Download Chapter 14. Biogenic and authigenic sediment

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Biogenic sediment
1. Introduction
a. Neritic Environments - carbonates
i. Coralgal reef limestones, like the Florida Keys and the Bahamas
ii. Coquina limestones of mollusk shells (i.e., oyster reefs off Bay St. Louis)
iii. Bryozoan-rich limestones, like the Great Australian Bight
b. Deep-water environments - Biogenic oozes
i. Can be carbonate or opal silica
ii. Oozes contain >60% skeletal remains of pelagic organisms
iii. Found from the outer shelf to abyssal depths of the oceans.
iv. Distribution is controlled by
(1) production of shell-bearing plankton. Production is controlled in turn by fertility
of the sea (upwelling)
(2) dissolution of shells and skeletal material by deep water.
(3) dilution by other sediment types, like terrigenous sediment
(4) Also affected by post-depositional alteration of the ooze - diagenesis
2. Carbonate sediment
a. Constituents
i. planktonic foraminifers (sand-size protists with chambered calcite shells called tests)
ii. calcareous nannofossils (algal cells, called coccolithophorids, that are armored by
clay-size and fine silt-size platelets of calcite
iii. Other minor constituents - persistent but occur in trace quantities (i.e., ostracods,
pteropods, carbonate spicules from various kinds of critters, benthonic foraminifers...)
b. Distribution of carbonate ooze
i. bathymetric highs
ii. areas removed from dilution by terrigenous input
c. Production carbonate skeletal material - mostly in surface waters, plankton. Production of
planktonic foraminifers is given as an example below
i. Fast (2000 shells/m2/d)
(1) equatorial regions
(2) western margins of continents (peak events as fast as 30,000 shells/m2/d)
(3) subpolar regions (10,000 shells/m2/d)
(4) shelf-edge (yearly average of 2000 shells/m2/d)
ii. Slow - gyre centers like the Sargasso Sea (< 500 shells/m2/d)
d. Dissolution of carbonate ooze - Calcium carbonate compensation depth (CCD), below
which there is no more than a trace of calcium carbonate
i. Depth
(1) 4200-4500 m water depth in the Pacific Ocean
(2) >5000 m water depth in the Atlantic Ocean
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ii. Definition: CCD is the depth at which the rate of dissolution equals the rate of input
of calcium carbonate.
iii. Lysocline: Dissolution rate relative to input rate increases below ~3500 m water depth
to the top of the CCD. This gradient is called the lysocline.
iv. Controls on carbonate dissolution
(1) ocean water factors
(a) Reactions (i) CO2 + H2O X H2CO3 X H+1 + HCO3-1 X H+1 + CO3-2
1) CO2: carbon dioxide gas dissolved in seawater
2) H2CO3: carbonic acid
3) H+1: acid proton
4) HCO3-1: bicarbonate ion
5) CO3-2: carbonate ion
(ii) CaCO3 + H+1 X Ca+2 + HCO3-1
1) Add more carbon dioxide, then more acid (H+1) protons are produced
(equation (i)), which dissolve calcium carbonate (equation (ii))
2) the ocean is buffered by its carbonate oozes, which can dissolve to
take up acid protons and keep the ocean from changing its pH (defined
based on the concentration of acid protons)
(b) Controls of CO2 in the ocean
(i) CO2 more soluble in cold waters, which form at high latitudes, where it
dissolves readily at the surface from the atmosphere and is subsequently
transported to the deep-sea by deep water formation.
(ii) CO2 from respiration of benthic organisms, so the older the bottom water,
the more time is has to accumulate CO2 from respiration of benthic
organisms. At present, bottom waters have a residence time of 1000 y.
(iii) CaCO3 is an unusual solid in that it dissolves more readily with
increasing pressure and decreasing temperature. Below about 5500 m,
this thermodynamic effect is quite significant in the oceans.
(2) Sediment factors
(a) Respiration also occurs in surficial sediments (upper ~ 10 cm). There is a
series of respiration reactions that occur in the mixed layer of surficial
sediment. Respiration of various types of bacteria use a succession of electron
acceptors starting with oxygen, MnO, nitrate (very minor since there is not
very much nitrate in sediment pore water), iron oxides, sulphate. The first
reaction with oxygen produces a lot of acid and promotes dissolution of
carbonate already deposited in sediment. The others (with Mn and Fe)
actually enhance precipitation of carbonate. The last reaction with sulphate,
can produce acid which causes dissolution in some cases and in contrast, it
can promote precipitation of carbonate in other cases. The reaction can go
either way depending on what bacteria are active.
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(b) Respiration of bacteria and infauna requires food in addition to electron
acceptors for respiration. So, bacteria in sediments that receive lots of organic
carbon may use up all the electron acceptors until there is nothing but sulfate
to use. When even this runs out, then organics are used and this results in
production of methane as a by-product. It follows that bacteria in sediments
that receive little organic carbon may not get past the stage where oxygen or
manganese oxide is used as the electron acceptor before they run out of food.
(i) So, respiration of infauna in sediments can produce acid, which will
dissolve carbonate, especially if the sediment undergoes very little
respiration and very little input of organic carbon, or if it gets a lot of
organic carbon and reaches sulfate utilization.
(ii) So, gyre centers, which remain mostly oxic, undergo strong dissolution
(iii) And continental margins are locales where dissolution and
preservation are patchy depending on the input of organic carbon from
the land and shelf. Here there is enough carbon (food) so respiration
can proceed to iron, sulfate reduction, or methane production with
different consequences for calcite preservation.
(3) Depth of the CCD is controlled by both water column and sediment effects. Water
column factors describe things pretty well in the open ocean, but things get pretty
chaotic on continental margins, so the CCD is not a nice neat line in these locales.
That is why Wolf Berger doesn’t draw the CCD onto continental margins. Local
input of carbon is huge compared to the open ocean and it is highly variable,
raising havoc with carbonate preservation.
e. Settling and dissolution through the CCD and lysocline
i. How do nannofossil platelets get to the sea floor?
(1) It takes 3.3 years for a 10-micrometer particle (like a coccolithophorid nanolith)
to fall 4,000 m according to Stokes Law. A micrometer is one millionth of a meter
(10-6 m).
(2) It takes 12 days for a 100-micrometer particle (like a radiolarian) to fall 4,000 m
according to Stokes’ Law
(3) It takes 1 day for a 350-micrometer particle (like a planktonic foraminifer) to fall
4,000 m according to Stokes’ Law
(4) A nannofossil platelet would surely dissolve in the water column if it took so long
to reach the sea floor.
ii. “Fecal pellet express” (Honjo, 1976; Honjo and Roman, 1978)
(1) A fecal pellet is 100 Fm or more and will reach the sea floor in two weeks or less
according to Stokes’ Law.
(2) Marine snow is another way of forming and agglomerating big particles from
little ones.
(3) The two mechanisms (fecal pellets and marine snow) are responsible for fast
delivery of very small particles to the sea floor.
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f. Lithification of carbonate ooze
i. compaction and dewatering of ooze produces chalk and semiconsolidated foraminifer
ooze.
(1) chalk, which is semilithified, is produced from nannofossil ooze
(2) semiconsolidated foraminifer ooze
ii. recrystallization
(1) overburden pressure, heat, the right pore water chemistry results in carbonate
growing into larger crystals (=recrystallizing)
(2) the rock produced is this fashion is called limestone
(3) Different shells have different sensitivities, so some will preserve while others are
the source of calcite for crystal growth.
g. History of carbonate mass accumulation in the deep ocean.
i. Mitch Lyle (2003) updated studies done by van Andel and others (1975) and
Shackleton (1987) in the Pacific Ocean based on ODP and DSDP sites and the latest
revisions to the radiometric ages of Neogene datum levels. He found one basinwide
event of decreased carbonate burial at ~21 Ma presumed controlled by chemistry of
seawater (dissolution), because all sites sit in the same deep water mass (a reasonable
assumption, but could prove to be wrong). All other changes are regional and
presumed controlled by regional changes in production of carbonate shells in the
plankton (foraminifers and nannofossils).
3. Siliceous ooze
a. Constituents - the important constituents are planktonic
i. Radiolarians - sand-size skeletons of protists
ii. Diatoms - clay to sand size silicified cell walls of algae
iii. Other minor constituents include silicoflagellates, sponge spicules, other.
b. Production
i. Phytoplankton and the protists that eat them reproduce in abundance where there is
upwelling of nutrients (equator, western boundaries of continents, polar fronts and
polar and subpolar waters).
c. Dissolution
i. Ocean waters are everywhere undersaturated with respect to silica.
ii. Surficial waters are particularly undersaturated due to biologic uptake of silica, so
dissolution is fastest in surface waters and a bit slower in deep waters.
iii. Only about 1-3% of the diatoms produced in surface waters are preserved in deepsea
marine sediments (Heath, 1974; Treppke et al., 1996). The rest are recycled in the
water column or at the sediment surface via various processes.
d. Distribution of siliceous ooze on the sea floor correlates quite well with plankton
production centers.
e. Silica sinks
i. Diatom production and preservation has played an intriguing role in silica cycling in
the oceans. At present, the Antarctic shelf is a sink for biogenic silica. Possibly 1/3 of
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the dissolved silica supplied to the oceans is ultimately sequestered on the Antarctic
shelf in the present-day. About 50% of the silica produced in the overlying waters is
preserved in the shelf sediments (DeMaster, 1981; Zielinski and Gersonde, 1997).
ii. It is interesting to consider that the location of silica sinks has changed during
geologic history. For example, during the Miocene and Eocene, diatomites were
deposited in deep coastal basins of the circum-Pacific (i.e., Japan Sea, California
basins, Peru and Chile).
f. Diagenesis
i. Amorphous opal (opal-a) becomes crystalline during diagenesis. It changes to
tridymite and cristobalite (opal-ct), and finally to either chert, which is
microcrystalline quartz, or quartz. Chert is a rock made of interlocking crystals of
quartz that are less than 30 Fm is size. Chert may contain some amorphous silica as
well as quartz.
ii. opal-a turns to opal-ct, then chert or quartz.
iii. the diagenesis is a function of
(1) temperature from heat flow and pressure from overburden, etc., so backarc basins
like the Bering Sea and Japan Sea have great diatoms, but they are gone at depth
(changed to opal-ct and chert).
(2) sediment composition (clays, specifically those with lots of exchangable Mg ions,
can inhibit chert formation (Kastner and Gieskes, 1977). This is why chert
alternates with diatomite in the Monterey Formation of California. The parts that
remained diatomite oare also clay-rich with plnety of Mg. In the cherty strata,
which have no clay and little Mg, the diatom frustules are destroyed by the
crystallization to opal-ct. Delicate radiolarians are destroyed, too, and robust
radiolarian skeletons become frosted with opal-ct (Bramlette, 1946).
(3) Time. There are very few Cretaceous age deposits of diatoms (for example, the
Moreno Formation of California, Alpha Ridge in the Arctic). The opal is not
stable and given enough time something is bound to happen to trigger the
recrystallization.
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Authigenic Sediment
1. Authigenic means formed in situ.
a. Precipitated from seawater or pore water
i. Often precipitates in layers onto a nucleus, like a fish tooth.
ii. Ferromanganese oxides (Mn nodules) are a good example of this
b. Weathering, where a mineral is altered to another mineral by releasing ions into seawater
and taking up CO2
i. Smectite clays
ii. Zeolites
c. Reverse weathering where a mineral is altered to another mineral be taking up ions from
seawater and releasing CO2
i. Glauconite
ii. Possibly tropical deltaic sediments (See papers by Aller on reverse weathering)
d. Precipitated from hydrothermal and volcanic effluents
i. Hydrothermal sulfides
ii. Hydrothermal sulfates
e. Precipitated on sea floor with biological mediation
2. Hydrothermal sediments
a. Associated with midocean ridge processes
b. Sulfide (and sulfate) associated with iron and manganese and minor amounts of other
interesting elements, such as copper, zinc, lead, gold, arsenic, silver.
c. Hydrothermal sediments are made of two end-member constituents
i. Volcanic fluids from the mantle
ii. Seawater that has circulated through basaltic crust
d. Hydrothermal circulation
i. Volcanic fluids and volatiles arise from the magma chamber beneath ridge. The
magma originates from the mantle.
(1) The fluids are very acidic and hot, promoting high temperature acid solution as it
rises up through the ocean crust. It alters the basalt and exchanges some ions.
(2) Enriched in sulfides
ii. The volcanic fluids mix with ocean water circulating through fault fractures of the
spreading ridge. The "ground water" also exchanges ions with basalt. For example,
seawater loses Mg to basalt and picks up Ca from dissolving feldspar, a common
mineral of basalt. Ca sulfate (anhydrite and gypsum) are common precipitates at
hydrothermal vents. The basalt alters into a Mg-rich rock called serpentinite, which
you have seen in lab.
iii. The mixing between circulating ocean water and volcanic fluids occurs in varying
degrees, so you get a variety of results
(1) little addition of sea water and lots of volcanic fluids results in deposition of
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massive sulfides (which include iron-rich sediments with FeS) at the surface
(2) lots of sea water with a little volcanic fluid (dilution)
(a) sulfides deposited only deep in the crust, within the conduits between the
surface vents and the magma chamber several kilometers below.
(b) manganese-rich and Ca-rich sediments are deposited at the sea floor surface
(3) intermediate mixing of sea water causes a mixture of iron- and manganese-rich
sediments at the surface.
iv. Venting rates correlate with spreading rates - fast spreading = lots of venting
(1) See German-C-R; Parson-L-M, 1998. Distributions of hydrothermal activity
along the Mid-Atlantic Ridge; interplay of magmatic and tectonic controls. Earth
and Planetary Science Letters.160; 3-4, Pages 327-341.
(2) high-temperature hydrothermal fluid flow estimated to be 1.8 X 1013 kg/yr
(Baker-Edward-T; Chen-Y-John; Phipps-Morgan-Jason. 1996. The relationship
between near-axis hydrothermal cooling and the spreading rate of mid-ocean
ridges. Earth and Planetary Science Letters.142; 1-2, Pages 137-145.)
v. Hydrothermal sediment is typically the first sediment type to be found in contact with
oceanic crust.
vi. Hydrothermal deposits are found at two types of ridge deposits
(1) unsedimented ridges
(2) sedimented ridges,
(a) where massive sulfide deposits are hosted by sediment rather than in or on
basalt.
(b) Metals are leached from the sediments and concentrated into the sulfides.
(c) Most sulfide deposits (with valuable traces of silver, etc.) that are mined on
land are sediment hosted.
(d) Examples of sedimented ridges include the Gulf of California, Middle Valley
at the narthern end of the Juan de Fuca Ridge, and the Escanaba trough at the
southern end of the Gorda Ridge.
(e) another interesting aspect of sedimented hosted deposits is an association with
petrochemicals through maturation of organic matter in the sediment.
3. Manganese nodules
a. Metals are precipitated directly from sea water and pore water
i. Metals include manganese oxide with iron, nickel, copper, cobalt, and traces of other
metals
ii. Chemistry
(1) 2Mn2+ (aq) + O2 (g) + 2H2O (l) = 2MnO2(s) + 4H+(aq)
(2) Mn+2 precipitates most readily onto surfaces and especially onto surfaces already
coated with itself (autocatalytic). Nodules almost always have a nucleus like a
fishtooth or otolith.
(3) Kinetics of precipitation dictate growth rates
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b.
c.
d.
e.
(a) Rate of growth is very slow (millimeters per million years) compared to most
rates for sedimentation of pelagic sediments, which is typically cm/y
(b) However, manganese-rich types can grow quite fast.
(4) Grow only in oxygenated waters and pore waters, where MnO2 can exist in solid
form. Remember that MnO2 is soluble in reducing conditions.
(5) Once buried, they cease to grow, but don't dissolve as long as pore waters remain
oxic.
Shapes
i. Spherical to subspherical nodules and micronudules
ii. Pavements rather than nodules of MnO2 form in some areas, especially areas swept
by bottom currents.
Mystery of nodules - not how they grow, but why they aren't covered up!
i. Questions
(1) For every nodule at the surface, only one will be found in the next 4 meters below
the surface: WHY SO MANY AT THE SURFACE?
(2) How do they keep from being buried?
(3) Why are they round?
ii. Answers
(1) best guess - organisms (benthic worms, fish, crustaceans, echinoids etc.) move
these things around and keep them at the surface. Probably do it just to get them
out of the way.
(2) Mn nodules are very low in density, float on the surface of sediment
(3) Dissolve at depth below oxic layer.
Distribution
i. Associated with slow sedimentation rates due to
(1) slow input of sediment
(2) or removal of sediment by bottom currents
(3) or steep surfaces (like scarps and sea mounts) where sediments can’t accumulate
(4) not related to source regions of Mn, for example, hydrothermal vents
ii. Patterns to composition
(1) beneath unproductive waters - composed mainly of iron and cobalt
(2) beneath moderately productive surface waters - composed of manganese, copper,
and nickel
(3) beneath productive waters where they grow quite fast - super-rich in manganese
(4) Valuable concentrations of valuable metals, higher than ore concentrations on
land, but expensive to recover
Paleoceanography from layers in Mn-pavements.
i. Frank et al. (2002, Paleoceanography, 17(2):12-1) show that differences in lead and
neodymium isotopes suggest a distinct decrease in NADW transport to the Southern
Ocean since the onset of glaciation ~3 Ma compared to the preceeding 11 m.y.
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4. Other authigenic constituents of sediments - biological mediation
a. phosphorite (fluorapatite; apatite) Ca5(PO4)3(F,Cl,OH)
i. Source is phosphorus in organic material and the distribtion is related to biloigically
productive areas, like upwelling regions on continental shelves.
ii. Appearance: Massive, cryptocrystalline, coarse granular, oolitic. Often brown.
Sometimes replaces fossils.
iii. Distribution: Associated with regions of high productivity, where phosphorous is
abundant in pore waters of the sediment. These conditions are most often found on
productive continental shelves like that of Peru - upwelling regions
iv. either direct sedimentation or by replacement of carbonate in sediments
v. There are valuable phosphorite deposits in Miocene neritic sediments of Florida
b. Biogenic pyrite - FeS2
i. Appearance
(1) yellow to black (sometimes with peacock blues and greens) metallic mineral
(2) usually granular, granules with a framboidal or raspberry texture
ii. Production
(1) Framboids form in anoxic porewater via bacterial reduction of sulfate to sulfide in
porewater followed by inorganic combination of iron with the bacterially
produced sulfide.
(2) Pyrite also forms inorganically from hydrothermal solutions at spreading centers.
Then it forms distinctive cubic crystals.
c. Biogenic magnetite - Fe3O4
i. Produced by some bacteria (Moskowitz-Bruce-M, 1997. Magnetism and microbes;
magnetic properties of biogenic iron minerals. Abstracts with Programs - Geological
Society of America. 29; 6, Pages 54; other papers in this session).
(1) Bacteria that produce iron minerals by biologically-controlled mineralization
exert strict control over nucleation and growth of intercellular particles of either
magnetite or greigite
(2) Bacteria using biologically-induced mineralization do not directly control the
mineralization process but instead induce the extracellular formation of iron
minerals by the reaction of metabolic products with ions in the environment.
ii. Important source of magnetism in marine pelagic sediments
d. Barites BaSO4
i. either by hydrothermal activity
ii. or by organic production
(1) barium correlates well with biological production patterns although it does not
appear that organisms use barium. It apparently adheres to organic matter.
(2) The connection may be useful in looking at paleoproductivity.
5. Weathering
a. zeolites - a weathering reaction with release of ions to seawater and uptake of CO2
i. A hydrated silicates of aluminum, calcium, sodium, and potassium formed by
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alteration of basalt and volcanic glass.
ii. common in red clays of the Pacific.
iii. For example, Phillipsite is a zeolite
(1) phillipsite = K2.8Na1.6Al4.4Si11.6O32 10H2O
(2) Appearance: elongate euhedral to subhedral prismatic crystals, often in rosettes,
colorless to yellow.
(3) Distribution: regions of low sedimentation rate in young, post-Miocene clay-rich
sediments.
(4) Source: an alteration product of tephra (volcanic ash), especially basaltic glass.
6. Reverse weathering - Formation of clay minerals in the marine environment
a. An example, Glauconite - K(Fe,Mg,Al)2(Si4O10)(OH)2
i. Appearance: earthy granules, green to black, sometimes as molds of fossils.
ii. Distribution and source: Formed in low oxygen conditions with low sedimentation
rates
(1) often associated with currents in the oxygen minimum on the upper slope.
(2) often associated with omission surfaces on continental margins (surfaces where
sedimentation ceased for a period of time, and where high input of organic matter
keeps pore water anoxic.
iii. Perhaps MnO would form in these areas if they were not low in oxygen.
b. Reverse weathering was proposed 30 years ago as a potentially important control on the
chemistry of the oceans by removal of sea water ions into solid clays and associated with
release of CO2.
i. You might know that chemical weathering (clay formation) on land is associated with
release of soluble cations and uptake of CO2. Reverse weathering does the opposite
(see below).
Weathering:
Feldspar + Carbonic acid + Water
2KAlSi3O8 + 2H2CO3 + H2O
\
Kaolinite + Dissolved silica + Potassium + Bicarbonate ion
Al2Si2O5(OH)4 + 4SiO2 + 2K+ + 2HCO3-
(1) Reverse weathering takes up ions and releases CO2
(2) Reverse weathering was proposed as a way to explain the removal of certain
soluble cations from seawater to balance the input from rivers due to chemical
weathering.
(3) A balance must also be struck for CO2. There must be a way to return to the
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atmosphere the CO2 combined into clays by weathering, or the atmosphere would
become depleted in CO2.. Reverse weathering would accomplish this.
Reverse Weathering:
Silica + Degraded aluminous clays +Iron oxide + Organic carbon + Soluble cations +
Bicarbonate
\
New clay material + Carbon dioxide + Water
ii. The idea was proposed in the late 1960s. This is why clay studies of marine clays
were so prevalent in the early 70's. In order to the understanding the geochemistry of
the ocean, including the long-term control of the carbon system (including carbonate
dissolution), we needed to know about oceanic clays to see if reverse weathering
happens.
(1) However, clay formation in marine sediments was not observed in quantities large
enough to be important.
(a) a survey of clays in surficial sediment of the deep ocean showed little
evidence of clays formed by reverse weathering. Glauconite was an exception,
but it was unimportant in terms of quantity.
(b) Researchers then focused on temperate deltas where rivers first bring products
that could participate in reverse weathering. However, the authigenic clays
were difficult to recognize from the flood of terrigenous clays typical of
deltas. Only a fairly small amount is needed (7%) to balance the equations. (It
also turned out they were looking at deltas in the wrong climate zone!)
(c) When hydrothermal circulation was discovered in the late 1970s, reactions
between seawater and basalt were thought to account for the budgets of most
major and minor elements, but discrepancies remained.
iii. Reverse weathering was NOT OBSERVED UNTIL NOW! (see below)
c. Michalopoulos-Panagiotis; Aller-Robert-C., 1995. Rapid clay mineral formation in
Amazon Delta sediments; reverse weathering and oceanic elemental cycles. Science.270;
5236, Pages 614-617.
i. M&A used lab experiments to show that reverse weathering (clay formation) could
take place readily in conditions found in tropical neritic environments, like the
Amazon Delta. Earlier work focused on temperate deltas and other environments, as
it turned out, the wrong places to look.
ii. K-Fe-Mg are the ions in question than combine with Al into clays on the surface of
SiO2 particles, like quartz grains, glass beads, etc.
iii. Much work remains to be done on other tropical systems to see if they also produce
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conditions where clays can be naturally synthsized from degraded clays plus silica
plus soluble ions etc. This has been a difficult hypothesis to test.
7. Red clay (abyssal clay) - a sediment with many authigenic constituents
a. Definition. Red clay is also called abyssal clay. The term, “red clay”, originated in
oceanographic studies more than 100 years ago and persists in the literature today. The
terms describe a sediment that is composed largely of hydrogenous minerals, eolian
debris, and other exotic constituents. The clay is generally barren of organic debris
except for very dissolution-resistant stuff like fish teeth, bones, and otoliths (ear bones of
marine mammals), and it is finer in texture than typical terrigenous sediment. Its rate of
sedimentation is very slow, generally less than 1 mm/1000 yr.
b. color
i. often brick red from oxidation of iron
ii. also chocolate brown
iii. but these colors occur in many other types of sediment and so are not especially
useful in recognizing "red" clays
c. composition
i. eolian debris blown from the continents and often altered to smectites and zeolites
ii. manganese nodules
iii. Fish teeth and otoliths (ear bones which are very dense and dissolution)
iv. Trace amounts of cosmogenic debris like tektites and dust from meteorites
v. Note that many of these constituents are hydrogenous.
d. distribution
i. found on sea floor isolated from terrigenous input
ii. typically far from sites of high biological productivity
iii. the sediment surface at the time of deposition is below the calcium carbonate
compensation depth (CCD)
iv. after deposition, the sediment at the surface is exposed to seawater for a very long
time allowing the dissolution of opal silica.
v. For example, surface sediments of gyre centers of the north and south Pacific Ocean
have red clay and the environment of those regions meet all the conditions listed
above.
Plate lithostratigraphy - the distribution of sediment types in space and time
e. Present-day locales of carbonate and siliceous oozes, terrigenous sediment, red clays
i. World map of distribution
(1) hemipelagic (terrigenous) sediment on the continental margins
(2) carbonate ooze on he bathymetric highs
(3) siliceous ooze beneath areas of strong upwelling
(a) eastern equatorial regions
(b) polar fronts
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(4) red clays in regions isolated from terrigenous input, at depths greater than the
CCD, and locales distant from oceanic upwelling
ii. Distribution across a bathymetric high, like an oceanic ridge
(1) Carbonate-siliceous ooze above the CCD
(2) Siliceous ooze near and below the CCD, provided input exceed dissolution.
(3) Red clay is the deepest facies found where dissolution of both carbonate and
biogenic silica exceed input rates.
iii. Pattern across the equator from gyre center to gyre center
(1) The depth of the CCD is deeper at the equator than in the gyre centers because of
enhanced input of carbonate by production due to equatorial upwelling
(2) Carbonate-siliceous ooze above the CCD
(3) Siliceous ooze near and below the CCD
(4) Red clay deepest
iv. Pattern down a continental margin
(1) to an abyssal plain
(a) neritic sediments on the shelf
(b) hemipelagic sediments on the slope and rise
(c) turbidites capped by Holocene pelagite or red clay on the abyssal plain
(2) to the abyssal hills
(a) neritic sediments on the shelf
(b) hemipelagic sediments on the slope and rise
(c) pelagic sediments on the abyssal hills (red clay or biogenic ooze depending on
the preservation conditions)
f. Lithostratigraphy - vertical succession of sediment facies
i. At a site in the Atlantic Ocean
(1) hydrothermal sediment admixed with carbonate ooze
(2) carbonate ooze at depth
(3) increasing terrigenous clastics up-section
(4) maybe turbidites at the top of the sequence (abyssal plain)
ii. At a site in the Pacific Ocean
(1) hydrothermal sediment admixed with carbonate ooze
(2) overlain by carbonate - siliceous ooze
(3) overlain by siliceous ooze
(4) red clay at the top of the section
g. Lithostratigraphy of a site on a moving plate
i. On an oceanic ridge
(1) hydrothermal sediment admixed with carbonate ooze
(2) overlain by carbonate - siliceous ooze
(3) overlain by siliceous ooze
(4) red clay at the top of the section
ii. A Pacific site that moves across the equator and approaches a deep sea trench
MAR581 - Geological Oceanography
Chapter 14 -p. 13-
The University of Southern Mississippi
Department of Marine Science
(1)
(2)
(3)
(4)
(5)
(6)
(7)
(8)
hydrothermal sediments above the basalt basement
overlain by carbonate siliceous ooze
overlain by carbonate ooze
overlain by red clay
overlain by carbonate siliceous ooze
overlain by carbonate ooze
overlain by carbonate siliceous ooze
red clay at the top of the section with increasing amounts of volcanic debris
MAR581 - Geological Oceanography
Chapter 14 -p. 14-