Spore tetrads, possible indicators of intense climatic regimes: case study from an early Permian stratum of Singrauli Coalfield, Son-Mahanadi Basin, India

A large number of naked, fossil spore tetrads assignable to the dispersed microspore genera Indotriradites, Microbaculispora and Microfoveolatispora are reported for the first time from an early Permian stratum (Lower Barakar Formation) of Singrauli Coalfield, Son-Mahanadi Basin, Central India. This is also the first record of tetrads from any Artinskian strata in the world. There is no evidence of any kind of sporangia or related plant parts in the present investigation that could ascertain the affinity of these tetrads; however, the presence of a trilete mark in the spores of the tetrads demonstrates their alliance at least with the pteridophyte group. The present study suggests possible factors affecting the sporogenesis process in the past, considering other available global records pertaining to fossil spore tetrads. The results of significant physiological and biochemical analyses performed on the anthers of modern plants related to reproductive biology, in order to understand the conditions and changes responsible for the formation of tetrads, are also considered. We analysed the globally occurring fossil tetrads and the palaeoclimates prevailing during their deposition. A correlation between extreme climatic conditions, specific pH values inside microsporangium and the formation of tetrad is envisaged. It is deduced that extreme climatic conditions (extreme cold/extreme hot) might have triggered some sort of malfunctioning in the sporogenesis process that altered the specific pH values inside the microsporangium. Any restraint of the activity of the callase enzyme, responsible for dissolution of callose walls laid between the individual spores, may therefore have apprehended the dissociation of tetrads into individual spores.