General Certificate of Education Tystysgrif Addysg GyffredinolAdvanced Subsidiary/Advanced Uwch Gyfrannol/Uwch

MARKING SCHEMES

SUMMER 2002

GEOLOGY

INTRODUCTION

The marking schemes which follow were those used by the WJEC for the 2002 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.

GL1

Question 1

(a) (i) A - North West – West.B - North West – West.C – East.(3 correct = 2 marks; 2 correct = 1 mark)

[2]

(ii) A. (1)Furthest from ridge. (1)(Credit reference to sea floor spreading.)

[2]

(b) (i) Basalt. (1)[1]

(ii) Labelled diagram

To include- Pillow lava;Rounded structures - 0.3 - 1m;Convex tops/tapered bottoms/sag structures;Glassy outer layers;Presence of vesicles.

[4]

(iii) Thinner towards B/thicker towards A. (1)Seafloor spreading from ridge towards A thus A has more time to accumulate sediment. (1)

[2]

(c) (i) Andesite. (1)(Credit basalt if explained correctly in (ii).)

[1]

(ii) Basaltic crust subducted at trench. (1)Partial melting of basalt produces andesite. (1)(Credit partial melting of mantle produces basalt.)Contamination of melt by oceanic sediment.(Credit labelled/annotated diagram.)

[2]

Total 14 marks

1

Question 2

(a) X – Stipe. (1)Y – Theca. (1)

[2]

(b) (i) On graph.Lower Ordovician (1) to extinction in Lower Silurian. (1)

[2]

(ii) Age - Middle Ordovician. (1)Only series in which all present. (1)

[2]

(c) 1. Change in number of stipes (1)- many to one. (1)2. Change in orientation of stipes (1) from pendent to scandent. (1)3. Change in complexity of thecae(1) Simple to complex. (1)

Max 2 each.[6]

(d) [4]

Factor Assessment of use as zone fossils Explanation

Evolutionary change with time

Good Rapid evolution in short time ranges

Widespread distribution

Quite good Planktonic - distributed by ocean currents

Ease of fossil identification (Very) good Easily identified, forms very

distinctive.

Ease of preservation

Poor Fragile, easily destroyed

Degree of facies independence

Poor/low Found preserved mainly in shales.

Total 16 marks

2

Question 3

(a) Lava flow. (1)Concordant. (1)One baked margin. (1)Upper weathered surface. (1)Included fragments in the mudstone.(3 max)

[3]

(b) (i) X - Mud crack/desiccation crack. (1)(Accept solution/karstic feature, or fossil plant root.)

Y - Cross bedding/dune bedding. (1)[2]

(ii) Limestone Shallow marine lagoon (1)or Terrestrial/lake (1)carbonate - evaporites (1)low energy - fine grained (1)plant remains - close to land (1)drying out/very shallow - mud cracks. (1)

ORSandstone - Wind dominated/arid/desert/aeolian –

red oxidation (1)rounded grains(1) well sorted grains (1)dune bedding. (1)

(Max 3 marks)[3]

(c) Marble - Base of Lava B/limestone. (1)Baked margin of lava flow/contact met. of limestone. (1)(Max 2.)

Spotted rock - Lava A/shale (1) or Xenolith in Lava A. (1)Baked margin of lava/contact met of shale. (1)(Max 2)

[4]

(d) (i) Must explain not just state:-

Baked margin on top of lava - not base. (1)Weathered/erosion surface underneath lava - not on top. (1)Included fragments of lava in mudstone /limestone - lava older. (1)Shale xenoliths in lava A -shale older. (1)Cross bedding is truncated at the bottom/ is convex upwards. (1)Mudcracks point upwards. (1)(Max 3)

[3]

3

(ii) Credit field diagram(s)/written description and explanation of different Sedimentary Structure that has:-

Named sedimentary structure; (1)A specific location; (1)Scale or other measurements e.g. dip etc.; (1)Quality of drawing/description; (2)Explanation of how it is used to indicate way up. [5]

Total 20 marks

Question 4(a)

Layer Description Mantle (1) The layer of similar composition to stony meteorites.

Outer Core (1) The layer of zero rigidity.

Inner Core (1) The solid layer of similar composition to iron meteorites.

Outer Core (1) The layer in which the Earth's magnetic field is generated.

[4]

(b) Incompressibility (bulk modulus) increases.Compressibility decreases.Rigidity (shear modulus) increases.Elasticity decreases. (1)

At greater rate than increase in density. (1)(2 max)

[2]

(c) Ocean (basalt) crust - 7km. (1)Continental (granite) crust – 65km(mean 35km). (1)Ocean crust is subducted at destructive plate boundaries. (1)Continental crust resists subduction. (1)Continental crust thickens with plate collisions/orogenesis. (1)Credit sedimentation effects. (1)Credit impact of erosion. (1)Credit impact of volcanic activity. (1)(4 max)

[4]

Total 10 marks

4

GL2

SPECIMENS

A = Sandstone (arkosic/Millstone Grit)

B = Dolerite

D1 = Goniatite

D2 = Pyrite

MarksQ.1 (a) Response

Must have reference to: 1fragmental/clastic (accept reference to grains)

State or develop: (1 or 2 of the following)size: medium or coarseshape: angular through to roundedsorting; moderate/no matrixcement/porosity. 2 max 3

(b) Asymmetrical ripple marks:Must have reference to:

current 1Development:

transporting bed loaderosion on upstream side,deposition on lee (accept diagram) 1

Cross-bedding:EitherMust have reference to:

current 1Development:

lee slopes of migrating ripples/aqueous dunes(steeper fronts) preserved 1

Or orMust have reference to:

point bar/slip off slope deposition 1Development:

lateral shift of meandering channel 1

Erosional base:Must have reference to:

erosion of channel (bed/banks) 1Development:

due to high energy conditionse.g. flood flow/lateral migration of channel 1 6

5

MarksQ.2 (a) crystalline

medium (1-2mm)mafic/dark colouredmineralogy (Fe-Mg /feldspar) any 2

Dolerite 1 3

(b) (i) Must have reference to:contraction (due to cooling) 1

Development:sheet of liquid magma cools and freezesjoints form due to internal stresses(polygonal pattern)columnar joints(accept diagrams) 2 max 3

(ii) has the same horizontal structure as the country rock (same outcrop pattern/ no cross-cutting) 1 1

(iii) intrusion shows moderate rate of cooling = medium texture 1 1

(iv) State or develop: (1 or 2 of the following)chilled margin at top and base of sillbaked margin above and below sill in the country rockoff-shoots or veins going up into country rockxenoliths at the top of the sillvesicles at the top of the silltransgressions(–ve arguments for lava are acceptable) 2 max 2

(v) Any 2 of the following: (accept any other reasonable statements)hard hatstout footwearno running /climbing on steep slopesdon't work immediately below another personwalk across scree in single filegoggles in context (e.g. acid test) 2 max 2 max

Q.3 (a) (i) 1 drawing 4 max2 drawings 5 maxTo include:scaleside shape ("circular")end shape ("squat")involute shellsuture line 5

6

Marks(ii) simple/early suture line

"angular' rather than "straight"/credit "saddles" and "lobes" 2 max(early suture) goniatite (accept ceratite but not ammonite) 1 3

(b) (i) colour: (brassy) yellow/gold 1lustre: metallic 1streak: dark/dark grey/black 1hardness: not scratched by steel pin/Mohs' Scale 5.5 1 4

(ii) pyrite 1 1

(iii) Must have reference to:Petrifaction/replacement/pyritisation 1(do not accept mould and cast)

Development:e.g. process: removal of outer shell/impregnatione.g. environmental: oxygen poor (anaerobic)

(deep sea) waters/muds 1 2

Q.4 (a) Folds are symmetrical (450 dip of limbs) 1but on a NE – SW trend (not NW-SE) 1and a wavelength of 450m (not 225m) 1 3

(b) (i) a sinous/(slightly) curved line 1vertical (90) 1to the east/south east/"right" 1 3

(ii) reversed 1 1

Q.5 (a) horizontal base of C to west of F1 and east of F2 2fault F1 (dip to north west e.g. 70-80) and arrows (downthrow SE) 2 maxfault F2 (90 dip) and arrows (downthrow W) west of F1 2 maxvertical fold axis (antiform); limbs 35-55 between F1

and F2 2 maxvertical fold axis (synform); limbs 35-55 east of F2vertical fold axis (antiform) (beneath uncon); limbs; 35-55 2 max 11

(b) F1 and F2B (emplacement/intrusion of sill) 1C 1Uncon 1folding (NE-SW trend) 1EDA 2 max 6

7

GL3

Question 1

(a) Landslip younger than glacial deposits/last 10,000 years. (1) [1]

(b) Explanation may include:

Presence of fault - movement/vibrations.Lithology (impermeable and/or weak shale/coal layers, permeable sandstones).Groundwater regime

Heavy rain/saturation- increase pore pressure/reduces friction (not water table alone - only if qualified e.g. high).

Weathering/load - gravity effect.Angle of slope (oversteepened valley side) - gravity effect.Shrinkage/expansion – stresses.Ground vibrations (not traffic) - reduces friction.Post-glacial melting of permafrost - saturated soil on slope.(2 for each explained)

[4]

(c) (i) Drain water from slip. (1)Lowers the water table. (1)Reduce pore pressure at slip surface/increase friction of grains/slip plane. (1)Lubrication reduced. (1)Other sensible.(2 max)

[2]

(ii) Increased weight/support for slip toe. (1)Prevent further movement/prevent erosion. (1)Other sensible.(2 max)

[2]

(iii) Stability will decrease. (1)Meandering river - will change its course. (1)Toe removal by erosion increases instability - no support. (1)River levels may rise - flooding & increase saturation/erosion. (1)Increase saturation - instability from lubrication/soil flow. (1)Other sensible. (1)Credit annotation of diagram.(Must explain for 3 marks; just stating =2 max.)(3 max)

[3]

Total 12 marks

8

Question 2

(a) (i) Description - e.g. 3 main area etc. (1)Area in North. (1)Description of associated rock ages. (1)

Associated with granite. (1)

Explain Granite Uranium rich. (1)Radioactive breakdown by-product. (1)Associated with granite (if not already given).(Describe 1, explain 1, plus 1 other.)

[3]

(ii) Radioactive. (1)Health risks (poisonous/toxic/cancerous etc. (1)(max 1)

[1]

(b) (i) One reserved from:Gas in solution in groundwater. (1)Lower pressure in cave - comes out of solution. (1)

Additional answers:Groundwater flows down fault/fracture zone. (1)Joints/bedding in limestone and granite provide pathway. (1)Credit annotation on diagram.(3 max)

[3]

(ii) 1. Clay Impermeable. (1)Clay particles/pores small. (1)

Pores not connected/sealed. (1)Few fractures/joints. (1)

or

2. S & G - Permeable. (1)High porosity/large pores/not cemented. (1)

Pores connected. (1)Characteristics of sediment (sorting/rounding). (1) [3]

(c) Prior to earthquake cracks open/stress increases. (1)Radon gas escapes. (1)Detected radon gas levels rise. (1)Dissolved gas levels in groundwater (wells) increases. (1)Radon levels level off until earthquake. (1) (3 max)

[3]

Total 13 marks

9

3. (a) Describe how porosity and permeability affect the suitability of a rock as an aquifer. [10]

(b) Explain how overuse of aquifers may result in two of the following:

1. local exhaustion of the water supply;2. saltwater incursion in coastal areas;3. surface subsidence. [15]

(a) Porosity/permeability/aquifer defined.

Porosity depends upon packing of grains;shape of grains;sorting of grains.

Permeability depends upon connectivity of pores;size of pores;joints and fractures.

Credit structures if related to permeability (artesian basins/confined/unconfined aquifer).Good aquifer depends upon good permeability/specific retention.Case studies given credit.

[10]

(b)1. Cones of exhaustion related to overpumping explained.

Pumping exceeds recharge.Credit case studies.(7 plus pos 1)

2. Cones of exhaustion result in pressure difference which draws in saline water in coastal areas.Credit case studies.(7 plus pos 1)

3. Reduction in pore pressure results in restructuring of particles subsidence.Credit case studies.(7 plus pos 1)

[15]

Total 25 marks

10

4. (a) Outline the geological problems associated with the disposal of highly toxic and radioactive waste. [10]

(b) Explain how these problems may be overcome by good site selection and engineering practice.

[15]

(a) Nature of toxic and radioactive waste. Defined.Length of time unstable, half-life - millions of years.Considerations:

Concentration and total containment.Patterns and consequences of environmental damage.Prediction p.f. natural hazards that may threaten containment.Site properties - groundwater flow and lithological characteristics.(Max 10 marks)

(b) Case studies credited. e.g. Sellafield.Examples of suitable lithologies, groundwater/site characteristics.

Disposal options include disposal in:Deep mined repository.Surface mined repository - easier monitoring but greater shielding.Deep wells.Ice sheets.Ocean trenches.Space.

Problems with each.(Max 18 marks)Holistic view overall as some overlap may occur.If not specific related to Toxic or Radio Active disposal. (max 5)

Total 25 marks

11

5. (a) Outline the potential benefits of living in a volcanically active region.[5]

(b) Explain why the hazards associated with lava flows depend upon the characteristics of the magma erupted. [10]

(c) Describe, with reference one or more case studies, how the destructive effects of volcanoes may be managed and controlled. [10]

(a) Good soils.Geothermal power. (3 marks max for stating)Tourism.Other (e.g. mineral water -Volvic).Explained/developed and/or using examples. (2 marks max)(Max 5 marks)

(b) Types of magma - mafic/intermediate/silicic.Various magmas have different characteristics that affect viscosity.- magma sources, (Divergent v Convergent with exceptions (Etna, Hawaii).- composition, (more silica rich - more viscous).- gas content, (higher gas - more viscous).- temperatures, (cooler at front of flow thus more viscous).

Viscous lava - Slow moving (10's m/hr to few m/day).- ample warning - confined to steep slopes.- erupt at lower temperature.- associated more with other hazards (pyroclastic flows/ash etc.).

Non viscous - Fluid - Fast moving (initially few Km/hr).- less warning but rarely kill (except - Nyirongongo, Zaire in 1971).- flows further - more hazard to property on lower slopes.- hotter initially.

Hazards associated with agricultural land, roads, bridges and buildings. Examples (Etna, Nyirongongo, Iceland, Hawaii etc.). (10 marks)

(c) Discussed using examples. Ultimately little management/control if people choose to live near volcanoes.Case studies - Iceland, Etna etc. No case studies (max 7).Evacuation, hazard mapping, diversion/blocks, dropping-spraying with water, explosion of flow margin, prediction devices. (10 marks)Holistic approach as (a), (b) and (c) may be linked.

Total 25 marks

12

GL4

Section A

Question 1

(a) (i) On graph. 1 mark between each chilled/baked margins.[2]

(ii) Upper baked margin. (1)[1]

(b)

Describe Explain

Large size - 280m. (1) Thus too big for lava flow. (1)

Metamorphism above sill.Two baked margins. (1)

Thus intrusive not extrusive orLava - only one, lower baked margin. (1)

Description of metamorphic evidence above sill - hornfels/index minerals. (1)

Must have been baked after mudstone deposited.

Differentiation is unlikely in a lava flow.  (1) Cools too quickly. (1)

Grain size large for a lava flow. (1) Lava cools quickly. (1)

No weathered top/sharp contact. (1) Not exposed to surface. (1)

Other sensible. (1) Explained. (1)

(1max for description if no explanation)[2]

(c) (i) Olivine rich layer between 30m - 60 m. (reserved 1)Olivine in the chilled margins. (1)Olivine increases from100m down to 60 m (or lower sill). (1)Olivine absent between 100m - 280 (or upper sill). (1)(Max 3 marks)

[3]

(ii) Olivine - first to crystallise in Bowens Reaction Series (1) - high crystallisation temp. (1)- more dense than other feldspar/augite. (1)- sinks in liquid magma/gravity differentiation. (1)- trapped at chilled margins/unable to differentiate/rapid cooling. (1)

No turbulence/thermal convection. (1)(Max 4 marks)

[4]

13

(d) (+ M) in either chilled margin. (1 reserved)Original melt cools quickly/crystallises. (1)No time for differentiation/crystal settling. (1)Partial melting of mantle peridotite gives plag/augite/olivine. (1)(1 reserved + other)Credit other explained possible alternatives.

[3]

Total 15 marks

Question 2

(a) (i) Stress - Force per unit area. (1)Strain - Change in volume or shape/deformation (1)

[2]

(ii) The higher the temperature:- the more ductile. (1)- the more stress needed to reach the fracture point. (2)- the greater the stain achieved prior to fracture. (2)(Or visa versa).(2 max)

[2]

(b) (i) 0 - A = Elastic. (1)B - C = Ductile flow/Plastic. (1)

[2]

(ii) A - same height as 0. (1)same width as 0. (1)Elastic - non permanent deformation explained. (1)(Max 2)

B - Smaller than 0 but taller than C. (1)Bulging (not fractured). (1)Ductile - permanent deformation explained. (1)(Max 2)

[4]

(c) Elastic up to fracture point. (1)No ductile zone/Brittle. (1)Permanent deformation/fracture/ruptures. (1)Stress proportional to strain. (2)(Max 2)

[2]

14

(d) Rocks that flow are ductile - fold (1) when stresses exceed yield strength. (1)Rocks that fracture are brittle - fault (1) when stress exceeds fracture strength. (1)Rocks near surface are colder/more brittle thus fault. (1)Rock deeper are hotter/more ductile thus fold. (1)

Credit also mention of:Effect of depth on greater confining pressures (folds). (1)Time - Slower application of stress (folds). (1)Elastic deformation - elastic rebound (earthquakes). (1)(Max. 3)

[3]

Total 15 marks

Question 3

(a) (i) Limestone – calcite/calcium carbonate/dolomite. (1)Mudstone – clay minerals or specific example-kaolinite etc. (1)(Max 2)

[2]

(ii) Mudstone. (1 mark)Explain (2 marks max). 2 valid statements from:

Clay minerals most chemically varied (complex silicates).Clay minerals most unstable under higher temperatures.Chemical elements re-combine to form more stable minerals.

(Credit examples such as andalusite/chiastolite).Sandstone and limestone recrystallise with little mineral change.(Credit sandstone - clay changes to mica - 2 max).

[3]

(b) (i) Increase in grain size. (1)Change from clastic to crystalline. (1)Loss of sedimentary structures/fossils (1)Credit reference to hornfelsic/porphyroblastic. (1)(Max 2)

[2]

(ii) Suggested example:

15

Credit - Mineralogy - Quartz and Clay (Reserved 1).(1 max)

Texture - to scale. (1)(3 max)Poor sorting. (1)Sub-rounded quartz grains. (1)

[4]

(c) (i) Xenolith/included frag. etc. (1)Explanation - ref to intrusion of ganite/stoping/detachment of

blocks of country rock (1)[2]

(ii) East side of intrusion very steeply inclined = narrow. (1)West side gently dipping = wider aureole. (Credit sketch up to 2 marks)Credit alternatives - thermal conductivity of rock effect of hydrothermal fluids to west.

[2]

Total 15 marks

Question 4

(a) A = Palaeozoic. (1)[1]

Mesozoic = Permo/Trias boundary to Cretaceous/Tertiary boundary. (1)[1]

(b) (i) Perm/Trias (1)[1]

(ii) 400 - 200 = 200 (1) method.200 * 100 = 50% (1) answer.400.

[2]

(c) (i) Cret/Tertiary boundary. (1)[1]

(ii) Dinosaurs. (1)Ammonites. (1)(Credit appropriate alternatives).

[2]

(iii) Two outlined from: Sea level variations. (2)Climatic change. (2)Vulcanicity. (2)Meteorite impact. (2)

[4]

16

(d) Life with hard parts had not yet developed/soft bodies. (1)Unfavourable preservation. (1)Only Algae, bacteria and medusoids. (1)Fossils destroyed with time (metamorphism, igneous activity, surface processes). (1)Fossils not yet found. (1)Fossil evidence is biased. (1)(3 max)

[3]

Total 15 marks

Section B

Question 5

(a) (i) Distribution - North and South. (1)West/Central/on Black Down/Shipham/Mendip Forest. (1)Confined/associated with valleys. (1)Irregular/ribbon-like /tongues/lobes. (1)Northern dip. (1)East-west strike. (1)Unconformable/cross cutting. (1)Other sensible.(Max 3 marks)

[3]

(ii) 64 (1) - 10 (1) = 54 degrees. (1)(Max. 2 marks)

[2]

(iii) Horizontal bedding drawn. (1)Beds viewed along strike/90o to dip. (1)

[2]

(b) (i) 1016m. (accept 1000 - 1030) (1 accuracy).25.4 or length * 40 (1 method).

[2]

(ii) Irregular unconformity. (1)Tongues of sediment in valleys. (1)Carboniferous valleys drain from anticline crest. (1)Folding and erosion of anticline prior to Triassic. (1)Conglomerate - high energy river. (1)Other sensible. (1)(3 max)

[3]

Total 12 marks

17

Question 6

(a) (i) Outcrop width (North)…..-338m (accept 320m - 350m). (1)Outcrop width (South) ….650m (accept 635m - 665m). (1)

[2]

(ii) Steeper dip (1) narrow outcrop (1) (visa versa).North nearer to true thickness (or equivalent). (1)Topography. (1)(2 max)

[2]

(b) Anticline/Antiform (oldest in centre) (reserved). (1)Asymmetric (variation in limb dips) (reserved). (1)

East - West axial planar trend. (1)Axial plane inclined to South. (1)Other descriptive (1 each) - hinge shape,

open,plunging,locally overturned

Erosion to expose core. (2 reserved plus any two)

[4]

(c) Way up criteria as identified by Described: coral/Lithostrotian (1)

wrong way up (reserved 1)Explained : beds are overturned/inverted. (1)

coral in life position only (1)not transported.(1)Credit diagram. (1)

Other creditable alternatives accepted if described and explained.e.g. desiccation cracks, facing from other fossils (brachiopods etc.) included fragments, etc.(4 max)

[4]

Total 12 marks

18

Question 7

(a) (i) Compare- both in Burrington Oolite. (1)- both dip south. (1)

Contrast- North is overturned/south not. (1)- South has lower dip/north steeper. (1)- Valley location/hill. (1)

Other sensible. (1)(4 max)

[4]

(ii) Steeper dip (1) - less stable friction angle. (1)Brecciated/contorted. (1)Dip variation in area. (1)Limited expansion eastwards – overburden. (1)Flooding in valley. (1)Narrow outcrop thus deep quarry. (1)(2 max)

[2]

(b) Must be geological:

Permeable limestone. (1)Needs to have artificial liner. (1)Leakage of leachate into groundwater/rock. (1)Southern dip of strata/flow of groundwater. (1)Pollution threat to springs/wells/boreholes/reservoir in South. (1)Leakage and problems of methane gas. (1)Subsidence problems. (1)Use of methane as a local fuel source. (1)Credit diagram. (1)Quality of assessment. (1)Other sensible. (1)(6 max)

[6]

Total 12 marks

19

GL5

Theme 1

Question 1

(a) (i) WNW-ESE (or bearing) accept E-W; NW/SE.[1]

(ii) The bearing of the long axis of the clast is identified/Compass is placed along the long axis. (1 reserved)Representative 50 multiple measurements made. (1)Sampling procedure/Random/systematic. (1)Site chosen to be free from mass movement. (1)(2 max)

[2]

(iii) Striations. (1)Drumlins. (1)Roches Moutonee. (1)Orientation of glacial trough. (1)Other sensible.(Any 2)

[2]

(b) End/terminal/recessional moraine – i.e. qualified moraine. (1)deposition at glacial snout. (1)across u shape valley. (1)orDrumlin /drift material (1) shaped by movement of ice form north. (1)orBand of hard rock (1) which has resisted glacial erosion. (1)

[2]

(c) For conclusion (one reserved) fromNo preferred orientation of clast/random. (1)Ice held up by moraine ridge at A. (1)Varved clay indicates dewasting ice. (1)

Critical assessment (one reserved) fromSample error (only 50 clasts measured).Could be several ice flows producing different orientations. (1)Ice from the north mixed with ice from the west. (1)Ablation till. (1)Solifluxion. (1)Freeze-thaw. (1)Fluvioglacial activity along valley margin might re-orientate. (1)(3 max)

[3]

20

(d) Any three from:

River erosion - cutting through moraine.River deposition - Alluvial/floodplain deposits. Scree/breccia - sub-aerial freeze thaw.Head deposits – solifluction.Breccia – landslip.

[3]

Accept - Varve - lake deposits from season ice melt as ice retreated trapping water in a pro-glacial lake.Kettle holes.

Total 13 marks

Question 2

(a) (i) 200 cm/sec.[1]

(ii) 15 mm (+/- 3mm) (1) (Range 12-18mm).[1]

(iii) Range 12-24hours. (1)Credit for evidence of correct method e.g. lines on graph/annotation. (1)

[2]Note:Accurate measurement shows this to be Vel of 124 cm/s. Thus 42 - 24 = 18hrs.Thus Accept 12 - 24 hrs.

(b) Particle shape. (1)Particle density (accept mass). (1)Examples given (1)

[2]

(c) Smaller particles have higher cohesion. (1)Greater charge per unit area. (1)Water can't get between/beneath grains. (1)Smaller particles do not stick up so far in flow. (1)thus present a smooth surface which is more resistant. (1)(Any 2)

[2]

(d) (Very) low energy/stagnant water - mud flats of estuary. (1)Flocculation of particles when they reach sea. (1)Sea is an ionic solution which reduces the charge on the particles which prevents particle collision. (1)Therefore clay particles collide and fall out of suspension. (1)(Any 2)

[2]

21

(e) Rapid deposition (1) causes velocity drops suddenly. (1)Poor sorting (1) because little time/energy to winnow away finer particles. (1)Examples (1 only)- Sudden change in river gradient.

River in flood entering still water (lake) etc.(Any 2)

[2]Total 12 marks

Question 3

(a) Describe and explain the evidence from 18O/16O isotope ratios for climatic change in the Quaternary.

(b) Using evidence from coastal areas, explain how eustatic sea level changes and isostatic changes in land levels may be linked to continental ice sheets.

(a) Discussion of 18O/16O ratios in shells of marine animals and their explanation in terms of glacial and interglacial periods.18O/16O trapped in CO2 in carbonate shells.As the temp. falls 18O/16O ratio increases (less16O) 18O is heavier than 16O thus more 16O is evaporated from sea during interglacials but returns via water cycle so ratio of 18O/16O during interglacials is constant.During glacials 16O is prevented from returning to sea as it is locked up in ice.Thus ratio of 18O in seawater increases during the colder glacial periods.

Reference to oxygen isotope ratios from ice cores.(14 marks max)

(b) Eustatic sea level changes result form growth and decline of continental ice sheets.Low sea levels during glacials (growth of large continental ice sheets).High sea levels during interglacials (ice retreat).Examples - drowned river valleys in Britain (Channel).

Isostatic changes result from ice loading and unloading.Land submerges with weight of large continental ice sheets (e.g. Scotland and Scandinavia).Land rises when ice retreats - local effect - e.g. raised beaches in Scotland.

Overall effect on sea level change is combination of Eustatic and Isostatic effects.Credit case study material.

If not coastal evidence – max 7 (14 marks max)Holistic.

Total 25 marks

22

Question 4

With reference to examples, describe how geological structures and bodies may produce different relief forms. You may wish to refer to your field observations.

[25]

Structures – sedimentary and/or tectonic

Answer depends upon field and other examples.Must give a minimum of two landforms associated with structures and geological bodies (e.g.  igneous, faults, folds etc.).Major or minor scale accepted (i.e. fold mountains or baked margin effects.).Credit field and other diagrams.

Examples - fault scarp.- igneous body (batholith/ dyke/sill).- folded rocks - breached anticline (Weald), inverted relief (Snowdon).- Basin and Range topography.- Flood Basalt Traps.

Volcanic cones Small scale – e.g. Lulworth Cove. Waterfalls. Coastlines. Fold Mountains/other large scale.

Structures and bodies – Holistic.

Care on glacial erosion features – not valid.Glacial deposition features (drumlins, kettle holes, moraines –credit).(Quality of case study).

Total 25 marks

23

Question 5

(a) Describe the nature, causes and erosional effects of turbidity currents commonly observed in modern aqueous environments.

(b) Discuss the origin of sedimentary features preserved in ancient turbidite sequences.

(a) Outline only needed:Nature Submarine density current that forms a slurry of sediment slightly

more dense than the surrounding sea. Flows far (continental shelf to abyssal plain), e.g. Grand Banks.

Causes Submarine slope failure associated with tectonic activity (earthquakes/volcanic activity). Unconsolidated/partly consolidated sediment on shelf typically becomes unstable and flows. Upward force of water (turbidity) keeping the sediment in suspension until energy is dissipated.

Erosional effectsLarge scale Submarine canyons e.g.Scale scale fluting of underlying sediments (turbulent action of flowing current

plus sedimentary load.) - flutes (eddies), grooves, prod and bounce marks (tool marks).

(14 max)

(b) Minimum of two features discussed from:

Graded Beds/fining up sequence (Bouma sequence).Sole structures - Flute/groove casts, bounce/prod marks preserved.Load cast/flame structures.Trace fossils - burrows/feeding trails

Credit examples, field diagrams etc.Depth v breadth.(14 max)Holistic approach to both sections.

Total 25marks

24

Theme 2

Answers

Section A

Question 1

(a) (i) north-south. (1)[1]

(ii) hydrothermal. (1)epigenetic. (1)

[1](credit tension to produce crack – i.e. faulting, do not credit folding).

(b) (i) sampling – qualified e.g. Grid. (1)sampling of river water. (1)or of stream sediment.or of soil.or of vegetation.(Max 1)

description (Max 2)e.g. analyse samples, plot on map, search for max value (just downstream of ore body), if zero value gone past mineral, also credit soil sampling (same technique), and vegetation sampling.

[3]

(ii) density of minerals high so found with coarser sediment (1),although some low on hardness scale (just break into tiny fragments) still concentrated when current slows/loses energy (reserved 1),inside of meander. (1), slump of spoil heap into stream. (1)flood deposit. (1)

[3]

(c) (i) working: 60 mill tonne over 40 years (1), answer: 1.5 mill tonnes per year. (1)(credit 1.48 if 0.7 t already taken out this year)

[2]

(ii) faster rate of extraction so mining processes increased/more environmental impact (reserved 1) increased blasting/vibration (1), increased noise/dust pollution (1), faster habitat destruction (1), more lorries using road (1)

[2]Total 12 marks

25

Question 2

(a) (i) Reservoir rock sandstone (1)

Relevant Physical Properties porous or permeable (1)connected pore spaces/allow to flow through (1)

Max (1)

Cap rock salt or shale (1)Relevant Physical Properties impermeable (1)

[4]

(ii) Correct position of labelled arrow ßT (in a sandstone bed in fault trap, anticline trap or salt dome trap) (1)Explanation of trap in terms of trap shape, and cap above reservoir.(2 max)

Name of Trap Explanation examplesFault Impermeable cap rock faulted (1) against reservoir rock to

collect oil/gas which has migrated up to this point so that oil/gas cannot by-pass it. (1)

Anticlinal fold

Impermeable cap rock bent in anticline fold shape (1) to collect oil/gas which has migrated up to this point so that oil/gas cannot by-pass it. (1)

Salt dome Salt dome has risen and deformed surrounding rocks (1), impermeable cap rock arranged to collect oil/gas which has migrated up to this point so that oil/gas cannot by-pass it. (1)

[3]

(b) (i) 18 milligals (1)[1]

(ii) z = 1.73 2/2 (1) Range 2-2.3

z = 1.73km (1) Range 1.73km – 2km.[2]

(c) seismic surveys. (1)shock waves reflected off geological boundaries. (1)computerised maps created/ 3D pictures. (1)

seismic velocities (1) speed of shock wave through rock decreases with fracturing. (1)[3]

(Boreholes - limited credit - since one borehole does not give surrounding structure details, mostly used for rock detail, not structure detail).

Total 13 marks

26

Section B

Question 3

Describe and explain the formation of the following economic deposits:-(a) residual;(b) precipitated.

[25]

(a) weathering removes soluble materials, leaves insoluble behind residual concentration by removal of surrounding non-economic material strong chemical weathering in hot and seasonally wet climates deep rotting profiles of soil laterites.Bauxite - concentration of Al.Feldspars (Al2O3) plus slightly acidic rainwater rot kaolinite contains Al so is concentrated.Secondary enrichment.Heavy deposits - gold, tin.(14 max)

(b) brine, evaporation>rainfall, high temperatures, evaporation process, halite. Barred basins/refilling basins to give thicknesses seen in UK, gypsum, anhydrite crystallise then deposit, then halite, finally potassium and magnesium salts. Evaporites (dolomite, gypsum/anhydrite, halite, bittern salts) - cycles of evaporation in basins (e.g. refill, basin and bar), and Sabkha deposits.

Banded Iron formations – Pre Cambrian before O2 freely available in atmosphere, shallow water but low energy (associated mud cracks and ripples), fine grains of silica and iron oxides precipitated in large basins.

Thin layers of metal sulphides deposited on sea floor when hot solutions rose through cracks in crust, hot fluids could dissolve metal sulphides, precipitated when meets cold sea water, sphalerite, galena, pyrite, silver.

Also credit vein precipitates, ironstones/nodules.

Looking for more than evaporation.(14 max)

Total 25 marks

27

Question 4

Evaluate the industrial application of one natural raw material with reference to its physical and/or chemical properties.

[25]

Depends on raw material selected:Evaluation - so expect reasoned arguments for why resource is good and bad for particular uses. Also expect comparisons perhaps.

Some examples of properties:Permeability /porosity /impermeability.Hardness (and ability to be hewn, carved for blocks and statues).Rigidity/strength.Resistance to chemical attack (and pollution) and its breakdown (and rotting).Purity.Colour.

Oil - residues, plastics industry, easy to split chains, so fractions can be derived (fractionating column - temperatures), stable don't rot, withstand variety of chemicals. Expensive. Environmental arguments for use.

Chalk - pure - chemical industry use, good colour as filler for paint, known chemistry, stability when not in contact with acid, cheap, readily available.

Impervious - slate (although not widely used nowadays!), roofing, easy to split, workable, thin layers minimal weight. Expensive - not used on all houses, no local sources, too bulky to transport. Often now used by traditionalists, or where cost is not an issue.

Hardness – "carvable" "shapeable" must not be too hard cannot be cut into required shape - sandstone, granite - also for decorative statues/purposes.

Porosity/permeability – "protected" under an overhanging roof - limestone, acid rain attack - rate slower than to threaten life of building.

Built environment uses: Facing stones - resistant minerals (usually calcite?), impermeable, hard. Dimension stone - strong, hard, resistant, impermeable. Limestone - building/facing, aggregate (hard, homogenous), cement (chemical properties). Clay - bricks, tiles (baking properties). Sand and gravel - in aggregate, concrete, cement, mortar, pebble dash, gravel drives (range of sizes, tough). Gypsum - plaster (chemical properties). Silica sand - glass (chemical/physical properties)

Max 15 if no evaluation.Total 25 marks

28

Question 5

(a) Describe the formation of coal deposits.

(b) Explain how environmental damage associated with the quarrying or mining of raw materials may be minimised.

[25]

(a) Swamps, plant material, hot and wet - maximum vegetation growth.Warm - luxuriant growthFresh water - vegetation (indicated by freshwater bivalves), tropical.Quiet - material not swept away.Stagnant - rotting not complete.Sinking - continued deposition.Rapid burial, exclude oxygen/anaerobic, minimise rotting.Burial raises temperature and pressure conditions.Time factor.Coalification proceeds from partially decomposing vegetable matter such as peat, through coal rank - lignite, bituminous coals to the highest grade of anthracite. During this process, the percentage of carbon increases, and volatiles and moisture are gradually eliminated.

(14 max)

(b) Any reasonable damage minimisation technique:open cast - large area lain to waste and habitat damage (eyesore - banks and screens, move endangered species, refurbish after), water pollution (monitor, dams), removal and replacement of topsoil, during extraction - range of measures to reduce dust (washing), noise (baffles), blast noise (restrict times), pollution of access roads (improve roads), back filling and eventual replacement of topsoil, landscaping/planting.

deep mining - rocks from deep underground brought to surface, may not be stable, subsidence (monitor and new buildings built with this in mind), pillars left under important buildings, at pithead, disposal of spoil in as friendly a way as possible (landscaped, planted), measures to reduce dust, acid mine drainage, groundwater contamination e.g. By pyrite etc.spoil heaps cover land surface, and water pollution risk (plus safety- Aberfan?).wheel washes for vehicles to remove dust.water sprays to damp dust down.tree screens.minimal buildings.credit examples.

(14 max)Total 25 marks

29

Theme 3

Answers

Section A

Question 1

(a)(i) (ii)

Tectonic Unit Name of Orogeny Trend of the orogenic beltA Caledonian (1) NE-SW (1)

Accept NNE-SSWDo not credit N-S

B Alpine E-W (1)

C Hercynian/Variscan/Armorican (1) WNW-ESE

[2] [2]

(b) (i) rock outcrops:P anticline, Q syncline. (1)orP older in younger, Q younger in older. (1)P younger material eroded, Q not (1)trend : P = N-S, Q = E-W. (1)

[2]

(ii) X -X unconformity. (1)

Y -Y (normal) fault. (1)Do not credit Thrust fault, nor fault if unqualified vertical movement).

Differenceunconformity is near horizontal/shallow dip, shown by irregular (undulating) outcrop pattern (1)fault is straight - steepish dip.

[3]

(c) Line Z-Z represents closure line / closing (1) of Iapetus. (1)Solway suture. (1)Destructive boundary/subduction zone/collision. (1)2 continents/land masses/continental plates. (1)

[3]Total 12 marks

30

Question 2

(a) (i) (ii)

Geological Period

Inclination (dip) of palaeomagnetic field

Palaeolatitude in degrees

Selected sedimentary rock types

Permo-Triassic 36° (1)Accept range 33°-39°

20°N Red sandstones with dune bedding, and evaporites

Carboniferous 0° (Equator) 0° (1)Coal deposits;Limestones with corals

Devonian20° 10°S Red sandstones, siltstones

and conglomerates[1] [1]

(iii) Magnetic inclination in basaltic rocks. (1)Magnetite orientates with respect to earth's magnetic field as it cools(1) below Curie Point. (1)Inclination locked in and remains if rocks move latitude. (1)Inclination horizontal at Equator, vertical at Poles. (1)Credit reference to formula Tan I = 2 tan 1.Credit reference to polar wandering curves.Sedimentary rocks - if iron rich - during deposition/sedimentation. (1)

[3]

(b) Limestones with corals:Tropical. (1)corals – tropics. (1)corals indicate shallow marine <50m deep (1) (not just marine).normal salinity 3.5%. (1)warm 25º - 28º C. (1)clear, sediment-free water which is well oxygenated. (1)nutrient supply from ocean current. (1)[Max 3]

Red sandstones with large scale cross bedding, and evaporites: ARID /very dry conditions. (1)Red Iron oxide = terrestrial oxidizing environment. (1)Dunes - wind/aeolian action. (1)Dune bedding = can establish palaeo-wind direction. (1)Evaporites – evaporation. (1)[Max 3]

[6]

(c) Climatic belts run parallel to lines of latitude, therefore all places on same latitude will have similar climatic conditions. (1)Rock types do not vary with longitude. (1)Magnetic inclination is the same along every line of latitude. (1)The distance to the North Pole is the same at any point along a line of latitude. (1)

[2]Total 13 marks

31

Section B

Question 3

Compare and contrast the sedimentary features and fossil assemblages of rocks formed in the following environments:

(a) deltaic(b) deep marine.

[25]

Similarities:Marine fossils; sandstones/mudstones/shales; feeding trails and burrows;

bedding/lamination/ripple marks, varying energy levels, deep sea and deltaic sediments can have turbidite sequences.

DifferencesDifferences in character of fossils and traces differences in fossil preservation; deltas

can have coarser sediments (channel conglomerates), cross bedding, cyclothems, coals; deep sea sediments - restricted sequences, oozes. Deltaic – foreset/topset/distal/proximal etc.

Deltaic Deep MarineCoarse Seds

Medium sedsFine seds

Rate ofsedimentation

Water effects

Fossils

Sea levels

Sands and gravels at proximal endFine sandsClays and silts at distal end

Rapid build up of sediment

Graded bedding, prograding delta

Freshwater fossils brought down by river, some estuarine fossilsPoor preservation potential due to coarse grain size

fluctuating

Very few, except in turbidite deposits

As aboveClays common

Slow build up

Laminations in fine sedimentScouring at base of turbidites, plus associated depositon features

Mostly forms which have fallen in on death (from above)

Good preservation, anoxic and fine sediments to preserve small details

Don’t fluctuate

Max 15 if no element of comparison.Holistic.

Total 25 marks

32

Question 4

Explain how investigations of sedimentary rocks and fossils have provided evidence of climatic change in Britain from the Jurassic to the present day.

[25]

U Mesoz (Jur-Cret) 35º N, warm seas similar to Bahamas – clues.Limestone - tropic of Cancer.Corals.Chalk seas -algal bloom, implying warm sea conditions.Coccoliths.

Cainoz (Tert/Rec) 50-60º N, clastic.Temperate - fossils - sabre tooth tiger etc, cold water fossils in Crag deposits at end.Credit - palaeomagnetic inclination from basalts (even though not sedimentary rocks).

Pleistocene Ice, Glacial - BUT not further drift north.Quaternary Glacials and interglacials - ice deposits and interglacial

deposits.Pollen.Warm and cold fossils (hippos, woolly rhinos).Sea level changes.Oxygen isotope data.

Total 25 marks

33

Question 5

Discuss the geological evidence for the type of plate boundary active in the British area, during the formation of the Tertiary Igneous Province.

[25]

Extrusive Igneous Activity:

Extensive upwelling of basalts - constructive margin e.g. centres in Scotland and NE Ireland.Basalt.Flood/plateaux basalts (low viscosity lava flowed substantial distances).Sub-aerial weathering of lava flows.Lava flows up to 15m thick.Antrim - 1500 square miles of lavas preserved.Mull - some 2000m thickness.Irish flows - olivine basalts with a middle succession of tholeiites consistent with melting of upper mantle and constructive plate boundary.Compare to Iceland.

Intrusive Igneous Activity:

Complex igneous intrusive centres. (Skye, Mull, Arran, Ardnamurchan, Rhum).magma rising, tension.concentric intrusions (ring dykes and cone sheets).Rising pluton of acid magma caused extension (thinning of crust), rifting and crustal extension.

Tension:

Dyke swarms trend NW-SE (same as current constructive margin).Extensive tension to account for great overall width covered by dyke material.

Credit arguments for why not other type of boundary:Not destructive plate boundary, no accretionary prism etc.Tension not compression.Basaltic volcanism prevalent not andesitic.

Rockall Trough - over 3000m of Mesozoic and Tertiary flat lying sediments.Important break under Upper Eocene sediments - unconformity due to changes in pattern of spreading in North Atlantic during the early Oligocene.Adjacent Atlantic with same sense of movement and the separation of NW Scotland from USA.

Rb-Sr isotopes.Melting of continental crust granite in Skye.

Total 25 marks

34

Theme 4

Question 1

(a) Base of Gabbro (layer 3). (1)[1]

(b) (i) Layer 2a - Pillow structure. (1)Layer 2b – Dyke. (1)

[2]

(ii) Pillow Lava underwater. (1)rapid cooling/chilled margin. (1)sag/neck structures. (1)other sensible.

or

Dyke Intrusion. (1)Conduit from magma chamber to surface. (1)Tension related structure. (1)

[2]

(c) Describe Increase in crust. (1)Increase at Moho. (1)Decrease at LVZ. (1)Credit use of numbers. (1)(2 plus 1)

Explain Changes in rigidity. (1)Changes in composition. (1)Partial melting of asthenosphere. (1)(2 plus 1)(5 max)

[5]

(d) (i) Base of lithosphere. (1)[1]

(ii) Older. (1)Colder. (1)Subduction. (1)Accretion. (1)Orogeny. (1)(2 max)

[2]Total 13 marks

35

Question 2

(a) (i) Normal. (1)[1]

↓(ii) P-max ↑ (1)

P-min →← (1)[2]

(iii) extension/tension. (1)step faulting/graben. (1)continued subsidence. (1)crustal thinning. (1)(any two)

[2]

(iv) Moho rises under rift. (1)[1]

(b) Rift is a lowland sediment trap. (1)Rift influences drainage. (1)Eroded material from sides of rift transported along valley to delta. (1)(Other sensible)(2 max )

[2]

(c) (i) Volcanoes.[1]

(ii) Crustal thinning (1)means base of lithosphere/asthenosphere is closer to the surface. (1)Rising convection currents. (1)Partial melting. (1)Mantle plume. (1)(Max 3)

[3]Total 12 marks

36

Question 3

(a) Features from:

Shield (Craton) - old, regionally metamorphosed, stable, thick, lower density.Form core of continents usually surrounded by younger provinces, e.g. Canadian etc.

Orogenic belts - Fold mts/collision zones, Cordilleran mountain belts.Crustal shortening (thrusting/folding/nappes) seismics/volcanics/ Metamorphism, e.g. Andes/Alpes. Foreland basins.Crustal extension, e.g. North Sea, East African Rift.Extensional basins.

Credit Ophiolite/accretionary prisms.

Continental Shelves/Slopes - Size depends upon boundary type - leading/trailing edges.

Ages distributions within a continent - e.g. North America.(14 max)

(b) Origins - Low density crust not subducted at Continent-continent.Continent-island arc collisions.

- Crustal melting and granite magmatism- Crustal thickening- Delamination, isotatic uplift and gravitational collapse.- Ophiolite formation- Lithospheric extension - extensional basins- Lithospheric loading - foreland basins.

(14 max)

Holistic approach - accept that (a) and (b) may be incorporated.Depth v breadth.

Total 25 marks

37

Question 4

Describe and explain the evidence for ocean basin evolution (formation, growth and destruction) as proposed in the J. Tuzo Wilson cycle.

Describe and explain evidence.

Magnetic stripes (dating), thickening sediment, distribution of ages, rifting and seafloor spreading as exemplified in Wilson cycle:

Formation - Continental rift - e.g. - East African - rifting/normal faults. Igneous activity associated with rising convection currents.Diagrams and use of maps

Growth - Narrow Sea - e.g. Red Sea. Constructive margin.Oceanic crust developing in rift. High heat flows.Rates of opening. Diagrams and use of map.

Mature Ocean - e.g. Atlantic - little subduction.Central axial ocean ridge.Rates of opening.Opening ocean basin.

Destruction - No ocean> 200Ma, evidence from Benioff zone, trench, gravity and heat readings, andesitic volcanics, accretionary prisms at destructive margins.Ophiolites.

- e.g. Pacific - Subduction associated with marginal trenches.Ocean ridge not central.Rates of opening faster.Closure of ocean basin.

Credit reference to past oceans - Iapetus, Closure of Tethys, formation of Himalayas.

Holistic approach.Total 25 marks

38

Question 5

(a) Account for the presence of linear magnetic anomalies in ocean basins.(b) Explain how mantle plume (hot spot) data from volcanic island chains (e.g. the

Hawaiian chain) can be used to calculate rates and direction of plate movement.

(a) Definition of magnetic anomaly. Principle of magnetometer/magnetic surveys.

Discussion of- remnant magnetism in ocean basalts (Earth's magnetic field, Curie temps etc.).- palaeomagnetic evidence for sea floor spreading based on magnetic reversals.

(stripes/patterns, extent, symmetry etc.)- Progressive formation related to sea floor spreading at ridges.- Effect and significance of transform faults in disturbing patterns.(14 max)

(b) Definition of mantle plume (hot spot).

Discussion of- rising plumes indicates position of plume at mid plate hot spot.- as plate moves over hot spot a chain of volcanoes is produced.- only recent volcanoes are active, older volcanoes sink (isostacy).- volcanoes can be dated (radiometric ages).- distance from hot-spot.- direction and rate thus established..- e.g. data from Hawaii-Emperor hot-spot track 8.2 cm/yr.(14 max)

Holistic approach.Total 25 marks

GCE Markschemes (June 2002)/GEOLOGY/AOB

39

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