24-Pet-A1 Principles of Stratigraphy and Sedimentation · December 2015
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
EGBC National Exam — Petroleum Engineering, 98-Pet-A1 Principles of Stratigraphy & Sedimentation, 2015-Dec. 3 hours duration; closed book, no calculator permitted. The paper has two parts: Part A (Questions 1–11, sediments/sedimentary rocks/sedimentary processes – Questions 1–4 at 10 marks each and Questions 5–11 at 5 marks each; answer any combination of questions totaling 45 marks) and Part B (Questions 12–18, stratigraphy – Questions 12–14 at 10 marks each and Questions 15–18 at 5 marks each; answer any combination totaling 30 marks) – a 75-mark maximum (45 for Part A + 30 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 (carbonate classification, diagenesis, dolomitization); Nichols, G., Sedimentology and Stratigraphy, 2nd ed., Wiley-Blackwell (fluvial systems, sequence stratigraphy, stratigraphic units); Reading, H.G. (ed.), Sedimentary Environments: Processes, Facies and Stratigraphy, 3rd ed., Blackwell (facies models, trace fossils, coastal processes); Selley, R.C. & Sonnenberg, S., Elements of Petroleum Geology, 3rd ed., Academic Press (source rocks, reservoir quality); 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. When waves approach a shoreline at an oblique angle, refraction bends the crests toward shore-parallel as they shoal, but a residual component of the wave's momentum remains directed along the shore; inside the surf zone this drives a steady current flowing parallel to the beach, whose strength scales with the angle of wave approach and breaker height.
Rip current. Waves breaking over an irregular nearshore bar/trough system pile up more water over shallow bar crests than over deeper troughs, creating an alongshore gradient in wave-driven water-surface elevation (radiation stress); the excess water escapes seaward as a narrow, fast, concentrated jet through a gap or low point in the bar, fed by longshore currents converging from both sides.
Effect on sediment dispersal. The longshore current is the primary engine of littoral drift, continuously entraining sand thrown into suspension by breaking waves and carrying it steadily along the coast, building spits, barrier islands and updrift-accreting beaches against obstructions. Rip currents, by contrast, are the main mechanism moving sediment seaward out of the surf zone entirely, cutting channels through longshore bars and depositing sediment lobes just offshore of the breaker zone.
