18-Geol-A3 Sedimentation and Stratigraphy · December 2018
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
EGBC National Exam — Geological Engineering, 18-Geol-A3, Sedimentation & Stratigraphy, 2018-Dec. Closed book, no calculator, 3 hours. Part 1: Sedimentology (Questions 1–12, 5 marks each) instructs "Answer questions 1 and 2, and any other 6 questions from the remaining 10 questions (i.e., questions 3–12)" for 40 marks total. Part 2: Stratigraphy and Sedimentary Basin Analysis (Questions 13–19, 5 marks each) instructs "Answer five of the following seven questions" for 25 marks total (65/65 maximum).
Reference texts: Nichols, Sedimentology and Stratigraphy, 2nd ed. (depositional environments, facies models, carbonate platforms, sequence stratigraphy, biostratigraphy and correlation); Boggs, Petrology of Sedimentary Rocks, 2nd ed. (sandstone and carbonate classification, weathering, diagenesis, grain-size analysis); Bjorlykke, Petroleum Geoscience: From Sedimentary Environments to Rock Physics, 2nd ed. (basin classification, reservoir facies).
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.
All four are defined below for completeness (the exam calls for any two).
(a) Diastem — a minor break in deposition of short duration (commonly a bedding-plane surface representing a brief pause, non-deposition, or minor erosion) that is too small in time and stratigraphic significance to be classified as a true unconformity; diastems are extremely common at bedding-plane scale and account for the fact that the sedimentary record everywhere contains far more "missing time" than continuous deposition.
(b) Microfacies — the total set of paleontological and sedimentological criteria observable in a thin section (or hand sample at small scale) — grain type, matrix/cement, texture, microfossil content — used to characterise carbonate rocks at a scale not visible in outcrop, commonly used to subdivide and correlate carbonate platform facies belts.
(c) Assemblage biozone — a biostratigraphic zone defined by the co-occurring group (assemblage) of three or more taxa, regardless of their individual total ranges, that together characterise a distinctive stratigraphic interval; distinguished from a range zone (defined by one taxon's total range) or an interval zone (defined by the interval between two biohorizons).
(d) Polarity zone (magnetozone) — a body of rock characterised by a consistent, dominant magnetic polarity (normal or reversed) recorded by remanent magnetisation of its constituent minerals at the time of deposition/crystallisation, used in magnetostratigraphy to correlate sections against the global magnetic-polarity time scale (GPTS).
