2000 GSA Annual Meeting -- Reno, Nevada
2000 GSA Annual Meeting -- Reno, Nevada
Author(s): UDDIN, Ashraf, Department of Geology and Geography, Auburn University, Auburn, AL 36849 (uddinas@auburn.edu); STRACKE, Andreas, and ODOM, A. Leroy, Department of Geological Sciences and National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL 32306
Keywords: Isotope, Himalayas, Bengal basin, Provenance
The formation of the Bengal basin of Bangladesh is directly related to orogenic activity in the Himalayas and the Indo-Burman ranges. Proximal deposition of a portion of these orogenic sediments in the Bengal basin has built a thick sequence (as high as 20 km) of deposits, which holds considerable potential for recording the erosion and thus the tectonic events in the Himalayan and the Indo-Burman mountain belts. Petrologic and subsurface studies reveal that orogenic sedimentation already had begun in the Bengal basin by the Miocene time. Isotope ratios of Miocene clastics from the Bengal basin provide constraints on sediment provenance. Kilometers of thick Miocene sediments from the Surma Group, deposited in fluvial, deltaic and shallow marine environments, have a relatively uniform 87Sr/86Sr isotope ratios (about 0.7212-0.7274). The Lesser Himalayan rocks from the Himalayas, dominated by Precambrian metasedimentary terranes, have 87Sr/86Sr ratios generally greater than 0.8. The High Himalayan Sedimentary Series, located above the Main Central Thrust, however have 87Sr/86Sr isotope ratios ranging from 0.7061-0.7290. Isotopic ratios of the rocks from the Indo-Burman ranges are yet known. These data are interpreted to indicate that the likely source(s) for the Miocene Surma Group is either located in the High Himalayas or the yet characterized Indo-Burman ranges. Distinctly higher 87Sr/86Sr ratios, reported for stratigraphically equivalent sediments sampled by ODP cores at more distal areas in the Bengal Fan, might indicate mineralogical sorting of sediment transported from the Himalayan and the Indo-Burman ranges, or contributions from Precambrian rocks of the Indian Peninsula.
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