ambientes sedimentarios

Definición:
Los ambientes sedimentarios son partes de la
superficie terrestre con propiedades físicas,
químicas y biológicas definidas y diferentes de las
que presentan las áreas adyacentes (Selley, 1970).
Los ambientes sedimentarios se clasifican en:
continentales, marinos y transicionales
Ambientes Sedimentarios Continentales
Ambientes
Sedimentarios
Continentales
Subaéreo
Subaéreo
Desértico
Glacial
Subacuático
Fluvial
Aluvial
Lacustre
Erosivos
Equilibrio
Depósito
Dominantes
Suelos
Locales
Desconocidos
Locales
Subacuático Locales
(Selley, 1976 en Arche ……)
Sedimentary Environments
Continental - Fluvial
Continental - Glacial
Continental Desert/Arid
Continental
Lacustrine
Swamp/Bog
Transitional (Coastlines):
Beach & Tidal Zone
Transitional: Deltas & Estuaries
Transitional: Tidal Glaciers
Transitional: Barrier Islands
Transitional: Reef & Lagoon
Shallow Marine
Marine
Deep Marine
AMBIENTE GLACIAL
GLACIAL
EaES 350-8
18
Ambiente Glacial
Restrictos a los polos Norte y Sur y a las
altas montañas
Asociados a bajas temperaturas, altas tasas
de precipitación y muy bajas tasas de
evaporación
El principal agente geológico es el
transporte por el hielo.
EaES 350-8
20
EaES 350-8
21
Glacial/eolian/lacustrine environments
Glacial environments
Glaciers and ice sheets form where precipitation rates, in the
form of snow (accumulation), exceed melting rates (ablation)
Ice flows as a result of gravity and essentially acts like a highhighviscosity fluid exhibiting laminar flow
Temperate (warm(warm-based) vs. polar (cold
(cold--based) glaciers reflect
the temperature regime within the ice
Ice shelves can form when a glacier or ice sheet reaches the
coast and extends offshore, and ultimately breaks up into
icebergs
EaES 350-8
22
EaES 350-8
23
Glacial/eolian/lacustrine environments
Glacial environments
Abrasion leads to the formation of rock flour (mineralogically
diverse siltsilt- and clay
clay--sized sediment grains); plucking results in
coarser (up to boulderboulder-sized) material
Warm--based ice tends to be more erosive (abrasive) than coldWarm
coldbased ice
Till/tillite (also known as diamict/diamictite) is poorly sorted,
angular, and immature
•
•
Lodgement till forms by active deposition under the ice (relatively
compact and usually fractured)
Meltout till forms passively during melting
EaES 350-8
24
EaES 350-8
25
EaES 350-8
26
EaES 350-8
27
EaES 350-8
28
EaES 350-8
29
Glacial/eolian/lacustrine environments
Glacial environments
Abrasion leads to the formation of rock flour (mineralogically
diverse siltsilt- and clay
clay--sized sediment grains); plucking results in
coarser (up to boulderboulder-sized) material
Warm--based ice tends to be more erosive (abrasive) than coldWarm
coldbased ice
Till/tillite (also known as diamict/diamictite) is poorly sorted,
angular, and immature
•
•
Lodgement till forms by active deposition under the ice (relatively
compact and usually fractured)
Meltout till forms passively during melting
EaES 350-8
30
EaES 350-8
31
EaES 350-8
32
EaES 350-8
33
EaES 350-8
34
Glacial/eolian/lacustrine environments
Glacial environments
Glaciofluvial or fluvioglacial deposits are sediments formed in
association with glacial meltwater (e.g., glacial outwash)
More distal glaciolacustrine and glaciomarine deposits are
typically dominated by finefine-grained sediment (rock flour), along
with iceice-rafted debris and dropstones
The preservation potential of glacial deposits is usually limited,
with the exception of tills and glaciomarine deposits associated
with big ice sheets
EaES 350-8
35
Tipo De Glaciares
Transporte Glaciar
Depósitos Glaciares
Depósitos no estratificados: acumulaciones
de morrena basal (depósitos basales, arcilla
conglomerádica o till)
Depósitos Glaciares
Depósitos estratificados: acumulaciones de morrenas internas
durante el rápido deshielo y sedimentos subacuosos formados
en contacto con el glaciar (kame, skerns, varves)
Insertar pdf
ABANICOS ALUVIALES
What is an alluvial fan?
… a fan-shaped deposit of alluvium found where a stream
flows out of a mountain onto flatter terrain.
An alluvial fan in Death Valley
Narrow outlet
(valley or gorge)
Fan apex
Radial spreading
alluvial fan
An alluvial fan in Death Valley
Coarse,
channelized
debris
Sediments
become finergrained
Ok, back to alluvial fans…..
The evolutionary stages of alluvial fans
Alluvial fans:
Steeper gradient than “normal” river profiles, thus are often
dominated by debris flow processes
Kosi megafan,
northern India
Migrating fluvial
channels
Debris flows
Shear stress vs. strain
So flow is plug like
and ceases as it
reaches shallower
surface, hence the
velocity diminishes
Flows also stop as
they thin or lose
water
Losing water and velocity caused the debris flow to
become more viscous and stop, creating a very steep front
Debris flow “channel”
on a talus in eastern
Sierra Nevada
A closer view
Note the existence
of the “levees”
The radial deposition
of alluvial fan
Active
depositional lobe
Period of active deposition, massive floods and
debris flows
Debris flow fan caused by typhoon, southern Taiwan, 2005
And afterwards…….
So, what will the stratigraphy look like?
Channels near apex of fan
Channel gravels
And suspended load
deposits on distal
portions of the fan
With bioturbation….
Downslope fining of alluvial fan deposits
Facies relationships, a
Devonian fan in Sweden,
showing characteristic
interfingering of
depositional facies
Pleasant Valley, Nevada
Pleasant Valley, Nevada
AMBIENTE FLUVIAL
Running water
Begins as sheetflow
Infiltration is controlled by
• Intensity and duration of rainfall
• Prior wetted condition of the soil
• Soil texture
• Slope of the land
• Nature of the vegetative cover
• Runoff of rain or spring snowmelt only
occurs when soil is saturated.
Running water
Streamflow
Factors that determine velocity
• Gradient
Gradient,, or slope
• Channel characteristics including
shape, size, and roughness
• Discharge – the volume of water
moving past a given point in a
certain amount of time
Running Water
Changes from upstream to downstream
Profile
• Cross
Cross--section of a stream
• From head (headwaters) to mouth of
stream
• Profile is a smooth curve
• Gradient decreases downstream
Factors that increase downstream
• Velocity
• Discharge
• Channel size
Longitudinal profile of a stream
Drainage Divide
Tributaries
Gradient decreases downstream
Factors that increase downstream:
Velocity
Discharge
Channel size
Trunk Stream
Distributaries
And Delta
Running water
Changes from upstream to downstream
Gradient and channel roughness decrease
downstream
Base level and graded streams
Base level is the lowest point to which a
stream can erode
Base level and graded streams
Two types of base level
• Ultimate (sea level)
• Local or temporary
Changing conditions causes adjustment
• Sudden extra sediment steeper gradient,
faster flow erosion, sediment removed and
equilibrium reestablished.
• Equilibrium is temporary
A waterfall results from change
in local base level
Local change in baselevel affects river profiles
Important definitions
Stream - Sediment Terminology
Transport of sediment by streams
Transported material is called load
Types of load
• Dissolved load – ions in solution from weathering
• Suspended load – fine particles
• Bed load Moves during high velocity events
Sandy Portion – Saltation (bouncing)
Cobbles – Traction (rolling)
Capacity –maximum load stream transports
Competence – Largest particles it can move
– Proportional to velocity squared
Suspended load - confluence Green & Colorado Rivers in Canyonlands, Utah
Competence
maximum particle size a stream transports
Proportional to velocity squared –K.E.
Deposition of sediment by a stream
Caused by a decrease in velocity
Competence is reduced
Sediment begins to drop out
Deposition of sediment by a stream
Channel deposits
• Pointbars
• Mid
Mid--channel bars in braided streams
• Deltas
Floodplain deposits
• Natural levees – form parallel to the stream
channel by successive floods over many years
Running water
Deposition of sediment by a stream
Alluvial fans
• Develop where a highhigh-gradient stream leaves a
narrow valley
• Slopes outward in a broad arc
Ambiente Fluvial
S = l/L
(Miall, 1974)
BP = función del número de islas o barras dentro de los canales
SISTEMA FLUVIAL BRAIDED
Sistema Fluvial Braided
Presentan cursos de agua múltiples de baja
sinuosidad
Amplio predomino de carga de fondo,
granulometría gruesa
Alta relación ancho / profundidad
Pendientes en general mayores a 5º
Variabilidad de descarga
Facilidad de erosión de los márgenes
Depósitos En Sistemas Fluviales Braided
Sistema
braided de
gravas
Sistemas braided
de arenas
Ej. en el Uruguay:
Fm. Salto
(C) buen desarrollo de artesas.
Ejemplo de dos tipos de elementos
arquitecturales de canal.
Calcos de carga rellenos de pequeños
canales abandonados.
Pisadas, frecuentes en planicies de
inundación.
Grietas de desecación, también presentes
en planicies de inundación.
Perfil esquemático mostrando los elementos
arquitecturales, litofacies y principales
subambientes en un sistema fluvial
meandriforme.
Aspectos de secuencias meandrosas de la
Formación Loma Larga. (A) depósitos de
canal con estratificación entrecruzada, (B)
facies de planicies de inundación (pelitas
carbonosas).
SISTEMA FLUVIAL MEANDRIFORME
Sistema Fluvial Meandriforme
Corresponden a un único canal con alta
sinuosidad
Baja relación ancho / profundidad
Pendientes suaves
Márgenes de canales estables
Transportan mayoritariamente carga en
suspensión
Depósitos En Sistemas Fluviales Meandriformes
Depósitos En Sistemas Fluviales Meandriformes
SISTEMA FLUVIAL ANASTOMOSADO
Complejo de canales de baja energía que se
separan y se unen, interconectándose entre
si
Baja relación ancho / profundidad
Pendientes suaves
Márgenes estabilizados por la vegetación
Detritos transportados por carga en
suspensión o mixta
Depósitos En Sistemas Fluviales Anastomosados
1 turberas; 2 pantano; 3 laguna de inundación; 4 dique marginal; 5
depósito de rompimiento de dique marginal; 6 canal fluvial; 7 depósito
de canal; 8 arena; 9 turba; 10 limo arenoso; 11 barro
Abanicos Aluviales
Morfología concoidal centrada en un ápice
Dimensiones métricas a kilométricas
Se localizan en áreas de importante rotura
de la pendiente
Presentan sedimentos gruesos en la
cabecera y finos en las partes distales
Presentan un perfil radial cóncavo y un
perfil transversal convexo
Depósitos En Abanicos Aluviales
Ej. en Uruguay: Fm. Cañada Solís
AMBIENTE LACUSTRE
Ambiente Lacustre
Lago: cuerpo de agua profunda, tan grande
como sea, que no presenta conexión con el
mar
La dinámica del medio lacustre está
controlada principalmente por: la geometría
de la cuenca, el clima, las propiedades del
agua y aportes externos
Ambiente Lacustre
En función de la predominancia de los factores
físicos, químicos y biológicos, los sedimentos
lacustres se clasifican en:
Sedimentos clásticos (predominancia de factores
físicos)
Sedimentos químicos (predominancia de factores
químicos)
Sedimentos bioquímicos y orgánicos
(predominancia de factores biológicos)
Lacustrine environments
Playa (saline) lakes are hydrologically closed, ephemeral water
bodies that form in arid environments and are characterized by
mud--evaporite couplets
mud
Freshwater lakes are permanent (commonly hydrologically
open) water bodies
•
•
Waves and relatively weak windwind-driven currents constitute the
main mechanisms of sediment transport
Density stratification develops under seasonal climate conditions
and when currents are limited
EaES 350-8
108
EaES 350-8
109
EaES 350-8
110
EaES 350-8
111
Glacial/eolian/lacustrine environments
Lacustrine environments
Coarse sediments mainly occur on lake margins (lacustrine
deltas, beaches)
In the central parts of lakes, deposition occurs from suspension
and by means of turbidity currents
Stratified lakes promote the accumulation of organic matter and
the formation of varves; organics are especially important in
small lakes
Carbonates of both chemical and biogenic origin can contribute
significantly to lake sediments
EaES 350-8
112
Lagos Con Predominancia De Sedimentos Clásticos
Ej. en Uruguay de ambiente fluvio-lacustre Fm. Tacuarembó, miembro inferir
Lagos Con Predominancia de Sedimentos Químicos
1 Halita; 2 Arcillas; 3 Anhidrita;4 Areniscas eólicas;
5 conglomerados, areniscas y arcillas fluviales (de
wadis) Glennie, 1972
EaES 350-8
115
EaES 350-8
116
EaES 350-8
117
EaES 350-8
118
Lacustrine environments
The final stage of filling of lakes commonly involves an
important organic component
Hydrosere:: vertical succession of organic deposits associated
Hydrosere
with the transition from a limnic, through a telmatic, to a
terrestrial environment
•
Gyttja -->
--> fen peat -->
--> wood peat -->
--> moss peat
EaES 350-8
119
Lacustrine environments
Playa (saline) lakes are hydrologically closed, ephemeral water
bodies that form in arid environments and are characterized by
mud--evaporite couplets
mud
Freshwater lakes are permanent (commonly hydrologically
open) water bodies
•
•
Waves and relatively weak windwind-driven currents constitute the
main mechanisms of sediment transport
Density stratification develops under seasonal climate conditions
and when currents are limited
EaES 350-8
120
EaES 350-8
121
EaES 350-8
122
EaES 350-8
123
EaES 350-8
124
AMBIENTE DESÉRTICO
Eolian environments
Eolian deposits dominate deserts (mostly at low latitudes, but
sometimes arctic), but are also important along shorelines
(coastal dunes) and in association with ice sheets (loess)
Air is a lowlow-density and lowlow-viscosity fluid; therefore high flow
velocities are required to enable sediment transport
Eolian deposits are mostly texturally and mineralogically mature,
due to the selective transport of specific grain sizes and the
large impact of graingrain-toto-grain collision
127
Ambiente Desértico
Area donde la tasa de evaporación potencial
excede la tasa de precipitación
El viento es el principal agente de transporte
Predomina la hipergénesis física
Depósitos en ambientes desérticos: wadis,
wadis,
sebkhas,, serir,
sebkhas
serir, reg,
reg, depósitos eólicos, entre
otros.
EaES 350-8
136
EaES 350-8
137
EaES 350-8
138
Eolian environments
Sand dunes are the most common eolian landforms; their
geometry and resulting sedimentary structures depend primarily
on sediment supply and prevailing wind direction
Large (>~5 m) sets of cross strata are very commonly eolian in
origin
Eolian sand sheets develop when sediment supply is limited
and are characterized by planar stratification; vegetation can
contribute to dune formation under such circumstances
Loess is a homogeneous, very well sorted, siltsilt-dominated
sediment that is deposited from suspension; it is commonly
associated with ice sheets that produce large quantities of
source material (rock flour)
139
EaES 350-8
140
EaES 350-8
141
EaES 350-8
142
Eolian environments
Sand dunes are the most common eolian landforms; their
geometry and resulting sedimentary structures depend primarily
on sediment supply and prevailing wind direction
Large (>~5 m) sets of cross strata are very commonly eolian in
origin
Eolian sand sheets develop when sediment supply is limited
and are characterized by planar stratification; vegetation can
contribute to dune formation under such circumstances
Loess is a homogeneous, very well sorted, siltsilt-dominated
sediment that is deposited from suspension; it is commonly
associated with ice sheets that produce large quantities of
source material (rock flour)
EaES 350-8
143
Depósitos Desérticos
Reg: depósitos de fragmentación in sitú
Serir: depósitos groseros, interdunas
Wadi: depósitos de ríos temporarios
Sebkhas: depósitos de lagos desérticos
Depósitos Desérticos - Eólicos
Sábanas de arena
Dunas de arena
EaES 350-8
146
EaES 350-8
147
EaES 350-8
148