Deep-sea Sediments

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Deep-sea Sediments Biogenic, Authigenic, and
Terrigenous Biogenic sediments biogenic-remains
of marine organisms vs. terrigenous-derived of
the earth shallow water biogenic sediments
(reefal limestones of various components)
vs. biogenic oozes pelagic- settle through
water column two primary types of biogenic oozes
carbonate vs. siliceou carbonate oozes (foram.,
nanno , pteropods) ooze CaCO3 constitutes gt30
primary constituents "Globigerina" ooze of
Challenger (1871) expedition
chlorophyll-bearing calcareous coccolithiphorid
ae foraminifera siliceous diatoms
radiolaria, silicoflagellates organic
wall dinoflagellates (red tides) foraminifera,
radiolaria, Kingdom Protista Coccolithiphoridae,
diatoms Kingdom Chromista also part of the red
line All Empire Eucaryota
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Calcareous nannoplankton Includes incerta sedis
discoasters Kingdom Chromista Division
Heterokonta Class Prymnesiophycae
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Planktonic Foraminifera Kingdom Protozoa? Order
Foraminifera
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Radiolaria
Diatoms, Kingdom Chromista, Division Haptophyta
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Marine Environments overhead Kennett p. 258
primary production CO2 H2O CH2On
O2 pelagic plankton and nekton neritic (green
water), oceanic (blue) zones epipelagic, meso-,
and bathy- don't worry about these nekton plankto
n floaters benthic/benthos bottom
dwellers lifestyles suspension feeders, grazer,
deposit feeders infaunal epifaunall depth zone
function of light, pressure (bars),
oceanography
zones supratidal,intertidal/littoral neritic
(i, m, o) or shelf or sublittoral (0-200 m)
bathyal 200-2000 (u 200-600, m 600-1000,
lo. 1000-2000) Abyssal (2000-5000 m) Hadyl
(gt5000 m)
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Big three processes for biogenic deep-sea
sediments 1) production 2) dissolution 3)
dilution (hemipelagic sediments) Carbonates Blatt
Middleton and Murray 10 stratigraphic record
"limestones" 50 oil in carbonates (20
U.S.) shallow water limestones versus pelagic
oozes, chalks, and limestones CaCO3 easier to
dissolve in colder water, _at_ high P CaCO3-makes
up 50 oceanic sediments Phases aragonites
unstable on 10-100 m.y. scale high Mg
Calcites unstable Mg2 substitutes for Ca low
Mg calcite
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Carbonate chemistry CaCO3 ????Ca CO3 CO2
280 ppm (0.03) pre-anthropogenic vs. 350 present
CO2gas ????CO2aq CO2aq H2O ???H2CO3 hydration
H2CO3 ?????? HCO3- Dissociation I ksp1 HCO3-
????? CO3 Dissociation II ksp2 buffered by
carbonate system, add n moles CO2aq, don't
release 2n mole H at oceanic pH (8.1), HCO3-
dominant species store H in HCO3- ?CO2 ?pCO2
HCO3- CO3 ??Henry's coeff.? H2CO3
neglected Ocean hold 40 x atmosphere Fig.
titration plot
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Alkalinity meq/liter
Fig. titration plot
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carbonate oozes tests of planktonic foraminifera
and the plates of calcareous nannofossil
coccolithiphorids found mostly in oligotropic
(low productivity) areas
CaCO3 near saturation CaCO3 saturation f(T,
depth, pH) dissolution increases with depth most
accumulation on (2-4 km) ridges comprise 50
ocean sediments
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input 0.11 gm/cm2/kyr riverine output 1.3
gm/cm2/kyr therefore must dissolve gt90
precipitated more easily dissolved with depth
CCD Calcite Compensation Depth snowline (e.g.,
Challenger noted carbonate oozes on highs) rate
input CaCO3 rate dissolution CaCO3, a kinetic,
not thermodynamic effect lt20 CaCO3
Aragonite compensation depth ACD lt 2000m
pteropods (aragonitic, more easily dissolved
only lt 1-2 km)
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CCD lower in Atlantic 4.5-5.5 km Fig. from
Berger CCD higher in Pacific 4.5 CCD lower
(depressed) in equatorial high productivity belt
(e.g., from 4.5 to 5 km in Pacific) Why?
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CCD not saturation/undersat. horizon lysocline
abrupt change in dissolution above
CCD foraminiferal lysocline abrupt drop in
foram. oreservation sedimentary lysocline abrupt
drop in CaCO3 hydrographic lysocline abrupt
increase in corrosivity
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does lysocline R0 (carbonate saturation level)
Fig. Berger 1) Broecker and Takahashi say yes 2)
field studies of beads R0 shallower due to
turbulence of water? 3) kinetically determined
level of critical undersaturation problem is
with determining ksp2 (thermodynamic solubility
product)
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• ?????aCa CO3)/ksp2
• 1 saturation,
• gt1 _at_ supersaturation,
• lt1 undersaturation
• Keir indicated that the lysocline is a response
  to 3-order kinetics
• Why? Has to do with the structure of CaCO3

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SiO2 Silica produced by planktonics
radiolarians and diatoms SiO2 is nutrient like
chemical (nutrients phosphates, nitrates
"fertilizers") supply riverine organisms still
secrete extremely undersaturated (10-fold) ltlt1
produced is preserved therefore, controlled
mostly by supply (production) siliceous oozes
mostly in heterotrophic regions (Upwelling) Fig.
nutrients-phosphates and nitrates. biolimiting.
lakes phosphorous biolim,
high nutrients in upwelling regions equatorial S
outhern Ocean general North Pacific upwelling
of deep waters
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Transport of pelagic sediments to bottom The role
of the fecal express p. 485 Kennett explains how
small, easily dissolved particles of calcite can
make it to bottom without dissolving or being
advected far from site of precipitation Diagenesi
s/lithification of biogenic sediments chalk,
limestone formation bring in sample ooze to chalk
200-400 m chalk to limestone 600-1000 m burial
loss of porosity reflects progressive dewatering
changes in packing, dissolution, cementation
(calcite precipitation f(burial depth, diagenetic
potential) chert formation transition from opal
(opal A, amorphous) to opal cristobalite (Opal
CT, cyptocrystalline) to chert
(microcrystalline) widespread late early to early
middle Eocene cherts
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Authigenic sediments maganese (Mn) nodules
very slow accumulation, found in areas of slow
accumulation p. 500 Kennett. often in regions of
swift bottom currents barite (BaSO4) deep
sea Phosphorites P apatite slow accumulation
on shelves Glauconites K-Al silicates, dysoxic,
slow accumulation shelves, slope
Maastrichtian glauconite sands (Navesink Fm.) and
silts (Red Bank Fm), Rt. 34, Matawan
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Organic rich p. 487 Kennett function of supply
organic matter and oxygen deep waters high supply
in upwelling zones oxygen minimum zone (300-1000
m) 0-3 ml/l FIG. 13 reaches 0 in upwelling zone
high organic matter uses O2 therefore more
organic matter preserved chicken and egg typical
deep sea sediments have lt 1 TOCV organic rich
gt1 why is there a min oxygen supplied from
atmosphere enters at air sea interface deep
water consumption throughout water (oxidation
regeneration) therefore, must be a
min. location closer to surface reflects vertical
advection diffusion