Difference between revisions of "Third-order sequences"

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==Third-order sequence deposition==
 
==Third-order sequence deposition==
  
[[file:exploring-for-stratigraphic-traps_fig21-8.png|thumb|{{figure number|1}}. Copyright: Hyne, 1995; courtesy Tulsa Geological Society.]]
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[[file:exploring-for-stratigraphic-traps_fig21-8.png|300px|thumb|{{figure number|1}}. Copyright: Hyne, 1995; courtesy Tulsa Geological Society.]]
  
 
The schematic cross section in [[:file:exploring-for-stratigraphic-traps_fig21-9.png|Figure 2]] is a third-order sequence model based on observations of the Tertiary of the Gulf of Mexico passive margin basin.<ref name=ch21r47>Van Wagoner, J., C., Mitchum, R., M., Campion, K., M., Rahmanian, V., D., 1990, Siliciclastic Sequence Stratigraphy in Well Logs, Cores and Outcrops: Concepts for High-Resolution Correlation of Time and Facies: [http://store.aapg.org/detail.aspx?id=1196 AAPG Methods in Exploration Series No. 7], 55 p.</ref> Although different basin types, i.e., foreland basins or active margin basins, require adjustments to the model, the Gulf of Mexico model still is useful for understanding third-order sequence deposition.
 
The schematic cross section in [[:file:exploring-for-stratigraphic-traps_fig21-9.png|Figure 2]] is a third-order sequence model based on observations of the Tertiary of the Gulf of Mexico passive margin basin.<ref name=ch21r47>Van Wagoner, J., C., Mitchum, R., M., Campion, K., M., Rahmanian, V., D., 1990, Siliciclastic Sequence Stratigraphy in Well Logs, Cores and Outcrops: Concepts for High-Resolution Correlation of Time and Facies: [http://store.aapg.org/detail.aspx?id=1196 AAPG Methods in Exploration Series No. 7], 55 p.</ref> Although different basin types, i.e., foreland basins or active margin basins, require adjustments to the model, the Gulf of Mexico model still is useful for understanding third-order sequence deposition.
  
[[file:exploring-for-stratigraphic-traps_fig21-9.png|thumb|{{figure number|2}}. Copyright: Haq, 1988; courtesy SEPM.]]
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[[file:exploring-for-stratigraphic-traps_fig21-9.png|300px|thumb|{{figure number|2}}. Copyright: Haq, 1988; courtesy SEPM.]]
  
 
The order of deposition for the sequence shown in [[:file:exploring-for-stratigraphic-traps_fig21-9.png|Figure 2]] is as follows:<ref name=ch21r47 />
 
The order of deposition for the sequence shown in [[:file:exploring-for-stratigraphic-traps_fig21-9.png|Figure 2]] is as follows:<ref name=ch21r47 />
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** Parasequences downlap onto the condensed section.
 
** Parasequences downlap onto the condensed section.
  
[[file:exploring-for-stratigraphic-traps_fig21-10.png|thumb|{{figure number|3}}. Copyright: Weber et al., 1995; courtesy SEPM.]]
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[[file:exploring-for-stratigraphic-traps_fig21-10.png|thumb|300px|{{figure number|3}}. Copyright: Weber et al., 1995; courtesy SEPM.]]
  
 
==Third-order sequence example==
 
==Third-order sequence example==
 
The Desmoinian of the Paradox basin, Utah, shown in [[:file:exploring-for-stratigraphic-traps_fig21-10.png|Figure 3]], is an example of a third-order depositional sequence.
 
The Desmoinian of the Paradox basin, Utah, shown in [[:file:exploring-for-stratigraphic-traps_fig21-10.png|Figure 3]], is an example of a third-order depositional sequence.
  
[[file:exploring-for-stratigraphic-traps_fig21-11.png|thumb|{{figure number|4}}.]]
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[[file:exploring-for-stratigraphic-traps_fig21-11.png|300px|thumb|{{figure number|4}}.]]
  
 
==Carbonate platform third-order sequence==
 
==Carbonate platform third-order sequence==

Revision as of 14:37, 7 July 2014

Exploring for Oil and Gas Traps
Series Treatise in Petroleum Geology
Part Predicting the occurrence of oil and gas traps
Chapter Exploring for stratigraphic traps
Author John C. Dolson, Mike S. Bahorich, Rick C. Tobin, Edward A. Beaumont, Louis J. Terlikoski, Michael L. Hendricks
Link Web page
Store AAPG Store

During a third-order sea level change, cycle amplitude is great enough (approximately 50–150 ft) to expose the shelf. Depositional sites range from coastal plain to deep basin. The unit of strata deposited during a third-order cycle is called a depositional sequence. A depositional sequence has three subdivisions: highstand systems tract (HST), transgressive systems tract (TST), and lowstand systems tract (LST). Figure 1 shows a schematic cross section of a third-order sequence and its various systems tracts.

Third-order sequence deposition[edit]

Figure 1 . Copyright: Hyne, 1995; courtesy Tulsa Geological Society.

The schematic cross section in Figure 2 is a third-order sequence model based on observations of the Tertiary of the Gulf of Mexico passive margin basin.[1] Although different basin types, i.e., foreland basins or active margin basins, require adjustments to the model, the Gulf of Mexico model still is useful for understanding third-order sequence deposition.

Figure 2 . Copyright: Haq, 1988; courtesy SEPM.

The order of deposition for the sequence shown in Figure 2 is as follows:[1]

  • Sequence boundary formation and lowstand systems tract; fan deposition
    • Rate of eustatic fall exceeds rate of subsidence.
    • Sea level falls to shelf break, shelf is exposed, incised; canyon cut.
    • Slope-perched deltas and submarine fans are deposited.
  • Lowstand systems tract; wedge deposition
    • Rate of eustatic fall decreases, reaches a stillstand, and rises slowly.
    • Submarine fan deposition ceases.
    • Incised valleys fill with coarse-grained, low-sinuosity channel or estuarine sandstones in response to sea level rise.
    • Shale-prone wedge with thin, fine-grained turbidites forms on the slope, then downlaps the top of the submarine fan.
  • Transgressive systems tract deposition
    • Rate of rise is at a maximum.
    • During brief slowdowns in the rate of rise, parasequences (fourth-order sequences) prograde; but overall they stack in a backstepping pattern.
    • Organic-rich (condensed) section moves up onto the shelf.
    • Fluvial systems typically shift from braided to meandering pattern.
  • Highstand systems tract deposition
    • Rate of sea level rise is at a minimum; in the late highstand, it falls slowly.
    • Depositional rates exceed rate of sea level rise, causing parasequences to build basinward in aggradational to progradational parasequence sets.
    • Parasequences downlap onto the condensed section.
Figure 3 . Copyright: Weber et al., 1995; courtesy SEPM.

Third-order sequence example[edit]

The Desmoinian of the Paradox basin, Utah, shown in Figure 3, is an example of a third-order depositional sequence.

Figure 4 .

Carbonate platform third-order sequence[edit]

The diagrams in Figure 4 outline the deposition of a sequence associated with a carbonate plat-form during a third-order sea level cycle. Sequence deposition begins with lowstand systems tract (2 and 3) and ends with the highstand systems tract (5).

See also[edit]

References[edit]

  1. 1.0 1.1 Van Wagoner, J., C., Mitchum, R., M., Campion, K., M., Rahmanian, V., D., 1990, Siliciclastic Sequence Stratigraphy in Well Logs, Cores and Outcrops: Concepts for High-Resolution Correlation of Time and Facies: AAPG Methods in Exploration Series No. 7, 55 p.

External links[edit]

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Third-order sequences
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