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Definitions of depositional system elements (view source)
Revision as of 19:14, 30 January 2014
, 19:14, 30 January 2014Initial import
{{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
}}
==Depositional cycle vs. sequence==
The term ''depositional cycle'' refers to time through which one complete cycle of relative sea level change occurs. The sediments deposited during one such cycle are called a ''depositional sequence''.
==Sequence boundaries==
A depositional sequence is bounded by unconformities or the correlative conformities and is subdivided by internal surfaces of transgression and maximum flooding;<ref name=ch04r68>Mitchum, R., M., Jr., 1977, Seismic stratigraphy and global changes in sea level, II: [[Glossary]] of terms used in seismic stratigraphy, in Seismic Stratigraphy—Applications in Hydrocarbon Exploration: AAPG Memoir 26, p. 205–212.</ref> see also .<ref name=ch04r99>Vail, P., R., 1987, Seismic stratigraphy interpretation procedure, in Bally, A., W., ed., Atlas of Seismic Stratigraphy: AAPG, p. 1–10.</ref><ref name=ch04r79>Posamentier, H., W., Vail, P., R., 1988, Eustatic controls on clastic deposition II—sequence and systems tract models: SEPM Special Publication 42, p. 125–154.</ref><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> Each of these surfaces is chronostratigraphically significant, separating consistently older strata from younger strata.
An alternative concept of defining a depositional sequence is that of Galloway.<ref name=ch04r34>Galloway, W., E., 1989a, Genetic stratigraphic sequences in basin analysis I: architecture and genesis of flooding-surface bounded depositional units: AAPG Bulletin, vol. 73, p. 125–142.</ref><ref name=ch04r35>Galloway, W., E., 1989b, Genetic stratigraphic sequences in basin analysis II: application to northwest Gulf of Mexico Cenozoic basin: AAPG Bulletin, vol. 73, p. 143–154.</ref> Galloway uses the maximum flooding surface and correlative condensed section as the bounding surface of the “genetic” depositional sequence. Both sequence concepts use the erosional unconformities, maximum flooding surface, and transgressive surface as interpretation horizons for partitioning each sequence. Sequence surfaces are often best recognized on seismic reflection profiles by stratal terminations called ''lapouts'', such as downlap and onlap.
==Maximum flooding surface==
The maximum flooding surface represents the greatest transgression of shallow marine facies within a sequence.<ref name=ch04r68 /> This is typically associated with a downlap surface formed by the progradation of the overlying highstand systems tract. Not all downlap surfaces are associated with maximum flooding surfaces.
==Transgressive surface==
The transgressive surface is the first significant marine flooding surface across the shelf.<ref name=ch04r68 /> Above this surface, shallow marine facies shift landward dramatically.
==Systems tracts==
Systems tracts are composed of all deposits accumulating during one phase of relative sea level cycle, such as lowstand systems tract or highstand systems tract. [[Attributes]] of each systems tract are discussed in section D.
==Age model==
An age model is the chronostratigraphic relationship of different depositional sequences.
==Biofacies==
A biofacies is an assemblage of organisms (living or fossil) found together because they responded to similar environmental conditions.
==Microfossil abundance patterns==
Microfossil abundance patterns are relative high and low peaks in the number of microfossils found in a sample or set of samples. They most often indicate sedimentation rates.<ref name=ch04r10>Armentrout, J., M., Clement, J., F., 1990, Biostratigraphic calibration of depositional cycles: a case study in High Island–Galveston–East Breaks areas, offshore Texas: Proceedings, Gulf Coast Section SEPM 11th Annual Research Conference, p. 21–51.</ref> Intervals with slow rates of sediment accumulation have consequent concentrations of abundant fossils and are associated with maximum flooding and transgressive surfaces. Intervals with high rates of sedimentation usually have low fossil abundances due to dilution and are often associated with sequence boundaries.
==Illustration of sequence boundaries==
The following figure illustrates the bounding surfaces for sequences. The GOM basin analysis example in this chapter is based primarily on well log and [[seismic data]] interpretation using this passive margin sequence stratigraphic model. Different models are necessary for different settings, such as a foreland basin (see .<ref name=ch04r104>Van Wagoner, J., C., Bertram, G., T., eds., 1995, [[Sequence stratigraphy]] of Foreland Basin Deposits: AAPG Memoir 64, 487 p.</ref> or a rift basin<ref name=ch04r82>Prosser, S., 1993, Rift-related linked depositional systems and their seismic expression, in Williams, C., D., Dobb, A., eds., Tectonic and Seismic Sequence Stratigraphy: Geological Society Special Publication 71, p. 35–66.</ref>
==See also==
* [[Depositional sequences]]
* [[Identifying depositional sequences]]
* [[Identifying depositional sequences in seismic sections]]
* [[Identifying depositional sequences from biostratigraphic data]]
* [[Recognizing stacked depositional sequences in seismic profiles]]
* [[Recognizing stacked depositional sequences from well data]]
==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
}}
==Depositional cycle vs. sequence==
The term ''depositional cycle'' refers to time through which one complete cycle of relative sea level change occurs. The sediments deposited during one such cycle are called a ''depositional sequence''.
==Sequence boundaries==
A depositional sequence is bounded by unconformities or the correlative conformities and is subdivided by internal surfaces of transgression and maximum flooding;<ref name=ch04r68>Mitchum, R., M., Jr., 1977, Seismic stratigraphy and global changes in sea level, II: [[Glossary]] of terms used in seismic stratigraphy, in Seismic Stratigraphy—Applications in Hydrocarbon Exploration: AAPG Memoir 26, p. 205–212.</ref> see also .<ref name=ch04r99>Vail, P., R., 1987, Seismic stratigraphy interpretation procedure, in Bally, A., W., ed., Atlas of Seismic Stratigraphy: AAPG, p. 1–10.</ref><ref name=ch04r79>Posamentier, H., W., Vail, P., R., 1988, Eustatic controls on clastic deposition II—sequence and systems tract models: SEPM Special Publication 42, p. 125–154.</ref><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> Each of these surfaces is chronostratigraphically significant, separating consistently older strata from younger strata.
An alternative concept of defining a depositional sequence is that of Galloway.<ref name=ch04r34>Galloway, W., E., 1989a, Genetic stratigraphic sequences in basin analysis I: architecture and genesis of flooding-surface bounded depositional units: AAPG Bulletin, vol. 73, p. 125–142.</ref><ref name=ch04r35>Galloway, W., E., 1989b, Genetic stratigraphic sequences in basin analysis II: application to northwest Gulf of Mexico Cenozoic basin: AAPG Bulletin, vol. 73, p. 143–154.</ref> Galloway uses the maximum flooding surface and correlative condensed section as the bounding surface of the “genetic” depositional sequence. Both sequence concepts use the erosional unconformities, maximum flooding surface, and transgressive surface as interpretation horizons for partitioning each sequence. Sequence surfaces are often best recognized on seismic reflection profiles by stratal terminations called ''lapouts'', such as downlap and onlap.
==Maximum flooding surface==
The maximum flooding surface represents the greatest transgression of shallow marine facies within a sequence.<ref name=ch04r68 /> This is typically associated with a downlap surface formed by the progradation of the overlying highstand systems tract. Not all downlap surfaces are associated with maximum flooding surfaces.
==Transgressive surface==
The transgressive surface is the first significant marine flooding surface across the shelf.<ref name=ch04r68 /> Above this surface, shallow marine facies shift landward dramatically.
==Systems tracts==
Systems tracts are composed of all deposits accumulating during one phase of relative sea level cycle, such as lowstand systems tract or highstand systems tract. [[Attributes]] of each systems tract are discussed in section D.
==Age model==
An age model is the chronostratigraphic relationship of different depositional sequences.
==Biofacies==
A biofacies is an assemblage of organisms (living or fossil) found together because they responded to similar environmental conditions.
==Microfossil abundance patterns==
Microfossil abundance patterns are relative high and low peaks in the number of microfossils found in a sample or set of samples. They most often indicate sedimentation rates.<ref name=ch04r10>Armentrout, J., M., Clement, J., F., 1990, Biostratigraphic calibration of depositional cycles: a case study in High Island–Galveston–East Breaks areas, offshore Texas: Proceedings, Gulf Coast Section SEPM 11th Annual Research Conference, p. 21–51.</ref> Intervals with slow rates of sediment accumulation have consequent concentrations of abundant fossils and are associated with maximum flooding and transgressive surfaces. Intervals with high rates of sedimentation usually have low fossil abundances due to dilution and are often associated with sequence boundaries.
==Illustration of sequence boundaries==
The following figure illustrates the bounding surfaces for sequences. The GOM basin analysis example in this chapter is based primarily on well log and [[seismic data]] interpretation using this passive margin sequence stratigraphic model. Different models are necessary for different settings, such as a foreland basin (see .<ref name=ch04r104>Van Wagoner, J., C., Bertram, G., T., eds., 1995, [[Sequence stratigraphy]] of Foreland Basin Deposits: AAPG Memoir 64, 487 p.</ref> or a rift basin<ref name=ch04r82>Prosser, S., 1993, Rift-related linked depositional systems and their seismic expression, in Williams, C., D., Dobb, A., eds., Tectonic and Seismic Sequence Stratigraphy: Geological Society Special Publication 71, p. 35–66.</ref>
==See also==
* [[Depositional sequences]]
* [[Identifying depositional sequences]]
* [[Identifying depositional sequences in seismic sections]]
* [[Identifying depositional sequences from biostratigraphic data]]
* [[Recognizing stacked depositional sequences in seismic profiles]]
* [[Recognizing stacked depositional sequences from well data]]
==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]]