Abstract:
The present study deals with the Neoproterozoic mat-infested substrate sculptured by inferred bioturbations,
excellently preserved within the ca. 600 Ma Sonia Sandstone, northwest India. The bioturbations
are horizontal, being preserved on the bed-surfaces and have been classified into linear
grooves and discoidal structures. The linear grooves are of two types, one group represents a straight
to meandering pattern with raised sand ridges on either side, while the other group represents a mostly
meandering pattern with changing width along the length, without raised ridges. Both types of grooves
resemble trails of advanced organisms. The discoidal structures have five internal lobes emerging from
the centre and merging with the outer ring and may represent body impressions of an organism; alternatively
may represent variants of Ediacara or other soft bodied organisms. The interaction of the substrate
with these possible bioturbators has great significance in establishing the evolutionary history
of the substrate and resulting bioturbations during the Proterozoic. Microbial mats possibly provided
oxygen and nutrients to the organisms and played an important role in their preservation. The study also
tries to extrapolate the life style of these trace-makers. All these traces may raise speculation about the
onset-time of some higher order organisms.
