Trace Fossils and Sedimentary Depositional Environment: A Case Study from Early Permian Barakar Formation, Raniganj Basin, India

Abstract

Behavioral responses of organisms with respect to changing environment have a wide area of research possibility. For a palaeontologist it is a challenge to interpret the organism-sediment interaction from the study of the trace fossils preserved in the ancient rock record. The ethological significance which is derived out of different intentional or accidental activities of the organisms may be preserved within the rock and is largely controlled by the substrate stability, grain size of the sediments, energy and rate of sedimentation of the driving process, types of nutrients and its supply, salinity, temperature and oxic/sub-oxic/an-oxic conditions etc. So, the viability of this study in sensu stricto depends on the preservation potential of the organism as a whole or in parts or its activities (indirect evidences) on or within the substrate upon which they have survived thousands and millions of years ago. The indirect evidences of the organism’s activities may be its locomotory/respiration/feeding/resting/dwelling/predating traces etc. which have different nomenclature based on their morphological classification. The study area encompassing the major river section of the Barakar, Khudia, Ajoy holds partly enriched and partly impoverished trace fossils within the sedimentary rocks hosting huge reserves of coal. There are several concepts regarding the depositional setting of the studied basin like formerly interpreted fluvio-lacustrine depositional model to recently reinterpreted fluvio-tide-wave dominated depositional model. Several invertebrate traces have been recorded from the study area namely Planolites, Thalassinoides, Ophiomorpha, Palaeophycus, Cylindrichnus, Diplocraterion which indicates diverse environmental settings ranging from supratidal/intertidal/subtidal to continental shelves whereas other solo/uniform traces observed like Chondrites, Skolithos, Rhizocorallium etc. are indicator of shallow subtidal to marine quite water setting. Here the additional challenges include the lack of ample exposures, weathered exposed rock sections, inaccessible mine cut sections, absence of body fossils and controversial identification of trace fossils in differential erosive surfaces. This chapter in short has tried to mitigate these problems by the integrated sedimentary and ichnological facies association studies in delineating the depositional environment of the studied basin.