24-Pet-A1 Principles of Stratigraphy and Sedimentation · December 2014
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
EGBC National Exam — Petroleum Engineering, 98-Pet-A1 Principles of Stratigraphy & Sedimentation, 2014-Dec. 3 hours duration; closed book, no calculator permitted. The paper has three parts: Part A1 (Questions 1–7, sedimentary processes, 5 marks each, answer any 4 of 7 for 20 marks), Part A2 (Questions 8–15, brief/multiple-choice, 3 marks each, answer any 5 of 8 for 15 marks), and Part B (Questions 16–24, stratigraphy, 5 marks each, answer any 6 of 9 for 30 marks) – a 65-mark maximum.
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); 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.
Calcium carbonate solubility increases with depth because increasing pressure and decreasing temperature both raise the solubility of CO₂ and hence of CaCO₃ in seawater, while the supply of CO₂ from respiring organisms accumulates with depth – together making deep water progressively more undersaturated with respect to calcite. Near the surface, seawater is supersaturated and calcitic hard parts (e.g. coccolithophores, foraminifera) are stable and accumulate freely as they settle. Below the lysocline (the depth where the dissolution rate sharply accelerates), these hard parts begin measurably dissolving as they sink or after deposition; below the calcite compensation depth (CCD) – where the rate of calcite dissolution equals or exceeds the rate of supply – essentially no calcite accumulates at all, and the sea floor there is dominated by non-carbonate (siliceous ooze or red clay) sediment. The CCD averages roughly 4–5 km in the modern ocean, though it varies with latitude, productivity and ocean basin.
