Stratigraphic Analysis & Sedimentology Flashcards

Which stratigraphic principle states that in undisturbed sedimentary sequences, older strata lie beneath younger strata?

Answer: Principle of superposition

The principle of superposition, formulated by Nicolas Steno, states that in undisturbed sequences younger layers are deposited above older layers.

In sequence stratigraphy, a sequence boundary (SB) is most commonly characterized by which feature?

Answer: Subaerial exposure and incised valley formation during sea-level lowstand

Sequence boundaries form during relative sea-level falls when the shoreline migrates basinward, causing subaerial exposure, soil formation, and incised valley cutting.

What sedimentary structure is most diagnostic of bidirectional tidal currents?

Answer: Herringbone cross-stratification

Herringbone cross-stratification forms from alternating flood and ebb tidal currents that deposit cross-beds in opposing directions, creating the characteristic V-shape pattern.

In sequence stratigraphy, the maximum flooding surface (MFS) represents:

Answer: The deepest water conditions and maximum landward extent of marine transgression

The maximum flooding surface marks the time of greatest landward extent of marine conditions, typically rich in condensed pelagic sediment and organic matter.

Which depositional environment most commonly produces a coarsening-upward (shallowing-upward) succession?

Answer: Prograding deltaic system

Prograding deltas build seaward over prodelta muds, producing a coarsening-upward succession from offshore silts to distributary mouth bar sands.

The bioturbation index (BI) used in core description quantifies:

Answer: The degree to which burrowing organisms have disrupted primary sedimentary structures

The bioturbation index (BI) ranges from 0 to 6, measuring the extent to which infaunal organisms have obliterated original sedimentary fabric such as lamination.

Large-scale, high-angle cross-bedding with bimodal paleocurrent patterns is most characteristic of which depositional environment?

Answer: Aeolian (wind-deposited) dune field

Aeolian dunes produce large-scale cross-beds exceeding 25° dip with bimodal paleocurrents reflecting seasonal wind reversals, which are not typical of aqueous environments.