Professor John Platt
Material covered in this lecture: Understanding Earth, Ch 5
Sedimentary Rocks
• Sedimentary rocks are produced by the deposition of sediment on the Earth s surface • Sediment includes:
– solid particles of rock or mineral material – material precipitated out of solution – biological materials
• Sedimentation can take place on land, in lakes and rivers, or beneath the sea • Sedimentary rocks cover 75% of continental area, and nearly all the ocean floor
The Persian Gulf: A large sedimentary basin
The Sedimentary Rock Cycle
• Weathering and erosion of preexisting rock • Transport of sediment by water, wind, or ice • Deposition • Burial • Diagenesis: processes that convert sediment into rock
Types of sediment
1. clastic sediments
– particles of pre-existing rocks and minerals
4. organic accumulations
– coal – petroleum (oil and gas)
1. Clastic sedimentary rocks
"coarse-grained sediment (gravel -- conglomerate) requires a high energy transport mechanism
– steep, fast-running rivers (alluvial deposits) – glacial deposits (till) – debris flows – storm waves on beaches
conglomerate
Alluvial fan, Death Valley
alluvial cycles
glacial till
Clastic sedimentary rocks
"medium-grained sediment (sand -sandstone) requires a medium energy transport mechanism
– Wind – slow streams – Deltas – submarine turbidity currents – Fair weather beaches
Sand dunes
Sand spit
tidal flat
Clastic sedimentary rocks
"fine-grained sediment (clay -- shale) requires low energy transport mechanism
– lakes, lagoons – flood-plains – tidal flats – deep sea
lagoon with salt marshes
river with floodplain
Marine shale and limestone
Sedimentary rocks, structures, and environments
• Sedimentary rocks contain information that tells us about the environment they formed in:
– Grainsize – Composition – sedimentary textures and structures
