295 D22. From Processes to Stratigraphy

Wednesday, 25 October 2017
8:00 AM - 12:00 PM
Ballroom 6C

SEDIMENTATION AND TECTONICS OF PLIOCENE-PLEISTOCENE HIMALAYAN CLASTIC WEDGES IN THE BENGAL BASIN

Paper number: 295-7
Program: Technical Sessions
Time: 9:30 AM – 9:45 AM

Authors

Abstract

Depositional history of Pliocene-Pleistocene clastic wedges in the Bengal basin provides data pertaining to uplift and erosional history of the hinterland areas (i.e., Himalayas, Indo-Burman Ranges and Shillong Plateau). Nearly 2.5-km-thick molassic Dupi Tila sediments deposited into the Bengal foreland basin as a result of a continent-continent (Eurasia-India) collision with the closing of the oceanic crust. Clastic wedges are composed of yellow, light brown, and pink, coarse- to very fine-grained, sandstone, siltstone, silty clay, mudstone and shale with some pebble beds.

Sandstone petrographic studies, heavy mineral analyses, sandstone chemistry, and bulk rock chemistry of mudrocks depict an orogenic detrital history for clastic wedges. Modal analyses of the sandstones from the Sitapahar anticline, Garo hills, Stable Platform, Sylhet Trough and Lalmai hills provide a quartzolithic composition which indicates that the sandstones were derived from orogenic provenance. The distribution of sedimentary and metamorphic lithic fragments in the provenance field indicates a source of low- to intermediate-grade metamorphic terrains. The relative abundance of aluminosilicates and ultra-stable minerals in the sediments throughout the Bengal basin reflect unroofing of deeper crustal levels. Garnet, epidote and chloritoid chemistry also support derivation from a low- to high-grade metamorphic facies rocks. Finally, the chemical indices of alteration from the bulk rock chemistry of mudrocks reflect an active continental provenance of felsic rocks.

Comparison of clastic detritus from the Eocene through Pliocene-Pleistocene reflects a progressive unroofing of the orogenic source regions. Lithic fragments in Eocene sandstones are mostly sedimentary, reflecting supracrustal sources whereas metamorphic lithic fragments, particularly intermediate- to higher-grade types, become increasingly more abundant through time, reflecting unroofing to deeper crustal levels.

Geological Society of America Abstracts with Programs. Vol. 49, No. 6

doi: 10.1130/abs/2017AM-306121

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