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.
Between fair-weather wave base (FWWB, the depth below which normal day-to-day waves no longer stir the bed) and storm wave base (SWB, the greater depth reached only by large storm waves), the shelf sits in an intermediate, episodically energetic zone. Under fair-weather conditions this zone is quiet enough to accumulate bioturbated mud (background suspension settling, reworked by burrowing organisms), but each storm event generates strong combined wave-and-current energy that erodes the sea floor and deposits a distinct storm bed (tempestite) before waning back to fair-weather conditions. A single ideal storm bed, base to top: a sharp, often gutter-cast-marked erosional base → hummocky cross-stratification (HCS, produced by the combined oscillatory-plus-unidirectional storm flow) in its lower, coarser part → grading upward into wave-ripple cross-lamination as storm energy wanes → capped by a thin bioturbated mud drape once fair-weather conditions resume. Stacking many such beds gives amalgamated (storm-on-storm) HCS sandstone nearer SWB, transitioning to thinner, more isolated storm beds separated by thicker bioturbated mud intervals nearer FWWB.
