EOSC : Petrology MID TERM minutes

Transcription

1 EOSC : Petrology MID TERM minutes PART 1: Individual Exam (42 marks) FAMILY NAME: (please print) GIVEN NAME: (please print) STUDENT NUMBER: (print CLEARLY) INSTRUCTOR: Dr. Stuart Sutherland Rules governing formal examinations READ AND SIGN BELOW! 1. Each candidate must be prepared to produce, upon request, a UBC card for identification. 2. Candidates are not permitted to ask questions of the invigilators, except in cases of supposed errors or ambiguities in examination questions 3. Candidates suspected of any of the following, or similar, dishonest practices shall be immediately dismissed from the examination and shall be liable to disciplinary action: Having at the place of writing any books, papers or memoranda, computers, sound or image players/recorders/transmitters (including telephones), or other memory aid devices, other than those authorized by the examiners; Speaking or communicating with other candidates; Purposely exposing written papers to the view of other candidates or imaging devices. The plea of accident or forgetfulness shall not be received. 5. Candidates must not destroy or mutilate any examination material; must hand in all examination papers; and must not take any examination material from the examination room 6. Candidates must follow any additional examination rules or directions communicated by the instructor or invigilator I have read and understood these instructions: SIGNATURE OF CANDIDATE:

2 QUESTION 1 (4 marks) a) Into which broad category of sedimentary rock would you place the sediments in the image below? (1 mark) Ring one of the following options: Terrigenous Orthochemical Allochemical b) Draw arrows from the items listed in the feature column to areas on the photograph where they can be CLEARLY seen. Note you have to use a vertical bar to define the area. (3marks) Photograph Feature SEDIMENT (any of the clasts you can see) BED (any individual stratum ) STRATA (any grouping of beds) QUESTION 2 (6 marks) i. In the spaces provided name the following sedimentary structure and indicate with an arrow the way up (2 marks) Structure Name: Graded Bedding Way up

3 ii. Describe how this sedimentary structure forms AND suggest a possible environment of deposition. (4 marks) Formation: Deposition of sediments in a waning flow such that the coarse heavy material settles out first and the finer lighter sediment settles out as flow velocity decreases. Environment of deposition: Anywhere with episodic flows of clastic material for example: turbidite events down a slope in an open body of water; during a flood event when a river breaks it s banks and deposits sediment on a floor plain; during flash flood events in an alluvial type of environment. QUESTION 3 (8 marks) a) Provide a name for each of the following rocks using the Pettijohn (1973) scheme. (1.5marks) Grain proportions as % seen in hand specimen Matrix Rock name A 80% Lithics / 10% Quartz / 10% Feldspar 0 Lithic Arenite B 0% Lithics / 98% Quartz / 2% Feldspar 20% Quartz Wacke C Too small too see in hand specimen 90% Mudstone b) Plot APPROXIMATE locations for each of these rocks (A/B/C) on the following QFL diagram (1.5 marks) B Q" 5# 25# 50# 5# 15# %#MATRIX## <#30microns# 75# C F" 50# 0# L" A

4 c) Assume that rock C was black, has a high organic and pyrite content and is very fissile. With this information provide a more specific name for rock C. (1 mark) Sulfidic black shale (0.5 mark for organic rich mudrock) In what type of environment might this sediment have been deposited? (2 marks) Restricted- circulation, reduced sedimentary rate, ANOXIC MARINE settings How does the pyrite form in these sediments? (2 marks) Metabolism of organics by sulfate reducing bacteria produce H 2 S by reduction of sulfate combines with Fe to from pyrite (FeS 2 ) QUESTION 4 (8 marks) REEF OS OS W OS OR W NC Refer to the figure above of a carbonate shelf margin environment. i. On the figure mark with OS just ONE possible location where you might find an oosparite.(1) ii Explain why an oosparite might form in this location (1): Form in areas of agitated water needs shallow conditions above wave base iii On the figure mark an area with OR that are MOST LIKELY form good oil reservoirs (1) LARGE REEFS ARE THE MOST LIKELY PLACE TO GET OIL ACCUMULATION RESERVOIRS! iv. Name one type or rock (using the Dunham scheme) that might be common in in the area you have defined as OR (1): Boundstones: Framestone, Bindstone, Rudstone, floatstones, Bafflestones,

5 v. On the figure mark with W just ONE possible location where you might get a Wackestone being deposited (1). vi. Explain why a wackestone might form in this location (1): Requires quiet conditions below wave base or behind a barrier vii. On the figure mark one area with NC where you would NOT expect to find carbonate rocks deposited (1). viii. Explain why you would not expect carbonates in this area (1): Bellow the CCD Due to pressure / temp / CO2 levels get net dissolution rather than deposition of carbonates. Dissolved CO2 in water increases dissolution of carbonates. QUESTION 5 (5 marks) A B i. Consider the figure above Name the zone at A (0.5): Vadose Zone Name the zone at B (0.5): Phreatic Zone ii. Name 4 processes that can occur to a sandy sediment in zone A (4 marks) - Wash clay grade material into the pore spaces - Continued degradation of unstable components - Growth of clays - Diagenetic redding of grain surfaces with hematite - possibly some compaction (4 out of this list of 5)

6 QUESTION 6 (7 marks) Draw lines that BEST connect the rocks or deposits on the left with the various statements / concepts on the right. An example has been provided for you. Thick variable evaporite deposit Brine Reflux Model Aragonite Great Oxygenation Event Chert Bitter Lakes Sodium Carbonate Cooler Oceanic State Halite Volcanic setting Lahar Salt lakes Banded Iron Formation microcrystalline silica Chicken wire Gypsum Sabkha

7 QUESTION 7: True / False Questions based on readings Circle the correct response (4 marks) i. Intracratonic basins develop on oceanic crust. ii. The most durable type of quartz is undulatory monocrystalline quartz without inclusions iii. Older mudrocks tend to contain more illite than younger mudrocks. iv. Peloids can only be formed when algae and other microbes bore into a carbonate grain. v. Micrite can only form by biological and inorganic processes. vi. Abundant muscovite in a sandstone suggests derivation from metamorphic rocks. vii. The Gulf Coast Salt Basin is mostly filled with gypsum. viii. The distribution of the sedimentary rocks in the Delaware basin show a crude concentric zonation with carbonates and clastics in the centre of the basin followed by gypsum and halite and finally potassium salts on the basin margins.