Study of stratigraphic distribution and lithology of Phanerozoic rocks of India with reference to fauna, flora and economic importance

  • The PhanerozoicEon is the current geologic eon in the geologic time scale, and the one during which abundant animal and plant life has existed.
  • It covers 541 million years to the present, and began with the Cambrian Period when animals first developed hard shells preserved in the fossil record.
  • The time span of the Phanerozoic starts with the sudden appearance of fossilized evidence of a number of animal phyla; the evolutionof those phyla into diverse forms; the emergence and development of complex plants; the evolution of fish; the emergence of insects and tetrapods; and the development of modern fauna.
  • Plant life on land appeared in the early Phanerozoic eon.
  • Tectonic forcescaused the continents to move and eventually collect into a single landmass known as Pangaea (the most recent supercontinent), which then separated into the current continental landmasses.
    • The Phanerozoic is divided into three eras: the Paleozoic, Mesozoic, and Cenozoic, which are further subdivided into 12 periods.
    • The Paleozoic features the rise of fish, amphibians and reptiles.
    • The Mesozoic is ruled by the reptiles, and features the evolution of mammals, and more famously, dinosaurs, including birds.
    • The Cenozoic is the time of the mammals, and more recently, humans.

Phanerozoic Rocks of Indian Subcontinent

  • Phanerozoic sedimentation in the Indian subcontinent in the backdrop of long geodynamic history.
  • Basins with varying tectonic affinity opened and evolved.
  • The Andaman-Nicobar outer arc tectonic prism formed on the leading edge of subducting Indian plate.
  • Quaternary deposits in Indian subcontinent offer scope to assess role of tectonics and climate.
  • The Paleozoic formations of India belong to the period from 570 to 245 million years. These are called as Dravidian systems, in India.
  • Most of them are distributed over the Extra-Peninsular region, and are very little in the Peninsular shield.

Cambrian System

  • The Cambrian System of India consists of the following formations:
    • The Salt Range containing the Salt Marl and Saline Series
    • The Spiti area containing the Haimanta System
    • The formations of Kashmir Valley.
  • The Cambrian period is the period in which plenty of fossil evidences have been obtained in India.
  • These are seen in all geological formations from this period.
  • Corals, Foraminifers, sponges, echinoderms, worms, gastropods, pelecypods, trilobites and brachiopods are the notable fossil assemblages found in these beds.
  • They also indicated marine conditions in these Palaeozoic rocks in India. Salt marl, purple sandstone, shales, slates, dolomites and quartzites, are the notable rocks of this system.

Ordovician System

  • The Ordovician system is exposed in the Northern Kumaon-Shimla regions containing mainly shales.
  • The Ordovician rocks of in Kashmir is exposed in the Lidar valley.

Silurian System

  • The Silurian rocks are seen in Spiti region.
  • They containg Red Crinoidal limestone of Griesbach and Zanskar Range.
  • The Silurian rocks of Kashmir are exposed in the Lidar valley.

Devonian System

  • The Devonian system of rocks are represented by the Muth Quartzites of Spiti, Kumaon and Kashmir.
  • Limestones with brachiopods and corals that are exposed in these rocks.

Carboniferous System

  • The Carboniferous system of rocks in India are distributed only in a few places in the Himalayan region in Kashmir. They contain fossiliferous limstones and shales.  They are called as Lipak and PO Series.

Gondwana System

  • The Gondwana System [derives its name Gonds, the most primitive people of Telangana and Andhra Pradesh.
  • They are deposits laid down in synclinal troughs on ancient plateau surface.
  • As the sediments accumulated, the loaded troughs subsided.
  • Fresh water and sediments accumulated in these trough and terrestrial plants and animals thrived.
  • This happened since Permian period (250 million years ago).
  • The notable coal deposits observed are:
    • Barakar Series
    • Jharia coal fields
    • Raniganj series
    • Panchet series
    • Mahadeva series
    • Rajmahal series and
    • Jabalpur series.
  • The upper carboniferous and Permian systems of India contain unique fauna and flora.
  • They are exposed in Spiti, Kumaon, Mount Everest  Region, Assam Himalaya,  Kashmir-Panjal Volcanic Series,  Simla-Garhwal-Krol series and in Eastern Himalayan regions like Sikkim
  • These are followed by the geological formations of Mesozoic era.

Mesozoic Era

  • The Mesozoic geological formations belong to the period between 245  million years and 66 million years.
  • It encompasses the formations of the Triassic, Jurassic and Cretaceous ages.
  • The formations are:
    • The Triassic System
    • The Jurassic System
    • The Cretaceous System and
    • The Deccan Traps.
  • The Triassic System is the earliest of all these systems in the Mesozoic era.

  • This period has shown a very rich and varied fauna and flora.
  • Numerous invertebrate fossils, including ceratites, ammonoids, brachiopods, Crinoids, echinoids and pelecypods have been observed in the rocks of this age. Amongst the vertebrates, fishes are quite abundant.  
  • In India, they are exposed as 
    • The Lilang system in Spiti
    • Northern Kumaon
    • The Chocolate Series
    • The Kalapani limstone
    • The Kuti shales and The Kioto limestone.
  • The Jurassic System is exposed as Spiti Shales, Laptal Series of Kumaon, Mount Everest Region, sub-Himalaya of Garhwal, Kutch and Rajasthan areas.
  • The Jurassic and Cretaceous Systems are known for their marine transgression.
  • Forminifera play an important part in Cretaceous stratigraphy.  The rocks contain limestones, sandstones and shales.

Deccan Trap

  • Volcanic outburst over a vast area of the Peninsular India from the end of the Cretaceous till the beginning of the Eocene gave rise to Deccan Traps.
  • Basaltic lava flowed out of fissures covering a vast area of about ten lakh sq km.
  • These volcanic deposits have flat top and steep sides and therefore called ‘trap’ meaning a ‘stair’ or ‘step’ in Swedish.
  • The process of weathering and erosion (denudation) since millions of years has reduced the Deccan Trap to almost half of its original size.
  • Present Deccan Trap covers about 5 lakh sq km mainly in parts of Kuchchh, Saurashtra, Maharashtra, the Malwa plateau and northern Karnataka.
  • Thickness of the Deccan Traps is 3,000 metres along the west which is reduced to 600-800 metres towards the south, 800 metres in Kuchchh and only 150 metres at the eastern limit.
  • The weathering of these rocks for a long time has given birth to black cotton soil known as ‘regur’.
  • Valuable resources of Quartz minerals, amethyst, agate, Onyx and many good gemstones occur in these volcanic rocks

The Cenozoic Era

  • The Cenozoic era of geological formations in India belong to the period from 66 million years to the present day.
  • The formations belonging to this age are:
    • The Tertiary Systems
    • The Eocene System
    • The Oligocene System
    • The Lower and the Middle Miocene
    • The Pliocene System and
    • The Pleistocene System.
  • The Tertiaries in India are called as Marine Tertiaries.
  • In the Tertiary period, in India, the Himalayan orogenic movements began.
  • It is also observed that the volcanism associated with the Deccan Traps has continued.
  • The rocks of this era have shown much valuable resources of petroleum and coal.
  • They are found in the Salt Range, Potwar Plateau, outer Himalayan regions of Jammu and Punjab, Assam, Sind and Baluchistan.
  • The Eocene System includes the rocks found in Sind and Baluchistan regions.
  • It includes the following unique geologic series of formations:
    • Ranikot Series,
    • Laki Series,
    • Kirthar Series,
    • Kashmir ranges,
    • Eocene Formations of Simla, Rajasthan, Kutch, Assam, Gujarat region
    • The Eocene beds of Cauvery Basin and Bengal Basin.
  • Oligocene and lower Miocene systems are exposed in the Cauvery Basin, Kutch and Rajasthan, Sind and Baluchistan, Potwar Plateau, Jammu, Simla Himalaya and Assam.
  • A lot of coal and petroleum resources of India are found in most of these formations.
  • The Miocene to Pleistocene formations are exposed as several unique systems and series.
  • The mammalian  fauna  are  represented  by  many  fossil 
  • The fossil  man  appeared  in  the Pleistocene period only. 
  • They geological formation of this period are :
    • The Siwalik System in north western India.
    • The Manchhar Series in Sindh
    • The Tipam and Dihing Series in Assam
    • The Dwarka Beds in Kathiawar
    • The Khar series in Kutch
    • The Varkala Beds in Coastal Kerala
    • The Cuddalore Sandstones in Tamil Nadu and
    • The Rajamahendri Sandstones in Andhra Pradesh.
  • Lignite, fire clays, ball clays, terra cotta clay, sandstones, shell-limestone, Kaolin and petroleum are the major economic natural resources of these formations.
  • The alluvium which is found in the Indo-Gangetic plain are all belonging to this era..
  • Human culture and global diversity in faunal and floral assemblages happened during the Pleistocene period.
  • Five major episodes of glaciation happened during the last 1 million years. The post glacial environment has indicated the development of Mesolithic human culture, in India, approximately about 20,000 years Before Christ.