24-Pet-A1 Principles of Stratigraphy and Sedimentation · December 2014
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
EGBC National Exam — Petroleum Engineering, 98-Pet-A1 Principles of Stratigraphy & Sedimentation, 2014-Dec. 3 hours duration; closed book, no calculator permitted. The paper has three parts: Part A1 (Questions 1–7, sedimentary processes, 5 marks each, answer any 4 of 7 for 20 marks), Part A2 (Questions 8–15, brief/multiple-choice, 3 marks each, answer any 5 of 8 for 15 marks), and Part B (Questions 16–24, stratigraphy, 5 marks each, answer any 6 of 9 for 30 marks) – a 65-mark maximum.
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); 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.
On a cumulative curve (phi on the X-axis, cumulative weight % retained/passing on the Y-axis), the slope directly records sorting: a steep curve rises from 0% to 100% over a narrow phi interval, meaning almost all the sample's mass falls within a small range of grain sizes – the sediment is well sorted. A gently-sloping curve climbs gradually across a wide phi interval, meaning the mass is spread over many size classes – the sediment is poorly sorted.
A steep curve reflects sustained, uniform-energy reworking that winnows out all but a narrow size range – typical of an aeolian dune or a wave-washed beach, where continuous, size-selective transport removes both fines (blown or washed away) and coarse outliers, leaving a tightly clustered, well-sorted deposit. A gently-sloping curve reflects a single depositional event with little or no post-depositional winnowing across a wide range of available grain sizes – typical of a glacial till or a debris flow / alluvial fan, where sediment of all sizes, from clay to boulders, is deposited essentially together as bulk mass movement with minimal fluid sorting.
