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) Carbonate platform types. Ramp – a gently sloping (<1°) surface with no abrupt break in slope, passing gradually from a shallow inner ramp to a deeper outer ramp. Rimmed shelf – a flat-topped platform with a distinct, elevated margin (a reef or shoal-sand rim) separating a protected, shallow lagoon from an abrupt slope break into deeper water. Isolated platform – an atoll-like carbonate body (e.g., the Bahama Banks) surrounded by deep water on all sides, with margins on every side exposed to open-ocean energy. Epeiric (epicontinental) platform – a very large, low-relief, shallow sea flooding a craton interior, far from any open-ocean margin.
(b) Energy distribution and facies effect.
On a ramp, energy decreases gradually offshore with no abrupt break, so facies grade continuously from high-energy grainstone/shoal sands (inner ramp) to progressively muddier, lower-energy wackestone/mudstone (outer ramp), without a sharp facies boundary. On a rimmed shelf, wave and current energy is concentrated at the rim itself (reef or ooid/skeletal shoal – grainstone/boundstone), producing a sharp facies contrast with the low-energy, mud-rich lagoon behind it and the quiet, deep slope/basin beyond it. On an isolated platform, the same rim-controlled zonation applies, but because the platform is surrounded by open ocean, energy (and reef/shoal development) is typically highest on the windward margin and lower on the leeward side, with steep margins shedding debris aprons into the surrounding deep water. On an epeiric platform, the very large area and generally low relief keep wave/tidal energy low and relatively uniform across most of the platform, favoring widespread muddy carbonate accumulation punctuated only locally by higher-energy shoal belts.
