S.Berndet al.- ErosionalOtfshore
SandRldgesandlawstandaroundFrance
ORIGINOF SOMEOFFSHORE
SANDBODIESAROUNDFRANCE
SergeBrRN€1,Tania MnnssETl,GillesLERlcoLArsl,
Jean FrangoisBo.pnulert,Marc de Bnrtsr2,
Jean Yves REyNAUD"
& BernadetteTEssrER"
'IFREMER,centrede Brest,BP70;29280Plouzan6,
France;
Tel.: +33-298.22.42/q
Fax:+33-298.22.45.7O;
E-mail:
sberne@ifremer.fr
3universite
deLire1,Laboratoire
r. rrolilff"tJrti"9,t3:ff.t""Ttre,
5e65s
Vlreneuve
d'Ascq,
France;
Fax:+33-320.43.49.10;
Tel: +33-320.43.43.96;
E-mail:bernadette.tessier@univJillel
.fr
Abstract.Offshoresancibodiesare describedin manycontinental
shelvesin the world,as well as in the stratigraphicrecordwherethey
representinterestingreservoirs.Many of the latest,initiallyinterpretedas sand ridges built by physicalprocesses,are now re-interpreted
as lowstandshorefacies.In contrast,relativelyfew attentionhas been paid to the origin of recenf offshoresand ridges, mainlybecauseof
the lack of data abouttheir internalstructure.lmprovedtechniquesin acquisitionand processingof very high resolutionseismic and some
shallowcores allow to reconstructthe architectureof "offshoresand bodies"from the Celtic Sea (tide dominated)and the Gulf of Lions
demonstrates
that the sand bodiesmainlyconsistof lowstand
iwavedominated)shelvesaroundFrance.In bothcases,our investigation
deposits(estuarine/deitaicsystems, sharp-basedshorefaces),insteadof transgressivedepositsas proposed by severalworkers. However,the shapeand positionof the "ridges"mainlyresultsfrom controlby physicalprocesses.In the CelticSea, intenseerosionresulted
in the shaping of shore-normalridges "cannibalizing"lowstanddeposits,while the shore-parallelorientationof the lowstandshorefaces
has been preservedin the Gulf of Lions. The understandingof the architectureand distributionof offshore sand bodies requiresto take
intoaccountnot only the classicalsequencestratigraphicconcepts(relativesea-levelchanges,sedimentsupply...)but also hydrodynamic
processes.The erosionalsand bodieswe describe representa new categoryof outer shelf sand bodies, in betweenthe purely hydrodynamicexamplesdescribedby Houbolt(1968)in the SouthernNorthSeaand the purely"allocyclic"lowstandshorefacesmainlydescribed
in the stratigraphicrecord of the Western InteriorSeaway.This finding may have interestingapplicationsfor predictingthe geometry,
orientationand positionof fossil sand bodies with respectto paleo-shorelines.
The magnitudeof erosionalprocesseaevidencedby our
investigationsalso impliesthat a largeamountof shelf sediments(mainlysand) has beentransferredto the adjacent.deepsea fans.
R6sum6. Des corps sableuxde plate-formesont d6critsen diversesr6gionsdu monde,ainsi que dans de nombreusesrochess6dimentairesoi ils constituentdes rdservoirsint6ressants.
En Mer Celtiqueet dans le Golfedu lion, on observeainsi,i des profondeurs
comprisesentre l00 et 160 m mdtres,des accumulations
sableusesd'Epaisseur
impodante(>30m).L'analysesismiqued hauter6solution et quelquescarottagessuggdrentque ces accumulationscorrespondentd des d6p6ts r6gressifsou de bas niveau,remani6set torpost-glaciaire.
tement6rod6spar la transgression
Unenouvellecat6goriede corpssableux,r6sultanti la fois de processusautocycliques
(remaniementpar des courants) et allocycliques(glacio-eustatisme)est ainsi mise en 6vidence.Cette d6couverted des implications
quantd la g6om6trieet ir I'orientation
de ces corpss6dimentaires
importanta 6t6 6rod6et
; elleimpliqueaussiqu'unvolumes6dimentaire
transferr6au domaineprofond.
Key-words: sand body,outershelf,lowstandshoreface-_ _
INTRODUCTION
generallyencased
Shallowmarinesandstone,
in shales,are commonin the stratigraphic
record,
wherethey representinterestingreservoirs,especially in the Western InteriorBasinsof North
America.Comparison
withQuaternary
shelvesled
severalauthorsto interpretthesesandbodiesas
transgressive(tide- or wave-dominated)sand
ridgessimilarto thatdescribed
aroundNW Europe
(Strideet al., 1982)and the Atlanticcoastof the
US (Swift,1975;Swiftand Field,1981).Mostof
thesesand bodiesare now re-interpreted
as lowwhose isostand and transgressive
shorefaces,
laled positionon the shelf can be relatedto
(forced)regressions
(Plint,1988;Posamentier
et
al.,1992;WalkerandBergman,1993;Walkerand
Plint,1992;WalkerandWiseman,
1995).Surprisingly,few attentionhas beenpaidto the structure
andoriginof modern(Quaternary)
outershelfsand
bodies,in orderto examinewhethersuch a reinterpretation
also could be applied.This paper
documentstwo outer shelf case studiesaround
France,with distinctsedimentaryand hydrodynamicalregimes.Highresolution
seismicdataand
someshallowcoressuggeslthat erosionalprocessesmay have had a very importantrole in remodellinglowstanddeposits,resultingin the formationof a new"hybrid"typeof shelfsedimentary
bodyin-between
classical
ridgesand classical
lowstandshorelines.
BACKGROUND
It has longbeenobservedthat sedimentscoveringmostof the outerpartof continental
shelves
aroundthe worlddo not matchthe presentday
hydrodynamical regimes (Bourcart, 1945;
Dangeard,
1928;Shepard,1932).ln particular,
these authorsobservedthe presenceof coarse
grainedsediments(mainlysands)in area where
currentvelocitiesnearthe bedwere (or weresupposedto be) lowerthanthe velocitythresholdfor
sedimenttransport(the presentsource of sand
beingalongthe coastline).
This contradiction
led
QEO-ECO-MARINA,2/1997
Nationallnstituteof Maine Geologyand Geo-ecologyof Romania
Proc. lntern. Workshopon "Fluvial-Marine
lnteractions"in Malnas,Romania,Oct.1-7, 1996
S.Bernd et al. - ErosionalOffshoreSand Ridgesand lowstandaroundFrance
Emery (1968)to proposethat the sandscoveringa tide-dominatedSouthern Celtic Sea (A in Fig.1)
large part of the continentalshelves were relict and the wave-dominatedGulf of Lions in the
depositsinheritedfrom periodsof low sea levels. Western MediterraneanSea (B in Fig.1). The
However, Swift et al., (1971) suggestedthat the seismic data were acquired with a SIG sparker
energy availableduring subsequentsea level rise seismicdevice,using an ELICS DELPH 2 digital
and highstand was sufficient for re-distributing recorder.All the records presentedin this article
sediments, these reworked sediments being were posprocessedusing the "SITHERE" proet al., 1990).
named "palimpsests".More recently, Swift and gramme(Lericolais
Thorne (1991)developedthe conceptof equilib"Moribund" sand ridges in the Southern
rium shelf, where the shelf surfaceis viewed as a
Celtic Sea
surface of dynamic equilibrium over geological
General setting
time-scales.From a wide range of seismic data,
One of the largestand best studiedsand ridge
Field and Trincardi (1991) demonstrated that
Quaternaryregressivecoastaldepositswere more field in the world is in the SouthernCeltic Sea. lt
likely to be preserved offshore of the lowstand was firstly mapped by Berthois (1974) and
shoreline,whereas those depositedinshorewere Bouysseet al., (1976). Up to 60m in height,
generally truncated and reworked by the trans- 200 km in length, 7 km in width, without clear
gressiveerosion.
asymmetryin cross-section,
these ridges,trending
lie
at
water depths comNortheast-Southwest,
One particulartype of "offshoresands" is repprised
between
120
m
and
170
m (Fig.2).Their
resentedby sand ridges(or sand banksof several
superficial
lithology
consists
of
medium
to coarse
authors),which have been extensivelystudiedon
grained
(mainly
sand
whose
carbonate
content
(Stride
et al., 1982,for
moderncontinental
shelves
about
60%,
the
remaining
fraction
shell
hash)
is
Swift
and
Field,
1981).
They
are
eloninstance;
gated sand bodies (several km or tenths of km consistingof terrigenousgrains. Current measlong, several hundredof rnetersor km wide and urementsover a 2 month period in the vicinity of
one to several tenth of meters thick). They are the Kaiser I Hind at a point where water depth is
generally subdivided into storm-dominatedsand 165m (point C in Fig.2), indicatethat, during
ridgesand tide-dominatedsand ridges.Both types springtides,surfacevelocitiesare higherthan 100
are generally referredto as "offshore bars" by ge- cm/s, whereasthose measured 50 m above the
ologistsstudyingthe stratigraphicrecord, but this bed reach 80 cm/s (Chapelier,1986).Even if one
term does not refer to any processnor any given take into accountthe attenuationof currentvelocsedimentary environment and should be disre- ity near the bed, there is no doubt that the tidal
currentis able to maintainthe mobilityof the sand
garded.
fractionon the floor, as demonstratedby side scan
The tidal sand ridges have generallybeen in- sonar imaging over the Kaiser I Hind, showing
terpreted as the result of "autocyclic"processes large dunes circulatingclockwisearoundthe ridge
(formation of residual eddies generaied by the ( R e y n a u d , 1 9 9 6 ) ,
Coriolisforce and botiom friction (Hulscheret al.,
In additionto the tidal current, storm waves
1993;Huthnance,1982a;Huthnance,1982b).This
may
also have sorneeffect on sedimenttransport.
interpretation
was supportedby the seismicdata of
Side
scan imagingreveals,at the top of the ridges
Houbolt(1968)were the sand ridgesof the South(depth
about 120 m), the occurrenceof symmetriern North Sea appearedas sand bodiesrestingon
a flat surface (the post-glacialtransgressivesur- cal small dunes,about 2 m in length,whose crest
face). In contrast,on the other side of the Atlantic is orientedN20". These bed forms are similar to
Ocean, sand ridges of the sform-daminatedmiddle the "wave ripples"formed in many coarse-grained
(see the review by
AtlanticBight were interpretedas the resultof the sedimentsof modern shelves
(1988).
fact
that
Leckie
The
tnawling
marks are
evolutionof sand bodiesformed on the shoreface,
by
these
bed
forms
confirms
their
reworked
recent
position
at the
eventually resting in an offshore
(Field,1980; origin.
"leadingedge of the transgression"
Few shallow cores, mainly sampled by the
Swiftet al., 1991).Thus,these"sand"bodiescould
incorporateback barriersands and lagoonalmuds, BritishGeologicalSurvey, are available.They reand should be the result of a partly "allocyclic" veal that the sandy mobile layer previouslymenprocess.lt is worth noting that most of the atten- tionedis underlainedby a lag pavementconsisting
tion was paid to inner shelf sand ridges,and that of coarsesand and gravel, dating from the Flanfew studiesdescribeouter shelf offshoreridgesat drian (post-glacial)sea level rise (Evans, 1990).
waterdepthmorethan 90 m (Bouysseet al., 1976; As to the inner part of the ridges,named the MelMoslowet al., 1989;Yang and Sun, 1988).In this ville Formationby the British oceanographers,it
paper, we examine data recently collectedfrom consistsof clean, sporadicallygravely, sand. lt is
two contrastedouter shelves around France:The dated late Devansian/ Weichseilian(Pantin and
Evans, 1984). lt must be emphasised
GEO.ECO.MARINA,
U1997
Nationallnstituteof Marine Geologyand Geo-ecologyof Romania
Prac. Intern. Workshopon "Fluvial-Mainelnteractions"in Malnas,Romania,Oct.1-7, 1996
s.Bern6 et at.- Erosionaloffshore sand Rldges and lowstandaraund France
=i9.1)
10'
r the
The
rarker
ligital
rrticle
pro"
N50'
:hern
ridge
ea.lt
and
right,
clear
rding
c0mTheir
)arse
ainly
ction
leasity of
[h is
uring
r100
r the
'one
eloctidal
san0
scan
rWir'19
ridge
At lantic
Ocean
Lions
editerranean
N40'
Gulf of Lions
CelticSea (A) and the wave-dominaied
Fig.1 positionof the studiedareason the outershelvesof the tide-dominated
mappedon the shelves The dark lines in the EnglishChannelcorre(B).The dottedareascorrespondto the majorsand accumulations
spondto the majorincisionsby riversduringlow standsof the sea'
7'30'
7"
6'30'
6'
aves
iport.
dges
retricrest
ar to
rined
w0y
i afe
)cent
the
y renensting
=lan-
)e0).
Melrs, it
It is
and
iised
for the sand ridgesare from Bouysseet al''
Fig,z Bathymetricmap of the Southernterminationof the CelticSea.(the contourlines
marginare from Bourilletand Loubrieu(1995).C is the positionof currentmeas'
1976,thoseforthe La Chapelleareaand the continental
4 and 5a'
urementsby chapelier(1986).Thick linesgivethe positionof seismicprofilesin Figs
GEO.ECO-MARINA, 2/1997
NationalInstituteof Maine Geotogyand Geo-ecologyof Romania
1996
Proc.lntern. wor4shop on "Fluvial-Mainelnteractions"in Malnas, Romania,oct.1-7,
S,Bernd et al. - ErosionalOffshoreSand Rldges and lowstandaround France
that only the upper part of the ridges has been appears that the bottom of the ridge does not
reached by vibrocoresto date; consequently,all match the surroundingsea floor: a "core",characthe proposedstratigraphicreconstructions
are very terised by strong acoustic impedance and subspeculative.
horizontalinternalreflectors,separatesthe Upper
Evidence of glacial sedimentson the ridge Little Sole Formation (Plioceneto early Quaterflanks (probablytransportedby ice-rafting)dem- nary)from the ridge itself(Reynaudet al., 1995).
onstrates that the ridges exisied before glacial The most strikingfeature is the presenceof deep
conditionsretreatedfrom the surroundingregion. (up to 30 m) channelsincisedinto the ridge.SevDetailedsedimentological
and micropaleontologi-eral phasesof incisionmay be identified,but the
cal studiessuggestthat, during Weichseilian,
an best preservedchannelsare the most recent,their
ice lobe advancedin the CelticSea from the lrish upper terminationbeing the erosionalsurface of
Sea, with groundedice as far south as N49"30' the ridge.Their infill consistsof oblique reflectors
(Scourseet al., 1990),but there is no evidenceof (maximumangle of dip about 12") (Fig.Sb)sugglaciationin the study area, which is located gestinglateralaccretionwithin a fluvial -or estuarine/deltaic
tidal-channel.Mappedin 3D from the
aroundN48'.
densegrid of seismiclines,they appear as relaBased on the presenttidal regime and the
tivelystraight,about500 m wide, roughlyoriented
sparse dated samples, the sand ridges in the
North-South,pinchingout towardthe two flanks of
Celtic Sea have been interpretedas tidal sand
the ridge (Pagnol 1995)"The lowest positionof
bodiesformed betweenthe last low sea level and
their incisionis about 150 m below presentsea
the early stage of the Flandriansea level rise,
level.
(Bouysseet al., 1976, Pantin and Evans, 1984;
Below the topographicbottom of the ridge, a
is supported
Strideet al., 1982).This interpretation
(more than 10km) and deep (more than
large
by numericalmodellingof M2 tidal constituent
for
200
m
below present sea level) incision is oba sea level loweredby 100 m, whichindicates
that
The infill is characterisedby several cut
served.
currentwould have been abouttwice strongerthan
phases
(Figs 4 and 5a). Correlationwith
and
fill
present
(Belderson
one
et al., 1986). lt has
the
been proposedthat southern ridges formed first, investigationsin the British sector indicate that
and the ones farther north formed progressively these depositsbelong to the Upper Little Sole
later, in relationwith the northwardpassageof a Formation,dated Plioceneto Early Quaternary
glacialforebulge(Wingfield,1995).However,such (Pantinand Evans, 1984, Evans, 1990, p.659).
a forebulgeis not predictedby numericalglacio- The mappingof this unitoverthe wholestudyarea
suggestsa link betweenthe positionof the ridges
hydro-isostatic
models(Lambeck,1995).
and that of the infills(Vanhauwaert,
1993,Fig.6).
In any of these interpretations,the inferrecj
Origin and evolution of the Kaiser-l-Hind
mechanismfor ridge formationis an up-building
process controlled by tidal currents, as in the
It is not possibleto explain the internalstrucHuthnance(1982a,b)numericalmodel.
ture of the Kaiser-l-Hindas the productof the formationof a "classical"
sand ridge.In the Southern
lnternal structure of the Kaiser I Hind
North Sea, the gently dipping reflectorsobserved
conductedin 1992,1993
Seismicinvestigations
by Houbolt resultedfrom combined aggradation
and 1994 reveal with great detail the internal
and progradation,
with (a) sand circulatingaround
structureof the Kaiser-l-Hind,
one of the ridgesof
the bankand (b) slow migrationof the ridge in the
the CelticSea. This ridgeis 60 km in length,5 km
directionof (or slightly obliquelywith respect to)
in width and up to 35 m thick. As many other
the dominanttidal current.The incisedchannels
ridgesin the area, it is separatedinto 2 sub-units,
evidencedon the seismicprofilesin the upperpart
each of them culminatingat -115 m and separated
of
the ridge can only be interpretedas fluvial
by a depressionat -135 m (Fig.3).On the seismic
and/or estuarineor deltaic tidal channelswhich
profiles,the ridge does not exhibitthe low angle
must have formed during Quaternarylowstands.
clinoformscommonlydescribedwithin tidal sand
As the upper channels almost outcrop (at the
ridges,as the Well Bank and the Smith Knoll in
resolutionof the seismicdevice),it is most likely
the SouthernNorth Sea (Houbolt.1968), but a
that they would correspondto the last lowstand
very complexpatternof cut and fill structures(Figs
(stage2). lf we interpretthese features as fluvial
4 and 5). Major boundingsurfacesare gentlydipchannels,
this implies a sea level lower than, or
ping toward the East. As a result,the major seisequalto, 150 m. lt can be notedthat a geometric
mic unitsthey delimitare shiftedin that direction
model of sea-levelduringihe end-Pleistocene
to
from the bottom to the top of the bank. Most of
Holocenetransitionlocatesa peakforebulgein the
these units exhibit clinoformswhose true angle of
soulhernCeltic Sea, al 12 ka BP, at a present
dip (determinedfrom measurementsalong 2 perwater
depth 160 m below presentmean sea level
pendiculardirections)reachesup to 10'. Most of
(Wingfield,
1995).In contrast,numericalmodelsof
theseclinoformsdip towardthe Souffi tzllesf.lt also
GEO-ECO-MARINA, 2/1997
Natlonallnstituteof Maine Geologyand Geo-ecologyof Romania
Proc. lntern. Workshopon "Fluvial-Mainelnteractions"in Malnas,Romania,Oct.1-7, 1996
L--
QffshoreSendRldgesandlowstandaroundFrance
S.Bemeet al.- Erosianal
)es not
characrd subUpper
]uater19e5).
rf deep
l. Sevrut the
t, their
ace of
lectors
r) Sugestuarmthe
; relaiented
nksof
ion of
rt sea
-100m
K a i s er - l - H i n
SW
NE
-200m
Sholf break
-300m
-400m_Tr+-T-__---l--i
k m 10
ll
20
30
40
II
50
60
70
80
90
and the adjacentcontinenialslope(Sedimanche1 cruise).
Fig.3 Topographicprofilealongihe Kaiser-l-Hind
200
lge,a
than
s obal cut
h
2so
t
t with
r that
Sole
rnary
65e).
area
idges
6).
i
itrucl for:hern
rved
ation
lund
r the
t to)
nets
part
rvial
hich
nds.
the
kely
and
tvial
| 50 E
F
L
U
o
F
F
e
u
F
t
F
. o o$
of the stratigraphicunits
The identification
ridge(positionin Fig.1)and interpretation.
Fag.4Seismicsectionacrossthe Kaiser,l-Hind
is baseOon correlationwith boreholesfromthe Britishsectorof the CelticSea (Evans,1990).CF: CockburnFormation(upperMiocene);
M.F: Melville
bottomof the ridge;B.S: "base-system";
T.B: topographic
ULSF:UpperLittleSoleFormation(Plioceneto EarlyQuaternary);
(see discussionin the text for the age of the formations).
formation
E
E
F
'Of
rtric
lto
the
;ent
rvel
;of
arethesameas in Fig.4Theabbreviations
of the KaiserI Hindridgein analongcrest(correct?) directionstructure
Fig.dInternal
givestheposition
of Fig'5b'
Therectangle
in Fig.2).
ridge(position
(a)Lini drawing
fora profilealongtheKaiser-l-Hind
GEO.ECO-MARINA,Yl997
Nationatlnstituteof Maine Geologyand Geo-ecologyof Romania
in Malnas,Romania,Oot l-7' 1996
Proc. lnterrr.Workshopon'Fluvial-Mainelnteractions"
S.Bern6et al.- Erosional
OffshoreSandRldgesandlowstand
aroundFrance
o
E
F
F
120
g
F
E
130 E
F
otJ'J
o
:---.-=-=-\
140 ffi
/,"/'
/t
,'
F
,/
t
r50
=_-\-.<
Fig.5 (b) Detailof the internalstructureof a recentinfill
glacio-hydro-isostatic
rebound around the British
lsles do not suggest the existenceof any major
forebulgein the southernCeltic Sea or of paleoshorelines at positionsto the west of 5'30' W
(Lambeck; Lambeck,1995).This meansthat, in
this area, sea level since -20,000 B.P. was never
deeper than about -120 m, not -160 m as suggestedby Wingfield(1995).
In any case, the cut and fill morphologydoes
not requirea base level as low as the deepestincision if we considerthat incision may also take
place in a submarine(esluarineor deltaic)setting,
the erosionbeing enhancedby tidal scouringas
observedin "highstand"estuariessuch as the Gi'
ronde estuary(Allen and Posamentier,1993).The
presenceof incisedchannelswithinthe ridgesimplies an origin different from the "classical"upbuilding process, as well as different lithologic
constituentsand sedimentarystructures.lt means
that a large amount of the ridge constituentsare
not shelf-tidalsands but fluvial, or more likely es62
tuarine/deltaic
deposits.The numerousphases of
erosionand depositionpreservedin the ridge suggesi that several high frequency eustatic cycles
have been preserved.However,the lack of correlationof boundingsurfacesat a regionalscale and
the absenceof ground truthing prevent from distinguishingpossibleautocyclicprocesses(lobe or
channel migrations)from global, glacio-eustatic
forcing.
Most irnportantly,the present morphology of
the ridgeappearsas the resultof an erosionalprocess (the top of the ridge is an erosionalsurface).
This does not rnean that the ridge morphology
cannot be the result of tidal processesbut that,
becauseof the availabilityof sedimentin this particular area, the tidal currents"shaped"deltaic or
estuarinedepositsinto sand ridges. At a smaller
scale,largedunes migratingwith a negativeangle
of climb and incorporatingunderlying deposits
have alreadybeen mentionedin aeolian(Rubin,
1987,p. 25) or subtidal(Bern6et al., 1991,Fig.7)
GEO-ECO-MARINA,2/1997
National lnstituteof Maine Geologyand Geo-ecologyof Ramania
Proc. lntern. Workshopon "Fluvial-Mailnelnteructions"in Malnas,Romania,OcL1-7, 1996
^L-
S.Bem6 et al. - ErosionalOffshoreSand Ridges and lowstandaround France
6'40'
6"20'
48'?o',
48"00'
E
I
-t'
47"4}',
F
o-
r.lJ
o
x,
tJ.l
F-
*
;of
ug;les
Te-
rnd
lis0r
ttic
of
r0e).
g}/
at,
tr0r
FT
tle
its
n,
I
Fig.6 Relationbetweenthe positionof the crest of the ridges
(thicklines,mappedfrom Bouysseet al., 1976,see Fig.2)and that
of the tJpper Little Sole incised valley-fill(doted area) modified
from Vanhauwaert(1993).The positionof seismicprofilesis representedby thin lines.
environments.This "tidal" interpretationis supportedby the shape and orientationof the ridges,
which match the orientationof modelledlowstand
tidal ellipse(Beldersonet al., 1986),and also by
the presentday tidal bed forms circulatingaround
the ridge. lt is also in agreementwith the Huthnance model (1982a, b), which implies higher
bottom friction (and consequentlypossible substrate erosion)in betweenthe ridges.Considering
that the ridge morphologymainlyresultsfrom an
erosionalprocessalso provide an explanationfor
the depressionobserved along most of the ridge
profiles,at a water depth about 135 m belowpresent sea level. This could be the result of a stillstand favouringthe action of ravinement(both by
wave and tidal scouring),this particulartype of
wave-cutterrace being only observablewhere the
sedimentswere not rernovedby subsequenttidal
erosion.
sandridgeappearsas
Finally,the Kaiser-l-Hind
a sedimentarybody resultingfrom remodellingby
tidal (or combined tidal/wave)processesof preexisting estuarine or deltaic lowstand deposits.
Seismicfaciessuggestthat sand is the dominant
constituentof this sedimentarybody.The timing of
depositionalevents is not possibleat this stage,
but ages proposed by previous workers are very
probably underestimated.The possible relationship betweenthe positionof the ridgesand that of
Late Plioceneto early Quaternaryincisions has
also to be considered.lt could mean that the zone
has been a depo-centerduringglacial periods,fed
by the rivers from NW Europe, especiallywhen
the Southern North Sea was dammed by icesheets, favouring the development of a major
drainage system called the "Channel River" by
Gibbard(1988).This hypothesisis also supported
and micro-paleontological
by the sedimentological
observationsof Scourse et al., (1990), who proposed that the sands in the Central and Southwestern Celtic Sea were deposited previous to
sand ridgeformationas glacialoutwash.
Offshore sand bodies in the Gulf of Lions
The Gulf of Lions, in the Western MediterraneanSea, is regardedas a "low energy"shelf.The
tidal range is only a few cm, and the waves have
moderateenergy.The largestswells are from the
Southeast,with maximumwave heightof 5 m and
associatedperiodsof about 8 s, occurring0.1 % of
the time. The generalcirculationin the Gulf is related to the Liguro-provencalcurrent, flowing
alongthe continentalslope.On the
southwestward
outer shelf, the average current velocity near the
bed is only about 5 cm/s, but the orientationand
magnitudeof this currentmay be modifiedby seasonal stratificationand wind effects (Millot, 1981).
In additioir,internalwaves and associatedinertial
currents,triggeredby wind increasesor wind decreasesunder stratifiedconditions(summer) may
have significanteffect on sediment transport at
any depths,with maximumcurrentvelocitiesnear
the bed on the shelf of about 20-30 cm/s (Millot
a n d C r 6 p o n1, 9 8 1 ) .
The shelf,about 50 km wide in the centralarea
of the Gulf of Lions,narrowsto the east and to the
west (Fig.7).The shelf break is located at water
depths rangingbetween 120 and 150 m, depending on the occurrenceor not of recent slope failures within the canyons. Seismic investigations
show that, on the outer and median shelf, Late
Quaternarysediments form a wedge thickening
seaward and pinching out landward at a water
depth of about 80 m (Aloisi,1986; Tessonet al.,
1990).This wedge consistsof several prograding
units, each of them being interpretedas a shelf
perched lowstandwedge related to forced regressions (Posamentieret al., 1992; Tesson et al.,
1993).Between80 and 100 m water depth,large
sand accumulations,named "sab/es du large"
("offshore sands") by Bourcart (1945) occur
(Fig.7).They cover a large part of the outer shelf
(Aloisi, 1986, Gensous, 1993, p.780; Monaco,
1971).Shallowcores indicatethat their upper part
GEO-ECO-MARINA,
A1997
Nationallnstituteof Maine Geologyand Geo-ecologyof Ronrania
Proc. lntern. Workshopon "Fluvial-MaineInteractions"in Malnas, Romania,Oct.1-7, 1996
S.Bern6et al. - ErosionalOffshoreSand Rldoesand lowstandaroundFrance
is fine grained(meangrainsize about200 mm) to
the West, coarser (mean grain size between400
and 500 mm) and less well sorted to the East
(AloTsi,
1986;Monaco,1971).The carbonatecontent of these sands, mainly of biogenicorigin,is
comprisedbetween25 and 500/o(Aloisi,1986).
Faunal analysisand carbon dating of the upper
part of thesesandsled Monaco(1971)to interpret
them as littoral sands deposited during the last
glacialmaximumand duringa shortstillstand(at 85 or -90 m) within the overall post glacial sea
levelrise.
an acousticvelocity of 1800m/s within sands)
(150s in Fig.8). This unit has a posdrvetapagraphy, and its offshoreterminationis generallywell
markedby a step (up Io 22 m high) in the sea floor
topography.The depth of this step is not perfectly
constantrelativeto the present sea-level, but is
comprisedbetween1001120
and 110/130m.
prograding
Landward,
unit pinchesout at a
the
fairly constantdepth of about 95 m. The width of
the sand wedge in the shore-normaldirection
rangesbetween7 and 18 km. This progradingunit
is characterised
by relativelysteep clinoformsdipping
in
an
offshore
direction.The maximumangle
NEW RESULTS
of
dip
of
these
reflectors,
determinedfrom two apprevious
hydrographic
surveysand
Compilationof
swath bathymetryover selectedareas,as well as a parentanglesmeasuredalong two perpendicular
reaches9', with an averageof 4'. The
dense grid of seismic profiling,over a zone of directions,
about 1200 kmz and some shallowcoresallowus directionof progradationis systematicallyoriented
to reconstructthe architectureof the nrost recent in the offshoredirection.The top of the sand
wedge is, at the resolutionof the sparkerseismic
sand units.
data, an irregularerosionalsurface.lt is possible
Seismic profilesacrossthe "offshoresands"of
to distinguishseveral sub-unitswithin the sand
Bourcart (1945) indicatethat they consist of a
wedge, all of them forming a "sand belt"
large progradingunit, up to 32 m thick (assuming
Sea).The dottedareacorrespondsto the e)densionof the "offshore
Fig.7 Morphoiogyof the Gulf of Lions(WesternMediterranean
Canyon;PvC:PruvotCanyon;AC: AudeCanyon;HC:
sands".FC: FoneraCanyon;CCC: Capde CreusCanyon;LDC:Lacaze-Duthiers
Canyon,GRC:Grand-Rhone
Canyon;EC: EstocadeCanyon;
HeraultCanyon;SC:SdteCanyon;MaC:MartiCanyon;PRC:Petit-Rh6ne
canyonsdeepsedimentary
body.The position
Canyon.PCDSB,Pyrenean
Canyon;PC: PlanierCanyon;CC: Cassidaigne
MC: Marseille
of offshoresandsrs frornAloisi(1986)and Gensouset al.,(1993).
o+
GEO-ECO-MARINA,
41997
of Romania
Nationalinstituteof Maine Geologyand Geo-ecology
lnteractions"
in Malnas,Romania,Oct.1-7,1996
Proc. lntern.Workshopon "Fluvial-Maine
L-
S.Berndet al. - ErosionatOffshoreSand Ridqesand lowstandaroundFrance
;ands)
)ogray well
r floor
fectly
but is
r00
t
T
U
o
tata
ith of
:ction
g unit
s dipangle
'0apicular
. The
snted
sand
ismic
;sible
sand
belt"
t50
x
U
F
i
E
F
U
r50 fr
F
=
Fig.8 Seismic(dip)sectionacrossthe "offshoresands"of Bourcart(1945).The uppersand unit (unit 15s) forms a positivetopography.Notesimilarunderlyingsand wedges(especially
is 4O.Positionin
unit 80s),whichwill be describedelsewhere.Verticalexaggeration
Fig.8.
hore
HC:
yon;
ition
whose lateral extent is more than 40 km. The
seismic profiles also indicate that several very
similar sand wedges can be detectedunderneath
(the characteristics
of these older unitswill be detailed elsewhere).Shallow (3 m) cores indicate
that the upper part of this sand wedge consistsof
medium to coarse olive-greysand (mean grain
size between 150 and 350 mm). Within some of
the cores,a coarselag, with large shell debrisand
pebbles, is observed. This coarse unit overlies
sandssimilarto the upper deposits.The dating of
one well preserved(not transported)shell yield an
AMS 14C age of 12,710r 80 y. 8,P., -1.80m below the surface(waterdepth -93 m). At the bottom
of the sand wedge,the clinoformsdownlapover a
generallyerosionalsurface,cuttingacrossanother
seismic unit consistingof parallel,sub-horizontal
continuousreflectors(150m in Fig.8). In some
other situations,they pass progressivelyto the
sub-horizontalreflectors. Seaward of the sand
wedge, the upper part of these sub-horizontalre'
flectors outcrops and it has been sampled by
shallow(5m) cores. lt consistsmainly of dark grey
clayey silts (mean grain size about 30 mm), with
fine sand layers.One
numerousthin interstratified
dating at -4.50 m within this core (water depth 126 m) gave an AMS 14C age of 20,440 t 400
Y.BP.
Beside this general organisation,differences
may be observedfrom the west to the east of the
study area.To the West, the top of the upper sand
wedge becomes more and more erosional (the
preservedthicknessof unit 150s decreasesalong
this directionand the erosionalsurface becomes
more undulated),The importanceof erosionalprocesses is confirmed by the presence of cemented
sandsat the top of the sand wedge,in the vicinity
GEO-ECA-MARINA,
41997
Nationallnstituteof Maine Gealogyand Geo-ecologyof Romania
Proc lntern. Workshopon "Fluvial-Marine
lnteractions''in Malnas,Romania,Oct.1-7, 1996
S.Bern6et al. - ErosionalQffshoreSand Rldoesand lowstandaroundFrance
ming,1988),not of that of linearsand bodies(Off,
1963).They are probablynot active as their morphologyis roundedand they don'tdisplayany superimposedbed form (smalldune or megaripple).
The seismicdata (Fig.10b)clearlyshow that both
the large sand bodies and the transversedunes
are not resultingfrom an up-buildingprocessbecause (a) their top is an erosionalsunfacetruncating gently dipping reflectorsand (b) these reflecgentlydipping
tors are in continuity
with underlying
The swath bathymetrymaps show, in the same
reflectors(insteadof downlappingovera bounding
weslern area, two type of large elongated"sand
surfaceas in classicalprogradingbed forms)"Latbodies" oriented ENE-WSW. Sorne large sand
eral correlationshow that the upper part of these
bodies(LSB in Fig.10a)severalkm long, up to 1
sand bodies correspondsto sands of unit 150s
km wide and 10 m high are observedin the shaldefinedpreviously,whereastheir lower part correlowerzones,culminatingat about 90 m belowprespondsto unit 150m, i.e. silty sediments.In consent sea level. Around the seawardlimit of the
trast with this erosional area, the sand wedge
sand wedge (waterdepth about 110 m), asymmetthickensto the East and is overlainedby an addiric bed forms, up to 7 m in height,500 m in spact i o n a ls e i s m i cu n i t ( u n i t1 5 5 si n F i g . 1 1 b )T. h i s u n i t
ing with a lateralextent about 2.5 km are also ob- is alsoshapedintobed forms,orientedN10', up to
served, especiallyin the vicinity of canyonssuch
10 m high, with a lateral extent about 1 km
as the Aude canyon(ASB in Fig.10a).These bed (Fig.11a).
Because they have no well defined
forms have a "steep"side (about5") facing to the asymmetryand because their spacing is not as
South-south-east;
their L/H ratio (about 60) is in regularas that of the first type, it is difficultto dethe range of that of transversebed forms (Flemof the Aude canyon (C.S. in Fig.9).These cementedsands,which consistof coarsegrain sands
cemented by a calcareousmatrix (Duplaix and
Olivet ), form a relief above the sand wedge up to
22 m in height, indicating that sediment was
erodedby a thicknessof at least about 22 m, and
probablysuppliedto ihe "Pyreneancanyonsdeep
sedimentarybody" (Alonsoet al., 1991) through
the Aude canyon.
e3 30
E3 t0
Et 50
Fig.9 Bathymetricmap (DigitalTerrainModel)of the centralpart of the Gulf of Lions.This map has been obtainedby compiling
Service(SHOM)originally
at the'l/20000scale,and surveysby IFREMERin 1994and 1995.
soundingsfromthe FrenchHydrographic
CS : cementedsands;WCT: Wave Cut Terrace.
GEO-ECA.MARINA,
U1997
Nationallnstituteof Maine Geologyand Geo-ecologyof Ramania
Proc. lntern. Workshopon "Fluvial-Mainelnteractions"in Malnas,Romania.Oct.1-7, 1996
S.Berndet al. - ErosionalOffshoreSand Rldges and lowstandaround France
t.3 ilB
u3 36
1 . .I .
(off,
m0r/ suple).
both
lnes
bercatflecping
ding
Lat
rese
50s
)rre-
N42 44"
N42 44.-
30n'dge
ddi-
unit
pt0
km
ned
:as
deE3 32.
J00!_._r
I'::t :r I
E3 38
!t3 36.
F i g , 1 0 a S w a t h b a t h y m e t r y ( S I M R A D 9 5 0 ) m a p o f a z o n e w i t h l a r g e s a n d b o d i e s i n t h e v i c i n i t y o f t h e A u d e c a n y o n ( p oTshi tei oi rni si naFv iegr.y7 )
goodconelationbetweensurficialsedimentdistributionand topography:the highs correspondto mediumsands (remainsof unit 15s), whereas (coriect ?) the surroundinglows consistof silly sands.Comparewilhseismicdala in Fig.'l0b).LSB: Largesand bodies;ASB: Asymelricsand bodies;CS:
to the seawatdlerminationo{lhe progradingsands (unit 15s)
CementedsandsiWCT: Wave cut terrace,corresponding
f-
F
\-r---,'
\\ \
ro'5'z
E
T
B
F
iling
=.-r\ffi
\:\>\\805
100
I
I
F
l50m
-
iAr]:::ES:S
rsoH
3
200
Fig.10b Seismic (dip) sectionin the vicinityof the Aude canyon(positionin Fig.10a).Note thal the gentlydippingclinoformsare truncatedby lhe
(erosional)sea floor.
/1997
GEA.ECO.MARINA,
Nationatlnstituteof Maine Geologyand Geo-ecologyof Romania
lnteractions"ln Malnas, Romania,Oct.1-7, 1996
Prac. lntern. Workshopon "Fluvial-Marine
67
S.Bern6 et al. - ErosionalOffshoreSand Rldoesand lowstandaroundFrance
termine whether they are linear or transverse
bedforms.In contrastwith the first category,they
are separatedfrom the underlyingdeposits (unit
150s) by a well-markedsub-horizontalerosional
surface(Fig.11b)and they onlyconsistof sand.
sive sand bodieswere built.The differencebetweenthe westernand easternpart of the zone
may be explainedboth by a largeramountof
sedimentsuppliedto the East (from the Rh6ne
river)andby the enhancement
of geostrophic
currentsto the West.As to the overallpositivetopographyof the sandwedge,whichmimicsin crosssectionthe shapeof a sandridge,it mightbe primarilyexplained
by differential
erosion,the sands
beinglesssensitive
to erosionthanthe surroundingfinegrainedsediments.
Formation and evolution of "offshore sand
bodies" in the Gulf of Lions
The two major seismic facies observedin the
area,sampledwith shallowcores.are attributedto
two differentsedimentaryenvironments.The unit
with medium sands and steep clinoforms(unit
It must me notedthat the erosionsurfaceat the
150s in Fig.8)is similarto presentdepositsof the
top of the sand wedge is polygenic.lt formed as
of the
uppefshoreface,high energyenvironments
sea level fell, both as a regressive submarine
Gulf of Lions.The occurrenceof cementedsands
surface
of erosionand as a subaeriansurface of
at the top of the seawardterminationof this sand
erosion. During the subsequentrise, it was rewedge is anothercriteriasupportinga very shallow
moulded by, and merged with, the transgressive
environmentinterpretation:such cementedsands
surface
of erosion,at least at the scale of resolupresentlyfonn as "beach rocks" in several places
of the seismic data. However, some true
tion
in the intertidalzone of the Mediterraneanafea
transgressivesand bodies (sand bodies with cli(Afexandersson,
1972), andthey are consideredas
good indicatorsfor the positionof paleo-shorelines noforms downlappingover a transgressivesurface) exist to the east of the study area(Fig.11b),
(Stefanon,1969).
Thesesand bodiesmainlydevelop at water depth
Consideringthe available dates, the present about 90 m and follow another, not very well
water depth of this unit and the seawarddirection marked,step in the topography(Fig.11a).A genof progradation,it is interpretedas lowstandupper eral investigation
of the detailedmorphologyof the
shorefacesands, depositedat the end of the last entirearea could permitto determinewhetherthis
sea level fall and during subsequent lowstand secondstep representsa second,shallowerwave
(Last Glacial Maximum) in responseto a forced cut terrace,or simplythe seawardterminationof a
regression(Posamentieret al., 1992).
sand body formed by hydrodynamicalprocesses.
The gently dipping clinoformswith alterning In the first case, unit 155s would represent a
fine sand and silty layers(unit 150m in Fig.8)are transgressiveparasequenceformed during a stillsimilar to prodeltaicsedimentspresentlydeposit- stand taking place during the overall post glacial
ing at water depths between20-44m.In such de- sea level rise. Except these sand bodies, the
posits,changesin grain size are generallyresult- transgressivedeposits are only represented,in
ing from seasonalvariationof the fluvial sediment most of the area, by a thin (0-2 m) veneer of sand.
load. This unit is interpretedas lower shoreface The coarselag observedwithin some of the cores
(low energy)sedimentsdepositedduringthe same might be the sedimentologicalexpressionof the
time intervalas unit 150s.In that case,the surface transgressive
surface.
sometimesboundingthese two units corresponds The offshoreterminationof the sand wedge (unit
to a submarineregressivesurfaceof erosion.The 150s),marked by a step in the topography,may
mechanismresponsiblefor the formationof such representthe seawardterminationof the progradsharp-basedsand bodieshas been explainedfrom ing shoreline,
at the maximumof sea level fall or,
the interpretationof the stratigraphicrecord, for more likely,the wave-cutterracedevelopedduring
sand bodiesinitiallyinterpretedas sand ridgesand a stillstandduringthe subsequentrise, followinga
now consideredas low stand shorefaces(Plint, mechanism similar to that described by Swift
sandssup- (1e68).
1988).As the sea level fall proceeded,
plied by rivers and littoraldrift were depositedin a
It is clear that hydrodynamical processes
high energy environment,then partly eroded in playedan importantrole in the shapingof the sand
subaerianenvironment(and possiblycemented). bodies, as demonstratedby the regular spacing
Seaward of the sand shorefaces,a regressive and asymmetric cross section of bed forms
surface of erosion developed above the fair (Fig.10a).lt must be noted that elongated bed
weatherwave base, cutting across distal silts de- forms are mainly observedin the vicinity of canposited previously when sea level was slightly yons (not only the Aude canyon presentedhere,
(postglacial)sea levelrise but also the LacazeDuthierscanyonfurtherto the
higher.The subsequent
was marked by subrnarinereworking,especiallyin west),suggestingthat irregularitiesin the topograzones where the energy was concentratedby the phy enhancedcurrentsnear the bottom. Several
topography(suchas in the vicinityof the Aude and processesmay be invoked for explainingthe foLacaze-Duthierscanyons), and some transgres- cusing of the energy by canyons (Huthnance,
GEO-ECO.MARINA,
41997
Nalionallnstituteof Maine Geologyand Geo-ecologyof Romania
Proc. lntern. Wor4shopon "Fluvial-Mainelnteractions"in Malnas, Romania,Oct.1-7, 1996
L-_
S.Bern1et al. - ErosionalOffshoreSand Rldgesand lowstandaraund France
,?
be0ne
tof
6ne
cur)og0ssprirnds
5
*
.&
bb
.lnd. the
las
rine
eof
resive
olutrue
cli-
sur1b).
rpth
well
Ienthe
this
'ave
ofa
ses.
.:'
1000m ,
a
arn"
+s
of the sandwedge(unit 15b) is better(positionin Fig.7).
Fig.11aSvvathbathymetry(SIMRAD950) map of a zonewherepreservation
Notethe step in the topography(between100 and 120 meters),which correspondsto the seawardpinch out of the sand wedge.Other,
to stillstandsduringthe followingsea levelrise, but
lesswell developedsteps are observedbetween90 and 95 m. Theycouldcorrespond
sand body,WCT: wave
TS8: transgressive
surveysnot alreadyperformed.
wouldrequireextensiveswathbathymetric
regionalcorrelation
cut terrace.
r00
E
I
F
Ita
rtillrcial
the
,tn
rnd.
.-^
| )u
d
I
=
)res
the
unit
nay
ad0r,
'ing
ga
rvift
tes
rnd
ing
ms
ed
tnre,
he
raral
fo)e,
'. \ \\,
o'5'
\"
2'
B
wcT
100
i
E
F
o
L
lF -
--i--i---:
---'.........-.-.-..-.-----'--'-
---.-:-i
V.E - 40
r s oF
=
200
erostonal
Fig,11b (positionin Fig.10a)Seismicsectionacrossthe sandwedge(unit'15s)a; sparkersection.Notethe sub-horizontal
surfaceboundingthe bulkof the sandwedgeand ihe overlyingsandbody.
GEA-ECA.MARINA,2/1997
Nationallnstituteof Maine Geologyand Geo-ecalogyof Romania
Proc. Intern. Workshopon "Fluvial-Mainelnteractions"in Malnas.Romania,Oct.1-7, 1996
S.Berndet al. - ErosionalOffshoreSand Rldgesand lowstandaroundFrance
1995).lt has been shownthat the Lacaze-Duthiers
canyon, in particular,is a "conduit"focusingthe
transfer between shelf and the deep Mediterranean Sea (Monacoet al., 1990).This effect is observed on the along shore geostrophicLiguroprovencalcurrent,which tends to be deviated in
an offshore direction. lt was also demonstrated
that the Lacaze-Duthiers
favouredthe trappingof
internalwaves (Millot,1990).This secondprocess
was probablyintensifiedduring low sea-levelperiods, when the coastlineapproachedthe deep canyons which concentratedthe wave action by refractingincomingwaves.
Synthesisand conclusions
Boththe CelticSea and the Gulf of Lionspresent elongatedsand bodies with positivetopographies, whose shape can be related to hydrodynamical processes.However, these "bed forms"
differ from the "classical"sand ridgesin the sense
that they mainly resultfrom erosionof pre-existing
deposits.The "classical"sand ridges,whose internal structurehas been mainlydescribedin the inner shelf on the Southern North Sea (Houbolt,
1968) resultfrom an up buildingprocess,and rest
over a flat erosionalsurface which is generallya
polygenic (regressive, lowstand, transgressive)
surfaceof erosion(Fig.12a).The "classical"ridges
are transgressiveas they formed duringthe Holocene sea-levelrise. They are topped by a surface
which can be consideredas a maximum flooding
surface,over whichtidal dunes in equilibrium
with
presentflows migrate(highstanddeposits).
fru rxe Cetnc SEA, erosion removed a large
amount of Quaternary lowstand deltaic/estuarine
sediments,probably transferredto the basrn. The
tidal currents(or tidal currentscombinedwith wave
action during storms) moulded Quaternary lowstand deposits into shore-normal sedimentary
bodiesseveraltenths of km long,severalkm wide
and several tenths of m high. The processesinvolved in their formationmay be similarto that
involved in the formation of modern shorefaceconnected ridges in combined (tide/wave)flows
along the Dutch coast (Van de Meene, 1996).
Even if the shape of the ridges can be explained
by purely autocyclic(hydrodynamical)processes,
some other morphologicalfeatures are probably
processes.The
due to allocyclic (glacio-eustatic)
landwardpinch-outof the ridges,about 120 m below presentsea-levelin the SouthernCeltic Sea,
could representthe positionof the attachmentof
the ridgesto a previouslowstandshoreline.However, despite several seismic investigations,no
remnants of such paleo-shorelinehas been observedso far, probablybecauseof the high hydrodynamicconditionsprevailingin the zone.As already mentioned,the depressionobservedacross
most of the ridgescould mark the positionof some
erosionalwave/tidalscouring during a stillstand.
The relativelyabrupt offshore terminationof the
Kaiser-l-Hind(Fig.3),which can be regarded as
the shallowestpositionfor the offshoretermination
of the progradinglowstandsedimentarybodies (if
no erosion took place) is presentlyabout 170m
below sea level, much deeper than the possible
positionof the sea during Last Glacial Maximum.
Consideringthe subsidence and glacio-isostatic
historyin the zone,this impliesa Lowerto Middle
Quaternaryage for these lowstanddeposits.As to
the upper incisionswithin the ridge (4 in Fig.12b)
they may be interpreted either as sequence
boundaryformed during sea level drop by fluvial
incision or as tidal ravinement surface formed
duringsea level rise.They may also be polygenic
surfacesresultingfrom the merging of both surfaces if no fluvial sediments were preserved.
Theseincisionsbeingcomprisedbetween115 and
150 m water depth, the first hypothesisimplies a
Lowerto Middle Quaternaryorigin. In the second
case, more recentperiodsmay be proposed(Middle to Late Quaternary)as tidal ravinementtakes
place below sea level. Anyhow, even if no exact
chronostratigraphic
framework is presentlyavailable, it is clear that several glacio-eustaticcycles
have been necessaryto shape the ridges. The
surface of the ridge (6 in Fig.12) is an erosional
surface with a lag pavement resultingfrom enhanced tidal (or combined tidal and wave) currents.From a seguencestratigraphicpoint of view,
it could be named a transgressivesurface in the
senseof Vail et al., (1987);however,it is probably
not synchronousfrom the deeper to the shallower
part of the ridge, as the erosion progressively
moved landwardas the sea level rise proceeded.
For this reason, this surface could be named
ravinement surtace in the sense of Swift (1968),
but such a surface is generallyformed by the retreat of a shoreface under the action of wave
scouring.As tidal currentis, in our case, the main
factorcontrollingthe erosionof lowstanddeposits,
this surface could also be consideredas a particular type of tidal ravinement surtace, but this
term is generally restrictedto concave-up ero*
sionalsurfacesformedwithin estuarinesettingsby
tidal scouring (Allen, 1991, Dalrymple, 1992,
p.883). Finally,the more appropriateterm is or7shore marine erosion surtace, as defined by
Nummedal and Swift (Nummedal and Swift,
1987):accordingto these authors,such surfaces
form offshore at the beginningof sea level rise
becausesedimentsupply drops (becausedeltaic
coaststurn into sedimenttrapping estuaries)and
becauseenhancedwinnowingby wave and currents. The transgressiveand highstand deposits
are only representedby a thin veneer of relatively
fine grainedsand, mouldedinto dunes active at
least when spring tidal currentsand storm wave
GEO-ECO.MARINA,
A1997
National lnstituteof Maine Geologyand Geo-ecologyof Romania
Proc. lntern. Workshopon "Fluvial-Marine
lnteractions"in Malnas,Romania,Oct.1-7, 1996
L.
S.Bofid et at.- ErasionalOffshoreSand Rt'dgesand lowstandaroundFrance
lno.
the
*-l
la3o
ion
(if
0m
ble
tm.
rtic
dle
'to
2b)
tce
rial
red
nic
I
I
20'7C km
€)
ur:d.
nd
;a
rnd
id(es
act
ailles
'he
$,,
l 7 0 r ni
shelf breaK
t-200 m)
17 *,nr
NW
STRIKESECTION
nal
b2
)nur-
-*
}W,
,ne
,l
0ty
rer
ely
rr{
ed
8),
retve
lin
':41:+
tq
arris
roby
,2,
tff-
by
ift,
;8S
qF
tic
nd
tr-
its
)ly
Fig.12 Simpl;fiedarchitectureof sand ridges(a) In the SouthernNcrth Sea (Houbolt,1968),(b) in the CelticSea and (c) in the Gulf
of Lions.
,'Classical"tidal sand ridge structurefrom the SouthernNorth Sea (from Houbolt,1968).1. coarselag (palimpsestsediments'with
a;
(subaerialsurfaceof erosion+ ravinementsurface);3:
deposits);2: Erosionalunconformity
reworkecj
e$tuarine,and-nrarine
mixedfluryial,
5:
tidal
dunes
surface;
active
flooding
4:
rnaximum
sand ridge;
iransgressive
euaternarylovrstandwedges;2: Plioceneor earlyQuaternaryincisedvalleyfills, 3: cut and fill structures
b: CelticSea 1. pliocenelearly
relatedto euaternarylowstanddeltaicor estuarinesystems;4: incisedvalley(dueto eitheror bothfluvialincisiondufing relativesea-level
surfacefcrmedduringrelativesea levelrise;5: estuarine(?) mud and sand infili;6: offshore
fail (sequenceboundary)or tidal ravinement
dune (sandwave)activewhen tidal currentcomcycle,7 . Transgressive
marineerosionsurfacerelatedto a subsequenfglacio-eustatic
wavecurrents.
with presentdaytidal/internal
dunes(sandwaves)in equilibrium
bineswith storm;B: shelf breaktransgressive
The depositsbetweenthe presentsea lloorand the dashedline(strikesectionb2) havebeeneroded.
shorefaoesor deltajclobes;3. canyoninfill;4: regressiveerosionsurface,becorninga correlative
c, Gulf of Lions:1,2: Formerlorirstand
conformiiyin an oifshoredirection.Notethat it may becomeagainan erosionalsurfacein the vicinityof the shelf break becauseof en*
hancedrryaveactionandlor nrasswasting.5: regressivesurface<lferosion;this surfacecuts acrosstime lines,separatingsandy from
muddyfacies.6. Lowstandshorelinewith targescaleprogradingclinoforms(topsetsgenerallynot preserved);7. offshorernarineerosion
parasequence;
10: polygenicerosionsurface(subaerialerosion
dunesand/ortranigressive
surfaie; g: erosionaldunes;9: transgressive
surface+ offshoremarineerosionsuiface).Notetlre positiveiopographyof this offshore"sand body".N.B.:the erosionaland "transgressive"dunesgenerallydo not coexist;the formerare observedto the west,the latestto the eastof the studyarea.
\,4
U1997
GEO-ECO.MARINA,
Nationaltnsrituteaf Marine Geotagyand Geo^ocologyof Romania
in Malnas'Romania,Oct.l-7, 1996
lnteractions"
Proc. lntern.Workshapon "Fluvial-Maine
S.Bern6et al. - ErosionalOffshoreSand Rldgesand lowstandaroundFrance
rT
orbitalcurrentsare combined(7 in Fig,12b).The moribund (rounded shape, no superimposed
depositsin megaripples).
most importanttransgressive/highstand
that area are trapped aroundthe shelf break (8 in
CONCLUDINGREMARKS
Fig.1?b),where strong internal waves and tidal
- As mentionedby Dalrymple(1992), most
currentsconcentratesediments,especiallyin the
La Chapellearea (see Fig.2) (Heathershawand of the concepts of sequence stratigraphywere
primarilydeveloped in wave-dominatedsettings.
Codd,1985).
Our
investigationsdemonstratethat, even in the
hri rne Gulr or Ltotts, lowstand prograding
very energetictide-dominatedsettingof the Celtic
shorelineshave been partly preservedas a result
Sea, some lowstand deposits have been preof less intensephysicalprocesses.However,wave
served
below the lowstand shoreline, implying an
energy, probably enhancedduring low stands of
allocyclic inlerpretation for the ridge internal
the sea by internal waves and inertial currents,
structure.On the other hand, the physicalregime
was able to remove more than 20 m of sediments.
controlspartlyor entirelythe shape and orientation
As a result of differentialerosion,sometimesfaof the offshoresand bodieswe have studied.
voured by early cementationof lowstandshore- Besidethe "classical"sand ridge structure
lines (beachrocks),these sand bodies have a
positivetopographywith respectto the surround- describedby Houlbolt(1968)in the SouthernNorth
ing environment.In two dimensions,they mimic Sea, a wide spectrum of internal structuresand
"classical"sand ridges(elongatedsand bodieswith relatedprocessesexist. There is not one "model"
large clinoformswith an angle of dip about 5", (or two models) of sand ridge formation but a
suchas in Fig.8),but their3D geometryand shore- spectrumof structuresfrom entirely"erosional"to
correspondingto several
parallel orientationindicate that they formed in entirely"constructional",
responseto an allocyclicprocess.Shallow cores combinationsof sediment supply, relative searegimes.Even
and seismic interpretationsuggestthat the upper level changesand hydrodynamical
pattern
and most offshoresand body (6 in Fig.12c)formed in a given area, the depositional/erosional
change
drastically,
for instancein the Gulf of
immediatelybefore and/or during Last Glacial may
Maximum.The erosionalsuface at the base of Lions where "classical" sharp based lowstand
this sand body (5 in Fig.12c)is not a transgressive shorefacespass laterally to much thinner sedisurfaceas in the "classical"sand ridges,but a re- mentarybodiesshapedinto erosionalsand ridges.
- Becauseof extremelyhigh combinedtidal
gressive or lowstand surface of erosion. In alr offprogresdirection,
surface
becomes
shore
this
and wave currents,the CelticSea is an end memsively a correlativeconformity(4 in Fig.12c)as it ber where ridges have been sculpted into former
becomesless sensitiveto wave action. However, lowstanddeposits.Betweenthe classicalHoubolt
it may become erosive again further offshore in "model"and the Celtic Sea case. some intermedithe vicinity of the shelf break, because of en- ary cases of tide or wave dominated shelf sand
hancedphysicalprocessesin that area, as well as bodies incorporatinga "core" of former deposits
slumpings.The sand body is toppedby an offshore have alreadybeing describedon inner shelves in
marine erosion surface, which is a particulartype the Southern North Sea (Bern6 et al., 1994;
of transgressivesurface, as defined previously. D ' O l i e r1, 9 8 1 ; L a b a a
n n dS c h u t t e n h e l m
19
, 8 1 ) t, h e
This surface moulded the lowstanddepositsand southernYellow Sea (Yang and Sun, 1988) and
shaped erosionaldunes in some places (8 in the Gulf of Mexico(Penlandet al., 1988),as well
Fig.12c).In other places,true transgressive
sand as in shoreface-attached
ridges (Sneddenei al.,
bodies(resultingfrom an up-buildingprocessand 199/t).lt must also be noted that Stubblefieldet
developed over a transgressivesurface-theoff- al., (1984) interpretedthe ridges of the wave
shore marine erosion surtace-- are observed (9 in dominated outer shelf of New Jersey as relict
Fig.12c).lt is not clear at the momentif they only nearshoreridgesand degradedbarrierislands.
representscatteredtransgressivedunes,or if they
- The architectureof the erosional sand
formed during a stillstandduring the overall post- ridgesin the CelticSea is not in contradictionwith
glacialsea-levelrise. ln that case,they would rep- the Huthnance(1982a,b)nurnericalmodel for
resent a recent analogue to the sharp-based ridge formation"This model requiresinitial seatransgressiveshorefacedescribedfor instancein floor irregularity,inducingdifferentialbottom fricthe Cardiumand VikingFormationsin Albertaand tion betweenthe swalesand the ridge. lf the bed is
the Shannon Sandstonesin Wyoming (Pattison erodible,this processmay conductto scouringof
and Walker, 1992; Walker and Bergman,1993; the sea-floor,insteadof sand pilling-upwhen the
Walker and Eyles, 1991; Walker and Wiseman, floor consistsof a very coarselag.
1995).Becauseof relativelyweak physicalregime
- Many shelf sand bodies present a (geprevailingpresently,both the dunes mouldedinto
netic?)link with underlyingincisedvalley fills. lt is
the lowstanddepositsand those developedsubseclear whetherthis is only due to the fact that
not
quently as true transgressivesand bodies are
al
t
ir
e
fi
s
e
s
tl
li
It
n
G
c
€
r
r
t
t
I
I
GEO.ECO-MARINA,A1997
Nationallnstituteof Maine Geologyand Geo-ecologyof Romania
Proc. lntern. Workshopon "Fluvial-Mainelnteractions"in Malnas,Romania,Oct.1-7, 1996
LL
S.Bern6 et al. - ErosionalOflshore Sand Rldges and lowstandaroundFrance
posed
most
were
ttings.
in the
Celtic
I preng an
Iternal
egime
rtation
ucture
North
s and
nodel"
but a
lal"to
everal
I seaEven
)attern
iulf of
vstand
' sediidges.
d tidat
memformer
loubolt
rmedif sand
lposits
ves in
1994;
1 ) ,t h e
8) and
rs well
et al.,
ieldet
WAVE
i relict
,s.
I sand
ln with
lel for
tl seam fricbed is
ring of
en the
a (gels. lt is
rctthat
moresedimentis availablein the vicinityof estu- shoremarineerosionsurface)is almostat theirtop
ariesor if the topography
of thesevalleysprovides (atthe resolution
of the seismicdevices)insteadof
the initialvorticityfor ridgeaccretion,
as required beingat theirbottom.
in theHuthnance
model.
- In some cases,it is possibleto identify
- In contrastwith the CelticSea whereno "true"transgressive
sandsat the top of the sand
evidenceof paleo-shoreline
hasbeenobserved
so bodies.In thetide-dominated
settingsof the Celtic
far, the Gulf of Lionsis a casewherelowstand Sea,sandwaves(largedunes),in equilibrium
with
shorefaces
still have a morphological
expression, presentday dynamics,are observedover the
eventhoughthey urerepaftlyreworkedinto ero- ridgesand alongthe shelf break.Moribundbed
sionalor constructional
dunes.
formsare observedin the relativelylow energy,
Gulfof Lions.
- In the sequencestratigraphic
terminology, wave-dominated
- In our scenariofor both tidal and wavethe offshoresand bodiesdescribedin this paper
largelyresultfrom the erosionof "shelfperched dominatedenvironments,
the beginningof sea
lowstandwedges" (Posamentieret al., 1988) levelriseis a periodwherea largeamountof sand
(Posamentier
formedduringforcedregressions
et is transferred
to the basinbecauseof enhanced
al., 1992).They are transgressive
only in the winnowingof lowstanddepositsnear the shelf
sensethattheirshapemoreor lessresultsfroman break.Considering
the very largeamountof sediprocessdominantly
erosional
takingplaceduring ment erodedfrom the lowstanddepositsof the
relativesea-levelrise (or duringstillstandoccur- Gulfof Lions(about20 m to the Eastof the study
ring duringthe overallsea-levelrise).However, area)andthe CelticSea (morethan25 m between
theymainlyconsistof lowstanddepositsand the the ridges),it may be predictthat largesandydeep
transgressive
surface(or more preciselythe off- seafansarepresentin bothareas.
REFERENCES
AlrxnNoenssott,T., 1972, Mediterraneanbeachrock
cementation:marine precipitationof Mg-calcite,ln:
S t a n l e yD
, . J . ,e d . ,T h e M e d i t e r r a n e aSne a :a n a t u r a l
sedimentation laboratory. Stroudsburg, Dowden,
Hutchinson& Ross, lnc.,203-223.
A*eru,G.P., '1991, Sedimentaryprocessesand faciesin
the Girondeestuary;a Recentmodel for macrotidal
, .E.,
e s t u a r i n es y s t e m s ,l n : S m i t h , D G . , R e i n s o n D
Zaitlin8
, . A . , a n d R h a m a n i ,R . A , ,e d s . ,C l a s t i cT r d a l
Sedimentology,Calgary, Canadian Society of PetroleumGeologistsMemoir 16, 29-44
AluN, G.P., RruoPosnMerurrrn,
H.W., 1993, Sequence
stratigraphyand facies model of an incisedvalley
fill: the Gironde estuary,France.J. Sediment,Petr o l . .6 3 . 3 7 8 - 3 9 1 .
A l o i s r ,J . C . , 1 9 8 6 , S u r u n m o d d l e d e s 6 d i m e n t a t i o n
deltaique:contributiond la connaissancedes marg e s p a s s i v e sU
. npublisheD
d o c t o r aT
t h e s i s ,U n i v e r s i t yo f P e r p i g n a n1, 6 2 p .
Ar-or.rso,
8., CANALS,
M., Gor, H,, ANDMnloorunao,
A.,
' 1 9 9 1S
, e a v a l i e y sa n d r e l a t e dd e p o s i t i o n asly s t e m s
i n t h e G u l f o f L i o n a n d E b r o c o n t i n e n t am
l argin.
AmericanAssociationof PetroleumGeolooistsBulletin.75. 1195-1214.
BrlorRsor.r,
R.H., Prruonre,R.D., RruoGRtrnrts, D.K.,
1986, Low sea-leveltidal origin of Celtic sea sand
b a n k s -E v i d e n c ef r o m n u m e r i c a lm o d e l l i n go f M 2
t i d a ls t r e a m s M
. a r .G e o l . ,7 3 , 9 9 - 1 0 8 .
Brnrur,S., Dunnruo,
J., ANDWeeen,O., 1991, Architect u r e o f m o d e r nt i d a l d u n e s ( s a n d w a v e s ) ,B a y o f
B o u r g n e u fF, r a n c e ,I n : M i a l l , A . D . , a n d T y l e r , N . ,
eds.,Three dimensionalfacies architectureof terrigenous clastic sediments and its implicationsfor
hydrocarbondiscoveryand recovery:Concepts in
s e d i m e n t o l o gayn d p a l e o n t o l o g yT.u l s a , O k l a h o m a ,
SEPM,245-264.
BennE,S., TRrxrcsnux,A., Srou, A., MrssrAEN,
T., aruo
DE BArsr, M., 1994, Architectureand long-term
evolutionof a tidal sandbank:the MiddelkerkeBank,
SouthernNorthSea. MarineGeology.
Berthois,1974, Carte bathym6triquedu Golfe de Gascogne.Brest,CNEXO.
BouRceRr,J , 1945, Etude des s6dimentspliocdneset
quaternairesdu Roussillon.Bull. Serv. Carte G6ol.
France.45.395-476.
Bounlr-ler,J.F., aruoLouaRreu,8., 1995, Bathymetry
and physiographyof the western approachesmarg i n .l f r e m e r .
Bouvsse,P., Honu, R., LAPTERRE,
F., nruoLe LnruN,F.,
1 9 7 6 ,E t u d ed e s g r a n d sb a n c sd e s a b l ed u S u d - E s t
d e l a M e r C e l t i q u eM
. a r i n eG e o l o g y 2
, 0,251-275.
C n a p r u e RJ, . M . , 1 9 8 6 , R 6 s u l t a t sd e s m e s u r e sd ' o c 6 - temp6rature)
anographiephysique(courantom6trie
r 6 a l i s 6 e s o u s l a r e s p o n s a b i l i td6e l ' U B O l o r s d e l a
campagneONDINE 85, Universit6BretagneOccidentale.
D'OLIER
8 ., , 1 9 8 1 ,S e d i m e n t a r ey v e n t sd u r i n gF l a n d r i a n
sea-levelrise in the south-westcorner of the North
S e a , I n : N i o , E . D . , S c h 0 t t e n h e l mR, . T . E . ,a n d V a n
V e e r i n gT
, . C E . , e d s . ,H o l o c e n eM a r i n eS e d i m e n t a tion in the Nofth Sea Basin. Specialpub. of the InternationalAssociationof Sedimentolooists.
Oxford.
B l a c k w e l2
l ,2 1 - 2 2 7 .
DALRvMeLE,
R.W., '1992, Tidal depositionalsystems,In:
W a l k e r ,R . W . , a n d J a m e s ,N . P . ,e d s . , F a c i e sm o d els. responseto sea level change. St John's, Cana d a ,A s s o c i a t i o G
n 6ologique
d u C a n a d a ,1 9 5 - 2 3 8 .
DnruoenRo,
L., 1928, Observationsde g6ologie sousm a r i n e e t d ' o c 6 a n o g r a p h iree l a t i v e sd l a M a n c h e .
GEO-ECO-MARINA,
41997
Nationallnstituteof Maine Geologyand Geo-ecologyof Romania
Proc. lntern. WorkshoBon "Fluvial-MaineInteractions"in Malnas.Romania.Oct.1-7. 1996
73
S.Bern6 et al. - ErosionalOffshoreSand Rldgesand lowstandaround France
A n n a l e sd e l ' l n s t i t uO
t c 6 a n o g r a p h i q u6e,,P a r i s ,2 9 5
p.
et
S., ANDOLTvET,
J.L., Etudes6dimentologique
DuFLArx,
morphologique
de la t6te du rech Bourcart(Golfedu
L i o n ) .C a h i e r sO c 6 a n o g r a p h i q u e s .
Errlenv,K.O., 1368, Relict sediments on continental
shelvesof the world. Bull. Am. Assoc. Petrol.Geol.,
52,445-464.
Ev*Ns,C.D.R., 1990, The geologyof the westernEngl i s h C h a n n e la n d i t s w e s t e r na p p r o a c h e sL. o n d o n ,
HMSO for the BritishGeologicalSurvey.
F I E L D ,M . E . , 1 9 8 0 , S a n d b o d i e s o n c o a s t a l p l a r n
shelves:Holocenerecord of the U.S. Atlantic lnner
,0
s h e l fo f f M a r y l a n dJ. o u r n a lo f S e d i m e n tP
. etrol.5
2,505-528.
F., 1991,Regressivecoastal
Frelo,M.E.,nxoTRrmcnRor,
depositson Quaternarycontinentalshelves:preserv a t i o n a n d l e g a c y , l n : O s b o r n e ,R . H . , e d . , F r o m
s h o r e l i n et o a b y s s :c o n t r i b u t i o nisn m a r i n eg e o l o g y
i n h o n o r o f F r a n c i sP a r k e rS h e p a r d .T u l s a , S E P M
n ' 46,107-122
speciap
l ublicatioN
klassifikation
1988,
7ur
FLEMMTNG, 8.W.,
subaquatischer,stromungstransversalerTransportkorperB
. o c h .g e o l .u . g e o t e c h n4. r b . , 2 9 , 4 4 - 4 7 .
Gtannno,P.L., 1988, The historyof the great northwest
E u r o p e a nr i v e r sd u r i n gt h e p a s tt h r e e m i l l i o ny e a r s .
P h i l .T r a n s .R . S o c , L o n d o nS e r .B , 3 1 8 ,5 5 9 - 6 0 2 .
Lecrte,D., 1988,Wave-formed,Coarse-grained
ripples
and their relationship to hummocky crossstratification.
Journalof SedimentaryPetrology,58,
ou | -ozz.
LeRrcomrs,
G., ALLENoU,
J.P., BERNE,
S., ANDMonvnn,
P., 1990, A new system for acquisitionand processing of very high-resolutionseismic reflection
d a t a .G e o p h y s i c s5,5 , 1 0 3 6 - 1 0 4 6 .
M t l l o r , C . , 1 9 8 1 , L a d y n a m i q u em a r i n e d u p l a t e a u
c o n t i n e n t adl u g o l f e d u L i o n e n 6 t 6 . U n p u b l i s h e d
Doctorthesis,Universityof Paris6, 175 p.
Mtllor, C., 1990,The Gulf of Lions' hydrodynamics.
ContinentalShelfResearch,10, 885-894"
M t l l o r , C . , l t i o C R e p o r uM, . , 1 9 8 1 , I n e r t i a lo s c i l l a t i o n s
on the continentalshelf of the Gulf of Lions. Observationsand theory.Journalof PhysicalOceanograp h y , 11 , 6 3 9 - 6 5 7 .
MorvRco,
A., 1971,Contributiond l'6tudeg6ologiqueet
s 6 d i m e n t o l o g i q udeu p l a t e a uc o n t i n e n t adl u R o u s s i l l o nI u n p u b l i s h eDdo c t o r t h e s i s ]P. e r p i g n a n2, 9 5 p .
Morunco,
A., Brscnve,P.E., SoyER,J., Pocxurttctoru,
R.,
ANDHEUSSNER,
S., 1990, Particulefluxes and ecosystemresponseon a continentalmargin:the 19851988 Mediterranean
ECOMARGEexperiment.ContinentalShelfResearch,10, 809-839.
Mosr-ow, T.F., Bnnnre,J.V., nruo LurenrunueR,J.L.,
1989, Sedimentaryfacies of a high energy, tidedominatedcontinentalshell Western canada, In:
H r n r n e n s n e wA, . D . ,n n o C o n o ,J , M . , 1 9 8 5 ,S a n d w a v e s ,
R e i n s o nG
, . E . ,e d . ,M o d e r na n d a n c i e n te x a m p l e so f
internalwaves and sediment mobility at the shelfclastictidal deposits- A core and peel workshop,
e d g ei n t h e C e l t i cS e a .O c e a n o l o g i cAac t a ,I 4 , 3 9 1 Calgary,CanadianSocietyof PetroleumGeologists,
402.
25-36.
H o u e o l r , J . J . H . C . , 1 9 6 8 , R e c e n t s e d i m e n t si n t h e
Nutvtueont,
D., ANDSwrrr, D.J.P., 1987, Transgressive
Southern Bight of the North Sea. Geologie en
stratigraphy
at sequence-bounding
unconformities:
Mijnbouw,47, 245-273"
some principlesderivedfrom Holoceneand CretaHurscneR,S.J.M.H DE SwARr, H,E., ANDDE VRTEND,
c e o u s e x a m p l e s ,I n : N u m m e d a l ,D . , P i l k e y ,O . H . ,
H . J . , 1 9 9 3 , T h e g e n e r a t i o no f o f f s h o r et i d a l s a n d
and Howard, J.D., eds., Sea-levelfluctuationand
banks and sand waves. ContinentalShelf Research.
coastalevolution.Tulsa, Societyof EconomicPale13, 1183-1204.
ontologistsand Mineralogists,
242-260.
J.M., 1982a, On one mechanismforming
Hurnrunruce,
, h y t h m i cl i n e a rs a n d b o d i e sc a u s e db y
O r r , T . , ' 1 9 6 3R
l i n e a r s a n d b a n k s . E s t u a r i n e ,C o a s t a l a n d S h e l f
tidal currents.American Associationof Petroleum
Science,14. 279-99
GeologistsBulletin,47, 324-341.
HurnrusncE,J.M., 1982b, On the formation of sand Pncnor, C., '1995,Stratigraphiesismique d
trds haute
banks of finite extent.Estuarine,Coastaland Shelf
r 6 s o l u t i o nd u b a n c d u K a i s e r - l - H i n d . I F R E M E R ,
Science.15,277-29930.
Hurnrunruce,
J.M., 1995, Circulation,exchangeand waC.D.R.,1984, The Quaternary
Pnrurrn,
H.M.,nNoEvnrus,
ter massesat the ocean margin:the role of physical
historyof the Centraland SouthwesternCeltic Sea.
processesat the shelf edge. Prog. Oceanog.,35,
Mar. Geol.,57, 259-293.
353-431.
Pntlrsor.r,S.A.J , ANDWALKER,
R.G., 1992, Deposition
ScnUrreNHELM,
R.T.E.,1981,Some new
Lnanru,
C., Rrrro
and interpretationof long, narrow sandbodiesune v i d e n c eo n t h e o r i g i no f t h e Z e a l a n dr l d g e s ,I n : N i o ,
derlain by a basinwideerosion surface: Cardium
E . D . , S c h U t t e n h e l mR
, .TE., and Van Veering,
Formation, CretaceousWestern Interior Seaway,
T . C . E . .e d s . .H o l o c e n eM a r i n eS e d i m e n t a t i oin t h e
Alberla,Canada.J. Sediment.Petrol.,62,292-309.
N o r t h S e a B a s i n .S p e c i a lp u b . n o . 5 , I n t e r n a t i o n a l
S., Bovo, R., nuo SureR,J., 1988,TransgresOxford,Blackwell, Perumruo,
Associationof Sedimentologists.
depositional
sive
systems of the Mississippidelta
239-245.
p l a i n :a m o d e lf o r b a r r i e rs h o r e l i n ea n d s h e l f s a n d
Lnnqeecr,K., 1995, Late Devensian and Holocene
development.
Journalof SedimentaryPetrology,58,
shorelinesof the British lsles and North Sea from
932-949.
m o d e l s o f g l a c i o - h y d r o - i s o s t artei cb o u n d .J . G e o l .
Puur, A.G., 1988, Sharp-basedshorefacesequences
Soc. London.152. 437-448.
and "offshorebars" in the Cardium Formationof Al74
GEO.ECA.M ARINA, 2/1997
Nationallnstituteof Maine Geologyand Geo-ecologyaf Romania
Proc. lntern. Workshopon "Fluvial-Mainelnteractions"in Malnas.Romania.Oct.1-7. 1996
S.Bern6et al. - ErosionalOffshoreSand Rr'dgesand lowstandaroundFrance
ipples
)rossy, 58,
'RVAN,
proc:ctlon
ateau
ished
mics.
rtions
bser0graue et
lousl5 p.
r,R,,
eco985ConJ.1.,
tide, In:
as of
hop,
1ists,
;sive
ities:
reta).H.,
and
)aleiby
9Um
rute
ER,
tary
iea.
tion
unrum
Ey,
'eselta
rnd
58,
3es
At-
berta; their relationshipto relativechanges in sea
l e v e l ,I n : W i l g u s ,C . K . ,H a s t i n g s8, . S . , P o s a m e n t i e r ,
H., and Van Wagoner,J., eds., Sea-levelchanges.
l ublian integratea
d p p r o a c hT. u l s a ,S E P MS p e c i a P
c a t i o nN o . 4 2 , 3 5 7 - 3 7 0 .
PosnveNrren,H.W., Ar-t-er.r,
G.P., Jmrrs, D.P., nro
Tessoru,M., 1992,Forcedregressionsin a sequence
stratigraphicframework; concepts, examples and
explorationsignificance.American Association of
Petroleu
m GeologistsBuIletin,76, 1687-1709.
PoSAMENTT
HE. W
R ,. , J e n v e v ,M . T . ,e r u o V e t ,P . R . ,1 9 8 8 ,
Eustaticcontrolson clasticdepositionll. Sequences
a n d s y s t e mt r a c tm o d e l s ,I n : W i l g u s ,C . K . ,H a s t i n g s ,
8 . S . , K e n d a l l ,C . G . S . C . ,P o s a m e n t i e rH, . W . , R o s s ,
C.A., and Van Wagoner, J.C., eds, Sea-Level
C h a n g e s -a n I n t e g r a t e dA p p r o a c h .T u l s a , S E P M
S p e c .P u b .4 2 , 1 2 5 - 1 5 4 .
Reyt'nuo,J.Y., 1996,Architectureet 6voiutiond'un banc
s a b l e u xd e M e r C e l t i q u eM 6 r i d i o n a l e2,5 6 p .
, . E . , 1 9 8 1 , E v o l u t i o no f a
S w r r r , D . J . P . ,A N DF I E L DM
classic sand ridge field: Maryland sector, North
americaninnershelf.Sedimentology,
28, 461-482.
S w r F T ,D . J . P . , P n t u p s , S . , A N DT r - l o R n eJ,. A . , 1 9 9 1 ,
Sedimentationon continentalmargins, lV: lithofacies and depositionalsystems, In: Swift, D.J.P.,
O e r t e l ,G . F . ,T i l l m a n ,R . W . , a n d T h o r n e ,J . A . , e d s . ,
Shelfsand and sandstonebodies,Geometry,Facies
and SequenceStratigraphy.Oxford, Blackwell,89152.
S w r F r ,D . J . P . ,S r e m l e y ,D . J . , e r u oC u R R n vJ, . R . , 1 9 7 ' ,1
Relictsedimentson continentalshelves:a reconsideration.J. Geol.,79, 322-346.
S w r r , D . J , P . ,A N DT H o R N eJ, . A . , 1 9 9 1 , S e d i m e n t a t i o n
o n c o n t i n e n t aml a r g i n s ,l : a g e n e r a lm o d e l f o r s h e l f
s e d i m e n t a t i o nI n
, : S w i f t , D . J . P . ,O e r t e l ,G . F . , T i l l m a n , R . W . , a n d T h o r n e ,J . A . , e d s . ,S h e l f s a n d a n d
sandstonebodies,Geometry,Facies and Sequence
Oxford,Blackwell,3-31.
Stratigraphy.
REyrunuo,
J.Y., Trssren, 8., PRousr, J.N., Lrnrcomrs, Tessot'r,M., Ar-1rru,
G.P., aruoRnverurue,
C., 1993, Late
G., MnRssrr,T., Benrue,S., ANDCHAMLEy,
H , 1995,
Pleistoceneshelf-perchedlowstandwedges on the
A p p o r t sd e l a s i s m i q u et r d s h a u t er 6 s o l u t i o nA l ' i n R h O n e c o n t i n e n t a sl h e l f , I n : P o s a m e n t i e r ,H . W . ,
terpr6tationg6n6tiqued'un banc sableuxde la Mer
S u m m e r h a y e sC
, .P., Haq, 8.A., and Allen, G.P.,
eds., Sequence stratigraphyand facies associaCeltique.C.R. Acad. Sci. Paris,320,125-132.
trons. Oxford, IAS Spec. Pub. 18, Blackwell Sci.
R u e t mD
, . M . , ' 1 9 8 7 ,C r o s s - b e d d i n gb,e d f o r m s a
, nd paPub.,183-196.
leocurrents.SEPM Conceptsin Sedimentologyand
P a l e o n t o l o gsye r i e sN o . 3 . T u l s a ,O k l a h o m a1, 8 7 p .
Tessor.r,
M , GENSous,
8., Al1eru,G.P.,xvo RAVENNE,
C.,
quaternary
1990,
Late
Lowstand
Wedges
on
the
S c o u R s eJ, . D , A u s r N , W . E . N . , B A T E M AR
N.,M . , C n r r ,
Rh6ne ContinentalShelf, France. Marine Geology,
J.A., Evnrus,C.D.R., Rosrr{soN,J.E., nxo Yourlc,
91, 325-332.
J . R . ,1 9 9 0 ,S e d i m e n t o l o gayn d m i c r o p a l e o n t o l oogfy
glacimarinesedimentsfrom the Centraland South- Vnl, P.R,, Cot-tt't,J.P., Du Cnerur,R.J., Kucxt-v, J.,
western Celtic Sea, In: Dowdeswell, J.A., and
Meonvutn, F., AND Tnrnuerr, V., 1987, La
S c o u r s e , J . D . , e d s . , G l a c i m a r i n ee n v i r o n m e n t s :
s6quentielle
et son applicationaux corstratigraphie
Processesand sedimentation.London, Geological
r6lationschronostratigraphiques
dans le Jurassique
Society, 329-347.
d u B a s s i n d e P a r i s . B u l l " S o c . G 6 o l . F r a n c e .8 .
1301-1321.
Snepnno, F.P., '1932, Sediments on the continental
shelves.Geol.Assoc.Am. Bull., 43, 1017-1040.
Vnruoe Meerur,J.W.H., 'l996, Sedimentarystructuresof
combined flow deposits from the shorefaceSNEDDEN,J.W., TILLMAN,R.W., KRTIsn, R.D..
connected
ridgesalongthe centralDutch coast. MaScHWELLER,
W.J., Culvrn, S.J.,nruoWrr.l'r,
R.W., Jr,
, 3 1, 1 5 1 - 1 7 5 .
r i n eG e o l o g y 1
1994, Stratigraphy and genesis of a modern
shoreface-attached
sand ridge,PeahalaRidge,New VnrurnuwneRr,P., 1993, Hoge-resolutie reflectieseisJersey.Journalof SedimentaryResearch,864, 560mischestudievan Neogeneen Kwartaireafzettingen
581.
in de KeltischeZee, Universitvof Gent Internalreport,
97 p.
role
in
the
study
Slernruoru,
A., 1969,The
of beachrocks
of the NorthAdriaticSea. Memoriede Bioqeoqrafica WnlxeR, R,G., ANDBeRovnN,K.M., 1993, Shannon
Adriatica,B. 7S-87.
sandstonein Wyoming: a shelf-ridgecomplex reinterpretedas lowstandshorefacedeposits.J. SediSrRror, AH., Belornsoru, R.H., KENyoN,N.H., nruo
ment. Petrol. 63. 839-851.
JonNsoru,M.A., 1982, Offshoretidal deposits:sand
s h e e t a n d s a n d b a n k f a c i e s .I n : S t r i d e .A . H . . e d . . W e l x e n ,R . G . ,A N DE v l r s , C . H , , 1 9 9 1 ,T o p o g r a p h ya n d
Offshoretidal sands: processesand deposits.New
signifiance
o f a b a s i n w i d es e q u e n c e - b o u n d i nsgu r Y o r k ,C h a p m a na n d H a l l ,9 5 - 1 2 5 .
face in the cretaceousCardium Formation,Canada,
Alberta.J. Sediment.Petrol.,61,473-496.
SrueaLrrrELo,
W.L., McGnru-,D.W., nNoKensev,D.G.,
1984, Recognition of transgressive and post- Welxrn, R.G.,nuo Plrrur,A.G., 1992,Wave- and stormtransgressivesand ridgeson the New Jerseycontidominated shallow marine systems, In: Walker,
n e n t a ls h e l t I n : T i l l m a n ,R . W . , a n d S i e m e r s ,C . T . ,
R . G . ,a n d J a m e s , N . P . , e d s . , F a c i e sm o d e l s- R e e d s . , S i l i c i c l a s t i cs h e l f s e d i r n e n t s .T u l s a , S E P M
s p o n s et o s e a l e v e l c h a n g e s .S t J o h n , G e o l o g i c a l
Associationof Canada,219-238.
S p e c i aP
l u b l i c a t i oN
n '34, 1-23.
Swrrr, D.J.P., 1968, Coastalerosionand transgressive Wnxen, R.G., nno Wsenltnru,
T.R., 1995, Lowstand
Journalof Geology,76, 444-456.
stratigraphy.
shorefaces,transgressiveincised shorefaces,and
forced regressions.examplesfrom the Viking ForS w l F TD
, . J . P, 1 9 7 5 , T i d a ls a n d r i d g e sa n d s h o a l - r e t r e a t
massifsM
. a r i n eG e o l o g y 1
, 8,105-133.
GEO-ECO-MA RINA, 2J1997
NationalInstituteof Maine Geologyand Gao-ecologyof Romania
Proc. lntem. Workshapon "Fluvial-Mainelnteractions"in Malnas, Romania,Oct.1-7, 1996
75
S,&md et al, - Erodsrsl OfibhoreSand FJ6gEs
andtortstand€roundFarlca
Fla{ioniJoarcam area, Alberta. Journal of Sedi- Yrurc,C.8., Af'{D
&JN,J.S., 1988,Tidal sand fidgesaft
mentaryResearch,
805, 132-141.
the East China.$aa shelf, In: de Boer,,P,L,,yall
Gelder,A., and Nio, S.D;, eds., Tide-influene*d
Wrueneto,R.T.R.,1995,A modelof sea-levelsin the
sedimentary
environments
and facies.Sedimentol*
lrish and Celticseas duringthe end-Pleistocene
to
ogy
and
Petroleum
Geology.Dordrecht,D. Reidd,
Holocenetransition,In: Preece,R.C",ed., lsland
23-38.
Britain:a Quaternaryperspective.
London,Geological SpecialPublication,
209-242.
76
GEO.ECO-MARINA,41997
NationalInstituteof Maine GeologyandGeo-ecology
of Romania
Proc.lntem.Workshop
on "Fluvial-Maine
lnteractions'in
Malnas,Romania,
Oct.l-7,1996