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GL1 III KI 3

GL1 III KI 3. *The recognition on geological problem maps and description of: (i) Horizontal beds, dipping beds, strike and dip. Folds and faults as products of tectonic stresses Folds : limb, hinge, axis, anticline, syncline, axial plane trace, symmetrical and asymmetrical folds.

austin-chaney
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GL1 III KI 3

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  1. GL1 III KI 3 • *The recognition on geological problem maps and description of: • (i) Horizontal beds, dipping beds, strike and dip. • Folds and faults as products of tectonic stresses • Folds: limb, hinge, axis, anticline, syncline, axial plane trace, symmetrical and asymmetrical folds. • Faults: (i) dip-slip: normal, reverse, thrust; throw – amount, relative movement of footwall/hanging wall (ii) strike-slip: transcurrent. • Fault displacement (=net slip). • (ii) Unconformities as hiatuses in the geological record. The formation of unconformities by Earth movements and sea level changes. The use of unconformities in dating Earth movements • Unconformities with or without angular discordance • (iii) Intrusive and extrusive bodies (dyke, sill, pluton, lava flow); metamorphic aureoles; mineral veins; superficial deposits (alluvial, glacial).

  2. Main terms • *The recognition on geological problem maps and description of: • (i) Horizontal beds, dipping beds, strike and dip. • Folds and faults as products of tectonic stresses • Folds: limb, hinge, axis, anticline, syncline, axial plane trace, symmetrical and asymmetrical folds. • Faults: (i) dip-slip: normal, reverse, thrust; throw – amount, relative movement of footwall/hanging wall (ii) strike-slip: transcurrent. Fault displacement (=net slip). • (ii) Unconformities as hiatuses in the geological record. The formation of unconformities by Earth movements and sea level changes. The use of unconformities in dating Earth movements • Unconformitieswith or without angular discordance • (iii) Intrusive and extrusive bodies (dyke, sill, pluton, lava flow); metamorphic aureoles; mineral veins; superficial deposits (alluvial, glacial).

  3. a BED of rock • A layer • Stratum • Plural – strata • Top and bottom defined by bedding planes • Usually represents a minor gap in deposition, allowing the sediment to settle

  4. Law of original horizontality • All beds deposited horizontally to start with

  5. Superposition • Oldest beds on the base, younger on the top • Which is why way up structures are so useful – so we can work out which way up the rocks are

  6. Law of SUPERPOSITION (oldest rocks at the base) younger older Trevor Quarry, Llangollen

  7. Geological events can be placed in relativetime scales…. • OLDER THAN • YOUNGER THAN

  8. WAY-UP CRITERIA • Small features on bedding planes which tell us where the surface was

  9. RAIN IMPRINTS Rain falling onto soft sediment may leave a small CRATER Show sediment was pliable, dry and it rained!

  10. GRADED BEDDING • Heavier fragments fall fastest • In deep marine environments, turbidity currents bring unsorted material in, this settles out, largest particles first

  11. MUD CRACKS • Drying out of mud • Curls up at edges • Polygonal pattern

  12. LOAD CASTS / SOLE STUCTURES / mud volcanoes / flame structures • Sandy layer of sediment deposited over a muddy layer of sediment • Sand is more dense and pushes downwards into the mud layer • Mud layer “erupts” through

  13. WASHOUTS • Older bed eroded as river washes out sediment

  14. Cross bedding/dune bedding • Formation of a sand dune ….. • http://www.youtube.com/watch?v=yRRl3HyR3mc (NB: note animal adaptions to living in such climates) • http://www.youtube.com/watch?v=iMCY9WMnzaw&feature=channel (Namibian desert)

  15. Ripples • Symmetrical – bi-directional current – tidal area, waves • Asymmetrical – uni-directional current – river • http://www.youtube.com/watch?v=KYvWwbEi0A0&feature=related • http://www.youtube.com/watch?v=-sS-h_EjCwg&feature=related • http://www.youtube.com/watch?v=bVSH1q-2vhI&feature=related

  16. http://www.youtube.com/watch?v=DdIUuUY0L9c PILLOW LAVA • Underwater eruption • Pillow shapes – rapid solidification in contact with cold water • Convex upper surface • Sag on lower surface

  17. Revision: • Use GeoScience: • Page 191 – superposition • Page 192 – way up structures • Page 193 – included fragments

  18. What is the name given to this way up structure?

  19. INCLUDED FRAGMENTS Older rock

  20. INCLUDED FRAGMENTS • PEBBLES – are fragments from an OLDER bed of rock which has been eroded • Conglomerate • Breccia

  21. Included fragments – older than the bed they are contained in Fragments of Rock A younger Rock A older

  22. They can also be cut by igneous dykesbut more later!

  23. BGS map of Kirby Stephen How do you know that the beds are horizontal?

  24. BGS map of Kirby Stephen Bedding is parallel to the contours How do you know that the beds are horizontal?

  25. Rocks ORIGINALLY DEPOSITED HORIZONTALLY can get DEFORMED • Tilting (FROM THE HORIZONTAL) we call DIPPING • And the wavy patterns we call FOLDING • Push the edges of the page in front of you together …. You’ll notice it buckles up into wavy patterns

  26. Geologists MEASURE the dip of the rock from the horizontal = the ANGLE OF DIPand we also record which direction that points = DIP DIRECTION

  27. Dip, strike and apparent dip. • The strike is a horizontal line drawn on a bedding plane. • Can be measured by using a compass to give a direction. • The Dip is the maximum amount that the bed is inclined from the horizontal. • It can be measured by using a clinometer to measure the angle and a compass to give the direction.

  28. MARKER BED • We tend to use a MARKER BED to see where the layer is

  29. Wenlock Edge BGS map shows gently dipping rocks. Which way are the rocks dipping? Ordovician Silurian

  30. diagram of an escarpment Dip slope Scarp slope More resistant rock Less resistant rock Escarpments have a dip of 5-10o

  31. Escarpments are formed by gently dipping rocks. The angle of dip is usually 5o – 10o. Limestone dips away from the viewer Eglwyseg limestone escarpment, Llangollen, N. Wales

  32. Rocks can also be tilted to be nearly vertical

  33. Vertical beds exposed on coast. Three Chimneys, Marloes Bay, Dyfed

  34. Natural arch produced by tough limestones which are near vertical. Durdle Door, Dorset Postcard from BGS

  35. Remind yourself ….. • What have you learned so far today?

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