Two times lowering of lake water at around 48 and 38 ka, caused by possible earthquakes, recorded in the Paleo-Kathmandu lake, central Nepal Himalaya

Harutaka Sakai,Ryoko Setoguchi,Misa Sugimoto,Mukunda Raj Paudel,Rie Fujii

doi:10.1186/s40623-016-0413-5

Harutaka Sakai, Ryoko Setoguchi + Show 3 more

Open Access

https://doi.org/10.1186/s40623-016-0413-5

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Abstract

Sedimentary facies and micro-fossil analyses, and AMS14C dating were performed in order to reveal the water-level fall events and draining process of the lake (Paleo-Kathmandu Lake) that existed in the past in the Central Nepal Himalaya. The sedimentary facies change from the lacustrine Kalimati Formation to the deltaic Sunakothi Formation in the southern and central Kathmandu basin, and the abrupt and prominent increase of phytoliths Bambusoideae and Pediastrum, and contemporaneous decrease of sponge spicule and charcoal grains around 48 and 38 ka support the lowering of water level at these times. According to the pollen analysis, both events occurred under rather warm and wet climate, thus supporting that they were triggered by tectonic cause and not by climate change. The first event might be linked to a possible occurrence of a large earthquake with an epicenter in the vicinity of the Paleo-Kathmandu Lake. The occurrence of a mega landslide in Langtang area close to the north of the Kathmandu Valley producing pseudotachylite dated at 51 ± 13 ka could be linked to this earthquake. Finally, the water was completely drained out from the remnant lake at the central part of the Kathmandu basin by ca.12 ka.

Highlights

Basin-fill sediments of intermontane basins are good archives of past climate changes, tectonics, and depositional environments within the valleys and surrounding mountains
Lowering of lake‐water level at 48 and 38 ka indicated by micro‐fossils Abrupt and prominent increase of Phytoliths Bambusoideae at 48 and 38 ka is interpreted to indicate lowering of lake-water level, because preferable habitat of Bambusoideae is swampy lowland where it is not submerged under water
Lowering of lake-water events recorded in the Late Pleistocene lacustrine sediments of the Paleo-Kathmandu Lake were studied by means of micro-fossil and sedimentary facies analyses of five drilled cores dated by Accelerator mass spectrometer (AMS) 14C

Summary

Introduction

Basin-fill sediments of intermontane basins are good archives of past climate changes, tectonics, and depositional environments within the valleys and surrounding mountains. The basin-fill sediments of the Kathmandu Valley in Central Nepal Himalaya (Fig. 1) are excellent archives of changes in monsoonal climate, terrestrial depositional environments, and tectonics of the Himalaya (Sakai 2001a). From a view point of the past earthquake in Central Nepal, the basin-fill sediments of the Kathmandu Valley is a valuable archive which recorded crustal deformation and fault rupture caused by large. In order to reconstruct geologic history of the Kathmandu Valley, we undertook core drilling of the sediments under the name of Paleo-Kathmandu Lake project, and have conducted multi-proxy analyses of the cores. Stratigraphic and sedimentological study of the basin-fill sediments revealed that the lake was born at around 1 Ma by damming of the Paleo-Bagmati river, and

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