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Palaeoecology of Quaternary Shorelines and Sea-Level Change in Mallorca Author(s): G. W. Richards Source: The Geographical Journal, Vol. 151, No. 3 (Nov., 1985), pp. 356-364Published by: geographicalj Stable URL: http://www.jstor.org/stable/633018Accessed: 06-03-2016 19:36 UTC
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The Geographical Journal, Vol. 151, No. 3, November 1985, pp. 356-364
PALAEOECOLOGY OF QUATERNARY SHORELINES AND
SEA-LEVEL CHANGE IN MALLORCA
G. W. RICHARDS
Quaternary raised shorelines in Mallorca have been cited as evidence of complex
eustatic sea-level changes. Investigation of the molluscan fauna of the shorelines
allowed the height at which they formed to be identified very accurately, showing
that comparatively little relative sea-level change has occurred. No unambiguous
Tyrrhenian beaches were found higher than 2.5 m above present sea level. The
faunal evidence suggests the presence of a single Tyrrhenian shoreline which has
been deformed by subsequent tectonic activity.
THE QUATERNARY SHORELINES of Mallorca have been subject to close
scrutiny in recent years, but in spite of numerous publications on the sea-level
chronology of the shorelines, little consideration has been given to possible tectonic
deformation. This study attempts to identify former sea levels with a high degree of
accuracy, using molluscan remains as sea-level indicators (Richards, 1982; in press), in
order to trace tectonic deformation.
Over the past three decades, the work of Butzer and Cuerda (Cuerda, 1957; Butzer
and Cuerda, 1962; Butzer, 1975) has helped to push Mallorca to the forefront of
Mediterranean sea-level studies. Much of the initial work on the raised shorelines was
descriptive, and merely attempted to fit the shorelines into the classic Tyrrhenian
framework of Deperet (1918). This placed the shorelines in the last interglacial period,
and related their formation to periods of high eustatic sea levels. The interglacial origin
of the shorelines was supported by the presence of the thermophilous gastropod
Strombus latus {-bubonious), which is today found living in West Africa.
A Tyrrhenian I 'transgressive complex' was recognized by Butzer and Cuerda (1962)
at heights between +4 m and +34 m; two stages of the Tyrrhenian II were identified
with shorelines at +10.5 m, +12.5 m and +2 m to 9 m; and Tyrrhenian III deposits were
found at +0.5 m to +2.8 m. The fauna associated with the shorelines is similar to that
reported from many other areas of the Mediterranean, with a rich Strombus fauna
characterizing the Tyrrhenian II shoreline.
Following this initial stratigraphic analysis, 15 Thorium/Uranium (Th/U) dates were
obtained for shell material in the shorelines (Stearns and Thurber, 1965). The dates fell
into three basic age ranges which tended to support the threefold division of the
Tyrrhenian, but the spread of dates also indicated that the sequence of marine and
terrestrial deposits was far more complex than was originally thought. Six major marine
transgressions were eventually recognized in the Mallorcan sequence (Table I). Each
marine hemicycle was identified by a beach overlain by a palaeosol, and the terrestrial
hemicycle was equated with a silt/aeolianite complex followed by a pedocal.
A useful review of the Mallorcan literature is presented in the Quaternary Research
Association field guide for the island (Crabtree et al, 1978). The guide also contains
location maps and sections of all the key sites. Most of the sites were visited in the
present study, and their molluscan fauna was sampled.
Methods
Samples of the fossil molluscan fauna were collected from each site over a set time
period of one hour. This method provides comparability with abundance data obtained
for modern live and dead molluscan assemblages in the Mediterranean (Richards,
1982; in press). Thus each site could be matched with a modern analogue with a known
relationship to sea level, allowing the position of the contemporaneous sea level to be
established to within ?0.5 m or better.
-^ Dr G. W. Richards is a Lecturer in Geography in the Department of General Education,
Southwark College, Tanner Street, London SE1 3DP. This paper was accepted for publication in
October 1983.
0016-7398/85/003-0356/$00.20/0 ? 1985 The Royal Geographical Society
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QUATERNARY SHORELINES IN MALLORCA
TABLE I
357
Pleistocene high shorelines of Mallorca, after Butzer (1975). Cycles X and Y correspond to
Tyrrhenian 11 and 111 respectively
100-105
The elevation of each site was obtained by levelling with an Abney level to a fixed
point on the shore, which could then be related to a measured tidal datum (usually
extreme high water). The position of the site relative to mean tidal level (MTL) could
then be obtained from tide tables. This method gives a root square sum error of less
than ?4 cm (Richards, 1982).
Cluster analysis of fossil assemblages was made using an indicator species computer
package, INSPAN2, based on the reciprocal averaging method of numerical ordination
(Hill et al, 1975). Collected material was identified using the comparative collections of
the British Museum (Natural History).
Faunal analyses
Thirteen sites reported by Crabtree et al. (1978) as containing Tyrrhenian fauna were
sampled, as were two other sites where no beach material was recorded (Figure 1). The
Tyrrhenian sites were found to contain both rocky and sandy shore assemblages and a
total of 22 species was recovered, of which only Strombus latus is not found living in the
Mediterranean today, although other immigrant species have been reported from these
sites (Cuerda, 1975).
Cluster analysis of the fauna reveals a high degree of homogeneity, although there is
some separation of sites into predominantly rocky and sandy shore assemblages. No
muddy shore or lagoonal elements could be traced in the fauna. Such a pattern might be
expected from a rocky shore with sandy embayments with a comparatively short time
span between the formation of the assemblages.
Although analysis of the depth distribution ofthe species collected showed that many
individuals would have lived in the sublittoral zone, most of the sublittoral individuals
were Glycymeris violasecens, a bivalve which is washed up in large numbers on modern
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358 QUATERNARY SHORELINES IN MALLORCA
10 km
i-1
Cala Estany
Camp
deMar
Fig. 1. Location of sample sites
beaches in Mallorca and other parts of the Mediterranean. This would suggest that
most of the assemblages formed close to sea level. In addition, the uniformity of the
zonal distribution between sites in different parts of the island indicates that the
deposits represent a single shoreline in which only a small part of the transgression has
been preserved. This view is supported by the fact that the shallow sublittoral species
Strombus latus was seldom found in life position, whereas it is frequently found in place
in sublittoral deposits in Tunisia (Richards, 1982).
In view of the overall similarity of the fauna, and the fact that many of the sites are
close together, it seems appropriate to deal with them in groups.
Site analyses
Col d'en Rabassa.?The eastern shore of the Bay of Palma is rich in Tyrrhenian
shorelines, which generally outcrop between +3 m and MTL. Four ofthe six sites which
have been described in the area (Crabtree et al, 1978) were sampled. The sites at Col
d'en Rabassa, Clot d'en Bernadet, Carnatage and Camp de Tir (Figures 2-5) were
similar both in terms of fauna and stratigraphy. An analysis of the site at Col d'en
Rabassa serves to illustrate the salient features of all four.
The shoreline at the Col d'en Rabassa site is underlain by dunes which dip below
modern MTL. The beach itself extends from +40 cm to +80 cm, and is composed of
two distinct layers. The lowest, at +40 cm, is composed of good-sized cobbles in a sand
matrix with numerous large shell fragments. The most common species represented are
Thais haemastoma, Glycymeris violasecens and Cerastoderma glaucum and most ofthe
shells are more than 15mm long. The deposit also contains a great number of columella
fragments of Strombus latus, although no whole shells were found. The mixture of
rocky and sandy substrate species from different depths and the amount of shell
breakage indicate a transported assemblage. Both C. glaucum and G. violasecens are
common in modern death assemblages on sandy shores between +50 cm and +1.5 m,
and this seems the most likely formation height for the fossil assemblage. This would
also be consistent with the presence of large cobbles in the deposit.
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OUATERNARY SHORELINES IN MALLORCA 359
The upper layer of the beach sediments contains numerous small gastropods, such as
Columbella rustica, Conus ventricosus and Vermetus triqueter. These are embedded in a
deposit of fine sand and gravel 25 cm thick. Similar assemblages are found on modern
sandy shores within the gravel lag deposits which often form at -30 cm to -50 cm. The
predominance of rocky shore species is typical of such deposits and indicates the
proximity of a rocky shore. Thus the sequence of deposits in the beach would seem to
indicate progressive submergence, which, in its latter stages, inundated areas of solid
rock.
The other sites in the area have a similar stratigraphy, except that some are directly
overlain by dunes. The fauna is also similar, with the lower beach deposit being
common to all sites. Only the site at Carnatage has a slightly anomalous fauna in being
composed almost entirely of Glycymeris violasecens. In view of the patchy distribution
of live and dead molluscan species on modern coastlines, this anomaly would be
consistent with changing concentrations of particular species along a sandy shoreline.
The general sequence of deposits at the sites around Col d'en Rabassa, therefore,
appears to represent a single transgression, with a dune overlain by a series of
transgressive beach deposits covered by another set of dunes. The regression between
the beach and the dune is shown very clearly at Camp de Tir and Carnatage, with a thin
layer of fine orange sand containing small fragments of both land and marine snails.
Thus the preserved beach sections represent only the upper stages of the transgression,
which is to be expected in view of the steep profile of the Mallorcan coastline.
Southern Arenal.?The second group of sites is located just south of Arenal, about
5 km south east of the previous sample areas. Once again the sites are found close
together and there is a high degree of faunal and stratigraphical similarity between
them. The basic stratigraphy in this area consists of a beach overlain by limons rouges,
containing shell fragments of land and marine molluscs, which are also covered by
extensive dune deposits.
The first of the three sites sampled is located close to Arenal, and consists of a beach
and dune sequence exposed in a small quarry (Figure 6). The beach has been ascribed
to Tyrrhenian II age (Crabtree et al., 1978). A large number of shells are exposed in
distinct bands in a coarse to fine sand matrix, which exhibits strong cross-bedding. The
fauna is dominated by the bivalves Cerastoderma glaucum, Glycymeris violasecens and
Spondylus gaederopus, and thus is composed largely of sublittoral species. This was the
only site at which Strombus latus was recorded in life position. As similar modern S.
latus are usually found living between -1 m and -5 m (Bernard, 1982), it seems likely
that the assemblage formed in the shallow sublittoral zone.
The site at Cala Moscas has a similar series of deposits, but at the northern end of this
quarried section there is a lens of fine sand and shell fragments dominated by small
gastropods such as Cerithium vulgatum (Figure 7). This assemblage is similar to
accumulations of shell material found on modern shores in Djerba at heights of +30 cm
to +75 cm on sheltered sandy shores (Richards, 1982). The deposit is stratigraphically
continuous with the rest of the beach whereas a sublittoral origin is suggested by the
fauna in the main beach. The latter may instead represent a beach on which a large
number of sublittoral species had been deposited.
A section at Cala Blava (Figure 8), 400 m further south, exhibits the same general
sequence of beach sands and shell lenses. The main shell band outcrops at about
+0.75 m, and is composed almost entirely of sandy shore bivalves, especially large
individuals of Cerastoderma glaucum, with a maximum shell length of 60 mm. Large
shells of this species are found on modern sandy shores on the east coast of Mallorca,
with the highest concentrations occurring at -25 cm to -50 cm. The lack of rocky
shore species indicates that this assemblage formed on an extensive sandy shore at some
distance from the nearest rocky outcrop. Above the beach deposits there is a thin layer
of orange sand containing small fragments of marine and land snails, which represents a
transition between the beach and the overlying dunes. No trace could be found of the
Tyrrhenian III beach deposits previously recorded at this site (Crabtree et al, 1978).
The sequence at this group of sites seems to represent a simple transgression, with the
entire sequence of facies changes from beach to dune present. As with the sites at Col
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360 QUATERNARY SHORELINES IN MALLORCA
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QUATERNARY SHORELINES IN MALLORCA 361
d'en Rabassa there is no evidence of deep sublittoral deposits which might indicate a
sea-level stand significantly higher than the present.
Camp de Mar.?Cuerda (1957) reports that the key sections of this site are located on
an offshore islet which could only be reached by boat, but, since his study, the islet has
been joined to the mainland by a bridge.
The beach deposits are best exposed in a small undercut between 0.5 m and 1 m
above MTL, on the northern side of the islet (Figure 9). The beach deposit is composed
of large pebbles and shell fragments in a coarse sand matrix. The fauna is similar to that
at Camp de Tir, with Strombus latus, Spondylus gaederopus and Cerastoderma glaucum
recorded as the most numerous species. The presence of these species in a fragmented
form suggests a death assemblage, and the cobbles in the deposit indicate that it was
formed in a high energy environment. Analogous modern death assemblages are
usually found between +0.5 m and +1.5 m. The overlying deposits of unbedded sand
with small shell fragments tend to support this hypothesis, as they would have formed
between 2 m and 3 m above MTL. As the sands are in turn overlain by dunes, the
sequence is seen to represent a regressive transition. Cuerda (1957) records the
maximum height of the beach as 2 m, but no deposits were found above +0.75 m in the
present study.
Magalluf.?A similar sequence of deposits is exposed in a small sea cave to the
south west of Magalluf (Figure 10). A beach deposit with large cobbles in a sand matrix
outcrops at about +0.5 m. No complete shells were recovered from the site and most of
the bivalve fragments present could not be identified at the species level. A single
internal east of Strombus latus was found, but it seems likely that the deposit formed
from a mobile cobble beach in which shell survival was low. This would place the
formation height of the deposit between -25 cm and +25 cm. The overlying sequence
of deposits is similar to those found at Camp de Mar, with a thin layer of fine sand and
small shell fragments overlain by dunes.
Andratx.?A series of exposures at Puerto Andratx, first reported by Sole Sabaris
(1962), purports to exhibit a sequence of 'aeolianites, angular head and colluvial silts'
(Crabtree et al., 1978). The stratigraphy has been interpreted as two dunes separated by
head deposits and a calcareous crust, the latter being supposedly of Tyrrhenian II age.
There is no report of marine shells at the site.
At the northern end of the site, fragmented shells of Cerastoderma glaucum and
whole shells of Conus ventricosus and small Cerithium vulgatum were found in a
medium sand matrix. The deposit grades upwards into sands which are manifestly
aeolian, and the small size of the shell fragments indicates that they accumulated
between 1 m and 1.5 m above MTL. The shelly deposit is absent from the rest of the
site, and its position is occupied by bedded cobbles in a silt/sand matrix which seems to
represent an alluvial deposit. Hence it is reasonable to conclude that the shell deposit is
a small surviving portion of the beach sequence found on other parts of the island and
that the beach itself has been eroded by fluvial action. There is no evidence to suggest
that the alluvial deposits are of Tyrrhenian II age.
South-east coast.?A number of high-level Tyrrhenian deposits have been reported
from the cliffs around the south-east coast of the island, of which two were studied, at
Cala Pi and S'Estalella. According to Butzer and Cuerda (1962), S'Estalella has two
Tyrrhenian shorelines and Cala Pi exhibits a Tyrrhenian II shoreline along with three
older ones.
At S'Estalella, erosion surfaces reported by Crabtree et al. (1978), close to the
medieval tower, were all identified, but no fossil deposits were found on either the
lower Tyrrhenian I or the upper Tyrrhenian II surfaces (Figure 11). The section was
carefully surveyed and compared with the site description provided by Crabtree etal. to
ensure that the right area was being investigated. The only shell material found
comprised modern shells such as the rocky shore gastropod Thais heamastoma, which
had been thrown up by storms. There was no trace of Strombus fauna on the high-level
platform.
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362 QUATERNARY SHORELINES IN MALLORCA
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QUATERNARY SHORELINES IN MALLORCA 363
A similar pattern emerged at Cala Pi, although some fossil material was found. The
Tyrrhenian I shoreline reported at 15 m (Crabtree et al, 1978) was readily identifiable
by the presence of numerous Patella ferruginea, but the supposed Strombus fauna at
15 m was represented only by unrecognizable shell fragments in an indurated sand
matrix found in very small patches on the platform surface. It seems unwise to use such
ambiguous and undatable material for the purpose of environmental reconstruction or
to chart sea-level changes. On the basis of present evidence, the relationship of these
shoreline traces to the deposits in the other parts of the island cannot be established.
Cala Estany.?With the exception of a single Tyrrhenian beach in the Bay of Alucida
(Cuerda and Galliana, 1976) the eastern coast of the island is devoid of marine deposits,
but a sequence of dune and alluvial deposits at Cala Estany relates closely to the
stratigraphic sequence of sites in the Bay of Palma.
The base of the deposit is composed of cemented cobbles which extend about 3 m
below MTL (Figure 12). The bedding of this deposit indicates an alluvial origin. It is
overlain by a limestone calcarenite, succeeded by 1.5 m of terra rossa, indicating drier,
terrestrial conditions. These sediments grade seawards into dunes which are piled up
against the valley side. The dunes are cut above MTL by a sea cave in which is preserved
a series of sediments which have been removed from the open valley sides.
At the base of the cave there is a thin layer of orange sands with marine and land shell
fragments similar to those that overlie beach deposits at other sites. The sands are
overlain by angular cobbles in a sand matrix which represents the remains of an alluvial
deposit. The sequence is very similar to that at Andratx, and at both sites the
indications are that beach deposits have been removed by subsequent fluvial erosion.
General stratigraphy and sea-level change
The indications from all the sites studied are that the Quaternary marine stratigraphy
of Mallorca is far more simple than has previously been suggested. The differences in
faunal composition between sites are relatively small, as is the range of zonal variation.
If the marine deposits were representative of the large number of sea-level fluctuations
proposed by Butzer (1975), a much more varied set of environments and fauna might be
expected.
The faunal evidence is strongly supported by the general stratigraphic sequence for
the island (Figure 13). At sites without alluvial deposits, the basal deposit is usually a
dune, overlain either directly by a beach or by a transition layer containing land and
marine shells. The beach is in turn overlain by a further transition layer which grades
into the most recent set of dunes. The entire sequence represents a very small change in
relative sea level. The shells found in each of the transition layers indicate an origin at
about 2-3 m above MTL, whilst the beach deposits were formed at between +1.5 m
and -5 m at the most. Therefore there is a very slight negative change in relative sea
level between the two sets of dunes and the beach deposits.
The elevations of beach deposits (Table II) and shoreline traces around the island do
indicate some tectonic deformation. The highest shorelines occur in the south-eastern
TABLE II
Past and present sea-level relationships of fossil deposits in Mallorca {in metres)
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364 QUATERNARY SHORELINES IN MALLORCA
corner of the island, reaching 12 m above MTL at S' Estalella and 15 m at Cala Pi. The
maximum height of beach deposits in the Bay of Palma is 2.5 m, and 2 m on the
south-western coast. Thus it seems that only the south-eastern corner of the island has
undergone any appreciable change in relative sea level.
Conclusion
The evidence for shoreline deformation presented above is compatible with the
model of small-scale block-type tectonic movements suggested for other areas of the
Mediterranean (Flemming, 1978).
It must be emphasized, however, that the evidence for a single deformed shoreline is
at present largely circumstantial. The stratigraphy, fauna and morphology of the
Mallorcan beach accord well with the single 'Tyrrhenian' shoreline identified in Tunisia
and dated radiometrically to between 35 000 and 25 000yrs BP (Richards, 1982).
However, more absolute dating is required to establish the origin of the Mallorcan
beach conclusively. Without dating, it is easy to construct a more complex sequence
from the same evidence by assuming that beach deposits at different sites are of
different age.
Nevertheless, only a single Tyrrhenian transgression can be postulated from the
evidence presented above, and although the Mallorcan shoreline has not been dated
during the present study, the faunal and stratigraphic similarities between it and the
Tyrrhenian beach of Tunisia do not rule out a much younger age for the Mallorcan
beaches than has previously been postulated. If this is the case, the correlation of the
Tyrrhenian raised shorelines with warm 'interglacial' conditions may be erroneous, a
possibility which underlines the importance of using molluscan evidence for identifying
shoreline environments rather than for climatic dating.
A c kno wledgements
I thank Chris Devereux and Jerry Murray for field assistance, John Taylor and the
Mollusca Section of the British Museum (Natural History) for advice and Claudio
Vita-Finzi for comments on the manuscript. The work was funded by a Natural
Environment Research Council CASE Studentship.
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