op ch07 lecture_earth3, sedimentary rocks

Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 7: A Surface Veneer: Sediments, Soils and Sedimentary Rocks

Chapter 7A Surface Veneer: Sediments, Soils, and

Sedimentary Rocks

©2008 W. W. Norton & Company, Inc.

Portrait of a PlanetThird Edition

earthearth

LECTURE OUTLINE

A Surface Veneer:Sediments, Soils, and Sedimentary RocksA Surface Veneer:Sediments, Soils, and Sedimentary Rocks

Prepared by

Ron Parker Earlham College Department of Geosciences

Richmond, Indiana


SedimentsSediments The Nile flows over a canyon filled by thick sediments.The Nile flows over a canyon filled by thick sediments.

The size of Grand Canyon.The size of Grand Canyon. The canyon was carved by the Nile.The canyon was carved by the Nile. Indicates the Mediterranean has evaporated and re-filled. Indicates the Mediterranean has evaporated and re-filled.

Sediment:Sediment: Rock and mineral fragments.Rock and mineral fragments. Shells.Shells. Mineral precipitates.Mineral precipitates.

Cemented into rocks.Cemented into rocks.


Sedimentary CoverSedimentary Cover Earth is covered by a thin “veneer” of sediment.Earth is covered by a thin “veneer” of sediment. The veneer caps igneous and metamorphic “basement.” The veneer caps igneous and metamorphic “basement.” Sediment cover varies in thickness from 0 to 20 km.Sediment cover varies in thickness from 0 to 20 km.

Thinner (or missing) where ig and meta rocks outcrop.Thinner (or missing) where ig and meta rocks outcrop. Thicker in sedimentary basins.Thicker in sedimentary basins.


WeatheringWeathering Processes that break up rock to create sediment.Processes that break up rock to create sediment.

Physical - Mechanical breakage and disintegration.Physical - Mechanical breakage and disintegration. Chemical - Decomposition by reaction with water. Chemical - Decomposition by reaction with water.

Weathering processes occur at Earth’s surface.Weathering processes occur at Earth’s surface. Rocks react with hydrosphere, atmosphere, and biosphere. Rocks react with hydrosphere, atmosphere, and biosphere. Low temperature and pressure.Low temperature and pressure.


Physical WeatheringPhysical Weathering Mechanical breakup; doesn’t change mineral makeup.Mechanical breakup; doesn’t change mineral makeup. Creates broken fragments or “detritus.”Creates broken fragments or “detritus.” Detrital fragments classified by size.Detrital fragments classified by size.

Coarse-grained – Boulders, cobbles, and pebbles.Coarse-grained – Boulders, cobbles, and pebbles. Medium-grained – Sand-sized.Medium-grained – Sand-sized. Fine-grained – Silt and clay (mud).Fine-grained – Silt and clay (mud).


Physical WeatheringPhysical Weathering Types of physical weathering.Types of physical weathering.

Jointing.Jointing. Frost wedging.Frost wedging. Root wedging.Root wedging. Salt wedging.Salt wedging. Thermal expansion.Thermal expansion. Animal activity.Animal activity.

Physically weathered rock fragments move by gravity. Physically weathered rock fragments move by gravity. Large blocks often accumulate as talus below a cliff.Large blocks often accumulate as talus below a cliff. Smaller fragments are carried away by water and wind.Smaller fragments are carried away by water and wind.


JointingJointing Deep crustal rocks are hot and under high pressure. Deep crustal rocks are hot and under high pressure. Erosion removes material; deep rocks become exposed. Erosion removes material; deep rocks become exposed. At the surface, crustal rocks cool and expand. At the surface, crustal rocks cool and expand. This causes through-going fractures called This causes through-going fractures called jointsjoints.. Joints may exhibit a variety of geometries.Joints may exhibit a variety of geometries.


JointingJointing Igneous plutons crack in onionlike “exfoliation” layers.Igneous plutons crack in onionlike “exfoliation” layers. These layers break off as sheets that slide off of a These layers break off as sheets that slide off of a

pluton. pluton. Over time, this process creates domed remnants. Over time, this process creates domed remnants. Examples: Half-Dome (Ca.) and Stone Mountain (Ga.). Examples: Half-Dome (Ca.) and Stone Mountain (Ga.).

W. W. NortonW. W. Norton


Chemical WeatheringChemical Weathering Reaction with water disintegrates many minerals. Reaction with water disintegrates many minerals. Water is the universal solvent. Water is the universal solvent.

Maximized under warm and wet conditions. Maximized under warm and wet conditions. Tropical weathering is intensive.Tropical weathering is intensive.Turns rock into heavily decomposed “saprolite.”Turns rock into heavily decomposed “saprolite.”

Chemical weathering is virtually absent in deserts.Chemical weathering is virtually absent in deserts.


Chemical WeatheringChemical Weathering Forms stable minerals from unstable precursors.Forms stable minerals from unstable precursors. Common chemical weathering reactions include:Common chemical weathering reactions include:

Dissolution.Dissolution. Hydrolysis.Hydrolysis. Oxidation.Oxidation. Hydration.Hydration.


Chemical WeatheringChemical Weathering DissolutionDissolution

Some minerals (halite, gypsum, calcite) dissolve.Some minerals (halite, gypsum, calcite) dissolve.CaCOCaCO33 + H + H22COCO33 +2H +2H++ = 2H = 2H22O + 2COO + 2CO22 +Ca +Ca2+2+

(calcite) + (carbonic acid) + (hydrogen ion) = (water) + (carbon dioxide) + (calcium ion)(calcite) + (carbonic acid) + (hydrogen ion) = (water) + (carbon dioxide) + (calcium ion)

Acidity (Acidity (i.e.i.e. acid rain) enhances this effect. acid rain) enhances this effect.


HydrolysisHydrolysis Water breaks cation bonds in silicate minerals. Yields…Water breaks cation bonds in silicate minerals. Yields…

Dissolved cations.Dissolved cations. Alteration residues.Alteration residues.

Clay minerals.Clay minerals.Iron oxides (rust).Iron oxides (rust).


Chemical WeatheringChemical Weathering OxidationOxidation

A reaction whereby a metal loses electrons.A reaction whereby a metal loses electrons. Important process in mafic silicate decomposition.Important process in mafic silicate decomposition. Rusting is a familiar example.Rusting is a familiar example.

Hydration Hydration Absorption of water into a mineral structure.Absorption of water into a mineral structure. Results in a volume increase (expansion).Results in a volume increase (expansion). Important processes in some clay minerals. Important processes in some clay minerals.


Chemical WeatheringChemical Weathering Minerals differ in their tendency to weather chemically.Minerals differ in their tendency to weather chemically. Silicate weathering susceptibility predicted by stability.Silicate weathering susceptibility predicted by stability.

Temperature (T) and pressure (P) are a dominant control.Temperature (T) and pressure (P) are a dominant control.High T and P minerals tend to weather quickly at low T and P.High T and P minerals tend to weather quickly at low T and P.Low T and P minerals are more stable at Earth’s surface.Low T and P minerals are more stable at Earth’s surface.


Organisms often important chemical weathering agents.Organisms often important chemical weathering agents. Plant roots.Plant roots. Fungi.Fungi. Lichens.Lichens. Bacteria.Bacteria.

Organic acids Organic acids

attack minerals.attack minerals.

Biological WeatheringBiological Weathering


Weathering FeedbacksWeathering Feedbacks Weathering processes often work as a positive feedback. Weathering processes often work as a positive feedback.

Physical weathering speeds chemical weathering. How? Physical weathering speeds chemical weathering. How?

An increase in surface area accelerates chemical attack.An increase in surface area accelerates chemical attack. Chemical weakening increases surface area via breakage. Chemical weakening increases surface area via breakage.


Chemical Weathering RateChemical Weathering Rate Block geometry influences weathering. Block geometry influences weathering.

Corners weather fastest; 3 sides of attack.Corners weather fastest; 3 sides of attack. Edges weather at a moderate rate (2 sides).Edges weather at a moderate rate (2 sides). Flat faces weather slowest (1 side). Flat faces weather slowest (1 side).

Cube-shaped rocks develop “spheroidal weathering.”Cube-shaped rocks develop “spheroidal weathering.”


Differential WeatheringDifferential Weathering Rates of weathering attack vary due to changes in… Rates of weathering attack vary due to changes in…

Mineral stability.Mineral stability. Degree of compaction or cementation. Degree of compaction or cementation. Subtle differences in texture, etc. Subtle differences in texture, etc.

Major control on surficial expression.Major control on surficial expression.


SoilSoil ““Soil consists of rock and sediment that has been Soil consists of rock and sediment that has been

modified by physical and chemical interaction with modified by physical and chemical interaction with organic material and rainwater, over time, to produce a organic material and rainwater, over time, to produce a substrate that can support the growth of plants.”substrate that can support the growth of plants.”

Soil-forming processes require long periods of time. Soil-forming processes require long periods of time. Soil may be easily destroyed by human activities.Soil may be easily destroyed by human activities. Soil is a crucial natural resource in need of protection. Soil is a crucial natural resource in need of protection.


The Soil ProfileThe Soil Profile Soil forms a vertical sequence of layers called a profile.Soil forms a vertical sequence of layers called a profile. Profiles develop from the surface downward. Profiles develop from the surface downward.

Weathering generates detritus. Weathering generates detritus. Rainwater alters the detritus. Rainwater alters the detritus.

Individual layers are horizons.Individual layers are horizons. The upper horizons form topsoil. The upper horizons form topsoil.

The only fertile part of the profile.The only fertile part of the profile. Easily removed by erosion.Easily removed by erosion. 1000s of years in the making.1000s of years in the making.


Soil-Forming ProcessesSoil-Forming Processes Coffee is a direct analogue.Coffee is a direct analogue. Zone of leaching – Upper soil Zone of leaching – Upper soil

profile.profile. Ions from chemical weatheringIons from chemical weathering Fine silts and clays infiltrate.Fine silts and clays infiltrate.

Zone of accumulation – Zone of accumulation – Lower soil profile. Lower soil profile.

Ions form new minerals.Ions form new minerals.Silts and clays clog pore Silts and clays clog pore spaces. spaces.


Soil HorizonsSoil Horizons Distinct horizons reflect soil-Distinct horizons reflect soil-

forming processes.forming processes. O Horizon – Dark organic O Horizon – Dark organic

matter-rich surface layer.matter-rich surface layer. A Horizon – Organic and mineral A Horizon – Organic and mineral

matter.matter. E Horizon – Transitional layer E Horizon – Transitional layer

leached by organic acids. leached by organic acids. B Horizon – Organic-poor B Horizon – Organic-poor

mineral rich layer. mineral rich layer. C Horizon – Slightly altered C Horizon – Slightly altered

bedrock. bedrock.


Soil-Forming FactorsSoil-Forming Factors Soil genesis influenced by a number of factors. Soil genesis influenced by a number of factors.

Climate – Amount of water and warmth.Climate – Amount of water and warmth. Substrate composition – Soil parent minerals. Substrate composition – Soil parent minerals. Slope steepness – Soils develop best on low slopes. Slope steepness – Soils develop best on low slopes. Drainage – Wet soils are more organic-rich.Drainage – Wet soils are more organic-rich. Time – Older soils are more developed. Time – Older soils are more developed. Vegetation – Controls type of organic matter added.Vegetation – Controls type of organic matter added.


Soil vs. ClimateSoil vs. Climate Climate exerts a dominant control on soil development.Climate exerts a dominant control on soil development.

Latitude.Latitude. Elevation.Elevation.


Human activities can make soil unproductive.Human activities can make soil unproductive. Crops can strip soil nutrients. Crops can strip soil nutrients. Topsoil erodes away when vegetation is removed. Topsoil erodes away when vegetation is removed.

Topsoil is sometimes mined and sold; usually a bad Topsoil is sometimes mined and sold; usually a bad idea.idea.

Soil quality is degraded by…Soil quality is degraded by… Overuse of pesticides.Overuse of pesticides. Industrial contamination.Industrial contamination. Salt build-up.Salt build-up.

It is wise to protect soils.It is wise to protect soils.

Soil Use and MisuseSoil Use and Misuse


Sedimentary RocksSedimentary Rocks Sediments are the building blocks of sedimentary rocks.Sediments are the building blocks of sedimentary rocks. Sediments are diverse, as are the rocks made from them. Sediments are diverse, as are the rocks made from them. 4 classes: 4 classes:

Clastic – Made from weathered rock fragments (clasts). Clastic – Made from weathered rock fragments (clasts). Biochemical – Cemented shells of organisms.Biochemical – Cemented shells of organisms. Organic – The carbon-rich remains of plants.Organic – The carbon-rich remains of plants. Chemical – Minerals that crystallize directly from water. Chemical – Minerals that crystallize directly from water.

ClasticClastic ChemicalChemicalOrganicOrganicBiochemicalBiochemical


Clastic Sedimentary RocksClastic Sedimentary Rocks Clastic sedimentary rocks reflect several processes. Clastic sedimentary rocks reflect several processes.

Weathering – Generation of detritus via rock disintegration.Weathering – Generation of detritus via rock disintegration. Erosion – Removal of sediment grains from rock.Erosion – Removal of sediment grains from rock. Transportation – Dispersal by wind, water, and ice.Transportation – Dispersal by wind, water, and ice. Deposition – Accumulation after transport stops. Deposition – Accumulation after transport stops. Lithification – Transformation into solid rock.Lithification – Transformation into solid rock.


Clastic Sedimentary RocksClastic Sedimentary Rocks Lithification – Transforms loose sediment into solid rock.Lithification – Transforms loose sediment into solid rock.

Burial – More sediment is added onto a previous layer.Burial – More sediment is added onto a previous layer. Compaction – Overburden weight reduces pore space.Compaction – Overburden weight reduces pore space.

Sand – 10-20%Sand – 10-20%Clay – 50-80%Clay – 50-80%

Cement – Minerals from groundwater that “glue” sediment.Cement – Minerals from groundwater that “glue” sediment.


Clastic Sedimentary RocksClastic Sedimentary Rocks Classified on the basis of texture and composition.Classified on the basis of texture and composition.

Clast (grain) size.Clast (grain) size. Clast composition. Clast composition. Angularity and sphericity.Angularity and sphericity. Sorting.Sorting. Character of cement.Character of cement.

These variables produce a diversity of clastic rocks.These variables produce a diversity of clastic rocks.


Clastic Sedimentary RocksClastic Sedimentary Rocks Clast (grain) size – The average diameter of clasts.Clast (grain) size – The average diameter of clasts. Range from very coarse to very fine.Range from very coarse to very fine.

Boulder, cobble, pebble, and pea gravel.Boulder, cobble, pebble, and pea gravel. Coarse, medium, and fine sand.Coarse, medium, and fine sand. Coarse, medium, and fine silt.Coarse, medium, and fine silt. Coarse and fine clay.Coarse and fine clay.

With increasing transport, average grain size decreases. With increasing transport, average grain size decreases.


Clastic Sedimentary RocksClastic Sedimentary Rocks Clast composition – Mineral makeup of clasts.Clast composition – Mineral makeup of clasts.

May be individual minerals or rock fragments.May be individual minerals or rock fragments. Mineral identity important. Mineral identity important.

Stable end-products of weathering (quartz, Fe-oxides, clays).Stable end-products of weathering (quartz, Fe-oxides, clays).Unstable minerals signify special conditions (feldspars).Unstable minerals signify special conditions (feldspars).

Composition helps to decipher depositional history.Composition helps to decipher depositional history.


Clastic Sedimentary RocksClastic Sedimentary Rocks Angularity and sphericity – Indicate degree of transport.Angularity and sphericity – Indicate degree of transport. Fresh detritus is usually angular and non-spherical. Fresh detritus is usually angular and non-spherical. Grain roundness and sphericity increases with transport. Grain roundness and sphericity increases with transport.

Well-rounded – Long transport distances.Well-rounded – Long transport distances. Angular – Negligible transport.Angular – Negligible transport.


Clastic Sedimentary RocksClastic Sedimentary Rocks Sorting – The uniformity of grain size. Sorting – The uniformity of grain size.

Well-sorted – Uniform grain size.Well-sorted – Uniform grain size. Poorly sorted – Wide variety of grain sizes.Poorly sorted – Wide variety of grain sizes.

Sorting indicates the constancy of environmental Sorting indicates the constancy of environmental energy.energy. Well-sorted – Uniform energy (i.e., a beach).Well-sorted – Uniform energy (i.e., a beach). Poorly sorted – Variable energy (i.e., an alluvial fan).Poorly sorted – Variable energy (i.e., an alluvial fan).


Clastic Sedimentary RocksClastic Sedimentary Rocks Cement – Minerals that fill sediment pores.Cement – Minerals that fill sediment pores.

Fluids with dissolved solids flush through pore system. Fluids with dissolved solids flush through pore system. Dissolved ions slowly crystallize in (and fill) pores.Dissolved ions slowly crystallize in (and fill) pores.

Cementation varies in degree.Cementation varies in degree. Weakly cemented (friable) – Grains easily pulled from rock. Weakly cemented (friable) – Grains easily pulled from rock. Strongly cemented (indurated) – Grains hard to dislodge.Strongly cemented (indurated) – Grains hard to dislodge.

Common cements:Common cements: QuartzQuartz CalciteCalcite HematiteHematite Clay minerals Clay minerals


Clastic Sedimentary RocksClastic Sedimentary Rocks Maturity – A measure of the degree of “processing.”Maturity – A measure of the degree of “processing.”

Textural maturity – Degree of roundness and sorting.Textural maturity – Degree of roundness and sorting. Mineral maturity – Degree of unstable mineral removal. Mineral maturity – Degree of unstable mineral removal.

Time and transport causes sediment evolution. Time and transport causes sediment evolution. Texture - Average grain size Texture - Average grain size ; roundness and sorting ; roundness and sorting .. Composition - Unstable minerals Composition - Unstable minerals ; Stable minerals ; Stable minerals . .

Maturity is used to reconstruct depositional conditions. Maturity is used to reconstruct depositional conditions.


Clastic Sedimentary RocksClastic Sedimentary Rocks Coarse clastics - Composed of gravel-sized clasts. Coarse clastics - Composed of gravel-sized clasts.

Breccia – Comprised of angular clasts.Breccia – Comprised of angular clasts.Indicates lack of transport processing.Indicates lack of transport processing.Deposited close to source.Deposited close to source.

Conglomerate – Comprised of rounded clasts. Conglomerate – Comprised of rounded clasts. Indicates processing by transport. Indicates processing by transport. Deposited away from source area.Deposited away from source area.


These are sediments derived from living organisms. These are sediments derived from living organisms. Biochemical limestone – Made from Biochemical limestone – Made from CaCOCaCO33 shell remains. shell remains.

Carbonate grains accumulate in the “carbonate factory.” Carbonate grains accumulate in the “carbonate factory.” Warm (tropical and subtropical). Warm (tropical and subtropical). Normal-salinity marine water. Normal-salinity marine water. Wave-agitated.Wave-agitated.Oxygenated.Oxygenated.Shallow. Shallow. Clear.Clear.

Biochemical and Organic RocksBiochemical and Organic Rocks


Organic rocks – Made from organic carbon. Organic rocks – Made from organic carbon. Coal – Altered remains of fossil vegetation. Coal – Altered remains of fossil vegetation.

Accumulates in lush tropical wetland settings. Accumulates in lush tropical wetland settings. Requires deposition in the absence of oxygen.Requires deposition in the absence of oxygen.

Oil shale – Shale with heat-altered organic matter.Oil shale – Shale with heat-altered organic matter.

Biochemical and Organic RocksBiochemical and Organic Rocks


Chemical Sedimentary RocksChemical Sedimentary Rocks Comprised of minerals precipitated from water solution.Comprised of minerals precipitated from water solution. Evaporites – Created from evaporated seawater.Evaporites – Created from evaporated seawater.

Evaporation triggers deposition of chemical precipitates.Evaporation triggers deposition of chemical precipitates. Examples include halite (rock salt) and gypsum.Examples include halite (rock salt) and gypsum.


Sedimentary StructuresSedimentary Structures Sedimentary rocks are usually layered or “stratified.” Sedimentary rocks are usually layered or “stratified.”

Arranged in planar, horizontal “beds.”Arranged in planar, horizontal “beds.” Bedding is often laterally continuous for long distances.Bedding is often laterally continuous for long distances. Beds are often similar in composition, color, and texture.Beds are often similar in composition, color, and texture.


Sedimentary StructuresSedimentary Structures Bedding caused by changing conditions during Bedding caused by changing conditions during

deposition.deposition. These can be changes in…These can be changes in…

Energy conditions, and hence, grain size.Energy conditions, and hence, grain size. Disturbance by organisms.Disturbance by organisms.

Bedding may also reflect non-deposition or erosion.Bedding may also reflect non-deposition or erosion.


Sedimentary StructuresSedimentary Structures A series of beds are referred to as strata.A series of beds are referred to as strata. A sequence of strata that is sufficiently unique to be A sequence of strata that is sufficiently unique to be

recognized on a regional scale is termed a formation. recognized on a regional scale is termed a formation. The formation is the fundamental geologic mapping unit. The formation is the fundamental geologic mapping unit.

Example: Note how the prominent Example: Note how the prominent white cliff-forming band of the white cliff-forming band of the Coconino Formation can be visibly Coconino Formation can be visibly traced across Grand Canyon.traced across Grand Canyon.


Sedimentary StructuresSedimentary Structures Water flowing over loose sediment creates bedforms.Water flowing over loose sediment creates bedforms. Bedforms are linked to flow velocity and sediment size.Bedforms are linked to flow velocity and sediment size.

Ripples, cm-scale ridges, and troughs indicate flow. Ripples, cm-scale ridges, and troughs indicate flow. Asymmetric ripples – Unidirectional flow. Asymmetric ripples – Unidirectional flow. Symmetric ripples – Wave oscillation.Symmetric ripples – Wave oscillation.Ripples are commonly preserved in sedimentary rocks.Ripples are commonly preserved in sedimentary rocks.


BedformsBedforms Dunes – Similar to ripples except much larger.Dunes – Similar to ripples except much larger. Cross-bedding – Created by ripple and dune migration.Cross-bedding – Created by ripple and dune migration.

Sediment moves up the gentle side of a ripple or dune.Sediment moves up the gentle side of a ripple or dune. Sediment piles up, then slips down the steep face.Sediment piles up, then slips down the steep face.

The slip face continually moves downstream.The slip face continually moves downstream.Added sediment forms sloping “cross-bedded” layers.Added sediment forms sloping “cross-bedded” layers.


BedformsBedforms Graded Beds – Bedding layers that fine upward. Graded Beds – Bedding layers that fine upward.

Transition from coarse to medium to fine grain sizes. Transition from coarse to medium to fine grain sizes. Base of coarse sand and gravel. Base of coarse sand and gravel. Mid-level sands.Mid-level sands.A fine silt and clay cap. A fine silt and clay cap. Abrupt contact with overlying coarse base. Abrupt contact with overlying coarse base.


Depositional EnvironmentsDepositional Environments Locations where sediment accumulates. They differ in…Locations where sediment accumulates. They differ in…

Energy regime (mostly comes from the sun; gravitational Energy regime (mostly comes from the sun; gravitational and chemical potential energy)and chemical potential energy)

Sediment delivery, transport and depositional conditions.Sediment delivery, transport and depositional conditions. Chemical, physical and biological characteristics.Chemical, physical and biological characteristics.

Environments range from continental to marine.Environments range from continental to marine.

Depositional conditions may be inferred from sediments.Depositional conditions may be inferred from sediments.


Depositional EnvironmentsDepositional Environments Terrestrial environments – Deposited above sea level.Terrestrial environments – Deposited above sea level.

Glacial – Due to movement of ice.Glacial – Due to movement of ice.Ice carries and dumps every grain size.Ice carries and dumps every grain size.Creates glacial till; poorly sorted gravel, sand, silt, and clay.Creates glacial till; poorly sorted gravel, sand, silt, and clay.


Depositional EnvironmentsDepositional Environments Terrestrial environments.Terrestrial environments.

Mountain streams.Mountain streams.Water carries large clasts during floods. Water carries large clasts during floods. During low flow, boulders are immobile.During low flow, boulders are immobile.Course conglomerate is characteristic. Course conglomerate is characteristic.



Alluvial fan - Sediments that pile up at a mountain front. Alluvial fan - Sediments that pile up at a mountain front. Rapid drop in stream velocity creates a cone-shaped wedge. Rapid drop in stream velocity creates a cone-shaped wedge. Sediments are immature conglomerates and arkoses. Sediments are immature conglomerates and arkoses.



Rivers – Channelized flow transports sediment.Rivers – Channelized flow transports sediment.Sand and gravel fills concave-up channels.Sand and gravel fills concave-up channels.Fine sand, silt, and clay is deposited on flood plains.Fine sand, silt, and clay is deposited on flood plains.


Depositional EnvironmentsDepositional Environments Marine environments – Deposited at or below sea-level.Marine environments – Deposited at or below sea-level.

Deltas – Sediments dropped where a river enters the sea.Deltas – Sediments dropped where a river enters the sea.River flow halts at the ocean. River flow halts at the ocean. Sediment carried by the river is dumped when velocity drops.Sediment carried by the river is dumped when velocity drops.Deltas grow over time, building out into the basin.Deltas grow over time, building out into the basin.Often develop a topset – foreset – bottomset geometry.Often develop a topset – foreset – bottomset geometry.


Depositional EnvironmentsDepositional Environments Marine environments.Marine environments.

Shallow marine – Finer version of beach sediment.Shallow marine – Finer version of beach sediment.Fine silts and muds.Fine silts and muds.Biologically active. Biologically active. Siltstone and mudstone.Siltstone and mudstone.



Shallow water carbonates – Tropical.Shallow water carbonates – Tropical.Skeletons of marine invertebrates.Skeletons of marine invertebrates.Born in the carbonate factory.Born in the carbonate factory.Warm, clear, shallow, normal salinity marine water.Warm, clear, shallow, normal salinity marine water.



Deep marine – Fines predominate far from land sources.Deep marine – Fines predominate far from land sources.Skeletons of planktonic organisms make chalk or chert.Skeletons of planktonic organisms make chalk or chert.Fine silts and clays turn to shale.Fine silts and clays turn to shale.


Sedimentary BasinsSedimentary Basins Sediments vary in thickness across Earth’s surface.Sediments vary in thickness across Earth’s surface.

Thin to a zero edge where non-sedimentary rocks outcrop.Thin to a zero edge where non-sedimentary rocks outcrop. Thicken to 10 to 20+ km where the surface has subsided. Thicken to 10 to 20+ km where the surface has subsided.

Subsidence – Sinking of the land during sedimentation. Subsidence – Sinking of the land during sedimentation. Due to crustal flexure and faulting. Due to crustal flexure and faulting. Compounded by the weight of added sediments. Compounded by the weight of added sediments.

Basins are important locations for natural resources.Basins are important locations for natural resources. Coal Coal PetroleumPetroleum Natural gasNatural gas UraniumUranium


Sedimentary BasinsSedimentary Basins Basins form where tectonic activity creates space. Basins form where tectonic activity creates space.

Rift basins – Divergent (pull-apart) plate boundaries.Rift basins – Divergent (pull-apart) plate boundaries.Crust thins by stretching and rotational normal faulting.Crust thins by stretching and rotational normal faulting.Thinned crust subsides. Thinned crust subsides. Sediment fills the down-dropped basin.Sediment fills the down-dropped basin.


Sedimentary BasinsSedimentary Basins Basins form where tectonic activity creates space. Basins form where tectonic activity creates space.

Passive margins – Non-plate boundary continental edge.Passive margins – Non-plate boundary continental edge.Underlain by crust thinned by previous rifting.Underlain by crust thinned by previous rifting.Thinned crust subsides as it cools.Thinned crust subsides as it cools.


DiagenesisDiagenesis Physical, chemical, and biological changes to sediment. Physical, chemical, and biological changes to sediment.

Bioturbation (The stirring or mixing of sediment or soil by Bioturbation (The stirring or mixing of sediment or soil by organisms)organisms)

Lithification.Lithification. Dissolution.Dissolution. Mineral precipitation.Mineral precipitation. Pressure solution.Pressure solution.

Temp range between burial and metamorphism (~300Temp range between burial and metamorphism (~300ooC).C). Integrates changes across the entire sediment history.Integrates changes across the entire sediment history.


Chapter 7A Surface Veneer: Sediments, Soils, and

Sedimentary Rocks

©2008 W. W. Norton & Company, Inc.

Portrait of a PlanetThird Edition

earthearth

LECTURE OUTLINE

This concludes the

op ch07 lecture_earth3, sedimentary rocks

Technology

surface veneer

stephen marshakchapter

sedimentary cover earth

veneer of sediment

chemical weathering

thick sediments

earths surface

sedimentary basins