WVU POLS 103 - test 3 (12 pages)

7 1 What sedimentary enviroments occur on land Main sedimentary elements on land o Mountain enviroments steep slopes developed on bedrock Erosion is vigourous on slopes and provides a large amount of sediment such as large angular blocks Once its produced it can be transported to other settings o Streams and rivers and mountains typically have steep gradients and are confined by bedrock canyons As streams and rivers leave the mountains they carve channels that split apart and rejoin This is described as fluival o High mountains develop glaciers as the snow melts down the mountain carrying the sediment and water and the sediment in the water is released at the terminus end of glacier o In dry climates wind picks up and moves fine particals Movement of the grains form sand dunes which in some places can go for hundreds of kms o Flood plains of meandering rivers are built layer upon layer by mud and sand carried by flood waters o When stream or river enters a body of water its current slows which causes most of its sediment to spread out and be depositied This forms a delta o Lakes contain a range of enviroments Some are always filled with others but others are completely dry when water seeps in or evaporates o Wetlands for adjacent to lakes and contain an abundance of vegetation which may become an important component of sediment 7 2 What sedimentary enviroments are near shorelines and in oceans Skdf o o o o o o o o Beaches are stretches of coastline where sedimentary has accumulated Water near the shoreline may be sheltered by offshore reefs or islands Sheltered water is called a lagoon and is commonly shallow and possibly warm The creatures construct reefs which can parallel the coast and circle islands or form irregular mounds or pllatforms Away from coastline many landmasses are flanked my contentintal shelves and slopes consisting of layers of mud and carbonate minerals Deep ocean parts commonly receive less more fine sediment than areas closer to land And its sediment is mostly made up of single cell organisms Coastal dunes are sandy dunes that are inland from beaches These dunes commonly form where sand and finer sediment have been blown and reshaped by the wind Low areas off the shore that are flooded by the sea during hightide and are exposed to the air during low tide are called tidal flats Submarine deltas extend in some places for ten kms offshore The material on the delta may be unstable and can slide into deeper water 7 3 Where do clasts come from Describe the main processes of physical and chemical weathering o Physical weathering is the physical breaking apart of rocks that are exposed to the environment Near surface fracturing many processes on or near the surface break rock into smaller pieces Fractures result when rocks expand as they are uplifted toward the surface and are exposed to less pressure Frost and mineral wedging rocks can be broken as water freezes and expands in fractures Crystals of salt and other minerals that grow in thin fractures can also cause rocks to break apart Thermal expansion rocks are heated bby wildfires and sun as rocks heat up they expand often irregularly and may crack This is the least important of physical weathering Biological activity roots can grow downward into fractures and pry rocks apart o Chemical weathering includes several types of chemical reactions that effect a rock by breaking down minerals causing new minerals to form or by removing soluable material from the rock Dissolution some minerals are soluable to water esp the weakly acidic waters These minerals along with rock and sediment that contain them can dissolve and be carried away by streams or rivers Oxidation minerals containing iron are unstable when exposed to earths aatmosphere These minerals can combine with oxygen to form oxide minerals which compose the reddish and yellow materials that form when metal rusts Hydrolysis when sylicite minerals are exposed to water esp water that is somewhat acidic this process commonly converts original materials into clay minerals and produces leftover dissolved materal that is carried away by water Biological reactions decaying plants produce acids that can attack rocks and some bacteria consumes certain parts of rocks These biological processes cause the minerals to break down into their constituent elements 7 4 What are the characteristics of clastic sediments describe how sediments are classified according to size sorting and shape of clasts o Size largest are boulders Cobbles are smaller than boulders Sand is smaller than cobbles Clay is smaller than sand o Shapes angular have sharps corners and edges Rounded have smooth curves edges like eggs Explain four factors that influence the type of sediment that is transported o Steepness of the slope o Strength of the current o Sediment supply river beach can only transport available sediment o Agents of transport eg wind can carry sand but not a boulder 7 5 What type of rocks to clastic sediments form Describe or diagram the classification of common sedimentary rocks o Read pg 180 o Describe what happens to clastic sediment as it becomes buried and converted into rock Compaction as sediment is buried beneath more sediment or other materials increasing pressure pushes clasts together Sand grains and clay particles o Summarize the natural cements that are common in sedimentary rocks There are 4 main types of natural cements Calcite common in sandstone Holds them together moderately well but is easily redissolved Silica forms strong cement that forms strong grains Clay minerals cement together larger grains including sand Iron oxides precipitate from water as a natural cement between the grains Gives sediment deposited on land a reddish color 7 6 What Are Nonclastic Sedimentary Rocks and How Do They Form Describe how limestone forms o Limestone forms inorganically by precipitation from water or through other chemical reactions Describe how some sedimentary rocks form from the accumulation of plant materials o Plant debris can accumulate in great thickness in wetlands where it partially or wholly decays and can be compacted into sedimentary rock 7 11 How do carbonate rocks form Characteristics of limestone o Typically grey Ranges from almost white to dark grey Soluble dissolved appearance Frequently includes fossils of shells corals fish and other marine organisms Characteristcs of dolostone o Made mostly of the mineral dolomite Resembles limestone but is more resistant and