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.
A carbonate platform is a broad, shallow area of the sea floor, typically within the photic zone, on which carbonate-secreting organisms (corals, algae, foraminifera, molluscs) and physico-chemical precipitation (ooids, carbonate mud) produce carbonate sediment faster than it can be removed – the sediment is essentially generated in place rather than transported in from elsewhere, unlike a siliciclastic shelf.
| Type | Geometry | Example setting |
|---|---|---|
| Rimmed shelf | Broad, gently-dipping platform top protected from open-ocean waves by a raised organic (reef) or shoal-sand rim at the platform edge, behind which a lower-energy lagoon accumulates | Modern Florida/Belize shelf-margin reef systems |
| Homoclinal ramp | Gentle, uniform, unbroken slope from shoreline to basin with no distinct shelf-break; energy and facies grade continuously offshore | Many Paleozoic epeiric-sea carbonate ramps (e.g. parts of the Western Canada Sedimentary Basin) |
| Distally-steepened ramp | Gentle inner ramp that steepens abruptly toward the basin, without a rigid organic rim | Transitional between homoclinal ramp and rimmed shelf |
| Isolated platform | An isolated carbonate build-up, commonly atop a submerged volcanic edifice or fault block, surrounded on all sides by deep water; may be rimmed (atoll-like) itself | Modern Bahama Banks; Pacific atolls |
| Epeiric (interior) platform | Very large, very low-relief platform flooding a continental interior during high sea-level stands, with extremely gentle gradients and restricted circulation | Ancient epicontinental seas (e.g. Ordovician–Devonian interior seaways of North America) |
The type that develops at a given time and place is controlled mainly by antecedent topography, tectonic setting, and the balance of carbonate production rate against the rate of relative sea-level rise (accommodation) – a rim can only build where wave/current energy is strong and organisms can keep pace with subsidence, whereas a ramp persists where slopes are too gentle or energy too uniform for a discrete organic barrier to localize.
