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WELSH JOINT EDUCATION COMMITTEE CYD-BWYLLGOR ADDYSG CYMRU General Certificate of Education Tystysgrif Addysg Gyffredinol Advanced Subsidiary/Advanced Uwch Gyfrannol/Uwch MARKING SCHEMES SUMMER 2003 GEOLOGY INTRODUCTION The marking schemes which follow were those used by the WJEC for the 2003 examination in GCE GEOLOGY. They were finalised after detailed discussion at examiners' conferences by all the examiners involved in the assessment. The conferences were held shortly after the papers were taken so that reference could be made to the full range of candidates' responses, with photocopied scripts forming the basis of discussion. The aim of the conferences was to ensure that the marking schemes were interpreted and applied in the same way by all examiners. It is hoped that this information will be of assistance to centres but it is recognised at the same time that, without the benefit of participation in the examiners' conferences, teachers may have different views on certain matters of detail or interpretation. The WJEC regrets that it cannot enter into any discussion or correspondence about these marking schemes. GEOLOGY GL1 Marks Q.1 (a) A = Joint/Fracture [1] B = Bedding plane/Bed [1] (b) Calcite. [1] (c) Erosion. Weathering. Weathering. Erosion. 4 correct = 2 marks, 3 correct = 1 mark (d) [2] Freeze thaw reference to moisture expansion (on freezing), causing opening up of joints/block separation/breaking off. Also credit related to temperatures at altitude fluctuating above and below freezing, [4] Solution/carbonation acidic, rainwater solubility of/reacts with limestone causing opening up of joints/block separation/breaking off. [4] or (e) (i) Reduction in size. Rounding. [1] [1] (ii) Abrasion or corrosion/attrition. Collision between transported particle and bed/bank. Collision between two transported particle. "Knocks off corners". [3] 14 marks 1 Q.2 (a) 1 2 Arrow parallel to horizontal line (pointing North). Arrow dipping away from diagram at approximately 67 degrees from the horizontal. [1] [1] (b) Iron. Moving/convection current/fluid/self exciting dynamo. (c) (i) Iron/mafic/magnetic minerals. Alignment. Become fixed/solid/Curie temp. Remnant magnetism. (ii) Shade of bar SB 180-65 Ma-part of 65 Ma. [1] (iii) India was decreasing its latitude/ moving towards the equator/ moving Northwards. [1] (d) [1] [1] Credit the following on diagram or text. Strong.weak/positive.negative/above.below average magnetic readings Normal and reverse magnetism Magnetic poles reversal/flip Take on alignment of magnetic field at time of eruption MOR or constructive/divergent plate boundary Stripe anomalies are parallel to MOR Stripe anomalies are symmetrical about MOR Rising magma/lava is erupted at MOR Movement of ocean floor away from MOR/older away from MOR. [5] 14 marks (N.B. MOR = mid ocean ridge) 2 Q.3 (a) E = Solar energy/the sun. I = Radioactive decay/geothermal. [1] [1] (b) (i) Crystalline/crystals. Foliated/schistose. Porphyroblastic. Only credit "groundmass" if supported by "medium grained" or "finer" or size measurements. [2] (ii) Metamorphic. Foliation/schistocity/alignment. Presence of garnet. [1] [1] (i) Pre-existing rock (mantle, metamorphic, subducted). Heat source. Partial melting. Minerals with lower melting points melt. Minerals with higher melting points remain solid. Melted portion forms the magma. [3] Plate tectonic activity/mountain building/uplift. Erosion. Xenolith in a lava/intrusive igneous body. [1] (c) (ii) (d) Accept reference to Folding, Faulting, Slickensiding, Dipping beds. Credit: Quality of diagram/fieldsketch. Reference to Scale. Detail of feature, e.g. "normal fault", "anticline". Specific location of feature, e.g. field location. Nature of stress involved, e.g. compression or tension. Labelled or descriptive features of the structure. Total 16 marks 3 Q.4 (a) (i) (ii) Trilobite. Trace fossil/track/trail/print/burrow/imprint. [1] [1] (b) (i) Random orientation/no alignment. (accept that they all lie flat on the bed). [1] (ii) (c) Weak current because: they would be aligned by a strong current they are unmoved/still present they are undamaged. [1] [1] Annotations to include some of the following: Original shell buried/trapped. Soft parts already destroyed. Lithification (of sediment to sedimentary rock) shell dissolved/decomposed by acidic fluids. Minerals infill Precipitated from fluids passing through the rock. **Cast (reserved mark) Cast is a replica of the original. Original hard parts no longer exist. ** Mould (reserved mark). External mould. [6] N.B. Mould and cast are both reserved marks; they have to be present to achieve full marks. (d) (i) (ii) Transported. [1] From life position/before burial/after death/before fossilised. [1] 3 of the following [3] Death assemblage broken aligned sorted can be derived out of life habitat Life assemblage unbroken non-aligned unsorted never derived in life habitat 16 marks 4 MARK SCHEME GL2(a) SUMMER 2003 SPECIMENS A = QUARTZ B = SPOTTED ROCK C= BIVALVE (ONE VALVE OF A COCKLE SHELL) 5 Q 1 response a b mark (i) cuts across folded/horizontal/tilted beds 1 1 (ii) (porphyritic) crystalline texture 1 1 (i) scrape mineral across an unglazed tile 1 white powder 1 scratch mineral with equipment specified 1 no scratch with any 1 (accept > 5.5 but not = 7) look for regular breakage c 2 1 quartz 1 (i) patches of new mineral growth 1 rock recrystallised (waterproof) loss of bedding, etc 1 mark spotted rock/hornfels 1 3 (ii) (contact) metamorphism (not regional) 1 1 (iii) position on Map 2 (anywhere with B in SE corner 1 of map) 1 a drawing shape square (or rectangular ) quality of detail scale labels pallial line/teeth and sockets/ hinge/muscle scars/ligament/ crenulated margin (not ribs or pallial sinus) 1 2 max 1 2 max 6 bivalves are equivalve, inequilateral (including plane of symmetry) 3 max brachiopods are inequivalve, equilateral (including plane of symmetry) 3 max 4 (i) Completion of beds 2 – 5 (treat labels as a guide to the beds) 1 reserved mark for thicknesses shale texture/irregular base bed 4/coarse bed 4/grading beds 2 + 4 (any 3) 1 4 (ii) 15/20mm 1 1 Graptolite But 2 stipes/pendant habit/Didymograptus Therefore Ordovician (not Silurian) (older than Silurian) 1 1 1 3 look for diagrams which suggest that a b 6 (ii) b 3 1 only irregular fracture 1 6 c (flutes) scour and fill passage of turbidity current d 4 a 1+1 1 2 2 max 2 3 correct for 2 marks 2 correct for 1 mark 3 in right place but wrongly labelled = 1 2 marks 2 inclined folds are asymmetrical 1 1 2 east 1 younger beds on downthrow (hanging wall goes down) 1 2 the azimuth/bearing measured from north NW (315º) to SE (135º) south west 1 1 1 3 thrust/reversed 1 1 horizontal base of C and labeled (uncon) discordant edge of pluton 1+1 1 fault F1 (dip/arrows/label) 2 max folding 4 max graptolite graded beds shale fossils replaced by pyrite black colour greywackes/turbidites (i) (ii) b c (i) (ii) 5 a b antiform and synform/labelled axes = 1 limbs to show asymmetry = 1 inclined axes 1 = 1 base of Unit B beneath synform = 1 either fold beneath uncon superposition: E dips beneath G therefore apparently older cross-cutting: dyke (rock unit A) younger than other units/fault F3; x-cut: fault younger than Units include fragments: G contained in E therefore older (superposition: cannot apply as beds are overturned) other explanation for fossils in E = 7 1 max 10 1 1 1 1 1 4 GEOLOGY GL3 Q.1 (a) Ash fall Lahar (1) (water from lake or melted ice cap) Pyroclastic flow (1) (nuees ardente) Volcanic gas (1) [3] (b) A- Ash FallWeight of ash (1) Ash from fine powder - bombs (1) Rapid - can be up to 1 metre /hour (1) Often mixed with water from torrential rain (1) Causes roofs/walls to collapse (1) Examples - Pinatubo, Vesuvius, Krakatoa (1) Other sensible qualification (1) B- Lahar Rapid burial by forceful flow of mud/ash plus rock (1) Rapid Speed - qualified (45km/hr) (1) Hot (1) Caused by lake overflowing/torrential rain/melting ice cap (1) Little warning given to evacuate (1) Sets like cement (1) Examples - Nevado del Ruiz/Mount Ruapehu (NZ)/Pinatubo (1) Other sensible qualification (1) C- Pyroclastic flow (Nuees ardentes)Rapid flow of hot gas/debris (1) Rapid - 100km/hr (1) Hot - 800degC (1) Little warning (1) Moves over water (1) Examples : Pinatubo//St. Pierre/Monserrat etc (1) Other sensible qualification (1) D- Volcanic gas Flow of volcanic gas causes suffocation (1) Rapid (1) quiet (1) Little or no warning (1) Gases include Carbon dioxide, Carbon monoxide and chlorine.(1) Gas disperses to leave no trace/no damage to buildings (1) Example - Lake Nyos, Cameroon (1) Other sensible qualification (1) e.g. Overturn of volcanic lake, density of gases in hollows (max 3 each) 8 [6] (c) Reference to particular hazard Holistic - 3 valid points/examples. e.g. Lava Evacuation, hazard mapping, diversion/blocks, dropping-spraying with water, explosion of flow margin, prediction devices. e.g. Etna [3] Total 12 marks Q.2 (a) (i) 22 - 23hrs (1) [1] (ii) 9750/15 (1) = 650 km/hr (1) [2] Too close to epicentre/no time for warning (1) [1] (iii) (b) (i) Wavelength wavelength decreases (1) Amplitude amplitude increases (1) Velocity slows (1) [3] (ii) (c) A- B- C- Small amplitude (1) Large wavelength (1) Indistinguishable from other waves/swell (1) Evacuation road/Access for relief work (1) Barrier (1) Above projected height of flood (1) Associated with Chamel for flood water (1) Barrier to inland flooding (1) Above projected height of flood (1) Absorb energy of wave (1) Associated with Chamel for flood water (1) Waves pass through piles/easily drains (1) Offer least resistance to force of water (1) Strength of Orientation (1) Above protected wave height (1) 9 [2] D- Trees dissipate wave energy (1) as they are flexible (1) Trees – barrier (1) Slow/breaking waves (1) No development to destroy (1) Provide run-up for waves to dissipate energy (1) (Max 2 each) [4] Total 13 marks Q.3 (a) Describe the geological hazards that may result when engineering activities associated with a major construction project interfere with natural processes in coastal areas. [10] Holistic approach. Problems of interference with coastal systems - erosion/deposition Engineering activities include coastal defences (groynes, rip rap, sea walls etc) Hazards areas Coastal deposition – longshore drift pattern changed in unprotected Reduction in amount of sediment deposition available to provide a beach to protect the coast. Increased marine erosion in unprotected area. Base of cliff undercut - loss of stability for toe of landslide etc increase in mass movement Increase lubrication of coastal sediments by sea water - mass movement Reference to case studies credited. [10] (b) Explain the geological factors that need to be considered when selecting a suitable site for a dam and associated reservoir. [15] Size & shape of valley and catchment Rock strength of dam site Porosity and permeability of reservoir site Structure Stability of site Examples Holistic approach Long, narrow, deep to reduce evaporation Suitable rock types explained. Clay/shale v limestone/sandstone/crystalline rock Leaking, need for grouting. Suitable rock types - shale/clay/crystalline rock Fold/faults/cleavage (related to stability/seepage) Favourable and unfavourable features – sedimentation rate Rock beneath, mass movement on sides. Earthquake risk Credited [15] Total 25 marks 10 Q.4 (a) Describe the distribution of earthquake epicentres around the world. Describe: (b) Definition of epicentre Narrow zones (few hundred kms wide, thousands of kms long) in oceans Wider zones on continents (Himalayas - Asia) Sometimes join/divide e.g. Indian ocean Associated with belts of mountains, ocean ridges, volcanoes, rift valleys, island arcs, trenches. (e.g. Himalayas/ Atlantic, Circum-Pacific) Associated with plate boundaries - crustal tension/compression Divergent (constructive) - plates moving apart (MOR/rift valley) Convergent (destructive)- plates coming together (trenches, fold mts) Conservative - plates sliding past (San Andreas) Mid plate examples/volcanic origin. (max 5) [5] (1) Groundwater levels and pressure – Water in pores migrates into cracks prior to earthquake (dilation) water levels decrease. Water levels increase as more water diffuses prior to earthquake. Pore pressure changes with water diffusion. Earthquake following increase in well levels/pore pressure. Credit actual examples (max 7 plus 1) (2) Tilting and ground elevation- expansion of ground (by opening of microcracks formed by stress) prior to an earthquake. Recorded by changes in angles of slope and elevation . Use of tiltmeters/laser beams to accurately measure variation across faults. EDM (electronic distance measurements) from known fixed points. Credit actual examples (max 7 plus 1) (3) Seismic activity - Variation in the seismic rate. Increase in the background rate of minor earthquakes prior to a major quake. Seismic gap. The Measurement of the velocities of P and S waves passing through and area. Reduction indicates influx of water into rock as micro-fractures open. On returning to normal, pore pressure rises = quake. Rate of return to normal = Prediction of timing imminent. Duration of anomaly = predicted magnitude of quake. (max 7 plus 1) [15] (c) Explain how the destructive effects of earthquakes might be partly managed by controlled stress release along faults. Release of "locked" areas of fault by injecting fluids along fault to produce smaller controlled earthquakes or underground explosions. Denver - waste fluids injected into deep wells in fractured rock triggered minor earthquakes until pumping stopped. Water lubricates fault zone. Colorado - pumping water from deep wells - reduced water pressure/decreased earthquakes Both considered as a possible method of releasing the strain in "locked" parts of San Andreas fault. Very expensive and not proven to be safe or feasible yet. [5] Total 25 marks 11 Q.5 (a) Explain how the geological problems associated with domestic waste disposal in landfill sites might be overcome by good site selection and engineering practice. Site selection Site capable of retaining waste Free from disturbance (tectonic or subsidence). Topography and structure- Existing hole/quarry-stable slopes Bedrock and surface geology -Impermeable rock base to site – clay with low permeability rates for leachate containment. Hydrological regime - Dry site - above water table is preferred- (pore pressure Gradient and rate of groundwater flow. Proximity to groundwater extraction. Engineering Practice Permanent containment – clay lining by compaction of clay, plastic/geomembrane Careful monitoring of hydrological system – wells outside landfill Venting of methane gas – boreholes within the landfill Leachate management system – porous pipes for removal/recycling of leachate Holistic approach. Combination (max 15 marks) Max 10 only if only site OR engineering. (b) Describe the potential uses of former landfill sites after waste disposal ceases and the problems associated with their development. Uses - Parkland, recreation, open spaces, greenbelt, low level industrial development. Domestic development limited - problems of methane gas hazard- leakage through permeable rock. (e.g. Loscoe - Derbyshire) Ground instability on completion - subsidence. Other problems associated with maintaining containment - groundwater pollution. Must be accessible over 25 years to maintain. Credit examples. Total 25 marks 12 [15] GEOLOGY GL4 Question 1 (i) Temperature at base of the crust (Moho) Actual temperature. Temperature at which dry (non-hydrous) granite would begin to melt. Temperature at which wet (hydrous) granite would begin to melt. Temp 0C 720 (710 - 730) 1075 (1065 - 1085) 740 (630-650) [3] (ii) (iii) (b) 275/10 (accept 250 to 300/10) (1) = 300 C/km (1) [2] Less/lower in mantle (1) Gradient is steeper in crust (1) Rate of temp change with depth decreases (1) (max 1) [1] (i) (ii) (iii) Geothermal gradient is not high enough/crust not hot enough (1) Temperature at Moho/base of Crust is not hot enough (1) to cross the melting point curve (1) Water reduces melting point (1) [2] Area above melting point curve (1) below geothermal gradient (1) [2] The rising magma falls below/crosses the melting point curve (1) It will crystallise before reaching the surface (1) Between 8 -12 km from surface (1) (2 max) [2] (c) Gas content affects - Viscosity (1) - Buoyancy (1) - Explosion (1) - Density (controls buoyancy) (1) - Fluid pressure (forcible intrusion if fluid pressure exceeds confining pressure) (1) (Max 3) Total 15 marks 13 [3] Question 2 (a) (i) (i) 500 0C (1) 3.70 k bar (3.60 – 3.80) (1) [2] Pathway A1 → A2 Type - contact or thermal metamorphism (1) adjacent to igneous intrusions/metamorphic/aureole/ baked margins (1) plutons, magma chambers, sills, dykes (1) range/high temperature – low pressure Pathway B1 → B2 Type - regional (or dynamothermal/burial) metamorphism (1) subduction zones/fold mountain root/deep burial orogenic (1) associated with destructive plate margins/organic belt (1) high temperature – high pressure (1) [1] [2] [1] [2] (b) Rock in Figure 2b (formed at X on Fig 2a) Texture Rock name Rock in Figure 2c (formed at Y on Fig 2a) Porphyroblastic or Texture Foliated or gneissose Hornfelsic (1) Non foliated banding (1) Hornfels or spotted rock (1) Rock name Gneiss (1) [4] (c) (i) clay (1) [1] (ii) most chemically diverse of rocks (1) composed of clay minerals (1) clay is rich in Al, Si and O (1) other rocks do not contain aluminium (1) mica from clay minerals (1) Accept reasons for not including others (max 1) (max 2) [2] Total 15 marks 14 Question 3 (a) (i) (ii) (iii) (b) (c) [2] Thorax are free, pygidium are fused (1) Other sensible (e.g. shape, number etc) [1] Function - Allows for movement - rolling up (1) - Protection/support internal viscera (1) [2] Benthonic –crawler (credit swimmer/burrower if qualified) (reserve 1) Evidence: Eyes on dorsal surface – can only see above (1) Eyes small – lives on muddy bottom (1) Eyes - light enough to see (sometimes) (1) Flattened with wide cephalon/pygidium - stop sinking into soft mud (1) Cephalon shape as a shovel for burrowing in mud (1) Other sensible - must relate to evidence (1) (i) [3] Correct plot Length – 20-22mm/Width – 30-32mm [1] Distribution in clusters (reserve 1) Positive correlation/width/length directly proportional (1) Credit range giving values (2-22/5-32) (1) [2] B (1) Reasons - any two from: Clumping representing successive moults (1) Range from small (infant) to large (adults) (1) Shows steady growth (1) or A - Death Assemblage would give only one area of clustering/ sorting (1) C - Gradual evolution unlikely to be preserved on same bedding plane/would show continuous development. (1) (3 max) [3] Trilobites extinct or Fossil bivalves and brachiopods have modern living forms (1 max) – do not double credit Allowing direct comparisons to be made from modern to ancient or Uniformitarianism (Present is the key to the past) (1) (max 1) [2] (ii) (iii) (d) Feature X - Eye (1) Feature Y - Glabella (1) Total 16 marks 15 Question 4 (a) (i) Fold element Amplitude (in metres) Description 6m Wavelength (in metres) 40 m Hinge shape Angular Axial plane attitude UPRIGHT Axis orientation PLUNGING to NORTH [3] (ii) Anticline "v'ing" in direction of plunge (1) Syncline "v'ing" opposite direction to plunge (1) [2] (b) (c) Stresses at X = tension/extension (1 plus 1) Stresses at Z = compression (1 plus 1) (max 3) [3] (i) Arrows on CORRECT side of fault showing movement (1) [1] (ii) Tension/extension (1 plus 1) W-E or σ max (1) [2] Describe Upthrow to the West/downthrow to East (1) Reversed fault movement/ (1) Reference to displacement of unconformity (1) Account Fault reactivation (reserve 1) Post unconformity (1) Compression (1) (Max 3 - 1+ 1 (reserve) + 1) [3] (iii) Total 14 marks 16 SECTION B Question 5 (a) (i) Quaternary/recent sediment cover (1) [1] (ii) Till (1) [1] (iii) 3. Youngest Alluvium 2. Till ROCK HEAD 1. Oldest Ing (Silt/Sandstone Conglomerate) [2] (b) (i) (ii) Describe: Along valley floor (1) Dimensions: 4500 - 5000m long by 250m (widest point) (1) Trend – NE to SW (1) Explain: Flood plain deposit/meandering river (1) (Max 1 describe plus 1 explain) [2] Describe: Follows contours (1) Parallel to valley sides (1) Explain: Horizontal/near horizontal/very gentle dip (1) (Max 1 describe plus 1 explain) [2] Total 8 marks 17 Question 6 (a) (i) (ii) (iii) B (1) 60o dip to the SW (1) (or reasons why others are incorrect involving dip and bed orientation) (max 2) [2] Unconformity (reserve 1) Limestone (Garsdale) (1) Ing (silt/sand/cong) (1) Dip of beds - 60o (1) and horizontal (1) Accept many others - swallow hole, joints, bedding planes, limestone pavement, resurgence, clints, grikes, irregular base to unconformity (1 mark each) (max 3) [3] Limestone permeable/jointed (1) Allows water to move vertically (1) Ing. Impermeable (1) Forces groundwater/water table to surface (1) (max 3) [3] Total 8 marks 18 Question 7 (a) (i) (ii) [6] NW - SE Fault characteristics RF Hollintree Fault Direction Angle (degrees) SW 74 Dip direction and angle (degrees) Downthrow direction Throw (in metres) N.E Orientation (direction) of the principal stress component (σmax) Fault type (b) [1] South Craven Fault Direction Angle (degrees) SW 82 SW. 325 m (300-350) SW-NE (or either) No data Not required Reversed/compressional/ normal tensional (i) Graben/rift valley (1) [1] (ii) Rocks are less resistant to south (1) UCM are mudstones/ more prone to erosion (1) GL DBL are limestones/less prone to erosion (1) No credit for they have been downfaulted) (max 2) [2] Total 10 marks 19 Question 8 (a) (b) (i) Horizontal line at ~250 m (1) [1] (ii) Overlying horizontal limestone (1) Description of folding (1) - NE - SW axial plane trend (1) - overturned in places (1) - isoclinal/vertical/steeply folded Ing.(1) - anticlines/synclines (1) Reference to faulting (1) (max 3) [3] Dam site Advantage - Limestone and Ing. - strong suitable support for dam Disadvantage - Limestone may be prone to collapse - Carbonation, underground caverns, karst features - Leakage through/under dam - dam site wide - large dam needed - boulder clay impermeable but questionable stability - strongly folded rock may be prone to fracturing Reservoir Advantage - elongated, deep glacial valley that narrows reduces evaporation - Ing. proven to be impermeable (spring line) - Spring/river to provide water supply - clean water supply through limestone - Boulder clay - impermeable. Disadvantage - leakage through limestone - permeable/pervious - will not fill to capacity above unconformity - need for grouting joints/fractures/faults - river silting - faulting (reactivation!) leakage along shatter zone - mineral vein contains lead – pollution (max 6 marks) [6] Total 10 marks 20 GEOLOGY GL5 THEMATIC UNIT 1 QUATERNARY GEOLOGY Q.1 (a) (b) Western terminal moraine identified (Reserved 1) Till (lodgement) showing orientation stops at terminal moraine (1) (No till west of) terminal/end moraine (1) Fluvio-glacial deposits to west of terminal moraine (1) Fluvio-glacial deposits show flow to the west. (1) (Max 2) (i) (ii) (c) (d) [2] Fluvio-glacial/river (1) Outwash from melting glacier/meltwater (1) Cross bedding/produced/indicates river direction (1) [2] Ice deposition/recessional moraine (1) Formed when glacier was static (1) During deglaciation/ablation/warmer period (1) (Max 2) [2] Laminated clay = low energy of lake (1) Pebbles = drop stone from ice blocks adrift in the lake (1) (Alternating layers =) seasonal fluctuation in melting/energy level (1) Coarse - spring melt (1) Fine winter freeze.(1) More energy / less energy related to grain size (1) (Max 4) [4] Radiocarbon / radiometric dating (1) of organic material washed in (1) from top and bottom of the sequence (1) Counting annual varve layers (1) (Max 2) [2] Total 12 21 Q.2 (a) (i) (ii) (iii) Current ripples (1) No bedload movement/not enough energy / velocity (1) Greater amplitude / thickness / depth (1) Greater wavelength/distance between crests (1) [1] [1] [2] (b) Internal structure (1 Reserved) Current (wind accepted) flow direction (either direction to match sketch) (1) Erosion of stoss slope (1) Deposition on lee slope by eddies (1) Evidence of advancing ripple crests relating to internal structure (1) (Max 3) [3] (c) Coarse-grain (lag deposit) on base = Upper planar beds. (1) = High velocity flow/energy conditions of deeper channel (thalweg) (1) Medium-grained sand = Cross bedded aqueous dunes (1) = Moderate energy of point bar/ lower water velocity (1) Fine-grained sand = Cross laminated current ripples (1) = lowest energy / velocity shallowest water at top of point bar (1) Fining up sequence - as meander migrates and energy decreases. (1) Cycle repeated with subsequent meander (1) (Max 4) [4] (d) Difference - symmetrical ripples formed by waves (1) Reason - orbital movement of water rather than unidirectional (1) [2] Total 13 22 Q.3 Describe and explain how variations in the Earth's rotation and orbit (as proposed by Milankovitch) and the distribution of continents and mountains in the Quaternary may affect global climate. Eccentricity of orbit - shape of the Earth's orbit changes over 100,000yrs from circular to elliptical Axial Tilt - angle varies between 24.5 and 21.5 deg every 41,000yrs Procession of equinoxes - Earth wobbles on its axis. The time of the year at which Earth is nearest to sun changes over 23,000yrs. Effect of each is minor but they may combine to significantly alter distribution of solar energy between hemispheres. Results in climatic fluctuations - warmer and colder conditions (Interglacial/glacial). Credit diagrams. Distribution of continents and mountain ranges controls oceanic and atmospheric circulation. Climatic belts influenced. Continents at poles/surrounding poles - Ice Caps form (Antarctic/Arctic.) Northern Hemisphere - continents surround the Arctic Ocean preventing warm influence of major ocean circulation from Tropics. Southern Hemisphere - Antarctica - land cold covers S Pole. (radiant energy from sun at low angle / reflected) Position of mountain ranges - restricts or encourages the movement of winds e.g. Himalayas Rain shadow effects. Total 25 23 Q.4 With reference to examples, describe and explain how geological structure and lithology control river drainage patterns, underground river courses and groundwater flow. Structure - joints, folds, faults, bedding planes, other boundaries (unconformities, igneous contacts etc.) Dip of strata. Lithology - resistance of rock to weathering/erosion. Examples - crystalline rock versus drift/sedimentary rock. Degree of lithification/cementation. Composition of rock (e.g. sandstone versus clay) Related to above: Drainage patterns - Radial drainage (Lake District, volcanic peak etc.) - Trellised drainage (e.g. related to cuestas). - Effect of dip/joints. Underground river systems - Limestone caverns and water courses. - Dry valleys. Springs. Groundwater flow - nature of rock - porosity/permeability. Credit examples and diagrams. Holistic - depth v breadth. Total 25 24 Q.5 (a) Describe the principles of the radiocarbon (14C) dating technique. 14 N changed to 14C by cosmic rays. Decays back to 14N at a constant rate. 5730 years (half life) 14 C in atmosphere is constant - replenished by cosmic rays. 14 C is absorbed by living organisms - thus proportion in living organisms is constant with atmosphere. Detailed consideration of method of age determination sufficient for high/full marks: On death the 14C decays but is no longer absorbed. Proportion of 14C compared to non-radiogenic carbon decreases compared to atmosphere with time. Decay curve. Labelled/discussed. Used to date death of organism in years B.P. Unreliable over 50, 000 years - thus only recent organic material can be dated. Other errors - carbon pollution of the atmosphere etc. (b) Discuss the extent to which fossil plant remains provide evidence for climatic fluctuations in Britain during the Quaternary period. Fluctuations relate to changes from glacial to interglacial periods. Maximum marks only if discussion is made of the "extent." Plant - Pollen diagrams in particular Fluctuating climate causes changes in vegetation recorded in pollen samples Relative abundance of pollen species indicates climate (interglacial lake deposits) Glacial/pre-temperate climate - birch dominates As climate warms - oak, elm, alder and hazel become abundant As climate cools the pattern is reversed with deciduous trees replaced by evergreens (fir and pine) and finally birch. Plant fossils mainly on land - poorer environment for preservation but often washed into lakes/sea where preservation is better. Pollen is small and grains are tough - better for preservation. Pollen is very abundant and widespread. Other plant remains - leaves/ stems/ roots - evidence of type and climatic regimes based on Principle of Uniformitarianism. 25 marks 25 THEMATIC UNIT 2 Geology of Natural Resources Section A Q.1. (a) gravity (settling)/of dense /early-formed / high M. Pt. minerals / non-turbulent (1) e.g. Li / Be / Sn / W / U (1) hot aqueous (circulating) solutions/volcanic association/black smokers (1) Cu ( Mo / Au / Ag ) (1) (b) (i) [4] Description: 1 of : pockets where limestone well-jointed/weathered/eroded (1) Explanation: 2 of: due to jointing and faulting (1) increases porosity / permeability (1) increases water activity / solution (1) pockets restrict erosion of bauxite (1) [3] (ii) Wet and dry seasons (1) / intense chemical weathering (1) [2] (iii) 3 of: chemical weathering of limestone (1) /removed in solution (1)/ insoluble residue (1) / hydrated aluminium oxides (1) [3] 12 Marks 26 Q.2. (a) (i) (ii) (b) (i) (ii) thicknesses / dips (1) symbols (1) [2] fold (1) unconformity (1) [2] Cap rock: halite (1) Reason(s): permeable sandstone / reservoir rock / beneath impermeable (halite / shale) prevents upward migration of hydrocarbons (2) Name: [3] unconformity (1) Description : folded / antiformal / source and reservoir rocks eroded / truncated against(erosional) surface/ (plane of) unconformity (2) [3] (c) Small/abundant/preserve well/widedistribution/environment al indicators /easy to recover/age/stratigraphy/P-T indicator/use in identifying source rock. [3] 13 marks 27 28 Section B Q.3 (a) Describe briefly the method of extraction of one named geological raw material. (b) Discuss how the extraction might impact on a nearby community and how the impacts may be reduced or controlled. Named Method of extraction: e.g. Environmental problems : removal of overburden description of quarrying/mining methods strategy relate to shape of "deposit" blasting ? removal/machinery accept labelled diagrams waste/ground pollution including visual/ noise/dust / drainage / wildlife etc. conservation buffer banks/tree barriers/timings of blasts drainage/treatment/reclamation etc. Total 25 29 Q.4 Describe one geophysical and one geochemical technique use to prospect for mineral resources. In each case name a mineral for which the technique might be suitable and explain any limitations that the technique might have. Geophysical: Named resource Techniques - Description - e.g. e.g. oil / gas seismic gravity explosions/ land/ ship/ reflection/ record of 2way time/ graphical representation to identify structures/ oil traps - magnetometer/ land/ plane/ ship/ graphical representation of magnetic readings/ depends on changes in magnetic properties or distribution of rocks i.e. structures - gravimeter/ land/ plane/ ship/ changes in gravity/ changes in density of the underlying rocks/ reflects the structure(s) graphical representation (including labelled diagrams) Geochemical: Named resource - Technique - Limitations : e.g. tin / copper / (name of mineral) stream sampling / water / sediment / soil (auger) /(vegetation) laboratory investigation / chemical analysis (atomic absorption) spectrometer laboratory and site for mineral/sediment identification plotted on map to locate (approx?) location of source / deposit e.g. e.g. gravity requires sharp density contrast stream sampling / laboratory back-up Total 25 30 Q.5 Describe and explain how rock properties and geological structures influence the accumulation and flow of ground water. Properties: Porosity N.B. Need descriptions for full marks = Permeability = Grain size permeability % age pore space rate of flow of fluid through rock in m/s = smaller the grain size higher the porosity lower the (unless perfect spheres! – accept lower permeability but same porosity) Grain shape = greater the sphericity greater the porosity and permeability Sorting = greater the sorting higher the permeability / porosity (?) Packing = tighter the packing lower the porosity and permeability Compaction = greater the compaction lower the porosity and permeability Cementation = greater the cementation lower the porosity and permeability Structure: Structure of aquifers e.g. confined (as London Basin) (credit perched in correct context i.e. structure) Diagrams. Must be well-labelled or explained. (Properties/structure Macro / micro fracturing = greater the fracturing higher the porosity and permeability) Accumulation/flow Porosity = Permeability = %age pore space = accumulation rate of flow of fluid through rock in m/s = flow Holistic: breadth versus depth. Total 25 31 A2 THEMATIC UNIT 3 Geological Evolution of Britain Section A Q.1 (a) Evidence : Cross-cutting/truncation/overlie/overstep/overlap/strata (ages) missing e.g. between Skiddaw Slate and Mell Fell Conglomerate or between Ordovician/Devonian or Ordovician/Carboniferous or Devonian/Carboniferous) (Any 2) Stratigraphic age : as chosen (1). [3] (b) (i) (ii) (iii) Type of plate boundary: destructive/subductive (1 Reserved) Reasons: 2 of: volcanicity with qualification (e.g. andesitic/ pyroclastic etc) (1) plutonic igneous activity with qualification (e.g. granitic/silicic etc) (1) folding (1) regional metamorphism/slate (1) [3] Trend: NE/SW (1) Reason: strike of Ord strata / strike of axial planes / NW – SE compression (1) [2] Caledonian (1) [1] (c) Marked as a whole such that palaeoenvironment / evidence / explanation match. Palaeoenvironment: fluvial/deltaic/alluvial/(terrestrial) (1) Evidence: channels/rounding/sorting/fans/red/ cross-bedding to the east (1) Explanation: water transport / flash floods / red (oxidation) etc (2) [4] 13 marks 32 Q.2 (a) Description: Name: 3 of: angular (to sub-) (1) non-interlocking (1) (very) poorly sorted/unsorted / stated grain sizes (1) fine-grained matrix / matrix supported (1) sandstone/arkose/feldspathic sandstone (1) [4] (b) Two of: Fossil: Rock-type: Environment: poor preservation/destroyed/washed away (1) medium/coarse grains poor for preservation (1) subaerial (accept "float away" or equivalent) high energy/erosion (1) [2] (c) (d) Grain shape: little transport / close to source (1) high energy environment (1) variety of possible environments/no water or wind? (1) Mineralogy: feldspar = little chemical weathering of feldspar/ lack of water? (1) little transport/close to source (1) relevant (negative ?) comment with respect to quartz (e.g. very poor environmental indicator) (1) [5] (to match answers to (c) ) e.g. terrestria/fluvio/deltaic [1] 12 marks 33 Section B Q.3 Discuss the extent to which the occurrence of greywackes and their sedimentary structures, interbedded with black graptolitic shales, indicate that parts of Britain once experienced deep-water marine conditions. Greywackes description: texture/mineralogy turbidites/bottom of continental slope "any" environment/ rapid deposition Black anaerobic/lack of oxygen deep water/ocean floor could be shallow(er) – just lack of oxygen Graptolitic pelagic/fragile/pyritisation - float into deeper waters/lack scavengers/weathering/erosion found in deposits of all depths extinct - problematic preservation/shale key feature Shales fine-grained / travel distance /sorting - no current any depth Sedimentary grading structures description: fining upwards/rapid deposition from turbidity currents (Any valid sedimentary structure with context e.g. current bedding; bottom structures etc.) Early Palaeozoic age for deep water as indicated by graptolites = zone fossils Allow "negatives" e.g. lack of brachiopods, corals, trilobites, limestones etc, etc. Total 25 34 Q.4. Describe and explain the evidence that suggests the past existence of shallow, tropical marine conditions in what is now Britain. Where possible outline any other possible interpretations of the evidence. Rocks: Fossils : Limestones: Bioclastic: formation of: shelly/coral/reef (/crinoidal) Oolitic: Bahama Banks / warm seas rich in calcium carbonate Chalk: deep-water oceanic/some shallow fossils Corals warm, shallow, marine conditions Brachiopods warm, shallow, marine conditions / less reliable (Crinoids etc) All strong on Law of Uniformitarianism: present-day reef conditions tabulate/rugose extinct deep-water corals ? Accept evaporites in context. Dolomites. Total 25 35 Q.5 Describe and explain the palaeoclimatic and the palaeomagnetic evidence which suggest that Britain was much closer to the equator in the Permo-Triassic than it is today. Red sandstones/breccias : description/significance of textures/mineralogy (quartz/ haematite) sedimentary structures – dune bedding etc lack of fossils running-water deposits/braided streams/wadi deposits Red shales / evaporites : description sedimentary structures – desiccation etc. fossils absent (/rare/exotic) Pre and post Permo-Triassic evidence of low latitudes e.g. swamps of Carboniferous and warm, clear marine seas of the Jurassic. Palaeomagnetism: iron-rich/haematite-rich beds possible to get data from red sandstones but difficult any reliable data would give low angle of magnetic dip/inclination discussion of origin of remanent magnetism in sedimentary rock re depositional origin in water and post-depositional (e.g. cementation) Credit realisation of no igneous rocks on mainland Britain but: Credit outline of remanent magnetism in e.g. basalts re Curie Pt etc. Could use igneous rock in other regions of plate. Total 25 36 THEMATIC UNIT 4 GEOLOGY of the LITHOSPHERE Q.1 (a) (b) (c) (i) Arrow at appropriate location. (1) [1] (ii) ~90km (Accept 85 -95) (1) [1] (iii) magnetic / iron minerals in magma (1) orientation in direction of magnetic field (1) locked when magma falls below Curie Temp / solidifies (1) reversal in polarity from normal with time (Reserved 1) (1 Reserved plus any 2) [3] (i) Distance/Time in working (1) ~ 4.5 (accept 4.0 to 5.0 incl) cm/yr (1) (ii) Explanation of the radiometric dating of: Mantle plume (hotspot) volcanic island chains (2) Accept also Ocean floor sediments / thickness and distance from ridge (2) Basalt rock samples dated plus distance from ridge (2) Thickness of lithosphere v distance from ridge (2) (Max 2) [2] Pacific (1) Ocean ridge is not central in Pacific/MAR is central in Atlantic (1) Ocean basin biggest (wider) in Pacific (older)(1) Pacific surrounded by trenches (few in Atlantic) (1) Subduction well underway at edges/ minor in Atlantic (1) Faster spreading rate in the Pacific (1) (4 max) [4] Total 13 37 Q.2 (a) (i) Continental crust Ocean crust Upper mantle Composition ANDESITIC / Granitic (silicic) / granodiorite ("any" non-basic / ultrabasic) Basaltic (mafic) Peridotite (ultramafic) Relative Density 2.7 3.0 (accept 2.9 or 3.0) 3.2 [2] (ii) (iii) (b) Mass = density x volume. (1) Pressure related to mass above (1) M and N have different densities (1) and volumes above = same mass (1) Or equivalent (max 2) [2] Moho will rise beneath M (1) and sink beneath N (1) As lithosphere seeks to maintain isostatic equilibrium.(1)(max 2) [2] (i) (ii) 4. Top OCEAN SEDIMENT 3. PILLOW LAVA 2. SHEETED DYKES 1. Bottom LAYERED PERIDOTITE (4 correct = 2 marks, 2 correct = 1 mark) [2] Y is OLDER 1) Ophiolite represents Ocean crust (1) during subduction at convergent (destructive margin)(1) Obducted/scraped into accretionary prism (1) Younger deposits are thrust/faulted (1) beneath older (underthrusting) (1) Credit annotation of diagram. (1) (Max 4 marks) [4] Total 12 38 Q.3 Describe and explain how a study of earthquake body waves provides evidence for the variation in thickness and mechanical properties of the lithosphere and asthenosphere. Holistic approach Define earthquake body waves. Use of/explanation of formulae for P and S wave velocities. Incompressibility and rigidity versus density for P-waves Rigidity versus density for S-waves Depth profile of P and S waves to show velocity variation. Depth of the Low Velocity Zone with distance from spreading centre. Thickening of the lithosphere with age and distance from ridge. Diagrams credited Definition of the difference between Lithosphere and Asthenosphere in terms of mechanical properties. Lithosphere = plate. Cold (<1300o C isotherm). Brittle thus fractures. Asthenosphere = partially molten (5 %) - Ductile thus flows. Total 25 39 Q.4 (a) Describe the variation in surface heat flow across a spreading ocean basin and active continental margin. Ridge - (High) Thermally varied. High range of heat flow (high to low) temperatures. Above world average. Abyssal plain - (Lower) Thermally stable: low range of heat flow. Below average heat flow. Heat loss greater further from the ridge. May increase above average at a "hot spot" e.g. Hawaii etc. Trench - (Lowest) Coldest lithosphere. Lowest temperature range. Example. Continental margin – (May be) very high adjacent to trench. Moderately high at passive margin. Example Diagrams credited throughout. (b) Explain how surface heat flow relates to plate tectonic and mantle processes within the lithosphere. Ridge - Associated with rising convection current in the mantle at spreading centre. Constructive margin. Heat loss by conduction/convection/radiation. Results from rising magma, "black smoker". Examples credited Abyssal plain - Owing to heat loss by conduction and radiation of older lithosphere as plate moves further from spreading centre. Hot spot - relates to "mantle plume". Associated with "mantle dynamics" rather than "plate tectonics". Trench - as ocean plate descends before subduction. Descending currents. Oldest lithosphere - max time for heat loss. Continental margin - Melting of subducting plate (and/or overlying mantle/continental root). Rising andesitic magma. Examples. Effect of water on melting temperatures. Diagrams credited throughout. Holistic approach if there is overlap between (a) and (b). 40 Q.5 (a) Describe, with the aid of labelled diagrams, the differing geometry of flexural (parallel) and flow (similar) folds. Description of each using diagrams. Quality of the diagrams to show key features (limb and hinge thicknesses, inter limb angles etc.) Credit field evidence and examples. (b) Discuss the different conditions under which rocks of the same type can undergo either brittle or ductile deformation. Reference to: Brittle and ductile defined. Stress/strain curve. Hookes Law. Brittle deformation structures (jointing, faulting - related to earthquakes etc.) Ductile deformation structures (types of folding - flow, metamorphic effects) Deformation variations in SAME rock type depends upon: 1. Temperature 2. Confining pressure 3. Time 4. Pore fluids Stress/strain experiments illustrating above variables Total 25 GCE Geology MS/(June 2003) 41 Welsh Joint Education Committee 245 Western Avenue Cardiff. CF5 2YX Tel. No. 029 2026 5000 Fax. 029 2057 5994 E-mail: [email protected] website: www.wjec.co.uk/exams.html