24-Pet-A1 Principles of Stratigraphy and Sedimentation · December 2015
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
EGBC National Exam — Petroleum Engineering, 98-Pet-A1 Principles of Stratigraphy & Sedimentation, 2015-Dec. 3 hours duration; closed book, no calculator permitted. The paper has two parts: Part A (Questions 1–11, sediments/sedimentary rocks/sedimentary processes – Questions 1–4 at 10 marks each and Questions 5–11 at 5 marks each; answer any combination of questions totaling 45 marks) and Part B (Questions 12–18, stratigraphy – Questions 12–14 at 10 marks each and Questions 15–18 at 5 marks each; answer any combination totaling 30 marks) – a 75-mark maximum (45 for Part A + 30 for Part B).
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, 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.
(i) Transgression. The landward migration of the shoreline, and of the facies belts behind it, caused by a relative rise in sea level (eustatic rise and/or subsidence) outpacing sediment supply. A transgressive succession is retrogradational – each younger facies belt is deposited landward of, and generally in deeper water than, the one below it – producing an overall deepening-upward/fining-upward trend, often with a basal transgressive lag or ravinement surface where wave/tidal reworking cannibalizes the underlying substrate as the shoreline sweeps across it.
(ii) Regression. The seaward migration of the shoreline caused by a relative fall in sea level, or simply by sediment supply outpacing the rate of accommodation creation even while sea level itself is still rising (a "normal regression"). A regressive succession is progradational – each younger facies belt is deposited seaward of, and generally in shallower water than, the one below it – producing an overall shallowing-upward/coarsening-upward trend. A regression driven by an actual sea-level fall, rather than simple sediment oversupply, is termed a "forced regression."
