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24-Pet-A1 Principles of Stratigraphy and Sedimentation · May 2018

Question 11 of 19: Building Blocks of Sequence Stratigraphy and Relative Sea-Level Change

Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)

Notes on this paper

EGBC National Exam — Petroleum Engineering, 17-Pet-A1 Principles of Stratigraphy & Sedimentation, 2018-May. 3 hours duration; closed book, no 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 5 marks each, for a Part B total of 30 marks – an 80-mark maximum (50 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 (sandstone/carbonate classification, diagenesis, dolomitization); Nichols, G., Sedimentology and Stratigraphy, 2nd ed., Wiley-Blackwell (fluvial/deltaic systems, sequence stratigraphy, stratigraphic units); Reading, H.G. (ed.), Sedimentary Environments: Processes, Facies and Stratigraphy, 3rd ed., Blackwell (facies models, deep-marine and shelf systems); Selley, R.C. & Sonnenberg, S., Elements of Petroleum Geology, 3rd ed., Academic Press (source rocks, basin classification, reservoir quality); International Commission on Stratigraphy, International Chronostratigraphic Chart (geological time scale).

Question 11: Building Blocks of Sequence Stratigraphy and Relative Sea-Level Change (5 marks)

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.

Sequence stratigraphy interprets a stratal succession as the product of relative sea-level (base-level) cycles, built from a small set of recurring elements:

Parasequence – the fundamental building block: a relatively conformable, genetically related succession of beds bounded by marine flooding surfaces, typically recording a single progradational (shallowing-upward) pulse. Sequence boundary (SB) – an unconformity (or its correlative conformity) marking a relative sea-level fall, at which base level drops below the shelf edge and subaerial exposure/erosion occurs. Systems tract – a linkage of contemporaneous parasequences (a parasequence set) sharing a common position on the relative sea-level curve and internal stacking pattern.

Systems tracts and the relative sea-level curve Relative sea level LST lowstand, prograding TST transgressive, retrograding HST highstand, prograding/aggrading MFS SB SB
Systems tracts against the relative sea-level curve: lowstand (LST, base-level low, progrades) → maximum flooding surface (MFS, base-level rise stalls sediment supply, retrogradation ends) → transgressive (TST, base-level rising, retrogradational parasequence stacking) → highstand (HST, base-level high then falling, progradational/aggradational stacking) → next sequence boundary (SB).

Maximum flooding surface (MFS) – the surface of maximum landward transgression, where sediment supply is most starved (often a condensed section), marking the boundary between the retrogradational TST below and the progradational HST above.