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.
Chronostratigraphy deals with actual ROCK bodies, defined as all the rock formed during a specific interval of time (bounded above and below by time-planes/GSSP boundaries) — it is a materials-based (rock-unit) classification. Geochronology deals with the abstract TIME interval itself, with no rock body implied — it is a purely temporal classification, expressed in years or as the corresponding named time interval, used whether or not any rock of that age is actually preserved at a given location.
| Chronostratigraphic unit (rock) | Geochronologic unit (time) |
|---|---|
| Eonothem | Eon |
| Erathem | Era |
| System | Period |
| Series | Epoch |
| Stage | Age |
| Chronozone | Chron |
The distinction matters in practice: one can correctly say "the Jurassic Period lasted about 56 million years" (geochronology — a duration of time) but must say "these strata belong to the Jurassic System" (chronostratigraphy — the rock deposited during that period); at a location with a depositional hiatus, the Jurassic Period (time) still elapsed even though no Jurassic System (rock) is present to represent it there.
