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.
The Bouma Sequence is the idealized, five-division vertical succession (Ta–Tb–Tc–Td–Te) of sedimentary structures left by a single waning turbidity current – a dense, sediment-laden underwater density flow that decelerates as it moves down-slope and across the basin floor. From base to top: Ta – massive or normally-graded sand, deposited by rapid en-masse suspension fallout while the flow is still fast and turbulent; Tb – planar-laminated sand, deposited under upper-flow-regime plane-bed traction as the flow slows; Tc – ripple cross-laminated (locally convolute) fine sand/silt, deposited under lower-flow-regime current ripples as the flow weakens further; Td – faint, upper-flow-regime parallel-laminated silt/mud as the flow nearly stops; Te – structureless pelagic/hemipelagic mud deposited by slow background settling between turbidity-current events, unrelated to the flow itself.
What it represents. Because the current decelerates continuously from initiation to standstill, the vertical stack of structures is a compressed, ordered record of that single flow's waning energy. It is the diagnostic signature of deep-marine sediment-gravity-flow systems (submarine fans, channel-levee complexes, basin-floor lobes); since complete Ta–Te beds are rare (most are truncated, missing lower divisions distally or upper divisions where amalgamated), which divisions are present or missing in a given bed also indicates proximal versus distal position within the fan.
