Sedimentology & Stratigraphy Flashcards

According to Walther's Law, which statement correctly describes the relationship between vertical and lateral sedimentary facies?

Answer: Facies observed in vertical succession were deposited in laterally adjacent environments

Walther's Law states that facies found in conformable vertical succession once existed as laterally adjacent depositional environments, allowing vertical sections to be used to reconstruct lateral paleogeography.

The Bouma sequence (divisions Ta through Te) is the diagnostic sedimentary structure package of which depositional environment?

Answer: Turbidite (deep-water submarine fan)

The Bouma sequence records the successive hydrodynamic stages of a turbidity current, from massive graded sand (Ta) through laminated, rippled, and fine-grained upper divisions, making it diagnostic of turbidite deposition.

In the Wentworth grain-size classification, which size range defines 'sand'?

Answer: 0.0625–2 mm

The Wentworth scale defines sand as particles ranging from 0.0625 mm (very fine sand lower limit) to 2 mm (granule boundary), spanning four sub-classes from very fine to very coarse sand.

An angular unconformity is best described as a surface where:

Answer: Tilted or folded beds below are overlain by younger, more gently dipping or horizontal beds above, indicating intervening deformation and erosion

An angular unconformity records a sequence of deformation (tilting/folding), uplift, erosion, and subsequent deposition of horizontal strata, producing the characteristic angular discordance between lower and upper beds.

In Dunham's classification of carbonate rocks, a 'wackestone' is defined as:

Answer: Mud-supported fabric containing more than 10% carbonate grains

Dunham's wackestone is mud-supported with more than 10% grains; it contrasts with mudstone (mud-supported, fewer than 10% grains) and packstone/grainstone (grain-supported).

Tabular and trough cross-bedding dipping in the direction of paleoflow is most commonly formed by:

Answer: Migration of bedforms (dunes and ripples) downstream under unidirectional wind or water currents

Cross-bedding forms when bedforms (ripples, dunes) migrate downcurrent, with foresets deposited on the lee face dipping in the flow direction, making cross-bed geometry a powerful paleocurrent indicator.

Which systems tract in sequence stratigraphy is deposited during a relative sea-level fall, before the lowstand is reached?

Answer: Falling-stage systems tract (FSST)

The falling-stage systems tract (FSST), also called the forced regressive wedge systems tract, accumulates during active relative sea-level fall before sea level reaches its lowest point, often producing forced regressions and shelf-margin incision.