ASBOG Sedimentology and Stratigraphy 3

Question 1

Which trace fossil is most diagnostic of a high-energy, shallow subtidal to intertidal sandy environment?

Accepted Answer

Skolithos

Answer

Skolithos (vertical, cylindrical burrows) typifies the Skolithos ichnofacies, characteristic of high-energy sandy shoreface and intertidal zones.

Question 2

In sequence stratigraphy, a lowstand systems tract forms during:

Accepted Answer

Falling and low stage of sea level

Answer

The lowstand systems tract accumulates when sea level falls below the shelf edge and during the early stages of subsequent rise, depositing basin-floor fans and slope wedges.

Question 3

Stylolites in carbonate rocks form primarily by which diagenetic process?

Accepted Answer

Pressure dissolution (chemical compaction)

Answer

Stylolites are irregular surfaces of insoluble residue produced by pressure dissolution, where minerals dissolve under overburden stress at grain contacts.

Question 4

The contact between marine and non-marine strata where there is no physical evidence of erosion or time gap is called a:

Accepted Answer

Conformity

Answer

A conformity (or conformable contact) exists where strata were deposited continuously without significant interruption, erosion, or tilting between units.

Question 5

Which sedimentary environment is most likely to produce well-sorted, well-rounded, frosted quartz grains?

Accepted Answer

Aeolian (desert) dune

Answer

Aeolian transport repeatedly abrades and sorts grains by wind action, producing well-rounded, frosted quartz grains with excellent sorting.

ASBOG - Association of State Boards of Geology Practice Test

ASBOG - Association of State Boards of Geology Practice Test

ASBOG Sedimentology and Stratigraphy 3