GEOLOGICAL FIELD REPORT ON
Lesser Himalayan, Lower nauwakot complex : Malekhu
Prepared By: Tejendra Budhamagar GIT 2076 BatchABSTRACT
The report is prepared after conducting a field visit under the Geomatic institute of Technology Thapathali Kathmandu according to the curriculum of 6th semester Geology, on Baishak 30-31, 2080. In the field visit, we studied, observed, analyzed, and identified different types of rocks as per our theoretical course based on geology and structures.
The field visit was conducted in Bagmati State, Dhading district, Rorang VDC, Malekhu, It is situated in Lesser Himalayan, lower nauwakot complex which has availability of different rocks natural topography in small extent of area and easy accessibility from the Kathmandu valley, a three/four hours bus travel along the Prithvi Highway from Thapathali. It gives us a clear idea about the importance of geological structures in the field of Geomatic/Survey engineering. This visit also provided us the knowledge regarding the different geological problems that are likely to occur during engineering works.
The report includes all studies data, relevant photographs, theories, and discussion of geology of the site.
ACKNOWLEDGEMENT
The trip was most enjoyable and hilarious to us and certainly we got a lot of knowledge about the rocks and its structures, and also we got a chance to learn about the tunnel and geology use in tunneling.
Thank you, Dr. Bijay man Sakya sir, and Senior Lecture Buddiman Gaudel sir for sharing a part of his brain and to help us in field and giving complete suggestions, also express our deep sense of gratitude for guidance during field visit. Also thanks driver dai for taking us safely to the spot and back to college. At last, we would like to thank all our 6th semester friends for team work
All of you did a wonderful job to lay out these pages.
At last, we would like to express our gratitude to our college, for providing the 2 days good lodging and food.
Introduction of field work
The geological field of Malekhu refers to the study and analysis of the geological features, processes, and formations present in and around the region of Malekhu. Malekhu is a specific location that could be a town, village, or region known for its distinctive geological characteristics, such as rock formations, landforms, geological structures, and mineral deposits. Geologists in this field would investigate and interpret the geology of Malekhu, including its stratigraphy, tectonic history, sedimentary records, and potential geological hazards. They may also explore the region's geological resources, such as groundwater reserves, minerals, and fossils, while considering the geological evolution and dynamics that have shaped the area over time.
Objectives of the Study
❖ To measure strike of bedding plane
❖ To measure the dip direction and dip angle of the bedding planes and joints
❖ To identify the rock type and its property.
❖ To be clear enough about joints, faults and folds.
Location of study area
Malekhu lies on lesser Himalayan unit of Nepal. It has unique geological features within a small range of area. The Rorang Malekhu V.D.C. of Dhading district lies about 70 Kms south west of Kathmandu valley and is located at latitude of 27o 50' 38'' to 27o 45' 50'' and longitude of 24o49'5'' to 84o50' 50’’. It is situated on the bank of Trishuli and Malekhu river. The Trishuli river is running from the eastern direction to the western diredtion and the Malekhu river from south to north which mingles into the Trishuli river. Also, the Malekhu river has a tributary namely the Apakhola which meets the Malekhu river at a distance about 3 kms from the Malekhu bazzar. Climatically Malekhu is a sub-tropical zone. Mainly the rainfall is during the monsoon.
Measuring strike, dip direction and dip angle
Methodology
The geological field study was carried out in the following ways:
❖ Field reconnaissance and geological traverse of the study site,
❖ Sketch of the field topography and rocks,
❖ Photographs of the field topography and rocks,
❖ Description of the field topography and rocks.
The study team of students were accompanied and guided by our respected teachers during the field study. The rock samples were observed, the altitude and location were tentatively estimated using topographic map of malekhu. parameters of bedding planes were obtained by the use of Brunton Compass. The idea obtained was noted and photographs of important spots were taken. A film blow of hammer checks the strength and rock types (Igneous, Sedimentary and Metamorphic) were obtained and acid test were performed on the rocks
Limitations
Malekhu was the best possible spot for this geological study while the time allocated was not enough for the detail study . The study could have been more effective if a little more time was provided. The field work was carried out and completed within two days, which means the study couldn’t be very thorough due to lack of time available, and the areas to be covered were more.
Measurement of Rock
Measurement of rock by using the compass is to measurement of strike, dip direction and dip angle of rock
Types of compasses:
1. Clinometers compass: The compass, which can measure bearing and orientation with two sets. Since it doesn’t consist the sprit level, it should leveled by approximation and may not be accurate.
2. Brunton compass: It consists of sprit level and can measure bearing and inclination with relatively less error.
Example of Geological map
Instruments used during geographical field study of malekhu:
Geological compass (Brunton compass)
A geological compass is used to measure the attitudes of the geological features. The compass was mainly used for measuring the bearing of object with respect to north and to measure inclination. The main operation of geological compass consists of opening the compass carefully, leveling the spirit level and placing the compass on the planer feature for measurement.
A hammer was used to test the hardness of rock in the field. It was performed by striking the tip of the hammer and the surface of the rock whose hardness was to be determined and for the extraction of the sample.
HammerIDENTIFICATION OF ROCKS
Petrology is the scientific study of rocks.
Classification of rocks
1. Sedimentary rocks:
2. Metamorphic rocks:
3. Igneous rocks:
Sedimentary rocks:
The sedimentary rocks, as the name indicates, are those rocks which are derived from the consolidation of sediments of the preexisting rocks (igneous, sedimentary or metamorphic) under the influence of mechanical, chemical or organic activities of the denuding agents (i.e. wind, running water, glacier etc.)
The products of wear and tear of the rocks due to natural agencies like blowing wind, running water, percolating underground water etc when subjected, under favorable conditions to sedimentation and subsequent compaction results in the formation of rock masses due to pressure and temperature conditions which are known as the sedimentary rocks. Well
known examples are sandstone, lime stone, shale etc.
Metamorphic rocks:
The rocks formed from the pre-existing rocks (igneous, sedimentary or metamorphic) by the processes of metamorphism (Greek, Meta=Change, morphe=form). It is a process by which existing rocks are modified under the influence of heat pressure or both
The ultimate product of metamorphism of already existing igneous, sedimentary or even metamorphic rocks incorporating temperature, pressure, stress, chemically active substances are called metamorphic rocks, e.g. Slate, Marble, Schist, Gneiss, Phyllite.
Igneous rocks
Primary or first formed rocks are called igneous (Latin, Ignis=Fire) rocks. It has been observed in deep wells, borings, mines, etc. that the temperature increases with the depth, generally there is an increase of 1o C for every 40m. depth. The consolidation of magma results in the formation of igneous rocks e.g. of igneous rocks are granite, rhyolite. The magma remains in the molten state; so long its physical and chemical environments remain unchanged.
But whenever some changes (pressure, temperature etc) takes place; the magma no longer remains in molten state, but is changed into solid state called rock. Those rocks, which are formed directly by the solidification of magma on the earth's surface or below it, are called igneous rock.
S.N.
Physical Properties
1 Sample number 01
2 Color Bluish grey
3 Texture Crystalline
4 Grain size Fine
5 Mineral comp. Calcite
6 Scratch test Scratched by hammer
7 Origin/rock type Low grade metamorphic
8 Identification Limestone
5 Grain size
6 Sp. Gravity
7 Origin/rock type
to coarse
to medium
gradeMetamorphic
8 Engineering properties
strength
9 Identification Phyllite
Sample of garnetiferous schist rock
12 Uses
As face works like flooring, wall panels, statue making, tabletops and other decorative works
Sample of marble rock
S.N .
1 Sample number 05
Physical Properties
2 Color Light Grey
3 Texture Crystalline
4 Description It had a metallic sound
5 Origin/rock type Igneous Rock
6 Engineering properties High strength
7 Identification Granite
8 Uses As aggregates, foundations in the construction and as slab
S.N.
1 Sample number 06
Physical Properties
2 Origin/rock type Metamorphic
3 Identification Meta-sandstone
4 Structure Cross Lamination
5 Description Layer’s separated by color contrast
Sample of granite rock
Sample of metasandstone rock
S.N. Physical Properties
1 Sample number 07
2 Color Dark black line
3 Texture Crystalline Structures/cleavage Foliation plane/slaty
5 Sp. Gravity High
6 Mineral comp. 85% of metamorphic rock
7 Origin/rock type High grade Metamorphic rock
8 Engineering properties High strength
9 Identification Gneiss
Sample of gneiss rock
RECOGNITION OF GEOLOGICAL UNITS:
Nepal lies at active tectonic region. Indian plate has been penetrating the Asian plate continuously. Due to this several thrusts were formed and forming till today .the Himalayas also formed due to tectonic activity.
Geological structures
Geological structure is the study of the permanent deformation and rock failure created by the changes in stress through geologic time. It is by far the most important aspect of geology for the engineer to understand.
Tectonic processes are responsible for the many discontinuity planes (fractures, faults, joints) that permeate rock masses controlling their strength, stress- strain characteristics and the transmission and storage of fluids. The stress due to various geological processes such as tectonic activities, earthquake, volcanic activities, etc tends to displace and distort the rocks within the earth.
Phenomenon of geological structures
Phenomenon of structures may be conveniently subdivided into two groups:
Brittle structures - recording the brittle-elastic failure of rocks in the
past. Faults and joints fall in this broad category.
Ductile structures - preserving the permanent viscoplastic deformation of rock throughout geologic time. Folds and metamorphic foliations are the expression of this type of structure
5.0 Classification of Geological Structure
5.0.1 Primary Structures
Primary Structures are those which are formed at the time of rock formation. It often allows us to determine the original facing direction of strata and are also useful in age determination. Some major primary structures are as follows :
a) Bedding
b) Mudcrack
c) Ripple Mark
d) Cross Lamination
a. Bedding
Beds refer to the layers of sedimentary rock that posses almost planar top and bottom surfaces. These layers are often easily distinguished on the basis of variation in color, composition and grain size.
Beddings are planar top and bottom surface of the beds. These are the planes of weakness.
Beds are classified according to their thickness such as very thick bedded (above 100cm) , thick bedded (30com – 100cm),medium bedded (10cm- 30cm) and thin bedded (1cm-10cm).
Mudcrack are sedimentary structures which are formed as sediment dries and contracts .These primary tructure are concave in shape . They are concave toward original direction of bed.
These are the sedimentary structures in which the sediments are deposited in the form of wave by the action of flowing water . The shallow slope faces of source of flow create ripple marks. There are two types of ripple marks :
a) Oscillation Ripple Marks
b) Current Ripple Marks
d. Cross Lamination
Deposition of sediments in different sets that make an angle with each other is known as cross lamination . Truncation occurs on upper portion of bed. Younging direction is on concave side of cross lamination.
b. Mudcrack c. Ripple Mark5.0.2 Secondary Structures
Secondary structures are those which are formed after the time of rock formation. Secondary structures mainly consists of metamorphic rocks . Some of the secondary structures are as follows :
a) Fold
b) Fault
c) Thrust
a. Folds:
Folds are ductile deformation on the structure. They are the strata permanently deformed either by buckling or fracturing, if subjected to stress in a rock ass, and they cannot resist. Type of deformation depends upon mechanical properties of rocks and the nature of stress when applied slowly deep on the earth.
Folds are the ductile deformation which does not rupture or fracture the rock but instead caused them to permanently bend. Ductile deformation most often occurs well below the earth’s surface. The classifications of folds are:a) Based on upward and downward bend:
• Anticline fold
• Syncline fold
b) Based on the basis of relationship of axial plane to limbs:
• Symmetrical fold
• Assymetrical fold
• Recumbent fold
• Overturned fold
c) Based on the hinge line
• Non-Plunging fold
• Plunging fold
d) Based on the behavior of depth
• Similar fold
• Parallel fold
e) Based on the shape
• Rounded fold
• Angular fold
• Chevron fold
• Box fold
f) Based on the mode of occurrence
• Synclinorium
• Anticlinorium
b. Fault
Fault is a rupture plane along which the opposite walls are moved each
other. This movement may vary from a few cm to many km depending upon the magnitude and nature of the stress and the resistance offered by the rocks. The faults are also caused due to earthquake but it is still a complicated geological problem, which awaits satisfactory solution. Whether the earthquakes are caused due to faulting or faults are caused due to earthquake. The fault is occurred due to the plate movements, which creates the shear stress. The metamorphic form of gauge and breccia is called mylonite.
The classifications of faults are as:
a) Geometrical classification:
• Strike fault
• Dip fault
• Oblique fault
b) Genetic classification
• Normal fault
• Reverse fault
• Strike slip fault
c. Thrust
A kind of reversed fault in which the hanging wall has actually moved relative to the footwall is called thrust. It is also known as low angle reverse fault.
There are mainly following thrusts.
1) Main central thrust
2) Main boundary thrust
3) Main frontal thrust
The Mahabharat range lies between MFTand MBT. Similarly, siwalik range lies below MFT. Our Study area lies between Kathmandu complex and nuwakot complex, both is the member of Mahabharat synclonyrium.
The study area starts from Maleuku dolomite, robang formation (robang phyllite with rock quartzite) to raduwa formation ( garnetiferous schist). This is the boundary between nuwakot and Kathmandu complex and known as Mahabharat thrust.
5.1 Folds Observed
• Ptygmatic Fold
The folds are created when high pressure is applied on rocks. The pressure is applied due to compression ptygmatic fold is formed
• Boundinage Fold
The fold created due to tensile pressure boundinage fold is formed.
5.6 Engineering significance of the geological structures
The most striking features of rocks as engineering materials is that they are not simple, isotropic, elastic and continuous but very complex, strongly anisotropic, inelastic discontinuous. It is virtually impossible to deduce the stress history of rocks from their observed deformation. There are always many ambiguous deformation paths that could have been followed to produce what is observed.
CONCLUSIONS:
At last we had concluded the malekhu and its surrounding is the answer for geological curiosity. Actually, the malekhu is small in area but it has large amount or numbers of the geological phenomenon and hence it can provide broad knowledge for the learners Minimum knowledge require for engineers in geology field is fulfilled in this trip.
Along the Malekhu River, we found sedimentary rock and gradually metamorphosed from phyllite to crystalline schist and along the way to Dhading, it gradually metamorphosed to lime stone to phyllite and then to slate.
Every major bed was dipped in north direction. This proved the tectonic movement along the way from south to north.
Handling the compass and to measure the attitude of rock outcrop is now very easy to us.
Finally it will be better to say that if there had not been any geological trip,we would not have learnt a lot of these information as theoretical knowledge is not enough for field work. So this geological field work helped a lot us for study and later on during field works.
.Really ...........beyond expectation! We do salute to our respective teachers again!!
REFERENCES:
Data collected during the field visit Sketches drawn and photo taken in the field
www.wikipedia.com
http://www.geology.edu.np
Geology Note and books: A Text Book of Engineering Geology
Recent Publications related to the subject
2076 Batch With respected teachers
Multi Talent Gang
Group Discussion
