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.
Not all fossils are useful for dating because a fossil is only chronologically diagnostic if the organism's presence reliably narrows the possible time of deposition; many organisms lived across very long time spans, are restricted to a narrow, unusual environment (so their absence elsewhere is environmental, not chronological), or are too rare/poorly preserved to be reliably found and correctly identified in a section — using such a fossil for dating risks either an overly broad age range or a false absence.
An organism useful as a biostratigraphic index/zone fossil must meet several criteria: (1) rapid evolutionary turnover — a short stratigraphic (time) range, so its presence pins down a narrow interval; (2) wide geographic distribution — ideally cosmopolitan, so the same zone can be correlated between widely separated sections/basins; (3) abundance and ease of preservation/identification — common enough to be reliably found, with distinctive, easily-recognised morphology so identification is unambiguous; (4) facies independence — not restricted to one narrow environment (e.g. a planktonic organism, which is not tied to a particular substrate/water depth), so its range is a true time signal rather than an environmental (facies-controlled) artefact; (5) rapid, easily-recognised morphological change through its range, allowing the total range to be subdivided into multiple successive sub-zones for finer time resolution. Planktonic foraminifera, graptolites, and ammonites are classic examples meeting most or all of these criteria.
