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.
Morphology. An alluvial fan is an entirely subaerial, cone/fan-shaped body built where a confined mountain-front channel abruptly loses gradient and confinement onto a lowland; deposition radiates outward from a fixed apex, producing a radial drainage/distributary pattern and a fan that thins and fines away from the apex. A delta, by contrast, builds where a river enters and progrades into a standing body of water (a lake or sea); it has a lobate or bird's-foot plan form and three genetically linked subenvironments – a subaerial delta plain (distributary channels, interdistributary bays/marshes), a subaqueous, high-energy delta front (mouth-bar sands), and an offshore, low-energy prodelta (suspension muds) – so a delta, unlike a fan, always has a genuine subaqueous, marine/lacustrine-influenced component.
Sedimentology. Alluvial-fan deposits are dominated by high-energy, often ephemeral gravity-driven processes – debris flows, sheetfloods, braided-stream flows – producing coarse, poorly sorted, matrix- to clast-supported conglomerate and breccia with only minor interbedded finer sheetflood sand/mud; there are no marine/lacustrine fossils or bioturbation, and the coarsening is systematically apex-to-toe rather than time-driven. Delta deposits span the full grain-size spectrum, from coarse fluvial channel sand at the delta plain, through better-sorted mouth-bar sand at the delta front, to laminated offshore mud at the prodelta, producing a well-developed coarsening-upward parasequence as the delta progrades; prodelta and delta-front facies commonly carry marine/lacustrine trace fossils and bioturbation, a signature alluvial fans entirely lack. Delta morphology and facies proportions are further modified by the relative strength of fluvial, wave and tidal processes at the shoreline (fluvial-dominated "bird's-foot", wave-dominated "cuspate", tide-dominated "estuarine" deltas) – a control with no equivalent on a purely subaerial fan.
