A new acritarch spike of Leiosphaeridia dessicata comb. nov. emend. from the Upper Permian and Lower Triassic sequence of India (Pranhita-Godavari Basin): Its origin and palaeoecological significance

Abstract

The Permian–Triassic Mass Extinction (PTME) event was the largest bio crisis to date, adversely affecting life on land and sea. The PTME event is evidenced in India by the destruction of glossopterids with immense loss of peat-forming vegetation, its replacement by stress-tolerant lycopsids, Lilliput Effect and the presence of numerous acritarchs and abnormal pollen grains. However, there are no reports for algal or acritarch spikes. We document, for the first time, an acritarch spike in the Indian subcontinent from the uppermost Permian to Lower Triassic sequence from the Pranhita–Godavari (P-G) Basin. Lithostratigraphically, the late Permian and Early Triassic aged deposits in the P-G basin are designated as the Kamthi Formation. The formation has a very rich and diverse assemblage of pollen grains, spores and acritarchs. Based on a palynological study, an abundance of Leiosphaeridia dessicata comb. nov. emend. has been identified from sediment samples from the two bore cores (MCP-7 and MCP-8) of the Chintalapudi sub-basin, P-G basin. The acritarch appearance and abundance occurred in synchronization with the floral shift. The acritarch appears along with the stress-tolerant lycopsid spores in the uppermost Permian assemblage and increases in accordance with lycopsid spores in the Lower Triassic assemblages.The morphology of Leiosphaeridia dessicata comb. nov. emend. relates its close affinity with an extant marine algal cyst of Acetabularia acetabulum. Moreover, the presence of gammacerane and methylate chromans in the host sediment indicates the hypersaline water column during the deposition. Thus, based on the presence of marine and hypersaline biomarkers and affinity of L. dessicata comb. nov. emend. with marine alga (probably Prasinophyceae or Chlorophyceae) infer that the deposition during the uppermost Permian and Lower Triassic occurred under shallow marine conditions, contradictory to the earlier belief that Indian Upper Permian and Triassic deposits are entirely terrestrial. The possible marine incursion in the P-G basin may have occurred from the eastern continental margin along western Australia or through a passage between the Indian southern margin and the west margin of Antarctica.