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.
An unconformity is a buried surface of erosion or non-deposition that separates two rock units and represents a significant gap in the geological time record (a hiatus) – the interval of time needed to deposit and/or erode the missing section is simply not represented by any rock at that location. Four main types are recognized:
Angular unconformity – strata below the surface were tilted or folded and then eroded flat before the overlying strata were deposited horizontally on top, so the lower unit's bedding is at a discordant angle to the upper unit's. Disconformity – both units are parallel to the erosion surface and to each other, but the surface itself is visibly irregular or erosional (channels, karst relief) and/or marked by a basal lag, representing a substantial time gap despite the lack of angular discordance. Nonconformity – sedimentary strata overlie eroded igneous or metamorphic (crystalline) basement rock; the contrast in rock type, not bedding angle, marks the unconformity. Paraconformity (cryptic unconformity) – both units are perfectly parallel and the contact shows no obvious physical evidence of erosion or exposure; the significant time gap is recognized only through biostratigraphic or radiometric dating, not from field appearance.
