LAB Flashcards
Conglomerate/Breccia nomenclature:
“support, clast-type, average size of clasts, conglomerate/breccia”
EX: Clast-supported quartzite pebble conglomerate
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 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.
Allochems
These include ooids, pisoids, peloids, oncoids, and intrachlasts. It includes any carbonate clasts with D>fine sand (63microns)
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.
Arenites NEED PIC
Sandstones that are composed of distinct grains and cement with a maximum of 5% mud.
Authegenic minerals
Minerals produced at the surface. Minerals precipitated through biologic, supersaturation, oxidation, or other processes.
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.
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.
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
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.
Conglomerates/Breccias:
Rocks that are primarily composed of lithic fragments over 4mm (pebble size) (>10%). 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.
In cut sections clasts may appear overly touching.
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. Commonly with slumps on slopes and water saturated sediments.
Coquina
A mechanically sorted fossil hash
Debris flow deposits
Unsorted, chaotic (sorting requires turbulence), matrix supported, lacks cross-stratification and occasionally shows reverse grading
Desiccation
These structures show occasional wetting within arid environments and includes mudcracks, raindrops, salt casts, and teepee structures.
Dimensionless numbers
Numbers that describe a state change for the participants of the system.
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.
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.
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 there is a mixture of mud accumulates in the troughs of the cross strata in the intrabedding portions of the rock. Indicates that the hydraulic conditions favored sand preservation during episodic flows and variable flow conditions
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.
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.
hummocky cross stratification
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.
It is believed to be caused by chaotic storm flows.
imbrication
These are flat pebble “shingles” that indicate the flow direction. These indicate a rather regular and persistent flow.
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
Lithic Arenites
Siliclastic rocks with a large quantity of rock fragments.
Often immature, angular grains and indicates shallow marine enviroments or fold-thrust belts.
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.
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
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
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.
Peloids
Grains of micro or cryptocrystalline calcite/aragonite without a coherent internal structure. These are often composed of pellets and lack concentric layering. .03
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.
Pisoids
an ooid with a D>2 mm
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.
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.
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.
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
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.
In cross section 2d ripples will have planar beds in one direction and bed sets in the other. 3d ripples will have bed sets in one direction and trough cross strata in the other.
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 Maturity
Sphericity, Roundness/angularity (wind is very effective and depleting angles), and composition. A very mature sediment indicates that a greater amount of work has been done of the grains.
Sequence of bedforms in laminar flow
planar beds, ripples, sand waves, dunes. Steep side shows flow direction.
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.
Solution Breccia
When a solution dissolves the host rock and only the insoluble rocks remain to form the fragments present within the breccia.
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.
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)
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.
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.
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
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.
What does sorting and roundness represent?
Sorting is representative of the persistence of the energy input or process. Less sorting indicates proximal rocks and good sorting indicates distal sediments where sorting consistently occurs (beaches, dunes…)
Roundness accompanies sorting and reflects the transport distance of the grains.
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.
Naming mudrocks
- ) check clay or silt
- ) Check for laminae or fissility
a. ) if laminated then shale or laminated mudstone/siltstone
b,) if unlaminated then it is a mudstone/siltstone.
Goldich Stability Series
This is the reverse of Bowen’s Reaction Series and represents the resistance to weathering.
Carbonate Nomenclature
Modifier (optional), Allochem type, allochem abundance
Modifiers for Carbonates
Fossiliferous refers to the presence of “bio-clasts”
oolitic: indicates a highly agitated, shallow water enviroment
intraclasts
peloidal: Same as oolitic but without concentricity
Ooids
Spherical to ellipsoidal grains .25-2 mm with concentric coating. Nuclei of extra-formational nature. Indicates a high energy, shallow enviroment
Pisoids
A small spheroidal particle with concentricity D>2mm
Oncoid
A coated grain of algal or microbial origin that is coarser than 2 mm.
Floatstone vs. Rudstone
These terms describe carbonates that have more than 10% of sediments of allochems D>2mm.
Floatstones are matrix supported.
Rudstones are grain-supported.
Carbonates with an originally solid structure
These are rocks that were autochthenous and are boundstones
Framestones are composed of a rigid framework like a coral reef
Bindstone are composed of binding/encrusting organisms like stromatilites and other algae.
Bafflestones are made of organisms that baffled waves/currents
Oncoids and Pisoids
Large D>1 cm concentrically coated that were mobile during formation.
Pisoids are not concentric.
Chalk
Extremely fine grained light colored lime mud primarily derived from microfossils.
Tufa
Highly porous and weakly bedded limestone formed from spring deposits
Travertine
Dense, fibrous limestone formed by springs. Often formed with tufas.
Nodular soil carbonates
Small irregular lumpy balls of carbonate. May resemble root traces.
Coal Types
Anthracite: high grade shiny coal
Bituminous or lignite: dull/soft coal
Bituminous sands: grey or black sandstones
Chert
Microcrystaline silica derived from radiolarian or diatom skeletons. It can also form from volcanic ash.
Diatomites vs. Tephra
Diatomites are very homogenous wheras tephra will has heterogeneous glass shards.
Evaporites
Chemically precipitated salts like gypsum, anhydrite, halite, sylvite. They infrequently outcrop (weathering) and are banded from variable water inputs.
Bedding terminology
Massive: indistinct bedding
Very thick = >1m
Thick= .3-1m
Med = 10-30cm
Thin =3-10 cm
very thin = 1-3 cm
Laminated = .3-1 cm
finely laminated
Varves
This is seasonal variation in sediment production, usually annual. It is seen in finely laminated mudstones primarily in lakes.
Styolites
Usually formed by the high-pressure dissolution of carbonates along a surface. Appears as rigid zig-zags or teeth.
liesegang banding
Concentric and/or ring bands of cements (typically iron stained) that form through groundwater flows. They are more typical in porous sandstones.
