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.
Dunham (1962) classified carbonate rocks by depositional texture – mud- vs. grain-support and organic binding – and Embry & Klovan (1971/72) extended it to properly cover coarse (>2 mm) allochthonous grains and to subdivide the original "boundstone" class by binding mechanism.
| Class | Fabric | Origin |
|---|---|---|
| Mudstone | Mud-supported, <10% grains | Dunham (1962) |
| Wackestone | Mud-supported, ≥10% grains | Dunham (1962) |
| Packstone | Grain-supported with mud matrix | Dunham (1962) |
| Grainstone | Grain-supported, no mud | Dunham (1962) |
| Floatstone | Mud- or grain-supported matrix containing >10% grains >2 mm ("floating" coarse clasts) | Embry & Klovan (1971) addition |
| Rudstone | Grain-supported, >10% grains >2 mm (coarse clasts touching) | Embry & Klovan (1971) addition |
| Bafflestone | Organisms that acted as baffles, trapping sediment among stalk-like or branching forms (e.g. crinoids, some corals) | Embry & Klovan subdivision of boundstone |
| Bindstone | Organisms that encrusted and bound sediment together in place (e.g. encrusting algae) | Embry & Klovan subdivision of boundstone |
| Framestone | Rigid, load-bearing organisms that built a wave-resistant frame in place (e.g. corals, stromatoporoids) | Embry & Klovan subdivision of boundstone |
The scheme reads as an ordered, purely descriptive energy/texture ladder from mudstone (quiet, mud-dominated) through wackestone, packstone and grainstone (progressively more grain-supported and washed) to the boundstone family (organically bound in place, independent of current energy) – with floatstone and rudstone inserted as the coarse-clast (>2 mm) analogues of the mud- and grain-supported classes, needed because Dunham's original four terms could not describe rudite-scale carbonate breccias/conglomerates such as reef-talus deposits.
