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Sea level cycles and climate (view source)
Revision as of 21:46, 31 January 2014
, 21:46, 31 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 = Predicting the occurrence of oil and gas traps
| chapter = Predicting reservoir system quality and performance
| frompg = 9-1
| topg = 9-156
| author = Dan J. Hartmann, Edward A. Beaumont
| link = http://archives.datapages.com/data/specpubs/beaumont/ch09/ch09.htm
| pdf =
| store = http://store.aapg.org/detail.aspx?id=545
| isbn = 0-89181-602-X
}}
==Global climatic effect of cycles==
The earth's climate has ranged from times of cooler temperatures (icehouse) to times of warmer temperatures (greenhouse).<ref name=ch09r50>Read, J., F., Horbury, A., D., 1993, Eustatic and tectonic controls on [[porosity]] evolution beneath sequence-bounding unconformities and parasequence disconformities on carbonate platforms, in Horbury, A., D., Robinson, A., G., eds., Diagenesis and Basin Development: AAPG Studies in Geology 36, p. 155–197.</ref> Continental glaciation characterizes icehouse conditions and causes large sea level changes because ice ties up large volumes of water. Sea level rises rapidly during glaciation and falls gradually during deglaciation. Sea level changes are small during greenhouse times because the ice volume was smaller.
The table below summarizes characteristics of fourth- and fifth-order sea level cycles during icehouse, greenhouse, and transitional periods.
{| class = "wikitable"
|-
! Characteristic
! Icehouse
! Transition
! Greenhouse
|-
| Amplitude [[length::( m]])
| High (50–100)
| Moderate (20–50)
| Low (1–20)
|-
| Dominant frequency (k.y.)
| 100
| 50
| 20
|}
==Greenhouse vs. icehouse times==
The chart below shows periods of icehouse and greenhouse conditions. Also shown are age and paleolatitudes of ice-rafted deposits (bar chart), net climate forcing CO<sub>2</sub>+ solar luminosity (upper curved line), and the Vail sea level curve (lower curved line).
[[file:predicting-reservoir-system-quality-and-performance_fig9-80.png|thumb|{{figure number|9-80}}. Copyright: Read, 1995; courtesy SEPM.]]
==Regional climates==
Arid or humid conditions can occur simultaneously in different regions during icehouse or greenhouse periods. The aridity or humidity of a region strongly affects carbonate deposition and diagenesis. For example, carbonates deposited under arid conditions tend to be associated with evaporites, and carbonate sequences are partly to completely dolomitized. In humid regions where rainfall is greater, carbonates are subject to greater dissolution; therefore, vuggy porosity and karst features are common.
==Sea level and climate==
Long-term sea level cycles influence regional climates (Read, 1996). More humid conditions tend to prevail during deposition of transgressive system tracts, and more arid conditions tend to prevail during deposition of late highstand-lowstand system tracts. Climatic conditions of an area are likely to be arid when a platform interior is subaerially exposed during long-term, sea level late highstand and lowstand. From the Precambrian to the Silurian, the lack of land plants might have amplified this aridity. Humid conditions prevail when extensive shallow epicontinental seaways present during long-term transgressions cause increased rainfall.
==Sedimentation rate and climate==
Light is a critical element of carbonate sedimentation. The photic zone in tropical carbonate settings is only 20–30 m. This is contrasted to cooler water carbonate settings where the photic zone extends to [[length::100 m]] or deeper. Tropical carbonate faunal assemblages strongly depend on light, which is why sedimentation rates below [[length::10 m]] water depth drop rapidly. Carbonate-producing assemblages of temperate zones do not have a strong light dependence; hence, the sedimentation rate, although lower, is constant from the surface to more than [[length::100 m]] water depth (Read, 1996).
The table below contrasts features of tropical carbonate settings with temperate carbonate settings.
{| class = "wikitable"
|-
! Characteristic
! Tropical carbonate settings
! Temperate carbonate settings
|-
| Photic zone depth
| 20–30 m
| 100 m+
|-
| Sedimentation rate
| High in [[length::10 m]] or less of water, then rapid drop
| Low but more constant in water [[length::100 m]] or deeper
|-
| Dominant fauna
| Reef-building assemblages (light-dependent biota)
| Bryozoans, mollusks, forams, crinoids (biota not as light dependent)
|-
| Depositional topography
| Reef-rimmed platforms
| Gently sloping ramps on prograding seaward-thickening sediment wedges
|}
==See also==
* [[Predicting carbonate porosity and permeability]]
* [[Carbonate facies]]
* [[Carbonate diagenetic stages]]
* [[Early carbonate diagenesis]]
* [[Basics of carbonate porosity formation and preservation]]
* [[Sea level cycles and carbonate sequences]]
* [[Sea level cycles and carbonate diagenesis]]
* [[Sequences during low-amplitude, high-frequency cycles]]
* [[Sequences during moderate-amplitude, high-frequency cycles]]
* [[Sequences during high-amplitude, high-frequency cycles]]
* [[Predicting carbonate reservoir location and quality]]
==References==
{{reflist}}
==External links==
{{search}}
* [http://archives.datapages.com/data/specpubs/beaumont/ch09/ch09.htm Original content in Datapages]
* [http://store.aapg.org/detail.aspx?id=545 Find the book in the AAPG Store]
[[Category:Predicting the occurrence of oil and gas traps]]
[[Category:Predicting reservoir system quality and performance]]
| image = exploring-for-oil-and-gas-traps.png
| width = 120px
| series = Treatise in Petroleum Geology
| title = Exploring for Oil and Gas Traps
| part = Predicting the occurrence of oil and gas traps
| chapter = Predicting reservoir system quality and performance
| frompg = 9-1
| topg = 9-156
| author = Dan J. Hartmann, Edward A. Beaumont
| link = http://archives.datapages.com/data/specpubs/beaumont/ch09/ch09.htm
| pdf =
| store = http://store.aapg.org/detail.aspx?id=545
| isbn = 0-89181-602-X
}}
==Global climatic effect of cycles==
The earth's climate has ranged from times of cooler temperatures (icehouse) to times of warmer temperatures (greenhouse).<ref name=ch09r50>Read, J., F., Horbury, A., D., 1993, Eustatic and tectonic controls on [[porosity]] evolution beneath sequence-bounding unconformities and parasequence disconformities on carbonate platforms, in Horbury, A., D., Robinson, A., G., eds., Diagenesis and Basin Development: AAPG Studies in Geology 36, p. 155–197.</ref> Continental glaciation characterizes icehouse conditions and causes large sea level changes because ice ties up large volumes of water. Sea level rises rapidly during glaciation and falls gradually during deglaciation. Sea level changes are small during greenhouse times because the ice volume was smaller.
The table below summarizes characteristics of fourth- and fifth-order sea level cycles during icehouse, greenhouse, and transitional periods.
{| class = "wikitable"
|-
! Characteristic
! Icehouse
! Transition
! Greenhouse
|-
| Amplitude [[length::( m]])
| High (50–100)
| Moderate (20–50)
| Low (1–20)
|-
| Dominant frequency (k.y.)
| 100
| 50
| 20
|}
==Greenhouse vs. icehouse times==
The chart below shows periods of icehouse and greenhouse conditions. Also shown are age and paleolatitudes of ice-rafted deposits (bar chart), net climate forcing CO<sub>2</sub>+ solar luminosity (upper curved line), and the Vail sea level curve (lower curved line).
[[file:predicting-reservoir-system-quality-and-performance_fig9-80.png|thumb|{{figure number|9-80}}. Copyright: Read, 1995; courtesy SEPM.]]
==Regional climates==
Arid or humid conditions can occur simultaneously in different regions during icehouse or greenhouse periods. The aridity or humidity of a region strongly affects carbonate deposition and diagenesis. For example, carbonates deposited under arid conditions tend to be associated with evaporites, and carbonate sequences are partly to completely dolomitized. In humid regions where rainfall is greater, carbonates are subject to greater dissolution; therefore, vuggy porosity and karst features are common.
==Sea level and climate==
Long-term sea level cycles influence regional climates (Read, 1996). More humid conditions tend to prevail during deposition of transgressive system tracts, and more arid conditions tend to prevail during deposition of late highstand-lowstand system tracts. Climatic conditions of an area are likely to be arid when a platform interior is subaerially exposed during long-term, sea level late highstand and lowstand. From the Precambrian to the Silurian, the lack of land plants might have amplified this aridity. Humid conditions prevail when extensive shallow epicontinental seaways present during long-term transgressions cause increased rainfall.
==Sedimentation rate and climate==
Light is a critical element of carbonate sedimentation. The photic zone in tropical carbonate settings is only 20–30 m. This is contrasted to cooler water carbonate settings where the photic zone extends to [[length::100 m]] or deeper. Tropical carbonate faunal assemblages strongly depend on light, which is why sedimentation rates below [[length::10 m]] water depth drop rapidly. Carbonate-producing assemblages of temperate zones do not have a strong light dependence; hence, the sedimentation rate, although lower, is constant from the surface to more than [[length::100 m]] water depth (Read, 1996).
The table below contrasts features of tropical carbonate settings with temperate carbonate settings.
{| class = "wikitable"
|-
! Characteristic
! Tropical carbonate settings
! Temperate carbonate settings
|-
| Photic zone depth
| 20–30 m
| 100 m+
|-
| Sedimentation rate
| High in [[length::10 m]] or less of water, then rapid drop
| Low but more constant in water [[length::100 m]] or deeper
|-
| Dominant fauna
| Reef-building assemblages (light-dependent biota)
| Bryozoans, mollusks, forams, crinoids (biota not as light dependent)
|-
| Depositional topography
| Reef-rimmed platforms
| Gently sloping ramps on prograding seaward-thickening sediment wedges
|}
==See also==
* [[Predicting carbonate porosity and permeability]]
* [[Carbonate facies]]
* [[Carbonate diagenetic stages]]
* [[Early carbonate diagenesis]]
* [[Basics of carbonate porosity formation and preservation]]
* [[Sea level cycles and carbonate sequences]]
* [[Sea level cycles and carbonate diagenesis]]
* [[Sequences during low-amplitude, high-frequency cycles]]
* [[Sequences during moderate-amplitude, high-frequency cycles]]
* [[Sequences during high-amplitude, high-frequency cycles]]
* [[Predicting carbonate reservoir location and quality]]
==References==
{{reflist}}
==External links==
{{search}}
* [http://archives.datapages.com/data/specpubs/beaumont/ch09/ch09.htm Original content in Datapages]
* [http://store.aapg.org/detail.aspx?id=545 Find the book in the AAPG Store]
[[Category:Predicting the occurrence of oil and gas traps]]
[[Category:Predicting reservoir system quality and performance]]