Himalayan Geology, Vol. 44 (2), 2023, pp. 89-103, Printed in India

A revised Quaternary stratigraphy in and around Pokhara valley, Gandaki province, Nepal

DIPESH THAPA, KABI RAJ PAUDYAL*, RAM BAHADUR SAH, USHA DHUNGANA, RAJENDRA KUMAR CHETRI

Central Department of Geology, Tribhuwan University, Kathmandu, Nepal

*Email (Corresponding author): paudyalkabi1976@gmail.com

Abstract: Pokhara, situated in the Lesser Himalayan region of Nepal, is an intermontane basin known for its significant terraced landscape. It spans approximately 60 km in length from its upper to lower parts. In the central region of the Pokhara valley, a contemporary framework for the Quaternary stratigraphy has been developed. Several factors were considered during the development of the stratigraphy which includes the geomorphic characteristics of the deposits, the height of terraces relative to the riverbed, and the classification of sediments based on their composition, structure, and texture within the valley. Additionally, geological cross-sections and columnar sections are also utilized for the preparation of Quaternary stratigraphy. The sediments are classified into seven lithostratigraphic units namely, Gyarjati, Begnas, Siswa, Ghachok, Phewa, Pokhara with its two members, and Rupakot Formation, and two geomorphic units as Gravel veneer, and recent deposit. The names of these units are mostly derived from previous research, while some new units are established during the current study. Among these units, the Pokhara Formation is widespread in the valley and overlays most of the earlier Ghachok Formation. The sediments within the Pokhara Formation, along the tributaries, ranging from coarse to fine, are further divided into two members known as Pokhara A and Pokhara B. Type sections were established for each unit, and a comprehensive geological map at a scale of 1:25,000, along with corresponding cross-sections, was created. Notably, fine sediments, particularly those deposited after the formation of earlier units and within tributaries, bear a resemblance to the formation of lakes in the area. Consequently, this study proposes several models to explain the origin of the lakes within the valley.

Keywords: Intermontane basin, Quaternary stratigraphy, lakes, Pokhara