Sedimentary Rock

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…. Sedimentary rocks tend to form layers or strata…each layer records a depositional event Cross-beds – former dunes

Ripple marks Mud cracks modern 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 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 – CaCO 3 composition Chert – SiO 2 composition Coal – Carbon composition

Pressure forms coal How does coal form?

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 O 16 so that oceans are O 16 depleted in an ice age

+ O 18 /O 16 - CaCO 3 Layer by layer sampling of plankton reveals oxygen isotope record Periodicity of 100,000 yrs

100 kyrs 41 kyrs 21 kyrs

These were made during an ice age!