Sedimentary Rocks

• Sedimentary rocks are products of mechanical and chemical weathering of preexisting rocks

• They account for about 5% (by volume) of Earth’s outer 15 kilometers

• The account for 90% of the upper ½ kilometer• Contain evidence of past environments

• Provide information about sediment transport by one of the geologic fluids

• Often contain fossils

Sedimentary rocks are important for economic considerations because

they may contain

• Coal• Petroleum and natural gas• Sources of iron, aluminum, and manganese• Natural fertilizers • Materials for concrete and bitumen

Types of sedimentary rocks

• Sediment originates from mechanical and/or chemical weathering

• Rock types are based on the source of the material

• Detrital or clastic rocks – transported sediment as solid particles• Chemical rocks – sediment that was once in

solution

What is a sediment?

• A material deposited by one of the geologic fluids (wind, water, ice) at the earth’s surface.

Types of Sediments

• Clastics – Materials transported and deposited by wind,

water, or ice

• Chemical– Materials deposited by chemical precipitation

• Biologic –  Parts of living organisms

Clastic or Detridal

• Pieces of solid stuff transported ad deposited by a geologic fluid

• Size and amount is controlled by– Fluid

• Density, viscosity

– Velocity

Generalized Geologic Map

Evaporites

• Reduce the volume by 

44%    (CaMg)CO3  

(Limestone - Dolomite)  2.2 g/cm3

81%    (CaMg)SO4   

(Gypsum)   2.6 g/cm3

91%    (Na,K)Cl        

(Rock Salt)  1.8  g/cm3  

Sedimentary Sequence in the Mediterranean Basin

•                         ClasticsCycle 3            Salt                        Gypsum                        Limestone

•                        ClasticsCycle 2            Salt                        Gypsum                        Limestone

                        ClasticsCycle 1            Salt                        Gypsum                        Limestone

• Clastics         2.0 g/cm3Limestone     2.2 g/cm3Gypsum        2.6 g/cm3Salt                1.8  g/cm3

    Biologic

• Parts of living organism– Rock Forming organisms

• (coral, algae)     limestones

• Organic Rocks from dead organisms• Plants (coal)

• Fragments of organisms – (oozes, muds, fossils)  limestones

Rock forming Organisms

• Coral

• Blue-Green algee

Dead Coral

Distribution of reefs

• Clear warm water

• Normal salinity

Dead organisms

• Plants – Swamps (anoxic)

– Peat – lignite – subbituminous – bituminous – superbituminous

• Shells– Fragments

Shells

Coal Swamp

• Burpee Museum, Rockford, Illinois

Major Coal U.S. Basins

Sedimentary environments

• A geographic setting where sediment is accumulating

• The environment determines the nature of the sediments that accumulate (grain size, grain shape, etc.)

Types of sedimentary environments

• Continental– Dominated by stream erosion and deposition

– Glacial

–Wind (eolian)

• Marine– Shallow (to about 200 meters)

– Deep (seaward of continental shelves)

Types of sedimentary environments

• Transitional (shoreline)– Tidal flats

– Lagoons

– Deltas

Sedimentary Environments

• ..\POG Lect\sed environments.jpg

Sedimentary Facies

• Different sediments often accumulate adjacent to one another at the same time• Each unit (called a facies) possesses a

distinctive set of characteristics reflecting the conditions of a particular environment• The merging of adjacent facies is a gradual

transition

Sedimentary Facies

Big Bend, Texas

Sedimentary structures

• Strata, or beds (most characteristic of sedimentary rocks)• Bedding planes that separate strata

Sedimentary structures

•Cross-bedding

•Graded beds

•Ripple marks

•Mud cracks

• Fossils