Short notes on The Gondwana System

The Gondwana system is regarded as the last massive formation of the stratified sedimentary rocks in the trough-basins of the Peninsula which were formed during the middle Carboniferous period. Huge quantity of alluvial matter was deposited in these basins over a long period of time starting from the UpperCarboniferous to the Jurassic periods.

The basins behaved as small geosynclincs yielding place to enormous thickness of rocks. Under favourable conditions of climate luxuriant growth of vegetation took place which was also buried under the debris during the Hcrcenian movement giving rise to coal seams. This system is designated as the Gondwana system after the ancient Gond kingdom in Madhya Pradesh where these rocks were first studied. Such formations also occur in Malaysia, Australia, S. Africa, South America and Anatarcatica to which the Indian landmass was previously tied up prior to the rupture of the super continent of the Gondwanaland.

The Gondwana system which took a long period of formation from Upper Carboniferous to the Jurassic periods indicates climatic changes. The system rests over a glacial boulder bed indicating a cold climate. This is followed by a hot and moist climate during which luxuriant vegetation thrived to form beds of coal. This flora is called glossopteris flora. This is followed by cold climate giving birth to greenish sandstones of the Panchet series. Then comes a period of hot and dry climate during which red sandstones and shales were formed. This is succeeded by warm and moist climatic condition producing Pillophyllum flora and forming new coal- seams.

Distribution

The outcrops of the Gondwana rocks are found in four main areas of the country: (i) the Damodar valley region of Chotanagpur, (ii) the Mahanadi valley, (iii) the Godavari, Venganga and Wardha valleys, and (iv) Kachchh, Kathiawar, west­ern Rajasthan. Kashmir and Sikkim (Fig. 2.3.A).

Classification

The Gondwana system has a two-way classi­fication: vertical and horizontal. O. Fiest-mantal and Vredenberg on lithological basis, has divided the Gondwana system into three parts, the Lower, Middle and Upper corresponding to the Permian, Triassic and Jurassic of Europe respectively. Of these the lower and upper contain seams of coal and the middle devoid of it. C.S. Fox, M.S. Krishnan and R.C. Mehdiratta have classified the system on palaeobotanical basis into two parts, the lower con­taining glossopteris flora and the upper ptilophyllum flora. Horizontally the system is classified under two broad groups: (i) the Peninsular Gondwana which includes (a) the Damodar valley region, (b) the Mahadnadi valley region, and (c) the basin of the Godavari river; and (ii) the Extra-Peninsular Gondwana. Table 2. VI. Presents a vertical classifica­tion of the Gondwana system, its prominent series and stages.