Sedimentary Rock Classification

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Sedimentary Rock Classification
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Rock cycle
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What are Sedimentary Rocks?

• What are sediments?
• How do sediments form sedimentary rocks?
• Where do sedimentary rocks form?

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General Features

• sedimentary rocks usually come from SEDIMENTS
  (mud, sand, pebbles, etc.)
• sediments are pressed into layers (strata)

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Ernst TinajaBig Bend National Park
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Ernst Tinaja

• Thin-bedded orangish rock Del Rio Clay,
• Stratigraphically just below the Buda Limestone
• The massive white rock below the Del Rio is the
  Santa Elena Limestone
• Time lapse between the deposition of the Santa
  Elena and the Del Rio unconformity

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Formation

• sediment comes from the weathering and erosion of
  other rocks
• wind and water move sediment

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Formation ctd.

• once sediments are settled, lithification (making
  a rock) begins
• lithification can involve two main processes
• compaction sediments are pressed together by
  weight, and water is forced out
• cementation minerals deposit out of water and
  cement together sediments

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Rock Cycle
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Types of Sedimentary Rocks1. Clastic

• clastic rocks come from broken pieces of other
  rock (as was just described)
• they are further classified according to their
  pieces

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Clastic Rocks ctd.

• conglomerates have large, round, pieces (see last
  slide)
• breccias have large, angular pieces
• clastic rocks from smaller pieces can be
  sandstones or mudrocks
• Shale

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2. Organic Rocks

• form directly or indirectly from living material
  (despite our definition of minerals)
• example limestone is calcium carbonate from the
  shells of dead clams and oysters

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3. Chemical Rocks

• form by chemical processes (not regular
  compaction)
• Limestone
• a. grainstone
• b. boundstone
• evaporites form when water evaporates, leaving
  just minerals
• ex gypsum, halite, and even some limestone are
  from evaporating water

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FIELD GEOLOGY

• Tools of a Geologist
• Grain size scale
• Roundness scale
• Hand lens
• Field notebook
• Make good observations and notes

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Summary Questions

• What might tip you off that youre looking at a
  sedimentary rock?
• What are two ways that limestone can form?
• How are chemical rocks different from other
  sedimentary rocks?