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CAUSE EFFECT
Process
Physical
Chemical
Biological
Sedimentary
Environment
Erosional
Non-depositional
Depositional Sedimentary
Facies
Geometry
Lithology
Sedimentarystructures
Paleocurrents
Fossils
The relationship between sedimentary environments and sedimentary facies
CAUSE EFFECT
Process
Physical
Chemical
Biological
Sedimentary
Environment
Erosional
Non-depositional
Depositional Sedimentary
Facies
Geometry
Lithology
Sedimentarystructures
Paleocurrents
Fossils
The relationship between sedimentary environments and sedimentary facies
Terrestrial/Continental
Alluvial fan
FluvialLacustrine
Eolian
Glacial
Braided
Meandering
Transitional
(Shorelines)
Lobate (deltas)
Linear (beaches)
Lagoons
Marine
Reef
Shelf
Submarine channel andfanPelagic
Classification of Major Depositional Environments
Sedimentary Environments• A part of the earth’s surface, physically, chemically, and
biologically distinct from adjacent terrain.
• defined by, fauna and flora, geology, geomorphology,
climate, weather, temperature, and if sub-aqueous, the
depth, salinity, and current system of the water.
• could be a site of erosion, non-deposition, or deposition.
• Erosional/non-depositional environments
preserved in the rock
record as unconformities.
Sedimentary Facies• A mass of sedimentary rock which can be defined
and distinguished from other by its geometry,
lithology, sedimentary structures, paleocurrent
pattern, and fossils (Selley 1970).
TERRESTRIAL ENVIRONMENTS
Alluvial Fan Environment• What is an alluvial fan?
• a fan-shaped, terrestrial deposit
• Where is it found?
• At the transition of mountains and plains
• where there is tectonic movement which
maintains high relief between mountains and
plains
• How is it formed?
• mountains shed sediment off their flanks,
streams carry it away as alluvium.
• stream carries lots of alluvial sediment
easily when its slope is steep and energy is
abundant.
• As stream valley emerges into a basin
(plain), slope and energy decrease
deposition of sediments in an alluvial fan
• Deposits
• lots of coarse particles
• usually sandstone and conglomerate
• poor sorting
Fluvial (River) Environment
Rivers/streams are elongated bodies of water that flow through
channels
Three ways streams transport sediments:
• in solution (dissolved load)• in suspension (suspended load)
• along the bottom of the channel (bedload)
Type and amount of material in suspension is
controlled by:
• water velocity
• settling velocity of each grain which depend
on:
• size
• shape
• specific gravity
bedload
• composed of coarser particles - cannot becarried by suspension
• bedload particles move along by:
• rolling
• sliding
• Saltation
Ability of streams to carry sediments is described by:
• capacity - maximum load of sediment that a
stream can transport
• competence - measure of the maximum size
of particles it is capable of transporting
Two Types of Channels:
1. Meandering
• consist of a single channel and thalweg (deepest poin
in a channel cross section)
• low gradient(slope) and high sinuosity
(curved/sinuous shape in map view)
• sediments deposited at the inner sides of meanders
(channel bends)
• associated with vegetated areas under a humid
climate
• deposition of sediments takes place in the channel, on
the levees and in the basins.
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• gravel and coarse sand are normally found on the
channel floor (`lag deposits').
• finer sand settles along the inner bends of the river,
on so-called `point bars'.
• Associated with oxbow lakes
Evolution of an Oxbow lake (1) On the inside of the loop, the river travels more
slowly leading to deposition of silt.
(2) Meanwhile water on the outside edges tends to
flow faster, which erodes the banks making the
meander even wider.
(3) Over time the loop of the meander widens until
the neck vanishes altogether.
(4) Then the meander is removed from the river's
current and the horseshoe shaped oxbow lake is
formed.
Without a current to move the water along, sediment
builds up along the banks and fills in the lake.
2. Braided
• have a single channel of low sinuosity (almost
straight) and high slope, with multiple `thalwegs' and
bars.
• high sediment load
• During times of maximum discharge, the channel is
completely inundated
• In times of low discharge, multiple thalwegs and barsreappear within the channel
• occur in areas with a highly irregular water
regime, and abundant sediment supply
• Deposits contain alternating areas (lenses)
of coarse gravel and sand
Lacustrine Environment• From the word “lacuna”, meaning lake
• lake - landlocked body of standing, non-marine water
• formed in depressions or basins with internal
drainage or limited flow
• Geometry - circular or elongate in plan view;
lenticular (lens-like) in cross section
• Low energy laminated fine sediments
Eolian Environment• eolian (from Aeolus, Greek god of winds) - describes
activity of deposits of winds
• deserts (arid environment)
• wind
Point bar
deposits
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• a turbulent stream of air
• like water, it has the ability to erode,
transport and deposit
• two properties:
• low density - limits competence
• unrestricted flow - enables spread
over wide areas
• lack of rain allows more effective wind
work
• sand transport
• Creep - large particles are rolled to the
surface after coming into contact with
saltating particles.
• Saltation - bouncing and jumping movement
of grains. Involves bedload.
• Suspension - occurs when fine dust and dirt
are lifted into the wind. Involves suspended
load.
Wind Erosion• needs chemical and mechanical weathering to act
effectively
• two types of wind erosion:
• Abrasion
• Sandblasting• shaping of solid rock
surfaces by constant
impact of grains by wind.
• deflation
• erosion of ground
when dry, loose particles of
dust and salt are lifted and
blown away
Deserts• concentrated in two regions:
• subtropics
• middle-latitudes
• areas where rainfall is less than 250 mm (10 in.)/year
or where evaporation exceeds precipitation.
• Rainfall in deserts may vary from 0.2 cm./yr. to about
40 cm./yr. Rainfalls of 5-20 cm./yr. are common.
• Temperature extremes can vary from –60 degrees F.
in Mongolian deserts to 137 degrees F. in the SaharaDesert. Temperatures in excess of 180 degrees may
occur in sands exposed to full solar radiation.
• Great daily extremes can occur.
• Due to lack of vegetation, wind velocities are high.
Causes of Deserts
• caused by high mountains causing available moisture
to condense and precipitate on their higher parts,
reducing moisture available for lowlands in the lee of
mountains.
• Direct blocking of moisture may also occur.
Wind Deposits
• deflation lag deposits - Coarsest clasts (desertpavement)
• loess - Unconsolidated, unstratified aggregation of
small, angular mineral fragments, usually buff in
color. Generally believed to be wind-deposited.
• dunes - Sand dunes form when there is (1) a ready
supply of sand, (2) a steady wind, and (3) some kind
of obstacle such as vegetation, rocks, or fences, to
trap some of the sand. Sand dunes form when moving
air slows down on the downwind side of an obstacle.
Dunes may cover large areas and reach heights up to
500m.Ventifacts - sha ed b the wind
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Types of Sand Dunes:• Barchan dunes - crescent-shaped dunes. They
form in areas where there is a hard ground surface, a
moderate supply of sand, and a constant wind
direction.
• Transverse dunes- large fields of dunes that
resemble sand ripples on a large scale. Consist of
ridges of sand with a steep face in the downwind
side, form in areas where there is abundant supply of
sand and a constant wind direction.
• Linear dunes - long straight dunes that form in
areas with a limited sand supply and converging wind
directions.
• Parabolic dunes - are "U" shaped dunes with an
open end facing upwind. Form in areas with
abundant vegetation and constant wind. Most
common in coastal areas.
• Star dunes - dunes with variable arms and slip face
directions. Form in areas with abundant sand supply
and variable wind direction.
Glacial Environment
• Glaciers• permanent (on a human time scale) body of ice that
shows evidence of downward movement due to
gravitational pull.
• form at or above snowline
• Snowline - where ice can be created and
remain all year round
• The snowline, at present, lies at sea level in
polar latitudes and rises up to 6000 m in
tropical areas.
• formed by recrystallization of snow due to pressure
of overlying compacted snow.
• Recrystallized snow has decreased air and
increased grain size and density forming
solid blocks of ice.
Types of Glaciers
• Alpine/Mountain Glaciers
– Relatively small glaciers at higher
elevations in mountainous regions.
• Ice Sheets: (Continental glaciers):
– the largest types of glaciers on Earth.
– cover large areas of the land including
mountain areas.
– Modern ice sheets cover Greenland and
Antarctica.
• Ice Shelves:
– are sheets of ice floating on water and
attached to land.
– usually occupy coastal embayments.
• Glacial Erosion • Plucking -particle detachment by moving glacial ice
• Abrasion - debris in basal ice grinds into the bedrock
and produce:
– Glacial striations - long parallel scratchesand grooves that are produced by rocks
embedded in the ice scraping against
the rock underlying the glacier.
– Glacial polish - rock that has a smooth
surface produced as a result of fine
grained material embedded in the glacier
acting like sandpaper on the
underlying surface.
Landforms produced by mountain glaciers:
Cirques - bowl shaped depressions that occur at the heads of
mountain glaciers
Glacial Valleys - Valleys that once contained glacial ice
become eroded into a "U" shape in cross section.
Arêtes - If two adjacent valleys are filled with glacial ice, the
ridges between the valleys can be carved into a sharp knife-
edge ridge, called an arête.
Horns - Where three or more cirques are carved out of a
mountain, they can produce a sharp peak called a horn.
Hanging Valleys - A valley that has greater elevation than the
valley to which it is tributary.
Fjords - narrow inlets along seacoasts once occupied by a
fjord glacier.
Barchan
Transverse
Longitudinal
Parabolic
StarStar
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Glacial Deposits • Since glaciers are solid they can transport all sizes of
sediment, from huge house-sized boulders to fine-grained material.
• Glacial Drift – general term for glacial deposits
• Till - nonsorted glacial drift deposited directly from
melting ice. A till that has undergone diagenesis and
has turned into a rock is called a tillite.
• Moraines – linear deposits of till produced by the
movement or retreat of glaciers
• Glacial Marine drift • Unsorted chaotic deposits of
sediments/rocks on seafloor or lakebeds
brought by melted glaciers.
• Large single rock bodies at the floor of a
water body is called a dropstone.
TRANSITIONAL ENVIRONMENTS Transitional environments are those at or near the transition
between the land and the sea.
Delta• prograding depositional bodies that form at the point
where a river drains into a lake or sea.
Parts of a Delta:
• delta plain - composed of meandering flood plains,
swamps, and beach complex.
• delta front - steeper part.
• prodelta - broadly sloping that grades into the open
shelf.
Factors Affecting Delta Formation and Facies:• water and sediment yield of the river
• differences in river/sea water densities, buoyancy,
salinity
• shelf slope and topography
• wave and tidal energy acting on the coast
• along shore winds and currents,
• tectonics (subsidence) of the receiving basin.
Types of Deltas• River-dominated
– large sediment volume
– lobate shape = moderate sediment supply
– elongated when sediment supply is large
• Tide-dominated
– linear features parallel to tidal flow andperpendicular to shore.
• Wave-dominated delta
– smoothly arcuate; wave action reworks
sediment.
– much sandier than the other types of delta.
Delta sediments• Sand, mud, sometimes gravel
• Decrease in grain size as you move away from land
• General coarsening upward due to progradation
Lagoon• shallow salt water body separated from the deeper
sea by a shallow or exposed sandbank, coral reef, orsimilar feature
• quiet waters allow fine silt and clays to settle out of
suspension, forming sequence of mudstone and shale
• overgrown with vegetation forming salt marshes,
coal, and peat swamps, or algal mats.
• some cases, evaporites are formed.
Beach• shore of a body of water formed and washed by
waves and tides.
• usually covered by sandy or pebbly material
• usually well sorted sand and pebbles, accompanied
by mud, cobbles, boulders, smooth rocks and shell
fragments.
• Wave action
– Longshore current • a current that moves parallel to a
shore
• formed from the momentum of
breaking waves that approach shore
obliquely.
– Longshore drift
• the movement of sediment along a
beach by swash and backwash of
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waves that approach the shore
obliquely.
• Spit • long ridge of sand deposited by longshore
current and drift
• attached to a land at upstream end.
• Tombolo • a sand or gravel bar that connects an island
with the mainland or another island.
MARINE ENVIRONMENT• Shallow marine
– Reefs
– Continental shelf
• Deep marine
– Submarine canyons and fans
– Pelagic
Reefs• wave-resistant, mound-like structures usually made
of fossiliferous carbonates (coral reefs) and/or sand
• build up on continental shelves
• Fringing Reefs– coral reef that is directly attached or borders
the shore of an island or continent.
• Barrier Reefs
– a long narrow coral reef roughly parallel to
the shore
– separated from it at some distance by a
lagoon.
• Atoll
– continuous or broken circle of coral reef and
low coral islands surrounding a central
lagoon.
Evolution of reefs
Continental Shelf • continuous with the coastal plain sequences of the
continents
• part of the continental margin that is between the
shoreline and the continental slope (~200m)
• carbonates, sand and mud.
• fossils are mostly marine invertebratesCarbonate compensation depth
• CCD
• Depth where the rate of dissolution and
precipitation of carbonates is equal
• Below this depth very little or no carbonates
• Continental Slope• between the continental shelf and continental shelf
and continental rise (oceanic trench)
• Continental Rise• between continental slope and abyssal plain
• gentle incline and generally smooth topography
• may bear submarine canyons and fans
• TURBIDITES
• Deposited by sediment-laden currents flowing
down submarine canyons and fans
• Sand and mud
• Abyssal Plain• Pelagic open ocean
• flat region of the ocean floor
• covered with pelagic mud with fine sand layers
from nearby turbidites
• fine-grained limestones (micrite), chert