First Report of Trace Fossils from Palaeogene Succession (Namunagarh Grit) of Andaman and Nicobar Islands

The Namunagarh grit of Eocene age in South Andaman island is a submarine fan deposit where sedimentation occurred in deep marine environment mainly by turbidity currents. The mudstone and fine-grained sandstone of the turbidite sequence yielded three ichnogenera viz Thalassinoides, Teichichnus and Lorenzinia.

Typically shallow marine Thalassinoides burrows co-occur with deep water burrows represented by Teichichnus and Lorenzinia, indicating a dominant control of substrate, availability of food and rate of sedimentation against bathymetry on distribution of trace fossils. Trace fossils are particularly abundant in the mudstones pointing to a strong lithofacies control. A well-oxygenated muddy bottom with a low rate of sedimentation is envisaged.

An order in the succession of traces could be deciphered. Simply constructed burrows of Thalassinoides appeared initially followed by complex structures of Teichichnus and ornate Lorenzinia.