Gondwana flora and fauna and its importance

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Introduction

• Gondwana term was coined by B. Medlicolt.
• Based on ‘Gond tribe’ this is dominant in that area the name Gondwana has been suggested.
• Gondwana period is from Upper Carboniferous to lower Cretaceous.
• The Gondwanaland is the southern part of Pangea and separated from Laurasia during mid-Mesozoic era dated 200-180 Mya.
• These rocks represent one of the most important phases of Indian geology having dominance of coal formation.
• The Gondwana rock sequence represent almost 6 km thick succession of fluviatile (water body generated rock) and Lacustrine (Lake deposits), having a glacial deposited succession at the base.
• These rock sequences represent a long episode of continental sedimentation on which began in later Carboniferous and closed during early Cretaceous representing a total time of 180 my or more.
• The study of rock succession has revealed that the beginning of Gondwana sedimentation started with glacial phase having predominance of tillites.

Stratigraphy of Gondwana Supergroup

• The suturing of Gondwana has taken place in between 570 and 510 mya thus the east part of Gondwana joined with west Gondwana.
• The Gondwana sediments has overlying on the three tracts including-
  • Koel-Damodar
  • Son-Mahanadi
  • Pranhita-Godavari Basins

Distribution of Gondwana basin

The classification of Gondwana is of two type depends upon the difference in lithology and presence of fossils i.e. paleontological evidence such as-

• Two fold classification- This classification was given by Meddlicott and W.T Blanford. The classification was done by dividing Lower Gondwana from Upper Gondwana on the basis of presence of Glossopteris and Ptilophylum.
• Three fold classifications- The classification was given by Hughes and he had given the classification by identifying the mixed flora such as Dichroidium in between the beds of Glossopteris and Ptilophylum floras.

Two-Fold Classification System

Three-Fold Classification System

Talcher Formation

• The formation overlie unconformably on Archean schist and gneiss (Proterozoic age).
• The main lithology of the formation is
• Fossils of flora found here such as- Glossopteris indica and Gangamopteris cyclopteroides belongs to the category of seed ferns.

Karharbari Formation

• The lithology of this group is pebble beds, conglomerates, sandstone and siltstone with thin streak of coal beds.
• The characteristic fossil of this group is Gondwanidium burriada.

Barakar Formation

• The formation consist of approx 250 m thick sediments.
• The lithology consist of conglomerate, grits, sandstones and coal seams.
• China clay is of economic importance from this formation.
• Fossils: Glossopteris communis, G. Indica, Gangamopteris.

Barren Measure Formation

• The lithology of the group consist of alternating beds of ferrugineous sandstones, micaceous siltstone and ferrugineous shales.
• This formation of devoid of fossils.

Raniganj Formation

• The lithology of this group is sandstones, shale, coal seams.
• The coal of this group is very fine and of good quality.
• Fossils: Glossopteris flora reaches its acme.

Panchet Formation

• The lithology of this group consists of greenish-brownish type sandstone varieties with the presence of shales at its lower portion.
• The lower part of the formation is devoid of coal seams.
• Fossils: Various mega and micro-flora assemblages such as Pecopteris,Glossopteris, Schizoneura and also invertebrates living in fresh water such as thecodont, reptiles(Dicynodonts),amphibians(Gonioglyptus).

Mahadeva Formation

• The formation has divided into-
  • Panchmarhi Sandstone- Coarse-grained and cross-bedded sandstones.
  • Denwa Clays- Consist of fossils of Mastodonasaurus indicus.
  • Bagra Conglomerate- Coarse ferruginous sandstones and conglomerate.
• Fossils: Vertebraria, Glossopteris, Pacopteris, Conifer seeds.

Rajmahal Hills

• These hills are the plateau basalts.
• Lithology- Fine-coarse dolerite with groundmass consist of pigeonite, labrodorite, augite.
• Fossils- Intertrappean beds consist of plant fossils such as Dictyozamites - Pterophyllum and species of fishes, cycads, pteridophytes and conifers.

Jabalpur Formation

• Lithology- white clays, massive sandstones, sandy conglomerate.
• Fossils-  Pteridosperms, Gangamopteris, Vertebraria and mammalian fana, Amphibians and pisces.

Gondwana Flora and Fauna

• India was a member of the hypothetical supercontinent Gondwanaland existing toward the southern pole during Permo-Carboniferous- Lower cretaceous times.
• Gondwana flora of India is conventionally divided into two parts, Lower Gondwana flora or Glossopteris flora and Upper Gondwana flora or Ptillophyllum

Flora and Fauna of Gondwana Group

Lower Gondwana flora

• Glossopteris flora is the purest of the contemporaneous Permian flora showing least admixture.
• The earliest members of this flora are Gangamopteris, Glossopteris, and Noeggerathiopsis, which are found within the shales above the glaciogene Talcher tillites of lowermost Permian age.

Origin and geographic distribution

• Evidently, Glossopteris flora grew as an indigenous product from the few plants. It was left at the end of the carboniferous glaciation that affected the entire Gondwanaland.
• Occurance of dissacate pollens and presence of poorly preserved stems with growth rings from glacial tillites of Talchir formation indicate, that its earlier members were co-existing with late carboniferous glaciation, but Glossopteris itself and other members of this flora are believed to be post-glacial.
• In India Glossopteris flora are found localized within the sedimentary rocks deposited along the Son-Damodar basins (covering MP, Bihar, West Bengal), the Pranhita –Godavari basins of Andhra Pradesh and Maharastra and the Mahanadi basins of Odisha .

Botanical affinity

• Floral elements mostly include Pteridosperms, however pteridophytes like lycopsids, sphenopsids and filicales are also found but in less abundance.
• Most of the fossils are carboniferous. Carbonized and petrified fossils are also found.
• Close association of the leaf fossils Glossopteris , stem fossil Vertebraria , Fructication Dictyopteridium and dissacate pollen within rocks may indicate that those may be the parts of the same plant.

Fossil components and Stratigraphic distribution

Upper Gondwana flora

• Rich in cycad-conifer plant assemblage occurring within the Mesozoic Gondwana sediments. As the cycad Genus Ptillophylum is the most abundant member of the flora, it is also known as Ptillophyllum Flora.
• Geographical occurrence: Chief occurrences of upper Gondwana flora are scattered all over the main Gondwana province of peninsular India.

Gondwana Fauna

• Vertebrate fossils are considerable variety in the Gondwana formations, particularly in the upper gondwana.
• A majority of the vertebrate fossils were found in the Upper Gondwana sediments of the Pranhita – Godavari valley, though some species have been described from some of the other basins as well.
• The interesting finds include Crutaceans , insects , ostracods ,coprolites .                                                                                                                                       
• Kotatherium haldenii, a therian symmetridont from the kota formation is the first reported earliest mammal from India.
• Indochelys spatulata and the first ever record of flying reptile Campylognathoids indicus are both from this formation.
• Fossil reptile Lystrosaurus occurs in the panchet formation of Raniganj coalfield.