PETROCHEMICAL AND MINERALOGICAL STUDY OF PERMO-CARBONIFEROUS SILICICLASTIC GONDWANAN SEQUENCES FROM CENTRAL-EASTERN INDIAN PLATFORM

Permo-carboniferous discrepancy in climate lead to the termination of the late Carboniferous glaciation and successive marine transgression, triggering deposition of the Gondwanan sequences in multiple intracratonic basins of the Indian platform. Sediment samples collected from these basins show variability in both petrochemical and mineralogical characters indicating changes in the depositional environment and simultaneously providing information for possible source terrain composition for the sediments as well as their mixing.

A total of 15 sandstone samples were collected 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 and vary ~5-8% at most 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 possibly 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 the other samples have an average of less than ~10%. Electron microprobe analyses of 75 garnet grains from the samples indicate mixture of garnet grains from possible amphibolite and granulitic metamorphic terranes.

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 electron microprobe analyses of the heavy minerals would strengthen narrowing down the trend of source terranes that shredded these sediments and is expected to provide significant information that would help understand the tectonic evolution of the eastern Gondwana.