Re: Structural Geology By Haakon Fossen Pdf
Argimiro Krishnamoorthy
And by this I have reached the main point of this blog article; field observations. Field observations and fieldwork have been an important aspect of structural geology for me ever since. It is a necessity, a condition for life as a structural geologist the way I experience it. Physical and numerical models are indeed both interesting and useful, but they cannot replace the joy and importance that comes with real rocks and making your own field observations.
At the same time, the large number of models and interpretations that can be made from field observations, the large degree of freedom if you like, sometimes makes it frustrating to be a structural geologist. It is a well-known fact that a model that explains a given set of data does not have to be correct, simply because there may be other, usually many other reasonable models that fit the data equally well. Just think about infinite number of strain paths that conglomerate pebbles can follow to reach a given state of strain. From my own experience it seems that we tend to become more aware of this fact as we gain experience as geologists. And as this happens, it becomes even more important to go back to the rocks and outcrops to look for more clues through new observations and descriptions. This pushes me back to my first thrilling encounter of beautifully deformed conglomerates. Back to the roots, back to enjoying the beauty of deformed rocks, to observing and describing. And it feels right.
Then, once they discover the usefulness of sketching, the next thing that comes up is a request for a course in drawing techniques. Why do hardly any geology departments offer such courses? I guess some departments have skilled field instructors who teach some of the basics of field sketching, but few do this in a systematic way. If a field-oriented drawing course for geology students exists, then I would really like to know more about it. Interestingly enough, a student recently asked me if I would be kind enough to run a little workshop on field sketching, and lacking any good alternative teacher for such a class in our department, I reluctantly agreed. Well, the student posted it on Facebook, and after a day or two more than 100 students had signed up for it! It is happening this week, and students voluntarily come in to the U at night to spend time on this no-credit mini-course.
Comparing sketches and techniques is also interesting. Some prefer 3D sketches, while others are more comfortable working in 2D, producing cross-sections and map-view illustrations (Fig. 3). Some try to capture (sometimes too many) details, while others make very general or idealized sketches reminiscent of textbook or article illustrations typically found in early- to mid-20th century publications.
Let me share an example. During my PhD I did structural mapping in a part of the Caledonides where well-foliated protomylonitic rocks had been pervasively folded into asymmetric hinterland-verging folds and shear fabrics. These folds are extremely prominent and really eye-catching (even in the winter, see Fig. 4), occurring from microscale structures to kilometer-scale asymmetric folds. Still, the structural geologist who mapped the area and wrote two healthy books about the structural geology of this area hardly mentioned their existence. I suspect at least part of the reason was that the folds did not fit the general concept of foreland-directed Caledonian thrusting, and therefore were largely overlooked. The message here is that if you force yourself to sketch out the details of key exposures, you also force yourself to deal with the structures that are there.
The discovery of S-C and related kinematic structures found in shear zones and mylonites (Fig. 5) may serve as a more general, albeit related example. Detailed field-based descriptions were what made us realize that these structures relate to strain partitioning during shearing rather than representing classical crenulation cleavage. Shortly after the publication of some key papers on this issue, S-C structures were discovered in shear zones all over the world. The implications of the kinematic information that this provided were enormous, and helped among other things to distinguish between extensional and thrust-related detachments. It was also a valuable tool for me as a student, as it helped to link the aforementioned hinterland-verging folds and related shear fabrics to post-collisional extensional reversal of the basal dcollement of the Caledonian orogenic wedge, and to relate this extensional deformation to plate-scale divergent motions.
The interesting question is whether there are other secrets hidden in rocks, secrets that we are missing out on because we are too caught up in our preferred models and entrenched ways of thinking. Are there other simple and, once understood and pointed out, intuitive, easy-to-use structures that we need to discover? Or will future advance in our field solely rely on more indirect methods, such as sophisticated isotope or geophysical data?
Regardless, the importance of objective observations through field sketching and descriptions will always be important, making the foundation for more advanced secondary work. Hence we should keep training our students (and develop ourselves as teachers) in this important part of geological research.
I used to teach at a small liberal arts college in Wisconsin. My field methods students, too, had asked me for instruction in how to sketch. One year when I was heading to GSA, I took advantage of my time away by having one of my art department colleagues teach my class that week. We met in advance to discuss what makes a good field sketch. He built his exercises around those goals. The students loved it, and their field sketches on our next trip were vastly improved.
I remember that he translated my thoughts into the terminology he would use as an artist. I started by showing him some of my field sketches from a recent field trip and talking about what information they recorded for me.
I think that for my students, at that time, the most helpful advice he had was on how to keep things in proportion. Mastering that allowed them to do a better job of recording visual information in general.
Good points. Thanks for sharing. I think there are different approaches to field sketching, depending on the purpose. Sometimes you really want to emphasize a certain structure or feature, toning down other (distracting) stuff. Other times it may be useful to just sketch up anything that might be geologically relevant, being true to the outcrop, and see if it leads to new observations. Proportionality may be important in any case, and adding actual angles and orientations measured in the field may add to that (since angles are not always what they seem to be, depending on perspective).
You ask about a field-oriented drawing course for geology students. I use gigapans of geological structures (e.g. ) to train students at home and in class their drawing skills. And it works. Once in the field you see that they benefit of this drawing excercises.
Gigapan is great because of the ability to zoom in on details. I wonder how exactly you use it? Do you give them specific exercises where they use their own computer (so that they can zoom in/out individually)? It would be interesting to hear more about your experience with this.
Great post. This takes me back to rigorous classical field camp education many of us went through in the past and experienced the wonders of geology in natural setting. You highlighted the significance of such exposure and the value associated with field mapping techniques as these pertain to imparting hands-on and critical thinking undergraduate education through beautiful illustrations. For geologists, field experiences are deemed by many as the central thrust when it comes to successfully explaining the origin of a terrain. Thank you so much for bringing importance of field geology education with the help of text-book quality outcrops characterized by deformed, complexly folded, faulted and other geological features. Enjoyed it very much.
Dr. Haakon Fossen is an internationally renowned geologist who is particularly well known for making structural geology more accessible to students and professionals who use data and principles of structural geology in industry.
Dr. Fossen is a professor of geology at the University of Bergen. He has made significant contributions to topics that have fueled debate in earth sciences over the last several decades, including the mechanisms and consequences of oblique motion of tectonic plates and the collapse of mountain belts when extension follows contraction. In addition, he has provided leadership in the study of important structures that control porosity and permeability in sedimentary basins, with applications in groundwater, oil migration, and the sequestration of carbon dioxide.
Dr. Fossen has reached a worldwide audience through his textbooks and extensive website. He wrote the first textbook in Norwegian on structural geology, followed by an even more successful textbook that has been widely adopted throughout the world. His website includes video tutorials and other teaching aids, free for anyone to use. Dr. Fossen has also written a book for the public on geology, rocks, minerals, and fossils, and has organized and led professional development courses in Europe and North and South America.
As a scholar with almost 150 publications, Dr. Fossen has won multiple awards, including the Nordic Geoscientist Award in 2012 and the Outstanding Paper Award from the structural geology and tectonics division of the Geological Society of America.
In naming Dr. Fossen as a recipient of the Distinguished Leadership Award for Internationals, the selection committee acknowledges his wide-ranging contributions to the geology field in Norway and around the globe, and looks forward to his future work.
Haakon Fossen is Professor of Structural Geology at the University of Bergen, Norway, where he is affiliated with the Department of Earth Science, the Natural History Collections, and the Centre for Integrated Petroleum Research (CIPR). His professional career has involved work as an exploration and production geologist/geophysicist for Statoil and as a Professor at the University of Bergen (1996 to present), in addition to periods of geologic mapping and mineral exploration in Norway. His research ranges from hard to soft rocks and includes studies of folds, shear zones, formation and collapse of the Caledonian Orogen, numerical modeling of deformation (transpression), the evolution of the North Sea rift, and studies of deformed sandstones in the western United States. He has conducted extensive field work in various parts of the world, notably Norway, Utah/Colorado, and Sinai, and his research is based on field mapping, microscopy, physical and numerical modeling, geochronology and seismic interpretation. Professor Fossen has been involved in editing several international geology journals, has authored over 90 scientific publications, and has written two books and several book chapters. He has taught undergraduate structural geology courses for over ten years and has a keen interest in developing electronic teaching resources to aid student visualization and understanding of geological structures.
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