Geography of India (Geological Structure of India)

Geological Structure is the  study the formation of bedding system of rock structures and how these structures affect tectonic movement.

The Archean Era

The earliest phase of tectonic movement was marked by the cooling and solidification of the upper earth’s crust surface in the Archaean era (before 2.5 billion years).

This is represented by the exposure of gneisses and granites especially on the Peninsula.

The term Archaean was given by J.D. Dana in 1872 to designate the geological formations which are older than the Cambrian period.

The Geological structure of Archaean Era is divided into two divisions as:   1. Archaean   2. Proterozoic

The Archaean rocks were structured during the very early period when there was no signs life on the earth.

They are mostly igneous origin. They also consist of metamorphosed granitic and basaltic rocks together. They consists of granitic rocks, gneisses, schist, etc,.

The basic structure of life was originated on this planet nearly 2500 million years. From unicellular organisms like bacteria into multicellular one like Algae all were evolved during this time.

 The Archaean structure encompasses the southern and eastern India and parts of Assam, Madhya Pradesh, Rajasthan and Jharkhand.

These contain the following metamorphic rock formations: In the chronological order, from the oldest to youngest are

a) Unclassified crystalline rocks  

b) Charnockites 

c) Khondalites and 

d) Dharwar System of rocks 

The layers of Schistose rocks of the Dharwar system contain the oldest known rocks in India, existing in Karnataka state. The Dharwar system is classified in lower, middle and upper Dharwar.

The Lower Dharwar contains Rhyolites, felsites, Schists and gneisses. The Middle Dharwar contains the Granite Basic and ultrabasic intrusive igneous rocks, volcanic products. The Upper Dharwar contains cherts, silts, clay, conglomerates and quartzites.

This period also have some unclassified crystalline rocks. These unclassified crystalline rocks are concentrated over Tamil Nadu, parts of Kerala, Karnataka, Assam, Meghalaya, Sikkim, parts of Andhra Pradesh, Odisha, Jharkhand, parts of Madhya Pradesh and Rajasthan.

The Proterozic Era

The era of Proterozoic geological formations of India range from 2500 to 570 million years. The Proterozoic formations, , are also called as Purana Group of formations in India.

These are separated from the older Archaean formations by the different unconformity known as Eparchaean unconformity. They are further subdivided (from older to younger)as:

a) Old Granites 

b) Cuddapah system 

c) Delhi system 

d) Vindhyan System 

e) Younger Granites and the

f) Malani Volcanics.

The Aravalli Range is the remnant of an early Proterozoic mountain called the Aravali-Delhi orogen. It extends nearly 500 kilometres from its northern end as isolated hills and rocky ridges into the Haryana region and end near Delhi.

The erosion of the mountains, and further deformated structure of the Dharwar group (Bijawars) marks the second phase. The volcanic activities are associated with this second phase.

The Proterozoic rocks are located in the Cuddapah region of Andhra Pradesh. After a long period of time, the Cuddapah system of rocks includiing slates, quartzite and limestones were concentrated over the Deccan peninsula.

These are found in the upper Mahanadi valley, in the Aravallis mainly in Delhi system and in the Son valley. The Cuddapah System includes Quartzites, Limestones, Sandstones and slates without any fossils. The thickness of the Cuddapah formation is approx. 6100 m.

It is concentrated in the Kurnool district of Andhra Pradesh, southern parts of Chhattisgarh, Singhbhum district of Jharkhand, Kalahandi and Keonjhar district of Orissa and in Aravalli ranges extending from Delhi to Idar in Gujarat.

The economic importance of this is presence of mineral resources of the Cuddapah system include iron, manganese, copper, cobalt, etc,.

The Vindhyan System of India, derives its name from the famous Vindhyan mountains. It consists of the ancient sedimentary rocks. The Vindhyan system consists of Sandstones,  shales and limestones rocks. It is divided into two divisions as

a) Lower Vindhyan (which is 1300 and 1100 million years older) and

b) Upper Vindhyan (which is 1000 and 600 million years older).

The Vindhyan rocks are devoid of any metalliferous mineral deposits. But they are famous for good building stones, and ornamental stones. They contain very valuable glass making sands and gemstones.

Gwaliar System and Bijawar series are the two parts where Cuddapah system is distributed in north India. The Delhi system covers Aravalli mountains to Ajmer and Mewar, to Idar and Palanpur in the south.

These structures can be seen from Mewar and Jodhpur regions. It consists of gneisses, Schists, Phyllites, Quartzites and Arkose-grits. In the Extra Peninsular region, the parts of Cuddapahs and Delhi systems can be seen in parts of the Himalayan region.

The Palaeozoic formations of India originated in the period from 570 to 245 million years. These are called as Dravidian systems, in India. The Palaeozoic era of geological formations include the systems of the following geological ages:

1) The Cambrian System

2) The Silurian System 

3) The Devonian System

4)The Lower Carboniferous System

5) The Lower Gondwana system 

6) The Upper Carboniferous & The Permian systems.

The Mesozoic Era

Mesozoic geological formations were started in the period between 245 million years and 66 million years. It encompasses the formations of the Triassic, Jurassic and Cretaceous ages.

The Triassic System is the earliest in the chronology in this system in the Mesozoic era. This period has shown a very rich and varied fauna and flora.

The Cenozoic Era

The Cenozoic era of geological formations in India belong to the period from 66 million years to the present day. The formations belonging to this age are:

a) The Tertiary Systems 

b) The Eocene System 

c) The Oligocene System 

d) The Lower and the Middle Miocene

e) The Pliocene System and 

f) The Pleistocene System. 

 In the Tertiary period, in India, the Himalayan movements was started. The volcanism associated with the Deccan Traps has continued. The rocks of this era have various valuable resources such as- petroleum and coal.