Coastal sedimentary environments and sea-level changes
Cristino J. Dab rio
Depanamenlode EstratigrnfJa, Facultad de Ciencias Ge<llOgicas, Universidad Complulenseand lnstinuo de G«llogla Economica,CSIC,
28040 - Madrid (Espai'la). [email protected]
ABSTRACT
Key-words: coastal sedime ntation; eustatic cha nges; stratigraphic architec ture; tecto nics; 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 is
essential 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 profit in oil exploration. Sediment
supply, wave-and tidal processes, coastal morphology, and accommodation space generated by eustasy and tectonics govern the
highly 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 loci
very 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 coastal
units.
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 para
definir, 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 acarreio
sedimentar, os processes ondulatorios e de mares, a morfologia costeira e 0 espaco de acornodaejc gerado pela eustasia e pela
tectonica sAo os reepcnsaveis pela 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. Alem
dissc, a desjocaejo lateral da ercsac ou mesmo lacunas sedimentares conduzem, com frequencia, adestruiiVto de parte significativa
do registo sedimentar. Apresentam-seexemplcs que ilustram algunsarranjos frequentesde facies e cs seus parametres caractertsticos
com vista a obter os melhores resultados na analise sedimentol6gica das unidades costeiras.
INTROD UCTIO N
The litto ra l is an unstable zone that comprises marine
an d terrestri al do mains ve ry sensitive to a var iety of
geologica l p ro c es se s . Waves an d tides playa most
importan t role in the coastal dynamics, and their mutual
inte raction ac co unts for redistri bution of the sediment
budget causi ng accumulation o r erosion . Changes of sea
level gre atly mod ify the area reac hed by these agents in
the course of time.
Wave s move sedimen t and ten d to accumulate it in
beaches. T hus, the incoming waves are really a barrier to
th e sea wa rd movement o f sedime nt de rived from the
continents. Storm waves p rodu ce erosional surfaces. T he
erosive effect is particularly great during transgressions due
to the land ward displacement o f the surfzonc ac ross former
emergent parts of the coast tha t were topograp hica lly mo re
elevated.
Tides cau se per iod ic oscillations of sea level that are
felt mainly in areas where geographical co nstrictions such
as shoals and straits restrict the free movement of water
masses and gene ra te c urrents th ai sweep the bo ttom .
Astronomical tides ind uced b y the attraction of the SWl
and Moon in large bas ins ca use periodi c reversion o fflow
a nd oscillating cu rren t velo c itie s . I n contras t,
meteorological tides caused by piling up of water on the
coast, either periodically or not, are important in microtidal
or tid eless coasts because they increase the area reached by
the surf zone. From the a sedimentological poi nt o f view,
the main differences between beaches and tidal flats refer
39
1° Congresso sobre 0 Cenoz6ico de Portugal
EUSTASY AND CO ASTAL ENVIRONM ENTS
to slope, source of sediment and dominance o f waves or
tida l curren ts. But thi s simple scheme changes from cliffs
to beaches, barrier islands and lagoons, tidal flats, and
estuari es.
In o ther words, the (morpho-) sedimentary units
deposited in coasta l settings exhi bit a highl y va ria b le
stratigraphic architec ture, that is mainly governed by
factors as sedimen t supp ly, wave- and tidal processes,
c oas ta l mo rp h ology a nd a ccommod at ion spac e .
Seaward, these coastal sedimen tary un its interfi nger with
muddy she lf depo sit s, bu t landward these either en d
abru ptly, or show ra pid facies changes to tida l, lagoonal,
washover-fa n and fluvial depo sits. With time the pattern
becomes more co mplica ted as the abo ve mentioned factors
change , especially wh en landward erosional surfaces start
to playa prom inent ro le as soon as a position ab ove base
level is reached.
Despite da ily or we ekly oscillations, it is possible to
estab lish a mean sea leve l that is considered 's table' or
' fixed' at the scal e of human life and serves as refe rence
datum for topographic purp oses. Th e theoret ical da tum in
Spain is the mean level of th e Mediterran ean Sea in
AIicant e, but it actu ally fluctuates some 20 to 30 em/yr.
These sma ll-scale oscilla tio ns are a response to variations
of atmosph eri c pressure, evapo ration, vol ume of ocean ic
currents, and changes of wat er density due to varying
temperature and salinity. In the Northern Hemisph ere the
mean sea level is topographically higher in autumn and
lower in early spring.
Suess first used the term e ustasy in late 19 11l Ce ntury to
re fer to changes of level in ocean s ass uming that they were
coev al and of gl oba l ex te nt. Later realisation o f the
GLACIO·EUSTASY
DEFORMATIONS
, OF THE GEOID
_
/
10-30 mmlyr
-e-.......-
1000
/
, ',
" " ,
100
TECTO-EUSTASY
.sw
~
~
GEOIDAL EUSTASY
GLACIAL
10 mmf yr
10
EUSTATIC ·
VARIABLES
"
\
\
DYNAMIC
CHANGESi
1 m
r;
~
~ -::-AIJ
0.01
0.1
1
10
100 mmlyr
VELOCITY(mm/yr)
Fig. I -Types of eustasy (left) and rates of sea level change (right).
8
A
regression
input
tra nsgression
o
\..
--. f
~
marine
_
coast (beginning) '\
terrestrial
coast (end)
C
~ 1
eusta tic curve
~ 2
'\
~3
eroslon
~
~ ~~
..
'\
composite offlap + to /a
Fig. 2 _(A) Sediment input, transgression and regression during a rise of sea level. (B) Superimposition of eustatic curves with
variable periodicity and resulting composite curve. (C) Effects upon coastal units of eustatic oscillations with different amplitudes
(modi fied from Dabrio & Polo, 1996).
40
Cienciasda Terra (UNL), 14
tectonic and glacial components of eus tasy led to the
incorpo rati on of the terms glacio-eustasy and tectonoeustasy. Monier ( 1976) coined the term geoida l eustasy
after measurem ents from satellites revealed that the irregularity of the geoid also causes eustatic cha nges. At present
it is widcly ackno wle dged that the sea level mov es
con tinuously both vertical and horizontally forced by
changes in the lithosph ere and the hydrosphere and their
diffe re nt velocity o f response (Fig. I). Thus, the term
eustasy applies to any change of sea level regar dless of it
bein g or not global and coeval.
Global factors such as the "glacio-eustatic general sealevel rise" that took place after the Last G lacia l Maximum until ca. 7 000 yr. BP (Goy et al., 1996) control the
present position of coastlines, b ut reg ional factors also
contribute significantly to their evolution and trends . In
the coasts of the Southern IberianPeninsula, there are three
ma in region al fac to rs . (I) The geographic loc ation
(between 36°-40° N and 3°E-9°W) largely controls the
wea ther and climatic trends. (2) The tectonic framewor k
(boundary betwee n the European and African p lat es)
where numerous faults ac tive during the Late Pleistocene
and Holocene have affected the coastline producing
upli fting or subside nce (Zazo et al., 1994). (3) The effects
of the interc hange of Atlantic and Medite rranean waters
thro ugh die Gibraltar Stra it.
D uring eustatic oscillations thc coastal environments
move latera lly tens to hundreds of kilometres and vertically tens to hundreds of metres depositing sedimentary
units that very often are disconnected laterally and far away
from each ot her. Th e laterally shifting high-energy surf
and bre aker zones cut erosional surfaces. Eustatic falls
expose large areas to subaerial erosion.
Apart from presently known possibilities to discriminate
the vertical upward and downward relative movement of
se a level within sequences of coastal depos its, a more
complica ted effort is to incorporate the three-dimensional
evolution of the shore line . Another complexity is the
determination of the timeframe in which the distinguished
patterns ofcoastal sequences have been formed. Generally,
coastal depos its do not easily lend themselves for precise
d at ing of successive de posi tio nal steps. Rec ent and
subrecent depos its form an except ion, e.g. through 14C
dating possi bilities. Altho ugh seq uence stratigraphy helps
to dis tinguish related sedi ment packets deposited under
conditions o f varying accommodation space, careful
sedimentolog ical analys is sho uld precede a sequenc e
stratigra phic scheme (Van Wagoner & Bertrams, 1995).
Even then it is good to keep in mind that the number of
variati ons on the general sequence stratigraphic model is
limited only by the imagination (posamentier & Allen,
1993).
EUSTATIC CHANG ES AND STRATIGRAPHI C
ARCH ITECTURE
Sea level rises do not necessarily imply transgression
and sea-level falls regressions, because these terms refer
to lateral shits of the shorel ine (the coast indicated in maps)
towar d the contine nt or the sea re spe ct ivel y, becau se
another essential element is the sedime nt supply (Fig. 2A) .
High input can produ ce regression with stable or rising
sea le ve ls; in contrast, re duced input can fav o ur
transgression even with stab le sea levels.
Positive eustatic oscillations not always reach the same
topo graphical elevation. Th is implies that sedimen tary
units forming an apparently conformable succession of
coastal deposits separated by erosional surfaces formed
during "sea-level falls" record only a part of eustatic
histor y bet ween the depo sition of the oldest and the
youngest outcropping units. Most probably the erosiona l
surfaces represe nt one or mor e osc illations (Dabric, Zazo
et at ., 1996, Zazo et al., 199 6). Of course palaeontological
or radiometric controls may, at leas t theoretically, solve
this problem, but very ofte n the eustatic events are too
rapid as compared to organic evolution, or there are not
materia ls suita ble for radiometry. Besides, many eustatic
event s either leave no recognisable deposits (even if sea
levels reache d an adequate elevati on) or their depos its were
eroded later on. Last, but not least, it is not always easy or
possib le to discriminate be tween adjacent sedimentary
units due to simi larity of facies and fossil contents.
As eustatic oscillations take place superimposed at
various scales and have diverse wavelengths (Fig. 2B),
shifts of the shoreline may look chaotic and the resulting
sedi mentary record more or less unfo reseeable (Fig. 2C) .
Coastal sed iments occur spread on large areas ofthe basin
margins as the shorel ine shifts bac k and forth, and a good
part o f it is eroded by the moving shoreline, tidal channels
and subaerial processes during lowstands.
Tecto nic up lift and/or subsidence also control the
stratigraphica l architecture of coastal units (Fig. 3). For
this reaso n it is more adequate to speak about relative
changes of sea level. It is not difficult to recogn ise the
tectonic trends and the velocity of move ment by comparing the topographic elevations o f the coastline in two
geological ages (Zazo et al., 1993). Generally speaking,
coastal units are arranged in offiap or in staircase in stable
or uplifted areas whereas they occur stac ked or onlapping
in subs iding regions (Fig. 3).
Estimation of eus tatic magnitudes is relativel y easy
when con tinuous seismic profiles are available and the
lateral shift of the coastal onlep ca n be measured . However, surface studies (and more specifically the study of
Quaternary units) are based mostly in laterally disc ontin uous outcrops (cliffs, quarries, road cuts) and vertical sections . These require to study and interpre t the thickness ,
environmental and palaecological meani ng, and water
depth at which facies were depo sited, and ca reful use of
the so-called Walter 's ' law' (Dabrio & Polo, 1987). Th en
it is time to deduce the locat ion of the shoreli ne or ot her
features ab le to indicate water-depths .
T he most reliable indicator of the sea level (datwn) is
the plunge step found at the lower foreshore in microtidal
and tideless coasts (Fig. 4). In low energy coasts the breakers form a ste p at the base o f the swash zone whic h
prob ably marks the transition between upper and lower
flow regime of back swash. In fossil examples the step is
pre se rv ed mo stl y in tw o ways d epending on th e
41
1° Congresso sobre 0 Cenozoicc de Portugal
...-,
. . ......
,
~-
("
ATLANTIC
imesotldai)
MEDITERRANEAN (microtidal)
-
AUCANTE • MURCIA
_IER
_
lSL\NIl .
II 1til.Na) .
~
~~
~.
DAYOFCADlZ
~~.
-~
~
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FNlDB.'A11
~
SEllOUEI>'TARY
Al.MEJUA - NfJAR
MUR CIA
U. ....., ...
........ llVOO11
~
~
~-
~
~
,~
,~
~ ~
~ ~
~~m
-,
~"""""""'"
~
~
~-
~ ~-
VERYlOW IlUIlSlOENCE
""FlYlOW '-"'Sf.
~~ ~
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,.
'~~
,,~
~\~
~a ~
,,~
=
~~~
¥'Bl': ':'
,.
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SUBSI DENCE
-8
emnt~
(Law Pleistoeerlo!l)
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,~
cnVK~
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%
t
t
,~
.
,
--
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,~
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cm'K~;""""
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(Lalli Pleistocene)
(l.81e Pleisl ~ )
(Late
.7
cmIK~
~.
I
•
+
, +
., ,
. . SUBSIDENCE
0u1i\en (1~ .T.III)
~)
(ute PIei$tociene)
Fig. 3 - Geometry and sedimentary models ofTyrrhcnian marineunits as related to tectonics
and distance to thc sourceof sediment (after Zazo el af., 1993).
Fig. 4 - Usc cf cross bedding generated by the plunge-step in the
lower foreshore, to reconstru ct beach progradation and
retrogradation. and short-term trcnds of sea-level oscillations
(modified after Bardaj l et al., 1990).
predomi nant gra in size. In gravelly beaches it is marked
by an accumulation of the coarsest grain sizes available,
locally crude planar cross bedding po inting seawards is
preserved. In sandy beac hes it is evidenc ed by a change
from the sea ward-incl ined parallel lamination ofthe swash
zone to tabular crOSS beddi ng pointing to seaward.
The limit between shoreface and foreshore is used in
tidal coasts , but cons ide rably less p reci se. Finally, a
correction for compaction must be incorporated. Parti cular
attention must be paid to erosional surfaces. For instance,
the landward retreat of a barrier island produces two
erosiona l surfaces related to breaki ng wa ves in the
foreshore and to the base of tidal channels and inlets.
f iWl.l PUHl
sw
!JOT "
UQT .t14
+11m
Pre-Strombus bubon ius
T- lll
95.000yr
T"
T~
128.000 yr
160.000 yr
®
®
@
>250.000 y r
T
T~ rr!leoian lMtacIIes
C
ee.uvjlJ'T1
®
lJQl
I5ol<>pic 5139"5
U - _ meas.u_
WIIh
s. bu bonius
n1S (Hil a im-Ma..::ele1 a t.. 1986)
Fig. 5 - Sequence ofTyrrhenian beach deposits exposed along the western (righ t) margin ofRamblaAmoladeras. Offlapping facies
arrangement and sinistral (N40-4S0E) and dextral (N 140· 160 0E) wrench fault systems with vertical movement (modified
after Goy et af. , 1989).
42
Ciincias da Terra (UNL) , 14
EVIDENCE O F SEA ~ ~ E V E L C H AN G ES I N
COA RS E-G RAINED BEACH DEPOSITS
One of the best preserved seq uences o f prograd ing
Tyrrhenian deposits in the Western Mediterranean is nicely
exposed along the western (right) marginof Rambla [wadi]
Amo laderas (Zazo et aI., 1998). Th e Last Intergla cial (IS
5) is characterised by three see-level bigbstands during
ISS 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 climatic
instability. A marin e terrace corresponding to ISS 5e (ca.
95 Ka) is recorded in a ll coas tal sectors, and anothe r
marine un it representing ISS 5a (ca. 85 ka) in uplifting
tre nding sec tors ofAlmeria and Alicante.
In Ramb la Arno laderas, three Tyrrhenian morpho-sedimentary units correlated with the isotopic stages 7, 5e and
5c occur separated by eros ional surfaces with beach
features and evidence ofearly cementation (Fig. 5). Th ese
units represent highstand facies during the Next to Last
and Last In terglacials, and erosional surfaces ind icate the
intervening falls ofsea level. Aeolian dunes separate these
un its from the un derly ing un its o lder beach deposits
(IS 11 or 9).
Sed imentary units were depo sited in gravelly beaches
with a wann fauna of SlTombus bubonius, between 180
and 100 Ka. The outcrop is affected by a system of normal
faults directe d N 140 -160oE, that locally pr odu ces a
disp lacement o f the present coastline. A fa ult directed
N40-60" E con trols both the elevatio ns at which beac h
deposits occur at both sides of the ramb la and the sudden
inflexions o f tbe present coas t.
The offiapping pattern ofthe morpho-sedimentary units
and their variable elevations reflect tectonic act ivity with
mea n uplift rates o f 0 .068 mm1yr. This fact, tog ether with
isotopic da ta, sugg est that the sea level duri ng Isotopic
Substages 5c, 5e, and 7a was very close. Beach deposits
c on s ist mo stly o f c on gl o mer ates, sands to n es a n d
mudstones arranged in coarsening-upwards se quences
(Dabrio et al, 1984 , 1985) that include in ascending order
(F ig. 6): ( I) A lower unit o f parall el-laminated an d
wa ve -rip p le cross-lamina ted micaceou s sandsto nes,
commonly burrowed, representing the lower shoreface and
transition zones. (2) A middle uni t o f trough cross-bedded
sand and gra vel corresponding to shore face zone und er
wave action. Th ese two units are poorly expo sed. (3) An
acc wnulation of the coarsest gra in sizes available on the
coastl ine, decreasin g upwards up to well sorted fine gra vel.
(4) An upper interval of well sorted. parallel-laminated
gra vel, gently incl ined toward s the sea, rep resenting the
upper part of the foreshore and berm.
EUSTATIC C HANGES AND STRATIGRAP H I C
ARC HITECTURE OF G ILBERT-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 rgin a l to the Med iterranean Sea,
extended inland in an western direction and was filled
with a complex succession ofunits separated by erosional
s urfaces th at in some cases remo ved most of the
sedi mentary 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 occ ur under a gen eral
tabular geometry made up o f a large nwnber of interbedded marine (M -O to M·5) and terrestri al (T-O to T-3 )
depo sits arranged in a multi- storey trans ition zone. The
verti cal stacking of all these units gen erated a Gilb erttype delta which records a complex histo ry of relative
sea-level changes, tectonic trends and modifica tions of
sediment supp ly. Succe ssive delta lob es progressivel y
filled the bay during bighs tand s, but ero sion removed part
of the lobes during lowstends.
....
•
•
_ _ "'"" (sIOmI}
~ ~ - -- - - --- - - ~- -~;; - - -
~~
., -
------- I
_Ye baM (tak -fhlH1
~ ----:3
_
_
ltIminaIion
:t 2
.
-_.....
--
~­
#>. . lIII'awH Ipple ClOSS /amlns lioo
~
1rOOricat9d cl8sts
-~. ~--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
w
E
poles 01coastal limil
'"
······'M-2 ···········.....
·a···._2
""
1
"
--...
~.::.
.
Fig. 7 - Panorama of the Cuartelillo hill (modifi ed after Dabrio et at., 1991). Numbers indicate sedimentary units.
Th e proposed model is a delta connected to a coarsegrained ri ver plain with rapidly shifting channe ls, flowing
mostly from the north (line source ) (Fig. 8). Terrestrial
(fluv ial) deposits include coarse -grained (channel fill) and
fine-grai ned (flood pain) facies. The coarser gra in sizes
were retained in gravelly reflec tive beaches at the waveworke d de lta front. Terrestrial and coarse-grained coastal
depo sits overlay the foreset unit with an intervening flat,
erosional surface gently inclined in the average direc tion
ofdelta p rogradation (ESE). Adelta platfonn cove red with
burrowed sand and scattered pebb les and boulders
extended seaward ofthe wave-worked delta front. Shallow
marine to coasta l dep osits consis t of light yellow to grey,
well so rted , conglomerates with ro unded and notab ly
spherical clasts deposited in coarse-grained beaches ofthe
reflective type . A stee p slope with dips rang ing from 25"
to 12" connected the delta platform with the shelf.
C linoforms evidence the progradation of units under the
action of sediment -laden currents which supplied sand to
the basin margin and slope . Alternati on of short periods
with hyperpicnical flows down the de lta slope (dominance
of sedimentation) and longer periods of quietness (dominance of burrowing) conditione d the internal structure of
the foreset. The Cuatro Calas G ilbert delta is comp arable
to present-day de lta s of eph emer al strea ms feed ing
gravelly beaches in SE Spa in. Progradation of the delta
generated a two-fold large-scal e cross-stratification: a
topograph ically lower high- ang le related to the advan cing
delta-foreset and the upper one asso ciated to progradation
of beac h units (Fig. 8).
Ev idence of eustatic changes come from the seepsided, large-scale ero sional surfaces in the forese t facies
that progress deep into the previous foreset deposits with
varia ble orie ntations. These are interpre ted as incision and
partia l destruction o f delta-front and fo reset deposits
during relative falls ofsea level. New delta lobes deposi ted
during later highstands had to adapt to inherited topographies (Fig. 9) and prograded to E, ESE, SE, and E as shown
. ~
,... 0 '
'
l OW ANGLE CROSS BEDD ING
rogradation of beach
p1alfonn
foreshore
berm
gravel .....gravel
sand + pebbles
HIGH ANGLE CROSS BEDDING
progradation of delta foreset
Fig. 8 · Model of Gilbert-type delta in Cuarro Cates (modified after Dabrio el al., 1991).
44
Ciincituda Terra (UNL), 14
---
STAGE I
HIGHSTAND AND DEPOSITION OF A NEW LO BE
STAG E I
LOWSTAND AND EROSHJN
Fig. 9 - Generation ofa complex Gilbert-type delta (modified after Dabrio et ~l., 199 1).
TRANSITION-ZONE UNITS
Post-Gilbert
DELTA-FORESET UNITS
M-5
T-3
Marine ~LS
Marine
? F LS
~.
Marm
~
.=::""
~
~:::""~,~
M-4
L: :T
T-2
M-3
M-2
TST+HST
TST+HST
T-l
T-(,
M-'
M-<l
Fig. 10- Sequencestratigraphy in the Cuetrc Calas Gilbert-type delta (modified after Dabrio el al., 1991).
by dip of clinoforms in units I to 4 respectively. Sequence
stratigraphy of the foreset units is explained by fluctuations of sea level (Fig. 10), but only the highstand delta
deposits are expo sed; lowstand wedges lay und er the
present se a le vel. Ba cksets ov erl yin g the er osiona l
surfaces were deposited during relative lowstand and early
transgressive episod es.
Th us, the develo pment of the complex Gilbert-type delta
followed a repetitive pattern in response to fluctuations of
sea level: prograda tion ofhighstand Gilbert-type delta was
follo wed by entrenchment and coas tal wedge in lowstand
and early transgression (Fig. 10). The various parts of the
del ta reacted differently to these see-level changes and
generated variable facies associations. Progradation of
complex de lta pr isms does no t imply a continuo us
stillstand as previously assumed for simple Gilbert-type
deltas . The rapid evolution of the bay-fill can be related to
hi gh-frequen cy fluctuations o f se a level already
documented in SE Spain during La te Pl iocene and
Q ua ternary, supe ri mposed on longer-lasting tec tonic
activity.
T HE INFL UEN C E OFACCOM MODATI ON SPACE
GENERATED BY EUSTASY AN D T E CTONICS
It is well ill ustrated by the late Messinian Sorbas
Member in Almeria prov ince aro und the town of Sorbas
due to absence of burrowing by raised water salinity and
expo sure 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 para sequ ence set of three
prograding coastal barri ers (sequences I-III), assoc iated
with lagoon and washove r sedi ments (Dabrio, Roep et al.,
1996). Logging and car eful corre lation of fifteen vertical
sec tions perm it to reco nstru ct and d iscuss pattern s of
relat ive sea-level mo vements between decimetres, up to
15 m within a parasequence. Excellent examples of nontidal transgressive facies are characteris ed by lagoon and
washover sediments instea d o f the usual combination
of washover and tida l deposi ts (channel and flood-tidal
delta) .
The lower two sequences are deposited in a relatively
large, tec tonical ly enhanced wedge shaped acconunodalion sp ace . T he y sho w b oth fining-up, de epening
sequences,followed by prograd ing coarsening-up shoaling
sequences and can be compared to th e c lassical
parasequences of the Western In terior Basin (USA).
Progradation o f seq uence II was interrupted by a majo r
slide even t (most likely triggered by an earthquake). that
caused mo re than 400- m seaward slumping of a stretc h of
1 km of coastal sands.
The architec ture of seque nce III is more complex due
to limited acconunodation space characteristi c for the late
highstand, with a wedge-shape d acco mmodation space to
the east (" sea" ) that changed to a more box-shaped space
towards the wes t ("land") (Fig. II A). Therefore, th is
setting was very sensitive to sea leve l fluctuations and the
coastline reacted in a j umpy way.
Taking the thickness ofUnit III as an indicator of water
depth and magnitude of see-level fluctuations involved in
the cha nges of coas tlines, a water depth o f ca. 10m is
45
I- Congresso sobrc: 0 Cenoz6ico de Portugal
A ·_
--
_
""""-'11-
--_.~.-.
_
_
W"O~OIl ~
~ICC :
.ifhOdlIIIon...-
INR.UENCE OF ACCOMMODATION sPACE
INFLUENCE OF SUBRE DEFOR.....TIONS
Fig. 11 • (A) Influence ofthe available accorrunodation space in the generation c r coesiat units. 1 10 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 position
that occupy in the vertical sequence certai n sedimentary
featur es indicative of the coast line such as bird-foot tracks,
swas h zo nes , and beach-rock leve ls.
Next to relati ve sea-level chang es and differential
uplift also related geometrical factors such as gen tle and
loca lly occ urring synsed imentary fold ing appear to have
influe nced the stratigraphic architecture of the Somas
Me mber an d bad palaeogeo gra phic implications. The
crea tion of a roughly N-S tr en ding ridge and swell
morpholo gy around Somas contro lled the prominent N· S
orien ta tion of the beach ridges and lagoons (Fig. I I B). The
rising areas ("anticlines) acted as nuclea tion areas for
barrier islands, where as the intervening gentle depress ions
favoured the development of lagoons. A crucial point is
that th e (p res en t) differen ce in elevat ion s between
the se a reas is usu all y 3 or 4 m, and mo st o f the
irre gul arity wa s com pe nsa ted a fte r deposition of
Un it III (Fig. 12).
In the field, Sequence III is readily recognised as a
parase quence. Upon closer inspec tion, however, it appears
to co nsis t ofj uxtaposed transgressive and pro grading parts,
separa ted by erosional surfaces and flooding surfaces due
to sea leve l fluctuations within the limited accommodation space. Minor trans gress ions induced formation of
landw ard moving washove r fan systems intercalated in
lagoonal mud. which finally were partly erod ed by the
retrea ting barri er. Periods of forced regression caused the
seaward stepping of tcmporary barriers coastline over more
than J.5 km, lea ving behin d "s tranded" coastal barriers
(Fig. J t Al . During this process these may show landward
ero sion. or sea ward progradation depe ndant ofthe smaller
sea -le vel flucruations. The lateral jumping and erosional
surfaces in parasequence III seem to be good indicato rs
for a much more red uced accommodatio n sp ace, as is the
exaggera ted infl uence o f wa ves in the for esh ore as
d est ru ct ive agents. Du e to it s more co mpl ex facies
architecture, Sequence III might fonn a nomencl atorial
prob lem : is it one paraseq uence or in fact a composite of
4 stac ked parasequen ce s, i.e. of similar ran king as
se quences I and II, given the largest sea-level fluctuations
dedu ce d? A main conclusion is that erroneous sequential
(stratigraphic) interpretations are eas ily made when
acconunodation space is limited.
46
Til E RECORD OF ESTUARI NE INFILL DURIN G
TI l E LAST POSTGLACIAL T RAN SGRESSION
The late Pleistocene and Holocene evo lution of the
estuaries in the Gulf of Cadiz (SW Spain) has been studied
using dri ll co res, logs, trenches, and 38 new radiocarb on
data . The resu lts were compared with the shelf to obtain
the sedimentary interp retati on of the estuarine fill of the
incised valleys (Fig. 13) cre ated along the prese nt coast
of the Gulf of Cadiz during the Last Glacial fall of sea
level (Dah rio el al., 1999 , 2000 ).
The studied estuaries reco rd repeated incision during falls
of sea level with prese rved deposi tion duri ng at least two
higbstan ds of Late Ple istocene (I S 3) and Holocene ages.
The overall pattern co rrelates with the 4'-order eustatic
o scillations an d th e superi mposed 5 111-ord er cycles
recorded in depositional sequences found in the sh elf off
the study area (Som oza et al., 1997, Nelson et al., 1999,
Rodero et al., 1999).
Th e Odiel, Tin to an d Gu ad alete rivers deposited
co nglomerates during a highstand that did not reach the
present se a level dated at ca . 2 5- 3 0 Ka (I S 3),
co rresponding to a relatively humid period in the area .
Rivers incised these coarse-grained deposits durin g the
last main lowstand at ca. 18 Ka, when sea level dropped
to - 120 m and the coastline lay 14 km seawards from the
present. The erosiona l surface is a sequence boundary and
also the flooding surface of the postglacial eusta tic rise,
overlain by the valley-fill deposits of the transgressive and
highstand phases of the last 4111 and SIII-order depo sitional
sequences reco gnised in the shelf. Vanney et at. (I98S)
found erosional channels in the shelf of Pleistocene age
that have been cov ered by Holoce ne sediments
Acco rding to da ta from the shelf (Hernandez-Mo lina
et al.; 1994), at the beginning of the Holocene and the
F1andrian transgression (ca. 10,000 yr BP) the sea level in
the Gulf of Cad iz was 30-35 m below present MSL. The
first marine ev idence of the Holocene (Flandri an) trans.gression in the studied estuaries OCCW'S 30 m belo w present
MSL in Guadalete and 22 to 30 m below present MSL in
Od iel-Tinto inci sed va lleys. Th ese differences reveal
topograp hic irregularities alon g 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
0
7
6
94 8
12
13
14
_~-'{J.
2
11
I
3
S
·1
50 m
0
250
500
750
1000
white limestone layer
0
10
20
30
40
SEQUENCE II
50
m
SEQUENCE III
Time
•
Fig. 12 · Es timates of sea- leve l fluctuations in Sequences II and III through time relative to the po sition of the Zorreras
white limestone datu m plane. To facilitate descri ption th e sea- level pos itions 1- 14 are indicated o n inset. Because ofthe
unkno wn time constraints the distan ces 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 the
bay-head deltas and the axial zones of the estuaries .
After 6500 yr SP the evolution of the estuarine filling is
closely related to the decrease of the rate of sea-level rise
from 5.7 mm yr-' between WOOD and 6500 yr BP, to 2.6
mm yrl between 6500 and 40 00 yr BP recorded in the
central estuarine basin. The rate offluvial input to estuaries
surpasse d the rate of sea-level rise (l.e.• crea tion o f
accommod ation). favouring the vertica l accretion of tidal
flats and the accumulation of the spit unit ~ colonised by
human settlements (BOIj a et al.• 1999). Vegetation changed
10more arid conditi ons. T he increase in vertical accretion
caused a reductio n of the tidal prisms in the estuaries that
allowed the acc umulation of stable spit barri ers and the
app arent effect of waves was magnifi ed. The effect is
particular ly felt between 2500-2700 yr BP. when the spit
M it H) began to grow and the first associated aeolian
foredun e systems acc umulated. In Guadal ete, two fluvial
cou rses supplie d sediment to the active littoral drift and
favoured the gro wth of a broad H) spit barrier crossed by
a Roman way. In the last 500years, the confluence ofl ittoral
drift. large fluvial input magnified by deforestation, increasing
aridity favoured the accumulation ofthe large H~ spit units.
Historical data. particularly the present position of watch
lowers built in the 170, century AD, evidence rapid coastal
progradation rates up to 3 m ycl (Lario et aI., 1995).
The filling follows a twofold pattern in respo nse to
the progressive chan ge from vertical accretion to lateral
(centripetal) pro gradation. First, subaqueous sedi menta-
tion greatly reduces water depth and the accommod ation
space, but that does not have an appreciable effect in the
surface morpho logy, except near the bay-head delta. Then.
the surface occupied by the flood ed estuary diminishes
rapid ly due to fast expansion of th e emergent area s.
producing rapi d geo gra phical changes and landscape
modifications.
A main deri vation is that onl y the radiocarbondata
and depths for a single dri ll core can be used to co nstruct
reliable curves of subsidence rate. A single curve reflects
sedime nta tio n in a p articu lar spo t o f the est uar y.
Comparison of curves obtained in an estuary will give a
"m ean" curve of subs idence.
Three washover fans breaking the part ofthe spit active
at ca. 1750 AD may be the result of the tsunami associated
to the so-ca lled 1755 Lisbo n earthquake that reached a
Richter magnitude 8.5-9 (Dabrio, Goy et al., 1998. Luque
et al. , 1999). It is difficult to date accura tely the washover
fans becaus e of the lack of s ui ta ble fo ssil remains.
Continued sou thwards migration of the San Pedro River
channe l since 1755 has eroded the area immediately to
the south of the spit barring the chances of findin g other
preserved remains.
T H E RECORD O F EUSTATIC C HAN GES IN
PLEISTOCENE AEOLIAN DEPO SITS. GULF OF
CADIZ
Coasta l areas that re mained largely emerg ent during
eustatic osci llations under aeolian influence (Menantcau,
47
j"Congresso sobre o Ccnozoico de Portugal
1979, Borja 1997) also record the cha nges, although the
stratigraphic record is some what different. The Quater.
nary sa ndy de posits form ing th e E I Asp erillo cliffs
(Hue lva ) exem p lifi es thi s case stu dy. H ere . the
stra tigr aphic relat ionsh ip s, ge nesis and chronology
. includi ng ra diocar bon da ting were studie d with spec ial
emphas is on the influence of neotectonic activity, sea-level
changes and cl imate upon th e evo lution of a subaerial
coastal zone (Dabric, Borja et al., 1996, Zaz o etal., 1999).
Normal faults ac tive duri ng the Quaternary co nditioned
the sed imentation in the coastal zones of SW Spain. The
E-W trend ing Torre de l Lora norm al fault was a major
control on aeoli an sedi mentation in the area of the EI
Asperillo cliffs during the Late Pleistocene (Fig. 14) and
on the coastl ine direc tions during the Mid dle and Late
Pleistocene. The fault separates two tecton ic blocks but
its movement stopped before the Holocene. Tiltin g ofthe
upthrown fault bloc k (Torre de l Loro - Mazag6n) to the
No rthwest during the Ea rly and Mi dd le Pl ei st ocene
con trolled the displace men t towards the Northwest of
flu viatile cha nne ls o f a trib utar y o f the p al ae oGuada lquivir River. In this blo ck. mari ne de posits of
probable Last Interglacial age have bee n preserved, and
arc subaerially exposed nowadays. Their presence in the
area is mentioned for the first time in this paper. In our
model, the Torre del Lora fault created accommoda tion
space in the downthrown block where aeolian sedi ments
accum ulated during the Last Glacial period, and probably
during part ofthe Last Interglacial. The vertical offset along
this fault is 80 m since the Early Pleistocene, and 18 to 20
m during the Late Pleistocene.
At present, the most active normal-fault system trends
NW-SE, contro lling the direction of the shoreline and the
pattern offluviatile valleys on land and of drowned fluvial
valleys on th e she lf. Thi s sys tem and th e important
NNE-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 (U nits I
to 6, Fig. 14), stacked in the do wntbrown bloc k, ar e separated by bounding surfaces (supersurfaces) in response to
major changes in sand supply and wetness of the substratum which contro lled the dep th of the water table. In
contras t, the aeo lian depo sits below the iron crust in the
upthrown bloc k, thought to correspond to Units 1 to 3, are
th inner and dep osited on drier substrata, with severa l
supersurfaces marked by palaeosoils indica ting repeated
degradation and de flation.
Thus, the oldest depos its occu r in the upthrown block.
They are Early to Middle Pleistocene fluviatile depos its,
probable Late Pleistocene shallow-marine depos its along
an E-W trendi ng shore line , and Lat e P lei stocene and
H o locen e ae olian sa nds depos ited under prevailing
southerly winds. Six Plei stocene and Holocene aeo lian
units accumulated in the do wnthro wn block. Ofthese, Unit
I is separated from the overlying Un it 2 by a supersurface
th at re p rese nts the end of the L ast Intergl aci a l.
Accumul ation ofUn it 2 took place durin g the Last Glacial
under more arid co nditions than Unit I . The supersurface
Fig. 13 - Four palaeogeographical steps of the changing
separating
Units 2 and 3 was fonned between the Last
landscapes in the Guadalete (above) and Odiel-Tinto (below)
Glacial maximum at 18000 I·C yr BP and - 14 000 I_C yr
incised valleys(modified after Dabrio et a/.• 2000).
48
Ciencias da Terra (UNLJ, 14
BAsperilo{..... tion 103m)
.. - .! . . . _-- ~-~~
.....,.,..
I
NW
m
+ ..
"j.8:I . _.
U-S- - - ~ -':!~- - · _ - _ · - - _ · -
U-4 :.-.:; :.,-.: :.-,;;;.-,.;; :.: .: :.-.:-_ ____
25
Iia n
~~: -
?
24
Z3
.
1 " MAT·'o
~T-ll \
~T.H
__I" 1.44T- 18.J-
e
L
~_
l~
_~,...:--
-:!il\ ~~T~~ MAT" 5
•
mir l...
/'
22
:n
20
"
Ie
~':/ l e \ 1 5 ,,-\4
,.Jl,
'"
__ surtaoe wdh 0l'gllIIic mane,
._ - surtace will'lotJCl 0tg80ic man.<
l41 ...
.,,,
\
13
12
n
SE
..
~
U-6
•
IL
U-5
--- . ... .1'
U-4
...- - - - - - - - - - - - - ... ~ -.. - ... - U-3
MA.T~ ; ;;;'
'0
•
,
1
1.4"" ' 4
::_!
4:
~
" """" " ' "
'." . :-. : . _•• ·· U-2·._ •. •:".:"
eo
5
4
3
2
1
"~
E
!Ii:
_.~ d
0,,",
lolAT-t
.-sooZ
bl "' b4
.... ~ 0ItlI'il;:hed in iron oUI8s
Fig. 14 - Schematic profile showing di5lribution of un its in the EI Aspcri llo cliffs and sample positio ns, Distances in km from the
tower (Torre) o f La Higuera. No te strong vertica l exaggeration. Palaeocurrent and wind direction s 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 the
rise of sea level. Unit 3 records wet conditions . The
supersurfa ce separating Units 3 and 4 fossilised the Torre
del Lora fault and the two fault blocks. Units 4 (deposited
before the 4" millennium BC), 5 (> 2100 1'"C yr BP to
16th century) and 6 (16th century to present) record
relati vely arid conditions . Prevailing wind directions
changed with lime from W (Units 2--4) to WSW (Unit 5)
and SW (Unit 6).
The generation ofthe aeolian depos its started prior the
Last Glacial period and continued until the present day.
Aeolian Unit s 4, 5 and 6 are probably rel at ed to
progradation ofspit systems in estuarine barriers. The sedimentat ion gaps found in the spits may correspond to the
supersurfaces separating Units 4, 5 and 6. Both seem to
be related to short-lived (250-300 yr), relatively humid
periods with a relative rise of sea level.
Wind directions changed during the deposition of the
aeolian dunes: the oldest recorded (upthrown fault block)
blew towards the north and south. Units 2, 3, and 4 accumulated under prevailing westerly winds. Palaeowinds
blew from the WSW during Unit 5 and, as at present, from
the Southwest during Unit 6. The change in palaeowind
directions from Unit 4 to Unit 5 may be related to a change
from 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 related
to estuarine barriers in the Gulf of Cadiz (Borj a et al.,
1999). The oldest one, 0 1, accumulated under prevail ing
WSW winds during the 1st millennium Be overlays both
the 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, accumulated
between (?) 13" (1) -14* century and 17th century AD.
The youngest 0 3 system occurs associated to the time of
building of watchtowers in 17th century AD but extends
to the present. It is related to prevailing winds from the
sw. The absence of aeolian deposits prior to - 2700 cal
BP is the result of trapping ofa large part of the sediment
supply in the estuaries, which starved the neighbouring
beaches and aeoli an settings. Aeolian accumulation
reached significant values when sedimentation in the
coastal zone changed from being mainly aggradational in
the estuaries(-6500·nOO cal BP) to mainlyprogradational
in spit barriers and related dunes (post - 2100 cal BP).
The pre sent analysis of aeolian syste ms s uggests a
non-direct correlation, at least in some cases. between
coastal progradation of spit ba rr iers and aridity as
previously assumed.
CONCLUSIONS
Six conc e ptual mo de ls exe mp lify di verse in
stratigraphic architectures in response to various types of
relative sea-level change and associated lateral shift ofthe
shoreline (Fig. 16). Illustrated are 6 (I - VI) hypothetical
eustatic sea level curves (the sinuous lines in the middle)
deduced from these deposits and associa ted shifts of the
coast line that can be reconstructed from the lateral and
vertical stacking of the coastal sediments (left).
(I ) Coastal onlap records a steady rise of sea level
(which. in principle, is considered to be continuous, see
thick heavy line) during a single eustatic oscillation (sll ,
sl2, etc. indicate succ ess ive position s of sea le vel ).
However, a discontinuo us rise may produce the same
effect, particularly if scrutiny of sections is not careful
enough. During this process the shoreline moves landand upward.
(II) Discontinu ou s coastal onlap may refl ect a
continuous sea level rise with variable sediment input
(thick line at the left), a two-step rise with an intervening
interruption, or sudden jump upwards (line in the centre),
or(evcn) an intervening minor fall (line at the right). In the
meantime. the shoreline progresses as in the former case.
49
1° Co ngresso sobre
0
Cenozeico de Portu gal
AEO LI AN P H ASES AN D H UM AN SE T T LE M EN T S
AYAUONTE
ooNANA
PUNTAUMaRIA
PUNTAARENIUA
VAl.DELAGFlANA
CANTARRANAS
LAALGAIDA
~ ~
fiI~
\lo~
,
•
•
,,
~
.=.--.
.·1- ~•. .• - iiit
• iiit ,'
~
I,,~i-:l
·•• - .
,,
~
1
•
...--
T
,"
!=-3QOO
••
~"-I
••
<Q>
~
1000 9C
:. ,'~
_ 'v'
·
•
1
T
'~
.~
••
-
Eo
I'iI
WatehlOW9. '7thcenlufyAD
Uttoic worI<ahop ""'Db (4111 10 2nd mIJemium BC)
~
~al
Late NeoIilNc-ElUlyCoppe< (3&40-3130 Be)
iiir:
Lal" Roman (2IIl1o 5111 cent<>riesAOj
I•
~ Romanway (,..tcenlBeIo2ndeenlAOj
"CJ Bronz". (1850- 1650 Be)
••
0lde9I rnIrlIrrul ao- '" splI sedlmentalion
based upon an:IIaeological data
••
<:Q;> Pre-Roman (8lh 102nd cenlury BC)
t
0kIesI da le<l age ~ 4 C) '" splI sedi_1lon
SpIt bat units (t.lediI" ............. Atlantic:)
Fig. IS - Chro nostrat igraphy ofaeol ian phases and human senlements in the Gulf ofC:id iz. No te that italic typing ind icate
calibrated ages (after Borja el al.; 1999).
GEOMErRY
(ARCHITECT URE)
EUSTATIC
OSClI.UTlON
:7.~?
of
or,
01.
- -
__
.
-
"
- - --- - ; . - '
__
8-,. ~i;'
DISC(lNT1HllOUS
-~ -~
••
-~~
SHIFT Of
COA STUNE
GEOMET1'IY
(ARCHITECTURE)
SHIFT OF
COASTUNE
;;.?'... ...
...·ll4o _ _·
_ _ _.0.
...
W
.........
...-:;.~ ...
.-
... ........-
V
COAST... OHLAo• OI'n.A o
.----_
:to'
.... ...1····
~
III
Fig. 16· Conceptual models ofslTat igraphic architecture induced by a variety ofsea -level cha nges, and associated lateral shift of
shoreline (modified after Dabrio & Polo. 1996)_
50
Ciincias da Terra (lINL), 14
(III) Coastal offlap reco rds (q uasi) steady sea level.
Seaward shift of s horeline may (or may not) be preceded
by other shifts (dotted line with question mark).
( IV) A co mplex coastal offlap with three pro gra d ing
beach units (B·1, B -2, B·3) a t different topographic
elevations, each composed of minor prograding un its (a,
b, c), records at least a firs t sea le vel rise followed by
eustatic oscillations re achin g pro gre s sively lo we r
ele vations . The shore line fo llo ws a zigzagging pattern.
(V) Two beach units (B. I olde r than B-2), each with
minoroffla pping un its (a, b, c) record at least two sea-level
ma xima reach ing progre s sive ly higher ele vatio ns, with an
int ervening stillstand, or minor fa ll that comple te these
oscillatio ns. Th e shoreline fo llows a zigzaggi ng patt ern .
(VI) A combinat io n offormer cases may produ ce much
more co mp lex stratigraphical ar chite ctures, suc h as in the
d isc on tin uo us coastal on lap plus simple offlap.
These mode ls c an be applied to the former ease studies but it must be noted that differentiatio n in the field
be tween si tua tion IV an d V may be d iffi cult when the
bo undaries arc incomp lete ly e xpo sed. Furthcnnore, the
late ral and vertical relationships are much more complicated d ue to the interplay of various o rders of magnitude
of sea leve l changes.
The cases of gravelly beaches in RamblaAmoladeras
and the Gilbert-type delta of Cuatro Ca las are classified
as type IV forming a complex offiap o f several uni ts
separated b y erosional surfaces. T he main d iffere nce
between the two situations is tha t tectonic up lift was more
promi nen t in Amoladeras.
Sit ua tions I, II a nd III a nd th e ir combi na tion in
example VI a ll can be fo und in seq ue nce II of Sorbas,
whereas examples IV and V can be found in sequence III .
Situation VI applies to the po st-glacial e ustatic rise in
S W Iberian Peninsula . H ere, li mi ted p ro grada tio n o f
Iithosomcs during temporary stops o r times of reduced
rate o f rise in termina l Pleistoc ene ti mes produce d iscontinu ous coastal onlap plus offlap (V ), whereas progradat ion
with qua si stab le sea leve l in Ho locene promotes simple
offlap (III).
ACKNOWLEDG EME NT S
Fi n ancia l s u p port fro m S p anish MEC proj e cts
PB98-OS14 and PB 98-0265. and ProjecrAreces: "Cambios
climaticos y nivel de l mar" . It is a contr ibutio n to
IGCP437.
R E F ERENC ES
Bardaji, T.; Dabrio, C. J.; Goy, 1 L.; Somoza, L. & Zazo, c . ( 1990) - Pleistocene fan deltas is southeastern Iberian Peninsula:
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