River Systems

Four types, braided, meandering, anastamosing and straight

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