UNIVERSITY OF SOUTH ALABAMA
Last time we covered…
Proterozoic Evolution Discussion
(Isabella)
MAS 603: Geological Oceanography
Proterozoic Beasties
Lecture 12: Sedimentary Facies
(Beaches)
1)
2)
3)
Eukaryotes (Acritarchs)
Metazoans (Ediacarin Fauna)
A visit to the Burgess Shale
Proterozoic Fossils
Proterozoic Fossils
The first eukaryotes appeared around 2 GA. Archritarchs were
small, single celled silica beasties that floated in the oceans
(pelagic). They peaked in abundance at 750 MA and then went
away…
Another big change in the Proterozoic was the appearance of
the first Metazoans
0.1mm
Proterozoic Fossils
5 cm
The Cambrian Explosion
Burgess Shale Fauna
Chengjiang Fauna
What we know about the early
development of all of the
current phyla is limited to sites
where we have lots of beasties
preserved
http://www.snowballearth.org/end.html
http://arjournals.annualreviews.org/na101/home/literatum/publisher/
1
The Burgess Shale
Today’s Agenda
Sedimentary Facies
1)
2)
3)
Facies versus depositional environments
Walther’s Law
Beaches
http://home.earthlink.net/~airdpacoima/sitebuildercontent/sitebuilderpictures/burgess__s.jpg
Sedimentary Facies
There are literally dozens of different depositional environments
that cover every imaginable marine and non-marine situation.
Sedimentary Facies
And in most cases, there are multiple varieties of each basic
environment of deposition.
For example, rivers come
in at least 3 “flavors”:
http://earthsci.org/mineral/rockmin/sed/clastics.gif
1) Meandering
2) Braided
3) Anastimosing
Sedimentary Facies
Ultimately, depositional
environments are the sum of
their various components and
each of those components are
distinguished from one another
of the basis of geological
characteristics.
The components that
collectively define depositional
environments are called
sedimentary facies (or just
facies).
Sedimentary Facies
Defining characteristics for facies include:
™
™
™
™
™
™
Grain size
Lithology
Mineralogy
Paleontology
Sedimentary and biogenic structures
Palaeocurrent orientations
™
™
™
™
™
™
Obvious sedimentary trends
Bedding (Bed thickness)
Lamination
Bedding contacts
Lateral variations
Anything else that you can think of
http://www.kgs.ku.edu/PRS/publication/ofr2003-82/gif/figure1_06.gif
2
Facies modeling is
best done back at
your lab/office
where you can
consider your data…
…and drink a few
beers to really help
you think about your
data…
Facies Modeling
Prograding Open Beach
Facies Modeling
…and interpret what your data are implying
Sedimentary Facies
Facies can, and will, repeat
vertically through a
sedimentary sequence…
Sedimentary Facies
Facies can, and will, repeat
vertically through a
sedimentary sequence…but
may vary in character as a
result of environmental
and/or evolutionary change
through time
shoreface (5m)
swash zone
(0m)
shoreface (5m)
e.g., fossil content.
offshore (10m)
Sedimentary Facies
Walther’s Law
Facies may also change laterally through a deposit as a result
of changing environments with distance at the same time.
3
Walther’s Law
Named after Johannes Walther (18601937), a German geologist, who in 1894,
noted a fundamental relationship between
the vertical and lateral distribution of
facies.
Walther’s Law
Sedimentary environments that
started out side-by-side will end up
overlapping one another over time
due to transgressions and
regressions.
Walther’s Law
Sedimentary environments that
started out side-by-side will end up
overlapping one another over time
due to transgressions and
regressions.
The result is a
vertical sequence of
beds. The vertical
sequence of facies
mirrors the original
lateral distribution of
sedimentary
environments.
Walther’s Law
Sedimentary environments that
started out side-by-side will end up
overlapping one another over time
due to transgressions and
regressions.
Walther’s Law
Walther’s Law
But…
And…
• Walther's Law can only apply to sections without unconformities.
• Walther's Law can only apply to a section without subdividing
diachronous boundaries [e.g., transgressive surfaces (TS),
maximum flooding surfaces (mfs) etc.]
Tan and white layers
of Mesozoic Era
Period Pio Nono
Formation
in Georgia's Coastal
Plain Province.
http://itc.gsw.edu/faculty/daskren/fallline.htm
Aside
4
Sequence Stratigraphy
Sequence Stratigraphy
First utilized by the petroleum industry to interpret depositional
surfaces on seismic sections. Now used by all geologists to explain
vertical and lateral changes in sediment rock distribution.
First utilized by the petroleum industry to interpret depositional
surfaces on seismic sections. Now used by all geologists to explain
vertical and lateral changes in sediment rock distribution.
http://strata.geol.sc.edu/exerices/seismic/07SeqNo_LST_TST_HST.jpg
http://strata.geol.sc.edu/exerices/seismic/07SeqNo_LST_TST_HST.jpg
Sediment is deposited in distinct systems tracts.
Sequence Stratigraphy
Sequence Stratigraphy
First utilized by the petroleum industry to interpret depositional
surfaces on seismic sections. Now used by all geologists to explain
vertical and lateral changes in sediment rock distribution.
http://strata.geol.sc.edu/exerices/seismic/07SeqNo_LST_TST_HST.jpg
The 3 controls on system tract architecture are:
1) sea level position, 2) sediment input, 3) accommodation space.
Sedimentary Environments: Beaches
™Factors promoting beach development
™Beach profiles
™Beach facies & sedimentary sections
Ultimately, sedimentary “packages” are bounded by specific surfaces
(reflectors in the seismic lines), and this is where/when Walther’s
Law breaks down
Factors controlling beach development
™Steady supply of sand to the shoreline, by river,
delta or longshore drift
™Wave dominated setting (medium to high wave
energy is best; low tidal energy necessary)
™Stable, low gradient coastal plan and continental
shelf gradient
32,000 km of shoreline meet these requirements; best
studied beaches are along the US eastern and Gulf
coasts
5
Wave action
Wave action
Wind
Orbicular motion
Wave base
From Komar, P.D., 1998. Beach Processes and Sedimentation. Prentice Hall, New Jersey, 544p.
From Komar, P.D., 1998. Beach Processes and Sedimentation. Prentice Hall, New Jersey, 544p.
Overall beach dynamics
Longshore drift
From Walker, R.G. and James, N.P. (1992). Facies Models: Response to Sea Level Change. Geological Association of Canada, 409p.
From Walker, R.G. and James, N.P. (1992). Facies Models: Response to Sea Level Change. Geological Association of Canada,
409p.
Hydrodynamic
zones
Overall beach dynamics
Sedimentary
Facies
From Blatt, H, Middleton, G. and Murray, R., 1980. Origin of Sedimentary Rocks. Prentice Hill, 782 p.
From Komar, P.D., 1998. Beach Processes and Sedimentation. Prentice Hall, New Jersey, 544p.
6
From Walker, R.G. and James, N.P. (1992). Facies Models: Response to Sea Level Change. Geological
Association of Canada, 409p.
Beach Facies
From Walker, R.G. and James, N.P. (1992). Facies Models: Response to
Sea Level Change. Geological Association of Canada, 409p.
Beach Facies
Facies distribution on beaches is a ballet
between shoreline advance
(progradation) and retreat.
Beach change = construction-destruction
Beach
Facies &
Structures
From Walker, R.G. and James, N.P. (1992). Facies Models: Response to
Sea Level Change. Geological Association of Canada, 409p.
Beach Facies
Galveston Island; a prograding beach
From Walker, R.G. and James, N.P. (1992). Facies Models: Response to Sea Level Change.
Geological Association of Canada, 409p.
Beach Facies
From Walker, R.G. and James, N.P. (1992). Facies Models: Response to Sea
Level Change. Geological Association of Canada, 409p.
Sea level as a control on beach development
From Walker, R.G. and James, N.P. (1992). Facies Models: Response to Sea Level Change. Geological Association of
Canada, 409p.
7
Next Time
1. Monday: Shelf Sedimentation
2. Wednesday: Submarine Fans
8