Sedimentary Rocks

Rocks from clastic materials

What is a Sedimentary Rock?What is a Sedimentary Rock?

Sedimentary rocks are products of mechanical and chemical weathering

They account for about 5% (by volume) of Earth’s outer 10 miles, and 75% of surface rocks

Contain evidence of past environmentsProvide information about sediment

transportOften contain fossils

Sedimentary rocks are products of mechanical and chemical weathering

They account for about 5% (by volume) of Earth’s outer 10 miles, and 75% of surface rocks

Contain evidence of past environmentsProvide information about sediment

transportOften contain fossils

Sedimentary rocks are also important because they may contain economic resources such as:

CoalPetroleum and natural gasSources of iron, aluminum, and

manganese

Sedimentary rocks are also important because they may contain economic resources such as:

CoalPetroleum and natural gasSources of iron, aluminum, and

manganese

Types of WeatheringTypes of Weathering

Mechanical weathering is the physical breaking apart of Earth materials Frost wedging = splitting of rocks due

to alternate freezing and thawing of water in cracks or voids

Unloading = slabs of rock “peel” away due to a reduction in pressure when overlying rock is eroded away

Mechanical weathering is the physical breaking apart of Earth materials Frost wedging = splitting of rocks due

to alternate freezing and thawing of water in cracks or voids

Unloading = slabs of rock “peel” away due to a reduction in pressure when overlying rock is eroded away

Types of WeatheringTypes of Weathering

Chemical weathering Water is the most important agent of

chemical weathering Reactions such as oxidation or

dissolution by acids serve to decompose rocks

Clay minerals are the most abundant and stable product of chemical weathering

Chemical weathering Water is the most important agent of

chemical weathering Reactions such as oxidation or

dissolution by acids serve to decompose rocks

Clay minerals are the most abundant and stable product of chemical weathering

Sediments to RockSediments to Rock

Many changes occur to sediment after it is deposited

Diagenesis = chemical, physical, and biological changes that take place after sediments are deposited

Occurs within the upper few miles of Earth’s crust

Many changes occur to sediment after it is deposited

Diagenesis = chemical, physical, and biological changes that take place after sediments are deposited

Occurs within the upper few miles of Earth’s crust

Lithification – sediments are transformed into solid rock by compaction and cementationNatural cements include calcite,

silica, and iron oxide

Lithification – sediments are transformed into solid rock by compaction and cementationNatural cements include calcite,

silica, and iron oxide

Iron oxideIron oxide

SilicaSilica

Types of Sedimentary Rocks

Types of Sedimentary Rocks

Rock types are based on the source of the materialDetrital rocks – transported

sediment as solid particlesChemical rocks – sediment that was

once in solution

Rock types are based on the source of the materialDetrital rocks – transported

sediment as solid particlesChemical rocks – sediment that was

once in solution

Chemical Sedimentary RocksChemical Sedimentary Rocks

Consist of precipitated material that was once in solution (in a fluid)

Precipitation of material occurs byInorganic processesOrganic processes (biochemical

origin)

Consist of precipitated material that was once in solution (in a fluid)

Precipitation of material occurs byInorganic processesOrganic processes (biochemical

origin)

CoalCoal

Stages of Coal FormationStages of Coal Formation

ClassificationClassification

Sedimentary rocks are classified according to the type of material:

Detrital (mechanical weathering)Chemical (precipitation from fluid)

According to texture:Clastic (fragments and particles)

ALL detrital rocksNon-clastic (pattern of interlocking

crystals)

Sedimentary rocks are classified according to the type of material:

Detrital (mechanical weathering)Chemical (precipitation from fluid)

According to texture:Clastic (fragments and particles)

ALL detrital rocksNon-clastic (pattern of interlocking

crystals)

Sedimentary EnvironmentsSedimentary

EnvironmentsContinental

Dominated by stream erosion and deposition

GlacialWind (eolian)

MarineShallow (to about 200 meters)Deep (seaward of continental shelves)

ContinentalDominated by stream erosion and

deposition GlacialWind (eolian)

MarineShallow (to about 200 meters)Deep (seaward of continental shelves)

Transitional (shoreline)Tidal flats (estuaries)LagoonsDeltas

Transitional (shoreline)Tidal flats (estuaries)LagoonsDeltas

And finally, Caves! (cool!)And finally, Caves! (cool!)