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.
As sediment travels farther from its provenance (source) area, particles are progressively abraded by repeated collision with the bed and with each other during traction, saltation and suspension. Three systematic trends result. Size decreases with distance, both by mechanical attrition (chipping and grinding off corners and edges) and by selective sorting, since finer, more easily suspended grains are winnowed out and carried preferentially farther than coarse grains, which lag near source. Roundness increases with distance because abrasion first removes the sharpest, most vulnerable corners; the relationship is not linear – roundness rises fast over the first tens of kilometres and then increases only slowly thereafter, following a negative-exponential (asymptotic) curve, so most rounding happens early in transport. Sphericity changes far more slowly than roundness, because sphericity is largely inherited from the original grain shape and any inherited fracture/cleavage planes in the parent mineral; long transport nudges platy or elongate grains only gradually toward a more equant form. The rate of all three changes also depends on transport medium (river vs. wind vs. littoral drift – wind and beach transport round grains fastest) and on mineral hardness/cleavage, since softer or well-cleaved grains (e.g. carbonate bioclasts, feldspar) round and shrink far faster than hard, cleavage-free quartz.
