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SEDIMENTARY ROCKS
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TERMS Weathering: breakdown of pre-existing rock
Physical or chemical breakdown Transport: movement of sediment on Earth’s surface
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SEDIMENTARY ROCKS Introduction Detrital Rocks Chemical/Organic Rocks
Classification Lithification Sedimentary Environments Sedimentary Structures
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Sedimentary Rocks Introduction
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INTRODUCTION Origin Only form at Earth’s surface
GEOL 131: Sedimentary Rocks INTRODUCTION Origin Only form at Earth’s surface Weathering of pre-existing rock into soluble and insoluble sediments Transport of sediments Deposition of solid sediment or precipitation of dissolved sediment Diagenesis: includes compaction and lithification
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INTRODUCTION Importance Record of past surface conditions Fossils
GEOL 131: Sedimentary Rocks INTRODUCTION Importance Record of past surface conditions Fossils Economically important materials Fossil fuels, gypsum, phosphates, iron, gravel, etc.
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Sedimentary Rocks Detrital Rocks
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Detrital Rocks “Detrital” from “detritus” - debris
GEOL 131: Sedimentary Rocks Detrital Rocks “Detrital” from “detritus” - debris Composed of solid sediment grains Distinguished by size of grains Detrital rock with smaller grains Detrital rock with large grains
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Detrital Rocks: Common Minerals
GEOL 131: Sedimentary Rocks Detrital Rocks: Common Minerals Quartz Physically durable Feldspars Break down chemically into clays Clay minerals Chemically stable
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Shale Most abundant sedimentary rock Made of clay grains
GEOL 131: Sedimentary Rocks - Detrital Shale Most abundant sedimentary rock 2/3 of all sedimentary rock is shale Made of clay grains Microscopic sheets From chemical weathering of feldspar
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Shale GEOL 131: Sedimentary Rocks - Detrital
Scanning electron microscope image of shale showing flat clay grains. Scale bar is cm. From: claysandminerals.com
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Shale Formation Quiet environment Burial and compaction of clay grains
GEOL 131: Sedimentary Rocks - Detrital Shale Formation Quiet environment Burial and compaction of clay grains Not cemented Weak From: geoexpro.com
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Sandstone Cemented sand-size grains Sand: 1/16mm – 2mm diameter
GEOL 131: Sedimentary Rocks - Detrital Sandstone Cemented sand-size grains Sand: 1/16mm – 2mm diameter Quartz is predominant mineral
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CONGLOMERATE/BRECCIA
GEOL 131: Sedimentary Rocks - Detrital CONGLOMERATE/BRECCIA Cemented gravel-size grains Gravel: greater than 2mm CONGLOMERATE has rounded gravel BRECCIA has angular gravel
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Sedimentary Rocks Chemical Rocks
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GEOL 131: Sedimentary Rocks
Chemical Rocks Dissolved sediment precipitates out of solution as crystals “Inorganic” processes: e.g. evaporation, chemical activity “Biochemical” processes, e.g. growth of shells Bonneville Salt Flats, Utah From: rogerdhansen.wordpress.com
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Chemical Rocks: Limestones
GEOL 131: Sedimentary Rocks - Chemical Chemical Rocks: Limestones Composed mainly of calcite (CaCO3) Several kinds Some biochemical and some inorganic Most form in marine environments
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Biochemical Limestones
GEOL 131: Sedimentary Rocks - Chemical Biochemical Limestones From: From: seashellsbymillhill.com From: proprofs.com Chalk Microscopic plankton shells Very soft Fossil limestone Shells + matrix Hard Coquina Shells only Fragile
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Inorganic Limestones GEOL 131: Sedimentary Rocks - Chemical
From: russianriverschoolhouse.com From: www4.uwm.edu From: Oolitic limestone Round “ooids” + cement Precipitation of crystals from seawater around a nucleus Rolling back and forth Micrite Microscopic calcite crystals Precipitated from oversaturated seawater Travertine “Cave rock” Porous
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Inorganic Limestones: Ooids
GEOL 131: Sedimentary Rocks - Chemical Inorganic Limestones: Ooids Calcite layers Seafloor Nucleus Ooid forming Ooid cross-section Ooids form when calcite precipitates from oversaturated seawater onto nuclei being rolled around on seafloor by currents Nucleus can be any small solid particle: sand grain, piece of shell, etc.
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Chemical Rocks: Chert Biochemical
GEOL 131: Sedimentary Rocks - Chemical Chemical Rocks: Chert Biochemical Composed mainly of microcrystalline quartz Very hard; sharp edges Made from compacted microscopic plankton shells
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Chemical Rocks: Evaporites
GEOL 131: Sedimentary Rocks - Chemical Chemical Rocks: Evaporites Inorganic Evaporation of water (usually salt water) Rock salt, rock gypsum Bonneville Salt Flats, the ancient floor of Lake Bonneville, a salty lake now mostly evaporated
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Organic Rocks: Coal Organic, no minerals
GEOL 131: Sedimentary Rocks - Chemical Organic Rocks: Coal Organic, no minerals Chemically altered dead plant matter Need oxygen-poor water From: eis.uow.edu.au
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Sedimentary Rocks Classification
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Classification: Detrital
GEOL 131: Sedimentary Rocks Classification: Detrital
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Classification: Chemical
GEOL 131: Sedimentary Rocks Classification: Chemical
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Sedimentary Rocks Lithification
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Lithification How sediment becomes rock “Lith” = stone
GEOL 131: Sedimentary Rocks - Lithification Lithification How sediment becomes rock “Lith” = stone
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Lithification Processes
GEOL 131: Sedimentary Rocks - Lithification Lithification Processes Compaction Cementation
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GEOL 131: Sedimentary Rocks - Lithification
Begins with deposition & burial of sediment under more sediment
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Compaction Decreases porosity (empty space) Drives out water
GEOL 131: Sedimentary Rocks - Lithification Compaction Decreases porosity (empty space) Drives out water Can make flat grains stick together
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Cementation New crystals form between grains
GEOL 131: Sedimentary Rocks - Lithification Cementation New crystals form between grains Precipitation out of groundwater Fills in remaining porosity Original sand grain Cement crystals From: northstonematerials.com From: unibe.ch
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Sedimentary Environments
Sedimentary Rocks Sedimentary Environments
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Sedimentary Environments
GEOL 131: Sedimentary Rocks - Environments Sedimentary Environments Any place where sediments accumulate Rocks give clues to past environments Reconstruct what Earth’s surface looked like in the past
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GEOL 131: Sedimentary Rocks - Environments
From: neiu.edu Examples of some sedimentary environments
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Categories of Sed. Environments
GEOL 131: Sedimentary Rocks - Environments Categories of Sed. Environments Nonmarine Transitional Marine
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Sed. Rocks Represent Past Environments
GEOL 131: Sedimentary Rocks - Environments Sed. Rocks Represent Past Environments UTAH Bonneville Salt Flats (white areas): rock salt deposits represent ancient lake Ancient Lake Bonneville
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Sedimentary Structures
Sedimentary Rocks Sedimentary Structures
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Layers (aka beds or strata)
GEOL 131: Sedimentary Rocks - Sedimentary Structures Layers (aka beds or strata) Most common type of structure Bedding planes: contacts between layers
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Cross-bedding Cross-beds in a modern sand dune Cross-beds in sandstone
GEOL 131: Sedimentary Rocks - Sedimentary Structures Cross-bedding Cross-beds in a modern sand dune Cross-beds in sandstone
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Cross-bedding shows depositional current’s flow direction
GEOL 131: Sedimentary Rocks - Sedimentary Structures Cross-bedding shows depositional current’s flow direction Wind, river, waves, etc. Paleocurrent: ancient depositional current Flow direction Crossbeds
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Graded beds Grains are sorted by size within a single layer
GEOL 131: Sedimentary Rocks - Sedimentary Structures Graded beds Grains are sorted by size within a single layer video
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Ripple marks & mud cracks
GEOL 131: Sedimentary Rocks - Sedimentary Structures Ripple marks & mud cracks Mud cracks in modern sediment Ripple marks in sandstone
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Fossils Remains or traces of prehistoric life
GEOL 131: Sedimentary Rocks - Sedimentary Structures Fossils Remains or traces of prehistoric life Correlate rocks of similar ages that are from different places (Chapter 9) Crustacean in limestone from Germany, 150 million years old. Trilobite.
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FIELD TRIP! Capitol Reef National Park
Sedimentary Rocks FIELD TRIP! Capitol Reef National Park
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Sedimentary Rocks Economic Resources
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Nonmetallic Mineral Resources
GEOL 131: Sedimentary Rocks – Economic Resources Nonmetallic Mineral Resources Not used as fuels or processed for metals Extracted/processed for nonmetallic elements of physical/chemical properties Used in process of creating other products Fluorite and limestone for steel-making Abrasives for machine production Fertilizers (sylvite-KCl)
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Nonmetallic Mineral Resources
GEOL 131: Sedimentary Rocks – Economic Resources Nonmetallic Mineral Resources 2 groups Building materials Cut stone aggregate (sand, gravel, crushed stone) Plaster (gypsum) Tile and bricks (clay) Cement (limestone and shale) Concrete (cement and aggregate) Industrial materials Manufacturing steel (limestone) Abrasives (corundum and garnet) Agricultural (limestone, sylvite)
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Energy Resources What fuels our industrial society
GEOL 131: Sedimentary Rocks – Economic Resources Energy Resources What fuels our industrial society Fossil fuels: natural energy sources formed from remains of dead plants or animals Coal, natural gas, and petroleum represent 82% of energy consumed in US
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Energy Resources - Coal
GEOL 131: Sedimentary Rocks – Economic Resources Energy Resources - Coal
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Energy Resources - Coal
GEOL 131: Sedimentary Rocks – Economic Resources Energy Resources - Coal Coal is abundant, but there are complicating factors Surface mining Underground mining Acid precip CO2 production
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Energy Resources – Oil and Natural Gas
GEOL 131: Sedimentary Rocks – Economic Resources Energy Resources – Oil and Natural Gas Provide more than 60% of energy consumed in US. Formation: Derived from remains of marine plants and animals, deposited, and buried Chemical reactions create liquid and gaseous hydrocarbons Squeezed from source rock into permeable beds Rise through pore spaces of enclosing rock
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Energy Resources – Oil and Natural Gas
GEOL 131: Sedimentary Rocks – Economic Resources Energy Resources – Oil and Natural Gas Oil traps Any geologic environment where economically significant amounts accumulate underground 2 features: Reservoir rock: porous, permeable rock that yields petroleum and natural gas Cap rock: virtually impermeable to gas and oil
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Energy Resources – Hydraulic Fracturing
GEOL 131: Sedimentary Rocks – Economic Resources Energy Resources – Hydraulic Fracturing Some shales contain significant reserves of natural gas that cannot naturally leave Process: Shale is shattered by pumping in fluids at very high pressures, cracks opened allow gas to flow into wells that can then be tapped to bring gas to surface Controversial Groundwater contamination Increased earthquakes
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End of Sedimentary Rocks Chapter
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