CPG Sedimentology & Stratigraphy 3

Question 1

In Folk's (1954) textural classification of sandstones, a rock with more than 25% feldspar and feldspar exceeding rock fragments is classified as:

Accepted Answer

Arkose

Answer

Folk's classification defines an arkose (or arkosic arenite) by feldspar content exceeding 25% of the framework grains and surpassing the rock-fragment content, typically indicating rapid erosion of granitic or gneissic source terranes.

Question 2

Diagenesis encompasses which set of processes?

Accepted Answer

Physical and chemical changes in sediments occurring after deposition but prior to metamorphism, including compaction, cementation, and dissolution

Answer

Diagenesis covers all post-depositional, sub-metamorphic changes to sediment and sedimentary rock, including mechanical compaction, cementation by precipitated minerals, dissolution, replacement, and recrystallization at low temperatures.

Question 3

A stratigraphic cyclothem, as classically defined in Pennsylvanian coal-bearing sequences of the U.S. midcontinent, represents:

Accepted Answer

A repetitive cycle of marine and non-marine deposits linked to glacioeustatic sea-level fluctuations

Answer

Pennsylvanian cyclothems record repeated transgressive-regressive cycles driven by Gondwanan glacioeustasy, each cycle typically comprising non-marine clastics and coal overlain by marine limestones and shales.

Question 4

The principle of superposition, foundational to stratigraphy, states that:

Accepted Answer

In an undisturbed sequence of sedimentary rocks, older layers lie below younger layers

Answer

Steno's principle of superposition holds that in any undeformed sedimentary succession, each bed is younger than the one beneath it, providing the basis for relative age determination in stratigraphy.

Question 5

Which stratigraphic correlation method is generally regarded as the most powerful tool for global time correlation across widely separated basins?

Accepted Answer

Biostratigraphic correlation using index fossils with short stratigraphic ranges

Answer

Biostratigraphic correlation using index fossils — taxa with geographically widespread distributions and short temporal ranges — remains the primary global time-correlation framework because biozones can be calibrated to absolute timescales worldwide.

CPG - Certified Professional Geologist Practice Test

CPG - Certified Professional Geologist Practice Test

CPG Sedimentology & Stratigraphy 3