Types Of Sedimentary Rocks

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Sedimentary Rocks
Lecture by

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

2. chemical sediments
– evaporites

3. carbonate rocks
– skeletal material: shells, corals, etc. Mainly calcite.

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


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

Sedimentary structures
• • • • • • • bedding scours and channels cross-bedding ripples graded bedding bioturbation mud-cracks


Channel in river sediments

Trench cut in sand dune, Colorado Plateau

Cross bedding in dune sands

Trench cut in sand dune, Colorado Plateau

Cross-bedded sandstone

Modern rippled sand

Ripples on the sea floor

Ancient ripple-marked sandstone

Graded bedding

Bioturbation tracks and tunnels

Mudcracks mudcracks



2. Evaporites
• precipitates formed with increasing concentration