physiographic division of north east india
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The North East India region is physiographically not a homogenous unit and the present coniguration of this region has taken shape during geologically recent time. But the ultimate result of vaious geological events took place through the geological past. North East India consists of very ancient Archaean and Shillong series rocks exposed in several parts of the Garo, Khasi, Jaintia and Karbi Hills. These rocks are similar to rocks exposed in the rest of the peninsular in Bengal and Bihar of which this was a part at one geological time. All these old rocks form the basement for very much younger Tertiary sediments in upper Assam.
A large part of this region was a landmass upto the formation of the Himalayas about 2,000 million years ago. Then the easten part of the Khasi Hills, the Jaintia Hills and the Westen pat of the Karbi Hills became a basin of sedimentation in which sandstones and shales of the Shillong series were deposited. Due to tectonic reasons these were later uplifted and became a landmass.
recent scholars have divided North East India into five physiographic units on the basis of lithology, age and mode of evolution. The physiographic divisions of the region are:
(1) Karbi-Meghalaya Plateau
(2) North-Eastem frontier mountain ranges or Arunachal Himalaya
(3) Brahamputra Valley
(4) Barak Plain or Cachar Plain
(5) South-Eastem Hill Ranges