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{{publication
| image = exploring-for-oil-and-gas-traps.png
| width = 120px
| series = Treatise in Petroleum Geology
| title = Exploring for Oil and Gas Traps
| part = Critical elements of the petroleum system
| chapter = Sedimentary basin analysis
| frompg = 4-1
| topg = 4-123
| author = John M. Armentrout
| link = http://archives.datapages.com/data/specpubs/beaumont/ch04/ch04.htm
| pdf =
| store = http://store.aapg.org/detail.aspx?id=545
| isbn = 0-89181-602-X
}}
One aspect of basin analysis focuses on mapping specific systems tracts of third-, fourth-, or fifth-order sea level cycles and the relationship that stacked depositional sequences deposited during those cycles have to each other. Knowing the order of a cycle or the phase of a cycle represented by a rock sequence is important for predicting the location and type of reservoir and seal and the location of potential [[[[source rock]]s]].
==Procedure==
To determine cycle order of a sequence of sediments, we use biostratigraphic data, stratigraphic context (i.e., what part of a systems tract the interval is from), oxygen isotope curves, and published sea level curves. The table below suggests a procedure for determining cycle order of a rock sequence.
{| class = "wikitable"
|-
! Step
! Action
|-
| 1
| Determine the time span during which the sequence was deposited and compare to age ranges for cycle orders (see table below).
|-
| 2
| Determine the stratigraphic context of the sequence. What are the cycle orders for similar sequences above or below it?
|-
| 3
| Determine the age of the sequence and compare it to published sea level cycle curves (e.g., <ref name=ch04r43>Haq, B., Hardenbol, J., Vail, P., R., 1988, Mesozoic and Cenozoic chronostratigraphy and cycles of sea-level change: SEPM Special Publication 42, p. 71–108.</ref> ).
|}
==Cycle order from thickness and areal extent==
Because rates of sediment accumulation and areas of accommodation space vary, thickness and areal extent are of little use in establishing the order of depositional cycles. Most cycle hierarchies are based on duration. Establishing the duration of a sequence is difficult because of problems in high-resolution dating of rocks. However, with careful work an estimate can be made (see .<ref name=ch04r67>Miall, A., D., 1994, Paleocene 16: [[sequence stratigraphy]] and chronostratigraphy—problems of definition and precision in correlation, and their implications for global eustasy: Geoscience Canada, vol. 21, no. 1, p. 1–26.</ref><ref name=ch04r7>Armentrout, J., M., 1991, Paleontological constraints on depositional [[modeling]]: examples of integration of biostratigraphy and seismic stratigraphy, Pliocene–Pleistocene, Gulf of Mexico, in Weimer, P., Link, M., H., eds., Seismic Facies and Sedimentary Processes of Submarine Fans and Turbidite Systems: New York, Springer-Verlag, p. 137–170.</ref><ref name=ch04r9>Armentrout, J., M., 1996, High-resolution sequence biostratigraphy: examples from the Gulf of Mexico Plio–Pleistocene, in Howell, J., Aiken, J., eds., High Resolution [[Sequence stratigraphy]]: Innovations and Applications: The Geological Society of London Special Publication 104, p. 65–86.</ref>
==Table of cycle order==
Use the table below to help assess the sea level cycle order of a rock interval after .<ref name=ch04r70>Mitchum, R., M., Jr., Van Wagoner, J., C., 1990, High-frequency sequences and eustatic cycles in the Gulf of Mexico basin: Proceedings, Gulf Coast Section SEPM 11th Annual Research conference, p. 257–267.</ref>
{| class = "wikitable"
|-
! Cycle order
! Nomenclature
! Thickness range (ft)
! Aerial extent (mi2)
! Duration (Ma)
! Range
! Mode
|-
| 1st
| Megasequence
| 1000+
| Global
| 50–100+
| 80
|-
| 2nd
| Supersequence
| 500–5000+
| Regional
| 5–50
| 10
|-
| 3rd
| Sequence
| 500–1500
| 500–50,000
| 0.5-5
| 1
|-
| 4th
| Parasequence Set
| 20–800
| 20–2000
| 0.1-0.5
| 0.45
|-
| 5th
| Parasequence
| 10–200
| 20–2000
| 0.01-0.1
| 0.04
|}
==GOM basin example==
The figure below shows the correlation of the third-order eustatic curve of Haq et al.<ref name=ch04r43 />) and the oxygen isotope curve of Williams and Trainor<ref name=ch04r113>Williams, D., F., Trainor, D., M., 1987, Integrated chemical stratigraphy of deep-water frontier areas of the northern Gulf of Mexico: Proceedings, Gulf Coast Section SEPM 8th Annual Research conference, p. 151–158.</ref> with seven prograding clinoform intervals from the High Island South Addition in the GOM basin (see Figure 4-21). The correlations were established using the extinction events of the benthic foraminifera ''Hyalinea balthica (Hyal B)'' and ''Trimosina denticulata (Trim A)'' and the present-day sea floor as chronostratigraphic data. Six of the observed depositional cycles occur during the Tejas supersequence B 3.10 (0.8-0.0 Ma) third-order cycle of Haq et al.<ref name=ch04r43 />). This correlation suggests that the local cycles are fourth-order depositional cycles with a duration of approximately 130,000 years each (see <ref name=ch04r70 />).
[[file:sedimentary-basin-analysis_fig4-21.png|thumb|{{figure number|4-21}}. Copyright: Armentrout (1993, <ref name=ch04r9 />); courtesy Gulf Coast SEPM and Geological Society of London.]]
The seven fourth-order cycles occur at approximately the same frequency as the oxygen isotope warm and cold cycles. The oxygen isotope cycles are interpreted as glacial-inter-glacial cycles corresponding with relative high- and lowstands of sea level.<ref name=ch04r113 /> The clinoforms generally correlate with trends in upward enrichment in isotope values, suggesting progradation during onset of glacial climates as a consequence of lowering sea level as continental ice formed.
==See also==
* [[Sea level cycle phase]]
* [[Sea level cycle phase and systems tracts]]
* [[Identifying systems tracts]]
* [[Systems tracts and trap types]]
* [[Identifying sea level cycle phase with biostratigraphy]]
* [[Biofacies and changing sea level]]
* [[Constructing age model charts]]
* [[Superimposed sea level cycles]]
==References==
{{reflist}}
==External links==
{{search}}
* [http://archives.datapages.com/data/specpubs/beaumont/ch04/ch04.htm Original content in Datapages]
* [http://store.aapg.org/detail.aspx?id=545 Find the book in the AAPG Store]
[[Category:Critical elements of the petroleum system]]
[[Category:Sedimentary basin analysis]]
| image = exploring-for-oil-and-gas-traps.png
| width = 120px
| series = Treatise in Petroleum Geology
| title = Exploring for Oil and Gas Traps
| part = Critical elements of the petroleum system
| chapter = Sedimentary basin analysis
| frompg = 4-1
| topg = 4-123
| author = John M. Armentrout
| link = http://archives.datapages.com/data/specpubs/beaumont/ch04/ch04.htm
| pdf =
| store = http://store.aapg.org/detail.aspx?id=545
| isbn = 0-89181-602-X
}}
One aspect of basin analysis focuses on mapping specific systems tracts of third-, fourth-, or fifth-order sea level cycles and the relationship that stacked depositional sequences deposited during those cycles have to each other. Knowing the order of a cycle or the phase of a cycle represented by a rock sequence is important for predicting the location and type of reservoir and seal and the location of potential [[[[source rock]]s]].
==Procedure==
To determine cycle order of a sequence of sediments, we use biostratigraphic data, stratigraphic context (i.e., what part of a systems tract the interval is from), oxygen isotope curves, and published sea level curves. The table below suggests a procedure for determining cycle order of a rock sequence.
{| class = "wikitable"
|-
! Step
! Action
|-
| 1
| Determine the time span during which the sequence was deposited and compare to age ranges for cycle orders (see table below).
|-
| 2
| Determine the stratigraphic context of the sequence. What are the cycle orders for similar sequences above or below it?
|-
| 3
| Determine the age of the sequence and compare it to published sea level cycle curves (e.g., <ref name=ch04r43>Haq, B., Hardenbol, J., Vail, P., R., 1988, Mesozoic and Cenozoic chronostratigraphy and cycles of sea-level change: SEPM Special Publication 42, p. 71–108.</ref> ).
|}
==Cycle order from thickness and areal extent==
Because rates of sediment accumulation and areas of accommodation space vary, thickness and areal extent are of little use in establishing the order of depositional cycles. Most cycle hierarchies are based on duration. Establishing the duration of a sequence is difficult because of problems in high-resolution dating of rocks. However, with careful work an estimate can be made (see .<ref name=ch04r67>Miall, A., D., 1994, Paleocene 16: [[sequence stratigraphy]] and chronostratigraphy—problems of definition and precision in correlation, and their implications for global eustasy: Geoscience Canada, vol. 21, no. 1, p. 1–26.</ref><ref name=ch04r7>Armentrout, J., M., 1991, Paleontological constraints on depositional [[modeling]]: examples of integration of biostratigraphy and seismic stratigraphy, Pliocene–Pleistocene, Gulf of Mexico, in Weimer, P., Link, M., H., eds., Seismic Facies and Sedimentary Processes of Submarine Fans and Turbidite Systems: New York, Springer-Verlag, p. 137–170.</ref><ref name=ch04r9>Armentrout, J., M., 1996, High-resolution sequence biostratigraphy: examples from the Gulf of Mexico Plio–Pleistocene, in Howell, J., Aiken, J., eds., High Resolution [[Sequence stratigraphy]]: Innovations and Applications: The Geological Society of London Special Publication 104, p. 65–86.</ref>
==Table of cycle order==
Use the table below to help assess the sea level cycle order of a rock interval after .<ref name=ch04r70>Mitchum, R., M., Jr., Van Wagoner, J., C., 1990, High-frequency sequences and eustatic cycles in the Gulf of Mexico basin: Proceedings, Gulf Coast Section SEPM 11th Annual Research conference, p. 257–267.</ref>
{| class = "wikitable"
|-
! Cycle order
! Nomenclature
! Thickness range (ft)
! Aerial extent (mi2)
! Duration (Ma)
! Range
! Mode
|-
| 1st
| Megasequence
| 1000+
| Global
| 50–100+
| 80
|-
| 2nd
| Supersequence
| 500–5000+
| Regional
| 5–50
| 10
|-
| 3rd
| Sequence
| 500–1500
| 500–50,000
| 0.5-5
| 1
|-
| 4th
| Parasequence Set
| 20–800
| 20–2000
| 0.1-0.5
| 0.45
|-
| 5th
| Parasequence
| 10–200
| 20–2000
| 0.01-0.1
| 0.04
|}
==GOM basin example==
The figure below shows the correlation of the third-order eustatic curve of Haq et al.<ref name=ch04r43 />) and the oxygen isotope curve of Williams and Trainor<ref name=ch04r113>Williams, D., F., Trainor, D., M., 1987, Integrated chemical stratigraphy of deep-water frontier areas of the northern Gulf of Mexico: Proceedings, Gulf Coast Section SEPM 8th Annual Research conference, p. 151–158.</ref> with seven prograding clinoform intervals from the High Island South Addition in the GOM basin (see Figure 4-21). The correlations were established using the extinction events of the benthic foraminifera ''Hyalinea balthica (Hyal B)'' and ''Trimosina denticulata (Trim A)'' and the present-day sea floor as chronostratigraphic data. Six of the observed depositional cycles occur during the Tejas supersequence B 3.10 (0.8-0.0 Ma) third-order cycle of Haq et al.<ref name=ch04r43 />). This correlation suggests that the local cycles are fourth-order depositional cycles with a duration of approximately 130,000 years each (see <ref name=ch04r70 />).
[[file:sedimentary-basin-analysis_fig4-21.png|thumb|{{figure number|4-21}}. Copyright: Armentrout (1993, <ref name=ch04r9 />); courtesy Gulf Coast SEPM and Geological Society of London.]]
The seven fourth-order cycles occur at approximately the same frequency as the oxygen isotope warm and cold cycles. The oxygen isotope cycles are interpreted as glacial-inter-glacial cycles corresponding with relative high- and lowstands of sea level.<ref name=ch04r113 /> The clinoforms generally correlate with trends in upward enrichment in isotope values, suggesting progradation during onset of glacial climates as a consequence of lowering sea level as continental ice formed.
==See also==
* [[Sea level cycle phase]]
* [[Sea level cycle phase and systems tracts]]
* [[Identifying systems tracts]]
* [[Systems tracts and trap types]]
* [[Identifying sea level cycle phase with biostratigraphy]]
* [[Biofacies and changing sea level]]
* [[Constructing age model charts]]
* [[Superimposed sea level cycles]]
==References==
{{reflist}}
==External links==
{{search}}
* [http://archives.datapages.com/data/specpubs/beaumont/ch04/ch04.htm Original content in Datapages]
* [http://store.aapg.org/detail.aspx?id=545 Find the book in the AAPG Store]
[[Category:Critical elements of the petroleum system]]
[[Category:Sedimentary basin analysis]]