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.
Textural maturity describes how far a sandstone's grain fabric has progressed toward the physical end-product of prolonged reworking: good sorting, well-rounded grains, and little or no clay-sized matrix between them. Mineralogical maturity describes how far the sandstone's mineral composition has progressed toward the chemically/mechanically most stable residue: a high proportion of durable quartz relative to unstable, easily weathered or cleaved grains such as feldspar and rock fragments (a "quartz arenite" being the mineralogically most mature end-member).
Yes, a sandstone can be both texturally and mineralogically mature simultaneously – the classic example is a quartz arenite (e.g. the St. Peter Sandstone or many aeolian dune sandstones): well sorted and well rounded (texturally mature) AND composed almost entirely of monocrystalline quartz with negligible feldspar, lithics or matrix (mineralogically mature). This dual maturity typically requires either prolonged, repeated reworking in a high-energy environment (aeolian dunes, beach/shoreface systems) that has enough time and energy both to abrade/sort the grains and to mechanically/chemically destroy the softer, less stable minerals, or multiple sedimentary recycling events (erosion of an older, already mature sandstone, re-transport, and re-deposition), which compounds both kinds of maturity over successive cycles.
