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.
The correct answer is (a) Cruziana. The Seilacher ichnofacies scheme arranges characteristic trace-fossil assemblages along an onshore-to-offshore energy gradient: the Skolithos ichnofacies (b) — dominated by vertical dwelling burrows — marks high-energy, shifting, well-sorted sand in the shallow, above-fair-weather-wave-base nearshore. Moving offshore, below fair-weather wave base into the sublittoral (shelf) zone where wave and current energy is markedly lower but the substrate is still a normal, oxygenated, soft marine mud/sand, the Cruziana ichnofacies (arthropod grazing and resting traces, plus forms such as Rhizocorallium) is the defining low-energy, sublittoral assemblage. The Zoophycus ichnofacies (c) occupies still deeper, quieter, commonly lower-oxygen outer-shelf-to-upper-slope settings beyond the sublittoral zone proper, and Trypanites (d) is a substrate-controlled (not energy/depth-controlled) ichnofacies of borings into hard or lithified substrates (hardgrounds, rocky shores), which can occur at almost any water depth wherever a firm/hard substrate exists.
