general terms Flashcards
Allochems
These include ooids, pisoids, peloids, oncoids, and intrachlasts. It includes any carbonate clasts with D>fine sand (63microns)
2 Types of carbonate grains
Allochems: These are chemically precipitated CO3 minerals that have undergone transport.
Lithoclasts: These are carbonate rocks that have been weathered and redeposited. These are “carbonate clasts”
Further intra vs extra clasts designation for if the carbonates are from within the same basin as the resultant rock.
3D QFL diagram
%mud: <5%= arenites, 5>%mud<50%=wackes, %mud>50%=mudstones QFL: %qtz: %qtz>90%=qtz arenite, 75-90%=sublithic, sub-arkosic, <75%-arkosic or lithic
4 “minerals” of carbonates
low-Mg calcite: <4% Mg
High-Mg Calcite: >4% Mg
Stoichiometric dolomite: Calcite with (Mg/Ca)>1
Aragonite: CaCO3 with alternative crystal form. This is an unstable form of calcite that eventually reverts back to calcite. Rocks older than the Cretaceous have ~0% aragonite.
4 types of erosional bedding plane markings
- ) Sole markings: These are extruding features on the base of sandstones into shales (non-exclusive) and derived from erosional tools scraping the bed bottom.
- ) groove casts: “scraping” of tools along the floor, creates chevron or v shape dipping down-current.
- ) Saltation: bouncing…
- ) flute casts: These are shaped like yardangs and form in a similar way. The fat tail indicates flow direction.
A-Horizon
Zone of oxidation, leaching, organic reactions, humus, solutes, fine clay percolating. Approximately 5% rocks.
Actualism
The present processes approximate the past but it must be interpreted with a grain of salt.
Alfisols
Soils that are developped in moist, temperate climates. There is alot of insoluble cations (Fe + Al) in the alfisols. Chelation because of the high plant life increases the solubility of other cations. They are more temperate than oxisols.
Allochthonous carbonates
This is all carbonates with coarse grains (10% has D>2mm) that are not organically bound at deposition indicating that grains were transported.
If it is grain supported it is a packstone.
If it is matrix supported grainstone.
If there are more than 10% grains then it is a wackestone.
If there are less than 10% grains than it is a mudstone.
Are physical, biological, and chemical weathering discrete things?
They are not. Salt crystallization is an example of both chemical and physical weathering. Root wedging and fungal breakdown are biophysical and biophysiochemical.
Arenites NEED PIC
Sandstones that are composed of distinct grains and cement with a maximum of 5% mud.
Aridsols
Soils that form in deserts. They are poorly developed, solutes are relatively static because evaporation offsets any percolation. Many evaporites and dust.
Authegenic minerals
Minerals produced at the surface. Minerals precipitated through biologic, supersaturation, oxidation, or other processes.
Autochthonous carbonates
These describe carbonates that are bound together during deposition.
This includes framestones, bindstones (stromalites), and bafflestones
B-Horizon
Zone of accumulation (illuvial). Clay and solutes. Dark colors. ~80% mineral
Ball and Pillow Structures
Seemingly abnormal ball or kidney shaped bulbous structures protruding the base of a bed and likely derived from the liquification of surrounding sediment.
Bed Shear Stress
tau0=SW*h*S
SW=specific weight
h=flow depth
S=slope (gradient)
This represents the shear stress a flow exerts onto a bed it is flowing over.
Bedding Structure Matrix
Beds are either Parallel or Nonparallel and either Continuous or discontinuous. The three kinds of lineations apparent are Even, Wavy, and curved.
Bedforms
Mounds or troughs of loose sediment on a mobile bed forming @ sediment and fluid interface. They describe the relation of strata and are often similar in size/shape, perhaps show a pattern.
Turbulence produces bedforms.
Beds
Tabular or lenticular layers of sediment that share lithological, textural, or structural unity and have a heterogeneous nature when compared to other beds.
These include Sediment units, subdivisions, and amalgamation surfaces.
laminae<1cm thick
Structures are used to describe how layers are configured and aid identification of environments/depositional processes.
Bernoulli’s Principle
Derived from the conservation of energy and the principle of continuity where:
KE+PE+P(aka work)=Constant
If the path is obstructed by a grain and therefore V(flow) increases (see principle of continuity) and over a dx the PE is constant/~0 then the KE increases when traversing over the grain and therefore P (pressure) decreases. This forms hydraulic lift.
Biogenic Structures
These are the trace fossils of burrowing, boring, feeding, locomotion, cut-and-fill caving, and arise from bioturbation, biostratification (stromalites), bioersion, and excrement.
Vertical trace fossils indicate harsher environments that are more likely to be eroded.
Biological Weathering
The influence of plant life of the weathering process. Examples include root wedging and bioturbation. It creates a significant part of the weathering scheme.
Biological Weathering Examples
Chelation: The Bonding of metals with organic compounds with the effect of increasing their solubility.
C-Horizon
Chunky Bedrock, regolith. 100% rock
Calcium carbonate compensation depth
This is the depth in the ocean where supply=dissolution. It decreases towards the cold poles that can have more carbon dioxide in solution.
Dissolution is preferred in environments with low T, low pH (basic), and low CaCO3
Carbonate Rocks
Rocks that are primarily composed of CO3 minerals/sediments. These include calcite, aragonite, and dolomite that are precipitated our of solution.
These are the most abundant chemical/biochemical rock and accounts for ~20-25% of all sedimentary rocks.
Cataclastic Breccia
Refers to breccias formed due to land movement.
Landslide/Slump breccias form due to the tension of sliding material
Tectonic Breccias form from gouge
Collapse breccias are from cave-ins and other forms of ground failure
chalk
An earthy LS derived from ooze
Chelation
Biogenic weathering through organic compounds. It forms a metal compound that increases the solubility of the metal. It occurs with most cations except iron and aluminium.
Chemical Weathering
Break down of rock due to being at disequilibrium on Earth’s surface. Characterized by shifts in the chemical and/or mineralogic components of a rock.
7 Chemical Weathering Mechanisms
Carbonation because of rain being slightly acidic
Simple Solution: dissolution without precipitation
Hydrolysis: dissolution and precipitation of new minerals. Incurs a permanent composition/mineralogic shift.
REDOX: The oxidation of Mn and Fe to form hydro/oxides.
Hydration/dehydration: clays, hematite->goethite, and gypsum->anhydrite. Characterized by reversibility and impermanence.
Ion Exchange: shifting ions within clays/zeolites and solution
Chelation
Clay series
Clays constitute a significant potion of all grains in sedimentary rocks that host large metallic cations, strong, and stable structures.
illite alters to smectite (montmorillonite: expandable upon hydration)
kaolinite is a T-Oct Al-rich clay with the potential for bauxite (Al(OH)3) . It is the ultimate Alumino-silicate weathering product.
Climbing Ripples
During the de-escalation of flow ripples will stop migrating and start “mounding” Therefore downward flow will be up-dip. They form non-tangential and tabular cross-bredding.
Competence ADD FBD
The maximum particle size that a flow can move.
Determines by if the flow can exert a force that is greater than tauc
Conglomerates/Breccias:
Rocks that are primarily composed of lithic fragments over 2mm (>30%). If they are angular then it is considered a breccia. If they are more mature and rounded then they are conglomerates. Clast supported refers to if the individual clasts are touching and create the structure. Matrix supported refers to the concept of the clasts being suspended in the fine grained matrix material.
Continental Block Provenance
Typical exhumed continental material. It has a wide variety but primarily consists of quartzose, K-spar, sometimes volcanics.
Convolute Bedding and Laminations
Folding and crumpling of beds with irregular mircro anti/synclines that are restricted to a finite subdivision of the bed (~.05-.25 m) and the upper/lower bounds are clearly not convolute. This is a form of soft sediment deformation but it is concurrent to deposition not post post-depositional like tectonics are.
Coquina
A mechanically sorted fossil hash
Debris flow deposits
Unsorted, chaotic (sorting requires turbulence), matrix supported, lacks cross-stratification and occasionally shows reverse grading
Debris flows
A type of subarial/subaqueous flow that is dominated by a high viscosity, like a bingham plastic, that forms an internal structure and develops matrix supported rocks. The base of the flow has a relatively low velocity and thus is non-erosive on the base. It is characterized by “freezing” when shear at the base is less than the critical shear.
This can commonly occur in arid regions and with volcaniclastic deposits and include mud flows (~50% mud), muddy debris flows, and debris flows (0% mud)
Density Flows
A fluid flow that is formed due to a non-homogenous density. This is a type of gravity flow and includes turbidity flows.
Often influenced by turbulent flows entering stagnate water, temperature of water, salinity.
Diagenesis
The final step of lithification of sedimentary rocks that alters the rock due to pressure.
Name two forms of deformation
Plastic and Ductile Deformation: Characterized by the expansion of clays into adjacent quartz
Flexible Grain Deformation: Characterized by minerals restructuring and reducing the volume of other grains. Ex: mica forming a planar surface where a quartz grain once existed.
Dimensionless numbers
Numbers that describe a state change for the participants of the system.
Dolomite Problem
This is the issue that dolomite does not readily precipitate in normal conditions and requires a “pump” to be precipitated yet there seems to be a abnormally massive amount of natural dolomite in the geo-history of earth.
Dolomite Textures
Fundamentally between either planar (idotopic) and nonplanar (xenotopic) crystals.
Planar is described by discrete crystal forms and can be floating, euhedral, subhedral, or void/pore filling.
Non-planar includes non-rhombic grains and can be described as anhedral, porphyritic, or void-filling.
Dolomitization
This is the diagenetic alteration of LS to produce dolomite. It occurs at a depth of 500-3000 m and requires Mg rich water circulating through relatively porous LS and higher temperatures.
Dunham Carbonate Classification
A classification system that enables classification via hand specimen that emphasizes the grain packing, micrite abundance, and grain binding.
Mud-supported rocks include mudstone (<10% grains) and wackestone (>10% grains)
Grain supported rocks include packstone (>1% mud) and grainstone (<1%mud)
Allochthonous is for coarse sediment not bound at deposition wheras autochtonoous is for coarse grains that are bounded at deposition.
E-Horizon
Zone of intense remove of cations (eluviation) and chelation. The soil is a light color and depleted of metallic cations. ~50% mineral
Entrainment
The process of grains losing contact with the bed below and is determined by the critical shear threshold.
Epiclastic Breccia/Conglomerate
FIND EXAMPLE
Epiclastic conglomerate/breccia: An extraformational/intraformational rock that formed from a non-specific weathering and transport process.
Erosional Structures
These include sole marks which show a unidirectional flow that drags a particle across the base. Direction of flow cannot be determined.
Tool marks refer to dragging of “tools” on the surface.
Flute casts refer to the scouring of eddies behind large clasts that are not entrained the deepest part of the cast is at the front of the flow.
Paleochannels: These cross-cut bedding and can be tidal, underwater, and fluvial.
Scour and Fill: These are small lenses of coarse material whose long axis indicates flow direction where the bulbous end of the lens exists.
Example of hydrolysis
Alumino-silicate+ “acidified” water + water yields alkalai metal in solution + phyllosilicate + SiO2 (aq)
Ex: 2KAlSiO6(s) +H2CO3 + H2O-> K2CO3(aq) + Al2SiO5(OH)4 (s) + 8SiO2 (aq)
Orthoclase + carbonated rain + water -> Potassium carbonate + kaolinite + aqueous silica
Example of REDOX
2FeS2+15/2O2 + 4H2O -> Fe2O3 + 4SO4 2- + 8H+
Ferrous iron (soluble) forms ferric iron (3+) upon being exposed to the atmosphere and forms the hydrated Fe(OH)3 This then dehydrates to form hematite (above).
Factors of Weathering
Climate and Rock
Weathering in wet climates is dominated by chemical mechanisms. Low slope, higher grain size surface area, and warm climates all promote water retention and higher weathering.
Feature of immature clasts
Poor sorting, angular grains composed on relatively unstable minerals.
Features of mature clasts
homogenous composition, well rounded, well sorted
Feldspathic Arenite AKA Arkose
Less than 75% of the clasts are qtz and there is more spar than lith. They are generally immature and form clay-rich arenites. They often form on stable continental shelves/alluvial fans or in-situ when granite decays. They are promoted by arid/cold environments and were more common from Paleozoic and Mesozoic times.
Flaser Bedding
This is describing a bed form where mud accumulates in the troughs of the cross strata. Indicates that the hydraulic conditions favored sand preservation during episodic flows.
Folks carbonate classification
Named via “packing”+”major type of allochem”+mud/cement type. It is the cement-matrix-allochem classification scheme.
Ex: Sparse Oomicrite= matrix supported ooid with micrite mud.
Froude Number
A dimensionless unit that describes how a surface wave passes through a liquid. The denominator describes the velocity of a surface wave through water and the numerator is the velocity of flow. Therefore a Fr<1 means that the wave’s velocity is greater than the flow’s.
Fr=V/(gD).5 D=water depth
Grading
Normal Grading describes beds that are larger grained at the base and grade into finer sediments.
Reverse grading indicates that the largest grains are at the top of the bed and can occur due to kinetic sieving and dispersive pressures.
Grain flow deposits
Kinetic sieving causes reverse grading. Generally well sorted, and form wedge shapes with the upper surface = angle of repose.
In comparison to eolian settling this increase in thickness downwards. They are often adjacent to settling deposits though.
Grain Flows
These are relatively dry flows of individual grains that are induced when the weight exceeds the internal frictional cohesion. The dispersive pressure is derived from the collision of grains. Commonly is the “Avalanching” of grains on the lee-side of dunes.
tau/P=tan(a) where: a=angle of internal friction
P=dispersive pressure
“grapestone”
A rock that is composed of aggregate grains (lithoclasts that become cemented together)
Gravity Flows
Characterized by a mass of sediment forming a flow with or without significant fluid composition and is propelled by the particle mass.
This includes density flows (turbidity flows)
MOR weathering
A form of submarine chemical weathering where basalt reacts with seawater to form glaucanite (clay), phillipsite (zeolite), and palagamite.
Hjulstrom Diagram
A diagram that shows three phases of sediment transport and describes the maximum diameter of a particle that be entrained within a flow based on flow velocity. At small diameter the erosion potential decreases (v for entrainment) because the fine particle’s develop stronger van-der-waals cohesive forces. This occurs when particles diameter<100 microns.
The curve is calibrated for D=1 m and SiO2 particles.
How does CaCO3 extraction, photosynthesis, organic decay, feeding/deposition, and bacteria influence precipitation?
Extraction increases the amount of shells and exoskeletons which create more allochems/micrite.
Photosynthesis lowers carbon dioxide and increases pH. This increases the amount of ooids/micrite.
Decay of soft tissues increases pH and increases precipitation
Feeding and digestion creates pellets.
Bacteria conduct ion exchange and precipitas carbonates.
hummocks
Undulating cross-stratification that are both concave-up (swales) and convex-up (hummocks) with beds gently cutting one another and bounded by bioturbation. Includes large circular surface features. Basically they are mounds that occur within fine sands with both oscillatory and unidirectional flows.
Hydraulic Lift
Derived from the principle of continuity which says that the flux within a pipe is constant.
Flux 1=Q1*A1=Flux 2=Q2*A2
where Q=velocity.
Therefore if A21 then Q2>Q1
Ichnofacies
These are trace fossil assemblages that reflect unique depositional enviroments
Intraformational Conglomerates
These are conglomerates that form within a basin so the clasts are not from an external formation. Flat pebble conglomerates. Precontemporeneous clast formation includes the drying of mud, grain flows, and/or tides.
K-Horizon
A special form of the B-horizon for CaCO3 accumulation (caliche). It is a distinctly hard zone because of the cementing.
7 Key geothermometers
Color alteration
Vitrinite reflectance
graphitization of kerogen
clay mineralogy
zeolite assemblages
fluid inclusions
oxygen isotope ratios
Laminar flow
Particles move relatively parallel to each other and the overall flow vector. It is supported by a low reynolds number.
Lenticular Bedding
This is characterized by discontinuous mud lenses and can indicate tidal planes, deltas, shallow shelfs, that favor mud preservation. In general the flow is episodic. Often paired with flaser bedding.
Liquified flow deposits
Dish structures (concave up “dishes”)
Convolute laminae (“mushroom” shapes)
Flame structures (similar to convolute but not yet wider at the peak)
Mounds and vertical structures: “mud volcanoes” where the water was escaping the sediment
Liquified flows
This is a broad term describing the upward exhumation of liquid from sand and mud. In the process sediment is “liquified/fludized” (effective loss of cohesion) by settling and water escapes the pore space.
Lithic Arenites
Siliclastic rocks with a large quantity of rock fragments.
Often immature, angular grains and indicates shallow marine enviroments or fold-thrust belts.
Magmatic Arc Provenance
Sediments are derived from igneous rocks, lith, plag, and typical volcanics. It includes less quartz and K-spar.
Marl
A mudstone with interlayers of siliclastic mud or silt that is torigenous.
Maturity of sediment
Maturity is the extent to which grains have reached their final weathering product for a given environment.
Meteorite Impact Breccia
Breccias that form due to meteorite impacts.
Methods for Measuring Grain Size (6 kinds)
Pippette Analysis, Photohydrometer (transmission=F(settling)), Sedigraph (x-ray), laser diffraction, electroresistance, semi-autoimaging
Microcrystalline calcite
calcite mud that forms the material holding grains in place. Under a microscope it is semi-transparent and grainy
Migration of Ripples
Ripples migrate due to the avalanching on the lee-side of the slope. They produce cross stratification that is either linear (2D ripples) or concave (3D ripples).
In lower flow regimes the small avalanching indicates down stream and in upper flow lee-side avalanching is up stream
Components of Sediments and their meaning for provenance
SiO2: Overrepresented due to multi-cyclical nature and non-secondary alteration.
Spars: the most common mineral in the crust but underrepresented due to susceptibility to alter to clays. Feldspathic grain indicate that the rock is relatively immature.
clays: kaolinite is the most mature clay. Volumetrically clay is the majority of sed rocks and acts as an important reservoir for accumulating metals.
heavy minerals: Relatively stable high SG minerals. Zeolites and garnets are significant components of this.
mafic minerals: RARE indicates an extremely immature rock.
lithic fragments: commonly the most stable rocks like quartzite, volcanic glass, slate, phyllite, schist, or chert.
Mollisols
Temperate/Semi-Arid Soils. There is usually a thick humus, low water content. There is low removal of cations. The E-horizon is usually absent. The B-horizon has alot of caliche nodules.
Mudstones
Fine grained siliclastic rocks with more than 50% of the grains smaller than 1/256 mm. Phyllosilicates (kaolinite, illite, and smectite) and quartz are the primary mineral components. They are indicative of deep ocean/lakes where the turbulence is low.
Claystones (D<4 microm)
Siltstone (4-63 microns)
Shale: fissile bedded/brittle mudrocks. often with pyrites and other sulfides.
Argillite: a low-grade metamorphosed mudstone
Name the size range for clay, silt, and sand
Clay: D8 (too small to see)
Silt: .004
Sand: .06
Neomorphism
This is the process of inversion. This is relevant for the recrystallization of aragonite to calcite.
Newton’s Laws of Motion
1: inertia, a body @rest is @ rest 2: F=ma 3: every action has an equal and opposite reaction
O-Horizon
Zone of organic accumulation. Leaf litter without any bedrock. It is black and particularly dense in highly vegetated areas with conditions that prevent automatic recycling of nutrients.
Oligomect vs. polymict conglomerates/breccias
Oligoment conglomerates are composed of a single clast type whereas polyment have several types of clasts present.
Ooids
A general term describing carbonate grains that grow as rims on other particles. The term particularly describes rims with concentric grains D>63 microns. Ooze has D<4 microns.
They tend to form in high energy environments like warm water reef shelves.
paleosols
Lithified, ancient soils. Most commonly from the Quaternary but determined by the paleoclimate of the time/area.
Peloids
Grains of micro or cryptocrystalline calcite/aragonite without a coherent internal structure. These are often composed of pellets and lack concentric layering. .03
Petramict conglomerate nomenclature
Named by the primary clast type
Phi-scale
phi=-log2d so d=2(-phi)
In general when phi>0 the size decreases reflecting the tendency to see small and not large particles.
The levels of phi define the different clasts in a sedimentary rock and are markers for how sediment behaves when acted upon by an external shearing force.
Physical Weathering
Disintegration of rocks without significant chemical or mineralogic changes occurring. Mechanical degradation.
Physical Weathering Examples w/ mechanisms
freeze-thaw: Ice has a volume of 1.09*Vol(liq) which wedges rocks and produces large angular blocks or granular disintegration within granites. Insulation weathering: Solar expansion and contraction Hydration-dehydration cycles: oscillating pore pressures “Sheeting”: exfoliation due t decreasing P of exhumation
Pisoids
an ooid with a D>2 mm
Protodolomite
A high calcium dolomite produced @ STP
Provenence
The paleosetting of a sediment used to derive its origin.
Proximal vs. Distal Turbidites
Proximal turbidites refers to turbidites that have prominent A-C horizons and form on or near the continental shelf. They are up to a meter thick.
Distal turbidites have more intense C-E layers and refers to deeper ocean turbidites.
R-horizon
Bedrock layer
Reaction path for Carbonates and favored depositional environments
H2O + CO2 + CaCO3 Ca2++2HCO3-
This mechanism works to reach equilibrium for a given T and P. Therefore an increase of water or carbon dioxide decreases CaCO3 which can occur when temperature rises because gas is less soluble in warm liquids.
Authigenic precipitation of calcite is preferred in high Ph, low depth, high T, plant life, and low turbidity.
Reading Cross Sections
Grain Size: The wider the base the larger the grains.
Beds: Dark lines indicate beds.
Amalgamation Surface: Indicated by a dotted line
Recognizing paleosols GET A PHOTO for cutons and peds
Traces of life, soil horizons, soil structures (bioturbation, preciptation of nodules…), cutons and peds (irregular bedding within a granular “matrix”)
Recycled Orogen
this provenance indicates continental collisions and has a great deal of meta-sed lith, and quartz.
Regolith
Physically broken rock debris. Cracked and fractured but still chonky.
Reynolds Number
=inertial F/Viscosity= U(flow)*L*rho/(dynamic viscosity)
where: L~depth of flow
Fi = intertial forces and is related to the momentum of the fluid.
U=avg velocity
It is a dimensionless unit describing laminar (re<500) and turbulent flow (500) The shift from laminar to turbulent flow is determined by boundary conditions of the flow.
Ripple Classification
2D ripples: Parallel lines without lee-side indicates oscillatory motion. These create planar bedding. Up dip on the bed sets indicates the flow direction. This is the down dip direction on the interbedded curves that show the migration of ripples.
3D ripples: Tangential, trough lines, indicates turbulence. These create trough stratification. They indicate higher flow velocities.
Rose Diagrams
A tool for identifying directional trends of sedimentary structures. The proportion of total fluid flow direction measures are plotted to show the primary flow direction.
Sandstones
Primarily mineral grains of sand size. Arenites are sand+cement, wackes are sand+silt/mud.
Sediment Classes
Clastic: Physically transported and accumulated sediment
Carbonates: chemical/biorganic carbonate formation and consists of either unaltered primary sediments or secondary, altered, sediments.
Other biogenic sediments: cherts, diatomites
Chemical Sediments: Evaporites
Sediment Load Types (4 types)
Fluvial:
Bed Load: this includes large particles being transported by saltation or traction transport.
Suspended load: This is the layer that is within the turbulent part of the flow and has infrequent impact with the bed.
Wash load: This is silt and dissolved particles.
Elluvial:
Dustload: The fine particles that act as the air’s “wash load”
Sediment Maturity
Sphericity, Roundness/angularity (wind is very effective and depleting angles), and composition.
Sequence of bedforms in laminar flow
planar beds, ripples, sand waves, dunes. Steep side shows flow direction.
Shield’s Diagram
A similar diagram to the Hjulstrom diagram with greater applicability.
Shooting/supercritical flow
When Fr> 1 and there is not upward flow.
Siliciclastic Sedimentary Rocks
A broad group of sedimentary rocks (~75% of all) that are primarily composed of silica rich minerals. These include sandstones, shales, and conglomerates.
Siliciclastic cements
Silica overgrowths: These are characterized by the quartz grains having extended, slightly modified boundaries, but also exhibit homogenous extinction angles.
Microcrystalline fabric: “mini-geodes”
Slump Structures
Also known as synsedimentary folds/faults that are derived from less compacted sand/mudstones.
Soil
A complex material with physical and chemical composition that is derived from weathering.
Soil Horizons
Internal soil structure derived from regolith-atmosphere interactions
Solution Breccia
When a solution dissolves the host rock and only the insoluble rocks remain to form the fragments present within the breccia.
Sparry Calcite
.02-.1mm rhombohedral calcite crystals that looks very similar to cryptocrystalline calcite.
Stages of Diagenesis
- ) Eogenisis: 0
- ) Mesodiagensis: z<2000 m Characterized by increased compaction and thinning of beds. The expulsion of water may create structures. Cementation and dissolution. The grains react with the groundwater to form new compounds like oil.
- ) Telediagenisis Z>2000m this is characterized by the exhumation of the rock. Characterized by chemical weathering and decompression.
Stoke’s Law
The terminal velocity of a settling particle determined from the balance of gravity and drag forces. It can also be said to be proportional to the cross-sectional area of a flow (pressure effects) and the amount of fluid a particle displaces (drag)
U=cD2 = (1/(18*μ)[(ρs-ρf)*g*D2]
Where: U=terminal V of the falling particle
D=spherical diameter
c=constant=f(viscosity, rho(fluid),rho(solid)
stomalites
These are organic silt laminations within LS that form from algal plumes. If the laminations are too poor to recognize it is called a thrombalite.
Structureless/Massive Bedding
Bedding that shows a lack of internal structure that have little viable explanations to their creation. Oftentimes apparent massive bedding shows structures following x-ray analysis or acid staining.
Substantive Uniformatarianism
Hutton and Lyell’s idea where the present processes of geomorphology perfectly mimic the past.
Synesis and mudcracks
Subaqueous and subariel mudcracks that form from the alignment of clay minerals.
Terms of bedforms (flow separation, attachment, eddy erosion)
Flow separation: The point where the flow lines depart from the peak of the ripple
Attachment: the intersection of the falling flow line with the proceeding ripple
Eddy erosion is the scouring that is caused by the turbulence of eddies.
Tranquil flow
When Fr < 1 and waves can move up the flow
turbidite anatomy
Head: The erosive part of the flow that scours the base of the bed.
Body: A steady and uniform portion of flow that begins depositing a and b layers of the bouma sequence. It flows faster than the head.
Tail: Dilute part of the flow that can auto suspend fine particles.
Turbidite/Bouma Sequence
.2-.4 m deposits derived form turbidity currents with an a-layer that has a scoured base, massive granular sands, and normal grading of coarse particles.
b layer is planar bedding from the upper flow regime.
c layer has ripple structures and represents the shift from upper to lower flow regimes.
d is laminated silts with tail ripples (lower flow)
e is pelogic (oceanic) and hemipelogic muds.
turbidity flows
A type of gravity flow derived from sediment accumulation following seasonal floods, storms, quakes, or tsunamis and characterized by a shift from plastic to fluid flow. It has low viscosity, high turbulence, and lacks an internal structure.
Turbulent flow
A field of the flow lines created within this type of flow show no pattern of molecular flow and may not align with the average flow vector. It is characterized by lower rates of settling and increased erosive capacity.
These flows are characterized by an eddy viscosity which is their “apparent viscosity” where n=mew*10x and tau=(mew+n)(du/dy)
Types of Chemical Weathering
Simple solution: The dissolution of nutrients and metallic ions. Hydration/Dehydration: Gypsum->anhydrite Hydrolosis: the formation of clays RedOx: Fe/Mg alternate between 2+ and 3+ during hydration and dehydration.
Types of contacts
Sutured Contacts: This is where the cement creates a jagged look like they have been crudely stitched together.
Concavo-Convex: Where the rounded grain has a “bite” taken out of it by the cement.
Long Contact: This is where the cement does not create a spherical indent into the grain but follows a smooth curve.
Udden-Wentworth Scale
A geometric scale for measuring grain sizes that uses the rule 2*(n-1) so each size is two times the prior.
Ultisols/oxisols/ferrosols
Tropical soils that rapidly recycle the nutrients. There is typically a very large A-horizon. Red soils indicating only insoluble Al and Fe reside. This is common in rainforests or Africa.
Upper flow regime bedforms
planar beds, antidunes, chutes+pools. Steep side towards flow direction.
At Fr=1 the buffering of ripples ceases and they are cleaved off to form planar beds.
Differentiate upper flow regimes by the erosional shooting traces.
Volcanic Breccias
Pyroclastic: Quenching due to air and depositied within ashy formations
autobreccia: due to the fragmentation of highly viscous lava at the front of a continuous flow
Hyaloclastic: Quenching of hot magma
Volcanoclastic sandstones
A form of lithic arenites that are pyroclastic material like euhedral spars, pumice, glass, and low qtz.
Wackes NEED PIC
Sandstones with grains that are surrounded by mud/silt
Weathering
A process which breaks down rock at the Earth’s surface. It produces discrete sedimentary particles and dissolved solutes. It includes physical, chemical, and biological weathering.
What are the four types of grain textures?
- ) parallel flow orientations: The lengthwise of the grains indicates the direction and occurs within turbidites, gravity flows, and glacial transport.
- ) Perpindicular Orientation The grains align perpindicular to the flow vector and is common for river pebbles.
- ) Imbricated (Shingled): Similar to perpindicular where the grains “stack” upon each other. Occurs in turbidits, grain flows, and conglomerates.
- ) Random: Enough Said
What are the three models for early dolomite formations?
Hypersaline model says that there were very briny solutions forming in the sabkahs.
Mixing Zone Model says that freshwater interfering with the seawater ground line decreases calcite precipitation and the soil has increased magnesium
Seawater model says that shifting tides effectively pump the pore spaces with Mg rich seawater.
What are the three regimes of diagenisis?
Marine Realm: This is the seafloor and very shallow subsurface with conditions reflecting the ocean floor. This
What Grain Surface Texture relates to littoral (coastal) environments?
V-shaped fractures and conchoidal fractures.
What to red rocks indicate?
Red rocks indicate that the iron was in an oxidizing enviroment. Black/green indicate that the iron is reduced to ferric iron and was formed within a anoxic or low oxygen enviroment.
whitings
Seasonally influenced milky patches of water that are from an increase of organic activity during spring.
Why is dolomite difficult to precipitate?
Mg(OH)2 is stronger than ca(OH)2 making it much less likely to react with carbonic acid and the kinetics for Ca is much more favored.
Dolomite is favored in high Mg/Ca ratio, low Ca/CO3 ratio, low salinity or high T (T>100C)
Why are mudstones composed of the most weathered particles?
With a decreasing particle size there is an increased surface area which increases the probability of a mineral transitioning to a different weathering product.
Fabric
This is how sediments within a rock are related to one another. It can be said to be the internal organization of particles.
It is composed of grains, matrix, cement, porosity, permeability, grain contacts, and sorting.
Grain Transport in Fluids
Fluid Drag: This is the shear exerted on the particle that causes rolling.
Hydrodynamic lift: This is because of Bernoulli’s principle.
The drag creates a horizontal vector and lift is vertical. Together they create a diagonal vector. After being entrained though the negative pressure becomes hydrodynamic making the slope of descent much less than the upwards entrainment slope.
Principle of Continuity
Q1A1=Q2A2
This says that the net mass going through an area is constant. It assumes that there is no collection of fluid and that it is incompressible.
Traction
This is a term describing anytime that drag influences a particle.
Porosity and Permeability
Porosity describes how much of the rock is filled with a fluid, either air or liquid.
Permeability is the measure for how rapidly a fluid moves through a rock.
imbrication
These are flat pebble “shingles” that indicate the flow direction. These indicate a rather regular and persistent flow.
What does graded bedding indicate in fluvial deposition?
Graded bedding indicates a decelerating flow. The deceleration of flow decreases the size of particles able to be entrained within a flow.
Desiccation
These structures show occasional wetting within arid environments and includes mudcracks, raindrops, salt casts, and teepee structures.
