18-Geol-A3 Sedimentation and Stratigraphy · May 2016
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
EGBC National Exam — Geological Engineering, 04-Geol-A3, Sedimentation & Stratigraphy, 2016-May. Closed book, no calculator, 3 hours. Part 1 (Questions 1–12, Sedimentology and Sedimentary Processes) instructs "Answer eight questions of your choice" (8 × 5 = 40 marks) and Part 2 (Questions 13–19, Stratigraphy and Sedimentary Basin Analysis) instructs "Answer five of the following seven questions" (5 × 5 = 25 marks), for a maximum attainable grade of 65/65.
Reference texts: Nichols, Sedimentology and Stratigraphy, 2nd ed. (depositional environments, facies models, flow regime and bedforms, carbonate platforms, sequence stratigraphy, biostratigraphic correlation); Boggs, Petrology of Sedimentary Rocks, 2nd ed. (sandstone/carbonate classification, diagenesis, provenance); Selley & Sonnenberg, Elements of Petroleum Geology (turbidite reservoirs, trace-fossil facies context).
Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.
Diagenesis is the sum of all physical, chemical and biological changes a sediment undergoes after deposition and before metamorphism (i.e., at temperatures and pressures below those of the greenschist facies) — the processes that transform a loose sediment into a lithified sedimentary rock and continue to modify it thereafter.
Three stages are recognized, defined by burial history rather than absolute time. Eogenesis occurs near the surface, shortly after deposition, while the sediment is still in contact with meteoric or marine pore water at shallow depth; example processes include bioturbation, early calcite or aragonite cementation, and redox-controlled mottling. Mesogenesis occurs during progressive burial, once the sediment is isolated from surface fluids; example processes include mechanical compaction and pressure solution (stylolites), quartz and feldspar overgrowth cementation, and clay-mineral transformation such as smectite converting to illite as temperature rises. Telogenesis occurs when uplift and erosion return previously buried strata to the near-surface, meteoric-water environment; example processes include dissolution of earlier cements or unstable grains (creating secondary porosity) and oxidative weathering of iron-bearing minerals.
