Scribd
Upload
254 views33 pages

Subarnarekha Case Study

Uploaded by

Rajib Das
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PDF or read online on Scribd
254 views33 pages

Subarnarekha Case Study

Uploaded by

Rajib Das
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PDF or read online on Scribd
You are on page 1/ 33
» CHAPTER III THE EVOLUTION OF THE SUBARNAREKHA BASIN Before starting with the case of evolution of the Subarnarg basin occupying part of the south-eastern Chota Nagpur Platea, (mainly in the districts of Singhbhum and Ranchi, Bihar), aa author likes to present some relevant observations on geo-chronolo, of the Precambrian rocks of the area as a background to th, present development of the basin. On the basis of all available age data from the Indian Shieg (Aswathanarayana 1956, 1964; Holmes 1955; Sarkar and Saha 1963, 1966; Sarkar et al. 1964, 1967; Vinogrador and Tugarinoy 1967) it may be concluded that the Older Metamorphic Group of this part of Chota Nagpur Plateau represents the relic of the oldest recognisable orogenic belt (closing age C. 3200 m.y.) in India. The Older Metamorphic Group may be correlated with the Katarchean rocks (3500-3000 m.y.) of the Baltic. Shield (Pelkanov and Gerling 1960); Swaziland System (3400-3000 m.y-) in South Africa (Alsopp, Ulrych & Nicolaysen 1967) and granite-gneisses of the Minnesota River Valley (3500-3300 my.) in Lake Superior region (Goldich 1967). The Singhbhum Granite (C. 2700 m.y.) now drained by the tributaries like Kharkai and Garra (the Subarnarekha system) ma} be correlated with the Charnockites and Peninsular Gneiss 0 Southern India, since Rb-Sr isochron age of Peninsular Gneiss Bangalore, is 2635 m.y. and that of Charnockites of Nilgiri anc Tamilnadu (Madras) is 2650 m.y. Accompanying any satisfactor explanation of the landscape of the Subarnarekha basin must b an interpretation of its drainage history and this involves primatil the Subarnarekha and its tributaries. It has been discussed in association with the drainage-hypo theses (Chapter VII) the manner of the origin of the streams (th Subarnarekha system) on the upheaved tracts of the uplands withi! the Subarnarekha basin, and how they have been guided by strut ture, joints and areal gradients in order to fulfill the denudation? 24 GEOMORPHOLOGY OF THE SUBARNAREKHA: BAS! _- chronology of the basin. Tt may he mentioned that renewed uplift ig. in the late-Tertiary raised the surfaces (about 300 m. Vhs a rejuvenated the streams followed by several camsequersey (a capture ctc. ke river The Origin of the Subarnarekha Basin Some aspects on evolution of the Ranchi Plateau, Singh and Panch Pargana Plains covering a major part of the Chow Nagpur Plateau within the northeastern Peninsula has buen nt sented above. It has been observed also that the gencral eresierci history of the Subarnarekha basin section seems to correlate fairly well with that outlined for the Chota Nagpur Plateau where regional uplift in Jate-Tertiary time accompanied by warping led to renewal of erosion. With the available geological and geomorphological data and from the fields the following broad outline of the erosional history of the Subarnarekha basin may now be built up, Tewill be convenient to trace the evolution of the Subarnarekha basin forming part of the Ranchi and Singhbhum sections of the Chota Nagpur Plateau since Tertiary times. The author likes to start with the picture of the Subarnarckha drainage system of a peneplain surface equivalent to the surface of an early-Tertiary peneplain (Dunn 1942) or the structural plain resulting from lava flows. Normally in the course of its development the erosional surface was subject to upheavals extending up to 300 m. thus creating favourable conditions for the streams to increase the degrading capacity of the Subarnarckha river over this rejuvenated surface. Consequently the rejuvenation ultimately led to the development of a new erosion surface at an altitude of 300 m. below the former surface levels on the Ranchi Plateau as above. Then the Subarna- rekha basin occupying a major part of eastern Ranchi Plateau formed as a single catchment unit of a drainage system. It was aligned roughly along the course presented by the Subarnarekha- upper and Kangsabati (Purulia Upland) through the northern Panch Pargana Plain (Fig. 47a). To the south of this drainage course in the Panch Pargana Plain there was another stream flowing through the Dalma Kange which includes the lower reach of the Present Middle Subarnarekha valley. Further renewal of uplifts during late-Tertiary after the formation of the Chota Nagpur Planation surface, as above, was responsible for raising the prevalent Surface at an altitude of 300 m., and thus the Subarnarekha valley ‘THE EVOLUTION OF THE SUBARNAREKHA BASIN = Fr As a result of this rejuvenation of sche original drainage of old Subarnaygy’*} Kangsabati (Western. Purulia Upland) io wa captured i‘ tributary to the lower Subarnarckha at a ent in 7 he Souths Pench Pargana Plain. ‘That portion lying to the east of the comm” divide along Ajodhya-Baghmundi hills dividing the Subarnarey, (Wig. 47a ght-side top, B, and below rig Coils Asal to the ¢ : of Jhalida; 47) centre back-ground) Srom the present Kangsabat{ We Teli beheaded or misfit river (Mukhopadhyay 1973). Tt should jy noted that the rejuvenation that led to the stream piracy Progressive Stream Piracy, Chapter VIT) as referred here, actuay, was an affair of the whole Subarnarckha basin covering a wig npheaved-area drained by the Kharkai and Sanjai, Garra ee | tributaries to the Subarnarckha. Tt appears that considerable portions of the South Koel ang Baitarani drainage systems were also diverted to the north, north. east in the courses delineated by the present tributary rivers jn { the basin. The valley floor of the Middle Subarnarekha basin in the western Singhbhum Plains, initially part of the catchment of a drainage system at higher altitude, exists at present 200 m. below the surface of Kharkai-Baitarani-Koels (South) divide along the Saranda hills-Kolhan uplands. It should be remembered that the operation of ‘stream-piracy’ mainly by headward erosion being assisted by unequal gradients along the two opposed Subarnarekha- Kangsabati and lower Subarnarekha rivers (which is called by the author as the Dalma river) as competing streams in the tilted blocks of the eastern plateau (the Panch Pargana Plain) with scarp front and gentle back slopes certainly could not have been ‘regular’ every where in the whole basin. On the other hand the matter of stream diversion was likely to have varied in its progress both in Panch Pargana Plain and Singhbhum Plain sections of the Subarna- rekha hydrographic unit. It was much prominent for the streams flowing north of the Panch Pargana Plain area situated to the west of Ajodhya-Baghmundi hills with two small monadnocks on its flat surface, i.e. the Subarnarckha-Kangsabati divide (Fig. 4a). Therefore, it can be concluded that since late-Tertiary uplift which caused a rejuvenation of the topography formerly charac- terised by a very coarse texture of drainage, ultimately resulted in the creation of a south, south-casterly drainage. ‘The north, south- cast profile was duc to tilt of the plateau to the south-east consistent in rej ated. was again rejuvenated Subarnarckha, portion 0! ” 26 GEOMORPHOLOGY OF THE SUBARNAREKHA BASIN r bisa, jun the above uplift. This resulted in the development of gorges, se lls, terraces tC. and alsa initiation of te ee y shorter rater aller tributaries like Karkari, Kanchi, Raru, Sanka, Sobha an sma | which a vinings iy dating from the late New pattern of draj- tem which grew headward following the mn Fejuvenation mittant with the scarp recession was extend} further —thus a separate drainage pattern was evolved, Some be considered comparatively much ertiary uplift. A posibly 4 nage sys Subsequent to the latter Tertiary uplift the Subarnarekha t its valley started to be deeply mmenced along with its tributary alleys concurrently. Because of its nearness to the local base led ‘i st south of Dalma hills i.c. south of the latitude 22°55" North to to which an arm of the Tertiary bay is believed to have extended ithe basc of the Dalma hills Chapter VII), the incision by the lower reaches of the Middle Subarnarckha v, alley in the Singh- bhum and Panch Pargana Plains, was much more rapid than in is more upper reaches. Tt would be noted that the lower (prots) Subamarekha or the Dalma river (as has been called by the atithor) had an advantage over the Subarnarekha-Kangsabati because i¢ was cutting its valley in more easily crosible rocks of phyllite and schists in the southern Panch Parg: yeeame rejuvenated and as a resul pecame : incised when rapid crosion also coi incise ana Plain. The progress was accelerated further on account of much steeper gradient of the lower Subamarekha (Dalma river) than the Old Subarnarckha-Kangsabati valley. One of the best known examples of piracy in this area is that which resulted in the formation of Jhalida, Baghmundi and Ajodhya gaps etc. This represents an illustration of Progressive stream piracy by headward erosion. Now, Jhalida (23°22’ N; 85°59’ E), a gap town along with other Saps are at present ‘wind gaps’, a term applied ‘0 former water gaps through which the Subarnarekha-Kangsabati ® lis wibutaries no longer flow, but formerly those streams flowed “stward through Ajodhya-Baghmundi Ridge in each of them. » i: Sems reasonable to assume that erosion was carried one ae a Subarnarekha (the Dalma tracts above 500 m.) to ‘ =rgana “rms the upper edge of the southern extensions of Pa @ Plain from which the lower Subarnarekha with its steep ™, Nouv 27 LUTION OF THE SUBARNAREKHA BASIN. y gradient used to flow through Dalma Range to th nee of the arm of Tertiary bay. In the lower Subarnarckha_(Dalma river) commence =o being assisted by uplifts and the recession ° faces r= also Marka in association with the advancement of ae ovards reaches of the valleys in the northern Panch argana lain, : whole the crosive action of these rivers was responsi 4 le for lower the surface of Panch Pargana Plain where a number of Tesidual hills with lower altitude like Andadungri (375 m.), Gorga Bun (677 m.), Kadali Pahar (375 m.), Buratakur Pahar (335 nj Burudih (330 m.), Saparum Buru (400 m.), Burukande (439 mj, Raranda (460 m.), Ghosra Pahar (450 m.), Chamtu (709 m) Chadgarh Pahar (650 m.), Bansa (480 m,) ete the present cyclic surface. The most residual hills as above are of polycyclic forms and carry a number of distinct breaks in its slope the profile of which exhibit the form of do: me-on-dome residuak (Fig. 1%, 19). The erosion surface in the Middle Subarnareki, basin are rel fated to a complex geomorphological history involv several cycles of erosion with these hills or elevated land Masses. representing the relics of former planation surface. Here, all erosion surfaces at different altitudes (Fig. 18a) ave warped and much dissected as a result of the uplifts which inaugurated the successive cyeles (see Chapter V). The bold and steep bounding scarps occur. ring as series of steep slopes are due to uplift during Tertiary times (Mukhopadhyay 1970). Some Points about the evolution of these hills as mentioned above have been considered afterwards. Mode of buru-dungri (residual hills) bevelling is shown, in Figure 19¢. However, at the hue Period the floor of the lower Subarnarekht Valley itself was being lowered concurrently. As more and more down cutting has take of reduction e rj this Nig; Fins ete. rise steeply frog s of the ; ¥ (proto) Subarnarekha or the Dalma rivet le for pproaching towards the Subarnarekha- alley in the northern Panch Pargana Plain, It has bee ary ale. Water divide between the two rivers—the barnarekha and the Upper Kangsabati, there are 20 Hills coyenan8€® ard practically the hills (23°9)/ Ny. apo ts 1 eel ae E ) i ‘AC rising not more than 30 ms v ¢ streams ing in di oe e width of the divide in the north ess of Pane eet directions, TH ast of Panch Pargana Plain is ofl, 28 was responsib) Kangsabati y observed th, 4 CFOMORPHOLOGY oF Tp SUBARNAREKHA BASIN | r— cage. Therefore, it appears tha By eee of the town ‘Jhalida ase Nee Herren Ang HO Ce possible ‘elbow of capture” @iee gee ww, east OF *ME Pieracted Subarnarckha that origi hopadhyay bye the 60% ha that originally flowed Reangsabati river through the Jhalida gap (23°22' N; 95739 ange present the sharply intrenched valley almost tik “ ore developed in the normal course due to re. gence of their water courses below the ‘elbow of cantare angen peasedl BY valley widening. Therefore, (i) the abrupt wave led turn of the Subarnarekha before entering the Panch sight ain, the comparatively high gradient of the river pore ne arts, (il) the gorge-like features e.g. south cast of Silli in OW N; 5°51’ E) etc., (@) the almost straight course of the er aenarokha at the adjoining areas of the turning points, (v) Subarnare® Myind gaps ¢-g- Jhalida gap (23°22" N; 85°59’ E) in ‘and (vi) the existence of a low water divide between the gubarnarekha and the Kangsabati in the northern Panch Pargana Plain etc. all seem to indicate that the lower (proto) Subarnarekha river (the Dalma river) initially in the southern part of the plain might have flowed to the south of Dalma and subsequently captured the east-south-east flowing original upper Subarnarekha river by headward erosion. The lower Subarnarekha valley intially a part of another catchment area around the southern plateau edge of re Panch Pargana Plain, developed into a separate existence with the evolution of this new drainage pattern in the aforesaid plain which is characterised by gorges, the steep valley gradient, terraces, aterfalls along the bounding scarps (Fig. 13). he major rivers in the eastern part of nitiated over a structural plain SS e 7 art hav buru-dungris and wi Therefore, it appears that t the Ranchi planation surface were i with a common slope to the south and south-east, and these pro- gressively cut down water gaps etc. in the plains of Singhbhum and Panch Pargana within the basin. The altitudinal variation between the present river bed and the adjoining summits in upland or hills of each case appear to have resulted from the initial uplift, ion has experienced’ in stages (Mukhopadhyay 1970, 1973, hte a the uplift followed by rejuvenation in association with eee of base levels was mainly responsible for such redistri- of relief and drainage, and finally resulted in the evolution fey fs s ice ‘urent drainage system of the Subarnarekha basin— geomorphic: E EVOL 29 ‘UTION OF THE SUBARNAREKHA BASIN | | | wx of ancient polycyclic erosions. The oe 7 0 ss on the concept of tectonic ¢, aug | ri Ontroy Oe jy | tre vee ech stress of the C : veith rejuvenation of the dramage anq scarp-retreat processes accompanied by rigsted \ n recent time. This concept yor 1 Bia : e conditions of the evolyti St opt st interpretation of the con ‘olution, Off earl basin (Mukhopadhyay 1969). oF the MeOGo far the author has discussed some of the j, x regarding the evolution of the drainage systems sine Tontiary period, now some points on the development gt & hale lovally known as ‘bara or dungris’ which are bey’ arsed wo a complex geomorphological history invole™y Greles of erosion, with these hills or elevated lands speciag adjoining areas of scarp lands representing the remnanty ofp! planation surfaces, would be referred as follows: ny (i) Major change of base-level occurred in the e; present Ranchi Plateau around 450 m. contour and Singhyy.! Panch Pargana Plain above 150 m.,a.s.l. for example, duringTws and also in early Pleistocene times in connection with the movements eg. tilting, warping or faulting etc., (ii) it ings new cycle advancing rapidly inland from the eastern coastal 19, up to the rejuvenated Subarnarekha river and its tributarig} Dulung, Garra, Kharkai and Sanjai, Karkari, Kanchi, Sa Raru etc., (iii) gradual retreat of the bounding valley sides afixd provisions for further widening of valley floors of the Subarnand drainage system. It provided the scope for the extension of thelt ge cyclic'plains forming in the lower Subarnarekha basin, (i inland encroachment of the new cycle caused in fashioni landscape into a number of blocks in accordance with its logical characteristics, (v) these individual blocks were then shit by progressive retreat of the scarps and the valley sides. sent ‘ghats’ or scarps do not delineate the original warp ling scarps having receded by erosion accordingly, (vi) ay cycle reached up smaller tributaries the blocks were further # mented into smaller compartments giving rise an overall imps ofa highly dissected and pi if ne rest : is and picturesque country, (vii) then tt a Theat, being reduced by back and down wearing in 8% eee pace the onset of a new cycle selection by the Subar™ vd vetem OF lines of weakness led to the rapid dissection of the *% mass of weakness le situated in its basin, into compartments of varying si consistent vigorated a to earth movements 1 . ancient polycyclic erosions. The present author like region of r i 7 reenuch stress on the concept of ae ou oF of base jt put ith rejuvenation of the drainage and assista, Md consistent with rejuvenat d by in Jigorated scarp-retreat processes accompanied by river-pira, wees hh movements in recent time. This concept seems to Offer Me Bene of the conditions of the evolution of the Subarnarekha basin (Mukhopadhyay 1969). : So far the author has discussed some of the Important fey regarding the evolution of the drainage systems since the Carly, Tertiary period, now some points on the development of the residue hills locally known as ‘buru or dungris’ which are believed to by related t@ a complex geomorphological history involving seve cycles of erosion, with these hills or elevated lands specially in the adjoining areas of scarp lands representing the remnants Of former planation surfaces, would be referred as follows: (i) Major change of base-level occurred in the eastern part gf present Ranchi Plateau around 450 m. contour and Singhbhum.. Panch Pargana Plain above 150 m., a.s.l. for example, during Tertiary and also in early Pleistocene times in connection with the earth | movements e.g. tilting, warping or faulting etc., (ii) it initiated | new cycle advancing rapidly inland from the eastern coastal region up to the rejuvenated Subarnarekha river and its tributaries like Dulung, Garra, Kharkai and Sanjai, Karkari, Kanchi, Sobha, Raru ete., (iii) gradual retreat of the bounding valley sides afforded provisions for further widening of valley floors of the Subarnarekha drainage system. It provided the scope for the extension of the later cyclic ‘plains forming in the lower Subarnarekha basin, (iv) the inland encroachment of the new cycle caused in fashioning the landscape into a number of blocks in accordance logical characteristics, (») these individual blocks by semperestive. retreat of the scarps and the valley sides. The pre- . sent ‘ghats’ or scarps do not delineate the original warp line, the scarps having receded by erosion accordingly, (vi) - ee cycle reached up smaller tributaries the blocks ee fur ns mented into smaller compartments giving 4, lurther ae; of a highly dissected and picturesque country, (vis) — impression areas are being reduced by back andl down spy teh the residual aring in general. Therefore, with the onset ofa new cycle seleon + with select system of lines of weakness led t0 the tapi diesen’ Stbamarekin mass simated in it hatin, into comparemen eee” OF the residual Roe q Presey, with its petro- ere then shrunk 30 on the spacing of the major joints. Th Mf ewer developed into ‘burs’ and the robably nee or burw as a geomorphic te Eins Tole eet ee te Subarnarekha b; pa oa ae 1970). hould be mentioned that being prote

You might also like