Tracking temporal palynofloral changes close to Cretaceous-Paleogene boundary in Deccan volcanic associated sediments of eastern part of central Deccan volcanic province

摘要

Deccan volcanic sequences( DVS) in the central Deccan volcanic province( CDVP) are designated as Sahyadri Group having ~ 500 m thick lava pile associated with multiple sedimentary beds at different stratigraphic levels. In the eastern part of CDVP between the latitude 19 °55 '--20 °25 ' N and the longitudes 78 °15 '--78 °30 ' E,palynological investigation of the intertrappean sedimentary beds at five stratigraphic levels was carried out. The study was basically aimed for tracking the floral and environmental changes across the Deccan transition. The resulting finds indicate that the intertrappean sediments at the lowest stratigraphic level between the earliest lava flows are characterized by presence of marker Maastrichtian palynomorphs- Gabonisporis vigourouxii,Aquilapollenites bengalensis,Azolla cretacea and Farabeipollis associated with triporate and tricolpate pollen grains,phytoliths of Oryzeae of Poaceae family and peridinoid dinoflagellate cysts. The increasing volcanism deteriorated the existing flora as evident by absence of pollen-spores and presence of only structured biodegraded organic matter,fungal spores,acritarchs and algal( Botryococcus) remains in the sediments of higher-up in the sequence. For chronostratigraphic constraints on the lava flows magnetic polarity of the flows bracketing the intertrappean beds was investigated. The results indicated presence of N-R-N-R magnetic polarity in the basal lava pile that are interpreted as representing the magnetochron C30 N to C28 R( Maastrichtian-Paleogene). The floral change begins with the onset of volcanism in the chron C30 N and floral deterioration is observed in C29 N with increasing volcanism and it is only in the chron C28 R( Danian) that some evidence of recovery of flora is recorded. The current study shows that in eastern part of CDVP the post Cretaceous-Paleogene boundary eruptions represent the main phase of eruptions that triggered deterioration of the flora.