Coastal sedimentary environments and sea-level changes

Cristino J. Dabrio

Depanamenlode EstratigrnfJa, Facultadde Ciencias Ge<llOgicas, Universidad Complulenseand lnstinuo de G«llogla Economica,CSIC,28040 - Madrid (Espai'la).dabrio@cucmax.sim.ucm.es

ABSTRACT

Key-words: coastal sedime ntation; eustatic changes; stratigraphic architec ture; tectonics; accommodation space; Ca inozo ic.

A detai led knowledge of the 3-D arrangement and lateral facies relationships of the stac king patterns in coastal deposi ts isessential to approach many geo logical problems such as prec ise tracing ofsca level changes. pa rticular ly duri ng small scale fluctua­tio ns. These are useful data regarding the geodynamic evol ution of basin marg ins and yield profi t in oil exploration. Sedimentsupply, wave-and tidal processes, coastal morphology, and accommodation space generated by eustasy and tectonics govern thehighly variable architecture of sedimentary bodies deposited in coastal settings. But these parameters change with time, and ero ­sional surfaces may play a prominent role in areas located towards land. Besides, lateral shift oferosional or even depositional locivery often results in destruction oflarge parts of the sediment record. Several case studies illustrate some commonly found arrange­ments offaeies and their distinguishing features. The final aim is to get the best results from the sedimentological analysis of coastalunits.

RESUMO

Palavras-chave: sedimentaiVlio costeira;vari~ eustaricas;arquitectura estratigrifica; tect6nica;espaeode acomodacgo;Cenoz6ico.

o conhecimento dctalhado do acranjo tridimensional e das re!aiViks laterais de facies nos depositos costeiros sAo essenciais paradefinir, com precisao, as variaeoes do nlvel do mar,em especial as Ilutuacdes de pequena escala. Estas fomecem dedos uteis para 0

reconhecimento da evclueac geodinjmlca das margens des bacias berncomo para a pesquisa e explcracao de petrcleo. 0 acarreiosedimentar, os processes ondulatorios e de mares, a morfologia costeira e 0 espaco de acornodaejc gerado pela eustasia e pelatectonica sAo os reepcnsaveispela arquitectura muito variavel des corpos sedimentares depositados em ambientes costetros.Todavia,estes pardmetros variam no tempo, e as superficies de ercssc podem ter papel importante nas mas pr6ximas do oontinente. Alemdissc, a desjocaejo lateral da ercsac ou mesmo lacunas sedimentares conduzem, com frequencia, adestruiiVto de parte significativado registo sedimentar. Apresentam-seexemplcs que ilustram algunsarranjos frequentesde faciese cs seus parametres caractertsticoscom vista a obter os melhores resultados na analise sedimentol6gica das unidades costeiras.

INTROD UCTIO N

The littora l is an unstable zone that comprises marineand terrestri al domains ve ry sensitive to a var iety ofgeologica l processes . Waves and tides playa mostimportan t role in the coastal dynamics, and their mutualinte raction acco unts for redistri bution of the sedimentbudget causi ng accumulation or erosion . Changes of sealevel gre atly modify the area reac hed by these agents inthe course of time.

Waves move sediment and tend to accumulate it inbeaches. Thus, the incoming waves are really a barrier toth e sea ward movement of sedime nt derived from thecontinents. Storm waves produce erosional surfaces. Theerosive effect is particularly great during transgressions due

to the landward displacement of the surfzonc across formeremergent parts of the coast that were topographica lly moreelevated.

Tides cause per iod ic oscillations of sea level that arefelt mainly in areas where geographical constrictions suchas shoals and straits restrict the free movement of watermasses and genera te currents th ai sweep the bottom .Astronomical tides induced by the attraction of the SWland Moon in large bas ins cause periodic reversion offlowand oscillating cu rrent velo cities . In contras t ,meteorological tides caused by piling up of water on thecoast, either periodically or not, are important in microtidalor tideless coasts because they increase the area reached bythe surf zone. From the a sedimentological point of view,the main differences between beaches and tidal flats refer

39

1° Congresso sobre 0 Cenoz6ico de Portugal

to slope, source of sediment and dominance o f waves ortida l curren ts. But this simple scheme changes from cliffsto beaches, barrier islands and lagoons, tidal flats, andestuari es.

In o ther words, the (morpho-) sedimentary unitsdeposited in coasta l settings exhi bit a highly va riab lestratigraphic architec ture, that is mainly governed byfactors as sedimen t supp ly, wave- and tidal processes,c oasta l mo rp hology a nd a ccommod at ion spac e .Seaward, these coastal sedimen tary units interfi nger withmuddy she lf depo sit s, bu t landward these either endabruptly, or show ra pid facies changes to tida l, lagoonal,washover-fa n and fluvial deposits. With time the patternbecomes more co mplica ted as the abo ve mentioned factorschange , especially when landward erosional surfaces startto playa prominent ro le as soon as a position above baselevel is reached.

EUSTASY AND COASTAL ENVIRONMENTS

Despite da ily or weekly oscillations, it is possible toestablish a mean sea leve l that is considered 's table' or' fixed' at the scale of human life and serves as refe rencedatum for topographic purp oses. The theoret ical da tum inSpain is the mean level of the Mediterranean Sea inAIicante, but it actually fluctuates some 20 to 30 em/yr.These small-scale oscilla tions are a response to variationsof atmospheri c pressure, evaporation, volume of oceaniccurrents, and changes of wat er density due to varyingtemperature and salinity. In the Northern Hemisphere themean sea level is topographically higher in autumn andlower in early spring.

Suess first used the term eustasy in late 1911l Century tore fer to changes of level in oceans assuming that they werecoeval and of gl oba l ex te nt. Later realisation o f the

GLACIAL10 mmfyr

DYNAMICCHANGESi1 m r;

0.1 1 10 100 mmlyrVELOCITY(mm/yr)

DEFORMATIONS, OF THE GEOID

_ / 10-30 mmlyr-e-.......-/ , ', EUSTATIC ·

"" , VARIABLES

"\\

0.01

1000

100

.sw 10

~~~

TECTO-EUSTASY

GLACIO·EUSTASY

GEOIDAL EUSTASY

~-::-AIJFig. I -Types of eustasy (left) and rates of sea level change (right).

o marine _ terrestrial

\.. coast (beginning) '\ coast (end)

transgression--. f

~ C~ 1 ~ 2 ~3

eustatic curve '\ eroslon ~ '\

~~~ ..composite offlap + to /a

8

input

Aregression

Fig. 2 _(A) Sediment input, transgression and regression during a rise of sea level. (B) Superimposition of eustatic curves withvariable periodicity and resulting composite curve. (C) Effects upon coastal units of eustatic oscillations with different amplitudes

(modi fied from Dabrio & Polo, 1996).

40

tectonic and glacial components of eus tasy led to theincorporation of the terms glacio-eustasy and tectono­eustasy. Monier (1976) coined the term geoida l eustasyafter measurem ents from satellites revealed that the irregu­larity of the geoid also causes eustatic changes. At presentit is widcly ackno wledged that the sea level movescon tinuously both vertical and horizontally forced bychanges in the lithosphere and the hydrosphere and theirdiffe rent velocity of response (Fig. I). Thus, the termeustasy applies to any change ofsea level regardless of itbeing or not global and coeval.Global factors such as the "glacio-eustatic general sea­level rise" that took place after the Last Glacia l Maxi­mum until ca. 7 000 yr. BP (Goy et al., 1996) control thepresent position of coastlines, but reg ional factors alsocontribute significantly to their evolution and trends . Inthe coasts of the Southern IberianPeninsula, there are threema in region al fac to rs . (I) The geographic loc ation(between 36°-40° N and 3°E-9°W) largely controls thewea ther and climatic trends. (2) The tectonic framework(boundary betwee n the European and African plates)where numerous faults active during the Late Pleistoceneand Holocene have affected the coastline producingupli fting or subsidence (Zazo et al. , 1994). (3) The effectsof the interchange of Atlantic and Mediterranean watersthro ugh die Gibraltar Stra it.

During eustatic oscillations thc coastal environmentsmove laterally tens to hundreds of kilometres and verti­cally tens to hundreds of metres depositing sedimentaryunits that very often are disconnected laterally and far awayfrom each other. Th e laterally shifting high-energy surfand breaker zones cut erosional surfaces. Eustatic fallsexpose large areas to subaerial erosion.

Apart from presently known possibilities to discriminatethe vertical upward and downward relative movement ofsea level within sequences of coastal depos its, a morecomplica ted effort is to incorporate the three-dimensionalevolution of the shore line . Another complexity is thedetermination of the timeframe in which the distinguishedpatterns ofcoastal sequences have been formed. Generally,coastal depos its do not easily lend themselves for precisedat ing of successive de posi tio nal steps. Rec ent andsubrecent depos its form an except ion, e.g. through 14Cdating possibilities. Although seq uence stratigraphy helpsto dis tinguish related sediment packets deposited underconditions of varying accommodation space, carefulsedimentolog ical analys is sho uld precede a sequencestratigraphic scheme (Van Wagoner & Bertrams, 1995).Even then it is good to keep in mind that the number ofvariati ons on the general sequence stratigraphic model islimited only by the imagination (posamentier & Allen,1993).

EUSTATIC CHANGES AND STRATIGRAPHI C

ARCH ITECTURE

Sea level rises do not necessarily imply transgressionand sea-level falls regressions, because these terms referto lateral shits of the shorel ine (the coast indicated in maps)

Cienciasda Terra (UNL), 14

towar d the contine nt or the sea re spect ively, becau seanother essent ial element is the sediment supply (Fig. 2A) .High input can produce regression with stable or risingsea le ve ls; in contrast, re duced input can fav o urtransgression even with stab le sea levels.

Positive eustatic oscillations not always reach the sametopographical elevation. Th is implies that sedimen taryunits forming an apparently conformable succession ofcoastal deposits separated by erosional surfaces formedduring "sea-level falls" record only a part of eustatichistory between the deposition of the oldest and theyoungest outcropping units . Most probably the erosiona lsurfaces represe nt one or mor e osc illations (Dabric, Zazoet at ., 1996, Zazo et al., 199 6). Of course palaeontologicalor radiometric controls may, at leas t theoretically, solvethis problem, but very often the eustatic events are toorapid as compared to organic evolution, or there are notmateria ls suitable for radiometry. Besides, many eustaticevent s either leave no recognisable deposits (even if sealevels reached an adequate elevation) or their depos its wereeroded later on. Last, but not least, it is not always easy orpossib le to discriminate be tween adjacent sedimentaryunitsdue to simi larity of facies and fossil contents.

As eustatic oscillations take place superimposed atvarious scales and have diverse wavelengths (Fig. 2B),shifts of the shoreline may look chaotic and the resultingsedimentary record more or less unfo reseeable (Fig. 2C) .Coastal sed iments occur spread on large areas ofthe basinmargins as the shorel ine shifts back and forth, and a goodpart o f it is eroded by the moving shoreline, tidal channelsand subaerial processes during lowstands.

Tectonic up lift and/or subsidence also control thestratigraphica l architecture of coastal units (Fig. 3). Forthis reason it is more adequate to speak about relativechanges of sea level. It is not difficult to recogn ise thetectonic trends and the velocity of movement by compar­ing the topographic elevations of the coastline in twogeological ages (Zazo et al., 1993). Generally speaking,coastal units are arranged in offiap or in staircase in stableor uplifted areaswhereas they occur stacked or onlappingin subs iding regions (Fig. 3).

Estimation of eus tatic magnitudes is relatively easywhen continuous seismic profiles are available and thelateral shift of the coastal onlep can be measured . How­ever, surface studies (and more specifically the study ofQuaternary units) are based mostly in laterally disc ontinu­ous outcrops (cliffs, quarries, road cuts) and vertical sec­tions . These require to study and interpre t the thickness ,environmental and palaecological meani ng, and waterdepth at which facies were deposited, and careful use ofthe so-called Walter 's ' law' (Dabrio & Polo, 1987). Th enit is time to deduce the locat ion of the shoreli ne or otherfeatures able to indicate water-depths .

The most reliable indicator of the sea level (datwn) isthe plunge step found at the lower foreshore in microtidaland tideless coasts (Fig. 4). In low energy coasts the break­ers form a ste p at the base of the swash zone whichprobably marks the transition between upper and lowerflow regime of back swash. In fossil examples the step ispre se rv ed mostl y in tw o ways depending on th e

4 1

1° Congresso sobre 0 Cenozoicc de Portugal

MEDITERRANEAN(microtidal) ATLANTICimesotldai)

~- AUCANTE • MURCIA MURCIA Al.MEJUA - NfJAR("......,......-,........ llVOO11 U. ....., ... - ~ DAYOFCADlZ_IER lSL\NIl . _ II 1til.Na) .

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~ ~ ~ ~

SEllOUEI>'TARY

~ ~ ~~

~~

~-~~.

~~m

~- ~~-

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. ,~ ~..j, ,~ t t %

~a~ + • , -,,~ « SUBSIDENCE ,4 """" I .. SUBSIDENCE +~~~= -8 emnt~ I .1.2 cnVK~ 0 2.25 cm'K~;i .7 cmIK~ 0u1i\en (1~.T.III)

¥'Bl':':' (Law Pleistoeerlo!l) (l.81e Pleisl~) (Lalli Pleistocene) (Late~)., ,

(ute PIei$tociene)

Fig. 3 - Geometry and sedimentary models ofTyrrhcnian marineunits as related to tectonicsand distance to thc sourceof sediment (after Zazo el af., 1993).

Fig.4 - Usc cf cross bedding generated by the plunge-step in thelower foreshore, to reconstruct beach progradation andretrogradation. and short-term trcnds of sea-level oscillations

(modified after Bardaj l et al., 1990).

predominant gra in size. In gravelly beaches it is markedby an accumulation of the coarsest grain sizes available,locally crude planar cross bedding po inting seawards ispreserved. In sandy beac hes it is evidenced by a changefrom the seaward-incl ined parallel lamination ofthe swashzone to tabular crOSS bedding pointing to seaward.

The limit between shoreface and foreshore is used intidal coasts , but cons ide rably less preci se. Finally, acorrection for compaction must beincorporated. Parti cularattention must be paid to erosional surfaces. For instance,the landward retreat of a barrier island produces twoerosiona l surfaces related to breaki ng waves in theforeshore and to the base of tidal channels and inlets.

f iWl.l PUHl

sw

T- lll95.000yr

®

!JOT "UQT.t14

T"128.000 yr

®

+11m

T~

160.000 yr

@

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>250.000 yr

T T~rr!leoian lMtacIIes WIIh s. bu boniusC ee.uvjlJ'T1

® I5ol<>pic 5139"5

lJQl U-_ meas.u_ n1S (Hila im-Ma..::ele1 a t.. 1986)

Fig. 5- Sequence ofTyrrhenian beach deposits exposed along the western (righ t) margin ofRamblaAmoladeras.Offlapping faciesarrangementand sinistral (N40-4S0E) and dextral (N 140· 1600E) wrench fault systems with vertical movement (modified

after Goy et af. , 1989).

42

Ciincias da Terra (UNL) , 14

EVIDENCE O F SEA~~EVEL C HANG ES INCOA RSE-G RAINED BEACH DEPOSITS

One of the best preserved seq uences of prograd ingTyrrhenian deposits in the Western Mediterranean is nicelyexposed along the western (right) marginof Rambla [wadi]Amo laderas (Zazo et aI., 1998). Th e Last Interglacial (IS5) is characterised by three see-level bigbstands duringISS 5e, represented by three maiine terraces in Almeria(Zazo et al.• 1993) with a mean age of 128 ka (Goy et aI. ,1986, Hilla ire-Marcel et al., 1986), suggesting climaticinstability. A marin e terrace corresponding to ISS 5e (ca.95 Ka) is recorded in a ll coas tal sectors, and anothe rmarine un it representing ISS 5a (ca. 85 ka) in upliftingtrending sectors ofAlmeria and Alicante.

In Rambla Arnoladeras, three Tyrrhenian morpho-sedi­mentary units correlated with the isotopic stages 7, 5e and5c occur separated by eros ional surfaces with beachfeatures and evidence ofearly cementation (Fig. 5). Th eseunits represent highstand facies during the Next to Lastand Last In terglacials, and erosional surfaces ind icate theintervening falls ofsea level. Aeolian dunes separate theseun its from the un derly ing un its o lder beach deposits(IS 11 or 9).

Sed imentary units were deposited in gravelly beacheswith a wann fauna of SlTombus bubonius, between 180and 100 Ka.The outcrop is affected by a system of normalfaults directed N 140 -160oE, that locally pr odu ces adisp lacement o f the present coastline. A fault directedN40-60" E controls both the elevations at which beac hdeposits occur at both sides of the ramb la and the suddeninflexions of tbe present coas t.

The offiapping pattern ofthe morpho-sedimentary unitsand their variable elevations reflect tectonic act ivity withmea n uplift rates o f 0 .068 mm1yr. This fact, together withisotopic da ta, sugg est that the sea level duri ng IsotopicSubstages 5c, 5e, and 7a was very close. Beach deposits

con s ist mo stly of congl o merates, sands to nes a ndmudstones arranged in coarsening-upwards sequences(Dabrio et al, 1984, 1985) that include inascending order(F ig. 6): ( I) A lower unit o f parall el-laminated andwave -ripple cross-lamina ted micaceou s sandstones,commonly burrowed, representing the lower shoreface andtransition zones. (2) A middle uni t o f trough cross-beddedsand and gravel corresponding to shore face zone und erwave action. Th ese two units are poorly exposed. (3) Anaccwnulation of the coarsest gra in sizes available on thecoastl ine, decreasing upwards up to well sorted fine gravel.(4) An upper interval of well sorted. parallel-laminatedgravel, gently incl ined towards the sea, representing theupper part of the foreshore and berm.

EUSTATIC C HANGES AND STRATIGRAP HICARC HITECTURE OF GILBERT-TYPE DELTAS

Thc bay of Cuatro Calas (Aguilas, Murcia Province)was generated during Late Pliocene times by a local down­ward bending of olde r Neogene materials (Zazo et al.,1998) . Th e bay, ma rgina l to the Med iterranean Sea,extended inland in an western direction and was filledwith a complex succession ofunits separated by erosionals urfaces th at in some cases removed most of thesedimentary record. The four older units ( I to 4, Fig. 7)a re la rge-sc a le cross st ra ti fie d, with la rge foresets(clinoforms) . Th e younger units occur under a generaltabular geometry made up of a large nwnber of interbed­ded marine (M -O to M·5) and terrestri al (T-O to T-3 )deposits arranged in a multi- storey trans ition zone. Theverti cal stacking of all these units generated a Gilb ert­type delta which records a complex history of relativesea-level changes, tectonic trends and modifications ofsediment supply. Succe ssive delta lobes progressivelyfilled the bay during bighs tands, but erosion removed partof the lobes during lowstends.

....

.-~­_.....--

•

•

_Ye baM (tak -fhlH1 :t 2------- I

~ ----:3_ _ ltIminaIion

#>. . lIII'awH Ipple ClOSS /amlns lioo

~ 1rOOricat9d cl8sts

-~.~---

__"'"" (sIOmI}

~~-------- - -~--~;; - - --~~. , -

Fig. 6 - (A) Typical beach profile for Med iterranean gravelly coasts. (8) Composite sequence offac ies generated by

progradation of gravelly beaches. (Mod ified after Dabrio et a1.• 1984. 1985).

43

1° Congresso sobre 0 Cenoz6ieo de Portugal

E

'"······'M-2 ···········.....

poles 01coastal limil

" ...--

w

""·a···._21 ~.::. .

Fig. 7 - Panorama of the Cuartelillo hill (modifi ed after Dabrio etat., 1991). Numbers indicate sedimentaryunits.

Th e proposed model is a delta connected to a coarse­grained river plain with rapidly shifting channe ls, flowingmostly from the north (line source ) (Fig. 8). Terrestrial(fluv ial) deposits include coarse -grained (channel fill) andfine-grained (flood pain) facies. The coarser gra in sizeswere retained in gravelly reflec tive beaches at the wave­worked de lta front. Terrestrial and coarse-grained coastaldeposits overlay the foreset unit with an intervening flat,erosional surface gently inclined in the average direc tionofdelta progradation (ESE).Adelta platfonn covered withburrowed sand and scattered pebb les and bouldersextended seaward ofthe wave-worked delta front. Shallowmarine to coasta l deposits consis t of light yellow to grey,well sorted , conglomerates with ro unded and notab lyspherical clasts deposited in coarse-grained beaches ofthereflective type . A steep slope with dips rang ing from 25"to 12" connected the delta platform with the shelf.Clinoforms evidence the progradation of units under theaction of sediment-laden currents which supplied sand to

the basin margin and slope . Alternation of short periodswith hyperpicnical flows down the de lta slope (dominanceof sedimentation) and longer periods ofquietness (domi­nance of burrowing) conditioned the internal structure ofthe foreset. The Cuatro Calas Gilbert delta is comparableto present-day de lta s of ephemeral strea ms feed inggravelly beaches in SE Spain. Progradation of the deltagenerated a two-fold large-scale cross-stratification: atopograph ically lower high-ang le related to the advancingdelta-foreset and the upper one asso ciated to progradationof beac h units (Fig. 8).

Ev idence of eustatic changes come from the seep­sided, large-scale erosional surfaces in the forese t faciesthat progress deep into the previous foreset deposits withvariable orientations. These are interpre ted as incision andpartia l destruction of delta-front and foreset depositsduring relative falls ofsea level. New delta lobes deposi tedduring later highstands had to adapt to inherited topogra­phies (Fig.9) and prograded to E, ESE, SE, and E as shown

HIGH ANGLE CROSS BEDDINGprogradation of delta foreset

. ~

,. 0 '.. '

p1alfonnsand +pebbles

l OW ANGLE CROSS BEDDINGrogradation of beach

foreshore bermgravel .....gravel

Fig. 8 · Model of Gilbert-typedelta in CuarroCates (modified after Dabrio el al., 1991).

44

STAG E ILOWSTAND AND EROSHJN

Ciincituda Terra (UNL), 14

STAGE IHIGHSTAND AND DEPOSITION OF A NEW LO BE---

Fig.9 - Generation ofa complexGilbert-type delta (modified after Dabrio et ~l., 199 1).

TRANSITION-ZONE UNITS

Marine~LSMarine ?F LS L::T

~. TST+HST

Marm~.=::""~~:::""~,~ TST+HST

Post-Gilbert

M-5T-3

M-4T-2

M-3M-2

T-lM-'

T-(,

M-<l

DELTA-FORESET UNITS

Fig. 10- Sequencestratigraphy in the Cuetrc Calas Gilbert-typedelta (modified after Dabrio el al ., 1991).

by dip of clinoforms in units I to 4 respectively. Sequencestratigraphy of the foreset units is explained by fluctua­tions of sea level (Fig. 10), but only the highstand deltadeposits are exposed; lowstand wedges lay und er thepresent sea le vel. Backsets ov erl yin g the erosiona lsurfaces were deposited during relative lowstand and earlytransgressive episodes.Th us, the development of the complex Gilbert-type deltafollowed a repetitive pattern in response to fluctuations ofsea level: progradation ofhighstand Gilbert-type delta wasfollo wed by entrenchment and coas tal wedge in lowstandand early transgression (Fig. 10). The various parts of thedel ta reacted differently to these see-level changes andgenerated variable facies associations. Progradation ofcomplex de lta pr isms does no t imply a continuo ussti llstand as previously assumed for simple Gilbert-typedeltas . The rapid evolution of the bay-fill canberelated tohigh-frequency fluctuations of sea level alreadydocumented in SE Spain during La te Pl iocene andQua ternary, supe rimposed on longer-lasting tec tonicactivity.

T HE INFLUENCE OFACCOM MODATI ON SPACEGENERATED BY EUSTASY AN D TECTONICS

It is well illustrated by the late Messinian SorbasMember in Almeria prov ince aro und the town of Sorbasdue to absence of burrowing by raised water salinity andexposure along a network of up to 30·m deep canyons(Roep et al., 1979, 1998). Th is unit consists in its type

area of an up to 75 m thick parasequence set of threeprograding coastal barriers (sequences I-III), associatedwith lagoon and washover sedi ments (Dabrio, Roep et al.,1996). Logging and careful corre lation of fifteen verticalsec tions permit to reco nstruct and d iscuss patterns ofrelat ive sea-level movements between decimetres, up to15 m within a parasequence. Excellent examples of non­tidal transgressive facies are characterised by lagoon andwashover sediments instead of the usual combinationof washover and tida l deposi ts (channel and flood-tidaldelta) .

The lower two sequences are deposited in a relativelylarge, tectonical ly enhanced wedge shaped acconunoda­lion space . T he y sho w both fining-up, de epeningsequences,followed by prograd ing coarsening-up shoalingsequences and can be compared to th e c lassicalparasequences of the Western Interior Basin (USA).Progradation of seq uence II was interrupted by a majorslide even t (most likely triggered by an earthquake). thatcaused more than 400-m seaward slumping ofa stretch of1 km of coastal sands.

Thearchitec ture of seque nce III is more complex dueto limited acconunodation space characteristi c for the latehighstand, with a wedge-shape d acco mmodation space tothe east ("sea" ) that changed to a more box-shaped spacetowards the west ("land") (Fig. II A). Therefore, th issetting was very sensitive to sea leve l fluctuations and thecoastline reacted in a jumpy way.

Taking the thickness ofUnit III as an indicator of waterdepth and magnitude of see-level fluctuations involved inthe changes of coas tlines, a water depth of ca. 10m is

45

_ _ W"O~OIl~ ~ICC : .ifhOdlIIIon...-INR.UENCE OF ACCOMMODATION sPACE

I- Congresso sobrc: 0 Cenoz6ico de Portugal

A ·_ _----_.~.-.

""""-'11-

INFLUENCE OF SUBRE DEFOR.....TIONS

Fig. 11 • (A) Influence ofthe available accorrunodation space in the generation c rcoesiat units. 110 4: ideal steps during fluctuations(modi fied from Dabrio, Roep et af., 1996). (8 ) Influence of tectonicelly induced irregularities in the substratum on the location of

beach ridges and lagoons (modified after Dabrio, Fortu in et af., 1998).

deduced (Fig. 12). This is further supported by the positionthat occupy in the vertical sequence certai n sedimentaryfeatur es indicative of the coast line such as bird-foot tracks,swash zones, and beach-rock levels.

Next to relative sea-level changes and differentialuplift also related geometrical factors such as gen tle andloca lly occ urring synsed imentary fold ing appear to haveinflue nced the stratigraphic architecture of the SomasMe mber and bad palaeogeogra phic implications. Thecrea tion of a roughly N-S tren ding ridge and swellmorpholo gy around Somas contro lled the prominent N·Sorienta tion of the beach ridges and lagoons (Fig. I I B). Therising areas ("anticlines) acted as nuclea tion areas forbarrier islands, whereas the intervening gentle depress ionsfavoured the development of lagoons. A crucial point isthat the (p res ent) differen ce in elevat ion s betweenthe se a reas is usu all y 3 or 4 m, and mo st o f theirre gul arity wa s com pe nsa ted a fte r deposition ofUn it III (Fig. 12).

In the field, Sequence III is readily recognised as aparase quence. Upon closer inspec tion, however, it appearsto consis t ofj uxtaposed transgressive and prograding parts,separa ted by erosional surfaces and flooding surfaces dueto sea level fluctuations within the limited accommoda­tion space. Minor trans gress ions induced formation oflandward moving washove r fan systems intercalated inlagoonal mud. which finally were partly eroded by theretrea ting barri er. Periods of forced regression caused theseaward steppingof tcmporary barriers coastline over morethan J.5 km, leaving behind "s tranded" coastal barriers(Fig. Jt Al . During thisprocess these may show landwardero sion. or sea ward progradation depe ndant ofthe smallersea -le vel flucruations. The lateral jumping and erosionalsurfaces in parasequence III seem to be good indicato rsfor a much more reduced accommodatio n space, as is theexaggera ted infl uence o f wa ves in the foreshore asdest ru ct ive agents. Du e to it s more co mpl ex faciesarchitecture, Sequence III might fonn a nomenclatorialprob lem: is it one parasequence or in fact a composite of4 stac ked parasequen ce s, i.e. of similar ran king assequences I and II, given the largest sea-level fluctuationsdeduced? A main conclusion is that erroneous sequential(stratigraphic) interpretations are eas ily made whenacconunodation space is limited.

46

Til E RECORD OF ESTUARINE INFILL DURINGTI lE LAST POSTGLACIAL T RANSGRESSION

The late Pleistocene and Holocene evo lution of theestuaries in the Gulf of Cadiz (SW Spain) has been studiedusing dri ll cores, logs, trenches, and 38 new radiocarb ondata . The resu lts were compared with the shelf to obtainthe sedimentary interp retati on of the estuarine fill of theincised valleys (Fig. 13) cre ated along the prese nt coastof the Gulf of Cadiz during the Last Glacial fall of sealevel (Dah rio el al., 1999 , 2000).The studied estuaries record repeated incision during fallsof sea level with preserved deposi tion during at least twohigbstands of Late Ple istocene (IS 3) and Holocene ages.The overall pattern correlates with the 4'-order eustaticoscillations an d th e superimposed 5111-ord er cyclesrecorded in depositional sequences found in the shelf offthe study area (Som oza et al., 1997, Nelson et al., 1999,Rodero et al., 1999).

Th e Odiel, Tin to and Gu ad alete rivers depositedconglomerates during a highstand that did not reach thepresent se a level dated at ca . 25- 3 0 Ka (I S 3),corresponding to a relatively humid period in the area .Rivers incised these coarse-grained deposits durin g thelast main lowstand at ca. 18 Ka, when sea level droppedto - 120 m and the coastline lay 14 km seawards from thepresent. The erosional surface is a sequence boundary andalso the flooding surface of the postglacial eusta tic rise,overlain by the valley-fill deposits of the transgressive andhighstand phases of the last4111 and SIII-order depositionalsequences reco gnised in the shelf. Vanney et at. (I98S)found erosional channels in the shelf of Pleistocene agethat have been covered by Holoce ne sediments

Acco rding to data from the shelf (Hernandez-Molinaet al.; 1994), at the beginning of the Holocene and theF1andrian transgression (ca. 10,000 yr BP) the sea level inthe Gulf ofCadiz was 30-35 m below present MSL. Thefirst marine evidence of the Holocene (Flandrian) trans­

.gression in the studied estuaries OCCW'S 30 m below presentMSL in Guadalete and 22 to 30 m below present MSL inOd iel-Tinto incised va lleys. Th ese differences revealtopograp hic irregularities along the thalweg of the rivers.

The maximum flood ing occurred at ca. 6500 yr BP(Zazo et al., 1994) , coinciding with the maximum land-

Ciincias do Terra (UNL) , 14

Time •

13 14

_~-'{J. 11I

S

white limestone layer

SEQUENCE III

·1

94 8

1000

12

750

7

SEQUENCE II

500

3

250

602

50 m

0

0

10

20

30

40

50m

Fig. 12 · Es timates of sea- leve l fluctuations in Sequences II and III through time relative to the position of the Zorreraswhite limestone datu m plane. To facilitate description the sea- level pos itions 1- 14 are indicated on inset. Because ofthe

unkno wn time constraints the distances on the time axis an: arbitrary (modified after Roep et al.; 1998).

ward migration of the estuarine barrier in the Guadalete.Most of the input of fluvial sed iment was trapped in thebay-head deltas and the axial zones of the estuaries .After 6500 yr SP the evolution of the estuarine filling isclosely related to the decrease of the rate of sea-level risefrom 5.7 mm yr- ' between WOODand 6500 yr BP, to 2.6mm yrl between 6500 and 4000 yr BP recorded in thecentral estuarine basin. The rate offluvial input to estuariessurpasse d the rate of sea-level rise (l.e .• crea tion o faccommodation). favouring the vertica l accretion of tidalflats and the accumulation of the spit unit~ colonised byhuman settlements (BOIj a et al.• 1999). Vegetation changed10more arid conditions. T he increase in vertical accretioncaused a reduction of the tidal prisms in the estuaries thatallowed the acc umulation of stable spit barriers and theapp arent effect of waves was magnifi ed. The effect isparticular ly felt between 2500-2700 yr BP. when the spitM it H) began to grow and the first associated aeolianforedun e systems accumulated. In Guadalete, two fluvialcou rses supplied sediment to the active littoral drift andfavoured the gro wth of a broad H) spit barrier crossed bya Roman way. In the last 500years, the confluence ofl ittoraldrift. large fluvial input magnified by deforestation, increasingaridity favoured the accumulation ofthe largeH~ spit units.Historical data. particularly the present position of watchlowers built in the 170, century AD, evidence rapid coastalprogradat ion rates up to 3 m ycl (Lario et aI., 1995).

The filling follows a twofold pattern in respo nse tothe progressive change from vertical accretion to lateral(centripetal) pro gradation. First, subaqueous sedimenta-

tion greatly reduces water depth and the accommod ationspace, but that does not have an appreciable effect in thesurface morphology, except near the bay-head delta. Then.the surface occupied by the flooded estuary diminishesrapid ly due to fast expansion of the emergent areas.producing rapi d geogra phical changes and landscapemodifications.

A main deri vation is that only the radiocarbondataand depths for a single dri ll core can be used to constructreliable curves of subsidence rate. A single curve reflectssedime nta tio n in a particu lar spo t o f the est uar y.Comparison of curves obtained in an estuary will give a"mean" curve of subs idence.

Three washover fans breaking the part ofthe spit activeat ca. 1750 AD may be the result of the tsunami associatedto the so-ca lled 1755 Lisbon earthquake that reached aRichter magnitude 8.5-9 (Dabrio, Goy et al., 1998. Luqueetal. , 1999). It is difficult to date accura tely the washoverfans because of the lack of sui ta ble fossil remains.Continued southwards migration of the San Pedro Riverchanne l since 1755 has eroded the area immediately tothe south of the spit barring the chances of finding otherpreserved remains.

T HE RECORD OF EUSTATIC CHANGES INPLEISTOCENE AEOLIAN DEPOSITS. GULF OFCADIZ

Coasta l areas that remained largely emerg ent duringeustatic osci llations under aeolian influence (Menantcau,

47

j"Congresso sobreo Ccnozoico de Portugal

Fig. 13 - Four palaeogeographical steps of the changinglandscapes in the Guadalete (above) and Odiel-Tinto (below)

incised valleys(modified after Dabrio et a/.• 2000).

48

1979, Borja 1997) also record the changes, although thestratigraphic record is some what different. The Quater.nary sandy de posits forming th e EI Asperillo cliffs(Hue lva ) exemplifi es thi s case study. Here . thestra tigr aphic relat ionsh ips, ge nesis and chronology

. includi ng radiocar bon dating were studie d with spec ialemphas is on the influence of neotectonic activity, sea-levelchanges and cl imate upon the evo lution of a subaerialcoastal zone (Dabric, Borja et al., 1996, Zazo etal., 1999).Normal faults ac tive during the Quaternary conditionedthe sed imentation in the coastal zones of SW Spain. TheE-W trend ing Torre del Lora normal fault was a majorcontrol on aeoli an sedimentation in the area of the EIAsperi llo cliffs during the Late Pleistocene (Fig. 14) andon the coastl ine direc tions during the Middle and LatePleistocene. The fault separates two tecton ic blocks butits movement stopped before the Holocene. Tiltin g oftheupthrown fault bloc k (Torre de l Loro - Mazag6n) to theNo rthwest during the Ea rly and Mi dd le Pl eistocenecontrolled the displace ment towards the Northwest offlu viatile cha nne ls o f a tributary o f the pal ae o­Guada lquivir River. In this block. mari ne deposits ofprobable Last Interglacial age have been preserved, andarc subaerially exposed nowadays. Their presence in thearea is mentioned for the first time in this paper. In ourmodel, the Torre del Lora fault created accommodationspace in the downthrown block where aeolian sedimentsaccumulated during the Last Glacial period, and probablyduring partofthe Last Interglacial. The vertical offset alongthis fault is 80 m since the Early Pleistocene, and 18 to 20m during the Late Pleistocene.

At present, the most active normal-fault system trendsNW-SE, contro lling the direction of the shoreline and thepattern offluviatile valleys on land and of drowned fluvialvalleys on the she lf. Thi s sys tem and the importantNNE-SSW system separate blocks, like the Abalario sector,in 'domino tectonics' fashion along the Huelva coast.

Six aeol ian and aeo lian-re lated sand deposits (Units Ito 6, Fig. 14), stacked in the downtbrown block, are sepa­rated by bounding surfaces (supersurfaces) in response tomajor changes in sand supply and wetness of the substra­tum which contro lled the depth of the water table. Incontras t, the aeo lian deposits below the iron crust in theupthrown block, thought to correspond to Units 1 to 3, arethinner and deposited on drier substrata, with severalsupersurfaces marked by palaeosoils indica ting repeateddegradation and de flation.

Thus, the oldest deposits occur in the upthrown block.They are Early to Middle Pleistocene fluviatile depos its,probable Late Pleistocene shallow-marine depos its alongan E-W trending shore line , and Late P leistocene andHo locen e aeolian sands depos ited under prevailingsoutherly winds. Six Pleistocene and Holocene aeo lianunits accumulated in the downthro wn block. Ofthese, UnitI is separated from the overlying Un it 2 by a supersurfaceth at re p resents the end of the Last Intergl aci a l.Accumul ation ofUn it 2 took place durin g the Last Glacialunder more arid conditions than Unit I . The supersurfaceseparating Units 2 and 3 was fonned between the LastGlacial maximum at 18000 I·C yr BP and - 14 000 I_C yr

Ciencias da Terra (UNLJ, 14

SE

__ surtaoewdh 0l'gllIIic mane,

._ - surtace will'lotJCl 0tg80ic man.<

....~ 0ItlI'il;:hed in iron oUI8s

INW

BAsperilo{..... tion 103m)

!.. - . . . . _--~-~~.. ...,.,....m . ~

\1 " MAT· 'o U-6 • IL

~T-ll "j.8:I . _. ~T.H__I" 1.44T-18.J- U-5 --- . .. ..1'U-S- - - ~ -':!~- - · _ - _ · - - _ · - U-4 ...------------- ... ~ -.. -

U-4 :.-.:; :.,-.: :.-,;;;.-,.;; :.: .: :.-.:-_____ e - ... -- U-3 MA.T~; ;;;' ::::_!+ ....Iia n L ~_ l~ _~,...:-- ~ 4: E• 1.4"" ' 4 " """" " ' " " ~ !Ii:

? ~~: - /' mir l... -:!il\~~T~~MAT" 5 '." . :-. : . _•• ·· U-2·._ •. •:".:" _ .~ d

25 24 Z3 22 :n 20 " Ie ~':/ l e \ 1 5 ,,-\4 13 12 n ' 0 • , 1 eo 5 4 3 2 1 0,,",

'" \ lolAT-t,.Jl, l41 .-sooZ.,,, ...bl "' b4

Fig. 14 - Schematic profile showing di5lribution ofun its in the EI Aspcri llo cliffs and sample positions, Distances in km from thetower (Torre) o f La Higuera. No te strong vertica l exaggeration. Palaeocurrent and wind directions shown in map view. The Torre

del Loro fault cited in the text is placed between Km 16 and 17 (mod ified after Zazo et al., 1999).

8Pt the latter age corresponding to an acceleration of therise of sea level. Unit 3 records wet conditions . Thesupersurface separating Units 3 and 4 fossilised the Torredel Lora fault and the two fault blocks. Units 4 (depositedbefore the 4" millennium BC), 5 (> 2100 1'"C yr BP to16th century) and 6 (16th century to present) recordrelatively arid conditions . Prevailing wind directionschanged with lime from W (Units 2--4) to WSW (Unit 5)and SW (Unit 6).

The generation ofthe aeolian depos its started prior theLast Glacial period and continued until the present day.Aeolian Unit s 4, 5 and 6 are probably related toprogradationofspit systems in estuarine barriers.The sedi­mentat ion gaps found in the spits may correspond to thesupersurfaces separating Units 4, 5 and 6. Both seem tobe related to short-lived (250-300 yr), relatively humidperiods with a relative rise of sea level.

Wind directions changed during the deposition of theaeolian dunes: the oldest recorded (upthrown fault block)blew towards the north and south. Units 2, 3, and4 accu­mulated under prevailing westerly winds. Palaeowindsblew from theWSW during Unit 5 and, as at present, fromthe Southwest during Unit 6. The change in palaeowinddirections from Unit 4 to Unit 5 maybe related to a changefrom wetter to more arid conditions since 4000 I·C yr BP,as suggested by pollen in Las Madres peat bog.

There are also three systems of dune systems relatedto estuarine barriers in the Gulf of Cadiz (Borj a et al.,1999). The oldest one, 0 1, accumulated under prevail ingWSW winds during the 1st millennium Be overlays boththe occupational horizons of Late Neolithic-Early Copper(4th millennium BC) and the ' lithic workshop levels' (4th­2nd millennium BC). The middle dune system 02, con­taining both Roman and Medieval remains, accumulatedbetween (?) 13" (1) -14* century and 17th century AD.The youngest 0 3 system occurs associated to the time ofbuilding of watchtowers in 17th century AD but extendsto the present. It is related to prevailing winds from the

sw. The absence of aeolian deposits prior to - 2700 calBP is the result of trapping ofa large part of the sedimentsupply in the estuaries, which starved the neighbouringbeaches and aeoli an settings. Aeolian accumulationreached significant values when sedimentation in thecoastal zone changed from being mainly aggradational inthe estuaries(-6500·nOO cal BP) to mainlyprogradationalin spit barriers and related dunes (post - 2100 cal BP).The pre sent analysis of aeolian systems suggests anon-direct correlation, at least in some cases. betweencoastal progradation of spit barr iers and aridity aspreviously assumed.

CONCLUSIONS

Six conceptual mo de ls exemp lify diverse instratigraphic architectures in response to various types ofrelative sea-level change and associated lateral shift oftheshoreline (Fig. 16). Illustrated are 6 (I - VI) hypotheticaleustatic sea level curves (the sinuous lines in the middle)deduced from these deposits and associa ted shifts of thecoast line that can be reconstructed from the lateral andvertical stacking of the coastal sediments (left).

(I ) Coastal onlap records a steady rise of sea level(which. in principle, is considered to be continuous, seethick heavy line) during a single eustatic oscillation (sll ,sl2, etc. indicate success ive positions of sea level ).However, a discontinuo us rise may produce the sameeffect, particularly if scrutiny of sections is not carefulenough. During this process the shoreline moves land­and upward.

(II) Discontinu ous coastal onlap may refl ect acontinuous sea level rise with variable sediment input(thick line at the left), a two-step rise with an interveninginterruption, or sudden jump upwards (line in thecentre),or(evcn) an intervening minor fall (line at the right). In themeantime. the shoreline progresses as in the former case.

49

1° Congresso sobre 0 Cenozeico de Portugal

t••

Eo

!=- 3QOO 1000 9C

'~.~••-

.­••:. '-~• ,_ 'v'·

fiI~\lo~,

••• - iiit.=­.--.

·1- ~•.• <Q> ,". ~

Uttoic worI<ahop ""'Db (4111 10 2nd mIJemium BC)

Late NeoIilNc-ElUlyCoppe< (3&40-3130 Be)

0kIesI da le<lage ~ 4 C) '" splI sedi_1lon

0lde9I rnIrlIrrul ao- '" splI sedlmentalionbased upon an:IIaeological data

SpIt bat units (t.lediI" .............Atlantic:)

1T

•••

I

~"-I.­..­••

AYAUONTE

AEO LI AN PH ASES AN D H UM AN SE TT LEM EN TS

PUNTAUMaRIA ooNANA VAl.DELAGFlANA~~PUNTAARENIUA LAALGAIDA CANTARRANAS

,~ ,• iiit '~ ,

I , ,~i- :l,,·- .••

~ 1T

I'iI WatehlOW9. '7thcenlufyAD

~ ~al

iiir: Lal" Roman (2IIl1o5111 cent<>riesAOj

~ Romanway (,..tcenlBeIo2ndeenlAOj

<:Q;> Pre-Roman (8lh 102nd cenlury BC)

"CJ Bronz". (1850- 1650 Be)

Fig. IS - Chronostrat igraphy ofaeol ian phases and human senlements in the Gulf ofC:idiz. No te that italic typing indicatecalibrated ages (after Borja el al.; 1999).

GEOMErRY(ARCHITECTURE)

EUSTATICOSClI.UTlON

SHIFT OFCOASTUNE

GEOMET1'IY(ARCHITECTURE)

SHIFT OfCOASTUNE

:7.~? ;;.?' . -o f - - ----- -;.-' ...·ll4o __· W ... ........-or, __ __ _ __.0. ... ......01. - ~i;' ... ...-:;.~ ... V8-,. ... ...."

DISC(lNT1HllOUS COAST... OHLAo• OI'n.A o

-~-~••-~~

.----_:to'....~...1····

III

Fig. 16· Conceptual models ofslTat igraphic architecture induced by a variety ofsea-level changes, and associated lateral shift of

shoreline (modified after Dabrio & Polo. 1996)_

50

(III) Coastal offlap records (quasi) steady sea level.Seaward shift of shoreline may (or may not) be precededby other shifts (dotted line with question mark).

( IV) A co mplex coastal offlap with three pro gra ding

beach units (B·1, B -2, B·3) a t different topographicelevations, each composed of minor prograding un its (a,b, c), records at least a firs t sea level rise followed byeustatic oscillations re achin g progre ssively lo werelevations . The shoreline follows a zigzagging pattern.

(V) Two beach units (B. I olde r than B-2), each withminoroffla pping un its (a, b, c) record at least two sea-levelmaxima reach ing progre ssively higher elevations, with anint ervening sti lls tand, or minor fall that complete theseoscillations. Th e shoreline follows a zigzaggi ng patt ern .

(VI) A combinat ion offormer cases may produ ce muchmore comp lex stratigraphical ar chite ctures, suc h as in thedisc on tinuous coastal on lap plus simple offlap.

These models can be applied to the former ease stud­ies but it must be noted that differentiatio n in the fieldbe tween si tua tion IV an d V may be diffi cult when thebo undaries arc incomp lete ly expo sed. Furthcnnore, thelate ral and vertical relat ionships are much more compli­cated due to the interplay of various orders of magnitudeof sea level changes.

R E F ERENC ES

Ciincias da Terra (lINL), 14

The cases ofgravelly beaches in RamblaAmoladerasand the Gilbert-type delta of Cuatro Ca las are classifiedas type IV forming a complex offiap o f several uni tsseparated b y erosional surfaces. T he main d iffere ncebetween the two situations is tha t tectonic up lift wasmore

promi nen t in Amoladeras.Situa tions I, II and III and th e ir combi nation in

example VI all can be found in seq uence II of Sorbas,whereas examples IV and V can be found in sequence III .

Situation VI applies to the po st-glacial eustatic rise inSW Iberian Peninsula . H ere, limi ted p ro gradation o fIithosomcs during temporary stops or times of reducedrate o f r ise in terminal Pleistoc ene times produce discon­tinu ous coastal onlap plus offlap (V ), whereas progradat ionwith qua si stab le sea level in Holocene promotes simpleofflap (III).

ACKNOWLEDG EME NT S

Fi n ancia l su pport fro m Sp anish MEC proj ectsPB98-OS14 andPB 98-0265. and ProjecrAreces: "Cambiosclimaticos y nivel de l mar" . It is a contr ibution toIGCP437.

Bardaji, T.; Dabrio, C. J.; Goy, 1 L.; Somoza, L. & Zazo, c . ( 1990) - Pleistocene fan deltas is southeastern Iberian Peninsula:sedimentary controls and sea level changes. Spec. PubIs. lilt. Ass. Sedimem., 10: 129-1SI.

Borja, E ( 1997). Dunas litorales de Huelva (SW de Espana) Tipologla y secuencias Pleistoceno Superior-Holocene . In: Rodriguez­Vidal, J. (Ed.), Cuaternario Iberica, Untverstdad de Huetva , 84·97.

Borja, F.; Zazo, C.;Dabrio, C.1.; Diu del Olmo, F.; Goy, l L. & Larin, J. (1999) - Holocene aeolian phases and human sett lementsalong the Atlantic coast of soulhem Spain. The Holocene 9 (3): 333·339.

Dabrio, C.1.; Bardajl, T.; Zazo, C. & Goy, lL. (1991) - Effects ofsc:a- Ievel changes on a wave-worked Gilberf.type delta (LatePliocene . Aguilas Basin. SE Spain). Cuadernos de Geologia Iberica, IS : 103· 137 .

Dabrio, C.1.; Borja, E ; Zazo, C.; Boersma, I R.; Lario, 1.; Goy. 1.L. & Polo. M.D. (1996) - DImas eelicas y facies asociadaspleistocenas y holocenas en el acantilado del Asperillo (Huelva). Geogacela 20 (S): 1089- 1092.

Dabrio, C. 1.; Fortuin, A.R.; Polo, M. D. & Roep, T.B. (1998) - Subtle controls ofsedimentation and sequence stratigraphyofcoastalsettings: the Late Messinian Sorbas Member (SE. Spain). In: Caiiavc:ns., l C , Garcia del CUTa, M.A. and Soria, J. (Eds.) ,Sedimelltology at the dawn of the 17Iird Millenllium. Abstracts. Publicaciones de la Universidad de Alicante: 279-28 1.

Dabrio , C.1.; Goy. 1.L. & Zazo. C. (1984) • Dinirn ica litoral y ambientes sedimentarios en el Golfo de Almeria desde el «TtrrenienSClta la actualidad . 1Congreso Espaiiolde Geologia, I: S07-S22.

Dabrio, CJ .; Goy,It. & Zazo. C. ( 198S) - A modelofcollglomerat ic beaches in tectonically aatve areas (Late Pleistocene-actual.Almeria, Spa in). 6th European Meeting of Sedimentology lA S.: 104- 107.

Dabrio, C.1.; Goy, 1.L. & Zazo, C. (1998)· The record of the tsunami produced by the 17SS Lisbon earthquake in Valdelagrana spit(Gulf of Cadiz, southern Spain). Geogaceta 23: 3 1-34.

Dabrio ,c.1. & Polo, M.D. (1987) - Holocene sea-level changes, coastaldynamics and human impacts in southern Iberian Peninsula.In: Zaze, C. (Ed.), Late Quaternary Sea-level Challges in Spai n. Musco Nal. Ciencias Naturales, CSIC., 10: 227· 247.

Dabrio , C.1. & Polo, M.D. (1996) - Cambios eustariccs y arquitectura estratignifica de unidades costeras. Geogaceta 20 (3) :438-441.

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\ - Congresso sobre 0 Cc:noz6ico de Portugal

D abrio, CJ .; Roep , T.o.; Polo , M.D. & Fortu in, A.R. ( 1996) - Late Messinian coas tal barrier and washover fan sed imentation inSorbas (SE Spain). Geogaceta, 2 1: 9 1-94.

Dabrio, CJ.; Zazo, C.; Goy, l L ; Sierrc, FJ .; Borj a, F.; Lario, l ; GonzAlez, lA. & Flores, l A (2000) - Depositional history ofestuarine infill during the last postglacial transgression (Gulf ofCidiz, sou thern Spain). Mar. Geo/., 162: 38 1-404.

Dab rio, CJ .; Zazo, C.; Lario, 1 ; Goy, l L ; Sic:rro, FJ.; Borja, F.; Gonzalez, lA. & Flores, l A. (1999) - Sequence strati graphy ofHolocen e incised-valley fills and coastal evo lutio n in the Gulfofadiz (southern Spain). Geol. Mijn., 77: 209-224 .

Dabrio, CJ.; Zazo , C.; Somoza, L; Goy, l L; Bardaji, T.; Lario, J. & Silva, P.G ( 1996) - Oscilaciones del mar de largo y corto

p lazo: indicadores morfosc:dimentarios en zonas costeras. Geogacela. 20 (5): 1078- 1079.

Goy, J.L ; Zazo, C.; Dab rio, CJ.; Lario , 1.; Borja, F.; Sierro, FJ . & Flores, lA. (1996) - Global and regional factors controllingchanges ofcoastl ines in southern Iberia (Spain) duri ng the Holocene. Qualc:mary Sci. R",., IS; 773-780.

Goy, 11..; Zazo, C.; Hillaire-Mercel, C. & Causse, C. ( 1986) - Stratigraphie et chronologie (U1Th) del Tyrrehmien du SE deL'Espagne. Zc:itschrift flu Geomorphology, 62; 71-82.

Goy, lL; Zazo, c.;Somoza, L ; Dabrio, CJ. & Ban:iaji, T. ( 1989) - LitoralBhjcas oriOliales.ln: . £JnniOn B-l liloral Mc:diJc:nWreo(Ed. by C. Zazo, CJ . Dabrio, J.L GoY), :ZO ReuniOn del Cuaternario lberico, Sept. 1989, Editorial E.T.S. Ing. lOOustriales,Madrid: 37-98.

Hernandez.Molina, FJ .; Somon, L ; Rey, J. & Pomer, 1.. (1994) - Late Pleistocene-Holocene sed iments on the Spanish continentalshel ves: I model for very high-reso lution sequence stratigraphy. Mar. Geol.. 120; 129-174.

Hill aire-Marcc l, C.; Carro. 0 .; Causse , C.; Goy, I.L & Zazo, C. ( 1986) - ThIU dati ng ofStrombus bubonius-bearing marine terracesin southeastern Spain. Geology, 14: 6 13-616.

Lario, 1 ; Zazo, C.; Dabrio, CJ.; Somoza, t .; Goy, lL; Bardaji, T. & Silva. P.G (1995) - Reco rd crrecent Holocen e sedime nt inputon spi t bars and deltas of south Spain. 1. Coastal Res., Spec. Issue 17: 24 1-245.

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