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Sediments and Sedimentary Rocks Chapter 5
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Concepts you will need to know for the exams Weathering Erosion Transportation Sorting Angularity Sedimentary environments, Cross-bedding (sedimentary structures) Bioturbation, bedding sequences, diagenesis Classes of sediments and sedimentary rock: -based on grain size -based on chemical composition, e.g., carbonate rocks ("carbonates") and evaporitic rocks ("evaporites")
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Lecture Outline 1. Sedimentary rocks 2. Your sedimentary environment and Burial Diagenesis 3. Interpretation of clastic texture 4. Sedimentary structures 5. Sedimentary Rock classification
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1. Sedimentary Rocks Cover most of the land surface and seafloor sedimentary rock cycleYour physical geography determines the dominant process at work in the sedimentary rock cycle weathering and/or erosione.g. (1) Mountains => weathering and/or erosion e.g., (2) Southern Louisiana => e.g., (3) offshore Louisiana =>
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1. Sedimentary Rocks Cover most of the land surface and seafloor Your physical geography determines the dominant process at work in the sedimentary rock cycle e.g. (1) Mountains => weathering and/or erosion transportation or deposition or erosione.g., (2) Southern Louisiana => transportation or deposition or erosion e.g., (3) offshore Louisiana =>
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1. Sedimentary Rocks Cover most of the land surface and seafloor Your physical geography determines the dominant process at work in the sedimentary rock cycle e.g. (1) Mountains => weathering and/or erosion e.g., (2) Southern Louisiana => transportation or deposition or erosion erosion or sedimentatione.g., (3) offshore Louisiana => erosion or sedimentation
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erosion weathering transportation Erosion includes BOTH weathering and transportation
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Sedimentary rocks are typically layered, (although layering is not diagnostic of only sedimentary rocks)
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Lecture Outline 1. Sedimentary rocks; surface processes 2. Your sedimentary environment and Burial and diagenesis 3. Interpretation of clastic texture 4. Sedimentary structures 5. Sedimentary Rock classification
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A sedimentary environment is a geographic location that has a peculiar combination of geological processes
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Walther’s Rule (1894) “The different (sedimentary) rocks (types) were formed beside each other in space, but in a crustal profile we see them lying on top of each other….”
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Bedding sequences--- are successions of rock ( in a vertical profile) that help geologists work out the past environment
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Where do you live? What dominant sedimentary process is at work where you live?
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If deposition is the dominant process, e.g., offshore Lousiana then rocks are in the process of being formed: Diagnesis Diagnesis includes compaction (1) compaction = volume loss (mechanical squeezing) dewatering and is accompanied by dewatering (= water loss) (by chemical or physical means) (2) changes in mineral composition (chemical process with heat and or fluids) cementation (3) cementation (physical) lithified If a sediment eventually becomes a rock we say it is lithified.
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compaction DIAGENESIS
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compaction dewatering DIAGENESIS
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compaction dewatering Cementation & mineral changes DIAGENESIS
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Lecture Outline 1. Sedimentary rocks; surface processes 2. Your sedimentary environment and Burial and diagenesis 3. Interpretation of clastic texture 4. Sedimentary structures 5. Chemical and biological classification
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degree of weathering and transport Geological FUZZY rules for determining degree of weathering and transport a rock or sediment has experienced respectively
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(1) Product composition
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(2) Degree of sorting
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Sortinghow similarSorting is a measure of how similar grain sizes are within a sediment or rock and tells us about the relative strength of the current before it dropped (deposited) it cargo. size settling velocityIn a current of water or air, the larger and denser grains fall faster than the smaller grains. That is, for the same density, size determines settling velocity.
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(3) Angularity or roundness (antonym) is a measure of the distance of transportation
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Lecture Outline 1. Sedimentary rocks; surface processes 2. Your sedimentary environment and Burial and diagenesis 3. Interpretation of clastic texture 4. Sedimentary structures 5. Chemical and biological classification
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Which of the following sediment characteristics is best used to determine former current speed? 1.sorting 2.angularity or roundness 3.Cross-bedding 4.diagenesis
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Cross-bedding Cross-bedding: Cross-bedding: sets of bedded material within rock layers that are inclined at angles as large as 35 degrees from the horizontal. These latter indicate wind- blown conditions in either a desert or a beach.
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2 directions of fluid movement
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Fossil example of the past activity of organisms mixing sediment --- an example of fossil BIOTURBATION
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Lecture Outline 1. Sedimentary rocks; surface processes 2. Your sedimentary environment and Burial and diagenesis 3. Interpretation of clastic texture 4. Sedimentary structures 5. Sedimentary Rock classification
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Three types of sedimentary Rocks Clastic Biochemical Chemical
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Major Classes of sediments and sedimentary rocks For clastic sedimentary rocks there is a classification scheme based on the SIZE of their clasts, (or rock fragments) that comprise them.
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Clst size indicates ancient relative current velocity >=1.8 km/hr (strong currents)weakmoderate
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240-channel Sercel 388 radio- telemetric seismic acquisition system Radio antenna Electrical- mechanically detonated surface seismic shear source MOBILE SEISMIC LABORATORY
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~16 m (Adapted from Rogers et al., 2008; Nelson, 2006) WE ~6m NS 17 th St Canal Breach sand ~6-9.00 a.m., Aug. 29, 2005
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What type of sediment is peat? 1.chemical 2.clastic 3.biological
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The End of Chapter 5
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