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==Shorelines and barrier islands==

==Shorelines and barrier islands==

[[File:M91FG191.JPG|thumb|300px|{{figure number|1}}The photograph shows a shoreface profile on St. Cyrus Beach, Scotland. The beach is just over a hundred meters wide. Reservoir properties are influenced by the degree of wave reworking up the shoreface profile. Lower figure from McCubbin (1982). Reprinted with permission from the AAPG.]]

[[File:M91FG191.JPG|thumb|300px|{{figure number|1}}The photograph shows a shoreface profile on St. Cyrus Beach, Scotland. The beach is just over a hundred meters wide. Reservoir properties are influenced by the degree of wave reworking up the shoreface profile. Lower figure from McCubbin.<ref name=McCubbin>McCubbin, D. G., 1992, Barrier Islands, strand-plains, in P. A. Scholle and D. R. Spearing, eds., Sandstone depositional environments: AAPG Memoir 31, p. 247–279.</ref> Reprinted with permission from the AAPG.]]

Shoreface sands are deposited along shorelines, and they generally form extensive, high-quality reservoir systems ([[:File:M91FG191.JPG|Figure 1]]). Wave action and occasional storms act to deposit sand along the shoreface. The lower shoreface lies below fair-weather wave base but can be affected by storms; the sands tend to be siltier and more poorly sorted by comparison to the upper shoreface, where the sands have been subjected to wave winnowing. A shoreface deposit separated by a lagoon from the land is known as a barrier island.

Shoreface sands are deposited along shorelines, and they generally form extensive, high-quality reservoir systems ([[:File:M91FG191.JPG|Figure 1]]). Wave action and occasional storms act to deposit sand along the shoreface. The lower shoreface lies below fair-weather wave base but can be affected by storms; the sands tend to be siltier and more poorly sorted by comparison to the upper shoreface, where the sands have been subjected to wave winnowing. A shoreface deposit separated by a lagoon from the land is known as a barrier island.

[[File:M91FG117.JPG|thumb|300px|{{figure number|6}}Time series of water cut maps from the West Cornelius reservoir, North Markham-North Bay City field, Texas. In this strand-plain reservoir, east-northeastndashwest-southwest-oriented beach ridge macroforms are fairways for water ingress. Tidal mud flat deposits south of the field restrict water influx from this direction (from Tyler and Ambrose, reprinted with permission from the AAPG.<ref name=TA1986 />)]]

[[File:M91FG117.JPG|thumb|300px|{{figure number|6}}Time series of water cut maps from the West Cornelius reservoir, North Markham-North Bay City field, Texas. In this strand-plain reservoir, east-northeastndashwest-southwest-oriented beach ridge macroforms are fairways for water ingress. Tidal mud flat deposits south of the field restrict water influx from this direction (from Tyler and Ambrose, reprinted with permission from the AAPG.<ref name=TA1986 />)]]

Beach sandstones form as single belts or accrete laterally to form strand plains many kilometers long and several kilometers wide. Modern strand plains such as the Nayarit strand plain of western Mexico show a ridge and swale topography on their surfaces (McCubbin, 1982). Mud fills in the interridge swales can act as permeability barriers to lateral flow in the subsurface. One example in the Frio Formation of south Texas is known to have caused the compartmentalization of a beach ridge interval containing several million barrels of recoverable oil (Reistroffer and Tyler, 1991). Water ingress may preferentially occur along the low-lying swales<ref name=TA1986 /> ([[:File:M91FG117.JPG|Figure 6]]).

Beach sandstones form as single belts or accrete laterally to form strand plains many kilometers long and several kilometers wide. Modern strand plains such as the Nayarit strand plain of western Mexico show a ridge and swale topography on their surfaces.<ref name=McCubbin /> Mud fills in the interridge swales can act as permeability barriers to lateral flow in the subsurface. One example in the Frio Formation of south Texas is known to have caused the compartmentalization of a beach ridge interval containing several million barrels of recoverable oil (Reistroffer and Tyler, 1991). Water ingress may preferentially occur along the low-lying swales<ref name=TA1986 /> ([[:File:M91FG117.JPG|Figure 6]]).

==Tidal channels==

==Tidal channels==

==Barrier Islands==

==Barrier Islands==

[[File:M91FG192.JPG|thumb|300px|{{figure number|7}}Generalized map and cross sections showing major environments and facies associations of a barrier island-lagoonal system (from McCubbin, 1982). Reprinted with permission from the AAPG.]]

[[File:M91FG192.JPG|thumb|300px|{{figure number|7}}Generalized map and cross sections showing major environments and facies associations of a barrier island-lagoonal system (from McCubbin<ref name=McCubbin />). Reprinted with permission from the AAPG.]]

Barrier islands form thick, well-sorted sand bodies with a tabular geometry ([[:File:M91FG192.JPG|Figure 7]]). They typically comprise a composite of beach, dune, and upper shoreface sandstones (Galloway, 1986). Barrier islands can be continuous for tens of kilometers along strike but may only be a few kilometers wide. Local heterogeneity can be provided by tidal channel inlet deposits. These form crosscutting lenticular pods, disrupting the layer-cake continuity of the barrier island body. Recent barrier island sediments on the South Carolina coast provide a modern analog and are described in detail by Sexton and Hayes (1996).

Barrier islands form thick, well-sorted sand bodies with a tabular geometry ([[:File:M91FG192.JPG|Figure 7]]). They typically comprise a composite of beach, dune, and upper shoreface sandstones (Galloway, 1986). Barrier islands can be continuous for tens of kilometers along strike but may only be a few kilometers wide. Local heterogeneity can be provided by tidal channel inlet deposits. These form crosscutting lenticular pods, disrupting the layer-cake continuity of the barrier island body. Recent barrier island sediments on the South Carolina coast provide a modern analog and are described in detail by Sexton and Hayes (1996).