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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
F i e l d R e p o r t | 1
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.
F i e l d R e p o r t | 2
Submitted to:
Dr. Hrishikesh Samant
Submitted by:
Russell Menezes Seat No: _______
T.Y.B.Sc. Geology, St. Xaviers College.
Date:
3rd January 2011
F i e l d R e p o r t | 3
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
F i e l d R e p o r t | 4
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
F i e l d R e p o r t | 5
INTRODUCTION __________________________________________________________________________________
F i e l d R e p o r t | 6
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.
F i e l d R e p o r t | 7
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.
F i e l d R e p o r t | 8
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.
F i e l d R e p o r t | 9
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.
F i e l d R e p o r t | 10
Methods Used For
Field Work __________________________________________________________________________________
F i e l d R e p o r t | 11
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.
F i e l d R e p o r t | 12
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.
F i e l d R e p o r t | 13
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.
F i e l d R e p o r t | 14
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.
F i e l d R e p o r t | 15
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
F i e l d R e p o r t | 16
F i e l d R e p o r t | 17
Mapping Exercises __________________________________________________________________________________
F i e l d R e p o r t | 18
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.
F i e l d R e p o r t | 19
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
F i e l d R e p o r t | 20
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
F i e l d R e p o r t | 21
Images:
Bearing being taken on the Brunton
Tape Stretched towards Staff held at Contact
F i e l d R e p o r t | 22
F i e l d R e p o r t | 23
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.
F i e l d R e p o r t | 24
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
F i e l d R e p o r t | 25
F i e l d R e p o r t | 26
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.
F i e l d R e p o r t | 27
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
F i e l d R e p o r t | 28
F i e l d R e p o r t | 29
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.
F i e l d R e p o r t | 30
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:
No. Distance (m) Sighting Remark
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:
No. Distance (m) Sighting Remark
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
F i e l d R e p o r t | 31
Set IV:
No. Distance (m) Sighting Remark
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:
No. Distance (m) Sighting Remark
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:
No. Distance (m) Sighting Remark
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
F i e l d R e p o r t | 32
F i e l d R e p o r t | 33
Structural Geology __________________________________________________________________________________
F i e l d R e p o r t | 34
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.
F i e l d R e p o r t | 35
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]
F i e l d R e p o r t | 36
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 -
F i e l d R e p o r t | 37
F i e l d R e p o r t | 38
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.
F i e l d R e p o r t | 39
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
F i e l d R e p o r t | 40
F i e l d R e p o r t | 41
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.
F i e l d R e p o r t | 42
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]
F i e l d R e p o r t | 43
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
F i e l d R e p o r t | 44
F i e l d R e p o r t | 45
Geology of
Malvan
F i e l d R e p o r t | 46
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
F i e l d R e p o r t | 47
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)
F i e l d R e p o r t | 48
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.
F i e l d R e p o r t | 49
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:
F i e l d R e p o r t | 50
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).
F i e l d R e p o r t | 51
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.
F i e l d R e p o r t | 52
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.
F i e l d R e p o r t | 53
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.
F i e l d R e p o r t | 54
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.
F i e l d R e p o r t | 55
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.
F i e l d R e p o r t | 56
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.
F i e l d R e p o r t | 57
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.
F i e l d R e p o r t | 58
Coastal
Geomorphology and
Features
F i e l d R e p o r t | 59
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.
F i e l d R e p o r t | 60
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.
F i e l d R e p o r t | 61
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.
F i e l d R e p o r t | 62
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.
F i e l d R e p o r t | 63
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.
F i e l d R e p o r t | 64
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.
F i e l d R e p o r t | 65
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.
F i e l d R e p o r t | 66
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.
F i e l d R e p o r t | 67
F i e l d R e p o r t | 68
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.
F i e l d R e p o r t | 69
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.
F i e l d R e p o r t | 70
Bibliography:
Google (www.google.com)
Wikipedia (www.wikipedia.org)
Structural Geology by Marland P. Billings.
Geology of Maharashtra by G. G. Deshpande.