PROVENANCE OF SANDSTONE OF TISTA FAN, NORTHWESTERN BANGLADESH

摘要

The Tista fan in Bangladesh is extended for about 181km from Banglabandha (apex) to Hakimpur (toe) in Dinajpur district with a south to southeasterly slope. Petrography of sandstone was carried out from trough cross-stratified sandstone fades (St) with grain size in between coarse to fine sand (Mesh No. 30 and 120) and the fades is exposed in majority of stations on the Tista fan. The sandstones of the Tista fan are composed of quartz fav. 31.3 percent), feldspar (av. 24.32 percent), rock fragments (av. 9.62 percent), mica (ar. 13 percent), heavy minerals (av. 7.37 percent) and some unidentified minerals (av. 14.39 percent). The rock fragment includes granule- and pebble- and cobble-sized clasts of gneiss, schist, slate, quartzite, pegmatite, granite, sandstone, sillstone, shale, etc. These sandstones are classified as arkosic wacke. The source of these minerals and rock fragments are the igneous-metamorphic, and pre-existing sedimentary rocks. The southerly paleocurrent along with the textural and mineralogical maturity and mineralogical composition indicate that the Himalayas, located to the north of the Tista fan, is the prime source of the sediments. Tectonic provenance of recycled orogene, dissented arc. transitional continent and basement uplift in the Himalayan zone are suggested for the derivation of sediments of the Tista fan.