GENERAL

GEOLOGY

[The section on Geology has been contributed by Shri. S. S. Deshmukh Geologist (Jr.) of the Geological Survey of India, Maharashtra Circle.]

The earliest reference to the geology of the area is by Hughes (18771 who manned the Penganga beds in the southern part of the Yeotmal district. Later, King (1881) and Heron (1949) also carried out some mapping of Penganga beds. In recent years the Geological Survey of India have carried out systematic mapping and mineral investigations in Yeotmal district and the geology of Yeotmal district as given in the following pages is mainly based upon these investigations. Detailed investigations of a few mineral deposits, particularly those of limestones have also been carried out by the Directorate of Mining and Geology, Government of Maharashtra.

Description of Rock Unit.

The stratigraphic succession of the rock formations met within the district is given below in the chronological sequence:-

Penganga Formation.

The Penganga beds are represented by a sequence of limestones and red shales, which are exposed in Penganga and Khuni river section, in the southern part of the district. In this part they form a part of enormous inlier in Deccan basalts, which extends southwards in the Adilabad district of Andhra Pradesh. The Penganga formation consists of a lower limestone member and an upper' shaly member. The limestone is prominently exposed in the western and south-western parts along Penganga river while the shale member is more dominant in the southeastern and eastern parts along Penganga and Khuni rivers. A prominent outcrop of greenish white dolomitic limestone, conformably overlying the red shales between Piwardol (19° 53': 78° 37') and Matharjun (19° 54': 78° 40') about 5 km. northeast of Bori (19° 52': 78° 40') is considered to be probably forming the uppermost horizon of this formation.

The Penganga formation generally exhibits low dips of 5° to 10° towards north-east and are relatively undisturbed. They are overlain by Deccan basalt flows on all sides except towards south.

The controversy, whether Penganga formation is equivalent to Vindhyans or to Cuddapahs, is not yet resolved. Hughes (1877) equates them with Vindhyans, whereas King (1881) considers them of Cuddapah age. Heron found them continuous with the lower Vindhyans of the Central Provinces (M. P.) to the north and to the south they are continuous with the Pakhals, which however are more folded formations.

Vindhyan Group.

Vindhyans comprise mainly of dolomites and limestones. These occur as three major inliers in the north-eastern part of the district in Wani tahsil (55 L/16). The northern most inlier is around Kagaon (20° 15': 78° 50') along the Wardha river valley. The central inlier extends south-eastwards from Dol Dongargaon (20° 10': 78° 53') in the north-west to Wanjri (20° 06': 78° 56') in the south-east. The third inlier occurs around Dahigaon (20° 03': 78° 52'), Wirkund (20° 02': 78° 52') and Maregaon (20° 00': 78° 53'). The northern inlier is surrounded by Deccan basalts and alluvium. Gondwana rocks border the central inlier along northwest-southeast boundary. In the north it is surrounded by basalts whereas in the western part alluvium and Lametas are seen bordering the inlier.

Outcrops of well bedded, chocolate coloured Vindhyan limestones are also observed in the Khuni river section (55 L/12) near Kelapur (20° 00': 78° 32') overlain by flows of Deccan basalt.

Dolomites.-The dolomites constitute the major rock unit of Vindhyan rocks. These are intimately interbedded with limestones and thin partings of shale. The dolomites are compact grey to blackish grey in colour, with fine sacharoidal texture and elephant back weathering on the surface.

Limestones.-Limestones, intercalated with dolomites, occur as thin bands, throughout the Vindhyan inliers. They are light buff, dark grey, and blackish in colour, fine grained, dense, hard and compact in nature. These limestones are traversed by thin calcite and silica veins in most of the areas mentioned earlier.

Shales.-These are exceedingly fine grained, greenish black coloured rocks and occur as thin partings in dolomite and limestones. These are well exposed in limestone bands south-west of Wanjri (20°08': 78°54'), Lakhapur and Sonapur (20°07':78°54') areas.

The Vindhyan rocks exhibit NW-SE regional trend with south westerly dips ranging from 10° to 70°. A fault trending in NW-SE direction between Manki (20°01':78°56') and Gowrla (20°07':78°52') has been inferred in 1965 from the repetition of Vindhyan rocks along the dip direction.

Gondwanas.

The Gondwana sediments rest unconformably on the Vindhyan rocks and are referable to Talchir, Barakar and Kamthi formations of lower Gondwana group. The rocks forming the Gondwana group are of fluviatile or lacustrine origin and were laid down in a series of large river or lake basins which sank along trough faults amidst the ancient rocks. Gondwana rocks are of special importance because of the presence of coal seams in them. Due to faulting and sinking in older rocks, the Gondwana rocks with their rich coal seams were preserved. The basins in which the Gondwana sediments have been deposited, have faulted margins roughly trending in NW-SE direction.

Talchir Series.-The Talchir formation comprises of boulder bed at the bottom followed by shales and sandstones successively. Boulder bed rests directly upon the Vindhyan rocks and indicate a great time gap.

Boulder Bed.-The boulder bed is composed of pebbles and cobbles of limestones, shales, pink granites, quartzites, chert and jasper cemented together in a soft friable quartzose matrix. The size of these varies from coarse sand to boulders of about 60 cm. across. Generally the boulders are grooved or striated indicating evidence of glaciation.

Occurrence of boulder bed bellow the Talchir shales is restricted to a few localities in Yeotmal district and is not of widespread nature as seen towards east, in Chanda district. A good exposure of Talchir conglomerate is seen along the bank of Wardha river to the west of Belsani (19°59':79°07'), along the border of Yeotmal and Chanda districts. The striated boulders are exposed to the north of Wirai (19°53':79°8'50") and south of Jugad (19°53'40":79°8'45"). The striated surface is generally covered by a thin calcerous layer.

Shales.-The Talchir shales are greenish grey to olive green, fine grained rocks which break along the joint planes into thin minute, angular or pencil like fragments, exhibiting a characteristic feature called needle shales. The shales are traversed by innumerable, closely spaced joints and are essentially horizontally bedded or with low dips at places. The Talchir shales are exposed around Kalman, north of Rajur railway station and Chichala (20°08':78°51').

Barakars.-The Barakar formation in Yeotmal district, is represented by sandstones. The sandstones rest on Talchir rocks and occupy a thin strip, about 11 km. long and 1 km. wide, between Kalman (20°06': 78°56') and Kinhal (20°10': 78°50^'). The exposures of Barakar sandstones are also met with about 0.5 km. east and north of Rajur railway station.

Talchir rocks appear to have undergone some erosion before the deposition of Barakar sediments, as seen near Kalman and Rajur. On the basis of this observation an erosional unconformity was interpreted in 1965 between Talchirs and Barakars. Another mapping which was carried out in 1947 in the adjacent areas, did not however indicate any erosional unconformity between these two formations.

The Barakar sandstones are fawn to yellowish grey or white, medium grained, loose textured, with subangular to rounded grains of quartz in a felspathic matrix. They are generally horizontally bedded, but at places display low westerly or south westerly dips. Barakar sandstones are coal bearing. In the coal bearing areas, the sandstones are followed by coal seams and clays in succession, with coarse grained brownish white; sand stone at the top.

The important coal bearing field in Barakar sandstones is Rajur Wani area, where a narrow coal field extending from Pisgaon (20°09':78°48') Rajur, Parsora to Wani Ganeshpur has been known since 1871.

Kamthi Formation.

The rocks of Kamthi formation rest unconformably over Barakars. It is at times difficult to separate these from lithologically similar upper Gondwana formations. According to some investigation in 1947 the lower Kamthis in Yeotmal district may be equivalent in age to the rocks of Ranigung and the Iron-Stone shales. Kamthi formation is extensively developed in the district covering large stretches of several square kilo-metres. Good outcrops of Kamthis are observed over a length of 24 km. from Mandar (20°00':78^o58') to Pijgaon (20°09: 78°50'). They also occur to the north-east of Kegaon (20°15':78^o50'); Bhalewadi (20°08':78^o49') east of Naigaon Khurd, north of Manki (20°01:78°56') and west of Palsoni (20°04':78°54').

Kamthis consist of sandstones and shales. The occurrence of clays and conglomerates from this formation was reported in 1947 in the eastern part of Yeotmal district (56 M/1).

Sandstones.-Sandstones are fawn to yellowish, dark brown and brick red in colour. They are medium to coarse grained in texture with subangular to subrounded grains of smoky and milky quartz. Sandstones are generally highly ferruginous, some being calcerous also. In some cases angular pieces of shales ranging from 1 cm. to 9 cm. in length and 1 cm. to 3 cm. in width are noticed. Towards the base, the sandstones become coarse grained and ferruginous. White ferruginous sandstones, very similar to those of Barakars, occur in the Malhargarh hills (56 M/1).

Some clays and shales are interstratified with these sandstones in the upper parts. Good exposures of clays are noticed to the north of Sirpur (19°57'45":79°00'15") and north-east' of Malhargarh hill. Conglomerates (56 M/1) form a very small part of the series and generally occur higher up in the series along with the compact, blotchy coloured sandstone, in the Malhargarh hill.

Shales.-Shales occur as intercalations in the sandstones and are purple red to brick red in colour. They are soft or compact, fine grained and frequently iron stained. They vary in thickness from a few cms. to a metre. Good intercalations of shales in sandstones are seen north of Wagdhara (20°02':78°58^;)_!, north-west of Chikhalgaon (20°04':78°56'), Palsoni (20°04'; 78°54') north-east of Sursi (20°00': 78°45') etc.

Kamthis in general have NW-SE strike with low south westerly dips. South west of Sirpur (19°57'45":79°00'15") along the boundary with Vindhyan sediments, the dip increases to 25°" or more. This evidence of disturbance is considered to be indicative of a fault along the boundary. Kamthi rocks exhibit higher dips than the underlying Barakars at Rajur and Wun, suggesting an erosional break in the continuity of the sedimentation. The Vindhyan rocks abut against Kamthi sandstones in the nallah west of Palsoni and north-west of Manki and exhibit variable attitudes and brecciation along the contact, perhaps indicating a boundary fault.

Some fossil plant remains, generally badly preserved, are reported from this formation near village Kawadsi (79°04': 19°55'40"). Some of the important plant fossils identified are Clossopteris indica and Phyllotheca sp. an equisetalean. Shells of Estheria minuta var. Brodiena, a phyllopod crustacean, are also found in the same area. This genus is known to occur mostly in shore facies.

Lameta Formation.

The Lameta rocks, which are infra-trappean in position, unconformably overlie the Kamthi sediments and comprise a sequence of green to brick red clays with intercalated horizons of limestones and sandstones. The clays are usually sandy with sporadic pieces of calcite and chert and on weathering disintegrates into coarse rubble and concretions of calcareous matter. A structure simulating box work is observed in these clays due to inter-section of thin ramifying calcereous veins.

Exposures of lameta clays are seen in nallah sections north and south of Nimbhala (20°06':78°53'), near Gowrala (20°07': 78°52') and east and west of Wanjri (20°06': 78°56'). Exposures of Lameta limestones overlying the clays are seen south of Dapori (20°15':78°48^'). A few exposures of Lameta sandstones are observed south of Wadgaon (20°07':78°58') and north-east of Nandepara (20^o09':78°56').

This formation is characterised by the presence of a rich assemblage of fossil remains. Lamellibranch shells of sp. Cardite beaumonti are seen well preserved in brick red clays about 2.5 km. north of Kumbha (20°11':78°50'). In the limestone beds south of Dapori, fossils of fresh water mollusca Physa prinsepii are seen well preserved along with other fossil shells which are not well preserved and cannot be easily identified.

Deccan Basalts.

Close of Mesozoic era was marked by the outpouring of enormous lava flows which spread over vast areas in western, central and southern India. These lava flows which are basic in composition are called Deccan basalts or Deccan traps, the latter name being due to their step-like or terraced appearance in outcrops. It is considered that the trap started erupting in late Cretaceous and continued up to early Eocene.

Deccan basalts form a major geological formation in the district and cover nearly about ⅔rd of the area, almost entirely occupying the northern, western and south-western parts of the district. The lava flows are generally horizontally disposed, overlying most of the older formations. They have unconformable relationship with the Vindhyans, Gondwanas, Penganga formation and Lameta beds.

The Deccan basalts form a thick sequence of lava pile consisting of several flows, varying in thickness from 7 m to 32 m and are separated by intertrappean beds or red clays (red bole beds?). The flows are generally composed of dark grey, dense, fine to medium grained prophyritic basalt with phenocrysts of plagioclase felspar. The flows generally become vesicular towards the top, the vesicles and cavities being filled with secondary silica, quartz, calcite, zeolites, etc. Some of the vesicles are partially filled or lined with dark greenish, black, glassy and chloritic material.

The flows are traversed by well spaced horizontal and vertical joints, some exhibiting well developed columnar jointing. Some flows are characterised by well developed spheroidal weathering, giving rise to large spheroidal boulders.

Intertrappeans.

Intertrappean beds, separating the lava flows, serve as good marker horizons for differentiating the different flows. They are generally made up of dark green, compact chert with abundant jasper, impure, earthy, silicified limestones. They generally occur as discontinuous outcrops of limited lateral extent and range in thickness from less than a metre to about 5 m. Some of the areas where good exposures of intertrappean beds are noticed are near Gargoti (20°09':78°45'), north of Narsala (20°07':78°46'), north-west of Bhand Umbri (19°58':78°26'), hill faces around Pahapal (20°00r:78°30'), near Kahelgaon (20°05': 78°39'), Medni (20°03': 78°42') and Pimpri (20°15':78°44').

The intertrappean beds are characterised by rich assemblage of fresh water mollusca. The exposures in areas mentioned above are all fossil bearing. The most characteristic fossil is gastropod shell Physa Prinsepii (bullinus). The other fossils present are Lymnacea, Paludine, Viviparus Normalis Hisl., Natica Stodaardi hisl. and Unio Deccanesis sow etc.

Some basalt flows are separated by red laminated, plastic clays in parts of Wani and Kelapur tahsils. These clays are at times associated with cherty, calcareous intertrappean beds.

A greyish white to brownish white, weathered sandstone occurs at a number of places, which was mapped as Lameta beds by Hughes, since he considered it as infra-trappean in position. Later in 1967 it was, however, considered as an intertrappean bed occurring between the two basalt flows, north of Sagola (19°53':78°22') where large blocks of undisturbed sandstone are seen overlying the basalt flow east of Bori (19°52': 78°35').

Isolated outcrops of compact green rock, intertrappean in position, 3 km. south-west of Buranda (20°06':78°44') and 1 km. north-west of Khadki (20°06': 78°45'), is composed of aggregates of secondary silica, glass and zeolites with shards or greenish glassy material. This was considered to be an ash bed when, an investigation was carried out in 1965.

Alluvium and Soil.

These form recent. and sub-recent deposits in the district. Recent alluvium is mainly confined to the flood plains of Penganga, Wardha and Khuni rivers. The soils can be classified as red soils, brownish sandy soils and black cotton soils. The red soils and the brownish sandy soils are derived from the disintegration of the older Vindhyan and Gondwana sediments. The Talchirs and Barakars generally form poor soils and support sparse vegetation.

The most important soil in the district, supporting the agriculture, is the black cotton soil or Regur. This is clayey or loamy soil, black in colour, and contains high alumina, lime and magnesia with a variable amount of potash, low nitrogen and phosphorous. It is generally porous and swells considerably on addition of water and dries up with conspicuous cracks on loosing the moisture.

Recent Conglomerates.

An occurrence of thin beds of recent conglomerates along the Wardha river near Thorma Nangaon (20°09':78°59'), Jolha (20°07':78°59') etc. was reported in 1965. The rocks are made up of ill-sorted pebbles of quartz, flint, felspar, jasper, and fragments of types set in a greyish black cement.

Economic Minerals.

Limestone.

The limestone deposits in Yeotmal district occupy large areas in Wani and Kelapur tahsils. The deposits occur in a number of belts, striking NW-SE. The limestone is suitable for cement manufacture and can also be used as flux in the metallurgical industry. The total reserves of all grades of limestone and dolomites are given below with the description of each deposit, along with the average chemical composition. The figures are based on the investigations carried out by the Directorate of Mining and Geology, Government of Maharashtra.

Rajur Belt.

The deposit lies 3.2.km. east of Rajur railway station and covers the villages of Kalmna, Wanjri, Majra, Magla, Pohana, Nandepara, Sonapur, Lakhapur, Wanoja, Akapur, Rhiski reserve forest area etc. The general strike of the limestone belt is NW-SE with dips up to 30° towards south-west.

The deposit contains medium grained, white dolomite, grey dolomite limestone, whitish to greyish coloured siliceous limestone and dark grey fine grained limestone. The prospecting operations of the limestone belt near Rajur have proved 31.5 million tonnes of workable reserve of limestone which can be used as flux in foundries as also 50 million tonnes of flux grade dolomite. The details of location and quality of the deposit in the Rajur area are given below:

Wanjri Block.-This block covers an area, 1,976 m. long and 456 m. wide. The limestone has an average thickness of 14 m., the total available reserves being 21.5 million tonnes of the following average chemical composition:-

CaO -47.18 % SiO₂ -5.44 % and MgO -3.16 %.

Majra-Pohana Block.-This block is 2,280 m. long and 213 m. wide, average thickness of limestone being 6.4 m. The reserves of limestone have been estimated at 5.5 million tonnes averaging 50.87 per cent CaO, 4.91 per cent SiO₂ and 1.23 per cent MgO.

Sonapur-Lakhapur Block.-This block has a length of 1,976 m. and width of 213 m., with 6.4 m. of average thickness of limestone. The total reserves are estimated to be about 4.6 million tonnes with the following range of composition:-

CaO -45.5 to 48.72 % Si0₂-1.50 to 4.26 % and MgO-1.33 to 5.39 %.

Flux grade Dolomite.

Dol-Lakhapur Block.-The block is 4,560 m. long and 912 m. wide, with average 14.6 m. thick dolomite. The reserves have been estimated at 36 million tonnes, having the following average composition:

MgO -20.05 % and SiO₂ -2.71 %.

Pohna-Majra Block.-The length of the block is 1,216 m. and width is 608 m. with 10.6 m. average thickness of dolomite. The reserves are estimated at 14 million tonnes averaging 19.69 per cent MgO and 3.58 per cent SiO₂.

Limestone Deposits of Mukutban Area.

The limestone deposits of Mukutban (19° 45' to 19° 47' 30": 78° 49' 45") are located south-west of Wani at a distance of nearly 35 km. Prospecting operations have been carried out in an area of about 4.87 sq. km. south of Mukutban in which 15.68 million tonnes of flux grade limestone averaging in composition 43.53 per cent CaO, 7.02 per cent SiO₂, 3.34 per cent MgO and 2.27 per cent R₂O₃, have been proved. The deposit also contains an estimated reserves of 150 million tonnes of dolomite averaging 34.87 per cent CaO, 12.79 per cent MgO, 6.56 per cent SiO₂ and 2.19 per cent R₂O₃. In addition to this, another 10 million tonnes of flux grade limestone and 24 million tonnes of dolomitic limestone are expected from the areas which are not as yet fully prospected.

Sindola Chanaka and Paramdoh belt.

The limestone deposits in this belt occur near the village Khandala, Kurli, Sindola, Chanaka (19° 50' 50": 79° 4' 20") and Paramdoh (19° 50' 50": 79° 05') in the southern part of Wani tahsil, about 22 km. from Wani town. The limestones form a strip of low lying ridges and knolls over a length of about 12 km. The width of the belt is about 200 m. The general strike of the limestone exposures is north-west, south-east with dips varying from 60° to 90°, in the major part of the belt starting from Khandala to Chanaka; while in the remaining part the dips vary from 10° to 30°.

Three distinct types of limestone are seen in this deposit viz., (a) greyish black limestone, (b) greenish to pinkish limestone and (c) shaly limestone. Generally the limestone is fine grained, massive and breaks with a conchoidal fracture. Some veins of barytes occurring in the limestone are also reported in some bore holes in this area.

The deposit has been proved up to a depth of about 45 m. The reserves of cement grade limestone indicated in this area are of the order of 76 million tonnes out of which 35.7 million tonnes have been proved. The limestone shows the following range in chemical composition:

1.43 to 2.21 per cent MgO, 9.85 to 10.20 per cent SiO₂ and 45.82 to 47.88 per cent CaO.

Chanaka-Bhimkund Belt.

This is an extensive, low magnesia limestone belt, in the vicinity of Chanaka in the Kelapur tahsil. The limestone belt extends mostly through the forest area from Chanaka village in a westerly direction up to Bhimkund village and beyond over a length of 17 km. The width of the belt varies from 1.6 km. to 3.2 km. the average width being 2.4 km. The deposit contains predominantly two varieties of limestones viz., cream coloured and dark grey coloured. The deposit is devoid of dolomite and dolomitic limestone intercalations. The limestone deposit forms the lowermost unit of Penganga formation.

The Directorate of Mining and Geology, Government of Maharashtra have carried out detailed prospecting of the deposit and have given the following reserves and grade of the limestone.

Proved reserves.

The reserves of cement grade limestone in the Chanaka area are estimated to be of the order of 31.9 million tonnes with a composition range of CaO -43 to 44 %, M_gO-1.09 to 1.35 %, SiO₂-14.8 to 14.9%, and R₂O₃- 3 to 4%. Reserves of inferior grade limestone of Chanaka area are estimated at 57.47 million tonnes with composition variation in the range of CaO 40 to 43 %, MgO 1.5 to 2 % SiO₂ 16 to 19% and  R₂O₃ 3 to 4 %.

Indicated reserves.

Indicated reserves of cement grade limestone of Chanaka-Gubri area are estimated at 25.20 million tonnes with composition range of 43 to 44 % CaO, 1.6 to 1.9 per cent MgO, and 14 to 15 % SiO₂. Reserves of inferior grade limestone in this area are 39.6 million tonnes with composition range of 39 to 40 per cent CaO, 1.5 to 1.7 per cent MgO and 15 to 19 per cent SiO₂.

Inferred reserves.

In the entire Chanaka-Bhimkund belt, excluding the areas prospected, as indicated above, the reserves of limestone up to a depth of 20 m. have been estimated to be of the order of 1,300 million tonnes.

Coal.

The only occurrence of coal in Yeotmal district is in Rajura-Wani area forming part of the Wardha Valley coal field. A narrow coal field extending from Pisgaon, Rajura, Parsora to Wani-Ganeshpur has been known since 1871. An old colliery of Rajura, (C.R.) has been closed down since last 15 years. The thickness of coal seam varies from 8.2 m. to 9.1 m. at Pisgaon, while at Rajura the thickness varies from 5.4 m. to 9.1 m. The proximate analysis of coal at Rajura is given below:-

The probable reserves of coal in the tract beyond Pisgaon up to Warora in 31 sq. km. area, are estimated at 240 million tonnes.

Groundwater.

Groundwater conditions in the district vary with the geological formations present in the different areas. The district receives an annual rainfall of 150 cm., most of which precipitates during the short monsoon period.

Large area of the district is covered by Deccan basalt flows in which water level varies from 3 m. to 12 m. below the ground level in summer months. Parts of the basalt flows with closely spaced joints and vesicular weathered tops of the flows form good acquifers and wells dug in such zones yield copious supply of water. The intertrappean beds and red clay horizons between the basalt flows also help locally in yielding good supply of water. The Lameta beds below the traps form good acquifer horizons.

The Penganga shales and limestones do not form good acquifer horizons. The highly jointed parts in the shales help percolation and storage of water, but the water from these horizons is generally brackish in nature. Groundwater conditions are in general similar in Vindhyan rocks.

The best groundwater conditions prevail in areas covered by Kamthi sandstones. Barakar sandstones also form good acquifer horizons. The level of water table appreciably goes down in summer in most of the wells, many of them becoming completely dry.

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