SEDIMENTARY PETROLOGY (WEATHERING AND EROSION) Flashcards
Weathering vs Erosion
Weathering process involve insitu breakdown of rock material in a particular location while
Erosion is the removal of rock material from a geographic location which intitiates its transport to another location
Disintegration vs Decomposition
Disintergration - physical breakdown into smaller fragments of same composition can be caused by mechanical or bioligical processes while Decomposition - breakdown of rock material that changes its chemical composition and alters rock mineralogy
Factors that affect Rate and Type of Weathering
- Climate
- Rock Type
- Slope
- Time
Climate of Disintegration
Cold and Dry Climate
Climate of Decomposition
Warm and wetter Climate
Source of Sed Rocks
Provenance
What type of slope favors long term decomposition?
Gentle Slopes
Fractures with no tangential movement has taken place
Joints
Joints during weathering are mostly formed due to
Decrease in Confining Pressure
another name for hoodos
spires
Pressure exterted on buried rock objects
Lithostatic or Confining Pressure
Decrease in Lithostatic Pressure
Unloading or decompression
When rocks expand by this much they tend to fracture
1-2%
Rocks fractures that open sub-parallel to Earth’s Surface and tend to form under upwardly convex surfaces such as domes and ridges in homogenous rocks like granites
Sheet joints
In rocks experience sheet joints what is the direction of the maximum tensile stress
Perpendicular to the convex Surface
Used to describe sheet joints that resemble the curved surface of an onion
Exfoliation
occurs when preexisting fractures and weak surfaces are enlarged by the expansion of water as it freezes
Frost Action or Shattering
Frost Wedging vs Frost Heaving
FW occurs along fractures oriented steeply (Perpendicular) to Earth’s Surace FH occurs on surfaces parallel to the earth’s surface
Process which may pry rock material apart as the crystal grows in farcture or pore spaces
Crystal Growth
Occurs when minerals such as clays and micas EXPAND when wetted
Slaking
This results from daily or seasonal changes in rock temperature and may cause significant amounts of disintegration
Thermal Volume Change (Insolation)
Disintegration of rock due to heating or change in temp
Spalling
How does Disintegration enhances decomposition
By increasing the surface area
An interplay between Disint and Decom in which massive, well jointed rocks such as granite, grabbro and basalts weather in spheroidal forms
Spheroidal Weathering
this is wehere three chemical active faces intersect
Corner
The most significant agent in decomposition
Downwad Percolating Water
Occurs when a mineral or other soil component is wholly or partially dissovled during chemical decomposition
Dissolution
When CO2 gas dissolves in water this form
Carbonic Acid H2CO3 (aq)
When carbonic acid reacts with calcite it produced calclum ions dissolved in Bicabonate Ions in the process called
Carbonation
In what place is karst topography named after?
Karst Region, Slovenia
Occurs when ions are directly exhanged between a mineral and a solution
Ion Exchange
IN what climate is feldspar decomposition faster?
Warm because soil waters are rich in H-ions and thus acidic
Most abundant mineral in the crust
Feldspars
Removal of Potassium from Illite converts it into
Kaolinite common in acidic soils
A chemical reaction between a mineral and water in which dissolved Hydrogen ions and/or hydroxyl ions are added to form one or more new minerals
Hydrolysis
In most hydrolysis reaction whats mostly the orig mineral?
Silicic
What mostly is the resulting product?
Hydroxide or Clay Mineral
The most abunant group of new minerals produce during chemical decomposition and the most abudant constituent of mud fraction of detrital sediments in soil
Clay minerals
Size of Clay sediments
<4micrometer
Hydrolysis of Mn bearing olivine produceds
Pyrolusite (MnO2)
This involves addition of water to a crystal structure during reaction between a mineral and the aqueous solution
Hydration
Reverse of hydration and reults from the removal or loss of water
Dehydration
When hematite undergo hydration it produces what mineral? Hydrated Hematite
Goethite
A chemical reaction in which one or more electrons are transferred from a cation in the mineral to oxygen thus increasing the valence cation.
Oxidation
Is the production of an oxide mineral required in oxidation reaction?
No, only the loss of electron
Oxidation of Fayalite results to
Hematite
During such reaction the valence of iron increases from what to what
Fe+2 to Fe+3
Oxidation of Manganese Silicate (Rhodonite) results to the formation of
Manganite
Oxidation of Pyrite results to the formation of
Hematite
Reaction which involve the loss of electrons
Reduction
Example of Reduction reaction
Hematite to Pyrite Tranformation
Organic hydrocarbon ring complex produced directly by LICHEN (algae) and indirectly by deacy of humus and which tend to bind metallic elements thus removing them from solution
Chelates
Process w/c often involves the exchange of Hydrogen ions from the chelating agen to the soluton and metal ions from the solution to the chelate (Hydrogen in excange of Metal)
Chelattion
Implication of the release of hydrogen ion and addition to soil water
Lowers the pH of the Solution and makes it more acidic
The higher the CO2 content of the soil
The more acidic the soil water would be since there is a higher conc. Of dissolved Hydrogen
Concenration of dissolved solids in mineral water
250ppm
concentration of dissolved solids in Rain water
10ppm
Addition of this mineral in soluble form is used to produce water in breweries
Gypsum
large scale dissoluton result in the formation of large cavities known as that frequently contain underground streams that enter the subsurface down disslution features and emerge as cave springs
Cave
Circular ovoid depression formed by dissoluton or collapse
Dolines or sinkholes
Solid inorganic components of residual soils
Detrital Seds
Detritas which are residual minerals and lithic fragments of orig parent rock which have survived decomposition
Resistates
New Mineral produced by Oxidation?
Hem, Goethite, Pyrolusite
New minerals produced by Hydrolysis?
Clay
Minerals that resist decomposition are
chemically stable
What is the bond of resistant minerals
Covalent
Chemical stability of minerals depend on
1) Climate
2) Soil Geochem
Inverted Bowens and applied to geological processes involving mienral stability
Goldich Stability Series
What is Goldich Rules
Susceptibility of Common Igneous Minerals is inversely proportional to their crystalliztaion Temp.
Minerals which crystallizes at high temp is prone to dissolution and or less table under surface temp
High temp minerals which are unstable at lower temp and low pressure environments at the surface
Oli, Pyx, Amph Ca-Plag
Mineral which becomes depleted from the resistate Population
Halite, Calciete, Olivine, Pyx
Minerals which are enriched in the resitate po
Qtx, Clay, FeO
Malakas Grp
Hematite, Gibbsite, Qtx, Rutile, Toutmaline, Zircon
Saks Group
Clay, Muscovite, Orthoclase, Biot, NaPlag, Amph
Mahina Grp
Ca Plag, Pyx, Oliv, Halite, Calcite
What is the relationship between erosion rates and population or distribution of Unstable Minerals?
The lower the erosion rate the lesser the concentration of Unstable minerals in the resistate because of enanced decomposition
Higher Erosionn rates promote dispersion of unstable mienrals in areas of deposition and thus higher proportion
Factors affecting Erosion (RVPEA)
Relief
Vegetaion
Precipitation
Erosional Agent
How do relief affect erosion
High Relief High Erosion
How does vegetation affect erosion
High Vegetation Low Erosion Rate
Agen which is most powerfull in terms of erosion
Glacier or Ice
Where is wind erosion most effective?
areas which are sparsely convered by vegetation and with low rainfall (rel.dry)
Rate at which precipitation increases erosion
350-400 mm/yr because eof the presence of hardpan soil, minimal inflitation, poorly vegetated soil
Rate at which precipitation decreases erosion
350-400 - 890-1015/mm yr thich vegetative cover retard erosion
Most abundant new minerals produced by decomposition, particularly of hydrolysis
Clay mienrals
IN terms of composition, Clay is under what mineral group ?
Phyllosilicates
In terms of texture, whats the size of clay particles?
<0.004 mm in diameter which may or may not be clay in mineralogy
Structures of Phyllosilicates?
?two or more sheets or layers connected by shared bondings
?separated by interlayer sites
Three major types of Sheets or layers in Clay Structures
1) S-Layer (Silica rich)/ T-layer
2) G-Layer (Gibbsite)/ O-layer Al-rich
3) B-Layer (Brucite)Fe-Mg Rich
How many nodes are there in an octahedral Layer?
6
How many nodes are there in a tetrahedral layer?
4
How many major groups of clay are there?
4
The distance between layers hich can be extremeley helpful in distinguishing between clay minerals in XRD
Repeat Distance
Clay major Groups
Group
Hybrid clays which contains layers sequence of more than one type
Mixed Layer Clays
Clays that lack interlayer constituents which may have been removed by pore waters during decomposition or other types of alteration
Degraded Clay mienrals
Conditions at which degraded clay minerals occu
Acidic conditions
aka lateritic soils
oxisols
Formation of insoluble Fe and Mn oxides and hydroxides
Decomposition of Ferromag silicates and Fe bearing sulfides
Mineral responsible for reddish color of soil
Hematite
mineral responsible for yellow brown color of soil
Limonite and goethite
What coloration does manganese mineral produce to soild
Black to dark gray
How does Bauxite form?
when decomposition of clay mienrls dissolve silica leaving Al combined with Hydroxyl and Oygen and some water
IN what conditions does bauxite form?
Acidic, Warm, Arid Climates
Common minerals in Bauxite
Gibbsite
Why is bauxite considered more as an ore mineral?
Because Al can be easily isolated from Oxide and hydroxide than from Silica
Solid in which Calcite and Aragonite, Gypsum and Anhydrite are abundant
Caliche Soil/ Aridosols
Soils which develop in ANOXIC, REDUCING environments and contains Pyrite
Histosols
small clumps of partially indurated material composed of precipiatted minerals in Soils
Soil Peds
Soild Crusts produced by precipitation of minerals from soils
Durisols or Petrosols or Hardpan
Largely unconsolidated surficial deposits produced by weathering processes capable of supporting rooted plant life
Soils
Soils produced from weathering of bedrock
Residual Soils
Transported sediments
Transported or Alluvial Soils
Proportoions of major component of soil
5 25 25 45
Organic Matter
Air
Water
Mineral and Rock Particles
Partially decayed, dead oranic matter
Humus
Contains more clay than sand and silt
Clay soil
A term used for soil that contain subequal proportion of Sand, Silt and Clay Soils
Loam
Importance of Soil
Natural Resources
Structure Bearing Materials
Water Flters and Contamenant Sinks
Soil layers produced by in-situ weathering
Soil Horizons
Vertical Layers of multiple soil horizons
Soil Profile
Top layer of soil profile which have not been truncated by later erosion
Epipedons
Sequence of Soil Horizons from Top to Bottom
O,A,E,B,C, R
Horizon consisting largely of organic material and said to be formed by dark brown to brown epipedon
O horizon
Differentiate Upper O and Lower O
Upper O is mainly plant litter such as loose leaves and other recognizable organic debris while the lower O is made up of partly decomposed organic matters (Humus) in which plant structures are no longer indetifiable
Horizon largely composed of mineral matter with up to 30% humus
A Horizon
O and A horizon combines
Topsoil
A light colored layer contains little organic material and where finer mterials are washed our or carried away mostly compose of quartz
E Horizon
Other term for E horizon
Zone of Eluviation
Washing out of fine soil components or the downard removal of solid particles and dissolved ions
Eluviation
This is the process of depletion of inroganic soluble materials from the upper soil with the aid of meteoric water percolation downward
Leaching
The process by which materials are translocated downward to be added to the lower part of the soil
Illuviation
This is where muh of the material removed from E horizon is deposited and is characterized by reddish to yellowish color and where bauxies are formed
B Horizon
Other term for B horizon
subsoil and Zone of Accumulation
What is the effect of the accumulation of fine clay particles
Enhancement of water retention in subsoil
This forms in extreme cases in B hoizon in which clay accumulation form a very compact and impermeable layer
Hardpan
Mineral precipitation in Bhorizon binds the soil particles together into hard, nodular zones, or into completely induratedsubhorizons
Duricrust
Duricrust compose primarily of calcium carbonate
Calcrete/Petrocalcic/Caliche Soil
Duricrust composed of Gypsum
PetroGypsic
Duricrust composed of Silica
Silcrete
Partially cemented clods of soil particles of various size that give soil crumbly lump apperance
Peds
Concentrations of Illuviated materials such as clays or iron oxides that occur as layers or that enveloped less altered cores
Cutans
Prolate to equant hard lumps formed by mineral precipitation and include concretions and nodules of all sizes
Glaebules
This is where the soil-forming processes are Active and that living roots and other plant and animal life are largely confined
Solum or “True Soil”
Horizons that make up the True Soil
O,A,E,B
Soil layer characterized by partially altered parent material which makes it easily identifiable compared to other layers known also as Soil Mantle
C Horizon
Largely unweathered bedrock
R Horizon or Reholith Horizon
Soils which have well developed profile due to stable conditions over an extended time span
Mature
Soils which lacks horizon altogether
Immature
Soils that contain more than 50% sand and gravel by weight
Corase-grained Sand
CoarSe grained sand with less than 5% fines
Clean Soils
Coarse grained sand with more than 12% fines
Dirty Soil
Soils that contain more than 50% Silt plus clay
Fine Grained Sand
amount of Stress a soil can bear without failing by rupture or plastic flow
Soil Strength
the measure of change in soil strength that results from changes in Water Content or other external disturbances such as vibrations, excavation,and loading that stress soils
Soil Sensitivity
Classfiication of soils in terms of behaviour when moisture content changes
Atterberg Limits
Four classification of Atterberg Limits
1) Brittle Solids
2) Semi-Solid Soils
3) Plastic Soils
4) Liquid Soils
Boundary between Brittle Solid and Semi Solid Soils below which soils do not shrink as additional moisture is lost during drying
Shrinkage Limit
Boundary between Semi Solid Soils and Plastic Soil and is the water content at w/c soil defroamtion changes from rupture to plastic flow
Plastic Limit
Characteristics of a plastic soil
Decreases strength, deform more easily and less cohesive in increasing moisture content
The measure of a soil’s cohesiveness, which is sense as a sticky cohesive feel to the touch
Plasticity
Whats the characteristics of Soils with low clay content
Non-cohesive, low plastic limits
Plasticity and Clay content
The more the clay the more plastiic the soil is the poorer its quality in terms of engg use
separates plastic soil from liquid soil and conditions in which soil lose their shear strength and begin to flow
Liquid Limit
Soils with low liquid limit
Non cohesive Sands and Coarse Silts
Soils with higher liquid limit
Cohesive Clay rich soils
Phenonmenon in which on non cohesive water saturated sands and coarse silts lose their strent during an eathquake and soil is turned into a quicksand-like material
Liquefaction
The range of water contents over which the soil behaves as plastic substance
Plasticity Index
Formula for Plasticity Index
PI=LL-PL
PI of of Sand and Silt rich soils which are not very cohesive
<5%, small changes in water content can cange the soil from semi solid to a liquid state
PI of Clay?
High which means soils are rich in Smectite and are extreely unstable
expresses the tendency of soils to change volume when wetted
shrink-swell potential
Characteristics of poor soil that musnt be used as substrates for structure
1) High sensitivity
2) High Shrink Swell ration
3) High Plasticity Index
Plots which sows behaviour of soil, its plasticity index versus liquid limit
Casagrande Diagrams
The tendency of the soild to consolidate and lose volumes
Compressibility
Soils with variable compresibility tend to?
settle unevenly causing variations in the subsidence of the surfaces
The capacity of a material to hold water in its intergranular spaces
Porosity
Formular of Porosity
(Volumer of %Pores/Total Rock Vol) *100
expresses the rate of fluid flow through a material
Permeability
Expression of Permeability
Darcy’s Law
Who formulated Darcy’s Law?
Henry Darcy
What does Darcy’s Law states?
Flow rate = Cross Sec Area (Hydraulic Conductivity x (hydraulic gradient (delta h/L))
Q= A [K x (h/L)]
Slope of the water table which is change in height divided by distance
Hydraulic Head
A measure of permeability that varies depending upong viscosity, density and effective permeability and acceleration due to gravity
Hydraulic Conductivity = (DensityxAcc due to Gravity xEffective permeability)/Fluid Viscosity
What indicates higher permeability
higher pore size and interconnectedness which increases as partice size and sorting increases
Hydraulic Conductivity of Clays
10^-6 cm/s
Hydr. Conductivity for Silts
10^-4 cm/S
Hydraulic conductivity for Sands
10^-2 to 10^-3 cm/s
Hydraulic conductivity for Gravels
10^-1 to 10^1 cm/s
Rocks layers with high permeability such as Sands and Gravels which permit storage and tranmission of water
Aquifers
Rocks layers with low permeability such as Clay-rich layers and retard fluid flow
Aquitard
Practical use of Permeability
1) Contaminant Studies in te subsurface
2) Determination of water flow in aquifers
3) Efficient Dispersion of Water Materials in Septic Tanks
3) Rate and Direction of Disperson of Water Borne Pollutants
Former soils which have been buried beneath the surface by subsequent deposition and are common along regional unconformities where long term weathering in continental environments is followed by period of deposition
Buried Soils
Buried soils that have been uncovered and exposed at the earth surface
Exhumed Soils
Soils that formed under conditions not related to the present climate ancient soils
Paleosols
Study of Ancient Soils
Paleopedology
study of Soils
Pedology
Time marked when free oxygen became first abundant in the atmosphere as evident with a green to gray-white reduced paleosol
2.0Ga (Paleoproterozoic)
What can imply presence of organisms in a soil
Low C13/C12 Ratio or depressed compared to the current background values because high ang C12
marks the early miocene
Wispread of Grasslands and mollisols
A global cooling attributed to depletion of CO2 in the atmosphre
L. Eocene
