GEOLOGY - GL4 INTERPRETING THE GEOLOGICAL RECORD

Transcription

1 Candidate Name Centre Number 2 Candidate Number GCE A level 1214/01 GEOLOGY - GL4 INTERPRETING THE GEOLOGICAL RECORD A.M. MONDAY, 21 June hours Section A Section B ADDITIONAL MATERIALS In addition to this examination paper, you will need: the Geological Map Extract (New Cumnock); a hand-lens or magnifier to study the map (optional); a calculator; a protractor. Total 100 INSTRUCTIONS TO CANDIDATES Write your name, centre number and candidate number in the spaces at the top of this page. Answer all questions. Write your answers in the spaces provided in this booklet. INFORMATION FOR CANDIDATES The number of marks is given in brackets at the end of each question or part-question. Candidates are reminded that marking will take into account the quality of communication used in their answers. JD*(S )

2 2 SECTION A Answer all questions in the space provided. This section should take approximately 1 hour to complete. 1. Figure 1a shows different tectonic settings for the generation of magma. Figures 1b and 1c are temperature/pressure diagrams showing the geothermal gradient and melting temperatures for dry (anhydrous) and wet (hydrous) peridotite, obtained by laboratory experimentation. Depth (km) partial melting in rising column mid-ocean ridge volcano A X magma Moho oceanic crust Location X (dry peridotite) ocean mantle peridotite showing convection currents trench Location Y (wet peridotite) volcano B continental crust Y magma Depth (km) 200 Source: S236 Geology Book 2, reproduced by permission of The Open University Figure 1a TEMP C TEMP C MELT MELT Depth (km) SOLID location X Melting point curve at which dry (anhydrous) peridotite begins to melt Depth (km) SOLID Melting point curve at which wet (hydrous) peridotite begins to melt location Y 400 geothermal gradient Figure 1b 400 geothermal gradient Figure 1c (a) Refer to Figure 1a. State the lava type most likely to be erupted from volcanoes A and B. [2] Volcano Lava type A B ( )

3 3 (b) Refer to Figures 1a and 1b. (i) Using Figure 1b, give the temperature and describe the probable state of the mantle at location X (solid, partially molten or molten). [2] Mantle temperature at location X... C State of the mantle at location X.... (iii) Draw a line on Figure 1b to represent dry peridotite rising by convection, from location X (beneath the ocean ridge), and erupting onto the surface at a temperature of 1200 C. [2] With reference to Figure 1b, explain how mantle convection may result in the generation of magma from dry peridotite beneath ocean ridges. [3] (c) Refer to Figures 1a and 1c Location Y is at the same depth as location X but composed of wet peridotite. Describe the probable origin and effect of the water in the generation of magma from wet peridotite at location Y. [3] Origin... Effect... (d) Using your knowledge, describe one process by which the composition of magma may change from its original composition as it rises through the lithosphere at convergent (destructive) margins. [3] Total 15 marks ( ) Turn over.

4 4 2. Figure 2a shows the changes in diversity of fauna (Sepkoski s curves) during the Phanerozoic. Number of faunal families in the fossil record Total number of faunal families Cambrian fauna End-Ordovician extinction End-Devonian extinction Palaeozoic fauna End-Permian (P/T) extinction Modern fauna End-Cretaceous (K/T) extinction 0 Precambrian Cambrian Ordovician Silurian Devonian Carboniferous Permian Triassic Jurassic Cretaceous Cenozoic Refer to Figure 2a. Phanerozoic Source: Milsom & Rigby Fossils at a Glance (2009) Figure 2a (a) (i) State the total number of faunal families at the end of the Cambrian. [1] State the most abundant Phanerozoic fauna ( Cambrian, Palaeozoic or Modern fauna) that existed during the Devonian. [1] (iii) Describe the changes in relative abundance of Phanerozoic faunas between the end-devonian and end-cretaceous (K/T) mass extinction events. [3] (b) (i) Using Figure 2a, calculate the percentage of faunal families that became extinct during the end-permian mass extinction (P/T). Show your working. [2] ) Percentage of families extinct...%

5 5 From your knowledge, describe one possible mechanism for the end-permian (P/T) mass extinction. [3] (c) Figure 2b and Figure 2c show sketches of the diversity within typical Cambrian and Modern faunas (in Figure 2a) based on fossil evidence. Cambrian fauna Modern fauna Source: Milsom & Rigby Fossils at a Glance (2009) Figure 2b Figure 2c (i) With reference to Figure 2b and Figure 2c, describe two differences in the modes of life of Cambrian and Modern fauna which help explain the greater diversity during the Phanerozoic. [2] Some Cambrian fossil formations (e.g. Burgess Shale) have recorded higher diversity of faunas than in Figure 2b. Explain the factors that may lead to an underestimation of the true diversity of fauna in the Cambrian. [3] Total 15 marks Turn over.

6 6 3. Figure 3 is a partly completed block diagram of a plunging fold cut by a dip slip fault and a dyke. dip-slip fault N shale layer dolerite dyke sandstone Key minor folds within shale Figure 3 (a) (i) Complete the table below to describe the fold elements of the major fold. [3] Fold element Description Fold type Symmetry Orientation (strike) of the axial plane trace Direction of plunge of fold axis Symmetrical - limbs the same length Describe how the following two characteristics of the minor folds within the shale differ from the fold in the sandstone. [2] Wavelength... Symmetry )

7 7 (iii) Account for the difference in the way the shale and sandstone have responded to stress during folding. [3] (b) Complete Figure 3, to the north of the fault outcrop, by sketching, on the top surface (i) the outcrop of the dyke, [1] the probable outcrop of the shale. [2] (c) A student concluded that: 1. the fault and fold were both formed by compressional stresses, during the same crustal shortening event; 2. the dyke formed after the folding, before the faulting. Evaluate these statements explaining the evidence for your conclusions. [4] Total 15 marks ( ) Turn over.

8 8 4. Figure 4a is a palaeogeographical map of the late Carboniferous showing the general distribution of the continents and climatic zones. Figure 4a Source: adapted from 2000, PALEOMAP project Refer to Figure 4a. (a) (i) Describe the global distribution of continents during the late Carboniferous. [2] Explain how the global distribution of continents may have influenced the development of ice sheets at both poles (icehouse conditions) in the Carboniferous. [2] (iii) Describe two characteristics of ancient glacial deposits that provide evidence of icehouse conditions in the Carboniferous. [2] ( )

9 9 (b) Figure 4b shows a generalised section of Carboniferous coal measure cyclothems, consisting of repeated cycles of sedimentation ending in a coal seam. The change in sedimentation within each cyclothem is interpreted as a change in the energy and environment of deposition. Source: Adapted from Bulletins/102_1/gifs/fig2.gif Figure 4b (i) Using the evidence from Figure 4b, describe the changes in energy and depositional environment within the cyclothem indicated. [3] Energy Environment (iii) Mark a cross (+C) on the map (Figure 4a) to show the most likely location of a depositional environment and climate suitable for the accumulation of coal. [2] Explain how repeated coal cyclothems may reflect global changes in size of continental ice sheets sea level changes variations in Earth s orbit during the Carboniferous. [4] Total 15 marks Turn over.

10 10 SECTION B Questions 5-7 relate to the British Geological Survey 1: geological map extract from the New Cumnock (Solid) Sheet. Answer all questions in the spaces provided. This section should take approximately 1 hour to complete. 5. (a) Refer to the Geological Map. (i) State the angle of dip of the inclined strata within the Kirkcolm Formation (KKF), shown by the dip symbol close to grid reference (GR) [1] Dip... degrees Describe the measurements that must have been made at this locality so that the dip symbol could be plotted. You may wish to use an annotated diagram(s). [3] (b) The Southern Upland Fault (grid square 7518) has been active since the Early Palaeozoic and has a long history of reactivation into the Tertiary. Complete Table 5 to describe the main fault characteristics shown by map evidence alone. [3] Fault characteristics on geological map Dip direction and angle (degrees) Strike directions Downthrow direction Fault type Southern Upland Fault NW at approximately 85 ( ) Table 5

11 11 (c) The granodiorite (G D - grid square 7718) is part of a large igneous pluton. (i) State the maximum and minimum width of outcrop of the metamorphic aureole south of gridline 18. Give your answer in metres (m). [2] Metamorphic aureole outcrop width (m) Maximum Minimum Draw an annotated diagram(s) to explain how the width of outcrop of the metamorphic aureole may reflect a variation in the dip of the contact between the pluton and the country rock. [2] (iii) Give one other possible explanation for the variation in outcrop width of the metamorphic aureole. [2] Total 13 marks ( ) Turn over.

12 12 6. Figure 6a shows a vertical cliff section through a Siluro-Devonian conglomerate (cg), typical of those within the Auchtitench Formation (AUC), grid square The pebbles show an imbrication a sedimentary structure in which pebbles are stacked-up on top of each other and aligned roughly parallel to the current that deposited them. The pebbles dip upstream, in the opposite direction from which the palaeocurrent was flowing. Figure 6a (a) (i) Describe the evidence from Figure 6a that suggests these conglomerates were deposited by flash floods. [3] With reference to the cross-section (P-Q), describe and suggest an explanation for the variation in thickness of the conglomerates (cg) within the Auchtitench Formation (AUC), north of the Southern Upland Fault. [2] ( )

13 13 (b) Table 6 shows the result of an analysis of 144 pebble orientations typical of the Auchtitench conglomerates (cg). Figure 6b is a partly completed rose diagram of palaeocurrent directions associated with these data. Direction Total pebbles N 48 NE 25 E 10 SE 3 S 8 SW 0 W 15 NW 35 Table 6 Figure 6b (i) Complete the rose diagram (Figure 6b) to show the palaeocurrent directions typical of this conglomerate. [3] Describe the variations in palaeocurrent directions shown by the completed Figure 6b. [2] (iii) Figure 6a represents the most typical palaeocurrent direction. Estimate the probable direction in which the camera (Figure 6a) was pointed. [1] (c) Explain how the Southern Upland Fault may have influenced palaeocurrent directions during the deposition of Siluro-Devonian sediments. [2] Total 13 marks Turn over.

14 14 7. Figure 7 is part of the Geological Map (Box A) showing the boundaries of the existing Glenmuckloch Opencast Coal site. Two extensions to this pit were proposed in 2007 for opencast development: the Samsiston and Knowe sites. Existing Glenmuckloch Opencast Coal site (fd T ) N Proposed Samsiston opencast extension site Excavation depths of 35 m (above current water table) are estimated and the removal of tonnes of coal from the Lower Coal Measure Swallowcraig coals (SC). The general dip is 20 degrees to the South GR Proposed Knowe opencast extension site Excavation depths of 90 m (below current water table) are estimated and the removal of tonnes of coal from three Middle Coal Measure seams, dipping approximately 5 degrees East. Figure 7 Refer to the Geological Map, Figure 7 and generalised Geological Column. (a) State the rock type (fd T ) and name the geological feature that controls the northern boundary of the Glenmuckloch Opencast site. [2] Rock type (fd T ) Geological feature )

15 15 (b) (i) Complete Table 7 below to indicate the order of superposition of the three coals first encountered during the proposed mining operations beneath the Knowe site. [2] Dip direction Average angle of dip (degrees) Name of coal seam Relative age of coal seam youngest East 5 degrees oldest Table 7 The generalised Geological Column shows three coal seams within the Lower Coal Measures (LCMS). Explain why the Kirkconnel Splint coal (KSP), as seen at GR , would not be expected beneath the Samsiston site. [2] (iii) Suggest two geological factors that may affect the accuracy of coal reserve estimates and excavation depths beneath the two proposed sites. [2] (c) Using the information given and your knowledge, identify the possible environmental issues associated with the further extraction of coal resources from the Glenmuckloch Opencast site. [6] Turn over.

16 Total 14 marks ( )