A History of Agriculture in India v1.c7.8

v1.c7.8

The middle and the upper Cretaceous were periods of great marine transgression. A palaeogeographic map of the Gondwanaland during the middle and upper Cretaceous is shown in Fig. 1. While the uppermost Cretaceous beds were being deposited along the south-eastern coast of India, stupendous volcanic outbursts overwhelmed a vast area, comprising the present Gujarat, Maharashtra and Madhya Pradesh, the like of which are not known anywhere else in the world (Fig. 2). Several hundred thousand square kilometres were flooded by the outpourings of extremely mobile lava from fissures. The hills formed by the lava are in some places over 1,200 metres high and are known as the Deccan traps. They are peculiar in appearance, being frequently flat on the top and with steep sides so that they appear from a distance as gigantic steps and, therefore, are called traps, a name derived from the Swedish word, meaning a stair or step. The individual lava flows that make up the Deccan trap plateau vary greatly from a fraction of a metre to 36 metres in thickness. During the periods of quiescence that intervened between successive outbursts, lakes were formed, probably because the lava streams had blocked the rivers. In these lakes, fishes, frogs, small crustaceans, etc., flourished, whereas the flowering plants, including palms and other vegetation, grew on the adjoining land. In the marshy areas dinosaurs thrived, and on the beaches tortoises crawled. As time went on, the lakes were filled up with sediments washed down from the land. Then came another period of volcanic outbursts and lava flows when lakes were formed again, and plants and animals reappeared. Thus, volcanism and sedimentation were repeated many times until a great thickness of lavas and interbedded sediments, called the Intertrappeans, had accumulated, containing the petrified remains of organisms which bear [Figure: Cratonic areas Freshwater facies Mixed facies Marine facies 1,000 — 1 5,000 — 5 Isopach form lines in feet 10,000 — 10 1 foot = 0.3048 metre]