2835: Sedimentary Classification and processes

1
2835 Sedimentary Classification and processes

• Classify mechanically-, chemically- and
  biologically-formed sedimentary rocks by grain
  size, shape, mineral composition and fossil
  content.
• We will cover this during this module but it is a
  goods idea to clarify what mechanically-,
  chemically- and biologically-formed sedimentary
  rocks actually are?
• Any ideas?

2
Mechanically-formed sedimentary rocks

• What are they?
• These are clastic sedimentary rocks.
• Those formed by transport of solid
  material/clasts by agents of erosion which are
  subsequently deposited.
• Examples include
• Sandstone
• Mudstone
• Siltstone
• Conglomerates
• Breccias.
• How are they classified?
• Mainly by grain size.

3
Chemically-formed sedimentary rocks

• What are these?
• They are rocks that are chemically precipitated
  such as
• Limestones (of various kinds such as oolites)
• Evaporites (like halite, gypsum etc.)
• Banded Iron Formation (BIF)
• They are non-clastic and the material is derived
  from elements in solution.
• How do many of these elements in solution get
  into solution?
• Chemical weathering.

4
Biologically-formed sedimentary rocks

• These are formed from the activity of animals or
  plants.
• Examples are
• Coral limestones
• Chalk
• Coal
• Stromatolites