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GEOL 440Sedimentology and stratigraphy:

processes, environments anddeposits

Lecture 5: Bedforms andsedimentary structures inunidirectional flows movie

http://bedforms%20at%20cremation%20creek.mov/http://bedforms%20at%20cremation%20creek.mov/

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Today: UNIDIRCTIONAL FLOW BEDFORMS

character?formation? flow type?

palaeoenvironment?

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Uses of

sedimentarystructures

Rogers flute imagedepositional environments palaeoflow - e.g.magnitude/direction way-up of beds affects porosity &permeability (important fordiagenesis/fluid flow)

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Depositional Sedimentary

Structures

Bedform: a morphological featuregenerated by sediment movement

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Depositional Sedimentary

Structures - Unidirectional flowsBedform

phasediagram

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Ripples & dunes:

flow transverse bedforms

Ripples: height ~4 cm (height

dependent on flow depth);wavelength dm - m

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ripples

flow

steepleeside

lower-anglestoss side Leeside: angle-of-

repose of sediment

(~20-35)

Stoss side: (~5-10)

Asymmetrical bedforms

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flow

coarsersand intrough

sinuous crestline

lee

stoss

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Flow over transverse bedforms

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Transverse bedforms (ripples/dunes):

terminology

Bridge and Demicco, 5.35

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Transverse bedforms (ripples/dunes):

planform shape

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deposits: cross-stratification

but to get preservation you need aggradation

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Quicktime Rubin 2Dla

An ESSENTIAL and SUPERB

and ADDICTIVE! website:http://walrus.wr.usgs.gov/seds/bedforms

http://movie%201%20fig.05/http://fig5new%20rubin%202d%20subcritical.mov/http://movie%201%20fig.05/http://fig5new%20rubin%202d%20subcritical.mov/http://movie%201%20fig.05/

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deposits: cross-stratification

planarcross-stratification

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trough cross-stratification..here a desert dune

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planar & trough cross-stratification

Bridge and Demicco, 5.60

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..what we see preserved is a function of

migration rate andaggradation rate

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and stosssidedeposits

leesides

( aggradationrate high)

d

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planar cross-stratification

erosion(bounding)surfaces

between dunecross-sets

dunes

ifi i i l

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cross-stratification: set terminology

Lindholm - 1.17 & HO

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the transition to uspb

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Bridge and Demicco, 5.64

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and eventually an upper-stage plane bed

t l b d

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upper-stage plane beds

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uspb in a flume.

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but on uspbs

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upper-stage plane beds: in section

parallel laminae(mm thick; cm-m long)

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uspb laminae - formation by bedwaves

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but turbulentimpacts on bed existto produce primarycurrent lineations

(pcl)

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upper-stage plane beds: in plan

primary current lineationparallel to flow

(mm wide; cm long)

antidunes

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antidunes

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Note:lower stage plane beds

only for sandswhat aboutgravels?

Transverse ribs

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Transverse ribs

Pebble Clusters

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Pebble Clusters

Pebble Clusters

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Pebble Clusters

..and bedform superimposition

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7

9050100150200250300

5

m

flow

.. f m p mp

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Things to take away from this lecture.

The BEDFORM PHASE diagram2D and 3D transverse bedforms/structures

Bedform transitionsMajor flow processesThink of palaeoflow directions

Reading: B&D: Chapter 5, p.157-192Leeder: Chapter 7Collinson and ThompsonBoggs Chapter 4, 74-92

Rubins websiteyoull be hooked!