DISCOVERY OF A JUVENILE MASS MORTALITY BED OF FRESHWATER VIVIPARID GASTROPODS IN DECCAN INTERTRAPPEAN HORIZON OF BARGA, MADHYA PRADESH, INDIA

Mass mortality event (MME), in general, reflects catastrophic demographic events (global or regional) affecting all or nearly all existing organic groups due to climatic extremes and/or other environmental influences like pollution irrespective of size. But it may often happen that certain age groups of an organism, particularly the juveniles are affected by biotic and/or abiotic factors resulting in juvenile mass mortality events and preserved as a mass mortality bed. The present study is on such a local juvenile mass mortality niche in the Upper Cretaceous Intertrappean strata that is exposed at Barga in Madhya Pradesh, India; where fossil juveniles of freshwater gastropod Viviparus are clustered in a bed. In modern environments, Viviparids usually occur in clusters, not with special dissemination and prefer perennial shallow energy freshwater environments with some vegetation as habitat, i.e. slow flowing parts of the rivers and ox-bow lakes. Viviparids being ovoviviparous genus, there is greater chance of survival of the young, as those are born with well-developed shells of about 5-7mm in diameter on an average and represents the first month representatives of the youngest individuals. This recent data correspond well with our sample. But encountering a mass mortality bed of juveniles in preferred habitat reveals the opposite, as the MMEs appear to be associated with a rise in disease emergence, biotoxicity and events produced by multiple stressors. But the stratum encountered in the present study is apparently solely affected by Deccan Trap intrusion and the related events. The gaseous emanations might have enhanced significantly toxicity of the aquatic environment which was subsequently incremented by sudden rise in temperature (temperature hike due to Deccan Trap volcanism was many times higher than the accepted Late Cretaceous Hothouse temperature 25.5°C). So, the juvenile mass mortality bed might be representing an anoxic environment produced due to thermal as well as chemical stress.