3/7/2012 1 Sedimentary Rocks Fossils Sedimentary rocks Two main types Rocks formed by deposition of sediment Clastic Rocks formed by precipitation from water Chemical (includes rocks formed by organisms) Clastic Sediment Grains Particle loosened from pre‐existing rock Transported to place of deposition Shape, size, and sorting of grains can tell about the environment of deposition Lithification Process of becoming stone Burial and compaction Precipitation of cement Each reduces ‘pore space’ Cement Brought in by water Mineral material between grains Fills in pore spaces Commonly calcite, silica, and sometimes iron oxide Bedding and bedding planes STRATA • http://www.birdandhike.com/Hike/General_Info/Glossary/Gloss4.htm
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Sedimentary RocksFossils
Sedimentary rocks
Two main types
Rocks formed by deposition of sedimentClastic
Rocks formed by precipitation from waterChemical (includes rocks formed by organisms)
Clastic Sediment Grains
Particle loosened from pre‐existing rock
Transported to place of deposition
Shape, size, and sorting of grains can tell about the environment of deposition
Lithification
Process of becoming stone Burial and compaction
Precipitation of cementp
Each reduces ‘pore space’
Cement
Brought in by water
Mineral material between grains
Fills in pore spaces
Commonly calcite, silica, and sometimes iron oxide
Classification of sedimentary rocks Features of sedimentary
rocks Porosity
Permeability
Sedimentary rocks
Economic importance
• Coal
• Petroleum and natural gas
• Precipitation of iron and aluminum
• Deposition of gold and tin
• Sand, gravel, clay
Fossils: evidence of past life
Remains or traces of prehistoric life
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Petrified
Cavities and pores are filled with precipitated mineral matter
Petrified
Formed by replacement
Cell material is removed and replaced with mineral matter
Mold
Shell or other structure is buried and then dissolved by underground water
Shape is preserved in the surrounding sediment http://www.ammonoid.com/Manning.html
Cast
Hollow space of a mold is filled with mineral matter
Carbonization
Organic matter becomes a thin residue of carbon. This is a
f‘compression’ of the original organism
Impression
Replica of the fossil's surface preserved in ffine‐grained sediment
http://www.lfbuffalo.org/exhibitions/map/t/
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Preservation in amber
Hardened resin of ancient trees surrounds an organism
Indirect Evidence Includes
Tracks
Burrows
Coprolites
fossil dung and stomach contents
Gastroliths
stomach stones used to grind food by some extinct reptiles
Tracks
Dinosaur footprint in fine‐grained limestone near Tuba City, Arizona.
Types of fossils
Petrified
Formed by replacement
Carbonization
Impression
i ireplacement
Mold
Cast
Preservation in amber
Indirect evidence
Conditions favoring preservation
Rapid burial
Possession of hard parts
Fossils and correlation
Principle of faunal succession
Index fossils
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Principle of faunal succession
Proposed by William Smith –late 1700s
Fossil organisms succeed one another in a definite and d bl d h fdeterminable order, therefore any geologic time interval can be recognized by its fossil content