Dendropoma Lower Intertidal Reef Formations and Their Palaeoclimatological Significance, NW Sicily

Marine Geology 161Ž 1999. 155–170 www.elsevier.nlrlocatermargeo

Dendropoma lower intertidal reef formations and their palaeoclimatological significance, NW Sicily

Fabrizio Antonioli a,), Renato Chemello b,1, Salvatore Improta c,2, Silvano Riggio b a ENEA, EnÕironmental Department, Õia Anguillarese 301, I-00060 S. Maria di Galeria, Rome, Italy b Department of Animal Biology, UniÕersity of Palermo, Õia Archirafi 18, I-90123 Palermo, Italy c Physics Department, UniÕersity ‘‘La Sapienza’’, p.le Aldo Moro 5, I-00198 Rome, Italy Received 20 May 1998; accepted 23 March 1999

Abstract

Most carbonate rocky shores of NW Sicily are marked by a coalescence of shells of the gastropod Dendropoma in a construction that is variably developed as a response to wave impact. Here, we review all the available information on these constructions and find that the fossil reefs are reliable sea-level indicators. The thickness of the reef samples never exceeds 30–40 cm below sea-level, whereas all 14C dates fall within a range of few centuries. Some small fragments ejected by violent sea storms date back to 2500 years cal BP. No samples older than 6200 years cal BP have been detected so far. The present distribution of Mediterranean vermetid platforms should result from a northward migration related to the long term effect of the Holocene sea surface temperatureŽ SST. warming. Some consideration on the morphology of the reefs and the comparison with the available data point out that Dendropoma reefs are excellent biological indicators of sea-level fluctuations especially when detected and sampled in tectonically stable areas as those in NW Sicily. q 1999 Elsevier Science B.V. All rights reserved.

Keywords: Dendropoma petraeum; vermetidae; sea-level indicator; palaeoclimatology; Mediterranean

1. Introduction patterns from those due to man’s activity. No reconstruction of Holocene climatic changes based on the The ultimate goal of palaeoclimatic studies is to analysis of palaeoclimatic indicators is possible un- make predictions about future climatic trends from less continuity of the geologic records and precision the knowledge of past geological events. Acquisition of the dating methods is ensured. of precise data on the range of climate variability Fluctuations of sea-level and sea surface tempera- through the Holocene is a necessary prerequisite to turesŽ SST. have been successfully interpreted by distinguish naturally occurring changes in weather analysing the oxygen isotopic compositionŽ Aharon, 1983; Bard et al., 1996. and strontiumrcalcium ratio ŽGuilderson et al., 1994. of tropical corals, the oxy-

) gen isotopic composition of planktonic foraminifers Corresponding author. Fax: q00-39-6-3048-4029; E-mail: Ž [email protected] contained in sediments from deep sea cores Keig- 1 E-mail: [email protected]. win, 1996; Kallel et al., 1997. , and oxygen isotope 2 E-mail: [email protected]. composition of marine overgrowths observed at dif-

0025-3227r99r$ - see front matter q 1999 Elsevier Science B.V. All rights reserved. PII: S0025-3227Ž 99. 00038-9 156 F. Antonioli et al.rMarine Geology 161() 1999 155–170 ferent depths on submerged speleothemsŽ Alessio et al., 1994; Antonioli and Oliverio, 1996. . In temperate mid latitude sea, where coral reefs do not develop, vermetid platforms — wherever they occur — are among the most reliable archives of climatic information about Late Holocene time slice. Further- more, these bioconstructions can be sampled at relatively low cost with respect to deep core drillings, and provide the parallel record of SST changes and sea-level fluctuations. In our work, Holocene fluctuations in sea-level have been tracked back using literature and original data on 14C ages as well as morphological features of vermetid reefs sampled in different regions of the world. All published 14C dates of vermetid platform and ledges have been calibratedŽ 1s. via the program Calib 3.0Ž Stuiver and Reimer, 1993. . The calibration enabled us to compare all radiocarbon ages recorded on vermetid bioconstructions, and to track the time sequence of sea-level fluctuations. Comparison of the ages obtained from Dendropoma reefs in NW Sicily with the data from literature has given an insight into the Holocene dispersion of Fig. 1.Ž a. Distribution of vermetid platforms along the Atlantic these gastropods through the Mediterranean Basin. coasts. Numbers are relative to the citations of:Ž 1. Stephenson Due to the lack of palaeoclimatic indicators com- and StephensonŽ 1954. ;Ž 2. Van Andel and LaborelŽ 1964. ;Ž 3. parable to coral reefs, geologists investigating recent Kemp and LaborelŽ 1968. ;Ž 4. Laborel and DelibriasŽ 1976. ;Ž 5. climatic changes in temperate areas like the Mediter- FockeŽ 1977. ;Ž 6. Jones and HunterŽ 1995. .Ž b. Distribution of ranean sea must rely on substitute reef-like indica- vermetid platforms in the Mediterranean sea. Dashed line indi- cates the 148C winter isotherm. Numbers are relative to the tors. Dendropoma platforms exhibit many character- citations of:Ž 7. De QuadrefagesŽ 1854. ;Ž 8. Molinier and Picard istics pertaining to good indicators: first of all, their Ž1953. ;Ž 9. Peres´ and PicardŽ 1952. ;Ž 10. SafrielŽ 1966; 1975. ; localization in warm-temperate areas such as the Ž11. Fevret et al.Ž 1967. ;Ž 12. SanlavilleŽ 1977. ;Ž 13. Tzur and Atlantic Ocean and the Mediterranean SeaŽ Fig. 1a. , SafrielŽ 1978. ;Ž 14. Pirazzoli et al.Ž 1991. ;Ž 15. Delongeville et al. their easy access for sampling and dating purposes Ž1993. ;Ž 16. Pirazzoli et al.Ž 1982. ;Ž 17. Pirazzoli and Montag- 14 gioniŽ 1989. ;Ž 18. Pirazzoli et al.Ž 1994a. ;Ž 19. Pirazzoli et al. using C techniques, then their limited range of Ž1994b. ;Ž 20. Pirazzoli et al.Ž 1996. ;Ž 21. Chemello et al.Ž 1990a, vertical growth, restricted to the intertidal level and, b.. occasionally, to the uppermost part of the infralittoral zone. VerrillŽ 1906. , PratŽ 1935. and Stephenson and years cal BP. Kemp and LaborelŽ 1968. gave a short StephensonŽ 1954. envisioned the possibility of account of the morphology of vermetid reefs located tracking recent sea-level fluctuations using vermetid along the coasts of Brazil and the island of Fernando ‘reefs’ at the Bermuda Islands while LaborelŽ 1986. de Norona,˜ and subsequently stressed their impor- pointed out the widest use of vermetid reefs as tance as biological markers for sea-level changes. sea-level indicators. Laborel and DelibriasŽ 1976. identified, described Van Andel and LaborelŽ 1964. applied radiocar- and dated fossil remains of vermetid reefs recovered bon dating to remains of fossil vermetid reefs which along the coasts of SenegalŽ West Africa. and Brazil. they identified along the Brazilian coast, and sug- Radiocarbon dating on remains located between 0.5 gested a sea-level rise of 2.2 to 3.4 m above the and 3 m above sea levelŽ a.s.l.. yielded ages from present mean sea-levelŽ MSL. from 1130 to 3764 subactual to 4847 years cal BP. On the basis of this F. Antonioli et al.rMarine Geology 161() 1999 155–170 157

Fig. 2. Investigated areas in Sicily. Starred dots indicate the stations of sampling established on Dendropoma platforms. 158 F. Antonioli et al.rMarine Geology 161() 1999 155–170 information, Laborel and DelibriasŽ 1976. suggested Femmine, near PalermoŽ northern Sicily, central a rise of sea-level taking place during the Late Mediterranean. by the French naturalist De Holocene, but cautioned about the possibility that QuadrefagesŽ 1854. . A century later, Molinier and external disturbances, such as exceptional tides on a PicardŽ 1953. gave a detailed description of the same 6-month scale, might invalidate the inferred vertical locality and suggested a correlation with similar extent of sea-level rise. Furthermore, they warned bioconstructions located along the Algerian coast that the radiocarbon ages may be older than the real ŽPeres´ and Picard, 1952. . age of the reefs as a result of contamination by In the eastern Mediterranean, SafrielŽ 1966; 1975. biogenic carbon derived from limestone particles described intertidal reef-like structures from along trapped within the empty spaces of the vermetid the coasts of Israel and identified vermetid reefs with bioconstruction. a peculiar microatoll morphology, and a diameter up The detection of vermetid platforms along the to 2 m, which he compared with the vermetid atolls coast of CuracaoŽ Focke, 1977. indicated a of the Bermudan archipelago. Fevret et al.Ž 1967. widespread distribution along the temperate and trop- described some vermetid platforms located along the ical Atlantic coasts. Jones and HunterŽ 1995. de- coast of Lebanon at about 1 m a.s.l., whose ages scribed some fossil Dendropoma platforms located were estimated from 1335 to 1735 years cal BP. along the coasts of Grand CaymanŽ British West SanlavilleŽ 1977. reported that radiocarbon dating Indies. . Those reefs, 0.3 to 1 m thick, are located at on vermetid platforms located at an elevation of depths from y0.3 to 0.8 m. Radiocarbon dating q2.2 m along the coast of Lebanon yielded an age yielded ages from 300 to 200 years cal BP. Conse- of 3270–3445 years cal BP. The study of Tzur and quently, Jones and HunterŽ 1995. inferred that the SafrielŽ 1978. on vermetid reefs in Israel concluded bioconstructive action of Dendropoma took place that these bioconstructions develop only on coasts during the Little Ice AgeŽ 1625–1740. and that the composed of rocks which can be easily erodedŽ e.g., depths of vermetid buildup mark the actual differ- loosely cemented calcarenites. and subjected to rapid ence of sea-level between 300 years ago and the uplift. Furthermore, they provided a model of plat- present. The radiocarbon ages of reworked fragments form breaking and reconstruction under the impact of Dendropoma buildups which were found on the of strong waves. Pirazzoli et al.Ž 1991. analysed beach, yielded 678 years BP. Unfortunately, in Jones some Dendropoma ledges and dated several and Hunter’s paper, it is not clear whether these Holocene shorelines from the Hatay coast in Turkey. older dates were calibrated or not. The ledges, sampled between q2.5 and q3 m a.s.l. In the MediterraneanŽ Fig. 1b. , the gastropod showed 14C ages of 2994 to 6177 years cal BP, and reef-builder species is the vermetid Dendropoma those sampled between q0.7 and q0.8 m a.s.l. petraeum ŽMonterosato, 1892. . Vermetid reefs were yielded ages of 1237 and 2084 years cal BP. The first reported from along the coasts of Isola delle relationships between ages and elevation of the ledges

Table 1 List of dated samples in SicilyŽ Italy. . In situ refers to fossils samples collected from living platforms. On the beach refers to samples from fragment of dead platform Program no. Sample Setting Lab code Conventional Calendar d 13 C age14 CŽ BP. age 14 CŽ BP. 1 s ŽPDB. 1 Mancina In situ y0.3 m R-2741 531"32 232–106 q1.40 2 Mancina In situ y0.3 m R-2742 527"36 232–94 q1.33 3 Calazza In situ y0.3 m R-2764 554"35 251–127 q1.31 4 Barcarello In situ y0.4 m R-2580 784"37 461–400 q1.76 5 Calazza On the beach R-2582 2651"51 2350–2293 q2.17 6 Isulidda On the beach R-2765 1352"34 923–876 q1.34 7 Castelluzzo On the beach R-2963 2084"39 1695–1586 q0.72 8 Castelluzzo On the beach R-2964 1563"40 1156–1055 q1.45 F. Antonioli et al.rMarine Geology 161() 1999 155–170 159

longeville et al.Ž 1993. dated two ancient shorelines located at q1.2 and q0.6 m along the Syrian coast. They used Dendropoma ledges as palaeotectonic indicators and obtained ages from 817 to 6089 years cal BP. In the central Mediterranean, Pirazzoli et al.Ž 1982. used remains of vermetid bioconstructions to date the recent tectonic uplift of the coasts of the islands of Crete and AntykithiraŽ Greece. . The vermetid reef fragments were detected between 1.45 and 7 m a.s.l. and yielded ages of 1317 to 4867 years cal BP. Pirazzoli and MontaggioniŽ 1989. used vermetids, as well as other biological indicators, to date eight seismic events which caused shoreline shifts in the island of Rhodes during the Holocene. Radiocarbon dating recovered up to the elevation of q3.45 m a.s.l. which yielded ages centred ;5500 years BP. Pirazzoli et al.Ž 1994a. identified and dated several Fig. 3. Sampling site in the innermost part of the Dendropoma platform. ancient shorelines at about q0.8 and 1.2 m a.s.l. which they noticed along the coasts of the islands in were subsequently used to reassess the rates of rela- the Ionian Sea. The Dendropoma ledges found at the tive sea-level fall for the entire Hatay coast. De- islands of Zante and Cephalonia were used for radio-

Fig. 4. Broad Dendropoma platforms at Cape S. Vito. 160 F. Antonioli et al.rMarine Geology 161() 1999 155–170 carbon dating, and yielded ages between 1283 and ing the coast of NW Sicily, and stated that there is a 4507 years cal BP. Pirazzoli et al.Ž 1994b. dated direct relationship between the structure of Den- vermetids located on a palaeoshoreline between 1.1 dropoma bioconstructions, the coastal morphology and 3.1 m a.s.l. in the Corinthian Gulf which yielded Ži.e., wave energy. and the bedrock lithology. La- ages between 1331 and 6284 years cal BP. Pirazzoli borel and Laborel DeguenŽ 1994; Laborel and La- et al.Ž 1996. identified a Holocene coseismic uplift in borelŽ 1996. stressed that Dendropoma bioconstruc- Greece and the eastern Mediterranean, by correlating tions can be used as a reliable tool to mark changes several studies which had utilised radiocarbon dating of sea-level because of their narrow vertical range on Dendropoma colonies. They calibratedŽ 2s. hun- and because they can be preserved even in case of dreds of radiocarbon data with the program of Stu- rapid coastal uplift. Consequently, they defined Den- iver and ReimerŽ 1993. and obtained important re- dropoma as Bio.S.L.I., which means biological sea- sults on a relatively short-lived period known as the level indicators, i.e., marker of past sea-level changes. Early Byzantine tectonic paroxysm, which took place in a time interval between the fourth and the sixtieth century A.D. In the paper of Pirazzoli et al.Ž 1996. , 2. Study area original dates were also obtained for vermetid buildups located between q0.4 and q0.7 m along The north coast of SicilyŽ southern Italy, central the ancient shorelines of the Corinthian Gulf and Mediterranean. between the north tip of the Gulf of Thessaly. These yielded ages between 1250 and Palermo and Cape San VitoŽ Fig. 2. is tectonically 1685 years cal BP. stable, and has been subjected to an average, long Chemello et al.Ž 1990a; b. described the distribu- term uplift of about 5=10y3 m kay1 since isotope tion and structure of Dendropoma platforms border- stage 5eŽ Antonioli et al., 1994. .

Fig. 5. Mushroom-like Dendropoma formation. F. Antonioli et al.rMarine Geology 161() 1999 155–170 161

When considering the maximum magnitude of the uplift of the Eutyrrhenian 3 inner margins and notches of the San Vito coastline, the uplift rate related to the time interval following 125 kaŽ stage 5e. , is 0.072 mm yry1, measured using a Total Station. Conse- quently, assuming that the crustal movements have been constant from the stage 5e to the present, the palaeoeustatic elevation which can be reconstructed from the Holocene Dendropoma reef should be di- minished of about 0.01 mŽ see Table 2 with the age of the Dendropoma reef. . These corrections are negligible, because they are small compared to errors stemming from dating and sampling inaccuracy. Its tectonic stability makes the northern coast of Sicily an optimum site to identify actual Holocene sea-level fluctuations. The survey of the coast revealed the presence of several Dendropoma reefs and platforms which developed onto Mesozoic limestones and well cemented calcarenites of Early Pleistocene ageŽ Abate et al., 1991, 1993; Antonioli et al., 1994. .

3. Material and methods

3.1. Morphology of Dendropoma reefs in Sicily

The survey of the Sicilian coast was addressed to the recognition of platform structures, of the relationship between platform and substrate, and as well as of the extent of geographic exposure of the platforms. Dating analysis by radiocarbonŽ Table 1. was performed on samples selected from freshly broken surfaces. The samples to be dated were collected on flat areas where the Dendropoma reefs are mostly developed in broadness and thicknessŽ Fig. 3. . On limestone promontories, Dendropoma ledges are smaller, up to 1 m long and 10 cm thick. In flat Fig. 6. Outline of the mechanisms of the mushroom-like Den- coastal areas, Dendropoma platforms, from 5 to 10 dropoma concretioning. Light grey rightward arrows indicate the m broad, coalesce to form a single, uninterrupted rim effects of erosion on coastal morphology. Black arrow upward stretching for several kilometres. Each platform is 20 points out the sea-level rise. SymbolŽU . marks the starting to 40 cm thick, and the upper 8 to 10 cm consist of position in mushroom formation. living organisms. The upper, living part lies at MSL

and, consequently, is exposed during low tide and submerged during high tide. A vertical section was 3 The recognition of a worldwide constant datum for the isotopic substage 5e highstand of the sea-levelŽ Eutyrrhenian, 125 ka. excavated in the reef to make morphological obser- at q7 m a.s.l. "1 mŽ Ku et al., 1974. provides an essential, and vations and sampling for radiocarbon dating feasible. precise, marker to characterize Late Quaternary deformations. Radiocarbon dating was carried out on the most 162 F. Antonioli et al.rMarine Geology 161() 1999 155–170

Table 2 Available data on vermetid reefs and ledges from Atlantic and Mediterranean coasts. All data were calibrated by using the program of Stuiver and ReimerŽ 1993. . Data are arranged by authors, sampling locations, elevation a.s.l., conventional ages, calibrated ages and sample laboratory code Program Reference Locality Metres Conventional Calibrated Laboratory no. on m.s.l.14 C 14 C 1 s no. Žyr BP.Ž yr BP. 1 Van Andel and Laborel, 1964 Brazil 3 2790"150 2721–2317 A-16 Recife 2.2 1190"130 1459–1130 A-17 3.4 3660"170 3764–3356 A-22 2 Laborel and Delibrias, 1976 West Africa 1 530"90 267–0 Gif-2196 Ghana, Ivory 1 650"90 387–228 2404 Coast, Cabo 1 700"90 436–262 2197 Verde Islands 1.5 740"90 466–280 2406 2.5 1420"100 1055–880 2405 2.5 1630"90 1268–1071 1675 3 2040"90 1700–1510 2195 2.5 2050"90 1708–1505 1676 3 Brazil 0.5 380"90 subactual Gif-1061 Sao Paulo, 0.5 380"90 subactual Gif-1063 Pernambuco 1.6 1190"130 881–630 Gif-2406 1.5 1670"100 1296–1115 Gif-1060 1.4 1750"170 1459–1130 Gif-2405 2 2400"95 2128–1894 Gif-1935 2 2450"95 2190–1954 Gif-1933 2.2 2790"150 2721–2317 A-16 3 3420"150 3391–3145 Gif-1059 2.6 3660"170 3764–3356 A-22 3 3900"110 3989–3697 Gif-1934 3 4480"180 4847–4406 Gif-2147 4 Fevret et al., 1967 Lebanon 0.8 1880"50 1479–1343 Mc-146 Tripoli, Tabarja 0.8 1960"140 1677–1335 Mc-64 0.8 2035"130 1735–1425 Mc-63 5 Sanlaville, 1977 2.2 3490"80 3445–3270 Mc-145 6 Pirazzoli et al., 1982 Greece 2 1870"70 1489–1317 Mc-2437b Creta, 2.2 1890"90 1522–1317 Mc-2438 Antikityra 2.7 1890"90 1522–1317 Mc-2435 2.7 1930"70 1538–1381 Mc-2430 7.8 1955"70 1538–1381 Mc-2110II 7.9 1950"80 1557–1398 Mc-2238 7.8 1965"70 1576–1412 Mc-2110 6.5 1975"70 1591–1424 Mc-2114 7 1980"70 1600–1435 Mc-21209 7.8 1995"70 1615–1465 Mc-2110I 7.7 2110"80 1793–1555 Mc-2195 2 2200"70 1863–1698 Mc-2437 5.2 2210"70 1871–1706 Mc-2116 3.1 2250"70 1917–1757 Mc-2115 7 2250"70 1917–1757 Mc-2101 2.5 2270"70 1938–1789 Mc-2436 2 2280"70 1949–1801 Mc-2439 6.4 2275"100 1979–1748 Mc-2193 2.15 2323"70 1996–1841 Mc-2431 7.2 2400"70 2107–1926 Mc-2272 1.5 2430"70 2132–1959 Mc-2100 4.4 2430"70 2132–1959 Mc-2107 F. Antonioli et al.rMarine Geology 161() 1999 155–170 163

Table 2Ž continued. Program Reference Locality Metres Conventional Calibrated Laboratory no. on m.s.l.14 C 14 C 1 s no. Žyr BP.Ž yr BP. 3.1 2450"70 2150–1983 Mc-2104 4.3 2380"70 2200–2018 Mc-2106 3.8 2480"70 2200–2018 Mc-2108 1.7 2580"80 2296–2088 Mc-2440 7.3 2625"70 2346–1926 Mc-2111 7.3 2650"70 2363–2280 Mc-2273 7.1 2680"70 2434–2300 Mc-2274 2 2740"80 2581–2327 Mc-2434 2.5 2800"70 2684–2378 Mc-1378 2.5 2800"70 2684–2378 Mc-1379 7.1 2900"70 2737–2610 Mc-2500 5.9 3200"70 3083–2877 Mc-2279 5.6 3230"70 3132–2928 Mc-2420 6.5 3300"80 3238–3003 Mc-2276 1.45 3370"70 3304–3157 Mc-2432 7 3400"70 3342–3172 Mc-2112 6.8 3450"70 3381–3234 Mc-2275 5.9 3800"100 3581–3602 Mc-2194 6.7 3690"70 3672–3480 Mc-2113 6.5 3730"80 3721–3543 Mc-2421 5.6 3820"90 3863–3630 Mc-2429 4.8 4330"80 4533–4354 Mc-2428 4 4600"90 4867–4700 Mc-2427 7 Pirazzoli et al., 1991 Turkey 0.75 1745"70 1333–1234 Pa-771 Hatay coast 0.4 2110"100 1804–1544 Pa-781 0.8 2450"60 2140–1993 Pa-823 0.8 2440"80 2150–1959 Pa-782 0.7 2690"95 2490–2290 Pa-769 1.2 2715"80 2494–2314 Pa-822 0.8 2810"60 2684–2432 Pa-776 3 2995"100 2990–2687 Pa-775 0.8 3230"60 3114–2938 Pa-774 2 3310"95 3266–2994 Pa-780 2.5 5200"80 5627–5468 Pa-779 2 5570"190 6177–5729 Pa-773 8 Delongeville et al., 1993 Syria 0.65 1335"50 922–817 Ly-5622 Guverdjne 0.65 1450"60 1047–924 Gif AMS Kaya, Arab 0 1675"55 1274–1168 Ly-5625 al Malek 0.6 1820"60 1401–1288 Ly-5621 0.6 1890"55 1495–1349 Ly-5623 0.4 2010"50 1610–1505 Gif AMS 0.5 2590"45 2314–2186 Ly-5621 0.9 5275"65 5694–5575 Ly-5631 1.2 5595"85 6086–5892 Ly-5624 9 Pirazzoli et al., 1994a Greece 1.2 1820"70 1410–1283 GifA-91114 Zante, 0.8 1960"60 1557–1417 GifA-92142 Cephalonia 1.05 2290"70 1960–1810 GifA-92283 1.05 2360"70 2051–1877 GifA-91112 0.8 2560"60 2306–2131 GifA-92141 1.3 4290"90 4507–4272 GifA-92073 164 F. Antonioli et al.rMarine Geology 161() 1999 155–170

Table 2Ž continued. Program Reference Locality Metres Conventional Calibrated Laboratory no. on m.s.l.14 C 14 C 1 s no. Žyr BP.Ž yr BP. 10 Pirazzoli et al., 1994b Greece 1.1 1865"55 1460–1331 GifA-92PE1 Corinth 2.2 4120"60 4245–4075 GifA-92PE5 3 4705"50 4976–4842 GifA-92PE8 3.1 5820"60 6284–6176 GifA-92PE3 11 Jones and Hunter, 1995 Grand y0.8 208"80 subactual – Cayman y1.4 318"90 subactual – 0 278"90 subactual – on the beach 678"90 420–250 – 12 Pirazzoli et al., 1996 Greece 0.7 1780"42 1310–1290 GifA-90SS3 Corinth, 0.4 1790"80 1390–1250 GifA-92TH2 Thessaly 0.6 2050"60 1685–1550 GifA-92TH3 13 Present research Italy y0.3 531"32 232–106 R-2741 Sicily y0.3 527"36 232–94 R-2742 y0.3 554"35 251–127 R-2764 y0.4 784"37 461–400 R-2580 on the beach 1352"34 923–876 R-2582 on the beach 1563"40 1156–1055 R-2964 on the beach 2084"39 1695–586 R-2963 on the beach 2651"51 2350–2293 R-2765

ancient, fossil part of the reefs, which is located at development of vermetid bioconstructions is partially 30–40 cm below the present sea-level. Because the hindered by the unfavourable morphology of coasts whole studied area is tectonically stable, the 30–40 exposed to high-energy breakers. cm which separate the living individuals from the Ž2. Platform or ‘‘true reef’’. This structure is fossil Dendropoma are here deemed as indicative of similar to a coral fringing reef, and corresponds to the actual sea-level rise for the last 400–460 calen- the classical vermetid reefs described by Peres´ and dar years. PicardŽ 1952. and Molinier and PicardŽ 1953. . Plat- forms are G10 m wide and F45 cm thick at the 3.2. Morphological types and the classification of the outer margin. The basement of the structure is com- Dendropoma reefs monly eroded, and takes the shape of a continuous vertical wall 0.40 to 1 m high. Vermetid reefs com- The Dendropoma bioconstructions in the monly colonise abrasion platforms generated through Mediterranean and, namely, those lying along the the action of high tide surf. Alternatively, these Sicilian coasts developed the following morpholo- structures acquired their morphology through contin- gies. uous, layered bioconstruction on several single col- Ž1. Ledge. This structure develops on unprotected lapse blocks. Dendropoma vermetid platforms con- headlands, promontories and cliffs exposed to surf. stitute about 90% of all the vermetid structures of the The biogenic buildings are typically -1 m wide and Sicilian coastŽ Fig. 4. . 10 to 20 cm thick at the outer margin. The mecha- Ž3. ‘‘Mushroom-like’’ pillars. These morpholo- nisms of formation of a Dendropoma ledge were gies seem to be the outcome of two different pro- described by LaborelŽ 1987. for the structures ob- cesses of formation. The primary cause for the devel- served along the coasts of Corsica. Ledges and en- opment of mushroom morphology is the different crustations are a common feature in coastal areas degree of resistance to erosion of the bedrock and subjected to vermetid colonisation. Ledges are also overlying vermetid bioconstruction. The bedrock is found in areas already colonised, but where the eroded at a higher rate than the vermetid structures, F. Antonioli et al.rMarine Geology 161() 1999 155–170 165

Fig. 7. Close view of Dendropoma fragment ejected on an inland beach by sea storms. which compensates for the loss due to erosion through the radiocarbon ages, we calibratedŽ 1s. all the data the continuous growth of the outer ledge. At the end by using the program Calib 3.0 of Stuiver and Reimer of the process, the morphology of the buildup is that Ž1993. . of a large round overgrowth tapering toward its base With respect to calibration, it must be stressed ŽFigs. 5 and 6. . In the second case, vermetid ledges that the regional effect was not taken into account grow on the abrasion blocks scattered at the base of ŽDRs0. . For this reason, comparison between abso- the cliff. The subsequent evolution yields mushroom lute calibrated ages of samples from different regions structures similar to those developed through the first is biased by the possible influence of the local mechanism. effects whereby a sample can be a few years more Ž4. Microatolls and reefs. A detailed description recent or older with respect to a calibrated age with of these structures is reported in the paper of Safriel DRs0. Consequently, each comparison should take Ž1966. on the vermetid microatolls and offshore into account for this bias. reefs in Israel. During the Late Holocene, which is the time span encompassed by the oldest age shown so far by Dendropoma bioconstructions, 4 vermetid reefs de- 4. Ages of Dendropoma vermetid reefs 14 4.1. Calibration of C dates 4 The radiometric ages of some datationsŽ Pirazzoli, 1996. Many radiocarbon age dates available from At- range from 12,300 to 18,860 years BP. Dating has been obtained lantic an Mediterranean areas for vermetid reefs from vermetids dredged from a submerged cliff 117 to 160 m deep off western Sardinia. We argue that the samples do not Žmostly Dendropoma. which have been published include the genus Dendropoma, but other vermetidae, living at since 1964 are listed in Table 2. In order to compare higher depths. 166 F. Antonioli et al.rMarine Geology 161() 1999 155–170

Fig. 8. Cross-section of a living Dendropoma platform.

veloped and were preserved in both tropical and from carbonates and activity measurements were car- temperate areas. ried out by means of CO2 proportional counters. The inner, fossil part of in situ Dendropoma 4.2. Radiocarbon dating of the Sicilian Dendropoma vermetid reefs yielded relatively young ages, typi- reefs cally ranging between 461 and 94 years cal BP. Reef fragments collected from the beaches and reworked The samples used for radiocarbon datingŽ samples by wave action proved to be much older, and typi- 1–2–3–4. were collected from coastal, D. petraeum cally their ages ranged from 2350 to 876 years cal reefs. Some samples were collected from blocks, BP. 0.20 to 0.50 m in diameter, which were ejected on The assessed age ranges are similar to those the shore by exceptional events, such as storm waves yielded by the 14C dating of fossil Dendropoma or tsunamiŽ samples 5–6–7–8. . These reef frag- reefs from Grand CaymanŽ Jones and Hunter, 1995. mentsŽ Fig. 7. have been observed over a wide area and to the 14C ages of fossil vermetid reefs located along the northern coast of Sicily and form a storm several tens of metres a.s.l. in rapidly uplifting zones layer bar 10 to 20 m off the present day shoreline. Žsee Table 2. . Samples 7 and 8 have been collected ;500 m off the shoreline, and very likely this relatively large displacement is the outcome of human activities. 5. Discussion Dating was performed on samples about 2 cm thickŽ weight ;30 g. , cut along planes parallel to From the observations on the morphology coupled the surfaceŽ Fig. 8. . Carbon dioxide was extracted with the analysis of new and previous calibrated data F. Antonioli et al.rMarine Geology 161() 1999 155–170 167 on vermetid reefs from the Atlantic and the Mediter- cm data, see Table 2. is of outstanding interest. In ranean, we can infer that vermetid reefs can attain fact, the curves describing the Holocene rise in their maximum growth only when they develop on sea-level are based on a small number of reliable coasts characterised by uplift rates of at least 0.1 cm data from the Late HoloceneŽ e.g., Bard et al., 1996 yry1. Conversely, vermetid reefs which developed present for the last 6 ka BP, two dates; Alessio et al., on stable coasts were demolished by storm waves, 1994 show four dates. . The only other case known of and their complete destruction occurred in 2r3000- fossil Dendropoma reefs of the same age, occurring year cycles. below present MSL, is that of Grand Cayman. On Along the coasts of Sicily, small, fossil Den- the basis of age vs. depth data, Jones and Hunter dropoma ledges, up to a few centimetres thick, were Ž1995. suggested a lowering of MSL during the found at depths of y2.5 to y3 m with respect to the Little Ice Age, which caused the death of most MSL. These fossil ledges probably marked the MSL vermetid colonies in South America. Some of the of the Mediterranean sea between 4000 and 5000 fossil reefs which should have been killed by the years cal agoŽ Alessio et al., 1994. . Along the east- catastrophic LIA event are located at y0.8 m below ern Mediterranean coasts, fossil vermetid reefs, dated sea-levelŽ b.s.l.. . However, the data from the present 6000 years cal BP, were preserved in areas subjected study indicate that between 1600 and 1700 A.D., the to rapid uplift. The observed occurrence of mechani- sea-level was higher than that proposed by Jones and cally eroded vermetid reef fragments which were HunterŽ 1995. . Some dataŽ Schmiedt, 1972; Leoni brought onto the beach support the ‘‘involuntary and Dai Pra, 1996. indeed indicate that the sea-level suicide’’ theory proposed by SafrielŽ 1966; 1974. . reached between y0.6 and y0.5 m at about 2000 This theory predicts that catastrophic events with years BP, and that the Sicilian Dendropoma reefs of decadal cyclesŽ e.g., storms. caused the mechanical LIA age are located only 0.30 to 0.40 m below destruction of vermetid reefs. In the interval between present MSL. two catastrophic events, the outer margin of the On the basis of the calibrated 14C ages reported in platform grows too much with respect to the carrying Table 2, the Dendropoma reef colonisation pattern capacity of the reef itself. Consequently, even in the Mediterranean can be reconstructed. The old- medium energy waves can easily break off this est radiocarbon ages referring to about 6000 years cantilever and transport the fragments onto the shore, cal BP, or slightly older, pertain to Dendropoma where their accumulate pile up to form storm layers. colonies which were sampled along the coasts of Most of the fossil fragments of the Dendropoma Turkey Žq2 m. , in Syria Žq1.2 m. , in the Gulf of platforms which were dated by other authors are Corinth Žq3.1. , in the southern Mediterranean. Fos- located from a few decimetres up to 7.9 m a.s.l., sil vermetid reefs which developed, typically yield because these reefs were sampled along coasts sub- ages between 6177 and 5729 years cal BP. The jected to uplift. Conversely, in-situ Dendropoma oldest specimens collected on the coasts of southern reefs which were sampled along the Sicilian coast Italy, about 2350 years cal BP old, are Dendropoma are in tectonically stable areasŽ Antonioli et al., reef fragments which were ejected onto the shore. 1994. . Consequently, these reefs are reliable indica- Prior to 6500 years BP, the rate of sea-level rise was tors of Holocene sea-level fluctuations. Although the very high, up to 2 m per century. The rapid rise of potential of vermetid reefs as indicators of sea-level the water level prevented the construction of ver- change has been acknowledged in the past, only a metid reef, because the habitat of these gastropods is few of these structures have been dated and used for restricted to the intertidal zone, and this zone was that purpose. short-lived in a period of fast sea-level rise. Alterna- Along the coasts of Sicily, in-situ vermetid reefs tively, if some vermetid reefs developed prior to are found to a depth of y40 cm below MSL and 6500 years ago, their remains would now be located their oldest, fossil part yielded calibrated ages of 400 several tens of metres b.s.l. to 461 years. These data indicate that between 400 The aforementioned considerations, and the avail- and 461 years ago, the sea-level was 40"8 cm able data, shed some light on both provenance and lower than today. This datumŽ together with the 30 distribution of the vermetid reefs in the Mediter- 168 F. Antonioli et al.rMarine Geology 161() 1999 155–170 ranean. Coastal stratigraphic records and fossil asso- ciations relative to marine transgressions which took place in the Middle and Late PleistoceneŽ isotope ‘‘warm’’ stages 11, 9, 7 and 5. , and in the Mediter- ranean region, indicate that fossil Dendropoma reefs were absent at that time. Probably, D. petraeum started only in the Holocene to build colonies with a typical reef-like structure. Alternatively, the fragility of vermetid bioconstructions may have prevented the preservation of colonies older than the Holocene. Vermetid reefs do indeed collapse under the impact Fig. 9. Diagrammatic curve of sea-level rise during 2 ka BP. Each sample is represented with an error box corresponding to the of storm waves and hurricanes. Due to the lack of 14 vertical estimation error Ž"8 cm. and C dating error. data from stable areas, we cannot rely on this nega- tive evidence to infer whether Dendropoma reefs did or did not exist before the Holocene. More observations and dates on Dendropoma reefs would be MediterraneanŽ about 12 cm of relative sea-level rise necessary to solve the problem. in the last century; Pirazzoli, 1993. those coming The oldest platforms are located in the SE part of from the dating of Dendropoma reefs and the ar- the Mediterranean region, whereas the most recent chaeological dataŽ Schmiedt, 1972; Leoni and Dai ones occur in the central Mediterranean. Den- Pra, 1996. , it is possible to plot a curve of the dropoma bioconstructions are extremely rare in the Mediterranean sea-level rise during the last 2 ka BP North, and the only ones in this area are some small ŽFig. 9. similar to those published by Laborel et al. ledges reported from the coasts of Corsica which are Ž1994. . now extinctŽ Laborel, 1987. . The Dendropoma As a conclusion, Dendropoma reefs appear to be colonisation pattern, from southeast to northwest, one of the best suited palaeoclimatic indicators for a may be the result of the SST trends, and especially slice key-time, i.e., the last 500 years, when man’s of the SST rise which characterized the Mediter- activities may have considerably altered the natural ranean during the Late Glacial and HoloceneŽ last 12 biogeochemical cycles and thus enhanced the green- ka cal BP. . If this were the case, Dendropoma house effectŽ IPCC Climate Change, 1994. . gastropods would be thermophilic. In addition, there is evidence that Dendropoma identify a valuable biological indicator of SST trends. Preliminary d18 O Acknowledgements data inferred from specimens collected in Sicily ac- tually indicate that Dendropoma are reliable records The authors would like to thank Dr. Silvia Frisia of SST fluctuationsŽ Antonioli et al., 1998. . for a general critical revision and Dr. Paolo Pirazzoli for his helpful comments which greatly improve the manuscript. Special thanks are due to Ignazio Ciuna 6. Conclusions and Sergio Silenzi for their invaluable field assis- tance. The overview of studies on Dendropoma reefs put into evidence that these gastropods have been widely used in tectonically unstable areas as indica- References tors of uplift rates. Alternatively, the occurrence of vermetid reefs has been simply reported and dated. Abate, B., Di Maggio, C., Incandela, A., Renda, P., 1991. Nuovi The results presented in this study should suggest dati sulla penisola di Capo San VitoŽ Sicilia nord-occidentale. . Mem. Soc. Geol. Ital. 47, 15–25. that the use of Dendropoma reefs in stable areas to Abate, B., Di Maggio, C., Incandela, A., Renda, P., 1993. Carta evaluate sea-level fluctuations is reliable for the past Geologica dei monti di Capo San Vito. Dipartimento di Geolo- 500–1000 ka. Using the tide-gauges data for the gia e Geodesia dell’Universita` di Palermo. F. Antonioli et al.rMarine Geology 161() 1999 155–170 169

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