Depotitioanal Environment

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Continental

FluvialAlluvial Fan, Braided River, Meandering River

Desert/Aeolian,LacustrineGlacialDeltaic

Delta Plain, Delta Front, Pro-deltaMarginal Marine

Beach, Barrier Island, Estuary, Tidal FlatMarine

Continental ShelfCarbonate Reefs and associated environments,Siliciclastic Shelves

Continental Slope and Ocean Floor

DEPOSITIONAL ENVIRONMENTS

Content

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Fluvial

Alluvial Fan

Braided RiverMeandering

River

Desert/Aeolian

DepositionalEnvironment

Marine

ContinentalShelf

CarbonateReefs and

associatedenvironments,

SiliciclasticShelves

Continental

Slope andOcean Floor MarginalMarine

Beach

BarrierIsland

Estuary

TidalFlat

Lacustrine

Deltaic

DeltaPlain

DeltaFront

Pro-delta

Glacial

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An Environment: a distinctive kind ofgeographic setting characterized by a

distinctive set of physical and/or chemicaland/or biological conditions.

Characteristics of Depositional Environment:

Heres a list of what you can look for in a sediment rock or a

sedimentary bed that might tell you something about depositional

environment:

grain size

grain shape

grain surface texture

grain fabric

sedimentary structurescomposition (siliciclastic; carbonate, evaporite, coal, chert)

fossils (body fossils, trace fossils)

stratification sequence

sediment-body geometry/architecture

CONTINENTAL DEPOSITIONAL ENVIRONMENTS

Environment

Environments

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CONTINENTAL DEPOSITIONAL ENVIRONMENTS

What Happens

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CONTINENTAL DEPOSITIONAL ENVIRONMENTS

What we Want

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Continental depositional environments &Characteristic Deposits:

Glacial :till, moraines, deltas, lakes, outwash, kames, drumlins

Desert :arroyo (wadi) deposits, eolian sands, sand dunes, dust, loess

Lake :clastic deposits (bedded), chemical (salts, carbonates)

Fluvial :channels, banks, flood basins

DEPOSITIONAL ENVIRONMENTS

Continental Depositional Environment

CharacteristicDeposits

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Continental Depositional Environment- Glacial Environment

Glaciers are important agents of erosion of bedrockand mechanisms of transport of detritus in mountainregions. Deposition of this material on land produces characteristiclandforms and distinctive sediment character, but these continentalglacial deposits generally have a low preservation potential in the longterm and are rarely incorporated into the stratigraphic record.

Processes in glacial environmentsGlaciers radically transform landscapes because they carry out fourtypes of geomorphological work.glacial erosion: erosion of rock by the direct action of moving glaciers.

glacial transportation: movement of debris that is either frozen within the

glacier or lying on the surface.

glacial deposition: occurs when rock debris, either frozen within theglacier or lying on the surface, is deposited onto the ground by meltingof ice.

glaciofluvial activity: processes (erosion, transportation, deposition)caused action of meltwater streams.

CONTINENTAL DEPOSITIONAL ENVIRONMENTS

GlacialEnvironments

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Another important process that operates within glacialareas is frost weathering or freeze-thaw action. Frostweathering causes the disintegration of rock masses intofragmented debris due to the growth and expansion ofice in joints and pores. Once a rock mass has been

weakened by frost weathering it collapses under theforce of gravity. If this occurs on a steep slope theloosened debris moves down the slope as rockfall.Frost weathering of rock slopes on the flanks of glacialvalleys supplies debris to the surface of a glacier. This

debris may eventually be deposited as till or may betransported down to the base of a glacier to become tothe tools of erosion.The action of these glacial environment processes isshaping and has shaped the landscapes in

contemporary glacial areas and regions that wereglaciated during the Ice Ages

CONTINENTAL DEPOSITIONAL ENVIRONMENTS

Continental Depositional Environment- Glacial Environment

GlacialEnvironments

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Characteristics of glacial deposits:lithologiesconglomerate, sandstone andmudstone.mineralogyvariable, compositionally immature.textureextremely poorly sorted in till to poorlysorted in fluvio-glacial facies.bed geometrybedding absent to indistinct in manycontinental deposits, glaciomarine deposits may belaminated.sedimentary structuresusually none in tills,crossbedding in fluvio-glacial facies.

palaeocurrentsorientation of clasts can indicateice flow direction.fossilsnormally absent in continental deposits, maybe present in glaciomarine facies.colourvariable, but deposits are not usuallyoxidised.

facies associationsmay be associated with fluvialfacies or with shallow-marine deposits

CONTINENTAL DEPOSITIONAL ENVIRONMENTS

Continental Depositional Environment- Glacial Environment

Characteristics

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CONTINENTAL DEPOSITIONAL ENVIRONMENTS

Continental Depositional Environment- Fluvial Environment

Fluvial - RiversMake up a very large fraction of terrestrial sedimentary rocksRivers are largely erosive, but some relatively continuous (pointbar) andperiodic (flood) deposition

Braided streams - horizontal beds of conglomerates and sandswith unidirectional crossbeds, almost no mud.

Meandering streamsProduce very distinctive sediments:

Channel conglomerates

Cross-bedded channel sandstones, well-sortedPointbar sands, somewhat finer than channel sandsLevee sands, ripple marks and finer grainsBackswamp, non-laminated mudstones

This package of sediments produces a sequence that fines upwards.Also associated with meandering streams

Fluvial Environment

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Cut-off meanders (ox-bow lakes) with lacustrinesediments

Additionally, meandering stream sequencessurrounded by flood-plain deposits of paleosolsinterrupted by layers of flood muds. The whole packageof stream deposits, paleosols, and ox-bow lakes

formfluviolacustrine deposits.In the above, each particular subenvironmentproduces rocks of a particularfacies (particularcombination of sedimentological, structural, andbiological features).Walther's Law: As depositionalenvironments migrate laterally, the sediments of one

environment come to lie on top of sediments of theadjacent environment.

CONTINENTAL DEPOSITIONAL ENVIRONMENTS

Fluvial Environment

Fluvial Environment

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Fluvial Environment

CONTINENTAL DEPOSITIONAL ENVIRONMENTS

Identification of Fluvial Environment :

absence of marine fossils

presence of plant fossils

red beds

scoured channels

unidirectional-flow cross-stratification

broadly unidirectional paleocurrents

paleosols

desiccation cracks

plant fossils

Charateristic

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Fluvial Environment

CONTINENTAL DEPOSITIONAL ENVIRONMENTS

Alluvial fansAlluvial fans are fan-shaped deposits ofwater-transported material (alluvium).They typically form at the base oftopographic features where there is amarked break in slope. Consequently,alluvial fans tend to be coarse-grained,especially at their mouths. At theiredges, however, they can be relativelyfine-grained.Gravel Deposit --on an alluvial fan in Death Valley, California.

Note how the upper half of the depositis coarser than the lower half. Itprobably marks a former channel thatmigrated over the non-channelled partof the fan. It is now stranded above theactive channel and is being eroded.

Fluvial EnvironmentTypes

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Fluvial Environment

CONTINENTAL DEPOSITIONAL ENVIRONMENTS

Channel Deposits

When seen in cross-section, channels (red arrow)

have elliptical profiles and are filled with sediment

that is generally coarser than the surrounding rock.

They also cut into (by erosion) the underlying rock.Hammer (circled) shows scale.Channel deposits indicate running water: they form

on alluvial fans, in rivers, on deltas, even in

submarine fans.Both of these photos are of channels in alluvial fan

deposits (note how coarse the rock is).The red dashed line on the right shows the channel.

the orange lines show bedding beneath the channel.

Notice how it is cut by the channel.

Fluvial EnvironmentTypes

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Braided RiverSome rivers have lots of smallchannels that continually split andjoin. These are called braided rivers.Braided rivers are usually wide butshallow. They form on fairly steep

slopes and where the river bank iseasily eroded.Braided Rivers exhibit numerouschannels that split off and rejoin eachother to give a braided appearance.They typically carry fairly coarse-grained sediment down a fairly steepgradient. Additionally, the waterdischarge tends to be highly variable.Consequently, braided rivers usuallyexist near mountainous regions,

especially those with glaciers.

When it rains really hard youcan find little braided riversflowing across building sites

and paths made of sand orfine ravel.

Braided rivers have a lotofrock , gravel and sandthat is carried along theriver bottom. When theamountofwater flowingthrough individual channelsdeceases the river dumpsthis material creatingislands and bars.

CONTINENTAL DEPOSITIONAL ENVIRONMENTS

Fluvial Environment

Fluvial EnvironmentTypes

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Braided-river systems

Characteristics:moderately steep gradefairly straightmany channels, bars, and islandscoarse-grained sediments

CONTINENTAL DEPOSITIONAL ENVIRONMENTS

Fluvial Environment

Fluvial EnvironmentTypes

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Meandering riversRivers flowing over

gently sloping ground beginto curve back and forth across thelandscape. These are calledmeandering rivers.Meandering rivers erode sedimentfrom the outer curve of each

meander bend and deposit it onan inner curve furtherdownstream. This causes individualmeanders to grow larger andlarger over time.

Oxbow lakes form when ameander grows so big and

loopy that two bends of theriver join together. Once themeander bends join, the flowof water reduces andsediment begins to build up.Over time oxbow lakes will fill

with sediment and can evendisappear. The point wherethe two bends intersect iscalled a meander cut-off.The low-lying area on either side of

a river is called a floodplain. Thefloodplain is covered with water

when the river overflows it banksduring spring floods or periods ofheavy rain. Sediment is depositedon the floodplain each time theriver floods. Mud deposited on thefloodplain can make the soil reallygood for agriculture

Meandering river channels areasymmetrical. The deepest part of the

channel is on the outside of each bend.The water flows faster in these deepersections and erodes material from theriver bank. The water flows more slowlyin the shallow areas near the inside ofeach bend. The slower water can't carryas much sediment and deposits its loadon a series of point bars.

CONTINENTAL DEPOSITIONAL ENVIRONMENTS

Environment

Fluvial EnvironmentTypes

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Aeolian sedimentary processes are those

involving transport and deposition of material by thewind.

Characteristics of Aeolian Deposits:

lithologies : sand and silt only.

mineralogy : mainly quartz, with rare examples of carbonate orother grains.texture : well- to very well-sorted silt to medium sand.fossils : rare in desert dune deposits, occasional vertebrate bones.bed geometry : sheets or lenses of sand.sedimentary structures : large-scale dune crossbedding and parallel

stratification in sands.palaeocurrents : dune orientations reconstructed from cross-bedding indicate wind direction.colour : yellow to red due to iron hydroxides and oxidesfacies associations : occur with alluvial fans, ephemeral river andlake facies in deserts, also with beach deposits or glacial outwashfacies

DEPOSITIONAL ENVIRONMENTS

Continental Depositional Environment- Aeolian Environments

AeolianEnvironments

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Lakes

Lakes form where there is a supply of water to atopographic low on the land surface. They are fed mainly byrivers and lose water by flow out into a river and/orevaporation from the surface. There are, however, importantdifferences with marine settings: the fauna and flora aredistinct, the chemistry of lake waters varies from lake to lake

and certain physical processes of temperature and densitystratification are unique to lacustrine environments.

CONTINENTAL DEPOSITIONAL ENVIRONMENTS

Continental Depositional Environment- Lakes

Lakes

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Characteristics of lake deposits

lithologiessandstone, mudstone, fine-grained limestones andevaporates.

mineralogyvariable.

texturesands moderately well sorted.

bed geometryoften very thin-bedded.

sedimentary structureswave ripples and very fine parallellamination.

palaeocurrentsfew with palaeoenvironmental significance

fossilsalgal and microbial plus uncommon shells

colourvariable, but may be dark grey in deep lake deposits

facies associationscommonly occur with fluvial deposits, evaporitesand associated with Aeolian facies

CONTINENTAL DEPOSITIONAL ENVIRONMENTS

Continental Depositional Environment- Lake

Characteristics

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Deltas

The mouths of rivers may be places where theaccumulation of detritus brought down by

the flow forms a sediment body that builds out into the sea or a

lake. Deltas are almost

exclusively sites of clastic deposition ranging from fine muds to

coarse gravels. Deposits

formed in deltaic environments are important in the stratigraphic

record as sites for the

formation and accumulation of fossil fuels.

CONTINENTAL DEPOSITIONAL ENVIRONMENTS

Continental Depositional Environment- Deltaic Environments

DeltaicEnvironments

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Delta-front sub-environments:

At the mouth of the channels the flow velocity is abruptlyreduced as the water enters the standing water of the lake orsea. The delta front immediately forward of the channel mouth isthe site of deposition of bedload material as a subaqueousmouth bar.

CONTINENTAL DEPOSITIONAL ENVIRONMENTS

Continental Depositional Environment- Deltaic Environments

DeltaicEnvironments

Delta-top sub-environments:Deltas are fed by a river or an alluvial fan and there is a transitionbetween the area that is considered part of the fluvial/alluvialenvironment and the region that is considered to be the delta topor delta plain.

Pro-Delta sub-environmentThe furthest offshore portion of a delta, lying at the toe of thedelta front, and characterized by a relatively slow rate of fine-grained deposition.

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Characteristics of Deltaic Deposits

Lithologies: conglomerate, sandstone and mudstoneMineralogy: variable, delta-front facies may be compositionallymatureTexture: moderately mature in delta-top sands and gravels, mature inwave-Reworked Delta: front depositsBed Geometry: lens-shaped delta channels, mouthbar lenses variablyelongate, prodelta deposits thin beddedSedimentary structures: cross-bedding and lamination in delta-topand mouth-bar facies.Palaeo-currents: topset facies indicate direction of progradation,wave and tidal reworking variable on delta frontFossils: association of terrestrial plants and animals of the delta topwith marine fauna of the delta frontColour: not diagnostic, delta-top deposits may be oxidised

CONTINENTAL DEPOSITIONAL ENVIRONMENTS

Continental Depositional Environment- Deltaic Environments

Characteristics

CONTINENTAL DEPOSITIONAL ENVIRONMENTS

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Principal depositional environmentsDeltas

Beaches and barrier island systems:Beaches Strandplains,

barrier islands/bars ,Estuaries(characteristic of transgressive coasts)

Lagoons (characteristic oftransgressive coasts)

Tidal flats

CONTINENTAL DEPOSITIONAL ENVIRONMENTS

Marginal-Marine Environments

Marginal-MarineEnvironments

CONTINENTAL DEPOSITIONAL ENVIRONMENTS

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. lithologysand and conglomerate

. mineralogymature quartz sands and shelly sands

. texturewell sorted, well rounded clasts

. bed geometryelongate lenses

. sedimentary structureslow-angle stratification and wavereworking. palaeocurrentsmainly wave-formed structures. fossilsrobust shelly debris. colournot diagnostic. facies associationsmay be associated with coastal plain,

lagoonal or shallow-marine facies

CONTINENTAL DEPOSITIONAL ENVIRONMENTS

Marginal-Marine Environments

Beach/barriersystems

CONTINENTAL DEPOSITIONAL ENVIRONMENTS

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. lithologymainly mud with some sand

. mineralogyvariable

. texturefine-grained, moderately to poorly sorted

. bed geometrythinly bedded mud with thin sheets and

lenses of sand. sedimentary structuresmay be laminated and waverippled. palaeocurrentsrare, not diagnostic. fossilsoften monospecific assemblages of hypersaline orbrackish tolerant organisms

. colourmay be dark due to anaerobic conditions

. facies associationsmay be associated with coastalplain or beach barrier deposits

CONTINENTAL DEPOSITIONAL ENVIRONMENTS

Marginal-Marine Environments

Lagoons

CONTINENTAL DEPOSITIONAL ENVIRONMENTS

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. lithologymud, sand and less commonlyconglomerate. mineralogyvariable. texturemay be well sorted in high energy settings. bed geometrylenses with erosional bases

. sedimentary structurescross-bedding andcrosslaminationand inclined heterolithic stratification. palaeocurrentsbimodal in tidal estuaries. fossilsshallow marine. colournot diagnostic

. facies associationsmay be overlain by fluvial,shallow marine, continental or delta

CONTINENTAL DEPOSITIONAL ENVIRONMENTS

Marginal-Marine Environments

Tidal channelsystems

CONTINENTAL DEPOSITIONAL ENVIRONMENTS

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. lithologymud and sand

. mineralogyclay and shelly sand

. texturefine-grained, not diagnostic

. bed geometrytabular muds with thin sheets and lenses of sand

. sedimentary structuresripple cross lamination and flaser/lenticularbedding

. palaeocurrentsbimodal in tidal estuaries

. fossilsshallow marine fauna and salt marsh vegetation

. colouroften dark due to anaerobic conditions

. facies associationsmay be overlain by shallow marine or

continental facies

CONTINENTAL DEPOSITIONAL ENVIRONMENTS

Marginal-Marine Environments

Tidal mudflats

DEPOSITIONAL ENVIRONMENTS

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Depositional characteristics for marginal-marine environments

River, wave, and tidalprocesses are dominantsedimentary processes

Salinity varies significantlySome environments are ofintermittent to nearlyconstant subaerial exposure,others are continuouslycovered by shallow water.

Wide variety of sedimenttypes includingconglomerates, sandstones,shales, carbonates, andevaporites.

DEPOSITIONAL ENVIRONMENTS

Marginal-Marine Environments

Characteristics

CONTINENTAL DEPOSITIONAL ENVIRONMENTS

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CONTINENTAL DEPOSITIONAL ENVIRONMENTS

Environment

CONTINENTAL DEPOSITIONAL ENVIRONMENTS

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CONTINENTAL DEPOSITIONAL ENVIRONMENTS

Environment

CONTINENTAL DEPOSITIONAL ENVIRONMENTS

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CONTINENTAL DEPOSITIONAL ENVIRONMENTS

Environment