Geology Field Report Malvan, Sindhudurg District

Geology Field Report Malvan 2010

Department of Geology, St. Xavier’s

College.

F i e l d R e p o r t | 1

Date: ____________

This is to certify that Russell Menezes has

attended the field work at Malvan, Sindhudurg

District of Maharashtra India from 24th October

2010 to 4th November 2010.

Dr. H. P. Samant Dr. G. Bandopadhya

Field Instructors


Acknowledgments:

We thank our professors

Dr. H. P. Samant

and Dr. Gautam Bandopadhya for

taking us for our field trip and guiding

us through this report.


Submitted to:

Dr. Hrishikesh Samant

Submitted by:

Russell Menezes Seat No: _______

T.Y.B.Sc. Geology, St. Xaviers College.

Date:

3rd January 2011


Contents

Acknowledgments: ................................................................................................................................. 1

INTRODUCTION ....................................................................................................................................... 5

Malvan: ............................................................................................................................................... 6

Geography and Climate: ..................................................................................................................... 6

Coordinates: ........................................................................................................................................ 7

Accessibility: ........................................................................................................................................ 7

Outline of Field Work at Malvan: ........................................................................................................ 8

Methods Used For Field Work .............................................................................................................. 10

Triangulation Method: ...................................................................................................................... 11

Average Pace Length (APL): .............................................................................................................. 13

Gneissosity: ....................................................................................................................................... 15

Mapping Exercises ................................................................................................................................ 17

Tape and Compass Method: ............................................................................................................. 18

Plane Table Survey: ........................................................................................................................... 23

Dumpee Level: .................................................................................................................................. 26

Beach Profiling: ................................................................................................................................. 29

Structural Geology ................................................................................................................................ 33

Joints: ................................................................................................................................................ 34

Joint Plane Exercise: ...................................................................................................................... 36

Folds: ................................................................................................................................................. 38

Strike and Dip of Plunging Folds: .................................................................................................. 39

Faults: ................................................................................................................................................ 41

Pebble Elongation: ............................................................................................................................ 42

Geology of Malvan ................................................................................................................................ 45

Stratigraphy of the Area around Katta, Malvan:............................................................................... 46

Stratigraphic Log: .............................................................................................................................. 47

Rocks Found in Malvan: .................................................................................................................... 48

Quartzites: ..................................................................................................................................... 48

Fuchsite Quartzite: ........................................................................................................................ 49

Kaladgi Quartzite: .......................................................................................................................... 49


Conglomerate: .............................................................................................................................. 51

Peninsular Gneiss: ......................................................................................................................... 52

Basalt: ............................................................................................................................................ 53

Metadolerite Dyke: ....................................................................................................................... 54

Garnets: ......................................................................................................................................... 55

Phlogopite: .................................................................................................................................... 56

Magnetite: ..................................................................................................................................... 57

Coastal Geomorphology and Features ................................................................................................. 58

Ripple Marks: .................................................................................................................................... 59

Marine Transgression and Regression: ............................................................................................. 61

Blowholes: ......................................................................................................................................... 63

Sea Caves: ......................................................................................................................................... 64

Sea Cliffs: ........................................................................................................................................... 65

Topple and Slip: ............................................................................................................................. 66

Sea Arches and Stacks: ...................................................................................................................... 68

Cross Bedding:................................................................................................................................... 69

Bibliography: ......................................................................................................................................... 70


INTRODUCTION __________________________________________________________________________________


Malvan:

Malvan is a fishing port on western coast of Sindhudurga District,

Maharashtra, India in a region of magnificent white beaches. It is the

southernmost town in Maharashtra. It is a southern part of the Konkan coastline

with a long stretch of shimmering sand & fringed with thick coconut, jack fruit,

bamboo and Supari trees. Rocky lands with overhanging cliffs, projecting

sandbanks, rocky shoals, coral reefs and boulders with a rib type coast are the

various geological features seen. On the north of Malvan the most striking

feature is the 'littoral concrete' or 'beach rock' which gives protection against the

harsh waves.

Geography and Climate:

Malvan is a compact town situated on the coast of Western India and boasts

some beautiful beaches. Sindhudurg fort, Tarkarli beach, Mobar point, Chiwala

beach, Tondavali beach are the places of attraction. Malvan town is bound by

three small creeks namely Karli, Kolamb and Kalavali.

The climate of Malvan can be generally classified as warm and moderately

humid. Average temperatures range between 16 - 33 °C while relative humidity

ranges from 69 to 98%. The annual average rainfall of Malvan is 2275 mm.


Coordinates:

WGS84 16° 3′ 23.53″ N; 73° 28′ 7.51″ E

Accessibility:

Malvan is easily accessible by Road. By road, Malvan is 514 km away from

Mumbai, 200 km from Ratnagiri. When arriving from Mumbai or Goa, take

National Highway NH-17 till Kasaal and then take a State Transport bus or

Rickshaw for an approximately 35 km ride to Malvan.

Nearest railway station is at Kudal/Kankawali and nearest Airport is at

Dabolim in Goa. You can also reach there by your own vehicle.


Outline of Field Work at Malvan:

Department of Geology, St. Xavier’s College arranged a field trip of twelve

days for the T.Y.B.Sc students from October 24th to November 3rd 2010. The

field trip was related to the subjects of Stratigraphy and Geomorphology and

Structural Geology. The objectives for that field trip were to study and observe

the lithology, depositional condition, sedimentary structures, contacts and

perform specific field and mapping exercises in those areas. Another objective of

our field trip was to enhance our knowledge and to strengthen our grip on field

techniques, especially to concentrate on geology of Malvan .The areas were

easily accessible and we used the local transport. The journey was pleasant and

smooth.

Our first day {25th Oct.} started near Malvan Jetty [16° 3'18.67"N; 73°27'49.83"E]

at Chivla Beach where we observed and studied the coastal features. Then we

moved along the coast to west where we performed the Triangulation Exercise.

[ 16° 3'21.11"N; 73°27'39.17"E] On moving further a small we arrived at a small patch

of grassy land [16° 3'15.98"N; 73°27'29.87"E] where we performed the Pace Length

exercise. We then moved north to the limbs of a plunging fold [16° 3'20.94"N;

73°27'25.53"E] where we found out the Attitude of the Plunging Beds.

On the second day {26th Oct.} we performed the Joint Plane and Pebble

Elongation exercises on a barren outcrop at Rajkot [16° 3'18.10"N; 73°27'21.26"E].

On the third day {27th Oct.} we did a mapping exercise using the tape and

compass at Rajkot [16° 3'14.28"N; 73°27'26.33"E].

On the fourth day {28th Oct.} we did a Sedimentary Log exercise at the

same place.

On the fifth day {29th Oct} we went to Amberi [16° 0'34.12"N; 73°33'40.85"E] to

explore the possibility of finding Garnets in the Sand Bars.


On the sixth day {30th Oct.} we went to an igneous rock quarry [16° 0'56.60"N;

73°30'10.17"E] to study the igneous rocks of that area. We then climbed up a dry

river bed [16° 1'10.60"N; 73°29'50.92"E] to study potholes. We then walked a great

distance over a peneplain [16° 1'38.83"N; 73°29'43.75"E] to get to a Fault zone

[16° 2'36.42"N; 73°29'16.57"E]. We then went to a laterite quarry [16° 3'48.74"N;

73°28'49.20"E].

On the seventh day {31st Oct.} we walked to a river bed [16° 3'57.84"N;

73°30'14.38"E] to study Gneissosity.

On the eighth day {1st Nov.} we did a mapping exercise using the Plane

Table and Dumpy Level at [16° 3'41.35"N; 73°27'22.76"E].

On the ninth day {2nd Nov.} we checked the dump from a newly dug well

at Stony Waste [16° 5'42.49"N; 73°28'53.78"E] and then we headed over to a Spit [16°

6'16.72"N; 73°27'26.07"E] where we performed a Beach Profiling exercise. On the way

back we witnessed the gigantic coastal cliffs and arches [16° 5'1.27"N; 73°27'33.14"E].

On the tenth and final day {3rd Nov.} we visited the Sindhudurg Fort

[16° 2'27.71"N; 73°27'40.81"E] where we got to see good quality samples of Kaladgi

Quartzite.


Methods Used For

Field Work __________________________________________________________________________________


Triangulation Method:

Aim: To determine ones location on the map using a

Compass.

Requirements: Compass, map of the area, drawing stationary.

Procedure:

The first step in triangulation is to pick three

topographic features that you can see and can

identify on your map (mountains are ideal). Start

with the first feature you have chosen and

determine the bearing between you and it, as

outlined above. Once you have determined its

bearing, pencil in a line with the same bearing on

your map that runs through the chosen feature

(make use of a protractor).

Repeat this for the other two features, drawing lines

for each. The point where the three lines intersect

on the map is where you are. Depending on how

accurate your sightings were and how accurately

you drew your lines through the features, there will

probably be some error in your location. Be sure to

double check the map and reconcile it with what

you see.

Note:

The three points should be in different directions.

The pencil point should be very fine.

If the size of triangle is big then something has gone

wrong.

Location: Malvan Jetty.


Map:

Result: Coordinates of area enclosed within the triangle is

[16° 3'20.91"N; 73°27'39.00"E ] which matches the GPS coordinates.


Average Pace Length (APL):

Aim: To determine average pace length on average ground.

Procedure:

A 30m tape is stretched between two points A and B.

The distance is then paced (with standard field gear on

the person). The number of paces are counted from

point A to B and back to A.

APL in meters =

Note:

Certain conditions affect your pace count in the field

and you must allow for them by making adjustments.

Slopes: Your pace lengthens on a downslope and

shortens on an upgrade.

Winds: A head wind shortens the pace and a tail wind

increases it.

Surfaces: Sand, gravel, mud, snow, and similar surface

materials tend to shorten the pace.

Elements: Falling snow, rain, or ice causes the pace to

be reduced in length.

Clothing: Excess clothing and boots with poor traction

affect the pace length.

Visibility: Poor visibility, such as in fog, rain, or

darkness, will shorten your pace.


Uses:

It helps in finding the approximate length of a huge

outcrop by walking over the distance and multiplying it

by ones pace length.

Observations:

Number of paces = 82

Therefore Pace length =

= 0.73m.

Images:

Student measuring his Pace Length with field

gear on.


Gneissosity:

Aim: To determine direction of Gneissosity of the Augen

Gneiss.

Procedure:

Three readings are taken each on the two adjacent faces

of the Augen gneiss outcrop. Each reading consists of the

attitude of the plane and the angle made by the

Gneissosity with the horizontal.

The mean of the attitude and the Gneissosity are

calculated and plotted as a beta diagram onto a

stereonet. The angle of Gneissosity is marked as point on

the beta curve in the direction of its dip.

Joining the points of Gneissosity of both the beta curves,

we will get the plane of regional Gneissosity.

Observations:

No. Strike Dip Amt. Dip Dir. Rake

Plane I N 235° 55° NW 81° Plane II N 132° 65° SW 25°

Attitude of the Metadolerite Dyke cutting through the gneiss is:

Strike: N 146°

Dip: 220°

Solution: Gneissosity is:

Strike: N 320°

Dip: 80°

Dip Direction: SW


Mapping Exercises __________________________________________________________________________________


Tape and Compass Method:

Aim: To survey the given area using a Tape and Brunton

Compass.

Requirements: 30 meter tape, Brunton Compass, tripod stand, clamping

screws, pebble, staff or rod.

Procedure:

Clamp the Brunton on the tripod and arrange it is

such a way that the bulls eye spirit level is in the

center.

Take a pebble and release it from the center,

under the Brunton. The place where it hits the

ground is the center. Hammer the chisel in there

and mark the desired area you want to survey

(radius =5m).

Take readings of every outcrop in the designated

area, the rock type, the distance from the center,

the contact and the bearing of that outcrop. Now

plot the readings on paper using an appropriate

scale.


Observations: Map Scale: 1: 50

No. Bearing° Dist. (cm)

Remarks Joint Plane Readings

T° Da° D

1.

N 185 4.32 SQC 1 N25 90 E

N 187 4.21 SQC 2 N210 90 W

N 189 4.30 SQC 3

N 182 4.36 SQC 4

2.

N 206 3.6 SQC 1 N351 63 E

N 209 3.41 SQC 2 N 210 3.33 SQC 3

N 217 3.17 SQC 4

N 222 3.34 SQC 5 N244 54 N

N 204 3.35 SQC 6 N163 58 W

3.

N 225 4.58 SQC 1 N113 72 E

N 233 3.52 SQC 2 N75 67 N

N 244 3.64 SQC 3 N266 90 N

N 245 4.05 SQC 4 N340 90 E

N 226 4.98 SQC 5

N 245 5.00 SQC 6

4.

N 241 3.37 SQC 1 N197 67 W

N 270 3.46 SQC 2 N255 55 N

N 269 3.92 SQC 3 N244 73 N

N 250 3.82 SQC 4

N 245 3.70 SQC 5

5.

N 254 4.05 SQC 1 N341 90 W

N 284 4.69 SQC 2 N245 90 N

N 278 5.00 SQC 3 N125 72 E

N251 5.00 SQC 4

6.

N 269 2.38 SQC 1 N 275 2.05 SQC 2

N 290 2.53 SQC 3

N 296 2.80 SQC 4

N 300 3.15 SQC 5

N 303 3.54 SQC 6 N 304 2.36 SQC 7

N 314 4.12 SQC 8

N 314 5.00 SQC 9

N 295 5.00 SQC 10

N 299 4.16 SQC 11

N 290 5.00 SQC 12

N 276 4.02 SQC 13


7.

N 316 3.63 SQC 1 N261 51 N

N 314 3.18 SQC 2 N161 90 W

N 318 3.26 SQC 3 N 321 3.40 SQC 4

N 320 3.57 SQC 5

8.

N 337 3.28 SQC 1 N23 90 N

N 338 3.96 SQC 2 N302 31 S

N 334 3.99 SQC 3

9.

N 83 3.66 SC 1 N75 62 S

N 86 3.80 SC 2 N251 90 S

N 87 4.58 SC 3 N71 56 S

N 74 4.20 SC 4

N 79 3.81 SC 5

10.

N 96 4.38 SC 1 N63 52 S

N 96 4.48 SC 2

N 96 4.60 SC 3

N 94 4.48 SC 4

11.

N 115 5.00 SQ 1

N 113 4.68 SQ 2 N311 23 N

N 114 5.53 SQ 3 N60 90 N

N 119 4.75 SQ 4

N 120 5.00 SQ 5

12.

N 124 5.00 SQ 1

N 123 4.81 SQ 2 N159 53 E

N 125 4.49 SQ 3 N124 90 W

N 134 4.98 SQ 4

13.

N 133 4.39 SQ 1

N 137 4.45 SQ 2 N 138 4.70 SQ 3

N 136 4.68 SQ 4

14.

N 55 4.69 SC 1 N302 72 E

N 50 4.80 SC 2

N 28 4.37 SC 3 N 18 4.51 SC 4

N 10 4.38 SC 5

N 7 3.31 SC 6 N62 90 S

N 38 2.94 SC 7 N60 90 S

15.

N 18 5.00 SC 1 N 17 4.50 SC 2 N334 42 N

N 7 3.98 SC 3 N53 23 W

N 2 4.40 SC 4

N 6 5.00 SC 5


Images:

Bearing being taken on the Brunton

Tape Stretched towards Staff held at Contact


Plane Table Survey:

Aim: To survey the area of the plunging folds using a Plane

Table and a Telescopic Alidade.

Requirements: Plane table, tripod stand, telescopic alidade, measuring tape,

tracing paper, drawing stationary, centering fork, staff.

Procedure:

Set the tripod up in the area in such a way that it

is steady and mount the plane table on it. Level

the tripod using a spirit level. Place the tracing

paper on the table and clamp it.

Using the centering fork mark the center on the

ground as well as on the paper.

Now start sighting the staff placed at the object

using the telescope and also measure the distance

of that object from the center.

Using an appropriate scale mark the distance on

the sheet. In this manner the entire area can be

surveyed.

Note:

The telescopic alidade and be substituted with a

Brunton compass. The readings are then taken by

getting the trend of the object and marking that

angle on the sheet from a line pointing north.


Observations:

Images:

Student using Telescopic alidade

No. Dist. Bearing Strike Dip Dip Amt.

a. 5.55 N 4 N 320 SW 64

b. 5.03 N 256 N 306 NE 21 c. 4.87 N 352 N 243 SE 7

d. 4.78 N 363 N 229 NW 11 e. 4.03 N 340 N 68 SE 16

f. 4.01 N 334 N 42 NW 10

g. 3.98 N 229 N 150 NE 26

h. 4.39 N 313 N 249 NW 7

i. 5.50 N 284 N 216 SE 10


Dumpee Level:

Aim: To survey the area and find the ground elevation with the

help of a Dumpee Level and Staff.

Requirements: Dumpee Level, Tripod Stand, Calibrated Staff,

Measuring Tape.

Procedure:

Adjust the Dumpee Level and mount it on the

tripod stand and level it with the help of the spirit

level. The rule of adjusting the Dumpee level is

simple, i.e. Left in, right out. This is how the two

knobs on the dumpee level should be adjusted.

Take one point in front of the dumpee level which

is fixed. Using the staff take a reading from the

telescope. This is the height of the instrument.

Find the center of the instrument on the ground

by dropping a pebble from the center of the

dumpee level. Readings must be taken of the

entire area that one wants to survey.

To take readings stretch the tape in one direction

from the center and hold the staff at the boundary

of the area. Use the telescope to see the

calibrations on the staff and get the height at that

level.

Similarly take readings at various intervals.

Change the angle of the dumpee level and take a

new set of readings. Plot the readings on paper

using an appropriate scale.


Note:

The instrument position is always fixed.

The instrument must always be turned clockwise.

The staff must always be vertical and not bend

towards or away from the instrument.

Observations:

Images:

Laser pointer being used with Dumpee level.

Dist. 120° 130° 140° 150° 160° 170° 1 11.41 11.46 11.45 1146. 11.48 11.44 2 11.34 11.34 11.38 11.45 11.47 11.47 3 11.31 11.36 11.39 11.34 11.46 11.44 4 11.30 11.30 11.30 11.40 11.42 11.52 5 11.23 11.28 11.33 11.26 11.43 11.52 6 11.23 11.29 11.37 11.35 11.40 11.51 7 11.32 11.42 11.47 11.44 11.41 11.64 8 11.48 11.54 11.54 11.53 11.46 11.53 9 11.58 11.58 11.61 11.58 11.55 11.45 10 11.58 11.62 11.34 11.28 11.65 11.60 11 11.52 11.68 11.58 11.20 11.70 11.73 12 11.62 11.62 11.72 11.22 11.73 11.72 13 11.64 11.69 11.74 11.83 11.75 11.70 14 11.62 11.68 11.75 11.80 11.71 11.67 15 11.34 11.68 11.73 11.70 11.78 11.60


Beach Profiling:

Aim: To draw the beach profile and understand the mode of

deposition and erosion.

Requirements: Brunton compass, measuring tape, staff, a bright strip of

cloth (to be used as a marker).

Procedure:

Using a Brunton compass, check the direction of

waves entering the beach. Take readings in that

direction at regular intervals along the beach.

To take readings sight the marker tied to the staff

which is placed vertically at some distance from

you. Using the tape find the distance from you to

the staff. Also find the angle of dip due to the

change in elevation of the ground.

Start taking readings from the pace where the

waves splash up to the place where vegetation

cover begins and no sand is deposited.

When taking dip readings note down whether

ground elevation is increasing or decreasing.


Observations: Set I:

No. Distance (m) Sighting Remark

1. 6.9 5° 30’ Elevation 2. 25.51 1° 50’ Depression 3. 7.40 3° 10’ Elevation 4. 4.49 6° 40’ Elevation 5. 11.38 1° 10’ Depression 6. 1.54 23° 30’ Elevation 7. 9.27 1° 40’ Depression 8. 4.25 17° 50’ Elevation 9. 8.39 4° 20’ Depression

Set II:


1. 15.86 3° 40’ Depression 2. 5.68 5° 50’ Elevation 3. 19.54 7° 50’ Depression 4. 1.74 11° 30’ Depression 5. 16.05 2° 20’ Elevation 6. 13.35 2° 40’ Depression 7. 2.76 21° 10’ Elevation 8. 5.41 2° 30’ Elevation

Set III:


1. 26.31 1° Elevation 2. 20.62 3° 10’ Depression 3. 5.2 4° 20’ Depression 4. 9.16 4° 10’ Elevation 5. 12.45 1° 20’ Depression 6. 10.54 6° 50’ Elevation 7. 2.8 23° 40’ Elevation


Set IV:


1. 14.43 2° 50 Elevation 2. 5.75 1 20 Depression 3. 4.76 5 20 Elevation 4. 26.16 2 30 Depression 5. 5.70 5 50 Elevation 6. 25 2 10 Elevation 7. 2.58 17 40 Elevation

Set V:


1. 11.07 4° 10’ Elevation 2. 6.11 1° 20’ Depression 3. 3.54 4° 10’ Elevation 4. 25.28 1° 50’ Depression 5. 4.98 6° 30’ Elevation 6. 25.44 1° 20’ Elevation 7. 4.36 10° 20’ Elevation

Set VI:


1. 18.9 4° 50’ Elevation 2. 4 3° 10’ Elevation 3. 21.80 1° 20’ Depression 4. 2.50 6° 30’ Elevation 5. 12.90 1° 50’ Depression 6. 21.90 2° 40’ Elevation 7. 1 18° Elevation


Structural Geology __________________________________________________________________________________


Joints:

A joint refers to a fracture in rock where the displacement associated with

the opening of the fracture is greater than the displacement due to lateral

movement in the plane of the fracture (up, down or sideways) of one side

relative to the other. Typically, there is little to no lateral movement across

them. Joints normally have a regular spacing related to either the mechanical

properties of the individual rock or the thickness of the layer involved. Joints

generally occur as sets, with each set consisting of joints sub-parallel to each

other.

Joints form in solid, hard rock that is stretched such that its brittle strength

is exceeded (the point at which it breaks). When this happens the rock fractures

in a plane parallel to the maximum principal stress and perpendicular to the

minimum principal stress (the direction in which the rock is being stretched).

This leads to the development of a single sub-parallel joint set. Continued

deformation may lead to development of one or more additional joint sets. The

presence of the first set strongly affects the stress orientation in the rock layer,

often causing subsequent sets to form at a high angle to the first set.

Joint sets are commonly observed to have relatively constant spacing,

which is roughly proportional to the thickness of the layer.

Location:

At Malvan, joints were seen in the Rajkot area near the jetty.


Type of Joints seen at Malvan:

Joint sets seen at Rajkot [16° 3'20.15"N; 73°27'19.14"E]

XX - Parallel Joints

OO – Conjugate Joints

Parallel Joints: When two or more joint sets are parallel to each other.

Conjugate Joints: When two joint sets intersect at a high angle.

Joint Plane Rajkot [16° 3'18.36"N; 73°27'20.74"E]


Joint Plane Exercise:

Aim: To determine the type of joint planes along the joints.

Procedure:

Take 30 readings each of strike, dip and dip

amount of suitable joint planes. Also note down if

the joint planes are parallel or conjugate.

Plot all the readings including readings from other

members of the group on a stereonet. Contour this

stereonet and interpret the type of joint.

Observations:

Number Strike° Dip° Dip Amount° Remark 1. N226 N136 71 - 2. N352 N262 82 - 3. N178 N88 56 - 4. N125 N35 58 Parallel 5. N120 N30 71 6. N110 N20 62 - 7. N105 N15 78 - 8. N60 N150 65 - 9. N337 N147 66 - 10. N157 N67 16 - 11. N153 N63 40 - 12. N183 N93 49 - 13. N185 N95 69 Parallel 14. N81 N171 67 15. N85 N176 44 Parallel 16. N188 N98 47 17. N217 N127 75 Parallel 18. N197 N107 56 19. N359 N269 76 - 20. N300 N290 52 Conjugate 21. N350 N260 48 22. N300 N210 41 - 23. N213 N183 34 - 24. N355 N265 51 - 25. N355 N265 76 - 26. N35 N125 56 - 27. N330 N240 60 Conjugate 28. N335 N245 54 29. N336 N246 62 - 30. N121 N31 62 -


Folds:

The term fold is used in geology when one or a stack of originally flat and

planar surfaces, such as sedimentary strata, are bent or curved as a result of

plastic deformation. Folds in rocks vary in size from microscopic crinkles to

mountain-sized folds. They occur singly as isolated folds and in extensive fold

trains of different sizes, on a variety of scales.

Folds form under varied conditions of stress, hydrostatic pressure, pore

pressure, and temperature - hydrothermal gradient, as evidenced by their

presence in soft sediments, the full spectrum of metamorphic rocks, and even as

primary flow structures in some igneous rocks. Folds are commonly formed by

shortening of existing layers, but may also be formed as a result of displacement

on a non-planar fault (fault bend fold), at the tip of a propagating fault (fault

propagation fold), by differential compaction or due to the effects of a high-level

igneous intrusion e.g. above a laccolith.

Folds seen at Rock Garden [16° 3'41.13"N; 73°27'21.47"E]

Strike and dip are marked above in white.


Strike and Dip of Plunging Folds:

Aim: To determine the strike and dip of plunging folds.

Procedure:

Take the Brunton Compass and hold it horizontally against the rock surface till the bubble in the bulls eye spirit level comes to the center. Check the direction

compass which is the strike of the bed.

The dip direction will be perpendicular to the strike direction depending on which side the bed is dipping. To find the dip amount, draw the strike line using a chalk

and then draw a perpendicular to that line. Keep the compass vertical and using the knob at the back get the

spirit level bubble to the center. Check the reading on the angular scale.

In this manner take 3 readings on each limb and plot it on a stereonet.

Observations: Left and right limb readings are as follows:

No Strike° Dip

a. N310 20°N

b. N292 24°N

c. N293 21°N

Limbs of a fold at Rajkot. [16° 3'21.02"N; 73°27'25.47"E]

No Strike° Dip

a. N258 12°N

b. N289 10°N

c. N253 13°N


Faults:

A fault is a planar fracture or discontinuity in a volume of rock, across

which there has been significant displacement. Large faults within the Earth's

crust result from the action of tectonic forces. Energy release associated with

rapid movement on active faults is the cause of most earthquakes.

A fault line is the surface trace of a fault, the line of intersection between

the fault plane and the Earth's surface.

Since faults do not usually consist of a single, clean fracture, the term fault

zone is used when referring to the zone of complex deformation associated with

the fault plane.

The relative motion of rocks on either side of the fault surface controls the

origin and behaviour of faults, in both an individual small fault and within the

greater fault zones which define the tectonic plates.

Because of friction and the rigidity of the rock, the rocks cannot simply glide

or flow past each other. Rather, stress builds up in rocks and when it reaches a

level that exceeds the strain threshold, the accumulated potential energy is

released as strain, which is focused into a plane along which relative motion is

accommodated.

A fault line shown my displacement across a quartz vein at [16° 3'37.06"N; 73°28'54.11"E]. Displacement is approximately 3 inches.


Pebble Elongation:

Aim: To study the direction of elongation of pebbles in stretched

pebble conglomerate.

Procedure:

Find in situ an outcrop of conglomerate and then measure

the length of the pebbles along at least 2 of the 3 axes. Also find out the trend and plunge of that pebble. Take at

least 30 readings in this manner. Also extract 5 to 6 pebbles from the rock marking the horizontal and direction of plunge of the pebble.

Plot all these readings including readings from other members of your group on a stereonet and then contour

them.

Image:

Quartzite Pebbles in the Conglomerate

[16° 3'17.97"N; 73°27'20.35"E]


Observations:

No. Shortest (x)

Intermediate (Y) Longest (Z)

L(cm) T° P° L (cm) T° P° L(cm) T° P°

1. 1 N252 10 - - - 6.5 N341 9

2. 1.2 N265 21 - - - 5.5 N352 8

3. 0.9 N82 11 - - - 3.9 N180 2

4. 1.3 N264 23 - - - 7.2 N351 3

5. - - - 1.5 N265 20 4.7 N165 22

6. - - - 1.7 N264 4 5.3 N355 9

7. - - - 2.2 N95 26 6.5 N163 11

8. - - - 2.1 N170 7 5.4 N175 4

9. - - - 1.7 N68 22 4.5 N355 2

10. 0.7 N265 33 - - - 4.3 N162 2

11. - - - 3.1 N81 35 5.1 N145 4

12. - - - 2.6 N78 12 8.5 N338 6

13. - - - 2.2 N88 6 5.2 N343 7

14. - - - 3.1 N87 41 5.2 N343 11

15. - - - 1.2 N86 32 5.4 N349 6

16. - - - 1 N70 20 6.5 N160 12

17. 0.8 N78 7 - - - 1.9 N153 9

18. 3.8 N235 2 - - - 6.7 N148 9

19. 3 N257 2 - - - 12 N348 14

20. - - - 1.1 N61 5 3.1 N152 8

21. - - - 3.5 N51 9 8.7 N143 2

22. - - - 2.3 N260 11 5.8 N351 7

23. - - - 1 N57 3 2.2 N142 27

24. - - - 0.9 N255 2 3 N342 2

25. - - - 2 N60 24 4.5 N153 10

26. - - - 1.1 N70 20 4.8 N340 14

27. - - - 2.5 N60 30 4 N148 10

28. - - - 1.8 N67 8 3.9 N156 10

29. - - - 1.1 N240 4 3.7 N160 18

30. 0.8 N700 9 - - - 2.3 N159 12


Geology of

Malvan


Stratigraphy of the Area around Katta, Malvan:

The regional succession of Malvan is somewhat similar to the Peninsular Gneiss

at the base of the rock succession of Malvan.

Laterite Primary

Secondary

Deccan Volcanics

Kaladgi Quartzite

Meta Conglomerate

Peninsular Gneiss

Laterites Pliocene - Pleistocene

Alluvium Holocene

Deccan Traps Upper Cretaceous - Eocene

Unconformity

Achara Sandstone – Shale Formation

Kaladgi Super Group Mid – Late Proterozoic

Unconformity

Basal Member of Baba Budan Series

2600 – 2400 my

Unconformity

Peninsular Gneiss 3000 – 2600 my


Stratigraphic Log: Area: Rajkot Scale: 1cm = 3m

Ferrugenitic Quartzite transgressing into quartzite showing inter-banding of conglomerate. (3m)

Grey to Ferrugenitic quartzite showing cross bedding with magnetite rich bands.(4m)

Polymictic conglomerate: Clasts of red Ferrugenitic quartzite and grey quartzite dominate. Minor presence of Conglomerate pebbles show elongation NNW – SSE. (8m)

Grey Quartzite transgressing into ferruginous quartzite. Magnetite bands are absent. (4m)

Massive Grey Quartzite. Intensely Jointed with at least three distinct cuts visible. Magnetite scarcely present. (12m)

Conglomerate: clasts of magnetite and red quartzite. Marked magnetite rich layers. Some are of considerable thickness. (8m)

Red ferruginous quartzite showing magnetite bands.(10m)

Conglomerate: Clasts mostly of grey quartzite, magnetite presence marked in conglomerate matrix. Intense jointing seen, many infilled by metamorphosed quartzite veins. Magnetite inter-bands also seen. (9m)

Grey Quartzite: Massive grey quartzite with minor presence of magnetite. Shows jointing some filled with coarser grained quartz. Complete lack of sedimentary structures. (>3m)


Rocks Found in Malvan:

Quartzites:

Quartzite

Quartzite is a hard metamorphic rock which was originally sandstone.

Sandstone is converted into quartzite through heating and pressure usually

related to tectonic compression within orogenic belts. Pure quartzite is usually

white to grey, though quartzites often occur in various shades of pink and red

due to varying amounts of iron oxide. Other colors, such as yellow and orange,

are due to other mineral impurities.

When sandstone is metamorphosed to quartzite, the individual quartz

grains recrystallize along with the former cementing material to form an

interlocking mosaic of quartz crystals. Most or all of the original texture and

sedimentary structures of the sandstone are erased by the metamorphism.

Minor amounts of former cementing materials, iron oxide, carbonate and clay,

often migrate during recrystallization and metamorphosis. This causes streaks

and lenses to form within the quartzite.


Fuchsite Quartzite:

Fuchsite Quartzite was seen at the Sindhudurg Fort.

Fuchsite Quartzites are green in colour due to alteration of mica to

chlorite.

Kaladgi Quartzite:


Laterite:

Laterite Quarry [16° 3'48.74"N; 73°28'49.20"E].

Laterites are soil types rich in iron and aluminium, formed in hot and wet

tropical areas. Nearly all laterites are rusty-red because of iron oxides.

They develop by intensive and long-lasting weathering of the underlying

parent rock. Tropical weathering (laterization) is a prolonged process of

chemical weathering which produces a wide variety in the thickness,

grade, chemistry and ore mineralogy of the resulting soils. The majority of

the land areas with laterites was or is between the tropics of Cancer and

Capricorn.

The laterites in the above quarry have formed as a result of weathering of

quartzite. A vertical gradation is seen with weathered quartzites at the

bottom with increasing grade of laterite towards the top. The difference is

visible as a colour gradation (from white to darker shades of red).


Conglomerate:

Conglomerate seen at Rajkot [16° 3'18.10"N; 73°27'21.26"E].

A conglomerate is a rock consisting of individual clasts within a finer-

grained matrix that have become cemented together. Conglomerates are

sedimentary rocks consisting of rounded fragments and are thus

differentiated from breccias, which consist of angular clasts. Both

conglomerates and breccias are characterized by clasts larger than sand

(>2 mm).

Metaconglomerate is a rock type which originated from conglomerate after

undergoing metamorphism. Conglomerate is easily identifiable by the

pebbles or larger clasts in a matrix of sand, silt, or clay.

Metaconglomerates look similar to conglomerate, although sometimes the

clasts are deformed. The cement matrix of conglomerate is not as durable

as the grains, and hence when broken, conglomerate breaks around the

grains. Metaconglomerate, however, breaks through the grains, as the

cement has recrystallized and may be as durable as the clasts.


Peninsular Gneiss:

Peninsular Gneiss is a term coined to highlight the older gneissic complex

of the abundant rock type found all over the Indian Peninsula. This term

was first fashioned by W.F.Smeeth of the Mysore Geological Department

in 1916 based on the first scientific study of this rare rock exposure.

Gneiss is a rock formed during regional metamorphism. It is generally a

coarse-grained granular textured rock which can develop from a wide

variety of igneous and sedimentary material. Gneisses consist of

alternating dark and light bands of minerals which can vary in thickness,

from millimetres up to a metre and can be highly contorted. Varieties are

distinguished by characteristic minerals, texture, structure or the parent

rock.

Augen gneiss, from the German Augen, meaning "eye", is a coarse-

grained gneiss, interpreted as resulting from metamorphism of granite,

which contains characteristic elliptic or lenticular shear bound feldspar

porphyroclasts, normally microcline, within the layering of the quartz,

biotite and magnetite bands.


Basalt:

Basalt with Inclusions of Glass

Basalt is a common extrusive volcanic rock. It is usually grey to black and

fine-grained due to rapid cooling of lava at the surface of a planet. It may

be porphyritic containing larger crystals in a fine matrix, or vesicular, or

frothy scoria. Unweathered basalt is black or grey.

The mineralogy of basalt is characterized by a preponderance of calcic

plagioclase feldspar and pyroxene. Olivine can also be a significant

constituent. Accessory minerals present in relatively minor amounts

include iron oxides and iron-titanium oxides, such as magnetite,

ulvospinel, and ilmenite.


Metadolerite Dyke:

While taking readings for Gneissosity, there was a Metamorphosed Dyke

cutting through the Gneiss. The trend of the dyke was N 146°.

A dyke is a type of sheet intrusion referring to any geologic body that cuts

discordantly across.

Dolerite is a medium-grained (hypabyssal) basalt and forms in shallow

intrusions, such as dykes, which cut across the rock strata, and sills,

which push between beds of sedimentary rock. When exposed at the

surface, dolerite weathers into spherical lumps.

Metadolerite is a Metamorphosed Dolerite.


Garnets:

Pyrope Garnets from Amberi [16° 0'34.12"N; 73°33'40.85"E].

The mineral pyrope is a member of the garnet group. Pyrope is the only

member of the garnet family to always display red colouration in natural

samples, and it is from this characteristic that it gets its name.The

composition of pure pyrope is Mg3Al2(SiO4)3, although typically other

elements are present in at least minor proportions -- these other elements

include Ca, Cr, Fe and Mn.

The garnets on breaking contained a red powder inside. This shows that

these garnets have undergone intense weathering. These garnets were

originally part of the Garnetiferrous Mica Schist rock which is a foliated,

fine to medium grained, shiny, medium grey rock. It is composed of

Muscovite, Biotite, Garnet, Quartz and Feldspar. It shows Small-sized dark

red-brown garnets on the foliation surfaces. These rocks were then broken

down due to the action of several weathering agents and were carried to

its current location by the streams.


Phlogopite:

Phlogopite from Amberi [16° 0'34.12"N; 73°33'40.85"E].

Phlogopite is a yellow, greenish, or reddish-brown Phlogopite is an

important and relatively common end-member composition of biotite.

Phlogopite micas are found primarily in igneous rocks, although it is also

common in contact metamorphic aureoles of intrusive igneous rocks with

magnesian country rocks.member of the mica family of phyllosilicates. It

is also known as magnesium mica.

Phlogopite is often found in association with ultramafic intrusions as a

secondary alteration phase within metasomatic margins of large layered

intrusions. In some cases the Phlogopite is considered to be produced by

autogenic alteration during cooling. In other instances, metasomatism has

resulted in Phlogopite formation within large volumes.Trace Phlogopite,

again considered the result of metasomatism, is common within coarse-

grained peridotite xenoliths carried up by kimberlite, and so phlogopite

appears to be a common trace mineral in the uppermost part of the

Earth's mantle. Phlogopite is encountered as a primary igneous

phenocryst within lamproites and lamprophyres, the result of highly fluid-

rich melt compositions within the deep mantle.


Magnetite:

Magnetite sample from a Dyke at Rajkot [16° 3'18.10"N; 73°27'21.26"E].

Magnetite is a ferromagnetic mineral with chemical formula Fe3O4, one of

several iron oxides and a member of the spinel group. Magnetite is the

most magnetic of all the naturally occurring minerals on Earth. Naturally

magnetized pieces of magnetite, called lodestone, will attract small pieces

of iron, and this was how ancient people first noticed the property of

magnetism.

Magnetite is sometimes found in large quantities in beach sand. The

magnetite is carried to the beach via rivers from erosion and is

concentrated via wave action and currents.

Huge deposits have been found in banded iron formations. These

sedimentary rocks have been used to infer changes in the oxygen content

of the atmosphere of the Earth.


Coastal

Geomorphology and

Features


Ripple Marks:

[16° 6'17.50"N; 73°27'28.34"E]

Ripple marks are sedimentary structures and indicate agitation by water

(current or waves) or wind.

Wave-formed ripple marks, also known as bidirectional ripples, or

symmetrical ripple marks, have a symmetrical, almost sinusoidal profile.

They indicate an environment with weak currents where water motion is

dominated by wave oscillations. Because of their distinct shape, with

pointy crests and gentle.

Wave ripples also tell the sedimentologist something about the water

depth. A problem here is however that the size of the ripples is not only a

function of the depth but the sand ripples vary directly with the size of the

generating waves (wave length and wave height), meaning that large

waves may produce the same size of ripple marks at considerable depth

than smaller waves produce at a lesser depth. Though, symmetric ripples

can be used as an indicator of stratigraphic top.


Current ripple marks, unidirectional ripples, or asymmetrical ripple marks

are asymmetrical in profile, with a gentle up-current slope and a steeper

down-current slope. The down-current slope is the angle of repose, which

depends on the shape of the sediment. These commonly form in fluvial

and aeolian depositional environments, and are a signifier of the lower

part of the Lower Flow Regime.


Marine Transgression and Regression:

A marine transgression is a geologic event during which sea level rises

relative to the land and the shoreline moves toward higher ground,

resulting in flooding. Transgressions can be caused either by the land

sinking or the ocean basins filling with water (or decreasing in capacity).

Transgressions and regressions may be caused by tectonic events such as

orogenies, severe climate change such as ice ages or isostatic

adjustments following removal of ice or sediment load.

The opposite of transgression is regression, in which the sea level falls

relative to the land and exposes former sea bottom.

Shells were seen on the ground at Stony Waste [16° 5'42.49"N; 73°28'53.78"E] which is

not very close to the sea. This is evidence of marine regression and tells us that

this area used to lay bellow the sea level at one time.


The sedimentary facies changes are indicative of transgressions and

regressions and are often easily identified, because of the unique

conditions required to deposit each type of sediment. For instance,

coarse-grained clastics like sand are usually deposited in near shore, high-

energy environments; fine-grained sediments however, such as silt and

carbonate muds, are deposited farther offshore, in deep, low-energy

waters.

Thus, a transgression reveals itself in the sedimentary column when there

is a change from near shore facies (such as sandstone) to offshore ones

(such as marl), from the oldest to the youngest rocks. A regression will

feature the opposite pattern, with offshore facies changing to near shore

ones. Regressions are less well-represented in the strata, as their upper

layers are often marked by an erosional unconformity.


Blowholes:

[16° 4'46.11"N; 73°27'47.38"E]

A Blowhole during the low tide

A blowhole is formed as sea caves grow landwards and upwards into

vertical shafts and expose themselves towards the surface, which can

result in quite spectacular blasts of water from the top of the blowhole if

the geometry of the cave and blowhole and state of the weather are

appropriate.

The blow holes activity varies with the tides.


Sea Caves:

[16° 4'47.15"N; 73°27'47.20"E]

A sea cave, also known as a littoral cave, is a type of cave formed

primarily by the wave action of the sea. The primary process involved is

erosion. Sea caves are found throughout the world, actively forming along

present coastlines and as relict sea caves on former coastlines.

Littoral caves may be found in a wide variety of host rocks, ranging from

sedimentary to metamorphic to igneous, but caves in the latter tend to be

larger due to the greater strength of the host rock.

In order to form a sea cave, the host rock must first contain a weak zone.

In metamorphic or igneous rock, this is typically either a fault or a dike. In

sedimentary rocks, this may be a bedding-plane, a parting or a contact

between layers of different hardness.

Rainwater may also influence sea-cave formation. Carbonic and organic

acids leached from the soil may assist in weakening rock within fissures.

As in solutional caves, small speleothems may develop in sea caves.


Sea Cliffs:

[16° 4'58.42"N; 73°27'29.83"E]

Sea cliffs are high, rocky coasts that plunge down to the sea's edge.

These harsh environments are subject to the battering of waves, wind,

and salt-laden sea spray. Conditions on a sea cliff vary as you move up

the cliff, with waves and sea spray playing larger parts in shaping the

communities at the base of a sea cliff while wind, weather, and sun

exposure are the driving forces that shape the communities towards the

top of a sea cliff.

At the base of the cliff, the pommeling by the surf prohibits all but the

most tenacious of animals from surviving there. Molluscs and other

invertebrates such as crabs and echinoderms occasionally find shelter

behind rocky outcrops or tucked within tiny crevices.


Topple and Slip:

A topple.

This is a common phenomenon seen in coastal areas along sea cliffs

where a protruding part of the sea cliff gets detached from the main land

and falls off.

It happens due to the crashing of waves on the wall of the cliff. If the

crack originates from the top, the mass of land slips and falls off. This is

called a slip.

If the area from under the land mass keeps getting eroded slowly, after a

span of time the land mass will topple down into the sea. This is called a

topple.

We can differentiate a topple from a slip by checking the vegetation cover

over the fallen land mass. If the vegetation is dying it is a slip as the land

gets detached from the mainland at the very beginning, cutting the supply

of nutrients from the mainland.


Sea Arches and Stacks:

Another spectacular type of erosional landform is the sea arch, which

forms as the result of different rates of erosion typically due to the varied

resistance of bedrock. These archways may have an arcuate or

rectangular shape, with the opening extending below water level. The

height of an arch can be up to tens of metres above sea level. It is

common for sea arches to form when a rocky coast undergoes erosion and

a wave-cut platform develops. Continued erosion can result in the collapse

of an arch, leaving an isolated sea stack on the platform.

A stack is a geological landform consisting of a steep and often vertical

column or columns of rock in the sea near a coast, isolated by erosion.

Stacks are formed through processes of coastal geomorphology, which are

entirely natural. Time, wind and water are the only factors involved in the

formation of a stack. They are formed when part of a headland is eroded

by hydraulic action, which is the force of the sea or water crashing against

the rock.


Cross Bedding:

[16° 3'41.35"N; 73°27'22.76"E]

Cross-bedding refers to inclined sedimentary structures in a horizontal

unit of rock. These tilted structures are deposits from bedforms such as

ripples and dunes, and they indicate that the depositional environment

contained a flowing fluid (typically, water or wind). This is a case in

geology in which original depositional layering is tilted, and the tilting is

not a result of post-depositional deformation.

Sediment grains bounce up the windward/upstream ("stoss") side of a

ripple, and then tumble down the lee side. The current erodes grains from

the crests and deposit them on the down current, or the lee face as it is

sometimes called, as the wave like sediment moves continually with the

current. The grains will fall down the side and roll a bit along the surface

until they lose momentum.

Cross beds are can tell geologists much about what an area was like in

ancient times. The direction the beds are dipping indicates paleocurrent.

The type and condition of sediments can tell geologists the type of

environment (rounding, sorting, composition…). Studying modern analogs

allows geologists to draw conclusions about ancient environments.


Bibliography:

Google (www.google.com)

Wikipedia (www.wikipedia.org)

Structural Geology by Marland P. Billings.

Geology of Maharashtra by G. G. Deshpande.

http://www.google.com/

http://www.wikipedia.org/

Geology Field Report Malvan, Sindhudurg District

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