Fluvial SystemsAlluvial Fan, Meandering

River, Braided River

Amy AsanumaZack St.Clair

Alluvial Fan

• Poorly Sorted Sediments with abundant gravel sized detritus

• Boulders – Sands• Cone Shaped with

network of branching distributary channels that cross the fan

Wrangell-St. Elias National Park, Alaska

Sedimentary Processes

• Debris-flow Deposits• Mud Flows• Landslides• Sheet flood• Incised-channel flow

Sedimentary Structures

• Cross beds• Steep gradient ~5-10 degrees• Building on top of itself• Coarsen Upwards

Braided River

• Poor sorting – better than alluvial fans• Gravels – Sands• Steep Channel Gradient

Resurrection River, Kenai Peninsula, Alaska

Sedimentary Structures

• Trough/Tabular Cross beds• Laminations• Sedimentary Load > Water• Fining Upwards and Repeats• Erodible Banks

Meandering River

• Sediment Load < Water• Gravels – Muds • Moderate Sorting

Owens River, CA

Sedimentary Structures

• Shallow Gradient• Fining Upwards• Ripples• Cross Beds• Bioturbidation

Oblique Dunes in a Meandering River System, Muddy Creek, Wyoming

Fossils

Stratigraphic Section

Fluvial System Example in History

• Alluvial Fan-Important in Precambrian and early Paleozoic time before land plants could provide vegetation cover to inhibit erosion

Present Day Fluvial System

• Alluvial Fan-common in areas of high relief, at the base of a mountain range, abundant supply of sediment needed

Present Day Braided River

• Extensive braided river systems are found in Alaska, Canada, New Zealand's South Island, and the Himalayas, which all contain young, rapidly eroding mountains

Works Cited

• Boggs Jr, Sam. Princiles of Sedimentology and Stratigraphy. Fifth Edition. New Jersey: Pearson Prentice Hall, 2011. 211-220. Print.