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.
Longshore current. A current that flows parallel to the shoreline, confined within the surf zone, generated when waves approach the coast at an oblique angle: as an oblique wave breaks, the momentum ("radiation stress") it carries has a component directed along the shore, and the sum of many breaking waves drives a net, persistent flow parallel to the beach.
Rip current. A narrow, fast, seaward-directed jet of water that flows through the surf zone, typically escaping through a gap or low point in a nearshore (longshore) sand bar. Rip currents are the "return flow" that balances the net onshore mass transport of breaking waves and the alongshore convergence of longshore currents – water piled up in the surf zone by wave setup finds its easiest seaward escape route through a bar gap, concentrating into a fast, localized jet rather than returning as a broad, diffuse undertow.
Effect on shallow-marine sediments. Longshore currents are the principal agent of littoral (longshore) drift, transporting sand progressively along a coast and building elongate features such as spits and barrier islands; interrupting this drift with an engineered structure (jetty, groin) causes updrift accretion and downdrift erosion. Rip currents locally erode a channel through the nearshore bar and can carry sand seaward, beyond the surf zone and sometimes beyond the influence of normal wave reworking, effectively short-circuiting sediment out of the beach system and depositing it as a "rip-head" lobe on the inner shelf.
