sedimentary rocks sedimentary rocks are products of mechanical and chemical weathering of...
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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
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