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.
Where two lithostratigraphic units are conformable (no significant time gap or unconformity between them), the physical nature of the boundary can still take several forms. A sharp (abrupt) contact changes lithology essentially instantaneously, over a thickness of millimetres or less, usually reflecting an abrupt change in depositional process or energy (e.g. a flooding surface or sudden facies change) even though no significant time is missing. A gradational contact changes lithology progressively over a measurable thickness, reflecting a gradual shift in depositional conditions such as a slow, continuous shallowing- or deepening-upward trend. An interbedded (interfingering) contact alternates the two lithologies in thin, repeated beds over a transitional interval before one finally dominates, typically recording a fluctuating or migrating boundary between two adjacent environments. A diastemic contact records a very brief, geologically insignificant pause in deposition (a diastem, not a true unconformity), marked by a subtle discontinuity such as a thin bioturbated horizon or minor scour, without any real hiatus in the stratigraphic record.
