Changes

===Deep sea sandstones===

===Deep sea sandstones===

Deep marine sandstones are formed by processes operating in deep oceanic environment such as gravity flows and turbidity currents, driven by down-slope movement of sediment under gravity, and ocean-bottom currents driven by movement of ocean water in three-dimensional circulation pattern, at depths of >200m and on the contential slope and adjoining abyssal plain, and are often associated with pelagic limestone, which represents carbonate ooze formed by accumulations of planktonic organisms, and are commonly part of a submarine fan deposit. These sub marine fans have a central feeder channel within which sediments move by debris flow from which lesser channels branch out onto the middle part of fan. The sands in lesser channel and the lower parts of the fan is transported by stirred-up suspensions of sediment in water thus forming a sharp erosive base with a fining up grain size sequence of a few centimeters or tens of centimeters thick and a distinctive sedimentary profile. Petroleum which is generated from pelagic beds associated with these sandstones, and channel up-dip towards the main fan feeder channel, can be trapped in the sand beds of deep-water marine sandstones. Examples of deep-sea sandstone reservoirs include Ventura and Los Angeles basins and Frigg field in Eocene of the North Sea.

Deep marine sandstones are formed by processes operating in deep oceanic environment such as gravity flows and turbidity currents, driven by down-slope movement of sediment under gravity, and ocean-bottom currents driven by movement of ocean water in three-dimensional circulation pattern, at depths of >200m and on the contential slope and adjoining abyssal plain, and are often associated with pelagic limestone, which represents carbonate ooze formed by accumulations of planktonic organisms, and are commonly part of a submarine fan deposit. These sub marine fans have a central feeder channel within which sediments move by debris flow from which lesser channels branch out onto the middle part of fan. The sands in lesser channel and the lower parts of the fan is transported by stirred-up suspensions of sediment in water thus forming a sharp erosive base with a fining up grain size sequence of a few centimeters or tens of centimeters thick and a distinctive sedimentary profile. Petroleum which is generated from pelagic beds associated with these sandstones, and channel up-[[dip]] towards the main fan feeder channel, can be trapped in the sand beds of deep-water marine sandstones. Examples of deep-sea sandstone reservoirs include Ventura and Los Angeles basins and Frigg field in Eocene of the North Sea.

===Glacial sandstones===

===Glacial sandstones===

===Aeolian sandstones===

===Aeolian sandstones===

Aeolian sandstones are wind-blown sand dunes of coastal and desert environments. Dunes are heaped-up shaped ridges of sand with crests either parallel to wind direction (longitudinal dunes) and perpendicular to the prevailing wind (transverse dunes) although they may also be crescent- shaped. Dunes advance down- wind direction by erosion of sand from up-wind side and depositing sand on the down-wind (lee side).the up-wind face clearly has a gentle inclination while the down- wind face has a steeper slope. sand added to this steeper slopes runs down this slope adding to it and building cross beds which when buried within the dune forms large scale high-angle cross beds (Figure 9); whose dips are in the same direction as wind direction, thus providing an indication of paleocurrent direction in ancient dune sands. Aeolian sandstones are extremely well sorted because of their wind-blown nature and hence have good porosity and permeability. However, with desert deposits, they are less likely than other types of sand to be associated with organic accumulations that would act as hydrocarbon source rocks and provide a petroleum charge. Aeolian sandstones are commonly associated with evaporites which are salt deposits. They can thus have a complex diagenetic history, which may in some cases block the pores of the sand with chemically precipitating cementing materials.

Aeolian sandstones are wind-blown sand dunes of coastal and desert environments. Dunes are heaped-up shaped ridges of sand with crests either parallel to wind direction (longitudinal dunes) and perpendicular to the prevailing wind (transverse dunes) although they may also be crescent- shaped. Dunes advance down- wind direction by erosion of sand from up-wind side and depositing sand on the down-wind (lee side).the up-wind face clearly has a gentle inclination while the down- wind face has a steeper slope. sand added to this steeper slopes runs down this slope adding to it and building cross beds which when buried within the dune forms large scale high-angle cross beds (Figure 9); whose [[dip]]s are in the same direction as wind direction, thus providing an indication of paleocurrent direction in ancient dune sands. Aeolian sandstones are extremely well sorted because of their wind-blown nature and hence have good porosity and permeability. However, with desert deposits, they are less likely than other types of sand to be associated with organic accumulations that would act as hydrocarbon source rocks and provide a petroleum charge. Aeolian sandstones are commonly associated with evaporites which are salt deposits. They can thus have a complex diagenetic history, which may in some cases block the pores of the sand with chemically precipitating cementing materials.

[[File:Sandstone-Fig-9.png|thumb|300px|Figure 9: Navajo Sandstone, Utah, USA (Modified from Pettijohn et al.<ref name=Pettijohn />).]]

[[File:Sandstone-Fig-9.png|thumb|300px|Figure 9: Navajo Sandstone, Utah, USA (Modified from Pettijohn et al.<ref name=Pettijohn />).]]