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.
Turbidite depositional system. A turbidite bed is deposited by a turbidity current – a sediment-gravity flow driven by the density contrast between sediment-laden water and the clearer ambient water – typically triggered by slope failure, flood-generated hyperpycnal river discharge, or seismic shaking on a continental slope or in a submarine canyon. The flow accelerates down-slope, then decelerates and deposits its load as it spreads out on reaching a base-of-slope or basin floor, producing a single graded bed.
Representative depositional model – the submarine fan. A canyon feeds an upper fan (a single, often leveed, incised feeder channel with coarse channel-fill conglomerate/sand), which passes down-fan into a mid-fan of bifurcating distributary channels flanked by channel-lobe complexes, and finally into a lower fan/basin plain of laterally continuous, sheet-like turbidite beds with no confining channel at all.
Proximal-to-distal facies change. In the proximal (upper-fan/channel) zone, beds are thick, coarse-grained and often amalgamated (stacked with no intervening mud), dominated by the lower Bouma divisions (Ta, Tb) with the finer upper divisions frequently eroded by the next flow – "proximal", incomplete turbidites. Moving down-fan into the mid-fan lobe complexes, flows are less erosive and beds preserve a more complete Ta–Te sequence, with a falling sand:mud ratio. In the distal basin-plain zone, only the dilute, waning tail of each flow arrives: beds are thin, fine-grained, laterally very continuous ("sheet" turbidites) and dominated by the upper divisions (Tc–Te), with the pelagic/hemipelagic Te mud cap forming a proportionally larger part of each bed.
