Geology Field Report Malvan 2010 Department of Geology, St. Xavier’s College. Field Report |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 Field Report |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. Field Report |2 Submitted to: Dr. Hrishikesh Samant Submitted by: Russell Menezes Seat No: _______ T.Y.B.Sc. Geology, St. Xaviers College. Date: 3rd January 2011 Field Report |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 Field Report |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 Field Report |5 INTRODUCTION __________________________________________________________________________________ Field Report |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. Field Report |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. Field Report |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 where we performed the Pace Length [16° 3'20.94"N; of grassy land [16° 3'15.98"N; 73°27'29.87"E] exercise. We then moved north to the limbs of a plunging fold 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. Field Report |9 On the sixth day {30th Oct.} we went to an igneous rock quarry 73°30'10.17"E] [16° 0'56.60"N; to study the igneous rocks of that area. We then climbed up a dry to study potholes. We then walked a great to get to a Fault zone [16° 3'48.74"N; river bed [16° 1'10.60"N; 73°29'50.92"E] distance over a peneplain [16° 2'36.42"N; 73°29'16.57"E]. 73°28'49.20"E]. [16° 1'38.83"N; 73°29'43.75"E] We then went to a laterite quarry On the seventh day {31st Oct.} we walked to a river bed 73°30'14.38"E] [16° 3'57.84"N; 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: Procedure: Compass, map of the area, drawing stationary. The first step in triangulation is to pick three topographic features that you c an 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 fea tures, 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 directi ons. 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) 4.32 4.21 4.30 4.36 3.6 3.41 3.33 3.17 3.34 3.35 4.58 3.52 3.64 4.05 4.98 5.00 3.37 3.46 3.92 3.82 3.70 4.05 4.69 5.00 5.00 2.38 2.05 2.53 2.80 3.15 3.54 2.36 4.12 5.00 5.00 4.16 5.00 4.02 Remarks Joint Plane Readings T° Da° D 1. 2. 3. 4. 5. 6. N 185 N 187 N 189 N 182 N 206 N 209 N 210 N 217 N 222 N 204 N 225 N 233 N 244 N 245 N 226 N 245 N 241 N 270 N 269 N 250 N 245 N 254 N 284 N 278 N251 N 269 N 275 N 290 N 296 N 300 N 303 N 304 N 314 N 314 N 295 N 299 N 290 N 276 SQC 1 SQC 2 SQC 3 SQC 4 SQC 1 SQC 2 SQC 3 SQC 4 SQC 5 SQC 6 SQC 1 SQC 2 SQC 3 SQC 4 SQC 5 SQC 6 SQC 1 SQC 2 SQC 3 SQC 4 SQC 5 SQC 1 SQC 2 SQC 3 SQC 4 SQC 1 SQC 2 SQC 3 SQC 4 SQC 5 SQC 6 SQC 7 SQC 8 SQC 9 SQC 10 SQC 11 SQC 12 SQC 13 N25 N210 90 90 E W N351 63 E N244 N163 N113 N75 N266 N340 54 58 72 67 90 90 N W E N N E N197 N255 N244 67 55 73 W N N N341 N245 N125 90 90 72 W N E F i e l d R e p o r t | 20 7. 8. 9. 10. 11. 12. 13. 14. 15. N 316 N 314 N 318 N 321 N 320 N 337 N 338 N 334 N 83 N 86 N 87 N 74 N 79 N 96 N 96 N 96 N 94 N 115 N 113 N 114 N 119 N 120 N 124 N 123 N 125 N 134 N 133 N 137 N 138 N 136 N 55 N 50 N 28 N 18 N 10 N7 N 38 N 18 N 17 N7 N2 N6 3.63 3.18 3.26 3.40 3.57 3.28 3.96 3.99 3.66 3.80 4.58 4.20 3.81 4.38 4.48 4.60 4.48 5.00 4.68 5.53 4.75 5.00 5.00 4.81 4.49 4.98 4.39 4.45 4.70 4.68 4.69 4.80 4.37 4.51 4.38 3.31 2.94 5.00 4.50 3.98 4.40 5.00 SQC 1 SQC 2 SQC 3 SQC 4 SQC 5 SQC 1 SQC 2 SQC 3 SC 1 SC 2 SC 3 SC 4 SC 5 SC 1 SC 2 SC 3 SC 4 SQ 1 SQ 2 SQ 3 SQ 4 SQ 5 SQ 1 SQ 2 SQ 3 SQ 4 SQ 1 SQ 2 SQ 3 SQ 4 SC 1 SC 2 SC 3 SC 4 SC 5 SC 6 SC 7 SC 1 SC 2 SC 3 SC 4 SC 5 N261 N161 51 90 N W N23 N302 N75 N251 N71 90 31 62 90 56 N S S S S N63 52 S N311 N60 23 90 N N N159 N124 53 90 E W N302 72 E N62 N60 N334 N53 90 90 42 23 S S N W 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: No. a. b. c. d. e. f. g. h. i. Dist. 5.55 5.03 4.87 4.78 4.03 4.01 3.98 4.39 5.50 Bearing N4 N 256 N 352 N 363 N 340 N 334 N 229 N 313 N 284 Strike N 320 N 306 N 243 N 229 N 68 N 42 N 150 N 249 N 216 Dip SW NE SE NW SE NW NE NW SE Dip Amt. 64 21 7 11 16 10 26 7 10 Images: Student using Telescopic alidade 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: Dist. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 120° 11.41 11.34 11.31 11.30 11.23 11.23 11.32 11.48 11.58 11.58 11.52 11.62 11.64 11.62 11.34 130° 11.46 11.34 11.36 11.30 11.28 11.29 11.42 11.54 11.58 11.62 11.68 11.62 11.69 11.68 11.68 140° 11.45 11.38 11.39 11.30 11.33 11.37 11.47 11.54 11.61 11.34 11.58 11.72 11.74 11.75 11.73 150° 1146. 11.45 11.34 11.40 11.26 11.35 11.44 11.53 11.58 11.28 11.20 11.22 11.83 11.80 11.70 160° 11.48 11.47 11.46 11.42 11.43 11.40 11.41 11.46 11.55 11.65 11.70 11.73 11.75 11.71 11.78 170° 11.44 11.47 11.44 11.52 11.52 11.51 11.64 11.53 11.45 11.60 11.73 11.72 11.70 11.67 11.60 Images: Laser pointer being used with Dumpee level. 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. 1. 2. 3. 4. 5. 6. 7. 8. 9. Distance (m) 6.9 25.51 7.40 4.49 11.38 1.54 9.27 4.25 8.39 Sighting 5° 30’ 1° 50’ 3° 10’ 6° 40’ 1° 10’ 23° 30’ 1° 40’ 17° 50’ 4° 20’ Remark Elevation Depression Elevation Elevation Depression Elevation Depression Elevation Depression Set II: No. 1. 2. 3. 4. 5. 6. 7. 8. Distance (m) 15.86 5.68 19.54 1.74 16.05 13.35 2.76 5.41 Sighting 3° 40’ 5° 50’ 7° 50’ 11° 30’ 2° 20’ 2° 40’ 21° 10’ 2° 30’ Remark Depression Elevation Depression Depression Elevation Depression Elevation Elevation Set III: No. 1. 2. 3. 4. 5. 6. 7. Distance (m) 26.31 20.62 5.2 9.16 12.45 10.54 2.8 Sighting 1° 3° 10’ 4° 20’ 4° 10’ 1° 20’ 6° 50’ 23° 40’ Remark Elevation Depression Depression Elevation Depression Elevation Elevation F i e l d R e p o r t | 31 Set IV: No. 1. 2. 3. 4. 5. 6. 7. Distance (m) 14.43 5.75 4.76 26.16 5.70 25 2.58 Sighting 2° 50 1 20 5 20 2 30 5 50 2 10 17 40 Remark Elevation Depression Elevation Depression Elevation Elevation Elevation Set V: No. 1. 2. 3. 4. 5. 6. 7. Distance (m) 11.07 6.11 3.54 25.28 4.98 25.44 4.36 Sighting 4° 10’ 1° 20’ 4° 10’ 1° 50’ 6° 30’ 1° 20’ 10° 20’ Remark Elevation Depression Elevation Depression Elevation Elevation Elevation Set VI: No. 1. 2. 3. 4. 5. 6. 7. Distance (m) 18.9 4 21.80 2.50 12.90 21.90 1 Sighting 4° 50’ 3° 10’ 1° 20’ 6° 30’ 1° 50’ 2° 40’ 18° Remark Elevation Elevation Depression Elevation Depression Elevation 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 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. Strike° N226 N352 N178 N125 N120 N110 N105 N60 N337 N157 N153 N183 N185 N81 N85 N188 N217 N197 N359 N300 N350 N300 N213 N355 N355 N35 N330 N335 N336 N121 Dip° Dip Amount° Remark N136 71 N262 82 N88 56 N35 58 Parallel N30 71 N20 62 N15 78 N150 65 N147 66 N67 16 N63 40 N93 49 N95 69 Parallel N171 67 N176 44 Parallel N98 47 N127 75 Parallel N107 56 N269 76 N290 52 Conjugate N260 48 N210 41 N183 34 N265 51 N265 76 N125 56 N240 60 Conjugate N245 54 N246 62 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: 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: To determine the strike and dip of plunging folds. No Strike° Dip a. b. c. N310 N292 N293 20°N 24°N 21°N No Strike° Dip a. b. c. N258 N289 N253 12°N 10°N 13°N Limbs of a fold at Rajkot. [16° 3'21.02"N; 73°27'25.47"E] 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. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. Shortest (x) L(cm) T° 1 N252 1.2 N265 0.9 N82 1.3 N264 0.7 N265 0.8 N78 3.8 N235 3 N257 0.8 N700 Intermediate (Y) P° L (cm) 10 21 11 23 1.5 1.7 2.2 2.1 1.7 33 3.1 2.6 2.2 3.1 1.2 1 7 2 2 1.1 3.5 2.3 1 0.9 2 1.1 2.5 1.8 1.1 9 T° N265 N264 N95 N170 N68 N81 N78 N88 N87 N86 N70 N61 N51 N260 N57 N255 N60 N70 N60 N67 N240 P° 20 4 26 7 22 35 12 6 41 32 20 5 9 11 3 2 24 20 30 8 4 - Longest (Z) L(cm) T° 6.5 N341 5.5 N352 3.9 N180 7.2 N351 4.7 N165 5.3 N355 6.5 N163 5.4 N175 4.5 N355 4.3 N162 5.1 N145 8.5 N338 5.2 N343 5.2 N343 5.4 N349 6.5 N160 1.9 N153 6.7 N148 12 N348 3.1 N152 8.7 N143 5.8 N351 2.2 N142 3 N342 4.5 N153 4.8 N340 4 N148 3.9 N156 3.7 N160 2.3 N159 P° 9 8 2 3 22 9 11 4 2 2 4 6 7 11 6 12 9 9 14 8 2 7 27 2 10 14 10 10 18 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: Laterites Alluvium Deccan Traps Achara Sandstone – Shale Formation Kaladgi Super Group Basal Member of Baba Budan Series Unconformity Peninsular Gneiss 3000 – 2600 my Mid – Late Proterozoic 2600 – 2400 my Unconformity Pliocene - Pleistocene Holocene Upper Cretaceous - Eocene Unconformity 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 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 finergrained 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 coarsegrained 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 coarsegrained 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 fluidrich 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, highenergy 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.
Comments
Report "Geology Field Report Malvan, Sindhudurg District"