Karharbari: a formation or biozone

Abstract

In the initial identification of the Karharbari sediment in Giridih Coalfield both litho- and bio- characters of the sediments were emphasized. Later, Karharbari has been considered as lithologically distinct unit, a definite palaeontological zone and both combined as a chronostratigraphic unit in between Talchir and Barakar. Karharbari is quite distinct in lithological composition, heavy mineral assemblage and coal seam characteristics. Stratigraphic delineation is not always distinct but from careful observation, Karharbari is identified as ‘formations’ in some of the basins or considered as basal member of Barakar Formation. Age of Karharbari has been suggested as Upper Sakmarian to Artinskian. The characteristic bioassemblage of Karharbari is more similar to Talchir bioassemblage in mega and palyno-floral compositional pattern. Botrychiopsis, one of the characteristic members of Karharbari bioassemblage and also a dominant member of the Pre-Gondwana Botrychiopsis Flora (Middle Carboniferous-Lower Permian) of South America (Brazil, Argentina) and Australia is not recorded from any other Indian Lower Gondwana horizions so far. Karharbari environmental facies (both climatic and ecological) were initiated during Talchir sedimentation. Terminologies, e.g., Karharbari megafloral assemblage and Karharbari palynofloral assemblage are proposed in the Karharbari biozone. Macroenvironment zone for Talchir- Karharbari and microenvironment zone of Lower Karharbari are recognized considering the environment of deposition. Talchir and Karharbari are considered as a biostratigraphic zone. The continuation of the marine transgressional phase during Karharbari is suggested by the occurrence of brackish water acritarchs.