Natural Casts of Early Eocene Entobia from the Kachchh Basin, India

摘要

Excellently preserved natural casts of sponge borings Entobia Bronn from the Early Eocene rocks of the Kachchh basin, India are reported for the first time. The entobian bioerosion is represented by four ichnospecies viz., Entobia cateniformis, E. geometrica, E. ovula, and E. paradoxa. Molds and casts of bivalves belonging to family Carditidae served as substrate for these sponge borings. The relation between mode of preservation of the natural casts, sea water chemistry, and time of emplacement of borings is discussed. The bored bioclasts are associated with Schaubcylindrichnus, Thalassinoides, and Rhizocorallium. This study indicates that the sediments of Assilina Limestone Member were deposited in turbidity-free, shallow water with nil or low rates of sedimentation.