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INTRODUCTION

The Panchkhal Valley, intermontane basin

developed in the southeast of the Kathmandu Valleyis located within the eastern flank of a synclinorium

in Kavre District (Stocklin 1980). The Jhiku Khola,

a tributary of the Sun Koshi River is characterised

by development of geomorphic surfaces at different

elevations formed after the last glacial retreat in the

area. Glacial strand retreat and fluvial incision led to

develop landscapes and evolve the area having a

relief of about 122 to 750 m. This paper describes

neotectonic framework and morphostratigraphic units

of the Panchkhal Valley. Aerial photographs and

satellite imagery of the valley were used to trace out

the lineaments.

NEOTECTONIC FRAMEWORK

Geomorphic surfaces show low relief and

continuous features. Terrace edges are considered as

indicators for the detection of neo-tectonic units. The

lineaments across the present basin cross-cut the

existing tectonic discontinuity such as the Mahabharat

Thrust (MT). Abrupt change in terrace elevation

associated with observed lineaments at Khok Village

and at Okhare Village signifies that they are

neotectonic in origin.

Two type of lineaments were recognised, of which

the first extends along NNW-SSE passing from the

east of the Panchkhal Valley along the Cha Khola

and eastern ridge. It has uplifted the southern block

of the valley during the Plio-Pleistocene time resulting

formation of an old Panchkhal valley with a thick

black clay. Regionally, the fault is sinuous and is

comparable with the Mahabharat Thrust (Stocklin

1980). The Mahabharat Thrust (MT) was active

during the Middle Pleistocene. The axis of the

elongated valley (NNW-SSE) is almost parallel to

the MT that also supports its genetic relationship

with the MT. The second group of NE-SE lineaments

extends almost right angle to the MT (Fig. 1). Three

major successive neo-tectonic lineaments, namely

Okhre Khola, Dhulikhel Khola and Punyamati-Cha

Khola Lineaments from south to north of Basukidada

are found to be associated with identified geomorphic

surfaces.

The Okhre Khola Lineament passes from the south

of the present valley floor. The Dhulikhel Khola

Bulletin of the Department of Geology, Tribhuvan University, Kathmandu, Nepal, Vol. 10, 2007, pp. 1–8

Quaternary stratigraphy of Panchkhal valley, Central Nepal

*Yadu Nath Timsina and Prakash Chandra Adhikary

Central Department of Geology, Tribhuvan University, Kathmandu, Nepal

ABSTRACT

The Panchkhal Valley is one of intermontane basins in the Central Nepal east of Kathmandu with two sets of neo-tectonic

lineaments sited from satellite imagery and aerial photographs. One extending NNW–SSE east of the valley results the old Panchkhal

Valley uplifting along south during Plio-Pleistocene age and second one NE–SW has ultimately uplifted the old valley. The

Panchkhal Clay, Ratopairo Formation, Rampur Formation and Tamaghat Formation are four depositional lithostratigraphical units.

Similarly, Tamaghat, Rampur, Thumka, and Chisapani surfaces are depositional and Basukidada, Sano-Tinghare, Sumara-Thulo

Tinghare, Dhulikhel, Koiralathumka and Bhamarkot surfaces are erosional morphostratigraphic geomorphic surfaces. Geomorphic

terrace cutting level is around 1400–1440 m and all surfaces and deposits above and below are relatively young.

*Corresponding author:

E-mail address: [email protected]

Bulletin of the Department of Geology

C e n

t r a l D e p a r t

m e n t

o f G e

o l o

g y

K ir t i p u r



Lineament passes through the Dhulikhel River. These

lineaments have raised the Panchkhal Clay. After the

depost of thick black clay, the fluvial sediments were

deposited in the central part of the valley covering

the clay, and debris flow deposited at the periphery.

This gave rise to a wide intermotane basin between

the lineaments. The lake would have drained

momentarily along the Jhiku Khola gorge at the

southern part of the valley. Punyamati-Cha KholaLineament triggered rejuvenated fluvial incision

which in its course led to headward nick-point

migration very near to the water divids clearing the

last glacial geomorphic surface. The neotectonic

activities along the faluts sculptured the existing

geomorphic surfaces. The activities continue even

at present.

QUATERNARY STRATIGRAPHY

The quaternary stratigraphy of the Panchkhal

Valley has been established based on field work

focused on the northern area of the valley, however

the stratigraphic units are also distributed in other

parts of the valley. The deposit in the area is

represented by terraces and debris flow at different

elevations including thick buried black clay which

does not form present-day landform. The geomrohphic

higher elevations suffer intense erosion and mass

movements erasing former evidences of landform

development, which are difficult to date absolutely.

These surfaces were dated relatively on the assumption

that landform assemblages are a palimpset of

superimposed part of different erosional cycles each

initiated by a change of base level of tectonic or

eustatic origin (Chorley et al. 1985). Geomorphic

height of a particular surface can be dated relatively

by morphostratigraphical criteria as described by

Adhikary and Thapa (2001).

Morphostratigraphy

Morphostratigraphy units were first identified

geomorphic surfaces in the aerial photographs

(1:50,000) and topographical map (1:25,000) which

was verified by field ground-truthing and were

relatively dated on the basis of their absolute heights,

general soil rubification, and terrace cutting levels.

The geomorphic surface of 1400 m was considered

as the terrace cutting level, a marker surface for the

area, as other geomorphic surfaces above and below

were relatively younger and were similar in

composition and elevation with the oldest geomorphic

surfaces of Middle Pleistocene age (?), which are

represented by the erosional Kotol Formation and

Swayambhu/Kirtipur Surface in the adjacent

Kathmandu Valley (Adhikary and Thapa 2001).

Morphostratigraphic units of the Panchkhal Valley

and its surrounding hills were broadly classified into

the depositional and erosional surfaces (Fig. 2; Tables

1 and 2).

Depositional morphostratigraphy

Morphological depositional surfaces are

represented by a series of terraces between 880 m

2

Y. N. Timsina and P. C. Adhikary / Bulletin of the Department of Geology, Vol. 10, 2007, pp. 1–8

Fig. 1 Major tectonic

lineaments in the

Panchkhal Valley



a n d > 1 1 6 0 m . T h r e e d e p o s i t i o n a l

morphostratigraphical landforms of the Pleistoceneage and the remaining one of the Holocene age were

observed as shown in Table 1. The Tamaghat Surface

(present-day floodplain and braided channels of the

Jhiku Khola) below 880 m above mean sea level

(amsl) represents the lowermost and the youngest

geomorphic surface in the valley (Fig. 3). The next

Rampur Surface represents the first raised old river

terrace forming prominent geomorphic surface at an

elevation 880-920 m and is distribtuted around

Tamaghat, Rampur and Takadihi Villages (Fig. 3).

The Thumka Surface represents the next surface at

1000-1140 m amsl. The uppermost surface is

represented by the Chisapani Surface at 1200–1220m amsl. The Chisapani surface is underlain by debris

flow deposit.

Erosional morphostratigraphy

Erosional surfaces of Pleistocene age are widely

distributed at different elevations from 1360 to 2053

m on hills surrounding the Panchkhal Valley. They

represent patchy remnants of gently slopping to almost

flat surfaces and are occupied by debris flow deposits

of varying age. Six erosional geomorphic surfaces

were identified in the area and are as shown in Table 2.

3

Fig. 2 Morphostratigraphic surfaces of the Panchkhal Valley

Table 1: Depositional morphostratigraphic units

Table 2: Erosional morphostratigraphic units

Unit Thickness (m) Type Probable age

Tamaghat Surface <880 River terrace Holocene

Rampur Surface 880-920 Old river terrace Last glacial stage (?)

Thumka Surface 1000-1140 Debris deposit Middle Pleistocene (?)

Chisapani Surface 1200-1220 Debris deposit Middle Pleistocene (?)

Unit Thickness (m) Type

Basukidada Surface 2053 Debris deposit

Sano-Tinghare Surface 1960 Debris deposit

Sumara-Thulo Tinghare Surface 1865 Debris deposit

Dhulikhel Surface 1505-1600 Debris deposit

Kairalathumka Surface 1400-1420 Debris deposit

Bhamarkot Surface 1340-1360 Debris deposit




Basukidada and Sano-Tinghare surfaces are made

up of Basukidada morrains, eskers, kames and debris

flows exhibiting U-shaped trough and glacial arrets

above 2000 m. U-shaped troughs on the surface at

the higher elevations in the Himalaya are the good

evidences of the last glacial stage (Adhikary 1993).

The age of the Basukidada geomorphic surface is

estimated to be of the last glacial stage. Widespread

Sumara-Thulo Tinghare and Dhulikhel geomorphicsurfaces respectively at 1865 m and 1505–1600 m,

are covered by Nala and Dhulikhel debris flow

deposits. Similarly, Koiralathumka and Bhmarkot

geomorphic surfaces between the Basukidada

geomorphic surface and the terrace cutting level are

estimated to be of the Middle Pleistocene age.

Depositional lithostratigraphy

Quarternary depositis distributed in the study area

were classified into seven units of formation level

(Fig. 4; Tables 3a and b).

Panchkhal Clay

West of Tamaghat, the Phanchkhal Clay is represented

by weakly consolidated thick black clay with thin silt

and fine sand layers in a dug well of more than eight

meters. The Panchkhal Clay is buried and does not crop

out on the surface. It also does not make significant

relief but forms a basal stratigraphic unit that can be

compared to the Lukundol Formation of age ranging

from the Late Pliocene to Early Pleistocene (Tuladhar

1982; Yoshida and Igarashi 1984).

Ratopairo Formation

The ratopairo Formation is an unconsolidated

debris flow deposit that overlies the Panchkhal Clay.

At present it lies at the toe often covering the top of

the low hills. It is primarily represented by the slopping

debris flow terraces distributed at the lower elevations

north of the Pachkhal Valley. The type locality of the

formation is located at Ratopairo about 2 km north

of Tamaghat. About 5 m thick debris and mud flowdeposits cover the low-lying hilly areas around

Ratopairo. The formation comprises deeply weathered

red soil at top and matrix-supported angular rock

fragments at bottm (Figs. 5 and 6). The formation

has been severely eroded and intensely rubified. The

Ratopairo Formation is older than the Rampur

Formation because the former is more rubified. The

age that could be attributed to the Ratopairo Formation

could be Middle Pleistocene to Early Pleistocene

(?) and could be correlated to Middle Pleistocene

Champi Formation in the Kathmandu Valley(Adhikary and Thapa 2001).

Rampur Formation

The Rampur Formation exhibits old gentle

slopping river terrace widely distributed at Rampur,

Dwaredhihi, Takadihi and northeast slope of Lamdihi

and east of Tamaghat. The formation comprises thick

and loose sand deposit with more than 8 m thickness

overlying the lower portion of debris deposit of the

Ratopairo Formation (Fig. 7) at west of Tamaghat in

newly dug well which was more than 8 m deep. The

4

Fig. 3 Rampur Surface

and Tamaghat Surface

north of Tamaghat




5

Fig. 4 Quaternary geological map of northwester region of the Panchkhal Valley

Fig. 5 Debris deposit of the Ratopairo Formation Fig. 6 Columnar section of the Ratopairo Formation

1 . 5

1 . 0

0 . 5

0 m

Light brown, angular rockfragments upto 70 mm witha sandy matrix

Red, angular rock fragmentsupto 60 mm with a sandymatrix




6

T a b l e 3 a : Q u a t e r n a r y s t r a t i g r a p h i c d i v i s i o n s o f P a n c h k h a l a r e a a

n d c o r r e l a t i o n w i t h t h e K a h m a n d u V a l l e y

a f t e r A d h i k a r y a n d T h a p a ( 2 0 0 1 )

K a t h m a n d u V a l l e y , A d h i k a r y a n d T h a p a ( 2 0 0 1 )

G e o c h r o n o l o g y

N e o t e c t o n i s m

E r o s i o n a l

D e p o s i t i o n a l

E r o s i o n a l


E r o s i o n a l

E r o s i o n a l D e p o s i t i o n a l

F o r m a t i o n

F o r m a t i o n

F o r m a t i o n

F o r m a t i o n M e m b e r

1 0 , 0 0 0

H o l o c e n e

T a m a g h a t

T u n d i k h e l

T h a p a t h a l i

2 4 , 0 0 0

U p p e r

P l e i s t o c e n e ?

B a s u k i d a d a

R a m p u r

B a s u k i d a d a

S a n o - T i n g h a r e

R a m p u r

T h e u p l i f t m e n t o f t h e

w a t e r s h e d a l o n g t h e

P u n y a m a t i - C h a K h o l a

L i n e a m e n t , e x i s t i n g

r i v e r s e n t r e n c h e d

f o r m i n g t h e R a m p u r

F o r m a t i o n a n d

d e p o s i t e d t h e T a m a g h a t

F o r m a t i o n a l o n g t h e

v a l l e y a x i s

G o k a r n a

T i l a n g a t a r

D h a p a s i

T o k h a

S h e o p u r i

M a n i c h u r

N a g a r k o t

I n d r a s t h a n

T u n d i k h e l

T i l i n g a t a r

D h a p

a s i

T o k h a

1 2 0 , 0 0 0

M i d d l e


N a l a D h u l i k h e l

K o i r a l a t h u m k a

R a t o p a i r o

S u m a r a - T h u l o

T i n g h a r e

D h u l i k h e l

K o i r a l a t h u m k a

B h a m a r k o t

T u m k a

C h i s a p a n i

T h e O k h r e a n d t h e

D h u l i k h e l L i n e a m e n t s

u p l i f t i n g t h e P a n c h k h a l

C l a y a n d r e s u l t i n g t h e

d e p o s i t i o n o f t h e

R a t o p a i r o D e b r i s F l o w

D a l k a p

T h a r t h o k

K o t o l

C h u n i k h e l

N a g a r j u n

K i r t i p u r

9 0 0 , 0 0 0

L o w e r


P a c h k h a l C l a y

( n o t e x p o s e d t o

t h e s u r f a c e

U p h e a v a l o f t h e

M a h a b h a r a t R a n g e

a l o n g t h e M T a n d

s o u t h e a s t a n d s o u t h o f

t h e p r e s e n t v a l l e y

r e s u l t i n g t h e f o r m a t i o n

o f o l d P a n c h k h a l b a s i n

C h a m p i

L u k u n d o l

M o r p h o s t r a t i g

r a p h y


L i t h o s t r a t i g r a p h y

A g e Y r .

B P

L i t h o s t r a t i g r a p h y

M o r p h o s t r a t i g r a p h y

P a n c h k h a l A r e a , p r e s e n t s t u d y

K A R E W A S G R O U P

1 3 , 0 0 0

3 0 , 0 0 0

T a m a g h a t




formation is represented by old river terace and fan

deposits at the foothills. The soil profile is poorly

developed. The formation lies upto about 20 m above

the present riverbed with higher terraces than of the

Holocene terraces in the area. This leads the most

suitable age for the Rampur Formation is the Late

Pleistocene (?) comparable to the Gokarna Formationof the Kathmandu Valley (Adhikary and Thapa 2001).

Tamaghat Formation

The Tamaghat Formation is represented by

Holocene deposits, present floodplain, channels and

minor natural levee just above the present Jhiku

Khola. The series of Holocene fluvial terraces of

height less than meters are characterised by alternate

layers of loose gravel and coarse to fine sand from

the bottom to the top. The gravel is matrix-supported

with lithology of quartzite, gneiss, granite and few

schists fragments. Holocene deposit is not

differentiated during this study and included in a

single unit.

Erosional lithostratigraphy

Debris flow deposits are widely distributed at the

gentle hill slopes and capping low-lying surrounding

hills around the Panchkhal Valley. They are found

as patches of hanging elongated bodies over steep

hillslopes and isolated hummocky hills. The debris

flow deposits contain matrix-supported poorly sorted rock

fragments distributed as wide extensive hanging terraces.

Koiralathumka Debris Flow

Koiralathumka Debris Flow, the oldest debris flow

in the Panchkhal Valley, is located at elevation 1420

to 1460 m amsl at the toe of surrounding hills as a

blanket of elongated bodies. The deposits are highlyweathered with intense rubification with reddish

colour. The deposits comprise poory soted boulders.

The Koiralathumka Debris Flow forms the oldest

deposit in the valley as evidenced by its distribution

around the distinct terrace cutting around the elevation

1400 m. The type locality is proposed at

Koiralathumka along the Rabi-Opi road. The deposit

is also exposed around Bhamarkot and Khewa

Villages. The Koiralathumka Debris Flow is

interpreted as an evidence of extensive glaciations in

the Himalayas representing the Gurkha Glacial Stage

(Adhikari 1993). It is correlated with the Kotol Debris

Flow of the Kathmandu Valley (Adhikary and Thapa

2001).

Dhulikhel Debris Flow

The Dhulikhel Debris Flow maintains an elevation

between 1550 and 1700 m amsl particularly at foothills

surrounding the Panchkhal Valley and comprises

poorly sorted sediments with less intense rubification.

The sediment includes sandy matrix-supported

boulders. The type locality of the formation is

7

Age Yr. BP Geochronology Formation Thickness Lithology Neotectonism

10,000Holocene Tamaghat Thin ?

24,000

Upper Pleistocene? Rampur 20 m

120,000Middle Pleistocene? Ratopairo 5 m

The Dhulikhel Lineament uplifted the Panchkhal

Clay and resulting the deposition of the

Ratopairo Debris Flow sediment

900,000

Lower Pleistocene?

Pachkhal Clay (notexposed to the

surface ?

Upheaval of the Mahabharat Range along the

MT and southeast and south of the presentvalley resulting the formation of old Panchkhal

basin

The upliftment of the watershed along the

Punyamati-Cha Khola Lineament, existing rivers

entrenched forming the Rampur Formation and

deposited the Tamaghat Formation along the

valley axis

30,000

13,000

Table 3b: Stratigraphic divisions of the Quaternary sediments in the Panchkhal Valley




proposed at Dhulikhel and is widespread in Thakla,

Thadagau, Kalthumki Bhanjyang and Manegau.

Nala Debris Flow

Nala Debris Flow is widely distributed at an

elevation from 1820 to 1990 m amsl. It is distributed

in the upper part of the Jhiku Khola watershed at the

toe of Basukidada. The debris flow has similar

lithology as the earlier two deposits, but shows no

soil profile and rubification. The type locality isproposed at Nala where the the dissected flat erosional

terrace at 1840 amsl represents the deposit.

Basukidada Morrains and Debris Flow

The Basukidada Morrains and Debris Flow

occupies the highest elevation in the valley above

1994 to 2053 m amsl. It covers the hill tops of the

valley. The unit contains sandy and gravely eskers

and kame glacial deposits with almost no soil profile.

The landscape reflected by U-shaped smooth glacial

valleys at the ridges surrounding the Panchkhal Valley

holds evidence of the last glacial stage. These strong

glacial evidences represent the last glaciation, the

Sherpa Glacial Stage in the Himalaya (Adhikary

1993). It is comparable to the Sheopuri Debris Flow

of the Kathmandu Valley (Adhikary and Thapa 2001).

CONCLUSIONS

The Panchkhal Valley is one of the intermontane

basins in the Central Nepal forming its landscape by

the Quaternary sediments. The area bears two sets

of tectonic lineaments, one extends NNW–SSE east

of the Panchkhal Valley, while the second group of

NE–SW lineaments has uplifted southern part of the

valley forming old valley at the beginning of Plio-Pleistocene. The basin drained after activation of the

second group of lineaments and started to deposit

river sediment and raised river terraces above the

present floodplain accompanied by retreating

hillslopes, and therefore erasing the Pleistocene

signatures. Geomorphic terrace cutting level in the

area is around 1400–1440 m amsl and all surfaces

and deposits above and below are relatively younging

(?). The Panchkhal Clay, Ratopairo Formation,

Rampur Formation, and Tamaghat Formations are

depositional lithostratigraphic units. Tamaghat,Rampur, Thumka and Chisapani surfaces are

depositional morphostratigraphic units while

Basukidada, Sano Tinghare, Sumara-Thulo Tinghare,

Dhulikhel, Koiralathumka and Bhamarkot surfaces

are erosional morphostratigraphic units .

ACKNOWLEDGEMENTS

Authors are thankful to Central Department of

Geology for providing facilities. Authors thank B.

D. Shrestha, Department of Electricity Development,

Kathmandu for providing suggestions.

REFERENCES

Adhikary, P.C., 1993. The monsoon circulation in Nepalese

Himalaya: evolution and environmental thrust, Bull.

Dept. Geol., Tribhuvan Univ., Kirtipur, Kathmandu,

Nepal, v. 3, Special Issue, pp. 1–10.

Adhikary, P.C. and Thapa, H.B., 2001. Pleistocene geology

of the Kathmandu Valley. Trivubhan University,

Kirtipur, Kathmandu, Nepal, v. 8, pp. 61–72.

Chorley, R.J., Schumm, S.A. and Sugden, D.E., 1985.

Geomorphology. Third Avenue, Methuen & Co., New

York, pp. 22–28.

Stocklin, J. and Bhattarai, K.D., 1977. Geology of

Kathmandu area and central Mahabharat Range, Nepal

Himalayas. Technical Report (Unpublished), UNDP

Mineral exploration project, Kathmandu, 86p.

Tuladhar, R.M., 1982. A note to the lignite occurrence in

Lukundol, Kthmandu, Jour. Nepal Geol. Soc., v. 2, no.

1, pp. 47–51.

Yoshida, M. and Gautam, P,. 1988. Neogene to Quaternary

lacustrine sediments in the Kathmandu Valley, Nepal.

Journal of Nepal Geological Society, v. 4, pp. 73–100.

8

Fig. 7 Columnar section of the Rampur Formation

2

0 m

Light brown pebbly fine sand,rounded pebble upto 17 mm

Light brown, clayey silt,planar

1

3

5

4

6

Brown grey with patches of yellowcolor, fine sand, planar

Black, clayey silt, planarGrey with yellowish patches, fine sand


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