ASBOG Sedimentology and Stratigraphy 4 — Questions and Answers
Question 1: Which cement type in sandstone forms early in shallow burial and is commonly dissolved during deeper burial to create secondary porosity?
- Quartz overgrowth
- Calcite cement (Correct answer)
- Illite clay cement
- Anhydrite cement
Correct answer: Calcite cement
Calcite cement precipitates early in sandstone diagenesis and is readily dissolved by acidic fluids during burial, creating significant secondary porosity.
Question 2: The ASBOG Fundamentals of Geology exam emphasizes which stratigraphic principle when establishing the relative age of an intrusive igneous body?
- Original horizontality
- Lateral continuity
- Cross-cutting relationships (Correct answer)
- Superposition
Correct answer: Cross-cutting relationships
The principle of cross-cutting relationships states that an igneous intrusion is younger than the rocks it cuts, establishing relative age.
Question 3: Which paleoenvironment is indicated by the co-occurrence of coal seams, seat earths (underclays), and freshwater limestones in a cyclothem?
- Coastal swamp / paralic environment (Correct answer)
- Deep anoxic basin
- Evaporite lagoon
- Carbonate ramp
Correct answer: Coastal swamp / paralic environment
Cyclothems with coal (peat swamp), seat earth (paleosol), and freshwater limestone record repeated coastal swamp (paralic) cycles driven by sea-level fluctuations.
Question 4: Graded bedding where grain size decreases upward in a single bed is described as:
- Inverse grading
- Normal grading (Correct answer)
- Bi-directional grading
- Laminar grading
Correct answer: Normal grading
Normal grading (coarse-to-fine upward) records waning flow energy, where heavy grains settle first and finer grains settle last from suspension.
Question 5: When correlated globally, the base of the Cambrian System is defined by the first appearance of which fossil?
- Trilobites
- Archaeocyathids
- Cloudina
- Treptichnus pedum (ichnofossil) (Correct answer)
Correct answer: Treptichnus pedum (ichnofossil)
The base of the Cambrian (GSSP at Fortune Head, Newfoundland) is defined by the first appearance of the trace fossil Treptichnus pedum.
Question 6: Which depositional model best explains thick, laterally extensive beds of clean quartz sandstone interbedded with shale on a continental shelf?
- Alluvial fan
- Storm-dominated shelf (hummocky cross-stratification) (Correct answer)
- Point bar accretion
- Evaporite basin
Correct answer: Storm-dominated shelf (hummocky cross-stratification)
Storm-dominated shelves produce hummocky cross-stratified (HCS) sands interbedded with fair-weather muds, creating thick laterally continuous sheet-sand bodies.
Question 7: In carbonate stratigraphy, what term describes a carbonate body that grew to sea level and shows flat top geometry?
- Pinnacle reef
- Atoll
- Carbonate platform (flat-topped) (Correct answer)
- Carbonate ramp
Correct answer: Carbonate platform (flat-topped)
A flat-topped carbonate platform (or rimmed shelf) develops when carbonate production keeps pace with sea-level rise and the top is truncated at sea level.
ASBOG Sedimentology and Stratigraphy 4
Which cement type in sandstone forms early in shallow burial and is commonly dissolved during deeper burial to create secondary porosity?