7_Sedimentary environments

7_Sedimentary environments - Lecture 7 Sedimentary...

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Lecture 7 Sedimentary Environments •A part of the earth’s surface, physically, chemically, and biologically distinct from adjacent terrain. defined by, fauna and flora, geology, geomorphology, climate, weather, temperature, and if sub-aqueous, the depth, salinity, and current system of the water. could be a site of erosion, non-deposition, or deposition. Erosional environments - occur in dissected mountain chains and rocky shores. Equilibria/non-depositional environments - occur both on land and under the sea - commonly preserved in the stratigraphic records as unconformities. Sedimentary Facies: •A mass of sedimentary rock which can be defined and distinguished from other by its geometry, lithology, sedimentary structures, paleocurrent pattern, and fossils (Selley 1970). The relationship between sedimentary environments and sedimentary facies Classification of Major Depositional Environments 1 CAUS E EFFE CT Proce ss Physi cal Che mical Biolo gical Sedime ntary Environ ment Erosional Non- depositional Depositional Sediment ary Facies Geometry Lithology Sedimenta ry structures Paleocurr ents Fossils Continen tal Alluvial fan Fluviatile Lacustrine Eolian Braided Meanderi ng Transiti onal (Shoreli nes) Lobate (deltas) Linear Terrigenous Mixed carbonate: terrigenous Carbonate Marine Reef Shelf Submarine channel and fan Pelagic Alluvial Fan Environment lots of coarse particles usually sandstone and conglomerate poor sorting deposited by high energy floods or mudflows cone-shaped typically found in tectonically active regions (rifting continental grabens and foreland basins) What is an alluvial fan? •non-marine sedimentary body • a fan-shaped deposit
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How it is formed? •When mountains shed sediment off their flanks, streams carry it away as alluvium. •A mountain stream carries lots of alluvial sediment easily when its gradient is steep and energy is abundant . Where are alluvial fans found? •They can be found in places where the stream or mass-flow emerges from a valley into a basin. Fluvial Environment Three ways streams transport sediments: • in solution (dissolved load) • in suspension (suspended load) • along the bottom of the channel (bedload) Type and amount of material in suspension is controlled by: • water velocity • settling velocity of each grain Factors affecting settling velocity • size • shape • specific gravity bedload composed of coarser particles - cannot be carried by suspension bedload particles move along by: • rolling • sliding • saltation Ability of streams to carry sediments is described by: • capacity - maximum load of sediment that a stream can transport • competence - measure of the maximum size of particles it is capable of transporting A longitudinal profile can be divided in three parts: -drainage system (tributary, head) -transport system -distributary system (mouth) Meandering System consist of one single channel and thalweg low gradient and high sinuosity
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This note was uploaded on 11/20/2010 for the course LIR 30 taught by Professor Thornley,k during the Spring '08 term at Santa Rosa.

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7_Sedimentary environments - Lecture 7 Sedimentary...

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