Sedimentary Rocks

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Queen's University
Geological Sciences and Geological Engineering
GEOL 104
Michael T.Mc Bride

Sedimentary Rocks What is a Sedimentary Rock?  After weathering, particles of rock are carried away from the source via wind, rain etc. and deposit in a new location  upon burial, this sediment becomes lithified and transformed into rock  bottom layer of sediment becomes compacted and cemented together by mineral matter deposited in spaces between particles  Diagenesis describes the chemical, physical, and biologic change that occur after sediments are deposited, but before metamorphism  burial encourages diagenesis due to increased temperature and pressure  occurs between 150-200°C within the upper few kilometers of the crust  Lithification is the process by which unconsolidated sediments are transformed into solid sedimentary rocks Types of Sedimentary Rocks:  Clastic Sedimentary Rocks: rocks composed of particles that originate as solid, derived from both physical and chemical weathering  Chemical Sedimentary Rocks: occur from dissolved ions that are precipitated from a solution  precipitated from an aqueous solution; often showing crystalline texture  Biochemical Sedimentary Rocks: rocks composed of organic matter from carbon-rich tissues of once living things  precipitated from an aqueous solution Clastic Sedimentary Rocks:  Mainly composed of clay and quartz, but also consist of feldspars and micas  Particle size is the primary basis for distinguishing clastic sedimentary rocks:  Gravel: 2mm (Conglomerate or Breccia)  Sand: 1/16th mm (Sandstones)  Mud: 1/256th mm (Silt, Mudrocks)  Mudrocks include shale, mudstone and siltstone and account for more than half of all sedimentary rocks:  tightly packed particles that are very small in size  shale is able to be split into thin layers along closely spaced planes (fissile)  if the rock breaks into chunks, it is a mudstone (NOT fissile)  Sandstones are rocks where sand grains are dominant and are mainly composed of quartz  well-sorted sandstone has particles that are about the same size  the better sorted a rock is, the longer the particles travelled for  well-rounded (angularity) particles are smoothed, whereas angular particles are edgy  degree of rounding indicates the distance, time, and conditions the sediment experienced during transport  Arenites: Well-sorted sandstones with little/no matrix (matrix=smaller grains between larger particles)  Wacke: Sandstone with lots of matrix  Conglomerates consist or largely rounded pebbles (gravel size = >2mm) that often have a finer matrix and requires high energy to transport  Coquina if composed of shell fragments  Breccia are similar to conglomerates but have angular particles rather than rounded  rare and rubble is not transported far Chemical Sedimentary Rocks:  derived from material that is carried in solution to lakes and seas where some of it precipitates to form chemical sediments (ie. dripstone from water dripping f
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