Gondwana S.G. (Damodar, Satpura, Mahanadi & Godavari basin)

Gondwana Supergroup is made up of continental sediments that were deposited in fluvial and lacustrine basins in different parts of the Indian Peninsula. This deposition begins from Late-carboniferous/ Early Permian (300 Ma) and continued until the Early Cretaceous Epoch (100 Ma). Lower part of the Gondwana sequences contain rich coal deposits. Barakar formation is the major storehouse of coal in all the basins.

Flora of the Gondwana Basin

Plant remains that are abundant in all parts of the Gondwana Supergroup are drifted materials that are deposited in the lacustrine and fluvial basins. Floral assemblages differ in the lower and upper parts of the sequence. Assemblage of lower part is referred to as Glossopteris-Gangmopteris flora and those of upper part comprises the Dicroidium-Lepidopteris-Ptillophyllum flora.

• Equisetaceous plants were common in swamps and damp woods during the deposition of the lower part of the sequence.
• Cycads and conifers are the dominant in the upper part of the Gondwana Supergroup.
• The Gondwana flora consists of predominantly seed ferns, such as Glossopteris, Gangmopteris, Sphenopteris and Sphenophyllum.
• Glossopteris is the foliage or the front of a tree whose rhizome (underground stem) is preserved as a fossil known as Vertibraria.
• The dominant land plants of the Triassic Period were the Cycadales that ranged in height from one to 18 meters, resembling modern palm tree in their appearance.

Cycodeoidales belong to the extinct class of plants that were common in Mesozoic forests. The flowering plants evolved from this class of extinct plant during the Cretaceous Period.

Generalized stratigraphy of Gondwana Supergroup

The term Gondwana is used for the sequence of continental rocks that is exposed below the Deccan Traps in the region south of the Narmada River.

• Major Gondwana basins of India occupy the three major tectonic belts of the Indian Peninsula.
  • Narmada-Son Damodar Graben
  • Mahanadi Graben
  • Prahnita-Godavari Graben

Basin wise Stratigraphy of the Gondwana Deposits

Talchir Formation (Talchir Boulder Beds) :

This formation rests unconformably over the basement of either Archaean gneisses and schists or proterozoic age and it found in all basins.

They are also known as Talchir Tillites since they show some features of glacial origin. The Talchir formation contains a few fossils of seed ferns, such as Gangmopteris cyclopteroides and Glossopteris indica and it’s characteristic stem Vertebraria indica.

• Marine intercalation : Intercalation of marine beds in the basal part of the Gondwana succession has been reported from Umaria District in Madhya Pradesh and at Manendragarh in Koriya District of Chhattisgarh. These bed contains marine fossils such as Products, Spiriferina and Reticularia, which suggests a Lower Permian age. The faunal assemblage also indicates a warmer climate. It shows that the deposition of the talchir formation began with glacial condition that was soon followed by warmer climate and marine transgression covering some aprts of the Gondwana basins.
  • First marine transgression is represented by the marine beds at Manendragarh, a extended arm of Tethys Sea through sikkim to Central India.
  • Second marine transgression is represented by the marine beds at Umaria, along the Narmada-Son Lineament as an engulfment of the sea from the west.
• Bap and Badhaura Formation : The boulder beds that are exposed near Bap NE of Jaisalmer have been correlated with the Talchir Boulder Beds. The boulder beds of conglomerate, sandstone and varved clays of fluvio-glacial origin that is named as Bap Formation. The Bap Formation is conformably overlain by succession of alternation of sandstone and clay, which is named as Badhaura Formaion.

Damuda Group

The Damuda Group of the type section has been divided into four lithostratigraphic units named as Karharbari Formation, Barkar Formation, Kulti Formation and Raniganj Formation. The pebbly and arkosic sandstones of the Karharbari Formation and basal Barakar Fromation were deposited in channels of braided streams.

• The lower most subdivision of the Damuda Group, Karharbari Formation is comprised of sandstone of sandstone, grit, conglomerate and coal seams.
• Barakar Formation : It rests unconformably over the Karharbari Formation is named after the river in Jharkhand. The Coal beds were deposited in peat swamps in distal floodpains and lakes of meandering streams.
• Kulti Formation / Barren Measures : It gradationally overlie the Barakar Formation. It consists of channnel like cross-bedded sandstone interbedded with siltstone and ironstone shale deposited in meandering streams. Facies variants are the lower Pali Formation in the Umaria area and Motur Formation in Satpura areas. The formation is devoid of workable coal seams and have Ironstone Shale Formation.
  • The Kulti Formaitonl; and Motur Formation have yielded scanty megaflora. The mega flora assemblager consists of Cyclodendron, Glossopteris indica and G. conspicua.
• The youngest unit of Damuda Group is known as Raniganj Formation consists of cyclic succession of sandstone-shale-coal beds. The floral assemblage is characterised by a maximum growth of the Glossopteris flora.
• The Kamathi Formation of the PG Basin has been correlated with the Raniganj Formation. The micaceous and fine-grained sandstone-shale sequence of the Satpura Basin is also known as Bijori Formation, which has beed also correlated with the Raniganj.

“The total thickness of the coal seams adds up to about 5% of the total thickness of the Damuda Group “

Upper Gondwana Sequence

The floral record shows a rapid change with the culmination of the Glossopteris Flora during the Permian-Triassic transition. This was rapidly followed by the appearance and growth of the Lepidtoris-Dicrodium flora in the lower part and Ptillophyllum flora in the upper part of the Upper Gondwana seqnences.

• Damodar Basin : The Raniganj Formation of the Damodar basin is overlain with a slight unconformity by the Panchet Formation. The Lower Triassic age for the formation has been inferred mainly on the basis of its vertebrate fauna.
• Satpura Basin : The Kamthi Formation of the Lower Gondwana Group is unconformably overlain by a thick succession of red beds of continental facies, which has been named as Mahadeo Group. The Mahadeo Group of central India is conconformably overlain by a clastic sequence known as Jabalpur Group.
  • Mahadeo Group is further divided into three formations, Pachmarhi sandstone, Denwa Clays and Bangra Conglomerate. They line one over other and also shows lateral gradation from one to another.
  • Jabalpur Group is further divided into Chaogaon beds, Jabalpur beds, Bansa beds.
• Rajmahal Hills : The Barakar Formation of the Lower Gondwana Group in the Rajmahal Hills is unconformably overlain by succession of Dubrajpur Formation of Upper Triassic. The Dubrajpur Formation is conformably overlain by a succession of volcanic flows of traps called as Rajmahal Formation.
• Mahanadi Valley Basin : The Kamathi Formation of Lower Triassic age in the Mandla Plateau in MP. is overlain by thick succession of cross-bedded, immature, feldspathic sandstone and arkose with abundant amount of brick-red shale and siltstone, this succession was earlier referred to as Pali/ Tikri beds. Tjis formation is rests over the coal measures of Damodar Group in Son Valley.
  • The Pali Formation is overlain by coarse sandstone of violet and red shades. This succession has been named as Parsora Formation. It yields Dicrodium.
• Godavari Basin : A continuous succession of Lower and Upper Gondwana rocks is exposed in the Godavari Basin. The Upper Gondwana that conformably rests over the Kamathi Formation of the Godavari basin is named as Maleri Stage.
  • Maleri stage is further divided into Yerrapalli, Bhimasaram, Maleri, Dharmaram, Kota and Gangpur beds. The lower three formation was also referred to as “Mangli Beds”.