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Sedimentary Rocks are the product of sediment deposition, diagenesis, and lithification Sedimentary Rock http://soest.hawaii.edu/coasts/cgg_main.html 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” 1 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 Glacial Environment – grains very coarse with no sorting, but usually rounded Eolian Environment – grains of uniform size “well sorted” Landslide Environment – grains very coarse with no sorting, with no rounding Coastal Environment – grains coarser and of mixed size Marsh/Mudflat Environment – grains very fine Stream Environment – grains much coarser and “poorly sorted” Sedimentary Structures…. Evaporite environment – chemical sediments Cross-beds – former dunes Reef environment – biological sediments Sedimentary rocks tend to form layers or strata…each layer records a depositional event Deep sea environment?? – Plankton sediment and clays from land 2 Sediment becomes sedimentary rock…the texture and composition of the sediment determine the type of sedimentary rock Ripple marks modern Mud cracks ancient Two types of sedimentary rock – Clastic Sedimentary Rock – made of pieces of broken crust Biochemical Sedimentary Rock – made of precipitated minerals Clastic Sedimentary Rock Biochemical Sedimentary Rock Conglomerate/Breccia – gravel texture Limestone – CaCO3 composition Sandstone – sand texture Conglomerate Rock Salt Chert – SiO2 composition Shale – silt/clay texture Coal – Carbon composition 3 How does coal form? Coal strip mine… Pressure forms coal 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 4 But why was there an ice age? 5 Ice stores O16 so that oceans are O16 depleted in an ice age + O18/O16 - Periodicity y of 100,000 , yrs y CaCO3 41 kyrs 21 kyrs Layer by layer sampling of plankton reveals oxygen isotope record 100 kyrs 6 These were made during an ice age! 7