Lithology and Age of the Tal Formation in Garhwal, and Implication on Stratigraphic Scheme of Krol Belt in Kumaun Himalaya

Abstract

The Tal Formation, containing datable fossil assemblages in the Lansdowne hills in Garhwal, occupies a crucial position at the top of the 6100-metre thick succession of predominantly unfossiliferous sediments constituting the Krol Nappe. The lithostratigraphic unit comprising of (i) Lower Permian fossil-bearing black shale (often phosphatic), mudstone, conglomeratic greywacke and mudstone, (ii) a variety of sandstone of varied colour and (iii) sandy, oolitic and shelly limestone, lithologically indistinguishable and tectonically inseparable from the formation recognized as the Tal, the limestone of the upper horizon of which has yielded Upper Permian fossils. The lower member of the Tal progressively thins out southward until finally disappearing so that the considerably attenuated middle member and the upper limestone member rest directly on the Krol, thus exhibiting transgressive overlap.

The Permian Tal is unconformably capped by the Subathu of Eocene age, implying that the whole of Mesozoic group is missing in the Lesser Himalaya. The Krol which conformably underlies the Tal is not Permo-Triassic as commonly believed and the Blaini that rests upon the Nagthat cannot be equated with the Upper Carboniferous Talchir formation of Peninsular India. The occurrence of Lower Palaeozoic bryozoan remains in the slate and calcareous beds resting on the Nagthat quartzite in the Nandhaur valley, southeast of Nainital, corroborates the Lower Palaeozoic age assigned to the Blaini.