Palpa Field Report (B.Sc Geology 4th year)

6.8. Mass Movement StudY ………………………………………………………………………………………………………… 52

SUMMARY AND CONCLUSION…………………………………………………………... 54

REFERENCE…………………………………………………………………………………. 56

CHAPTER-1

1.1 Introduction

Geology is essentially an applied science, therefore it needs intensive fieldwork. To enhance the theoretical and practical knowledge, it is compulsory that a student of geology must follow usual procedure of geological fieldwork for the partial fulfillment of the requirement of Bachelor Degree of Science in Geology. Hence, a fieldwork was carried out in Butwal-Tansen-Palpa area for three weeks.

The report of three weeks’ fieldwork has been broadly separated into two sections: general geology and engineering geology. The general geology section includes stratigraphy and geological structure of the study area. On the other hand, engineering geological section focuses on the engineering properties of soil and rock mass, slope stability analysis and mass movement.

1.2 Location

Butwal-Tansen area is about 270 km west of Kathmandu. The study area extends from latitude 27º 40' 30" N to 27º 52' 53" N and longitude 83º 26' 33" E to 83º 35' 04" E (Fig. 1.1). The field area is situated partly in Rupandehi and Palpa Districts of Lumbini Zone and Syangja District of Gandaki Zone. Geologically, the studied area lies in the Siwalik and Lesser Himalayan zone.

Fig: 1.1 Location Map of Study Area

1.3 Accessibility

Most of the study area lies along the Siddhartha highway. So the study area is easily accessible. However, some of the area located along the rivers and in the mountain slopes and ridges are accessed by foot trails.

1.4 Topography and drainage system

The study area lies in Siwalik and Lesser Himalaya with a small part of Terai plain. Hence, it consists of flat plains to low hills, river valleys and high mountains reaching up to 3000 m in altitude. TinauRiver is the main drainage of the area. Its tributaries like Hulandi Khola, Bhainskati Khola, Jhumsa Khola, Dobhan Khola etc. drain various parts of the area and join to the Tinau River.Other small gullies are active only during the rainy season.

1.5 Land use

Most of the study area is covered by trees, shrubs and grasses. The plain area is cultivated by the local residents. In the mountainous region, river valley floodplains and terraces are cultivated by the local people. The remaining land is either barren or covered with forest.

1.6 Objectives

The main objectives of the study are as follows:

Ø To understand the stratigraphy of the Siwalik Group and the Lesser Himalayan rocks of the study area, To acquire knowledge on geological structures of the area,

Ø To study sedimentology including depositional environment of Siwaliks and the Lesser Himalayan sequence of the study area,

Ø To prepare detailed route map and columnar section of the study area

Ø To prepare geological map of the study area in 1:25,000 scale

Ø To carry out engineering geological study of the area

1.7 Methodology

Topo-sheets (099-09, 099-05 and 098-12) were used for map purpose during the field.Different equipments and accessories like Brunton Compass , Geological Hammer, Measuring Tape, Hand Lens, Chisel etc were used for the rock and soil testing and data collection. Various data were collected at different location on the field routes. Detailed rote maps and columnar sections were prepared on the basis of the collected data. Finally, geological map of the study area and its cross section were prepared. For the engineering geological investigations, soil properties, rock mass properties were studied and rock slope stability analysis was done at different study sites. Mass movement study was also carried out in addition. An engineering geological route map was also prepared.

CHAPTER-2

Geology of Nepal Himalaya

2.1 Himalaya in general

Himalaya is a massive geological structure in Asia which is formed as a result of collision between two great tectonic plates which are Indian plate and Eurasian plate. The process was initiate at about 50-55 million years ago. Indian plate is moving northward and is continuously subducting below Eurasian plate at the rate of 5cm/year. Numbers of strike slip faults are developed during that period. MHT (Main Himalayan Thrust) is major strike slip fault which is the major source of other thrust and faults in Himalaya. The total length of Himalaya is 2400km.

The entire Himalaya is divided into 5 different regions from west to east according to the location and lithological properties. They are:

Ø Punjab Himalaya

Ø Kumaon Himalaya

Ø Nepal Himalaya

Ø Sikkim-Bhutan Himalaya

Ø NEFA (North East Frontier Agency) Himalaya

2.2 Geology of Nepal Himalaya in General

The physiographic sub-divisions of Nepal discussed below are after Hagen (1969) with some modifications.Fig2.1

Ø Terai

Ø Churia Range (siwalik) or Sub-Himalaya

Ø Lesser Himalaya

Ø Higher Himalaya

Ø Tibetan Tethys Himalaya

himalaya-gansser

Fig. 2.1 Tectonic sub-division of Nepal Himalaya

2.2.1 Terai

This zone represents the northern edge of the Indo Gangetic Plain and forms the southernmost tectonic division of Nepal. Though, physiologically, this zone does not belong to the main part of Himalaya, it is a foreland basin and owes its origin to rise of the Himalaya and thus genetically inseparable (Upreti 2000). In the north, it is delineated by Himalayan Frontal Thrust (HFT) which is exposed at many places. Along the thrust, the churia rocks are found to rest over the sediments of the Terai (Upreti 2000). The Terai plain gradually rises from 100 m in the south to 200 m in the north. However, there seems to be also a gradual regional slope from west to east in further south so that the Ganges river system flows towards east to the Bay of Bengal. All the rivers emerging from the Nepal Himalaya first flow to south and finally head eastward towards the Bay of Bengal.

Geologically the Terai plain is covered by Pleistocene – Recent alluvium.The average thickness of alluvium is 1500m. The basement topography of the Ganges basin is not uniform.There appears to have a number of traverse ridges and valleys below the alluvium and therefore the depth of basement widely varies. The alluvial sediments were deposited over the siwaliks which in turn rest over the Precambrian and Gondwanas or the rocks of Eocene – Oligocene age (Toler et al 1989, Sharma 1990). The Terai sediments which in turn rest over the gondwanas or younger rocks. The recent alluvium in Terai is brought in by the rivers coming from the hills in the north.Tarai zone is divided into three groups.They are as follows:

2.2.1.1 Northern Terai (Bhavar Zone)

The Northern Terai or Bhavar Zone lies adjacent to foothills of churia and extends southward to a maximum width of about 12km.Thezone is composed of thick pile of sediments of boulder, cobble, pebble and coarse sands derived mainly from the rock of Himalaya. This zone has thick tropical forests.

2.2.1.2 Middle Terai Zone

This zone represents the intermediate zone between the Bhavar Zone and Southern Terai Zone. This zone is characterized by pebbly and sandy sediments with few clay layers. Difference in porosity and permeability between the sediments of Bhavar Zone and southern Terai and mark change in elevation has caused the development of spring, natural ponds and marshy lands.

2.2.1.3 Southern Terai Zone

This zone lies to the south of the middle terai and extends southward to the India Nepal boarder. This zone is mainly composed of finer sediments consisting of sand, silt and clays. The region often suffers from devastating flood and droughts.

2.2.2 Churia Range

This zone is bounded to the north by the Main Boundary Thrust(MBT)and to the south by theHimalayan Frontal Thrust(HFT).The Churia Range (sub –Himalayan Zone) consists basically the rocks of fluvial origin belonging to Neogene age. The Lower siwaliks consist of finely laminated sandstone, siltstone and mudstone. The middle siwaliks are made up of medium to coarse grained salt and pepper type Him sandstone.the upper siwaliks comprise conglomerate and boulders beds.

2.2.3 Lesser Himalaya

The Lesser Himalayan Zone is bordered in the south by the MBT and in the north by the Main central Thrust (MCT).The MBT has brought the older Lesser Himalayan rocks over the much younger siwalik. The lesser Himalayan is made up mostly of the unfossiliferous sedimentary and metasedimentary rocks like slate, phyllite, schist, quartzite, dolomite etc

2.2.4 Higher Himalaya

This zone has been mapped and traced along the entire Himalayan region and has been named differently at different places. Geologically, the higher Himalayan zone includes the rocks lying to the north of the MCT and below the fossiliferous Tibetan- Tethys zone. This zone consists of about 10km thick crystalline units of the higher Himalayan extend continuously along the entire length of the country. The high-grade Kyanite, Sillimanite bearing gneisses, schist, and marbles of the zone form the basement of the Tibetan Tethys Zones.

2.2.4 Tibetan Tethys Himalaya

The Tibetan Tethys Zone generally begins from the higher Himalayan Zone and extends to the north in Tibet. In Nepal, the fossiliferous rocks of the Tibetan- Tethys Zone are well developed in Thak Khola(Mustang), Manang and Dolpa.Most of the Great Himalayan peaks of Nepal including Mt.Everest, Manaslu, Annapurna and Dhaulagiri belong to the Tibetan-Tethys zone Composes of sedimentary rocks such as shale, limestone and sandstone, ranging age from Lower palaeozoic to palaeogene.

CHAPTER -3

The Siwalik Group

3.1 Introduction

The Siwalik group is bounded by the Main Boundary Thrust (MBT) to the north and the Main Frontal Thrust (MFT) to the south. This group is composed of the fluvial sediments derived from the rising Himalaya during middle Miocene and early Pleistocene. This foreland basin lies on the southern flank of the Himalaya. This group is lithologically divided into three groups namely Lower, Middle, and Upper Siwaliks having increasing grain size towards the top. Geologically, this group is subdivided into southern belt and the northern belt by Central Churia Thrust (CCT). The Siwalik sediments exhibit coarsening upward sequence in general. The geological map of siwalik from Butwal to Kerabari showin fig 3.1 and its columnar section show in fig: 3.2.

3.2 Previous Works

Many studies and researches have been conducted in Siwalik group throughout the country. Different classifications of this group have been suggested in different areas by different researchers. Auden (1935) was one of the earliest to work in Siwalik group and he classified this zone into three groups namely Lower, Middle and Upper Siwalik. This classification scheme was later followed by Hagen (1959) and Yoshida and Arita (1982) in their studies. Glennie and Ziegler (1964) divided the group into conglomerate facies and sandstone facies which are correlated with the Upper Churia Group and Lower Churia Group of Sharma (1977). Tokuoka et al. (1986) presented fourfold classification system of Siwalik as Arung Khola Formation, Binai Khola Formation, Chitwan Formation and Deorali Formation in Arung Khola-Binai Khola section. Shah et al. (1994) classified this zone into Rapti Formation, Amlekhganj Formation, Churia Khola Formation and ChuriamaiFormation. This classification was later followed by Ulak and Nakayama (1998) in Hetauda-Bakiya Khola area. In Surai Khola section Corvinus and Rimal (1994) and Dhital et al. (1995) classified the Siwalik group in five formations namely Bankas Formation, Chor Khola Formation, Surai Khola Formation, Dobatta Formation and Dhan Khola Formation.

3.3 Stratigraphy

On the basis of lithology and the grain size, the Siwalik Group in the study section has been slightly modified from the previous established stratigraphy and sub-divided mainly in to the Lower Siwalik (lower and upper member) and Middle Siwalik (Lower and Upper Members). The typical Upper Siwalik are absent.In Eastern, central and Western Nepal, the Churia rocks have been studied by a number of geologists. In eastern Nepal along Bagmati, Marin, Kamala and Trijuga valleys Churia Group has been well studied by French Geologist (Herail and Mascle, 1980). They have recognized a number of the Thrust with in the Siwaliks. In some areas they also reported the presence of thrust bound pre-siwalik rock witin the Siwalik group.In the central Nepal, Curia group is very well exposed along Birjung-Heatuda.Lithologically it can be divided into Lower Siwalik, Middle Siwalik and Upper Siwalik according to field study as in the Table 3.1.

Table3.1 :Stratigraphy and Lithology of Siwalik Unit

Group	Belt	Unit	Member	Lithology
Siwalik Group	Northern Belt	Upper Siwalik	No Exposure
		Middle Siwalik	Upper Member	Pebbly sandstone, 'pepper and salt' textured sandstone
			Lower Member	Medium-grained sandstone with 'pepper and salt' texture
		Lower Siwalik Lower Siwalik	Upper Member	Variegated mudstone interbedded with thickly bedded sandstone
			Lower Member	Variegated bioturbated mudstone interbedded with thinly bedded fine-grained sandstone.
	----------------------------Central Churia Thrust (CCT)--------------------------------
	Southern Belt	Upper Siwalik	Pebble-cobble sized conglomerates with lenses of muds and sands
		Middle Siwalik	Upper Member	Pebbly sandstone, 'pepper and salt' textured sandstone.
			Lower Member	Medium grained sandstone with 'pepper and salt' texture
		Lower Siwalik	Upper Member	Variegated mudstone is interbedded with thickly bedded sandstone
			Lower Member	Variegated bioturbated mudstone interbedded with thinly bedded fine-grained sandstone.

3.3.1 Lower Siwalik

`The Lower Siwalik is composed of very fine to medium grained grey sandstones and bioturbated, variegated mudstones. It has an average thickness of about 1500 m. It is further subdivided into three members namely lower, middle and upper member.

In the lower member of Lower Siwalik, the proportion of mudstone is greater than sandstone. Mudstone is variegated and bioturbated and often contains calcareous cementing material. In the middle member, sandstone and mudstone are present in roughly equal proportions. Bioturbation and variegated mudstone is comparatively rare in this zone. The upper member comprises mainly of fine to coarse grained sandstone beds with associated dark grey to variegated mudstone. Some plant fossils are found in lower Siwalik which were observed on the right bank of Tinau Khola near the confluence of Tinau Khola and Dobhan Khola.

It is interpreted that the Lower Siwalik sediments were deposited by meandering river system and its long exposure in the sun after the deposition caused the variegation in mudstone. Petrographic analysis shows that most of the sediments in lower Siwalik were derived from the low grade metamorphic rocks of the Lesser Himalaya (Chaudhari, 1982; Hisatomi, 1990).

3.3.2 Middle Siwalik

The Middle Siwalik is about 1600 m thick and it is characterized by presence of thick bedded, coarse to very coarse grained, “salt and pepper” sandstone rarely alternating with dark grey mudstone. There is lack of variegation in mudstone and the proportion of sandstone is much greater than that of mudstone. The pebbly sandstone is occasionally found in the upper part of the Middle Siwalik. Due to presence of “salt and pepper” sandstone, the sediments of Middle Siwalik are thought to be derived from the Higher Himalaya and are deposited by sandy braided river system.

Fossils of plant leaves, vertebrate teeth and mollusk shells are found in middle member of Middle Siwalik.

3.3.3 Upper Siwalik

The Upper Siwalik is characterized by presence of well-sorted, rounded to sub-rounded, clast supported cobble to pebble-sized conglomerates with coarse grained sand in the lower part and poorly sorted boulder-sized conglomerates with subordinate dark grey mudstone in the upper part. In the lower part the clasts are mostly of quartzite and limestone from the Lesser Himalaya. On the other hand, in the upper part of the Upper Siwalik, the boulder conglomerates are derived from the Siwalik itself. The sediments in the Upper Siwalik are deposited by gravelly braided river system flowing southward from the Himalaya.

The fining upward sequence of sediment deposit is observed in individual members of the Siwalik but in general the coarsening upward succession of the whole group supports the upheaval of the Himalaya during Neogene Epoch, caused by movement of the thrusts.

3.4 Geological Structures

Geologically the Siwalik Group is bounded by Main Frontal Thrust (MFT) in the south and by the Main Boundary Thrust (MBT) in the north. MFT separates it from the Indo-Gangetic Plain in the south and MBT separates it from the Lesser Himalaya in the North. Another thrust called Central Churia Thrust (CCT) (Tokuoka et al., 1984) is developed within the Siwaliks. Along this thrust the lower Siwalik with the middle Siwalik on top of it, overrides the upper Siwalik. Thus the upper, middle and lower Siwalik on the south of the CCT is named as southern belt of the Siwalik whereas the lower and middle Siwalik exposed on the north of CCT is named as northern belt.

Except the major thrusts other geological structures are rare in Siwalik Group. However, in some places e.g. at the bank of Tinau Khola near Butwal, minor anticline and syncline folds can be observed.

3.4 Sedimentology

Sedimentology deals with the processes and products of the sedimentation by the mechanical or chemical processes. such as river system, flow direction, provenience or sediment source.

Lower Siwalik was deposited by meandering river system. Here the sediments were derived from Tibetan Tethys Himalaya and Higher Himalaya. The flow of river from north to south. Here, we find variegated mudstone and fine-grained sandstone.

Middle Siwalik was deposited by sandy braided river system. The sediments were derived from higher and lesser Himalaya. The flow of river was from northeast to southwest. Here, we find the medium to coarse-grained sandstone with ‘pepper and salt’ texture and pebbly sandstone. Upper Siwalik was deposited by gravelly braided river as well as debris Flow River. Here, we find the sediments from lesser Himalaya and from the Siwalik it self, which are deposits by east to west and northeast to southwest flow direction.

3.5 Fossils Occurrence

The Siwalik Group is well known for the presence of various fossils. The Siwalik Group has fossil assemblages at many places. (West et al, 1981) reported few vertebrate remains in the Lower Siwalik mudstone beds. Munthe (1983) also reported Ramapithecus fossil (jaw) in the Middle Siwalik. Apart from them fossils horizons with biocoenose (fossils of gastropods), bivalve, plant logs, petrified tree trunk fossils, leaf impressions were also found in the lower and Middle Siwalik. The plant fossils are most common in the mudstone of the Lower Siwalik. They contain clear visible midrib, reticulated venations and crenulated margins. The trace fossils like bioturbations and raindrops were also observed in the Chidiya Khola in the Lower Siddhababa Temple.

The Upper Siwalik being deposited by gravelly braided river system and having sediments of pebbles, cobble is not suitable for fossil formation. So, no fossils are reported in the Upper Siwalik.

3.6 Depositional environment

The rocks of the Siwalik Group are deposited by the fluvial system. The sedimentary basin of the Siwalik Group was much far from the Himalaya today.

According to Ulak and Nakayama (1998, 1999, 2001) the Lower Siwalik was deposited by meandering river. The Middle Siwalik was deposited by the sandy braided river system.The Upper Siwalik was deposited by gravelly braided river system. The river system changed from meandering to braided river system (Ulak and Nakayama, 2001).

Predominace of bioturbated, variegated and thick bedded mudstone beds, presence of calcareous nodules, abundance of trace fossils in fine grained sandstone and mudstone beds in lower and upper members of the Lower Siwalik indicates that they are produced in the low discharge, low relief meandering fluvial system. Significance amount of Paleosoles, presence of lateral accretion and mud cracks suggest the extensive flood plain deposits and the sediments were exposed for a long time on the flood plain.

The Upper Member of the Lower Siwalik is interpreted by the presence of medium to coarse grained; light grey sandstone interbedded with thinly laminated mudstone which belongs to a flood flow dominated meandering river system. Laminated sandy mudstone and fine grained sandstone represents deposition from the suspension and weak current. Climbing ripples indicates the gradual decrease in the velocity of flood flow.

The lower member of the Middle Siwalik is represented by the presence of thick bedded, medium to coarse grained sandstone interbedded with dark grey mudstone. These are considered to be the products of the sandy meandering river system with flood flow dominant deposits. The upper member is represented by the presence of thick bedded, coarse to very coarse grained sandstone, pebbly sandstone and dark grey mudstone beds. The pebbly sandstone beds have sheet like geometry. The sub-rounded pebbles in these sandstone beds are derived from the Lesser Himalayan rocks. The clasts of quartz are about 1 to 5cm in diameter. Presence of bed load in sandstone with downstream and lateral accretion indicatesthe deep sandy braided river system. The upper member of the Middle Siwalik is developed by the shallow sandy braided river system.

CHAPTE-4

geology of weatern nepal lesser himalaya

4.1 Introduction

Rocks of the Lesser Himalaya are very well exposed in the western Nepal in Palpa-Tansen area Fig: 4.2. The rocks of Kaligandaki Supergroup are extensively distributed in the MahabharatRange and the Midlands area whereas the rocks of Tansen Group are exposed in Palpa and Dumre area. The sequence of Kaligandaki Supergroup attains a thickness of more than 10 km ranging in age from Late Precambrian to early Paleozoic, and is unconformably overlain by the Tansen Group of Gondwana rocks. There is no stratigraphic break throughout the whole sequence.

4.2 Previous Works

Geology of the western Nepal has been studied by Bordet (1961), Bordet et al. (1964), Boudenshesen et al. (1964), Nadgir and Nanda (1966), Fuchs (1964), Hagen (1969), Fuchs and Frank (1970), Hashimoto (1973), Sharma (1977, 1980), Upreti and Merh (1978), Upreti et al. (1984), Sharma et al. (1984) and Dhital and Kizaki (1987). The Tansen Group and Kaligandaki Supergroup of the western Nepal have been studied thoroughly by Sakai (1983-1985). The Palpa Klippe in this zone was introduced by Sakai (1983, 84) and the recumbent fold was also recognized by him in 1985.

The rocks of Kaligandaki Supergroup of Western Nepal can be correlated with Nawakot Complex of central Nepal.

4.3 Stratigraphy of the Western Nepal Lesser Himalaya

The geology of western Nepal Lesser Himalaya has been studied by many researchers and the stratigraphy proposed by them is almost same for the area. The stratigraphy of Western Nepal Lesser Himalaya is divided into following two major divisions. Geological map of Lesser Himalaya around Butwal-Tansen area show in fig: 4.1

1. Kaligandaki Supergroup and

2. Tansen Group

Lithology of the western Nepal Lesser Himalaya is described below:

4.3.1 Kaligandaki Supergroup

Kaligandaki Supergroup is separated from the Siwalik Group in the south by MBT and from the Higher Himalaya in the north by MCT. This super group is composed of low to medium grade metamorphic rocks. The supergroup is sub-divided into three sub-groups namely lower, middle and upper group.

4.3.1.1 Lower Group

It consists of oldest rock of Kaligandaki Supergroup. Lithologically it is divided into following two formations:

4.3.1.1.1 Andhi Formation

The name of this formation is derived from the Andhi Khola of Syangja district (Sakai, 1983). It consists of thinly laminated, grey-light green Phyllite and gritty Phyllite. It is over 2000 m thick and its age is late Precambrian. This formation is correlated with the Kunchha Formation of central Nepal.

4.3.1.1.2 Naudanda Formation

The name of this formation is derived from the Naudada cliffs of Syangja district (Sakai, 1977). It consists of strongly rippled, cross laminated, fine to coarse grained, milky quartzite with metabasics and several intercalations of Phyllite and conglomerate. It is about 400 m thick and the rocks of this formation belong to late Precambrian. This formation is correlated with the Fagfog Quartzite of central Nepal.

4.3.1.2 Middle Group

This group is separated from the Lower Group by a thrust. This group comprises by rocks of Late Precambrian age. It consists of following five formations:

4.3.1.2.1 Heklang Formation

Heklang Formation is named after Heklang Village (Sakai, 1983). This formation is mainly exposed in the north and northwest of Tansen in a narrow belt along the Barigad Fault. It is composed of green-light brown phyllitic slate with fine laminae of marl beds. It is over 800 m thick. This formation is correlated with Dadagaon Phyllite of central Nepal.

4.3.1.2.2 Virkot Formation

Virkot Formation is named after Virkot Village (Sakai, 1983). It contains white pink quartzite and red brown shale having ripple marks, sun-cracks and stromatolites. The lower part of the formation is predominantly red purple shale and upper part comprises predominantly by quartzite. It is about 510 m thick and the age is Paleozoic. The Virkot Formation is correlable with Nourpul Formation of central Nepal.

4.3.1.2.3 Chappani Formation

Chappani Formation is named after Chappani village. It consists of quartzite with suncracks and grey colored slate consisting of stromatolites. It has average thickness of about 400 m. The Chappani Formation is correlated with Nourpul Formation of central Nepal. The age is Paleozoic.

4.3.1.2.4 Khoraidi Formation

Khoraidi Formation gets its name after the Khoraidi village. It consists of dolomite with stromatolites of various types. It also contains oolite, quartzite and rhythmite 350 m thick and the age is Paleozoic.

4.3.1.2.5 Saidi Khola Formation

Saidi Formation is named after the Saidi Khola. It consists of black and green slate with bioturbated rhythmite Flute cast, load cast, cross lamination, cross bedding and drag folds can be observed in this formation. It is about 180 m thick and the age is Paleozoic. It is correlated with the Hugdi bed of Dhading Dolomite.

4.3.1.3 Upper Group

The Upper Group of Kaligandaki Supergroup contains rock of early Paleozoic age. It consists of following formations:

4.3.1.3.1 Ramdighat Formation

The Ramdighat Formation is named after Ramdighat village on the southern bank of the Kaligandaki River (Sakai, 1983). This formation consists of variegated, laminated calcareous slate with thin layer of limestone. It also consists of bluish grey shiny phyllite and greyish white quartzite. This formation is divided into three members; the lower member of this formation consists of mainly black slate passing upward into brown slate. The middle member is characterized by marked color banding of reddish-purple calcareous slate and white limestone. The upper member is composed of calcareous and argillaceous grey slate. Thickness is about 750 m. The Ramdighat Formation is correlated with Benighat Slate of central Nepal. The age is Paleozoic.

4.3.1.3.2 Kerabari Formation

It is the topmost formation of Kaligandaki Supergroup. The name of this formation is derived from the Kerabari village (Sakai, 1983). The lower part of this formation consists of sheet-form algal limestone, intraformational dolomicrite, pebbly conglomerate, bedded dolomicrite with ripple marks and flute cast. The lower part contains Riri Member, which is composed of about 150 m thick slate.

The middle part comprises of bedded grey dolomicrite with chert beds and lenses whereas the upper part is composed of bedded grey dolomicrite with red-purple shale, thin sandstone, dolomite and chert beds.

The total thickness of this formation is about 2000 m and geological age is early Paleozoic. It is correlated with Malekhu limestone of central Nepal.

4.3.2 Tansen Group

Rocks of Tansen Group rest over the Kaligandaki Supergroup. This is fossiliferrous group largely formed in non-marine environment. The total thickness of this unit is about 2 km. The rock of Tansen Group is divided into following five formations:

4.3.2.1 Sisne Formation

It is the lower-most formation of Tansen Unit with average thickness of about 1000 km. It lies disconformably above the Kerabari Dolomite. It consists of conglomerate having fragments of dolomite, claystone, metamorphosed mudstone (slate) at basal part of disconformity. Slate and Phyllite is observed in this formation and diamictite of glacio-marine origin and sediments of glacio-fluvial origin also frequently occurs. Age of this formation ranges from late Carboniferous to Permian.

4.3.2.2 Taltung formation

Taltung Formation begins with beds of conglomerate having clast of subrounded sandstone, quartzite and trachyte, which are densely packed. The pebble-cobble conglomerate is known as Charchare conglomerate. Volcanic rock (Aulis trachyte) is also observed in this formation. The top of this formation consists of sandstone followed by silty shale, which indicates the fluvial nature of the sequence. The age of this formation ranges from Late Jurassic to Early Cretaceous (Sakai, 1983).

4.3.2.3 Amile formation

Amile Formation rests unconformablely over Taltung Formation. It is composed of sandstone with subordinate shale and limestone. It contains some lenticular interbeds of argillaceous limestone, which abundantly yield marine bivalve, gastropods, corals etc. Some conglomerate beds are also observed. Fossiliferrous siltstone containing shark teeth, coral, vertebrate bones can be observed. Its thickness is about 200 m. The age of this formation is supposed of Late Cretaceous to Paleozoic (?).

4.3.2.4 Bhainskati formation

Bhainskati Formation is well exposed around the Tansen Synclinorium. It is mainly composed of marine sediments. Dark muddy limestone and shale with fossils of bivalve, gastropods and foraminifera are found in this formation. Red purple mudstone and green sandstone are also present on the upper part of this formation. This formation is separated from the overlying Dumri Formation by Hematite bed. Its thickness is about 160 m and the age is Middle to Late Eocene (Sakai, 1983).

4.3.2.5 Dumri formation

It is the youngest formation of Tansen Group. This formation is also termed as pre-Siwalik rocks as it was deposited just after the upliftment of the Himalaya. It is characterized by massive quartzose sandstone, shale and pebble conglomerate having rhythmic sequence. Wedge shaped cross bedding and strong bioturbation on the mottled shale are observed in this formation. Tree trunk, vertebrate fossils are also found. Its thickness is about 725 m. The age of this formation ranges from Oligocene to Early Miocene.

CHAPTER-5

GEOLOGICAL FIELD STUDY in TANSEN ARea

Introduction

The field study was carried out in the Butwal, Palpa and Tansen area covering the Siwalik Group and Tansen Unit and Kaligandaki Supergroup of the Lesser Himalaya in western Nepal. The study was along the Siddhartha Highway and around Masyam-Dumre area. All the formations of Siwalik Group, Tansen Group and lower and middle group of Kaligandaki Supergroup were observed during the study. The stratigraphy of these areas is described in brief in the following sections.

5.1 The Siwalik Group Along the Tinau Khola Section

5.1.1 Stratigraphy and Lithology

Siwalik group of Nepal is situated in between indo-Gangetic plain (Terai) in the south and lesser Himalaya in north.Siwalk group is divided into two parts by a thrust called Central Churia Thrust (CCT). One is northern belt and other is southern belt.

5.1.1.1 Southern Belt

Southern Belt of the Siwalik Group is bounded by HFT in the South and CCT in the North. In the study area, this belt consists of following three parts:

5.1.1.1.1 Lower Siwalik

This is an approximately 2250m thick sequence of sandstone and mudstone lying in the lowermost part of Siwalik Group. On the basis of lithofacies observed in the area, the Lower Siwalik is also subdivided into two members as Lower Member and Upper Member.

5.1.1.1.1.1 Lower Member of Lower Siwalik

The lower member of the Lower Siwalik was observed on the right bank of Tinau Khola at about 700m west of Golpark underneath a suspension bridge and along the Chidiya Khola. This member is composed of fine grained, variegated and bioturbated mudstone interbedded with fine grained sandstone beds. The proportion of mudstone is greater than sandstone and the ratio of the two is about 63:35 (Ulak and Nakayama, 1980). Fining upward sequence is observed all along the unit. Trace fossils, plant fossils and bioturbations were observed in the mudstone on the bank of Tinau Khola whereas sedimentary features like lateral accretion, vertical accretion and pinching and swelling beds were observed near the Chidiya Khola. This suggests the depositional environment of this member to be of low relief meandering river system. Thickness of the mudstone bed ranges from 0.5m to 4m and that of sandstone beds from 0.1 to 1m. Attitude of the beds were measured 300/18⁰.

5.1.1.1.1.2 Upper Member of Lower Siwalik

First appearance of thick bedded, medium grained sandstone beds in the Chidiya Khola section marks the boundary between lower and upper member of lower Siwalik. This member was well observed near the Mathillo Siddhababa Temple. Proportion of sandstone and mudstone is nearly equal in this member. Sandstone is fine to medium grained, grey colored and calcareous whereas mudstone is variegated and bioturbated with some trace fossils. Pseudo ‘pepper and salt’ sandstone is observed in this member. Architectural elements like load-cast, lateral and vertical accretion cross lamination are observed throughout the member in various locations. This indicates that this member was deposited by flood dominated meandering river system with crevasse splay deposits. Thickness of sandstone beds ranges from 2 to 3m and that of mudstone ranges from 0.5 to 1m. Attitude of the beds were measured 290/24⁰(Fig. 5.1)

5.1.1.1.2 Middle Siwalik

The first appearance of coarse grained ‘pepper and salt’ sandstone marked the boundary between lower and middle Siwalik near the Butwal Hydropower Station. The middle Siwalik is composed of coarse grained sandstone and pebbly sandstone interbedded with dark grey mudstone. The proportion of sandstone is much greater than that of mudstone.

The average thickness of the middle Siwalik is about 1600m. On the basis of lithofacies the middle Siwalik is also divided into two members namely lower and middle member.

5.1.1.1.2.1 Lower member of Middle Siwalik

In the southern belt of the Siwalik Group the lower member of the middle Siwalik is well observed in the Dobhan village and Dobhan Khola area. This member is composed of medium to coarse grained, thick bedded ‘pepper and salt’ sandstone with rarely alternating dark grey mudstone beds. Thickness of sandstone beds range from 2-7m whereas that of the mudstone beds from 0.5-1m. Fining upward succession is observed in the individual beds. The ‘pepper and salt’ appearance in the sandstone is due to feldspar, quartz, muscovite and biotite minerals derived from the granites and gneiss of Higher Himalaya during the deposition of the sequence. The increase in thickness of sandstone beds, increasing grain size and ‘pepper and salt’ appearance indicates the rapid upliftment of the Himalaya during the deposition of this member. Sedimentary features like lateral accretion and loadcast were observed in this member. These features suggest that this member was deposited by flood dominated meandering river system. The thin fine grained mudstone beds within the thick sandstone beds indicate the start of monsoon in the Himalayan region during the deposition of this member. Attitude of the beds was 275/45⁰

S.N	Sample No.	Roundness		Sphericity
S.N	Sample No.	R=(∑r/n)/R	Result	a	b	c	b/a	c/b	Result
1	PC₁	0.430	Sub-rounded	5.5	5.4	5	0.98	0.920	Equant
2	PC₂	0.404	Sub-rounded	6.4	5.5	3.7	0.85	0.627	Equant
3	PC₃	0.909	Well-rounded	7	5.3	3.8	0.75	0.710	Equant
4	PC₄	0.680	Rounded	6.4	5.5	3.7	0.850	0.670	Equant
5	PC₅	0.869	Well-rounded	6.1	5.2	3.4	0.850	0.650	Oblant
6	PC₆	0.527	Rounded	5	4	2.5	0.80	0.625	Oblant
7	PC₇	0.772	Rounded	5.3	4.5	2.5	0.849	0.543	Oblant
8	PC₈	0.850	Rounded	5	3.8	2.9	0.760	0.763	Equant
9	PC₉	0.930	Well-rounded	5.3	4	3.4	0.754	0.850	Equant
10	PC₁₀	0.617	Rounded	4.4	3.8	2.4	0.860	0.630	Oblant

Table 5.1 Sphericity and roundness of the pebble of conglomerate of the Upper Member of Middle Siwalik.

5.1.1.1.2.2 Upper Member of Middle Siwalik

The upper member of middle Siwalik is marked by first appearance of pebbly sandstone at about 500m downstream of the confluence of Dobhan Khola and Tinau Khola. This member is composed of thick bedded, coarse grained pebbly sandstone with alternating dark grey mudstone beds. Roundness and nature of shape of the pebbles from this unit is shown in table 5.1 below.

Thickness of sandstone beds ranges from 3-10m. Trough cross lamination, ripple lamination and downstream accretion are observed in the sandstone beds and immature concretion is observed in mudstone. The sediments are derived from the Lesser Himalaya and Higher Himalaya. The upliftment of the Himalaya was very rapid which changed the meandering river system to braided river system in the area. The deposits of the upper member of middle Siwalik is deposited by the sandy braided river system. Attitude of the beds is 292/55⁰.

5.1.1.1.3 Upper Siwalik

Upper Siwalik is observed at Dobhantar on the left bank of Dobhan Khola. The lower part of this formation consists of well sorted, clast supported, moderately indurated, pebble-cobble-conglomerate. The clasts are mainly composed of quartzite and are believed to be derived from the Lesser Himalaya. The attitude of the conglomerate bed was measured 295/38⁰ in the study location. A minor fault was also observed there.

The upper part of upper Siwalik is composed of poorly sorted, matrix supported, boulder sized loose conglomerate with lenses of sand and mud. The sediments in this part are derived from the Siwalik itself and are very poorly indurated. However this part was not observed in our field work.

The sediments of upper Siwalik are deposited by gravelly braided river system. Thickness of conglomerate beds reaches upto 200m. Age of this unit is early Pleistocene.

5.1.1.2 Northern Belt

Northern belt lies in the north of the CCT and in the south of Main Boundary Thrust (MBT) i.e. it is bounded by CCT and MBT. It is also further divided into three parts, Lower Siwalik, Middle Siwalik and Upper Siwalik.

5.1.1.2.1 Lower Siwalik

It is the oldest subgroup of siwalik group of northern belt. It mainly consists of mudstone followed by sandstone. It is subdivided into,

Ø lower member of lower siwalik

Ø upper member of lower siwalik

5.1.1.2.1.1 Lower Member of Lower Siwalik

This member was observed about 50 m northward from the confluence of Jhumsa Khola and Tinau Khola. Alternation of thinly bedded mudstone and fine grained sandstone was observed in this member. Proportion of mudstone was greater than sandstone. Mudstone and sandstone both were calcareous. Bioturbation and concretion were observed in mudstone as in the southern belt. A 10m thick fossiliferous horizon of bivalve and gastropods was observed in this member which was absent in the equivalent Southern belt. The detailed columnar section of this member along Siddhartha Highway is show in fig: 5.2.and at right bank of Tinau khola, Khoshyauli show in fig 5.3.Attitude of the beds was measured 018 / 73^0.

5.1.1.2.1.2 Upper Member of Lower Siwalik

About 50m north from Siddhababa temple along Siddhartha Highway, we observed thick bed of sandstone that suggest the boundary between the lower member of lower siwalik and upper member of lower siwalik. General Attitude of bedding plane is N50S/40SW. Proportion of sandstone and mudstone is nearly equal.Pseudo ‘pepper salt’ sandstone is observed in this member. This member deposited by flood dominated meandering river system. Structures like lateral accretion, load accretion, load cast, immature concretion etc.

5.1.1.2.2 Middle Siwalik

The thickness of the Middle Siwalik in the Northern belt is about 1200 m. It is also divided into two members as lower and upper member.

5.1.1.2.2.1 Lower Member of Middle Siwalik

Thick beds of coarse grained, ‘salt and pepper’ appearance sandstone was observed in this member. It ranged up to 4 m with alternating thin bedded greenish-grey colored concreted and calcareous mudstone. The proportion of sandstone was very much greater than mudstone. Columnar section of a part of this member along Siddhartha Highway is shown in fig 5.6. Attitude: 020 / 60⁰.

5.1.1.2.2.2 Upper Member of Middle Siwalik

In this member the proportion of sandstone was too much greater than mudstone. Very thick beds of sandstone were observed. Similar to that of the Southern belt, pebbly sandstone with ‘salt and pepper’ appearance sandstone was observed. Grey calcareous mudstone of very thin bedding was observed. Columnar section of a part of this member along Tinau Khola is shown in fig 5.5. Attitude: 18 / 58⁰

5.1.1.2.3 Upper Siwalik

It is not exposed in the study area.

5.1.2 Sedimentology and Sedimentary Structures

Sedimentology deals with the process and products of sedimentation. Sediments are produced either by disintegration and alteration of pre-existing rock or by precipitation from solution. Sediments are transported by running water, wind or moving ice to various depositional environments. The nature of sedimentation provides the clue to the paleocurrent and paleo-enviroment.

In siwalik different types of sedimentation were occurred in past. Siwalik is mainly comprises of fluvial sediment. Middle Miocene to Pleistocene fluvial sediments of siwalik group is widely distributed in the southern frontal area of Himalaya. The group is separated in to northern and southern belts by the Central Churia Thrust (CCT).there are different depositional environment are recognized in the siwalik group. it is found that lower siwalik was deposited by meandering river system whose sediments were transported from Lesser Himalaya and Tibetan Tethys Himalaya. The middle siwalik was deposited by sandy braided river system and pepper and salt appearance sandstone of this formation explain sedimentary environment of this area. Upper Siwalik comprise of course grained to gravelly sedimented beds. So it was deposited by gravelly braided river system.

Structures formed during the formation of rocks having secondary origin are termed as primary sedimentary structures. Bedding is the most prominent and important primary structure. Beside these, the rocks of the Siwalik Group have primary sedimentary structures like cross-stratification, mud cracks, concretion, raindrop imprints and ripple marks. Some of the major sedimentary structures are mentioned below:

Lateral and Vertical accretion

Lateral and Vertical accretions are one of the characteristic architectural elements of the meandering river system. It was observed in the Lower Siwalik along the Chidiya Khola

Bioturbation

The reworking and alteration of sediments by organisms, which are marked by the transverse holes made by worms at the bottom of the depositional environment or the structures made by the locomotory organs and by their habitat. Bioturbations (fig; 5.8) were seen in the mudstone of the Lower and Middle Siwalik.

100_3087

Fig.5.8 Bioturbations in middle siwalik

Cross Bedding

The cross bedding is produced by migration of bed form, mainly ripples, mega ripples and sand waves. It is commonly seen in sedimentary rock. It is found in sandstone bed in the Lower and Middle Siwalik.Cross limination also found in lower siwalik,fig:(5.9).

These are one of the series of lake or revering topographic features, consisting of repeated wave like forms with symmetrical slopes, sharp peaks and rounded troughs. These are formed on sandy bottoms by current or oscillation waves. Ripple laminations were seen in fine grained sandstones of Lower and Middle Siwalik. (Fig5.10).

Load Cast

Loads may leave a sand bed intact on it may totally disrupt the bed. When not completely disrupted the loading is shown by botryoidally protuberances on the base of sand beds. The load is called load cast. It is found in the sandstone in the Siwalik Group.

Pebble Imbrications

Pebble imbrications were observed in conglomerate of Upper Siwalik. This shows the direction of flow of river.

Amalgamated Structure

These structures, observed in fining upward sequence of river deposit in upper member of Middle Siwalik, developed due to rapid uplift of the area and rapid deposition of sands.

Concretion/ Caliches

These were observed in the beds of mudstone in the Lower and Middle Siwalik Groups and in some beds of sandstone in the Middle Siwalik.

5.1.3 Fossil occurrence

Siwalik is a fluvial sedimentary sequence. Fossil occurrence is not so abundant. In our study area mainly fossil horizon has found in two places .on the right bank of Tianu khola, plant fossils have fond on the mudstone bed. This is belong to lower member of lower siwalik. Similarly two meter thick fossil horizon compri.sing pelecypod and gastropods has hound on the right bank of Jhumsa khola which is belonging to middle siwalik.

5.1.4 Paleocurrent Analysis

The paleocurrent analysis deals with the past river flow direction of the particular area. Different sedimentary structures used for analyzing the flow direction of the paleo river.the ripple marks, pebble imbrications, crossbedding are the important tools of paleocurrent analysis.

5.1.5 Depositional environment

The rocks of the Siwalik Group are deposited by the fluvial system. The sedimentary basin of the Siwalik Group was much far from the Himalaya today.

The Upper Member of the Lower Siwalik is interpreted by the presence of medium to coarse grained, light grey sandstone interbedded with thinly laminated mudstone which belongs to a flood flow dominated meandering river system. Laminated sandy mudstone and fine grained sandstone represents deposition from the suspension and weak current. Climbing ripples indicates the gradual decrease in the velocity of flood flow.

The lower member of the Middle Siwalik is represented by the presence of thick bedded, medium to coarse grained sandstone interbedded with dark grey mudstone. These are considered to be the products of the sandy meandering river system with flood flow dominant deposits. The upper member is represented by the presence of thick bedded, coarse to very coarse grained sandstone, pebbly sandstone and dark grey mudstone beds. The pebbly sandstone beds have sheet like geometry. The sub-rounded pebbles in these sandstone beds are derived from the Lesser Himalayan rocks. The clasts of quartz are about 1 to 5cm in diameter. Presence of bed load in sandstone with downstream and lateral accretion indicates the deep sandy braided river system. The upper member of the Middle Siwalik is developed by the shallow sandy braided river system

5.1.6 Tectonic structure

The structures formed after formation of rocks are known as secondary structures. The secondary structures found in the Siwalik Group are the Main Frontal Thrust (MFT); Central Churia Thrust (CCT) and Main Boundary Thrust (MBT).

HFT: The Himalayan Frontal Thrust divides the Indo-Gangetic Plain in south and the Siwalik Group in north. The boundary was not clearly observed. In Nepal, the Siwalik forms for 20-30km wide foot hill belt and extends beneath Gangetic alluvium in the south. The HFT was traced out at downstream of the Tinau Khola just below the hills of Siwalik near Butwal Bazar.

CCT: The Central Churia Thrust divides the Siwalik Group in northern and southern belts. Dun Valleys are formed due to the movement of this thrust. It was observed at the confluence of Jhusma Khola and Tinau Khola and also along the Dobhan Khola 350m upstream from the Suketar Village. Repetition of same lithology of the Lower and Middle Siwalik upward sequence is the evidence for the presence of CCT. (Fig 5.11).

Fig.5.11- CCT Near Tinau Khola

MBT: The Main Boundary Thrust divides the Siwalik Group in south and the Leser Himalaya in north. The thrust is supposed to be a low angle thrust but at the study area it is found to be dipping about 40-60 N at some distance near the Kerabari Village. Because of the subduction of Siwalik and upliftment of Lesser Himalayan the angle becomes high.

The Lesser Himalayan Sediments are highly sheared and drag folds developed near the thrust zone.(fig 5.12).

Fig. 5.12- MBT Near Kerabari Village.

5.2 Lithology and Stratigraphy of the Tansen Group

The Tansen group rests over the older Kaligandaki Supergroup with a marked unconformity. The rocks of this group are well exposed along the study area. On the basis of lithology found in this group, the Tansen Group is subdivided into five formations namely Sisne Formation, Taltung Formation, Amile Formation, Bhainskati Formation and Dumri Formation. The stratigraphy of this unit is shown in table 5.2.Brief description of each of the formation is given below.

Table 5.2: Established Lithostratigraphy of the rocks of the Tansen Group

Formation	Thickness (m)	Age	Lithological Characters	Depositional Environment
Dumri Formation	more than 350	Oligocene- Early Miocene	Red purple shale interbedded with fine-grained greenish-grey sandstone.	Meandering river system
Bhainskati Formation	45	Eocene	Pencil cleavage, black shale with bivalve, gastropod and Gondwana plant fossils.	Shallow marine to brackish water deposits.
Amile Formation	100-140	Cretaceous- Paleocene	Ferruginous and carbonaceous Quartzite with ripple marks and cross laminations.	Fluvial deltaic deposits.
Taltung Formation	160-240	Late Jurassic – Early Cretaceous	Fine-grained grey sandstone shale and conglomerate.	Gravelly braided to meandering river system.
Sisne Formation	more than 300	Late Carboniferous	Diamictite, slate, pebbly sandstone, rythmite beds.	Tidal flat deposits, Glaciofluvial, Glaciomarine.

5.2.1 Sisne Formation

The name of this formation was derived from Sisne Village (Sakai, 1983). This formation overlies the Kerabari Formation of Kaligandaki Supergroup with an unconformity. It is mainly composed of diamictite, slate, sandstone and sandstone-mudstone rythmite beds. Diamictite is matrix supported. Various size and shapes of the clasts were observed in the diamictite. The presence of angular and rounded both shape of clasts, dropstones and sandstone beds over fine grained shale indicates that the sediments of this formation are inter-glacial spring deposit. On the upper part of the formation, sandstone-mudstone rythmite beds were observed.On the top part, bioturbated mudstone appears which is called Ritung Bioturbated Mudstone

The name of this formation was derived from Sisne Village (Sakai, 1983). This formation overlies the Kerabari Formation of Kaligandaki Supergroup with an unconformity. It is mainly composed of diamictite, slate, sandstone and sandstone-mudstone rythmite beds. Diamictite is matrix supported. Various size and shapes of the clasts were observed in the diamictite. The presence of angular and rounded both shape of clasts, dropstones and sandstone beds over fine grained shale indicates that the sediments of this formation are inter-glacial spring deposit. On the upper part of the formation, sandstone-mudstone rythmite beds were observed. On the top part, bioturbated mudstone appears which is called Ritung Bioturbated Mudstone member (Sakai, 1983, 1985).The thickness of this formation is more than 300m and the age ranges from Late Carboniferous to Permian.The columnar section of contact between Sisne and Taltung formation is show in fig: 5.13. Attitude of the beds were measured 190/35⁰.

5.2.2 Taltung Formation

The name of this formation was derived from the village Taltung (Sakai, 1983). This formation overlies the Sisne Formation with a disconformity. Basal part of Taltung Formation consists of conglomerate known as Charchare conglomerate which was observed near the confluence of Tinau Khola and Bhainskatta Khola. The conglomerate is matrix supported and the clasts are well rounded with medium to high sphericity. Clasts are quartzite pebbles and volcanic pebbles of aulis trachite whereas matrix is composed of medium grained, dark grey sandstone. Thickness of this bed is about 10m.

The upper part of this formation is composed of carbonaceous shale rich in upper Gondwana plant fossils. Reddish brown to reddish purple shale is commonly interbedded in this part. This formation was deposited by gravelly braided and meandering river systems. The total thickness of this formation ranges from 160-240m and geological age is late Jurassic to early cretaceous.Attitude of the bed was measured 210/70⁰..

5.2.3 Amile Formation

This formation is named after Amile Khola (Sakai, 1983). This formation was observed on the left bank of Bhainskatta Khola at about 10 m upstream from the confluence of Bhainskatta Khola and Tinau Khola. A disconformity separates this formation with the Taltung formation. It is mainly composed of cross-bedded and wedge bedded quartzite mottled, black carbonaceous sandstone and ferruginous mottled quartzite. The quartzite contains carbonaceous wood fragments. Wedge shaped swelling and pinching beds were observed along the Bhainskatta Khola. Massive fossiliferrous siltstone, limestone and thinly laminated black shale are also observed in this formation. The sandy limestone contains molluscan fossils and also coal in minor amount. The Detailed columnar section of Upper member of Lower Siwalik in Chidiya Khola show in fig: 5.15. Attitude was measured 190/57⁰.

The Amile Formation was deposited in deltaic environment. Its thickness ranges between 100 and 140m and its age is late Cretaceous to Paleocene

5.2.4 Bhainskati Formation

This Formation was observed on the right bank of the Bhainskatta Khola about 100 m upstream from the confluence of Bhainskatta Khola and Tinau Khola. It is named after the Bhainskatta Khola (Sakai, 1983). Abrupt change in lithofacies marks the boundary between Amile and Bhainskati Formation. This formation consists of black shale and calcareous beds with abundant marine bivalve and gastropod fossil. The upper part contains green and reddish-purple and mottled shale with characteristic pencil cleavage. On the topmost part hematite with oolites was observed.The columnar section of contact between the Bhainskati formation and Dumre formation is show in fig 9.12, Thickness of this formation is about 45m and age is Eocene. Attitude of the beds was measured 355/55⁰.

5.2.5 Dumri Formation

A disconformity separates this formation from the Bhainskati Formation. It is named after the Dumre village (Sakai, 1983). This formation contains typical green sandstone and green to purple shale and mudstone. The sandstone beds were thick, massive, and fine to coarse grained. Shale is bioturbated and mottled. Petrified tree trunks and coalified wood fragments were observed on the uphill side of the road near the bridge. This formation is composed of river channel deposits, point-bar deposits and over-bank deposits. Coconite, a bivalve fossil was observed in this Formation.

Thickness of this formation is more than 350m. Its age ranges from Oligocene to early Miocene. Attitude of the beds was measured 188/75⁰.

5.3 Lithology and Stratigraphy of Kaligandaki Supergroup

The Kaligandaki Supergroup is extensively distributed in the lesser Himalaya and midlands o western Nepal. In the study area this group can be observed from Dumre to Ramdighat with the Tansen Group within it. This super group forms a large Synclinorium with the Tansen Group on it. In the south it is separated from the Siwaliks by the Main Boundary Thrust (MBT) and in the north it is separated from the Higher Himalaya by the Main Central Thrust (MCT). Another thrust separates this group from the Tansen Group.

The Kaligandaki Supergroup is composed of low to medium grade metamorphic rocks. Stratigraphically this super group is divided into Lower, Middle and Upper Groups. These groups are further subdivided into different formations according to the lithology observed in the area. The stratigraphy of this super group is shown in the table 5.3.

In the study are the Andhi Khola Formation and Naudanda Formation were not observed. Brief description of each formation is given below

Table.. 5.3: Established Lithostratigraphy of the rocks of the Kaligandaki Supergroup

Formation	Member	Thickness (m)	Age	Lithological Characters	Depositional Environment
Kerabari Formation	Riri	more than 2,000 150	Early Paleozoic	Bedded grey dolomicrite with chert beds, sheet form algal limestone and intraformational dolomicrite pebble conglomerate at lower part Black laminated limy slate at Riri member.	Neritic to uppermost of Bathyl zone
Ramdighat Formation		750	Late Pre-Cambrian	Light brown to varicolored calcareous slate with thin limestone.	Neritic zone
Saidi khola Formation		180		Bioturbated, rhythmite of sandstone and shale	Tidal flat
Khoraidi Formation		350		Dolomitic stromatolite of various types. oolite, quartzite, rhythmite	Neritic to upper most of bathyl zone
Chappani Formation		400		Quartzite with suncracks, grey clay slate with stromatolite	Aerial to upper most of Bathyl zone
Virkot Formation		510		White pink quartzite and red purple shale with ripple mark, sun crack and stromatolite	Aerial to sub-aerial zone
Heklang Formation		more than 800		Green to light brown phyllitic slate with fine laminae and marl bed.	Neritic zone
Naudanda Quartzite		400		Strongly rippled, white quartzite with metabasite	------
Andhi Formation		more than 2,000		Grey to light green phyllite with fine laminae	------

5.3.1 Andhi Formation

This formation is composed of monotonous thick sequence of grey to light green Phyllite and greenish grey to brownish grey slate with occasional interbeds of thin calcareous siltstone. The slate has silvery luster. The thickness of this formation is thought to be more than 2,000m. The rocks are of Late Pre-Cambrian age.

5.3.2 Naudanda Formation

It consists of strongly rippled and cross bedded, fine to coarse grained white quartz arenite and bluish grey to greenish grey phyllites. The phyllite shows silty luster. This formation has the thickness of about 400m and the age of the rocks are thought to be Late Pre- Cambrian.

5.3.3 Heklang Formation

This formation was observed on the right bank of Hulandi Khola near Bartung. Tectonite is observed between the Dumri Formation of Tansen Group and Heklang Formation. It is again seen near MalungaVillage where tiger stripe pattern can be seen in phyllite of this formation

This formation is mainly composed of dark green slate or phyllite occasionally associated with calcareous sandstone, marl and dolomite. The rocks in this formation were deposited in neritic zone in marine environment. Its age is late Precambrian. Attitude: 155/60⁰.

5.3.4 Virkot Formation

This formation is observed near Bhalebas along the Siddhartha Highway. It is composed of white to pink quartzite and reddish purple phyllitic slate. However bioturbated shale beds and reworked shale and dolomite can also be found. Pebble layers are also occasionally observed. In some parts rhythmically alternating beds of quartzose sandstone and reddish purple shale with algal dolomites are observed. Ripple marks, suncracks and occasionally stromatolites can be observed in this formation.

The Virkot Formation lies in the core of Tansen Synclinorium which can be easily recognized in the study area by the two limbs of the formation dipping toward each other.

This formation was deposited in shallow marine environment with the sea level falling and rising periodically. Its age is late Precambrian.

5.3.5 Chappani Formation

This formation was observed along the Siddhartha Highway north of Malunga. It is composed of grey shale and stromatolitic limestone in the lower part and thinly laminated light purple green claystone at the middle part. The upper part is composed of shale. In some places, white, light green and pale orange quartzite can also be observed. Mudcracks can also be seen. This formation is shallow marine deposit of late Precambrian age.

Attitude: the attitude of ceneral bed is 145/50⁰.

5.3.6 Khoraidi Formation

This formation overlies the Chappani Formation. It is composed of dolomitic stromatolites with oolitic quartzose sandstone, quartzite, rythmite of thinly bedded sandstone and intraformational reworked pebble conglomerate. Concave upward stromatolites observed in this formation indicate the overturned beds. It is a Precambrian shallow marine deposit with some gaps in the deposition periods. Attitude: 145/50⁰.

5.3.7 Saidi Khola Formation

This formation was observed at Ramdighat below the Kaligandaki Bridge. It is mainly composed of quartzose sandstone and black shale with rythmite. The shale is bioturbated. Oolitic sandstone beds and stromatolitic limestone beds are also present in this formation. The stromatolite observed in this formation is shown in fig 5.17. The cross and plan view of stromatolite were observed frequently. Flute cast, load cast, cross lamination, cross bedding and drag folds can be observed in this formation. The depositional environment of Saidi Khola formation was tidal flat deposit.

Attitude: 180 / 57⁰

Stromatolite

Fig; 5.17Stromatolite observed in Saidhi Khola Formation.

5.3.8 Ramdighat Formation

This formation is observed along the Siddhartha Highway near the Kaligandaki Bridge. It consists of black slate at the lower part and green slate at the top of the lower part. Middle part consists of reddish purple, pink and green calcareous slate and white limestone. The upper part of this formation is composed of white limestone and grey calcareous slate.This formation was deposited in neritic zone and its age is late Precambrian. Attitude: 85 / 37⁰.

5.3.9 Kerabari Formation

This is the topmost formation of Kaligandaki Supergroup. It overlies the Siwalik Group and separated from it by the MBT. It is mainly composed of dolomite. At the basal part of this formation black calcareous slate and a minor amount of limestone is found. These beds are termed as Riri Member of Kerabari Formation. In the middle part grey dolomite and thinly laminated shale with intraformational-pebble-conglomerate and dolomite are observed. Pink to light purple shale and dolomite is observed on top. At the MBT, near the Kerabari village, slickenside structure was observed.

The Kerabari formation was deposited in neritic and uppermost bathyl zone and its age is early Paleozoic. Attitude: 190/75⁰.

5.4 Geological structure of Tansen Area

Geologically Tansen area is divided into two groups.

Ø Tansen Group

Ø Kaligandaaki Supper Group

There are different Geological structures, sedimentary structures and tectonic structures are found in this area.

5.4.1 Geological Structure of Tansen group.

Geological structure of Tansen group is divided into two types.

Ø Sedimentary structures

Ø Tectonic structures

Sedimentary Structures

A lot of sedimentary structures are observed in the Tansen group along the study area. Bioturbation is found in Sisne Formation. The kink band is observed in the diamictite bed of Sisne Formation. Here fining upward sequence is observed within conglomerate of Taltung Formation. Quartize of Amile Formation is strongly cross bedded. Black shale of Bhainsekati Formation shows parallel lamination and cross bedding. Lateral accretion is observed within the Dumri Formation.

Tectonic Structures

In the Tansen group several tectonic structures can be observed. This group is rich in presence of erosional unconformities which has formed in several places along Siddhartha Highway from Charchare to Dumri and also in Bhainsekati Khola.

All of the formations are separated with adjacent formation by disconformities. Similarly ,one of the micro tectonic structure has seen on shale of Sisne Formation at the right bank of Bhainsekati Khola knows as tensional gash which is S or Z shaped and is useful on identifying the stress direction. The sheared structured so formed is called tectonite which is observed on the right bank of Hulandi Khola.

5.4.2 Geological Structure of Kalikgandaki Super Group

Geological structures of Kaligandaki super group is divided into two types.

Ø Sedimentary structures

Ø Tectonic structure

5.4.2.1 Sedimentary structure of Kaligandaki Super group

The Kaligandaki super group is reach in consisting of lots o sedimentary structures. The stromatlytic structure is dominants in dolomite of various formations of the kaligandaki super group. i.e Kerabari formation, Khorid formation and Chappani formation. Suncracks were observed within the beds of red shale in Virkot formation. Parallel laminations were observed in thick-bedded grey dolomite of Kerabari formation. Ripple marks were observed in quartzite of the Virkot formation.Rhythmite structure seen at the bank of the Kaligandaki River (Fig: 5.18).

Rhytmite

Fig: 5.18 Rhythmite structure seen at the bank of the Kaligandaki River

5.4.2.2 Tectonic structures of Kaligandaki Supergroup

The Kaligandaki Super group comprises a lot of tectonic structures. The structures observed in study area suggest that the rock of this super group have undergone the phase of deformation. The major tectonic structures observed are as follows.

CHAPTER-6

ENGINEERING GEOLOGICAL STUDY

6.1 Introduction

Engineering geology is an applied field of geology in which geological knowledge is used in engineering. Engineering geology deals with the engineering properties of rock and soil. Result from the engineering geological study is applied to the civil engineering, like road, tunnel, dam, bridge etc. therefore engineering geology is an opportunity and challenge profession. In this field, studies engineering geological investigation were carried out to measured basis of rock and soil mechanics.

6.2 Study of soil

Engineering geology and soil scientist have different definition for the term soil. Engineering soil is roughly equivalent to regolith, a term used by geologist to describe all unconsolidated material mantling the surface of the earth.

The importance of soil in engineering geology is in construction. Such as use of building materials, use for the construction of levee and earth dams.

Soil mechanics describes the behaviors of soils. That behavior determines the nature of construction; the soil type determines the natural slope management. Change occurred in soil slope creates problem in down slopes and nearby area.

6.2.1 Field Identification

Description: breaking%20test There are various tests to identify the properties of soil directly in the field and some properties can be test only in the lab. According to A. Casagrande (Graduate School of Engineering, Harvard University), Soil can be test by the following way without equipment;

6.2.1.1 Dry Strength Test

Dry strength test is a measure of the character and quantity of the colloidal fraction contained in the soil. The dry strength increases with increasing plasticity. High dry strength is characteristics of the inorganic clay of CH groups. Typical inorganic silts posses’ medium and low dry strength. Silty fine sands and silt have low dry strength but can be distinguish by powdering the specimen. However, sand feels gritty and typical silt have smooth feel of flour.

After selecting the particles smaller than 300µm size (No. 4 sieve size), a part of soil was added to consistency of putty, adding some water. The part was allowed to sundry completely and its strength was tested by breaking and crumbling between fingers. Typical inorganic silt posses’ slight dry strength, silty fine sand and silt have about same slight dry strength, but can be distinguished by feel when powdering the dry specimens. Fine sand feels gritty where as typical silt has smooth feel of flour. The result obtained is sown in the table no.6.1.

6.2.1.2 Dilatancy Test

It is the measure of finesse and quality of soil very fine clean sands given the quickest and moist distinct reaction where as plastic clay has no reaction. Inorganic silts such as typical rock flour shows a moderately quick reaction.

After removing the particles larger than No. 40 sieve size, prepare a part of moist soil with a volume of about 10 cc. add enough water, if necessary, to make the soil soft but not sticky.

The appearance of water on the surface the part was observed. The sample was squeezed between the fingers, the water and gloss disappeared from the surface, the part stiffened and finally crumbled. The rapidly appearance of water during the squeezing assisted in identifying the characters of fines in a soil. Very fine clean sands give the quickest and most distinct reaction where as plastic clay has no reaction. Inorganic silts, such as a typical rock flour, show a moderately quick reaction. The result is shown in table no.6.1

Table6.1: Observation table for dry strength test and Dilatancy test of the soil

Sample No.

Sample

location

Soil description

Reactions shaking(Dilatancy)

Dry strength

Remark

Quick

Intermediate

Sluggish

High

Medium

Low

On the right bank of the Hulandi Khola

Grey color, fine grain

Silt contain soil

On the right bank of the Hulandi Khola

Fine-grained, grey color

Silt contain soil

On the right bank of the Hulandi Khola

Fine-grained, gray color

Clay contain soil

6.3 Soil Unit

Generally we concerned with genetic classification of soil.

6.3.1 Alluvial soil

This is that type of soil formed by river action and hence angularities are changed into rounded and spherical rockball.

Soil description

They are rounded, well graded, densely packed Sandy gravel with different sizes ranging from cobbles to boulders of dolomite, limestone, slate and sandstone of lesser Himalayas. Somewhere these clastic fragments are cemented by sandy and calcareous cement.

Distribution

According to engineering geological map, alluvial soils are dominant near riverbank. In Masyam area, it is distributed around Tinau and Bhainskatte River.

Thickness

Thickness ranges from 0.5m- 15m

Seepage Condition

Generally this area is dry in summer season but discharge is very prominent in rainy seasons and hence there is seasonal variation discharge.

Slope Stability

It is stable because it is located near the river valley and bank but if present far from river bank it may not be stable.

6.3.2 Colluvial Soil

soil Description:

Poorly graded, angular rock fragments with many cms thickness.

Distribution:

It is found in landslide zone, below the large rock unit exposure.

Thickness:

It ranges from 2m-20m in different areas.

Seepage Condition: seepage varies with season increasing toward rainy season.

Slope Stability:

It is not stable because it lacks compaction.

6.3.3 Residual Soil

Soil Description:

The soil is present in high elevated but flat land as there is no area to form soil unit. It is well graded, rounded to angular with varying grain size

Distribution:

It is found in flat land far from river and far from high sloppy land.

Thickness:

It ranges from 1m-50m in different areas.

Seepage Condition:

Discharge varies with season increasing toward rainy season.

Slope Stability:

It is very stable then the areas having other type of soil.

6.4 Study of Rock

Rock is the aggration of minerals. Rock involved in many civil engineering projects. Rock properties inherently are a part of the exploration, design, construction and post construction phases of such projects. In addition to the rock properties including the classifications, engineering uses of rock requires classifications that are more generic. These are intact rock and rock mass.

6.4.1 Intact Rock

It is the rock unit having homogeneous properties without any discontinuities. It may be described by standard geologic terms such as rock name, mineralogy texture, degree and kind of cementation and weathering. Rock strength, rock deformation and weathering condition are some important properties of the intact rock.

6.4.1.1 Field Test of Intact Rock

Location is about 150 m uphill from the right bank of the Bhainskati Khola to the North West of Masayam high school. The result from the field study is shown in table 6.2:

Table 6.2: Field Test of intact rock

S. No.	Properties of intact rock	Description
1.	Rock name	Sand stone
2.	Mineralogy	Mica, quartz, feldspar
3.	Texture	Medium grain
4.	Degree and kind of cementation	Highly cemented by silica
5.	Weathering condition	Slightly weathered
6.	Moisture content	Dry
7.	Grade	R4
8.	Term	Strong
9.	USC (MPa)	50-100
10.	Point load index	2-4 (Hand held specimen broken by a single blow of geological hammer)

6.4.2 Rock Mass

It is the large volume of rock mass having discontinuities like bedding, fault, joint etc. It is typically more heterogeneous and anisotropic than intact rock mass is described on the basis of discontinuities.

Orientation

It refers to dip direction and dip amount of the discontinuity. The most readily apparent influence of the orientation of discontinuities on rock mass strength is evident in the failure of rock slopes along one or more discontinuities. Two factors of primary importance relative to the influence of joint orientation on rock slope stability are: Whether joint or joint intersection cut the slope at less than the natural or manmade slope angle and whether the dip angles of the joints or the plunge angle of the joint intersections exceed the angle of friction along the joint surface. The orientation of joints within a rock mass also influences the strength anisotropy of the mass. Rock masses with irregularly oriented joints have a greater degree of block interlock and less mechanical anisotropy than those masses with regularly oriented joints (Goodman 1964).

Spacing

It is the perpendicular distance between two adjacent discontinuities. It affects overall rock mass strength, excavation methods and support system. Spacing increases with depth except in faulting regions. Even the strongest intact rock is reduced to one of little strength when closely spaced joints are encountered whereas when spacing increases, the behavior of rock mass will be strongly influenced by intact rock properties.

Continuity (Persistence)

It refers to the continuity or aerial extent of a discontinuity and is particularly important because it defines the potential volume of the failure mass. Intact rocks or rock bridges may interrupt persistence.

Surface Characteristics

Waviness or undulation of surface, smaller scale roughness of the surface, and physical properties of any infill materials are important surface characteristics. Waviness has a greater influence on rock mass strength than roughness where slope stability is involved. For two adjacent blocks to move along a way intervening surface, there must be displacement normal to the surface.

Separation and Filling of Joints

The amount of separation or space between joint surfaces and presence of filling material may have a profound influence on the strength of a jointed rock mass, where separations occur, the space may be empty, partially filled or completely filled. The filling material may be clay, silt, sand or coarse fragmental material or mixtures of them resulting from depositional filling, faulting or wall-rock weathering.

Ground Water Condition

The water present in the discontinuities affects the total rock mass strength. High amount of water present in the opening or joints reduces the total strength of the rock mass in situ.

RQD

Rock quality designation is probably the most commonly used method for characterizing the degree of jointing in borehole core. It can be regarded as indirect measurement of block size. The RQD percentages are directly proportional to the various measures of rock mass quality such as fracture frequency and in situ modulus of deformation.

6.5 Engineering Geological Route Mapping

6.5.1 Study Site

An engineering geological route map was prepared for a section of Dumre-Masyam road near Masayam Higher Secondary School Masayam, Palpa. The location is shown in the map.

6.5.2 Methodology

First of all a route map of the study site was prepared by compass traverse method using Brunton compass and measuring tape. Appropriate sites were selected to study the engineering properties of rocks and soil. Since no considerable soil deposit was found, only the rock mass properties were observed. ASTM system of rock mass classification (1983) was used for this purpose. Kinematic analysis using stereographic projection was used to analyze the rock slope stability of various sites.

6.6 Estimation of Rock Mass Strength

Strength is a fundamental quantitative engineering property of a rock specimen. By definition it is the amount of applied stress at rock failure or rupture. The strength of rock mass is influenced by different characteristics of discontinuities: such as orientation, spacing, continuity, surface characteristics, separation and filling of joints. The rock mass was estimated at different locations along the Siddhartha Highway. Initially bedding planes were recognized and their attitudes were measured. Then joints sets were recognized and their attitudes were measured. The width of spacing the joints was measured and their surface characteristics like roughness, waviness and infilling materials were noted. Attitude of cut slope as also measured. Then the rock mass strength was estimated by using data of Table shown below 6.3.

Table 6.3: Measurement of discontinuities properties and Estimation of Rock Mass Strength

Location	Rock Type	Discontinuities	Orientation	Persistency (In m)	Spacing (In cm)	Surface roughness	Aperture	Infill	Seepage
Section of the Dumre-Masyam road section	Sandstone	Bedding plane	139/81	2	1	Undulating rough	Narrow	Absent	Dry
		Joint J₁	035/55	1.5	7	Planar smooth	Extremely narrow	Soil	Dry
		Joint J₂	280/61	1	4	Planar rough	Tight	Absent	Dry

6.6.1 Rock mass classification

Study of Rock mass classification was carried out to get idea about tunneling on road section of Masayam area. Area used for study of rock mass discontinuities was used for the study of rock mass classification also. Depending on the collected information we calculated RMR (Rock Mass Rating) value. Rock mass rating system (After Bieniawski, 1989) and Q- system classification of Barton et al. (1974) was used for the calculation of the RMR value.

Results after calculation are shown below:

1) RQD = 16

2) Spacing of discontinuities = 20 m

3) Condition of discontinuities = 25

4) Ground water = 15

5) Strength of intact rock material = ( very strong) (100-250 mpa) =12

6) Rating Adjustment for Discontinuity Orientations = -12

Total = 61

ROCK MASS CLASSES DETERMINED FROM TOTAL RATINGS

Rating	80 61
Class number	II
Description	Good rock

6.3.1 Table defining the rock class using total RMR value

GUIDELINES FOR EXCAVATION AND SUPPORT OF 10M SPAN ROCK TUNNELS IN ACCORDANCE WITH THE RMR SYSTEM (AFTER BIENIAWSKI, 1998)

6.3.1. Table showing guidelines for excavation and support for tunneling in accordance with the RMR system

Rock mass class

Excavation

Rock bolts (20mm diameter, fully grouted)

Shotcrete

Steel sets

II-Good rock

RMR: 61-80

Full face, 1-1.5m advance. complete support 20 m from face

Locally, bolts in crown 3m long, spaced 2.5m with occasional wire mesh

50mm in crown where required

None

6.7 Rock unit

Our study area belongs to the Dumre formation of Tansen group. The rocks units in this area are Dumre Slate and Dumre limestone.

6.7.1. Dumre Sandstone

This rock belongs to the Dumre formation of lower Tansen Group.

Intact Rock Description

The rock without any cracks is known as intact rock. In our study area we found light to dark brown, fine to medium grained moderately strong slightly weathered sandstone .

Distribution:

The rock is well exposed only on some place on the side of Bhainskatte Khola. At about 1 Km upstream from Dumre Bazzar on its right bank it is well exposed.

Thickness

The thickness of this rock unit is about 1-2 km.

Discontinuities:

The given table provides all information about discontinuities:

No.	Orientation	Spacing	Persistence	Surface Characteristic	Aperture	Infill Material
J1	N80°W/82SW	50cm	10cm	Undulated Surface	Tightly joined	Absent
J2	N10°E/70SE	30cm	50cm	Stepped rough	3-5 cm	Clay
J3	S15°W/25NW	40cm	35cm	Planar	Tight	Absent

Weathering

The intact rock i.e. sandstone is slightly weathered.

Seepage Condition:

As our study time was hot sunny day the amount of water discharged was very low.

Slope Stability:

Though most of the slopes were stale, but in some place we find plane failure, wedge failure and toppling failure.

Rock Mass Rating:

According to Bieniawski’s Geomechanics Classification the rocks were classified on the basis of different parameter like strength of intact rocks, Drill core qualities etc are found to be very Low.

6.8 Mass Movement Study:

It is a general term used for a variety of processes due to which large masses of earth material move under gravity, either slow or fast in downward slope. The term 'landslide' is used to denote the downward and outward movement of slope forming materials along surfaces of separation by falling, sliding, flowing etc. with high rate of moving. Although they are primarily associated with mountainous regions they can also occur in low relief during rainy seasons and especially, in surface excavations for highways, buildings etc.

Types of Mass movements

According to Varnes (1978), the slope movements are classified on the basis of the nature of the movement and the type of material involved in the process (annex).

Falls: The abrupt movement of slope material that becomes detached from steep slopes or cliffs is fall. The movement may be free fall or a series of leaps and bounds down the steep slope. The relatively free character and lack of a slide plane differentiates the rock fall and rockslide. Depending upon the type of slope material involved, it may be a rock fall, soil fall, earth fall, debris fall and boulder fall and so on.

Topple: A topple is a block of rock that tilts or rotates forward on a pivot or hinge and then separates from the main mass falling on the slope and subsequently bouncing or rolling down the slope.

Slides: The term slides refer to the mass movement with a distinct surface of rupture or zone of weakness separating the slide material from the more stable underlying material. The two major types of slides are rotational and transitional slides.

Spread:The failure in this case is caused by liquefaction, the process whereby saturated, loose, cohesion-less sediment is transformed into a liquefied state. Rapid ground motions such as earthquakes usually trigger the failure.

Flow: Flows involve an aspect of flow in unconsolidated materials with low or high rates under saturated or drained conditions. Flows are characteristics feature of movement in unstable areas.

Creep: These are extremely slow movements, which are imperceptible if measurements are not carried out over a long period of time, particularly in fine-grained materials.

Complex Movements

Slope movements involving two or more principal types of movement are called Complex Movement. Often landslides dams are formed because of a combination of movement. Often landslides dams are formed because of a combination of movement of some of the following types: Rock and Earth Slides, Debris and Mudflows and Rock and Debris avalanches. The landslide observed in the field excursion was slide. The type of the slide was Rotational Slide.

Landslide study:

We studied one landslide, nearly one km west from Dumre Bazaar, Palpa district. It is at left bank of Bhainskatte khola and at 20 m altitude than that from the river bank. Generally we observed gravelly sand and clayey sand with low plastic type soil.

Causes of this landslide are as follows:

i) Construction of road

ii) High slope of related area

iii) Weathered rock

iv) Seasonal Discharge

Preventive measures are as follows:

i) Bioengineering

ii) Deviation of water route.

SUMMaRY And CONCLUSION

The study area mostly lies along the Siddhartha Highway. It extends from Butwal in the south to Tansen and Syanja in the north where the Siwalik and the Lesser Himalayan rocks were studied. Geological as well as engineering geological works were done during field period.

The Siwalik Group is separated from the Terai region of Indo-Gangetic Plain by the Himalayan Frontal Thrust (HFT). The main lithology of the Siwalik Group is represented by mudstone, sandstone and conglomerate with coarsening grain size toward the top part of the Siwalik. Fossil of plants and invertebrates are also abundant in rock of Siwalik. The Siwalik Group is divided into the Lower Siwalik, Middle Siwalik and Upper Siwalik from bottom to the top. The sedimentary sequence of Siwalik Group was deposited by the river system. Meandering river system was prevailed during the deposition of Lower Siwalik as evidenced by sedimentological criteria noted in the rocks of Lower Siwalik whereas the river system was changed to the braided that indicated by sediments like coarse grained sandstone, pebbly sandstone and conglomerate with typical sedimentary structures. The northern and southern belts of the Siwalik Group are separated by the Central Churia Thrust (CCT). The depositional age of the Siwalik sediments ranges from Middle Miocene to Early Pleistocene. In the study area rocks of Tansen Group and Kaligandaki Supergroup are exposed. These Lesser Himalayan rocks are separated from the Siwalik by the Main Boundary Thrust (MBT). The Tansen Group consists of the Sisne, Taltung, Amile, Bhainskati and Dumri Formations in ascending order. The main lithology of the Tansen Group is diamictite, trachyte, quartzite, hematite and red shale. Plant and invertebrates fossils are also abundant in rocks of the Group. The sedimentology of the rocks of Tansen Group shows that Sisne Formation was deposited by glacio–marine to glacio–fluvial system. Then, the sediments of Taltung Formation were accumulated by braided to meandering river system. Quartzite of the Amile formation was deposited in deltaic setting as illustrated by the sedimentological characters of the rock, while black shale Bhainskati Formation was deposited in the sea. The youngest Dumri Formation consisting dominant sandstone lithology was deposited by the meandering system. The age of Tansen group ranges from Cambrian to early Miocene.

The Kaligandaki Supergroup is extensively distributed in the Mahabharat Range and Midlands of the Lesser Himalaya in the study area. It is divided into lower, middle and upper groups. Lower group consists of Andhi Formation and Naudanda Formation; middle group consists of Heklang, Virkot, Chappani, Khoraidi and Saidi Khola Formations and the upper group consists of Ramdighat and Kerabari Formations. The Kaligandaki Super Group is made up of thick sequences of argillite, carbonate rocks containing stromatolites of various types, and quartzite having ripple marks, mudcracks, load casts and flute casts. There is a thrust contact between the Kaligandaki Supergroup and Tansen Group. The rock of Kaligandaki Supergroup rest over the rocks of Tansen Groups and they form a huge Tansen Synclinorium. The oldest rocks of Kaligandaki Supergroup (Virkot and Heklang Formations) are exposed in the middle part of Tansen Synclinorium. Palpa Klippe is developed by thrusting the rocks of Kaligandaki Supergroup over the rocks of Tansen Group near Tansen area.

References

-Ulak, P.D and others 2012, Field Guide book for BSc-III year geology student, along Butwal - Tansen -Palpa, Sidartha Highway

-Upetri, B.N., 2000, 'Geology of Nepal Himalaya', Tribhuvan University, Tri-Chandra Campus, Department of Geology

-Sakai, H, 1985. Geology of the Kali Gandaki Supergroup of the Lesser Himalaya in Nepal Memoirs of the Faculty of Science Kyushu University series D Geology 25.

-Cassagrande, A., 1948, Classification and Identification of Soil, Am. Soc. Civ. Eng., Trans., v 113, pp. 901-930.

-Dhital, M.R., Gajurel, A.P., Pathak, D., Paudel, L.P. and Kizaki, K., 1995, Geology and structure of the Siwaliks and Lesser Himalaya in the Surai khola-Bardanda area, mid-western Nepal. Bulletin of the Department of Geology, Tribhuvan University, Kathmandu, v. 4, 1-70.

-Johnson Robert B, Degraff Jerome V. 'Principles of Engineering Geology', John Wiley & Sons, New York Chichester Brisbane Toronto Singapore

-Tokuoka, T, Takaysu, K. Hisatomi, K, Yamasaki, H. Tanaka, S. Konomatsu, M. Sah R.B. and Rai, S.M. (1990) Stratigraphy and Geological structures of the Churia (Siwalik) Group in the Tinau Khola- Binai Khola area, west central Nepal. Memo. Vac, sci. Shimane University, 24, pp. 71-88.

-Ulak, P.D., and Nakayama, K., 1998, Lithostratigraphy and Evolution of the fluvial system of the Siwalik Group in the Hetauda-Bakiya Khola, Central Nepal Bull.Dept Geol.T.U.6, pp. 1-14.

Palpa Field Report (B.Sc Geology 4th year)

4.3.1.1.2 Naudanda Formation

4.3.1.2.1 Heklang Formation

4.3.1.2.2 Virkot Formation

4.3.1.2.3 Chappani Formation

4.3.1.2.4 Khoraidi Formation

4.3.1.2.5 Saidi Khola Formation

4.3.1.3.1 Ramdighat Formation

4.3.1.3.2 Kerabari Formation

4.3.2.2 Taltung formation

5.1.1.1.1 Lower Siwalik

5.1.1.1.1.1 Lower Member of Lower Siwalik

5.1.1.1.1.2 Upper Member of Lower Siwalik

5.1.1.1.2 Middle Siwalik

5.1.1.1.2.1 Lower member of Middle Siwalik

5.1.1.1.2.2 Upper Member of Middle Siwalik

5.1.1.1.3 Upper Siwalik

5.1.1.2.1 Lower Siwalik

5.1.1.2.1.1 Lower Member of Lower Siwalik

5.1.1.2.1.2 Upper Member of Lower Siwalik

5.1.1.2.2 Middle Siwalik

5.1.1.2.2.1 Lower Member of Middle Siwalik

5.1.1.2.2.2 Upper Member of Middle Siwalik

5.1.1.2.3 Upper Siwalik

5.2.2 Taltung Formation

CHAPTER-6

ENGINEERING GEOLOGICAL STUDY

6.1 Introduction

6.2 Study of soil

6.4 Study of Rock

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