Middleton G.V. (Ed.) Encyclopedia of Sediments and Sedimentary Rocks

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TSUNAMI DEPOSITS

755

Ford, T,D., and Pedley, H,M,, 1996, A review of tufa and travertine

deposits ofthe World. Earth Science Reviews, 41; 117-175,

Freytet, P,, and Plet, A,, t996. Modern freshwater microbial

carbonates: the Plwnnidium stromatolites (tufa-travertine) of

southeastern Burgundy (Paris Basin, France), Facies, 34:

219-238,

Golubie, S., t969. Cyclic and noncyclic mechanisms in the formation

of travertine, Verhandlungen der Internationalen

Vereinigung

fuer

Theoretische undAngewandte Limnologie, 17:

956-961,

Guo,

L,, and Riding, R,, t998. Plot-spring travertine facies and

sequences. Late Pleistocene, Rapolano Terme, Italy. Sedimentol-

ogy, 45: 163-180,

Henning, G,J., Grun, R., and Brunnacker, K,, 1983, Speleothems

Travertines and Paleoctimates, Quaternary

Re.search,

20: t-29,

Lorah, M,M., and Herman, J,S., 1988. The chemical evolution of a

travertine depositing stream: geochemical processes and mass

transfer reactions.

Water

Resources

Research.

U\ t54t-1552,

Ordonez, S., Gonzalez-Martin, J.-A,, and Garcia del Cura, M.A.,

1983,

Recent and tertiary fluviat carbonates in central Spain, tn

Collinson, J.D., and Lewin, J. (eds,). Ancient and Modern Fluvial

Systems, tnternational Association of Sedimentologists, spec, publ.

Special Publication, 6, pp. 485-497,

Pedley, tH.M,, 1990. Classification and environmental models of cool

freshwater tufas. Sedimentary Geology, 68: t43-154,

Pedley, H.M., t994, Prokaryote-microphyte biofilms and tufas: a

sedimentological perspective. Kaupia. Darmstadter Beitrage zur

Naturgesehichte, 4: 45-60,

Pedtey, tl,M,, Hill, t., and Denton, P., 2000, Three dimensional

modelling of a Holocene tufa system in the Lathkill valley, north

Derbyshire, using ground penetrating radar, Sedimentoiogy, 47:

721-735.

Pentecost, A,, 1995. The Quaternary travertine deposits of Europe and

Asia Minor, Quaternary Science Reviews, 14: i005-1028.

Pentecost, A,, and Viles, H,A,, 1994. A review and reassessment of

travertine classification, Geographie Physique et Quaternaire, 48:

305-314,

Preece, R,C., t991. Radiocarbon-dated molluscan successions from

the Holocene of central Spain, Journal of Biogeography, 18: 409-

426.

Srdoc, D,, Horvatincic, N,, Obelic, B,, Krajcar-Bronic, L, and

O'Malley, P,, 1986, The effects of contamination of calca-

reous sediments on their radiocarbon ages. Radiocarbon, 25:

510-514.

Taylor, D.M,, Pedley, H.M,, Davies, P., and Wright, M,W., 1998,

Pollen and mollusc records for environmental change in central

Spain during the mid- and late Holocene, The

Holocene,

8 (5): 605-

612,

Thompson, J,B,, 2000, Microbial whitings. In Riding, R.E., and

Awramik, S.M. (eds.), Microhial Sediments. Springer-Verlag,

pp.

250-260,

Vadour, J., 1994, Evolution Holocene des vallees dans le Midi

Mediteranee Francais, Geographie physique et Quaternaire, 48(3):

315-326.

Violante, C, Ferreri, V,, D'Argenio, B,, and Golubie, S,, 1994,

Quaternary travertines at Rochetta a Volturno (Isernia, Central

Italy):

facies analysis and sedimentary model of an organogenic

carbonate system, tn Fietdtrip Guidebook Al. International Asso-

ciation of Sedimentolgists Ischia 94, 15th Regional Meeting, Italy,

pp,

3-23.

Waring, G.A., 1965. Thermal springs ofthe United States and other

countries of the World, U.S. Geological Survey Professional Paper,

Volume 492, 383pp,

Cross-references

Algal and Bacterial Carbonate Sediments

Bacteria in Sediments

Micritization

Speleothems

Stromatolites

TSUNAMI DEPOSITS

A tsunami deposit is a sedimentary layer deposited in low-lying

coast regions by a tsunami generated by some form of seafloor

deformation, such as earthquakes and submarine landslides,

or by a subaerial event that significantly disturbs the water

surface, such as a landslide or glacier calving event. Tsunami

deposits most commonly form sheets of well-sorted sand that

extend inland as much as several kilometers across coastal

lowlands. Sheets of coral gravel or pebbles have also been

reported. The sand sheets typically contain marine fossils, lack

bedform sedimentary structures, and tine both upward and

landward, A tsunami may produce a single upward-fining bed,

or its waves may produce a vertical series of such beds.

Tsunamis may also deposit boulders. Modern tsunamis are

known to have moved boulders as much as 30 m in diameter

(Simpkin and Fiske, 1983), Diamicts and imbricated boulder

fields have also been ascribed to tsunami, but they so far lack

modern analogs.

Although early scientific papers about tsunamis mention

their deposits (Platania, 1909; Billings, 1915), tsunami sedi-

mentology probably begins with a paper describing onshore

erosion and deposition by the 1960 Chile tsunami on the

northeastern coast of Japan (Konno, 1961), The 1960 locally

deposited a sheet of sand up to 20 cm thick blanketing coastal

lowlands. The sand is described as structureless except for

vertical grading, which formed one or more cycles within the

bed (Figure T17), The sand filled low places, such as furrows in

plowed fields, but it also thinned landward in some places,

Konno interpreted the sand as depositing from suspended

load.

Tsunamis since 1960 have also produced sand "sheets" on

coastal lowlands (Dawson etal., 1996; Minoura etal., 1997;

Goldsmith et al., 1999; Caminade et al., 2000), In general,

"modern" tsunami deposits have consisted of well-sorted sand

sheets up to about

cm thick extending inland up to about

300 m inland. The sand source is generally inferred to have

been either at the shoreline or just offshore, and the presence

of erosional features along the shoreline tends to support the

idea that sand is mined from the coastline and moved inland.

These later surveys have shown that individual fining upward

"pulses" of sedimentation can be traced in the deposit,

possibly correlated to individual waves in the tsunami train,

and have established the concept of overall landward fining in

the direction of wave motion. One result of these recent

surveys is a set of criteria for identifying ancient tsunami

deposits (Dawson and Shi, 2000),

Criteria for identifying tsunami deposits include both

sediment composition and physical properties, tn addition to

deposit fining landward and upward, researchers have noted

that modern tsunami deposits appear to be well-sorted to

moderately well sorted and positively skewed (Dawson etal.,

1996),

Local overwash fans caused by tsunami typically show

foreset bedding, but sand sheets have not yielded sedimentary

structures other than normal grading. Tsunami deposits

contain marine microfossils (Hemphill-Haley, 1996) and often

retain evidence of landward movement in the form of bent-

over plant debris at the base of the deposit (Atwater and

Hemphill-Haley, 1997), Like their modern counterparts,

ancient tsunami deposits show some subset of these criteria.

756

TSUNAMI DEPOSITS

HIGHEST WATER LEVEL OF TSUNAMI WAVES

^ MEAN SEA LEVEL

-0

-10

-20

-30

10 20 30 40 5D

METERS

HEAVY LINE INDICATES DEPOSITION AREA

SILT AND SANDY SILT

FINE-

GRAINED SAND

SOIL

Figure T17 Deposil from lhe 1960 Chile tsunnmi ne^r Miytiko, lapan, showinj; four ^r^idecl units (Konno ct a/.,

19611,

and are genertilly closely iissociatcd with a geologically inferred

causal mechanism (e,g.. earthquake evidence such as coastal

subsidence for sitbduction zone related tsunamis) (Atwater.

1987).

As early as 1984, onshore deposits ascribed to tstinami have

been described in sequences of coastal sediments, and have

often served as the tirst warning of the tstinami hazard faced

by coastal cotiimuniiies, Sandy paleotsitnatiii deposits have

been deseribed frotn Scotland (Dawson

i'lal..

1988). Norway

(Bondevik vt at.. 1997). Kamchatka. Japan {Minoura and

Nakaya. 1991). New Zealand (Goft" cl at.. 2000). the

Mediterranean (Dominey-Howes etut.. 1999), and the Pacific

coast of North America (Clague clot.. 2000), Most are sand

sheets in sequences of peaty or muddy deposits of coastal

lowlands.

As with sandy deposits, onshoie movement of large

boulders has been noted in many early descriptions of tsunatnis

(Makino. 1980; Simpkin and Fiske, 1983; Yamashita. 1997).

Modern tsunamis have also rnoved boulders (MeSaveney etat..

2000).

and (Yeh etat.. 1993) describe boulders frotn the 1992

Flores tsunami within sandy deposits. These deposits differ.

however, from poorly sorted diatnietons ascribed to tsitnami

{Bryant, 2001) in thaf the Flores boulders lie as individual

large blocks protruding IVotn an extensive, thin sand sheet

rather Uian incorporated into the deposit. Ancient tsunamis

have also been inferred based solely

ov\

the presence ofonshore

boulder deposits {Bryant ct at., 1992; Moore et at.. 1994;

Hearty, 1997). but these ideas remain controversial because

boulders can be transported inland by coastal processes other

than tsunatni. such as storms,

Andrew Moore

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Dawson. A.G,. Long. D,. and Smith. D.F,. 1988, The Sloregga slides:

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TURBIDITES

7,57

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for an earthquake and tsunami ahoul 3100-3400 years ago. and

other cauistrophic saltwater inundalions reeorded in a coastal

lagoon. New Zealand, \farinc Geology. 170; 231-24*).

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Papua New Guinea, Butietin of the Sew '/.calami Society for Earlh-

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\^)'-)l.

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liiterglaciation on North Eleiithera. Bahamas, Quuicrnarv Rc-

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lo ihc Insiiiule of

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ami

Paleontology Tohnku

('ni-

ver.'iity.

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So Mciwa Olsunami jihc

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naniiinlheYaeyanta

f.slanilsj.

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Seqttcnce of sedimentation processes eaused by the 1992 Elores

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intcr-tidal lacustrine and marsh deposits: some examples fiom

noriheasi Japan, Journal

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Moore. J,G,. Bryan. W,B,. and ' Ludwig. K.,R.. 1994, Chaotic

deposition by a iiiant wave. Moiokai. Hawaii,

Gt'oloi-ical

Society

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Platania, (i.. h)(W. II maiemoto dello Stretto di Messina del 28

Dicembre 1908, Bottciiino detta Socicla Sistiiologica Indiana. 13:

369 458,

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1993.

The Elores Island tsunamis,

Fo.s.'tran.sadioti.s.

Antcri( an Gco-

phyiscat

Union.

74: 371-373,

Cross-reference

Storm Depo^its

They are amongst lhe commonest of sedimentary deposits, and

lurbidite depositional systems siteh us submarine fans and

basin plaitis form the largest individual seditnentary accittnula-

tions on the Earth, Thiek sequences ol" synorogenic turbidite.s

{fty.\cti)

are comtnon in the ancient record.

Turbidity cttrrents were lirst so named in

I9.'^8.

allhougli lhe

existence of density ttnderllous in lakes had been recognized

earlier (see review by Walker. 1973). Their potential impor-

tance as agents of seditnent transport into deep water was not

fully reeognized till Kuenen and Migliorini (1950) (see Sedi-

i}U'ntol(/^l.sis:

Kiicncn) combined e,\peritnental work with ftcld

observations to suggest that tttrbidity ctitfcnts were the cause

of graded sandstone beds deposited in deep water. The natne

turbidite for the deposits

i)['

turbidity currents eame into use

abotit 1960, and Bouma's (I9fi2) analysis of sandstone

turbidites shot"tly thereafter generated the tirst and. for sotne

time,

the sole depositional model. The last three decades of

the 20ih Century saw an exponential increase in lurbidite

research. This was driven in part by new techniques of

investigation in the deep sea. including the deveiopment of

side-scan sonar, and drilling by the Deep Sea Drilling Project

and its successor., the Ocean Drilling Program, However this

increase was also due to the rising importance of turbidites as

hydrocarbon reservoirs. Turbidites eonlain some ofthe worlds

largest and tnost prolific reservoirs outside of lhe Middle East.

and Cenozoic turbidite systetns of the conlinental margins are

a major target for hydrocarbon exploration.

Turbidity currents tnove by virtue of gravity acting upon the

density excess due to the ptesence of sttspended seditnent. and

flow down-slope, or spread by collapse over low-gradient basin

floors. Coneentrations o\' suspended sediment range from a

few parts per thousand tip to 10 percent or more, though the

upper litnit for what can truly be regarded as a turbidity

current is a matter of debate. Deposition of sedimeni from the

current occurs when fluid turbulence decays, generally as a

result of deceleration of the current. Although turbidily

currents tend to flow toward gravity base (i,e.. the lowest

point on the transport path), deposition especially of coarser

grained seditnent mav also occur on the slope, Turbidite

deposits thus occur on submarine slopes (see StopcScdiincni.s).

in canyons, slope channels, submarine fans (see Sutinntrine

FansamtCtunuH'ts). slope aprons and ramps, and basin plains.

They also occur as fans and bitsin plain deposits in lakes and

artifieial reservoirs.

TURBIDITES

Turbidites are the deposits of turbidity currents, which arc

gravity-driven turbid sitspensions of fluid (ttsually water) and

scdittietit. They fortn a class of subaqueous seditnent gravity

flow (see Crayily-Driyeii

Ma.ss

Ftows) in which the suspended

seditnent is stipported during tratispori largely or wholly by

fluid turbulence. Turbidites range in grain-size from mud to

giiivel. and may be of any composition- siliciclasiic, carbo-

tiate,

or even sulfide near deep-sea hydrothertnal vents,

Turbidite beds range in thickness from millitneters to tens of

melers. and individual events ean, in extreme cases, involve the

resediinentation of hundreds of cubic kilometers of sediment.

Initiation

lurbidity curtents are commonly initiated by the failure of

unstable tnateriat on subaqueous slopes, the faiiure being

triggered by earthquakes, pore fluid pressure imbalance,

decotnposition of clathrate

(q.v.).

or simply by over-steepening

of the slope by deposition (Normark ct at.. 1991: Rothwell

ct at.. !99f^). In these eircumstanccs turbidity currents tnay

arise by the enlrainment of waler into flows that were initially

more viscous and concentrated (such as slumps and debris

flows, q.v.) that were generated high on the slope or within a

submarine canyon. Such currents may deposit sediment o\er

the course of hours. However, sotne turbidity currents tnay be

generated by highly seditnent-eharged river outflow where the

concentration of suspended material is sufficiently high to

render the river effluent denser than the water into which it

Hows,

and where the river discharges directly onto a slope

(Mttlder and Syvitskl. 1995), Such hyperpycnal flows are

758

BOUMA (1962) DtVISIONS

E Laminated to

homogeneous mud

D Uppei mud/Bill laminae

C Ripples, climbing ripples,

wavy or convolute

laminae

B Plane laminae

A Structureless or graded

sand to granule

INTERPRETATION

Deposit ion trom low-dans ity tall

ot turbidity current 1

settlmg ot pelagic o'

hernipelagic particles

Shear sorllna o( grams 8 IIOCS

Lower part ot lower flow

regime of Simons »i •'.

(1965)

Upper flow regime plane bed

Rapid depostlion wItti no

traction transport,

possible quick (liquetied) bed

Figure T18 The Bouma sequence of sedimentary structures (ond its

interprets lion) formed by lurbidity currents of low to moderate density

(after Pickering el al., 1989, reproduced with permission).

tiiore comtnonly achieved in fresh walcr. but may occur in

the marine realm its frequently as annually in association

with "dirty" rivers, or less frequently in assoeiation with

catastrophic events in the subaerial realm such as major floods,

landslides or glacial lake outbreaks (e.g., ZulTa ctal., 2000).

On their passage down submarine canyons and channels,

turbidity currents may erode substantial amounts of sediment

from the seatloor. increasing their momentum and erosive

power in a positive feedback loop known as autosuspension

(t/.v.) or ignition (Bagnold. 1962; Fnikushima ct ctf. 1985).

In this way. coarse sediment introduced into canyons between

turbidily current events is flushed out, significantly increasing

the volume and altering the grain-size mix of the resulting

eiirrent (e.g., Hughes Clarke

eiaf.

1990).

Depositional models

Turbidites commonly show graded bedding

((/.

v.)

and a

sequence of sedimentary structures indicative of waning flow

during passage of the turbidity current, and progressively

declining bed shear stress during deposition of the bed. The

rather common occurrence of these struetures in a particular

order led Bouma (1962) lo propose an idealized vertical

sequence for graded sand-to-niud turbidites (Figure TIS) that

remains the standard for comparison in normally-graded

sandy turbidites. These divisions have been interpreted in

terms of the hydraulic regime that produced them (Figure T18;

Walker, 1973) and reflect the longitudinal structure oi the

current (Allen, 1991). The lowest part of the bed (often

overlying a basal erosion surface) commonly consists of

structureless graded sandstone—Bouma's Ty division. This is

interpreted as the result of deposition from suspension so

rapidly as to inhibit movement of material in traction; this

may occur via a tratisient liquefied bed (Middleton, 1967) or

zone of hindered scaling

Iq.y.).

This precludes the formation

of traction-generated structures (Allen. 1991, Knellcr and

Branney. 1995). The Tb division consists of a parallel-

laminated interval (see Plane and Parallel Lamination)

indicative of an upper stage plane bed. indieating slower

deposition rates and an extended period of traction. The

ripple-laminated T^. division (see Ripples) commonly shows

upward-increasing rates of climb, and by inlerence increasing

rates of deposition. Convolute lamination is common but by

Figure T19 The ide-ilized sequence of sedimentary structures formed

by turbidity currents of high densily lafter Lowe. 1982. reproduced

wilh permissionl.

no means universal within the T^. division. The T^, division

consists oi parallel laminated silt or hydraulically equivalent

flocculated clay formed under the weakest of eurrents, while

the T^ division represents sedimentation of mud from

suspension in the absence (or virtual absence) ofa curt"ent.

Complete Bouma sequences are rather uncoEiimon. Partial

sequences In which lower divisions may be missing ('"base-

absent") are widespread, especially in the distal parts oi

turbidite systems, or in overbank settings where the finer-

grained upper parts of turbidity currents have spilled out of

channels (see Submarine Fans and Channels). Divisions within

the sequence may also be absent or poorly developed (e.g.,

T.,ht.^.), sometimes with a sharp grain-size break at the level of

the missing division.

The Bouma sequence describes some of the features

associated with deposits of currents oi low to moderate

density. An analogous model for the deposits of high density

turbidity currents was proposed by (Lowe, 1982) (Figure TI9).

A louermost S| division is dominated by traction of coarse-

grained material. This is overlain by an S^ division dominated

by inverse-graded layers, interpreted by Lowe as the deposits

ofa succession of "frozen"" traction carpets: subtle inverse-lo-

normally graded layers corresponding to this division may

TURRIDITES

759

rcprcscni deposiiion during ihe passage of large eddies

(Hiscott. 1994: KncIIcr (7 (//.. 1999). Corresponding Rl and

R2 interviils arc dincrcntiLitcd in gr<ivelly turbidites. The

ovLTlying S-, division (more or less corresponding to an

e.\p;nidcd T., division) consists of sand that is structureless or

dominated by fiuid escape structures

(i/.

r.). The ensuing T,

division Is dominated by traction and in part this corresponds

to Bouma's Th and/or

T^.

divisions, but may also include cross-

siriitilied sands, sometimes well-sorted, that reflect partial

bypassing of the How (Mutti. 1992). As with the Bouma

sequence, the model for high-density turbidity current deposits

is ideali/ed. Basal divisions may be absent, and the deposit

may include grain-size breaks, especially common above or

below intervals with cross-stratification

((/.

v.).

Comparable models for fine grained turbidites have been

developed by. amongst others. Piper (1978) and Stow and

Shanmugam (19S(1). Facies ciassiJications of turbidites attest to

the wide di\ersity of depositionai facies (Ghibaudo. 1992;

Mutti. 1992: Pickering ct al.. 1989). most of which do not

conlbrm to the idealized models, and reflecl the range of

variables thai affect deposition (Kneller, 1995).

Other depositional and post-depositional features

The base of coarse-grained uirbidites commonly reveals

evidence of erosion. This may take the form o'i casts of

erosional strucltires such as flutes (see Scour. Scour Murks) ov

tool marks ((/.v.) formed in fine grained substrate (eommonly

ihe muddy lop o\' ihe underlying lurbidite) during passage

the frontal, iiondepositional parts of the How (Dzulynski

and Sanders. 1959). These form good paleocurrent indicators

(see Paleocurrent Analy.si.s). Such structures often contain

grains that are significantly coarser than those in Ihe remainder

of the bed. suggesting that the head of the current carries the

coarsest grains. Trace fossils preserved on the sole ol' ihe bed

also bear u ilness to ihis erosion. Where erosion has completely

removed ihe muddy lop of an tinderlying graded sand-to-mud

bed. the sandy portions of stiecesslve beds become amalga-

maicd. Where repealed this can produce composite "beds" o\'

sand many meters thick in which the amalgamation surfaces

may be hard to discern. Such amalgamated beds are common

in ihick-bedded sandy and gravelly lurbidite sequenees such as

those found in submarine canyons and channels.

Bases of turbidite sandstones cotnmonly show load struc-

tures

((/.!.).

often associated with liquefaction structures (see

Uquclaciioii and Fluidizatioii) in the underlying and/or over-

lying bed. The load easts often amplify pre-existing perturb-

ations of the bed. such as llute easts. Dewatering structures

(eommonly developed in Si divisions) may be arranged in a

vertical sequence trom consolidation laminae (wavy and/or

anastomosing) near the base, through dish structures (q.w) to

pipes or sheets, which in some instances may be inclined down-

current due to shear wiihin the dewatering sediment mass.

Liquefaclion of the deposit can result in the creation of sand

volcanoes on the tops

o\~

beds (where liquefaction of the bed

occurred at the surface) or injection of clastic dykes and sills

(c/.

V.)

into surrounding sediments (Nicholls. 1995). upward,

downward or sideways from the parent bed. Another common

feature of the deposits of presumed moderate to high

concentration turbidity currents is the presence o\' shale clasls.

some of which may have experienced considerable transport

after incorporatit)n into the llou' during initiation or b\

erosion of the bed. while others tnay be incorporated during

deposition via a highly concentrated (perhaps liquefieJ)

depositionai layer that may behave as a transient debris flow

(Stow and Johansson. 2000).

Some turbidity currents e.\perience reflection from basin-

bounding surfaces and intrabasinal topography, resulting in

distinctive current changes within the bed. commonly asso-

ciated with small reversals in gradinii (Pickerinc and Hiscott.

1985:

McCaffrey and Kneller. 2001).^

Current controversies

Considerable debate exists about what constitutes a turbidity

current, and thus what may or may not correctly be interpreted

as a turbidile (Shanmugam. 2000). Some authors (e.g..

Middleton and Hampton. 1973; Mulder and Alexander,

2001) restrict their definition of turbidity currents to flows in

which the grains are supported almost exclusively by fluid

turbulenee, whereas others (e.g.. Lowe. 1982) take a broader

view. It is useful to recall that the root of the term turbidity

current is the word turbid (i.e.. opaque with sediment) as

distinet from turbulent (i.e.. disturbed by eddies). Much

uncertainty arises tVom the lack of direct observations from

large natural currents, and from the difliculty in producing in

the laboratory nondepositional sand-bearing currents of even

moderate density. This renders (he debate largely speculative.

Ben C. Kneller

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El^cvier.

D7uiynski. S.. ;ind Sanders. J.E.. 1959. Boilom marks on tirm lulite

suhslraluni underlying lurbidite beds. GeologicalSocielyof America

Hiilh'iin. 70: 1594.

Kiikusliimii. V.. Parker, G.. and Pantin. H.M.. 1985. Prediction of

ignitive luibidity currents iti Scripps submarine canyon. Marine

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67:

55'81.

Ghibaudo. G-. 1992. Subiiquoous sedimeni gravity How deposits;

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lolofiy. 39: 423 454.

Ihiniptoii. M.A.. 1972. The role of subaqueous debris How in

ueneriitini; turbidity currents. Joitrniil ol .Setlimenha-v Perrolu^v.

42:

775-793.

Hiscott. R.N.. 1994. Traction-carpet slratilic;ilion in lurbidites; fact or

liction.' Journal of Setlimentiiry

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Hughes Clarke. J.F... Shor. A.N.. Piper, D.J.W., and Mciycr. L-A..

1990.

Large-scale current-induced erosion and deposition in ihe

path of the 1929 Grand Banks turbidii> current. Scdimciuolo^w

37:

613 629.

Kneller. B.. 1995. Beyond ihc lurbidite paradigm: physical models for

deposition of luibidiles and tbeir impliciitions for reservoir

prediction. In Hartley. A.. ;md Prossor. D.J. (eds.). Cbariiclerii'a-

lion of deep marine clastic systems. Gcolo^iad Si'cicly SpecictlPuh-

/iiiiiion.s. Volume 94. pp. 31 49.

Kneller. B.C.. Bennett. S.J.. and McCiifTrey. W.D., 199'). VekKily

siruclurc. turbulence and lluid stresses in experimental gravity

currents. Jourmilol

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Research.

Oix'tins. tO4: 5281 5291,

KnclL-r, B.C.. and Bratincy. M.J.. 1995. Sustained high-density

turbidiiy currents and the deposition of thick massive sands, Sedi-

nieniohi-y. 42: 6(17 616.

760

TURBIDITES

Kucncii. P,H,. ;md Migliorini. Cl,. 1950. Turbidily currents as a cause

of graded bedding, ./ournalof Gctdogy. 58: 91 127.

Lowe. D,R,, 1982- Sediment gravity flows: II. deposilioniil models with

special reference \o the deposits of high-density Uirbidily currents.

Journal of Scdimeniarv Petrology. 52: 279 297.

McCaffrey, W,. and Knellor. B,. 2()UI, Proeess eontrols on iJio

development of stratigraphic Irap poieiuial on the margins of

contined Itirbidite syslems and aids to reservoir evaluation, .4AFG

Hulleiln, 85: 971 988,

Middleton. G.V.. 19d7, Experiments on densiiy and lurbidily eurrenis:

[Part] 3. deposition of sediment, Catiadian Journal ot tJarih

Sciences, 4: 475- 505.

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mechanics of How and deposition. In Middleton. G,V,. and

Botmia. A,H,. (eds.).

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and Decp-Waler Sedintenialion.

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stibaqueous sedimentary densiiy fiows and iheir deposits. Sedi-

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river mouths during exception;^ discharges to the world oceans.

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275pp,

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the deposiiional record. In Osborne. R,H,. (ed.).

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Formation. Quchce. Canada; an alternative to lhe antidune

hypothesis, Scdinicniology. 32: 373 394.

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ikininStdmuirine

Canyons,

l^ans.

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& Ross. pp. 163 175,

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Pclrotcunt

Gcotogy, 17: 2S5 342,

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nature, origin and hydrocarbon implicalions. Marine and

Petrolvuni

Geology. 17: 145-174,

Stow. D,A,V,. and Shanmugiim. G,. 1980. Seqtienec of structures in

line-grained turbidiles: eomparison of Recent deep-sea und ancieni

flysch sediments, Scditucniary Geology. 25: 23-42,

Walker. R,G,. 1973, Mopping up ihe lurbidite mess. In Ginsburg.

R.N. (ed,). Evolving Comcpts in Sedinicniology. Johns Hopkins

University. Studies in Geology. Volume 21. pp, 1 37,

Zuffa. G,G,.' Normark. W,R,. Scrra. F,. and Brunner. CA,. 2000,

Turbidite mcgabcds in an oceanic rift valley recording jokulhlaups

of lale Pleistocene glaeial lakes of the Western L'nited Stales,

Jourtud of Geology. 108: 253 274.

Cross-references

Autosuspension

Bedding and Inlcrnai Structures

Clasiic (Neptunian) Dykes and Sills

Clathrates

Convolute Lamination

Cross-Slralilicalion

Debris Flow

Dish StrticUire

Fluid Escape Structures

Grading. Graded Bedding

Grain Flow

Gravity-Driven Mass Flows

Hindered Settling

Liqucfaelion and FluidJzation

Load Sliuciures

Paleocurrenl Analysis

Planar and Parallel Lamination

Ripple. Ripple Mark. Ripple Structures

Scdimciilologisis

Slide and Slump Siruclures

Slope Sedinienls

Submarine Fans and Channels

Tool Marks

UPWELLING

Introduction

One principle characteristic of upweiling systems is that they

occur predominantly in the same location due to the

combination of physiographic factors (coastline, shelf bathy-

metry) and seasonal features such as wind strength and

direction. Upwelling may occur in the open ocean as a

consequence of divergence between major current and frontal

systems, or along contincnial margins (often referred to as

coastal upwelling). Although both open ocean and coastal

upwelling intiuencc the imderlying sedimentary record, the

predominant diagnostic sedimentary facies relation to upwel-

ling are developed along continental margins. The hydro-

graphic features of an upwelling system commonly drive

undepletcd nutrients (especially nitrate and phosphate) into

the eupholic zone resulting in intense, and often seasonal,

primary production oi phytoplankton and related trophic

grazing by zooplankton. fish, and higher predators. This high

primary and secondary production produces large quantities

oi biomass whicli subsequently sinks and decays during transit

through the water column resulting in major decreases in

dissolved oxygen levels caused by aerobic microbial respiration

of the decomposing organic matter. Where the "oxygen

minimum zone" impinges on the seafloor the accumulating

sediments are commonly anaerobic giving rise to a particular

set of fiicics relationships and diiigenetic processes (Figure Ul).

FrcquL'ntly. at continental margins where wind-driven upwel-

ling occurs, there arc high levels of lithogenic detritus derived

from ihe adjacent land mass added to the organic-rich

anaerobic sediment. At the present day, such coastal upwelling

systems are characteristic of continental margins otT Califor-

nia, Peru, Mauritania, Namibia. Oman. Pakistan, and

Australia with open ocean upwelling systems characterized

by the Eastern Equatorial Pacific and the Antarctic Polar

Front.

Historical development

The study of upwelling systems and their resulting imprint on

sealloor sediments has long attracted significant scienlilic study

(e.g.. sec the following edited volumes: Theide and Suess, 1983;

Summerhayes ctal.. 1992; Sumnierhayes ctal.. 1995). In part,

this has been due to the long-known association between

organic matter, black metalliferous shales and siliceous

deposits characteristic of petroleum source rocks (e.g.. the

Miocene Monterey f-\irmation of the western USA), but more

latterly, the emerging significance of upwelling systems as

part of the oceanic carbon cycle and resulting implication for

the climate system. Through the study oi such systems, there

have grown up Important geological paradigms, such as the

enhanced preservation of organic matter under anaerobic

depositionai conditions (Dcmaison and Moore. 1980). and

subsequent challenges to the paradigm based on detailed

modern oceanographic studies (Pedersen and Calvert, 199(1).

Other major areas of study have centered on the issues of

allocthonous versus autocthonous carbon burial at shelf

depocenters (Walsh. 1991: Jahnkc and Shimmield. 1995). and

increased levels of carbon burial at upwelling centers during

past glacial episodes (Muller eta/.. 1983). Current research

aims to use the complex composition of biogenic microfossils,

sediment organic and inorganic geochemistry, and microfabric

lithology (laminalions) to reconstruct the history of upwelling

systems over a variety of timescales from decades (e.g..

reconstructing El Nino variations), to tens of thousands of

years relevant to the study of the waxing and waning of the ice

sheets and associated climatic change.

Current understanding and applications to

paleoceanography

Coastal upwelling systems, although small in arcal extent

compared to whole ocean, account for over 50 percent of

oceanic primary pioduction and more than 95 percent of the

sedimentary accumulation of organic carbon (Romankevitch.

1984).

The accumulating sediment, derived from organic

matter, biogenic skeletal material (calcite and opal), iish scales

and bones, and lithogenic minerals carried by wind and nu\ial

762

UPWELLING

500-

1000-

1500-

;rusts antm • * ^*^ * * * ^*^ * Primary * * ^*^ *

P nodule^Hgi * * * *

» production* * *

Laminated

^^^^r*

Mn^*

Oxvqen minimum zone

Manganese-rich

silts and muds

Figure Ul Schematic diagram illuslrating the effect of

intense oxygen minimum zone, produced as a consequence of upwelling water fuelling

primary [iroduclion and subsequent microbial decay of the organic matter, on the sediment lithotomy and geochemistry. Such OMZ formalion can

result in substantial le-ikage of dissolved Mn into the water column and resulting recycling and reprecipitation in underlying sediments. The

profiles of dissolved oxygen <ind manganese are typical of a modern upwelling system, such as in the northwest Arabian Sea,

diseharge. become juigmented hy diagenetic processes leading

to the concentration o\' phosphorites and sullidc minerals

under the suboxic and anoxic sedimentary conditions prevail-

ing. Linking the processes sediment supply to the locus of

sedimentary deposition is notoriously difficult at continental

margins (Jahnke and Shimmield, 1995; Bertrand eliil. 1996).

Frequently, the organic matter actually accumulating may be

older than the surrounding sediment based on ^\' age dating

(Anderson ei al., 1994). or the quantity of carbon in the

sediment does not appear to be related to the bottom water

oxygen (Pedersen etai. 1992). but instead to the inieiisity of

sediment resuspension and reworking. Such physical rework-

ing may be relatively common at coastal upwelling centers

the Oman margin is characterized by refractory carbon

diagenesis (Pedersen ci al., 1992) and deep sulfatc reduction

in the pore waters, and the Peru margin has large areas of hard

pavemeiU and phosphorite pellet beds (Jahnke and Shimmield,

1995).

In contrast, the absence of oxygen in bottom wiiters at

continental niiirgin upwelling sites can lead to an absence of

bentiiic infaunal and minimal sediment disturbance through

bioturbation. Under these conditions quite labile organic

matter is found and the sediment retains a remarkable

microfabric with annual laminations related lo the changing

surface ocean productivity (Brodie and Kemp. 1994). Even the

changing percentages of diatoms, radiohuia, and foraminifera

in the sedimentary laminations may be used to interpret

intcrannual variablity in upwelling associated with events such

as El Nino (Langc ci al.. 19S7). Even under open occiin

upwelling eonditions. such as those associated with the eastern

equatorial Pacific divergence, Kemp and Baldauf (1993) have

found historical evidenee for very rapid deposition of giant

diatom mats and resulting excellent preservation in the

sedimentary record.

The geochemistry of sediments imderlying upwelling centers

is varied and fascinating. A wide range uf redox environments

are commonly found, often with redox gradients in the

sediments that can be measured on a scale of millimeters.

rather than meters commonly found in open ocean sedimen-

tary settings. Rapid consumption of oxygen, nitrate, and

sulfatc is commonly observed with attendant dissolution of

carbonaie and degradation o\' the organic matter. Sulfide

mineral precipitation occurs during sulfate reduction and the

release of iron

111

from the oxidized coatings on mineral grains

transported by winds from the adjacent, often arid, landmass.

One key factor influencing organic matter preservation under

upwelling systems is burial rale. Often the sediments are

aeeumulating relatively rapidly {say >5em ky ') giving rise to

burial efiiciencics of greater than 10 percent. The elemental

and Isotopie composition ofthe organic matter {Kcro^cn. q.y.)

has long been used as a proxy for the changes in upwelling,

circulation, and bottom water oxygen (Reimers and Sucss.

1983).

Over the past 15 years the discovery that changes in the

C.17 alkenone unsaturation index (U^y) could be related to the

water temperature in which the phytoplankton lived, as

enabled reconstructions of past upwelling history such as for

the Peru margin (McCaffrey

i'lai.

1990). Upwelling centers

also provide inorganie proxy indicators of changes in oceanic

productivity, such as the sedimentary concentration of the

element barium in the mineral phase, barite. Bishop (1988)

showed the precipitation of barite in the decaying organic

matter within frustules of sinking diatoms. Von Breymann

ct III. (1992) summarized the known Information on high

barium in hemipelagie sediments but also identified the

potential Achilles' heel for (he use o^ Ba as a paleoproduetivity

proxy in organic-rich sediments: namely that strong sulfate

reduction diagenesis caused sedimentary barite to dissolve.

The ehanges in the faunal eomposition of the upwelling

sedimenfs can give imporlant clues as to the temperature ofthe

upwelled waters, the intensity of the primary and secondary

production, and the species succession through a .seasonal

upwelling event. Typically, the calcareous tests of the

Ibraminiferit are most often studied, both for species diversity

and abundance, and the oxygen and earbon isotopie record

they contain. Partieular species have now come to be

UPWELLINC

iissociated typically with upwelling L'onditions, such as Globi-

gcrimi hiilloiilcs (Prcll and Curry. 1981). However, close

cxjniination of bolli the species succession, and the isotopic

make-up (pai*ticiil;trl\ the

'C signature) reveals complexity in

the response ol' production of the Ibraminifera. the depth of

the ihermoeline, and the origin ol'the upwellcd water (Kroon

and Gunssen. 1989).

Summary

The sediments underlying upwelling systems, and partieularly

(hose at conlinentui margins, are a very important repository

of organic matter in the world's biogeochcmical cycle of

earbon- The upwelling process fuels high levels of marine

primary productivity whieh induces low levels of dissolved

oxygen in tlie overlying water column dtiring decomposition of

Ihe sinking organic matter. The resulting sediment, rich in

organic carbon and with accelerated diageneiie reaelions,

ultimately forms some of the most valuable hydrocarbon

source roek. In certain cases, phosphorite formation augments

the mineralogical \alue. Modern upwelling systems have

become the type areas for testing paradigms on organic tnatter

preser\ation and for proving inorganic and organic proxy

paleo-indicators of pcodueti\ ity and ocean temperature.

liHeiise episodes of oeeanie produeiivity have been recorded

in massive diatom mat accumulations, and under certain

conditions, well preserved laminated sediments deposited

under anaerobic eonditions are helping to provide a detailed

historie record of inlerannual climatic variability, such as that

associated with the El Nino episodes in the Pacitie.

Graham Shimmield

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Cross-references

Black Shales

Kerogen

Mudroeks

Phosphorites

Sa propel

Slope Sediments

VARVES

A varve is a demonstrably annual sedimentary deposit.

Implied is rhythmicity in one or more observable character-

istics occurring as a response to seasonal fluctuations of

physical, chemieal, or biological processes. The term origi-

nated with de Geer (1912) from the Swedish word vary

meaning a cyclic event or form regardless of periodicity.

However, de Geer and others since have emphasized that a

varve represents a yearly cycle, and this remains fundamental

to the value ofthe eoneept.

The depositional environment is normally aquatic, although

varves may occur subaerially, for example, as a result of

seasonally varying eolian processes (Stokes. 1964) or snowfall

as it transforms to glaeial ice. Aquatic varves are best known

from lacustrine sediments, although they have also been

reported extensively in marine deposits (Fisher. 1990). Clasiic

varves normally consist of fine-grained sediment deposited

in low-energy eonditions when inflow of water and sediment

is small, and coarser sediment deposited in response to large

inflows and vigorotis circulation. This produces the respective

dark and light couplets that distinguish classical glaeilacustrine

varves (Figure Vl) but clastic varves are also produced in non-

glacial lakes where there is a large seasonal variation in

sediment input, for example in the monsoon climate of

southeast Asia (Ross and Gilbert, 1998). Very low settling

rates of clay-sized particles (about

mm/d to

m/d) aeeording

to Stokes Law, necessitate flocculation to permit deposition in

one winter, especially in deep lakes. In summer, turbidity

currents eommonly transport eoarser sediment throughout the

lake to create numerous graded laminae.

Bioi^enic

varve.s

form by deposition of allochthonous and

autochthonous organic matter produced in seasonal cycles,

ineluding pollen in lakes and diatoms in the sea. In lakes

having water charged with dissolved sediments, chemogenic

varves may form by precipitation of salts, especially calcium

earbonate, from supersaturated solution, tor example during

summer when water temperature is elevated (Anderson, 1988).

In some situations, higher concentration of earbonate in

summer deposits is due to rapid settling and quiek buria! of

larger partieles, whereas in winter, fine particles settle slowly

and carbonate is dissolved in the cold lake water. Changes in

redox conditions in glacimarine environments have been

shown to produce varves in glacimarine sediments (Stevens,

1986).

In both lakes and the ocean, tine-scale varves are best

preserved in the absenee of bioturbation, commonly in

permanently or intermittently anoxic basins.

The value of varves depends on demonstrating that the

observed cyclicity is annual. This may be done from

independent evidence, including radiometrie dating, eorrela-

tion to other time series proxies such as tree-ring reeords,

relation to dated time-stratigraphie markers such as tephra,

comparison to measured or calculated rates of sediment

aecumulation (e.g.. in sediment traps), or by comparison of

characteristics of the deposits with hydrologic or climatic

controls (Figure VI). However, many accounts of varves

depend only on the inference that strong, regular cyclicity must

be annual. Where the annual character cannot be established,

cyclic deposits should be referred to as rhyilimires.

Counting varves provides an important dating tool.

although errors may occur if more than one rhythmite occurs

in a given year, or if seasonal variation is sufficiently muted

in one or more years that a varve is not recognized. The former

is common where extreme events, such as major storms

(Figure Vl), interspaced with low-energy eonditions occur

irregularly. The latter may occur, for example, when a mild

winter maintains water and sediment input to the lake or sea,

or during a cool dry summer when inflow is reduced or

precipitation of salts fails to occur. Over- or under-counting of

varve time scries can be reduced by comparison of the

thickness time series of varve records both from the same

depositional environment (e.g., a single lake) and from

different, widely separated environments.

More valuable, however, is the application of varve records

as proxies in paleoenvironmental assessment. Thickness ofthe

whole varve or of its seasonal components provides a measure

of the inter-annual variations of the climatic, hydrologic or

aquatic processes that produced it (Kemp. 1996). Thickness

variation also provides a measure of the fluctuations in the