Indian Rock Systems: A Geological Journey from Vindhyan to Anthropocene

Unearthing India's Geological Tapestry: A Journey Through Rock Systems from Vindhyan to Anthropocene

Introduction

The Indian subcontinent presents a geological narrative of extraordinary depth and complexity. Its crust bears witness to billions of years of Earth's history, from ancient cratonic nuclei to dynamic plate collisions and recent human-induced transformations. Understanding India's rock systems is fundamental not only for deciphering its geological evolution but also for appreciating the distribution of its natural resources, the formation of its diverse landscapes, and the nature of its geological hazards. This journey delves into the major rock systems of India, focusing on the vast span from the Proterozoic Vindhyan Supergroup to the ongoing, human-influenced Anthropocene epoch. We will explore their formation, characteristics, distribution, economic significance, and the profound stories they tell about our planet's past and present.

While the Archaean and early Proterozoic systems (like the Dharwar Supergroup and the Bundelkhand Gneiss Complex) form the ancient basement upon which later sequences were deposited, our detailed exploration begins with the widespread and relatively undeformed Vindhyan strata, marking a significant chapter in India's Proterozoic history.

1. The Vindhyan Supergroup (Late Proterozoic)

Geological Time: Primarily Mesoproterozoic to Neoproterozoic (~1400 to 600 Million Years Ago - Ma). The precise age range, especially the upper boundary, is still debated but firmly places it within the Proterozoic Eon.
Distribution: Occupies a vast, crescent-shaped basin stretching across central India, including parts of Rajasthan, Madhya Pradesh, Uttar Pradesh, Bihar, and Chhattisgarh. The Vindhyan Range lends its name to this system.
Formation and Tectonic Setting: Deposited in a large intracratonic (or pericratonic) basin that developed over the eroded Archaean-Paleoproterozoic basement. The basin likely formed due to crustal sagging or slow rifting. Sedimentation occurred primarily in shallow marine, deltaic, and fluvial environments under relatively stable tectonic conditions, explaining the generally unmetamorphosed and undeformed nature of these rocks compared to older systems like the Dharwars or Aravallis.
Stratigraphy: The Vindhyan Supergroup is traditionally divided into two main parts, separated by a significant unconformity:
- Lower Vindhyan (Semri Group): Characterized by a mix of carbonate rocks (limestones, dolomites), shales, sandstones, and some volcanic tuffs (porcellanites). This sequence suggests fluctuating marine and non-marine conditions. Key formations include the Deoland, Kajrahat Limestone, Rohtas Limestone, and Bhagwar Shale. Evidence of early life, primarily microbial mats (stromatolites), is abundant in the carbonate layers.
- Upper Vindhyan: Dominated by thick sequences of arenaceous (sandy) and argillaceous (clayey) rocks, indicating a shift towards more extensive fluvial and deltaic deposition, possibly related to basin rejuvenation or changes in sediment supply. It is further subdivided into:
  - Kaimur Group: Predominantly sandstones (e.g., Dhandraul Quartzite) and shales.
  - Rewa Group: Sandstones, shales, and prominent diamondiferous conglomerates (source of Panna diamonds).
  - Bhander Group: Uppermost group, featuring extensive sandstones (Upper Bhander Sandstone – a major building stone), shales, and thick limestone and evaporite sequences (Sirbu Shale, Nagod Limestone), suggesting episodes of marine transgression and restricted basin conditions.
Lithology: Predominantly sedimentary rocks: Sandstones (quartz arenites, feldspathic sandstones), Shales, Limestones, Dolomites, Conglomerates. Minor occurrences of volcanic ash beds (Porcellanites). Remarkably unmetamorphosed and gently dipping over large areas, except near major fault zones like the Great Boundary Fault (GBF) in Rajasthan.
Economic Significance: Immense reserves of building and ornamental stones (e.g., red sandstone used in many historical monuments like the Red Fort, limestone for cement industry), raw materials for glass manufacturing (silica sand), diamonds (Panna belt), and potential for phosphate deposits.
Paleontological Significance: Crucial record of Proterozoic life, including diverse stromatolites, acritarchs, and potential early metazoan traces (though debated). Provides insights into the environment preceding the Cambrian explosion.

2. The Palaeozoic Era: A Period of Relative Quiescence (in Peninsular India)

Following the Vindhyan deposition, much of Peninsular India appears to have experienced a prolonged period of erosion and non-deposition during the early to middle Palaeozoic (Cambrian, Ordovician, Silurian, Devonian, Early Carboniferous). While marine Palaeozoic sequences are well-developed in the extra-peninsular regions (Himalayas, Salt Range in Pakistan), they are largely absent over the stable cratonic interior of the Peninsula. This "Palaeozoic gap" signifies that the Peninsular shield was largely emergent landmass during this time. The major geological activity relevant to this era begins in the Late Carboniferous with the initiation of the Gondwana sedimentation.

3. The Gondwana Supergroup (Late Carboniferous to Early Cretaceous)

Geological Time: Spanning from the Late Carboniferous (~300 Ma) through the Permian, Triassic, Jurassic, and into the Early Cretaceous (~145 Ma).
Distribution: Primarily confined to major linear rift valleys or grabens within the Peninsular shield, formed due to tensional tectonics related to the assembly and eventual breakup of the Gondwana supercontinent. Key basins include the Damodar Valley, Mahanadi Valley, Godavari Valley, Satpura Basin (Narmada-Son Valley). Smaller patches occur elsewhere.
Formation and Tectonic Setting: Developed within fault-bounded troughs (grabens) on the older basement. The initial sedimentation (Talchir Formation) was triggered by widespread glaciation (Permo-Carboniferous Gondwana glaciation). Subsequent deposition occurred in fluvial (riverine), lacustrine (lake), and paludal (swampy) environments within these subsiding basins. The climate evolved from cold glacial conditions to warmer, more humid conditions conducive to lush vegetation (leading to coal formation), and later to semi-arid conditions.
Stratigraphy: A thick sequence (often exceeding several kilometers) divided broadly into Lower and Upper Gondwana:
- Lower Gondwana (Permian): Represents the major coal-bearing sequence of India.
  - Talchir Formation: Basal unit, characterized by glacial tillites (boulder beds), varved clays, and cold-climate sandstones/shales, indicating the Permo-Carboniferous ice age.
  - Barakar Formation: The primary coal-bearing unit in India. Consists of thick seams of high-quality bituminous coal interbedded with coarse feldspathic sandstones, shales, and fireclays. Deposited under warmer, humid, fluvial, and swampy conditions.
  - Barren Measures (or Motur Formation): As the name suggests, largely devoid of workable coal seams. Dominated by sandstones and shales, often reddish, suggesting a shift towards slightly drier or better-drained conditions.
  - Raniganj Formation (or Kamthi Formation in some basins): Another significant coal-bearing sequence, though coal quality is often inferior to Barakar. Contains finer sandstones, carbonaceous shales, and coal seams. Represents a return to extensive swampy environments. Famous for its rich Glossopteris flora.
- Upper Gondwana (Triassic - Early Cretaceous): Generally lacks significant coal deposits and often shows reddish colours, indicating more oxidizing, possibly semi-arid conditions. Represents continued continental deposition.
  - Panchet Formation (Triassic): Greenish and khaki shales, sandstones, indicating fluvial and lacustrine environments. Contains early reptile and amphibian fossils (Lystrosaurus fauna).
  - Mahadeva Formation/Group (Triassic-Jurassic): Coarse sandstones, conglomerates, clays, often red. Represents higher energy fluvial systems, possibly related to tectonic adjustments.
  - Rajmahal Formation (Jurassic): Notable for extensive basaltic lava flows (Rajmahal Traps) interbedded with sedimentary layers containing rich plant fossils (Ptilophyllum flora). Represents significant volcanic activity preceding the Deccan Traps.
  - Jabalpur Formation (Jurassic-Cretaceous): Sandstones, white clays, and carbonaceous shales with plant fossils.
  - Umia Formation (Kutch Basin - Cretaceous): Includes marine intercalations, indicating proximity to the coast during the final stages of Gondwana deposition in western India.
Lithology: Sandstones (often feldspathic), Shales (grey, black, red), Coal seams, Fireclays, Conglomerates, Glacial Tillites. Basaltic flows in the Rajmahal Formation.
Economic Significance: The Gondwana Supergroup is paramount for India's economy, hosting over 98% of its coal reserves. It also provides valuable fireclay, silica sand, building stones, and some iron ore deposits.
Paleontological Significance: Crucial record of Permian to Cretaceous terrestrial life on the Gondwana supercontinent. Famous for the Glossopteris flora (Lower Gondwana) and the Ptilophyllum flora (Upper Gondwana), as well as vertebrate fossils (amphibians, reptiles, early mammals).

4. The Deccan Traps (Late Cretaceous - Early Paleogene)

Geological Time: Spanning the Cretaceous-Paleogene (K-Pg) boundary, primarily erupted between ~66.5 and 65 Ma, with peak activity possibly lasting less than a million years.
Distribution: Covers a massive area (over 500,000 sq km) of western, central, and southern India, forming the Deccan Plateau. Originally, the extent might have been much larger. Outliers exist in Rajahmundry (East coast) and potentially offshore.
Formation and Tectonic Setting: Represents one of the largest flood basalt provinces on Earth. Formed by colossal outpourings of basaltic lava through fissures (linear vents) rather than central volcanoes. The eruptions are widely linked to the Réunion hotspot, over which the Indian plate migrated during its rapid northward journey after separating from Gondwana. The sheer volume and rate of eruption suggest deep mantle plume activity.
Lithology: Overwhelmingly composed of Tholeiitic Basalt. The lava flows accumulated layer upon layer, creating the characteristic 'trap' (meaning 'step' or 'stair' in Swedish) topography. Individual flows can vary in thickness from a few meters to over 50 meters. The total thickness exceeds 2 km in the western Ghats, thinning towards the east and south.
- Compound Flows: Common pahoehoe flows, often thinner and more widespread.
- Simple Flows: Thicker aa flows, often forming prominent escarpments.
- Intertrappean Beds: Sedimentary layers (clays, sandstones, limestones, cherts) deposited between successive lava flows during periods of volcanic quiescence. These beds are crucial for dating the flows and contain valuable fossil remains.
- Dykes: Numerous basaltic dykes acted as feeders for the surface flows.
Impact on Landscape: Created the vast Deccan Plateau. Weathering of the basalt under tropical conditions led to the formation of fertile Black Cotton Soils (Regur), vital for agriculture. The step-like topography influences drainage patterns and geomorphology.
Economic Significance: Provides abundant rock material for construction (aggregates, building stones). Some secondary minerals (zeolites, agate, calcite) found in vesicles are of economic or aesthetic value. The weathering product, black soil, is economically crucial. Potential for geothermal energy.
Paleontological Significance: The Intertrappean beds preserve fossils of organisms that lived between eruptions, including freshwater molluscs, ostracods, frogs, turtles, crocodiles, dinosaurs (found just below or within the lowermost flows), and early mammals, providing snapshots of life around the K-Pg boundary.
K-Pg Boundary Event: The timing of the Deccan eruptions coincides closely with the K-Pg mass extinction event. While the Chicxulub impact is considered the primary trigger, the massive release of volcanic gases (CO2, SO2) from the Deccan Traps likely contributed significantly to environmental stress and climate change, potentially exacerbating the extinction event.

5. The Tertiary System (Cenozoic Era: Paleogene & Neogene)

Geological Time: ~66 Ma to 2.6 Ma (Paleocene, Eocene, Oligocene, Miocene, Pliocene).
Formation and Tectonic Setting: This era is dominated by the tectonic consequences of the Indian plate's collision with the Eurasian plate, which began around 50-55 Ma. This monumental event led to:
- Himalayan Orogeny: Intense folding, faulting, thrusting, and uplift of the Tethyan sediments and parts of the Indian plate margin, forming the Himalayan mountain range.
- Foredeep Development: Creation of a deep trough (foredeep basin) south of the rising Himalayas due to the crustal load. This basin became the site of deposition for the Indo-Gangetic Plain sediments.
- Peninsular Adjustments: Reactivation of older faults, minor uplift, and coastal tilting in response to the collision stresses.
Distribution and Characteristics:
- Extra-Peninsular Region (Himalayas):
  - Paleogene Marine Sediments: Thick sequences of marine limestones (often rich in Nummulites – large foraminifera), shales, and sandstones deposited in the shrinking Tethys Sea just before and during the initial collision (e.g., Subathu Formation, Murree Formation).
  - Neogene Molasse Deposits (Siwalik Group): As the Himalayas rose rapidly, vast amounts of eroded material were shed southward into the foredeep basin. These form the Siwalik Group – thick sequences (up to 6 km) of river-deposited sandstones, conglomerates, and mudstones. They represent the erosional products of the rising mountains and contain abundant vertebrate fossils (mammals, reptiles). They are progressively younger towards the south (Lower, Middle, Upper Siwaliks).
- Peninsular Region:
  - Coastal Deposits: Marine transgressions led to deposition of limestones, clays, and sandstones along the East and West coasts (e.g., Cuddalore Sandstone, Quilon Beds). These often contain lignite (brown coal) deposits, notably at Neyveli (Tamil Nadu).
  - Inland Basins: Some sedimentation occurred in smaller inland basins (e.g., parts of Rajasthan, Gujarat).
  - Lateritization: Extensive chemical weathering under tropical conditions led to the formation of thick laterite cappings over various older rocks (especially Deccan Traps, Khondalites) across the Peninsula. Laterites are residual soils rich in iron and aluminium oxides/hydroxides.
Lithology: Highly variable: Limestones (Nummulitic), Shales, Sandstones, Conglomerates (Siwaliks), Clays, Lignite, Laterite/Bauxite. Rocks in the Himalayas are intensely deformed (folded, faulted, metamorphosed to varying degrees), while Peninsular deposits are relatively less disturbed.
Economic Significance: Major source of petroleum and natural gas (Assam-Arakan basin, Cambay basin, Mumbai High offshore basin, KG basin). Significant lignite deposits (Neyveli). Bauxite (aluminium ore) derived from laterites. Building stones and materials. Groundwater resources in coastal plains.
Paleontological Significance: Excellent record of early Cenozoic marine life (Nummulites) and Neogene terrestrial mammalian evolution (Siwalik fauna).

6. The Quaternary System (Late Cenozoic - Present)

Geological Time: ~2.6 Ma to Present (Pleistocene and Holocene epochs).
Formation and Tectonic Setting: Characterized by ongoing Himalayan uplift, continued subsidence of the Indo-Gangetic foredeep, significant climatic fluctuations (Pleistocene Ice Ages and interglacials), and associated sea-level changes. Fluvial, aeolian, glacial, and coastal processes became dominant landscape shapers.
Distribution and Characteristics:
- Indo-Gangetic-Brahmaputra Plains: Vast alluvial plains formed by the deposition of enormous volumes of silt, clay, sand, and gravel carried by the Indus, Ganga, Brahmaputra, and their tributaries eroding the Himalayas. Sediment thickness can exceed 2 km. The plains are differentiated into:
  - Bhabar: Coarse gravelly zone at the Himalayan foothills.
  - Terai: Poorly drained marshy tract south of Bhabar.
  - Bhangar: Older alluvial terraces, above flood levels.
  - Khadar: Younger alluvial deposits within active floodplains.
- Coastal Plains: Alluvial deposits along the East and West coasts, delta formations (Ganga-Brahmaputra, Mahanadi, Godavari, Krishna, Cauvery), beach sands, and lagoonal muds. Affected by sea-level fluctuations.
- Thar Desert: Extensive aeolian (wind-blown) sand deposits (dunes, sheets) covering western Rajasthan and adjoining areas.
- River Valleys (Peninsula): Alluvial fills along major peninsular rivers.
- Glacial Deposits (Himalayas): Moraines, fluvio-glacial outwash deposits in high-altitude valleys, indicative of past glaciations.
- Karewas (Kashmir Valley): Thick sequences of Pleistocene lacustrine (lake) and fluvial deposits, famous for saffron cultivation. They provide valuable records of Quaternary climate change.
- Laterite: Continued formation and modification of laterite profiles.
Lithology: Predominantly unconsolidated or semi-consolidated sediments: Alluvium (silt, clay, sand, gravel - Kankar nodules common), Aeolian Sand, Glacial Till, Loess (minor), Coastal Sands and Muds, Peat.
Economic Significance: The Indo-Gangetic plains represent India's most fertile agricultural land. Vast groundwater resources are stored in these alluvial aquifers. Sand and gravel are essential construction materials. Placer deposits (gold, heavy minerals) occur in some riverbeds and beach sands. Peat and diatomaceous earth are also found.
Paleontological/Archaeological Significance: Contains fossils of Quaternary fauna, pollen records indicating climate shifts, and crucial archaeological evidence of human evolution and settlement (Stone Age tools, early settlements).

7. The Anthropocene (Informal Epoch - Present)

Concept: While not yet formally ratified as a distinct geological epoch, the Anthropocene signifies the period during which human activities have become a dominant geological force, significantly altering Earth's systems, including the lithosphere, hydrosphere, atmosphere, and biosphere. Its starting point is debated (Industrial Revolution, mid-20th century 'Great Acceleration').
Manifestations in the Indian Geological Context:
- Landscape Modification: Large-scale urbanization, infrastructure development (roads, railways, dams), extensive mining and quarrying activities, deforestation, and agricultural land conversion drastically alter topography, erosion rates, and sediment transport pathways. Dams trap vast quantities of sediment, starving deltas.
- Altered Sedimentary Systems: Increased soil erosion due to agriculture and deforestation leads to higher sediment loads in some rivers, while dam construction alters deposition patterns downstream. Coastal erosion is exacerbated by sea-level rise and human interference (e.g., port construction).
- Novel Deposits ('Technofossils'): Creation and deposition of entirely new materials like plastics, concrete, fly ash, and various industrial wastes, which are becoming incorporated into the sedimentary record. These act as unique markers of the Anthropocene. Altered soil profiles ('anthrosols') due to agriculture and pollution.
- Hydrological Changes: Extensive groundwater extraction leading to aquifer depletion and land subsidence in regions like the Indo-Gangetic Plains. Surface water pollution altering water chemistry and sedimentation in rivers and lakes.
- Climate Change Impacts: Anthropogenic climate change is accelerating glacial melt in the Himalayas, altering river regimes, increasing the frequency/intensity of extreme weather events (floods, droughts), and causing sea-level rise impacting coastal geomorphology and sedimentation.
Significance: Recognizing the Anthropocene emphasizes the profound and potentially long-lasting impact of human civilization on the geological framework of India and the planet. It necessitates integrating human activities into the understanding of contemporary geological processes.

Conclusion

The journey through India's rock systems, from the ancient Proterozoic platforms of the Vindhyans to the human-modified landscapes of the Anthropocene, reveals a dynamic geological history. The stability of the Peninsula, punctuated by rifting (Gondwana), massive volcanism (Deccan Traps), and peripheral impacts of plate collision, contrasts sharply with the intense dynamism of the Himalayan orogeny. Each system – Vindhyan, Gondwana, Deccan, Tertiary, Quaternary – tells a unique story of environmental conditions, tectonic events, biological evolution, and resource formation. The recent imprint of the Anthropocene adds a critical, ongoing chapter, highlighting the responsibility that comes with being a dominant geological agent. Studying these rock systems is not merely an academic exercise; it is crucial for sustainable resource management, hazard mitigation, and understanding the very foundation upon which Indian civilization has developed and continues to evolve.

Practice Exercises

Here are some exercises to test your understanding of the Indian Rock Systems discussed:

Part 1: Multiple-Choice Questions (MCQs)

The Vindhyan Supergroup is primarily known for which type of economic resource? (a) High-quality bituminous coal (b) Petroleum and natural gas (c) Building stones (sandstone, limestone) and diamonds (d) Bauxite (aluminium ore)
The Gondwana Supergroup sediments were predominantly deposited in which tectonic setting? (a) Volcanic arcs (b) Deep ocean trenches (c) Intracratonic rift valleys (grabens) (d) Fold-and-thrust belts
The Deccan Traps are a classic example of: (a) An ancient mountain range eroded flat (b) A large igneous province formed by flood basalts (c) Sediments deposited in a shallow sea (d) Metamorphic rocks formed under high pressure
Which geological event is most directly responsible for the formation of the Siwalik Group? (a) The eruption of the Deccan Traps (b) Glaciation during the Talchir period (c) The collision of the Indian and Eurasian plates and subsequent Himalayan uplift (d) Marine transgression during the Eocene
Fertile alluvial soils, crucial for Indian agriculture, are characteristic of which system? (a) Vindhyan Supergroup (b) Gondwana Supergroup (c) Deccan Traps (weathered product) (d) Quaternary System (Indo-Gangetic Plains)

Part 2: Scenario-Based Questions

Scenario: An oil exploration company is drilling a deep well in the offshore Mumbai High region. Describe the likely sequence of major rock systems they might encounter, starting from the seabed downwards, and explain why.
Scenario: Imagine you are a geologist mapping an area in the Damodar Valley. You find sequences containing glacial tillites at the base, overlain by thick coal seams associated with Glossopteris fossils, followed by sandstones largely devoid of coal. To which major rock system do these sequences belong, and what formations might they represent? What does this sequence tell you about the changing environment over time?

Part 3: Map/Diagram-Based Exercise

(Imagine a simplified geological map of India showing major geological provinces)

Map Exercise: On the provided simplified map outline of India: (a) Shade the approximate area dominated by the Deccan Traps. (b) Mark the general location of the Vindhyan Basin. (c) Indicate the primary belt where Gondwana coalfields are found (e.g., Damodar Valley). (d) Outline the vast expanse of the Quaternary Indo-Gangetic Alluvial Plains. (e) Roughly delineate the Himalayan mountain belt (Tertiary and older rocks, intensely deformed).

(Self-Assessment: Compare your sketched map to a standard geological map of India).

Detailed Explanations for Answers

Part 1: MCQs Explanations

(c) Building stones (sandstone, limestone) and diamonds: The Vindhyan Supergroup is famous for its extensive, relatively undeformed sandstones (like the red sandstone) and limestones used in construction and cement. The diamondiferous conglomerates occur within the Rewa Group (Upper Vindhyan). (a) Coal is characteristic of the Gondwana Supergroup. (b) Petroleum is primarily found in Tertiary basins. (d) Bauxite is typically associated with laterites formed by weathering, often over Deccan Traps or other suitable parent rocks during the Tertiary/Quaternary.
(c) Intracratonic rift valleys (grabens): The Gondwana sediments accumulated in linear troughs or basins (like the Damodar, Mahanadi, Godavari valleys) that formed due to faulting and subsidence within the stable Indian craton during the fragmentation of the Gondwana supercontinent.
(b) A large igneous province formed by flood basalts: The Deccan Traps resulted from massive fissure eruptions pouring out fluid basaltic lava over a vast area in a relatively short geological time, characteristic of a Large Igneous Province (LIP) linked to a mantle hotspot.
(c) The collision of the Indian and Eurasian plates and subsequent Himalayan uplift: The Siwalik Group consists of thick molasse deposits – sediments eroded from the rapidly rising Himalayas following the India-Eurasia collision. These sediments were deposited in the foredeep basin south of the mountains.
(d) Quaternary System (Indo-Gangetic Plains): The vast, fertile Indo-Gangetic plains are formed by thick alluvial deposits (silt, clay, sand) laid down by the Indus, Ganga, and Brahmaputra river systems during the Quaternary period. While weathered Deccan Traps form fertile black soil (c), the term 'alluvial soils' most directly refers to the river-deposited sediments of the Quaternary plains.

Part 2: Scenario Explanations

Mumbai High Drilling Sequence: Starting from the seabed (Quaternary), a drill would likely encounter:
- Quaternary Sediments: Recent marine muds, sands. Relatively thin.
- Tertiary Sediments: Thick sequences of Paleogene and Neogene marine shales, limestones (often porous, acting as reservoirs), and sandstones. These host the oil and gas deposits of Mumbai High. These were deposited in the developing passive margin basin after India rifted from Seychelles and during its northward drift, before and during the initial phases of collision far to the north.
- Deccan Traps: Below the Tertiary sediments, basaltic lava flows of the Deccan Traps are expected, as the eruptions extended offshore into this region.
- Mesozoic Sediments (Pre-Deccan): Potentially Cretaceous or older Mesozoic sediments deposited before the volcanism.
- Basement: Eventually, the drill would hit the Precambrian crystalline basement rocks of the Indian Shield.
- Reasoning: This sequence reflects the geological history: ancient basement, possible Mesozoic deposition, massive Deccan volcanism covering the area, followed by thick Tertiary marine sedimentation in the subsiding offshore basin as India moved north and the Himalayas formed, capped by recent Quaternary deposits.
Damodar Valley Mapping:
- Major Rock System: Gondwana Supergroup.
- Formations: The sequence described strongly suggests:
  - Glacial Tillites: Talchir Formation (basal Gondwana, Permo-Carboniferous glaciation).
  - Thick Coal Seams & Glossopteris: Barakar Formation (Lower Permian, major coal deposition under warm, humid, swampy conditions).
  - Sandstones without Coal: Barren Measures (or Motur Formation) (Mid-Permian, indicating a shift away from coal-forming swampy environments, possibly drier or better-drained fluvial systems).
- Environmental Change: The sequence clearly indicates a dramatic climate shift from ice-age glacial conditions (Talchir) to warm, humid, vegetative swamps conducive to coal formation (Barakar), followed by a period less favourable for thick peat accumulation (Barren Measures). This reflects the northward drift of India away from the South Pole and changing climatic and depositional conditions within the rift valley.

Part 3: Map Exercise Explanation

A correct sketch would show: (a) Deccan Traps: A large area covering much of Maharashtra, western Madhya Pradesh, parts of Gujarat, Karnataka, and Andhra Pradesh. (b) Vindhyan Basin: A crescent-shaped area across central India, north of the Narmada River, encompassing the Vindhya Range. (c) Gondwana Coalfields: Linear belts primarily along the Damodar Valley (West Bengal, Jharkhand), Mahanadi Valley (Odisha, Chhattisgarh), Godavari Valley (Andhra Pradesh, Telangana), and Satpura Basin (Madhya Pradesh). (d) Indo-Gangetic Plains: The vast plains stretching from Punjab in the west, across Haryana, UP, Bihar, West Bengal, to Assam in the east, south of the Himalayas. (e) Himalayan Belt: The northernmost fringe of India, forming an arc from Jammu & Kashmir/Ladakh through Himachal Pradesh, Uttarakhand, Nepal (border), Sikkim, Bhutan (border), Arunachal Pradesh.

Indian Rock Systems: A Geological Journey from Vindhyan to Anthropocene

Unearthing India's Geological Tapestry: A Journey Through Rock Systems from Vindhyan to Anthropocene

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