Lecture 2 - Sedimentary course notes PDF

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Lecture 2: Bedforms- Bedforms are sedimentary structures that form by the interaction between a flow and sedimenton the bed- Bedload transport is defined as that during which sediment particles are in contact with the bedat least some of the time. It can occur by traction/rolling when particles rema...

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Lecture 2: Bedforms

- Bedforms are sedimentary structures that form by the interaction between a flow and sediment on the bed

- Bedload transport is defined as that during which sediment particles are in contact with the bed

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at least some of the time. It can occur by traction/rolling when particles remain in direct contact with the bed all the time or by saltation when particles are entrained into the flow before dropping back onto the sediment bed once again. Hjulstrom curve flows the velocity over grain size and see the points where sediments are: deposited, transported or eroded Lower flow regime = everything blow subaqueous dunes Upper flow regime = antidotes and upper flat bed

Bed-load transport: - Bed-load transport can be described in terms of mean stream velocity, depth, particle and fluid parameters (density, shape, size) and surface roughness - Can be observed from flume tanks - The Boundary layer — major thing that determines the nature of the bed forms, forms from interference - Fluids tend to flow in channels and pipes — are contained - Surfaces that constrains the flow causes the boundary layer - Interaction between walls, floors and pipes and cause velocity to vary - Man made structures such as pipes able us to predict contacts with pipes compared to natural structures - Atoms that are closest to floors/walls stick to it and not move — velocity is slowest - Next layer below is slowed down by the stationary ones - Third layer is slowed by the second later until there is a point where the flow isn't effected by the solid — fastest flow - Increase in velocity upward — the solid retarded layer = boundary layer - The free moving layer = free/ external stream - Prandtl experiment is used to observe the flow - Contact with a bed will slow the flow

- Any grain that is >0.6mm is always rough - Any grain that is 0.6 mm grainsize with no bursts or streaks. Upper stage plane beds: - Upper stage plane beds form at higher velocities for all grain sizes where welldefined planar laminae 5-20 grain sizes thick, and elongate ridges parallel to the flow direction (primary current lineation) form as the result of streaks. Ripples: - Current ripples formed when the critical boundary stress for bedload motion is exceeded, grain motion starts with small numbers of grains moving in little clusters — These clusters will form local irregularities in the bed that can lead to boundary layer separation from smooth boundaries, these are to grow and spread across the bed through time - Stream lines will by pass the trough as low energy area - Ripples — formed from boundary layer processes and formed with any depth of flow - Anything 5-30mm high and wavelength of 500-400mm - Wavelength of the ripple is dependent on grain size - As they move they generate cross bedding — ripples migrate forward Cross bed stratification: - Left behind from the ripples - Cross stratification is any layering in sedimentary rock or sediment that is orientated at an angle to the depositional (near horizontal) surface — can be high angle or low angle — velocity dependent — more rapid = less steep - For ripples this is referred to as cross lamination — max height is...