Palynology of the Jurassic-Cretaceous transition in the Rajmahal Formation,West Bengal,India

Borehole PGD-1A penetrated Cretaceous Rajmahal Formation and underlying Triassic Panchet Formation between 288–423.51 m. Palynoassemblages recovered within the Mesozoic sequence are assigned to three palynozones closely comparable to Australian assemblages. The oldest palynozone is the Verrucosisporites-Lundbladispora zone, which occurs between 373.5–376 m in the uppermost Panchet Formation. The first occurrence of Callialasporites turbatus occurs at 373.5 m and signals the presence of Jurassic deposits. The overlying Infratrappean greyshales (371.5–354 m) of the Rajmahal Formation is represented by the Murospora florida palynozone of Late Jurassic age. The youngest palynozone identified is the Cicatricosisporites australiensis zone which occurs within the Inter-trappeans (346.35–295.0 m) of the Rajmahal Formation. Based on ages assigned to the M. florida and C. australiensis zones in Australia, the Rajmahal Formation is dated as Oxfordian-Berriasian. The first appearance datums (FADs) of Cicatricosisporites australiensis, Crybelosporites stylolsus, Aequitriradites spinulosus and Lycopodiacidites dettmannae suggest that the Jurassic-Cretaceous boundary probably lies just within the interval 346.35–328.81 m in Inter-trappean bed II.