CPG Stratigraphic Analysis & Sedimentology 1 — Questions and Answers
Question 1: Which stratigraphic principle states that in undisturbed sedimentary sequences, older strata lie beneath younger strata?
- Principle of original horizontality
- Principle of superposition (Correct answer)
- Principle of cross-cutting relationships
- Principle of faunal succession
Correct answer: Principle of superposition
The principle of superposition, formulated by Nicolas Steno, states that in undisturbed sequences younger layers are deposited above older layers.
Question 2: In sequence stratigraphy, a sequence boundary (SB) is most commonly characterized by which feature?
- Maximum marine flooding and deepest water conditions
- Subaerial exposure and incised valley formation during sea-level lowstand (Correct answer)
- Rapid transgression over a wave-ravinement surface
- Maximum progradation of deltaic systems
Correct 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.
Question 3: What sedimentary structure is most diagnostic of bidirectional tidal currents?
- Graded bedding
- Large-scale planar cross-bedding
- Herringbone cross-stratification (Correct answer)
- Parallel lamination
Correct 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.
Question 4: In sequence stratigraphy, the maximum flooding surface (MFS) represents:
- The base of a lowstand systems tract
- The maximum seaward extent of regression
- The deepest water conditions and maximum landward extent of marine transgression (Correct answer)
- An unconformity surface formed during sea-level fall
Correct 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.
Question 5: Which depositional environment most commonly produces a coarsening-upward (shallowing-upward) succession?
- Meandering river channel fill
- Deep-water turbidite lobe
- Prograding deltaic system (Correct answer)
- Transgressive barrier island
Correct answer: Prograding deltaic system
Prograding deltas build seaward over prodelta muds, producing a coarsening-upward succession from offshore silts to distributary mouth bar sands.
Question 6: The bioturbation index (BI) used in core description quantifies:
- The percentage of organic carbon in sedimentary rock
- The degree to which burrowing organisms have disrupted primary sedimentary structures (Correct answer)
- The density of fossil shells in carbonate rocks
- The ratio of sand to shale in a mixed clastic sequence
Correct 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.
Question 7: Large-scale, high-angle cross-bedding with bimodal paleocurrent patterns is most characteristic of which depositional environment?
- Shallow marine shoreface
- Tidal flat
- Aeolian (wind-deposited) dune field (Correct answer)
- Fluvial braided system
Correct 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.
CPG Stratigraphic Analysis & Sedimentology 1
Which stratigraphic principle states that in undisturbed sedimentary sequences, older strata lie beneath younger strata?