Paragenesis describes the relative sequence or timing of “events” in the diagenetic history of a rock. “Events” refers to any and all of the diagenetic processes discussed in this book: compaction, cementation by one or more minerals, dissolution, replacement, structural deformation, hydrocarbon emplacement and others. As with any geological dating, paragenesis can include relative age determinations (Event B happened before Event C but after Event A), or radiometric dating (Event A happened 426.8 m.y. ago; B occurred 316.5 m.y. ago) or a combination of the two (Event A happened 426.8 m.y. ago and B occurred at some later time). Paragenesis is not just a petrographic exercise; it almost requires integration with other geologic information such as regional depositional models and sequence stratigraphy, burial history, thermal history, timing of tectonic events, and the like. From an economic perspective, that integration may lead to valuable insights on the presence or absence of porosity in units of interest relative to the timing of hydrocarbon generation and migration—the essence of petrographic value in petroleum systems analysis.
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.