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Abstract

F ive well -preserved trace fossil species namely Thalassinoides, Ophiomorpha, Tube burrows, Rhizocorallium, and Halymenidium are reported from calcareous sandstone of Mandai Formation of the Barmer Basin, Mandai area, western Rajasthan. This is the first record from Barmer Basin. The Mandai Formation is about 24 -26m thick lithostratigraphic unit deposited in the north -western part of the Barmer Basin. It is unconformably overlies on Early Palaeocene Bariyara -Dharvi -Sajit Member of the Akli Formation and overlain by Giral- Thumbli Member of Akli Formation. Its upper sequences namely pebbly sandstone, coarse grained sandstone, coarse to medium grained sandstone and medium to fine grained sandstone are correlated with Mataji Ka Dugar Formation by Parihar, 2009. The lithology of the Mandai Formation, it has mixed siliciclastic, minor carbonate and phosphorite facies. Here Mandai Formation starts with calcareous sandstone which are indicate extensive bioturbation. These trace fossils are preserved of full relief in white calcareous sandstone and reddish brown ferruginous sandstone around Mandai village. The present investigation area is located about 15km from Fatehgarh on Fatehgarh to Jhinghiyali tar road. They are identified as Thalassinoides suevicus isp. (Y -shaped branching, full relief, smooth wall tubes, horizontal to slightly oblique, displaying a network of triple junction, produced by decapods crustaceans), Ophiomorpha isp . (Commonly occur as vertical or horizontal, cylindrical tunnels system, sometimes its branched and covered by elongate or irregular pellets arranged perpendicular to the long axis and produced by crustaceans), Tube burrows isp . (do not show any spreite structure possibly made by allied organisms), Halymenidium isp. (they show back fill structure (spreite) indicate activity by the animal for either feeding or dwelling purpose, the pattern formed by ribblets approaches pigtail design, ribblets move distinct and straight) and Rhizocorallium isp. (horizontally or obliquely oriented, U -shaped dwelling and feeding burrow that show spreite between the limbs of the U, produced by some kind of annelids). Heterodonts Bivalve fossils are also reported here by Parihar, 2009. The entire ichnogenera shows shallow marine depositional environment. No age can be assigned on the basis of these trace fossil species as they range from Cambrian to Recent. The present investigations are continuing to get more fossils and index fossils which will solve the status of Mandai Formation of Barmer Basin of Western Rajasthan.

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