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”

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….

Sedimentary rocks tend to formlayers or strata…each layer recordsa depositional event

Cross-beds – former dunes

Ripple marks

Mud cracks

modern

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

Sandstone – sand texture

Shale – silt/clay texture

Biochemical Sedimentary Rock

Limestone – CaCO3 composition

Chert – SiO2 composition

Coal – Carbon composition

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

But why was there an ice age?

Ice stores O16 so that oceans are O16 depleted in an ice age

+ O18/O16 -

CaCO3

Layer by layer sampling of plankton reveals oxygenisotope record

Periodicity of 100,000 yrs

100 kyrs

41 kyrs

21 kyrs

These were madeduring an ice age!