18-Geol-A3 Sedimentation and Stratigraphy · May 2018
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
EGBC National Exam — Geological Engineering, 04-Geol-A3, Sedimentation & Stratigraphy, 2018-May. Closed book, no calculator, 3 hours, 80 marks total. Part 1 (Questions 1–10, Sedimentology and Sedimentary Processes, 50 marks) instructs "Questions 1 and 2 must be answered (10 points each); answer any FIVE of Questions 3–10 (6 points each)." Part 2 (Questions 11–19, Stratigraphy, 30 marks) instructs "Answer any FIVE of Questions 11 to 19 (6 points each)."
Reference texts: Nichols, Sedimentology and Stratigraphy, 2nd ed. (depositional environments, facies models, sequence stratigraphy, biostratigraphy and correlation); Boggs, Petrology of Sedimentary Rocks, 2nd ed. (sandstone and carbonate classification, weathering, diagenesis); Bjorlykke, Petroleum Geoscience: From Sedimentary Environments to Rock Physics, 2nd ed. (basin settings, 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.
An index (zone/guide) fossil is a fossil taxon used to define and correlate a specific, narrow interval of geologic time between widely separated rock sections — the practical tool that makes biozones (Question 11) usable for correlation.
A useful index fossil must satisfy several criteria simultaneously: (1) a short stratigraphic (time) range, ideally the product of rapid evolutionary turnover, so its presence pins down a narrow interval rather than a broad swath of time; (2) wide geographic distribution, so the same taxon can be found and used to correlate across many widely separated sections/basins; (3) abundance and ease of preservation — it must actually be common enough, and have hard/durable parts, to be reliably found in outcrop or core; (4) ease and reliability of identification, with distinctive, unambiguous morphology that is not easily confused with related taxa; and (5) facies independence — ideally a free-swimming or planktonic organism unrestricted to one particular depositional environment, so its occurrence reflects time rather than local facies control (a facies-restricted benthic organism instead risks being "time-transgressive," appearing wherever/whenever the right facies occurs rather than at one synchronous horizon).
Ammonites, graptolites and planktonic foraminifera are classic examples because they combine rapid evolution, wide (often pelagic, basin-independent) dispersal, and morphology that changes distinctively and quickly through their lineage.
