STUDY GUIDE FOR EXAM #3, GEOS 304, SPRING, 2015 Exam #3 will cover Folds (Chapter 7), Fault-Fold-Salt Models (Chapter 8), Cleavage, Foliations, and Lineations (Chapter 9), and Shear Zones (Chapter 10). As in the case for preparing for Exams #1 and #2, my study guide for Exam #3 presents three sets of questions, one of which I will ask you to answer on the Essay part of the exam. By preparing hard for all 3, you won’t be testing your luck in predicting which of the questions sets I will ‘pull out of the hat’. Moreover, you will be advancing your general knowledge in ways that will be helpful in other parts of Exam #3. Remember that Exam #3 will cover everything we have studied since Exam #2. Moreover, you probably realize that some of the material for Exam #3 brings back into focus some of the fundamentals, such as strain and stress, and rock strength, etc. Also it is hard to be strong in Fault-Fold models without being up to speed on Faults (Chapter 6). When during your preparation you see that concepts and substance in the material that we have covered for this exam draws upon certain specific ‘fundamentals’ learned earlier, it will be good to review again those specific fundamentals. *If you haven’t learned the geological time scale, it is time to do so. Know the succession of periods in the Paleozoic and in the Mesozoic. Know the succession of epochs (e.g., Paleocene, Eocene, …) in the Cenozoic. Both in evaluating fault throw and in distinguishing anticlines and synclines from antiforms and synforms, knowledge of the age-ordering of formations and epochs is key. Bring to Exam #2 a calculator, a scale-protractor, and a stereographic projection and tracing paper. Possibility A. Imagine in your mind a horizontally-bedded sedimentary rock sequence composed of the kinds of strata you mapped at G8 and in Arrastre Wash. Recall that there are sandstones, siltstones, thin limestone beds, mudstones, and shales. Imagine that this sequence of interbedded strata is on the order of 100 m. Now imagine that this sequence is going to be shortened by 30%, due to horizontal compression oriented NE/SW. Take me through how this sequence will respond as the shortening progresses. What kinds of structures are likely to form in the very early stages, versus the intermediate stages (say, 10%-20% shortening), versus the end stages (25% to 30%). Be specific about the mechanics and the kinematics involved. Be open to combinations of folding and faulting and cleavage development. Have your answer be a combination of prose and pictures. Possibility B. Imagine in your mind a sequence of horizontally-bedded sedimentary rocks ~1km thick. The sedimentary rocks consist mainly of siltstone, sandstone, and shale. Now picture that a third of the way from the base of the sequence there is a very thick layer of salt (several hundred meters thick. Describe how this salt layer is likely to behave as more and more sediment is deposited in this same sedimentary basin. Also describe how this salt layer is likely to behave as the sedimentary sequence, still containing the salt, is subjected to either extensional stretching and normal faulting, OR contraction shortening marked by thrusting and/or detachment folding. Through words and pictures help me visualize the kind of deformation that takes place and the structures that form. Help me understand more about the mechanics of how salt behaves during deformation.

Possibility C. Shear zones represent a structure that causes us to bring a lot of different kinds of structures and concepts together to achieve understanding. We know that shear zone deformation of rocks under elevated temperature and pressure conditions create foliations and lineations. We know that fault rocks such as mylonites can be formed during shearing. Moreover, we know that shear zones are expressions of non-coaxial shear. Write about the physical nature of shear zones and how we recognize very large ones with lots of displacement (map scale). Discuss also the physical nature of rocks and fabrics within shear zones as they might appear in outcrops or in microscopic view. What fabric/texture/mineral features within a shear zone help us to determine ‘sense of shear’ (e.g., delta porphyroclasts). Now explain how non-coaxial strain kinematics help us understand the character of shear zones and the interrelationships of foliations and lineations and strain within shear zones.