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Two or three weeks of the course are dedicated to studying diagenesis. Lectures start with a general definition of diagenesis, the range of conditions under which it occurs, and examples of diverse diagenetic environments and features. I use rice crispy cereal and rice crispy treats to introduce cement (the marshmellow is the cement that "glues" the rice krispies together). I also incorporate basic hydrogeology to show how pores filled with (or partially filled with) groundwater provide both the space and the material for cementation. As part of this lecture, I show the students various rock samples and photomicrographs in which they can see cement examples. I outline the different cement minerals and shapes and how they can be used to interpret past diagenetic conditions (eg., gravitational "pendant" calcite cements indicate that the host sediment was once in a vadose zone with groundwater rich in calcium and carbonate). I also discuss types of pores during these lectures and the ways that pores form. We also discuss criteria for recognizing cements. After two one-hour lectures about cements, we have a lab exercise in which the students are given ~10 samples (including hand samples and thin sections) and asked to sketch and describe the cement types. The next one-hour lecture focuses on neomorphic processes and their products, including replacement, recrystallization, and polymorphic transition. As part of the lecture, we look at photomicrographs and hand samples that illstrate various neomorphic features, such as replacement dolomite and replacement chert. We establish criteria for distinguishing cements from neomorphic fabrics. This lecture is followed by a lab exercise that presents the students with ~10 rocks and thin sections and asks them to sketch and identify neomorphic fabrics. This lab is follwed by another one-hour lecture on compaction features, dissolution evidence, and determining paragentic sequences. If I am short on time, that is all I do for diagenesis. However, ideally, I continue with a lecture focused on the "dolomite problem" and some case studies of other types of diagenesis, as well as a third lab assignment that combines cementation, neomorphism, compaction, dissolution, and paragenetic sequences. As part of this section, I also try to incorporate examples of methods other than petrology (eg., fluid inclusion studies, stable isotope studies, dating) that are used for diagenetic studies. Later in the course, we take several field trips in which the students examine diagenetic features.
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