Chapter 3. Chapter 3. Sources and composition Sources and composition

of Marine Sedimentsof Marine Sediments

The sediment cycleThe sediment cycle Sources of sedimentSources of sediment Sediments and sea water compositionSediments and sea water composition Major sediment typesMajor sediment types

Lithogenous sedimentsLithogenous sedimentsBiogenous sedimentsBiogenous sedimentsNon-skeletal carbonatesNon-skeletal carbonatesHydrogenous sedimentsHydrogenous sediments

Sedimentation ratesSedimentation rates

Fig.3.1 Sources, transport, and destination of marine sediments

3.1 The Sediment Cycle

3.2 Sources of Sediment- 1. River Input

The dissolved and particulate load of riversThe dissolved and particulate load of rivers Particulate load; continental shelf & slope depositsParticulate load; continental shelf & slope deposits Dissolved load; precipitates (CaCODissolved load; precipitates (CaCO33 and opal, SiO and opal, SiO22

..nHnH22

O)O)

Deep sea sedimentation rate = 1~20mm/kyrDeep sea sedimentation rate = 1~20mm/kyr Slope sedimentation rate = up to 100mm/kyrSlope sedimentation rate = up to 100mm/kyr Taking the value of 100mm/kyr for 10% of the ocean, aTaking the value of 100mm/kyr for 10% of the ocean, a

nd a value of 5mm/kyr for the rest; the average is near 1nd a value of 5mm/kyr for the rest; the average is near 15 mm/kyr.5 mm/kyr.

1. River Input1. River Input The ocean floor covers more than twice the area of the laThe ocean floor covers more than twice the area of the la

nd.nd. Hence, the continents, if they are the ultimate source of aHence, the continents, if they are the ultimate source of a

ll sediment, must wear down at a rate of near 30 mm/kyr.ll sediment, must wear down at a rate of near 30 mm/kyr.

Another rough calculation may be based on an estimated Another rough calculation may be based on an estimated sediment supply from rivers of 12 kmsediment supply from rivers of 12 km33/yr./yr.

If we distribute this amount on the 362 million kmIf we distribute this amount on the 362 million km22 of se of sea floor, we get a sedimentation rate of about 30 mm/kyr, a floor, we get a sedimentation rate of about 30 mm/kyr, and a corresponding erosion rate of 60 mm/kyr for the cand a corresponding erosion rate of 60 mm/kyr for the continents.ontinents.

Mechanical weathering dominates in high latitudes.Mechanical weathering dominates in high latitudes. Chemical weathering (leaching) is favored by high Chemical weathering (leaching) is favored by high

rainfall and temperatures and dominates in tropical rainfall and temperatures and dominates in tropical areas.areas.

We live in a highly unusual period.We live in a highly unusual period. High mountain ranges and the powerful abrasive action High mountain ranges and the powerful abrasive action

of the continental ice masses have greatly increased of the continental ice masses have greatly increased mechanical erosion for the last several million years.mechanical erosion for the last several million years.

1. River Input1. River Input

Fig.3.2 Distribution of ice-rafted materials in the North Atlantic. {resent limits of drift ice (normal and extreme ) run from around Newfoundland toward Greenland and Iceland. During the last ice age, this limit went form New York straight across to Portugal. Triangles Surface samples; dashes dredge samples; circles core samples. [H. R. Kudrass, 1973, Meteor Forschungserg Reihe C 13:1]

3.2 Sources of Sediment – 2. Glacier Input

In high latitude, the immense In high latitude, the immense masses of outwash material masses of outwash material are brought to the shore.are brought to the shore.

Calving glaciers can Calving glaciers can transport both fine and very transport both fine and very coarse material far out to coarse material far out to sea.sea.

Around Antarctica this type Around Antarctica this type of transport reaches about of transport reaches about 40°S.40°S.

In the North Atlantic the In the North Atlantic the transport boundary roughly transport boundary roughly follows the present boundary follows the present boundary b/w very cold and temperate b/w very cold and temperate waters.waters.

At present about 20% of the At present about 20% of the sea floor receives at least sea floor receives at least some ice-transported some ice-transported sediments.sediments.

Fig.3.3 Abundance of haze from dust, over the Atlantic Ocean. Numbers are % of observations. [ G. O. S. Arrhenius, 1963, in M. N. Hill, Sea 3: 695]

3.2 Sources of Sediment – 3. Input from Wind

Wind can only move Wind can only move the fine material.the fine material.

The rate of dust fall The rate of dust fall from the air can best from the air can best be measured in be measured in snowfields and ice snowfields and ice cores.cores.

Even in the Antarctic and in Greenland, far from desert sources, the rate iEven in the Antarctic and in Greenland, far from desert sources, the rate is quite appreciable; 0.1~1 mm/kyr.s quite appreciable; 0.1~1 mm/kyr.

Exactly how much dust is falling is not known.Exactly how much dust is falling is not known. Some estimate suggest that much or most of the deep sea clay is derived frSome estimate suggest that much or most of the deep sea clay is derived fr

om wind input.om wind input. Such clay accumulates at 1 mm/kyr in the North Pacific and at 2.5 mm/kySuch clay accumulates at 1 mm/kyr in the North Pacific and at 2.5 mm/ky

r in the Atlantic.r in the Atlantic.

Fig.3.4 Distribution of volcanic ash produced by two large volcanic explosions in the Aegean Sea, Presumably of Santorini. The lower ash layer marks a prehistoric event (> 25000 yrs.). The upper layer is less than 5000 yrs old; the volcanic explosion creating it may be the one which brought catastrophe to the Minoan culture, sine 36000 year ago. [D. Ninkovich, B. C. Heezen, Nature London 213: 1968. Oceans, Prentice-Hall, New Jersey]

3.2 Sources of Sediment – 4. Volcanic Input

A substantial amount of A substantial amount of material is delivered by material is delivered by volcanoes, especially thvolcanoes, especially those associated with actiose associated with active oceanic margins.ve oceanic margins.

Volcanoes have a short Volcanoes have a short live, and single eruptiolive, and single eruptions are ns are flash-like eventsflash-like events..

Therefore, ash layers caTherefore, ash layers can be used for regional sn be used for regional stratigraphic purposestratigraphic purposes

TephrachronologyTephrachronology

백두산백두산

3.3 Sediments and Seawater Composition

3.3.1 Acid-Base Titration3.3.1 Acid-Base Titration Sea water is a solution of sodium chloride (NaCl).Sea water is a solution of sodium chloride (NaCl). Sodium and chloride make up 86% of the ions presenSodium and chloride make up 86% of the ions presen

t by weight.t by weight. Since the major cations form strong bases, but bicarbSince the major cations form strong bases, but bicarb

onate forms a weak acid, the ocean is slightly alkalinonate forms a weak acid, the ocean is slightly alkaline, with pH of near 8.e, with pH of near 8.

ClCl-- > Na > Na++ > SO > SO442-2- > Mg > Mg2+2+ > Ca > Ca2+2+> K> K++ > HCO > HCO33

--

Table 3.1 Comparison between seawater and river water

3.3 Sediments and Seawater Composition

The salty ocean may be understood as the prodThe salty ocean may be understood as the product of emission of acid gases from volcanoes uct of emission of acid gases from volcanoes (hydrochloric, sulfuric and carbonic acid) (hydrochloric, sulfuric and carbonic acid)

and the leaching of common silicate rocks whoand the leaching of common silicate rocks whose minerals have the form [MeSise minerals have the form [MeSiaaAlAlbbOOcc] ]

where Me stands for the metals, Na, K, Mg, anwhere Me stands for the metals, Na, K, Mg, and Ca, and the remainder makes insoluble silicad Ca, and the remainder makes insoluble silica-aluminum oxides, clay minerals.-aluminum oxides, clay minerals.

How stable was the composition of How stable was the composition of seawater through geologic time?seawater through geologic time?

Seawater salt in the ancient salt depositsSeawater salt in the ancient salt deposits Their composition indicates that sea salt did not vary Their composition indicates that sea salt did not vary

much over the last 600 million years.much over the last 600 million years. Paleontologic evidence certainly agrees with this.Paleontologic evidence certainly agrees with this. Already in the early Paleozoic there were organisms Already in the early Paleozoic there were organisms

whose closest modern relatives have rather narrow salwhose closest modern relatives have rather narrow salt tolerances; radiolarians, corals, brachiopos, cephalot tolerances; radiolarians, corals, brachiopos, cephalopods, echinoderms.pods, echinoderms.

On comparing the average composition of river water On comparing the average composition of river water with that of seawater, one notes drastic difference.with that of seawater, one notes drastic difference.

River water is a solution of calcium bicarbonate and sRiver water is a solution of calcium bicarbonate and silicic acid, with a small admixture of the familiar salts.ilicic acid, with a small admixture of the familiar salts.

The river influx is irrelevant to the make-up of sea salThe river influx is irrelevant to the make-up of sea salt.t.

But But steady-state conditionsteady-state condition

3.3.2 Interstitial Water and Diagenesis3.3.2 Interstitial Water and Diagenesis

Fine-grained sediments; porosities of 70~90%, while Fine-grained sediments; porosities of 70~90%, while sands have around 50%.sands have around 50%.

Chemical reactions; diagenesisChemical reactions; diagenesis Redox reactionsRedox reactions These reactions are the more intense the more organic These reactions are the more intense the more organic

carbon is present.carbon is present. Stripping oxygen from dissolved nitrate and from soliStripping oxygen from dissolved nitrate and from soli

d iron oxides and hydroxidesd iron oxides and hydroxides Sufate reductionSufate reduction MethanogenesisMethanogenesis There reactions are all mediated by bacteria.There reactions are all mediated by bacteria.

Fig.3.5 Mud volcano. Side scan record from the Black Sea bottom. ( Side scan principle see Fig.4.15). [Courtesy Dr. Glunow, Moscow, UNESCO-IMS-Newsletter 61, Paris]

In the process, gases are produced (carbon dioxide, ammonia, hydIn the process, gases are produced (carbon dioxide, ammonia, hydrogen sulfide), as well as iron sulfide (pyrite).rogen sulfide), as well as iron sulfide (pyrite).

Methane can react with water (low temperature and high pressure) Methane can react with water (low temperature and high pressure) to make to make clathratesclathrates..

The massive escape of gases from organic-rich muds can produce The massive escape of gases from organic-rich muds can produce mud volcanoesmud volcanoes..

3.3.3 Residence Time3.3.3 Residence Time

For steady-state conditions, output must equal For steady-state conditions, output must equal input.input.

The seawater has to rid itself of all new salt The seawater has to rid itself of all new salt coming in, in the same proportions as they are coming in, in the same proportions as they are added.added.

SinksSinks

Calcium carbonate; calcareous skeletons built by orgaCalcium carbonate; calcareous skeletons built by organismsnisms

Silica; opaline skeletonsSilica; opaline skeletons Metals leave the ocean as newly formed minerals sucMetals leave the ocean as newly formed minerals suc

h as authigenic clay, oxides, and sulfides and as zeolith as authigenic clay, oxides, and sulfides and as zeolites, also by hydrothermal alteration at the ridge crestes, also by hydrothermal alteration at the ridge crest

Sulfur; heavy metal sulfides in anaerobic sedimentsSulfur; heavy metal sulfides in anaerobic sediments Salt; pore waters in the sedimentsSalt; pore waters in the sediments

Residence timeResidence time

The average time a seawater component remains in The average time a seawater component remains in the water, before going out as sedimentthe water, before going out as sediment

T = A/rT = A/r Where A is the amount present, r is the inputWhere A is the amount present, r is the input

Salt age for the ocean, under the assumption that the Salt age for the ocean, under the assumption that the ocean started out fresh and retained all sodium since ocean started out fresh and retained all sodium since … near 100 million years!… near 100 million years!

Fig.3.6 a, b. Familiar examples of two major types of beach sand a medium sand, lithogenous, La Jolla b coarse sand, biogenous, Hawaii. (Photos: W.H.B.)

3.4 Major Sediment Types

Lithogenous, Hydrogenous, Biogenous Lithogenous, Hydrogenous, Biogenous

Fig.3.7 Heavy mineral provinces of the Gulf of Mexico, based on typical mineral associations. East Gulf; Ⅰ ⅡMississippi; Central Texas; Rio Grande; Mexico. carbonate particles are dominant off Mexico and YucatⅢ Ⅳ Ⅴan. The heavy mineral patterns contain clues about the sources and transport paths of terrigenous sediments. [D. K. Davies, W, R. Moore, 1970, J Sediment Petrol 40: 339]

3.5 Lithogenous Sediments

3.6 Biogenous Sediments

Fig.3.8 Recent hemipelagic sediment  from Continental Rise off NW Africa (Cape Verde Rise). SEM photos, bar 20μm. Left Fine-silt fraction (2-6μm) predominantly composed of coccoliths (c) and of some detrital mica (m) and quartz (q); Right coarse silt fraction, mainly detrital grains (q quartz) and foraminifera tests and fragments (f). [Photo courtesy D. Futterer]

Fig.3.9. Calcareous oolites, produced within tidal zone by algal activity. Upper Air photo of oolite sand bars, Bahama Banks. Note tidal channels.[Photo courtesy D. L. Eicher]. Lower SEM photos of ooids, scale bar 5μm; left slightly etched section. Three secondarily filled borings (b) intersect the concentric laminae of primary oolite coating; right close-up of oolite laminae, showing acicular aragonite needles. [Photos courtesy D. Futterer]

3.7 Nonskeletal Carbonates

Fig.3.10 Present-day dolomite formation. Lagoon on the southern coast of the Persian/Arabian Gulf (a), floor covered with calcareous mud. Intertidal zone (b) and  algal mats of uppermost littoral (c)  rim the lagoon. Intermittently flooded evaporite flats (d, sabkhas) follow landward [After L. V, Illing et al 1965, Soc Econ Paleontol Mineral Spec Publ 13:89, Simplified]

Hydrogenous Sediment - Marine evaporitesHydrogenous Sediment - Marine evaporites

Form on evaporation of seawaterForm on evaporation of seawater Where?Where?1)1) Coastal lagoonCoastal lagoon2)2) Salt seas on the shelvesSalt seas on the shelves3)3) Early rift oceans in the deep seaEarly rift oceans in the deep sea

How much salt can be produced by evaporating a How much salt can be produced by evaporating a 1000m-high column of seawater?1000m-high column of seawater?

Salt constitutes 3.5% of the weight of the column, its Salt constitutes 3.5% of the weight of the column, its density is about 2.5 times that of water.density is about 2.5 times that of water.

About 14m of saltAbout 14m of salt

Marine EvaporitesMarine Evaporites The least soluble salts precipitates first: calcium The least soluble salts precipitates first: calcium

carbonate (aragonite) and calcium sulphate (gypcarbonate (aragonite) and calcium sulphate (gypsum)sum)

To precipitate halite, the brine needs to be concTo precipitate halite, the brine needs to be concentrated about 10 foldentrated about 10 fold

Many evaporites only contain carbonate and gyMany evaporites only contain carbonate and gypsum (or anhydrite), others have thick deposits psum (or anhydrite), others have thick deposits of halite or of the valuable (and very soluble) poof halite or of the valuable (and very soluble) potassium salts.tassium salts.

Fig.3.11 Possible models for marine evaporite formation. a Serial fractionation in very shallow and extended basins. Saturation of different salts is reached in a series ocean to land. Terrigenous particles may be supplied from land. Recent example: Adshi-darja Lagoon attached to the Caspian Sea by Kara Bogaz Inlet (chemical conditions there are not fully comparable with open sea). b Serial fractionation and differential preservation in deeper basins divided by sills. Saturation of differents salt is reached in a  series shallow to deep water. Derail Only gypsum is precipitated near the sill. Halite saturation is not reached, because brine sinks down to the basin escaping further evaporation. Sill depths can be considerably reduced by carbonate and /or gypsum precipitation. No Recent example known. [ G. Richter-Bernburg, 1955, Dtsch Geol Ges 105 [4]: 59] 

3.8 Hydrogenous Sediments

Fig. 3.12 Model of concentric serial fractionation in the uppermost Miocene underneath the Western Mediterranean. G Gibraltar Region, where the connection with the Atlantic was closed for half a million years; M Mallorca; C Corsica; S Sardinia [K. J. Hsu et al., 1973 in Ryan, W. B. F. et al. eds. Initial Repts. DSDP 13, 695, Washington D. C]

Differential preservation and serial fractionation are the key processes in controlling the chemistry of salt deposits.

PhosphoritesPhosphorites Phosphorites deserve special attention for the rePhosphorites deserve special attention for the re

ason of this tie-in to ocean fertility, but also becason of this tie-in to ocean fertility, but also because of their economic valueause of their economic value

Marine phosphorites vary in compositionMarine phosphorites vary in composition A general formula is CaA general formula is Ca1010(PO(PO44,CO,CO33))66FF2-32-3, with in, with in

creases in carbonates going parallel to increase icreases in carbonates going parallel to increase in fluoriden fluoride

PhosphoritesPhosphorites

Modern phosphorites typically occur in areas of high pModern phosphorites typically occur in areas of high productivity.roductivity.

Occurs as nodules or crusts up to head size and as irregOccurs as nodules or crusts up to head size and as irregularly shaped cakesularly shaped cakes

In the geologic record, they occur as replacement of prIn the geologic record, they occur as replacement of previously deposited carbonates, or as mineralization of eviously deposited carbonates, or as mineralization of pre-existing organic matterpre-existing organic matter

The common depth of deposition is on the shelf and upThe common depth of deposition is on the shelf and upper slope.per slope.

PhosphoritesPhosphorites The association of geologically young phosphorites deposits with The association of geologically young phosphorites deposits with

present-day regions of upwelling suggests that the source of the phpresent-day regions of upwelling suggests that the source of the phosphorous is organic matter.osphorous is organic matter.

Apparently the algae growing in these regions, in the surface waterApparently the algae growing in these regions, in the surface waters, extract the phosphorous from the water, and crustacesn and fish s, extract the phosphorous from the water, and crustacesn and fish concentrate it further in their bodies and excrement.concentrate it further in their bodies and excrement.

During decomposition of organic debris, much phosphate is releasDuring decomposition of organic debris, much phosphate is released to the interstitial water (and also to seawater)ed to the interstitial water (and also to seawater)

Thus, interstitial waters may become saturated with the phophate Thus, interstitial waters may become saturated with the phophate mineral apatite.mineral apatite.

Precipitation of apatite replacement of pre-existing carbonate minePrecipitation of apatite replacement of pre-existing carbonate mineral, and impregnation of sediment can then proceed.ral, and impregnation of sediment can then proceed.

Iron CompoundsIron Compounds Abundant in both oceanic margin sediments and in the Abundant in both oceanic margin sediments and in the

deep ea since iron is one of the most abundant elements deep ea since iron is one of the most abundant elements on Earthon Earth

On the slopes, the high supply of organic matter On the slopes, the high supply of organic matter commonly leads to oxygen deficiency, and to sulfate commonly leads to oxygen deficiency, and to sulfate reduction by bacteria, in the uppermost sediment layers.reduction by bacteria, in the uppermost sediment layers.

This process results in This process results in HH22SS formation, and in the formation, and in the precipitation of iron sulfide (pyrite).precipitation of iron sulfide (pyrite).

In the deep sea, oxygen is generally plentiful, and In the deep sea, oxygen is generally plentiful, and essentially all iron occurs in its oxidized form, as iron-essentially all iron occurs in its oxidized form, as iron-oxide/hydroxide (goethite)oxide/hydroxide (goethite)

Iron CompoundsIron Compounds An iron-mineral which has been much studies is glauconiteAn iron-mineral which has been much studies is glauconite It is greenish silicate common in shallow marine areas.It is greenish silicate common in shallow marine areas. Chemically it is a poorly crystallized mica, rich in potassium Chemically it is a poorly crystallized mica, rich in potassium

(7-8%) and in iron (20-25%)(7-8%) and in iron (20-25%) Apparently the association with decaying organic matter (fecaApparently the association with decaying organic matter (feca

l pellets, interior of shells) is a necessary condition of growth: l pellets, interior of shells) is a necessary condition of growth: part of the iron in glauconite is reduced iron.part of the iron in glauconite is reduced iron.

A high concentration in interstitial waters (at conditions interA high concentration in interstitial waters (at conditions intermediate between reduction of iron oxide and precipitation of smediate between reduction of iron oxide and precipitation of sulfide) appears to be favorable for glauconite formation, as is ulfide) appears to be favorable for glauconite formation, as is the presence of the right kind of clay to convert into the glaucthe presence of the right kind of clay to convert into the glauconite mica.onite mica.

Fig.3.13 Rates of vertical crustal motion, of denudation, and of sedimentation rates. Scale in mm/1000 years. also called "Bubnoffs" (B), of m/million years. Postglacial sea level rise for comparison: 100 m in 5000 yrs. Note interaction with recently deglaciated land (arrow left) and with coral growth rates (arrows right).

3.9 Sedimentation Rates High rates at the edges of the coHigh rates at the edges of the continents, especially in estuaries antinents, especially in estuaries and marginal basins with river infnd marginal basins with river influxlux

The lower rates in abyssal regioThe lower rates in abyssal regionsns

C. slopes = 40-200mm/kyrC. slopes = 40-200mm/kyr Deep sea = 1-20 mm/kyrDeep sea = 1-20 mm/kyr Coral reef = 10m/kyrCoral reef = 10m/kyr

Fig.3.14 Annual layers (varves) in the sediment of a bay in the Adriatic Sea (Mljet Island). The photo shows light and dark laminae. One light-dark pair corresponds to one year. The lower boundary of light layers are generally sharp; they are due to  precipitation of carbonate by phytoplanktom, which bloom in early summer (record to the right) as temperature rises. In fall and winter, rains bring terrigenous matter which- together with organic detritus- provides for dark colors. the interpretation of the varves is a complicated matter: recent studies use statistical procedures to reconstruct climatic conditions in detail.(photo E. S.)