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3 Types of weathering
Mechanical, Chemical and Biogenic
Paleosols
Ancient soils that have become preserved in the strata as a part of the fossil record
Clastic Sedimentary rock
Made up of clasts of pre-existing rocks. Pieces of rock loosened by weathering then transported to a basin/depression where sediment is trapped and compacted/cemented
Biochemical (Organic) Sedimentary rocks
Formed from cemented pieces of once living organisms. Chert from diatoms, limestone from calcareous organisms/precipitation, and coal from water-laden fossilized plants
Chemical Inorganic Sedimentary Rocks
Mineral constituents in solution become supersaturated and inorganically precipitate. Most commonly evaporites: Gypsum, halite, etc
Subaqueous and Subaereal
Subaqueous is weathering that occurs under water, and subaerial is weathering that occurs out of water
Mechanical Weathering (Definition)
Produces smaller constituents without altered chemistry or mineralogy, usually by exceeding the tensile strength of the rock
Stress-release weathering
Freeze-thaw weathering
Physical breakdown of rocks by the invasion of water into cracks or planes of weakness and expansion when water freezes
Insolation Weathering
Sun-heated rock surfaces expand and then contract in the sun's absence, weakening bounding planes and grain boundaries
Salt weathering
Generation of internal pressure when high-salt concentrated water invades the pores or weakness planes of a rock and forms salt evaporates
Wetting and Drying weathering
Weakening of tensile stresses by causing negative pore pressure in the process of removing water and swelling pressures in the process of adding water to a rock.
Hydration weathering
Expanding of clay minerals due to absorption of water
Stress-release weathering
When buried rocks under high pressure suddenly experience offloading (a portion of the rock weight above is removed) and the compacted stones will begin to expand and may experience brittle pressures
Exfoliation weathering
Flaking of the outer layers of sediment in a bed. Mainly caused by repeated cycles of heating and cooling.
Chemical weathering
Changes in composition and mineralogy with a net loss of material and/or a change in particle size.
3 types of chemical weathering
Congruent dissolution
Hydrolysis
Oxidation and Reduction (Redox)
Congruent Dissolution weathering
Completely dissolving a mineral into solution without precipitation of it or any other mineral out of solution. Often due to rainwater.
hydrolysis weathering
Chemical reaction between silicate minerals and acids leading to the mineral's breakdown along with release of metal ions from solution.
Redox weathering
Chemical alteration of metal ions (ie iron and manganese) in silicate minerals due to interactions of oxygen in contacting water. Oxidation (Loss of electron) of the metal and reduction of the water will cause the metal cation to fall out of the crystal lattice and may cause the crystal lattice to become unstable.
Hydration/dehydration weathering
Hydration: Water molecules are added to a mineral's crystal structure to form a new mineral
Dehydration: Water molecules removed from a mineral's crystal structure to form a new mineral
Bowen's Reaction Series (In regards to weathering)
Minerals that form at high temperatures, such as olivine, will have significantly less stable at surface conditions than minerals formed at low temperatures such as quartz.
Products of subaerial weathering
Source rock residues, secondary minerals and soluble constituents
Source rock residues
Found in immature soils
Includes igneous and metamorphic rocks, fragments and assemblages of unstable rocks such as olivine, hornblende, calcitic plagioclase, etc. Mature soils would only include the most stable minerals.
Secondary minerals
New minerals formed in the same area during chemical weathering
Soluble materials
Extracted from rocks by chemical weathering and removed from the weathering site by soil or groundwater. End deposition site will be the ocean.
Processes of subaqueous weathering
Exposed seafloor rocks will experience chemical reactions with sea water.
Temperature percolation through cracks in the oceanic plate may bring water to high-temperature/pressure forming minerals and allow them to dissolve said minerals. When the water is heated and returns to the surface, the minerals are deposited out of solution in vents of sulfide, sulfate, and oxide deposits.
Soil forming factors
Parent material, time, climate, relief, organisms
Soil Profile Horizons
O: Organic
A: Topsoil
E: Eluviated horizon
B: Subsoil
C: Parent material
R: Bedrock
Bioturbation
Disturbance of sedimentary deposits by organisms
mass wasting
the downhill movement of a large mass of rocks or soil due to gravity
Fluid Density
Mass per unit volume.
Affects forces that act in a fluid: temperature, rate of particle settling, response to gravity, etc.
Fluid Viscosity
Ability of a fluid to flow.
Low flows easily, high flows with difficulty. Affects turbulence and changes with temperature.
Turbulent Fluids
Support Mechanism: Turbulent fluid
Observed Type of Flow: Turbidity Flow
Newtonian Fluids
Support mechanism: Upwards escape of intergranular fluid
Observed type of flow: Liquefied flow
Non-Newtonian Fluids
Support mechanism: Grain interaction through dispersive pressures
Observed type of flow: Grain flow
Bingham Plastic Fluids
Support mechanism: Matrix
Observed type of flow: Mud or debris flow
laminar flow
Streamlines are parallel and don't intertwine, predictable flow lines.
turbulent flow
Streamlines twist and turn and cross each other. There is significant movement in directions other than the overall direction of the flow
Eddies
swirling fluid in the reverse direction of a current created in a turbulent flow regime
Reynolds number
Dimensionless numbers used to determine if a flow is laminar or turbulent. Used to assess the magnitude and turbulence (low Re= laminar, high Re= turbulent).
Transitional Flow
A flow that alternates between being laminar and turbulent.
Boundary Layers
Layers of a flowing fluid in contact with a surface, such as a riverbed. From bottom to top there is an increase in flow velocity followed by a zone of consistent velocity.
Laminar/viscous sublayer
Present in smooth beds, characterized by an unmoving section at the bed boundary where viscous forces dominate. Within the underlying layer, flow is laminar and is traced by overlying layers
Froude Number
Dimensionless number defined as the ratio of the flow inertia to the gravitational forces used to measure flow regimes of open channel flow
Entrainment (of Sediments)
The process by which sediment is picked up from a surface and carried some distance by a overpassing fluid flow. Fluid drag and fluid lift push the sediment into suspension, while gravitational forces will pull it out of suspension.
critical threshold
The passing of positive entrainment forces beyond the negative entrainment forces that will result in pushing a particle into suspension
Bernoulli Effect
When a fluid is overpassing the top of an exposed particle, the pressure above it will be lower than the pressure below it due to the difference in fluid speeds. This will allow the particle to move off the surface more easily.
Hjulstrom diagram
A diagram of critical flow velocity against mean grain size.
Velocity decreases with increase of size from Clay to fine sand.
Velocity then increases with the increase of size from fine sand onwards
Kurtosis
A measure of the skewness of a graph. When a grain sized graph is positively skewed, The mode sediment is coarse and when it is negatively skewed, the mode sediment is fine.
Stoke's Law of Settling
An object falling through a fluid experiences the force of gravity, buoyancy and drag.
Bed load, Suspended load and Dissolved load
Bed Load: Portion that cannot be kept in constant suspension but still moves with the current through either saltation or traction
Suspended Load: low enough density/small enough size that is kept in contact suspension by electrostatic and viscous interactions with the surrounding water
Dissolved load: Ions that are dissolved in moving solution
Wash load
clay-sized portion of suspended load
Sediment Transport by Wind
Surface creep, saltation, and suspension. Due to air's low density, much more positive entrainment forces are required to lift clasts, and clasts will always be smaller than those transported by water.
Sediment transport by glacial ice
Less positive entrainment forces required to suspend clasts, and the size threshold of clasts that can be transported is significantly larger than water due to ice's high density.
Rock Fall
Free falling movement of massive rocks from a cliff or steep slopes
Slides
Mass movements of large portions of sediment due to shear failure with little to no internal deformation
Sediment Gravity Flow
A mass movement mimicking fluid flow where sediment undergoes mass internal deformation
Turbidity current
A subaqueous downslope movement of dense, sediment-laden water created when sand and mud on the continental shelf and slope are dislodged and thrown into suspension
Turbidites
Graded layers of sand interbedded with finer pelagic sediments typical of the deep sea floor.
Bouma Sequence
An idealised sequence of sediments and sedimentary structures that could be seen in a turbidite deposit
Liquified flow
Sediment-gravity flows in which grains within the flow are kept suspension by the upward movement of fluid.
Normal vs Reverse grading
Normal grading: A transition from coarse to fine grained sediments moving up in a depositional unit.
Reverse grading: A transition from fine grained to coarse sediments moving up in a depositional unit. This is much more uncommon and typically only occurs due to kinetic seiving.
Debris flow
A downslope movement of mud mixed with large rock fragments and biological material
Udden-Wentworth Scale
A grade scale for classifying the diameters of sediments.
Particles larger than 64 mm in diameter are classified as cobbles.
Smaller particles are pebbles (16mm), granules(2-4mm), sand(2-1/16mm) and silt (1/16-1/265.)
Those smaller than 1/256 mm are clay.
Phi Scale
Expresses grain size on a logarithmic scale. Phi values increase arithmetically as the grain size decreases geometrically.
64 mm= cobbles, -6 phi
32-4mm= gravel, -5 to -2 phi
2mm-125um= sand, -1 to 3 phi
63-4um=silt, 4-8 phi
Below 4um=clay, 9+ phi
Measuring Grain size
Thin sections, estimations or measurements (larger clasts), sieving of loose sediment
Particle Form
Sphericity or "Particle shape". From equant to platy.
oblate(disc)
Bladed (asymmetrical)
Prolate (roller)