River Systems Four types, braided, meandering, anastamosing and straight


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River Systems


Grand Canyon, erosion



River incision in Indus Suture Zone



River types



Links between sinuosity and slope



Anastomosing river stratigraphy



Braided rivers

  • Typically developed in mountainous terrain on higher gradients. Typified by high degree of seasonality. Permanent channels with ripple crossed bedded sands develop during periods of low flow. These channels meander between sand bars that are active only during flood stage, these develop larger scale cross beds. Sediments are typically sandy and pebbly, usually moderate to well sorted, texturally moderately mature. Ancient example- Devonian Old Red Sandstone. Modern example - Saskatchewan River.



Braided River Model



Braided River Model and stratigraphy



Braided River



Braided geometry, Matanuksa River, Alaska



Braided River, Nubra, India



Braided River, Shyok River, India



Anastomosing River, Indian foreland



Channel sandstone facies



Meandering Rivers

  • Typically developed in coastal plain areas, lower gradient. More continuous flow, finer grained sediment than braided. Channel sediment is marked by the deep stream migration of meanders and the construction of cross laminated sands on point bars in the inner bends of meanders. Channels are separated by levees from flood plains that are comprised of finer grained muds and sands deposited after breach of levee during flood stage, usually vegetated. Flood stage can lead to cut-off of meanders and break-through of river.



Meandering Rivers, contd.

  • Abandoned meanders become Ox-bow lakes, filled by clays. Meandering river deposits typified by fining-upward stratigraphy. Sediments are typically sandy, silty and clayey. Well sorted. Sandstones form isolated channels in finer background. Ancient example- Jurassic, Brent Group of North Sea. Modern example - Brazos and Mississippi Rivers.



Meanders in the Amazon Basin



McKenzie River meanders and glacial lakes



Ox Bow Lake/meanders



Point bar deposits



Braided versus meandering river type sections



Impact of sinuosity on stratigraphy



Channel migration-Ganges



Ganges and Himalaya thrust front



Indus River and tectonic uplift, Kohat Plateau



Effect of tectonism on location of rivers



Fluvial facies examples



Indus Molasse, fluvial sandstone



Slumped sediment, modern Indus River



Climbing wave ripples, Indus River



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