Sedimentary Rocks

• Detrital/Clastic sediments are results of mechanical (physical) weathering.
• Chemical sediments are made of minerals precipitated from solutions by inorganic processes and by organism activities through chemical weathering.
• What is a depositional environment?

  A geographic setting where sediment is accumulating. It determines the nature of a sediment.
• DETRITAL (CLASTIC) SEDIMENTARY ROCK

  1. Weathered (physically or chemically)
  2. Eroded
  3. Deposited
  4. Lithified
• CLAST SIZES

  Boulder

  Cobble

  Pebble

  Sand (coarse, medium, fine)

  Silt

  Clay
• CLAST SHAPES

  Angular

  Rounded (interacted with large amount of water)
• what are the sorting of clasts?

  Poor, moderate, well
• TRANSPORTATION

  Boulder is transported by ice

  Pebble is transported by water

  Sand is transported by wind
• DEPOSITION

  Low areas like basins accumulate sediments.
• BURIED AND LITHIFIED INTO ROCKS

  Uncompacted (loose) sediment slowly becomes rock
• Diagenesis is the physical (compaction) or chemical (cementation) changes in pressure, heat, and/or chemistry.
• Conglomerate

  Well rounded pebble-sized clasts in a matrix of sand, silt, and/or clay.
• Where can conglomerate rocks be found?

  Streams, rivers, beaches, turbidity
• Breccia

  An angular pebble-sized clasts with a sand, silt, or clay matrix.
• Breccia can be found in alluvial fans.
• Sandstones are sand-sized grains. Different compositions of sand clasts give the stone a different name.
• Shale is a very fine-grained, clay-sized, particles (form layers, breaks in chips). It id from still or slow-moving water.
• Chemical/Biochemical sedimentary rocks

  Substances derived from solution by inorganic or biochemistry process. Some have crystalline texture
• What id the clastic textuse of chemical/biochem rocks?

  Fragments, like shells, that are glued together.
• Chemical/biochem sedimentary rocks are classified on the basis of composition.
• Evaporites include rock salt and rock gypsum.
• The chemical sediments in evaporites are formed by precipitations. Evaporites forms in playa.
• What is a playa?

  A dried up lakebed in a desert.
• Carbonate rocks primarily consists of carbonate ion, such as calcite and dolomite. They often forms in calm saltwater.
• What is an example of carbonate rocks and where are they formed?

  Limestone and dolostone forms in calm saltwater (Deep ocean, lagoons, and reefs).
• Limestones formed in reefs often contain fossils of sea creature.
• Coal is a biochemistry sedimentary rock composed largely of altered land plant remains.
• Peat is a partially decayed plant remains found in low-oxygen waters in swamps.
• Chert is microcrystalline quartz formed in deep marine
• Dark chert = flint

  Red cHERT = jasper
• Sedimentary facies

  Sediment/sedimentary rocks that are recognizably different from adjacent sediment/sedimentary rocks and deposited in a different environment
• Sedimentary facies are used to identify ancient changes in sea level.
• Marine transgressions

  Sea level rises. As a result, offshore fancies overlies nearshore facies
• Marine regressions

  Sea level drops. As a result, nearshore facies overlies offshore facies.
• Textures describe the shape, size, and sorting of grains.
• STRUCTURES

  • Ripple marks
  • Bedding
  • Mud cracks
• Ripple marks

  Current ripple marks have asymmetric streams.

  Wave-formed ripple marks have symmetrical oceanic streams
• Bedding

  Cross—bedding preserves layers deposited at angle .

  Parallel bedding—one layer in top of another.

  Graded bedding-coarse s material at bottom of bed, then finer sediments on top.
• Mud cracks

  Deposited in lagoons and mudflats when mud dries, contracts, and cracks.
• Fossils are the remains and traces of ancient life. It correlates strata, dates rocks, and interpret depositional environment.