Lecture 11
Sedimentary Environments
Goals
1. understand the relationship between
sediments, the structures that the contain
and the environment in which they were
deposited
2. Recognize the environment from rock
outcops
3. Use knowledge of environment to
constrain tectonic history
Depositional Environments
Load
Stream environments
Hjulstrom curve
Alluvial fan
Alluvial fan deposits
Meandering River
Meandering river
deposits
Flood plain
Flood plain deposits
Deltas
Growth of Deltas
distributary
levy
bay
distributary
mouth bar
Mississippi Delta
Shoreline Environment
Sediment transport by wave action
Wave Action
Longshore current
Example of migraton
Barrier Island
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
Bay
Barrier
Island
Continental Shelf
Why so flat?
Continental Slope Environment
Sediment transport by mass wasting
“turbidity currents”
Continental slope
Continental rise
Most of the sea floor…boring!
Turbidity Currents
Grand Banks Turbidite
Turbidites
transport
sediment to
great
distances
offshore
Turbidites in core
Bouma Sequence
Ancient Turbidites
Wind-blown environment
Dominated by sand dunes
dune
Dune transport
Navajo Sandstone – dune deposit
Dune sediments
foam
Coarse grained environments
Fine grained environments
Biogenic
reefs
Bahamas
Buried reef on continental margin
Bioclastic Limestone
Fine-Grained
Limestone
Deep sea limestones will not
have visible fossils, because
they are made up of the shells of
little dead bugs like these:
foraminifera.
This specimen
(viewed by scanning electron
microscope) is about
100 microns long
(0.1 millimeter).
Coccoliths – another type of
organisms with a CaCO3 test
Dover
Deep water marine environment
Evaporites
Calcite, halite and gypsum are
common precipitates from
dried lakes in arid
environments.
the white is halite, the red are
bacteria that love salt
Owens Valley, CA
Evaporites in Death
Valley
Martin G. Miller
Evaporites formed during rifting
Restricted basin: more
evaporation than inflow
Limited sea
water
evaporation
Very salty water
Deposition of evaporites
Limited river
water
No hole
no deposition
Processes that create holes
rifting
faulting
thermal subsidence
glacial
ocean growth
Etc.