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Transcript
Sedimentary Rock
http://soest.hawaii.edu/coasts/cgg_main.html
Sedimentary Rocks are the product of
sediment deposition, diagenesis,
and lithification
Oceans rise and fall, lakes come and go, streams run and disappear, deserts
become forests and forest become swamps…all these changes will be recorded
in sedimentary rocks
Sedimentary rock contains sediment grains, cement holding them together,
and empty space called “pores”
To understand Earth history, a geologist seeks to interpret the
“Environment of Deposition” of a sedimentary rock…this reveals
something about changes occurring on Earth’s surface
Eolian Environment – grains of uniform size “well sorted”
Coastal Environment – grains coarser and of mixed size
Stream Environment – grains much coarser and “poorly sorted”
Glacial Environment – grains very coarse
with no sorting, but
usually rounded
Landslide Environment – grains very coarse
with no sorting, with no
rounding
Marsh/Mudflat Environment – grains very fine
Evaporite environment – chemical sediments
Reef environment – biological sediments
Deep sea environment?? – Plankton sediment and
clays from land
Sedimentary Structures….
Cross-beds – former dunes
Sedimentary rocks tend to form
layers or strata…each layer records
a depositional event
Ripple
marks
modern
Mud
cracks
ancient
Sediment becomes sedimentary rock…the texture and composition
of the sediment determine the type of sedimentary rock
Two types of sedimentary rock –
Clastic Sedimentary Rock –
made of pieces of broken crust
Conglomerate
Biochemical Sedimentary Rock –
made of precipitated minerals
Rock Salt
Clastic Sedimentary Rock
Biochemical Sedimentary Rock
Conglomerate/Breccia –
gravel texture
Limestone –
CaCO3 composition
Sandstone –
sand texture
Chert –
SiO2 composition
Shale –
silt/clay texture
Coal –
Carbon composition
How
does
coal
form?
Pressure forms coal
Coal strip mine…
Environments of deposition
Sedimentary texture
Sediment composition
Global Climate history
Clastic – Biochemical sedimentary rox
Breccia/Conglomerate
Sandstone
Shale
Limestone
Chert
Coal
How does coal form?
Sedimentary structures
But why was there an ice age?
Ice stores O16 so that oceans are O16
depleted in an ice age
+ O18/O16 -
Periodicity of 100,000 yrs
CaCO3
Layer by layer
sampling of plankton
reveals oxygen
isotope record
41 kyrs
21 kyrs
100 kyrs
These were made
during an ice age!