Sedimentary rocks

• Sediments


  Transported by water, ice, wind, or gravity. The ultimate fate of most sediment is burial and conversion to sedimentary rock.
• Sedimentation, Stratification, and Bedding

  Stratification or bedding is the arrangement of sedimentary particles in layers. Each stratum or bed is a distinct layer of sediment. The top or bottom surface of a bed is a bedding plane.
• Sediment classification


  • Non-Clastic sediment: Chemical sediment precipitates from solution in water, Biogenic sediment is composed of the fossilized remains of plants or animals
  • Clastic sediment: Gravel (>2mm), Sand (1/16 - 2mm), Silt (1/256 - 1/16mm), Clay (<1/256mm)
• Sorting


  Identifies sediment in terms of the variability (std dev) in the size of its particles. Poorly sorted has a range of particle sizes, well sorted has a small range of particle sizes.

  
• Flow speed


  Faster flow can transport larger or heavier particles, slower flow deposits heavier and denser particles first while lighter particles are transported onward.
• Roundness


  A measure of the sharpness of a particle's edges
• Sphericity

  A measure of how closely the shape of a particle approaches that of a sphere

  
• Sorting, roundness and sphericity are a reflection of the transport processes sediments undertake before conversion into rock. Unpacking these features enables the interpretation and identification of past environments.
• Sedimentary structures


  • Graded bedding, Cross bedding

  
• How cross beds form


  Cross bedding is the work of turbulent flow in the transporting agency.
• Lithification


  The overall process of creating sedimentary rock
• Diagenesis


  The collective term for all the chemical, physical, and biological processes that cause lithification
• Diagenesis processes


  • Compaction, Cementation, Recrystallization, Dissolution, Chemical alteration
• Clastic Sedimentary Rocks


  • Conglomerate, Breccia, Sandstone, Siltstone, Mudstone/Shale
• Sedimentary structures


  • Erosional, Depositional, Biogenic, Post-depositional
• Erosional structures


  • Flute marks, Groove marks, Gutter casts, Impact marks
• Flute marks


  Spatulate/heel shaped, asymmetric in cross section, formed by localized erosion by sand laden currents
• Groove marks


  Linear ridges on base of sandstone beds formed by infilling of groove cut into underlying mudstone, formed by "tools" carried by current cutting through sediment
• Depositional structures


  • Bedding & lamination, Ripples, dunes & cross stratification
• Ripples


  Wavelength <30cm, height <3cm, can be straight, sinuous, or linguoid
• Dunes


  Can be straight, sinuous, catenary, or lunate
• Biogenic structures


  Trace fossils, bioturbation
• Post-depositional structures


  • Mud cracks
• Mud cracks form when mud dries out
• Non-clastic rocks


  • Evaporites, Biochemical sediments, Chert and Flint, Limestones, Coal
• Evaporites


  Rocks made from salts produced by evaporation of seawater or lake water
• Biochemical sediments


  Contain the fossil remains of plants and animals, can be bioclastic if the remains are broken and scattered
• Biochemical sediments


  • Calcareous ooze, Siliceous ooze, Stromatolites
• Banded iron formations (BIFs)


  Some of the Earth's most important iron concentrations are in sedimentary rocks that formed from around 3.5 billion years ago, indicating chemical precipitation
• Chert and Flint


  Hard, very compact sedimentary rock composed almost entirely of very fine-grained quartz, tend to occur in limestones

  
• Chalk


  Composed of the compacted carbonate shells of minute floating organisms called coccolithophores
• Limestone


  The most important biogenic rock, formed from the precipitation of calcium carbonate
• Limestone types


  • Reef limestone, Shelly limestone, Oolitic limestone
• Oolitic limestone


  Limestone containing 0.5-2mm spherical grains of carbonate that form when carbonate particles are rolled backwards and forwards in a tidal environment
• Coal


  Formed from the accumulation and compression of plant remains
• Photosynthesis and carbon burial over the Phanerozoic has been a major control on atmospheric oxygen levels