GENERAL

[The section on Geology is contributed by Shri D. Subramanian, Geologist (Jr.) of the Geological Survey of India, Maharashtra Circle.]

GEOLOGY.

Physiographically, the district is divided into two divisions; while the northern part of the district is occupied by clusters of hills forming the water shed of the area, the southern part presents a gently undulating terrain intersected by numerous streams with occasional hills. The Wardha, the Wunna and the Pothra rivers with their tributaries drain the district.

The earliest reference to the trap rocks of Hinganghat area, was made by W. T. Blanford (1868). T. W. Hughes (1877) has mapped parts of Arvi, Wardha and Hinganghat tahsils; and D. Bhattacharjee (1923) has mapped portions of Arvi tahsil. In recent years A. K. R. Hemmady (1964-65), A. R. Patil (1964-65) and G. Suryanarayana (1963-64) have summarised the geology of portions of Hinganghat tahsil of Wardha district.

The geological formations met within the district, are arranged in descending order of antiquity as under:

Infra-trappeans (Lametas) :

Sedimentary rocks referable to the Lametas occurring below the traps are called infra-trappeans. These beds were laid down under fluviatile to estuarine environments in this area and are considered to be of Middle Cretaceous age. A prominent horizon of the Infra-trappean is exposed in the Pothra nala at Khambad (20° 26': 78° 59'). A few detached out-crops of similar rocks are also noticed elsewhere in the Wardha valley. They comprise red and grey clays, limestones and sandstones, which usually grade into each other. The sandstones are composed of angular to sub-rounded grains of quartz, orthoclase, micro-cline and plagioclase felspars cemented together by an aphanitic or cryptocrystalline brownish calcareous and ferruginous material. The limestones are composed of cryptocrystalline aggregate of carbonates, minor quartz, potash felspar and patches of chert.

Fragmentary fossil remains of mollusca, fishes and dinosaurian reptiles have been reported from other areas from rocks of similar age, and hence the possibility of coming across similar fossils from this area cannot be ruled out.

Deccan Traps :

The Deccan Traps are so designated on account of their step like or terraced appearance and their extensive distribution in South India (Deccan) besides Central and Western India. This district is mostly covered by Deccan Traps; on the south the boundary of Wardha and Chanda districts almost marks the termination of this extensive rocks and on the east, north and west, it extends beyond the limits of the district.

The rocks are basaltic in composition; in all seven flows have so far been recognised within a vertical column of about 120 metres from Girar area of Hinganghat tahsil. The individual flows vary in thickness from 10 to 30 metres. The rocks are well jointed. Besides vertical and inclined joints, sheet joints are also common. The traps show the typical exfoliation or spheroidal weathering. The traps are usually hard, compact, greenish grey to black in colour. Thus fine to medium grained traps can be grouped into two varieties non-vesicular and vesicular.

The vesicular variety carried lot of cavities which are often filled with secondary minerals such as quartz, chalcedony, calcite, agate and zeolites. This type is called as amygdaloidal basalt and is often soft and chocolate brown in colour. At times, the basalt exhibits a porphyritic texture with the development of large lath shaped crystals of plagioclase felspar set in a comparatively fine grained matrix. The rock is composed of pyroxene (augite), plagioclase felspar (Labrodorite), and interstitial glass. At places, the glass is devitrified and altered to pale green mineral, palagonite. Magnetite and ilmentite are amongst the common accessory minerals.

Inter-trappeans:

The fluviatile and lacustrine beds deposited during the time interval between two successive lava flows are called inter-trappeans. They generally consist of red and green clays, green chert and buff coloured limestone and vary in thickness between 0.5 and 3 metres. They are fossiliferous at times. The occurrence of Inter-trappean beds are reported from Hewa (20°40': 79°03'), Girar (20°39'; 79°09'), Kora (20°31': 79°06'), Dasoda (20°32': 79°10'), Khursipar (20°42': 79°04'), Selu (20°20': 78°47') and Daroda (20°28': 78°46') of Hinganghat tahsil, but they are unfossiliferous. The only fossiliferous locality in the area occur south of Sindhi Vihira (21°03': 78°33') of Arvi tahsil.

Laterite:

A few small and isolated patches of laterite overlying the traps are seen on plateau tops near Nagjhari, Dhanoli, Garamsur and Nawargaon in Arvi tahsil.

Alluvium:

Four important alluvial tracts covering the following villages are reported from this district:—

(1) Pulgaon (20°44': 78°19'), Saongi (20°35': 78°16'), Sirpur (20°32': 78°23'), Andori (20°32': 78°29'), Bhidi (20°34': 78°24'), and Saiod Fakir (20°34': 78°20').

(2) Talegaon (20°31': 78°30'):—West of Khamgaon-Pipalgaon and Kolhapur (20°34': 78°28').

(3) Sonegaon (20°41': 78°26'), Giroli (20°33': 78°35'), Takli (20°26': 78°40'), Alipur (20°33': 78°42'), Waigaon (20°38': 78°36'), Salod (20°42': 78°33'), Nimgaon (20°43': 78°29'), and Deoli (20°39': 78°29').

(4) South of Hinganghat near Pipalgaon (20°32': 78°52').

The first two patches occur on the right bank of the Wardha river, the third on the banks of the Asoda nala and the fourth south of Hinganghat near Pipalgaon (20°32': 78°52'). The thickness of alluvium in the Pulgaon (20°43': 78°19') area is estimated at about 18 metres.

Soil :

Black cotton soil, generally formed by the weathering of the Deccan Traps occurs as thin veneer over the country. It is fertile and rich in plant nutrients such as lime, iron and alkalies.

Economic Geology :

No minerals of economic value are reported from this district except building stones. The basalts quarried near Umri, Segaon and Wasi (Hinganghat tahsil) are commonly used as dimension block in building construction and as road metal. Calcite associated with inter-trappean beds and kankar in the black cotton soil are burnt for lime locally and is used for white washing purpose.

Groundwater:

The joints and fissures present in the massive traps aid movement and percolation of groundwater; but by and large the traps are generally found unsuitable for ground water storage except where there is either a zone of weathered, or/and highly vesicular trap or horizon of inter-trappean beds, which may serve as a source of ground water. Generally water in the area is tapped from wells, which yield very limited quantities and most of them are reported to go dry during the summer months. The chemical analysis of water samples collected from a few wells and the Wardha river, near Pulgaon show that the water is mildly alkaline and very low in chlorite content and is potable. The chemical analysis is given in the following statement.

CHEMICAL ANALYSIS OF WATER SAMPLES FROM PULGAON AREA

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