Sedimentology and Stratigraphy Flashcards

Which stratigraphic surface in sequence stratigraphy represents the deepest water conditions and maximum landward extent of marine flooding?

Answer: Maximum flooding surface (MFS)

The maximum flooding surface (MFS) marks the turnaround from transgression to regression, corresponding to the deepest water and most landward marine conditions.

The conversion of smectite to illite during burial diagenesis is significant because it:

Answer: Releases silica and potassium that can alter reservoir quality

Smectite-to-illite conversion releases silica (which can precipitate as quartz cement) and consumes potassium, significantly reducing sandstone reservoir quality.

What is the primary control on the preservation of sedimentary structures in tidal flat deposits?

Answer: Bioturbation intensity

High bioturbation by burrowing organisms in tidal flat environments can completely destroy primary sedimentary structures, so low bioturbation is essential for preservation.

Which method of stratigraphic correlation relies on matching distinctive chemical signatures (e.g., carbon isotope excursions) across rock units?

Answer: Chemostratigraphy

Chemostratigraphy correlates rock units using geochemical signatures such as carbon, oxygen, or strontium isotope ratios that reflect global oceanographic or climatic events.

A lacustrine (lake) deposit is most likely to be identified by which characteristic combination of features?

Answer: Varved laminae, non-marine fossils, and absence of tidal structures

Lacustrine deposits characteristically show finely varved (seasonally laminated) sediment, freshwater or brackish fossils, and lack marine or tidal indicators.

Which term describes the decrease in porosity and permeability of sediment due to physical compaction and cementation with increasing burial depth?

Answer: Lithification

Lithification is the suite of processes (compaction + cementation) that convert loose sediment into solid sedimentary rock, progressively reducing porosity.

When using gamma-ray logs to identify shale versus clean sand in subsurface correlation, which response is expected for a clean quartz sandstone?

Answer: Low gamma-ray reading due to low radioactive mineral content

Clean quartz sandstones have very low concentrations of radioactive elements (K, U, Th), producing a low gamma-ray deflection to the left on the log track.