Palynostratigraphic correlation of lower Gondwana sediments in the Chuparbhita and Hura Basins, Rajmahal Hills, Eastern India

Abstract

Correlation of palynostratigraphic zones of the adjacent Chuparbhita and Hura Basins reveals similar depositional environments. Distinct changes in climatic and ecological phases are key features of the depositional environment in the two adjacent basins. Three climatic phases recognised in the Chuparbhita Basin are (I) monosaccate Plicatipollenites-Parasaccites, (II) nonstriate disaccate Scheuringipollenites and (III) striate disaccate Striatopodocarpites-Striatites, while a single climatic phase of nonstriate disaccate Scheuringipollenites is recognized in the Hura Basin. Climatic phases are suggested from the relative abudance of the different saccate types viz., monosaccates, nonstriate disaccates and striate disaccates as cool, temperate and warm humid conditions respectively. Ten ecological phases have been identified in the Chuparbhita Basin within the three climatic phases and seven in the single climatic phase of the Hura Basin. Scheuringipollenites is the most extensive climatic phase of deposition in both the basins in which identical ecological phases are recognised at some corresponding horizons. Two marker horizons are recognised within the Scheuringipollenites climatic phase in the Chuparbhita and one in the Hura Basin. The marker horizons contain a distinctive assemblage of trilete and monolete taxa in addition to diverse acritarchs and prasinophytes viz., Peltacystia, Circulisporites, Tetraporina, Kagulubeites, Haplocystia and Maculatasporites. The Marker horizon I of PN H-5 of Hura is distinguished by the occurrence of diverse acritarch suites along with the key trilete genus Lalmatiasporites. PN C-9, with the key trilete genus Ghoshiatriletes and diverse acritarch suites identified as Marker horizon II, has not been encountered in the Hura Basin. The marker horizons may be considered as representing phases of brackish water transgression in the essentially continental sequence of deposition. Palynological evidence indicates an Early Permian age for both basins.