Stratigraphy and depositional environments of basin-fill sediments in southern Kathmandu Valley, Central Nepal

Paudel, Mukunda Raj; Sakai, Harutaka

doi:10.3126/bdg.v11i0.1544

Cited by 8 publications

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References 4 publications

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“…It is extensively distributed in the southern part of the Kathmandu Basin ranging in altitude from ~1420m in the southern margin to 1300m in the central part of the basin. The type locality of this formation is at the Sunakothi, 3 km to the south of the Patan (Paudel and Sakai 2004). Well-exposed sub-type sections of this formation are exposed at the upstream of the Godawari Khola at Damaitar in the east, both side of the Nakhu Khola in the west, at the confl uence between the tributary fl owing from Dhapakhel and Kodkhu Khola, and Khayakadol Khola between Jorkhu and Parigaon at the southern most part of the Kathmandu Basin.…”

Section: Study Areamentioning

confidence: 99%

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Soft sediments deformation structures: Implication for draining of Paleo-Kathmandu Lake

Paudel

2015

Journal of Nepal Geological Society

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Kathmandu basin is one of the Quaternary intermontane basins in the central Nepal Himalaya. It is bounded by several faults on both southern and northern margins. The basin is fi lled with Plio-Pliestocene terrestrial sediments and their characteristics indicate four types of unconsolidated successions within the basin. These are before lake succession, during lake succession, draining stage lake succession and fl uvial succession. Late Pleistocene aged Sunakothi Formation crops out along the southern part of the basin. It is a typical fl uviolacustrine delta succession that extended from 1390 m in the southern margin to nearly 1300 m toward center of the basin. It is composed by poorly consolidated sand, gravelly sand, silt and mud beds. Various soft-sediment deformation structures occur in the formation, especially in fi ne-to medium -grained sands, silts and mud: load structures, fl ame structures, clastic dikes (sand dike), disturbed layers, convolute beds, slumps and synsedimentary faulting. The deformation mechanism and driving force for the soft-sediment deformation are related, essentially, to gravitational instability, dewatering, liquefaction and brittle deformation. Field data and the wide lateral extent of the structures as well as regional geological data show that most of the deformation is related to seismicity and the structures are interpreted as seismites. In addition, there have also been experimental studies undertaken by various authors within the different sedimentary basin.Soft-sediments deformation structure in Kathmandu basin are mainly considered to be part of the initial diagenetic changes of the sediments and include: Slump structure which occurred on the slope like delta-front area, dewatering structures which occurred by the processes of upward escape of water commonly due to loading, load structures which occurred due to density contrasts between sand and underlying wet mud. The existence of seismites in the Sunakothi Formation is evidence of continuing tectonic activity in the study area during the late Pleistocene and is a main factor for draining of the Paleo-Kathmandu lake water.

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Section: Study Areamentioning

confidence: 99%

“…Other slope of the valley and fl oor of the valley consist of metasediments. Therefore, sources of the basin-fi ll sediments are either metasediments zone or granite gneiss and schist to the north (Sakai 2001, Paudel 2004, 2008.…”

Section: Study Areamentioning

confidence: 99%

Soft sediments deformation structures: Implication for draining of Paleo-Kathmandu Lake

Paudel

2015

Journal of Nepal Geological Society

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“…Sunakothi Formation is extensively distributed in the southern part of the Kathmandu basin ranging in altitude from 1400 m in south to 1300 m in the central part of the basin (Fig.2). Type locality is found at Sunakothi village, 3 km to the south from Patan (Paudel, 2008). Well-exposed sub-type sections are encountered at upstream of the Godawari Khola around Damaitar, around the Nakhu Khola, around the confl uence of the tributary fl owing from Dhapakhel and Kodkhu Khola, and around Khayakadol Khola between Jorkhu and Parigaon (Fig.…”

Section: Stratigraphy and Distributionmentioning

confidence: 99%

Facies analysis of Sunakothi Formation, Kathmandu basin, Nepal and its significance

Paudel

2014

Journal of Nepal Geological Society

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This study decipher facies characteristic of Sunakothi Formation at southern part of Kathmandu Basin. Thick sandy and muddy sequence is found on an open lacustrine facies of the Kalimati Formation. Five facies associations have been recognized within the sandy and muddy facies. These are: (a) muddy rhythmites and silt and laminated to ripple sand bed of the prodeltaic origin (pd), (b) association of cross-stratification, rippledrift and parallel lamination in the lacustrine delta front origin (df), (c) muddy flood-plain and alteration of the fine and coarse sediments of delta-plain origin (dp), (d) sandy to silty rhythmites of the marginal shallow lacustrine origin above the delta-plain (ml), and (e) association of fluvial origin (fl ). Former three associations are interbeded by the thick gravel deposits, which is gravelly braided river origin. Transition from lacustrine to alluvial system is characterized by fluvial and deltaic system in the south. Sedimentology of the Sunakothi Formation indicates deposition during rapid lake level rise and also the thick channelized fluvial gravel beds within the sandy and muddy sequence indicate lake level fall. The cause could be climatic as well as activity of the basin margin tectonics. Sunakothi Formation is the southern counterpart of the Thimi-Gokarna Formations distributed in the northern part of the basin.

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“…The sediments of the northwest region also indicate sandy deltaic foresets. The sediments of the southern margin of the Paleo-Kathmandu Lake were deposited from allvial fan (Paudel and Sakai 2008). Existence of pedimont debris overlying organic rich mud were reported from the northwestern and southwestern margins of the Kathmandu Basin (Saijo and Kimura 2007).…”

Section: Introductionmentioning

confidence: 99%

Facies association and depositional environment of fan-delta sequence in southwest Kathmandu Basin, Nepal

Tamrakar

Shrestha

Maharjan³

1970

Bull. Dept. Geol.

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Lake marginal sedimentation prevailed around the Paleo-Kathmandu Lake. Owing to the difference in local basin conditions; tectonics, source rock types and river systems therein, the lake marginal environments and sedimentary facies associations differ around the Paleo-Kathmandu Lake. In this study, the basin-fill sediments of southwestern margin of the Kathmandu Basin were studied for the sediments recorded in vertical sequences at various localities and facies analysis was made. Mainly eight facies were recognised. They were matrix-supported massive gravel (Gmm), matrix-supported graded gravel (Gmg), gravelly fine or mud (GF), massive silt (Fsm), massive mud (Fm), ripple-laminated silt or laminated silt/mud/clay (Fl), carbonaceous clay (C), and incipient soil with roots (Fr). Four facies associations that were identified were proximal fan-delta facies association (FA1), mid fan-delta facies associaiton (FA2), distal fan-delta facies association (FA3), and gravelly sinuous river facies association (FA4). Remarkably, these facies associations do not contain any sandy facies and foreset bedding of Gilbert-type. The fan-delta region was characterised by flood-dominated flows and vertical accretion of fines in the flood basins, and vegetated swamps rich in organic sediments. The distribution of facies associations suggests extensive lake transgression followed by rapid lake regression. The recent river system then incised the valley against local upliftment due to faulting or lowering of base level of the main river in the Kathmandu Basin probably related to draining out of the lake water. doi: Bulletin of the Department of Geology, Vol. 12, 2009, pp. 1-16

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Stratigraphy and depositional environments of basin-fill sediments in southern Kathmandu Valley, Central Nepal

Cited by 8 publications

References 4 publications

Soft sediments deformation structures: Implication for draining of Paleo-Kathmandu Lake

Soft sediments deformation structures: Implication for draining of Paleo-Kathmandu Lake

Facies analysis of Sunakothi Formation, Kathmandu basin, Nepal and its significance

Facies association and depositional environment of fan-delta sequence in southwest Kathmandu Basin, Nepal

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