Changes

[[file:M31F3.jpg|thumb|300px|{{figure number|2}}Summary diagrams illustrating the major characteristics of braided channel deposits (letters on the vertical section refer to core or outcrop photographs).<ref name=Colemanandprior_1981 />]]

[[file:M31F3.jpg|thumb|300px|{{figure number|2}}Summary diagrams illustrating the major characteristics of braided channel deposits (letters on the vertical section refer to core or outcrop photographs).<ref name=Colemanandprior_1981 />]]

[[:file:M31F3.jpg|Figure 2]] summarizes the major characteristics of braided-channel deposits, including lateral relationships (block diagram in upper left); typical vertical sequence (upper right), including grain size, directional properties, dip angles, relative porosity, and sedimentary structures; sand body isopach map (lower left); and representative electric logs (lower right) at selected sites to show variation in log shape. As this diagram illustrates, the typical vertical sequence is characterized by multiple stacked fining-upward cycles of deposition (each representing deposition by a migratory channel). Directional properties within each cycle often display narrow directional spread and are fairly representative of the long-axis orientation or downstream direction of the channel. High dip angles are most often associated with large-scale cross-bedding and distorted layers.

[[:file:M31F3.jpg|Figure 2]] summarizes the major characteristics of braided-channel deposits, including lateral relationships (block diagram in upper left); typical vertical sequence (upper right), including grain size, directional properties, [[dip]] angles, relative porosity, and sedimentary structures; sand body isopach map (lower left); and representative electric logs (lower right) at selected sites to show variation in log shape. As this diagram illustrates, the typical vertical sequence is characterized by multiple stacked fining-upward cycles of deposition (each representing deposition by a migratory channel). Directional properties within each cycle often display narrow directional spread and are fairly representative of the long-axis orientation or downstream direction of the channel. High dip angles are most often associated with large-scale cross-bedding and distorted layers.

The isopach map shows a laterally continuous sand body, often extending 20-50 km laterally in a direction perpendicular to the downslope channel direction. Most braided channels display rather uniform thicknesses across the entire sand body (averaging 15 to 25 m thick) and localized deeper sand-filled scoured pods. Log response often shows an overall blocky shape, with numerous sharp "kickouts" representing local coarse-sand-filled scours. Locally numerous fining-upward cycles can be well defined on the logs. Although distinctive cycles can often be discerned from log data, it is very likely that individual units cannot be carried laterally any great distance, and presence of the numerous thin silt and clay layers discourages thinking that reservoir continuity may extend for great dis ances. Exposures in some of the tar sands in Canada show a lack of reservoir continuity as tars are concentrated along distinct layers within the overall sand body. Potential for porosity traps is great in the braided-channel environment.

The isopach map shows a laterally continuous sand body, often extending 20-50 km laterally in a direction perpendicular to the downslope channel direction. Most braided channels display rather uniform thicknesses across the entire sand body (averaging 15 to 25 m thick) and localized deeper sand-filled scoured pods. Log response often shows an overall blocky shape, with numerous sharp "kickouts" representing local coarse-sand-filled scours. Locally numerous fining-upward cycles can be well defined on the logs. Although distinctive cycles can often be discerned from log data, it is very likely that individual units cannot be carried laterally any great distance, and presence of the numerous thin silt and clay layers discourages thinking that reservoir continuity may extend for great dis ances. Exposures in some of the tar sands in Canada show a lack of reservoir continuity as tars are concentrated along distinct layers within the overall sand body. Potential for porosity traps is great in the braided-channel environment.