Depositional Environments: L4 Chapter 8 PDF

Transport and Deposition of Sediment Sediment is transported by: Water Figure 8.5 diagram only Wind Ice Mass wasting The Navajo Sandstone The Wave Navajo sandstone formation i...

Transport and Deposition of Sediment Sediment is transported by: Water Figure 8.5 diagram only Wind Ice Mass wasting The Navajo Sandstone The Wave Navajo sandstone formation in Arizona: © Gb11111 Large exposure of pink and white Navajo Sandstone on Zion's east side NPS photo/Adrienne Fitzgerald Transport and Deposition of Sediment Figure 8.6 – Deposition of sediment Deposition, the process of laying down of sediment; occurs on land and in the ocean Many different environments exist on the surface of the earth and each one will have typical types of sediment (facies) associated with it. We will now look at each environment and the types of sediment which accumulate in it starting with upland areas and working our way to the deep ocean. Depositional Environments, Land Four principal sites of deposition on land: Margins of glaciers In streams Figure 8.7(a) – Glacier margin In Lakes Wherever wind blows strongly and intermittently Glacier margin >  Alluvial fan, braided river, meandering river, glacial, sand dune, playa lake and glacial deposits Alluvial Fan River Systems Braided stream with gravel bars  The braided Waimakariri river in New Zealand. The Cauto River in Cuba. Note the sinuosity in the river, which is meandering. https://www.bbc.co.uk/bitesize/guides/z6jx382/revision/3 https://www.bbc.co.uk/bitesize/guides/z6jx382/revision/4 Floodplain Glacial Depositional Environments Land Playas (dry lakebeds) Dunes, formed by wind transport Figure 8.7(c) - Playa Figure 8.7(d) - Dunes Playa Lake Deep Springs Lake, eastern California. As the lake dries, it leaves behind evaporites. John Stan Coats  Depositional Environments Land In dry windy environments, eolian (wind) processes dominate Eolian sediment Figure 8.7(d) - Dunes Sediment that is carried and deposited by wind Loess Type of wind-blown sediment Coastal Deposits Depositional Environments In and Near the Ocean Sediment can be deposited in and around the edges of the ocean Typically occurs where current velocity decreases Figure 8.9(a) - Estuary Estuary: A semi-enclosed body of coastal water, in which fresh water mixes with seawater Depositional Environments, Land Delta, a sedimentary Figure 8.7(b) -Delta deposit, commonly fan- shaped, that forms where a stream enters a standing body of water The Mississippi River’s deltaic plain begins near Baton Rouge, Louisiana Ancient Deltaic deposits Depositional Environments In and Near the Ocean Beaches: quartz is the most common Carbonate reefs accumulate biogenic component of beach sand (calcium carbonate) sediment Figure 8.9(b) - Beach Figure 8.9(c) – Carbonate shelf Beaches Barrier Islands Barrier Islands, a coastal landform and a type of dune system, are exceptionally flat or lumpy areas of sand, that are parallel to the mainland coast. Origin? waves transport sand landward until a sand bar is formed when the sand bar reaches near sea level, waves will break over the bar, scour and deposit… longshore drift, storms etc.. Arid tidal flat In warm coastal areas shell debris and reefs commonly dominate the sediment When turned to rock this will produce? Photograph by Luis Marden Illustration courtesy USGS Limestone! We will finish by looking at environments in the deep ocean. Depositional Environments In and Near the Ocean Continental Slopes and Abyssal Plains Thick deposits found at the foot of a continental slope, created by turbidity currents Turbidity current: A turbulent, Figure 8.9(d) – Deep-sea turbidities gravity-driven flow consisting of a mixture of sediment and water Conveys sediment from the continental shelf to the deep sea The Grand Banks turbidity current in 1929 An earthquake that occurred south of Newfoundland caused loose sediment on the continental slope to move in a submarine landslide Submarine cables were broken up to 600 Km downslope Based on the times at which the transmissions ceased the maximum speed of the turbidity current was estimated at about 95 Km/h Approximately 100 Km3 of sediment was moved and eventually spread over an area of 100 000 Km2 Plate Boundaries Divergent Plate Boundaries Rift valleys: A linear, fault-bounded valley along a divergent plate boundary or spreading center Plate Boundaries Convergent Plate Boundaries Continental Collisions Plate Boundaries Pillow lavas in the Oman Ophiolite. Convergent plate boundaries Collisional type Subduction type Back-arc basin Accretionary wedges Syracuse University Ophiolites