Multidirectional Flows - Stratigraphy - Lecture Slides, Slides of Geology

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GEOL 440

Sedimentology and stratigraphy:

processes, environments and

deposits

Lectures 6 & 7: Flow, bedformsand sedimentary structures inoscillatory and multidirectionalflows

Today, aim to examine: •Main flow features

in oscillatory boundary layers •Sediment transport under waves •Bedforms and sedimentary structures under oscillatoryflows •Combined flows

(oscillation and superimposed unidirectional

flow) •Multidirectional flows

(linked to shelf storms sometimes?)

h

λ/2) y = λ/ Rick Cheel Brock U

Rick Cheel Brock U (λ/20 < h < λ/2) h < λ/

Wave Orbits Deep water wave (h> λ

C=1.

λ Shallow waterwave C=

gd where C is celerity(speed)

Stoke’s Drift

Unidirectional Component A unidirectionalcomponent

Bedform Phase Diagram 0.15- 0.22mm sand T = time taken for a wave to travel 1 wavelength i.e., T= λ /C What bedforms are generated under short-period waves?? Wave ripples

Types of Oscillation Ripple

Wave

Ripples

• Boggs, Fig. 10.
• Wave Ripples

Cross-lamination types In cross-section some wave ripples can look very similar to unidirectional ripples BUT………………….

draping & undulating boundaries - crestlines frequently bifurcate in planform - Up to 25 cm high - Ripple index ~6-7 rather than ~8-

As always, need to account for aggradationrate and bedform migration