24-Pet-A1 Principles of Stratigraphy and Sedimentation · May 2016
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
EGBC National Exam — Petroleum Engineering, 98-Pet-A1 Principles of Stratigraphy & Sedimentation, 2016-May. 3 hours duration; closed book, no calculator permitted. The paper has two parts: Part 1 (Questions 1–12, Sedimentology and Sedimentary Processes – 10 marks each; answer any eight of the twelve, 80 marks total) and Part 2 (Questions 13–20, Stratigraphy and Sedimentary Basin Analysis – 10 marks each; answer any five of the eight, 50 marks total) – a 130-mark maximum (80 for Part 1 + 50 for Part 2).
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, 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.
(a) Primary versus diagenetic components. Framework grains and matrix are both primary, syn-sedimentary particles – they are transported and deposited together as part of the original detrital sediment, the framework grains forming the sand-sized load-bearing skeleton and the matrix being the finer (silt/clay) material trapped between them at the time of deposition. Cement is diagenetically added and post-sedimentary – it is precipitated chemically from circulating pore fluids after burial, binding the framework grains together; it was never part of the original detrital sediment.
(b) Common framework grains. Quartz (monocrystalline and polycrystalline, the most chemically and mechanically durable common rock-forming mineral); feldspar (K-feldspar and plagioclase, derived from granitic/gneissic or volcanic sources); and lithic (rock) fragments – small pieces of the parent rock itself (volcanic, sedimentary or metamorphic clasts).
(c) Most reliable provenance indicator. Lithic (rock) fragments are the most reliable indicator of source-rock (provenance), because each fragment is a miniature sample of the parent rock and retains its distinctive mineralogy and texture (e.g., a volcanic lithic with a felted microlite texture, or a slate lithic with visible cleavage). Quartz, by contrast, is mechanically and chemically so durable that it survives multiple cycles of erosion and redeposition and is common to almost every source terrane, so a quartz grain by itself carries little specific information about which rock it ultimately came from.
