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) diamictite. A diamictite is, by definition, a poorly sorted, non-genetic textural term for a terrigenous sedimentary rock in which a wide range of clast sizes — including gravel and larger — is suspended (matrix-supported, "floating") within an abundant fine-grained (muddy) matrix, with no implication of a specific origin (it may form by glacial deposition, debris flow, or slump). A petromictic conglomerate (a) is instead a compositional term describing a clast-supported conglomerate whose gravel clasts are of many different rock types — it says nothing about matrix support and would normally be clast-supported, not floating in mud. A pyroclast (c) is fragmental material ejected explosively by a volcano, an origin term unrelated to matrix support. A mylonite (d) is a fault-related metamorphic rock produced by ductile shearing, not a sedimentary rock at all.
