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 framework grains of a sandstone — the load-bearing, sand-size particles that make up its skeleton — are principally quartz (both monocrystalline and polycrystalline), feldspar (K-feldspar and plagioclase), lithic (rock) fragments (fine-grained pieces of the parent volcanic, sedimentary or metamorphic rock), and lesser amounts of mica and heavy minerals.
Lithic fragments are the most useful indicator of provenance, because a rock fragment preserves the parent rock's original texture and full mineral assemblage intact within a single grain — a volcanic lithic instantly signals a volcanic source, a slate or phyllite fragment signals a low-grade metamorphic source, and a fine-grained sedimentary lithic signals recycling of an older sedimentary sequence. By contrast, an isolated monocrystalline quartz grain could have come from almost any igneous, metamorphic or recycled sedimentary source and carries very little diagnostic information on its own; polycrystalline quartz and feldspar are intermediate in usefulness (twinning style, exsolution texture and grain shape can narrow the source but still require more inference than a lithic fragment does).
