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.
The answer is (c) parasequence. This is the standard sequence-stratigraphic definition (Van Wagoner et al., 1988): a parasequence is a relatively conformable, genetically related succession of beds/bedsets bounded above and below by marine flooding surfaces (or their correlative surfaces) — typically representing one progradational (shallowing-upward) cycle, the basic building block of a systems tract.
The other options are wrong because each names a coarser or differently-bounded unit: (a) a depositional system is a three-dimensional assemblage of process-related facies (e.g. "fluvial-deltaic system"), defined by depositional PROCESS/environment, not by flooding-surface boundaries; (b) a system(s) tract is a linkage of contemporaneous depositional systems interpreted from stratal-stacking pattern and position within a sequence (e.g. lowstand, transgressive, highstand systems tract) — composed of MANY parasequences, not itself bounded by a single pair of flooding surfaces; (d) a depositional sequence is the largest of these units, bounded by unconformities and their correlative conformities (Question 18/19), and contains an entire succession of systems tracts, each in turn built from many parasequences. The hierarchy from smallest to largest is therefore: parasequence → parasequence set → systems tract → depositional sequence.
