0 slip face forms
Sand sheets, stringers, and domes. These are accumulated lumps of sand that tend to form a bell shape. They form in areas with low sand supply.
1+ slipface bedforms
Blowout dunes: sand accumulating ~haphazardly near vegatation
Parabolic dunes: These occur due to plants securing soil at the edges of a barchan dune and reversing the “U” shape so the curve is in the direction of the wind.
2 slipface bedforms
Symmetric Ridge/linear dunes: These are long lines that sometimes undulate. They form due to two subparallel dominant winds. The wind can become helical.
3+ slipface bedforms
These are Star dunes that form due to variable wind directions
Accumulation and preservation space
The accumulation space is the area of elevation available for accumulating material.
There is an erosional line that defines the preservation space by being the space where migration will not erode the material.
Preservation space can change due to compression/subsidence, rising water table, or changes in migration.
Alluvial Fan Depositional Environment
Principle of continuity dominates. The area of flow rapidly increases as slope decreases and competence falls fast. Near the interface, proximal fans, there are debris flow deposits (poor sorting, large clasts, matrix supported conglomerates/breccias). Further down, mid-fan, there is sheetflood deposits and incised channels that vary the deposition from fluvial to find sands down slope. Then there is there distal fan that merges with the alluvial plane below.
Alluvial fan depositional processes
Wet Fans: Channelized confined flows deposit fluvial sediments. This produces scour and fill, imbrication. Sheet floods create well sorted materials that fine outwards
Dry fans: Debris flows and rock avalanches (differ in presence of mud)
Alluvial fan geometry
Parallel to the mountains they are like a bell curve (convex up). Normal to the mountains they are like a channel and are concave up.
Alluvial fan types (4)
wet fans: stream dominated and have fluvial facies
Dry fans: These are arid fans that are dominated by debris flows and sheet floods.
Mega fans: These are low slope, stream dominated fans common in monsoonal areas.
Fan-deltas: Fans that empty into standing water. Common in glacial enviroments.
Alluvial Fan vertical sections
These tend to have autocyclical channel switching and abatement related to tectonic processes and climactic factors. This creates two superimposed cycles of sediments.
On a large scale there are cycles of coarsening upwards due to the progradation of the fan combined with subsidence resetting the cycle and on a small scale there is a fining upwards due to the loss of competence within the flow.
Alluvial Fans
These are conical prisms/wedges of sediments that form at the mouths of canyons and high relief areas with little vegetation. They are flow dominated or stream dominated and typically transport large quantities of sediment into a basin.
They tend to form in either tectonically active or glacial areas.
Alluvial fans distinguishing character
On a transect they have lobes of muddy large flow deposits with gravelly channel incisions. They also have sieve deposits which are gravel dominated subsurface deposits from sub-surface water flow removing mud.
Anastomosing channels
These are channels that form multiple stable channels with prominent levees and vegatated islands. They do not meander.
Anastomosing river deposits
These form on low slopes and generally have greater deposition than erosion. They can avulse (rapidly change course). Vegetation on the levees encourages muds and organics.
When compared to anastomosing rivers they show vertical continuity.
Anatomy of a carbonate platform
These are ~circular platforms of boundstones and fossiliferous rudstones and bafflestones that encapsulate a low energy center area that is filled with micrite and flanked by steep cliffs.
Back Barrier deposits
The sub-enviroments of this area vary with the barrier island configuration but can show signs of being marshy (anoxic, organics) to bidirectional channelized flow that produces lenticular and flaser bedding.
Backshore sediments
These are often eolian deposits or paleosols.
Bajadas
These are distal fans that merge with one another because of adjacent alluvial fans.
Barrier island facies from backshore to offshore
root traces within fine sands. coals and other lagoon deposits
Eolian dunes (trough cross beds, 3d ripples)
Swash-related deposits (planar beds or multidirectional trough cross beds). Well-sorted, mature sediments.
There are increasingly massive beds of coarse sediments as the breaker zone is at a lower depth.
alternating muds and sands grading into fine sands with bioturbation
Barrier Island Facies Model
General shift from eolian to shallow marine.
Barrier Island Reaction to Eustatic SL Shifts
Transgression: The Barrier islands erode and slump into deeper water
Regression: They prograde like shores or dunes. The Back-barrier becomes increasingly brackish and is capped by evaporites.
Barrier Island Subenviroments
There is the subtidal/subaerial barrier-beach complex: Sand islands about 1-20 m thick and long. This protects the coast from high energy waves.
Back-barrier region: calm, swampy/marshy areas aka a lagoon
Inlet-Channel complex: This is the calmish breaks in the barrier islands that allow for water to transfer between the back and front areas.
Beach Deposit Character
Fine grained sands with parallel planar laminae dipping at about 2-3 degrees. Placers are association with upper flow regimes. Within coarse sediment beaches there can be imbrication towards the shore.
Backshore beaches on barrier islands are more likely to be interbedded with muds and hummocks from storm surges.
Beach Morphology
Moving seaward:
- Eolian dunes (backshore) grade into the beach that starts with the foreshore this area is below the high tide line
- This grades into a steeper subaqueous zone that is the surf zone
- The base of the surf zone is at the low tide line where another steep dip occurs and this is the breaker zone
- There is then another sloe and that becomes the transition zone and grades into offshore
- Nearshore describes the areas in the surf, breaker, and transition zone.
Bioherms
These are hills that form from reefs. They depict the progradation of reefs are generally underlain by a massive boundstone lump flanked by massive framestones with beds of micrite in the center.
Braided channels
These are channels that have many sub-channels. They are highly unstable with many unvegetated islands aka sandbars. They tend to not have levees but instead are incised into the landscape.
Braided River Deposits
These channels have more gravel-like sediments, less fossils/organics, less mud, and pervasive longitudinal bars (tear-drop shaped lobes that migrate downstream and coarsen upwards)
Breaker Zone sediments
These have isolated trough cross stratification and finer sediments. They often have planar horizontal laminae with many vertical burrows.
Carbonate ramps
These are similar to continental ramps but with carbonates. This occurs on the inside of Florida. They differ from reefs sedimentologically by not having framestones or boundstones.
Channel Form Factors (4 total)
Sinuosity: the channel’s deviation from a straight line
of channels: Degree of subdivision
Braiding: Prevalence of bars/islands
anastomosing: The prevalence of flood-plains
Channel formation variables
Flow character, slope, sediment source, discharge, continuity, bed roughness, and human activity.
Generally as discharge and slope increases channels move from anastomosing to meandering, to braided.
Clast age on alluvial fans.
Because alluvial fans most often form at the interface of rising mountain faces the youngest clasts are at the base of fan because these are eroded first. The oldest clasts are eroded last and are on the top of the fan.
Coastal Sand Belt
These are barrier islands. They form in wave dominated coastal systems.
Coastal Sedimentology
Sources: These are generally fluvial or reworking from continental shelves
Progradaiton: There is episodic deposition
Keep in mind that all the current processes we observe are in an age of major trangression
Common subenviroments within deltas
Transgressive: tidal flats, estuaries, lagoons,
Regressive: tidal flats, deltaic sands/muds, and strandplains.
Correlation chart
Compares one or more stratigraphic section to time and not to depth.
Crevasse Splay deposits
These are lobes of coarse sands or gravels. They have climbing ripples because of the principle of continuity. They may show flaser bedding.
Deflation pavement
Lag deposits of large gravels. These are the materials that remain after small material is eroded away.
Delta
This describes a deposit of any subaerial or subaqueous deposit formed by fluvial sediments prograding into a standing water body.
The transgression we are currently within enable delta progradation. During regression the channels erode the deltas.
Delta Classification
Deltas are either river, wave, or tidal dominated. This is along the spectrum of mixed mud/siilts, fine sand, sand, and gravel. This second axis is dependent on how close the delta is to the source.
Deltaic Facies
These broadly have marine sediments that grade into marshy muds, organics, and channel sands. This grades into fluvial sediments. This is because regressive sequences are more likely to be preserved.
At the base of prograding deltas there are often turbidites and beach sands. These are overlain by marshy sediments and fluvial sediments.
Deltaic sub-enviroments and deposits
Overall they are heterogeneous and complex.
Overbank deposits are like crevasse splays. These will likely subside to marshy sediments.
Interdistributary bays/marshes: These form inbetween the lobes of a river dominated delta. They have high organic content, bioturbation, fine grained muds, oftentimes with oyster beds.
Distributary mouth bars: These are sub-aqueous sand/mud bars from the rapid loss of competence when entering the water.
Subaqueous levees: These also form due to the rapid loss of competence and underflow of denser material.
Entrenchment
This describe the lenses of fining upwards strata within alluvial fan deposits that reflect incision within alluvial fans.
Eolian facies model
These have high angle bedset with small-scale trough cross beds. They often have grain fall/flows. This is adjacent to low angle translatent ripple laminae. This is above fine grained silts, muds, clays, evaporites with bioturbation and fossils from interdune periods.
Eolian strata
These have grainfall slides, lag gravels, erosional bases with gravels, kinetic sieving, trough cross stratification.
Eolian structures
Excellent sorting, large scale trough cross beds.
Compared to fluvial systems they have translatent ripple stratification which describes that the planar beds are more likely to be preserved than the cross-strata of fluvial deposits. On a large scale they form sub-parallel parallel bedsets with lenses of trough cross bedding.
Epicontintental Seaways
These are like pericontinental seas but they are within the continent and are surrounded by land on both sides. They differ from normal seas because of limitted fetch. This results in a large amount of organic shales similar to lakes. They also can have storm dominated coastlines.
Ergs
These are areas that are larger than 125 km2 they encompass about 20% of modern deserts or 6% of earth’s surface.
They require ample sand and wind.
Estuaries
This is a term that describes drowned river valleys. They only occur during transgression because they fill with sediment and become a delta causing a transgressive lag of progradation elsewhere. This includes both fluvial and marine sediments. They can be classified by being wave, tide, or river dominant.
Estuaries facies
Because of ample accumulation space these deposits are often preserved. They are similar to deltas with a general shift from fluvial sediments to marine muds but differ in that the lowest energy area is in the middle of the estuary which is reflected in the progradation too.
Facies
This is a recognizable lithology or group of lithologies. It is the “sum of a sedimentary rocks lithologic character and acts as a class of deposit type.”
They are not dependent on locale only on the nature of the rocks. They can be lumped together to create sequences of facies (Bouma Sequence).
These are objective observations of rocks that do not vary with time. interpretations vary with time.
Facies features (10)
This includes grain size/maturity/composition, beforms, structures, geochemical character, diagenetic alternations, fossils, or geophysical character (polarity or magnetic susceptibility)
Facies of storm dominated Coastlines
These generally have hummocky shelf muds with fine sands and storm based “lag gravels” This occurs along usually passive margins where the fair-weather waves do not transport or impact sediment.
Fan Deltas
These are coastal prisms of alluvial sediments that are derived from density flows.
Ferestrae
These are fossil algea with holes.
Fetch
This is the surface area that wind is able to blow along the interface of a standing body of water and the air. Limitted fetch limits the turbidity of the surface and decreases the amount of waves that are seen on the surface.
This is why beaches are sandy but lake shores are mucky.
Floodplain Deposits
These are bioturbated muds with lots of organics.
They often include crevasse splay deposits which represent a break in the levee with similar character to a Bouma sequence.
Floodplains
These are natural flats adjecent to the flow that are periodically flooded during avulsions. They are particularily prevelant in single channel systems.
Fluvial channel deposits
There is a gradual fining upwards of sediments that represent the decreased competence of the flow near the top. The outer corner is erosional, the inner is depositional. The bases has trough cross stratification which grade into 2d ripples.
Fluvial System Deposits
These will be large U-shaped valleys with fine laminated planar muds that are intercepted by troughs of coarser normally graded sands with epsilon cross beds that shift throughout the basin due to the changing position of the channel/s. These also have “shoestring” sands that are from point bars and levees. There are abundant paleosols.
fluvial system subenvrioments
Channels: where water flows
Levees: these are high embankments that channelize the flow.
floodplains: large areas that are periodically flooded
Lakes/swamps
Fluvial-Eolian Deposits
These form due to the point that very often the water table below a dune is very high so the interdune enviroments will flood.
These will have eolian cross beds with mud laminae, ripples, and fluvial pebbles between eolian sections.
Foreshore sediments
The primary process that dominates sediments is wave breaking and this is because as the wave depth approaches 0 the Froude Number approaches infinity (Fr=V/(gD)^.5) Which results in fine upper flow planar bed laminae with good sorting.
If there are larger particles there may be imbrication that is leaning in the foreshore direction.
Foreshore, Backshore, nearshore, shoreface and offshore
Foreshore is the area that is flooded by tides daily
Backshore is the coast
nearshore is always underwater but waves occur
shoreface is the subtidal to wave base area
offshore is the region prior to breaking
Form Types
Compound Dunes: these are when the same type of dune is superimposed on itself (EX: barchan on a barchan dune)
Complex dunes: these are when there are dissimilar types superimposed on one another (star on a linear dune)
Formations
This is a deposit that can be mapped on the surface. They are observed from the surface or mapped with seismology. They are gross lithology (sequence of facies) of a rock mass and represent a unit of stratigraphy.
They differ from facies by being a facies because they can be deposited in different sedimentary deposystems. Within a formation a facies may grade or extend beyond the formation and because it is an objective description the same facies can be found in multiple formations across the flobe.
Forms with 1 slipface
Barchan dunes (Large U shaped dunes)
Barchanoid dunes (Large U shaped dunes that are ~interconnected)
Transverse Ridges (Long parallel rows of dunes)
These indicate one dominant direction of wind.
General character of eolian deposits
These tend to have very mature sediments that are also well-rounded.
They are generally quartz but there are also carbonate dunes.
Grain fall and grain flow
grain fall alludes to the falling of grains that are swept over the top of the dune. These taper down slope. Grain flows are avalanches. They thicken towards the base and taper up slope.
Haboobs
These are low density gravity flows that arise from suspended silt moving downslope.
Hadley Circulation
This is the rising warm air (equator) and falling cold, dry air (@ +-30 degrees).
This is the reason deserts form at +-30 degrees. This helps paleogeographers understand continental shifts by finding how large sand seas shifted with time.
Helical Flow
This describes that when fluids are moving around a bend like in an anastomosing channel the outer edge has a higher elevation than the inner which causes a helical flow.
Hemipelagic muds
These are muds that are partly from continental sources. They are usually ~5% organics, ~40% silt and deposit through suspension settling.
Hierarchy of sand bedforms
Drass: these are massive dunes with a wavelength on the scale of km and heights of up to 400 m
Dunes: these form on the scale of tens to hundreds of meters with heights up to ~100 m
Ripples: these are undulating sand bodies with wavelengths less than tens of meters
Ripples can form on dunes that form on drass.
Hybrid/interpretive maps
These are maps that may show the paleogeography or other interpretations of facies. They are helpful hypotheses.
Inclined foresets
These are dipping beds that form off of sand-bars. They are identified by being well defined wavy sub-parallel fine sand laminae.
Isolith Maps
These show how one unit shifts in thickness laterally.
Isopach maps
These show lines of equal sediment thickness not of equal lithology
Lagoon facies models
When compared to an estuary there are less indicators of freshwater aka restricted flow and circulation. They tend to have massive deposits of silty muds that grade into a tidal inlet and eventually offshore deposits. They are similar to lakes in that they fine upwards as they fill their accumulation space. They have limited biodiversity because of their unique chemistry.
Lagoons
These are shallow stretches of seawater adjacent to the sea but they are not fed by a river and are protected by coastal features like barrier islands. They are like oceanic quasi-lakes.
They are generally more saline than the oceans but their chemistry can either be hypo or hyper saline.
loess
This is very fine silt that tends to accumulate far from the source and is very well sorted.
Long term lacustrine deposition
Lakes fill with sediment to become floodplains. This generates thinner laminae and finer material with more organics.
Longshore currents
This is when waves do not directly impact the beach normal to the water beach interface. This causes a sub-parallel current along the beach.
This is also a reason for the “zig-zag” motion of sediment transport down a beachfront
Longshore trough
This describes the longshore drift that causes the zig-zag motion of particles. The flow that is parallel to the coast can create a helical flow that creates subaqueous dunes in the breaker zone too.
Lacustrine Systems
These are lake related deposits.
lakes are any and all bodies of still water within a continental environment
These are very uncommon in the grand stratigraphic record but are rich in information, oil, evaporites, coal, iron, and uranium. They tend to have formed due to volcanic calderas, oxbow lakes, and tectonics although right now they are formed from infill of glaciers.
Max low sea level in Pleistocenes
100-120 m below current sea level
Meandering channels
These have a sinuosity index greater than 2 and tend to form in humid, flat areas. They are singular channels with wide floodplains, moderate stability, and migration.
Meandering channels facies models
On the outside of bends point bars form. These sand bodies fine upwards and show large wavy bedsets with ripples in cross strata which decrease in size up-section. They have erosional bases too. During progradation there is epsilon cross bedding which describes the parallelogram shaped bedsets.
On a bigger scale they also have alternating zone of anoxix marshes from oxbow lakes and lobes of sand from crevasse splays.
Migration of facies
Progradation which is simply the building out through lateral deposition.
Tectonics and quake shifts can alter rivers, cause subsidence, and change erosional features. This is common with large scale avulsions and autocyclic alluvial fan deposits.
Climate change shifts the environment but the processes do not change. This is simply adaptation.
Biotic succession/modification: As biologic features grow they can shift facies.
Model and function
This is a simplified version of reality that only contains features of concern. It helps us relate observations to interpretations.
Modern reef controls
Reef formers aka Corals: Hermatypic corals are tropical shallow corals that rapidly build
Ahermatypic corals are deep water corals that are very slow to build
Reef Binders: These are algaes that laterall bind things
Neritic Zone
This is the area from the shore to the continental break where the pericontinental sea forms. This has a unidirectional sediment flow to deep ocean.
This is broken into the inner, middle, and outer shelf.
Net transport of sediment due to waves
There is an assymmetry of velocity where it peaks when moving beachward. This means that there is only transport in the forward motion of sediments.
Ocean Anatomy
Starting at a passive margin there is the Continental shelf (low dip), which then has the shelf break at ~100 km from the shore and depths of ~130 m. This is followed by the continental slope (~4o slope) and meets the continental rise which is subaqueous fans. This grades into the Abyssal Plane until the MOR is reached.
The only difference in an active margin is everything is called a trench.
Oceanic/Deep-Water sedimentology
These are rarely studied because they only exist as ompholites, have very low sedimentation rates, and economic value.
Generally along the continental slope submarine canyons have turbidity flows and in the deep oceans there is very slow sediment accumulation from loess, glaciers/icebergs, and MOR’s.
Orbital Velocity
This is the cyclical change in velocity of the wave’s velocity. It is significant because it peaks towards the shore and can only cause traction transport towards the shore. An integral of the oscillation yields zero.
Pelagic sedimens
These are derived from the ocean. They include pelagic clays that are derived from loess and calcareous/siliceous ooze.
pH controlling factor
Biology controls pH by extracting CO2, bioturbing the base, producing organic acids, and producing shells.
Physical Processes within Lakes
Entering flow either floats has a middling (where there is a density gradient in the lake) or dense turbid underflow The first two create slow precipitation of particles the last creates turbidity flows.
Bioproduction also creates carbonates, shells, other carbon material that settles slowly to the lake base.
Primary formation of lakes
Because we are in an interglacial period many of our lakes are glacial but preivously lakes were largely due to rifting and transverse faults.
Prograding delta facies
U. Section: bioturbated bay/marsh
Crevasse splays and indistributary bay lenticular beds
Overbank sands interbedded with beach sands
Beach sands (cross strata dunes)
Fines into finer sands/muds for offshelf enviroment
Reef facies models from inner to off-reef
The inner reef is the calmest enviroment with shifting salinity. There are few corals and mainly micrite.
The outer back-reef are skeletal grain/packstones with some bioturbation.
The Reef crest is made of boundstones, framestones, and bafflestones that are resistant to waves. This is the area of optimal growth because it faces the ocean and the ocean chemistry is most constant.
The deeper fore reef is made from gravity flows off the reef crest and will be more likely to have slumps of rudstone that may end up in deep water.
Reef progradation
There is the combination of subsidence and reefs growing towards the ocean where chemistry is stable. This creates a concave up shape.
Regressive Phase
This is when the sea level lowers.
River dominated delta
These have large elongated lobes of sediment. There is significant evulsion and mud dykes on these deltas. These will form deposits that are similar to a meandering river.
Shelf Break cause
There is usually a basement ridge that fills with sediment off the shores of continents that creates the continental shelf. This can be from tectonics, reefs, faulting, volcanics, diapars or folds.
Currently, because of transgression the shelf on the East coast is not depositing sediments which is why people are able to fish mammoth bones.
shoreface
This is the subtidal to wave base part of the beach.
Shoreface Deposits
These occur in the area between the low-tide zone and storm base.
Their upper portions are defined by high energy wave breaking processes that create multidirectional torugh cross beds. This grads into the area below the wave base which is very fine sand laminae. These deposits tend to have vertical burrows.
Sinuosity index
This is an index that increases as channels become less straight.
S=Lthalweg*Dmax/Lvalley where the thalweg length is the total path distance in the deepest part of the channel. D is depth and valley length is the distance downvalley within one wavelength of the channel.
Slipface
This refers to the lee edge/s of a dune. It is used to classify dunes. These occur in the downwind direction.
Storm Geomorphology and Impacts
Low pressure cells create storm urges/swell that are very longwave and deep waves which erode beaches, create muddy sediment plumes, and flood the shores. This creates hummocks because of the changing flow conditions.
Surf zone sediments
These are mostly very well sorted mature sediments that form ripples and the associated bedforms. There can be troughs and undulations in this area with coarser sediments.
Tempesites
These are sandy cross bedded beds that form from storms where the suspended sands rapidly settle out of suspension. Oftentimes this is couples with mudstones.
Terrigenous Sediments
This is sediment derived terrestial sources
Three types of lake deposits
Overfilled lakes: These have persistantly open hydrology and show progradational shores, interbedded fluvial sediments.
Balance filled: These are open and sometimes overfilled. They have fluctuating conditions with mixed shorelines, oxic vs anoxic enviroments, and varied siliclastic and carbonate bedding
Underfilled: These are closed lakes that are chemically stratified with high solutes, evaporites, and aggradational shores.
Tidal Flat Anatomy
There is the subtidal zone below the mean low tide level. It has the highest velocity of tidal shifts and will have bedload deposits. These often have herringbone cross stratification and 2D ripples.
intertidal zone: this is the area within the average tidal flux where there is a mix of bedload and settling. This creates wavy shales, flaser and lenticular beds.
supratidal zone: This is the area only flooded at extreme tides and can form sabkahs in arid regions. This will range from organic rich shales to evaporites. They tend to have high bioturbation.
Tidal flats and inlets
These are common within macrotidal coastal systems with low wave energy (usually along low relief or protected coasts). These have extensive mud flats that have tidal channels normal to the coastline or parallel to the tidal channel flow.
Tidal flat deposits are important for oil, gas, uranium and can be siliclastic or carbonates.
Tidal Flats Unique Features
These will include bi-directional flow, tidal rhythmites (bi-directional channelized flow deposits with herringbone x-strata that occur in groups of 7 related to tidal cycles), flaser bedding, fossil hash, many reactivation surfaces in SS, the uppermost strata has algaes and desiccation features.
Because the rising tide has a low velocity there may be indications of assymetric flows in the herringbone crosss strata.
Tide dominant deltas
These deltas have periodic oscillatory flow that redistributes fluvial sediments across the coast. They have bars that are parallel to tidal channels. They are defined in rock by having significant sand bars that are parallel to the flow.
Topsets, Foresets. and Bottomsets
Topsets are fluvial deposits from the river. They are dominated by sands, gravels, muds, organics (from interweaved lagoons and marshes)
Foresets are silty sands with lightly dipping beds. Also called subaqueous delta plain.
Bottomsets are from suspension settling that are fine laminae that dip more steeply seaward. This is also called the prodelta.
Transgression
This is the rise of ocean levels. It is unlikely to be preserved than regressive phases.
Transgressive/regressive barrier island deposits
During periods of transgression the islands are eroded away and will often “slump” into the ocean creating soft sediment deformation structures
During periods of regression the barrier islands prograde to form lee side dune cross beds, sand avalanches, and slump structures. Of significance is that the back-barrier environment
can become isolated and thus grades into evaporites.
Transition zone sediments
Finer very finely laminated sands that dip seawards
Transverse bars
These are like sand sheets or barchan dunes that form on braided rivers that are calmer. They create 3d and climbing ripples. Updip on bedset indicates paleoflow direction.
Transverse dunes
These are “barchanoid ridges” with one slipface that form because of unidirectional wind.
Delta Forms
Generally the form of a delta is a function of the climate, river, and water body
Tidal dominated seasonal discharges creates large triangular, slightly fan-like deltas. (the Nile)
Large sediment loads with harsh coasts creates a rather flat delta (the coast does not shift) this is like the Copper River
River dominant with weak tides creates large lobey tidal flats (Missippi)
Types of Density Flows
Homopycnal flow: This is when the density of the river ~ density of the water. This leads to rapid deposition (v~0)
Hyperpycnal flow: This is when the river is more dense than the water. It leads to currents that deposit fluvial materials at the basin base. This can create an anoxic environment in the base of the lake
This occurs in fluvial deltas.
Types of Eolian Systems
Dry systems: This is when the water table is below the depositional surface. There is no water-related stabilization.
Wet Systems: This is when the water table is at or on the depositional surface and deposition is only related to water stabilization
Stabilized system: This is when there is not migration and vegetation, cement, muds help to stabilize the system
Types of lakes and implications for deposition
Open/external lakes: These have ready input/output of water and are more like to be oxic
Closed/internal lakes: These lakes lack an exit which may create anoxic environments and encourages the development of evaporites. They form in arid environments.
Types of tides
Diurnal: daily
semi-diurnal: 2x/day of relatively similar heights
mixed: unequal lows and highs.
Varves
These are thin laminae of light and dark sediment primarily from cool lakes.
The light material is siliclastic from summer floods and the thin dark laminae are from winter organics settling.
In lake sediments autumn produces white micrite. Summer produces white calcite crystals. Spring produces diatoms. Winter is when only settling occurs so it is dark organics.
Walther’s Law
The deposits that form together laterally are superimposed on others vertically if deposition is continuous and post-depositional structure does not shift. The failure of walther’s law is when facies “pinch-out” which indicated that the sedimentological process has terminated laterally when deposition occured.
The implication is that vertical sections reveal lateral relationships.
Water circulation mechanisms and impacts in lakes
Temperature gradients within lakes creates circulation that is often seasonal. This helps to oxidize the base of the lake and increase the amount of organic matter.
In closed lakes or lakes with internal feeding systems there may be a denser layer at the base of the lake due to dissolved solutes that prevents this mixing. This leads to an anoxic base of the lake that will diable bioturbation and have microlaminae. This is very important for oil.
Wave Base
This is the depth where wave oscillation ceases. It is roughly .5*wavelength.
Near the shore the interaction of the oscillation of the wave causes shearing.
Wave Dominant Delta
These deltas get smeared by longshore currents that creates a less obvious lobe of sediment that is more parallel with the coast. These don’t violently protrude but are morphed into the coastline.
The resulting deposits have trough cross beds, barrier island deposits, and significant evidence of reworked sediment.
Wave Dominant deltas
Wave height
Wave depth is one half of the wavelength of the wave.
Why do reefs not form near river mouths?
There is too much siliclastic sediment that fluctuates the water composition and blocks sunlight.
Wind form of transport
For any sediment with D>.05 mm the material saltates. This causes “creep”
Threshold wind values “throw” particles through collisions.
d
Cross section
This is the observed sequence of rocks as a function of depth.
Correlation chart
This relates formations or facies to time at various locations.
fluvial systems chart
River avulsion
This is when a river abandons a channel. Meandering refers to when the river migrates laterally and gradationally.
Point bars
These are the deposition that occurs on the inside corner of meandering channels. In the sedimentary record they look like parallelagrams fining upwards/
Stratigraphic Unroofing
This refers to how the youngest clasts will be at the base of a fan and the oldest will be at the top because this is how they are eroded.
Geologically significant types of lakes
Tectonic lakes, Volcanic lakes, fluvial lakes (oxbow stuff)
Large scale high angle cross stratification
This is a term that describes the large troughs that form due to grain fall during dune migration. In comparison the low angle trough cross stratification is because of translatent ripple migration.
Syndepositional deformation
This is related to soft sediment deformation common on deltas.
Transgressional Lag
This is the term that underpins the idea that transgression is often not preserved within the sedimentological record. This is because the sediment will be deposited laterally and not vertically.
ahermatypic coral deposits
These will be more likely be framestones where the allochems are bound at deposition because of the calmer enviroment.
