lab 1 prep

• Siliciclastics include breccia, conglomerate, sandstone, siltstone, claystone, and shale
• Carbonates include limestone and dolomite
• Evaporates include halite, gypsum, and gypsum anhydrite
• Biogenics include coal, limestones, opal
• Clasts are individual particles of a sedimentary rock produced by physical disintegration of a larger mass
• Siliciclastic rocks are mixtures of mineral grains and rock fragments derived by weathering and erosion of pre-existing silicate rocks
• Siliciclastic rock process:

  • Parent rock undergoes chemical or physical weathering, producing smaller particles
  • Small particles are transported by ice, air, or water to a region of lower energy and accumulate in a sedimentary basin
  • Deposition takes place due to lowering of hydraulic energy, chemical change, or organic biochemical activity
  • Sediments are lithified through compaction and cementation
  • Compaction is decrease in rock volume due to weight of overlying sediment
  • Cementation is chemical precipitation in pore spaces between grains that glue the rock together
• The grains in siliciclastic rock tend to be minerals most resistant to breakdown by chemical weathering

  • Quartz is one of the most resistant minerals to chemical weathering, resulting in many sandstones being predominately quartz grains
  • Feldspar is less resistant than quartz but is the primary mineral grain in feldspathic sandstone and arkose
• Conglomerates may contain multiple minerals called lithic fragments
• The most common grain types for siliciclastic sedimentary rocks are quartz, feldspar, and lithic fragments
• Clay minerals are an important component of many siliclastic rocks but clay-size particles are too small to be seen by the naked eye
• Grain size indicates the energy level of the depositional environment

  • Gravel-sized sediment requires significant energy to transport
  • Clay-sized particles settle out in calm, low-energy environments
  • Sand's grain size ranges between 0.06 and 2 mm
  • Silt's grain size ranges between 0.004 and 0.06 mm
  • Clay grain size is smaller than 0.004 mm
• Sand lithifies into sandstone
• Grain sorting refers to the uniformity in grain size

  • Well-sorted sediment consists of uniform grain size
  • Poorly sorted sediment contains particles of many grain sizes
  • Environments with constant energy flow result in well-sorted sediment
  • Turbulent environments result in poorly-sorted sediments
• More rounded grains have been transported farther from their source rock

  • Rocks transported further are finer, rounded, well-sorted, and have more quartz
  • Rocks transported less far are coarser, angular, poorly sorted, and have more lithics
• Course sand ranges between the grain sizes of 0.5 and 2mm

  • Medium sand ranges between the grain sizes of 0.25 and 0.5mm
  • Fine sand ranges between the grain sizes of 0.06 and 0.25mm
• The most stable minerals indicate more mature rocks and less stable minerals indicate less mature rocks

  • Stability of minerals from most stable to least stable:
  • Clay minerals
  • Quartz
  • Mica
  • Potassium feldspar/orthoclase
  • Sodium-rich feldspar (albite)
  • Amphibole
  • Pyroxene
  • Calcium-rich feldspar (anorthite)
  • Olivine
  • Calcite
• Lithic fragments are individual pieces of rock within a sedimentary rock
• Gravel lithifies into conglomerate
• Silt lithifies into siltstone
• Clay lithifies into shale and mudstone