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.
The ratio of the two stable oxygen isotopes, expressed as δ18O (the per-mil deviation of the 18O/16O ratio from a standard), measured in the calcite tests of marine (especially benthic and planktonic) foraminifera, is controlled mainly by global ice volume: the lighter isotope 16O evaporates preferentially and is sequestered in continental ice sheets during glacial periods, leaving the ocean (and the calcite precipitated from it) progressively enriched in the heavier 18O. δ18O therefore rises during glacial (cold) intervals and falls during interglacial (warm) intervals, giving a continuous, globally-correlatable proxy for ice volume/climate that is independent of local lithology or facies.
Stacking many deep-sea core δ18O records produces the standard Marine Isotope Stage (MIS) curve, in which odd-numbered stages are warm (interglacial, low δ18O) and even-numbered stages are cold (glacial, high δ18O). Because the glacial-interglacial cyclicity is paced by Milankovitch orbital forcing (eccentricity, obliquity, precession), the MIS curve can be astronomically (orbitally) tuned to an absolute age model, giving Quaternary stratigraphy a high-resolution chronostratigraphic framework that works even in settings with no useful biostratigraphy, and that can be correlated directly against ice-core, loess and speleothem records that show the same cyclicity.
