Algal Structures from the Upper Krol-Lower Tal Formations of Garhwal and Mussoorie Synclines and their Palaeo-Environmental Significance

Abstract

Algal pisolites, oncoids, columnar stromatolites and columnar layered stromatolites have been recorded from cherty dolomitic limestones from Upper Krol and Lower Tal formations. The algal mat facies show bird's eye structures and irregular fenestral fabric suggesting an intertidal supratidal environment of deposition for Upper Krol (D and E) Formation of Garhwal syncline. The basal Lower Tal Formation of Mussoorie syncline also represents a complex algal oncoidal-stromatolitic (protected tidal flat/lagoonal) facies with restricted circulation. The association of phosphorite with stromatolites and oncoids proves the phosphorite to be deposited in a shallow water environment. The presence of pyrite and associated black shales indicate an erobic condition.