatic changes. This, especially after the advent of Earth Observing Satellites, Available online 20 January 2011 has attracted the geoscientists from all over the world, for studying such drainage anomalies. In this connection, a study has been undertaken in parts of South India falling south of 14° south latitude to Keywords: fl Lineament comprehensively map some drainage anomalies like de ected drainages, eyed drainages and compressed Drainage anomalies meanders and to evolve the tectonic scenario therefrom. The mapping of such mega drainage anomalies and Active faults the related lineaments/faults from the satellite digital data and the integration of such lineaments/faults with Post collision tectonics the overall lineament map of South India showed that the study area is marked by active N–S block faults and South India NE–SW sinistral and NW–SE dextral strike slip faults. Such an architecture of active tectonic grains indicates that the northerly directed compressive force which has originally drifted the Indian plate towards northerly is still active and deforming the Indian plate. © 2011 Elsevier B.V. All rights reserved.

1. Introduction sea level changes, these drainage anomalies have the credibility of providing information on the flood histories, seismic vulnerability, past Rivers have characteristic pattern and life histories with (1) short climates and anthropogenic phenomenon too (Chitale, 1970; Chen and and straight drainages performing only erosion in the hilly catchments, Stanley, 1995; Lillesand, 1989; Matmon et al., 1999; Miller, 1937; Reid, (2) meandering and sinuous paths doing both erosion and deposition in 1992; Saintot et al., 1999; Smith et al., 1997; Twidale, 2004; Thornbury, the plains and (3) Brownian pattern of movement doing only dumping 1985 and many others). In different parts of the Indian sub continent of sediments and building up of deltas in the coastal zones. Such too, studies have been carried out on the drainage anomalies using characteristic life history of the rivers with youthful stage in the hills, topographic sheets, black and white panchromatic aerial photographs mature stage in the plains and the old stage in the coastal zones in and orbital multimode and multispectral satellite data, to elucidate the general are controlled by the base level of erosion or Mean Sea Level structural fabric, tectonic processes, climatological and other phenom- (Thornbury, 1985). But, the rock types and the geological structures of enon of especially the Quaternary period (Amalkar, 1988; Babu, 1975; the terrain related to palaeo, time transgressive and ongoing tectonisms Bakliwal and Sharma, 1980; Barooah and Bhattacharya, 1989; Mitra et too significantly control the drainage pattern and the related river flow al., 2005; Murty and Mishra, 1981; Narasimhan, 1990; Oldham et al., dynamics in all these three stages. Hence, geoscientists from all over the 1901; Philip et al., 1989; Rajaguru and Kale, 1985; Ramasamy, 1991, world have all along been showing greater interest in understanding the 2006; Ramasamy and Kumanan, 2000; Ramasamy et al., 1987, 1991, drainage architecture in general and their anomalies in particular. That 2006; Singh et al., 1996; Sood et al., 1982; Thirunaranan, 1938; too, after the advent of Earth Observing Satellite technology, mapping of Vaidyanadhan, 1971; Yashpal et al., 1980). drainage pattern and their anomalies like dentritic, semi dentritic, But, despite these, no detailed and comprehensive information is trellis, parallel, annular, radial, deflected, pirated, avulted, eyed, available on the various drainage anomalies and the related tectonics, compressed, preferentially migrated and other drainage anomalies especially for the southern part of the Indian Peninsular, under the have gained greater momentum, since, besides lithology, tectonics and present context of recurring seismicities in the region. Hence, a remote sensing based study has been carried out in the southern part of the Indian Peninsular falling south of 14° south latitude in parts of ⁎ Corresponding author. Tel.: +91 451 2452305 (office), +91 9442105116 (mobile); four states, namely , Andhra Pradesh, and Tamil fax: +91 451 2454535. Nadu for comprehensively mapping the selected major drainage E-mail addresses: [email protected], [email protected] (S.M. Ramasamy), [email protected] (C.J. Kumanan), [email protected] (R. Selvakumar), anomalies and to evolve a holistic picture on tectonics there from [email protected] (J. Saravanavel). (Fig. 1).

0040-1951/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.tecto.2011.01.011 Author's personal copy

42 S.M. Ramasamy et al. / Tectonophysics 501 (2011) 41–51

Fig. 1. IRS satellite mosaic-study area map.

2. Methodology dors related to such deflected drainages. Similarly, some major drainages flowed as a single channel in the upstream, split up into two In the present study, 21 number of scenes of IRS IB LISS II satellite or more drainages and either finally joined together or showed the data of different paths and dates (February, 1993; April, 1994; March, tendency of rejoining in their downstreams. This assigned conspic- 1995 and May, 1995), with spatial resolution of 36.25 m and spectral uous eyed shapes with entrapped lensoidal/crescent shaped islands resolutions of band1 (0.45–0.52 μm), band2 (0.52–0.59 μm), band3 within them. Such eyed drainages (ED) were mapped as significant (0.62–0.68 μm) and band4 (0.77–0.86 μm) were loaded in the ENVI drainage anomalies, provided these were found either at the crossing image processing software. These independent scenes were georefer- points of some major lineaments or confined within sub parallel enced, false color composites (FCC) were generated by exposing systems of lineaments. Accordingly, these lineaments were also band2 under blue, band3 under green and band4 under red filters and mapped as neo-active tectonic grains related to such eyed drainages. the FCC images were generated independently for 21 scenes and then In the same way, the otherwise normally flowing rivers and major the mosaic was prepared for the study area (Fig. 1). Such digital streams showed anomalous compressed meandering pattern at some mosaic of false color composite data was zoomed up to 1:25,000 scale places in a restricted zone, either at their intersections with some in the computer and scanned in detail for selected, significant and lineaments or confined within sub parallel systems of lineaments. major drainage anomalies viz: deflected drainages, eyed drainages These anomalies were interpreted as compressed meanders (CM) and and compressed meanders. Most of the previous workers from the associated lineaments as neo-active faults related to them. different parts of the world have attributed such drainage anomalies Such prominent and major drainage anomalies say, over 31 to neo-active tectonics. So wherever the major drainages were deflected drainages (DD), 12 eyed drainages (ED) and 20 compressed abruptly deflected by some lineaments, those drainages were marked meanders (CM) and the related neo-active tectonic faults interpreted as deflected drainages (DD). In case, if the original flow of the from different parts of the study area were transferred on to three drainages were already controlled by some lineaments prior to such independent planimetrically controlled GIS overlays using ARCGIS deflections, then both the original controlling lineaments and the software. These three GIS layers were further integrated with the deflecting lineaments were interpreted as neo-active tectonic corri- lineament map of Ramasamy et al. (1999) and the regional probable Author's personal copy

S.M. Ramasamy et al. / Tectonophysics 501 (2011) 41–51 43 neo-tectonic picture revealed by such drainage anomalies were deflected rivers/streams and the related neo-active tectonic linea- brought out. From it, the pattern of regional recent stress field was ments are shown in Table 1. also brought out (Fig. 2). For example, in DD1, the northeasterly flowing river Cauvery has been sharply deflected by a NW–SE trending lineament near Mercara in its youthful stage whereas in the case of DD8, the Cauvery river was 3. Geology and drainage systems of South India subjected to multiple deflections in the Hogenekkal–Stanley reservoir region. The river seems to have flowed along E–W lineaments both Geologically, the southern part of the Indian Peninsular is a near Hogenekkal and Stanley reservoir and at both locations, the river characteristic shield area exposing complex igneous and metamor- was deflected by two different N–S lineaments (DD8, Fig. 2). So, all the phic rocks of Archaeozoic–Proterozoic Era in its major parts and four lineaments were interpreted as probable neo-active tectonic Mesozoic, Tertiary and Quaternary sediments along the eastern and grains related to the deflected drainage DD8. Similarly, at further the western coastal fringes (Fig. 1). downstream, the south southwesterly flowing Cauvery river has The major rivers flowing in the study area are Palar, Ponnaiyar, taken a southeasterly flow along a major lineament near Bhavani Northern Vellar, Cauvery, Southern Vellar, Vaigai and Tambraparani. (DD10, Fig. 2). In the Nagari region, the easterly flowing Nagari river Though the study area falls in parts of the four states of Southern along an E–W lineament has been sharply deflected towards Indian Peninsular, detailed satellite imagery interpretation was southeasterly by a NW–SE trending lineament (DD13, Fig. 2). In the carried out mostly for Tamil Nadu part, as the rivers showed full same way, various deflected drainages were mapped and 31 such evolutionary history with youthful, mature and old stage character- major deflected drainages and the related Neo-Active Tectonics istics only in Tamil Nadu due to the low easterly slope of the terrain. Lineaments (NATL) were brought under a GIS database in their true geographical positions. The overall pattern of the (NATL) related to 4. Drainage anomalies and the related neo-active tectonic such deflected lineaments showed that the lineaments controlling lineaments original drainage flow were mostly aligned in general E–W direction and the deflecting lineaments were generally oriented in NNE–SSW 4.1. Deflected drainages direction (Rose diagram, Fig. 3).

Twidale (2004) has observed deflections in the Murry river of 4.2. Eyed drainages Australia and identified lineaments/faults and related them to active tectonics. Babu (1975) has observed anomalous drainage deflections As stated earlier, the otherwise singularly flowing drainages split in river Godavari, Andhra Pradesh and attributed these to various up into two or more and rejoin again in their downstreams thus lineaments related to tectonic upliftments. The interpretation of displaying eye shapes, especially at their intersections with linea- satellite IRS digital data has revealed prominent deflected drainages in ments or within sub parallel set of lineaments were mapped as eyed over 31 locations (DD1–DD31, Fig. 3). Almost all these 31 deflected drainages. Smith et al. (1997) have observed similar anomalies in the drainages were not only deflected abruptly by some lineaments but Okavango river, Botswana, called it as “drainage anastomosis” and also controlled by lineaments of different orientations. So, all such attributed the same to ongoing tectonic subsidence. Thornbury controlling lineaments and the deflecting ones were marked as zones (1985) also inferred earlier that wherever land undergoes emergence, of neo-active tectonics related to such deflected drainages (Fig. 3). The the drainages will get incised and cause vertical cutting and gullying geographical locations of such deflected drainages, the names of the and in contrast, when land subsides, the drainages will struggle to

Generation of digital FCC mosaic of IRS IB LISS II satellite data of South India

Interpretation of enlarged digital images for drainage anomalies and related lineaments

Deflected drainages Eyed drainages (ED) Compressed meanders (DD) where the where the drainages split (CM) wherever the drainages are deflected up into 2 or 3 and rejoin drainages abruptly show by lineaments providing eyed shape compressed pattern at with lineaments at their their intersection with axes or lineaments lineaments confining them

Filter out such lineaments / neo tectonic faults deduced from such drainage anomalies

Integrate such neo tectonic faults with regional lineament map of South India and build the comprehensive neo tectonic cartoon along with possible driving force

Fig. 2. Methodology flow chart. Author's personal copy

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Fig. 3. Deflected drainages and related lineaments.

flow and hence will conversely get split up. Ramasamy and Kumanan ED1, Fig. 4). Such restricted flood plain within such lineaments too (2000) have similarly observed such split up drainages conspicuously substantiates probable land subsidence. along the crossing points of lineaments in a few places in Tamil Nadu, In general, these eyed drainages showed simple lensoidal shapes, called them as “eyed drainages” and doubted possible ongoing but in certain cases, these eyes displayed some dragging effects. For tectonic subsidence along the lineaments. example, in ED2, the river Cauvery showed two prominent eyed Hence in the present study, attempts were made to identify similar drainages in the Madavalli area near (2A–2B, Fig. 4). These eyed drainages and the same revealed major eyed drainages in 12 two eyed drainages were not only bisected by two major N–S sub locations (ED1–ED12, Fig. 4, Table 2). These eyed drainages seem to parallel lineaments but also displayed “S” shaped drags. So, in addition have an eye length of 3 to as long as 25 km and were invariably either to probable tectonic subsidence, sinistral couple has also been bisected by some lineaments or confined within sub parallel systems visualized along these lineaments/faults. Similarly, in the Kanchi- of lineaments. For example, the river Cauvery has developed two eyed puram area (ED6, Fig. 3), the river Palar has branched off into two and drainages near Mysore with eye lengths of 3 and 5 km and both were run colinearly for over 16 km and rejoin in the downstream, thus bisected by NNE–SSW trending lineaments (ED1, Fig. 4). So, tectonic displaying a mega eyed drainage. Significantly, this mega eyed subsidence along these lineaments was inferred to be the stimuli for drainage was confined within two major NE–SW trending sub parallel the origin of such eyed drainages. In addition, the river Cauvery has lineaments. In addition, at the point of crossing of these lineaments also showed a very wide flood plain within these two lineaments (FP, with the drainage, “S” shaped drags were seen at both ends of the eye. Author's personal copy

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Table 1 dominantly aligned in N–StoNE–SW and all with sinistral strike slip Deflected drainages. movements (Rose diagram, Fig. 4). Drain. Area River Related neo-active no. tectonic lineaments 4.3. Compressed meanders DD1 Mercara Cauvery.r NE–SW and NW–SE DD2 Mysore Cauvery.r E–W and NW–SE The otherwise normally flowing drainages exhibit anomalous DD3 Sivasamudram Cauvery.r N–S and ENE–WSW compressed meanders abruptly in a restricted domain, such drainage – – DD4 Heggadadevankote Kabani.r ENE WSW and N S segments were interpreted as compressed meanders (CM). These DD5 Nanjangud Kabani.r NW–SE and NE–SW DD6 Badagara Chaliyar.r N–S and E–W types of compressed meanders have been demonstrated to be DD7 Kollegal and Cauvery.r N–S and E–W indicative of active tectonics. Bakliwal and Sharma (1980) have Pennagaram explained the intense, acute and restricted compressed meandering in DD8 Stanely Cauvery.r Multiple deflections E–W river Yamuna in the Agra region of the Indo-Gangetic plains to active and N–S scissor fault tectonics along two sub parallel lineaments of the Great DD9 Nallur Palar N–S and E–W DD10 Bhavani Cauvery.r N–S and NW–SE Boundary Fault System. Murthy and Sastri (1981), Barooah and DD11 Near Maddivallapalle Mandavi.r N–S and ENE–WSW Bhattacharya (1989) and many others have interpreted a large DD12 Chittoor Ponnanai.r ENE–WSW and NW–SE number of drainage anomalies in the form of compressed meandering – – DD13 Nagari Nagari.r ENE WSW and NW SE in Brahmaputra river and explained them to be due to still ongoing DD14 Kalahasti Kalangi.r NE–SW and NW–SE DD15 Walajapet Ponnanai and N–S and E–W collision of the Indian plate. Jain and Sinha (2005) have attributed the palar acute compressed meandering in river Baghmati, Himalayan foreland DD16 Tiruvallur Cooum.r NE–SW and E–W basin to active block faulting. DD17 Arani Cheyyar.r WNW–ESE and NE–SW Hence in the present study, the enlarged IRS IB digital FCC mosaic – – DD18 Chengalpattu Palar.r E W and N S was studied critically and in that process, 20 such compressed meanders DD19 Harur Pambar.r NW–SE, NNE–SSW and NE–SW were interpreted from different parts of South India (Fig. 5). Such DD20 Tirukkovilur Ponnaiyar NW–SE and ENE–WSW compressed patterns were mapped as drainage anomalies only when DD21 Valavanur Warahanadi.r NW–SE, NE–SW and these were found either at the intersections of lineaments and the – NW SE drainages or confined within sub parallel systems of lineaments. In DD22 Pennadam Vellar.r NE–SW and WNW–ESE DD23 Pugalur Cauvery.r NNW–SSE, E–W and addition, the pattern of drainage compressions were also interpreted as NE–SW “normal (N)”, wherever the drainages were symmetrically compressed DD24 Aravakurichi Amaravati.r NE–SW and E–W and “Z” and “S” shaped, when the drainages were asymmetrically DD25 Udumalaipettai Amaravati.r N–S and NE–SW compressed with respective shapes. Further in the case of “Z” and “S” – – DD26 Kollidam.r E W and NNE SSW shaped compressed meanders, probable dextral and sinistral move- DD27 Karambakkudi Agniar.r NE–SW and NW–SE DD28 Devakottai Manimuttar.r NW–SE and ENE–WSW ments were respectively visualized along the related faults. The details DD29 Paramagudi Vaigai.r E–W and NNW–SSE on their geographical locations, the rivers in which the compressed DD30 Palayamkottai Tambraparani NE–SW and NNW–SSE meanders were interpreted, the pattern of compression (“N”, “Z” and – – DD31 Tenkasi Nellar NE SW and E W “S”), width of such zones of compressed meanders and the probable NATL related to them are shown in Table 3. For example, the northern Vellar showed anomalous and abrupt compressed meanders (CM11, Fig. 5) in the Bhuvanagiri region with Hence, in addition to tectonic subsidence, sinistral movements were symmetrically compressed drainage segments within two N–Strending also visualized along these two sub parallel faults, indicating active sub parallel lineaments. So, it was marked as “Normal” (N) compressed tectonic movements along them. meander and probable scissor type of tectonic movements along these In the case of ED10 (Fig. 3) of the Tiruchirappalli region, river lineaments were accordingly visualized. But in contrast, the southeast- Cauvery has branched off into two as Coleroon in the north and erly flowing Vaigai river, in the area north of Ramanathapuram, showed Cauvery in the south at upper Anicut in the west and flowed colinearly an “S” shaped compressed meandering pattern within two N–Ssub for over 26 km and showed the tendency of rejoining in the parallel lineaments (CM19, Fig. 5), whereas away from these two downstream near Grand Anicut in the east, thus forming a mega lineaments, the river showed a southeasterly linear flow. In addition, eyed drainage. Again, the eye was bounded by two major NE–SW along these two lineaments, the coast has also been shifted sinistrally in trending sub parallel lineaments and strikingly, the western linea- their southern extension. So, a probable sinistral couple was conceived ment intersects the river at its branch off point near upper Anicut in along these two N–S sub parallel lineaments/faults. Similarly, the the west and the eastern lineament cuts across the river at the general easterly flowing Korttalaiyar river suddenly displayed a series of rejoining point at Grand Anicut in the east. Hence, these two “Z” shaped compressed meanders in Tiruvallur area within two NW–SE lineaments were interpreted as active faults causing probable trending sub parallel lineaments (CM8, Fig. 5) denoting a possible grabening in the entrapped land segment of Tiruchirappalli plains. It dextral couple along these two bounding lineaments/faults. But in has also been inferred by the authors that the river Cauvery gets contrast, the east southeasterly flowing Arani river, flowing just north of flooded periodically in the faults bounded eyed segment only. This Korttalaiyar river exhibited “S” shaped compressed meanders, but here further substantiates the phenomenon of ongoing land subsidence within two NE–SW oriented lineaments, indicating the possible sinistral along the NE–SW sub parallel lineaments/faults, which in turn must strike movements along these two sub parallel lineaments (CM7, Fig. 5). be disturbing the base level of erosion leading to such flooding. A In the same way, a possible dextral couple was identified along the two similar phenomenon of flooding has also been witnessed in another NW–SE trending sub parallel lineaments as within which , a major eyed drainage of Cauvery in its downstream (ED11, Fig. 4), tributary of Cauvery, displayed conspicuous “Z” shaped compressed where a number of minor eyelets were observed with “S” shaped meander (CM3, Fig. 5). But, in certain cases, along the crossing points of drags indicating ongoing sinistral couple along the intersecting faults. single lineament too, even some major rivers displayed compressed Thus, all the 12 eyed drainages along with related lineaments/faults courses. (For example river Cauvery near — CM12, Fig. 5). In and the directions of movements wherever possible were brought on to such cases, probable active transverse tectonic movements were a common GIS database (Fig. 4, Table 2). Significantly, the Neo-Active conceived along such lineaments. In the same way, such major Tectonics Lineaments (NATL) deduced from such drainages were compressed meanders were identified in over 20 places and the Author's personal copy

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Fig. 4. Eyed drainages and related lineaments.

comprehensive pictorial information on their distribution is shown in Table 2 Fig. 5. Other details on the geographical locations, names of the rivers, Eyed drainages. pattern of compressions, the related NATL etc., are shown in Table 3. NB: NATL: Neo-Active Tectonic Lineaments — Drain. Area River Orientation Length Related NATL 5. Drainage anomalies and tectonics discussions no. of eye of eye and their (in km) orientations Various neo-active tectonics/faults deduced from deflected ED1A Mysore Cauvery.r E–W3Along NNE–SSW drainages, eyed drainages and the compressed meanders domi- 1B 5 Along NNE–SSW nantly fell in N–S/NNE–SSW, NE–SW, NW–SE and E–Wdirections ED2A Madavalli Cauvery.r N–S 3 Along N–S (Rose diagrams, Figs. 3–5). These were individually transferred on – 2B (dragged) 6 Along N S to the lineament map of South India prepared by Ramasamy et al. ED3A Nattam Cauvery.r E–W2Along NNE–SSW 3B 2 Along NNE–SSW (1999) along with the related drainage anomalies (Fig. 6A, B and C). 3C 3 Along NNE–SSW After plotting so, wherever such NATL deduced from the drainage ED4 Cauvery.r N–S 3 Along N–S anomalies have coincided with major and regional lineaments of ED5 Vellore Palar.r E–W 10 Along NNE–SSW South India, those were extrapolated as regional active faults. Such ED6 Kanchipuram Palar.r E–W 16 Within NE–SW an analysis has revealed over 32 regional probable active faults in sub parallel – – – ED7 Madurantakam Palar.r E–W 5 Along NNE–SSW South India viz: 8 in N S with oscillations to NNE SSW (1 8, ED8 Tiruvettiputam Cheyyar.r E–W 3 Along NE–SW Fig. 5A), 8 in NE–SW (9–16, Fig. 5B), 7 in NW–SE (17–23, Fig. 5C) and ED9 Villupuram Ponnaiyar.r E–W 6 Along NNE–SSW remaining 9 in E–W(24–32, Fig. 5C) directions. ED10 Trichy Coleroon.r E–W 26 Within NE–SW (Kollidam) and Sub parallel – Cauvery.r 5.1. N S faults ED11 Trichy Coleroon.r E–W 5 Within NE–SW Sub parallel Among the N–S faults, the fault no. 1 formed a NNE–SSW to N–S ED12A Kumbakonnam Coleroon.r NE–SW 4 Along N–S system of over 7–8 sub parallel active faults in Mysore–Sivasamudram– 12B Coleroon.r 3 Along N–S Biligiri Rangan hill ranges. These faults were basically deduced from a Author's personal copy

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Fig. 5. Compressed meanders and related lineaments. number of deflected drainages (DD3–5, DD7–10, Fig. 3), eyed drainages has taken an acute southerly turn towards Tiruchirappalli plains only due (ED1–4, Fig. 4) and compressed meanders (CM4, Fig. 5), all belonging to to active N–S systems of faulting and cymatogeny. Again, Radhakrishna river Cauvery and its tributaries. The frequent deflections of Cauvery from (1992) and Ramasamy et al. (1992) inferred that the northeasterly its east–west tectonically controlled flow by the system of N–S/NNE–SSW flowing river Cauvery in Hogenekkal area was drafted towards southerly trending faults indicated that the river Cauvery and its tributaries tried to towards the present path of Ponnaiyar river and again further down flow towards easterly, but the N–Sactivefaultsseemtohavevery towards Tiruchirappalli plains due to the N–S fault opening. Valdiya frequently abberated and deflected them towards southerly. But, while (1998) too has observed that most of the easterly flowing rivers of some eyed drainages (ED 1–4, Fig. 4) indicated tectonic subsidence along Karnataka in Mysore plateau were obstructed by N–S active faults and such N–S faults, certain eyed drainages (ED2, Fig. 4) suggested sinistral caused ponding along them due to block faulting. movements whereas some compressed meanders (CM4, Fig. 5)revealed Whereas, the fault no. 2 (Fig. 6A) was characterized mostly by dextral movements. Thus, the N–SandNNE–SSW oriented spectrum of deflected drainages (DD8, 10, 24, 25 etc.,). In fact, this is the lineaments/faults distilled from these drainage anomalies of Mysore– easternmost one among the above sub parallel system of faults 1 Stanley Reservoir area showed active tectonics along these NATL with along which only the southerly drafted river Cauvery is now flowing land subsidence and also dextral and sinistral movements all indicating in the Stanley Reservoir region. Further, this fault and its associated that the Biligirirangan–Stanley reservoir area must be under the grip of sub parallel fault have deflected the too in their block faulting with differential vertical and horizontal movements. southern extension (DD2, 4 and DD25, Figs. 3 and 6A). The N–S faults Radhakrishna (1992) has inferred that the Cauvery river, which has 3,4 and 5 interpreted in the coastal region in between Pondicherry earlier flowed northeasterly, in the Biligirirangan–Stanley Reservoir area and Vedaranniyam (Fig. 6A) were deduced from the prominent Author's personal copy

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Table 3 as evidenced from the “S” shaped drag in the meanders. Thus, the N–S Compressed meanders. faults interpreted from various drainage anomalies in South India in Drain. Area River Meander Width of the Related general showed block faulting and upliftment along with dextral and no. pattern zone of NATL sinistral strike slip movements at places. compressed and their meander orientations 5.2. NE–SW sinistral faults (in km)

CM1 Mercara Cauvery.r Z 19 Within Whereas, the NE–SW spectrum of lineaments/faults deduced from NW–SE CM2 Kannanur Cauvery.r Z 15 Within various drainage anomalies have predominantly expressed evidences of NNW–SSE sinistral strike slip movements. For example, the fault no. 9 exhibited CM3 Kabani reservoir Kabani.r Z 19 Within eyed drainage (ED5, Fig. 6B) with “S” shaped dragging in Palar river and NNW–SSE an “S” shaped compressed meander (CM5, Fig. 6B) to a breadth of 23 km CM4 Talakad Cauvery.r Z 14 Within in Ponnaiyar river, both signifying sinistral morphology of the fault. N–S – CM5 Uttangarai Ponnaiyar.r S 23 Within Similarly, the NE SW fault no. 10 and the related sympathetic faults NE–SW have a number of drainage anomalies viz: “S” shaped compressed CM6 Vaniyambadi Palar.r S 12 Within meanders of Arani river near Arani (CM7, Figs. 5 and 6B), sinistrally – N S dragged eyed drainage in Palar near Kanchipuram (ED6, Figs. 4 and 6B), – CM7 Uttukkottai Arani.r S 29 NNE SSW “ ” and S shaped dragged eyed drainage in Ponnaiyar near Villupuram (ED9, ENE–WSW Figs. 4 and 6B), deflected drainage (DD19, Figs. 3 and 6B) in Pambar in CM8 Tiruvallur Korttalaiyar.r Z 24 Within Harur area etc. Most of these drainage anomalies are very characteristic NW–SE evidences for sinistral strike slip morphology of this fault no. 10. – CM9 Cuddalore Ponnaiyar.r S 11 Along NE The integration of faults distilled from drainage anomalies and the SW – CM10 Vriddhachalam Vellar.r N 15 Within lineament map of South India has brought out yet another NE SW NE–SW trending sub parallel lineaments (no. 12 and 13) extending from CM11 Chidambaram Vellar.r N 13 Within Chennai in the northeast to almost Cape Comorin in the southwest – N S having varied drainage anomalies such as deflected drainages (DD18, CM12 Sirkazhi Coleroon Z 5 Along (kollidam) NW–SE 21, 22, 28 and 30, Figs. 3 and 6B) and an eyed drainage (ED8, Fig. 6B) CM13 Ariyalur Marudaiyar.r S 21 Within along another sub parallel fault all indicating active tectonism along NE–SW these lineaments with probable tectonic subsidence as evidenced CM14 Coonoor Bhavani.r Z 24 Within from the eyed drainage (ED8). Balaji (1995) too has doubted for a – NW SE possible graben along NNE–SSW sub parallel lineaments of Tamil CM15 Dharapuram Amaravati.r N 24 Within – NE–SW Nadu coast. Again, Vemban et al. (1977) inferred that the NNE SSW CM16 Palakad Aliyar.r Z 23 Within faults of Tamil Nadu coast act as crystalline–sedimentary contact and NW–SE also seismic prone. Similarly, the NE–SW trending sub parallel CM17 Periyakulam Vaiagai.r S 21 Within lineaments 14 and 15 that emerged from the drainage anomalies NE–SW CM18 Tiruvalla Manimala.r Z 26 Within have a series of drainage anomalies along them. Besides many, the NW–SE eyed drainage (ED10, Figs. 4 and 6B) seen in the Tiruchirappalli area in CM19 Ramanathapuram Vaigai.r S 7 Within river Cauvery with an eye length of over 25 km (Table 3) is a major N–S anomaly signifying possible grabening. In addition at both ends of the CM20 Kallidaikurichi Tambraparani.r S 12 Within eye, “S” shaped drags were found in Cauvery signifying sinistral NE–SW movements or sinistral couple too along these faults. Ramasamy and —“ ” —“ ” — NB: S S Shape, Z Z Shape, N Normal Shape. Karthikeyan (1998) have inferred many geomorphological and NATL: Neo-Active Tectonic Lineaments. hydrological anomalies in the Tiruchirappalli region and inferred a Holocene graben along Pondicherry in the northeast to Cumbum valley in the southwest passing through Tiruchirappalli. Ramasamy normal and symmetrically compressed meanders in Vellar river near (2006) has observed a sinistral strike slip shift along a NE–SW fault in Bhuvanagiri (CM11, Fig. 5) Bakliwal and Sharma (1980) have Neyveli Mio-Pliocene sandstone which also coincides with the observed similar acute normal and symmetrically compressed mean- present fault no. 14. Thus, almost all the NE–SW trending NATL ders in Yamuna river within ENE–WSW set of sub parallel lineaments inferred from such varied drainage anomalies and extrapolated from related to Great Boundary Fault and attributed the same to the scissor the regional lineament map of South India, have indicated the regional fault tectonics. Hence, such compressed meanders in Vellar in CM11 strike slip component. significantly confined within faults 4 and 5 can be attributed to scissor fault tectonics along these N–S faults. There seems to be another sub 5.3. NW–SE faults parallel fault (no. 3) to the west of faults 4 and 5 along which the Vellar river shows minor compressed meander too. This seems to On the contrary, the NW–SE trending NATL inferred from various continue further down south up to west of Vedaranniyam as fault 6 drainage anomalies emerged to be mostly dextral strike slip faults (Fig. 6A). Ramasamy et al. (2006) have also inferred that the N–S (Fig. 6C). For example, the fault no. 16 seen in between Cochin in the faults are major tectonic grains in the Vedaranniyam area, along west coast and Tuticorin in the east coast has many compressed which the Mio-Pliocene sandstone has undergone upliftment causing meanders with “Z” shaped dragging such as CM18 near Tiruvalla in rapid land progradation in the Vedaranniyam coast. While Agarwal Manimala river with a compressed segment of 26 km (Table 3). It is and Mitra (1991) have inferred that the N–S to NNE–SSW faults of the also significant that this fault coincides with Achankoil shear which Cauvery basin must be the youngest and are hydrocarbon bearing, was worked extensively by many earlier workers (Chetty, 2006; Guru Prabaharan et al. (1995) have observed some curvilinear N–S faults in Rajesh and Chetty, 2006; Sacks et al., 1997) Similarly, the faults no. 17 the Cauvery basin and attributed them to the post drift kinematics. In and its sympathetic failure 17A, deduced from the drainage anomalies contrast, the sub parallel faults 7 and 8 deduced from a well defined has a prominent “Z” shaped compressed meander in Aliyar river in the compressed meander (CM19, Fig. 5) in Vaigai river are sinistral faults Palakad area with the width of compressed meander having 23 km Author's personal copy

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Fig. 6. Lineament tectonics.

(CM16, Figs. 5 and 6C). The fault no. 18 and 18A have many prominent indicated that the N–S, NE–SW, NW–SE and E–Wtrendingsystemof compressed meanders with “Z” shaped drags viz: CM4 in Talakad, lineaments are very prominent and important active tectonic grains CM3 in Kabani reservoir and CM14 in Coonoor area (Figs. 5 and 6C). In rather neo-tectonic. Further, the N–S faults are overall vertical block the same way, a major dextral strike slip fault has also been faults with subordinate transverse movements, NE–SW are sinistral deciphered in the area east of Tiruchirappalli (19, Fig. 6C) which has and NW–SE dextral strike slip faults. Such an architecture of the caused acute “Z” shaped compression in Cauvery river (locally faults indicates that the NE–SW faults, could be the left lateral Coleroon) (CM12, Figs. 5 and 6 C). Similarly, the CM8 seen in wrench faults, while the NW–SE ones could be the right lateral Korttalaiyar river at Tiruvallur near Chennai with “Z” shaped drag wrench faults. And if so, a general northerly directed active (CM8, Figs. 5 and 6C) is again a very clear documentary evidence for compressive force could be visualized (Anderson, 1951). As the the dextral strike slip movements along the NW–SE system of faults N–Sfaultsfallintheacutebisectoroftheseabovetwowrenchfaults, (Fig. 6C). the same could be extensional failure related to such North–South The integration of NATL extracted from various drainage anoma- aligned compressive force. lies with lineament map of South India, again have indicated large The dextral and sinistral movements inferred along some of the N–S number of E–W tectonic grains (24–31, Fig. 6C). But, significantly all of faults indicate the still ongoing and progressive compression and the them bear only deflected drainages, not even a single fault had eyed resultant deformation. The occurrence of E–W lineaments prominently drainage or the compressed meanders. This indicates that these could reflected by the deflected drainages, under such an architecture of be mostly vertical/block faults. tectonic grains may hence be the release fractures. The conspicuous Thus, the assembly of various drainage anomalies, the related absence of either eyed drainages or the compressed meanders further NATL and their integration with lineament map of South India has substantiates the same. Author's personal copy

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