Gl1 iii ki 3
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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.

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GL1 III KI 3

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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.

  • 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).


Main terms

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).


A bed of rock

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


Law of original horizontality

Law of original horizontality

  • All beds deposited horizontally to start with


Superposition

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


Law of superposition oldest rocks at the base

Law of SUPERPOSITION (oldest rocks at the base)

younger

older

Trevor Quarry, Llangollen


Geological events can be placed in relative time scales

Geological events can be placed in relativetime scales….

  • OLDER THAN

  • YOUNGER THAN


Way up criteria

WAY-UP CRITERIA

  • Small features on bedding planes which tell us where the surface was


Rain imprints

RAIN IMPRINTS

Rain falling onto soft sediment may leave a small CRATER

Show sediment was pliable,

dry and it rained!


Graded bedding

GRADED BEDDING

  • Heavier fragments fall fastest

  • In deep marine environments, turbidity currents bring unsorted material in, this settles out, largest particles first


Mud cracks

MUD CRACKS

  • Drying out of mud

  • Curls up at edges

  • Polygonal pattern


Load casts sole stuctures mud volcanoes flame structures

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


Washouts

WASHOUTS

  • Older bed eroded as river washes out sediment


Cross bedding dune bedding

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)


Ripples

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


Pillow lava

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


Revision

Revision:

  • Use GeoScience:

  • Page 191 – superposition

  • Page 192 – way up structures

  • Page 193 – included fragments


What is the name given to this way up structure

What is the name given to this way up structure?


Included fragments

INCLUDED FRAGMENTS

Older rock


Included fragments1

INCLUDED FRAGMENTS

  • PEBBLES – are fragments from an OLDER bed of rock which has been eroded

  • Conglomerate

  • Breccia


Included fragments older than the bed they are contained in

Included fragments – older than the bed they are contained in

Fragments of

Rock A

younger

Rock A

older


They can also be cut by igneous dykes but more later

They can also be cut by igneous dykesbut more later!


Bgs map of kirby stephen

BGS map of Kirby Stephen

How do you know that the beds are horizontal?


Bgs map of kirby stephen1

BGS map of Kirby Stephen

Bedding is parallel to the contours

How do you know that the beds are horizontal?


Rocks originally deposited horizontally can get deformed

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


Gl1 iii ki 3

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


Dip strike and apparent dip

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.


Marker bed

MARKER BED

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


Wenlock edge bgs map shows gently dipping rocks

Wenlock Edge BGS map shows gently dipping rocks.

Which way are the rocks dipping?

Ordovician

Silurian


Diagram of an escarpment

diagram of an escarpment

Dip slope

Scarp slope

More resistant rock

Less resistant rock

Escarpments have a dip of 5-10o


Escarpments are formed by gently dipping rocks the angle of dip is usually 5 o 10 o

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


Rocks can also be tilted to be nearly vertical

Rocks can also be tilted to be nearly vertical


Vertical beds exposed on coast

Vertical beds exposed on coast.

Three Chimneys, Marloes Bay, Dyfed


Natural arch produced by tough limestones which are near vertical

Natural arch produced by tough limestones which are near vertical.

Durdle Door, Dorset

Postcard from BGS


Remind yourself

Remind yourself …..

  • What have you learned so far today?


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