Drawing Geological Structures

 
 
Wiley-Blackwell (Verlag)
  • erschienen am 20. Juli 2017
  • |
  • 232 Seiten
 
E-Book | ePUB mit Adobe-DRM | Systemvoraussetzungen
978-1-119-38724-4 (ISBN)
 
Despite the modern dominance of computer graphics programs and digital cameras, the ability todraw geological structures manually remains a necessity in academic geology and beyond. Drawings serve for quick and simple documentation in the field or at the microscope. They can be applied as a language of their own as well as be adapted to suit specific requirements. Moreover, geological drawing improves observational ability and contributes to the understanding of geological structures and structure-forming processes. Geological drawing is assisted scientific thinking.
Drawing Geological Structures provides undergraduate as well as graduate and practicing geologists with a thorough, step-by-step practical guide to the art of geological drawing. Beginning with the basics, the book covers thin sections, sample sections, samples and geological stereograms. The chapters provide examples of how drawings evolve and are complemented by exercises, allowing the reader to practice their drawing prior to going out into the field or working at the microscope. Users of this unique guide will develop their knowledge and technical vocabulary whilst also improving their drawing skills.
1. Auflage
  • Englisch
John Wiley & Sons
  • 22,40 MB
978-1-119-38724-4 (9781119387244)
weitere Ausgaben werden ermittelt
Jörn H. Kruhl is retired professor of geology at Technische Universität München, Germany. He received his Dr. rer. nat. from Rheinische Friedrich-Wilhelms-Universität Bonn and held appointments in research and teaching at universities in Mainz, Salzburg, Berlin and Frankfurt/M. For decades, he worked on rock structures in numerous regions and orogens, from macro to micro, in the field and at the microscope.
About the Author vii
Preface ix
1 Introduction 1
1.1 Why Do We Need Drawings? 5
1.2 The Tools 11
1.3 Sizes of Drawings 12
1.4 Geological Versus Artistic Drawing 13
1.5 Drawing With Symbols 15
1.6 Realistic Drawing 21
1.7 The Fractal Geometry of Geological Fabrics 26
1.8 Basic Rules of Geological Drawing 29
References 30
2 Rock Thin Sections 33
2.1 Drawing as a Form of Microscopy 35
2.2 Drawing with Various Tools 35
2.3 Foundations of Thin-Section Drawing 36
2.4 Minerals and Their Characteristic Fabrics Under the Microscope 41
2.5 Sketches for Fast Documentation 52
2.6 Development of Precise Thin-Section Drawings 60
2.7 Digital Reworking of Manual Thin-Section Drawings 82
2.8 Digital Drawing 83
Summary 90
References 93
3 Specimen Sections 95
3.1 The Geological Message of a Drawing 95
3.2 Schematic Representation of Minerals 97
3.3 Schematizing Rocks and their Structures 100
3.4 Development of Drawings 104
3.5 Illustration on Different Scales 107
3.6 Detailed Drawings of Sample Cuts 110
Summary 116
4 Drawing Rock Structures in Three Dimensions 117
4.1 Foundations 118
4.2 The Development of Schematic 3D Drawings 125
4.3 Field Drawing 156
4.4 Digital Processing 169
4.5 Rules of Labeling 172
Summary 174
References 177
5 Geological Stereograms 179
5.1 Foundations 179
5.2 Orientation and Extension 181
5.3 Additions and Labeling 189
5.4 Digital Processing 193
Summary 195
References 196
6 Solutions 199
Index 207

Chapter 1
Introduction


"Of course you should draw! You should draw everything that can be drawn." "But, Professor, I have no artistic talent!"-"You do not need it! You aren't supposed to make art, but simply draw as well as you write. Firstly, so that you can learn to better see and observe, because the drawing pencil forces the eye to look closely and give a detailed account of the facts, for drawing is guided seeing; secondly, because drawing is often the shortest and best form of description. For this you need no talent, only diligence and a little guidance."

(Hans Cloos, 1938)

Drawing is one of the elementary human abilities. It requires practice. But one must not draw with the skill of a Leonardo da Vinci or an Albrecht Dürer to be able to create drawings that are informative, aesthetic, and a joy to others. The drawing of geological objects is at a level that anyone can reach with a little practice and by following a few rules (Figure 1.1).

Figure 1.1 One of the author's early, but failed, attempts to draw samples and outcrops in the field, and a better version of the same drawing. (a) Monoclinic fold in psammopelite and quartzite layers of the Moinian (Grampian Highlands at Loch Leven, Scotland); field drawing; outcrop KR513; field book 6 (Kruhl, 1973). The drawing contains numerous shortcomings; above all, imprecise layout of lines, a sloppy perspective, and an incorrect positioning of foliation planes in the metapsammopelitic layers. (b) The same drawing redrawn years later. Cross bedding and S1 foliation planes are more precisely placed; the perspective is correct and, consequently, the 3D appearance of the drawing is better; the carbonate spots are more realistically illustrated; and the labeling is more closely related to the structures. Circles L and K indicate positions of samples. Both drawings ca. A6; black ballpoint pen.

When we talk about drawing, we usually mean artistic drawing. In the case of Leonardo da Vinci-the brilliant painter, sculptor, architect, naturalist, and engineer of the Renaissance-this includes technical or scientific drawing. But in later times, the artists were rarely scientists and the scientists rarely artists. The tasks were distributed. Alexander von Humboldt "measured the world" and Aimé Bonpland drew it. Carl von Linné systematized species classification, while Maria Sibylla Merian painted insect and flower pictures, and John James Audubon left behind "The Birds of America." Only a few artists sketched geology (apart from the omnipresent Goethe), like Robert Bateman, for example: "I enjoyed painting the rock, a kind of granite called gneiss, using little trickles of turquoise and pink and yellow and gray. When I paint rocks I like to convey their characteristics and to make sure that they belong in the landscape and are recognizable geologically" (Terry, 1981); it is the geoscientists, rather, like Clarence E. Dutton (1882) or Albert Heim (1921), that have seen rocks and their structures with the eyes of artists (Figure 1.2).

Figure 1.2 Drawing of part of the Grand Canyon, "Vishnu's Temple" (Dutton, 1882, plate XXXIV): a felicitous combination of artistic, geological, and geomorphological representation.

Today, constructive drawing is what is meant by the term technical drawing, and that is done almost exclusively by computers. Academic (or scholarly), in particular scientific and specifically geological, drawing resists automation, because nature knows no straight lines. Geological objects, like rock layers, folds, volcanic dykes, foliation planes, joints, and the outlines of crystals cannot be represented using the shapes of Euclidean geometry. This is not a question of precision, since the shapes of all these objects don't just vary by chance from the Euclidean form. We know today that many natural processes are not linear and produce shapes of non-Euclidean, fractal geometry (Mandelbrot, 1983). Many geological shapes appear complex and are usually described qualitatively (sutured, rounded, amoeboid) or are represented with the help of picture plates, like the degree of rounding of sand grains, for example. These images are usually paired with specific names (angular, subangular, subrounded, rounded) to ensure the transition to a written description. Complex structures can be captured truly precisely only when they are quantified using fractal geometry. Using these rules while sketching geological structures is well worthwhile. The gain in naturalness and closeness to reality is big.

While scientific drawing is based on a number of rules of artistic drawing, it has many of its own laws. Therefore, geological drawing requires different rules, in part, from artistic drawing. However, the principally irregular form of geological objects does not necessarily mean that it must always be drawn "irregularly" or "fractally." There are reasons for schematic, Euclidean drawing. This is why geological drawing must shuttle between lifelike and abstract representation. This is not easy, and the questions of when is it better to draw realistically, when is an abstract representation more effective, and how can a balance be established between the two, will be discussed in detail.

What is drawn must, however, already be technically understood and interpreted. This is the only way to select and distinguish between what is geologically important and unimportant. "It is the theory that determines what we can observe" (Einstein, 1955). Or, in other words: "You only see what you know" (Weizsäcker, 1955). When transferred to the drawing of geological structures, this means: We only see what we already have as a mental model. We only see the geological structures we expect and that already belong to our knowledge base. Although this may seem a little bit strict, it is true that we have difficulty perceiving and often dismiss structures that we do not know and that aren't part of our empirical knowledge.

Of course it is fundamentally possible to perceive even the unexpected or unusual, but it's hard, and we therefore do well to look at structures exactly before drawing them. If we interpret first, it will be easier to perceive the unexpected and unusual, and incorporate it into our knowledge and experience. This can be time consuming, and causes difficulties. Nevertheless, drawing itself, the physical process of seeing and sketching geological objects, is on a level of craftsmanship that anyone can achieve with a little practice, and, in any case, a "bad" drawing is still better than no drawing!

There are some aspects of geological drawing relating to geological maps and the construction of profiles that we will not touch upon, because they veer too much into the field of technical drawing. For this, there are a sufficient number of good books and, above all, websites where these techniques can be trained online. Furthermore, this book is not about drawing fossils. Although the drawing of fossils coincides in many ways with the drawing of geological structures, there are still some fundamental differences, like the object fidelity, which is essential to the drawing of fossils but more of a hindrance when drawing geological structures. The present book is mainly about:

  • the way in which one must represent geological objects at different scales,
  • how the purpose of the representation affects the nature of the representation,
  • the way in which a balance between detailed and symbolic representation must be maintained in such drawings, and
  • how one can practice all of this.

We will go from small to large, from thin section to outcrop, especially the ensemble of outcrops, and from the two-dimensional representation to the three-dimensional. This order has been chosen in part because two-dimensional representations are technically and in their principles easier, and because the two-dimensional surfaces of three-dimensional objects are seen first. Secondly, big geological objects are made up of many small pieces, and the bigger picture is best understood, if we understand the details.

This book is intended as an exercise book for the purpose of self-study. It should encourage the playful retention of structures, the anchoring of one's own geological data collection in the form of graphic representations, and the occasional replacement of the camera with paper and pen in the field. In addition, this book is meant to encourage the use of the benefits of exact drawings especially when it comes to precision and conciseness (e.g., in publications). Finally, I would like the representations in this book to show that geological structures have not only scientific value but also deserve our attention for their complexity and aesthetics.

1.1 Why Do We Need Drawings?


Anyone who has tried to describe a thin section, a rock sample, or an outcrop without the help of drawings (or photos), would probably not pose such a question. Compared to the expressiveness and the rich detail of graphic representations, the spoken or written word is an inadequate tool. Drawings and photos can document things that would otherwise take much more time to describe, in no time. And since graphics can be digitized, the electronic storage and processing of graphic information is not a problem.

There is no strong conflict between drawing and photo. Photography is a quick and easy type of...

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