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Barail Gr
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Barail Gr base reconstruction

Barail Gr

Period: 
Paleogene

Age Interval: 
Oligocene


Province: 
North East Basins of India, Bangladesh SE

Type Locality and Naming

Evans named the rock unit as the Barail Series after the Barail Range of Assam and this was later emended by B Biswas to the Barail Group. It represents the geosynclinal development of Oligocene.


Lithology and Thickness

Clayey sandstone. The unit comprises arenaceous and in places shaly and carbonaceous rocks. It has three formations, from bottom to top: the clayey sandstone Laisong Fm, sandy claystone Jenam Fm and sandstone Renji Fm.


Lithology Pattern: 
Clayey sandstone


Relationships and Distribution

Lower contact

It lies conformably overlies the Kopili Fm shale of the Jaintai Gr

Upper contact

It has a sharp unconformably to the Bhuban Fm (lowest formation in Surma Gr)

Regional extent

Khasi & Jaintia Hills, Naga Schuppen Belt, Tripura Cachar, SE Bangladesh: It is well developed in the Surma valley, north Cachar and the Khasi and Jaintia hills of Assam. In Bangladesh the area between Jaintiapur in the east and the Dauki Nala in the west belongs to the Renji Fm based on the lithology and the fossil content of the exposed rocks. Rocks belonging to the Jenam Fm were encountered in the well Atgram-iX at depths ranging from 4,740 to 4,980 m without reaching the base of the formation. Also rocks lithologically comparable to the Renji Fm are penetrated in the well Atgram-iX between 4,015 and 4,740 m depth.


GeoJSON

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Fossils


Age 

Oligocene

Age Span: 

    Beginning stage: 
Priabonian

    Fraction up in beginning stage: 
0.0

    Beginning date (Ma): 
37.71

    Ending stage: 
Chattian

    Fraction up in the ending stage: 
0.8

    Ending date (Ma):  
23.89

Depositional setting


Depositional pattern:  


Additional Information

The unit has economic importance for its workable coal seams and oil-producing horizon in Upper Assam.


Compiler:  

Largely copy-pasted from Banglapedia (National Encyclopedia of Bangladesh as compiled by several geologists; http://en.banglapedia.org/index.php/Geological_Group-Formation; 2015)