Type 1 and type 2 sequence

In sequence stratigraphy, a sub discipline of geology, type 1 sequences and type 2 sequences are special sequences that are defined by having by distinct types of sequence boundaries. In modern literature, the distinction in type 1 sequences and type 2 sequences was abandoned.[1][2]

Definition

Type 1 and 2 sequence boundary

A type 1 sequence boundary is defined to be a sequence boundary "characterized by subaerial exposure and concurrent subaerial erosion associated with stream rejuvenation, a basinward shift of facies, a downward shift in coastal onlap, and onlap of overlying strata".[3] Similarly, a type 2 sequence boundary is "marked by subaerial exposure and a downward shift in coastal onlap landward of the depositional-shoreline break; however, it lacks both subaerial erosion associated with stream rejuvenation and a basinward shift in facies"[3]

So the main distinction between type 1 and type 2 sequence boundaries is the amount of subaerial exposure. Type 2 sequence boundaries display, in contrast to type 1 sequence boundaries, only little subaerial exposure.

Type 1 and 2 sequence

With the notions introduced above, a type 1 sequence is a sequence that is bounded by a type 1 sequence boundary below and a type 1 or a type 2 sequence boundary above.[3]

Similarly, a type 2 sequence is a sequence that is bounded by a type 2 sequence boundary below and a type 1 or a type 2 sequence boundary above.[3]

Usage

The definition of a type 1 and type 2 sequence was first introduced by Vail et al. (1984).[4] Since they were hard to recognize, they were redefined in 1990 by Van Wagoner et al.. However even with this new definition, type 2 sequence boundaries were hard to recognize in the field due to their lack of subaerial exposure. Therefore, the abandonment of this nomenclature was recommended by Posamentier and Allen in 1999.[5]

References

  1. ↑ Catuneanu, Octavian (2011). "Sequence stratigraphy: methodology and nomenclature". Newsletters on stratigraphy. E. Schweizerbart'sche Verlagsbuchhandlung. 44 (3): 185.
  2. ↑ Patzkowsky, Mark E.; Holland, Steven M. (2012). Stratigraphic Paleobiology. Chicago: University of Chicago University Press. p. 221.
  3. 1 2 3 4 Van Wagoner, JC (1988). "An overview of the fundamentals of sequence stratigraphy and key definitions". Special Publications of SEPM.
  4. ↑ Catuneanu, Octavian (2006). Principles of sequence stratigraphy. Amsterdam: Elsevier. p. 165.
  5. ↑ Patzkowsky, Mark E.; Holland, Steven M. (2012). Stratigraphic Paleobiology. Chicago: University of Chicago University Press. p. 43.
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