Earth Mat Flashcards - Ch 11
__________________ are the solid products of weathering, the breakdown of rocks at or near Earth’s surface.
Detrital sediments
are the solid products of organic synthesis or precipitation and include hard materials such as shells, bones, and teeth, and soft materials such as cellular materials composed of organic molecules.
Organic sediments
are the solid products of inorganic precipitation, such as mineral crystals precipitated from solution.
Chemical sediments
is a general term for solid sedimentary particles regardless of origin.
Clastic
The term _________ is used for clastic sediment that is transported as solid particles across Earth’s surface.
epiclastic
clastic particles of organic origin such as shell fragments transported by waves or currents.
bioclastic
refers to clastic particles composed of silicate minerals.
Siliciclastic
is used for clastic particles produced initially by volcanic processes.
Volcaniclastic
refers to clastic sediment derived from a land mass.
Terrigenous
The _____________is a simple model of the processes responsible for the production of sediments and sedimentary rocks.
sedimentary cycle
Two major types of weathering processes are recognized:
Disintegration processes, which break rock materials down into smaller pieces of the original material without changing their composition.
Decomposition processes, which change the composition of the original material, producing new materials
The products of a second sedimentary cycle are referred to as ____________ sediments and sedimentary rocks.
polycyclic
Cross strata form when sediments accumulate on steeper slopes of up to
35°.
depositional environments may be broadly subdivided
into terrestrial, transitional (paralic), and marine environments.
environments typically occur in the terrestrial-marine transition and include coastal-deltaic environments such as deltas, estuaries, tidal flats, beaches and back-beach dunes, and barrier island-lagoon systems.
Transitional (paralic)
In _________________ which possess shear strength, the major stress that initiates flow is the tangential force of gravity (gₜ), which increases with increasing slope angle.
plastic flows,
Flows may also be distinguished as
laminar or turbulent flows
In __________ flow, adjacent parcels of the flow move roughly parallel to one another in a well-organized pattern, with negligible mixing between them.
laminar
In __________ flow, adjacent parcels of the flow move in chaotic patterns, and random mixing between parcels is common.
turbulent
Water is a Newtonian fluid.
T or F
T
Like all fluids, Newtonian fluids lack shear strength, but they are characterized by a constant resistance to shear stress, called
dynamic viscosity (μ).
Colder water possesses more molecular bonds between molecules, resulting in
higher viscosity or resistance to flow.
is essentially a ratio between the inertial forces and the viscous forces in a fluid medium.
Reynolds’ number
The Reynolds’ number can be used to predict
whether flow will be laminar or turbulent.
Viscous forces tend to damp out turbulence and favor
laminar flow.
Inertial forces tend to favor the development of
fluid turbulence.
For any situation, there is a critical Reynolds’ number below which flow is ________ and above which flow is ___________.
laminar; turbulent
The process by which epiclastic sediment transportation is initiated by erosion is called
entrainment.
Hjulstrom’s diagram contains two curves that divide the diagram into three fields.
Upper Curve : Erosion/Entrainment Curve
Lower Curve : Threshhold Depositional Velocity
Why does the critical entrainment velocity increase with decreasing particle size for silt and clay?
Due to increasing cohesiveness from higher surface area-to-volume ratios and electric charge on particles.
Their cohesiveness makes them more difficult to entrain, similar to larger particles.
What does the central field between the critical entrainment and deposition curves on Hjulstrom’s diagram represent?
The transportation or at rest field.
What happens to particles in the central field of Hjulstrom’s diagram when flow velocity is decreasing? increasing?
Particles continue to move until the velocity drops below the threshold velocity for deposition:
Particles continue to be deposited until the velocity surpasses the critical entrainment velocity
Once entrained, the _______________ of different particle sizes tends to be carried in different parts of the flow.
sediment load
The ________________ is carried in continual or intermittent contact with the bed over which the water is flowing.
bed load
The bed load is subdivided into:
A traction load, which is in continual contact with the bottom.
A saltation load, which is in intermittent contact with the bottom.
contains the coarsest particles, those with sufficient mass that they are not lifted from the bottom by turbulence and lift forces.
The traction load
Particles in the traction load move down-current by:
Rolling, sliding, creep
Where the traction load is more than one particle deep, the term ___________ can be used.
traction carpet
The_____________ contains smaller, less massive particles that can be lifted from the bottom by turbulence, lift forces, and particle impacts but quickly settle back to the bed before being lifted again.
saltation load
The ___________ contains the smallest, least massive particles—those particles that, once lifted from the bed, have such small settling velocities that they remain suspended above the bed for long periods.
suspension load
Water also transports a _that consists of the dissolved solids produced by the dissolution of rocks and minerals with which the water has been in contact.
solution load
two major types of aqueous flow are recognized in sedimentary environments:
Unidirectional flows.
Oscillatory flows.
are characterized by flow in one direction over a period of time.
Unidirectional flows
A qualitative measure of the speed of a fluid flow, with different amounts of flow corresponding to different sedimentary structures, called bedforms.
Flow regime
Two flow regimes are recognized:
The lower flow regime, where the bed is out of phase with the flow surface
The upper flow regime, where the bed is generally in phase with the flow surface
Increasing transition of a lower flow regime
Stationary Flat Bed
Current Ripples (Straight Crested then to curved)
Sand waves/dunes on Bed
Increasing transition of a upper flow regime
Plane Bed
Antidunes
Chutes and Pools
Ripple Indices
Wavelength to Height ratio
are straight-crested two-dimensional bed forms where, ideally, every two-dimensional cross-section parallel to flow is the same;
Sand waves
are curved-crested three-dimensional bed forms where cross-sections parallel to flow vary.
dunes
dunes begin to be sheared out into a flat or plane bed that is parallel to the nearly flat flow surface, marking the transition to lower to higher flow regime
plane bed or the plane bed transition.
They migrate with the standing wave in an up-flow direction by lee-side erosion and stoss-side deposition.
antidunes
Net aggradation of sediment on a flat or plane bed produces
horizontal stratification.
sand waves and dunes do not form on what grain sizes
Coarse silt to fine sand
sequence of bed forms for coarse silt to fine sand
(1) lower flow regime current ripples,
(2) upper flow regime plane bed transition, and
(3) antidunes.
Current ripples do not form in beds composed of
coarse sand or gravel.
sequence of bed forms for coarse sand or gravel.
(1) lower flow regime flat bed,
(2) sand waves or dunes,
(3) upper flow regime plane bed, and
(4) antidunes.
troughs climb at angles equal the stoss-side slope.
the entire ripple form is preserved as sequences of lee-side cross-laminations
type I climbing ripple laminations.
Critically climbing ripples
troughs climb at angles higher than the stoss-side slope angle
preserve both stoss-side and lee-side laminations and entire ripple forms
type II climbing ripple laminations
Supercritically climbing ripples
“troughs climb at angles less the stoss-side slope.
only toe of foresets is preserved
Cosets of small scale ripple laminations
Subcritically climbing ripples
As fallout from above increases from zero to extreme during the migration of ripple trains, the sequence of preserved structures evolves from:
(1) isolated ripple marks,
(2) horizontal laminations,
(3) small-scale cross-laminations,
(4) type I climbing ripple laminations, to
(5) type II climbing ripple laminations
result from the erosion of preceding dunes by offset “scoop-shaped” troughs during bed aggradation.
Trough sets
record the curvature of lee faces in cross-sections perpendicular to flow.
Festoon cross-strata
Flow direction in festoon cross-strata
is roughly perpendicular to the place of maximum curvature in plan view (Figure 11.17).
Waves moving through water whose depth is less than the wave base (< L/2) are called
transitional and/or shallow water waves.
are straight-crested forms with small ripple indices (length: height ratios) produced by the back-and-forth movement of sand across the bed and across the ripple forms
Oscillation ripples
is produced in protected areas with low sand : mud ratios and contains isolated lenses of ripple-laminated sand deposited from traction encased in dominant muds deposited from suspension
Lenticular stratification
is characterized by subequal amounts of relatively continuous ripple-laminated sand and mud layers with the rippled sand giving the mud layers a wavy appearanc
Wavy stratification
is produced in less protected areas with high sand : mud ratios.
Flaser stratification
are thin mud drapes deposited from suspension that partially preserve ripple forms in areas dominated by the deposition of ripple-laminated sand
Flaser
______________ characterized by gently inclined, convex-up cross-strata, whereas ________________is characterized by gently inclined, convex-down cross-strata, both in sets with thicknesses less than 0.5 m
hummocky cross stratification; swaley cross stratification
where does HCS and SCS commonly occure
between the normal wave base and the storm wave base
During major wind storms, the saltation load moves in part by _________ in which many saltating sand grains collide in mid-air, before reaching the bed, and stay suspended for longer than normal times.
sheet flow
Larger grains are transported in a traction load by the process called _____, which is maintained by grain-to-grain collisions.
creep
Coarse silt to medium sand is transported primarily by
saltation
are transported slowly by creep in the traction load,
Fine to coarse sand and perhaps fine gravel
repeated entrainment, transportation, and deposition produce a down-wind sequence from:
Coarse lag gravels
Well - Sorted sand deposits
Well-Sorted mud deposits
examples of well sorted mud deposits caused by aeolian processes
poorly stratified loess deposits
explain ripple indices
A measure of the symmetry of a ripple form, expressed by the ratio of ripple wavelength to ripple height.
Wavelenth / Height
How does wind ripples differ from aqueous reipples
Wind ripples tend to have lower heights relative to wavelengths and thus larger ripple indices (RI > 12).
Wind ripples are strongly asymmetrical.
Unlike continuous-crested subaqueous current ripples, wind ripples show branching crests (Figure 11.29).
are larger features (2.0 × 10² to 2.0 × 10⁴ m) composed of multiple dune forms with complex cross-stratification.
Dras
Cold Dry Glacier vs Warm Wer glacier
Cold, dry glaciers occur in very cold regions where ice remains frozen most of the year.
processes involve flowing ice.
—
Warm, wet glaciers occur in regions that partially thaw for extended periods so that glacial ice is melted
mix of glacial ice flow and unidirectional aqueous flow.
Glacial entrainment occurs primarily by some combination of three processes:
(1) erosion of unconsolidated sediment; (2) plucking; and (3) abrasion of bedrock.
occurs when a glacier encounters an obstruction in an uneven bedrock surface, often where it is flowing downhill across bedrock.
Plucking
In the glacial flow, what does Larger, medium, and small size particles in contact with bed rock produce,
Grooves, Strations, Polish
Small particles entrained from glacier
rock flour
No matter which set of depositional processes is involved, sediment deposited directly from glaciers is called
glacial till
poorply sorted, boulder bearing and polymictic lithified glacial tills
tillites
When icebergs melt, ice-rafted debris sinks to the bottom.
Large clasts dropped from icebergs are called
dropstones.
are characterized by large proportions of sedimentary particles (≥ 80%) relative to water (≤ 20%), though they may contain significant air.
Granular flows
are characterized by smaller amounts of sedimentary particles (∼ 60–80%) and larger amounts of liquid (∼ 20–40%) and are sometimes called liquefied flows.
Slurry flows
possess lower sediment (∼ 20–60%) to water (∼ 40–80%) ratios and include hyperconcentrated stream flows and many, but not all, subaqueous turbidity currents.
Hyperconcentrated flows
sediment concentration that separates high concentration and low concentration turbiditiry currents;
locations
> 60%; <20%
Proximal; Distal
