Changes

Deposition by gravity-flow processes occurs within physiographic lows.<ref name=ch04r53>Kneller, B., 1995, Beyond the turbidite paradign: physical models for deposition of turbidites and their implications for reservoir prediction, in Hartley, A., J., Prosser, D., J., eds., Characterization of Deep Marine Clastic Systems: Geological Society, London, Special Publication 94, p. 31–49.</ref><ref name=ch04r53 /> Although each field occurs within a local structural high, most have a major stratigraphic component related to their transport through slope channels and deposition as a gravity-flow deposit within the axis of a salt-withdrawal valley (see [[:file:sedimentary-basin-analysis_fig4-42.png|Figures 3]], [[:file:sedimentary-basin-analysis_fig4-43.png|4]], and [[:file:sedimentary-basin-analysis_fig4-56.png|5]] for the East Breaks 160-161 field). The sands within these valleys were deposited with a slope-parallel orientation. The trapping structure develops after reservoir deposition as the dip-oriented sand bodies are tilted along the flanks of the salt-cored anticlines ([[:file:sedimentary-basin-analysis_fig4-41.png|Figure 2]]). The anticlines continue to grow, and the tilt of the sand body becomes progressively more accentuated as each successive cycle of [[Syncline|synclinal]] fill accumulates and displaces the underlying salt.

Deposition by gravity-flow processes occurs within physiographic lows.<ref name=ch04r53>Kneller, B., 1995, Beyond the turbidite paradign: physical models for deposition of turbidites and their implications for reservoir prediction, in Hartley, A., J., Prosser, D., J., eds., Characterization of Deep Marine Clastic Systems: Geological Society, London, Special Publication 94, p. 31–49.</ref><ref name=ch04r53 /> Although each field occurs within a local structural high, most have a major stratigraphic component related to their transport through slope channels and deposition as a gravity-flow deposit within the axis of a salt-withdrawal valley (see [[:file:sedimentary-basin-analysis_fig4-42.png|Figures 3]], [[:file:sedimentary-basin-analysis_fig4-43.png|4]], and [[:file:sedimentary-basin-analysis_fig4-56.png|5]] for the East Breaks 160-161 field). The sands within these valleys were deposited with a slope-parallel orientation. The trapping structure develops after reservoir deposition as the dip-oriented sand bodies are tilted along the flanks of the salt-cored anticlines ([[:file:sedimentary-basin-analysis_fig4-41.png|Figure 2]]). The anticlines continue to grow, and the tilt of the sand body becomes progressively more accentuated as each successive cycle of [[Syncline|synclinal]] fill accumulates and displaces the underlying salt.

This process accelerates during relative lowstand of sea level when the river systems discharge their loads near to or into the heads of the slope valleys.<ref name=ch04r3>Anderson, R., N., Abdulah, K., Sarzalejo, S., Siringan, F., Thomas, M., A., 1996, Late Quaternary sedimentation and high-resolution [[sequence stratigraphy]] of the East Texas shelf, in DeBatist, M., Jacobs, P., eds., Geology of Siliciclastic Shelf Seas: Geological Society of London Special Publication 117, p. 94–124.</ref><ref name=ch04r115>Winker, C., D., 1996, High-resolution seismic stratigraphy of a late Pleistocene submarine fan ponded by salt-withdrawl minibasins on the Gulf of Mexico contentental slope: Proceedings, Offshore Technology conference, no. 38, vol. 1, p. 619–628.</ref>

This process accelerates during relative lowstand of sea level when the river systems discharge their loads near to or into the heads of the slope valleys.<ref name=ch04r3>Anderson, R., N., Abdulah, K., Sarzalejo, S., Siringan, F., Thomas, M., A., 1996, Late Quaternary sedimentation and high-resolution sequence stratigraphy of the East Texas shelf, in DeBatist, M., Jacobs, P., eds., Geology of Siliciclastic Shelf Seas: Geological Society of London Special Publication 117, p. 94–124.</ref><ref name=ch04r115>Winker, C., D., 1996, High-resolution seismic stratigraphy of a late Pleistocene submarine fan ponded by salt-withdrawal minibasins on the Gulf of Mexico contentental slope: Proceedings, Offshore Technology conference, no. 38, vol. 1, p. 619–628.</ref>

==Explanation of example==

==Explanation of example==

In Figure 4-40, producing fields are along the 200-ft (60-m) net sand contour or beyond rather than in the axial thick. This is because of gravity-flow sands accumulating within the [[Syncline|synclinal]] valley axes, which continue to subside through time.

In Figure 4-40, producing fields are along the 200-ft (60-m) net sand contour or beyond rather than in the axial thick. This is because of gravity-flow sands accumulating within the [[Syncline|synclinal]] valley axes, which continue to subside through time.

The following figure shows a depositional strike seismic reflection profile across one of these valleys. The high-amplitude, more continuous reflections correlate with condensed-section claystones and often bracket [[pressure compartments]] due to their very low [[permeability]]. Between the condensed sections are the sand-prone early lowstand systems tract, sometimes with hummocky-mounded facies suggesting channel complexes, overlain by silt-prone late lowstand deposits. The differential loading of salt by sediment accumulation along the synclinal valley axis results in differential rotation of each depositional sequence. This rotation along the synclinal flanks results in the early lowstand gravity-flow sands pinching-out structurally upward, providing potential hydrocarbon traps along the valley margins (;<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><ref name=ch04r20>Bilinski, P., W., McGee, D., T., Pfeiffer, D., S., Shew, R., S., 1995, Reservoir characterization of the “S” sand, Auger field, Garden Banks 426, 427, 470, and 471, in Winn, R., D. Jr., Armentrout, J., M., eds., Turbidites and Associated Deep-water Facies: SEPM (Society for Sedimentary Geology) Core Workshop No. 20, p. 75–93.</ref><ref name=ch04r65>McGee, D., T., Bilinski, P., W., Gary, P., S., Pfeiffer, D., S., Sheiman, J., L., 1994, Geologic models and reservoir geometries of Auger field, deepwater Gulf of Mexico: Proceedings, Gulf Coast Section SEPM 15th Annual Research conference, p. 245–256.</ref> ''see also'' Weimer and Bouma, 1995).

The following figure shows a depositional strike seismic reflection profile across one of these valleys. The high-amplitude, more continuous reflections correlate with condensed-section claystones and often bracket [[pressure compartments]] due to their very low [[permeability]]. Between the condensed sections are the sand-prone early lowstand systems tract, sometimes with hummocky-mounded facies suggesting channel complexes, overlain by silt-prone late lowstand deposits. The differential loading of salt by sediment accumulation along the synclinal valley axis results in differential rotation of each depositional sequence. This rotation along the synclinal flanks results in the early lowstand gravity-flow sands pinching-out structurally upward, providing potential hydrocarbon traps along the valley margins (;<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><ref name=ch04r20>Bilinski, P., W., McGee, D., T., Pfeiffer, D., S., Shew, R., S., 1995, Reservoir characterization of the “S” sand, Auger field, Garden Banks 426, 427, 470, and 471, in Winn, R., D. Jr., Armentrout, J., M., eds., Turbidites and Associated Deep-water Facies: SEPM (Society for Sedimentary Geology) Core Workshop No. 20, p. 75–93.</ref><ref name=ch04r65>McGee, D., T., Bilinski, P., W., Gary, P., S., Pfeiffer, D., S., Sheiman, J., L., 1994, Geologic models and reservoir geometries of Auger field, deepwater Gulf of Mexico: Proceedings, Gulf Coast Section SEPM 15th Annual Research conference, p. 245–256.</ref> ''see also'' Weimer and Bouma, 1995).

The [[isochron]] thick of the ''Glob alt'' sands in the figure represents the sand-prone slope/valley fill of the ''Glob alt'' sequence. Understanding the interplay of depositional processes and tectonic [[deformation]] is essential to hydrocarbon exploration in GOM minibasins.

The [[isochron]] thick of the ''Glob alt'' sands in the figure represents the sand-prone slope/valley fill of the ''Glob alt'' sequence. Understanding the interplay of depositional processes and tectonic [[deformation]] is essential to hydrocarbon exploration in GOM minibasins.