Transcript GL1 III KI 3

GL1 III KI 3
SPECIFICATION
*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).
a BED of rock
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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
• All beds deposited horizontally to start with
SEDIMENTARY
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
SO WHAT WOULD
THAT LOOK LIKE FROM
ABOVE?
• Concentric shapes
• Like contour lines
This would
be the MAP
version
Law of SUPERPOSITION
(oldest rocks at the base)
younger
older
Trevor Quarry, Llangollen
Geological events can be placed in relative
time scales….
• OLDER THAN
• YOUNGER THAN
WAY-UP CRITERIA
• Small features on bedding planes which
tell us where the surface was
• 2 minutes … In pairs … take it in turns
to draw a diagram and for the other to
name the structure and how it forms
and a scale!
RAIN IMPRINTS
Rain falling onto soft sediment
may leave a small CRATER
Show sediment was pliable,
dry and it rained heavily! But
not too much to turn the area
to mush.
GRADED BEDDING
• Heavier fragments fall fastest
• In deep marine environments, turbidity
currents bring unsorted material in, this
settles out, largest particles first
MUD CRACKS
• Drying out of mud
• Curls up at edges
• Polygonal pattern
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
• Older bed eroded as river washes out
sediment
Cross bedding/dune bedding
• Formation of a sand dune …..
• http://www.youtube.com/watch?v=yRRl3HyR
3mc (NB: note animal adaptions to living in
such climates)
• http://www.youtube.com/watch?v=iMCY9W
Mnzaw&feature=channel (Namibian desert)
Ripples
• Symmetrical – bi-directional current – tidal area,
waves
• Asymmetrical – uni-directional current – river
• http://www.youtube.com/watch?v=KYvWwbEi0A0&feature=r
elated
• http://www.youtube.com/watch?v=-sSh_EjCwg&feature=related
• http://www.youtube.com/watch?v=bVSH1q2vhI&feature=related
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:
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Use GeoScience:
Page 191 – superposition
Page 192 – way up structures
Page 193 – included fragments
What is the name given to this
structure which could tell you an age
relationship and the way up of the
beds?
INCLUDED FRAGMENTS
Older rock
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
Fragments of
Rock A
younger
Rock A
older
They can also be cut by igneous dykes
but more later!
BGS map of Kirby Stephen
How do you know that the beds
are horizontal?
BGS map of Kirby Stephen
How do you know that the beds
are horizontal?
Bedding is
parallel to the
contours
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
Geologists MEASURE the dip of the rock
from the horizontal = the ANGLE OF DIP
and we also record which direction that
points = DIP DIRECTION
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
• We tend to use a MARKER BED to see where
the layer is
Wenlock Edge BGS map shows gently dipping
rocks.
Which way are the rocks dipping?
Ordovician
Silurian
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 5o – 10o.
Limestone dips away
from the viewer
Eglwyseg limestone escarpment,
Llangollen, N. Wales
Rocks can also be tilted to be nearly
vertical
Vertical
beds
exposed
on
coast.
Three Chimneys,
Marloes Bay,
Dyfed
Natural arch produced by tough
limestones which are near vertical.
Durdle Door, Dorset
Postcard from BGS
Remind yourself …..
• What have you learned so far today?
• Revision here ….
http://www.geologyin.com/2014/11/terminology-of-brittle-
deformation.html?utm_source=feedburner&utm_medium=email&utm_campaign=Feed%3A+AmazingGeologist+%28Amazing+Geologist%29