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.
A parasequence is a relatively conformable succession of genetically related beds bounded by marine flooding surfaces, each individually recording a shallowing-upward cycle. A parasequence set is a succession of several parasequences stacked with a consistent, systematic pattern, controlled by the ratio of the rate of sediment supply to the rate of accommodation-space creation (relative sea-level rise).
A progradational parasequence set forms when sediment supply rate exceeds the rate of accommodation creation: each successive parasequence's shoreline is deposited basinward of the one below it, so progressively shallower-water (more proximal) facies stack directly on top of deeper-water facies at any fixed location — net shallowing-upward through the whole set. An aggradational parasequence set forms when sediment supply approximately balances accommodation creation: successive parasequences stack essentially vertically with little lateral shoreline shift, so a similar facies belt repeats through the set with no strong shallowing or deepening trend. A retrogradational parasequence set forms when the rate of accommodation creation exceeds sediment supply: each successive parasequence's shoreline is deposited landward of the one below it (marine flooding outpaces sediment infill), so progressively deeper-water (more distal) facies stack on top — net deepening-upward (backstepping) through the whole set.
