Architecture and Sedimenology Gilber-Delta Corinth-Rift

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Architecture and sedimentology of the Kerinitis Gilbert-type fandelta, Corinth Rift, Greece

NICOLAS BACKERT*, MARY FORD* and FABRICE MALARTRE*Centre de Recherches Petrographiques et Geochimiques, University Lille 1, CNRS, 15 rue Notre Damedes Pauvres, B.P. 20, F-54501 Vandoeuvre-les-Nancy, France (E-mail: [email protected])G2R, Nancy-Universite, CNRS, INPL, Ecole Nationale Superieure de Geologie, Rue Doyen MarcelRoubault, B.P. 40, F-54501 Vandoeuvre-les-Nancy, France

Associate Editor Mariano Marzo

ABSTRACT

The Kerinitis Delta in the Corinth Rift, Greece, is a footwall derived, coarse-grained, Gilbert-type fan delta deposited in the hangingwall of a linked normal

fault system. This giant Gilbert-type delta (radius 38 km, thickness > 600 m)was supplied by an antecedent river and built into a brackish to marine basin.Although as yet poorly dated, correlation with neighbouring deltas suggeststhat the Kerinitis Delta was deposited during a period of 500 to 800 ka in theEarly to early Middle Pleistocene. Facies characterizing a range of depositionalprocesses are assigned to four facies associations (topset, foreset, bottomsetand prodelta). The dominantly fluvial topset facies association has locallydeveloped shallow marine (limestone) and fluvial-shoreface sub-associations.This delta represents a subsidence-dominated system in which high faultdisplacement overwhelmed base-level falls (creation of accommodationpredominantly 0). Stratal geometries and facies stacking patterns were usedto identify 11 key stratal surfaces separating 11 stratal units. Each key stratal

surface records a landward shift in the topset breakpoint path, indicating arapid increase in accommodation/sediment supply. Each stratal unit records agradual decrease in accommodation/sediment supply during deposition. Thecyclic stratal units and key stratal surfaces are interpreted as recording eustaticfalls and rises, respectively. A 30 m thick package of foresets below the maindelta records the nucleation of a small Proto-delta probably on an early relayramp. Based on changes in stratal unit geometries, the main delta is dividedinto three packages, interpreted as recording the initiation, growth and deathof the controlling fault system. The Lower delta comprises stacked, relativelythin, progradational stratal units recording low displacement on the youngfault system (relay ramp). The Middle delta comprises vertically stacked stratalunits, each recording initial aggradationprogradation followed by

progradation; their aggradational component increases up through theMiddle delta, which records the main phase of increasing rate of faultdisplacement. The Upper delta records pure progradation, recording abruptcessation of movement on the fault. A major erosion surface incisingbasinward 120 m through the Lower and Middle delta records anexceptional submarine erosion process (canyon or delta collapse).

Keywords Corinth Rift, facies analysis, Kerinitis Gilbert-type fan delta,normal fault growth, stratal architecture, tectonics versus eustasy.

Sedimentology (2010) 57, 543586 doi: 10.1111/j.1365-3091.2009.01105.x

2009 The Authors. Journal compilation 2009 International Association of Sedimentologists 543


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INTRODUCTION

The Kerinitis Delta is one of eight conglomeraticGilbert-type fan deltas of exceptionally largedimensions that are preserved within the Plio-Pleistocene syn-rift stratigraphy of the Corinth

Rift, Greece (Fig. 1). It is one of the best knownand most frequently described examples of afootwall derived, coarse-grained, Gilbert-type fandelta deposited in the hangingwall of an activenormal fault. Several studies have used theexceptional exposures of this delta to examinethe interplay between tectonics and eustasy incontrolling stratigraphic architecture in a highsubsidence setting (e.g. Gawthorpe & Colella,1990; Ori et al., 1991; Poulimenos et al., 1993;Dart et al., 1994; Gawthorpe et al., 1994, 2003;Ulicny et al., 2002). Gawthorpe & Colella (1990)

and Hardy et al. (1994) argue that tectonic subsi-dence is the primary control on delta architecture,while Ulicny et al. (2002) emphasize eustaticcontrol. Dart et al. (1994) relate architecturalevolution to the ratio of rate of creation ofaccommodation over rate of sediment supply(A/S). Ori et al. (1991) associate architecturalfeatures to variations in accommodation only.

This study presents the first detailed study ofthe sedimentology and stratal architecture of thecomplete 38 km long Kerinitis River sectionbased on field mapping at 1:5000 scale, loggingand facies analysis. Sediment facies analysiscompletes initial descriptions by Ori et al.

(1991) and Dart et al. (1994). As demonstratedin the numerical models of Gawthorpe et al.(2003), in subsidence-dominated systems, rela-tive base-level falls may not be recorded, makingthe application of sequence stratigraphic modelsdifficult. For example, sequence boundaries,related to relative sea-level fall, are lacking orcryptic. Therefore, sequence stratigraphic termi-nology is not used in describing the delta and ininterpreting the controlling factors. A singlemajor erosional surface is observed in the deltaand it is argued that it records submarine erosion.

Eleven stratal units (SUs) separated by key stratalsurfaces (KSSs) are identified and interpreted interms of variations of A/S. Changes in the relativeimportance through time of tectonic subsidence,eustasy and sediment supply are discussed. Pos-sible climate controls on sediment supply areidentified. The presence of a small Proto-delta,some 30 m high, below the main delta records the

Fig. 1. Map of the southern coast of the Gulf of Corinth showing the distribution of pre-rift and syn-rift litho-stratigraphic units. Three generations of syn-rift Gilbert-type deltas are distinguished. The principal normal faults areshown, with dip-direction and throw indicated by small ticks. The progradation directions of the principal Lower toMiddle (L-M) Pleistocene Gilbert-type fan deltas are shown by large arrows. This map is based on Ghisetti & Vezzani(2004, 2005), Rohais et al. (2008) and the authors own work. Positions of Figs 2A and 6H and of the cross-section inFig. 2B are shown. KOL, Kolokotronis Gilbert delta; K, Kerinia village; KF, Kato Fteri village. Inset: tectonic map ofthe Aegean region showing the location of the Corinth Rift and the study area. NAF (S), southern branch of the NorthAnatolian Fault; KF, Kephalonia Fault.

544 N. Backert et al.

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earliest nucleation of Gilbert-type foresets.Changes in the geometric characteristics of thevertically stacked SUs define three stages in deltagrowth, that are related to the initiation, growthand sudden death of the controlling normalfault system, allowing insight into fault linkage

history. The increase in height of clinoformswas gradual as basin water depth increaseddue to cumulative subsidence during faultgrowth.

REGIONAL SETTING AND SYN-RIFTSTRATIGRAPHY

The Corinth Rift comprises the Gulf of Corinth, arapidly-opening, seismically active graben (cur-rently accommodating 11 t o 16 cm year)1 of

northsouth extension; Bernard et al., 2006) anda 30 km wide early rift zone exhumed andpreserved in the northernmost Peloponnesos(Fig. 1), where up to 2800 m of syn-rift strati-graphy are preserved in a series of fault blocksdefined by a complex normal fault networktrending on average N110 (Rohais et al., 2007a).Due to uplift of the northern Peloponnesos at arate of 1 to 15 mm year)1 (e.g. De Martini et al.,2004; McNeill & Collier, 2004), syn-rift strata areexposed spectacularly in a deeply incised land-scape with altitudes reaching over 2000 m. Therift probably initiated in the Late Pliocene (Dout-

sos & Piper, 1990; Collier & Dart, 1991) but itsclastic infill is, as yet, poorly dated. South of thecity of Aigion (Fig. 1), the rift basement com-prises Mesozoic carbonates, radiolarites andsandy turbidites of the Pindos thrust sheet,emplaced towards the west and intensely de-formed under sub-greenschist conditions duringthe Oligo-Miocene Hellenic orogeny (Doutsoset al., 1993). The basal rift units infill a consid-erable inherited palaeotopography.

The present study focuses on the 6 km widePirgakiMamoussia fault block, bounded to the

south by the Pirgaki Fault (N107) and theMamoussia Fault, hard linked by the Kerinitisfault trending N050 (Fig. 2A). The Pirgaki Faulthas a maximum throw of 1475 m (Fig. 2B). Thefault block is limited to the north by the HelikeFault (Fig. 1), which is a younger structure(Goldsworthy & Jackson, 2001; De Martini et al.,2004). The Kerinitis Delta nestles between thePirgaki and Kerinitis Faults (Figs 1 and 2).

No sediments belonging to the Kerinitis Deltaare found in the footwall of the Kerinitis Fault(Fig. 2A; Ford et al., 2007). Kerinitis topsets are

tilted 10 to 18 south-east towards the KerinitisFault. These observations imply that both thePirgaki Fault and the oblique Kerinitis Faultcontrolled the creation of accommodation spacefor the Kerinitis Delta.

The syn-rift stratigraphy is divided into three

informal groups, the Lower, Middle and Uppergroups that can be correlated into adjacent areas(Ford et al., 2007; Rohais et al., 2007a). In thestudy area, stratigraphic thicknesses vary across aseries of second-order tilted fault blocks, locallyreaching a maximum thickness of 1624 m(Fig. 3). The presence of erosional unconformi-ties and the lensoid form of delta bodies con-tribute to a complex three-dimensional (3D)stratigraphic architecture. The Lower group hasan average thickness of 250 to 500 m and consistsof the fine-grained (mainly fine sandstone to

siltstone) fluvio-lacustrine Melisia Formation.The Middle group (> 600 m) includes the silt-stone-dominated Zoodhochos Formation andlaterally equivalent conglomeratic fan deltas(Kerinitis and Selinous). The Upper group has avariable thickness up to 312 m and includesconglomeratic fan deltas (Figs 1 to 3) as well asother units believed to have been depositedlocally since the early Middle Pleistocene whenuplift of the northern Peloponnesos began(Rohais et al., 2007a). Plio-Pleistocene syn-riftdeposits are being cannibalized by present-dayrivers such as the Vouraikos, Kerinitis, Selinous

and Meganitas to supply major deltas that arebuilding out into the Gulf in the hangingwall ofthe Helike Fault (Fig. 1).

Within the Middle group, the ZoodhochosFormation is characterized by cyclic, finely lam-inated siltstones and fine sandstones, showinggrading, leaf prints, occasional floating pebblesand rare conglomerates forming thick massivelenses or thin ribbons. This formation overlies theMelisia Formation on an erosive contact. Itsthickness is highly variable and can reach500 m in the northern Kerinitis valley. These

sediments are interpreted as distal turbidites andsuspension deposits that were deposited in thedeep basin in front of Middle group fan deltas;however, they cannot be correlated to any specificdelta. Preliminary palynological results suggestbrackish to marine conditions. Recent biostrati-graphic dating further east in laterally equivalentdeltas indicates that the Middle group wasdeposited from Early to early Middle Pleistoceneover a period of between 500 and 800 ka (Malartreet al., 2004; Ford et al., 2007; Rohais et al.,2007b).

Corinth Rift Kerinitis Gilbert-type fan delta 545



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MiddleGroup

LowerGroup

LadopotamosFo

rmation

MelisiaFormation

Zoodhochos

Formation

KatoFteriForma

tion

KERINITISDELT

A

SelinousDelta

VouraikosDelta

KolokotronisDelta

UpliftedDeltas

KerinitisRiver

SelinousRiver

Palaeo-Kerinitis

River

Achlad

iaFault

KerinitisFault

Wes

tKeriniaFault

MamousiaFault

PirgakiFault

MinorFault

MajorFault

UpperGroup

Fig.2.

(A)Geologicalmapofthe

KerinitisDeltaareabasedon1:500

0mapping.

Themainclifffacesarelabelled1to3(Zone2includesfour

cliffs,2W,

2N,

2E

and2C).TheProto-deltaisinfer

redwithasemi-circleform.

TheinferredQuaternaryKerinitisRiverco

urseimpliesasubsequenteastward

shiftintheriver

course.

Thisfigureshowsthepositionsofthefourstratigraphiccolum

nsdetailedinFig.

3AtoD.

ThelocationofFig.

5isgivenintheblackfr

ame.

Locationsof

theFigs9Band10Aareshownw

ithblackdottedlines.(B)NNE

SSW

cross-sectionthroughthesyn-r

ift

fillofthePirgakiMamoussiafaultb

lockshowingthe

syn-r

iftstratigraphyincludingerosionalcontactsbetweengroups.ThePirgakiFaultpresentsanestimat

edthrowof1475m.




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THE KERINITIS DELTA

With a basal radius of 38 km and an arc of 125,the Kerinitis Delta, covers a surface area of 15 km2

and contains ca 9 km3 of (preserved) coarse-

grained sediment. It is very well-exposed along a38 km long, 600 m high, natural cliff section cutsouth-west to north-east by the Kerinitis River(Fig. 2A). This seismic-scale cliff represents asection through the south-east side of the delta,which prograded towards the north. Foresets onthis river section dip on average 25 towardsN042. The point source for the delta was inher-ited from an antecedent drainage system thatcoincided approximately with the present dayKerinitis River, where it incises into footwallcarbonates (Fig. 2A). As the base of the delta is

not exposed in the Kerinitis valley and thus liesbelow 200 m altitude, the delta is assigned aminimum thickness of 600 m. In the Selinousvalley to the west (Figs 1 and 2A), the delta base isat 500 m altitude implying that this contact erodesdown to the east. Erosion must have occurredbefore emplacement of the delta in a similar way tothe adjacent Vouraikos Delta, which also has ahighly erosive base (Ford et al., 2007). Clasts aredominantly carbonates with minor radiolarites(Upper Trias to Upper Cretaceous) and someflysch sandstones (Upper Cretaceous to Eocene),

principally derived from the underlying Pindosthrust sheet (Sebrier, 1977).

The Kerinitis Delta is separated from the Vou-raikos Delta to the east by the Kerinitis Fault(Ford et al., 2007). To the west, its uppermost

west-dipping foresets interfinger with the east-dipping foresets on the east side of the SelinousDelta (Fig. 3), suggesting that the two deltas wereconstructed synchronously. The KolokotronisDelta (Upper group) overlies the Kerinitis Delta,with a significant erosional boundary (Figs 2Aand 3).

The Kerinitis River profile is divided into threezones, similar to those of Ori et al. (1991)(Fig. 2A). Zone 1, abuts the Pirgaki Fault to thesouth and is 15 km long. Here, up to 440 m ofstacked topsets represent the most proximal part

of the delta edifice. Zone 2 is 900 m long andcomprises the most complex stratal architectureof the delta. A north-west to south-east trendingvalley, ca 1600 m deep, cuts at right angles to themain cliff (Fig. 2A). Zone 3 (14 km long) exposes600 m of stacked foresets, which pass rapidlynorth-eastward into bottomset and prodelta fa-cies. Eleven SUs, labelled SU1 to SU11, havebeen identified in the Kerinitis Delta. These unitsare separated by 11 KSSs labelled KSS1 to KSS11(see Stratal architecture of the Kerinitis Deltasection).

Upper

Group ConglomeraticKolokotronis

fan delta

ConglomeraticSelinousfan delta

Kato FteriFormation

KeriniaConglomerate

ZoodhochosFormation

(Kerinitis and Vouraikos fines)

ZoodhochosFormation

(Kerinitis andVouraikos fines)

ZoodhochosFormation

MelisiaFormation

ConglomeraticKerinitisfan delta

ConglomeraticKerinitisfan delta

SelinousValley (A)

MiddleGroup

LowerGroup

Fig. 3. Syn-rift stratigraphy of the study area south of Aigion presented in four stratigraphic columns A to D, locatedon Fig. 2A. The column (B) represents the most complete stratigraphic succession of 1624 m.




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FACIES DESCRIPTIONS ANDINTERPRETATIONS

Nineteen elementary facies are identified withinthe Kerinitis Delta. The detailed description(lithology, stratification and sedimentary struc-

tures), relative volumetric proportion and inter-pretation of each facies are given in Table 1.Facies abbreviations used here are as follows: Gfor conglomerates, S for sandstones, F for silt-stones and claystones, and M for carbonates.Some elementary facies may be formed by a rangeof depositional processes found within fluvial todeep-marine environments. The relative volumet-ric proportion of each facies with respect to allfacies is given.

Facies G1a: Well to poorly sorted structureless

conglomerate

This clast-supported conglomerate is well topoorly sorted with a granule to cobble range inclast sizes. Clasts are angular to well-rounded witha fine to very coarse sand matrix. Bed thicknessranges from 3 cm to 42 m and beds can haveerosional or non-erosional bases and planar tops.Beds can be structureless or they can show aslightly normal grading and, locally, open-frame-work textures. The relative volumetric proportionof facies G1a is ca 20%.

The characteristics of facies G1a are consistent

with bedload transport in high flow regimes.Variations in grain-size and sorting reflect theextreme changeability of flow and transportrates.

Facies G1b: Steeply dipping conglomerate

This clast-supported, poorly sorted conglomeratehas a mean clast size of 15 cm (from granule tocobble grade). The facies is characterized princi-pally by primary bedding dips of 20 to 35. Thematrix of poorly sorted coarse sand represents

less than 10% of rock volume. Beds have athickness of 60 to 70 cm with planar bases andtops. Beds can contain a horizontal or weaklydipping clast (cobble grade) alignment [a(p)a(i)-type] and local pockets of open-frameworktexture. The relative volumetric proportion offacies G1b is ca 30%. Facies G1b is interpreted asGilbert delta foresets, deposited by sedimentgravity flows (Postma, 1983, 1984; Postma &Roep, 1985; Colella et al., 1987; Nemec, 1990;Chough & Hwang, 1997; Kleinhans, 2004) or bydebris-falls (Nemec, 1990).

Facies G1c: Crudely stratified conglomerate

Facies G1c is made of very poorly sorted (pebbleto cobble), clast-supported conglomerate. Clastsare well-rounded and have a low sphericity. Bedslocally have oversized clasts (> 30 cm in dia-

meter). The matrix is made of very coarse sandand comprises less than 5% of rock volume. Bedthickness varies between 1 and 25 m and bedsare stacked to form SUs of 40 to 120 m. Beds canhave non-erosional or locally erosional bases.Typical sedimentary structures are crude hori-zontal bedding and a weak low angle cross-bedding. Beds locally show clast imbrication[a(t)b(i)-type] and an open-framework texture.Facies G1c represents 45% of all facies. FaciesG1c is interpreted as longitudinal bedform depos-its (Miall, 1996) and is typical of rapid gravelsheet transport processes (Hein, 1984).

Facies G1d: Variably graded conglomerate

Facies G1d is made of well to poorly sorted,clast-supported conglomerate. Pebble to cobblegrade clasts are well-rounded and have lowsphericity. Beds can contain rare intraforma-tional clasts of silt composition. The matrix ismade of medium to very coarse sand. Bedthickness varies between 7 cm and 14 m. Bedshave erosional or non-erosional bases and pla-nar or wavy tops. Observed sedimentary struc-

tures often include subtle inverse grading andrare weak normal grading, sub-horizontal bed-ding and, locally, cross-strata at the bases ofbeds. Open-framework texture has rarely beenrecognized. The relative volumetric proportionof facies G1d is ca 015%.

The normal grading leads to the interpretationof facies G1d as longitudinal bedform deposits(downstream growth; Hein & Walker, 1977; Hein,1984). However, inverse grading may be indica-tive of a clast-rich debris flow process.

Facies G1e: Cross-stratified conglomerateFacies G1e is divided into sub-facies (1) and (2).Sub-facies (1) consists of a poorly sorted, clast-supported conglomerate. Clast sizes range fromgranule to cobble. The matrix is made of verycoarse sand and never comprises more than 10%of sediment volume. Bed thickness is from 78 cmto 1 m and beds have erosional or non-erosionalbases and planar tops. Cobble-size clasts havebeen observed at the top of some beds. Thissub-facies shows cross-bedding and tangential




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Table

1.

(Continued)

Facies

Lithologyandstratification

Sedimentarystructures

Interpretationandp

rocesses

G2:Matrix-supported

conglomerate

Welltopoorlysorted,

matrix-supported

Pebblegradeclasts,well-rounded

Matrix:mediumtoverycoarsesand

Bedthickness:decimetrescale,

sharpbas

es,

planartops,lensshape

Weaknormalgradingand

lateral

fining

Crudehorizontalbedding

Sedimentgravityflo

w(debrisflow)

G3:Algal

clast-supported

conglomerate

Poorlysorted,

clast-supported,

sandy

Coarsesandtogranulegradeclasts

Redalgaeclasts,locallyabundant

Spariticormicrospariticcementpoorly

developed

Bedthickness:decimetrescale,

planarbases

ProgressivetransitiontofaciesM1bya

gradualdisappearanceoflithoclasts

Crudehorizontalbedding

Reworkedcarbonate

sediments

Brackishtomarineenvironments

Highenergyenviron

ment(grainstone

andalgalclasts)

S1:Structureless

sandstone

Welltopoorlysorted,

finetoverycoarse,s

ome

floatin

glithoclasts(verycoarsesandto

pebble)

Bedthickness:centimetretodecimetresc

ale,

erosio

nalornon-erosionalbases,planaro

r

wavy

tops,sometimeslenticular

Rareamalgamatedripples

Convolutebedding

Waterescapestructures

Bioturbation(Exichnia-typ

e)

Sedimentgravityflo

w

SubdivisionA(Ta)oftheBouma

sequence

S2:Laminated

sandstone

Well-sorted,

finetomedium

Bedthickness:centimetrescale,

erosionalor

non-erosionalbases,planartops

Horizontaltolowreliefun

dulating

lamination,

sometimes

discontinuous


Upperflow-regimeplanarbed

S3:Cross-bedded

sandstone

Welltopoorlysorted,

finetoverycoarse,s

ome

lithoc

lasts,sometimesshellfragments

Sometimesinterbeddedwithfine-grained

facies

(from

silttoclay)


maybe

lenticular,erosionalornon-erosionalbases,

planartowavytops

Obliquelamination,

withchangesin

grain-s

izebetweenlamina

e

Obliquetangentiallamination

(ripples)

Troughcross-bedding

Asymmetricripples

Climbingripplecross-lamination

Reactivationsurfaces


Loadstructures

Variabletexturecon

trolledby

variationsinsorting

resultingfrom

changinghydraulic

conditions

Migrationofsubaerial3Dbedforms

Tractivepartofhigh

-densityturbidity

currents

S4:Inverselyor

normallygraded

sandstone

Welltopoorlysorted,

finetocoarse,

some

floatin

glithoclasts


sometimes

sharp

toerosionalbases,wavytops

Inversegrading

normalgradingandlateralfining

Horizontalbedding

Unidirectionnalcross-lamination

(ripples)

Bioturbation(mainlyonsoles)

Fluid-r

ich,

cohesion

-lesssediment

gravityflow

High-densityorlow-densityturbidity

current

Grainflow




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Table

1.

(Continued)

Facies

Lithology

andstratification


Interpretationandproce

sses

F1:Structureles

siltstone

Well-sorte

d

Bedthickness:centimetrescale

Structureless

Depositionfromsuspensionfallout,

lowvelocityflow

Continualsteadydeposition

Drapedeposits

F2:Laminated

siltstone

Well-sorte

d,

intraformationalclastsofreddish

clay(sometimesabundant)


millimetre

scalelaminae

Horizontaltowavylaminati

on

Symmetricorasymmetricripple

cross-lamination

Fluctuationinthesupplyof

suspendedsedimentand/or

Suddenincursionsoftu

rbidity

currents

Intraformationalclasts=

local

erosionalevents

F3a:Interbedded

siltstone

(1)Well-s

ortedsiltandfinesand,

millimetre

to

centimetrescalestrata

(2)Siltsw

ithfineorcoarsesandylenses,

centimetresinthickness

(3)Siltsw

ithshellsandfineshellysands,a

fewdecim

etresinthickness

(4)Siltsw

ithshellsandfineshellysands,fin

e

sandylen

ses(centimetre),afewdecimetresin

thickness

(5)Siltsandfinesand,

sandwithshells,

charcoalc

lasts,leavesandstemfragments,

metresin

thickness

(1)Wavymillimetriclamina

tions

(2)Wavylamination

(3)Horizontaltowavylamination

(4)Weakinversegradingwi

thin

silts

Wavylamination

Bioturbation

(5)Horizontallamination

Symmetricalripples

HCS-l

ikestructures

Convolutebedding

Bioturbation

(1)Fine-grainedturbidi

tes

(2)Alternationofsuspensionfallout

andweakcurrent

(3),(4),(5)Suspensionfalloutsometimes

disturbedbysmallweak

turbiditic

depositionalprocesses

Hypopycnalsuspension

plumes

Stormwavesandcurren

ts(5)

F3b:Variegated

siltstone

Finegrain

ed

Variegatedcolour(green,

grey,

purple)

Irregular,

crudelyroundedcarbonatenodules

orglaebules(millimetretocentimetrescale)

withundifferentiatedinternalfabrics

Bedthickness:afewdecimetrescale

Roottraces(pedotubules)

Charcoalfragments

Repeatedimmaturepala

eosol

development

F4a:Claystone

Uniform

Bedthickness:centimetrescale

Structureless

Settlingfromsuspension

Veryhomogenous(andpossibly

rapid)depositionalproc

ess

F4b:Laminated

claystone

Reddishc

oloured

Bedthickness:decimetrescale

Veryfinehorizontaltowavy

lamination

Episodicsuspensionfalloutinastill

waterenvironment




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Table

1.

(Continued)

Facies

Lithologyandstratification


Interpretationandp

rocesses

M1:Bioclastic

calcareousbeds

(1)Grai

nstonewithcorallineredalgae

(Lithophyllum,

Lithothamnion)micritic

fragmen

ts,

gastropodsshells,bedthickness

is

decimetretometrescale,

planarbases

orprogressivetransitionfromG3,

slightly

wavyto

ps,locallynodularaspect.Locally,

decimetrescaleshellypackstonewithalgal

fragmen

ts

(2)Interbeddedsiltstone(centimetrescale)

andgrainstonebeds(centimetretodecimet

re

scale),erosionalornon-erosionalbases,

planartops,differentkindsofgastropods,

locallyslightlynodularaspect

Weakhorizontalbeddin

g

Alternationofhigh

tomoderate

energycarbonateen

vironment

M2:Calcareous

spheroid

accumulations

(1)Accumulationofindividualspheroids

(centim

etresindiameter)insmallmounds

(decime

tresindiameter).

Spheroids

compos

edofconcentricmicriticlaminae

around

acoreofbioclastic(redalgae)

grainsto

ne

(2)Shellysiltstonewithconglomeraticlens

es

comprisingpre-r

iftclastsandrarespheroid

s

Bulboussurfaceaspect

Verydiscontinuoushorizontal

bedding

Biologicalconstruct

ionbycoralline

redalgaeinbrackishtomarine

conditions

Reefmound-typeo

rganization

Depositionduringp

eriodsoflittleor

noclasticinput




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foresets with normal graded beds. Open-frame-work texture is observed sometimes.

Sub-facies (2) is a well to poorly sorted, clast-supported conglomerate with rare sands. Bedthickness ranges from 05 t o 26 m. Beds haveerosional or non-erosional planar bases and pla-

nar tops. Beds display tangential foresets alterna-tively made of sands (locally laminated) orgravels. Foresets can show sigmoidal geometry.Some conglomeratic cross-beds pass laterally intosandstones. The relative volumetric proportion offacies G1e is ca 05%.

Foresets identified represent gravel dunes.Facies G1e records a grain flow depositionalprocess. Foresets of gravel dunes record bedformmigration. Facies G1e(1) is related to high-con-centration turbidity current transport processes(Pickering et al., 1989), in particular traction

transport of gravel bedload. Alternating beds ofsand and gravel [facies G1e(2)] reflect extremelyunsteady flow and transport rates. Grain-sizevariation in individual cross-strata is due mainlyto superimposed bedforms.

Facies G2: Matrix-supported conglomerate

Facies G2 comprises well to poorly sorted, well-rounded pebble grade clasts (mean clast size2 cm). The matrix is made of medium to verycoarse sand and forms 50% to 80% of rock volume,corresponding to a matrix-supported conglomer-

ate. Bed thickness is between 15 and 60 cm, bedshave sharp bases, planar tops and can be lenticularin form. Observed sedimentary structures includepoorly developed normal grading and lateralfining, crude horizontal bedding. The relativevolumetric proportion of facies G2 is ca 05%.

Sedimentary structures suggest a sedimentgravity flow depositional process. Poor sortingassociated with normal grading suggests a debrisflow process with clasts floating in an abundantmatrix. Development of a crude stratification maybe the result of either an upward decrease in

matrix strength or an increase in water content(Hampton, 1972; Larsen & Steel, 1978). Normalgrading is probably due to incorporation of water(Eyles, 1987) allowing increased clast mobilitywithin the flow (Morgenstern, 1967; Larsen &Steel, 1978; Nemec & Steel, 1984; Nemec et al.,1984; Walker, 1984).

Facies G3: Algal clast-supported conglomerate

Facies G3 is a poorly sorted, clast-supportedsandy conglomerate that is found at two locali-

ties. Clast-size ranges from coarse sand to granulegrades. The cement is made of sparitic ormicrosparitic calcite and is poorly developed,representing less than 10% of rock volume. Themain characteristic of this facies is that it containsbioclasts of red algae in variable amounts,

increasing upward in each bed to up to 70% ofall clasts. Bed thickness ranges between 02 and1 m. Beds have planar bases. G3 progressivelypasses vertically into facies M1(1) by the gradualdisappearance of lithoclasts. A crude horizontalbedding constitutes the only internal sedimentarystructure. The relative volumetric proportion offacies G3 is ca 01%.

Although reworked, the presence of red algaebioclasts suggests brackish to marine deposits.Reworking of algal fragments is assumed tohave been in situ. The sparitic cement precip-

itated in primary porosity of sediments em-placed under high-energy conditions (Dunham,1962).

Facies S1: Structureless sandstone

This fine to very coarse sandstone is well topoorly sorted, with or without floating lithoclasts.Lithoclast size ranges from very coarse sand topebble grade. Bed thickness is between 1 cm and50 cm with erosional or non-erosional bases andplanar or wavy tops. Beds can sometimes belenticular. Locally observed sedimentary struc-

tures include rare amalgamated ripples, convo-lute bedding, water escape structures andbioturbation. Bioturbation comprises small-scaleburrows on bed bases (simple arcuate forms ofcentimetre length and ca 2 cm in diameter) ofExichnia-type. The relative volumetric proportionof facies S1 is ca 2%.

S1 is encountered within a wide range ofdepositional processes in subaerial to deep-water settings. This facies can record a sedimentgravity flow depositional process (Eyles, 1987)with rare tractive features and post-depositional

modification by dewatering and bioturbation. S1could correspond to Subdivision A (Ta) of theBouma sequence (1962) interpreted as due torapid deposition from suspension, with littleor no bed transport (Collinson et al., 2006).Floating gravel clasts commonly occur withinsandy facies in a turbidity current depositionalprocess (Postma et al., 1988; Shanmugam,2000). S1 can also represent subaerial overbanksand deposits where it is associated with apalaeosol (facies F3b) and other fluvial facies[F3a(2), F4a].




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Facies S2: Laminated sandstone

Facies S2 is a well-sorted, fine to medium sand.Bed thickness ranges from 15 cm to 6 cm. Bedshave erosional or non-erosional bases and planartops. S2 contains horizontal to low-relief un-

dulating lamination, sometimes discontinuousand locally disturbed by water escape structures.The relative volumetric proportion of facies S2 isca 03%.

Facies S2 is interpreted as representing anupper flow-regime planar bed (Collinson et al.,2006). Collinson et al. (2006) proposed that,although formation of lamination could be theresult of fluctuations in flow strength, it is alsopossible that grain segregation on the bed pro-duces layers of moving grains with different sizecharacteristics. The origin of the low-relief un-dulating lamination can be explained by an

increase in velocity of water flowing above anupper flow-regime planar bed (Collinson et al.,2006).

Facies S3: Cross-bedded sandstone

Facies S3 corresponds to a well to poorly sorted,fine to very coarse sand that may contain litho-clasts, from granule to cobble size and sometimesshell fragments. S3 can be interbedded with bedsmade of silt to clay. Bed thickness varies from2 mm to 50 cm. Beds can have erosional or non-

erosional bases and planar to wavy tops. Beds canbe lenticular in shape. Facies S3 is characterizedby a wide range of sedimentary structures,including oblique lamination of dunes withchanges in grain-size between laminae, obliquetangential lamination of ripples, trough cross-bedding, asymmetric ripples, climbing ripplecross-lamination, reactivation surfaces, waterescape structures and load structures. Therelative volumetric proportion of facies S3 is ca03%.

Facies S3 shows a variable texture due tovariations in sorting resulting from changinghydraulic conditions. Trough cross-beddingdevelops by the migration of 3D bedforms (arcu-ate-crested bedforms). Erosional surfaces can beproduced by bedform migration (with time-vary-ing geometry) or when bedform migration ceasedfor a long time and then re-started as the flowstage increased. Tractive structures can be inter-preted as representing the tractive part of high-density turbidity currents (Lowe, 1982), whenfound within bottomset to prodelta facies associ-ations.

Facies S4: Inversely or normally gradedsandstone

Facies S4 is a well to poorly sorted, fine to coarsesand, with or without floating lithoclasts (verycoarse sand to pebble in size). Bed thickness

ranges from 5 to 30 cm. Beds sometimes showsharp to erosional bases and have wavy tops.Sedimentary structures include inverse grading,normal grading associated with lateral fining,horizontal bedding, unidirectional cross-lamina-tion (ripples) and bioturbation mainly recordedon the soles of beds. The relative volumetricproportion of facies S4 is ca 03%.

Normally graded beds record deposition frommore fluid, less cohesive sediment gravity flowsin which limited sorting occurred (Hein &Walker, 1982; Walker, 1984). Normal gradingalso suggests a high-density or low-density

turbidity current depositional process (Bouma,1962; Middleton & Hampton, 1976; Lowe, 1982;Hein, 1984; Nemec & Steel, 1984). Inversegrading can be the result of a grain flowdepositional process. Horizontal and obliquelamination indicates deposition in bedforms ofvariable shape. The grading of beds can be theresult of a decrease or an increase in currentenergy.

Facies F1: Structureless siltstone

Facies F1 corresponds to a well-sorted structure-less siltstone with bed thickness from 1 to 75 cm.The relative volumetric proportion of facies F1 isca 01%.

Facies F1 represents deposition from suspen-sion in a standing body of water during a periodof low velocity flow. The structureless textureindicates a continual, steady deposition by sus-pension fallout. Locally, thin beds of facies F1can represent drape deposits.

Facies F2: Laminated siltstone

Facies F2 is a well-sorted siltstone which con-tains intraformational clasts made of reddish clay(< 1 cm in size), sometimes in abundance. Bedthickness ranges from 2 to 20 cm. Individuallaminations reach 1 mm in thickness. Observedsedimentary structures include horizontal towavy lamination, symmetric or asymmetric ripplecross-lamination. The relative volumetric propor-tion of facies F2 is ca 01%.

Facies F2 records fluctuations in the supply ofsuspended sediment by high discharge episodes




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and/or sudden incursions of turbidity currents.The intraformational clasts could be related toepisodic local erosional events superimposedupon a constant and calm deposition by suspen-sion fallout.

Facies F3a: Interbedded siltstone andsandstone

Facies F3a is composed of five sub-facies:

Subfacies (1) corresponds to a well-sorted silt-stone and fine sandstone with bed thickness from3 mm to 4 cm. Wavy millimetric laminationshave been observed.

Subfacies (2) is a siltstone with fine or coarsesandy lenses with a bed thickness of 15 to 25 cm.Wavy lamination constitutes the main sedimen-tary structure.

Subfacies (3) is a siltstone with shells (gastro-pods and bivalves) and fine shelly sands. Bedthickness is 30 cm. Horizontal to wavy lamina-tion has been observed.

Subfacies (4) represents a siltstone containingshells and fine shelly sands with fine sandy lenses(15 cmin thickness). Bedthicknessreaches 20 cm.Sedimentary structures include weak inversegrading, wavy lamination and bioturbation.

Subfacies (5) is represented by siltstones andfine sandstones. Sandstones can contain shells,charcoal clasts, leaves and stem fragments. Bed

thickness ranges from 2 to 4 m. Sedimentarystructures include horizontal lamination, sym-metric ripples, hummocky cross-stratification-like structures identified by local truncations andwedging-out associated with hummocky struc-tures with a wavelength of 15 to 2 m and a heightof 15 to 20 cm, convolute bedding and bioturba-tion. The relative volumetric proportion of faciesF3a is ca 03%.

Sub-facies (1) bears a strong similarity to fine-grained turbidites defined by Stow & Shanmu-gam (1980). In this case, thin regular or irregular

beds indicate low-energy current and thick andirregular beds suggest a higher energy current(Stow & Shanmugam, 1980). Sub-facies (2) is theresult of an alternation of suspension fallout andweak current. Sub-facies (3), (4) and (5) suggestdeposition by suspension fallout sometimesdisturbed by small and weak turbiditic deposi-tional processes. These three sub-facies areinterpreted as deposits of hypopycnal suspen-sion plumes events (Mackiewicz et al., 1984;Hansen, 2004). Hummocky cross-stratification-like structures record waves and currents gen-

erated by storm activity. Hummocky cross-strat-ification (HCS) affects siltstones primarilydeposited by turbidity currents above stormwave base, as HCS has been considered asdiagnostic of storm influence (Harms et al.,1975; Cheel & Leckie, 1993). Nevertheless, HCS

has already been described in turbidite deposits(Walker et al., 1983; Guillocheau et al., 2005;Mulder et al., 2009).

Facies F3b: Variegated siltstone

This facies is composed of fine-grained siltstonesof variegated colour (green, grey and purple).Beds of F3b contain irregular (diffuse boundaries)but crudely rounded carbonate nodules or glae-bules (millimetres to centimetres in size) with nointernal fabrics. Beds are structureless and with a

thickness of 30 cm. Beds contain root traces(pedotubules) and charcoal fragments. The rela-tive volumetric proportion of facies F3b isca 01%. Variegated colours, the presenceof glaebules and root traces indicate repeatedimmature palaeosol development (Retallack,1988, 1990; Bridge, 2003).

Facies F4a: Claystone

This facies is a homogenous structureless clay-stone. Bed thickness ranges from 05 cm to 4 cm.It represents a relative volumetric proportion of

all facies of ca 01%. Facies F4a represents thesettling of clays from suspension. The lack oforiginal lamination may be due to very homo-geneous (continuous) and, possibly, rapiddeposition.

Facies F4b: Laminated claystone

The reddish colour of this claystone may be dueto recent weathering. Bed thickness is decimet-ric. Sedimentary structures are represented byvery fine horizontal to wavy lamination. The

relative volumetric proportion of facies F4b isca 01%. Facies F4b records the episodic set-tling of clays from suspension in a still waterenvironment.

Facies M1: Bioclastic calcareous beds

This facies is composed of two sub-facies. Sub-facies (1) is a grainstone with coralline red algae(Lithophyllum and Lithothamnion) micritic frag-ments and gastropod shells. Bed thickness rangesfrom 015 to 15 m. Beds of sub-facies (1) have




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planar bases or show a progressive transition fromfacies G3 and slightly wavy tops. Beds can locallyshow a slightly nodular aspect. Within SU2topsets of Zone 3 (Fig. 2A), two thin bioclasticpackstone beds (20 and 80 cm thick) containmollusc shells and some algal fragments.

Sub-facies (2) represents interbedded siltstone(thickness < 10 cm) and grainstone beds (5 to70 cm in thickness). Beds show erosional or non-erosional bases, planar tops and contain differentkinds of unidentified gastropods. Beds of thissub-facies can also locally show a slightly nodularaspect. Both sub-facies display weak horizontalbedding. The relative volumetric proportion offacies M1 is ca 003%.

Grainstone beds and interbedded grainstoneand silty beds suggest deposition in an alternatinghigh-energy to moderate-energy carbonate envi-

ronment. The weak nodular characteristic may bedue to a weakly developed bioturbation.

Facies M2: Calcareous spheroid accumulations

Facies M2 is composed of two sub-facies. Sub-facies (1) represents an accumulation of individ-ual (domal-shape to bulbous-shape) spheroids (5to 10 cm in diameter) in small mounds (20 to25 cm in diameter). These spheroid mounds passlaterally into well-bedded carbonates (grainstone-dominated). Spheroids are composed of concen-tric micritic laminae around a core of bioclastic

grainstone. M2(1) contains crustose coralline(red) algae (Melobesoideae), dominated by Litho-thamnion and Lithophyllum. Sub-facies (2) is ashelly siltstone with conglomeratic lenses com-prising pre-rift clasts and rare spheroids (asdefined above). Both sub-facies have a bulboussurface texture and present a very discontinuoushorizontal bedding. The relative volumetric pro-portion of facies M2 is ca 002%.

Facies M2 records a biological construction bycoralline red algae in brackish to marine condi-tions. The small mounds of sub-facies (1)

suggest a reef mound-type organization (James,1983). This carbonate-dominated facies recordsdeposition during a period of little or no clasticinput.

SEDIMENTARY FACIES ASSOCIATIONS

Gilbert-type fan deltas

Gilbert-type fan deltas were first described fromthe Pleistocene of Lake Bonneville by G.K. Gilbert

(1885) who recognized their tripartite associationof topsets, foresets and bottomsets. Interestingly,at around the same time, similar deltas in theCarboniferous-Permian of the French Massif Cen-tral (Centre of France) were described by Fayolet al. (1886) who reached similar conclusions to

Gilbert.Topsets are defined as predominantly fluvial

deposits representing the top of the delta withdepositional dips < 6. Foresets dip radially atangles between 10 and 35 (Flores, 1990) andcomprise gravitational deposits on the curveddelta front.

Bottomsets were defined by Gilbert (1885, 1890)as gently inclined (< 10) fine-grained sediments.There has since been some divergence in thedefinition of bottomsets, with some authors em-phasising their low angle dip (Rhine, 1984;

Colella, 1988b; Nemec, 1990; Rohais et al., 2008)while others insist on their fine-grained nature(Massari & Parea, 1990; Chough & Hwang, 1997;Hansen, 2004). In the present study, bottomsetsare defined as the down-dip terminations offoresets where the facies association is transi-tional, deposited by both gravitational flow andsuspension fallout processes (Ford et al., 2007;Fig. 4A). The fine-grained sediments depositedby suspension fallout and turbidity currentsfurther out in the basin are termed prodeltadeposits. Bottomsets can be low angle to hori-zontal. The facies transition can be abrupt (< 5 m)

or very gradual (up to 300 m). In the latter casehorizontal bottomsets extend out into the basin.In summary, in this study, bottomsets represent atransitional facies association both in grain-sizeand in dip value between foreset and prodeltafacies associations (Fig. 4).

The conditions necessary for the formation ofGilbert-type fan deltas include: (i) high sedimentsupply; (ii) high water flux; and (iii) high creationof accommodation space (Postma, 1990).

Gilbert-type fan deltas are found in fresh waterand marine basins of all types. These deltas have

been described from numerous rift basins andtranstensional basins, for example, the Gulf ofSuez (Gawthorpe & Colella, 1990; Young et al.,2002; Jackson et al., 2005), the Crati Basin in theApennines (Colella et al., 1987; Colella,1988a,b,c), the Corinth Rift (Prior & Bornhold,1989; Ori et al., 1991; Poulimenos et al., 1993;Seger & Alexander, 1993; Dart et al., 1994; Zelil-idis & Kontopoulos, 1996; Malartre et al., 2004;Ford et al., 2007; Rohais et al., 2007a, 2008), theLa Miel Basin, Spain (transtension; Garcia-Mondejar, 1990), the Loreto Basin, Mexico (Dor-




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sey & Umhoefer, 2000; Mortimer et al., 2005) andbasins in the Betic Cordillera, Southern Spain(van der Straaten, 1990; Fernandez & Guerra-Merchan, 1996; Garcia-Garcia et al., 2006).

In this study, the topset breakpoint is a pointdefined as the transition from topset to foreset andcorresponds to a slope break (Fig. 4). In moderndeltas, this transition is characterized by a gentlesub-aqueous slope between shallow water topsets(< 50 m, McNeill et al., 2005) and the beginningof steeply dipping foresets (see close-up in Fig. 4).When stacking patterns are described, successive

topset breakpoints are linked by a line named thetopset breakpoint path. The topset breakpointpath does not correspond to the shoreline trajec-tory (sensu Helland-Hansen & Martinsen, 1996);however, the shoreline will migrate in the sameway. Equivalents of the topset breakpoint pathhave been used by other authors as a tool todescribe and interpret the architecture andsequential stratigraphic arrangement in Gilbert-type delta systems, for example, the Roda Sand-stone (Lopez-Blanco, 1996a,b; Lopez-Blanco &Marzo, 1998), the Kerinitis Delta in the Corinth

Rift and the Jizera and Teplice Formations in theBohemian Cretaceous Basin, Czech Republic(Ulicny et al., 2002), and Pliocene Loreto basindeltas, Mexico (Mortimer et al., 2005).

Facies association descriptions andinterpretations

The nineteen facies are organized into four faciesassociations (topset, foreset, bottomset and pro-delta; Table 2). These facies associations and sub-associations correspond to several depositional

environments, from fluvial to deep water thatdescribe a complete (proximal to distal) Gilbert-type fan delta profile (Fig. 4). Logs illustratingeach facies association and each facies sub-asso-ciation are located on Fig. 5 and presented inFigs 6 and 7. The terms topset, foreset, bottomsetand prodelta are used in this study as geometricterms for the large-scale architectural elements.

Topset facies associationTopset facies are related to a wide range ofdepositional processes and thus represent the

most diverse facies association. Three sub-associations are distinguished, T1, T2 and T3(Table 2). T1 is related to a fluvial depositionalenvironment, T2 to a shallow marine environ-ment and T3 to a transition zone betweenfluvial and marine environments (Fig. 4). T1 isthe overwhelmingly dominant facies sub-associ-ation, representing at least 99% of Kerinitistopsets.

Fluvial topset facies sub-association (T1). Thissub-association is composed of thirteen facies

(Table 2). Gravels of various grades (Facies G1a,G1c and G1d; Table 1) volumetrically dominate,in particular, facies G1c (crudely stratified con-glomerate, representing ca 99% of all the compo-nent facies). Facies G1c, F3a(2), F3b and F4a arefound only in this sub-association. Gravel pack-ages consist mainly of tabular bodies withdiscrete minor internal erosion surfaces. Themost prominent sedimentary structure is crudehorizontal stratification (Fig. 6A).

Rare channel morphologies are preserved,mainly at the top of SU5 and SU6 and within

Fig. 4. Simplified Gilbert-type fan delta profile showing the position of the four facies associations: topset, foreset,bottomset and prodelta. The inset shows positions of the three topset facies sub-associations. The transition fromtopset to foreset is represented by the topset breakpoint.




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SU9 (Fig. 6A). SU5 and SU6 channel forms arebest observed in Zone 2W (Fig. 2A and B); theyhave nearly the same size (thickness, 10 m; width,60 to 70 m) and architecture. On Zone 2W(Figs 2A and 5), channel morphologies arerecognized by their incision into underlying strata.SU9 channel forms are smaller (depth, 3 m; width,20 m), locally display a discrete stacked geometry

and are more developed. Channel infill is made ofhorizontal to undulate conglomeratic bedsdisplaying no internal structure (Fig. 6A). Allthese elements are interpreted as gravel-domi-nated fluvial channels.

Fine-grained facies (sand and silt) occur at thetop of SU1 to SU3 with a maximum thickness of4 m at the top of SU1 (Fig. 6B); they mainly show acoarsening-upward organization with sandstoneto siltstone at the bottom passing to pebblyconglomerates of facies G1a at the top (Fig. 6B).The contact between this conglomerate facies and

the overlying G1c conglomerates defines a KSS,and may be sharp or slightly erosive (Fig. 6B).Locally, coarse-grained facies may consist of int-erbedded pebble grade conglomerate beds and thinsandstone or pebbly sandstone beds (Fig. 6C).

Rare palaeosols of facies F3b are found in theless resistant intervals at the top of SU1 to SU3(Fig. 6A and B). Locally, a small-scale alternation

with facies S1 can be observed. F3b and S1represent facies deposited on the river floodplain.Facies F4a is interpreted as part of the most distalfloodplain. In summary, all these features lead tothe conclusion that this sub-association corre-sponds to a wide range of processes: bedload,traction and suspension transport in a gravel-dominated braided river environment.

Shallow marine topset facies sub-association(T2). Reported here for the first time, T2 is foundin three small outcrops (Figs 2A and 5). Strati-

Table 2. Facies associations corresponding to different processes and depositional environments.

Faciesassociations Facies (see Table 1) Processes and depositional environment

Topset (T1) G1aG1cG1dG2S1S2S3S4F1F2F3a(2)F3bF4a

Wide range of processes: bedload, traction and suspensiontransport

Poorly preserved floodplain and palaeosol depositsSubaerial delta segment: alluvial-dominated settingcomprising gravel-dominated fluvial channelsGravel-dominated braided river environment

Topset (T2) G1aG3S1M1(1)M1(2)M2(1) Variable energy levelBiohermal mound generated mainly by encrustatingred-algae genera (Lithophyllum and Lithothamnion)Shallow marine to brackish environment

Topset (T3) G1e(2)G1aS1S2S3S4 Initial fluvial deposits reworked by wave-actionTransitional between fluvial and marine environmentslocated in the surf zone

Foreset G1aG1bG1d Processes dominated by sediment gravity flows

Gravitational avalanches on the delta frontSubaqueous delta front: avalanching frontal slope withsteeply dipping beds

Bottomset G1aG1dG1e(1)S1S2S3S4F1F2

Dominated by sediment gravity flows, mainly low-densityand high-density turbidity processesTransitional in grain-size and dip valueSubaqueous delta segment: downslope asymptotictransition from asymptotic foresets

Prodelta G1aG2S1S2S3S4F1F2F3a(1)F3a(3)F3a(4)F3a(5)F4bM2(2)

Settling from suspension fallout interbedded withturbidity current depositsOccasional debris-flow processesDeep basin environment in front of deltas

The topset facies association is divided into a fluvial (T1), a shallow marine to brackish sub-association (T2, AghiosAndreas limestone member) and a transitional environment with fluvial and marine influences (T3). Facies that arerestricted to a specific facies association are in bold lettering.




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graphically, this white limestone is named theAghios Andreas limestone member. The mainoutcrop has a thickness of 154 m (Fig. 6D). It iscomposed of six facies (Table 2). Facies G3, M1and M2(1) are unique to this sub-association. M1and M2(1) are volumetrically dominant. At thebase, a well-defined, decimetre thick, continuous

conglomeratic bed with a non-erosive base isinterpreted as a beach conglomerate (facies G1a;b in Fig. 6D) because clasts are well-sorted insize and shape (Collinson & Thompson, 1982;Bourgeois & Leithold, 1984). The overlying lime-stone is divided into two units. The lower unit(67 m) comprises well-bedded bioclastic grain-stones (M1 facies). The upper unit (85 m) showsa biohermal mound (M2 facies, Fig. 6D and E)which is surrounded by bedded strata of M1facies (Fig. 6D). The biohermal mound was gen-erated mainly by Lithophyllum (Fig. 6F) and

Lithothamnion (a sub-family of the Corallinaceaefamily; Flugel, 2004), which consist mainly ofencrusting genera of variable size and form,which inhabit a wide range of high-energy (Bar-attolo, 1991) brackish to marine environments(Wray, 1977; Tucker & Wright, 1990; Riding,1991; Flugel, 2004). It is concluded that this

carbonate mound was built in a brackish tomarine environment during a period of very lowinput of terrigenous sediments, close to the topsetbreakpoint (Fig. 4). Carbonates lying over fluvialtopsets are common in many deltaic systems(Weimer, 1978; Coleman, 1981; Galloway & Hob-day, 1983; Giosan & Bhattacharya, 2005).

Foreshore to shoreface topset facies sub-asso-ciation (T3). This sub-association occurs at thetop of SU7 in two orthogonal exposures (Fig. 5),one of which has been described previously by

Fig. 5. Geographic location in the Kerinitis River valley of sedimentary logs presented on Figs 6 and 7. The Proto-delta package is also shown, showing an onlap surface between the Proto-delta and the Lower delta.




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A

B

C

05

1205

1205

KerinitisDelta

KolokotronisDelta

Verycoarsesand

Fig.6.

Logsofkeyfaciesinthetopsetfaciesassociation.

Alllogs[ex

cept(A)and(G)]representtrueoutcropslocatedonFig.

5.

Logs(A)and

(G)aresynthetic

logsofinaccessibleclifffaces.(A)Syntheticlogthroughfluvialtop

setunitsofZone1dominatedbyfaciesG1c[faciessub-associationT1;(T1a)onFig.

5].

Stratalunits(SU)inZone1aredominatedbythefaciesG1c.

(B)Detailedlogoffine-grainedfaciesofT1

subassociationdevelopedattheto

pofstratalunit1

(T1bonFig.

5).Stratalunit2isd

ominatedbyG1c(Fig.

6A).(C)Coar

se-grainedtopsetfaciesdominatedb

yG1dandwithsomesandstones(S1)(T1conFig.

5).

(D)LogthroughtheAghiosAndreaslimestonemember(T2faciessu

b-association)anddiagramofthem

ainoutcrop.

LocationsofFig.

6Ean

dFaregiven.

(E)

FieldphotographofthefaciesM

2(1)(Table1)organizedindecimetricmounds.(F)Thinsectionofthefa

ciesM2(1)showingconcentricmicritic(stromatolite-

like)laminaeencrustingacoreo

fbioclasticgrainstone.

L.

indicatesLithophyllum

redalgae.(G)SyntheticlogthroughtheT3sub-association.

(h)Photograph

illustratingwhereasimilarfacie

ssub-associationiscurrentlybeing

depositedatthemouthofthepres

ent-dayVouraikosRiver(seeFig.1

forlocation).See

Figs5,

9A,

9B,

11Band13Bfor

location.

Inset:symbolsusedinlogs.




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D

E

G

H

F

Fig. 6. (Continued)




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Ori et al. (1991) and Dart et al. (1994). A syntheticlog (Fig. 6G) has been made on the northsouthsection, not previously described, where T3 has athickness of 24 m.

The sub-association is composed of six facies.Facies G1a is volumetrically dominant. Conglo-

meratic beds of facies G1e(2), unique to this sub-association, show low angle cross-bedding withdepositional dips ranging between 6 and 18(average 13 with structural dip restored). Palaeo-currents are towards the north. T3 locally shows aslightly erosional base. The basal part of T3comprises conglomerates with progradationaloblique-bedding with laterally decreasing dips.Conglomerates laterally pass into alternatingsandstone and conglomerate beds. A successionof finely bedded alternating conglomerate andsandstone beds overlie the basal part of T3. The

top of T3 comprises well-bedded conglomeratebeds of variable thickness (05 to 33 m) whichcan have channellized bases.

The laterally continuous, non-lenticularwell-bedded conglomerates indicate a marineinfluence (Massari & Parea, 1990). Reading &Collinson (1996) argue that wave action mayshallow the dip of cross-bedding. The low anglecross-bedding plus the tabular conglomeraticbeds therefore are interpreted to indicateinteraction of fluvial and wave processes(Leithold & Bourgeois, 1984). Such an environ-ment is named the transition zone by Colella

(1988b,c) and is located in the surf zone (Fig. 4),where waves are efficient. The deposits aremainly fluvial in origin but reworked by waveaction (shoreface to foreshore). Figure 6H illus-trates where a similar facies sub-association iscurrently being deposited at the mouth of thepresent-day Vouraikos River (see Fig. 1 forlocation). Because of its position near the deltafront, this transition zone was very sensitive tovariations of relative sea-level. The T3 unitoverlies fluvial conglomerates (facies G1c) on aplanar bedding surface. In summary, this facies

sub-association is interpreted as a wave-re-worked gravel beach, located in the surf zoneon the delta front, at the transition betweenfluvial and marine environments.

Foreset facies associationThis facies association includes three facies(Table 2). Facies G1b is unique to this associationand volumetrically dominant. The outstandingcharacteristic of this facies association is thedepositional dip of 25 (mean value; Fig. 7A).The height of a foreset package indicates palaeo-

water depth and was up to 350 m. Stratification isdefined by subtle changes in sorting, open-frame-work texture or by beds containing oversizedclasts (Fig. 7A).

Foresets are observed in several places todownlap onto erosional surfaces (see Delta stratal

architecture and A/S section below). Foreset bedswere deposited mainly by gravitational ava-lanches on the delta front. Two types of internalstructure are observed: slumps (see SU9 descrip-tion below) and backset bedding possibly due tobackfilling of a slump scar (Ori et al., 1991).Similar structures are widely described on deltafronts (Dingle, 1977; Massari & Parea, 1990;Nemec, 1990; Ulicny, 2001; Longhitano, 2008).

Open-framework gravels are very commonwithin foreset beds (Hwang & Chough, 1990;Massari & Parea, 1990; Rohais et al., 2008). These

gravels form mainly by the separation of finerfacies from gravel on steep lee faces. The sandand finer facies are carried in suspension,whereas the gravel avalanches or rolls down thelee face (Lunt & Bridge, 2007). In summary, thisfacies association is interpreted as resulting fromsediment gravity flows, and gravitational ava-lanches on the sub-aqueous delta front, which arecharacterized by limiting slope inclination ofsteeply dipping beds.

Bottomset facies associationSU10 foresets show a downward asymptotic

decrease in dip angle, gradually passing intobottomset facies, with inclinations lower than10. The bottomset facies association comprisesnine facies (Table 2), which gradually fine basin-ward. The bottomset facies association is charac-terized mainly by thinly interbedded S2, S3 andG1d (Table 1). Inverse grading is assigned togravity flow processes. Erosion surfaces and/orscours are common. In some places, soft sedimentdeformation occurs with small-scale slump foldsand/or dewatering structures (Fig. 7B).

Gravel dune cross-bedding [facies G1e(1)],

unique to this facies association, is interpretedas due to the arrival of a high-density turbidityflow on the shallowly dipping delta front(Pickering et al., 1989). Mutti et al. (2003)describe similar tractional bedforms controlledby hyperpycnal flows of coarse-grained sedimentstransported by turbulent flow from the riveroutlet.

In summary, this facies association is domi-nated by sediment gravity flow processes, mainlylow-density and high-density turbidity processes.It corresponds to the subaqueous delta base where




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asymptotic foresets pass into more gently dippingto subhorizontal bottomsets.

Prodelta facies associationThe prodelta facies association is made of 14facies, six of which are unique to this faciesassociation (Table 2). That association is domi-nated by beige-coloured, structureless to parallel-laminated sandstones and silty sandstones, thinmatrix-supported pebble conglomerates and lam-inated siltstones (Fig. 7C). These deposits areinterpreted as the products of suspension fallout

(fine facies) and turbidity currents, and representthe most distal environment within the KerinitisDelta system. Rare matrix-supported conglomer-ates (facies G2) are interpreted as far-travelleddebris flow deposits. As well as forming theZoodochos Formation (up to 500 m thick), rem-nants of this facies association (up to 5 m thick)are preserved throughout the Kerinitis edifice,often with erosive upper boundaries. This faciesassociation is often affected by small normalfaults. Similar prodelta facies associations havebeen described and associated with other Corinth

A

B C

Fig. 7. (A) Log of typical gravel-dominated foreset facies association with steep sedimentary dips. (B) Log of typicalbottomset facies association (C) Log of typical prodelta facies association. See Figs 5, 9A and 11B for location.




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Gilbert deltas (Malartre et al., 2004; Ford et al.,2007; Rohais et al., 2008). In summary, this faciesassociation is interpreted as resulting from sus-pension fallout and turbidity current processesand represents the most distal (deep basin) envi-ronment of the Kerinitis Gilbert delta.

DELTA STRATAL ARCHITECTURE ANDA/S

Stratal architecture and stacking patterns are hereinterpreted in terms of A, which is the rate ofcreation of accommodation space, and S, thesediment supply rate (Schlager, 1993; Muto &Steel, 1997). Changes in A and S can only beappraised qualitatively in this study. When0 < A/S < 1, sequences show a progradational

stacking pattern. When A/S > 1, sequences canshow a retrogradational stacking pattern andwhen A/S = 1, sequences show an aggradationalstacking pattern (Shanley & McCabe, 1994).Abrupt changes in A/S cause changes in stratalarchitecture, in particular the position of thetopset breakpoint path.

The delta stratal architecture is analysed byidentifying and tracing SUs and the surfaces thatseparate them, here called key stratal surfaces.The subdivisions given here are not strictly thesame as those proposed by Dart et al. (1994) whodefine sequence stratigraphic surfaces (for exam-

ple, transgressive surfaces) and systems tracts. Inaddition, this analysis includes the whole deltawhile Dart et al. (1994) restrict their studyto Zones 2E and 3 as defined in this study(Fig. 2A).

Stratal units are bounded by KSSs and cancontain any combination or thickness of topsets,foresets, bottomsets and prodelta which are innormal geometrical succession (showing progra-dation, aggradation or retrogradation). The com-position and thickness of these units will varylaterally across the delta.

Key stratal surfaces are surfaces that can beidentified clearly and correlated across a largepart of the delta. Each surface represents a hiatusin sedimentation and a change in A/S ratio. Incharacter these surfaces:

(a) are either conformable (1) or erosive (2);(b) can separate topset (T), foreset (F) or prodelta

(P) packages;(c) which are in normal (when superposition of

topset, foreset and prodelta follows thestratigraphic order shown in Fig. 4) or

abnormal succession (for example, foresets ontop of topsets).

Using these three parameters, Fig. 8 representsall possible configurations of KSS geometries andjuxtaposed facies associations and assigns them a

code. For example, TF1 describes a non-erosive butabnormal contact between topsets and overlyingforesets while TF2 describes the erosive equiva-lent. Surfaces can show onlap, downlap or toplapgeometries along their length (as defined byMitchum et al., 1977). All three parameters canchange along an individual surface. Surfaces arebest defined in the area of the topset breakpointpath and thus it is important to trace surfacesacrossthe whole deltaicedifice whenever possible.

Changes in A/S are most clearly indicated by anabnormal succession of facies associations acrossa KSS. The presence or absence of erosion is a

secondary feature. Surfaces that superimpose thesame type of facies association (topset on topset,for example) are ambiguous and cannot be inter-preted in isolation.

Changes across KSS can record two major typesof change in A/S:

1 A landward shift in the topset breakpointpath across a KSS indicates an abrupt increase inA/S. TF2 and TF1 types are the most obviousexpressions of an increase in A/S. TP1 and TP2surfaces represent even more important landwardshifts in the topset breakpoint. FP1 and FP2

surfaces (Fig. 8), which occur at the foot of adelta edifice, may be interpreted in the same way(Rohais et al., 2008).

2 Basinward shifts in the topset breakpoint pathdue to a decrease in A/S are more difficult todetect as the sedimentary record is often pre-served in the deep offshore basin, not in the delta,where only erosion should be recorded. Theseshifts are recorded (in decreasing importance) byPT2 (onlap), PF2, PF1, FT2 (onlap), FT1 and TT2.

STRATAL ARCHITECTURE OF THEKERINITIS DELTA

The geometry and hierarchy of KSSs and SUs ofthe Kerinitis Delta have been identified andcorrelated on photographic montages of majorcliff sections. Delta architecture is simplified andprojected onto two profiles, one north-east tosouth-west (Fig. 9) and the other north-west tosouth-east (orthogonal to the transport directionin this part of the delta, Fig. 10A). Detailed




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drawings of cliff sections are shown in Figs 11 to14.

In Zone 1, topsets dip and thicken towards bothcontrolling faults. An important component of theobserved south-west tilting is post-KSS11 (Fig. 9).Thickening of Kerinitis topsets across Zone 1requires a syn-sedimentary tilting of 7 to 8towards the faults; however, tilting towards theKerinitis Fault is impossible to represent cor-

rectly in the south-west to north-east cross-section (Fig. 9B). When traced into Zone 2,topsets become horizontal, thus describing agentle anticline. The thinnest units lie at thecentre of the delta edifice at the western end ofZone 2N (Fig. 9A). Creation of accommodationspace was therefore at a minimum in the centre ofthe delta edifice and increased towards the faults.

All KSS in Zone 1 (Fig. 9) are slightly erosive tonon-erosive and separate conformable succes-sions of fluvial topsets (KSS type TT1, Fig. 8).Key stratal surfaces are underlain by fine-grained

facies forming a less resistant interval of variablethickness (Fig. 6A and B). Overlying conglomer-ates can have locally channellized bases. All SUs,except SU4, SU10 and SU11, are represented inZone 1. Key stratal surfaces are best identified inZone 2 where most topset breakpoint paths occur(Fig. 9B). The frontal part of the delta, Zone 3, isdominated by thick stacked foresets of SU7 toSU11. Here KSS are of type FF1 or FF2 and can

show local downlap and toplap (Fig. 8). Towardsthe foot of the edifice in Zone 3, bottomset andprodelta facies appear above and below the KSS.However, due to poor exposure, the position ofthe foresetbottomsetprodelta transitions andthus KSS frequently have to be inferred (Fig. 9B).

Three distinct packages of SUs are identified inthe delta, based on the characteristics of theirinternal geometries, facies and the nature of KSS.In addition, a small Proto-delta is identified belowtopsets in Zone 1. This foreset package is ca800 m long and ca 30 m thick. It occurs in the

Fig. 8. Synoptic table presenting all possible geometries and facies juxtapositions across key stratal surfaces in aGilbert-type fan delta. For the sake of clarity, the bottomset facies association and the prodelta facies association areregrouped under the name prodelta.




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A B

Fig.9.

(A)Panoramaofthewholesouth-westtonorth-eastKerinit

isRiversectionshowingselectedK

SSandSUoftheKerinitisDeltaa

ndtheoverlying

KolokotronisDelta.

Thispanoram

adoesnotincludethelower25%o

fthecross-sectionin(B).Themostw

esterlypointonthecliffofZone2N

liesverycloseto

thecoreofthedeltaedificewhil

ethecliffsofZone1and3lieclose

totheKerinitisFault.

Locationsof

variousfiguresareindicated.

Some

topsetbreakpoint

pathsareindicatedwithblackdo

ttedlines.Notethechangesinorien

tationbetweencliff2Eand3.

(B)Sy

ntheticnorth-easttosouth-westcros

s-sectionthrough

theKerinitisDeltashowingthek

eystratalsurfacesandstratalunits.Thisdiagram,

locatedonFig.

2A,pr

ojectsaverageunitthicknessesandp

ositionsoftopset

breakpointpathsontoasinglecross-sectionthatisatahighangletothePirgakiFaultbutrunsparalleltotheKerinitisFaultandpassesclosetothecentreofthe

delta.

Anycross-sectionalrepresentationofthecomplex3Ddeltaarc

hitecturerequiresconsiderablesimp

lificationbecausestrataaretilted(u

pto18)andcan

alsothickentowardscontrollingfaults.Notethatgeometrieshave

beensimplified.

Forexample,

SU5

toSU7geometriesarethoseobservedinZone2N;

however,theseunitsthickenanddiptowardstheKerinitisFault(Zone3;seeFigs13and14).SU2and

SU3onlapontotheProto-delta.




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A

A

A

B

KatoFteriFm.

Ko

loko

tron

isDe

lta

Fig.10.

(A)Syntheticnorth-we

sttosouth-eastcross-sectionthrou

ghthecentreoftheeasternKerin

itisDeltaparalleltothePirgakiF

aultandroughly

orthogonaltothedeltabuildingd

irection.

TheerosivecharacterofmanyoftheKSScanbeseenaswellas

thepositionofthetopsetbreakpointpathsofSU6and

SU7.

Thisdiagramislocatedon

Fig.

2A.

(B)PanoramaofthenorthernfrontoftheKerinitisDelta(SU10

andSU11)asexposedonthenorth-westtosouth-east

cliffsection(lookingtowardsthe

south-west).SU10foresetsshowad

ome-l

iketracesimilartothatproducedinmodelsofGawthorpeetal.(2003).Theyounger

KolokotronisDeltaliesunconformablyabovetheKerinitisDelta.D

isplacementontheWestKatoFteri

Fault,

usingthebaseofSU10,

isestimatedat37m.

WKaFF,

WestKatoFteriFault;E

KaFF,

EstKatoFteriFault(Fig.

2A).




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Fig.

7C

Fig.

11B

Fig

.11D

Fig.

6D

Fig.11.

Stratalarchitectureinth

eLowerdeltaandveryearlyMiddledelta(SU1toSU4)showingKSSgeometries(inboxes,seeFig.

8)andfaciesassociations

(incircles,seeTable2).(A)StratalgeometryofSU1toSU3inZone3.

SU1showsaprogradationalstackin

gpattern.

SU2comprisesstackedprogradationalunits

separatedbythintopsetfaciesincludingrarelimestones(packstone).SU3topsets,

includingtheAghiosAndreaslimestonemember(black),areincisedby

KSS5,

whichshowsastaircasep

rofile.

ThepositionofFig.

13Aiss

hown.

(B)Fieldphotographofthea

reainterpretedin(A).Locationsof

logspresentedin

Figs6C,

6D,

7A

and7Careindicated.

(C)LowestexposuresinZ

one2EshowingKSS5incisingintoSU4.

A

smallnormalfaultcuts

SU5(N172-6

0E).

Palaeocurrentdataindicatethat

theSU4GilbertdeltabuilttowardsN044E,

awayfromtheviewer.Loca

tionofFig.

11Disgivenbytheblackframe.

(D)Field

photographofthecentralpartof(C).Inset:locationofdiagrams(A)

and(C).




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Kerinitis valley close to the Pirgaki Fault(Figs 2A, 5 and 9A). Foreset trends indicate aprogradation towards the north. Topsets of SU2 toSU3 onlap onto the package (Figs 5, 9A and 9B).

Lower delta: stratal units 1 to 3The Lower delta is 150 to 200 m thick (base notexposed). SU1 and SU2 (Figs 9B, 11A and 11B)are dominated by stacked packages of foresetslimited by sub-horizontal KSS of type FF1b andFT1 (Fig. 8).

SU1 comprises a single package of north-east-dipping foresets, 65 m high, and at least 1100 mlong exposed at the base of Zone 1. The foresetsshow a toplap geometry with KSS1 (type FF1b).This package is cut internally by erosionalsurfaces, locally associated with packages of

bottomset to prodelta facies (Fig. 11A). Theseforesets are correlated with the lowest 40 m thickpackage of fluvial topsets in Zones 1 and 2(Fig. 9B). The topset breakpoint path wouldtherefore be strongly convex up before passingto a long sub-horizontal toplap boundary(Fig. 9B).

SU2 is a poorly exposed, 35 m thick unit inZone 3, comprising two stacked foreset pack-ages separated by thin topsets (with thin bio-clastic limestones) whose bounding surfaces arepoorly exposed and not laterally continuous(Fig. 11A and B). Therefore, all these surfaces

have not been interpreted as KSSs. SU2 isbounded above by KSS2 (type FT1; Fig. 11Aand B). A strongly convex up topset breakpointpath is inferred for each foreset package. TheSU2 topset package is 30 m thick across Zones1 and 2.

The lower part of SU3 (Figs 9B and 11A) isdominated by fluvial topsets (up to 45 m) inZones 1, 2 and 3. No equivalent foresets arepreserved as the unit is deeply incised by KSS5 oftype TF2 (Fig. 11C and D). The upper SU3comprises the Aghios Andreas limestone member

(Fig. 11A; T2 topset facies sub-association) whichis preserved in isolated remnants below KSS5 andis up to 154 m thick. The base of the beachconglomerate (b, Fig. 6D) corresponds to a sur-face which records a slow increase in A/S (sur-face a on Fig. 12A).

In summary, the Lower delta is dominated byvertically stacked packages of progradationalforesets (SU1 and SU2) overlain by fluvial andminor shallow marine (T2) topsets of SU3 in Zone3. All packages pass to stacked fluvial topsets inZone 1.

Middle delta: stratal units 4 to 9

The Middle delta is 400 to 450 m thick and startson KSS3, which is a non-erosional surface (TT1 toTF1), separating beds of T1 topset facies sub-association from a package some 20 m thick

comprising prodelta beds and bottomsets (SU4,Fig. 11C and D). Across KSS3 the topset break-point path took a landward step of more than1 km, the most significant landward shift in thewhole delta (Fig. 12A).

A landward shift in the topset breakpointpath of ca 200 m is recorded across the erosiveKSS4. SU5 is only preserved in Zones 1 and 2.In Zone 2 it is represented by 40 m highforesets that infill a 20 m incised topography(Fig. 11C and D); they are truncated above byKSS5, which is the most significant surface in

the exposed delta, incising downward towardsthe basin by over 120 m across Zones 2 and 3(Fig. 9). In the eastern part of Zone 2, KSS5 issub-horizontal and locally erosive (Fig. 13A). InZone 3, where it totally cuts out SU3 (60 m),the surface presents a staircase form suggestingthat the surface cut into already induratedconglomerates (Fig. 11A and B). No palaeosolswere found on or below this surface.

Across Zone 1, SU6 topsets thicken to 50 mtowards the Kerinitis Fault. Across Zone 2 thetopset breakpoint path has a shallow dip, becom-ing horizontal towards the north-east (Fig. 13A).

At the south-west end of Zone 3, SU6 is 20 mthick (Fig. 13A and B) where it terminates againstthe erosive KSS6. In detail, the SU6 topsetbreakpoint path comprises alternating toplapgeometries and packets of gently climbing topsetbreakpoints (Fig. 13C). SU6 foresets downlaponto the erosive KSS5, reaching heights of 55 m,but they did not reach the shelf break of the delta.

On the south-east to north-west cliff face (sec-tion 2E, Figs 2A and 10A), orthogonal to the maindelta construction direction, details of KSS6 showthat it has a composite history (Fig. 12B). The

erosive surface is wavy (wavelengths 30 to 80 m,Fig. 10A), incising by up 3 to 5 m sometimes witha staircase geometry. However, just below thissurface fine-grained beige facies [mainly F3a(5)]are preserved in the cusps between erosivelobes, (< 5 m in thickness) and lie in non-erosivecontact on SU6 fluvial topsets (T1 sub-faciesassociation). This fine-grained facies correspondsto a prodelta facies association, implying thattheir base records a major increase in A/S (surfaceb, Fig. 12B) that pre-dates the erosive surface(Fig. 10A; surface c, Fig. 12B).




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Across KSS6 the topset breakpoint path stepslandward by over 200 m. SU7 foresets build out(downlap) across the KSS6 and KSS5 surfaces(type TF2) and cross the shelf break on KSS5 toreach heights of over 250 m (Fig. 13A). Like SU6,

the SU7 topset breakpoint path comprises alter-nating toplap and aggradational geometries andclimbs gently towards the north-east following aconvex up path (Fig. 13D). SU7 has a thickness ofup to 80 m in Zone 3 thinning to 30 m (Zone 2N).




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From this point towards the south-east (acrossZones 2W and 1) SU7 topsets thicken to 90 mtowards the controlling faults (Fig. 9B).

At the south-east end of Zone 2E (Fig. 9) theupper 20 m of SU7 topsets record both wave andfluvial processes (T3 facies sub-association;Figs 6G and 13B). The planar base of this package(Fig. 13D) therefore records a small to modestincrease in A/S (identified by Dart et al., 1994 intheir fig. 8B; surface a on Fig. 12C).

On the north-west to south-east cliff face,KSS7 has the same composite characteristics asKSS6 (Fig. 10A). The upper erosional surface(surface c; Fig. 12C) is undulose with wave-lengths of 40 to 80 m, and erosive by up to 5 m.It cuts down into the T3 topsets of SU7(Fig. 13A). The same fine-grained beige prodeltafacies association is preserved in cusps below,lying in non-erosive contact on T3 topsets. Thebase of these prodelta beds records an abruptincrease in A/S (surface b, Fig. 12C). Thesefeatures again indicate that the erosive surface c

(Fig. 12C) post-dates the major increase in A/S(see Discussion). The lobate characteristics of theerosion surfaces (surface c, Figs 12B and C)may be related to local erosional processes at thefoot of prograding foresets.

SU8 is characterized by topsets (Fig. 9B) thatthicken considerably across Zone 1 (up to100 m) and high foresets (Figs 10A, 14A and14B) in Zone 3 (foreset maximum height: 260 m).However, in Zone 2N (Fig. 9A), the unit isonly 30 m thick (Fig. 14C to E). The topsetbreakpoint path has a very shallow dip passing

north-eastward to a toplap geometry (convex-upgeometry).

SU9 is very similar to SU8 (maximum foresetheight of 353 m; Figs 9B, 14A and 14B), however,its upper part has been eroded by KSS11 (base ofthe younger Kolokotronis Delta). Although itstopset breakpoint path geometry cannot be fullydefined, foreset height implies that the topsetbreakpoint path is convex-up with a high aggra-dational component. On Zone 2E, KSS8 and KSS9

are associated with small-scale local erosion.

Upper delta: stratal units 10 and 11

SU10 foresets (height 300 m) terminate upwardwith clear toplap geometry onto KSS10 (Figs 9Band 14A) and curve downward into long sub-horizontal bottomsets that can be traced north-ward (ca 1300 m) across the Kato Fteri horst(Fig. 10B), terminating against the East KatoFteri Fault (Fig. 2A). The thin overlying topsetpackage (20 m) is correlated with SU11 foresets

that are preserved in small outliers on the frontof the delta (Fig. 10B). SU11 is insufficientlypreserved to define its characteristics but seemsto record a weak late subsidence. The ESEWNW cliff forming the northern limit of thedelta provides a longitudinal section throughSU10 and SU11, both of which show a dome-like form (Fig. 10B), typical of a transverse cutthrough a curved delta front (e.g. Gawthorpeet al., 2003). The KSS11 surface is the erosivebase of the younger Kolokotronis Gilbert delta(Fig. 9A).

Fig. 12. Analysis of the composite characteristics of the boundaries KSS3, KSS6 and KSS7. (A) Simplified NW to SE/SW to NE cross-section of KSS3 c

Architecture and Sedimenology Gilber-Delta Corinth-Rift

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