Map Interpretation for Structural Geologists ( PDFDrive )

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MAP INTERPRETATION 
FOR STRUCTURAL GEOLOGISTS 
About the Series
“Developments in Structural Geology and Tectonics” is an Elsevier book series where potential authors are 
welcome to contact the Series Editor: Soumyajit Mukherjee (soumyajitm@gmail.com, smukherjee@iitb.ac.in) with 
new book proposals either as authors or editors. All theoretical, practical, regional and interdisciplinary topics of 
structural geology and tectonics are welcome as potential book proposals.
Developments in Structural Geology and Tectonics 
MAP INTERPRETATION 
FOR STRUCTURAL 
GEOLOGISTS 
Volume 1 
NARAYAN BosE & SouMYAJIT MUKHERJEE 
Indian Institute of Technology Bombay, Mumbai, India 
ELSEVIER 
Elsevier
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Notices
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ISBN: 978-0-12-809681-9
ISSN: 2542-9000
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Cover image: Reproduced from a part of map 7 of Platt (1951). The entire map has been solved as Map 6.8 in this book.
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S. Mukherjee dedicates this book in loving memory of his grandmother late Namita Mukherjee.
Dedication
Contents 
Preface ix 
Acknowledgments Xl 
1. Topography 1 
Map 1.1 4 
2. Horizontal and Inclined Beds 9 
Map 2.1 14 
Map 2.2 16 
Map 2.3 20 
Three-Point Problem to Deduce Attitude 20 
3. Unconformity 25 
Map 3.1 26 
Map 3.2 29 
4. Folds 35 
Map 4.1 37 
Map 4.2 40 
Map 4.3 43 
5. Faults 49 
Map 5.1 51 
Map 5.2 54 
Map 5.3 58 
6. Summary Maps 65 
Map 6.1 66 
Map 6.2 68 
Map 6.3 70 
Map 6.4 73 
Map 6.5 77 
Map 6.6 81 
Map 6.7 84 
Map 6.8 89 
Map 6.9 93 
Exercises 97 
7. Miscellaneous Maps 105 
Map 7.1 106 
Map 7.2 109 
Map 7.3 11 1 
Map 7.4 113 
Map 7.5 116 
Exercises 119 
References 127 
Index 129 
Vll 
Preface 
Interpreting topography and structures from geo-
logical maps is a fundamental and compulsory exer-
cise for Bachelors and Masters students in geosciences. 
This book presents how to interpret maps and draw 
their cross-section s. Stvdents are requested to consult 
standard textbooks of structural geology for definitions 
and diagrams for the common terms used in this book. 
A number of solved maps a.re provided along with few 
unsolved exercises for practice. This will help students 
to practice map interpretation with nominal guidance. 
lX 
Starting from preliminary concepts (e.g., topogra-
phy, horizontal, and inclined beds), maps with single 
'' components" (folds, faults, and unconformities) are 
explained. This is followed by maps with multiple com-
ponents and map completion exercises. We believe the 
book provides sufficient information for a single semes-
ter to teach beginners. We welcome any comments, sug-
gestions, or alternate explanations for the solved maps 
at: narayan.bghs@gmail.com and soumyajitm@gmail. 
com. 
Copyrighted material 
Acknowledgments 
Narayan Boseexpressesgra titude to his structural geol-
ogy instructors, Pr.ofs. Ananda K Chakrabarti, Alokesh 
Chatterjee, Gautam Ghosh, and NiJanjan Dasgupta, in 
the then Presidency College (Kolkata) for teaching the 
fundamentals of structural geology rigorously during 
the period 2008- 2011 in the BSc. programme. Soumyajit 
Mukherjee thanks Profs . Ananda K. Chakrabarti and 
Alokesh Chatterjee for building structural geological 
concepts, especially geometric, during his BSc days 
(1996- 1999) in the then Presidency College (Kolkata). 
The authors a lso acknowledge their BSc batch mates for 
helping in the learning procedure. Jn this connection, 
Soumyajit expresses gratitude especially to his batch-
mate, the late Sbovik Banerjee. Narayan and Soumyajit 
have been immensely benefited by several batches of 
Xl 
geology and geophysics students while teaching them 
sh·uctural geology inside classrooms and in the field, 
as <1 Teaching Assistant and an Instructor, respectively. 
PhD student Dripta Dutta clarified a few points on map 
interpretation. A Research Sabbatical provided by IIT 
Bombay to SoumyajH for the year 2017 helped him to 
coauthor this book. Amy Shapiro is owed additional 
thanks for conceptualizing a new book series in Elsevier: 
"Developments in Structural Geology and Tectonics" 
and including this book as the first book in the series. 
Tasha Frank and Marisa Laf leur (Elsevier) are thanked 
for numerous prompt supports. The Elsevier proofread-
ing team in Chennai headed by Anjtha Sivaraj worked 
diligently to publish the book. Authors express gratitude 
to the reviewers of this book's proposal. 
Copyrighted material 
1
Map Interpretation for Structural Geologists.
DOI: © Elsevier Inc. All rights reserved.2017http://dx.doi.org/10.1016/B978-0-12-809681-9.00001-2
1
In geological maps, the undulation of the topography is represented by height contours. These contours represent 
lines along which all the points have the same altitude. Height contours are represented usually by broken lines and 
the numbers attached to them indicate the altitude of the corresponding contour. A vertical cross-section (herein 
referred to as “cross-section”) accompanies a geological map, in almost all cases. Cross-sections represent various 
topographic and sub-surface structural geological features. Concept 1.1A exemplifies of how a three-dimensional 
topographic feature is presented in a map (as height contours) and in a cross-section. Concepts 1.1B and 1.1C show 
how various topographic features can be understood from height contours.
Map 1.1 has only height contours. The task is to describe different topographic features present in Map 1.1, as 
well as to draw a suitable cross-section.
C H A P T E R 
Topography
CONCEPT 1.1A Representation of a basin in various ways. Schematicdiagrams. (A) Three-dimensional view. Height horizons are marked. 
(B) Note how the height contours look similar to those in map view. The height increases as one moves away from the centre (as indicated by 
the arrow “i”). (C) Vertical section along MN marked in (A).
MAP INTERPRETATION FOR STRUCTURAL GEOLOGISTS
1. TopogrAphy2
CONCEPT 1.1B Contours of topographic features: (A) Basin, where height increases (“i”) away from the centre. (B) Dome, where altitude 
decreases (“d”) away from the centre. (C) Hill. Here the slope of the topography along E–W is much gentler than that along N–S (note spac-
ing between adjacent contours). (D) Plateau. Here an elevated flat surface is bound by “steep” slopes. (E) Water divide. Here elevated por-
tions together function as a water divide, since two oppositely draining valleys generate from this part. One drains towards NE and the other 
towards SW.
3
MAP INTERPRETATION FOR STRUCTURAL GEOLOGISTS
 TopogrAphy
CONCEPT 1.1C Contours for valley and spur. (A) A northerly draining valley. Note height increases from the central part towards the flanks (“i” 
direction). (B) A south sloping spur. Note height falls towards the flanks (“d” direction). (C) A north sloping spur. (D) A south draining valley. (E) A combi-
nation of valleys and spurs, where the valleys drain towards south. (F) A combination of valleys and spurs. All the valleys drain towards the central part.
MAP INTERPRETATION FOR STRUCTURAL GEOLOGISTS
1. TopogrAphy4
MAP 1.1
MAP 1.1 Part of a topographic map. Cropped from map 31 of Platt (1951).
Map 1.1 represents an undulating topography. The maximum height reaches 900 m or more, and the minimum 
height is 500 m or less. Six valleys are present (marked in Fig. 1.1A). The central elevated region works as a water 
divide (also see Concept 1.1B E) as two valleys (V5 and V6) slope in opposite directions. Fig. 1.1B: cross-section 
along the “MN” line in Fig. 1.1A.
● Cross-section 1: Drawing the topography. For drawing a vertical cross-section, first select the line along which the 
section will be drawn (Fig. 1.1A). The line should be selected in such a way, that it passes through the maximum 
number of (if possible, all) litho-units and structural-/topographic features in the map. The next job is to mark all 
the points of intersection on this line and transfer them to the x/horizontal-axis of the graph (Fig. 1.1B). The y/
vertical-axis represents elevation and here the scale should be the same as that of the map (in most of the cases/
unless stated otherwise). Now from the points marked on the x-axis, the topographic elevation points are marked 
accordingly (see the black solid circles in Fig. 1.1B). Finally, these points are joined by freehand drawing/by a 
smooth curve. The following things should always be mentioned in the cross-section: scale, a caption stating the 
line along which the cross-section has been drawn (such as line MN in Fig. 1.1B), and proper marking of the line 
on the x-axis.
● Points A–F: points A–C represent an elevation of 700 m. However, they were not joined by a straight line in 
the cross-section (Fig. 1.1B). The contour pattern indicates that the elevation ranges 700–800 m between points 
A and B. And similarly, the part between points “B” and “C” has 600–700 m elevation. A freehand curve joining 
points A–C therefore reflects the topography. Similar strategies have been followed for points D–F.
5MAp 1.1
MAP INTERPRETATION FOR STRUCTURAL GEOLOGISTS
FIGURE 1.1A Interpretation of Map 1.1. Valleys (V1–V5) marked by blue lines and arrows.
FIGURE 1.1B Cross-sections along MN. V2 and V4 mark the cross-section. See the text for a discussion on points (A–F).
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Map Interpretation for Structural Geologists.
DOI: © Elsevier Inc. All rights reserved.2017http://dx.doi.org/10.1016/B978-0-12-809681-9.00002-4
2
Map representation and interpretation of horizontal and inclined beds are discussed in this chapter. Few key 
points are given below:
1. A solid line on the map represents a plane (Concept 2.1A), and the plane is:
horizontal—if the line is parallel to the height contours (i.e., the broken lines);
inclined—if the solid line is curved and cuts the height contours;
vertical—if on a map of undulating topography, the plane is represented by a straight line that cuts across height 
contours.
2. On the map, the curvature of the solid line decreases as the bed steepens. A straight solid line indicates a vertical 
plane for an undulating topography. However, in a planar topography, both inclined and vertical planes appear 
as straight lines.
3. Concept 2.1B describes the concepts of strike lines and stratum contours associated with an inclined plane. Strike 
lines are present on the inclined plane and stratum contours are the orthographic/map projection of strike lines 
on a horizontal surface.
4. Strike lines of a single plane are mutually parallel. Successive strike lines of equal interval (500 m, 400 m, 300 m, 
etc.) are equidistant from each other. Steeper planes produce more close-spaced strike lines.
Concepts 2.1C and 2.1D demonstrate how the outcrop pattern changes in maps for two oppositely dipping beds. 
Three maps will be discussed in this chapter: Map 2.1 (horizontal beds), Map 2.2 (inclined beds), and Map 2.3 (three 
point construction of strike lines).
C H A P T E R 
Horizontal and Inclined Beds
MAP INTERPRETATION FOR STRUCTURAL GEOLOGISTS
2. HorIzontAl And InclInEd BEds10
CONCEPT 2.1A Horizontal and inclined beds as in hillocks and in maps. Schematic diagrams, not to scale. (A) Horizontal beds in a hill-
ock. (C) Inclined beds in a hillock. (E) Vertical beds cropping out in a hillock. B, D and F are the plan-/map- views of A, C and E, respectively.
11
MAP INTERPRETATION FOR STRUCTURAL GEOLOGISTS
HorIzontAl And InclInEd BEds
CONCEPT 2.1B Strike lines and stratum contours of a plane dipping towards the reader: towards south. Schematic diagrams, not to scale. 
(A) Block diagram showing an inclined plane, the strike lines and stratum contours. (B) Representation of the inclined plane in a map.
MAP INTERPRETATION FOR STRUCTURAL GEOLOGISTS
2. HorIzontAl And InclInEd BEds12
CONCEPT 2.1C (A) Exposure of an inclined plane (dipping in a direction opposite to the reader: towards north) in a valley. The valley 
slopes towards the reader: towards south. Thus, the dip direction of the plane is opposite to the slope of the valley. (B) Intersection between the 
outcrop of the bed and the height contours. The construction of the stratum contours is to be noted.
13
MAP INTERPRETATION FOR STRUCTURAL GEOLOGISTS
HorIzontAl And InclInEd BEds
CONCEPT 2.1D (A) Exposure of an inclined plane in a valley. The dip direction of the plane and the slope of the valley are in the same 
direction: towards the reader—towards south. (B) Intersection between the outcrop of the bed and the height contours.
MAP INTERPRETATION FOR STRUCTURAL GEOLOGISTS
2. HorIzontAl And InclInEd BEds14
MAP 2.1
MAP 2.1 Describe topography and structural geology. Draw a suitable cross-section.
15MAp 2.1
MAP INTERPRETATION FOR STRUCTURAL GEOLOGISTS
FIGURE 2.1 Cross-section along “PQ”: refer to Map 2.1.
The map represents an undulating topography with a western valley sloping south, and an eastern spur occurring 
side-by-side. Here the maximum height is 800 m or more, and the minimum height is 100 m or less. Four litho-units 
crop out: A, B, C, and D. The bed boundaries do not cross-cut the height contours, but they are sub-parallel. Hence 
the beds are horizontal. Fig. 2.1 shows a cross-section along PQ.
● Cross-section 2 (Fig. 2.1): Drawing horizontal beds in cross-section and modification of the topographic outline. Let us 
discuss this concept using the example of the litho-contact between the units A and B (A/B) in Map 2.1. On the line 
PQ, the A/B contact is exposed at ~ 550 m height, and this point is markedby “A/B” on the x-axis of the section. 
As the contact is horizontal, in the vertical cross-section it will be represented by a line parallel to the x-axis. In 
other words, the contact needs to be shown as a horizontal line. Therefore, ST is drawn at the 550 m elevation 
to represent the A/B contact. Now, at point A/B, a line perpendicular to the x-axis is drawn, which meets ST 
at the point T. Point T indicates the point where A/B contact cuts the topography. Hence, the A/B contact (i.e., 
the ST line) cannot be extended beyond point T. And the topographic outline should also pass through point T. 
A similar technique is followed to draw litho-contacts in subsequent cross-sections.
MAP INTERPRETATION FOR STRUCTURAL GEOLOGISTS
2. HorIzontAl And InclInEd BEds16
MAP 2.2 Describe topography and structural geology. Draw a suitable cross-section. Modified after map 4 of Simpson (1961).
MAP 2.2
17MAp 2.2
MAP INTERPRETATION FOR STRUCTURAL GEOLOGISTS
The map represents an undulating topography with a western valley and eastern spur occurring side-by-side. 
Here the maximum height is between 800 to 900 m and the minimum height is between 0 and 100 m. Four litho-
units crop out: A, B, C, and D.
Fig. 2.2A shows strike lines on the map. The attitude of the litho-contacts is 90°/20°→0° (i.e., strike: 90–270°, true 
dip amount: 20°, true dip direction: 0°/north) (Fig. 2.2B).
● Cross-section 3: Drawing an inclined bed in cross-section and modification of the topographic outline. Consider the C/D 
contact. The points where 300 m and 400 m strike lines of the C/D contact intersects PQ is marked on the cross-
section as C/D 300 and C/D 400, respectively. Vertically above these two points, the 300 m (for C/D 300) and 
400 m (for C/D 400) are marked by black solid circles. The straight line passing through these two black solid 
circles is the C/D contact on the cross-section. Now, the point where the C/D contact cuts the PQ line is marked 
by “C/D” on the x-axis of the cross-section. A line perpendicular to the x-axis and through the point “C/D” 
marks the extent up to which the C/D contact is actually present in this section. Following the similar argument 
made in “Cross-section 2”, the topographic outline is adjusted.
● Measuring true dip amount of an inclined planar surface from stratum contours: see Fig. 2.2C for detail.
● Measuring bed thickness: The line PQ is drawn perpendicular to the stratum contours (parallel to the true dip 
direction). A cross-section drawn along such a line represents the true thicknesses of the planar bodies. The 
orange lines in Fig. 2.2B show the true thickness for beds B, C, and D. According to the scale of the map, the 
true thicknesses of the beds B, C, and D are 190 m, 360 m, and 200 m, respectively. In Fig. 2.2A, the A/B 600 m 
stratum contour is superposed on the B/C 400 m stratum contour. This indicates that the upper surface of unit 
B (i.e., A/B) and the lower surface of unit B (i.e., B/C) are vertically 200 m apart. Hence, the vertical thickness 
of the unit B is 200 m, as also shown by the green line in Fig. 2.2B.
MAP INTERPRETATION FOR STRUCTURAL GEOLOGISTS
2. HorIzontAl And InclInEd BEds18
FIGURE 2.2A Solution of Map 2.2.
19MAp 2.2
MAP INTERPRETATION FOR STRUCTURAL GEOLOGISTS
FIGURE 2.2B Cross-section along “PQ”.
FIGURE 2.2C Calculation of true dip amount on the map. (A) Map view. (B) Cross-section view.
MAP INTERPRETATION FOR STRUCTURAL GEOLOGISTS
2. HorIzontAl And InclInEd BEds20
MAP 2.3 Measure the attitude of the contact between A and B units by the “three-point method”.
MAP 2.3
THREE-POINT PROBLEM TO DEDUCE ATTITUDE
In the previous map the stratum contour was drawn by joining the two points where the litho-contact intersects 
a particular height contour. However, in Map 2.3 the contact cuts each height contour only once. Here, the stratum 
contour is to be drawn by the “three-point method”. The solution is given in Fig. 2.3.
Consider that the A/B contact is planar. Hence the 600-, 700- and 800-m stratum contours for the A/B contact 
will be parallel and the distance between successive strike lines will be same. The points where the 800- and 600-m 
height contours cut the A/B contact is marked by points P and Q, respectively. The A/B 700-m stratum contour will 
pass through the mid-point of PQ, i.e., R. Now, the A/B 700-m contact also goes through the point of intersection 
between A/B contact and the 700-m height contour. Hence this point of interaction is joined with R to get the 700-m 
stratum contour of the A/B contact. Other stratum contours are drawn parallel to it. The attitude of the litho-contact 
between the units A and B is 153°/14°→243° (Fig. 2.3).
21tHrEE-poInt proBlEM to dEducE AttItudE
MAP INTERPRETATION FOR STRUCTURAL GEOLOGISTS
FIGURE 2.3 Solution for Map 2.3.
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25
Map Interpretation for Structural Geologists.
DOI: © Elsevier Inc. All rights reserved.2017http://dx.doi.org/10.1016/B978-0-12-809681-9.00003-6
3
Unconformities indicate a significant time gap in deposition. This time gap has not been quantified in geology. 
The details of unconformities can be found elsewhere (e.g., brief review by Ghosh, 1993). There are four main types 
of unconformities: angular unconformity, nonconformity, disconformity and para-conformity.
In geological exposures/successions, unconformities are surfaces along which much younger litho-units at top 
are found to be in contact with much older litho-units at bottom. At the same time, there was no movement or 
displacement along this discontinuity surface. In the case of angular unconformities, the overlying beds parallel 
the unconformity surface, whereas the underlying litho-units make an angle. Nonconformities generate when older 
plutonic/metamorphic bodies are buried under younger sedimentary depositions. Para- and disconformity surfaces 
parallel both the overlying and the underlying beds.
Two maps with angular unconformity are interpreted below. The unconformity surface is horizontal in Map 3.1 
and inclined in Map 3.2. Unconformity related maps have also been discussed in Chapter 6.
C H A P T E R 
Unconformity
MAP INTERPRETATION FOR STRUCTURAL GEOLOGISTS
3. UnconformIty26
MAP 3.1 Map with angular unconformity.
MAP 3.1
27mAp 3.1
MAP INTERPRETATION FOR STRUCTURAL GEOLOGISTS
FIGURE 3.1A Solution of Map 3.1.
MAP INTERPRETATION FOR STRUCTURAL GEOLOGISTS
3. UnconformIty28
FIGURE 3.2 Note that the cross-section is not perpendicular to the strike lines of litho-contacts and the unconformity. Therefore, not the true 
dip, but apparent dips of the contacts and the unconformity are presented.
This map represents an area of undulating topography with an eastern spur and a western valley, both sloping 
towards south. The minimum- and maximum heights are ~100 m and ~800 m, respectively. There are two litho-
groups: Group-1 consists of litho-units A, B, C and D and Group-2 with E and F. Attitude of the beds in Group 1 
is 90°/21°→0° (Fig. 3.1A). The base of E and the boundary between E and F parallel the height contours. Hence 
the Group-2 litho-units and the base of E are horizontal. The base of Group-2 is a discontinuity surface (blue line) 
where Group 1 litho-units truncate. The attitude of the discontinuity surface is same as that of the litho-contacts of 
the Group 2 rocks. Litho-units of Group-2 parallel the discontinuity surface. Therefore, the discontinuity surface 
is an angular unconformity. Beds of Group-1 litho-units make 21° with the angular unconformity (from stereo-net 
exercise). Fig. 3.1B presents a cross-section along PQ.
29mAp 3.2
MAP INTERPRETATION FOR STRUCTURAL GEOLOGISTS
MAP 3.2
MAP 3.2 Cropped from map no. 4 of Platt (1951).
MAP INTERPRETATION FOR STRUCTURAL GEOLOGISTS
3. UnconformIty30
FIGURE 3.2A Solution of Map 3.2.
31mAp 3.2
MAP INTERPRETATION FOR STRUCTURAL GEOLOGISTS
This map shows undulating topographyconsisting of an eastern valley and a western spur, both sloping towards 
south. The minimum and maximum heights are ~700 m and ~1000 m, respectively. Two litho-groups occur: Group 
1—gray shale, red shale and flags of Devonian Period; and Group 2—shale, mudstone, flagstone, sandstone, grit, 
and quartzite of Ordovician Period. The base of Group 1 is a discontinuity surface (blue line) where Group 2 litho-
units truncate. The attitude of the discontinuity surface is same as that of the litho-contacts of the Group 1 rocks. 
Beds of Group 1 parallel the discontinuity surface. Therefore, the discontinuity surface is an angular unconformity. 
Attitude of beds in Group 1 as well as the angular unconformity surface is 130°/33°→40°. Attitude of the beds in 
Group 2: 90°/42°→0°. Beds of the Group 2 rocks make a 33° angle with the angular unconformity (from stereonet 
calculations, not shown here) (Map 3.2).Cross-section drawn along PQ in Fig. 3.2A. Note in this case, the angular 
unconformity surface is tilted/non-horizontal (Fig. 3.2B).
FIGURE 3.2B Cross-section drawn along PQ. Note that the cross-section is not perpendicular to the strike lines of litho-contacts and the 
unconformity. Therefore, not the true dip, but apparent dips of the contacts and the unconformity are presented.
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35
Map Interpretation for Structural Geologists.
DOI: © Elsevier Inc. All rights reserved.2017http://dx.doi.org/10.1016/B978-0-12-809681-9.00004-8
4
The general information related to folds can be found in text book (e.g., Billings, 1954; Ghosh, 1993; Fossen, 2016). 
On the map, a fold is generally recognized by symmetrical repetition of beds (Concept 4.1A) across a line, i.e., the 
trace of axial plane (or the axial trace). Concept 4.1B distinguishes folded- and unfolded- terrains.
In the following part of the chapter, three fold-related maps will be interpreted: Map 4.1 (non-plunging fold), 
Map 4.2 (isoclinal fold) and Map 4.3 (plunging fold). More fold-related maps are presented in chapter 6.
C H A P T E R 
Folds
CONCEPT 4.1A Box diagrams of (A) non-plunging fold and (B) plunging fold. Surfaces ABCD (in “A”) and EFGH (in “B”) represent the 
map views of the folds. Red dash line indicates the axial plane.
MAP INTERPRETATION FOR STRUCTURAL GEOLOGISTS
4. Folds36
CONCEPT 4.1B General way to distinguish the folded and unfolded litho-contacts on the map. A. Litho-contacts separating the litho 
units P, Q, R crop out in a way that a dark blue line joining the hinges of the contour Vs and outcrop Vs (almost) coincides. This indicates the 
unfolded nature of the litho-contacts. B. Here a line joining the hinges of the contour Vs (red broken line) and that of the outcrop Vs (green 
broken line) are away from each other. This indicates that the litho-contacts are folded. A’. Strike lines drawn for case A. B’.Strike lines drawn 
(by the ‘three-point problem’) for case B.
37MAp 4.1
MAP 4.1
MAP 4.1 Map with fold. Cropped from map 17 of Simpson (1961).
4. Folds38
FIGURE 4.1A Solution for Map 4.1. “A/Bw” strike line indicates the strike line drawn for A/B contact at the western limb of the fold. 
Similarly, “B/Ce” indicates the strike line drawn for the B/C contact on the eastern limb of the fold.
Three litho-units: A, B, C crop out in Map 4.1. The A/B boundary is continuous and cuts the 700 m con-
tour at 5 non-collinear points. At places, the outcrop Vs for the contacts do not match the contour Vs (see also 
Concept 4.1B). For A/B boundary the blue boxes indicate the matches and the red box indicates mismatch 
(Fig. 4.1A). Hence, it indicates a fold. From the strike lines the limbs are drawn in the cross-section and the axial 
trace is plotted (Fig. 4.1B). The attitude of the limbs are 57°/23°→147° and 57°/23°→327°. The interlimb angle is 
134°. The axial plane is vertical. Hence, it is a symmetric gentle non-plunging upright synform.
FIGURE 4.1B Cross-section along MN.
4. Folds40
MAP 4.2
MAP 4.2 Map with fold. Reproduced from map 10 of Simpson (1961).
41MAp 4.2
There are four litho-units (A, B, C, D) cropping out in Map 4.2. From the symmetric repetition of outcrop and the 
values of the strike lines, it can be understood that, a fold is present in the map (Fig. 4.2A). It is an isoclinal fold. The 
attitude of the limbs and the axial plane is 0°/12°→90°. A cross-section drawn along MN line is presented in Fig. 4.2B.
FIGURE 4.2A Solution for Map 4.2.
FIGURE 4.2B Cross-section drawn for Map 4.2 along MN.
43MAp 4.3
MAP INTERPRETATION FOR STRUCTURAL GEOLOGISTS
MAP 4.3
MAP 4.3 Modified after map 10.11 of Borradaile (2014).
There are three litho-units (A, B, coal seam) cropping out in Map 4.3. The dissimilarity between outcrop V and 
height contours indicates the presence of a fold. The attitudes of the limbs indicate that this is a plunging fold. The 
strike lines for the eastern limb are drawn by “three point method” (Fig. 4.3A). The trends of the eastern and western 
limbs are 18°/48°→108° and 176°/56°→ 226°. The plunge of the fold axis is 18°→199°. A cross-section drawn along XY 
(in Fig. 4.3A) is presented in Fig. 4.3B.
MAP INTERPRETATION FOR STRUCTURAL GEOLOGISTS
4. Folds44
FIGURE 4.3A Solution for Map 4.3.
45MAp 4.3
MAP INTERPRETATION FOR STRUCTURAL GEOLOGISTS
FIGURE 4.3B Cross-section drawn for Map 4.2 along XY.
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49
Map Interpretation for Structural Geologists.
DOI: © Elsevier Inc. All rights reserved.2017http://dx.doi.org/10.1016/B978-0-12-809681-9.00005-X
5
Fault-related various terminologies and their explanations can be found in various text books such as Billings 
(1954), Ghosh (1993), and Fossen (2016). Before starting with the maps, a few concepts are discussed below: Concept 
5.1A shows apparent horizontal displacement of beds (along the fault plane) by dip slip movement of blocks. No 
horizontal movement was actually present. Similarly, apparent vertical displacement takes place as fault blocks slip 
horizontally. The method of net-slip calculation is shown in Concept 5.1B. Three maps are solved in this chapter: 
Map 5.1, Map 5.2 and Map 5.3.
C H A P T E R 
Faults
CONCEPT 5.1A Apparent strike-slip movement of beds due to dip-slip displacement of the blocks: (A) Before faulting. (B) After dip slip 
normal faulting. (C) After erosion brought the top surface of the footwall block at the same level as the hanging wall block.
MAP INTERPRETATION FOR STRUCTURAL GEOLOGISTS
5. FAults50
CONCEPT 5.1B Steps of net-slip calculation. (A) Block diagram showing two markers (here, dykes) before faulting. (B) Displacement/slip 
of blocks due to faulting. XY is the strike line of the fault. On this line the traces of the dykes are marked and the pitch (or rake, α and β) of 
the dykes on the fault plane is calculated. (C) Drawing is made on the fault pane. The displacement of the points of intersection of the dykes is 
marked by the line MN, which is the net-slip.
51MAp 5.1
MAP INTERPRETATION FOR STRUCTURAL GEOLOGISTS
MAP 5.1
MAP 5.1 Map with Fault. Reproduced from Map 15 of Simpson (1961).
MAP INTERPRETATION FOR STRUCTURAL GEOLOGISTS
5. FAults52
In Map 5.1, three lithounits—A, B, and C, crop out on an undulating topography. The calculations are presented in 
Fig. 5.1A. The trend and spacing of the strike lines for these litho-units indicate that they belong to a single sequence 
and their attitude is 90°/30°→180°. This sequence is disrupted by a fault (attitude 90°/71°→0°). The cross-section 
(Fig. 5.1B) shows that the northern block (hanging wall) is downthrown. Hence, it is a normal fault. On the cross-
section (Fig. 5.1B) MN (~170 m) and NO (~60 m) indicate throw and heave, respectively.
FIGURE 5.1A Solution of Map 5.3.
FIGURE 5.1B Cross-section drawn along PQ marked on Fig. 5.3A.
MAP INTERPRETATION FOR STRUCTURAL GEOLOGISTS5. FAults54
MAP 5.2 Map with fault and fold. Reproduced from Map 17 of Simpson (1961).
MAP 5.2
55MAp 5.2
MAP INTERPRETATION FOR STRUCTURAL GEOLOGISTS
In Map 5.2 four litho-units A, B, C, and D crop out on an undulating topography. The mismatch among the out-
crop and contour ‘V’s indicates the presence of a fold. The axial trace of the fold trends NE. The folded sequence is 
disrupted by a fault. Hence, faulting postdates folding.
Fig. 5.2A shows the necessary constructions for interpreting the map. The attitudes of the NW and SE limbs are 
33°/36°→123° and 33°/36°→303°, respectively. It is a nonplunging fold, with interlimb angle (180°–36°–36°=) 72°. 
The axial trace trends 33°. The axial plane is vertical (deduced from the cross-section in Fig. 5.2B). Hence, this is a 
nonplunging upright open synform. For the folded B/C contact on the southern block, the axial trace is drawn in 
the cross-section (Fig. 5.2B) by joining the hinge points “x” and “y.” This line also passes through the hinge point 
on the B/C contact on northern block (point “z”). So, the xy line represents the axial trace across the fault plane (at 
the hanging wall and the footwall block).
The attitude of the fault plane is 123°/72°→213°. The fault trends perpendicular to the axial trace of the fold, hence 
it is a transverse fault. The strike line values indicate that the southern block (hanging wall) is 100 m downthrown. 
For example, “B/Cn 700” and “B/Cs 600” are represented by the same line. The axial trace is not displaced by 
faulting. So, the net-slip is along the trace of axial plane on fault plane, i.e., along the true dip direction of the fault 
plane (cross-check by stereonet calculations). Hence, it is a transverse dip-slip normal fault.
MAP INTERPRETATION FOR STRUCTURAL GEOLOGISTS
5. FAults56
FIGURE 5.2A Solution of Map 5.2.
FIGURE 5.2B Cross-section drawn along PQ marked on Fig. 5.2A.
MAP INTERPRETATION FOR STRUCTURAL GEOLOGISTS
5. FAults58
MAP 5.3
Map 5.3 represents an undulating topography where valleys from north, west, and south meet at a central 
depressed region and finally slopes towards east. The maximum and minimum heights of the region are more than 
1100 m and less than 700 m, respectively.
Four litho-units crop out, viz., A, T, D, and N. Their conformable contacts and similarity in strike lines indicate that 
they constitute a single homoclinal sequence. The outcrop Vs of the litho-boundaries show two pairs of patterns—a 
pair of outcrop Vs pointing towards E/W matches with the contour Vs; but the another pair of outcrop Vs pointing 
N/S does not match with the contour Vs, hence indicate folds.
A plane of discontinuity disrupts the outcrop pattern. Similar litho-units truncate against the plane of discontinu-
ity at both sides. Hence it is a fault plane.
Cross-section drawn along XY (marked in Fig. 5.3A, B): perpendicular to the strike of the fault plane.
The attitude of the easterly dipping limb is 0°/26°→90°. The attitude of the westerly dipping limb is 0°/28°→270°. 
The interlimb angle is 126°. Therefore it is a gentle fold. The fold axis is horizontal and trends north–south. It is 
a nonplunging/horizontal fold. The attitude of axial plane trace is 0°/90° (dip measured from cross-section; indi-
cates upright geometry). The axial plane almost bisects the interlimb angle. Therefore, it is a symmetric antiform 
(or synform).
Hence, the fold can be termed as symmetric nonplunging upright open fold.
MAP 5.3 Map with fault. Modified after map 10 of Platt (1951).
59MAp 5.3
MAP INTERPRETATION FOR STRUCTURAL GEOLOGISTS
FIGURE 5.3A Solution for Map 5.1.
MAP INTERPRETATION FOR STRUCTURAL GEOLOGISTS
5. FAults60
Description of the fault:
Attitude of the fault plane is 10°/68°→100°. Here the eastern block (the hanging wall block) moved up with 
respect to the western block (the footwall block). Hence it is a reverse fault. It is almost a longitudinal fault since 
the fault parallels the axial trace of the fold. Since the section was drawn perpendicular to the strike of the fault 
plane, the distance PQ (in Fig. 5.3B) indicates dip separation for the lower surface of the bed D (i.e., the boundary 
between beds T and D). PQ is 400 m as per the scale of the map. The strike separation of the same surface is EF (see 
Fig. 5.3A). FG is perpendicular to EF. FG = PQ. Hence the magnitude of net-slip is EG = 3320 m (in map scale). The 
pitch of net slip on fault plane is 7° from 190° (Figs. 5.3A, B). Note that the triangle FGE was at first constructed on 
the fault plane itself, and then rotated so that the triangular plane becomes horizontal.
FIGURE 5.3B Cross-section drawn for Map 5.1, along XY.
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65
Map Interpretation for Structural Geologists.
DOI: © Elsevier Inc. All rights reserved.2017http://dx.doi.org/10.1016/B978-0-12-809681-9.00006-1
6
So far, we presented maps with only one structural feature (e.g., unconformity/fold/fault). In this chapter we will 
discuss maps with more than one such features. The objective is to describe the structural details, to draw suitable 
cross-sections and decipher time-wise sequence of events.
C H A P T E R  
Summary maps
MAP INTERPRETATION FOR STRUCTURAL GEOLOGISTS
6. SummAry mApS66
MAP 6.1
MAP 6.1 Reproduced from ‘maps without contours: 2’ of Bradshaw and Jarman (1969). Permission received by Elsevier.
67mAp 6.1
MAP INTERPRETATION FOR STRUCTURAL GEOLOGISTS
FIGURE 6.1 Solution of Map 6.1.
Six litho-units crop out in Map 6.1. Conglomerate, shales, sandy shale, and sandstone constitute a litho-group 
(Group A). This litho-group is folded and faulted. Group A is underlain by a horizontal basalt layer. The contact 
between Group A and this layer is an angular unconformity. Group A rocks are intruded by a 64° trending vertical 
quartz porphyry dyke. At two places alluvium deposits are observed.
Details of Group A: Group A rocks are synformally folded. The western limb dips 15° towards east and the east-
ern limb 15° towards west. It is a symmetric fold. The fold is disrupted by an E trending vertical transverse fault. 
Here the northern block is downthrown (as understood from the broadening of hinge of the synform). The solution 
is given in Fig. 6.1.
Sequence of events:
Deposition of alluvium (youngest)
Basalt layer
Intrusion of quartz porphyry dyke
Development of angular unconformity
Faulting of Group-A
Folding of Group-A
Deposition of Group-A (oldest)
MAP INTERPRETATION FOR STRUCTURAL GEOLOGISTS
6. SummAry mApS68
MAP 6.2
MAP 6.2 Reproduced from fig. 56 of Thomas (1966). Permission received by Elsevier.
Seven litho-units, viz. A, B, C, D, E, F, and G crop out in Map 6.2. Units A, B, and C belong to a litho-group 
(Group 1). Group 1 rocks are folded, faulted, and intruded by dyke D (Fig. 6.2). This sequence is separated from 
the overlying litho-unit E by an angular unconformity. Units F and G are sills intruded within E. Fault F5 affected 
the overall rock sequence. The ‘m’ symbol indicates contact metamorphism effects.
Details of Group 1: Group 1 rocks are antiformally folded with NE trending axial trace. The northern limb dips 
towards NW. These folded strata are disrupted by five faults. F1, F2, F3, and F4 disrupted only the Group 1 rocks. 
Fault F5 is youngest as it displaces/slips the overlying litho-unit E as well. From the broadening or narrowing of 
the hinge, the upthrown/downthrown blocks can be identified for those four faults. The upthrown block for these 
faults are: F1—western block, F2—eastern block, F3—western block, F4— western block.
Fault F5: This is a map of almost planar topography and the western block of F5 exposes only the top-most 
litho-unit, i.e., E. Whereas, in the eastern block all the other underlying litho-units expose. Hence, the eastern block 
is upthrown.
69mAp 6.2
MAP INTERPRETATION FOR STRUCTURAL GEOLOGISTS
Sequence of events (also consult Fig. 6.2):
Fault F5(youngest geological event)
Intrusion of F, G
Deposition of E
Development of angular unconformity
Intrusion of D
Faulting F1, F2, F3, F4
Folding of Group 1
Deposition of Group 1 (oldest geological event)
FIGURE 6.2 Solution of “Map 6.2. Alphabets denote different litho-units, which are referred in the structural/geological interpretation.”
MAP INTERPRETATION FOR STRUCTURAL GEOLOGISTS
6. SummAry mApS70
MAP 6.3 Reproduced from fig. 10.9 of Borradaile (2014). Permission received by Elsevier.
MAP 6.3
71mAp 6.3
MAP INTERPRETATION FOR STRUCTURAL GEOLOGISTS
FIGURE 6.3A Solution of Map 6.3.
Five litho-units, A, B, C, D, and E, crop out in Map 6.3 of undulating topography. Litho-units D and E belong to a 
single group (Group 1). Group 1 rocks are folded. The strike lines of the limbs are parallel. Hence it is a nonplung-
ing fold. The axial trace (trace of the axial plane) trends same as the limbs, i.e., 102°. The attitude of the southerly 
dipping limb is 102°/27°→192°, and that of the northerly dipping limb is 102°/27°→12°. The interlimb angle of the 
fold is {180°− (27° + 27°)} = 126°. Hence, it is also a gentle fold.
Folded D-E sequence gets truncated against the base of C. The base of C is not parallel with the base of the 
overlying unit B. Hence there is an angular relation between them. Again both B and C terminate below A. These 
indicate that the basal planes of the units C, B and A are angular unconformity surfaces. They have been marked 
as angular unconformity 1, 2, and 3 in Fig. 6.3A.
MAP INTERPRETATION FOR STRUCTURAL GEOLOGISTS
6. SummAry mApS72
The attitude of this basal plane of C is 27°/14°→297°. The attitude of the basal plane of B is 58°/12°→328°. The 
base of A is horizontal (as it is not intersected by any height contours). A cross-section drawn along LR is given in 
Fig. 6.3B.
Sequence of events (Fig. 6.3A):
Deposition of A (youngest)
Angular unconformity 3
Deposition of B
Angular unconformity 2
Deposition of C
Angular unconformity 1
Folding of D, E
Deposition of D, E (oldest)
FIGURE 6.3B Cross-section drawn for Map 6.3.
73mAp 6.4
MAP INTERPRETATION FOR STRUCTURAL GEOLOGISTS
MAP 6.4 Reproduced from Map no. 5 of Platt (1951). Permission received by Elsevier.
MAP 6.4
MAP INTERPRETATION FOR STRUCTURAL GEOLOGISTS
6. SummAry mApS74
In Map 6.4 of undulating topography, two groups of rocks crop out: Group-1: litho-units A, F, O, E, and T; and 
Group 2: litho-units R and S. The Group-1 rocks truncated at the base of Group 2 and the Group 2 rocks are parallel 
to this plane of truncation. Hence, the base of Group-2 rocks is an angular unconformity. The attitude of Group-1 
rocks is 130°/46° → 240°. The attitude of Group 2 rocks as well as the angular unconformity: 95°/19° → 5°.
Two vertical faults (F1 and F2) slipped these rocks. F1 affected Group-1 rocks only, whereas F2 affected both the 
groups. F1 trends 161° and F2 trends 12°. The eastern block is downthrown by F1 and the vertical separation is 
50 m (from Fig. 6.4). The western block is downthrown by F2 and the vertical separation is 100 m (from Fig. 6.4), 
which is also indicated by the superposition of the strike lines ‘A/F 500w’ and ‘A/F 600e’.
Sequence of events (Figs. 6.3, 6.4A,B):
Faulting F2 (youngest geological event)
Deposition of Group-2 rocks
…..Angular unconformity…..
Faulting F1
Deposition of Group-1 rocks (oldest geological event)
75mAp 6.4
MAP INTERPRETATION FOR STRUCTURAL GEOLOGISTS
FIGURE 6.4A Solution of Map 6.4.
MAP INTERPRETATION FOR STRUCTURAL GEOLOGISTS
6. SummAry mApS76
FIGURE 6.4B Cross-section drawn for Map 6.4.
77mAp 6.5
MAP INTERPRETATION FOR STRUCTURAL GEOLOGISTS
MAP 6.5
MAP 6.5 Reproduced from ‘advanced Map 3’ of Bradshaw and Jarman (1969). Permission received by Elsevier.
MAP INTERPRETATION FOR STRUCTURAL GEOLOGISTS
6. SummAry mApS78
Seven litho-units belonging to two groups crop out in this map (Map 6.5) of undulating topography. From bottom 
to top, the lower sequence (Group-1) consists of limestone, mudstone, sandstone and oolite. Group-2 is made up 
of arkose and sandstone. Group-1 rocks are folded with 104° trending axial plane. The axial plane dips 86° (found 
from Fig. 6.6). The trend of the northern limb is 149°/23° → 59°, and that of the southern limb is 61°/23° → 151°. 
The attitude of the fold axis is 17°→195°. The interlimb angle, deduced from stereo-net (not shown here), is 149°. 
The fold is a gently plunging-symmetric-gentle upright antiform.
An acidic igneous rock intruded the Group-1 rocks. From this massive intrusion, three dykes with trends 65°, 77°, 
115° emanated but remained within Group-1 rocks. The igneous intrusion and the the dykes created local contact 
metamorphism (indicated by ‘m’ in the map). Although the host rocks are folded, the dykes are not. Therefore, 
intrusion postdates folding.
The Group-1 rocks along with the intrusion truncates against the base of Group-2. Hence the base of Group-2 is an 
angular unconformity. The attitude of Group-2 rocks as well as that of the angular unconformity is 15°/13° → 105°.
Sequence of events (Figs. 6.5A,B):
Deposition of Group-2 rocks (youngest)
Development of angular unconformity
Igneous intrusion in Group-1 rocks
Folding of Group-1 rocks
Deposition of Group-1 rocks (oldest)
79mAp 6.5
MAP INTERPRETATION FOR STRUCTURAL GEOLOGISTS
FIGURE 6.5A Solution of Map 6.5.
MAP INTERPRETATION FOR STRUCTURAL GEOLOGISTS
6. SummAry mApS80
FIGURE 6.5B Cross-section drawn for Map 6.5.
81mAp 6.6
MAP INTERPRETATION FOR STRUCTURAL GEOLOGISTS
MAP 6.6
MAP 6.6 Reproduced from fig 10.12 of Borradaile (2014). Permission received by Elsevier.
MAP INTERPRETATION FOR STRUCTURAL GEOLOGISTS
6. SummAry mApS82
Litho-units A and B crop out in this map (Map 6.6) of undulating topography. Both of them are intruded by two 
vertical dykes D1 and D2. Litho-units A and B are folded and faulted. The fault plane is not folded and the strike-
line magnitudes on the either side of the fault indicate that the folded sequence is faulted. Hence folding predates 
faulting.
The solution is given in Fig. 6.6A. The trend of axial plane is 15°. The attitude of the west dipping limb is 15°/40° 
→ 285°, and that of the east dipping limb is 15°/40° → 105°. Hence the fold is a symmetric-nonplunging-open fold.
The attitude of the fault plane is 74°/63° → 164°. Magnitudes of the strike lines on either side of the fault indicates 
that the southern block (the hanging wall block) is upthrow. It is a reverse fault. In Fig. 6.6B, EF is the net slip and 
according to the scale of the map, it is 80 m. The pitch of net slip on the fault plane is 54° from 74°.
D1 and D2 trend 166° and 128°, respectively. Dyke D2 is faulted, but not folded. Hence, D2 intruded in between 
the folding and the faulting events. Dyke D1 is not displaced and it’s pitch on the fault plane (90°) does not match 
with the pitch of net slip on the fault plane (i.e. 54° from 74°). Hence, Dyke D1 intruded after faulting. A cross-
section has been presented in Fig. 6.6C.
Sequence of events (Figs. 6.6A,B):
Intrusion of dyke D1 (youngest)
Faulting
Intrusion of dyke D2
Folding of A and B
Deposition of A and B (oldest)
83mAp 6.6
MAP INTERPRETATION FOR STRUCTURAL GEOLOGISTS
FIGURE 6.6A Solution of Map 6.6.
MAP INTERPRETATION FOR STRUCTURAL GEOLOGISTS
6. SummAry mApS84
FIGURE 6.6B Net slip calculation for Map 6.6 and Fig. 6.6A.
FIGURE 6.6C Cross-section for Map 6.6.
85
m
A
p 6.7
M
A
P IN
T
E
R
PR
E
TA
T
IO
N
 FO
R
 ST
R
U
C
T
U
R
A
L G
E
O
L
O
G
IST
S
M
A
P
 6.7
MAP 6.7 Reproduced from Map 3 of Platt (1951). Permission received by Elsevier.
MAP INTERPRETATION FOR STRUCTURAL GEOLOGISTS
6. SummAry mApS86
Six litho-units crop out in Map 6.7. They can be subdivided into the following three groups: Group-1: litho-units 
L, N, and O; Group-2: litho-units A and E; and Group-3: a 59° trending vertical dyke (D) that intruded Group 1 
rocks only. Hence the dyke is younger than Group 1 rocks and olderthan Group 2 rocks.
The pattern of strike lines indicates that the Group-1 rocks are folded. The attitudes of the limbs are 0°/31°→90° 
and 0°/16°→270°. The Group-1 rocks truncates against the base of Group 2 rocks. Also, Group-2 rocks are parallel 
to this plane of truncation. Hence an angular unconformity separates Group-1 from Group-2 rocks.
The three rock groups are disrupted by a fault. The attitude of the fault plane is 97°/71°→187°. Here the northern 
block (the footwall block) is upthrown. Hence it is a normal fault. The amount of net slip is 100 m (Fig. 6.7B). The 
pitch of net slip on fault plane is 66° from 277°. A cross section drawn along XY line is shown in Fig. 6.7C.
Sequence of events (6.7A,C):
Faulting (youngest)
Deposition of Group-2 rocks
…angular unconformity…
Intrusion of dyke
Folding of Group-1 rocks
Deposition of Group-1 rocks (oldest)
FIGURE 6.7A Solution of Map 6.7.
MAP INTERPRETATION FOR STRUCTURAL GEOLOGISTS
6. SummAry mApS88
FIGURE 6.7B Calculation of net-slip for Map 6.7. The calculations are done on the fault plane, which trends 97–277 º (orange line). Pitch of 
dyke on fault plane 66° from 277° (black line, cuts the strike line of the fault plane at “P”). Pitch of the unconformity planes on fault plane is 7° 
from 97°. The traces of the unconformity planes for southern (blue line) and northern (green line) blocks intersect the strike of the fault plane at 
Q and R, respectively. Net slip: PS = 1 cm, which is 100 m, according to the map scale. The pitch of net slip (i.e., PS) on fault plane is 66º from 97º.
FIGURE 6.7C Cross-section for Map 6.7.
89mAp 6.8
MAP INTERPRETATION FOR STRUCTURAL GEOLOGISTS
MAP 6.8
MAP 6.8 Reproduced from Map 7 of Platt (1951). Permission received by Elsevier.
MAP INTERPRETATION FOR STRUCTURAL GEOLOGISTS
6. SummAry mApS90
FIGURE 6.8A Solution of Map 6.8.
91mAp 6.8
MAP INTERPRETATION FOR STRUCTURAL GEOLOGISTS
Two groups of rocks crop out in Map 6.8: Group-1: rock units M, N, and E. Group-2: rock units L and T. Besides, 
recent deposits O and A are also present at places.
Group-A rocks folded and faulted. The attitudes of the fold limbs are 0°/64°→90° and 0°/45°→270°. Hence, they 
are nonplunging asymmetric folds (antiform/synform). The interlimb angle of the folds are 71°. Therefore it is an 
open fold. The axial traces, that trend N in Fig. 6.8A, have been drawn in the cross-section (Fig. 6.8B) by locating 
(i) where the axial traces intersect (red dots) the topographic profile along the XY line, and (ii) joining the red dot 
in the central part of the diagram with the corresponding hinge point. The second axial trace (left to the former in 
Fig. 6.8B) is drawn parallel to the previous axial trace and passing through its corresponding red dot. Two faults 
Fault-1 and Fault-2 affected the folded sequence. Both of the faults are vertical and trends 90°. For Fault-1, the 
southern block (~the central block) is upthrown by 100 m. For Fault 2, the southern block is downthrown by 200 m.
The two groups of rocks are separated by an angular unconformity. Its attitude as well as that for Group-2 rocks 
is 43°/12°→133°.
Sequence of events (Fig. 6.8B):
Deposition of A and O (Youngest)
Tilting
Deposition of L and T
Angular unconformity
Folding of Group 1 rocks
Deposition of Group 1 rocks (M, N and E) (Oldest)
FIGURE 6.8B Cross-section drawn for Map 6.8.
93
m
A
p 6.9
M
A
P IN
T
E
R
PR
E
TA
T
IO
N
 FO
R
 ST
R
U
C
T
U
R
A
L G
E
O
L
O
G
IST
S
M
A
P
 6.9
MAP 6.9 Reproduced from Map 18 of Platt (1951). Permission received by Elsevier.
MAP INTERPRETATION FOR STRUCTURAL GEOLOGISTS
6. SummAry mApS94
Seven litho-units crop out in this map (Map 6.9) of undulating topography. They can be classified as: Group 1: 
Silurian units S1, S2, S3; Group 2: Old Red Sandstone (R) and Dolerite (D); Group 3- Trias (T) and Jurassic (J).
Based on the pattern of the strike lines, it is seen that the Group 1 units are folded. The trend of the axial planes is 
60–240° (Fig. 6.9A). The attitude of NW dipping limb is 60°/76°→330° and that of the SE dipping limb 60°/52°→150°. 
Folded Group 1 rocks (Silurian) truncate at the base of the unfolded Old Red Sandstones (mainly Devonian). Hence 
this basal plane (marked green in Fig. 6.9A) indicates a break in deposition and deformation as well. That means, 
this surface is an angular unconformity (attitude: 59°/11°→329°). The dolerite intrusion appears to be concordant 
with the host Old Red Sandstone, hence it is a sill (attitude 8°/179°→269°). Group 1 and Group 2 units truncate 
against the base of Group 3 (marked light blue). Group 3 units are parallel to this base. Hence, the base of Group 
3 is an angular unconformity surface (attitude 114°/7°→204°).
There are three faults—F1, F2, and F3 present in the map. F1 has affected Group 1 only. F1 is a vertical fault trend-
ing 82–262°and the eastern block is upthrown by 200 m. F2 has affected Group 1 and Group 2 units. F2 is a vertical 
fault trending 174–264° and the western block is upthrown by 300 m. F3 is a normal fault that has affected all three 
groups of rocks. The trend of F3 is 66°/77°→156°. Here the western block (i.e., the footwall block) is upthrown by 
100 m. Hence it is a normal fault. A cross-section is presented in Fig. 6.9B.
Sequence of events:
Fault 3 (Youngest)
Deposition of Group 2 rocks
Development of angular unconformity
Fault 2
Angular Unconformity
Fault 1
Folding of Group 1 rocks
Deposition of Group 1 rocks
Intrusion of Dolerite in Old Red Sandstone
Deposition of Old Red Sandstone (Oldest)
FIGURE 6.9A Solution of Map 6.9.
FIGURE 6.9B Cross-section drawn for Map 6.9.
97ExErcISES
MAP INTERPRETATION FOR STRUCTURAL GEOLOGISTS
EXERCISES
For each of the following maps (Maps 6.10–6.14): give geological and structural details, draw a proper cross-
sections, and find out the sequence of events along with explanations.
MAP 6.10 Reproduced from Map 8 of Simpson (1961). Permission received by Elsevier.
MAP INTERPRETATION FOR STRUCTURAL GEOLOGISTS
6. SummAry mApS98
MAP 6.11 Reproduced from Map 6 of Platt (1951). Permission received by Elsevier.
MAP 6.12 Reproduced from Map 9 of Platt (1951). Permission received by Elsevier.
MAP 6.13 Reproduced from “ADVANCED MAPS:1” of Bradshaw and Jarman (1969). Permission received by Elsevier.
MAP 6.14 Reproduced from Map 17 of Platt (1951). Permission received by Elsevier.
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105
Map Interpretation for Structural Geologists.
DOI: © Elsevier Inc. All rights reserved.2017http://dx.doi.org/10.1016/B978-0-12-809681-9.00007-3
7
This chapter deals with the completion of geological maps, maps with bore-hole-related problems, and various 
other calculations.
C H A P T E R 
Miscellaneous maps
MAP INTERPRETATION FOR STRUCTURAL GEOLOGISTS
7. MIscEllAnEous MAps106
MAP 7.1 A coal seam (solid line) crops out and cuts 300 m contour at three points. This coal seam occurs also at 200 m below the ground 
surface at +. 1. Complete the outcrop of the seam and describe its structural geology. 2. Determine the depths at which the coal will probably 
be found in the boreholes A and B. Reproduced from Map 30 of Platt (1951).
MAP 7.1
107MAp 7.1
MAP INTERPRETATION FOR STRUCTURAL GEOLOGISTS
1. The outcrop in Map 7.1 has been completed (marked red) (Fig. 7.1). Note: The line tx, ty and tz cannot be the 
strike lines since they become non-parallel: not possible for a plane with uniform attitude.
The points p, q, r, and s are 400, 300, 400, and 300 m elevations, respectively. At these points the coal seam occurs 
200 m below the surface. That means, at p, q, r, and s the coal seam can be encountered at 200, 100, 200, and 
100 m depths, respectively. ‘q’ and ‘t’ are the points where the coal seam is present at 100 m and 300 m elevations, 
respectively. Hence the coal seam is present at 200 m elevation at point u, which is equidistant fromq and t. Points 
p and u are joined to obtain the 200 m strike line of the coal seam. 
The necessary constructions are shown in Fig. 7.1. Parallel to this strike line, the 300 and 100 m strike lines 
are drawn through the points t and q, respectively. In the northern part of the map, another 300 m strike line of 
the coal seam can be drawn based on the pattern of exposure. The trend of this 300 m strike line does not match 
with the trend of previously drawn 300 m strike line. Hence, the coal seam is folded. The 200 and 100 m strike 
lines for the other limb are drawn through the points r and s, respectively. The rest of the strike lines for both 
the limbs are drawn maintaining the equal spacing of the strike lines. From the points of intersections between 
the strike lines and corresponding height contours, the outcrop of the coal seam is figured out (solid red line), 
and the axial trace is drawn as a broken red line. The attitudes of the limbs are 98°/29°→188° and 1°/37°→91°. 
The attitudes of the axial plane and the fold axis are 147°/90° and 23°→147°, respectively. The interlimb angle 
is 132°. Hence it is a plunging gentle upright synform. The plunge of the fold axis and the interlimb angle are 
deduced using stereo-net, not shown here.
2. Say points A and B are at an elevation of 450 m. Again, both the points locate on the hinge line of the folded coal 
seam. The zero m strike line of the coal seam passes near the point A. Hence, the coal seam is encountered at 
450 m depth at point A. Similarly, as the −100 m strike line passes near the point B, here coal seam will possibly 
be encountered at 550 m.
MAP INTERPRETATION FOR STRUCTURAL GEOLOGISTS
7. MIscEllAnEous MAps108
FIGURE 7.1 Solution of Map 7.1. Exercise: draw a suitable cross-section.
109
M
A
p 7.2
M
A
P
 7.2
MAP 7.2 The map represents an area where Triassic Rocks and Coal Measures crop out. The outcrop of the base of the Trias (T-T) and that of the Fault (F-F) are marked. A coal seam 
was encountered at 200 m depth in all the bore holes marked A. Determine: (I) the direction and amount of dip of the base of the Trias and of the Coal seam; (II) full particulars of the 
fault. Reproduced from Map 29 of Platt (1951).
MAP INTERPRETATION FOR STRUCTURAL GEOLOGISTS
7. MIscEllAnEous MAps110
The drawings required to complete Map 7.2 is shown in Fig. 7.2. From that, the following results are found:
1. Attitude of Trias: 60°/15°→330°
2. Attitude of Coal Measures:11°/21°→281°
3. This is a 171° striking vertical fault with 300 m vertical separation. The fault disrupted the Coal Measures, but 
not the Trias. Hence this fault is younger than the Coal Measures, but older than the Trias (Fig. 7.2).
Note: Dashed fault line indicates the part of the fault that runs below the undisturbed upper unit. The dashed 
line is drawn to infer the pattern of the faulted coal seam below the younger cover.
FIGURE 7.2. Solution of Map 7.2. Exercise: Draw a suitable cross-section.
111
M
A
p 7.3
M
A
P
 7.3
MAP 7.3 Complete the outcrops of the lithounits. Reproduced from “FOLDED ROCKS: 2” of Bradshaw and Jarman (1969).
MAP INTERPRETATION FOR STRUCTURAL GEOLOGISTS
7. MIscEllAnEous MAps112
The completion of Map 7.3 is presented in Fig. 7.3. The observations made from Fig. 7.3 is given below:
1. Two litho-groups crop out: Group-1: A, B, C, and D. Group-2: G.
2. In the NE corner and in the part covered by G, the outcrop Vs do not match with contour Vs. Hence they 
indicate folds.
3. From the outcrop Vs, that match with the contour Vs, the strike-lines have been drawn.
4. Two axial traces are drawn parallel to the strike lines. The axial traces divide the map into three segments with 
different dip amounts.
5. A/B x m strike line = B/C (x + 100) m strike line = C/D (x + 200) m strike line. Following this, other strike 
lines are drawn.
6. The attitudes of the limbs are 5°/21°→95° and 5°/41°→275°, respectively.
7. The base of G is horizontal and expose at ~ 900 m elevation. Based on this observation, the base of G is drawn 
in the SE part of the map.
FIGURE 7.3 Solution of Map 7.3. Exercise: draw a suitable cross-section.
113MAp 7.4
MAP 7.4
MAP 7.4 Reproduced from “THREE-POINT PROBLEM: 3” of Bradshaw and Jarman (1969). Red Sandstone rests unconformably on gently 
dipping Coal Measures containing three workable seams, which are mined by deep shafts at a, b and c, and an opencast working at x. The table 
below gives the depths (in m) of the seams in each mine. The task is to: (1) Draw in the outcrops the three seams by obtaining the strike lines. 
(2) Shade the area in which two, and only two seams can be mined. (3) At what depths would the various seams be met by a shaft sunk at d? 
Note: See Eskenazy and Vassilev (2001) for report on coal layers at great depth.
Seams
Upper Middle Lower
Mines a 80 280 680
b 25 425
c 250
MAP INTERPRETATION FOR STRUCTURAL GEOLOGISTS
7. MIscEllAnEous MAps114
Constructions to solve Map 7.4 are shown in Fig. 7.4, where the three strike lines are drawn. The following 
observations have been made:
1. The given chart says that the vertical distance between the upper and the middle coal seams is 200 m. Also, the 
vertical distance between the middle and the lower coal seams is 400 m.
2. The strike lines (in m) passing through the points a, b, and c are:
Upper Middle Lower
a 1600 1400 1000
b 1900 1700 1300
c 1800 1600 1200
3. For the lower coal seam, the 1000 m and 1300 m strike lines pass through the points “a” and “b” respectively. 
The point through which the 1200 m strike line of the lower coal seam passes, is marked on the ab line. This 
point is joined with “c” to obtain the 1200 m strike line for the lower coal seam. This strike line also indicates 
the 1600 m strike line for the middle coal seam and 1800 m strike line for the upper seam (from their vertical 
distances as mentioned in point 1). Now, the 1000 m and 1300 m strike lines for the lower coal seam are drawn 
through points “a” and “b”, respectively.
4. All other strike lines for the coal seams are drawn assuming constant attitude of the coal seams.
5. Finally, from the points of intersection between strike lines and a height contours the coal seams are drawn. 
Broken lines indicate the part of the corresponding coal seam buried under the Red Sandstone.
6. The attitude of the coal seams is 81°/19°→351°.
7. The area where two and only two coal seams can be mined has been shaded by translucent gray color in 
Fig. 7.4.
115MAp 7.4
MAP INTERPRETATION FOR STRUCTURAL GEOLOGISTS
FIGURE 7.4 Solution of Map 7.4. Exercise: Draw a suitable cross-section.
MAP INTERPRETATION FOR STRUCTURAL GEOLOGISTS
7. MIscEllAnEous MAps116
MAP 7.5
MAP 7.5 The map represents an area with horizontal surface; boreholes at A, B, C, and D show the following depths 
(in m) to the base of the Trias and Coal Measures: 
A B C D
Base of Trias 400 300 200 500
Base of Coal Measures 1000 400 600 ?
Determine the dip and strike of the beds. Shade the area where the Coal Measures are found. Determine the depth to the base of the Trias and 
Coal Measures at E. Describe the structure of the area. Reproduced from Map 41 of Simpson (1961).
117MAp 7.5
MAP INTERPRETATION FOR STRUCTURAL GEOLOGISTS
The attitude of Coal Measures is 101°/28°→191°. The attitude of the base of the Trias is 66°/14°→156°. The 
shaded area, at the SW corner of the map, indicates the place where Coal Measures can be found. The magnitudes 
of the strike lines indicate that the Coal Measures and the Trias are present at point E at 700 m and 400 m depths, 
respectively. In this map, the Coal Measures (mainly Carboniferous) truncates below the Trias. Hence, it indicates 
angular unconformity.
The −400 m and the −200 m strike lines of the base of Trias pass through the points A and C, respectively. Therefore, 
the −300 m strike line passes through the midpoint of AC, point F, and also through the point B (as given in the 
table). The -300m strike line is obtained by joining thetwo points F and B. Parallel to the line FB the −400 m and 
the −200 m strike lines are drawn. Other strike lines of the Trias are drawn keeping the equal strike spacing.
For the Coal Measures, the −1000 m and the −400 m strike lines passes through the points A and B, respectively. 
On the AB line, the point G is obtained through which the −600 m strike line passes through (1/3rd of AB length 
from B side). Point G is joined with C to get the −600 m strike line of the Coal Measures. Parallel to GC line, the 
−400 m and −1000 m strike lines are drawn. Other strike lines are drawn based on the principle of equal spacing.
The points of intersection between strike lines of equal magnitudes (−200 and −100) are joined by a straight line 
that represents the line of intersection between the base of the Coal Measures and that of the Trias.
MAP INTERPRETATION FOR STRUCTURAL GEOLOGISTS
7. MIscEllAnEous MAps118
FIGURE 7.5 Solution of Map 7.5.
119
Ex
Er
c
IsEs
M
A
P IN
T
E
R
PR
E
TA
T
IO
N
 FO
R
 ST
R
U
C
T
U
R
A
L G
E
O
L
O
G
IST
S
MAP 7.6 Exposures of a thin planar coal seam are encountered at A, B, and C, on the map above. Draw the outcrop and shade the area underlain by coal. Reproduced from Fig. 63 
of Thomas, (1966).
E
X
E
R
C
ISE
S
MAP 7.7 A field survey has plotted five outcrops of boundaries between the three rock-types shown in the key. The rocks dip at the same angle throughout the area. (A) Construct 
and label the strike lines. (B) Complete the outcrop pattern. (C) Present a detailed geological description. (D) Draw a suitable cross-section. (E) If a borehole is made at X, at what depth 
below ground will the bedding planes be encountered? Reproduced from “TILTED ROCKS: 3” of Bradshaw & Jarman (1969).
121ExErcIsEs
MAP INTERPRETATION FOR STRUCTURAL GEOLOGISTS
MAP 7.8 Complete the outcrop on the northern side of the fault and describe the Geological features. Draw a suitable cross-section. 
Reproduced from Fig. 10.11 of Borradaile (2014).
MAP 7.9 (1) Find the depth of the base of the grit below the surface at A. (2) Shade in the area under which coal occurs and find the dip of the seam in degrees. (3) Write a geologi-
cal history of the area. Reproduced from Fig. 78 of Thomas (1966). Exercises: (1) Find the depth of the base of the grit below the surface A. (2) Shade the area under which coal occurs, and find the 
attitude of the coal seam. What happens to the coal seam under the unconformable grit? (3) Write a geological history of the area.
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127
Billings, M. P. (1954). Structural geology. Prentice-Hall.
Borradaile, G. (2014). Understanding geology through maps. San Diego: Elsevier.
Bradshaw, M. J., & Jarman, E. A. (1969). Geological map exercises. London: The English Universities Press Ltd.
Eskenazy, G., & Vassilev, S. (2001). Geochemistry of chlorine and bromine in Bulgarian coals. Review of the Bulgarian Geological Society, 62, 37–46.
Fossen, H. (2016). Structural geology. Second Edition. Cambridge University Press.
Ghosh, S. K. (1993). Structural geology: Fundamentals and modern developments. Oxford: Pergamon Press.
Platt, J. I. (1951). Selected exercises upon geological maps. London: Thomas Murby and Co.
Simpson, B. (1961). Geological map exercises. London: George Philip & Sons Ltd.
Thomas, J. A. G. (1966). An introduction to geological maps. London: Thomas Murby and Co.
References
http://refhub.elsevier.com/B978-0-12-809681-9.00019-X/sbref9005
http://refhub.elsevier.com/B978-0-12-809681-9.00019-X/sbref1
http://refhub.elsevier.com/B978-0-12-809681-9.00019-X/sbref2
http://refhub.elsevier.com/B978-0-12-809681-9.00019-X/sbref901
http://refhub.elsevier.com/B978-0-12-809681-9.00019-X/sbref9007
http://refhub.elsevier.com/B978-0-12-809681-9.00019-X/sbref3
http://refhub.elsevier.com/B978-0-12-809681-9.00019-X/sbref4
http://refhub.elsevier.com/B978-0-12-809681-9.00019-X/sbref5
http://refhub.elsevier.com/B978-0-12-809681-9.00019-X/sbref6
129
Note: Page numbers followed by “f” refer to figures.
Index
A
Angular unconformity, 29f, 71, 73f, 75f, 76f
map with, 25–28, 26f
Axial plane, 35, 38
Axial trace, 35, 40f
B
Basalt, 65
Bed attitude, 28, 58
C
Coal seam, 107
Cross-section, 1, 4, 14f, 15–16, 16f, 37f, 58
E
Event chronology, 67–68, 72, 74, 82, 86, 94
F
Faults, 67, 72, 110
Dyke D1 intruded after faulting, 82, 87f, 
88f
plane attitude, 58
Folds, 35, 65
axial trace, 35, 40f
axis, 43
map with, 35f, 38f, 39f, 42f, 43f
G
Geological maps, 1
H
Horizontal beds, 9
I
Inclined beds, 9
in map, 10f
stratum contours, 11f
strike lines, 11f
three-point method, 19f, 20, 21f
topography and structural geology, 14f, 
15f, 16f, 19f, 20f
undulating topography, 14–17
Inter-limb angle, 38
L
Limbs, 38
Litho-contacts, 112
M
Map 1 interpretation, 4, 5f
Miscellaneous maps, 105
coal seam, 107, 108f
exposures of thin coal seam, 119f
fault, 109f, 110, 110f
reproduced from ‘TILTED ROCKS:3’, 120f
reproduced from “three-point problem”, 
113f
reproduced from folded rocks, 111f
N
Net-slip
calculation, 84f, 88f
magnitude, 58
Nonconformities, 25
O
Omission of beds, 49
map with fault, 49f, 50f, 51f
P
Planar topography, 68
Plane, 9
Plunging fold, 43
Plunging-symmetric-gentle fold, 74
S
Spur, 15–16, 28
contours for, 3f
Stratum contours, 9, 11f
Strike lines, 9, 11f, 38, 43, 69
Summary maps, 65
ADVANCED MAPS, 100f
angular unconformity, 71, 75f, 76f, 78, 91
Dyke D1 intruded after faulting, 82, 87f, 
88f
eastern block, upthrown, 68, 70f, 71f
maps without contours, 66f
northern block, downthrown, 65, 67f, 68f
pitch of net slip on fault, 86, 90f, 92f
western block, downthrown, 72, 77f, 79f
Symmetric nonplunging, 58
T
“Three-point method”, 43
Three-point problem to deduce attitude, 20, 
21f
Time gap, 25
Topography, 1
basin in various ways, 1f
contours for valley and spur, 3f
contours of topographic features, 2f
part of topographic map, 4f
topographic features, 4, 5f
U
Unconformity, 25
angular, 29f, 71, 75f, 76f, 78
map with angular, 26–28, 26f, 28f
V
Valley, 4, 5f, 15–17, 49
contours for, 3f
exposure of inclined plane, 13f
slopes, 12f
	Cover
	Title Page
	About the Series
	MAP INTERPRETATION FOR STRUCTURAL GEOLOGISTS
	Copyright
	Dedication
	Contents
	Preface
	Acknowledgments
	1 Topography
	2 Horizontal and Inclined Beds
	3 Unconformity
	4 Folds
	5 Faults
	6 Summary maps
	7 Miscellaneous maps
	References
	Index