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Indian Rock System

• The Indian Rock System involves the study of the geological structure and time scale of rocks in India. Geological structure refers to the arrangement and deposition of rocks in the earth's crust due to earth movements, or the absence of such movements. This can also include the morphological features of the rocks, such as the Gondwana structure. On the other hand, the geological time scale is a chronological dating system that categorizes various geological formations and life according to their time and place of origin, evolution, and extinction. Giovanni Ardunia first developed this concept in 1760, and the standard Geological Time Scale was established during the International Geological Congress held in Italy in 1881. T.S. Holland later advocated for the Indian Geological Time Scale.
• To understand the geological history of India, one must examine the geological structure and rock systems in relation to their geographical locations and historical context. India's geological formations can be grouped into two main physiographic divisions: Peninsular India and Extra Peninsular India. By studying these divisions, researchers can gain insights into the geological processes and events that have shaped India's landscape over millions of years.
• Major events in the geological history of India:
  • Peninsular India was a part of the old landmass since the formation of the Earth’s Crust
  • The upheaval of the Himalayas in the tertiary period.
  • Aggradational formation of the Indo-Gangetic plain during the Pleistocene period. It continues till today through sedimentation in the floodplains of the rivers and the lower part of the Gangetic plain.

Geological time scale

Based on this complex and varied geological history, the Geological Survey of India has classified rock systems of the country into 4 major divisions:

• The Archaean Rock System
• The Purana Rock System
• The Dravidian Rock System
• The Aryan Rock System

Archaean Rock System (Pre-Cambrian Rocks)

• The Archaean Rock System, also known as Pre-Cambrian Rocks, represents the earliest phase of tectonic evolution in Earth's history. This period, which occurred before 2.5 billion years ago during the Precambrian Era, is characterized by the cooling and solidification of the upper crust of the Earth's surface. The Archaean rocks, primarily made up of gneisses and granites, can be found predominantly in the Indian Peninsula and form the core of the Indian Craton, which is a block of the Indian Subcontinent that was once part of Gondwanaland.
• The term "Archaean" was first introduced by J.D. Dana in 1782 and refers to the oldest rocks found in the Earth's crust. The Archaean group of rocks is composed of two main systems: the Achaean System, which consists of granites and gneisses, and the Dharwar System, which includes the first sedimentary rocks.
• Gneiss is a type of rock whose mineral composition can range from granite to gabbro, while schists are mostly crystalline rocks that can include minerals such as mica, talc, hornblende, and chlorite. Together, these ancient rock formations provide valuable insight into the geological processes that took place during the early stages of the Earth's development.

Archaean Gneisses and Schists

• Archaean Gneisses and Schists are some of the oldest rocks on Earth, dating back to the Pre-Cambrian era, approximately 4 billion years ago. These rocks were formed as a result of molten magma solidifying, as the Earth's surface was extremely hot during that time.
• These ancient rocks are also known as the "Basement Complex," as they serve as the foundation for newer layers of rock that have formed over time. They are characterized by their lack of fossils, which is why they are sometimes referred to as Azoic or unfossiliferous rocks.
• Archaean Gneisses and Schists have a foliated structure, meaning they are composed of thin, sheet-like layers. Their thoroughly crystalline nature is due to their volcanic origins, and they can be classified as plutonic intrusions, which are volcanic rocks found deep within the Earth's crust.

Dharwar System

• The Dharwar System is a geological formation that dates back to a period ranging from 4 billion to 1 billion years ago. These rocks are primarily composed of highly metamorphosed sedimentary rocks, which were formed through the transformation of sediments from Archaean gneisses and schists.
• As the oldest known metamorphosed rocks, the Dharwar System is predominantly found in the Dharwar district of Karnataka, India. These rocks hold significant economic value due to the presence of various valuable minerals such as high-grade iron ore, manganese, copper, lead, and gold.

Purana Rock System

• The Purana rock system is a combined term for the Cuddapah and Vindhyan rock systems. These systems were formed through the erosion and deposition of the older Archean and Dharwar rocks, which occurred between 1,400 to 600 million years ago. 
• The Purana rock system primarily consists of sedimentary rocks.

Cuddapah System

• The Cuddapah System is named after the Cuddapah district in Andhra Pradesh, India, where there is a significant presence of Cuddapah rock outcrops. These rocks were formed through the deposition of sedimentary rocks such as sandstone, limestone, and clay in synclinal folds, which are the spaces between two mountain ranges. The most prominent examples of these outcrops can be observed in the Cuddapah district itself.
• These rocks are known to contain various valuable ores, including those of iron, manganese, copper, cobalt, and nickel. Additionally, the Cuddapah System is home to extensive deposits of limestone suitable for cement production.

Vindhyan System (1300-600 million years)

• This system derives its name from the great Vindhyan mountains.
• The system comprises of ancient sedimentary rocks (4000 m thick) superimposed on the Archaean base.
• Mostly Unfossiliferous rocks and a large area of this belt is covered by the Deccan trap.
• The Vindhayan system have diamond-bearing regions from which Panna and Golconda diamonds have been mined.
• It is devoid of metalliferous minerals but provides large quantities of durable stones, ornamental stones, limestone, pure glass making sand, etc.

Dravidian Rock System (Palaeozoic)

• The Dravidian Rock System, also known as the Paleozoic formation in India, dates back to the Paleozoic era, approximately 600-300 million years ago. This geological formation is also referred to as the Carboniferous Rock System due to the high-quality coal deposits formed during this time worldwide.
• These rock formations are predominantly found in the extra-peninsular regions of the Himalayas and the Gangetic plain, with limited presence in the Peninsular shield, such as in Umaria in Rewa. Significant areas with Dravidian rocks include Pir Panjal, Handwara, Lider valley, and Anantnag in Kashmir, as well as Spiti, Kangra, Shimla in Himachal Pradesh, and Garhwal and Kumaon in Uttarakhand.
• The Dravidian rocks are composed of various materials, such as shales, sandstones, clays, quartzites, slates, salts, talc, dolomite, and marble. This geological period marks the fragmentation of the supercontinent Pangaea and the formation of the Tethys Sea. It also represents the emergence of life on Earth, as evidenced by the abundance of fossils found in these rock formations. These fossils indicate marine conditions during the Paleozoic era in India.
• Although the Dravidian period initiated the formation of high-quality Carboniferous coal, these deposits are not found extensively in India. The Dravidian Rock System encompasses several geological ages, including the Cambrian, Ordovician, Silurian, Devonian (known for fossils and corals), and Carboniferous (comprising Lower and Middle Carboniferous) Systems.

Carboniferous rocks (350 million years)

• The Carboniferous rocks (350 million years) comprise mainly of limestone, shale, and quartzite.
• Mount Everest is composed of Upper Carboniferous limestones.
• Coal formation started in the Carboniferous age.
• Carboniferous in geology means coal-bearing. [most of the coal found in India is not of the Carboniferous period; High-quality coal of Great Lakes Region-USA, U.K and Ruhr region is Carboniferous coal].

Aryan Rock System

• The beginning of the Upper Carboniferous period is known as the Aryan Group, has come to the threshold of the last, longest, and most eventful era, extending from Upper Carboniferous to the Holocene period.
• The Aryan Group of Rock Formation classified in the following Group:
  • Upper Paleozoic Era—Upper Primary Epoch– Upper Carboniferous & Permian Period formation
  • Mesozoic Era —Secondary Epoch -Triassic, Jurassic & Cretaceous period Formation(Gondwana Rock system, Deccan trap, Jurassic system)
  • Cenozoic Era —Tertiary Epoch – Paleocene, Eocene, Oligocene-Miocene & Pliocene Period
  • Neozoic Era — Quaternary Epoch– Pleistocene & Holocene/recent Period.

Gondwana System

• The Gondwana System is named after the Gonds, who are among the most ancient inhabitants of Telangana and Andhra Pradesh in India. This geological system consists of deposits that have been laid down in synclinal troughs, which are depressions on the surface of an ancient plateau.
• Over time, as more and more sediments accumulated in these troughs, the weight of the deposits caused the troughs to sink further. This process led to the formation of freshwater bodies in these depressions, which in turn allowed terrestrial plants and animals to thrive in these areas.
• The development of the Gondwana System began during the Permian period, which occurred around 250 million years ago. As a result, this geological system provides valuable insights into the ancient ecosystems and environments that existed during that time.

Gondwana Coal

• Gondwana rocks contain nearly 98 per cent of India’s coal reserves.
• Gondwana coal is much younger than the Carboniferous coal and hence it’s carbon content is low.
• They have rich deposits of iron ore, copper, uranium and antimony also.
• Sandstones, slates and conglomerates are used as building materials.

Jurassic System

• The marine transgression in the latter part of the Jurassic gave rise to thick series of shallow water deposits in Rajasthan and in Kuchchh.
• Coral limestone, sandstone, conglomerates and shales occur in Kuchchh.
• Another transgression on the east coast of the Peninsula is found between Guntur and Rajahmundry.

Deccan Trap

• The Deccan Traps are a result of a massive volcanic eruption that occurred in the Peninsular India between the end of the Cretaceous period and the beginning of the Eocene epoch. Basaltic lava flowed through fissures, covering an extensive area of around ten lakh square kilometers.
• These volcanic deposits have flat tops and steep sides, which led to their name "trap," meaning "stair" or "step" in Swedish. Over millions of years, weathering and erosion (also known as denudation) have significantly reduced the size of the Deccan Traps to nearly half of their original extent.
• Today, the Deccan Traps cover approximately five lakh square kilometers, primarily in parts of Kutch, Saurashtra, Maharashtra, the Malwa plateau, and northern Karnataka. The thickness of these deposits varies, with 3,000 meters along the western region, decreasing to 600-800 meters in the south, 800 meters in Kutch, and a mere 150 meters at the eastern boundary.
• Long-term weathering of these rocks has led to the formation of black cotton soil, also known as "regur," which is found in the Deccan Traps region.

The Deccan Trap has been divided into three groups:

Tertiary System

• The Tertiary System, ranging from the Eocene to Pliocene epoch, occurred approximately 60 to 7 million years ago. This period is characterized by two significant events: the final breakup of the ancient Gondwana landmass and the uplift of the Tethys geosyncline, which led to the formation of the Himalayas. The Tertiary System is crucial in India's geological history, as it marked the birth of the Himalayas and the development of India's current geographical form.
• Tertiary rocks can be found throughout India, including the Bengal and Ganges delta, the East coast, the Andaman Islands, the Salt Range, Potwar Plateau, the outer Himalayan regions of Jammu and Punjab, Assam, Sind, and Baluchistan. Important rock formations from this period include the Karewas of Kashmir and the Bhangra and Khadar of the Gangetic plains.
• India's geological history is diverse and unique, with various regions containing rocks from different geological periods. The Indian Craton was once part of the supercontinent Pangaea. After the breakup of Gondwanaland (approximately 225 million years ago), the Indian Craton began to slide towards the Eurasian Craton, eventually leading to the formation of the Himalayan mountain range around 65 million years ago.
• Following the formation of the Outer Himalayas, the widespread alluvial plains began to form during the Upper Pliocene and Pleistocene periods, resulting in the Indo-Ganga-Brahmaputra plain region. Consequently, different parts of India contain rocks from nearly every type of geological structure and period.
• The stratigraphy of India can be divided into several systems, including the Archean, Dharwar, Cudappah, Vindhyan, Dravidian, and Aryan systems, which consist of Gondwana, Jurassic, Deccan Trap, Tertiary, and Quaternary rocks. India's geology features the oldest rocks from the Archaean period in peninsular India to the newest alluvial formations in the Indo-Gangetic plains. Sedimentary rocks formed by the deposition of sediments from the Indo-Gangetic plains can be found throughout the country, and a variety of sedimentary and metamorphic rocks can be traced within the great folded mountainous regions.

Conclusion

Frequently Asked Questions (FAQs) of Structure & Relief

What is the Indian Rock System?

The Indian Rock System involves the study of the geological structure and time scale of rocks in India. It includes the examination of rocks in relation to their geographical locations and historical context to understand the geological history of India.

What are the major events in the geological history of India?

The major events in the geological history of India include the formation of Peninsular India as a part of the old landmass, the upheaval of the Himalayas in the tertiary period, and the aggradational formation of the Indo-Gangetic plain during the Pleistocene period.

What are the four major divisions of the rock systems in India?

The Geological Survey of India has classified the rock systems of the country into four major divisions: The Archaean Rock System, The Purana Rock System, The Dravidian Rock System, and The Aryan Rock System.

What are the significant geological formations found in the Archaean Rock System?

The Archaean Rock System consists of two main geological formations: the Achaean System, which consists of granites and gneisses, and the Dharwar System, which includes the first sedimentary rocks.

What is the significance of the Gondwana System in India's geological history?

The Gondwana System is significant as it contains nearly 98% of India's coal reserves and has rich deposits of iron ore, copper, uranium, and antimony. The development of the Gondwana System began during the Permian period, around 250 million years ago, providing valuable insights into the ancient ecosystems and environments that existed during that time.