Distribution and classification of Precambrian rocks of India | Geology Optional Notes for UPSC PDF Download

Dharwar Craton Overview

• The Dharwar craton, an Archaean geological feature in Peninsular India, spans approximately 450,000 km².
• It is bordered to the south by the Pandyan mobile belt (PMB) and to the north by the Deccan Traps.
• To the northeast, it is bounded by the Karimnagar granulite belt (KGB), to the east by the Eastern Ghat Mobile Belt (EMBG), and to the west by the Arabian Sea.
• The Dharwar craton primarily consists of tonalite-trondhjemite-granodiorite (TTG) gneisses known as Peninsular gneisses.

Geographical Features Surrounding Dharwar Craton

• The Dharwar craton is surrounded by various geographical features and cities such as Ahmedabad, Mumbai, Hyderabad, Bangalore, Chennai, and Kolkata.
• It is flanked by the Arabian Sea on the west and the Indian Ocean on the east.

Significance of Dharwar Craton

• The Dharwar craton is a significant geological entity with a rich history that contributes to our understanding of the Earth's ancient past.
• It serves as a key area for studying the evolution of the Earth's crust and the processes that have shaped the planet over millions of years.

Major Cratons and Mobile Belts in India

• India hosts various cratons and mobile belts, including the Dharwar craton, Aravalli craton, Bundelkhand craton, Bastar craton, and Singhbhum craton.
• Mobile belts like the Pandyan mobile belt, Satpura mobile belt, and Eastern Ghat mobile belt are also integral parts of India's geological landscape.

Stratigraphy and Geological Significance

• The stratigraphy of India showcases a diverse range of geological formations, reflecting the country's complex geological history.
• The Palghat-Cauvery shear zone and other features play crucial roles in understanding the tectonic evolution of the region.

Unit 4 Summary: Dharwar Craton Rocks

• Greenstones and Schist Belts in Dharwar Craton

  The Dharwar Craton contains greenstones or schist belts with sedimentary associations. Greenstones consist mainly of basalts with some fine clastics and chemical sediments. In certain areas, greenstones also include basal conglomerates, shallow water clastics, and shelf sediments like limestones and dolomites. These greenstone belts, along with intercalated metasediments, are known as Dharwar Schist Belts.

  Key Points:

  • Greenstone belts have a regional trend NNW-SSE.
  • Metamorphic grade increases gradually from north to south.
  • Schists and gneisses transition into granulites like charnockites and khondalites in the southern part of the craton.

• Age of the Oldest Rocks in the Indian Plate

  Rocks in the Indian plate dating between 3.5 and 3.2 billion years ago (Ga) are considered the oldest. Zircons from felsic lavas in the Holenarsipur greenstone belts of the Dharwar Craton have been dated to be around 3.4 Ga. The Banded Gneissic Complex (BGC) of Rajasthan and the Older Metamorphic Group of Singhbhum craton also yield ages around 3.4 Ga.

  Insight:

  • The geological history of the Indian subcontinent does not extend beyond 3.5-3.4 Ga.

• Stratigraphic Classification of Dharwar Craton

  The term "Dharwar craton" was coined in 1978 by the Geological Survey of India to incorporate the Dharwar Supergroup and Sargur Schist complex. Various classification schemes were proposed over the years:

  • W.F. Smeeth (1915-16) suggested a two-fold division: the Hornblendic Division and the Chlorite Division.
  • B. Ramarao (1936) proposed a three-fold division: Lower, Middle, and Upper Dharwar.
  • Radhakrishan (1967) proposed a five-fold scheme.
  • S.V.P. Iyergar (1976) recommended a four-fold classification based on lithostratigraphy.

• Significance:

  • The classification and correlation of greenstone belts by the Geological Survey of India revolutionized the geology of the Dharwar craton.

• Tectonic Blocks in Dharwar Craton

  The Dharwar craton is divided into two tectonic blocks: the Western Block and the Eastern Block. These blocks were later designated as Western Dharwar Craton (WDC) and Eastern Dharwar Craton (EDC). The Grey gneisses, previously known as Peninsular gneisses, cover the EDC.

  Key Information:

  • The Western and Eastern Blocks were categorized based on differences in schist belts, metamorphic grades, and temporal evolution.
  • The term "Peninsular gneisses" now refers to gneisses older than 3000 million years.

Block 2: Stratigraphy of India

• The stratigraphy of India involves the Western Dharwar Craton (WDC) and the Eastern Dharwar Craton (EDC).
• The granitic terrain in the Eastern Dharwar Craton is referred to as the Dharwar Batholith, which dates back to more than 2500 million years.
• Chitradurga Shear Zone acts as the boundary between the WDC and EDC, located on the eastern edge of the Chitradurga schist belt near the Closepet Granite margin.
• The demarcation between WDC and EDC is not abrupt; instead, there exists a transition zone between them.
• Differences between WDC and EDC are outlined in Table 4.1, providing a clear comparison of the two regions.

Key Locations:

• Goa
• Mangalore
• Moyar-Bhavani Shear Zone
• Palghat-Cauvery Shear Zone
• Achankovil Shear Zone
• Chitradurga Shear Zone
• I Sargur
• Kochi
• Thiruvananthapuram
• Hyderabad
• Bangalore
• Pandyan mobile belt
• Madurai
• Chennai

Geological Features:

• Cuddapah basin
• Granite
• Migmatite
• Closepet granite
• Charnockite
• Greenstone/Schist belts
• Peninsular gneiss

Fig. 4.2: Essential features of the Dharwar craton. Abbreviations: WDC- Western Dharwar Craton; EDC-Eastern Dharwar Craton. (Source: simplified from Ramakrishnan and Vaidyanadhan, 2008)

Fig. 4.3: Peninsular Gneiss exposed at National Monument at Lalbagh, Bangalore.

Distinguishing Characteristics of the Western Block and the Eastern Block of Dharwar Craton

• Western Block

  • Consists of large schist belts of the Dharwar Supergroup with volcanics and subordinate sediments.
  • Three lithostratigraphic associations include:
    • Quartz-arenite-metabasalt-Banded Iron Formation (BIF)
    • Polymict conglomerate-stromatolitic carbonate-arenite-metapelite-BIF
    • Greywacke-submarine volcanics-BIF association
  • Peninsular Gneiss (>3000 Ma) forms the basement cover relation, with angular unconformity marked by Quartz Pebble Conglomerate (QPC).

• Eastern Block

  • Comprises narrow linear belts of the Dharwar Supergroup with dominant pillowed basalts.
  • Three lithostratigraphic associations include unclassified belts of different rock types.
  • Experiences intermediate pressure metamorphism mainly at 3000 Ma terrain.

• Western Dharwar Craton

  • Consists of two orogenic cycles: the Sargur Group (3100-3300 Ma) and the Dharwar Supergroup (2600-2800 Ma).
  • Majorly comprises Peninsular Gneiss forming the basement to Dharwar Supergroup.
  • Characterized by the presence of Dharwar Batholith (2500-2700 Ma) and diapiric gneiss domes.
  • Undergoes low pressure metamorphism and mainly comprises gneisses and younger granite remnants.

Block 2: Stratigraphy of India

• Western Dharwar Craton features vast Peninsular Gneiss along with two significant superbelts: Bababudan - Western Ghats - Shimoga and Chitradurga - Gadag.
• The greenstone belts of the Western Block are defined by supracrustal rocks primarily composed of mature sediments, some volcanism, and intermediate-pressure Barrovian metamorphism.
• The regional stratigraphy of the Western Dharwar Craton is represented by various lithological units as mentioned below:

Dharwar Supergroup (2600-2800 Ma)

• Chitradurga Group
• Bababudan Group
• Sargur Group (3100-3300 Ma)

Hiriyur Formation

• Consists of Greywacke-argillite suite with volcanics, pyroclastics, cherts, and polymict conglomerate.

Ingaldhal Formation

• Includes Mafic-felsic volcanics, pyroclastics, cherts, and phyllites.

Vanivilas Formation

• Comprises Manganese and iron formations, stromatolitic carbonates, biogenic cherts, pelites, quartzites, and polymict conglomerates.

Mulaingiri Formation

• Contains Metabasalts, felsic volcanics, ultramafic schists, and cross-bedded quartzite.

Santaveri Formation

• Consists of Metaproxenite, metabasalts, and cross-bedded quartzite.

Allampura Formation

• Involves Metabasalts, gabbros, ultramafic schists, phyllites, cross-bedded quartzite, and basal quartz pebble conglomerate.

Peninsular Gneiss (>3000Ma)

• Includes Ultramafic-mafic layered complexes, tholeiitic amphibolites, komatiites, and BIF.

Gorur Gneiss (3300-3400 Ma)

• Comprises Quartzites, pelites, marbles, and calc-silicate rocks.

Gorur Gneiss

• Oldest gneiss in the Western Dharwar Craton (WDC) dating back to 3300-3400 million years ago.
• Comprised of suite TTG gneisses; its connection with Sargur enclaves remains uncertain.

Sargur Group

• Consists of narrow linear belts like Holenarsipur, Nuggihalli, and Nagamangla within the Gorur gneissic complex.
• Lithology includes ultramafic-mafic layered complexes, tholeiitic amphibolites, komatiites, BIF, quartzites, pelites, marbles, and calc-silicate rocks.
• Similar to true greenstones due to high mafic-ultramafic content in rocks.

Dharwar Supergroup

• Divided into Upper Chitradurga and Lower Bababudan groups.
• Exposed in two large schist belts known as superbelts: Bababudan-W. Ghats-Shimoga and Chitradurga-Gadag.

Bababudan Group/Schist Belt

• Covers about 2500 sq. km in Karnataka's Bababudan region.
• Mainly comprises basaltic volcanics, detrital, and chemical sediments.
• Stratigraphy includes Mulaingiri, Santaveri, Allampura, and Kalsapura formations.

Chitradurga Group/Schist Belt

• Extends over 450 km from Gadag to Mysore, preserving volcano-sedimentary sequences.

Stratigraphy of India

• Schist Belt Composition:
  • Bimodal Volcanics: The schist belt in India is mainly composed of bimodal (mafic-felsic) volcanics, including pillow basalt, greywacke, conglomerates, phyllites, BIF, quartzite, and chert.
• Formations in the Schist Belt:
  • Hiriyur Formation: One of the formations in the schist belt.
  • Ingaldhal Formation: Another significant formation in the schist belt.
  • Vanivilas Formation: Corresponds to a volcanic formation containing manganese and iron formations, stromatolitic carbonates, biogenic cherts, pelites, quartzites, polymict conglomerates, and metabasites.
• Features of Vanivilas Formation:
  • Manganese and Iron Formations: Found within the Vanivilas Formation.
  • Stromatolitic Carbonates: These are part of the composition of the Vanivilas Formation.
  • Biogenic Cherts: Cherts formed through biological processes.
  • Pelites, Quartzites, and Conglomerates: Other components of the Vanivilas Formation.

Summary of Unit 4: Dharwar Craton Geology

Western Dharwar Craton (WDC)

• Consists of the Bababudan Group followed by the Ingaldhal Formation.
• Ingaldhal Formation includes bimodal volcanics, pyroclastics, cherts, and phyllites.
• The Hiriyur Formation is made up of a greywacke-argillite suite with various rock types.
• Sedimentary structures in these formations indicate characteristics of turbidites.
• The Chitradurga Subgroup is intruded by the Chitradurga granite, dating back to around 2600 million years.

Eastern Dharwar Craton (EDC)

• Characterized by volcanic-dominated, sediment-poor greenstone belts with significant gold content.
• Greenstone belts are surrounded by younger granitoids and form linear arcuate belts.
• Major lithological types in EDC include Greenstone Belts (GSB) and Tonalite Trondhjemite Granodiorite (TTG) Granitoids.
• Basement-cover unconformities are absent in EDC unlike in WDC.

Distinct Features of EDC

• Greenstone belts in EDC are known as superbelts.
• Yeshwantanagar Formation in the Sandur belt shares similarities with the Bababudan Group.
• Most greenstone belts in EDC can be correlated with the Chitradurga Group in WDC.
• The Kolar belt is a significant area in EDC, known for its gold content.

Geological Ages and Formations

• The Kolar schist belt and the Ramagiri schist belt have similar ages of around 2700 million years.
• The Champion Gneiss is a prominent felsic volcanic and volcaniclastic suite found at the eastern margin of the belt.

Dharwar Supergroup Stratigraphy

• Dharwar Supergroup (2600-2800 Ma)
  • Kolar Group (Chitradurga Group)
    • Yashantanagar Formation (Bababudan Group)
    • Champion Gneiss
  • Stratigraphy of India Goldfield Volcanics
  • Proterozoic mafic dykes
  • Charnockites (2500-2600Ma)
  • Dharwar Batholith (2500-2700 Ma)
  • Banded Iron Formation (BIF)
  • Official LE'S Bimodal mafic-felsic volcanics, pyroclastics, Komatiites, BIF, cherts, greywackes, pelites, carbonate rocks, minor polymict conglomerate, minor basalt, and BIF
  • Felsic volcanics with volcaniclastics, wacke, volcanogenic polymict conglomerate, minor metabasalt with quartzite, manganiferous marbles, stromatolitic carbonate rock, calc silicate rock, pelitic schists with cordierite, andalusite, staurolite, garnet, amphibolites, BIF, and basic-ultrabasic sills
  • Base not seen (>3000 Ma) Mafic-ultramafic rocks, quartzites, BIF

Greenstone Superbelts in Dharwar Supergroup

• Ramgiri - Penakacherla Belt - Hungund Superbelt
• Kolar - Kadiri - Hutti Superbelt
• Velligallu - Raichur - Gadwal Superbelt

Generalized Lithology of Greenstone Belts

• Pyroclastic rocks, quartzites, conglomerates
• Greywackes with BIF
• Limestones and dolomites
• Bimodal volcanics and ultramafics

Closepet Granite

Closepet Granite marks the end of the Dharwar cycle. It signifies a significant geological boundary between the western and eastern crustal blocks.

Life in Dharwar Craton

• The stromatolite Batiola indica in Chitradurga Group
• Microbial trichomes in a black chert band of Sandur Schist Belt
• Microbiotic remains in stromatolite structures of Bababudan Group

Stratigraphy of Archaean Dharwar Craton

• Western Dharwar Craton (WDC)
• Younger granite and charnockite
• Chitradurga and Bababudan Groups
• Peninsular Gneiss and other groups
• Eastern Dharwar Craton (EDC)
• Dharwar Supergroup and younger granite/gneiss
• Charnockite, Foum, Um, Kolar Group, Yashwantanagar Formation

Mineral Potential

The western block is rich in copper, iron, and manganese. Bababudan schist belt holds significant economic deposits such as iron ores at Kudremukh, alongside gold, uranium, and asbestos. Notable auriferous belts in EDC include Kolar, Ramagiri - Penakacherla, Hutti, and Maski.

Cuddapah Supergroup

Proterozoic sedimentary basins like the Cuddapah Supergroup were formed in peninsular India between Late Palaeoproterozoic and Mesoproterozoic times. Vindhyan, Chhattisgarh, and Cuddapah basins are extensively developed Proterozoic basins on Archaean cratons.

Summary: Stratigraphy of India

Overview

• The stratigraphy of India involves studying the sedimentary sequences of the Vindhyan and Cuddapah basins.

Cuddapah Basin

• The Cuddapah basin is a distinct crescent-shaped basin situated in the south-central region of Andhra Pradesh and Telangana.
• It spans approximately 44,500 square kilometers and runs about 450 kilometers along the eastern edge of the Indian peninsula.
• The basin primarily comprises orthoquartzite-carbonate sequences, basic to acidic volcanics, and sills in the lower section. In contrast, the upper part consists of siliceous shales with quartzites.
• The estimated thickness of the basin varies from 6 to 12 kilometers.

Lithostratigraphy

• The lithostratigraphy of the Cuddapah basin is categorized into the Cuddapah Supergroup and the Kurnool Group.

Cuddapah Supergroup

• It is predominantly composed of arenaceous to argillaceous rocks with some calcareous to dolomitic units.

Kurnool Group

• The Kurnool Group, part of the Upper Proterozoic succession, overlies the rocks of the Cuddapah Supergroup.
• It mainly consists of carbonate sediments with minor amounts of fine clastics.

Vindhyan Supergroup

• The Vindhyan Supergroup is another significant geological formation in India.

Basin Map

• A map displays the major Proterozoic basins of peninsular India, including the Cuddapah and Vindhyan basins.

Unit 4: Cuddapah Basin Stratigraphy

Kurnool and Cuddapah

• Kurnool and Cuddapah are regions within the Eastern Dharwar craton.

Legend of the Cuddapah Basin

• The Cuddapah Basin holds significant geological importance in the region.

Kurnool Group

• The Kurnool Group is a geological formation in the region.

Srisailam Quartzite

• Srisailam Quartzite is a prominent geological feature in the area.

Nallamalai Group

• The Nallamalai Group is another geological formation in the region.

Chitravati Group

• The Chitravati Group is a significant part of the geological history of the area.

Papaghni Group

• The Papaghni Group is an essential geological unit within the region.

Granite and Basement Gneissic Complex

• Granite and Basement Gneissic Complex are important components of the geological makeup in the region.

Cuddapah Supergroup

• The Cuddapah Supergroup is a collection of geological formations in the region.

Stratigraphic Classification

• A fourfold stratigraphic classification was initially proposed by King in 1872 and remained uncontested for over a century.
• In 1976, Narayanaswami proposed a five-fold classification, which was later revised by Nagaraja Rao et al. in 1987 to a three-fold classification in line with the stratigraphic code.

Classification of Cuddapah Supergroup

• The Cuddapah Supergroup is divided into three main groups: Papaghni, Chitravati, and Nallamalai.

Sequence of Groups

• Each group within the Cuddapah Supergroup starts with quartzite and concludes with a shale unit, representing a cycle of quartzite-shale sequences that indicate successive transgressions in the basin.

Table 4.5: Stratigraphy of Cuddapah Supergroup

• Table 4.5 presents the detailed stratigraphy of the Cuddapah Supergroup.

Fig. 4.7: Cuddapah basin in the Eastern Dharwar craton. (Source: GSI, 1981b)

Block 2: Stratigraphy of India

Lithology of Cuddapah Supergroup

• Papaghni Group:
  • Vempalle Formation
  • Gulcheru Quartzite

• The Gulcheru Quartzite, part of the Papaghni Group, is the lowest formation in the Cuddapah Supergroup. Situated above the Archaean granitic basement, it exhibits an angular unconformity known as the Eparchaean unconformity over the greenstone belts of the Eastern Dharwar Craton. This formation primarily comprises conglomerates, arkoses, and quartzites. The conglomerate contains pebbles sourced from the Archaean basement.

  The Vempalle Formation, overlying the Gulcheru Quartzite, is predominantly composed of calcareous materials like stromatolitic dolomites, dolomitic shales, sandstones, quartzites, and cherts. It also features phosphatic and uraniferous horizons in its lower section. The Kuppalapalle Volcanics, found at the top of the Vempalle Formation, consist of tholeiitic basalt and basaltic andesite, with mafic igneous activity dating back to approximately 1800 million years ago.

  The sedimentation process in the Papaghni subbasin commences with the deposition of fluvial quartzites and conglomerates, interspersed with minor sandstone-shale intercalations of peritidal origin.

• Chitravati Group:
  • Gandikota Quartzite
  • Tadpatri Formation
  • Pulivendla Quartzite

• The Chitravati Group, well exposed in the Chitravathi and Cheyiar rivers, consists of three formations. These formations showcase distinct lithological characteristics and play a crucial role in the stratigraphy of the region.

Unit 4: Stratigraphic Succession in the Cuddapah Supergroup

• Introduction to Cuddapah Supergroup
  • The Cuddapah Supergroup is composed of several distinct groups and formations, showcasing a wide range of lithologies and geological features.
• Components of the Cuddapah Supergroup
  • Nallamalai Group: A significant portion of the supergroup, ranging from 3500 to 6000 meters in thickness.
  • Chitravati Group: Comprising formations with a thickness of about 4900 to 5000 meters.
  • Papaghni Group: Notable for its formation called Kurnool Group, spanning from 200 to 450 meters.
• Key Formations and Lithologies
  • Srisailam Quartzite: A 300-meter formation found within the Cuddapah Supergroup.
  • Cumbum (Pullampet) Formation: Characterized by a variety of rock types, including slate, phyllite, quartzite, and dolomite.
  • Bairenkonda (Nagari) Quartzite: Consists of conglomerate, quartzite, and shale layers, sometimes with intrusions.
• Distinct Features and Unconformities
  • Angular Unconformity at Cumbum (Pullampet): Signifying a significant geological gap between rock layers.
  • Eparchaean Unconformity: Marks the boundary with the crystalline basement of the Dharwar Craton, indicating a major geological shift.
• Interpretation of Formations
  • Pulivendla Quartzite: Identified by its thin yet persistent horizon comprising quartzites and conglomerates.
  • Tadpatri Formation: Characterized as an argillaceous unit with intermittent quartzite layers.

Block 2: Stratigraphy of India

• Stromatolitic Dolomites and Volcanogenic Sediments

  India exhibits stromatolitic dolomites alongside volcanogenic sediments. The Tadpatri Formation notably contains substantial felsic pyroclastics.

• Gandikota Quartzite

  The Gandikota Quartzite, named after the Gandikota Fort, showcases a gradual transition with the Tadpatri Formation. Comprising shales, glauconite-bearing quartzites, and thick ripple-marked and cross-laminated quartzites, it reflects a depositional environment ranging from sub-tidal to shallow marine, with overlaps of carbonate tidal flats.

• Sandstone and Conglomerate

  • Sandstone

    Includes well-bedded and low-dipping Gulcheru sandstone, showcasing distinct features.

  • Conglomerate

    Features chertified stromatolites within cherty dolomite of the Vempalle Formation, as depicted in field photographs.

Unit 4: Nallamalai Group

• Nallamalai Group Overview

  The Nallamalai hill range showcases the Nallamalai Group, divided into two formations:

  • Cumbum Formation linked with Pullampet Formation
  • Bairenkonda Quartzite linked with Nagari Quartzite

• Bairenkonda Quartzite

  The lower Bairenkonda Quartzite formation, primarily found at Bairavunikonda, comprises a mix of quartzite-pelitic cycles and a substantial quartz arenite layer.

• Nagari Quartzite

  Nagari Quartzite is a thick-bedded sandy unit with basal conglomerates.

• Cumbum Formation

  The Cumbum Formation, named after Kambhan village, is a shaly sequence interspersed with quartzites and dolomites.

• Pullampet Formation

  The Pullampet Formation comprises purple and calcareous shales with layers of dolomite and quartzite, sitting above the Nagari Quartzite.

• Srisailam Quartzite

  Situated along the Krishna river, this formation contains red quartzites and ferruginous quartzites, suggesting deposition in a shallow marine to tidal flat environment.

• Igneous Activity

  The region experiences significant igneous activity including dolerite, picrite, gabbro sills, basaltic flows, ignimbrites, and ash fall tuffs.

• Life in Cuddapah Basin

  The Lower Cuddapah rocks feature notable columnar stromatolites, offering insight into ancient organic remains like Conophyton and algal mats.

• Mineral Potential

  The Cuddapah basin harbors various mineral deposits including the renowned Koh-i-noor diamond. It also boasts industrial minerals like chrysotile asbestos, baryte, base metals, diamond, phosphorite, uranium, steatite, clay, and ochre.

  • The basin's mineral richness extends to raw materials such as high-grade limestones, dolomite, flooring stones, and slate.

Block 2: Stratigraphy of India

G102

Fig. 4.10: Steatite mine in Vempalle Formation near Rayalacheruvru. (Photo credit: Prof. R.C. Hanumanthu)

Learners, you have learnt about the stratigraphic classification of Dharwar Craton and Cuddapah Supergroup. Before discussing the Vindhyan Supergroup, let's go through some questions to review your understanding.

Short Answer Questions (SAQ 1)

• a) Mention the basis for division of Dharwar into two blocks.
• b) What is the significance of quartz-pebble conglomerate (QPC)?
• c) List two greenstone belts of WDC and EDC.
• d) Write about the life reported in the Cuddapah Supergroup.
• e) List formations of Cuddapah Supergroup with igneous activity.

4.4 Vindhyan Supergroup

The Vindhyan basin is a significant Proterozoic basin located in the Indian Peninsular shield on the Bundelkhand craton. It is the largest single Proterozoic basin shaped like a sickle. The basin spans across Rajasthan, Madhya Pradesh, Uttar Pradesh, and Bihar. Vindhyan sediments cover an extensive area, with a portion directly observable while the rest is concealed by Deccan Traps and Indo-Gangetic alluvium.

The Vindhyan basin is divided into three sub-basins: Rajasthan, Bundelkhand, and Son valley sector. The Bundelkhand sector is primarily composed of carbonates, whereas the Son valley and Rajasthan sectors contain both siliciclastics and carbonates. The term 'Vindhyan' for this Supergroup was introduced by Thomas Oldham in 1856.

The Great Boundary Fault Zone separates the Vindhyan basin from the Aravalli-Delhi orogenic belt in the west. The basin's geological formations and structure vary across these sub-basins, showcasing a mix of different sediment types.

In summary, the Vindhyan Supergroup stands out as a remarkable geological feature in India, offering insights into the country's ancient geological history.

Vindhyan Supergroup

• Vindhyan derives its name from the Vindhyan Mountains in Central India.
• It consists of a 4500m thick sedimentary pile with sandstone, shale, and some carbonates.
• Vindhyan rocks exhibit exceptional preservation of sedimentary structures.

Stratigraphic Classification

• The Vindhyan basin studies began with D.H. Williams in 1848.
• T. Oldham proposed a three-fold division: Kaimur, Rewa, and Bhander in 1856.
• Lower Vindhyan was termed Semri by F.R. Mallet in 1869.
• Auden divided the Vindhyan Supergroup into four groups chronologically: Bhander, Rewa, Kaimur, and Semri.
• Common terms include Lower Vindhyan (Semri Group) and Upper Vindhyans (Kaimur, Rewa, and Bhander groups).

Lithology

• The lithology of the groups mentioned in the table is as follows:
• Bijawar Group
• Bundelkhand Granite/Archaean

Stratigraphy of India

• Vindhyan Supergroup (Meso-Neoproterozoic)
  • Bhander Group
    • Bhander Group consists of:
      • Maihar Sandstone
      • Sirbu Shale
      • Bundi Hill Sandstone
      • Lakheri Limestone
      • Ganurgarh Shale
      • Govindgarh Sandstone
      • Drummondganj Sandstone
      • Jhiri Shale
      • Asan Sandstone
      • Panna Shale
      • Simrawal Shale
  • Kaimur Group
    • Kaimur Group includes formations like:
      • Dhandraul Quartzite
      • Mangesar Formation
      • Bijaigarh Shale
      • Markundi Sandstone
      • Ghurma Shale
      • Sasaram Sandstone
  • Semri Group
    • Semri Group formations consist of:
      • Suket Shale
      • Rohtas Limestone
      • Chorhat Sandstone

Alternative Names

• Various formations in the Vindhyan Supergroup have alternative names such as:
  • Upper Bhander Sandstone
  • Bargawan Limestone
  • Lower Bhander Sandstone
  • Kheinjua Shale
  • Chopan Porcellanite
  • Kajrahat Limestone

Semri Group

• The Semri Group:
  • Derives its name from the Semri River near Bijawar
  • Rests with a non-conformity on the Bundelkhand granite and on the Banded Gneissic Complex
  • Basal succession includes conglomerates, ferruginous sandstones, and shales
  • Stromatolitic limestones and dolomites suggest a continental shelf setting

Unit 4 Summary: Pyroclastics and Volcanics

Chopan/Deonar Porcellanite Formation

• The Porcellanite comprises tuffaceous beds, pumice tuffs, agglomerates, breccia, bedded chert, and volcanic bombs.
• Olive Shale, also known as Kheinjua Shale, is characterized by its olive green color and distinct pencil fracture.
• Overlying the Olive Shale are stromatolite-bearing Fawn colored limestones or Bargawan Limestone, featuring prominent Collenia clappii and Conophyton garganicus.
• Fawn Limestone is succeeded by Glauconitic Sandstone (Chorhat Sandstone).

Rohtas Limestone and Sasaram Sandstone

• Rohtas Limestone of the Semri Group (Lower Vindhyan) is followed by the Sasaram Sandstone of the Kaimur Group (Upper Vindhyan).
• The lithologies of the Semri Group indicate a varied depositional environment ranging from lagoonal to subtidal.

Stratigraphy of India

• Bundelkhand Granite marks the unconformable contact with the sandstone of Lower Vindhyan.
• Upper Vindhyan consists of sandstone, while Lower Vindhyan features limestone.

Kaimur Group

• Kaimur Group, named after the Kaimur scarp, shows a conformable contact with the Semri Group.
• It primarily consists of an argillo-arenaceous succession.
• Sasaram Sandstone forms the base of the Kaimur Group, followed by the Markundi Sandstone, with the Ghurma Shale or Susnai Breccia in between.
• Block 2: Stratigraphy of India
  • Depositional Environments:
    • The stratigraphy of India indicates deposition in various environments like barrier beach dune, tidal flats, lagoons, and braided ephemeral streams.
    • For instance, the Bijaigarh pyritiferous shale near Amjhore, with significant sulfur content, suggests a tranquil lagoonal setting.
    • The Mangesar Formation and the overlying Dhandraul Quartzite, composed of arkosic and arenitic sandstones, are interpreted as braided ephemeral stream deposits or sandy intertidal flat or tidal channel deposits.
  • Kaimur Group Rocks in Son Valley, Sonbhadra District
    • The Kaimur Group rocks exhibit a range of depositional settings, including tidal channels and intertidal flats.
    • Fig. 4.13a provides a panoramic view of the geological formations in the region, offering insights into the sedimentary history of the area.
  • Rewa Group
    • Origin and Composition:
      • The Rewa Group derives its name from the historical Rewa State.
      • It comprises the Panna Shale and Asan Sandstone, characterized by red shales, limestones, barytes, and glauconitic siltstones, indicative of lagoonal environments.
    • Stratigraphic Sequence:
      • The basal Panna Shale, lacking a basal conglomerate, suggests uninterrupted deposition from the preceding Kaimur Group.
      • Distinctive Features:
        • The presence of diamondiferous conglomerate at Panna separates the Jhiri Shale from the Asan Sandstone.
        • Red shales with glauconitic siltstones signify lagoonal, lacustrine, or offshore conditions.
    • Geological Significance:
      • The Drummondganj Sandstone, located above the Jhiri Shale, is indicative of shore environments, emphasizing the diverse depositional history of the region.

Stratigraphy of the Vindhyan Group

• Vindhyan Group Overview:
  • Sedimentary Layers: The Vindhyan Group consists of various sedimentary formations that offer insights into past environments.
  • Govindgarh Sandstone: Represents a coarse, immature layer possibly formed in a fluvial, deltaic, or tidal flat setting.
  • Bhander Group:
    • Ganurgarh Shale: Contains chocolate-colored shale with stromatolitic limestone and sandstone interbeds, suggesting a complex depositional history.
    • Lakheri Limestone: Shows features like algal mats, stromatolites, and gypsum layers, indicating an evaporitic environment.
    • Bundi Hill Sandstone: Represents a sequence that fines upwards, possibly reflecting changing sediment sources.
    • Sirbu Shale: Contains halite casts, indicative of oxidizing to arid conditions.
    • Maihar Sandstone: Characterized by sedimentary structures and stromatolitic limestone beds, suggesting a specific depositional environment.
• Age of Vindhyan Group: Radiometric dating places the initiation of Vindhyan sedimentation around 1600-1720 Ma, with different units showing varying ages.
• Fossils and Life in Vindhyan:
  • Stromatolites: Fossils like Collenia clappii and Conophyton garganicus found in the Fawn Limestone provide evidence of ancient life forms.
  • Microfossils: Cyanobacterial, bacterial, algal, and fungal remains found in Semri and Bhander groups, along with trace fossils, indicate diverse life in the past.
  • Other Life Forms: Small shelly fauna, primitive brachiopods, Ediacaran fauna, and trace fossils further enrich the paleontological record of the Vindhyan Group.

Key Ages and Environments

• Environmental Interpretation: The lithological characteristics of the Bhander Group suggest a shoreline-lagoon-tidal flat environment.

Stratigraphy of Delhi Supergroup

• Delhi Supergroup is a significant part of the Aravalli craton, located in the northwestern region of the Indian shield.
• It extends over a distance of approximately 700 km from Gujarat in the southwest to Delhi in the northeast.

Geological Context

• The Aravalli craton, where the Delhi Supergroup is situated, is bordered by the Himalayas in the north, the Vindhyan basin and the Deccan Traps in the east, the Cambay graben in the southwest, and recent alluvium lies to the west.
• It is renowned for its rich base metal resources and is made up of the Banded Gneissic Complex, Aravalli Supergroup, and Delhi Supergroup.

Chronological Order

• The Delhi Supergroup is Mesoproterozoic in age and is part of the Aravalli Fold Belt.
• It consists of three main groups: Raialo, Alwar, and Ajabgarh. These groups are arranged chronologically.

Raialo Group

• At the base of the Delhi Supergroup, the Raialo Group comprises well-sorted Basal conglomerates indicating a beach environment.
• Basic volcanics with sedimentary interbeds are present, including agglomerates, volcanic breccia, and welded tuffs.

Mineral Potential

• The Delhi Supergroup is known for its mineral resources, including base metals, building stones, laterite, ochre, and glass sand.
• Noteworthy occurrences of mineralisation and native sulphur have been observed in the region.

Unit 4: Stratigraphic Sequences of Delhi Supergroup

• Delhi Supergroup Composition:
  • Ajabgarh Group:
  • 
    
    • Position: Youngest group in the Delhi Supergroup, overlying Alwar Group.
    • Composition: Primarily consists of carbonaceous shales, phyllites, and quartzites.
    • Formations: Kushalgarh, Sariska, Thanagazi, Bhakrol, and Arauli.
    • Sequence: Arauli Formation followed by basic and acid intrusives.
  • Alwar Group:
  • 
    
    • Position: Overlies the Raialo Group.
    • Composition: Predominantly arenaceous, comprising conglomerates, feldspathic quartzites, orthoquartzites, and arkoses, with minor shales.
    • Depositional Environments: Braided stream, subtidal, and tidal flat environments.
    • Formations: Rajgarh, Kankwarhi, and Pratapgarh.
  • Raialo Group:
  • 
    
    • Formations: Acids intrusives, basic intrusives, Arauli-Mandhan, Bharkol, Thana-Ghazi, Seriska/Weir, and more.
• Dogeta Formation:
• 
  
  • Composition: Includes brecciated and ferruginous quartzite, chert, breccia, carbon, phyllite, and marble.
  • Features: Contains impure marble with phosphorite lenses, back flows, agglomerate tuff, and more.
• Serrate Formation:
• 
  
  • Composition: Oligomictic conglomerate, quartzite, phyllite, and schist.
• Tehla Formation:
• 
  
  • Composition: Quartzite, marble, gritty quartzite, conglomerate, and more.

```In the Delhi Supergroup of northeastern Rajasthan, Unit 4 comprises formations such as Dogeta, Serrate, and Tehla in a specific order of superposition as detailed in Table 4.7. The stratigraphic sequence of the Delhi Supergroup is a key aspect to understand the geological history of the region. Here is a breakdown of the different groups and formations within the Delhi Supergroup:- Ajabgarh Group: This is the youngest group within the Delhi Supergroup and lies above the Alwar Group. It mainly consists of carbonaceous shales, phyllites, and quartzites. The Ajabgarh Group is further divided into formations like Kushalgarh, Sariska, Thanagazi, Bhakrol, and Arauli, with Arauli Formation being overlain by basic and acid intrusives.- Alwar Group: Positioned above the Raialo Group, the Alwar Group is primarily composed of conglomerates, feldspathic quartzites, orthoquartzites, and arkoses, with minor shales. These sedimentary rocks indicate deposition in braided stream, subtidal, and tidal flat environments. The Alwar Group consists of formations such as Rajgarh, Kankwarhi, and Pratapgarh.- Raialo Group: This group consists of various formations including acid intrusives, basic intrusives, Arauli-Mandhan, Bharkol, Thana-Ghazi, Seriska/Weir, and more, contributing to the stratigraphy of the region.- Dogeta Formation: Comprising brecciated and ferruginous quartzite, chert, breccia, carbon, phyllite, and marble, the Dogeta Formation also features impure marble with phosphorite lenses, back flows, and agglomerate tuff.- Serrate Formation: Characterized by oligomictic conglomerate, quartzite, phyllite, and schist, the Serrate Formation adds to the geological diversity of the region.- Tehla Formation: This formation includes quartzite, marble, gritty quartzite, and conglomerate, showcasing the varied lithological composition within the Delhi Supergroup.