Chapter 8 – FROM SEDIMENT INTO SEDIMENTARY ROCK
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Transcript of Chapter 8 – FROM SEDIMENT INTO SEDIMENTARY ROCK
Chapter 8 – FROM SEDIMENT INTO
SEDIMENTARY ROCK
Sediments and Sedimentation• Deposition
– Laying down of sediment• Separated into 3 broad
categories– Clastic (Detrital)– Chemical– Biogenic (Biochemical)
• Clastic sediment– Fragmented rock &
mineral debris from weathering & erosion
– Described by particle shape, angularity, & size
– Volcani-clastic sediments• Pyroclasts
– Distinguished by size (bombs, lapilli, ash)
Sediments and Sedimentation
• Chemical sediment– Precipitation of minerals dissolved in lake, river, or sea
water• Limestone
– Shallow sea water evaporation causes dissolved salts to precipitate
Sediments and Sedimentation
• Biogenic sediment– Primarily composed of plant or
animal remains• Shells, bones, teeth• Wood, roots, leaves
Sediments and Sedimentation
Sedimentary Rocks• Lithification
– Processes where loose sediment transforms into sedimentary rock• Bedding
– Layers of strata in sediment/sedimentary rock
• Bedding surface– Top or bottom of rock
bed• Graded bed
– Bed with large clasts at bottom, fining toward top
• Cross bedding– Beds are inclined
relative to layer they occur in
Lithification Processes• Compaction
– Reduced pore space due to weight of sediments above
• Cementation– Dissolved substances
precipitate out & act as glue
• Recrystallization– Form new crystalline
mineral grains from old ones
• Diagenesis– Low
temperature/pressure changes
Types of Sedimentary Rocks• Clastic sedimentary
rock– Conglomerate or breccia
• Large fragments in fine grained matrix
– Sandstones• Medium grained (sand
sized)• Arkose or Quartz
Sandstone– Mudstones
• Very fine grained rock• Same composition as
shale but lacks fissility– Shale
• Very fine grained fissile rock
• Fissile = breaks into layers
Particle Sizes in Clastic Sedimentary Rocks
Diameter (mm)
Particle Type
Sediment Name
Sedimentary Rock
More than 256 Boulder
Gravel Conglomerate or Breccia
64 to 256 Cobble
4 to 64 Pebble
2 to 4 Granule
1/16 to 2 Sand Sand Sandstone
1/256 to 1/16 Silt
Mud Siltstone, Shale or MudstoneLess than
1/256 Clay
Types of Sedimentary Rocks• Chemical sedimentary rocks
– Classified mainly by composition– Evaporite
• Formed by lake or sea water evaporation
• Rock salt; rock gypsum
– Limestone & related• Oolitic• Dolostone
– Chert
• Biogenic sedimentary rocks– Limestone
• Mostly made of calcite• Coquina• Chalk
– Peat• Formed by
accumulation & compaction of plant remains
– Coal• Formed by lithification
of plant-rich sediment• Bituminous coal
Types of Sedimentary Rocks
Depositional Environments• Interpreting
environmental clues– Patterns made by air
& water that moved over sediments
– Ripple marks– Fossils– Mud cracks
Depositional Environments on Land• Streams
– Alluvial fan• Forms where stream is not
constrained by valley walls• Fan-shaped
• Lakes– Delta
• Forms where stream enters standing body of water
• Usually triangle-shaped– Playa
• Seasonal lake
Depositional Environments on Land• Glacier
– Till• Mixed particles
sizes & shapes• Wind
– Eolian sediment• Sediments carried & deposited by
wind– Loess
• Wind-blown silt & clay sediment
Depositional environments in & near the ocean• Delta• Estutary
– Semi-enclosed body of coastal water
– Fresh water mixes with sea water• Beaches
– Mixed material; quartz common• Shelves
– Silt or sand sediment; numerous fossils
• Carbonate platforms and reefs– Reef: wave-resistant structure built
of marine invertebrate skeletons
Depositional environments in & near the ocean• Turbidites & turbidity currents
– Turbulent, gravity driven flow of sediment & water
– Moves sediment from continental shelf to deep sea
• Seafloor– Nutrient-rich
• Calcareous ooze• Siliceous ooze
Depositional environments in and near the ocean• Sedimentary facies
– Changes in the character of sediment from one environment to another
How Plate Tectonics Affect Sedimentation• Divergent plate
boundaries– Rift valleys
• Convergent plate boundaries– Collisional type – Subduction type
• Back-arc basin• Accretionary wedges