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Sedimentary EnvironmentsSedimentary Environments

ContinentalContinental•• rivers, lakes, caves, desert, glaciersrivers, lakes, caves, desert, glaciers-- mostly detritalmostly detrital

TransitionalTransitional-- coastalcoastal-- along ocean shoresalong ocean shores•• Estuaries and DeltasEstuaries and Deltas•• Offshore islands Offshore islands •• LagoonsLagoons•• SubductionSubduction zoneszones•• Submerged coastlinesSubmerged coastlines

Sedimentary EnvironmentsSedimentary EnvironmentsMarineMarine

•• Shallow marine environments (< 200m)Shallow marine environments (< 200m)•• Deep marine environments (beyond the continental Deep marine environments (beyond the continental

shelf)shelf)

Facies Model

Depositional Environment

FaciesFacies ModelModel

Depositional Depositional EnvironmentEnvironment

Alluvial Fan FaciesAlluvial Fan Alluvial Fan FaciesFacies

Alluvial fans can basically be described as fan shaped deposits that are fed by a channel emanating from a very narrow, steep valley in a region of

high topographic relief. This high relief is often due to the fact that most alluvial fans are found in association with regions of active faulting.

Braided River Facies

Braided River FaciesBraided River Braided River FaciesFacies

Braided riversGeneral Characteristics1) Generally not very sinuous2) Multiple channels separated by bars or islands3) Grain size decreases down stream from gravelly to sandy

Formation of a Braided riverUsually found in areas of high sediment influx, high water influx, and high gradientExamples include glacial discharge plains, distal portions of alluvial fans, and mountainous regionsDuring times of flooding the river is choked with a high amount of sediment and a new channel is formedMid channel bars result from sediment too large to be carried

Structure of a Braided river depositContain gravel in lower portions of bars and channels and sand throughout the rest of the deposit; mud is almost nonexistantLongitudinal bars present with some having horizons of plant rootsLinguoid and transverse bars also presentLateral bars possible, also with possible plants rootsLateral extent of a braided river deposit can be extensive because lateral migration of the system and the high sedimentation rate

Meandering River FaciesMeandering River Meandering River FaciesFacies

Meandering River Meandering River FaciesFacies

General Characteristics1) High sinuosity2) Composed mostly of sand and mud3) Confined to a single channel

Formation- The transition between a braided river system and a meandering river system is a difficult one to draw a line through- Further down stream the river has a much less sediment influx, and therefore, does not form bars as a result of sediment choking, but starts to deposit the smaller sediment in its system and also erodes the surrounding banks- The cut bank will erode the outside bank and cause the river to expand laterally while the point bar will deposit sediment from the system and accrete the river laterally with sandy silt deposits and sometimes mud- A meander will sometimes meet another and then form a faster way down stream so the abandoned channel will become an ox-bow lake- During flooding stages the river will spill over its banks and deposit on the levee and also on the flood plain depositing silts and muds

Structure of a Meandering river deposit

- The majority of the deposit will consist of the accretion of the point bar

- Some abandoned channels and deep channels will be preserved as dish shaped structures, up to hundreds of meters wide, in the outcrop

The point bar will have a fining upward succession starting from a channel deposit rising through trough cross bedding and sand stone lenses up to ripples and finally a flood plain deposit

- The flood plain forms by the deposition of fine material from the river during flood stages

- Deposits are usually laminated and may be oxidized

- Paleosols may also be present on floodplain, levee, and point bar (thoughmuch less common here)

- A crevasse-splay deposit will consist of a sheet flow with some cross bedding towards the upper section with rip up clasts present in the bottom of the section

Structure of a Meandering river deposit

- The majority of the deposit will consist of the accretion of the point bar

- Some abandoned channels and deep channels will be preserved as dish shaped structures, up to hundreds of meters wide, in the outcrop

The point bar will have a fining upward succession starting from a channel deposit rising through trough cross bedding and sand stone lenses up to ripples and finally a flood plain deposit

- The flood plain forms by the deposition of fine material from the river during flood stages

- Deposits are usually laminated and may be oxidized

- Paleosols may also be present on floodplain, levee, and point bar (thoughmuch less common here)

- A crevasse-splay deposit will consist of a sheet flow with some cross bedding towards the upper section with rip up clasts present in the bottom of the section

Shoreline and Coastal Systems

DefinitionsCoast - zone that spans from the landward limit of marine processes to the seaward limit of alluvial and shoreline processes.Shoreline - boundary line separating a body of water from an exposed beach.Significance - shoreline deposits are easy to identify using fossils and are crucial in documentation of sea-level changes and sequence stratigraphic analysis

ProcessesThe morphology of shorelines reflects the interaction between sediment supply and basinal reworking processes.Sediment supply - nature and volume determined by size, relief, tectonics, climate and deposits of the catchment area, majority of seds are land-derived and transported via alluvial processes, 5-10% comes from erosion of the coast or are transported from the shelf.Waves - the most significant modifier of shoreline deposits, waves sort and redistribute sediment into beaches, barriers and spits.

Transgressive systems:Barrier Islands - narrow barrier beach that is separated from the mainland by a lagoon or marsh. Generally associated with low sed supply and relative sea-level rise although can also form as a prograding system during stillstands. Deposits generally are preserved in washover features (i.e. washover fans).

Lagoons - areas of shallow water parallel to the shore between the barrier island and the mainland. Lagoons contain mostly fine-grained seds that are finely laminated (hyper saline) or are highly bioturbated (normal marine), also, symmetrical ripples (humid) or mudcracks (arid) may be present.

Estuaries - partially enclosed bodies of water where tidal processes interact with fresh-water stream currents. Differentiated from deltas by having a net landward movement of sediment. Estuarine faciesconsist of an outer coarse-grained sand body, a central fine-grained body and an inner sand and gravel facies composed of fluvial deposits.

Environments (excluding deltas)The type of environment that develops is a function of waves/tide energy, grain size, marine sedsupply, and relative sea-level change

Regressive systems:Beaches/strandplains - prograding sand-rich shorelines produced by longshore currents and fluvial processes. Deposits are therefore a mix of rounded marine-derived sand and angular fluvially-derived sand.

Chenier plains - extensive, prograding coastal mudflats with widely separated, subparallel beach ridges (cheniers).

Tidal Flats - form in all tidal settings, extent depends on tidal range, sed supply and shoreline gradient.

Barrier bar

Mangrove swamp

Estuaries

Tidal flat

Delta Facies

What is a delta?A delta, as defined by the USGS (U.S. Geological Survey), is the fan-shaped area at the mouth, or lower end, of a river, formed by eroded material that has been carried downstream and dropped in quantities that can not be carried off by tides or currents. Boggs defines a delta as any deposit, subaerial or subaqueous, formed by fluvial sediments that build into a standing body of water.

Where are deltas found?Deltas can occur in lakes and inland seas as well as in the ocean, but they are most important in the open ocean (Boggs). Deltas are particularly common in the modern ocean owing to post-Pleistocene sea-level rise coupled with high sediment loads carried by many rivers. They often contain extensive wetlands, whose high biological productivity makes them vital nursery grounds for fisheries. Huge amounts of coal, oil, and natural gas are found in subsurface ancient deltaic deposits. Deltas seldom form on active, subducting continental margins because there is no stable shallow shelf on which sediments can accumulate. Twenty-five (25) of the world’s largest deltas are found on passive margins of continents. They are categorized according to features within the delta plain and by energies acting on the delta (tide, wave, and fluvial). The size of a delta is dependent on the size of the drainage basin, the elevation of the land, and climate.

What does a typical delta look like?

What are the different types of deltas?

Tide-Dominated Deltas

The shape of a delta is influenced by sediment input, wave energy, and tidal energy. Deltas which undergo strong tidal interaction are classified as tide-dominated deltas. As sediment travels out of the delta into the sea, high tides and flood tides confine sediment on the delta

plain and low tides carry sediment seaward. Tide-dominated deltas typically occur in locations of large tidal ranges or high tidal current speeds. In situations such as these, where

the sediment supply is over powered by strong tidal currents, the delta tends to be very small. Another resulting feature of a tide-dominated delta is that it has many linear structures

parallel to the tidal flow and perpendicular to the shore (shown below).

The delta has a gradational, upward coarsening sequence of muds; interbedded sands, silts, and muds; and then fine to medium sands. Due to the eroding effect of tides, the sands display cross-bedding, the sand ridge field can be truncated through erosion, and the

distributary channel sediments contain more slack-water mud drapes than usual.

These tidal sand ridges are characteristic of the subaqueous delta plain. They may reach relief heights of up to 15-20 meters close to the shoreline. Relief of the ridges decrease with increasing distances from the distributaries. Ridges are also greater in relief and size when there is more tidal discharge than fluvial discharge. Sediments that make up the sand ridges are fine to medium sands. Characteristic of the lower delta plain are broad tidal flats that grade unidirectionally into the sand bars and the opposite direction into marshes or evaporative flats (depending on climate).

Tide-Dominated Deltas

Wave-Dominated Deltas

An open ocean basin accepts more water input, which means there is potential for greater wave energy, making wave-dominated deltas more likely. High wave interference causes conflicted or deflected river mouths.

There is less influence from fluvial sources. In wave-dominated delta regions, breaking waves cause immediate mixing of fresh and salt water. Typically, the fresh water flow velocity decelerates rapidly. A bar may form in the immediate vicinity of the distributarymouth, often supplemented by landward migrating swash bars. The wave action reworks the sediment, making it much sandier than other types of deltas, coarsening upward. Sediment is delivered by the river and is transported along the coast. The sediment is then deposited as beaches and bars and the development of distributaries is limited

1. More lobate and have smooth, arcuate to sharp margins. 2. Longshore drift may rework sediment along coastline. 3. Lobes strung out parallel to shoreline.

Geometry:

1. substrate gradient 2. wave energy vs. tidal energy 3. sediment supply vs. accommodation volume: supply-dominated areas

produce allochthonous shelves characterized by more rapid sedimentation and thick muddy sequences in which barrier sand bodies maybe encased while accommodation-dominated areas are associated with allochthonous shelves that have sandy sediments and experience extensive reworking.

4. rates of sea level change

Controls on the Geometry:

Wave-Dominated Deltas

Fluvially-dominated deltas are primarily controlled by the water density difference between the inflowing river water and the standing water on the basin.

Fluvial-Dominated Deltas

Homopycnal flow occurs when the density of the river water is equal to the density of the standing water in the basin.. Hyperpycnal flow is produced when the density of the river water entering the basin is greater than the density of the standing water in the ocean basin. This higher density river water will flow below the standing water in the basin because of the difference in density. Hypopycnal flow is associated with a lower river water density entering a higher density standing water in the basin. Under these conditions, the river water will flow out over the standing water, gradually depositing the suspended clay portion of the sediment load on the prodelta.

Different flow types that determine the distribution of sediment and sedimentary structures formed in the delta are homopycnal flow, hyperpycnal flow, and hypopycnal flow

Lacustrine Facies

Lakes are systems of fresh to saline waters contained in basins that are not in connection with the oceans. These lake systems may span an immense range of variability in arealsize, depth, geometry, water chemistry, biota, elevation, and latitude. External influences on lake sedimentation are also highly variable and encompass a spectrum of amounts of precipitation, evaporation, temperature, wind, storms and fluvial flux of both water and sediment. Even within one lake system, there is a large range of depositional environments ranging from a high energy shoreline, to the quiet water basin. Below is a listing of some of the most common of the facies of sediments deposited in these environments.

Controls on sedimentation:These controls will influence the nature of the lake system, and the resultant sediments deposited therein.Lake size Closed Basin vs. Open Basin Chemistry of Water Amount of sediment entering the basin Latitude (Seasonality) Shape of basin (shallow vs. deep) Regional tectonics Water temperature (lake and inflow) Wind

Economic Value of Lake DepositsGood source of evaporite minerals, gravels, oil shales, diatomites, zeolites, phosphates and metallic ores.Common site of discovery of vertebrate remains and archaeological sites.

Turbidite Facies

Turbidites are deposits of a turbidity current (density current moving downslopeon ocean floor driven by gravity that acts on the density difference between the current and the surrounding seawater due to suspended sediment)

Turbidity currents can be initiated by earth quakes, rivers in flood, and sediment failure in rapidly deposited delta fronts. The initial sediments in the current will reflect the source

Major features•Sandstones and shales are monotonously interbedded. •Beds tend to have sharp, flat bases, with no indication of erosion of sea floor. •The sharp bases of beds have abundant markings (tool marks carved by rigid objects). •Within sandstone beds, the grain size commonly decreases upward (graded bedding; see Bouma sequence).

Turbidite Facies

Walker divided deep water clastic rocks into 5 facies associations:

Classical Turbidites: characterized by monotonous interbeds of sandstone and shale, with no evidence of topography on the seafloor. All sandstones cab be described using the Boumasequence. In this sequence, deposits fine upward.

Massive Sandstones: Much more evidence of erosion of substrate; beds are commonly associated with channels many meters deep. The deposits of successive flows also join together (amalgamation) to make comosite beds (the monotonous aspect of sandstone-shale interbedding is lost). Most common sedimentary structure of this type is dish and pillar structure which indicate abundant fluid escape during deposition (see images from sedimenphica reference).

Pebbly sandstone: beds tend to be well graded with internal stratification fairly abundant and consists of coarse, crude horizontal stratification and commonly channeled and laterally discontinuous.

Conglomerates: Imbrication features which typified by clasts whose long axes lie parallel to flow and dip upstream. This signifies that clasts have not rolled on the bed.

Pebbly mudstone, debris flows, slumps and slides: Consist of pebbles and distorted clasts of sandstone and mudstone, dispersed in a silty mudstone matrix.

Bouma Sequence

SHALLOW WATER

CARBONATE

KlasifikasiDunham,1962

Klasifikasi

Embry & Klovan, 1971

Carbonate platforms

Sedimentary Sedimentary FaciesFacies

Sedimentary Sedimentary FaciesFacies-- the characteristics of a unit of the characteristics of a unit of sediments which can be used to interpret the depositional sediments which can be used to interpret the depositional environment.environment.

--sediments deposits at the same time but in different sediments deposits at the same time but in different environments.environments.

Sedimentary Sedimentary FaciesFacies can shift over timecan shift over time

Walther's Law

Conceived in 1894 by German geologist Johannes Walther.Conceived in 1894 by German geologist Johannes Walther.

Different kinds of sediments are deposited adjacent to each othDifferent kinds of sediments are deposited adjacent to each other as result of lateral variation in er as result of lateral variation in depositional environments. A vertical sequence of different sedidepositional environments. A vertical sequence of different sedimentary rocks must record the mentary rocks must record the superimposition of those same environments over time. superimposition of those same environments over time.

StratigraphicStratigraphic units containing unconformities may not follow this rule. units containing unconformities may not follow this rule.

The Facies Concept

A number of different depositional environments exist in any seA number of different depositional environments exist in any sedimentary basin.dimentary basin.

These environments represent local variation in physical, chemiThese environments represent local variation in physical, chemical and biological conditions as cal and biological conditions as well as distance and direction from depositional agents enteringwell as distance and direction from depositional agents entering basin (e.g. a river and its delta). basin (e.g. a river and its delta).

At any moment sediments being deposited may be correlated with At any moment sediments being deposited may be correlated with local depositional local depositional environments. environments.

These lateral variations are termed sedimentary These lateral variations are termed sedimentary faciesfacies. .

Sedimentary Sedimentary FaciesFacies