1. Chapter 8 – FROM SEDIMENT INTO SEDIMENTARY ROCK

2. Sediments and Sedimentation
Deposition
Laying down of sediment
Separated into 3 broad categories
Clastic (Detrital)
Chemical
Biogenic (Biochemical)

3. Sediments and Sedimentation
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)

4. 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

5. Sediments and Sedimentation
Biogenic sediment
Primarily composed of plant or animal remains
Shells, bones, teeth
Wood, roots, leaves

6. 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

7. 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

8. 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
Sandstone
1/256 to 1/16
Silt
Mud
Siltstone, Shale or Mudstone
Less than 1/256
Clay

9. 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

10. Types of Sedimentary Rocks
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

11. Depositional Environments
Interpreting environmental clues
Patterns made by air & water that moved over sediments
Ripple marks
Fossils
Mud cracks

12. 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

13. Depositional Environments on Land
Glacier
Till
Mixed particles sizes & shapes
Wind
Eolian sediment
Sediments carried & deposited by wind
Loess
Wind-blown silt & clay sediment

14. 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

15. 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

16. Depositional environments in and near the ocean
Sedimentary facies
Changes in the character of sediment from one environment to another

17. How Plate Tectonics Affect Sedimentation
Divergent plate boundaries
Rift valleys
Convergent plate boundaries
Collisional type
Subduction type
Back-arc basin
Accretionary wedges