PROVENANCE VARIATION IN PERMO-CARBONIFEROUS SILICICLASTIC SEQUENCES FROM CENTRAL-EASTERN INDIAN PLATFORM

Repeated fluctuations during Permo-Carboniferous climates lead to the termination of the late Carboniferous glaciation and successive marine transgressions, triggering deposition of thick Gondwanan sequences in multiple intracratonic basins at the Indian subcontinent. Sediment samples collected from these basins show variability in both petrochemical and mineralogical characters indicating changes in the depositional environment and their provenance.

A total of 15 sandstone samples were collected during previous field seasons from Jharia basin in eastern India and Barapukuria, Jamalgonj and Khalashpir and Dighipara basins in Bangladesh. Modal composition of the lower Gondwanan Talchir Formation in Jharia basin varies significantly with the upper quartzose samples of the Barakar Formation. In contrast, samples from Bangladesh are arkosic to sub-arkosic based on modal composition and vary ~5-8% in compositional modes. Heavy mineral analysis shows mixed assemblages of heavy minerals including garnet, apatite, rutile, spinel, tourmaline, zircon and opaque minerals which are mostly magnetite, hematite and possible limonite and ilmenite. Minor amount of epidote, sphene and staurolite were also observed in some samples. There is a significant increase in zircon-tourmaline-rutile (ZTR) percentage in the Barakar Formation ~34% whereas all other samples have an average of less than ~10%. Microprobe analyses of 75 garnet grains from the samples indicate a combination source terranes between amphibolite and granulitic metamorphic rocks.

Modal analysis of the sandstones suggests possible multiple source terrain and likely to be the Prydz Bay Belt and the Kuunga orogen in northeastern Antarctica, the Pinjarra and the Albany-Fraser orogen in southwestern Australia as well as the Indian craton. Ongoing whole rock geochemistry and microprobe analyses of the heavy minerals would strengthen narrowing down the trend of source terranes and is expected to provide additional information to understand the tectonic evolution of the eastern Gondwana.