Current%20Bedforms%20PDF

Current%20Bedforms%20PDF - Bedforms and Sedimentary...

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http:// www.youtube.com/watch?v=5ouKekqiRbs&feature=related Bedforms and Sedimentary Structures
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The video shows that when fluids pass over a bed of loose grains and cause grain transport, geometric forms develop in the loose sediment on the bed These are called bedforms. Ripples are an example.
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Bedforms develop whether the flow is in water or in air Here both the sand dunes and the ripples on the dunes are eolian bedforms
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Also whether flow moves in one direction or moves in two directions Wave ripples which are due to back and forth motion of the water
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Bidirectional or oscillatory flow in water 1. What do we mean by Bidirectional flow? Sometimes referred to as oscillatory flow 2. In what depositional environments do we see oscillatory flow?
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Unidirectional flow in water 1. What do we mean by unidirectional flow? 2. In what depositional environments do we see unidirectional flow?
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Unidirectional flow in water 1. What do we mean by unidirectional flow? 2. In what environments do we see unidirectional flow?
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We are going to focus first on unidirectional flow in water Different types of bedform develop depending on: the flow conditions, particularly flow velocity and the grain size of the sediment.
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The internal structure of the bedforms is what is generally preserved in the sedimentary record and this is called a sedimentary structure. Don’t see the whole ripple – See cross-stratification
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For a given grain size, we get a characteristic sequence of bedforms as flow velocity increases. For fine to medium sand the progression of bedforms with increasing flow velocity is: no movement ripples large ripples or megaripples plane bed antidunes
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Ripples and Megaripples – common attributes: • bedforms with a triangular cross- section • crests and troughs oriented perpendicular to flow Let’s draw a simple sketch of ripples & megaripples in x-section
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• bedforms migrate downstream due to erosion in the trough, transport up the stoss side (upflow side), and deposition on the lee side transport
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• deposition occurs on the lee (downflow) side, which
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This note was uploaded on 02/23/2010 for the course -1 -1 taught by Professor -1 during the Spring '10 term at Colorado.

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Current%20Bedforms%20PDF - Bedforms and Sedimentary...

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