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.
Carbonate sediments are built from four principal grain types, all formed largely in place within the depositional basin rather than delivered from land. Skeletal grains (bioclasts) are the calcareous hard parts — whole or fragmented — of organisms such as bivalves, brachiopods, corals, echinoderms and foraminifera; they are the most direct evidence of the biota that lived in, or was transported into, the depositional setting. Ooids are sand-size grains with a concentric (or occasionally radial) coating of aragonite or calcite precipitated in successive layers around a nucleus as the grain is repeatedly rolled by agitated, wave- or current-swept water; they indicate a high-energy, shallow, warm-water shoal environment. Peloids are structureless, well-rounded micritic grains lacking internal texture, most commonly produced as fecal pellets by grazing/deposit-feeding organisms, though some form by micritization (bioerosion and infilling) of other grain types; they typically indicate quieter, lower-energy settings than ooids. Intraclasts are fragments of penecontemporaneous, weakly lithified carbonate sediment that were eroded and reworked from elsewhere within the same depositional basin (e.g. desiccated mudflat rip-up clasts, storm-reworked seafloor crusts), recording local erosion during otherwise continuous carbonate deposition. A fifth, less common category, extraclasts, are fragments of older, fully lithified carbonate rock derived from outside the basin, signalling erosion of an exposed carbonate terrane.
