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Sedimentology and Stratigraphy Flashcards

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  1. Which trace fossil is most diagnostic of a high-energy, shallow subtidal to intertidal sandy environment?

    Answer: Skolithos

    Skolithos (vertical, cylindrical burrows) typifies the Skolithos ichnofacies, characteristic of high-energy sandy shoreface and intertidal zones.

  2. In sequence stratigraphy, a lowstand systems tract forms during:

    Answer: Falling and low stage of sea level

    The lowstand systems tract accumulates when sea level falls below the shelf edge and during the early stages of subsequent rise, depositing basin-floor fans and slope wedges.

  3. Stylolites in carbonate rocks form primarily by which diagenetic process?

    Answer: Pressure dissolution (chemical compaction)

    Stylolites are irregular surfaces of insoluble residue produced by pressure dissolution, where minerals dissolve under overburden stress at grain contacts.

  4. The contact between marine and non-marine strata where there is no physical evidence of erosion or time gap is called a:

    Answer: Conformity

    A conformity (or conformable contact) exists where strata were deposited continuously without significant interruption, erosion, or tilting between units.

  5. Which sedimentary environment is most likely to produce well-sorted, well-rounded, frosted quartz grains?

    Answer: Aeolian (desert) dune

    Aeolian transport repeatedly abrades and sorts grains by wind action, producing well-rounded, frosted quartz grains with excellent sorting.

  6. What stratigraphic tool is used to correlate subsurface rock units between boreholes based on physical rock properties measured downhole?

    Answer: Well log correlation

    Well log correlation uses downhole measurements (gamma ray, resistivity, SP, density) to match and correlate rock units between multiple boreholes.

  7. In a deltaic succession, which sub-environment is characterized by the finest-grained sediment and lowest energy?

    Answer: Prodelta

    The prodelta is the most distal, lowest-energy sub-environment where only fine clay and silt settle from suspension beyond the delta front.