Morpho‐sedimentary records at the Brahmaputra River exit, NE Himalaya: climate–tectonic interplay during the Late Pleistocene–Holocene

Abstract

2009. Morpho-sedimentary records at the Brahmaputra River exit, NE Himalaya: climate-tectonic interplay during the Late Pleistocene-Holocene.ABSTRACT: Morphological and sedimentary records at the exit of Brahmaputra River at Pasighat in the NE Himalaya inform about the climate-tectonic interplay during the past ca. 15 ka. The geomorphology of the area comprises (1) fan terrace T 3 , (2) a high-angle fan (3) terrace T 2 , (4) terrace T 1 and (5) a low-angle fan. Geomorphic consideration suggests that the fan terrace T 3 and high-angle fans are the oldest units and were coeval. The low-angle fan is the youngest geomorphic unit. Sedimentological studies and optically stimulated luminescence chronology suggest that (i) fan terrace T 3 formed between 13 and 10.5 ka and comprised multiple events of debris flows separated by the aggradation as channel bars in a braided river environment; (ii) the high-angle fan formed during 15-10 ka and comprises channel bar aggradation in braided river conditions; (iii) terrace T 2 formed during 10-8 ka due to aggradation in a braided channel environment with lesser events of debris flows; (iv) terrace T 1 formed during <7 and 3 ka took place as bars of the braided river. Sudden coarsening of the sediment indicated a tectonic rejuvenation in the provenance region between 7 and 3 ka; and (v) the low-angle fans dated to <3 ka formed due to aggradation in a small tributary joining the Brahmaputra River. This implies a phase when the main channel of the Brahmaputra did not flood regularly and the tributaries were actively aggrading. The sedimentation style and incision of these geomorphic units responded to contemporary climatic changes and uplift in the Siwalik range along the Himalayan Frontal Fault.

Neotectonic study along mountain front of northeast Himalaya, Arunachal Pradesh, India

“…20 ka by migrating 150 m eastward and by incising 48 m vertically (Mukul et al 2007). Similar observations of the latest Pleistocene (15-10 ka) to Holocene deformations associated with the tectonic-climatic interaction are also made by Luirei and Bhakuni (2008) and Srivastava et al (2009) at the Siang River exit, Arunachal Pradesh. The presence of upliftments was a result of thrusting, growing fold and by strike-slip faulting, indicating the activeness of the mountain front region of the study area.…”

Chronology of relict lake deposits in the Spiti River, NW Trans Himalaya: Implications to Late Pleistocene–Holocene climate-tectonic perturbations

“…A mean of at least 30% of ages was used as a caution against poor pre-depositional bleaching, if any. Published records suggest that in the Himalaya sufficient pre-depositional zeroing during the fluvial transport of sediment grains occurred (Srivastava and Misra, 2008;Srivastava et al, , 2009). Samples were pre-treated sequentially and clean Quartz grains were extracted using the method described in Aitken (1998).…”

Dating sediments using potassium feldspar single-grain IRSL: Initial methodological considerations

“…These limitations can include low quartz OSL signal sensitivity, high or variable thermal transfer signals, low saturation dose characteristics, or other forms of irregular behavior. Many publications have drawn attention to poor or limiting characteristics of quartz OSL in mountainous, glaciated and/or tectonically-active areas, for example Smith et al (1990; UK glacial sediments), Rhodes and Pownall (1994; Himalayan sediments), Preusser et al (2006;New Zealand and Alpine sediments), Srivastava et al (2009; Himalayan fluvial sediments).…”