a diverse and complex geology needs to be studied very
systematically. Stratigraphy covers study of rocks of a
region and tracing down the geological history. Rocks as
they occur now in the field have gone through some of
the events like deposition, compaction, deformation,
metamorphism and erosion. Some may experience many
phases of deformation and metamorphism. Most of these
events depend on the tectonic activities this part of
the earth's crust has witnessed over the ages.
erosion and later phases of tectonism tend to erase the
past, we can still get some evidence of the past
tectonic activities through study of rocks. From
whatever idea we have, we can build tectonic framework
of India and study each unit separately. The Himalayan
mountain-building is relatively recent tectonic activity
that India has experienced and because of this event we
have broad three tectonic units which coincide with the
three physiographic divisions - the Peninsula,
the Extra Peninsula and the Indo-Gangetic
Peninsula because of its uniqueness has been treated
separately as Himalayan Geology. The Indo-Gangetic
Alluvial Plains are mostly covered with recently
deposited alluvium carried by two major river systems --
the Ganga and the Indus.
Peninsula exhibits a geology that has not experienced
any major deformation since the beginning of the
Phanerozoic eon. The earliest rocks have been severely
deformed during the Archaean and Proterozoic times.
Eventually when they got stabilized, they formed
basement for other rocks to be laid over them. We will
study these earliest rocks under the heading Precambrian
Basement. Precambrian Basement rocks are
widespread in southern and south-eastern India and also
in Aravalli Range of mountains.
there were phases of deformation in some parts during
the Proterozoic, in some other places there had been
quiet depositional activities during this time and these
rocks still lie nearly flat covering large areas. We
group such successions under Proterozoic Cover.
Large basins with Proterozoic Cover rocks are exposed in
north-central India and parts of Andhra Pradesh,
Karnataka and Madhya Pradesh.
only occasional rock-building activities in Indian
Peninsula after the close of the Precambrian. The
central part remained above sea-level. Therefore, marine
depositional activities are normally not to be expected
there anymore. The Palaeozoic of Indian Peninsula
therefore is represented by river deposits laid down in
wide grabens. The deposition by ancient river systems
continued until the end of the Mesozoic. These rocks are
now exposed as Gondwana Supergroup in various
modern river systems such as Damodar, Godavari, Mahanadi,
Wardha and also in Satpura Hills of Madhya Pradesh.
the river deposits, the Mesozoic also witnessed a unique
event in Indian history. Close to the end of Mesozoic,
vast areas of western India were covered by lava flows
identified as Deccan flood basalt. Similar lava flows
were laid down in eastern India in Rajmahal Hills.
Sedimentary deposition was confined to coastal areas
which were occasionally flooded by the trangressing sea.
Mesozoic and Cenozoic marine formations are found
in coastal areas such as Kutch, Saurashtra, Jaisalmer,
Assam-Arakan, Cauvery Basin.