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.
A delta forms where a river enters a standing body of water (lake or sea) and its sediment load, no longer confined by channel banks, spreads out and is deposited faster than waves or currents can redistribute it. Three zones prograde basinward, in order:
Delta plain (subaerial, landward) – the largely non-marine part of the delta above mean sea level: distributary channels (fining-upward sand/gravel fills), natural levees (thin-bedded, ripple-laminated fine sand/silt flanking the channels), crevasse splays (thin sandy lobes where a levee breaches during flood), and interdistributary bays/marshes (organic-rich mud and peat accumulating in quiet, poorly-drained lows between channels).
Delta front (subaqueous, high-energy) – the site of most active sand deposition where distributary channels debouch into open water: distributary-mouth bars (a seaward-thinning, fining wedge of well-sorted sand deposited as flow expands and decelerates at the channel mouth), reworked by waves into shoreface sand where wave energy dominates or preserved as elongate bar-finger sand where the river dominates; overall coarsening-upward.
Prodelta (subaqueous, most distal) – the seaward-thinning apron of suspended clay and silt that settles beyond the reach of active channel and wave processes, grading basinward into normal open-water mud, and forming the base over which the delta front and delta plain prograde through time.
