Detrital Grain Contacts vs. Burial Depth: 24-Pet-A1 Principles of Stratigraphy and Sedimentation, December 2014, Q11

Question 11 of 24: Detrital Grain Contacts vs. Burial Depth

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

Notes on this paper

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 11: Detrital Grain Contacts vs. Burial Depth (3 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.

With increasing burial (overburden pressure), detrital grain contacts evolve through a progressive sequence: initially loose, unconsolidated grains touch only at scattered point contacts; mechanical compaction and grain rearrangement (rotation, better packing) produces long (planar) contacts where flattened contact faces meet; continued load drives pressure dissolution at grain boundaries, producing concavo-convex contacts (one grain's convex surface indents into another's concave, dissolved surface); and at the deepest, most advanced stage, extensive intergranular pressure dissolution produces interlocking, irregular sutured (stylolitic) contacts. This sequence – point → long → concavo-convex → sutured – is a widely-used relative indicator of compaction/burial history in a sandstone.

Topic. Compaction-driven progression of detrital grain contacts.

Key relations. Point → long → concavo-convex → sutured, with increasing burial depth/overburden stress.

Why this works. Early contacts record purely mechanical rearrangement (grains sliding/rotating into tighter packing), while later, more irregular contacts record chemical pressure dissolution at grain-to-grain stress points – a process that only becomes significant once overburden stress is high enough, i.e. at greater burial depth.

Common pitfall. Treating contact type as a precise depth thermometer – the SAME contact type can form at different absolute depths depending on mineralogy, grain size, sorting, pore-fluid chemistry and time, so contact progression indicates RELATIVE compaction/burial history, not an absolute depth.

Source. Boggs, Petrology of Sedimentary Rocks, 2nd ed., ch.9 (compaction and diagenesis).