Significance of Lockeia and associated trace fossils from the Bada Bagh Member, Jaisalmer Formation, Rajasthan

A Lockeia-Protovirgularia ichnofauna representing the Cruziana ichnofacies is reported from a calcareous sandstone horizon of the Callovian Bada Bagh Member, Jaisalmer Formation, Rajasthan. The ichnoassemblage is characterized by Lockeia cunctator, L. siliquaria, Protovirgularia? bidirectionalis, P. rugosa, Ptychoplasma vagans along with Palaeophycus tubularis, P. striatus, Heliophycus isp. and ?Lophoctenium isp. Use of numerical analysis yielding length to width ratio, slopes and coefficient of determination helps in confirming identification of ichnospecies of Lockeia. Fine morphological details of Lockeia and Protovirgularia, especially sharp and closely spaced chevrons of Protovirgularia, indicate that the substrate in which they were emplaced was stiff, resistant, dewatered and better consolidated. Therefore, it construes that this ichnoassemblage belonging to the classical Cruziana ichnofacies occurs in stiff softground and not a typical softground. Though the ichnofacies of this calcareous sandstone bed indicates low-medium energy condition under subtidal environment of deposition, underlying strata containing Arenicolites, Skolithos and Curvolithus of Skolithos ichnofacies indicate intertidal sandy shore environment with high energy conditions. Thus, it is concluded that this area was undergoing continuous, gradual deepening. However, the percentage of Thalassinoides, Ophiomorpha and Phycodes in the overlying bed is quite high suggesting an increase in the energy conditions resulting from a probable shallowing.