Indian Rock System
India's geological structure comprises four major rock systems: Archaean (oldest, >2.5 billion years), Purana (2.5 billion-700 million years), Dravidian (570-65 million years), and Aryan (youngest, <65 million years). These systems represent the complete geological timeline and are crucial for mineral exploration and engineering projects.
India has a complex and diverse geological structure that has evolved over billions of years. The Indian landmass contains rock formations from almost all geological periods, making it a natural laboratory for geological studies.
Classification of Indian Rock Systems
Based on their age and formation, Indian rocks are classified into four major systems:
Archaean Rock System: The oldest rocks in India, formed more than 2.5 billion years ago. They constitute the basement complex and are highly metamorphosed and crystalline in nature. Found predominantly in peninsular India, these rocks are rich in minerals like iron ore, manganese, gold, and mica.
Purana Rock System: Formed between 2.5 billion and 700 million years ago, these are ancient sedimentary rocks that overlie the Archaean basement. The Purana rocks are further divided into the Cuddapah and Vindhyan systems and contain valuable minerals including limestone, diamond, and copper.
Dravidian Rock System: Representing the Paleozoic and Mesozoic eras (570-65 million years ago), these rocks are found in limited areas, particularly in the extra-peninsular regions. They include important coal-bearing strata of Gondwana formations.
Aryan Rock System: The youngest rock system, formed during the Cenozoic era (65 million years ago to present). These rocks consist of sedimentary deposits found in the Himalayan region and the Indo-Gangetic plains, representing the most recent geological activities.
Understanding these rock systems is essential for geological surveys, mineral exploration, groundwater assessment, and various engineering projects across the Indian subcontinent.
Introduction to Indian Geological Structure
India's geological structure comprises diverse formations spanning billions of years, divided primarily into Peninsular (ancient, stable) and Extra-Peninsular (younger, dynamic) regions. This geological diversity influences the country's habitability, resources, and economic development through its rock formations, mineral deposits, and water resources.
Geological Structure
Geological structure refers primarily to the arrangements and deposition of the rocks in the earth's crust, resulting from various earth movements or their absence. This concept also encompasses the morphological features (morphology) of rocks, as exemplified by formations like the Gondwana structure. The study of geological structures involves analyzing folds, faults, joints, and other deformational features that provide insights into the tectonic history and stress patterns experienced by the region over millions of years.
Geological Time Scale
The Geological Time Scale provides a chronological dating of various geological formations (geological strata) and life forms according to their origin, evolution, and extinction periods. Giovanni Arduino pioneered this scale in 1760, which was later standardized at the International Geological Congress held in Italy in 1881. This scale divides Earth's history into eons, eras, periods, epochs, and ages, allowing geologists to establish relative ages of rock formations worldwide and correlate them across different regions.
The Indian Geological Time Scale, developed by T.S. Holland, adapts this global framework to India's unique geological context. Holland's contribution was significant as it allowed scientists to properly categorize and understand the complex and diverse geological formations found throughout the Indian subcontinent.
Geological History of India
The geological structure and rock systems of India are analyzed according to their geographical locations and historical formation. For better understanding, India's geological formations are typically studied within two major physiographic divisions:
Peninsular India - characterized by ancient, stable landmass with rock formations dating back over 3.8 billion years, making it one of the oldest geological formations on Earth
Extra Peninsular India - featuring younger, more dynamic formations that have undergone significant tectonic activity in relatively recent geological time
The contrast between these two divisions provides a fascinating study in geological processes and continental evolution. While the peninsula represents stability and prolonged weathering processes, the extra-peninsular region showcases active mountain building and sedimentation.
Major events in the geological history of India:
Peninsular India has remained a stable part of the ancient landmass since the formation of the Earth's crust. This stability has allowed for the preservation of some of the oldest rocks on Earth, particularly in regions like the Dharwar Craton, where rocks date back to the early Archaean period.
The dramatic upheaval of the Himalayas occurred during the tertiary period, creating one of the world's youngest mountain ranges. This mountain-building process (orogeny) began approximately 50 million years ago when the Indian Plate collided with the Eurasian Plate after traversing northward from Gondwanaland.
The aggradational formation of the Indo-Gangetic plain during the Pleistocene period continues to the present day through ongoing sedimentation in river floodplains and the lower Gangetic region. This vast alluvial plain formed as the Himalayan rivers deposited enormous volumes of sediment eroded from the young mountains.
The separation of India from Madagascar occurred around 88 million years ago, followed by its separation from the Seychelles approximately 65 million years ago, marking important stages in the northward journey of the Indian Plate.
The massive volcanic eruptions that formed the Deccan Traps around 66 million years ago covered a large portion of western and central India with basaltic lava flows, significantly altering the landscape and potentially contributing to the Cretaceous-Paleogene extinction event.
These geological events have shaped not only the physical landscape of India but also influenced its climate patterns, river systems, soil types, and ultimately human settlement patterns throughout history. The diversity of geological formations has blessed India with a wide range of mineral resources distributed across different geological provinces.
The study of India's geological structure continues to evolve with advances in technology and methodologies. Modern techniques such as radiometric dating, satellite imagery, and deep drilling projects have enhanced our understanding of the complex geological processes that have shaped the Indian subcontinent over billions of years.
Classification of Indian Rock Systems
Based on this complex and varied geological history, the Geological Survey of India has classified the rock systems of the country into four major chronological divisions, representing distinct geological epochs and formations:
The Aryan Rock System
The youngest rock system in India, formed during the Mesozoic and Cenozoic eras. These formations include the Himalayan mountain range and are rich in fossils and sedimentary deposits.
The Dravidian Rock System
Comprising primarily Palaeozoic formations, this system includes coal-bearing Gondwana beds and represents a crucial period in India's geological and economic mineral development.
The Purana Rock System
Predominantly featuring Cuddapah and Vindhyan formations, this system dates to the Proterozoic era and contains significant deposits of limestone, sandstone, and valuable minerals including diamonds.
The Archaean Rock System
Representing the oldest rock formations in India, dating back over 2.5 billion years. These highly metamorphosed crystalline and gneissic rocks form the foundation of the Indian Peninsula and contain valuable mineral deposits.
The Archaean Rock System
The earliest phase of tectonic evolution occurred during the Archaean era (prior to 2.5 billion years ago; Precambrian Period), marked by the cooling and solidification of the earth's upper crust. These ancient formations are prominently exposed as gneisses and granites across the Indian Peninsula.
These primordial rocks form the foundational core of the Indian Craton (a stable block of the Indian Subcontinent that was once part of Gondwanaland).
The term 'Archaean' was introduced by geologist J.D. Dana in 1782 to designate the oldest rocks comprising the earth's crust.
The Archaean group of rocks is classified into two primary systems:
(a) Achaean System: Predominantly Granites and Gneisses
(b) Dharwar System: Representing the First Sedimentary Rocks
Gneiss — A metamorphic rock with mineral composition varying from granite to gabbro, characterized by alternating bands of light and dark minerals.
Schists — Strongly foliated crystalline rocks that include minerals such as mica, talc, hornblende, chlorite, and others.
Archaean Gneisses and Schists
Key characteristics:
Oldest known rocks of the pre-Cambrian era, formed approximately 4 billion years ago
Formed through solidification of molten magma when the earth's surface maintained extremely high temperatures
Recognized as the 'Basement Complex' because they constitute the oldest foundation upon which younger rock layers rest
Azoic or unfossiliferous (containing no fossil remains)
Distinctly foliated structure (consisting of thin mineral sheets)
Thoroughly crystalline in nature (resulting from their volcanic origins)
Plutonic intrusions (volcanic rocks that solidified deep beneath the earth's surface)
Dharwar System
Formation period spans from approximately 4 billion to 1 billion years ago
Represents a highly metamorphosed sedimentary rock-system (formed through the metamorphosis of sediments derived from Archaean gneisses and schists)
Constitutes the oldest metamorphosed sedimentary formations in India
Found abundantly in Karnataka's Dharwar district, from which the system derives its name
Economically vital rock system containing valuable mineral deposits including high-grade iron-ore, manganese, copper, lead, gold, and other metallic resources
The Purana Rock System
The Cuddapah and Vindhyan rock systems collectively comprise the Purana rock system, representing a significant geological era in India's formation.
These rocks developed through the erosion and subsequent deposition of Archean and Dharwar materials, a geological process estimated to have occurred between 1400-600 million years ago.
The Purana system consists of rocks that are predominantly sedimentary in nature, marking an important transition in India's geological timeline.
Cuddapah System
Named after the Cuddapah district of Andhra Pradesh, where extensive outcrops of these rocks are prominently displayed
These formations developed when sedimentary materials including sandstone, limestone, and clay were deposited in synclinal folds (depressions between mountain ranges)
The most comprehensive exposures can be observed throughout the Cuddapah district of Andhra Pradesh
These rock formations harbor valuable mineral resources including ores of iron, manganese, copper, cobalt, and nickel
They are economically significant as they contain substantial deposits of cement-grade limestone
Vindhyan System (1300-600 million years)
This system derives its name from the magnificent Vindhyan mountain range
The formation consists of ancient sedimentary rock layers (approximately 4000 meters thick) overlying the Archaean foundation
Characterized by primarily unfossiliferous composition, with significant portions of this region covered by the Deccan trap volcanic formations
The Vindhyan system contains famous diamond-bearing regions that have yielded the renowned Panna and Golconda diamonds
While largely lacking metalliferous minerals, it provides abundant resources including durable building stones, ornamental materials, limestone, and high-quality sand suitable for glass manufacturing.
The Dravidian Rock System
The Paleozoic rock formations are known as Dravidian systems in India, developing during the Paleozoic era approximately 600-300 million years ago. This system is also referred to as the Carboniferous Rock System due to the high-quality coal formation that characterized this period globally.
Distribution
These rocks are predominantly found in the extra-Peninsular regions of the Himalayas and the Gangetic plain, with minimal presence in the Peninsular shield (notably in Umaria in Rewa).
Major Regions
The primary regions where Dravidian rocks are found include PirPanjal, Handwara, Lider valley, and Annatnag in Kashmir; Spiti, Kangra, and Shimla regions in Himachal Pradesh; and Garhwal and Kumaon areas in Uttarakhand.
Rock Types
The Dravidian rocks primarily consist of shales, sandstones, clays, quartzites, slates, salts, talc, dolomite, marble, etc.
This period coincided with the breakup of the supercontinent Pangaea and the formation of the Tethys Sea, marking significant geological transitions.
The Dravidian era represents a crucial milestone in Earth's history as it witnessed the beginning of abundant life on the planet's surface. These rock formations contain numerous fossil evidence, providing valuable insights into early life forms.
Fossils are prevalent throughout all geological formations from this period, indicating that marine conditions predominated in these Paleozoic rocks across India.
The Dravidian period marked the beginning of coal formation (high-quality Carboniferous coal), although these valuable coal deposits were not found abundantly within the Indian subcontinent.
The Dravidian system of geological formations encompasses rocks from the following geological ages:
The Cambrian System
The Ordovician Systems
The Silurian System
The Devonian System (characterized by abundant fossils and corals)
The Carboniferous Systems (divided into Lower and Middle Carboniferous)
Carboniferous rocks (350 million years)
The Carboniferous rocks (dating back 350 million years) consist primarily of limestone, shale, and quartzite
Mount Everest's summit is notably composed of Upper Carboniferous limestones
Significant coal formation processes initiated during the Carboniferous age
The term "Carboniferous" in geology literally means coal-bearing. [Interestingly, most coal deposits found in India are not from the Carboniferous period; the high-quality coal of the Great Lakes Region-USA, United Kingdom, and Ruhr region of Germany represents true Carboniferous coal]
The Aryan Rock System
The Aryan Group marks the beginning of the Upper Carboniferous period and represents the threshold of Earth's most eventful and longest geological era, spanning from the Upper Carboniferous to the Holocene period.
Upper Paleozoic Era
Upper Primary Epoch – characterized by Upper Carboniferous and Permian Period formations
Mesozoic Era
Secondary Epoch – featuring Triassic, Jurassic, and Cretaceous period formations (including the Gondwana Rock system, Deccan Trap, and Jurassic system)
Cenozoic Era
Tertiary Epoch – encompassing Paleocene, Eocene, Oligocene-Miocene, and Pliocene Periods
Neozoic Era
Quaternary Epoch – comprising Pleistocene and Holocene/Recent Periods
Gondwana System
The Gondwana System derives its name from the Gonds, indigenous people native to Telangana and Andhra Pradesh regions
These formations consist of deposits laid down in synclinal troughs on ancient plateau surfaces
As sediments accumulated over time, the loaded troughs gradually subsided
Freshwater and sediments collected in these depressions, creating environments where terrestrial plants and animals flourished
This geological process began during the Permian period approximately 250 million years ago
Gondwana Coal
Gondwana rock formations contain nearly 98 percent of India's total coal reserves
Gondwana coal is geologically younger than Carboniferous coal, resulting in lower carbon content
These formations also contain rich deposits of iron ore, copper, uranium, and antimony
The sandstones, slates, and conglomerates from this system serve as valuable building materials
Jurassic System
Marine transgression during the latter part of the Jurassic period created thick series of shallow water deposits in Rajasthan and Kutch regions
Kutch area features diverse formations including coral limestone, sandstone, conglomerates, and shales
Evidence of another transgression on the Peninsula's east coast appears in the region between Guntur and Rajahmundry
Deccan Trap and Tertiary System
Deccan Trap
Volcanic eruptions across vast areas of Peninsular India from the end of the Cretaceous to the beginning of the Eocene period created the Deccan Traps
Basaltic lava flowed from fissures, covering approximately ten lakh sq km of land
These volcanic deposits feature flat tops and steep sides, thus earning the name 'trap', meaning 'stair' or 'step' in Swedish
Millions of years of weathering and erosion (denudation) have reduced the Deccan Trap to nearly half its original extent
Today, the Deccan Trap spans about 5 lakh sq km, primarily across parts of Kuchchh, Saurashtra, Maharashtra, the Malwa plateau, and northern Karnataka
The Deccan Traps reach 3,000 meters in thickness along the western edge, thinning to 600-800 meters southward, 800 meters in Kuchchh, and merely 150 meters at its eastern boundary
Centuries of weathering of these volcanic rocks has produced the fertile black cotton soil known as 'regur'
Tertiary System
Spanning from Eocene to Pliocene (approximately 60 to 7 million years ago), this period was marked by two significant events: the final fragmentation of ancient Gondwana land and the upliftment of Tethys geosynclines, forming the Himalayas
The Tertiary represents the most pivotal period in India's geological history, as the Himalayan mountain range emerged and India assumed its present geographical configuration
Tertiary Succession deposits are extensively distributed across the Bengal and Ganges delta, East coast, and the Andaman Islands. They also appear in the Salt Range, Potwar Plateau, outer Himalayan regions of Jammu and Punjab, Assam, Sind, and Baluchistan. Notable rock formations include the Karewas of Kashmir and the Bhangra and Khadar of the Gangetic plains
India's geological history exhibits remarkable diversity and uniqueness. Different regions of the subcontinent contain rock formations from various geological periods, reflecting India's complex tectonic past. The Indian Craton was once integrated into the supercontinent of Pangaea.
The collision between the Indian plate and Eurasian plate following the breakup of Gondwanaland (225 million years ago) led to the formation of the Himalayan mountain range (65 million years ago).
The formation of the vast Indo-Gangetic-Brahmaputra alluvial plains began in the upper Pliocene and Pleistocene periods, following the development of the Outer Himalayas. Consequently, India's geological landscape encompasses virtually every type of rock structure from different geological epochs.
Indian stratigraphy can be classified into several major systems: the Archean System, Dharwar System, Cudappah System, Vindhyan System, Dravidian System, and Aryan System (including Gondwana, Jurassic, Deccan Trap, Tertiary, and Quaternary formations).
India's geological strata contain everything from the oldest rock formations to the newest alluvial deposits. The ancient rocks of the Archaean period are predominantly found in peninsular India, while younger sedimentary formations characterize the Indo-Gangetic plains. The Great Himalayan mountain belt features diverse sedimentary and metamorphic rock formations, further showcasing India's rich geological heritage.
