Palaeoecology of Quaternary Shorelines and Sea-Level Change in Mallorca

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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

QUATERNARY SHORELINES IN MALLORCA

TABLE I

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

358 QUATERNARY SHORELINES IN MALLORCA

Cala Estany

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.

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

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

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.

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)

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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Palaeoecology of Quaternary Shorelines and Sea-Level Change in Mallorca

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