In sequence stratigraphy, a sub discipline of geology, '''type 1 sequences''' and '''type 2 sequences''' are special sequences that are defined by having distinct types of sequence boundaries. In modern literature, the distinction in type 1 sequences and type 2 sequences was abandoned.<ref name="catuneanu185"/><ref name="patzkowsky221"/>
== 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".<ref name="vanwagoner41"/> 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"<ref name="vanwagoner41"/>
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.<ref name="vanwagoner41"/>
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.<ref name="vanwagoner41"/>
== Usage == The definition of a type 1 and type 2 sequence was first introduced by Vail et al. (1984).<ref name="catuneanu06165"/> 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.<ref name="patzkowsky43"/>
== References == <references> <ref name="catuneanu185">{{Cite journal|last=Catuneanu|first=Octavian|date=2011|title=Sequence stratigraphy: methodology and nomenclature|language=en|publisher=E. Schweizerbart'sche Verlagsbuchhandlung|journal=Newsletters on Stratigraphy|volume=44|number=3|pages=185|doi=10.1127/0078-0421/2011/0011 |url=http://doc.rero.ch/record/28034/files/str_ssm.pdf }}</ref> <ref name="patzkowsky221">{{cite book |last1=Patzkowsky |first1= Mark E. |first2=Steven M. |last2=Holland|year= 2012|title=Stratigraphic Paleobiology |location=Chicago |publisher=University of Chicago University Press|pages=221}}</ref> <ref name="vanwagoner41">{{Cite journal|last=Van Wagoner|first=JC|date=1988|title=An overview of the fundamentals of sequence stratigraphy and key definitions|language=en|publisher=Special Publications of SEPM}}</ref> <ref name="catuneanu06165">{{cite book |last1=Catuneanu |first1=Octavian |year= 2006|title=Principles of sequence stratigraphy |url=https://archive.org/details/principlesofsequ0000catu |url-access=registration |location=Amsterdam |publisher=Elsevier|pages=[https://archive.org/details/principlesofsequ0000catu/page/165 165]|isbn=9780444515681 }}</ref> <ref name="patzkowsky43">{{cite book |last1=Patzkowsky |first1= Mark E. |first2=Steven M. |last2=Holland|year= 2012|title=Stratigraphic Paleobiology |location=Chicago |publisher=University of Chicago University Press|pages=43}}</ref> </references>
Category:Sequence stratigraphy
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