geol 440 2011 lecture 5web
TRANSCRIPT
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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!