The Geologic Time Scale (Paleozoic–Mesozoic–Cenozoic): 24-Pet-A1 Principles of Stratigraphy and Sedimentation, May 2016, Q16

Question 16 of 20: The Geologic Time Scale (Paleozoic–Mesozoic–Cenozoic)

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, 2016-May. 3 hours duration; closed book, no calculator permitted. The paper has two parts: Part 1 (Questions 1–12, Sedimentology and Sedimentary Processes – 10 marks each; answer any eight of the twelve, 80 marks total) and Part 2 (Questions 13–20, Stratigraphy and Sedimentary Basin Analysis – 10 marks each; answer any five of the eight, 50 marks total) – a 130-mark maximum (80 for Part 1 + 50 for Part 2).

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, basin classification, reservoir quality); International Commission on Stratigraphy, International Chronostratigraphic Chart (geological time scale).

Question 16: The Geologic Time Scale (Paleozoic–Mesozoic–Cenozoic) (10 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.

Following the Precambrian (the informal super-eon comprising the Hadean, Archean and Proterozoic, ending at 541 million years ago), the Phanerozoic Eon is divided into three eras, each in turn divided into periods, listed here oldest to youngest:

Phanerozoic periods, oldest to youngest (ICS International Chronostratigraphic Chart)
Era	Periods (oldest → youngest)	Approx. base age
Paleozoic	Cambrian → Ordovician → Silurian → Devonian → Carboniferous → Permian	541–252 Ma
Mesozoic	Triassic → Jurassic → Cretaceous	252–66 Ma
Cenozoic	Paleogene → Neogene → Quaternary	66 Ma–present

Each era boundary marks a major biotic turnover recorded in the rock record: the Paleozoic-Mesozoic boundary (252 Ma) coincides with the end-Permian mass extinction, and the Mesozoic-Cenozoic boundary (66 Ma) coincides with the end-Cretaceous (K-Pg) mass extinction.

Topic. The Phanerozoic geologic time scale (Paleozoic, Mesozoic, Cenozoic periods).

Key relations. Paleozoic: Cambrian–Ordovician–Silurian–Devonian–Carboniferous–Permian; Mesozoic: Triassic–Jurassic–Cretaceous; Cenozoic: Paleogene–Neogene–Quaternary; era boundaries at 252 Ma and 66 Ma coincide with the two largest Phanerozoic mass extinctions.

Why this works. The time scale's period boundaries were originally defined by observable, correlatable breaks in the fossil record (major faunal turnovers), so the era names and their period subdivisions are not an arbitrary numbering scheme but a direct reflection of the biotic history preserved in the rock record.

Common pitfall. Using the term "Tertiary" (an older, informal, now-abandoned term roughly spanning the Paleogene and Neogene) in place of the current ICS-approved period names; the modern chart uses Paleogene and Neogene as the formal periods within the Cenozoic.

Source. International Commission on Stratigraphy, International Chronostratigraphic Chart; Boggs, Principles of Sedimentology and Stratigraphy, 5th ed., ch.15.