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Meandering fluvial reservoirs (view source)
Revision as of 18:16, 31 July 2015
, 18:16, 31 July 2015no edit summary
==Geometry of meander belts==
==Geometry of meander belts==
Meandering rivers deposit sand and mud within well-defined meander belts. The appearance of a meander belt in plan and cross section is of a complex labyrinth of interlocking sand bodies on the scale of hundreds of meters, embedded within varying volumes of mud ([[:file:M91FG173.JPG|Figure 2]]). The mud can make up 50% or more of the volume. Channel features, where they survive, tend to be plugged with clay ([[:file:M91FG173.JPG|Figure 2]], [[:file:M91FG174.JPG|Figure 3]]).
Meandering rivers deposit sand and mud within well-defined meander belts. The appearance of a meander belt in plan and cross section is of a complex labyrinth of interlocking sand bodies on the scale of hundreds of meters, embedded within varying volumes of mud ([[:file:M91FG173.JPG|Figure 2]]). The mud can make up 50% or more of the volume. Channel features, where they survive, tend to be plugged with clay ([[:file:M91FG173.JPG|Figure 2]], [[:file:M91FG174.JPG|Figure 3]]).
Gibling<ref name=Gibling_2006>Gibling, M. R. 2006, [http://jsedres.geoscienceworld.org/content/76/5/731?related-urls=yes&legid=jsedres;76/5/731 Width and thickness of fluvial channel bodies and valley fills in the geological record: A literature compilation and classification]: Journal of Sedimentary Research, v. 76, p. 731–770.</ref> provided data on width and thickness relationships for fluvial systems in various settings from Quaternary and older outcrops (Table 1). He found that meandering rivers do not generally create thick sedimentary packages. The maximum thickness for meandering river deposits in his database is only 38 m (124 ft), with 4–20 m (13–65 ft) as a common thickness range. Gibling makes the comment that despite their familiarity in the modern landscape, meandering river deposits probably constitute only a minor portion of the fluvial rock record by comparison to braided systems. This may be because the organized flow patterns associated with meandering rivers rarely persist for long periods.
{| class = "wikitable"
|-
|+ {{table number|1}}Width and thickness relationships of fluvial sediments in various settings.<sup>1</sup>
|-
! Depositional environment || Thickness || Width || Width/thickness ratio
|-
| Braided and low sinuousity rivers || 1-1200 m (3-3937 ft); most < 60 m (197 ft); common range 5-60 m (16-197 ft) || 50 m-1300+ km (164 ft-808+ mi); many > 1 km (0.62 mi); common range 0.5-10 km (0.3-6 mi) || 15-15,000+; some > 1000; common range 50-1000
|-
| Meandering rivers || 1-38 m (3-125 ft); common range 4-20 m (13-65 ft) || 30 m-15 km (98 ft-9 mi); most < 3 km (1.8 mi); common range 0.3-3 km (0.1-1.8 mi) || 7-940; most < 250; many < 100; common range 30-250
|-
| Delta distributaries || 1-35 m (3-115 ft); most < 20 m (65 ft); common range 3-20 m (10-65 ft) || 3 m-1 km (10 ft-0.6 mi); most < 500 m (1640 ft); common range 10-300 m (33-984 ft) || 2-245; most < 50; many < 15; common range 5-30
|-
| Channels in eolian settings || 1-19 m (3-62 ft) || 2.5-1500 m (8.2-4921 ft); most < 150 m (492 ft) || 1-90; most < 15
|-
| Valley fills on bedrock unconformities || 12-1400 m (39-4593 ft); most < 500 m (1640 ft) || 75 m-52 km (246 ft-32 mi); most < 10 km (6 mi) || 2-870; highly variable; mainly 2-100
|-
| Valley fills within alluvial and marine strata || 2-210 m (6-689 ft); most < 60 m (197 ft) || 0.1-105 km (0.06-65 mi); common range 0.2-25 km (0.1-15 mi) || 4.6-3640; highly variable; common range 10-1000; many from 100 to 1000
|-
| colspan="4" | <sup>1</sup>''From Gibling<ref name=Gibling_2006 />, Journal of Sedimentary Research. Reprinted with permission from, and © by, the SEPM (Society for Sedimentary Geologists).''
|}