24-Pet-A1 Principles of Stratigraphy and Sedimentation · May 2018
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
EGBC National Exam — Petroleum Engineering, 17-Pet-A1 Principles of Stratigraphy & Sedimentation, 2018-May. 3 hours duration; closed book, no calculator permitted. The paper has two parts: Part A (Questions 1–10, Sedimentology and Sedimentary Processes) – Questions 1 and 2 are mandatory (10 marks each, 20 marks), plus any five of the remaining eight (3–10) at 6 marks each (30 marks), for a Part A total of 50 marks; and Part B (Questions 11–19, Stratigraphy and Sedimentary Basin Analysis) – answer any six of the nine at 5 marks each, for a Part B total of 30 marks – an 80-mark maximum (50 for Part A + 30 for Part B).
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 (sandstone/carbonate classification, diagenesis, dolomitization); Nichols, G., Sedimentology and Stratigraphy, 2nd ed., Wiley-Blackwell (fluvial/deltaic systems, sequence stratigraphy, stratigraphic units); Reading, H.G. (ed.), Sedimentary Environments: Processes, Facies and Stratigraphy, 3rd ed., Blackwell (facies models, deep-marine and shelf systems); 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.
Conglomerate versus breccia. Both are coarse-grained sedimentary rocks composed predominantly of clasts >2 mm (gravel-grade). The distinction is purely one of clast roundness: a conglomerate is dominated by rounded to subrounded clasts, indicating a meaningful history of fluvial, littoral or other transport during which corners were abraded off; a breccia is dominated by angular to subangular clasts, indicating little or no transport (or a non-abrasive origin) – the clasts retain sharp, unworn edges.
Processes that generate breccia. Because angularity implies minimal transport, breccias form by several genetically distinct mechanisms rather than one:
| Type | Forming process |
|---|---|
| Sedimentary (talus/scree) breccia | Mass wasting – rockfall/rockslide accumulating angular debris at a cliff or fault-scarp base with essentially no transport |
| Fault (tectonic) breccia | Brittle crushing and fragmentation of rock within a fault zone by shear/frictional stress |
| Collapse (solution-collapse) breccia | Dissolution of an underlying soluble unit (evaporite or carbonate) removes support, causing the overlying strata to fracture and collapse in place |
| Volcanic breccia | Explosive pyroclastic eruption, or autobrecciation of the flow-top/base of a moving lava flow, shatters rock into angular fragments |
| Intraformational (sedimentary rip-up) breccia | Early, weakly lithified mud (e.g., desiccation-cracked mudflat) is ripped up in place or transported only a very short distance and redeposited as angular intraclasts within the same depositional system |
