Palaeosynecology Of Continental Molluscan Fossils In The Intertrappean Rocks Of Madhya Pradesh India A Multifaceted Approach

Abstract

Continental molluscan fossils of essentially cherty intertrappean rocks exposed at Deori,Karondi,Barga,Rajendragram,Bogwania,Ukala of Madhya Pradesh have been studied in terms of taxonomic refinement and ecologic precision. Previously,it was thought that the fossils represent different species of freshwater genera of gastropod like Physa,Viviparus,Lymnaea,and bivalve genus Unio.But,the present study reveals that the assemblage of fossils is a good example of ecophenotypic plasticity of single species of different molluscan genera.So,the entire gastropod genus is represented by single variable morphospecies.Bivalves have been renamed as Margaritifera and Shahpuranaiain the same family Unionidae.The fossils are in situ and the cherty rocks are petrographically proved to be transformed product of paleosols, tuffaceous materials and fine siliciclastic sediments.That is,broadly continental deposits and cementation occurred in vadose zone of phreatic environment.The aforesaid molluscan genera are inhabitant of very shallow small riverine environment of the present day.Cross stratification is very common in fluvial environment.The presence of cross stratification in the intertrappean is indicative of lotic environment having coarser than muddy sediments in the substratum of riverbasin. Discovery of stenothyrid gastropod from the intertrappean for the first time as well as presence of numerous palm plant fossils indicates that the areas were near the river mouth where it is infested with tidal seawater activity.The geochemical values of Ba,Sr,Vand Ni have been determined to understand environmental condition of deposition and the interpretation of those values indicate that the depositing milieu was freshwater,at times brackish water.The environment was humid,oxic in most of the areas except at Gandhwani,where the environment was arid and anoxic.The depositing area in Gandhwani was very shallow perennial waterbody.Miniature sized fossils of the preexisting genera probably are an artefact of environmental newline