Name(s): ______________________ ____________________________________
Section (please circle one):
Thurs-002
Lab 10: Geologic Structures, Maps and Block Diagrams: AGI 10th Ed. F2014
Read Chapter 10 in Busch and Tasa. Read the introduction and carefully review structural geology and
geologic mapping principles and symbols on Pages 259-282 plus the Figure 8.10, the Geologic time scale and
fossil succession chart on p 213.
Know and understand: original horizontality, continuity, correlations and stratigraphic sequences, superposition,
inclusions, and cross cutting relations.
Learn to recognize the three different types of unconformities, various types of folds and 4 major types of faults.
Use stratigraphy as the key to structure. Knowing the succession allows you to tell what was deeper.
Unconformities: always label which type it is: <Dis>, <Ang> or <Non>!
1. Disconformity – erosion or non-deposition generally lasting years to millions of years. Parallel beds above
and below but missing time, fossils and facies.
2. Angular unconformity requires deformation and erosion, generally millions of years or more. Underlying
beds are eroded at an angle before deposition resumes. As sea level rises, deposition may resume at one location
before others so the lowest stratum of the overlying sequence can vary laterally until sediments fill in across the
entire region.
3. Nonconformity marks erosion clear down to crystalline basement rocks below the sedimentary basin. Often
this is the basal unconformity for an entire sedimentary basin. The rocks below are deformed igneous and
metamorphic that are hundreds of millions or billions of years older than the overlying sedimentary succession.
These underlying rocks represent the roots of eroded mountain belts and they are often quite distant from a
modern plate margin.
Faults
All faults show up as break where the correlated strata or rock fabric is offset across a planar surface. They are
the trace of past earthquake rupture and tend to form near or adjacent to plate boundaries where stresses build.
Some faults moved only once and may have offsets of only a few centimeters. Major plate bounding fault zones
may be several tens of kilometers wide with many fault strands. Depending on the behavior and different
strengths in a stack of rocks, faults may laterally fade away into the axes of folds, or join up to make one big
master fault.
Dip Slip Faults: Here the fault motion slid up or down the slope or dip of the fault plane
1. Normal – This is the normal kind of fault to find in the top of the crust as erosion unloads the crust and it fails
in tension. Typically these are high angle faults where the footwall falls, as in rifts, volcanic settings, or the
basin and range. The dip on normal faults often decreases with depth in a “listric” fashion so that several normal
faults merge into one basal shear plane.
2. Reverse – high angle fault (dip > 45°) where the footwall rises, typical of convergent settings. Typical in
mountain fold and thrust belts like the Rockies or the Alps.
3. Thrust – low angle fault (dip < 45° and often <10°) typical of convergent settings, fold and thrust mountain
belts and overthrust ranges (Eastern Rockies, Wind River Mountains in Wyoming). This is also the fault type of
subduction zones which typically dip at 10-15° where they intersect the seafloor. The symbol for this fault on a
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map view has teeth along the fault on the side of the upper plate. In cross section use arrows only as with any
other fault type.
Strike-slip & Oblique Slip Faults: In these faults the motion is horizontal, along the strike of the fault and the
fault plane is usually vertical or nearly vertical.
4. Strike-slip are high angle faults with purely lateral motion or offset, named either right lateral or left lateral
for their sense of motion. This includes the major oceanic fracture zone transform faults that offset the mid
ocean ridge system (Mendocino, Blanco, Sovanco, Clipperton) and major plate boundary transform faults like
the San Andreas, Queen Charlotte-Fairweather, Alpine, Anatolian etc. Smaller scale strike-slip faults are found
as tears between thrust panels in fold and thrust belts like those in the foothills of the Canadian Rockies. Strike
slip transform faults take up differential rotation when blocks of crust slide or shear past each other.
5. Oblique-slip Faults: In these faults the motion is at an angle to both the horizontal and to the steepest line of
descent in the fault plane. The motion is oblique to the fault plane and is a combination of horizontal, along the
strike and vertical along dip motions. The fault planes are often curved and this type of faulting occurs along
curved contacts of mountain belts or where strike slip faults cut mountain ranges or are otherwise affected by
rocks of different strengths on both sides of the fault. Most of these occur in bends or raises along major strike
slip faults, or at the ends of thrust faults.
Strike and Dip and other common map symbols:
Please refer to the various map symbols and their definitions on p. 264-266.
Strike is the “long direction” on a geological map. This direction the trace of a horizontal line formed from the
intersection of a plane of rock and the surface of the earth. It is measured in degrees clockwise from North at 0°
in a circle with 360°. Strike is always parallel to the long direction of bedded formations on a geological map.
The strike direction of a fault, dyke or vein is along that feature as it crosses the surface of the Earth.
Dip is perpendicular to the strike line and points in the downhill direction. It is measured in degrees below the
horizontal ranging from 0° to a maximum of 90°.
Special cases: horizontal beds are denoted with a plus sign + or an X in a circle (also called quaquaversal
dip). Vertical beds like intrusive dykes are denoted with a short cross bar perpendicular to the strike symbol
With bedded rocks it is possible to tell the way up from the succession of fossils or local stratigraphy and also
from the orientation of cross beds, fossils, pebble imbrications and other sedimentary structures such as mud
cracks or graded beds. Because of this, it is possible to tell when beds are upside down. We use special symbols
for overturned strike and dip, fold axes etc. that pay attention to the overturning direction (vergence) as well as
angles. These symbols look like bent over croquet wickets or capital U’s or their upside down equivalent. The
open end of the line always points down dip.
Fault traces are shown by a bold line with either U and D for up and down on respective sides for normal and
reverse faults on a map or given by a laterally opposed pair of arrows pointing the direction of strike slip motion
(to the right or to the left) on top of the map. For faults shown in cross section always use arrows to indicate the
relative sense of motion across the fault.
For Thrust faults, a series of triangular teeth is drawn on the map edge of the upper plate (subduction zones)
When a fault has a compound motion that is neither purely dip slip nor purely strike slip, it is termed an oblique
slip fault. Because of the compound motion, both the UD and opposed arrows are shown on the map.
Fold axis symbols:
Anticlines have outwards facing arrows, antithetic to the strike along the fold hinge. (outwards dips for Domes).
Synclines have inwards facing arrows, synthetic to the strike, along the fold hinge. (inwards dips for basins)
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Recumbent folds lay down sideways and both limbs tend to be parallel, one is overturned
Monoclines drape across basement faults and resemble half of a syncline/half of an anticline
Unconformites: Hiatus and unconformities are denoted by bold wavy lines between stratigraphic packages,
whether these occur on a cross section or along a map surface.
Activity 10.1: Geological Structures Inquiry
Geological structures are broadly divided into those which form under brittle (cold, shallow,
dry, explosive, fast strain rates) conditions such as jointing, faulting, brecciation and those
which form under ductile conditions (deep, warm, fluid-rich, recrystallization or plastic-flow)
such as folding, diapirism, regional metamorphism. In some settings the rocks have experienced
more than one episode of deformation or experienced changing environmental conditions. For
example sedimentary salt beds can flow at 1-4 km depth then become uplifted and unloaded to
break along joints. In the photo below by Dr. Callan Bentley of Northern Virginia Community
College, there are dipping gravels and muds overlying a tilted angular unconformity, eroded
down onto the normally faulted and intensely folded sandstones and mudstones of the Harpers
Formation near Harper’s Ferry Virginia. It looks like the Appalachians Mountains were a
happening place, more than once!
A. Examine the geological photos 1-4 on p.273 in the AGI manual and indicate whether the rocks pictured are:
a) undeformed (horizontally layered) b) uniformly dipping (planar but tilted) c) faulted (offset layers) d)
jointed (fractured but not offset) e) folded (curved structures). Circle any answers that apply.
1. Grand Canyon (Cambrian-Permian): a) undeformed
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b) dipping c) faulted
d) jointed e) folded (2)
2. Cliff in South Central Alaska:
a) undeformed
b) dipping c) faulted
d) jointed e) folded (2)
3. Quartzite, Maria Mountains, CA:
a) undeformed
b) dipping c) faulted
d) jointed e) folded (2)
4. Sandstone, Little Colorado Gorge:
a) undeformed
b) dipping c) faulted
d) jointed e) folded (2)
B.1 Which of the images show ductile deformation?
2. Which of the images show evidence of brittle deformation?
1)
1)
2)
2)
3)
3)
4)
4)
(2)
(2)
Activity 10.2: Visualizing How Stresses Deform Rocks
A.Visualize all stresses or forces involved in the following deformations &complete the table below, checking
any which apply.
.
Object/Action
Confining Pressure
Directed Pressure
Compression Tension Shear
1.Smashed Carton
2. Sealed Soda Can
3. Stretched elastic
4. Rubbed hands
B. Illustrate these block diagrams as per instructions in 1-3 below.
a. _____________________
b. _______________________
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c. _____________________
1. On the Figure above trace on the stress directions as arrows on each of the 3 folded and faulted strata. (6)
2. On each of the 2 sides of the fault blocks in the bottom row of block diagrams, put the appropriate symbols
for the relative sense of fault motion across the fault. When you view a strike skip fault in cross section, the side
that comes towards you is labelled with a bullseye (circle with a dot in the middle) the side that moves away is
labelled with an x inside a circle. On the map view of the dip slip faults, put a U on the up-thrown side and a D
on the down-thrown side.
(6)
3. Below each of the 3 fault types, label the appropriate type of plate margin where these structures tend to
occur: Transform/Strike-Slip, Convergent/Subduction, Divergent/Rift.
(3)
C.1 All of the above diagrams a, b & c, the stresses dominantly seem to act in the horizontal plane, with a
direction parallel to the Earth’s surface. In each case there is also a vertical force. Name this force. ________
_____________________________________________________________________________________ (1)
2. For each of the 3 settings, explain how the vertical force manifests and describe what part of the deformation
in the block diagrams it aids or opposes.
a. ___________________________________________________________________________________ (2)
b. ___________________________________________________________________________________ (2)
c. ___________________________________________________________________________________ (2)
Activity 10.3: Map Contacts and Geological Formations
To make geological maps or cross sections and to trace out structures, we need
something to trace out or to correlate. The fundamental unit of stratigraphy and
mapping is called the formation. A formation must be laterally extensive, thick enough
to show up on a map and generally consists of a related stack of beds or lithologies
which contain fossils of the same age and a related set of environmental indicators.
Formations are organized into Groups and Supergroups. Formations usually are a
several metres to hundreds of metres thick and represent a few million to many tens of
millions of years of geological time.
A. The photo below is near the leading edge of the Rocky Mountains in Western Montana. The Rockies formed
in Late Cretaceous through Early Tertiary time because of rapid convergence between the Farallon Plate
(former Eastern Pacific seafloor) and North America. These forces were so great that mountains were built from
older rocks > 1000 km east of the subduction margin! Nearby, this same structure turns into the Lewis Thrust.
1 On the image below of Scapegoat Mountain trace in the upper and lower bedding plane contacts for the cliff
forming Lower Paleozoic limestones entirely across the width of the photo. __________________________ (2)
2. What is the geological name for this kind of structure? (two words) __________________ ___________ (2)
3. What kind of stresses formed this structure? ________________________________________________ (2)
4. Draw in arrows for the relative directions of those stresses above and below the photo. _______________ (2)
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West
East
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B.1 Draw in the contacts for the base of the buff coloured Cambrian Muav Limestone near the base of the
canyon and the base of the white coloured Pennsylvanian Watahomigi sandstone near the top of the plateau on
the oblique air photo above. _______________________________________________________________ (4)
2. Colour the region between the 2 contacts on your map above red, and above the Watahomigi as Blue.___ (2)
3. Look at your geological map here and the related images and topographic map in the manual on p. 275 to
decide whether the Watahomigi Formation is deformed into a geological structure to give it this shape or
whether it is flat lying. Choose one:
a) Deformed b) Flat Lying (2)
4. Explain your reasoning for the shape you found and why you interpreted its origin this way. ____________
_______________________________________________________________________________________
______________________________________________________________________________________ (2)
Activity 10.4: Determine the Attitude of Rock Layers & a Formation Contact
Strike is a map direction. Expressed as a map quadrant, it can be something general like
NNE, E, SE as per the Compass Rose on an old nautical chart. Azimuth is measured as
degrees east of north so the same strikes might be given as: N 22.5° E, N 90° E & N 135° E.
A.1 This page is just as flat as the top of the rock wall pictured in A.1 on p,276. Put the appropriate structural
symbol here to show its horizontal orientation and lack of dip. ___________________________________ (1)
Symbol:
2. This plan view photo A.2 p.276 is a dipping (tilted) slab of rock much like a boat ramp at the edge of the sea.
Assuming the top of this page is oriented North, Draw the Strike and Dip symbol here. After you draw it, give
the Compass direction of the Strike (Quadrant strike) for your symbol and give its Azimuth Strike (compass
bearing in degrees east of north).
Symbol:
(1)
Quadrant Strike: ___________________
(1)
Azimuth Strike:
(1)
___________________
3. This oblique view photo A.3 p.276 is a dipping (tilted) slab of rock much like a boat ramp at the edge of the
sea. You can see the dip direction by the wet line from the descending stream of water from the sqeeze bottle.
Assuming the top of this page is oriented North, Draw the Strike and Dip symbol here. After you draw it, give
the Compass direction of the Strike (Quadrant strike) for your symbol and give its Azimuth Strike (compass
bearing in degrees east of north).
Symbol:
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(1)
Quadrant Strike: ___________________
(1)
Azimuth Strike:
(1)
___________________
Judging Dips from Geological Maps: The Earth’s surface to a first approximation is a
horizontal plane. A bed of rock, a dyke, a sill or a thick mineral vein is also a planar object.
Where 2 planes intersect they make a single line. Take 2 sponges and do this. The orientation of
this linear geological contact on a map is called strike. Where land has a gentle slope, streams
erode and run downhill. A stream valley cuts down into the “horizontal” surface and allows you
to see a bit of the cross section. Streams tend to converge as tributaries come together enabling
us to see the flow direction. Rock beds which dip vertically show no offsets as they cross
streams. Dipping beds generally control the tilt of land and flow direction of streams. For
dipping beds having downstream dips, the strike of contacts is offset in the down-stream
direction, because the overlying bed is removed in the notch of the stream channel. Take a cut
pot scrubber and lay it on top of a dipping sponge to visualize how this works when you look
down on it from above. This trick that V’s point down dip is called “The Rule of V’s”
B. Grab some coloured sponges or scouring pads from our collection on the carts and use them to make the
maps and cross sections below. For each of the 2 maps below 1) Draw a possible cross section that agrees with
the map in the open rectangle below. 2) Draw the strike and dip symbol on the map and 3) Give the numerical
value of the strike azimuth with respect to North in the blank below the cross section. Hint use the Rule of V’s
to determine the dip direction and sketch this in on the cross sections below. Here the dip angle is approximate
as we do not have the topography nor the stream gradient to calculate a specific angle.
(6)
C. The following aerial photograph is 1 km square and taken from directly above the center of the photo in the
Great Basin. Dipping strata have outcrop patterns that resemble chevrons on a Sergeant’s sleeve. As these beds
differentially erode, the contacts between sandstones and shales obey the Rule of V’s. On the photo:
1.a (D in manual) Draw in the contact for 2 different beds which are about 200 m apart on the hillside.
(2)
1.b Circle a “V” shaped stream notch which points down dip.
(1)
2. Recall Strike is the “Long direction”. Add a strike and dip symbol on the face of a chevron.
(2)
3. What is the strike azimuth (degrees east of north)? _________________________________________ (2)
4. What is the dip direction (azimuth of the down dip vector) and how do you know this from just looking at the
aerial photo before you use the protractor? _____________ ___________________________________ (2)
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Activity 10.5: Cardboard Model (Paper Copies) Analysis and Interpretation
A.1 through F.1 Complete each of the geological maps placing all appropriate: faults, unconformities, strike
and dip symbols, dip degrees., fold axes etc. Make sure you draw in all beds, unconformities, intrusions etc. on
the ends or sides of the image if they are not drawn in already. Contacts need to match up where corners touch.
Do not fold these up for handing in. Submit them complete and flat.
(60 points)
Do this part of the lab on the models provided.
Once you have completed each model, give the stepwise geological instructions for forming each block of
geology as represented. Include sedimentation e,g, Cambrian Through Devonian strata were deposited.
Deformation: Those strata were tilted, folded faulted etc. Erosion: this structure was eroded. And any new
episodes of deposition etc.
A.2 Explain the sequence of geological events that led to this geological map and block diagram. If
sedimentation was in ordinary sequence without unconformities it is not necessary to list the deposition of each
stratum. Do include any structural deformation, name the structures formed and include any erosional
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unconformities. S through P denote the Geological time Periods Silurian through Permian respectively. ___
Structure Name: _______________________________________________________________________ (1)
_______________________________________________________________________________________
_______________________________________________________________________________________
_____________________________________________________________________________________ (3)
B.2 Explain the sequence of geological events that led to this geological map and block diagram. If
sedimentation was in ordinary sequence without unconformities it is not necessary to list the deposition of each
stratum. Do include any structural deformation, name the structures formed and include any erosional
unconformities. Bed B was deposited up the eroded surface of plutonic rock A. The block does not go far
enough east to show beds G or younger strata. Structure Name: __________________________________ (1)
________________________________________________________________________________________
________________________________________________________________________________________
_______________________________________________________________________________________
_____________________________________________________________________________________ (4)
C.2 Explain the sequence of geological events that led to this geological map and block diagram. If
sedimentation was in ordinary sequence without unconformities it is not necessary to list the deposition of each
stratum. Do include any structural deformation, name the structures formed and include any erosional
unconformities. Structure Name: __________________________________________________________ (1)
________________________________________________________________________________________
________________________________________________________________________________________
_____________________________________________________________________________________ (3)
D.2 Explain the sequence of geological events that led to this geological map and block diagram. If
sedimentation was in ordinary sequence without unconformities it is not necessary to list the deposition of each
stratum. Do include any structural deformation, name the structures formed and include any erosional
unconformities. Bed B was deposited up the eroded surface of plutonic rock A. Ensure that both ends of your
model show the same kind of fold! Structure Name: ___________________________________________ (1)
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
_____________________________________________________________________________________ (6)
E.2 Explain the sequence of geological events that led to this geological map and block diagram. If
sedimentation was in ordinary sequence without unconformities it is not necessary to list the deposition of each
stratum. Do include any structural deformation, name the structures formed and include any erosional
unconformities. My model has some extra steps compared to the one in the manual. Do mine!
Structure Name: _______________________________________________________________________ (1)
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
_____________________________________________________________________________________ (7)
F.2 Explain the sequence of geological events that led to this geological map and block diagram. If
sedimentation was in ordinary sequence without unconformities it is not necessary to list the deposition of each
stratum. Do include any structural deformation, name the structures formed and include any erosional
unconformities. Notice the different widths for the sandstone at the west edge and recall the rule of V’s.
Structure Name: ________________________________________________________________________ (1)
________________________________________________________________________________________
________________________________________________________________________________________
________________________________________________________________________________________
_____________________________________________________________________________________ (4)
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Activity 10.6 Block Diagram Analysis & Interpretation p. 279-280.
1. Complete all contacts 2. Add all structure symbols & #’s 3. Name each structure on line below (30)
E. _________________________________
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F. _______________________________________
Activity 10.7: Nevada Fault Analysis Using Ortho Images
A. Below is an orthophoto image of the Frenchman Mountain Quadrangle ~7 km east of Las Vegas NV. Google
Earth 36 09.5 N, 114 56.6W. Note the strike of the strata and note how they are cut and offset by a significant
Tertiary fault that was active between 11 and 6 Ma in the Late Miocene. 1-Use a coloured pen to mark in the
trace of this fault. Noting the offset of the strata, 2-draw in the half arrows on both sides of the fault to
indicate the directions of relative motion. Now be really observant and look for some V’s on both sides of the
fault and 3-put in one strike and dip symbol on 4-each side of this fault. The direction of dip is sufficient, you
do not need to estimate the angle.
Do steps 1-4 on the image below.
Finally name the type of fault you just mapped? (4 words) ________ ___________ _______ ______ fault (5)
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.
B. Go to Google Earth and download it if you have not already done so. Into the search bar type the coordinates
of the lower location and image on p. 281: 36 08 19.4N, 114 58 41.8W.
1. How many faults do you see here which have throws greater than 100 metres (note scale on image). ____ (2)
2. Give the numerical strike azimuth for these faults: __________________ and _____________________ (2)
3. Name these faults (type and throw direction) _________ __________________ _________ _______ (2)
C. At 11-6 Ma, interpret why this part of Nevada faulted instead of folding. Provide at least 2 viable reasons
relating to the strain rate and likely depth of this panel of rocks in Pliocene when the deformation occurred. __
________________________________________________________________________________________
______________________________________________________________________________________ (2)
Activity 10.8 Appalachian Mountains Geological Map p. 282
Examine the geological map from south central Pennsylvania near McConnellsburg in the
Valley and Ridge province of the Appalachian Mountains.
A. Complete the geological cross section as per figure 10.8B
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(10)
B. Label each of the geological structures present with the appropriate symbols.
(8)
C.Add half arrows to the fault near the center of the map which cuts the Bald Eagle and Tuscarora formations.
What type of fault is this? ___________________________ (2)
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Activity 10.9 Wapiti Pass 1:50,000 Geology Map by McMechan & Thompson
Use Map Sheet Provided in Lab to answer questions below:
A. What geographic region does this map represent? ____________________________________________ (1)
B. What geological feature or belt is represented here? __________________________________________ (1)
C. What is the name ____________________ & age ____________________ of the oldest formation here? (2)
D. What geologic structure or feature is associated with the outcrop of this formation? __________________
______________________________________________________________________________________ (2)
E. What is the name of the youngest geological formation on this map __________ and what structure or
feature is it associated with? _______________________________________________________________ (2)
F. How many angular unconformities are present in this stratigraphic succession? _______ & what units bound
them (denote: Name A/Name B etc.): __________________________________________________________
________________________________________________________________________________________
________________________________________________________________________________________
_____________________________________________________________________________________ (4)
G. During which intervals of geologic history was there the greatest amount of uplift and erosion in this region?
(age to age)_______________________________________________________________________________
________________________________________________________________________________________
_____________________________________________________________________________________ (3)
H. Throughout the Western Canada Sedimentary Basin, the Upper Devonian Palliser Formation and its facies
equivalents tend to host oil pools in its porous reef limestones. Explain why the TGS et al Narraway C76G well
was drilled in this location? __________________________________________________________________
______________________________________________________________________________________ (2)
I. Where would be a better location for an exploration well from McMechan and Thompson’s interpretation?
______________________________________________________________________________________ (2)
J. Explain why the Vreeland formation is only found in the SW of the map while the Gates formation is only
found in the NE? __________________________________________________________________________
________________________________________________________________________________________
______________________________________________________________________________________ (2)
K. The mountains in the SW corner of this map sheet are_____ than those in the NE. a) older b) younger (2)
Please staple your models from 10.5 to the back of your lab before handing it in.
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