DISTRBUTION, STRATIGRAPHY, ECONOMIC IMPORTANCE AND EQUIVALENTS OF THE VINDHYAN SYSTEM

 

INTRODUCTION

The Vindhyan basin is a classic example of Proterozoic intracontinental basin that developed in the central part of the Indian shield along with several other basins such as Cuddapah, Chattisgarh, etc. The Vindhyan Supergroup is the thickest Precambrian sedimentary succession of India and the duration of its deposition is one of the longest in the world. The Vindhyan System derives its name from the great Vindhyan Mountains, a part of which is found to form the prominent plateau-like range of sandstones to the north of the Narmada valley, particularly in Bundelkhand and Malwa. The Vindhyan system is a vast stratified formation of sandstones, shales and limestone encompassing a thickness of over 14,000 feet, developed principally in the Central Indian highlands which form the dividing ridge between Hindustan proper and the Deccan Traps.

The strata are exposed in three major sectors: Son valley, Bundelkhand and Rajasthan. They occupy a large extent of the country—a stretch of over 40,000 square miles from Sasaram and Rhotas in Western Bihar to Chittorgarh on the Aravallis, with the exception of a central tract in Bundelkhand. The outcrop has its maximum breadth in the country between Agra and Neemuch. Substantially thick Vindhyan rocks have also been recognized under the Gangetic alluvium. The Vindhyan Basin, containing more than 5000 m thick sequence of sandstones, shales and limestones, occupies an area of about 1,62,000 sq.km of which about 80,000 Sq.km extends into the Ganga valley in the north and northeast beneath the Tertiary sediment of the Himalayan foredeep. In the southwest, the Vindhyan rocks are covered by Deccan volcanics.

       

        The Vindhyan system, is composed of two distinct facies of rocks deposits, one calcareous and argillaceous, characteristically developed in the lower part, and the other almost exclusively arenaceous, forming the upper system. The shale, limestone and sandstone strata show very little structural displacement or disturbance of their primeval characters ;they have preserved almost their original horizontality of deposition over wide areas ; the rocks show no evidence of metamorphism, as one is led to expect from their extreme age, beyond induration or compacting. The shales have not developed cleavage nor have the limestones undergone any degree of crystallisation. The only locality structural where the Vindhyan strata show any marked structural disturbance is along the south-east edge of the Aravalli country, where they have been affected by folding and overthrust due to the crust-movements which succeeded their deposition, and their internal mineral structure considerably altered, especially in the case of the freestones which have become quartzites.

                        Tectonic Framework:.

          The Vindhyan Basin is one of several ‘‘Purana” (ancient) sedimentary basins of the Indian subcontinent. It is a sickle-shape basin that outcrops between the Archaean Aravalli–Bundelkhand province to the north and west and the Cretaceous Deccan Traps to the south; the Great Boundary Fault marks the western limit of this basin south of which occurs the Satpura orogeny. The Vindhyan Basin is composed of several smaller sub-basins; the largest of these are referred to as the Rajasthan sector and the Son Valley sectorThe basin is bounded by the Son-Narmada Geofracture in the south, the Great Boundary Fault in the west, the Monghyr-Saharsa Ridge in the east, and the Bundelkhand Massif and Indo-Gangetic Plains in the north. Bundelkhand Massif divides this basin into two parts – the Son Valley on the southeastern side and the Chambal Valley where exposures occur from Agra (Uttar Pradesh) to Chittorgarh (Rajasthan). The Vindhyan strata are unmetamorphosed and mostly undeformed. However, there exist large scale folds in the Son valley and several post depositional faults in Rajasthan. The Upper Vindhyans in the Bundi–Sapotra-Karauli sector in Rajasthan are significantly affected by reactivations of the Great Boundary Fault and hence stratigraphic correlation is tricky. Evidence for any global or local event found in these formations must therefore be linked carefully with those reported elsewhere in the basin

          The Vindhyan strata define a broad, regional syncline trending ENE–WSW. The axis of the syncline is slightly curved and plunges gently towards west. The average dip of the southern limb is greater than that of the northern limb rendering the axial plane to dip southerly.

                        Basin Evolution:.
          The Cuddapah were succeeded by the rocks of the Vindhyan system after a time interval marked by the earth movement and erosion. The Vindhyan Basin was formed as a result of a large crustal down warp in the northern part of the Indian Platform, after the Delhi orogeny. The Cuddapahs were then folded and metamorphosed to some extent through the intensity of the forces at play was feebler than that at the close of the Dharwarian era. In Rajasthan however, the post-Delhi movements were of great intensity along the Aravalli axis and were followed by the granitic intrusions on a large scale. The initial transgression of the sea from the north is inferred to have taken place in the eastern part of the basin over the Bijawars. The shallow sea appears to have established lagoonal conditions near the coastal part during the subsequent regressive phase. Initially, the Son-Narmada Lineament was dormant, but at the onset of Vindhyan sedimentation later, the fault system along this down warp became active with the formation of the southern limit of Vindhyan deposition.

          The structure of the Vindhyan area is that of a basin, the sandstones forming plateau. Over the greater part of the area the beds are nearly horizontal, but they show evidence of disturbance near the northwest and southeast margins. In the Dhar forest and near Jhalrapatan, the Vindhyan  are folded and show steep dips.

          After the deposition of Kajrahat Limestone, the Son-Narmada Lineament again became active resulting in emission of volcanic material, which was deposited as the Jardepahar Porcellanite. In the subsequent regression, the shore line shifted towards northwest. The Fawn Limestone was deposited over the shelf in a tidal flat environment. This was followed by shallowing of the basin as is evident from the overlying Glauconitic Sandstone. The fresh marine transgression resulted in the deposition of marine shales followed by Rohtas Limestone.

         

          The Vindhyan sandstones throughout their thickness give evidence of shallow-water deposition in their oft-recurring ripple-marked and sun-cracked surfaces, and in their conspicuous current-bending or diagonal lamination, characters which point to the shallow agitated water of the coast, and the constantly changing velocity and direction of its currents.

The epeirogenic upheaval which lifted up the Vindhyan deposits from the floor of the sea to form a continental land-area was the last serious earth movement recorded in the history of the Peninsula, no other disturbance of a similar nature having ever affected its stability as a land-mass during the long series of geological ages that we have yet to review. The Peninsula has remained an impassive solid block of the lithosphere, unsusceptible to any folding or placations, and only affected at its fringes by slight movements of secular upheaval and depression

                              

                         Evidence of Life

          Except for a few obscure traces of animal and vegetable life occasionally discernible in the Vindhyan system, this vast pile of sandstones, shales and limestone is characterized by an almost total absence of recognizable organic remains. The only animal fossils that have been hitherto discovered in these rocks are a few discs, the remains of some chitinous organisms, embedded in the lower part of the Bhander series. But the specimens are too imperfectly preserved, and of uncertain zoological affinities, to permit of their specific determination. Fucoid markings, belonging to indistinguishable thallophytic plants, are usually seen on the ripple-marked and sun-cracked surfaces of sandstones and shales.

 In recent years the Suket shales of Rampura in central India have yielded small discoid impression considered to be organic remains and assigned to the genus fermoria related to the primitive brachiopod acrothele. There is however, a difference of opinion as to whether they are inorganic or organic.

          Coaly matters with streaks of vitrain have been reported from the lower vindhyans at various times. Fox reported vitrain from the limestones at Japla several years ago. Fragments and streaks of coaly material are known to occur in the Bijaigarh shales.

                Age of Vindhyan Supergroup

With regard to the Vindhyan system there exists some difference of opinion. From its lithological agreement with the fossiliferous Cambrian of the Salt-Range, Mr. Vredenburg of the Indian Geological Survey has considered them to be Cambrian in age. Sir T. H. Holland, however, regards all the unfossiliferous peninsular formations resting above the Archaean-Dharwar complex as pre-Cambrian, occupying much the same position as the Torridon sandstone of Scotland, overlying the Lewisian gneisses, and groups them in his Purana group. The Purana group of this includes the unmetamorphosed but more or less disturbed and folded rock-system that intervenes between the crystalline Archaean and the fossiliferous younger systems of the Peninsula. The Purana group thus forms a sort of transition between the foliated and the highly metamorphosed Dharwar and Archaean gneisses and the fossiliferous Paleozoic strata. They include the major part of what, in the early days of Indian geology, was called the Transition System. Age control on Vindhyan sedimentation is still the subject of considerable controversy as are the ages of the other Purana basins. In general, the age of sedimentation for the Lower Vindhyan is far better constrained than that of the Upper Vindhyan. The lower Vindhyan units are collectively designated as Semri Group. The Semri Group is made up of five alternating formations of shale and carbonates with areas of sandstones and volcanic clastic units. The Semri sediments unconformably overlie basement rock of either the 1854 ± 7 Ma Hindoli Group or the 2492 ± 10 Ma Bundelkhand granites or terminal Archaean Berach Granite (2.5 Ba). Ages from the Semri Series include a Pb–Pb isochron from the lower Kajrahat Limestone of 1721 ± 90 Ma; U–Pb zircon ages from the Porcellanites and Rampur shale ranging from 1630.7 ± 4 to 1599 ± 8 Ma. The Rohtas limestone in the upper part of the Lower Vindhyan has Pb–Pb ages of 1599 and 1601 Ma. Most scientists agree with a Mesoproterozoic age for Lower Vindhyan sedimentation (_1750–1500 Ma).

          The Semri Series is separated from the Upper Vindhyan by a basin wide unconformity between the Rohtas limestone and the overlaying Kaimur Group. The Kaimur rocks are intruded by the 1073 ± 13.7 Ma Majhgawan kimberlite, that cross-cuts both the Semri Series and Kaimur Groups and is currently exposed in the Kaimur Group (Baghain sandstone). Up-section is the Rewa Group, a series of shale and sandstone formations that, in areas, contain kimberlite derived diamondiferous conglomerates. A thin shale unit marks the transition into the Bhander Group. The Bhander Group contains the only major carbonate unit in the upper Vindhyan system, a unit containing stromatolites, ooids, and micritic layers known as the Bhander or Lakheri limestone. The overlying lower Bhander sandstone marks a transition into shallower marine, sometimes fluvial, sandstone typical of the Bhander Group. The Sirbu shale overlies the lower Bhander sandstone, and is in turn overlain by the upper Bhander sandstone. Age control on the Upper Vindhyan sequences is more problematic. The best age estimates come from the Majhgawan kimberlite, that intrudes the Lower Vindhyan and into the Baghain sandstone (Kaimur Group – Upper Vindhyan) near Panna. Possible Ediacaran fossils have been described in the Lakheri and Sirbu formations of the Bhander Group and could indicate an age <635 Ma for the Bhander.

      However, a Mesoproterozoic age for these discoidal organisms would lead to questions regarding the depth of metazoan evolution. In an attempt to further constrain the age of the uppermost Vindhyan, Malone et al. (2008) conducted a study of detrital zircon populations from the Bhander and Rewa Groups in the Rajasthan sector along with samples from the Lower Marwar Supergroup in Rajasthan. In that study, note that the youngest population of zircons from the Upper Bhander is older than 1000 Ma. That observation, coupled with the similarity in paleomagnetic directions from the Upper Vindhyan sedimentary sequence and Majhgawan kimberlite led to conclude that Upper Vindhyan sedimentation was completed by _1000 Ma. This rather surprising conclusion is consistent with recent data from another of the Purana basins to the south.

                       

                             Stratigraphy:.

          The entire Vindhyan succession, maximum thickness estimated to be around 3 km, and comprising mainly sandstone, shale and limestone is assigned as the Vindhyan Supergroup. The Vindhyan have been separated into 2 division which, though of very unequal proportions, have been determined by important physical considerations. They are separable as much by an unconformable junction between the two divisions as by the sharp lithological contrast between them. The lower division consists of one group and upper divisions have three groups. Thus the Supergroup is divisible into four groups:

1. Semri Group,
2. Kaimur Group,
3. Rewa Group and
4. Bhander Group,

          From bottom to top. Each group is again subdivided into several formations. The Semri Group in the Son valley rests unconformably on a variety of pre-Vindhyan rocks such as granites and metamorphics. In the Bundelkhand area, the group overlies the Bundelkand Granite Gneisses and Bijawar Group of metamorphics, whereas in the southern Son valley, Mahakoshal is the basement in most places; however, in some localities (e.g., Deoland, M.P.) the basement is granite. The Semri succession of the Bundelkhand area has two detached outcrops around Chitrakut and Bijawar respectively, and is only a few tens of meters thick.

The Vindhyan Supergroup is composed mostly of low dipping formations of sandstone, shale and carbonate, with a few conglomerate and volcanoclastic beds, separated by a major regional and several local unconformities. The regional unconformity occurs at the base of the Kaimur Group and divides the sequence into two units: the Lower Vindhyans (Semri Group) and the Upper Vindhyans (Kaimur, Rewa and Bhander Groups). The outcrop pattern of the Supergroup resembles a simple saucer shaped syncline. It is generally believed that the Vindhyan basin was a vast intra-cratonic basin formed in response to intraplate stresses.
          The different depositional systems recognized in the Vindhyan succession are: alluvial fan, fan delta, braid delta, braidplain, eolian sand sheet, tidal flat (carbonate as well as siliciclastic), shoreface (tide and storm dominated), storm dominated shelf, homoclinal carbonate ramp, distally steepened carbonate ramp and epeiric peritidal flat (siliciclastic). The overall paleocurrent directions of the depositional systems in the Son valley are northerly suggesting a source towards south.

 The unconformities divide the Vindhyan succession of Son valley into five sequences. Each sequence consists of several systems tracts representing different paleogeographic settings and marking paleogeographic shifts. The different strata of the Vindhyan succession show evidences of soft-sediment deformation suggesting synsedimentary tectonic activity. The progressive and successive angular unconformities suggest that the deformation pattern shown by the Vindhyan strata is a reflection of synsedimentary tectonic activity. It is postulated that the individual sequences of the Vindhyan succession are related to discrete episodes of tectonism that induced the subsidence necessary for accumulation of sediments and resulted into deformation of the older strata. Angular unconformities resulted due to erosion of the uplifted crest of the anticlines on which the next sequence of strata was deposited with an angular discordance.

There are sediment packages at the northern part of the Vindhyan basin developed from a northerly source and thus representing different tracts and sequences from those of the southern part. These packages are represented intermittently in the succession and have been interpreted as representing periods of uplift of the Bundelkhand Granite and subsequent erosion in the north. The paleocurrents revealed by the Vindhyan strata are typically northerly suggesting that the evolving Satpura orogeny served as the source for the Vindhyan sediments. However, the source for the clastics occurring within the Semri and the lower parts of the Kaimur and Rewa Groups in the Bundelkhand sector was perhaps the Bundelkhand Granite Gneiss, Bijawar and Gwalior Group of rocks as manifested by the southerly paleocurrent.
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LOWER VINDHYANS

Semri Series

          From Sasaram westwards to the watershed between the sone and the Narmada. The lower Vindhyan are exposed underneath the prominent scarp of the Kaimur quartzite’s for a length of some 400 km. here the maximum width of this series is about 20 km, but farther east it narrows down to a width of less than 3 km. this is the type area of the Semri Series.

          The lowermost beds of this series in the Sone valley, called the basal stage, are 600 m thick and consist of basal conglomerates and the Kajrakhat limestone beds. They are followed by shales, sandstones and tuffs which have been silicified and converted to porcellanites(the porcellanite stage)

Attaining a thickness of about 100m. The Khenjua Stage overlying is about 180 m thick. Above this comes Rohtas stage, 120 to 210 m thick, consisting of alternating beds of limestone and shales.

          The Semri series is intruded by dykes of basalt in few places in the valley. The basic rocks contain the augite and rhombic pyroxene, zoned plagioclase, illemenite and pyrite, with patches of micrographic quartz ad feldspar and occasional glass.

          The Semri Series is found also in the Karauli area of Rajasthan where the Aravalli phyllites are overlain by sandstone and conglomerate and these in turn by the Triohan Limestone.

  

THE SEMRI SERIES AND ITS EQUIVALENTS :-

	Sone Valley	Karauli	Chitor
Rohtas Stage	Alternating limestones and shales	Tirohan breccia Tirohan limestone	Suket shales Nimbahera limestone
Khieinjua Stage	Glauconite beds Fawn limestone Olive shales	Glauconite-bearing beds	Nimbahera shales
Porcellanite Stage	Porcellanite and silicified rocks	Sandstones and conglomerates	Grits and conglomerates
Basal Stage	Kajrahat limesone Basal conglomerate

 

UPPER VINDHYAN Succession

Bhander Series	Upper Bhander sandstones
	Sirbu shales
	Lower Bhander sandstone
	Bhander limestone(Nagode)
	Ganurgarh shales
Diamond-bearing Conglomerate
Rewa Series	Upper Rewa sandstone
	Jhiri shales
	Lower Rewa sandstone
	Panna shales
Diamond-bearing Conglomerate
Kaimur Series	Upper	Dhandraul quartzite
		Scarp sandstone and conglomerate
	Lower	Bijaigarh shales
		Upper quartzites and sandstones
		Susnai breccia
		Lower quartzites and shales

UPPER VINDHYANS

         

          The upper Vindhyans are exposed in the great Vindhyan basin. They consist largely of sandstones and shales with subordinate limestones, the sandstones forming extensive plateau around and to the south of the Bundelkhand granite mass. The subdivisions are shown in the table..

KAIMUR SERIES

          In the Sone Valley the Kaimur Series contains two bands of quartzite in the lower division which may be gritty and even conglomerate and show current bedding. The lower quartzite passes upward into flagstones and shales showing ripple-marks and sun cracks, and these into thin bedded micaceous and carbonaceous shales with sideritic bands. Interbedded with these are banded and jointed porcellanites, fragments of which are found in the next succeeding gritty bed called as the Susnai Breccia, which is of epi-clastic origin.

          The Susnai Breccia is overlain by the upper silicified quartzite with marked current bedding and ripple marks, which forms a conspicuous scarp, 15m high, in the Sone valley. Thes pass upwards into the Bijaigarh shales which are carbonaceous, pyritiferous and micaceous and generally bleached or yellow in colour.

          The Upper Kaimurs, overlying the Bijaigarh shales, consist if greenish flagstones and sandy silt stones which crop out along the kaimur scarp and are exemplified in the Mangesar hill. Above these are the Dhandraul Quartzites which are white to purplish in colour. The upper kaimurs have a thickness varying from 150 to 300 m.

          In Bundelkhand, the Kaimurs show a basal conglomerate containing pebbles of jasper, the main formation being a fine grained quartzite of grayish or brownish colour with conspicuous current bedding.

REWA SERIES

          The Kaimurs are succeeded by the Rewa Series composed of somewhat coarser sand stones than those of the Kaimurs, and current-bedded flagstones. The two series are separated by a zone of diamond bearing conglomerate. The divisions recognized in central India in the Rewa and the overlying Bhander series are shown in the table given above.

          The existence, in Bundelkhand, of the lower Rewa sandstone and Panna shales ids questioned by Vredenburg who states that the diamond bearing conglomerate occurs at the base of the Jhiri shales. In Gwalior, however, there are two shales bands separated by sandstone, between the Kaimurs and the main rewa sandstone.

BHANDER SERIES

          The uppermost division of the Vindhyans is the Bhander series, which is separated from the Rewa series by a horizon of diamond-bearing conglomerate. The Bhander sandstones are fine grained and soft, usually of a red colour with white specks. When light coloured they often show red colour streaks. They are fairly thick bedded and yielded large blocks which are used in building. The upper Bhander frequently show ripple marks. The Bhander limestone is of variable thickness and quality, passing from a good limestone to calcareous shale. The Bhander contains veins and beds of gypsum.

          The Sirbu shales of this series bear a good resemblance to the salt pseudomorph shale of the salt range and contain salt pseudomorphs a certain places.

          The scarp near Sonia in rajasthan exposes 0m of basal conglomerates and grits, succeeded by 8m of purple shales, 30m of variegated shales and sandstones and 30m of pink to brown sandstones. The section is overlain by the Bilara Formation consisting of light to dark grey cherty limestone which is 40m thick. The whole section is equivalent of a part of the Cambrian of the Salt Range and of the upper part of the Upper Vindhyan. The structure of the Vindhyan area is that of a basin, the sandstones forming plateau. Over the greater part of the area the beds are nearly horizontal, but they show evidence of disturbance near the northwest and southeast margins. In the Dhar forest and near Jhalrapatan, the Vindhyan are folded and show steep dips.

          The Vindhyans probably continue to the north under the gangetic alluvium of Bihar, perhaps buckled down to form the basement of the Himalayan fore deep. It is not known whether they have equivalents in some of the unfossiliferous rocks of the sub Himalayan region in U.P. and Nepal, which are now found broken up and thrust southward over he Permo-Carbonifeous and Tertiary rocks.

ECONOMIC IMPORTANCE

DIAMOND

For many centuries past, diamonds have been won form the Vindhyan and Kurnool and in the conglomerates separating the different group of the Upper Vindhyans in Panna, Central India, as also just outside the Cuddapah basin in Sambhalpur in Orissa.  The original source of the diamond which came to be deposited I the conglomerates are apparently pipe like intrusions of ultrabasic rocks like one at the Majhgawan near Panna. Several; such pipes may be present in the Panna area and in the Cuddapah basin.

The wajra karur region in Anantpur is still reputed to yield occasional diamond to diligent searchers who visit and comb the area after the rains each year. Geophysical work by G.S.I. located a diamond bearing pipe here in 1962. Several more must be present in this region.

PYRITE

The Bijaigarh Shales of the lower Kaimurs contain a bed, 1 to 1.3m thick of sedimentary pyrite of fine grain. The bed has been found to crop out at two places about 5km apart, on the Kaimur scarp near Amjhor a few miles south of Dehri-Sone and at Kasisiya Koh about 14km from Amjhor. The material is of good quality, containing around 45% sulphur, without any arsenic. A part of this deposit has been proved to contain several million tons.

COAL

Streaks of coaly matter were found by Fox in 1928 in the Bijaigarh Shales on the Kaimur scarp near the Japla limestone quarries. Some years later the Kajrahat limestone was to found to contain some saucer-shaped carbonaceous discs with coaly matter in the centre. Since then the beds of coal and carbonaceous shales have been discovered in other places. The better part of the coal gave on analysis 9-13 percent volatile matter and 24-30 percent fixed carbon, the rest being ash. The material shows spores and cuticles and tracheids of vascular plants. These occurrences are of interest in proving that plant remains exist both in the Semris and Kaimurs though no workable coal; seam may be expected.

LIMESTONE

The limestone of the Vindhyans are among the most important sources of raw materials for the lime and cement industry in India like in the Sone Valley in Bihar and U.P., in Rewa, in Jabalpur, in Gunturana in the Bhima Valley in Hyderabad.

The flagstones quarried near jammalmadgu, yerrugntla, betamcherla and other place popularly known in madras as ‘Cuddapah slabs’ are widely used as paving stones, fence stones, steps and table tops.

BUILDING AND DECORATIVE STONES

Some of the limestones of the lower Vindhyan and lower Bhander stages show spherulitc structures, the concentric shells of which display different colours. Beautiful stone if these kinds are found at Sabalgarh near Gwalior have been used in the inlaid decorations in the buildings of Agra.

The Vindhyan sandstones, especially of the Bhander series, constitute a great storehouse of the excellent sandstones which, because of their regular bedding, uniform grain, colours, easy workability and durability have been very extensively used all over Northern India as building stone.

GLASS SAND

Some Vindhyan sandstones near Allahabad, U.P. on disintegrating by weathering yield good sands which are being used for the manufacture of glass. The deposits occupy an area of over 100 sq. miles and extend into the neighboring states. If specially purified, some of these sands can be used also for optical glass manufacture.

EQUIVALENTS OF THE VINDHYAN SYSTEM

KURNOOL SYSTEM

The Cuddapah basin in the Andhra Pradesh contains two areas of younger rocks resting unconformably on the Cuddapahs – one in the Kundair Valley stretching up to the Krishna, and the other in the Palnad tract. This younger group of rocks, constituting the Kurnool System, is about 400m thick in the west but much thicker in the Palnad area and has been affected by disturbances in the eastern part but by forces which were less intense than those which acted on the Cuddapahs. This system is regarded as the equivalent of the lower Vindhyan.

The Kurnool has been divided into fur series, composed mainly of limestones with subordinate shales and sandstones.

THE KURNOOL SYSTEM

Series	Stages
Kundair	Nandyal Shales
	Koilkuntla Limestones
Paniam	Pinnacled Quartzites
	Plateau Quartzites
Jammalamadugu	Auk Shales
	Narji Limestones
Banganapalali	Banganapalli Sandstones

JEYPORE – BASTAR – RAIPUR

          There are several exposures of sedimentary rocks of Purana aspect in the region between the Godavari and Mahanadi valleys. These are apparently the remnants of a large and continuous spread isolated by erosion. The sediments are to have been derived from the southward and west. They were originally regarded as mainly the equivalents of the Cuddapahs but now they were correlated with the Kurnools, particularly as lithological similarities are good.

Bastar – the succession in this area has been named the Indravati Series by V.B.S.Dutt who has divided them as below.

Jagadalpur Stage (=Nandyal) (200-250m)	Upper shale, with quartzite intercalations.
	Purple shales and limestones
	Purple, fine grained dolomite
	Basal purple shales
Kanger Stage (=Koilkuntla) Upto 140m	Grey laminated shales
Tiratgarh Stage (=paniam) 50-110m	Purple shale with layers of platy quartzite
	Basal quartzite, conglomerate, Sub-arkose

Chhattisgarh – the rocks in the large exposure of the Raipur-Durg-Bilaspur area were originally divided into a lower Chanderpur Stage and an upper Raipur Stage.

SUCCESSION IN RAIPUR SERIES

Stage	Description
Raipur(450m)	Greenish grey, shaly limestone fine grained in the lower part and purple in the upper
Khairagarh(variable)	Current beded sub-arkose with 10-15% feldspar. Outcrop is accurate.
Gunderdehi(180m)	Splinter calcareous shale, with thin sandstone laminae near the top
Charmuria(300m)	Grey, fine grained, thin bedded limestones; become shaly towards the top. The Mahanadi follows the junction of this with the lower sandstone between dhamtari and mohdi
Chandarpur(300m)	Medium feldspathic sandstone or sub-arkos with conglomerate at the base

BHIMA SERIES

Named after the Bhīma River, a tributary of the Krishna, the series is developed in the Gulberga and Bijaipur districts. It occupies an area of 4200sq km, lying over the Archaean formations.

          The lithology, horizontal disposition and unmetamorphosed nature of the Bhima, point to their being the equivalents of Kurnool Formation. The rocks are divided into a lower and an upper series by W. King and R.B. Foote, but recent work by C. Mahadeven shows that a three fold division is preferable.

Upper(100m)	Black, blue, buff and purple coloured shales with local sandstones at the bottom and flaggy limestone at the top
Middle(165m)	Creamy, grey, bluish, and buff limestones and flaggy limestones.
Lower(110m)	Sandstones and purple shales. The bottom beds are conglomerate while the topmost beds are often calcareous.

SULLAVAI SERIES

          There is a group of rocks called the Sullavai Series in the Godavari valley, consisting of slates, quartzites, sandstones and conglomerates. They are well exposed near Sullavai and in the Dewalmari hills, where the quartzites recall the appearance of the pinnacled quartzite’s of the Kurnools. They have a thickness of 360-480m, and overlie the Pakhals unconformably in the synclinal folds of the latter.

 MILLANI SERIES

          The Lower Vindhyan rocks of Western Rajputana deserve special notice. They show there a very much altered facies, being composed of a group of rhyolitic lavas with abundant pyroclastic material, resting unconformably on the Aravalli, The Malani schists. This volcanic series known as the Malani series,from the State of that name (near Jodhpur ia Marwar). The Malani rhyolites cover many thousands of square miles around Jodhpur. They are partly glassy, much devitrified, amygdaloidal lavas largely interstratified with tuff and volcanic breccia. The lavas vary in acidity from rhyolites to quartzandesites. In the majority of cases they have undergone such an amount of devitrification that they appear almost as felsite, the glassy ground-mass having completely disappeared. An outcrop of the Malani series composed of felsitic rhyolites and tuff occurs, remote from the Aravallis, in the plains of Northern India, in the Sangla hill in the Punjab, a small highly eroded outlier of the Aravalli chain.

          Connected with these lava-flows, as their subterranean plutonic roots or magma-reservoirs which supplied the materials of the eruptions, are bosses of granite, laid bare by denudation, in some parts of Rajputana. Two varieties of granite are recognized in them—one, hornblende-biotite-granite {Jalor granite), and the other, hornblende-granite [Siwana granite). The latter shows distinctly intrusive relations to both the Malani series and the Aravalli schists ; it rises to a height of nearly 3000 feet above sea-level.