Geological Time Scale with Indian Examples

The geological history of the Earth is divided into distinct chronological units: Eons, Eras, Periods, and Epochs. In Indian geology, these global time divisions correspond to specific stratigraphical systems categorized by the Geological Survey of India (GSI) into four major eras: Archean, Purana, Dravidian, and Aryan.

Archean Eon / Era (Early Precambrian)

The Archean represents the oldest geological phase, dating from the formation of the Earth’s crust (around 4,000 million years ago) up to 2,500 million years ago. It forms the structural foundation or “basement complex” of the Indian Peninsular shield.

Archean Gneisses and Schists (The Basement Complex)

• Chronology: Formed before 2,500 million years ago.
• Characteristics: Highly metamorphosed, crystalline rocks, devoid of any fossils due to their ancient origin.
• Indian Examples: The Bundelkhand Gneiss (Central India), Nilgiri Gneiss (South India), and Bengal Gneiss. These form the roots of the Indian Peninsula.

Dharwar System (Transition System)

• Chronology: Late Archean to Early Proterozoic (2,500 to 1,800 million years ago).
• Characteristics: The oldest metamorphosed sedimentary rock system in India. It is highly metalliferous but completely unfossiliferous.
• Indian Examples: Found extensively in the Dharwar and Shimoga districts of Karnataka, the Aravalli range (Rajasthan), and the Champion reef (famed for gold). This system contains India’s richest iron ore, manganese, copper, and gold deposits.

Proterozoic Era / Purana Rock System (Late Precambrian)

The Proterozoic or Purana era (2,500 to 541 million years ago) is characterized by the formation of thick sedimentary basins in large synclinal depressions over the Archean basement.

Cuddapah System

• Chronology: Early Proterozoic era.
• Characteristics: Unfossiliferous clay, slates, quartzites, and limestones deposited in ancient synclinal basins.
• Indian Examples: The Cuddapah basin of Andhra Pradesh. Other representations include the Delhi Ridge system and the Bijawar series in Madhya Pradesh. It is rich in building stones, asbestos, and barytes.

Vindhyan System

• Chronology: Late Proterozoic to Cambrian edge (1,300 to 600 million years ago).
• Characteristics: Vast sedimentary formations, largely unfossiliferous, though micro-fossils and primitive algae signatures have been traced.
• Indian Examples: Stretching from Sasaram (Bihar) to Chittorgarh (Rajasthan). It is famous for producing high-quality durable sandstones used in historical monuments (e.g., Sanchi Stupa, Red Fort) and diamond-bearing pipes (Panna in Madhya Pradesh and Golconda in Telangana).

Paleozoic Era / Dravidian Rock System

The Dravidian system spans from the Cambrian period to the Middle Carboniferous period (541 to 340 million years ago). This era is minimally represented in the Peninsular shield but is highly developed in the Extra-Peninsular (Himalayan) region.

Cambrian to Silurian Periods

• Characteristics: Abundant marine life fossils appear for the first time in Indian stratigraphy.
• Indian Examples: The Haimanta System in the Spiti Valley (Himachal Pradesh) and Kashmir. These strata contain rich marine fossils of trilobites, brachiopods, and primitive corals.

Devonian and Carboniferous Periods

• Characteristics: Marked by marine transgressions in the northern zone.
• Indian Examples: The Lipak and Po series in the Spiti Valley. The Muth Quartzite of the central Himalayas acts as a distinct chronological marker for the Devonian period in Indian stratigraphy.

Mesozoic to Cenozoic Eras / Aryan Rock System

The Aryan system begins from the Upper Carboniferous period and continues to the Holocene epoch. This is the most dynamic era in Indian geology, witnessing the disintegration of Gondwana Land, massive volcanism, and the uplift of the Himalayas.

Gondwana System (Upper Carboniferous to Jurassic)

• Chronology: 320 to 140 million years ago.
• Characteristics: Terrestrial Sedimentary deposits formed in structural sync-faults and river basins under humid climatic conditions, leading to rich swamp vegetation preservation.
• Indian Examples: The Damuda series (Raniganj and Jharia coalfields), Talchir series (Odisha), and Panchet series. This system holds nearly the entire workable coal reserves of India.

Triassic, Jurassic, and Cretaceous Sedimentary Systems

• Characteristics: Marine incursions into the continental interiors during plate drift.
• Indian Examples: The Triassic Lilang system of Spiti; the Jurassic Marine formations of Kutch (famous for ammonite fossils); and the Cretaceous beds of Trichinopoly (Tamil Nadu), rich in marine gastropods.

Deccan Traps (Late Cretaceous to Paleocene)

• Chronology: 67 to 60 million years ago.
• Characteristics: Intense, non-explosive fissure eruptions over the western and central peninsula as India passed over the Reunion hotspot, forming a stepped volcanic plateau.
• Indian Examples: The Deccan Plateau covering Maharashtra, parts of Gujarat, Madhya Pradesh, and northern Karnataka. Denudation of this basaltic lava has produced India’s fertile Regur (Black Cotton) soil.

Tertiary / Cenozoic System (Eocene to Pliocene)

• Chronology: 65 to 2.5 million years ago.
• Characteristics: The collision of the Indian and Eurasian plates resulting in the three distinct phases of Himalayan uplift.
• Indian Examples:
  • Oligocene-Miocene: Formation of the Greater Himalayas.
  • Mid-Miocene: Uplift of the Lesser/Middle Himalayas (Murree and Karewa formations).
  • Pliocene: Uplift of the Outer Himalayas / Siwalik System, containing rich mammalian fossils.

Quaternary System (Pleistocene to Holocene Epochs)

• Chronology: 2.5 million years ago to Present.
• Characteristics: Recent alluvial accumulations, glacial deposits, and hominid evolution.
• Indian Examples: The Indo-Gangetic-Brahmaputra alluvial plains; the Karewa formations of Kashmir (famous for saffron cultivation, preserving Pleistocene glacial-lacustrine sediments); and the older (Bhangar) and newer (Khadar) alluvial terraces.

Chronological Summary of Indian Rock Formations