24-Pet-A1 Principles of Stratigraphy and Sedimentation · Undated paper
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
EGBC National Exam — Petroleum Engineering, 17-Pet-A1 Principles of Stratigraphy & Sedimentation, 2019-May. 3 hours duration; closed book, approved Sharp/Casio calculator permitted. The paper has two parts: Part A (Questions 1–10, Sedimentology and Sedimentary Processes) – Questions 1 and 2 are mandatory (10 marks each, 20 marks), plus any five of the remaining eight (3–10) at 6 marks each (30 marks), for a Part A total of 50 marks; and Part B (Questions 11–19, Stratigraphy and Sedimentary Basin Analysis) – answer any six of the nine at 6 marks each, for a Part B total of 36 marks – an 86-mark maximum (50 for Part A + 36 for Part B).
Reference texts: Boggs, S. Jr., Principles of Sedimentology and Stratigraphy, 5th ed., Pearson (grain texture, sediment transport, bedforms, carbonate/evaporite systems, sequence stratigraphy, unconformities, stratigraphic principles); Tucker, M.E., Sedimentary Petrology, 3rd ed., Blackwell (sandstone/carbonate classification, diagenesis, porosity); Nichols, G., Sedimentology and Stratigraphy, 2nd ed., Wiley-Blackwell (fluvial/deltaic/deep-marine systems, sequence stratigraphy, stratigraphic units); Reading, H.G. (ed.), Sedimentary Environments: Processes, Facies and Stratigraphy, 3rd ed., Blackwell (facies models, alluvial fans, deltas, deep-marine systems); Selley, R.C. & Sonnenberg, S., Elements of Petroleum Geology, 3rd ed., Academic Press (basin analysis, well-log correlation, seismic/acoustic impedance); International Commission on Stratigraphy, International Chronostratigraphic Chart (geological time scale).
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.
Folk's classification (1959, 1962). Folk names a limestone by combining an allochem prefix (the dominant grain type) with a matrix/cement suffix that records depositional energy: mud-supported rocks take the suffix -micrite (lime mud, <4 μm), grain-supported rocks with sparry calcite cement take -sparite.
| Allochem prefix | Grain type | Mud-supported name | Grain-supported (cemented) name |
|---|---|---|---|
| Intra- | Intraclasts (reworked penecontemporaneous mud clasts) | Intramicrite | Intrasparite |
| Oo- | Ooids (concentrically coated grains) | Oomicrite | Oosparite |
| Bio- | Bioclasts (skeletal/fossil fragments) | Biomicrite | Biosparite |
| Pel- | Peloids/pellets (structureless micritic grains) | Pelmicrite | Pelsparite |
Dunham's classification (1962), extended by Embry & Klovan (1971/72). Dunham classifies limestone by depositional texture – whether the rock is mud-supported or grain-supported, and how much lime mud versus grains it contains – rather than by grain type. Embry & Klovan extended the scheme to name coarse (>2 mm) allochem fabrics and to subdivide organically-bound rocks by binding mechanism.
| Term | Support / fabric | Distinguishing feature |
|---|---|---|
| Mudstone | Mud-supported | <10% grains – almost pure lime mud |
| Wackestone | Mud-supported | ≥10% grains, but grains "float" within a load-bearing lime-mud matrix |
| Packstone | Grain-supported | Grains touch and form the load-bearing framework, but lime mud still fills the intergranular pores |
| Grainstone | Grain-supported | No lime-mud matrix – pores are empty or cement-filled; indicates thorough winnowing |
| Floatstone (E&K) | Mud-supported, coarse | >10% grains coarser than 2 mm, "floating" in a finer matrix |
| Rudstone (E&K) | Grain-supported, coarse | Grain-supported fabric of allochems coarser than 2 mm |
| Bafflestone / Bindstone / Framestone (E&K) | Organically bound | Sediment baffled by upright organisms / bound by encrusting organisms / rigid in-place skeletal framework, respectively |
The two schemes are complementary and broadly cross-correlate: a Folk "-micrite" rock is texturally equivalent to a Dunham mudstone/wackestone (mud-supported), and a Folk "-sparite" rock is equivalent to a Dunham grainstone (grain-supported, cement-filled); a rock with abundant mud AND touching grains (Dunham's packstone) corresponds to no single clean Folk term, which is one reason Dunham's scheme is now more widely used in the petroleum industry for its more direct link to depositional energy and reservoir quality.
