24-Pet-A1 Principles of Stratigraphy and Sedimentation · May 2018
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
EGBC National Exam — Petroleum Engineering, 17-Pet-A1 Principles of Stratigraphy & Sedimentation, 2018-May. 3 hours duration; closed book, no calculator permitted. The paper has two parts: Part A (Questions 1–10, Sedimentology and Sedimentary Processes) – Questions 1 and 2 are mandatory (10 marks each, 20 marks), plus any five of the remaining eight (3–10) at 6 marks each (30 marks), for a Part A total of 50 marks; and Part B (Questions 11–19, Stratigraphy and Sedimentary Basin Analysis) – answer any six of the nine at 5 marks each, for a Part B total of 30 marks – an 80-mark maximum (50 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 (sandstone/carbonate classification, diagenesis, dolomitization); Nichols, G., Sedimentology and Stratigraphy, 2nd ed., Wiley-Blackwell (fluvial/deltaic systems, sequence stratigraphy, stratigraphic units); Reading, H.G. (ed.), Sedimentary Environments: Processes, Facies and Stratigraphy, 3rd ed., Blackwell (facies models, deep-marine and shelf systems); 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.
Answer: (d) a, b & c. The observed (local) range of a taxon in a section is rarely identical to its true (total, global) range, and all three listed factors contribute independently to the mismatch: (a) differences in origination/evolution timing – a taxon may evolve and first appear at different times in different provinces before dispersing, so its earliest LOCAL appearance in any one basin postdates its true origination; (b) migration – even after a taxon exists, it takes finite time to migrate into a given area, so the local first appearance is time-lagged relative to the species' true first appearance elsewhere, and likewise a local "last appearance" may only record local extirpation/emigration rather than true global extinction; (c) local facies control – a taxon's preservation depends on the local depositional environment being suitable for both its habitat and its preservation, so it can appear to be locally absent (and its true range under-represented) in an unfavourable facies even though it existed there in time, then reappear once facies conditions become favourable again. Because all three effects act simultaneously and are difficult to separate from field data alone, first/last appearance data must always be treated as a minimum estimate of a taxon's true range, refined by integrating multiple sections and independent (e.g., isotopic) age control.
