CPG Stratigraphic Analysis & Sedimentology 3

Question 1

Eustasy, as used in sequence stratigraphy, refers to:

Accepted Answer

Worldwide changes in absolute sea level independent of local tectonics

Answer

Eustasy refers to global changes in sea level driven by changes in ocean basin volume or water volume, independent of local tectonic or isostatic effects.

Question 2

A lowstand submarine fan in sequence stratigraphy develops when:

Accepted Answer

Falling sea level exposes the shelf, forcing rivers to incise to the shelf edge and deliver sediment directly to deep water

Answer

Lowstand fans develop when sea-level fall exposes the continental shelf, causing rivers to incise and bypass the shelf, delivering coarse clastic sediment to the slope and basin floor.

Question 3

Evaporite minerals such as halite and anhydrite most commonly form in which depositional setting?

Accepted Answer

Restricted marine basins or coastal sabkhas with evaporation exceeding water input

Answer

Evaporites precipitate in restricted marine basins (sabkhas, salinas, evaporitic lagoons) where evaporation exceeds influx, concentrating brines until minerals precipitate in order of decreasing solubility.

Question 4

What is the key distinction between a stratigraphic trap and a structural trap in petroleum geology?

Accepted Answer

Structural traps depend on rock deformation geometry while stratigraphic traps rely on lateral changes in lithology or porosity

Answer

Structural traps form through tectonic deformation (anticlines, faults), while stratigraphic traps result from depositional or diagenetic changes in rock properties that create a seal without structural deformation.

Question 5

Accommodation space in sequence stratigraphy is controlled primarily by the interplay of:

Accepted Answer

Relative sea-level change (eustasy plus subsidence or uplift)

Answer

Accommodation is the space available for potential sediment fill, controlled by the sum of eustatic sea-level change and basin subsidence (or minus uplift), regardless of how much sediment is actually supplied.

(CPG) Certified Petroleum Geologist Practice Test

(CPG) Certified Petroleum Geologist Practice Test

CPG Stratigraphic Analysis & Sedimentology 3