ASBOG - Association of State Boards of Geology Sedimentology and Stratigraphy Questions and Answers

Question 1

A geologist examines a vertical sequence of sedimentary rocks.
From bottom to top, the sequence fines upward from a coarse-grained, cross-bedded sandstone to a fine-grained sandstone, then to siltstone, and finally to a deep-water shale.
Assuming no unconformities are present, which geological principle best explains this vertical succession?

Accepted Answer

Walther's Law of Facies

Answer

The Law of Superposition

Answer

The Principle of Original Horizontality

Answer

The Principle of Cross-Cutting Relationships

Question 2

While logging a core from a deep marine environment, you identify a repeating, fining-upward sequence. The base of each sequence is a massive, graded sandstone (Ta), overlain by parallel laminated sandstone (Tb), which is in turn overlain by ripple cross-laminated siltstone (Tc). This characteristic succession is known as a:

Accepted Answer

Bouma Sequence

Answer

Fining-upward fluvial cycle

Answer

Varve deposit

Answer

Cyclothem

Question 3

A field outcrop shows horizontally bedded Cenozoic sandstones directly overlying tilted and eroded Paleozoic shales. What type of unconformity is this?

Accepted Answer

Angular Unconformity

Answer

Disconformity

Answer

Paraconformity

Answer

Nonconformity

Question 4

Which of the following diagenetic processes is most likely to CREATE secondary porosity in a sandstone reservoir?

Accepted Answer

Dissolution of feldspar grains

Answer

Compaction

Answer

Cementation by calcite

Answer

Formation of quartz overgrowths

Question 5

Within the framework of sequence stratigraphy, which systems tract is characterized by a progradational to aggradational stacking pattern and is bounded below by a maximum flooding surface and above by the next sequence boundary?

Accepted Answer

Highstand Systems Tract (HST)

Answer

Lowstand Systems Tract (LST)

Answer

Transgressive Systems Tract (TST)

Answer

Falling Stage Systems Tract (FSST)

Question 6

A geologist identifies a stratigraphic surface where horizontally bedded marine shales directly overlie horizontally bedded marine sandstones. There is evidence of an erosional surface between them, such as scour marks and a lag deposit, but the beds above and below are parallel. This type of unconformity is best described as a:

Accepted Answer

Disconformity

Answer

Nonconformity

Answer

Angular Unconformity

Answer

Paraconformity