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GEOS100, Sedimentary cheat sheet
This is a draft cheat sheet. It is a work in progress and is not finished yet.
Classification of Sedimentary Rocks
Detrital
made of solid sedimentary fragments (eg, mudstone, siltstone, sandstone, and conglomerate/breccia)
Clastic - mainly for detrital rocks with distinct sized fragments
Chemical
made of minerals taken into a solution and reprecipitated without help from organisms (eg, evaporites like rock salt and iron formations)
Crystalline - mainly for chemical rocks with interlocking crystals
Biochemical
made of minerals of which organisms played a role in turning to sediment (eg, limestone made of calcite from coral, chert made of a planktonic micro-organism)
Bioclastic - rocks with skeletal remains |
Sedimentary Rock Textures
Clastic Texture Particle Size |
Sediment Name |
Rock Name |
Coarse (over 2mm) |
Gravel (rounded particles) Gravel (angular particles) |
Conglomerate Breccia |
Medium (1/16 to 2mm) |
Sand (or Arkose if abundant feldspar is present) |
Sandstone |
Fine (1/256 to 1/16 mm) |
Silt |
Siltstone |
Very fine (<1/256 mm) |
Clay |
Shale/Mudstone |
Sedimentary Facies
Lateral view of sedimentary rock reflects changes in past environments.
Characteristics of each facies reflect the environment in which it formed.
Different sediments often accumulate next to one another at the same time.
The merging of many facies is usually a gradual transition. |
Sedimentary Glossary
Sedimentary rock - one of the 3 rock types formed by the accumulation and cementation of inorganic or organic particles. |
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Sedimentary Environments
Continental - Dominated by erosion and deposition associated with streams; in frigid environments, glaciers can move large volumes and sizes of sediment; streams are a dominant factor in moving sediment; wind deposits are well sorted
Transitional (shoreline) - quiet water conditions may form tidal flats; higher energy water conditions tend to form beaches, spits, bars, and barrier islands; sheltered, brackish water conditions can form lagoons; deltas are common and form when river velocity slows at river/sea interface and sediment is deposited
Marine - Divided according to depth: shallow ≤200m - may include land derived sediment, skeletal debris, and coral reef accumulation; deep >200m: tiny skeletons rain down on sea floor and strong currents may move material from continental shelf to deeper environments |
Tidal flat - shallow, muddy, part of shore
Brackish water - salinized freshwater
Continental shelf - part of a continent submerged under shallow water
Sedimentary Rock Types
Biological Sediment
organic matter or biochemically produced materials (eg, limestone).
Chemical Sedimentary Rock
precipitates from a fluid (eg, rock salt),
Siliciclastic made off clasts (sediments or fragments) compacted and cemented together. (eg, sandstone, conglomerate); also called detrital |
Sedimentary Structures
Strata beds - Distinct layers of sedimentary rocks; formations include multiple individual strata
Bedding planes - horizontal cracks that separate strata
Surface impressions - mud cracks or trace fossils
Graded beds - rapid deposition through water; coarse settles first and progressively shrinks in grain size upward through a bed; commonly formed by turbidity currents
Cross-bedding - Inclined layers in relation to bed formed by movement.
Ripple marks - small waves of sand formed by moving water
Current ripple marks - stream currents (asymmetric)
Oscillation ripple marks - waves (symmetric) |
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