Sedimentary RocksSedimentary Rocks

Sedimentary RocksSedimentary Rocks

Rocks that form from an Rocks that form from an accumulation of sediments from pre-accumulation of sediments from pre-existing rocks and/or organic existing rocks and/or organic materialsmaterials

Most sedimentary rocks are formed Most sedimentary rocks are formed under large bodies of water (lakes, under large bodies of water (lakes, seas, oceans…) where sediments are seas, oceans…) where sediments are usually deposited in horizontal layersusually deposited in horizontal layers

Methods of FormationMethods of Formation Compaction and Cementation – When sand, Compaction and Cementation – When sand,

silt, pebbles, etc… are cemented together by silt, pebbles, etc… are cemented together by minerals that “glue” solid sediments minerals that “glue” solid sediments together. Sediments can also be compacted together. Sediments can also be compacted or compressed together. or compressed together. *** CLASTIC sedimentary *** CLASTIC sedimentary rocks are formed due to these two methods. rocks are formed due to these two methods. ******

CLASTIC SEDIMENTARY ROCKS are formed by CLASTIC SEDIMENTARY ROCKS are formed by compaction or cementation.compaction or cementation.

Clastic sedimentary rocks are sorted by the Clastic sedimentary rocks are sorted by the sizes of the sediment that compose the rocksizes of the sediment that compose the rock

Clastic Sedimentary Rock ExamplesClastic Sedimentary Rock Examples(see ESRT for exact sediment sizes)(see ESRT for exact sediment sizes)

Conglomerate (cemented pebbles)Conglomerate (cemented pebbles)

Clastic Sedimentary Rock Clastic Sedimentary Rock ExamplesExamples

Breccia (cemented jagged pebbles)Breccia (cemented jagged pebbles)

Clastic Sedimentary Rock Clastic Sedimentary Rock ExamplesExamples

Sandstone (larger sediments)Sandstone (larger sediments)

Clastic Sedimentary Rock Clastic Sedimentary Rock ExamplesExamples

Sandstone (BANDED sandstone Sandstone (BANDED sandstone example)example)

Clastic Sedimentary Rock Clastic Sedimentary Rock ExamplesExamples

Siltstone (finer sediments) and shale Siltstone (finer sediments) and shale (finest sediments)(finest sediments)

Methods of FormationMethods of Formation

Chemical Action –When water Chemical Action –When water evaporates, mineral crystals precipitate evaporates, mineral crystals precipitate out of the water, forming chemical out of the water, forming chemical sedimentary rock. These “rocks” are sedimentary rock. These “rocks” are often composed of just one mineral. often composed of just one mineral.

Examples: rock salt (composed of halite), Examples: rock salt (composed of halite), rock gypsum (composed of gypsum), rock gypsum (composed of gypsum), dolostone (composed of dolomite).dolostone (composed of dolomite).

Example: Chemically Formed Example: Chemically Formed Sedimentary RockSedimentary Rock

Rock Salt (formed from Halite)Rock Salt (formed from Halite)

Methods of FormationMethods of Formation

Organic Processes – Any rock made by Organic Processes – Any rock made by living organisms or mostly composed of living organisms or mostly composed of materials from life forms is an organic or materials from life forms is an organic or BIO-CLASTIC sedimentary rock. BIO-CLASTIC sedimentary rock.

Examples: Limestone (cemented shell Examples: Limestone (cemented shell fragments by calcite) and Coal (from fragments by calcite) and Coal (from plant remains, composed of carbon)plant remains, composed of carbon)

Example: Organic Sedimentary Example: Organic Sedimentary RockRock

Limestone from Calcite with FossilsLimestone from Calcite with Fossils

Example: Organic Sedimentary Example: Organic Sedimentary RockRock

Limestone from Calcite with FossilsLimestone from Calcite with Fossils

Example: Organic Sedimentary Example: Organic Sedimentary RockRock

LimestoneLimestone

Example: Organic Sedimentary Example: Organic Sedimentary RockRock

Coal Coal

Example: Organic Sedimentary Example: Organic Sedimentary RockRock

CoalCoal

Example: Organic Sedimentary Example: Organic Sedimentary RockRock

Coal FormationCoal Formation

Characteristics of Sedimentary Characteristics of Sedimentary RocksRocks

Most are Clastic Most are Clastic Contain horizontal sorting or Contain horizontal sorting or

layering… beds or stratalayering… beds or strata Some may contain mud cracks, Some may contain mud cracks,

raindrop impressions, ripple marks…raindrop impressions, ripple marks… Some organic sedimentary rocks Some organic sedimentary rocks

contain fossilscontain fossils