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.
Dunham's (1962) scheme classifies carbonate rocks by depositional texture — whether the rock is mud-supported or grain-supported, and whether original components were bound together during deposition — rather than by composition:
| Dunham class | Defining texture |
|---|---|
| Mudstone | Mud-supported, <10% grains >20µm (skeletal/non-skeletal particles) |
| Wackestone | Mud-supported, ≥10% grains |
| Packstone | Grain-supported, but with mud matrix filling the intergranular pores |
| Grainstone | Grain-supported, mud-free (open, cement- or void-filled pores) |
| Boundstone | Original components bound together in place during deposition (organic framework/binding) |
Embry & Klovan (1972) refined this scheme in two ways. First, they split boundstone into three sub-types by the specific binding mechanism: bafflestone (deposition-time sediment trapped between upright, baffle-like organisms, e.g. crinoid stems), bindstone (sediment encrusted and bound by laminar or crust-forming organisms, e.g. stromatolitic mats), and framestone (a rigid, load-bearing organic framework built in place, e.g. a true coral or archaeocyathid reef). Second, they extended the scheme to coarse allochthonous carbonate sediment composed of grains >2 mm (which the original Dunham scheme did not accommodate): floatstone (matrix-supported, ≥10% grains >2 mm) and rudstone (grain-supported, ≥10% grains >2 mm) — the coarse-grained analogues of wackestone/packstone-grainstone respectively.
