Small-amplitude lake-level fluctuations recorded in aggrading deltaic deposits of the Upper Pleistocene Thimi and Gokarna formations, Kathmandu Valley, Nepal

Authors

  • Tetsuya Sakai Department of Geology and Mineralogy, Division of Earth and Planetary Sciences, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan
  • Ananta Prasad Gajurel Department of Geology, Tri-Chandra Campus, Tribhuvan University, Ghantaghar, Kathmandu
  • Hideo Tabata Gifu Academy of Forest Science and Culture, Min o, Gifu 501-3 71-1, Japan
  • Bishal Nath Upreti Department of Geology, Tri-Chandra Campus, Tribhuvan University, Ghantaghar, Kathmandu

DOI:

https://doi.org/10.3126/jngs.v25i0.32049

Keywords:

Sedimentary Facies, Lake-level fluctuations, Thimi and Gokarna Formation, Kathmandu Valley

Abstract

Small-amplitude lake-level fluctuations have been recognized from the aggrading delta-plain deposits in the lower parts of the Thimi and Gokarna formations, Kathmandu Valley, Nepal. The delta-plain deposits consist or gravelly sand beds of fluvial channel origin (coarse-sediment interval) and alternation of' fine to very line sand and sandy silt beds (line-sediment interval). Wave generated structures occur in the sand beds or the fine sediment intervals.

The vertical and lateral facies changes suggest that the deposition or a set of coarse- and fine-sediment intervals associated with prograding delta front deposits was controlled by a lake-level rise and fall sequence superimposed on a long-term lake­ level rise trend. The aggradation of fluvial sediments occurred during a lake-level rise period with sufficient sediment supply to fill a newly created accommodation space on the delta plain. The observation or wave-generated structures in an overlying fine-sediment interval suggests that the delta plain was subsequently inundated due to further lake-level rise, exceeding the sedimentation rate. Subsequent delta progradation occurred during a lake-level stabilized phase after a lake­ level fall. The small-amplitude lake-level changes are thought to be attribute able to seasonal wet and dry cycles, as inferred based on the presence of peculiar aggrading delta successions, implying that lake-level fluctuations may have occurred over short time scales, and on the results of a previous palaeopalynological study in which a moist palacoclimate was inferred in the lower part of the Gokarna Formation in particular.

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Published

2001-12-01

How to Cite

Sakai, T., Gajurel, A. P., Tabata, H., & Upreti, B. N. (2001). Small-amplitude lake-level fluctuations recorded in aggrading deltaic deposits of the Upper Pleistocene Thimi and Gokarna formations, Kathmandu Valley, Nepal. Journal of Nepal Geological Society, 25, 43–51. https://doi.org/10.3126/jngs.v25i0.32049

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