Southeastern Section - 60th Annual Meeting (23–25 March 2011)

Paper No. 1
Presentation Time: 8:00 AM-12:00 PM


ALAM, Md.I.1, UDDIN, Ashraf2 and HAMES, Willis E.2, (1)Boone Pickens School of Geology, Oklahoma State University, 105 Noble Research Ctr, Stillwater, OK 74078, (2)Department of Geosciences, Auburn University, 210 Petrie Hall, Auburn, AL 36849,

Permo-carboniferous Gondwanan sequences are preserved well in Indian subcontinent which along with Australia and Antarctica constituted eastern Gondwanaland. These siliciclastic sequences are drilled in intra-cratonic basins in the northwestern Bengal basin of Bangladesh. Around several coal bands, this ~1 km thick sequence consists primarily of massive and trough cross-bedded sandstones, laminated mudstones, and occasional conglomerate layers.

The twelve sandstone samples analyzed from these sequences are primarily poorly sorted and sub-arkosic, with some compositions ranging from quartz-arenite to litharanites. Non-opaque heavy minerals constituted dominantly of rutile, followed by amphiboles, garnets and few serpentines.

Laser 40Ar/39Ar ages were determined for single crystals of detrital muscovite of the Gondwanan sequence in order to evaluate possible source(s). A total of 106 detrital muscovite crystals were analyzed from a sandstone sample collected at 375 m depth of GDH-58/01 well located at Khalashpir, northwest Bengal Basin. The distribution of age population in a probability plot represents a singular mode that is entirely confined to a range from 480 Ma to 500 Ma, which could be derived from an orogenic belt in Antarctica. As none of the muscovite crystals analyzed yielded Precambrian ages, it appears that the Indian and East Antarctic shield areas were not source terranes for the samples analyzed.

The Ross orogenic belt, with peak metamorphic events during 502-480 Ma, was the most likely source terrane for these sediments. Specifically, the pelitic schists and quartzofeldspathic gneisses from the Nimrod Group (499-496 Ma) in the Geologists Range, and the mica schists from the Lanterman Metamorphic Complex (482 Ma) in the Lanterman Range within the Ross orogenic belts were likely have been the source rocks.

Ongoing study on additional sediment samples will help provide detailed information on detrital history of these Gondwanan sequences.