CPG Sedimentology & Stratigraphy 2

Question 1

Graded bedding, with coarser grains at the base grading upward to finer grains at the top, is most commonly associated with which depositional process?

Accepted Answer

Turbidity current deceleration

Answer

Normal graded bedding is the hallmark of turbidity current deposits, as the flow decelerates and settling velocity sorts particles from coarsest at the base to finest at the top of a single event bed.

Question 2

Flute casts found on the base of a turbidite sandstone bed are most useful for paleoflow analysis because:

Accepted Answer

The deepest, closed (upstream) end of the scoop points into the paleoflow direction

Answer

Flute casts are erosional scour marks preserved as positive casts on bed bases; they are deepest and rounded at the upstream (stoss) end and flare open downstream, so the closed end points into the paleoflow.

Question 3

In sequence stratigraphy, a parasequence is formally defined as:

Accepted Answer

A relatively conformable succession of genetically related beds and bedsets bounded by marine flooding surfaces and their correlative surfaces

Answer

The parasequence is the fundamental building block of sequence stratigraphy, defined by Van Wagoner et al. (1988) as a shallowing-upward succession bounded by marine flooding surfaces that record abrupt deepening.

Question 4

Lithostratigraphy differs fundamentally from biostratigraphy in that lithostratigraphy classifies and correlates rock units based on:

Accepted Answer

Observable physical and compositional characteristics of the rocks themselves

Answer

Lithostratigraphy divides the rock record into formations and other units defined by observable lithologic properties (rock type, color, texture, mineralogy), independent of age or fossil content.

Question 5

Which sedimentary structure most reliably indicates oscillatory (wave) rather than unidirectional (current) flow?

Accepted Answer

Symmetrical (in-phase) ripple marks

Answer

Symmetrical ripple marks, with crests of equal steepness on both sides, are produced by the to-and-fro motion of oscillatory wave energy, whereas asymmetrical ripples indicate net unidirectional transport.

CPG - Certified Professional Geologist Practice Test

CPG - Certified Professional Geologist Practice Test

CPG Sedimentology & Stratigraphy 2