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Sedimentary Rock
http://soest.hawaii.edu/coasts/cgg_main.html
Sedimentary Rocks are the product ofsediment deposition, diagenesis,and lithification
Oceans rise and fall, lakes come and go, streams run and disappear, desertsbecome forests and forest become swamps…all these changes will be recordedin sedimentary rocks
Sedimentary rock contains sediment grains, cement holding them together,and empty space called “pores”
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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 norounding
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 formlayers or strata…each layer recordslayers or strata…each layer recordsa depositional event
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Ripple marks
modern
Mud cracks
ancient
Sediment becomes sedimentary rock…the texture and compositionof the sediment determine the type of sedimentary rock
Two types of sedimentary rock –
Clastic Sedimentary Rock –made of pieces of broken crust
Biochemical Sedimentary Rock –made of precipitated minerals
Conglomerate Rock Salt
Clastic Sedimentary Rock
Conglomerate/Breccia –gravel texture
Biochemical Sedimentary Rock
Limestone –CaCO3 composition
Sandstone –sand texture Chert –
SiO2 composition
Shale –silt/clay texture
Coal –Carbon composition
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Pressure forms coalHow does coal form?
Coal strip mine… Environments of depositionSedimentary texture
Sediment compositionGlobal Climate history
Clastic – Biochemical sedimentary roxBreccia/Conglomerate
SandstoneShale
LimestoneChertCoal
How does coal form?Sedimentary structures
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But why was there an ice age?
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Ice stores O16 so that oceans are O16
depleted in an ice age
+ O18/O16 -
Periodicity of 100,000 yrsCaCO3
Layer by layer sampling of plankton reveals oxygenisotope record
y , y41 kyrs
21 kyrs
100 kyrs
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These were madeduring an ice age!
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