MS3 WELSH JOINT EDUCATION COMMITTEE £3.00 CYD-BWYLLGOR ADDYSG CYMRU

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

MARKING SCHEMES

SUMMER 2007

GEOLOGY

INTRODUCTION The marking schemes which follow were those used by the WJEC for the 2007 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.

1

GL1 1. (a) (i)

Layer of ocean crust

Rock type Name of igneous structures

Q Basalt Pillow lavas

R Dolerite Dykes S Gabbro

[4] (ii) Plagioclase feldspar Pyroxene or Augite 2 of these Olivine [2] (iii) More rapid cooling causes finer crystal size (or equivalent) (1) More rapid cooling closer to the surface (or equivalent) (1) [2] (b) (i) Contact with seawater (1) Rapid cooling/quenched (1) Forms a crust/skin (1) Inflation/pushing through the pillow or equivalent (1) [2] (any two) (ii) Partial melting or equivalent (1) Of mantle/asthenosphere (1) Of ultramafic/peridotite (1) Lower melting temperature components melt (1) Credit other valid point (1) e.g. pressure release [3] (any three)

(c) (i) Points plotted showing positive correlation [1] (ii) Correct relative age of crust e.g. B older than C (1) Correct reason for relative age of crust (1) Thicker sediment = older. (I.e explicit statement of age thickness

relationship) (1) Because longer time for sediment accumulation/ will not have had as much sediment on it (1)

Credit link to sediment derived from the continent. (1) [3] (any three)

Total 17 marks

2

2. (a) (i) Age relative to something else/ older:younger (1) [1] (ii) Intrusion is younger than Carboniferous rocks because it cuts them or

equivalent (1)

Intrusion is older than Quaternary sediment because they overlie the intrusion or equivalent (1) [2]

(b) (i) Gaseous exchange between tree and atmosphere (1) [1] (ii) Decrease in the amount of 14C. (1) 14C decays radioactively (1) 14C not replenished from the atmosphere (1) [3] (iii)

Suitable for dating by

14C method. Yes/No

Reason(s)

Fossil tree in Quaternary sediment

Yes Organic matter (1) Young enough/not too old (1)

Fossil tree in Carboniferous sedimentary rock

No Too old (or stated age 350-275mya) so that too much 14C is lost (1)

Igneous intrusion No

Not organic (1)

3 correct = 2 marks 2 correct = 1 marks 1 correct = 0 mark [6]

Total 13 marks

3

3. (a) J located in the shale outside the metamorphic aureole (1) [1] (b) During folding (1)

Under NE-SW compression (1) (R one of these two as a link to Fig 3b) Regional metamorphism (1)

Low grade (1) (heat and) pressure 1) Of a fine grained/or named fine grained sedimentary rock (1) Aligned grains (1) [3]

(c) (i) shorter wavelength/ more intense in slate (1) or vice versa trend of axial plane trace NW-SE in slate

but NE-SW in shale (1) [2]

(ii) NW-SE (1) [1] (d) Downthrow to SE because: Younger rock on downthrow side (1) Shale is unmetamorphosed (1) [2] (e) specific type of fold/fault e.g. "reverse fault", "anticline" (1)

Quality of diagram/description (2) Reference to appropriate scale (1) Specific location of feature (1) Correct name of stress involved (1) R e.g. Extension/Tension for normal fault, Compression for reverse/thrust fault or fold Shear for tear fault [5] Total 14 marks

4

4. (a) (i) Trilobite (1) [1] (ii) Glabella (1) [1] (b) Brachiopods have: 2 different sized valves/inequivalve (1) plane of symmetry within 1 valve/equilateral (1) 2 of these pedicle foramen or pedicle (1) diductor muscle scars (1) or equivalent Bivalves have a pallial line/sinus (1) [2] (c) Soft parts absent (hard parts only present) R (1) Decay/decomposition/eaten/eroded/breakdown (1) [2] (d) Solution of calcite (1) Any ref to groundwater/ porewater/percolating water (1) Quartz/silica precipitated /crystallised (1) Replacement (atom by atom)/Impregnation/Petrifaction (1) [3] (e) (i) Not preserved in life position (2)

Moved/ transported (1) after death or before preservation (1) [2] (ii) Valves fragmented/disarticulated/separated (1) damaged Due to transport/current etc (1) Not in life position(1) [2] (iii) 1 for statement of environment (1)

e.g. high energy bed 1/low energy bed 2/fast deposition bed 2 1 for evidence (1)

e.g. fragmented in bed 1/whole in bed 2/well preserved bed 2/flipped in bed 1

at least 1 for cause of change (1 R)

e.g. – may indicate deepening water over time (1) – may indicate sudden high energy current event during bed 1

deposition (1) ) [3]

Credit other relevant answers Total 16 marks

5

GL2a SPECIMENS A = granite (for use in Q1) B = calcite (for use in Q2) C = schist (for use in Q3) 1. (a)

(b)

(i) (ii) (iii)

(texture only) crystalline porphyritic cooling and crystallisation of a magma 2-stages (larger phenocrysts first) TWINNING or CLEAVAGE is the only property which can gain the following marks:

description (e.g. use hand lense to see any regular breakage/twinning)

none seen in grey mineral (accept fracture) present in pink/white mineral

Photo 1 either (D) chilled margin (E) finer crystals than in Specimen A due to rapid

cooling against cold country rock or (D) dyke/vein (E) a melt intruding weaknesses in cold, brittle country

rock Photo 2 (D) random chiastolite/andalusite crystals (E) contact metamorphism of cold country rock as hot

melt cools Map 1 (D) radial dip (E) forceful intrusion domes country rock

1 1 1 1 1 1 1 1 1 1 1 1 1 1 1

2 2 3 6 (13)

6

2. (a)

(b) (c) (d)

(i) (ii) (i) (ii)

scaled drawing shape of ooliths structure of ooliths pore spaces positive acid test or rhombic cleavage Calcite non-frilled, showing lobes and saddles (e.g. "zig-zag", "angular", "rounded") Upper Palaeozoic Goniatitic (or similar e.g. early type of suture evolution) (No mark for evaluation only; mark reason only if evaluation is correct) Photo 3 False

limestones/ooliths form in shallow marine environments Photo 4 Correct

fossil group (cephalopod/ammonoid/goniatite) uniformitarianism (nautiloids) R

1 1 1 1 1 1 1 1 1 1 1 1 1

4 1 1 2 2 3 (13)

3. (a) (b) (c)

(i) (ii) (i) (ii) (iii) (iv) (v)

e.g. freeze-thaw water expands in cracks as it freezes cyclic process Textural – foliation/aligned crystals Mineralogical – micas or garnets b/a = 0.80 c/b = 0.12 or 0.13 plot and label the answer from part (i) foliation causes "thin" fragments when physically weathered spheres plutons/granites have cooling joints 3-D spacing produces “cubic” fragments

1 1 1 1 1 1 1 1 1 1 1

1 2 2 1 1 1 1 2 (11)

7

4. (a)

(b) (c)

(i) (ii) (i) (ii) (iii)

horizontal rock overlies folded rock units/ cross-cutting e.g. weathered surface beneath Rock Unit e.g. included fragments of older rocks (C, E, F) in Rock Unit B NE-SW line within Rock Unit C, but not cutting through the unconformity 25m F1 downthrows to the southeast F1 is normal F2 is vertical (straight line of outcrop) Dowthrows to northwest, but is this the hanging or footwall?

1 1 1 1 1 1 1 1 1

1 1 1 1 2 2 (8)

5. (a) (b)

see section see table

10 5

10 5 (15)

8

B base at 250m radial dip around the pluton

edge of pluton F2 dip

movement Antiform fold axis

symmetrical antiform fold

F1 dip movement

top & base of Rock Unit E either to west of F2 or east

← superficial deposits

← F2

← folding

← folding (alternative)

both F and C correct

both A and D correct

9

10

GL3 1. (a) Arrow (1R) Glacial till impermeable – sandstone permeable (1) – water forced to the surface.(1) (2 max) [2] (b) Rotational slip plane in tip debris. [1] (c) (i) Loading, groundwater (spring), rainfall, lithology, angle of slope (not dip), vibration, other (any 2) [2] (ii) Geological factor explained [2] (d) Monitored for creep, strain, groundwater pressure, Mapped for spring presence. Slope stabilisation, methods – drainage, diversion etc (3 max holistic) [3] (e) Stability of rock faces, rock falls, ground subsidence,

gas explosions, flooding, surface/groundwater pollution (2 max) [2] Total 12 marks

11

2. (a) As Richter scale increases energy increases (1) and frequency decreases (1) Credit use of numbers (2 max) [2] (b) (i) 32 million [1] (ii) Rare for energy to build up so high before slipping build up if strain takes time .

(2 max) [2]

(c) (i)

Name Distance (km)

S-P lag time (seconds)

Amplitude (mm)

Richter Magnitude

Earthquake A ~50 6 0.2 2 Earthquake B 20 5 Aftershock C

~225

(25-27)

25 2 4 Care with follow on [3] (ii) 1. 32 2. 10 [2] (d) Increase/decrease in background rate of minor quakes Seismic Gap. Measurement of P and S velocities passing through fault zone. Reduction indicates influx of water into rock as micro-fractures open. On returning to normal, pore pressure rises = quake. Duration of anomaly = predicted magnitude of quake. Holistic (3 max) [3] Total 13 marks

12

Section B 3. (a) Describe the properties of rock that control porosity and permeability in aquifers.

Aquifer, permeability, porosity (specific yield) defined. High POROSITY depends upon gaps between grains large/interconnected Primary and secondary porosity depends upon

Packing of grains – cubic v rhombic Fracture/joint spacing Shape/orientation of grains – angular v rounded Sorting of grains – small fit in between larger. Cementation

PERMEABILITY depends upon

Connectivity of pores Size of pores Joints and fractures

Interconnected joints, faults, fractures, solution cavities Examples – Limestone, sandstone, fractured/jointed igneous and met rock 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) Explain how geologically related problems may result from interference with

the hydrological system. Holistic – may include:

1. Local exhaustion of water table – cones of depression. Extraction exceeds recharge. Reduction of flow from springs/wells – dry wells and valleys

– loss of wetland habitat/domestic supply in arid region. Loss of artesian effect. Flooding if hydrological system is blocked/throughflow restricted.

2. Reduction in pore pressure causing surface subsidence. 3. Contamination as pollutants are drawn in – pollutants identified.

Sea water contamination in coastal areas Examples (e.g. London) and diagrams credited. Acid Mine Drainage – mining 4. Reference to interference with coastal processes – longshore drift,

coastal erosion/deposition. 5. Pumping water into faults – earthquake reactivation – Denver, building

reservoirs increases pore pressure and instability – Vaiont dam [15] Total 25 marks

13

4. (a) Using one or more case studies, describe how one of the following volcanic phenomena can be hazardous:

(i} lahars (ii) volcanic gas (iii) blast/explosion lahar Reworked ash from volcano. Melted snow and torrential rain.

Hot, liquid. Consistency of concrete – fast flowing. Suffocation/drowning/burial. Difficult to predict. Lasts for years.

E.G. Armero(Columbia)/Pinatobo etc. volcanic gases Variety – CO2, H2S, CO, SO2

etc – contain fluorine, sulphur, chlorine – noxious

Hot (1000C) – Suffocation/drowning/burial/burning/respiratory problems Effect on vegetation. – Not affecting buildings but kill people – silent killer E.G. Lake overturn – Lake Nyos – Cameroon.

blast/explosion Explosive index – Types – Hawaiian – Ultra Plinian. Lateral blast – e.g. Mt St. Helens – Heat, speed, force, distance travelled. Vertical blast – e.g. Pinatubo, Krakatoa Secondary effects – trees levelled, rivers blocked by debris, effect of

bombs/ash etc. tsunamis (Max 10 – No case study – max 7) (b) Explain how the risk to life and property associated with a major volcanic event

largely depends upon the extent to which an eruption can be predicted or its effect minimised.

Holistic approach

Volcanic hazard defined – i.e. Risk of the harmful effect to human life or property of an unavoidable volcanic event.

Minimising volcanic hazards and efficient/effective prediction reduces the risk and scale of the potential hazard.

Minimising may involve – evacuation, hazard mapping, diversion/blocks,

dropping-spraying with water, explosion of flow margin. Case studies credited – Iceland, Etna. Prediction may include – monitoring ground deformation, gravity and thermal

anolalies, gas emissions and seismic activity (harmonic tremors). Effectiveness discussed and case studies given credit – Pinatubo. Ultimately always risk of hazard if people choose to live near volcanoes. (Max 15 to include evaluation – 12 max if none) Total 25 marks

14

5. (a) Compare the changes in radon gas emissions before and after an earthquake with the changes in groundwater levels (identified in wells) over the same period of time. Explain your answer.

During build-up of elastic strain prior to earthquake (dilation) cracks open –

radon released and increase recorded. Water levels fall. Radon gas emissions stabilise in diffusion stage where no new cracks open. Water levels rise as water infills cracks. (Credit also – Radon gas increase also associated with the movement of groundwater into the micro-cracks as it is soluble in water.)

Fall to background levels after quake when micro-cracks close. Water levels rise further.

(Max 10 marks) (b) Account for the presence of high radon gas concentrations in some buildings

located in particular areas of the British Isles. You should consider the sources, and pathways of the gas to the surface, the surface geology in high risk areas and the risk involved in high concentrations. Radon defined. A dangerous (when in high concentrations) inert gas from

decay of uranium rich rock. Natural release from radioactive decay. Sources and pathways. – porosity, permeability examples. Granite – high risk areas (SW England). Other areas associated with

shale/limestone. Radon dissolves in water and transported in groundwater. Released when pressure drops/near surface. Trapped by some rock types (clay) but released to atmosphere to be trapped by

poorly ventilated/well insulated buildings (cellars, attics, roof and floor voids). (Max 15 marks) Total 25 marks

15

MARK BAND CRITERIA FOR AS ESSAYS.

Summary

Description Mark out of

25 Criteria

Excellent

21 - 25

Not the perfect answer but purposeful, demonstrating a secure grasp of knowledge and understanding and few significant omissions. Well-supported and illustrated with detailed examples selected from named geological situations. Ideas expressed fluently in logical form using appropriate geological terminology. Few errors in grammar, punctuation and spelling.

Good/Very good

16 - 20

Sound answers with relevant material providing evidence of good knowledge and understanding. May be limited in terms of supporting material and breadth of coverage but appropriate examples selected. Ideas expressed with clarity with only occasional errors in grammar, spelling and punctuation.

Modest/Quite Good

11 - 15

A reasonably secure grasp of basics but some deficiencies in knowledge and understanding although use is made of geological terminology. Examples and illustrations may lack detail or may not relate to real geological situations. Reasonable use of language with adequate spelling and punctuation.

Weak/Minimal

6 - 10

Answers show limited basic knowledge and understanding, lacking directness and organisation; tendency to rehash prepared material and answer by inference. Superficial use of examples. Deficiencies in use of language evident; weaknesses in spelling and punctuation apparent.

Very weak

1 - 5

Little evidence of knowledge and understanding with erroneous or repeated material evident. Candidate is unable to address the question. Largely irrelevant; possibly too brief. Language skills poor, with spelling, grammar and punctuation errors becoming obtrusive.

Incorporated into this mark scheme is the assessment of candidates on their ability to organise & present information, ideas, descriptions & argument clearly & logically, taking into account their use of spelling, punctuation & grammar.

16

GL4

1. (a) (i) Bivalve (1) [1] (ii) Laminated (1) Clay minerals (1) fine grained (1) Name: Shale (1) [3]

(iii) Marine/low energy/near land (1) Marine – cephalopod/marine fossil (1)

Near land – plants washed in (1) Low energy/deep – fine grained/clay (1) [3]

(b) Contact/thermal met only /high temp/heat/intrusion (1R) (don’t credit heat if in conjunction with pressure) – lacking pressure/no cleavage/foliation (1)

(Random) Chiastolite crystals/growth of new minerals/spotted rock (1)

Fossils destroyed/lacking (1) [3]

(c) Regional met/Temp & Pressure/Orogenic processes (1) Shale to slate (slatey cleavage/relic cleavage) (1) Then later (1R) contact met/intrusion/high temp (1) - Random chiastolite which cuts cleavage (1)

HOLISITIC [4] Total 14 marks

17

2. (a) (i)

Fault characteristics

Description

Strike direction

• N-S

Dip (degrees)

• 90

Throw (vertical displacement)

0 (zero) metres

Principal stress direction (σ max)

• SE-NW

Type of fault • Sinistral/strike slip/wrench/tear/transcurrent

[4] (ii) Scratches/grooves show orientation of movement (1) May not indicate actual direction (1) unless Smooth feel in downslip direction (2) Possibly indicates last direction of movement. (1) Horizontal in fig 2a (1) (2 max) [2]

(b) B (1) Fault breccia (1) Contains igneous material not likely at A/clasts of all rock types Unless reactivation(1) – A then accepted(1) (Accept explanation of why not C or D) [3] (c) (i) Dyke/discordant/igneous intrusion not lava flow/

concordant (1R) Other medium grained not fine as in lava flow size too small, controlled by joints/too regular no sag structures/spherical not pillow shaped (2 max) [3] (ii) Water along joints Chemical decay (rot/breakdown of feldspar to clay) of the

minerals/oxidation, hydrolysis etc Greater at the joint boundaries – larger surface area Rounding to produce core stones [3] Holistic Total 15 marks

18

3. (a) Viscosity increases (1) with increase in SiO2 %age (1)

Positive relationship (1) (2 max) [2] (b) (i) Similarity Both melts are less viscous at higher temperatures (melts more viscous at lower temps) (1) Difference Granite magmas are always more viscous than basaltic magmas at any temperature. (1) Granite increases/decrease faster (visa versa) (1) [2] (ii) 1100 oC (1) [1] (iii) Lower temp & higher viscosity range than basalt (1) Higher temp & lower viscosity range than granite (1) [2] (c) Basalt is non viscous (runny). Extruded hot, with low SiO2 content, Gas is readily able to escape in bubbles. Flows further before it cools. Runs in tunnels (lava tubes) many kilometres –insulated. Holistic(3 max) [3] (d) (i) Subduction of ocean lithosphere (basalt) at trench (1) Seawater dragged down (seawater within sediment) with descending plate(1) [2] (max 2 marks) (ii) Lowers the melting point (1) Allowing magma to be generated at shallower depths (1) Lower temperatures of magma (1) More explosive eruption (1) (max 2 marks) [2] Total 14 marks

19

4. (a) All true (1) but pygidium smaller than cephalon (1R) [2] (b) (i) Large eyes positioned on side – 360o vision (below) (1) Streamlined body – fast movement or equivalent (1) Limbs – paddles (1) Spines – stability in water/protect rear (1) Inflated glabella – buoyancy (1) (2 max – 1 if only described) [2] (ii)

Morphological feature

Possible function

Genal spines

• Help to stabilise during feeding /channel water towards fringe

Limbs

• Used to create a water current to allow food to be drawn towards mouth

NOT: propulsion/swimming Fringe on the Cephalon

• Filter food from water/shovel for burrowing/large surface area so more food can be gathered

Credit other sensible [3] (c) Can’t really use uniformitarianism Extinct group – no current forms that have similar morphology to study Exceptional preservation (example: eg. Burgess Shale, Solnhofen Limestone etc) allows soft parts preserved

Credit trace fossils for morphology/behaviour Holistic (3 max) [3] (d) (i) Constant/steady increase/straight line (1)

in morphology with time (1) No stasis (1) (max 2) [2] (ii) Stepped line (1) Stasis labelled (1) [2] (e) Fossil record is biased – rarely preserves soft parts Limited preservation - predation, scavengers, diagenesis Missing links may not be preserved . Fossils may not be representative of actual population Trilobites old - Palaeozoic age but hard shell preserved Trilobites not known to show major evolutionary changes Sample may not be valid/ representative

Grapt/amm/gon/cer/horse examples (Max 1) (Holistic – max 3) [3] Total 17 marks

20

Section B

5. (a) (i) Head (1) [1] (ii) Narrow, linear, dimensions (1km max, 300m min), N-S (max 2) [2] (b) (i) [4]

Formation Wyche Formation (Wy)

Malverns Complex (MvC)

Dip direction

West (WSW) None

Apparent dip angle (degrees)

75 (80-70) degrees None

Rock type (Igneous, sedimentary or metamorphic)

sedimentary Intrusive igneous

Age

Silurian Precambrian

(ii) No metamorphic/baked margin/aureole Included fragments Precambrian MvC older than Silurian Wyche (max 2 marks) [2] (iii) unconformity (1) [1] Total 10 marks

21

6. (a) (i) Rising (1), levelling (1), accuracy (1) [3] (ii) PT lower density – lower gravity Silurian higher density thicker sequence – lower gravity effect of faulting explained link to geol struct (isogals parallel to outcrop) (3 max) [3] Total 6 marks

22

7. (a)

Fold characteristic Description Fold type • Syncline/synform

Fold symmetry • Asymmetric/numbers

Orientation of axial plane trace

• NNW-SSE (N-S)

Plunge direction • South

[4] (b) (i) 55mm *10 (5.5cm* 100) = 550m (1) method (1) [2] (Range: 530m-570m and correct working) (ii) Similar dips to East (1) CF = Reverse movement (crustal shortening) (1) EMF – Normal (crustal extension) (1) Probably not contemporary/at same time – opposite stress

fields (1) Credit fault reactivation arguments

(max 4 marks) [4] Total 10 marks

23

8. (a) Joints/fractures/faults make it permeable(1R) High relief provides rainfall (1) Springs where water forced to the surface (1) At faults/unconformity/joints/fractures. (Max 2 marks) [2] (b) (i) Steep dipping mudstone/siltstone (Coalbrookdale) lmst (Woolhope) mudstone/siltstone (Wyche) List of rocks (not age) : max 2. Massive igneous (Malverns) Low dip mudstone (Mercia) Faults (three -four). Small made-ground/drift (max 4 marks) [4] (ii) Water problem in permeable strata Fault reactivation – water along fracture Igneous rock/lmst – strong/more difficult to work/but less

support needed Mudstone/made ground – weaker/easier to work/needs

support Wy Wyche overturned strata/steep dip – need support (Holistic max 4) [4] Total 10 marks

24

GL5 THEME 1 – QUATERNARY GEOLOGY

Section A

1. (a) (i) West of Andros Island (1) length of the island (1) shallow water (1) shelf (1) (distances and latitudes / longitudes credited)

(ii) Low energy (1) allows fine sediment to be deposited (1) warm (1)

shallow sea (1) evaporation and precipitation (1)

(b) High energy(1) nutrients brought by ocean currents(1) photic zone (1) oxgen (1)

(c) (i) Concentric structure (1) nucleus (1) to scale (1 reserve)

(ii) HOLISTIC : carbonate precipitating (1) confined to depths less than 180m(1) in higher energy environment (1) wave action moving the grains(1) flow depositing ooids in cross-beds (1)

2. (a) 2 of : Moraine / till present (1) corrie (1) ice-scratched rocks (1) arête (1)

pyramidal peak (1)

(b) (i) Eroded basin of corrie (1) impermeable till / bedrock (1) + (1) for development

(ii) 2 periods of glaciation (1) terminal (1) recessional moraine (1)

(c) (i) High on the mountains (1) above 700 m contour (1) south-facing

slope (1) edge of frost-shattered boulders (1) E-W (1) to the north (1)

(ii) Melting of frozen soil (permafrost) (1) on slopes exposed to sun (1) weakened soil flows down the slope (1) saturated (1)

(d) Holistic mark for argument. Reference to time (1 reserve) ice in Cwm Cau

with periglacial conditions higher than ice limit or periglacial conditions existed whenice had melted as climate ameliorated. High up because of steep slopes and more rain.

25

Section B

3. (a) Explain how Milankovitch Cycles are thought to cause climatic fluctuations in the Quaternary.

Eccentricity/Precession/Tilt - descriptions including diagrams Effects on seasons Combined - effects on climate Cyclical nature of climate change

(b) Discuss the importance of the distribution of continents and mountain belts in influencing global climate in the Quaternary.

Position of continents affects oceanic circulation (and atmospheric) Particularly with reference to Quaternary positioning in N hemisphere Mountain belts (particularly Alpine-Himalayan) affect atmospheric circulation Recognition of other factors - Milankovitch Cycles; solar activity; volcanic activity etc.

4. (a) Explain how fossils can provide evidence for Quaternary climatic fluctuations.

Consideration of one or more (breadth versus depth) of the following : Pollen & vegetation community reconstruction Beetles Mammoths and other vertebrates – use of adaptation to climate Foraminifera and oxygen isotope data Tree ring climate data

(b) Evaluate the use of radiocarbon (14C) dating in determining the duration of Quaternary climatic fluctuations.

Absolute dating Can only date organic material 5,730 half-life Can only date recent events accurately Limited use during glacials – lack of dateable material Cannot be used for much of the Quaternary period

5. “Geological structure and lithology of an area controls drainage patterns of water both above and below the surface.” Evaluate this statement with reference to examples you have studied.

Effects of structure and / or lithology in production of :

Radial drainage (domes, volcanoes etc) Trellised drainage (dipping rocks, basin & range etc) Dendritic drainage (homogenous geology) Superimposed drainage Dry valleys Groundwater flow (aquifers, aquicludes etc) Subterranean river courses Springs

Breadth versus depth but must cover surface and groundwater

Credit use of examples

26

GL5 THEMATIC UNIT 2 – NATURAL RESOURCES

Section A

1. (a) (i) oval or disc shaped (1) concentric structure (1) layered/bedded (1) bowl / basin (1) use of scales (1)

(ii) Calcite (1) First to precipitate from solution / least soluble (1) forms the lower

layer (1) Only 50-60% of seawater volume needs to be evaporated (1)

(b) (i) Tides (1) storm (1)

(ii) 5 cm ≡ 3 metres 100 cm (1 metre) ≡ 20 × 3 = 60 metres 200 × 60 = 12,000 metres

(iii) Repeated sequences (of replenishment, evaporation, precipitation) (1)

followed by subsidence (due to mass of accumulated evaporites) (1 reserve)

(c) Atlantic too deep - unable to evaporate >60% of volume to commence

precipitation from solution (1) climate too cool - rates of evaporation low (1) conditions (e.g., turbulence) unsuitable (1) lack of suitable environments for playa formation (1)

2. (a) (i) S = Base of Chalk-junction with Gault Clay (1)

A = Any location vertically through the Lower Tertiary to Chalk (1)

(ii) Synclinal structure (1) Impermeable Gault Clay beneath (1) Chilterns and N Downs chalk outcrops at surface acts as unconfined aquifer (1) higher ground - more rainfall (1)

(b) Discussion of the following in correct context re porosity (space) and / or permeability (interconnection). BOTH discussed for 3 marks : Coccoliths - disc shaped with holes in centres. Loose packing / compaction of coccoliths. Joints / bedding planes / faults.

(c) (i) (25 to 26) − (11 to 12) = 13 to 15 metres (or use of scale)

(ii) Chalk acts as a natural filter and has fewer suspended particles (1) less treatment is required (1) stored at a stable temperature, low oxygen levels, surface waters vary in temp (1) reservoir water more likely to contain contaminants that need treatment such as chemicals / nitrates / other pollution sources (1) organic matter/algal blooms, etc., in surface reservoirs (1)

27

Section B 3. "Igneous processes are the most important processes in the formation of epigenetic

and syngenetic mineral deposits." Evaluate this statement and illustrate your answer with reference to examples you have studied.

Igneous processes – related to cooling and solidification of magma/lava and pyroclastic activity Explanation of syngenetic - formed at same time as enclosing rock Explanation of epigenetic - formed later than enclosing rock Processes (case studies ) one or more (breadth versus depth) of : - cumulate/gravity settling - pegmatitic - porphyry copper - pneumatolysis - metasomatism - hydrothermal - black smokers - kimberlites

Description of processes with links to the actual minerals being formed: cassiterite, galena, sphalerite, diamonds, chalcopyrite. Description of form of deposits – veins, lodes, reefs, stockworks Other processes – surface processes/sedimentary part of the rock cycle. Weathering and residual deposits, placer deposits, evaporites, supergene enrichment. Formation of coal in tropical swamps. Oil and gas.

4. (a) Evaluate the relative importance of the geological factors that favour the

formation and accumulation of large scale oil and gas deposits.

(b) evaluate the importance of anticlinal traps in the formation of large scale oil and gas deposits.

Essential nature of :

Source Rock - for production of hydrocarbons

- origin of hydrocarbons - from marine plankton - significance of temperature and depth of burial - idea of the oil window - argillaceous shales/clays

Reservoir rock - for storing of hydrocarbons

- high porosity and permeability, e.g., well sorted sandstones

Cap rock - for stopping vertical migration of hydrocarbons

- impermeable strata to stop oil from flowing upwards to surface, e.g., clay/mudstone/ shale argillaceous rock type

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Oil Traps - for large scale accumulation of hydrocarbons - anticline - just one of several types of trap - fault - unconformity - lithological - salt dome

Earliest discoveries − many anticlinal traps – most now depleted Extraction of oil from oil shales and oil sands – future trend.

Credit diagrams and appropriate examples

5. Evaluate the role of geophysical and geochemical techniques in the search for energy

and mineral deposits.

First step narrow down search to 'potential areas' using remote sensing and satellites - infrared imaging/computer analysis plus study of already available geological maps/surveys.

Geophysical methods - seismic - most important for locating oil and gas

- magnetic (often airborne) - dense metallic minerals - magnetite

- gravity (often airborne) - salt domes + dense metallic minerals

- resistivity – sulphides

Geochemical methods - mainly metallic ores - soil sampling solids and gases - vegetation surveys - stream sediment surveys - stream water analysis - laboratory investigations

In context : - Borehole drilling most informative / slow / expensive / to

assess 3 dimensional shape and size of ore-body - Assessment of grade and tonnage of ore body – rock

geochemistry - Assessment of results – decision to mine or not

Credit descriptions and examples of the above methods. Breadth v depth Credit annotated diagrams

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GL5 THEMATIC UNIT 3 – GEOLOGICAL EVOLUTION OF BRITAIN

Section A 1. (a) (i) WNW-ESE (accept E-W) (1)

(ii) NNE-SSW (accept N-S) (1)

(b) (i) Angular (1) / chevron (1) / zig-zag (1) / pointed (1) 0-15° (1) 40-55° (1)

(ii) 1 : overfold / recumbent / smaller interlimb angle / scale (wavelength and amplitude) 3 : hinge rounded / axial plane vertical / larger interlimb angle / scale (1)

(c) 10 − 6.5 = 3.5 m 3.5/10 × 100 = 35%

(d) Evaluation - HOLISTIC

From Tables : decrease in intensity from S to N as shown by folding style (1) and cleavage (1) and degree of crustal shortening (1)

From Fig 1a : granites / thrusts / ophiolites / low-grade regional metamorphism explained Evidence conclusive ? suduction ? obduction ? Variscan orogeny - pre-Variscan rocks affected

2. (a) (i) cross bedding (or flute marks)

(ii) lose energy / velocity (1) large grains first (1) finest longer to settle(1)

(b) (i) shale fine grained low energy (1) far from land (1) graptolites fragile planktonic forms best preserved in low energy water (1) chert ooze deposit (1) black rich in carbon (1) deep sea (1) anaerobic (1)

HOLISTIC - 3 valid points

(ii) erupted under water (1 reserve) oceanic crust / ocean floor / basaltic

ridge volcanics (1)

(c) thickest turbidites adjacent (2) = trench position (1) deep ocean / ocean floor / spreading ridge to south east (1)

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Section B 3. (a) Interpret the geology of the Tertiary Igneous Province of north west Britain in

plate tectonic terms

(b) Describe the evidence for rifting and subsidence in the North Sea and evaluate its relationship to plate movements in the Mesozoic and Ttertiary.

(a) Related to tension / rifting and ocean floor production:

Late Cretaceous early Tertiary igneous activity to NW Basaltic dyke swarms and lavas Varied associated plutonic activity Mantle plumes develop under NW Britain / Greenland Opening of N.Atlantic (Later) Granites due to melting of continental crust.

(b) Tensional regime

Rifting and subsidence N-S orientated (Jurassic early Cretaceous - ends late Cretaceous) grabens

4. Palaeomagnetic evidence suggests that during the late palaeozoic (Devonian,

Carboniferous and Permian), drifted across the equator. (a) Describe the evidence from sedimentary rocks and fossils which suggests an

equatorial climate in Britain in the Late Palaeozoic. (b) Describe and evaluate the palaeomagnetic evidence.

Devonian - south of Equator / arid / red beds / alluvial / fluvial / lacustrine / lack of fossils

Carboniferous - Equatorial / limestones / associated fossils / coal / tropical

swamps / forests / associated fossils Permian - north of Equator / breccias / sandstones / dune-bedding /

haematite cement / evaporites / mudcracks / desert / hypersaline / lack of fossils

(b) Formation of remanent magnetism (Curie Point)

Angle of inclination - zero at Equator re late Palaeozoic Latitude not longitude Polar wandering curves Inaccuracies due to absolute ages

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5. (a) Describe a range of techniques for collecting geological data in the field and explain how the data can be presented in a variety of forms.

(b) Evaluate the usefulness of these techniques in the interpretation of the geology

of an area with which you are familiar.

(a) Sediments : Hand specimen descriptions / logs / sedimentary structures / histograms / fossils / field sketches

Igneous: Hand specimen descriptions / contacts / associated

metamorphism / textures re cooling history / field sketches Metamorphic: Hand specimen descriptions / foliations / field sketches Structure: Dip and strike / rose diagrams / field sketches

Maps / sections / geological column

(b) Case study. Reliability / accuracy of data / weathering - erosion effects Inferred boundaries / outcrop availability

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GL5 THEMATIC UNIT 4 – LITHOSPHERE

Section A

1. (a) (i) parallel (1) / irregular (1) / NE-SW (1) / variable widths of stripes (1) /symmetrical(1) aligned (1) linear (1) alternating N and R (1)

(ii) MUST BE PARALLEL TO STRIPES FOR ANY MARK

line through "central stripe" (2 marks) line within limits of 200 m contour (1)

(iii) must be normal (1) / parallel to stripes (1) / within ridge 200 m

contour (1) / symmetrical(1)

(b) (i) Bruhnes

(ii) 8

(iii) longer reversed than normal

(c) (i) 210 × 105 (1) / 2.6 × 106 (1) = 8.08 (1)

(ii) different rates of production of oceanic crust / lithosphere (1) varying forces (1) / ridge push (1) / slab pull (1) varying rates of movement of convection currents (1) plates of different sizes/masses (1) different types of plate boundaries on either sides (1)

2. (a) (i) max horizontal (1) / min vertical (1)

(ii) NE-SW / in-out of paper / at right angles to the other (1) (iii) thrust / reverse (1)

(b) graded bedding (1) / right way up (1)

cross-bedding (1) / upside down (1) conflicting evidence (1)

(c) HOLISTIC - both compressional thus probably same stresses / probably same

time (but fold not faulted)

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Section B 3. Describe how the use of seismic studies may contribute to an understanding of the

theory of plate tectonics. Discuss the importance of the different depths of earthquake foci to the theory.

Describe Importance Distribution of earthquakes related to plate boundaries.

Plate boundaries

Circum Pacific / Alpine - Himalayan / oceanic ridges = boundaries

Plate boundaries

Shallow foci at CPM Shallow re rising hot material / mantle / CPM / spreading / MOR and East African Rifting

Benioff Zone at DPM Subduction related to convection

Conservative (mainly)shallow / complex

San Andreas / complex / tear movement

(tomography including mantle ?)

(magma / plumes)

Labelled diagrams (almost certainly) essential. Must address "importance" for higher marks.

4. (a) Describe the J. Tuzo Wilson Cycle.

(b) Discuss how the present-day distribution of rift valleys might support the theory. Labelled diagrams (almost certainly) essential.

(a) Description of phases (number irrelevant). Rising mantle / tension / thinning / CPM Rifting / African Rifts / CPM / rifting of continental lithosphere Spreading ocean floor Subduction / DPM / closing ocean Collision (b) African rifting and mid-oceanic rifts re theory. Connection of both (Afar). Rifting "irrelevant" to collision / DPM = "third part of theory". (Midland Valley of Scotland, etc., in context)

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5. Describe how sedimentary basins may be formed. Evaluate the importance of isostasy in the formation of sedimentary basins.

Note: (re specification) only expect one example (compressional or tensional). Labelled diagrams (almost certainly) essential. Case study. Compressional : DPM / formation of lithosphere / orogenic belts / erosion

provides sediment (on either side ?) Faulting / thrusting / folding contribute towards basin formation.

Tensional : Rifting. (North Sea basin ?) Sediment from sides of rift. Infilling. Fault reactivation.

Isostasy : weight of sediment leads to subsidence ± fault reactivation.

Isostatic rebound re orogenesis leads to increased sediment production and erosion of basins.

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MARK BAND CRITERIA FOR A2 ESSAYS.

Summary Description

Marks out of 25

Criteria

Outstanding 25-23 Not the perfect answer, but a candidate could not be expected to produce better work at this level in the time allowed.

Very good 22-20 Arguments are purposeful, well supported & show both balance and style. Irrefutable evidence of a thorough grasp of concepts & principles. A hint of flair apparent in the work.

Good 19-17 The answer is direct & explicit; shows the ability to use knowledge & understanding & to discuss. May be limited in terms of supporting material & breadth of coverage.

Quite good 16-14 Shows a reasonably secure grasp of the basics, but answer may show some slight deficiencies in terms of either knowledge & understanding or directness & organisation.

Modest 13-11 Material is mainly relevant & sound, but points need more development(& support). Could be much more direct & explicit in approach.

Minimal 10-8 Work impoverished by limited knowledge & understanding; tendency to rehash prepared material & to answer by inference. Answer rather hit & miss.

Weak 7-5 Little evidence of knowledge or understanding; unable or unwilling to address the question; essentially random in approach.

Very weak 4-1 Largely irrelevant; too brief; abundant erroneous material.

Unacceptable 0 Wholly irrelevant or nothing written. Incorporated into this mark scheme is the assessment of candidates on their ability to organise & present information, ideas, descriptions & argument clearly & logically, taking into account their use of spelling, punctuation & grammar.

GCE Geology MS (Summer 2007)/JD

Welsh Joint Education Committee 245 Western Avenue Cardiff. CF5 2YX Tel. No. 029 2026 5000 Fax. 029 2057 5994 E-mail: exams@wjec.co.uk website: www.wjec.co.uk/exams.html