Sedimentology and Stratigraphy Flashcards

Which cement type in sandstone forms early in shallow burial and is commonly dissolved during deeper burial to create secondary porosity?

Answer: Calcite cement

Calcite cement precipitates early in sandstone diagenesis and is readily dissolved by acidic fluids during burial, creating significant secondary porosity.

The ASBOG Fundamentals of Geology exam emphasizes which stratigraphic principle when establishing the relative age of an intrusive igneous body?

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.

Which paleoenvironment is indicated by the co-occurrence of coal seams, seat earths (underclays), and freshwater limestones in a cyclothem?

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.

Graded bedding where grain size decreases upward in a single bed is described as:

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.

When correlated globally, the base of the Cambrian System is defined by the first appearance of which fossil?

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.

Which depositional model best explains thick, laterally extensive beds of clean quartz sandstone interbedded with shale on a continental shelf?

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.

In carbonate stratigraphy, what term describes a carbonate body that grew to sea level and shows flat top geometry?

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.