Arkell.1956.Jurassic..

CHAPTER 14
THE INDIAN PENINSULA, WITH CUTCH
AND THE SALT RANGE
THE FORELAND OF THE INDIAN* PENINSULA
Like the African shield and its extension the Arabo-Nubian massif,
peninsular India was dry land throughout the Jurassic. Its ancient
surface of pre-Cambrian and early Palaeozoic rocks had been denuded
and faulted in Upper Palaeozoic and Triassic times and has remained above
sea ever since. The Jurassic sea lay to the north-west, west and east and
there were minor marginal floodings in the Lower Cretaceous along the
present east coast and in the Upper Cretaceous there and on the NW.
Finally, at the end of the Cretaceous (probably Danian) came fissureeruptions
in the NW., producing vast lava flows, the Deccan traps (fig. 54).
Although the lavas have been exposed to denudation since the beginning
of the Eocene, they still cover about 200,000 square miles and near Bombay
they reach a thickness of about 2 miles. The similarity to the Abyssinian
lavas is striking, in both geological setting and age.
Nearly a third of the ancient surface of the peninsula is covered by the
Deccan traps, which conceal any Jurassic marginal sediments that may have
been deposited there and have survived Cretaceous erosion. To the north
an even larger area is buried below the Ganges alluvium, which is known
to extend at least 1000 ft. below sea-level, but has never been bottomed.
Although Archaean rocks come to the surface to the north of it at many
points along the Himalayan chain almost continuously, they have there
been upheaved and eroded. It is possible that Jurassic and other Mesozoic
rocks exist under the alluvium of the Ganges, where there has been subsidence
and protective deposition at least since Tertiary times, but for
reasons mentioned in the next chapter any such occurrence is unlikely.
THE GONDWANA SYSTEM
There are preserved considerable sedimentary records of the fluviatile
erosion undergone by the peninsula from Upper Palaeozoic times to the
outpouring of the Deccan traps. In trough faults at scattered points,
mainly in the north but intermittently as far south as Madras and Ceylon,
are thousands of feet of clastic sediments of continental facies, grouped
together as the Gondwana system. The beds, largely sandstones, were
laid down in deltas and lake basins in areas of subsidence. The commonest
fossils are plants, locally aggregated into coal seams; they supply nearly
* As always in this book, established English geographical terms are used without
political implications and may often cut across national frontiers.
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