Diagenesis: Deformation Features
2015. "Diagenesis: Deformation Features", A Color Guide to the Petrography of Sandstones, Siltstones, Shales and Associated Rocks, Dana S. Ulmer-Scholle, Peter A. Scholle, Juergen Schieber, Robert J. Raine
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This chapter covers a range of structural features that can occur at thin-section scale in terrigenous rocks, including natural fractures, deformation bands, grain-scale strain features, stylolites and cone-in-cone structures. However, soft-sediment deformation features are not substantially covered here, because they are visibleatthin-sectionlevelprimarilyinveryfine-grained strata, and thus were previously illustrated in Chapter 8); likewise, compaction-related deformation features were largely covered in Chapter 10. The structures discussed in this chapter, especially fractures and deformation bands, play a major role in porosity-permeability relationships and hydrocarbon reservoir performance of many sandstones and mudstones. Although tectonic processes are commonly inferred to be the causes of brittle deformation structures, elevated pore-fluid pressures (and rapid or episodic loss of such overpressures) also have been shown to play a major role in formation of many natural fractures and veins (e.g., Cartwright, 1994; Miller, 1995; Conybeare and Shaw, 2000; Cosgrove, 2001; Cobbold et al., 2013). Natural overpressures can be generated in a variety of settings as a result of rapid burial of low-permeability strata, hydrocarbon generation, expulsion of water from evaporites and other processes (e.g., Burrus, 1998; Swarbrick and Osborne, 1998), and artificial generation of elevated fluid pressures is the basis of modern induced hydraulic fracing.
Figures & Tables
AAPG Memoir 109 is designed as a practical guide for students and professionals to learn the fundamentals of microscopic examination of sandstones, mudrocks, and associated rocks. With more than 1100 color illustrations, it covers the identification of grains, textures, and structures of clastic terrigenous rocks as well as their diagenetic alteration (compaction, cementation, dissolution, and replacement) and porosity reduction or enhancement. It also provides classification diagrams for formal description of those rocks and their porosity. Although the majority of the outcrop and subsurface examples come from the United States (35 states and Puerto Rico), there are representative photographs from 32 other countries, including many from the offshore areas. The foldout birefringence chart and an included DVD with Powerpoint files of all of the petrographic images provide additional aids for instructors and students.