18-Geol-A3 Sedimentation and Stratigraphy · May 2016
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
EGBC National Exam — Geological Engineering, 04-Geol-A3, Sedimentation & Stratigraphy, 2016-May. Closed book, no calculator, 3 hours. Part 1 (Questions 1–12, Sedimentology and Sedimentary Processes) instructs "Answer eight questions of your choice" (8 × 5 = 40 marks) and Part 2 (Questions 13–19, Stratigraphy and Sedimentary Basin Analysis) instructs "Answer five of the following seven questions" (5 × 5 = 25 marks), for a maximum attainable grade of 65/65.
Reference texts: Nichols, Sedimentology and Stratigraphy, 2nd ed. (depositional environments, facies models, flow regime and bedforms, carbonate platforms, sequence stratigraphy, biostratigraphic correlation); Boggs, Petrology of Sedimentary Rocks, 2nd ed. (sandstone/carbonate classification, diagenesis, provenance); Selley & Sonnenberg, Elements of Petroleum Geology (turbidite reservoirs, trace-fossil facies context).
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.
Eustatic sea level is the global, absolute elevation of the ocean surface measured relative to a fixed datum (e.g. Earth's centre of mass), and by definition changes everywhere on Earth simultaneously and by the same amount. It is driven by processes that change either the volume of the ocean basins (tectono-eustasy — e.g. changes in mid-ocean ridge volume altering how much water the basins can hold) or the volume of water in the oceans (glacio-eustasy — growth or melting of continental ice sheets).
Relative sea level, by contrast, is the LOCAL position of sea level measured relative to the land surface at a specific point, and it integrates the eustatic signal together with local vertical land motion — tectonic subsidence or uplift, sediment compaction, isostatic adjustment (glacial or sediment-load related), and basin subsidence from thermal cooling or crustal loading. Because it is relative sea level, not eustasy alone, that actually determines accommodation space and therefore the local stratigraphic record, the two can diverge sharply: a location undergoing rapid tectonic subsidence can show a relative sea-level RISE (and a transgressive stratigraphic signature) even during a period of global eustatic FALL, while a rapidly uplifting location can show a relative sea-level fall even during global eustatic rise. This is why sequence stratigraphic interpretations made from a single local section cannot be assumed to record global eustasy directly without independent control on local subsidence/uplift history.
