18-Geol-A3 Sedimentation and Stratigraphy · May 2016
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
EGBC National Exam — Geological Engineering, 04-Geol-A3, Sedimentation & Stratigraphy, 2016-May. Closed book, no calculator, 3 hours. Part 1 (Questions 1–12, Sedimentology and Sedimentary Processes) instructs "Answer eight questions of your choice" (8 × 5 = 40 marks) and Part 2 (Questions 13–19, Stratigraphy and Sedimentary Basin Analysis) instructs "Answer five of the following seven questions" (5 × 5 = 25 marks), for a maximum attainable grade of 65/65.
Reference texts: Nichols, Sedimentology and Stratigraphy, 2nd ed. (depositional environments, facies models, flow regime and bedforms, carbonate platforms, sequence stratigraphy, biostratigraphic correlation); Boggs, Petrology of Sedimentary Rocks, 2nd ed. (sandstone/carbonate classification, diagenesis, provenance); Selley & Sonnenberg, Elements of Petroleum Geology (turbidite reservoirs, trace-fossil facies context).
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.
The correct answer is (b) Foreland basin. A foreland basin forms adjacent to (in front of) an actively growing fold-and-thrust belt at a convergent plate margin (continent-continent collision or continent-arc/subduction-related thrusting), where the flexural load of the thickening, advancing thrust sheets depresses the adjacent lithosphere and creates accommodation space that fills with synorogenic clastic sediment. By contrast, a passive margin basin (a) forms on a rifted, tectonically quiet continental margin far from any active plate boundary (a divergent-margin product, long after rifting ceased), an aulacogen (c) is a failed rift arm of a three-armed (triple-junction) rift system that did not go on to become a spreading ocean ridge — itself a divergent/extensional feature, not a convergent one — and an intracratonic basin (d) is a broad, slowly subsiding sag basin in a craton's stable interior, unrelated to any active plate margin.
