Infilling of the Younger Kathmandu–Banepa intermontane lake basin during the Late Quaternary (Lesser Himalaya, Nepal): a sedimentological study

Abstract

The Kathmandu and Banepa Basins, Central Nepal, are located in a large syncline of the Lesser Himalayas. The Older Kathmandu Lake evolved during the Pliocene and early Pleistocene; the Younger Kathmandu Lake, which is the focus of this study, is infilled with late Quaternary sediments. Three formations, arranged in stratigraphical order, the Kalimati, Gokarna and Thoka Formations formed during the infilling stage of this lacustrine basin. Structural and textural sedimentological analyses, a chemical survey across the basin and mineralogical investigations of fine-grained sediments form the basis of this palaeogeographical study. The basin under investigation was covered by a perennial freshwater lake before 30 000 yr BP. The lake was infilled with alluvial and fluvial sediments delivered mainly from the mountains north of the basin. A fairly low gradient was favourable for the formation of diatomaceous earths, carbonaceous mudstones and siltstones, which were laid down in the centre of the lake and in small ponds. Towards the basin edge, lacustrine sediments gave way to deltaic deposits spread across the delta plain. Crevasse splays and anastomosing rivers mainly delivered suspended load for the widespread siltstones and mudstones. The proximal parts of the alluvial-fluvial sedimentary wedge contain debris flows that interfinger with fine-grained floodplain deposits. Three highstands of the water-level (>30 000 yr BP, 28 000-19 000 yr BP, 11 000-4000 yr BP (?)) have been recognised in the sedimentary record of the younger Kathmandu Lake in the Late Quaternary. Second-order water-level fluctuations are assumed to be triggered by local processes (damming by tectonically induced landslides). First-order water-level fluctuations are the result of climatic changes.

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

“…12 ka BP and peaked at ca. 9 ka BP (Chauhan, 2003;Dill et al, 2003). Rivers originating in the sub-Himalaya experienced reduced discharge due to reduced rainfall at ca.…”

Morpho-sedimentary records of active tectonics at the Kameng river exit, NE Himalaya

“…Therefore, any incision occurring in such condition should be supported by increased channel gradient induced by tectonic uplift. The palaeoclimatic scenario during the last 15 ka, based on continental pollen and ocean records, suggests that following the Last Glacial Maxima (24-18 ka), Indian summer monsoon strengthened ∼ 12 ka B.P., with peak rainfall at ∼ 9 ka B.P., and has been stable since then (Swain et al, 1983;Dill et al, 2003;Sarkar et al, 2000;Chauhan, 2003). We argue that the incision in Kameng is more governed by increased river gradient due to tectonic uplift, and which is explained below and in Fig.…”

An Overview of Younger Kathmandu Lake, Nepal, during the Late Quaternary, with Special Reference to Ferruginous Structures in Carbonaceous Sediments

“…1B). Basin subsidence in Kathmandu Basin began by the end of the Tertiary and lasted into the Holocene (Corvinus and Sharma, 1984;Yoshida and Igarashi, 1984;Dangol, 1985;West et al, 1988;Dill et al, 2001Dill et al, , 2003a.…”