Group	Formation	Member	Lithological Description	Thickness (m)
Surma	Bokabil		Erosive contact Gray to light gray fine grained well-sorted sandstone with sandy shale and siltstone. Lenticular bedding, micro cross-lamination, ripple marks and concretion are present. Conformable surface.	330+
	Bhuban	Upper	Alternation of sandstone, silty shale and shale. Grayish white to grayish gray through yellowish gray medium to fine grained hard sandstone and siltstone which are massive as well as variously structured by graded bedding, flat bedding, ripple lamination and lenticular lamination. Bluish black thinly laminated silty shale to shale. Blue to black laminated and exfoliated weathered shale with massive mudstone.	260
	Bhuban	middle	Mainly shale with subordinate sandstone and siltstone. Black thinly laminated shale with lenses of sandstone and siltstone, which are grayish white. Bluish gray to gray massive and variously stratified sandstone. Matrix supported conglomerate locally present. Base not found.	130