S O M E A S P E C T S O F T H E P R E - V I N D H Y A N F O R M A T I O N S O F T H E S O N V A L L E Y , M.P .

BY S. LAKSHMANAN (Centre of Advanced Study in Geology, University of Saugar)

Received February 5, 1968

(Communicated by C. S. Pichamuthuw r.A.Se.)

ABSTRACT

The paper gives a general account of the stratigraphic position of the granite seen in the Son Valley, and also the age, extension, folding, up- lift, and denudation of the Bijawars. The author's study has led him to conclude that the granite is of post-Bijawar age, and that the Bijawars of the Son Valley show resemblance to the Bijawars of the type area, the only difference being that the Son Valley Bijawars are more disturbed and metamorphosed with the obliteration of sedimentary characters. The absence of any evidence for glaciation during Bijawar times is also pointed out.

INTRODUCTION

SINCE Oldham, Vredenburg and Datta's work in 1901 no published geologi- cal account has appeared, especially on the western portion of the Son Valley. In recent years, West (1962)emphasized the importance of a detailed study of this tract. Auden's work (1933) to the east of Long. 82 ° 30' was mainly concerned with the Vindhyan formation. The only paper on the geology and geomorphology of the Son Valley area is that of G. V. Rao (1965). The author remapped a portion of the vast Son Valley tract comprising parts of the Satna and Shahdol Districts of M.P. The area covered falls within the Survey of India one inch topo sheets 63 H/4, 63 H/8 and 63 D/16.

The pre-Vindhyan formations in the area (Fig. 1) include the Bijawar sub-metamorphics and the crystalline gneissose-granite. The author con- siders the Red Shale Series as Vindhyans, and hence this series is outside the scope of this study. The granitic complex which forms the middle exposed stratigraphic unit is contained in a lens-shaped area bounded by the basal quartzite of the Semri Series to the north and by the Bijawars to the south. The 29O

The Pre-Vindhyan Formations of the Son Valley, M.P. 291

crystalline rocks, because of their comparative rapidity of decomposition, occupy a featureless low country. Due to the large cover of recent deposits exposures are confined only to thz Son river section. The granitic plain at places like Sitkuri has a tendency to develop bad land topography. The complex and unfossiliferous meta-sediments to which the term 'Bijawars' was applied by the pioneer workers are similarly under a thick soil cover.

F, l° .g,d

GEOLOGIC,AL MAP OF THE AREA(AFTER.R.D.OLDHAM.)

FxG. I

(1) Bijawar-Granite Relationship

P. N. Bose during 1893-94 surveyed a large area in Rewa, and amongst the pre-Vindhyan formations he distinguished a schistose formation (metarnorphics) from the Bijawars and included a belt of gneiss with the former. R. D. Oldham, who had the opportunity of inspecting Bose's work, came to the conclusion that the so-called gneiss of Bose is in reality

292 S. LAKSHMANAN

an intrusive granite. According to Griesbach (1895) the differenc~ in lithology between the schistose rocks and the Bijawars is due to contact metamorphism.

On the geological map of the Son Valley, Oldham (1901) shows the granites as the oldest group of rocks. But while describing the rocks he states that the next succeeding formation in point of age (that is after the Bijawars) is the intrusive granite (1901, p. 5). The development of folia- tion in the granite giving it a gneissic appearance and the intercalation of schists in it led Oldham to" refer to it as a still structure. He believed the granite to be post-Bijawar in age.

Auden (1933, p. 145) also has expressed a similar view. Law (1954) after mapping parts of the Sidhi District (where the same granite gneiss is present) came to the conclusion that the granite gneisses are the oldest exposed rocks in the Son Valley.

On the geological map of India published in 1957 by the Geological Survey of India, the g~anite (gneiss) to the south of the belt of Bijawars is included under the "unclassified crystallines '" (oldest rocks), whereas the granite to the north of the Bijawars is shown as a granite of Purana and Archaean age.

Pascoe (1959, p. 293) regards the gneissose granite to be post-Bijawar in age. According to Krishnan, the gneissic granite intruded into the Bijawar is the same as the Chota Nagpur Granite-gneiss (1960, p. 149) (post-Bijawar in age).

Kedar Narain (1961, p. 7), who carried out systematic mapping of por- tions of the Sidhi District, states that the granites show distinct intrusive relationship with the Sidhi series (equivalent to the Bijawars). He considers the granite to be post-Bijawar in age.

Rao (1965) finds that the granites belong to two periods. The various xenoliths and intmsives found in the pink to grey granite-gneisses are the oldest rocks, which have later been intruded by pink coarse-grained granites. The Sidhi series (Bijawars) overlies the above assemblage with a distinct unconformity.

The problem appears similar to that of the problem of the Champion gneiss and Dharwars in Mysore (Pichamuthu, 1964). There is, however, unequivocal evidence here of distinct intrusive relationship of the granite with the Bijawars, as near Marai, Sejari and south of Chandola. The B1jawar phyllites near the granitic contacts have been converted to sc~sts. Th

The Pre-Vindhyan Formations of the Son Valley, M.P. 293

various xenoliths present in the granite gneiss are of Bijawars (metamor- phosed), and the metabasic rocks present are post-Bijawar intrusives, one is prone to ask as to what happened to the basement rocks on which the Bijawars were deposited ? The next group of rocks in the area being Red Shale Series into which the granites show no intrusive relationship, the author regards the granite gneiss as coming between the Bijawars and the Red Shale Series in age.

(2) Possible Extension of the Bijawars to the South during Vindhyan Times

The author is of the opinion that the present limit of the Bijawars was not the original limit during Vindhyan time, and it is considered likely that the Bijawars have extended somewhat further to the south on the following grounds.

The present belt of Bijawars in the Son Valley is believed to represent the southern limit of a large syncline with increasing disturbance and meta- morphism towards the south (Pascoe, 1959, p. 292; Vredenburg, p. 59). It is likely that during Vindhyan time the syncline was followed by an anticline to the south, since in a large tract of folded country a syncline as such does not occur alone.

The present limit of the Vindhyans is not far from the Bijawar-Gondwana boundary. It is believed that the Vindhyans were deposited on the eroded surfaces of the Bijawars with material composed definitely of Bijawar origin. There must have been some elevated landmass from where the materials were transported and deposited over the uneven Bijawar floor of the Vindhyan basin. This is further supported by the fact that the palaeo- current direction worked out from the various directional current structure for the Lower and Upper Vindhyans points to a lqN37¢ to north-westerly direction, indicating sediment transport from SSE or SE.

(3) Age and Correlation of the Bijawars

The correlation of an unfossiliferous and metamorphosed formation is beset with a lot of difficulty, and the correlation of the Archaeans espe- cially continues to be a problem. Till 1955, the conventional methods of correlation like lithology, order ot superposition, degree of metamorphism, stratigraphie continuity, etc., were used with little success. The position remains the same even after the advent of determination of ages of different organic cycles by radioactive minerals. This appears to be the case with the Bijawars also.

294 S. LAKSHMANAN

The general tendency among geologists is to correlate the the Dharwars or with the Cuddapahs, or to ascribe them orogenic cycle.

(a) Dharwar age.--Mollet considered the Bijawars in the Son Volley to be the equivalent of the Iron-ore series of Singhbhum.

The association and the intercalation of basic igneous rocks, lavas and pyroclastics, and also their metamorphosed nature, probably led Pascoe to regard them as the equivalents of the Dharwars.

According to Krishnan, "It is practically certain that the granite is identical with that occupying the Ranchi plateau and other parts of Chota Nagpur where it belongs to the period of post-Dharwar diastrophism. The granite, being thus pre-Cuddapah in age, the so-called Bijawars of the Son Valley must be equivalent to a part of the Dharwars. Since banded jaspers and associated epidiorites are an integral part of these, they should be regarded as similar to the Iron-ore series of Singhbhum" (considered equivalent to Upper Dharwars of South India) (1935, p. 187).

Auden is of the opinion (1933, p. 45) that the Bijawars of the Son Valley are to be classed with the Dharwars.

According to Fermor the Transitions of the Son Volley, although they were first thought to be the equivalents of the Bijawars, at least a large part must be assigned to the Dharwars (footnote by Fermor, Mem. Geol. Surv. Ind., (1933), 62, p. 145.

The main considerations for assigning a Dharwar age to the Bijawars, as could be seen from the above views, are the metamorphosed nature of the sediments, the presence of granite intrusions in them, and lithologioal resemblances (banded iron ores, red jasper, crystalline limestone, etc.) in addition to their containing basic igneous intrusives.

(b) Cuddapah age.--The fact of the Vindhyan sediments overlying the Bijawars, the basic igneous activity in them as in the Upper Cuddapahs, and to a certain extent lithology, favour a Cuddapah age. However, the argument that the Karnools (.equivalent to Lower Vindhyans) overlie the Cuddapahs in Andhra Pradesh and the Lower Vindhyans overlie the Bijawars in the Son Valley and hence the Bijawars might be of Cuddapah age, is not a very pertinent one.

Krishnan in assigning an age to the rocks of the Son Vallley and adjoin- ing areas states that "These may belong to the Dharwars or to the Cuddapahs"

Bijawars with to the Salpura

The Pre-Vindhyan F6rmations of the Son Valley, M.P. 295

(1960, p. 150). In the Geology of India and Burma he describes the Bijawars of the Son Valley and the Dhar forest area under the Archaean system, while the Bijawar system itself is described under the Cuddapahs. It seems that although he too favoured a Dharwar age for these rocks in the beginning, his recent view appears to be that they are all of Cuddapah age. In a recent article Krishnan and Swaminath (1959, p. 14) state that "The pre-Vindhyan formations closely associated with the Vindhyan formations in the Peninsula are the Delhis, Bijawars, Gwaliors and their equivalents. Because the outcrops of these rocks are not continuous and their lithology is variable, their correlation presents a difficult problem but they may be taken as probably of approximately the same age, i.e., Upper Pre-Cambrian.'"

According to Dubey's (1950) tripartite division, the Lower Bijawars include the Lower Cuddapahs and Delhi rocks, the Middle Bijawars include those with basic igneous activity as in the Bijawars of the type a'ea, and the Upper Cuddapahs of Andhra and the Upper Bijawars include the Semris of the Son Valley (Lower Vindhyans) which contain acid flows and tufts and the Lower Vindhyans of Rajasthan. " A point in favour of this idea is that all Cuddapahs a~d the Pre-Cambrian rocks associated with basic igneous activity would be relegated to the Cuddapahs, and that the Vindhyans of Northern India exclusive of the Semris would be the equivalents of the Kurnools which do not show any con.temporaneous volcanism. The well- marked unconformity between the Stmris and Upper Vindhyans would also support this idea " (Krishnan, 1960, p. 197).

(e) Bijawars of the Son Valley considered as equivalent to the Bijawars of the type area (Bundelkhand).--On the evidence of the lithology and the presence of granite intrusions, the Bijawars resemble the Dharwars. Similarly, if some other aspects like the presence of basic igneous intrusives and the overlying, Vindhyans, etc., are considered they resemble the Cuddapahs. But in no complete respects do they resemble either the Dharwars or the Cuddapahs. It might be argued that a Cuddapah age cannot be assigned since the Bijawars in the degree of metamorphism and disturbance and also on lithological grounds do not show any resemblance to the Cuddapahs. If the Dharwar age is applied, the vast time gap (including the eparchaean interval) between the Dharwars and the Lower Vindhyans, as represented by the great thickness of Cuddapah sediments and other intrusive rocks in South India, is to be accounted for. Therefore, a correlation of the Bijawars with the South Indian rocks when they do not agree broadly in all respects, is undesirable and unnecessary. The Bijawars can very well be considered as a separate entity. The Bijawars may not be equivalent to the Cuddapahs

296 S. LAKSI-IMANAN

or the Dharwars, but in the Son Valley area they constitute the oldest forma- tion (unfossiliferous recta-sediments, highly disturbed and intiuded by acidic and basic intrusives).

As early as 1901, the resemblance of the Transitions of the Son Valley to the Bijawars of the type area in Bundelkhand was recognised by workers like Oldham and Vredenburg. No attempt was made by them, however, to correlate the Bijawars with the Dharwars or with the Cuddapahs ; they retained the name Transitions as such.

After examining the rocks of the type area the author considers that the Bijawars of the Son Valley differ from the type area only in being more metamorphosed and disturbed with the obliteration of sedimentary charac- ters.

(4) Eolding Uplift and Denudation of the Bijawars The rocks of the Semri series and the Red Shale series are nowhere

found resting upon the Bijawar basement rocks in a conformable sequence. At the same time, the Bijawars with the prevailing strike of ENE, and dipping almost vertically towards the SSE, are overlain unconformably by younger formations with a regional dip towards the NW or NNW. The distinct unconformity and the presence of acid and basic igneous intrusives in the Bijawars suggest some disturbance before the younger sediments were de- posited. This indicates that the Bijawars were folded before the deposition of the Vindhyans.

The question now arises as to whether the Bijawars have been actually folded and uplifted or whether they have been only tilted and/or uplifted like the Vindhyans or Gondwanas which in general do not show any orogeny. The latter alternative does not appear probable.

The Bijawars must have been at great depth when folding and plutonic intrusion took place; they were later uplifted and subjected to erosion before the next series of rocks were deposited over them. It is not known whether the folding was concomitant with the igneous intrusion or the intrusion of the granites produced the folding and subsequent uplift; the intrusive granite was probably in the form of a great bathohth or laccolith.

The present extension and thickness of the Bijawars may be only a fraction of what they were before the deposition of the Lower Vindhyans. At many places the Bijawars have been denuded exposing the granite gneiss beneath it, over which the later sediments have been deposited and that is

The Pre-Vindhyan Formations of the Son Valley, M.P. 297

the reason why the/basal beds of the Semri series are sometimes seen resting directly upon tl=e granite gneiss without the intervention of the Bijawars. This indicates that the Bijawars had been eroded away locally producing an uneven gneissic floor over which deposition of the younger series took place.

(5) Glaciation during Bijawar Time

According to Ahmed (1958, p. 529) " I n the Son Valley the Bijawars themselves are associated with a distinct tillite and the possibility that the shales are glacial sediments cannot be ruled out" .

The author, in the area examined by him, has not observed any tillite or shale. The chloritic phyllites and schists, associated with vesicular lava flows, are considered to be altered tufts.

ACKNOWLEDGEMENT

The author is deeply indebted to Prof. W. D. West for guidance, facili- ties provided and for critically going through the manuscript. Grateful thanks are also due to Prof. C. S. Pichamuthu for his valuable comments and suggestions.

REFERENCES

1. . . "Palacogeography of Central India in the Vindhyan period," Ree. Geol. Surv. Ind., 1958, 87, 3.

2. . . "Vindhyan Sedimentation in Son Valley," Mere. Geol. Bury. Ind., 1933, 62, 2.

3. .. Curr. Sci., 1950, 20, 143.

4. .,. Annual Report of the Geological Survey of India and o f the Geological Museum, Calcutta, for 1894, 1895, 28, 1, 2.

5. . . "Gemeral Report of the Geological Survey of India for the year 1955," Rec. Geol. Surv. Ind., 1961, 89, 1, 7.

6. . . "Pr~idential Address," Prec. 22nd Ind. Sci. Congr., 1935, 187.

7. "The Great Yindhyan basin of Northern India," Jour. Geol. Soc. India, 1959, 1, 16.

8. Krishnan, M.S. .. ( Geology of India and Burma, 1960 (Madras).

9. Law, Y.D. . . "Contributions to the Geology of the Son Valley in Vindhya Pradesh," Quart. Jour. Geol. Min. Met. Soc. Ind., 1954, 26, 2.

10. Mallet, F . R . . . "Vindbyan Series as exhibited in the North and Central Pro- vinces of India," Mere. Geol. Surv. Ind., 1871, 7, 1.

Ahmcd, F.

Auden, 3. B.

Dub~y, v. s

Griesbach, C. L.

Ke, dar Narain

Krishnan, M. S.

and Swaminath, J.

298 S. LAKSItMANAN

11.

12. Pascoe, E. H.

13. Pichamuthu, C. S.

14. Rao, G. V.

15. West, W. D.

Oldham, R. D., Vredenburg, "Geology of the Son Valley in Rewah State and of parts of E. and Dutta, P.N. the adjoining districts of Jabalpur and Milzapur," Mere.

Geol. Sure. Ind., 1901, 31, 1.

. . Manual o f the Geology o f India and Burma, 19S9, 1 and 2.

. . "The Stratigraphic position of the Champion gneiss," Syrup. on Stratigraphy, Age and Correlation of the Archaean Pro- vinces of India, 1964, Andhra University, Waltair.

•. "Geology and Gvomorphology of the Son Valley area, M.P.," (unpublished), 1965, Seminar on "Geomoxphology," University of Saugar.

. . "The Line of Narmada and Son Valleys," Curr. Sci., 1962, 31, 143.

236-68. Printed at The Bangalote Press, Bangalore City, by M. S. Narayana Murthy, Secretary, Published by B. $. Venkatachar, Editor, "Proceediags of the Indian

Academy of Sdences," Bangalore