Marine Sedimentation - PowerPoint PPT Presentation

1 / 66
About This Presentation
Title:

Marine Sedimentation

Description:

Marine Sedimentation – PowerPoint PPT presentation

Number of Views:264
Avg rating:3.0/5.0
Slides: 67
Provided by: Lianne8
Category:

less

Transcript and Presenter's Notes

Title: Marine Sedimentation


1
Marine Sedimentation
2
(No Transcript)
3
(No Transcript)
4
(No Transcript)
5
(No Transcript)
6
(No Transcript)
7
(No Transcript)
8
(No Transcript)
9
(No Transcript)
10
  • Sediment Defined
  •  unconsolidated organic and inorganic particles
    that accumulate on the ocean floor
  • originate from numerous sources
  • weathering and erosion of the continents
  • volcanic eruptions
  • biological activity
  • chemical processes within the oceanic crust and
    seawater
  • impacts of extra-terrestrial objects
  •  classified by size according to the Wentworth
    scale

11
  • grain size indicates condition under which
    sediment is deposited
  • high energy environments characteristically yield
    sediments larger in size
  • small particles (silts, clays) indicate low
    energy environments
  • considered well-sorted if most particles appear
    in the same size classification
  • poorly sorted sediments comprised of multiple
    sizes
  •  sediment maturity is indicated by several
    factors
  • decreased silt and clay content
  • increased sorting
  • increased rounding of grains, as a result of
    weathering and abrasion
  • particle transport is controlled by grain size
    and velocity of transporting medium

12
4-1
Sediment in the Sea
  • Average grain size reflects the energy of the
    depositional environment.
  • Hjulstroms Diagram graphs the relationship
    between particle size and energy for erosion,
    transportation and deposition.

13
(No Transcript)
14
Classification of marine sediments can be based
upon size or origin.
4-1
Sediment in the Sea
  • Size classification divides sediment by grain
    size into gravel, sand and clay.
  • Mud is a mixture of silt and clay.
  • Origin classification divides sediment into five
    categories Terrigenous sediments, Biogenic
    sediments, Authigenic sediments, Volcanogenic
    sediments and Cosmogenic sediments.

15
  • Terrigenous (or Lithogenous Sediments)
  • derived from weathering of rocks at or above sea
    level (e.g., continents, islands)
  • two distinct chemical compositions
  • ferromagnesian, or iron-magnesium bearing
    minerals
  • non-ferromagnesian minerals e.g., quartz,
    feldspar, micas
  • largest deposits on continental margins (less
    than 40 reach abyssal plains)
  • transported by water, wind, gravity, and ice
  • transported as dissolved and suspended loads in
    rivers, waves, longshore currents

16
  • (LANDSAT images adapted from Geospace Images
    catalog).
  • sediment delivered to the open-ocean by wind
    activity as particulate matter (dust)
  • primary dust source is deserts in Asia and North
    Africa
  • comprise much of the fine-grained deposits in
    remote open-ocean areas (red clays)
  • volcanic eruptions contribute ash to the
    atmosphere which settles within the oceans

17
  • sediment also transported to the open-ocean by
    gravity-driven turbidity currents
  • dense 'slurries' of suspended sediment moved as
    turbulent underflows
  • typically initiated by storm activity or
    earthquakes 
  • first identified during 1929 Grand Banks
    earthquake
  • seismic activity triggered turbidity current
    which severed telegraph lines
  • initial flow often confined to submarine canyons
    of the continental shelf and slope
  • form deep-sea fans where the mouth of the canyon
    opens onto the continental rise

18
20 m s-1 near Grand Banks
19
  • boulder to clay size particles also eroded and
    transported to oceans via glacial ice
  • glacier termination in circum-polar oceans
    results in calving and iceberg formation
  • as ice (or icebergs) melt, entrained material is
    deposited on the ocean floor
  • termed 'ice-rafted' debris

20
(No Transcript)
21
  • Biogenous Sediments
  • composed primarily of marine microfossil remains
  • shells of one-celled plants and animals, skeletal
    fragments
  • median grain size typically less than 0.005 mm
    (i.e., silt or clay size particles)
  • characterized as CaCO3 (calcium carbonate) or
    SiO2 (silica) dominated systems
  • sediment with biogenic component less than 30
    termed calcareous, siliceous clay
  • calcareous or siliceous 'oozes' if biogenic
    component greater than 30 

22
(No Transcript)
23
  • siliceous oozes (primarily diatom oozes) cover
    15 of the ocean floor
  • distribution mirrors regions of high productivity
  • common at high latitudes, and zones of upwelling
  • radiolarian oozes more common in equatorial
    regions

24
  • calcareous oozes (foraminifera, coccolithophores)
    cover 50 of the ocean floor
  • distribution controlled largely by dissolution
    processes
  • cold, deep waters are undersaturated with respect
    to CaCO3
  • deep water is slightly acidic as a result of
    elevated CO2 concentrations
  • solubility of CaCO3 also increases in colder
    water and at greater pressures
  • CaCO3 therefore readily dissolved at depth 
  • level below which no CaCO3 is preserved is the
    'carbonate compensation depth'
  • typically occurs at a depth of 3000 to 4000 m

25
Microfossils in Paleoclimatology/Paleoceanography
26
  • DissolutionCalcium carbonate dissolves better in
    colder water, in acidic water, and at higher
    pressures. In the deep ocean, all three of these
    conditions exist. Therefore, the dissolution rate
    of calcium carbonate increases greatly below the
    thermocline. This change in dissolution rate is
    called the lysocline.Below the lysocline, more
    and more calcium carbonate dissolves, until
    eventually, there is none left. The depth below
    which all calcium carbonate is dissolved is
    called the carbonate compensation depth or CCD.

27
(No Transcript)
28
  • Hydrogenous (or Authigenic) Sediments
  • produced by chemical processes in seawater
  • essentially solid chemical precipitates of
    several common forms
  • non-biogenous carbonates
  • form in surface waters supersaturated with
    calcium carbonate
  • common forms include short aragonite crystals and
    oolites
  • phosphorites
  • phosphate crusts (containing greater than 30
    P2O5) occurring as nodules
  • formed as large quantities of organic phosphorous
    settle to the ocean floor
  • unoxidized material is transformed to phosphorite
    deposits
  • found on continental shelf and upper slope in
    regions of high productivity

29
  • manganese nodules
  • surficial deposits of manganese, iron, copper,
    cobalt, and nickel
  • accumulate only in areas of low sedimentation
    rate (e.g., the Pacific)
  • develop extremely slowly (1 to 10 mm/million
    years)

30
(No Transcript)
31
  • The term evaporites is used for all deposits,
    such as salt deposits, mainly chemical sediments
    that are composed of minerals that precipitated
    from saline solutions concentrated by
    evaporation. Evaporite deposits are composed
    dominantly of varying proportions of halite (rock
    salt) (NaCl), anhydrite (CaSo4) and gypsum
    (CaSo4.2H2O). Evaporites may be classified as
    chlorides, sulfates or carbonates on the basis of
    their chemical composition (Tucker, 1991).

32
evaporites ('salt' deposits') occur in regions
of enhanced evaporation (e.g., marginal seas)
evaporative process removes water and leaves a
salty brine e.g., Mediterranean 'Salinity
Crisis' between 5 and 6 million years ago
33
  • Cosmogenous Sediments
  • sediments derived from extraterrestrial
    materials 
  • includes micrometeorites and tektites
  • tektites result from collisions with
    extraterrestrial materials
  • fragments of earth's crust melt and spray outward
    from impact crater
  • crustal material re-melts as it falls back
    through the atmosphere
  • forms 'glassy' tektites

34
  • Distribution of Marine Sediments
  • sediments thickest along continental margins,
    thin at mid-ocean ridges 
  • coastlines
  • dominated by river-borne and wave reworked
    terrigenous sediments
  • shelf and slope characterized by turbidites and
    authigenic carbonate deposits
  • glacial deposits and ice-rafted debris common at
    high latitudes
  • high input of terrigenous sediments 'dilutes'
    biogenous components
  • deep-sea (pelagic) basins
  • abyssal clays (wind blown deposits) common
  • lower quantities of biogenic material
  • distribution of biogenous sediments dependent
    upon three primary factors
  • production in surface waters
  • dissolution in deep waters
  • dilution by other sediments types

35
  • high productivity in zones of upwelling and
    nutrient-rich high latitude waters
  • calcareous oozes more common in warmer or
    shallower water
  • siliceous oozes more common in colder or deeper
    water
  • terrigenous sedimentation rates range from 1 mm
    to 10's cm/1000 years
  • biogenous sedimentation rates typically 1
    cm/1000 years

Nearshore sediments, turbiditesUp to km/my
(kilometers/million years)Hemipelagic deposits
Tens to hundreds of m/myDrift deposits40-400
m/myMid-latitude eolian deposits 3 to 10
m/myIce rafted material 10 m/myCarbonate
oozes Up to 50 m/mySiliceous oozes Up to 10
m/myHydrothermal deposits (off ridge axes)About
0.5 m/myHydrogenous sediments Rarely exceed 0.2
m/myFerromanganese nodules 0.0002 to 0.005 m/my
(0.2 to 5 mm/my)
36
(No Transcript)
37
(No Transcript)
38
Shelf sedimentation is strongly controlled by
tides, waves and currents, but their influence
decreases with depth.
4-2
Sedimentation in the Ocean
  • Shoreline turbulence prevents small particles
    from settling and transports them seaward where
    they are deposited in deeper water.
  • Particle size decreases seaward for recent
    sediments.
  • Past fluctuations of sea level has stranded
    coarse sediment (relict sediment) across the
    shelf including most areas where only fine
    sediments are deposited today.

39
(No Transcript)
40
Geologic controls of continental shelf
sedimentation must be considered in terms of a
time frame.
4-2
Sedimentation in the Ocean
  • For a time frame up to 1000 years, waves,
    currents and tides control sedimentation.
  • For a time frame up to 1,000,000 years, sea level
    lowered by glaciation controlled sedimentation
    and caused rivers to deposit their sediments at
    the shelf edge and onto the upper continental
    slope.
  • For a time frame up to 100,000,000 years, plate
    tectonics has determined the type of margin that
    developed and controlled sedimentation.

41
60 of the worlds shelves are covered with
relict sediments that were formed about 15,000 y
BP under a different energy regime.
42
(No Transcript)
43
(No Transcript)
44
(No Transcript)
45
(No Transcript)
46
(No Transcript)
47
(No Transcript)
48
(No Transcript)
49
(No Transcript)
50
(No Transcript)
51
(No Transcript)
52
(No Transcript)
53
(No Transcript)
54
(No Transcript)
55
(No Transcript)
56
(No Transcript)
57
(No Transcript)
58
(No Transcript)
59
(No Transcript)
60
(No Transcript)
61
(No Transcript)
62
(No Transcript)
63
  • Gas Methane Hydrates (Clathrates)
  • Hydrates store immense amounts of methane, with
    major implications for energy resources and
    climate, but the natural controls on hydrates and
    their impacts on the environment are very poorly
    understood
  • The worldwide amounts of carbon bound in gas
    hydrates is conservatively estimated to total
    twice the amount of carbon to be found in all
    known fossil fuels on Earth (USGS).
  • Methane bound in hydrates amounts to
    approximately 3,000 times the volume of methane
    in the atmosphere.

64
(No Transcript)
65
(No Transcript)
66
(No Transcript)
Write a Comment
User Comments (0)
About PowerShow.com