24-Pet-A1 Principles of Stratigraphy and Sedimentation · May 2016
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
EGBC National Exam — Petroleum Engineering, 98-Pet-A1 Principles of Stratigraphy & Sedimentation, 2016-May. 3 hours duration; closed book, no calculator permitted. The paper has two parts: Part 1 (Questions 1–12, Sedimentology and Sedimentary Processes – 10 marks each; answer any eight of the twelve, 80 marks total) and Part 2 (Questions 13–20, Stratigraphy and Sedimentary Basin Analysis – 10 marks each; answer any five of the eight, 50 marks total) – a 130-mark maximum (80 for Part 1 + 50 for Part 2).
Reference texts: Boggs, S. Jr., Principles of Sedimentology and Stratigraphy, 5th ed., Pearson (grain texture, sediment transport, bedforms, carbonate/evaporite systems, sequence stratigraphy, unconformities, stratigraphic principles); Tucker, M.E., Sedimentary Petrology, 3rd ed., Blackwell (carbonate classification, diagenesis, dolomitization); Nichols, G., Sedimentology and Stratigraphy, 2nd ed., Wiley-Blackwell (fluvial systems, sequence stratigraphy, stratigraphic units); Reading, H.G. (ed.), Sedimentary Environments: Processes, Facies and Stratigraphy, 3rd ed., Blackwell (facies models, trace fossils, coastal processes); Selley, R.C. & Sonnenberg, S., Elements of Petroleum Geology, 3rd ed., Academic Press (source rocks, basin classification, reservoir quality); International Commission on Stratigraphy, International Chronostratigraphic Chart (geological time scale).
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.
(a) Diagenesis. Diagenesis is the sum of all physical, chemical and biological changes that a sediment undergoes after deposition, during and after lithification, at temperatures and pressures below those of metamorphism – broadly, everything that happens to a sediment or sedimentary rock from burial up to (but excluding) metamorphic conditions.
(b) Diagenetic stages. Three stages are conventionally recognized, defined by burial history rather than absolute depth or time:
| Stage | Setting | Example process/product |
|---|---|---|
| Eogenesis (early/near-surface diagenesis) | At or just below the sediment-water interface, before deep burial | Micritization of grains by boring algae/fungi; early marine cementation by aragonite or high-Mg calcite; bioturbation |
| Mesogenesis (burial diagenesis) | Subsurface, below the near-surface zone, with increasing temperature and effective stress | Mechanical and chemical compaction (pressure solution, stylolites); burial cementation (blocky calcite, quartz overgrowths); dissolution creating secondary (moldic/vuggy) porosity |
| Telogenesis (uplift/exposure diagenesis) | Previously buried rock re-exposed near-surface by uplift and erosion | Meteoric dissolution enlarging porosity; karstification of exposed limestone; near-surface weathering and oxidation |
