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

Marine Geology 161 Ž1999. 155–170 www.elsevier.nlrlocatermargeo

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

a,)

, Renato Chemello

b,1

, Salvatore Improta

c,2

, Silvano Riggio

b

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 temperature ŽSST. 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 The ultimate goal of palaeoclimatic studies is to make predictions about future climatic trends from the knowledge of past geological events. Acquisition of precise data on the range of climate variability through the Holocene is a necessary prerequisite to distinguish naturally occurring changes in weather

)

Corresponding author. Fax: q00-39-6-3048-4029; E-mail: [email protected] 1 E-mail: [email protected]. 2 E-mail: [email protected].

patterns from those due to man’s activity. No reconstruction of Holocene climatic changes based on the analysis of palaeoclimatic indicators is possible unless continuity of the geologic records and precision of the dating methods is ensured. Fluctuations of sea-level and sea surface temperatures ŽSST. have been successfully interpreted by analysing the oxygen isotopic composition ŽAharon, 1983; Bard et al., 1996. and strontiumrcalcium ratio ŽGuilderson et al., 1994. of tropical corals, the oxygen isotopic composition of planktonic foraminifers contained in sediments from deep sea cores ŽKeigwin, 1996; Kallel et al., 1997., and oxygen isotope composition of marine overgrowths observed at dif-

0025-3227r99r$ - see front matter q 1999 Elsevier Science B.V. All rights reserved. PII: S 0 0 2 5 - 3 2 2 7 Ž 9 9 . 0 0 0 3 8 - 9

156

F. Antonioli et al.r Marine Geology 161 (1999) 155–170

ferent depths on submerged speleothems ŽAlessio 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. Furthermore, 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 14 C ages as well as morphological features of vermetid reefs sampled in different regions of the world. All published 14 C dates of vermetid platform and ledges have been calibrated Ž1s . via the program Calib 3.0 ŽStuiver 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 these gastropods through the Mediterranean Basin. Due to the lack of palaeoclimatic indicators comparable to coral reefs, geologists investigating recent climatic changes in temperate areas like the Mediterranean sea must rely on substitute reef-like indicators. Dendropoma platforms exhibit many characteristics pertaining to good indicators: first of all, their localization in warm-temperate areas such as the Atlantic Ocean and the Mediterranean Sea ŽFig. 1a., their easy access for sampling and dating purposes using 14 C techniques, then their limited range of vertical growth, restricted to the intertidal level and, occasionally, to the uppermost part of the infralittoral zone. Verrill Ž1906., Prat Ž1935. and Stephenson and Stephenson Ž1954. envisioned the possibility of tracking recent sea-level fluctuations using vermetid ‘reefs’ at the Bermuda Islands while Laborel Ž1986. pointed out the widest use of vermetid reefs as sea-level indicators. Van Andel and Laborel Ž1964. applied radiocarbon dating to remains of fossil vermetid reefs which they identified along the Brazilian coast, and suggested a sea-level rise of 2.2 to 3.4 m above the present mean sea-level ŽMSL. from 1130 to 3764

Fig. 1. Ža. Distribution of vermetid platforms along the Atlantic coasts. Numbers are relative to the citations of: Ž1. Stephenson and Stephenson Ž1954.; Ž2. Van Andel and Laborel Ž1964.; Ž3. Kemp and Laborel Ž1968.; Ž4. Laborel and Delibrias Ž1976.; Ž5. Focke Ž1977.; Ž6. Jones and Hunter Ž1995.. Žb. Distribution of vermetid platforms in the Mediterranean sea. Dashed line indicates the 148C winter isotherm. Numbers are relative to the citations of: Ž7. De Quadrefages Ž1854.; Ž8. Molinier and Picard Ž1953.; Ž9. Peres ´ and Picard Ž1952.; Ž10. Safriel Ž1966; 1975.; Ž11. Fevret et al. Ž1967.; Ž12. Sanlaville Ž1977.; Ž13. Tzur and Safriel Ž1978.; Ž14. Pirazzoli et al. Ž1991.; Ž15. Delongeville et al. Ž1993.; Ž16. Pirazzoli et al. Ž1982.; Ž17. Pirazzoli and Montaggioni Ž1989.; Ž18. Pirazzoli et al. Ž1994a.; Ž19. Pirazzoli et al. Ž1994b.; Ž20. Pirazzoli et al. Ž1996.; Ž21. Chemello et al. Ž1990a, b..

years cal BP. Kemp and Laborel Ž1968. gave a short account of the morphology of vermetid reefs located along the coasts of Brazil and the island of Fernando de Norona, ˜ and subsequently stressed their importance as biological markers for sea-level changes. Laborel and Delibrias Ž1976. identified, described and dated fossil remains of vermetid reefs recovered along the coasts of Senegal ŽWest Africa. and Brazil. Radiocarbon dating on remains located between 0.5 and 3 m above sea level Ža.s.l.. yielded ages from subactual to 4847 years cal BP. On the basis of this

F. Antonioli et al.r Marine Geology 161 (1999) 155–170

Fig. 2. Investigated areas in Sicily. Starred dots indicate the stations of sampling established on Dendropoma platforms.

157

F. Antonioli et al.r Marine Geology 161 (1999) 155–170

158

information, Laborel and Delibrias Ž1976. suggested a rise of sea-level taking place during the Late Holocene, but cautioned about the possibility that external disturbances, such as exceptional tides on a 6-month scale, might invalidate the inferred vertical extent of sea-level rise. Furthermore, they warned that the radiocarbon ages may be older than the real age of the reefs as a result of contamination by biogenic carbon derived from limestone particles trapped within the empty spaces of the vermetid bioconstruction. The detection of vermetid platforms along the coast of Curacao ŽFocke, 1977. indicated a widespread distribution along the temperate and tropical Atlantic coasts. Jones and Hunter Ž1995. described some fossil Dendropoma platforms located along the coasts of Grand Cayman ŽBritish West Indies.. Those reefs, 0.3 to 1 m thick, are located at depths from y0.3 to 0.8 m. Radiocarbon dating yielded ages from 300 to 200 years cal BP. Consequently, Jones and Hunter Ž1995. inferred that the bioconstructive action of Dendropoma took place during the Little Ice Age Ž1625–1740. and that the depths of vermetid buildup mark the actual difference of sea-level between 300 years ago and the present. The radiocarbon ages of reworked fragments of Dendropoma buildups which were found on the beach, yielded 678 years BP. Unfortunately, in Jones and Hunter’s paper, it is not clear whether these older dates were calibrated or not. In the Mediterranean ŽFig. 1b., the gastropod reef-builder species is the vermetid Dendropoma petraeum ŽMonterosato, 1892.. Vermetid reefs were first reported from along the coasts of Isola delle

Femmine, near Palermo Žnorthern Sicily, central Mediterranean. by the French naturalist De Quadrefages Ž1854.. A century later, Molinier and Picard Ž1953. gave a detailed description of the same locality and suggested a correlation with similar bioconstructions located along the Algerian coast ŽPeres ´ and Picard, 1952.. In the eastern Mediterranean, Safriel Ž1966; 1975. described intertidal reef-like structures from along the coasts of Israel and identified vermetid reefs with a peculiar microatoll morphology, and a diameter up to 2 m, which he compared with the vermetid atolls of the Bermudan archipelago. Fevret et al. Ž1967. described some vermetid platforms located along the coast of Lebanon at about 1 m a.s.l., whose ages were estimated from 1335 to 1735 years cal BP. Sanlaville Ž1977. reported that radiocarbon dating on vermetid platforms located at an elevation of q2.2 m along the coast of Lebanon yielded an age of 3270–3445 years cal BP. The study of Tzur and Safriel Ž1978. on vermetid reefs in Israel concluded that these bioconstructions develop only on coasts composed of rocks which can be easily eroded Že.g., loosely cemented calcarenites. and subjected to rapid uplift. Furthermore, they provided a model of platform breaking and reconstruction under the impact of strong waves. Pirazzoli et al. Ž1991. analysed some Dendropoma ledges and dated several Holocene shorelines from the Hatay coast in Turkey. The ledges, sampled between q2.5 and q3 m a.s.l. showed 14 C ages of 2994 to 6177 years cal BP, and those sampled between q0.7 and q0.8 m a.s.l. yielded ages of 1237 and 2084 years cal BP. The relationships between ages and elevation of the ledges

Table 1 List of dated samples in Sicily ŽItaly.. 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 age 14 C ŽBP.

Calendar age 14 C ŽBP. 1 s

d 13 C ŽPDB.

1 2 3 4 5 6 7 8

Mancina Mancina Calazza Barcarello Calazza Isulidda Castelluzzo Castelluzzo

In situ y0.3 m In situ y0.3 m In situ y0.3 m In situ y0.4 m On the beach On the beach On the beach On the beach

R-2741 R-2742 R-2764 R-2580 R-2582 R-2765 R-2963 R-2964

531 " 32 527 " 36 554 " 35 784 " 37 2651 " 51 1352 " 34 2084 " 39 1563 " 40

232–106 232–94 251–127 461–400 2350–2293 923–876 1695–1586 1156–1055

q1.40 q1.33 q1.31 q1.76 q2.17 q1.34 q0.72 q1.45

F. Antonioli et al.r Marine Geology 161 (1999) 155–170

Fig. 3. Sampling site in the innermost part of the Dendropoma platform.

were subsequently used to reassess the rates of relative sea-level fall for the entire Hatay coast. De-

159

longeville et al. Ž1993. 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. Ž1982. used remains of vermetid bioconstructions to date the recent tectonic uplift of the coasts of the islands of Crete and Antykithira ŽGreece.. 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 Montaggioni Ž1989. 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. Ž1994a. identified and dated several ancient shorelines at about q0.8 and 1.2 m a.s.l. which they noticed along the coasts of the islands in the Ionian Sea. The Dendropoma ledges found at the islands of Zante and Cephalonia were used for radio-

Fig. 4. Broad Dendropoma platforms at Cape S. Vito.

160

F. Antonioli et al.r Marine Geology 161 (1999) 155–170

carbon dating, and yielded ages between 1283 and 4507 years cal BP. Pirazzoli et al. Ž1994b. dated vermetids located on a palaeoshoreline between 1.1 and 3.1 m a.s.l. in the Corinthian Gulf which yielded ages between 1331 and 6284 years cal BP. Pirazzoli et al. Ž1996. identified a Holocene coseismic uplift in Greece and the eastern Mediterranean, by correlating several studies which had utilised radiocarbon dating on Dendropoma colonies. They calibrated Ž2 s . hundreds of radiocarbon data with the program of Stuiver and Reimer Ž1993. and obtained important results on a relatively short-lived period known as the 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. Ž1996., original dates were also obtained for vermetid buildups located between q0.4 and q0.7 m along the ancient shorelines of the Corinthian Gulf and Thessaly. These yielded ages between 1250 and 1685 years cal BP. Chemello et al. Ž1990a; b. described the distribution and structure of Dendropoma platforms border-

ing the coast of NW Sicily, and stated that there is a direct relationship between the structure of Dendropoma bioconstructions, the coastal morphology Ži.e., wave energy. and the bedrock lithology. Laborel and Laborel Deguen Ž1994; Laborel and Laborel Ž1996. stressed that Dendropoma bioconstructions can be used as a reliable tool to mark changes of sea-level because of their narrow vertical range and because they can be preserved even in case of rapid coastal uplift. Consequently, they defined Dendropoma as Bio.S.L.I., which means biological sealevel indicators, i.e., marker of past sea-level changes.

2. Study area The north coast of Sicily Žsouthern Italy, central Mediterranean. between the north tip of the Gulf of Palermo and Cape San Vito ŽFig. 2. is tectonically stable, and has been subjected to an average, long term uplift of about 5 = 10y3 m kay1 since isotope stage 5e ŽAntonioli et al., 1994..

Fig. 5. Mushroom-like Dendropoma formation.

F. Antonioli et al.r Marine 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 ka Žstage 5e., is 0.072 mm yry1 , measured using a Total Station. Consequently, 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 diminished of about 0.01 m Žsee 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 age ŽAbate 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 radiocarbon ŽTable 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 thickness ŽFig. 3.. On limestone promontories, Dendropoma ledges are smaller, up to 1 m long and 10 cm thick. In flat coastal areas, Dendropoma platforms, from 5 to 10 m broad, coalesce to form a single, uninterrupted rim stretching for several kilometres. Each platform is 20 to 40 cm thick, and the upper 8 to 10 cm consist of living organisms. The upper, living part lies at MSL

3

The recognition of a worldwide constant datum for the isotopic substage 5e highstand of the sea-level ŽEutyrrhenian, 125 ka. at q7 m a.s.l. "1 m ŽKu et al., 1974. provides an essential, and precise, marker to characterize Late Quaternary deformations.

Fig. 6. Outline of the mechanisms of the mushroom-like Dendropoma concretioning. Light grey rightward arrows indicate the effects of erosion on coastal morphology. Black arrow upward points out the sea-level rise. Symbol ŽU . marks the starting position in mushroom formation.

and, consequently, is exposed during low tide and submerged during high tide. A vertical section was excavated in the reef to make morphological observations and sampling for radiocarbon dating feasible. Radiocarbon dating was carried out on the most

F. Antonioli et al.r Marine Geology 161 (1999) 155–170

162

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 Reimer Ž1993.. Data are arranged by authors, sampling locations, elevation a.s.l., conventional ages, calibrated ages and sample laboratory code Program no.

Reference

1

Van Andel and Laborel, 1964

Brazil Recife

2

Laborel and Delibrias, 1976

West Africa Ghana, Ivory Coast, Cabo Verde Islands

3

Locality

Brazil Sao Paulo, Pernambuco

4

Fevret et al., 1967

5 6

Sanlaville, 1977 Pirazzoli et al., 1982

Lebanon Tripoli, Tabarja

Greece Creta, Antikityra

Metres on m.s.l.

14

Conventional C Žyr BP.

14

Calibrated C1s Žyr BP.

Laboratory no.

3 2.2 3.4 1 1 1 1.5 2.5 2.5 3 2.5 0.5 0.5 1.6 1.5 1.4 2 2 2.2 3 2.6 3 3 0.8 0.8 0.8 2.2 2 2.2 2.7 2.7 7.8 7.9 7.8 6.5 7 7.8 7.7 2 5.2 3.1 7 2.5 2 6.4 2.15 7.2 1.5 4.4

2790 " 150 1190 " 130 3660 " 170 530 " 90 650 " 90 700 " 90 740 " 90 1420 " 100 1630 " 90 2040 " 90 2050 " 90 380 " 90 380 " 90 1190 " 130 1670 " 100 1750 " 170 2400 " 95 2450 " 95 2790 " 150 3420 " 150 3660 " 170 3900 " 110 4480 " 180 1880 " 50 1960 " 140 2035 " 130 3490 " 80 1870 " 70 1890 " 90 1890 " 90 1930 " 70 1955 " 70 1950 " 80 1965 " 70 1975 " 70 1980 " 70 1995 " 70 2110 " 80 2200 " 70 2210 " 70 2250 " 70 2250 " 70 2270 " 70 2280 " 70 2275 " 100 2323 " 70 2400 " 70 2430 " 70 2430 " 70

2721–2317 1459–1130 3764–3356 267–0 387–228 436–262 466–280 1055–880 1268–1071 1700–1510 1708–1505 subactual subactual 881–630 1296–1115 1459–1130 2128–1894 2190–1954 2721–2317 3391–3145 3764–3356 3989–3697 4847–4406 1479–1343 1677–1335 1735–1425 3445–3270 1489–1317 1522–1317 1522–1317 1538–1381 1538–1381 1557–1398 1576–1412 1591–1424 1600–1435 1615–1465 1793–1555 1863–1698 1871–1706 1917–1757 1917–1757 1938–1789 1949–1801 1979–1748 1996–1841 2107–1926 2132–1959 2132–1959

A-16 A-17 A-22 Gif-2196 2404 2197 2406 2405 1675 2195 1676 Gif-1061 Gif-1063 Gif-2406 Gif-1060 Gif-2405 Gif-1935 Gif-1933 A-16 Gif-1059 A-22 Gif-1934 Gif-2147 Mc-146 Mc-64 Mc-63 Mc-145 Mc-2437b Mc-2438 Mc-2435 Mc-2430 Mc-2110II Mc-2238 Mc-2110 Mc-2114 Mc-21209 Mc-2110I Mc-2195 Mc-2437 Mc-2116 Mc-2115 Mc-2101 Mc-2436 Mc-2439 Mc-2193 Mc-2431 Mc-2272 Mc-2100 Mc-2107

F. Antonioli et al.r Marine Geology 161 (1999) 155–170

163

Table 2 Žcontinued. Program no.

Reference

Locality

7

Pirazzoli et al., 1991

Turkey Hatay coast

8

Delongeville et al., 1993

Syria Guverdjne Kaya, Arab al Malek

9

Pirazzoli et al., 1994a

Greece Zante, Cephalonia

Metres on m.s.l.

Conventional 14 C Žyr BP.

14

Calibrated C1s Žyr BP.

Laboratory no.

3.1 4.3 3.8 1.7 7.3 7.3 7.1 2 2.5 2.5 7.1 5.9 5.6 6.5 1.45 7 6.8 5.9 6.7 6.5 5.6 4.8 4 0.75 0.4 0.8 0.8 0.7 1.2 0.8 3 0.8 2 2.5 2 0.65 0.65 0 0.6 0.6 0.4 0.5 0.9 1.2 1.2 0.8 1.05 1.05 0.8 1.3

2450 " 70 2380 " 70 2480 " 70 2580 " 80 2625 " 70 2650 " 70 2680 " 70 2740 " 80 2800 " 70 2800 " 70 2900 " 70 3200 " 70 3230 " 70 3300 " 80 3370 " 70 3400 " 70 3450 " 70 3800 " 100 3690 " 70 3730 " 80 3820 " 90 4330 " 80 4600 " 90 1745 " 70 2110 " 100 2450 " 60 2440 " 80 2690 " 95 2715 " 80 2810 " 60 2995 " 100 3230 " 60 3310 " 95 5200 " 80 5570 " 190 1335 " 50 1450 " 60 1675 " 55 1820 " 60 1890 " 55 2010 " 50 2590 " 45 5275 " 65 5595 " 85 1820 " 70 1960 " 60 2290 " 70 2360 " 70 2560 " 60 4290 " 90

2150–1983 2200–2018 2200–2018 2296–2088 2346–1926 2363–2280 2434–2300 2581–2327 2684–2378 2684–2378 2737–2610 3083–2877 3132–2928 3238–3003 3304–3157 3342–3172 3381–3234 3581–3602 3672–3480 3721–3543 3863–3630 4533–4354 4867–4700 1333–1234 1804–1544 2140–1993 2150–1959 2490–2290 2494–2314 2684–2432 2990–2687 3114–2938 3266–2994 5627–5468 6177–5729 922–817 1047–924 1274–1168 1401–1288 1495–1349 1610–1505 2314–2186 5694–5575 6086–5892 1410–1283 1557–1417 1960–1810 2051–1877 2306–2131 4507–4272

Mc-2104 Mc-2106 Mc-2108 Mc-2440 Mc-2111 Mc-2273 Mc-2274 Mc-2434 Mc-1378 Mc-1379 Mc-2500 Mc-2279 Mc-2420 Mc-2276 Mc-2432 Mc-2112 Mc-2275 Mc-2194 Mc-2113 Mc-2421 Mc-2429 Mc-2428 Mc-2427 Pa-771 Pa-781 Pa-823 Pa-782 Pa-769 Pa-822 Pa-776 Pa-775 Pa-774 Pa-780 Pa-779 Pa-773 Ly-5622 Gif AMS Ly-5625 Ly-5621 Ly-5623 Gif AMS Ly-5621 Ly-5631 Ly-5624 GifA-91114 GifA-92142 GifA-92283 GifA-91112 GifA-92141 GifA-92073

F. Antonioli et al.r Marine Geology 161 (1999) 155–170

164 Table 2 Žcontinued. Program no.

Reference

Locality

10

Pirazzoli et al., 1994b

Greece Corinth

11

Jones and Hunter, 1995

Grand Cayman

12

Pirazzoli et al., 1996

13

Present research

Greece Corinth, Thessaly Italy Sicily

Metres on m.s.l.

14

14

Calibrated C1s Žyr BP.

Laboratory no.

1.1 2.2 3 3.1 y0.8 y1.4 0 on the beach 0.7 0.4 0.6 y0.3 y0.3 y0.3 y0.4 on the beach on the beach on the beach on the beach

1865 " 55 4120 " 60 4705 " 50 5820 " 60 208 " 80 318 " 90 278 " 90 678 " 90 1780 " 42 1790 " 80 2050 " 60 531 " 32 527 " 36 554 " 35 784 " 37 1352 " 34 1563 " 40 2084 " 39 2651 " 51

1460–1331 4245–4075 4976–4842 6284–6176 subactual subactual subactual 420–250 1310–1290 1390–1250 1685–1550 232–106 232–94 251–127 461–400 923–876 1156–1055 1695–586 2350–2293

GifA-92PE1 GifA-92PE5 GifA-92PE8 GifA-92PE3 – – – – GifA-90SS3 GifA-92TH2 GifA-92TH3 R-2741 R-2742 R-2764 R-2580 R-2582 R-2964 R-2963 R-2765

ancient, fossil part of the reefs, which is located at 30–40 cm below the present sea-level. Because the whole studied area is tectonically stable, the 30–40 cm which separate the living individuals from the fossil Dendropoma are here deemed as indicative of the actual sea-level rise for the last 400–460 calendar years. 3.2. Morphological types and the classification of the Dendropoma reefs The Dendropoma bioconstructions in the Mediterranean and, namely, those lying along the Sicilian coasts developed the following morphologies. Ž1. Ledge. This structure develops on unprotected headlands, promontories and cliffs exposed to surf. The biogenic buildings are typically - 1 m wide and 10 to 20 cm thick at the outer margin. The mechanisms of formation of a Dendropoma ledge were described by Laborel Ž1987. for the structures observed along the coasts of Corsica. Ledges and encrustations are a common feature in coastal areas subjected to vermetid colonisation. Ledges are also found in areas already colonised, but where the

Conventional C Žyr BP.

development of vermetid bioconstructions is partially hindered by the unfavourable morphology of coasts exposed to high-energy breakers. Ž2. Platform or ‘‘true reef’’. This structure is similar to a coral fringing reef, and corresponds to the classical vermetid reefs described by Peres ´ and Picard Ž1952. and Molinier and Picard Ž1953.. Platforms are G 10 m wide and F 45 cm thick at the outer margin. The basement of the structure is commonly eroded, and takes the shape of a continuous vertical wall 0.40 to 1 m high. Vermetid reefs commonly colonise abrasion platforms generated through the action of high tide surf. Alternatively, these structures acquired their morphology through continuous, layered bioconstruction on several single collapse blocks. Dendropoma vermetid platforms constitute about 90% of all the vermetid structures of the Sicilian coast ŽFig. 4.. Ž3. ‘‘Mushroom-like’’ pillars. These morphologies seem to be the outcome of two different processes of formation. The primary cause for the development of mushroom morphology is the different degree of resistance to erosion of the bedrock and overlying vermetid bioconstruction. The bedrock is eroded at a higher rate than the vermetid structures,

F. Antonioli et al.r Marine 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 continuous growth of the outer ledge. At the end of the process, the morphology of the buildup is that of a large round overgrowth tapering toward its base ŽFigs. 5 and 6.. In the second case, vermetid ledges grow on the abrasion blocks scattered at the base of the cliff. The subsequent evolution yields mushroom structures similar to those developed through the first mechanism. Ž4. Microatolls and reefs. A detailed description of these structures is reported in the paper of Safriel Ž1966. on the vermetid microatolls and offshore reefs in Israel. 4. Ages of Dendropoma vermetid reefs 4.1. Calibration of

14

C dates

Many radiocarbon age dates available from Atlantic an Mediterranean areas for vermetid reefs Žmostly Dendropoma. which have been published since 1964 are listed in Table 2. In order to compare

the radiocarbon ages, we calibrated Ž1s . all the data by using the program Calib 3.0 of Stuiver and Reimer Ž1993.. With respect to calibration, it must be stressed that the regional effect was not taken into account ŽDR s 0.. For this reason, comparison between absolute calibrated ages of samples from different regions is biased by the possible influence of the local effects whereby a sample can be a few years more recent or older with respect to a calibrated age with DR s 0. Consequently, each comparison should take into account for this bias. During the Late Holocene, which is the time span encompassed by the oldest age shown so far by Dendropoma bioconstructions, 4 vermetid reefs de4

The radiometric ages of some datations ŽPirazzoli, 1996. range from 12,300 to 18,860 years BP. Dating has been obtained from vermetids dredged from a submerged cliff 117 to 160 m deep off western Sardinia. We argue that the samples do not include the genus Dendropoma, but other vermetidae, living at higher depths.

166

F. Antonioli et al.r Marine Geology 161 (1999) 155–170

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

veloped and were preserved in both tropical and temperate areas. 4.2. Radiocarbon dating of the Sicilian Dendropoma reefs The samples used for radiocarbon dating Žsamples 1–2–3–4. were collected from coastal, D. petraeum reefs. Some samples were collected from blocks, 0.20 to 0.50 m in diameter, which were ejected on the shore by exceptional events, such as storm waves or tsunami Žsamples 5–6–7–8.. These reef fragments ŽFig. 7. have been observed over a wide area along the northern coast of Sicily and form a storm layer bar 10 to 20 m off the present day shoreline. 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. Dating was performed on samples about 2 cm thick Žweight ; 30 g., cut along planes parallel to the surface ŽFig. 8.. Carbon dioxide was extracted

from carbonates and activity measurements were carried out by means of CO 2 proportional counters. The inner, fossil part of in situ Dendropoma vermetid reefs yielded relatively young ages, typically ranging between 461 and 94 years cal BP. Reef fragments collected from the beaches and reworked by wave action proved to be much older, and typically their ages ranged from 2350 to 876 years cal BP. The assessed age ranges are similar to those yielded by the 14 C dating of fossil Dendropoma reefs from Grand Cayman ŽJones and Hunter, 1995. and to the 14 C ages of fossil vermetid reefs located several tens of metres a.s.l. in rapidly uplifting zones Žsee Table 2..

5. Discussion From the observations on the morphology coupled with the analysis of new and previous calibrated data

F. Antonioli et al.r Marine Geology 161 (1999) 155–170

on vermetid reefs from the Atlantic and the Mediterranean, we can infer that vermetid reefs can attain their maximum growth only when they develop on coasts characterised by uplift rates of at least 0.1 cm yry1 . Conversely, vermetid reefs which developed on stable coasts were demolished by storm waves, and their complete destruction occurred in 2r3000year cycles. Along the coasts of Sicily, small, fossil Dendropoma ledges, up to a few centimetres thick, were found at depths of y2.5 to y3 m with respect to the MSL. These fossil ledges probably marked the MSL of the Mediterranean sea between 4000 and 5000 years cal ago ŽAlessio et al., 1994.. Along the eastern Mediterranean coasts, fossil vermetid reefs, dated 6000 years cal BP, were preserved in areas subjected to rapid uplift. The observed occurrence of mechanically eroded vermetid reef fragments which were brought onto the beach support the ‘‘involuntary suicide’’ theory proposed by Safriel Ž1966; 1974.. This theory predicts that catastrophic events with decadal cycles Že.g., storms. caused the mechanical destruction of vermetid reefs. In the interval between two catastrophic events, the outer margin of the platform grows too much with respect to the carrying capacity of the reef itself. Consequently, even medium energy waves can easily break off this cantilever and transport the fragments onto the shore, where their accumulate pile up to form storm layers. Most of the fossil fragments of the Dendropoma platforms which were dated by other authors are located from a few decimetres up to 7.9 m a.s.l., because these reefs were sampled along coasts subjected to uplift. Conversely, in-situ Dendropoma reefs which were sampled along the Sicilian coast are in tectonically stable areas ŽAntonioli et al., 1994.. Consequently, these reefs are reliable indicators of Holocene sea-level fluctuations. Although the potential of vermetid reefs as indicators of sea-level change has been acknowledged in the past, only a few of these structures have been dated and used for that purpose. Along the coasts of Sicily, in-situ vermetid reefs are found to a depth of y40 cm below MSL and their oldest, fossil part yielded calibrated ages of 400 to 461 years. These data indicate that between 400 and 461 years ago, the sea-level was 40 " 8 cm lower than today. This datum Žtogether with the 30

167

cm data, see Table 2. is of outstanding interest. In fact, the curves describing the Holocene rise in sea-level are based on a small number of reliable data from the Late Holocene Že.g., Bard et al., 1996 present for the last 6 ka BP, two dates; Alessio et al., 1994 show four dates.. The only other case known of fossil Dendropoma reefs of the same age, occurring below present MSL, is that of Grand Cayman. On the basis of age vs. depth data, Jones and Hunter Ž1995. suggested a lowering of MSL during the Little Ice Age, which caused the death of most vermetid colonies in South America. Some of the fossil reefs which should have been killed by the catastrophic LIA event are located at y0.8 m below sea-level Žb.s.l... However, the data from the present study indicate that between 1600 and 1700 A.D., the sea-level was higher than that proposed by Jones and Hunter Ž1995.. Some data ŽSchmiedt, 1972; Leoni and Dai Pra, 1996. indeed indicate that the sea-level reached between y0.6 and y0.5 m at about 2000 years BP, and that the Sicilian Dendropoma reefs of LIA age are located only 0.30 to 0.40 m below present MSL. On the basis of the calibrated 14 C ages reported in Table 2, the Dendropoma reef colonisation pattern in the Mediterranean can be reconstructed. The oldest radiocarbon ages referring to about 6000 years cal BP, or slightly older, pertain to Dendropoma colonies which were sampled along the coasts of Turkey Žq2 m., in Syria Žq1.2 m., in the Gulf of Corinth Žq3.1., in the southern Mediterranean. Fossil vermetid reefs which developed, typically yield ages between 6177 and 5729 years cal BP. The oldest specimens collected on the coasts of southern Italy, about 2350 years cal BP old, are Dendropoma reef fragments which were ejected onto the shore. Prior to 6500 years BP, the rate of sea-level rise was very high, up to 2 m per century. The rapid rise of the water level prevented the construction of vermetid reef, because the habitat of these gastropods is restricted to the intertidal zone, and this zone was short-lived in a period of fast sea-level rise. Alternatively, if some vermetid reefs developed prior to 6500 years ago, their remains would now be located several tens of metres b.s.l. The aforementioned considerations, and the available data, shed some light on both provenance and distribution of the vermetid reefs in the Mediter-

168

F. Antonioli et al.r Marine Geology 161 (1999) 155–170

ranean. Coastal stratigraphic records and fossil associations relative to marine transgressions which took place in the Middle and Late Pleistocene Žisotope ‘‘warm’’ stages 11, 9, 7 and 5., and in the Mediterranean 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 of storm waves and hurricanes. Due to the lack of data from stable areas, we cannot rely on this negative evidence to infer whether Dendropoma reefs did or did not exist before the Holocene. More observations and dates on Dendropoma reefs would be necessary to solve the problem. The oldest platforms are located in the SE part of the Mediterranean region, whereas the most recent ones occur in the central Mediterranean. Dendropoma bioconstructions are extremely rare in the North, and the only ones in this area are some small ledges reported from the coasts of Corsica which are now extinct ŽLaborel, 1987.. The Dendropoma colonisation pattern, from southeast to northwest, may be the result of the SST trends, and especially of the SST rise which characterized the Mediterranean during the Late Glacial and Holocene Žlast 12 ka cal BP.. If this were the case, Dendropoma gastropods would be thermophilic. In addition, there is evidence that Dendropoma identify a valuable biological indicator of SST trends. Preliminary d18 O data inferred from specimens collected in Sicily actually indicate that Dendropoma are reliable records of SST fluctuations ŽAntonioli et al., 1998..

6. Conclusions The overview of studies on Dendropoma reefs put into evidence that these gastropods have been widely used in tectonically unstable areas as indicators of uplift rates. Alternatively, the occurrence of vermetid reefs has been simply reported and dated. The results presented in this study should suggest that the use of Dendropoma reefs in stable areas to evaluate sea-level fluctuations is reliable for the past 500–1000 ka. Using the tide-gauges data for the

Fig. 9. Diagrammatic curve of sea-level rise during 2 ka BP. Each sample is represented with an error box corresponding to the vertical estimation error Ž"8 cm. and 14 C dating error.

Mediterranean Žabout 12 cm of relative sea-level rise in the last century; Pirazzoli, 1993. those coming from the dating of Dendropoma reefs and the archaeological data ŽSchmiedt, 1972; Leoni and Dai Pra, 1996., it is possible to plot a curve of the Mediterranean sea-level rise during the last 2 ka BP ŽFig. 9. similar to those published by Laborel et al. Ž1994.. As a conclusion, Dendropoma reefs appear to be one of the best suited palaeoclimatic indicators for a slice key-time, i.e., the last 500 years, when man’s activities may have considerably altered the natural biogeochemical cycles and thus enhanced the greenhouse effect ŽIPCC Climate Change, 1994..

Acknowledgements The authors would like to thank Dr. Silvia Frisia 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 and Sergio Silenzi for their invaluable field assistance.

References Abate, B., Di Maggio, C., Incandela, A., Renda, P., 1991. Nuovi dati sulla penisola di Capo San Vito ŽSicilia nord-occidentale.. Mem. Soc. Geol. Ital. 47, 15–25. Abate, B., Di Maggio, C., Incandela, A., Renda, P., 1993. Carta Geologica dei monti di Capo San Vito. Dipartimento di Geologia e Geodesia dell’Universita` di Palermo.

F. Antonioli et al.r Marine Geology 161 (1999) 155–170 Aharon, P., 1983. 140,000-yr isotope climatic record from raised coral reefs in New Guinea. Nature 304, 720–730. Alessio, M., Allegri, L., Antonioli, F., Belluomini, G., Improta, S., Manfra, L., Preite, M., 1994. La curva di risalita del mare Tirreno negli ultimi 43 ka ricavata da datazioni su speleotemi sommersi e dati archeologici. Mem. Descr. Carta Geol. Ital. 52, 279–292. Antonioli, F., Oliverio, M., 1996. Holocene sea-level rise record by a radiocarbon-dated mussel in a submerged speleothem beneath the Mediterranean sea. Quat. Res. 45, 241–244. Antonioli, F., Reitano, G., Puglisi, C., Tusa, S., 1994. Evoluzione geomorfologica pleistocenica del settore costiero di S. Vito Lo Capo. Mem. Descr. Carta Geol. Ital. 52, 251–277. Antonioli, F., Silenzi, S., Chemello, R., Parello, F., 1998. Oxygen isotopic analysis on vermetids reefs Ž Dendropoma. in central Mediterranean coastal zone ŽSicily, Italy.. Atti del 798 Congresso Soc. Geol. Ital., pp. 86–88. Bard, E., Hamelin, B., Arnold, M., Montaggioni, L., Cabioch, G., Faure, G., Rougerie, F., 1996. Deglacial sea-level record from Tahiti corals and the timing of global meltwater discharge. Nature 382, 241–244. Chemello, R., Pandolfo, A., Riggio, S., 1990. Le biocostruzioni a Molluschi Vermetidi nella Sicilia Nord-Occidentale. Atti 538 Congresso UZI, Palermo, p. 88. Chemello, R., Gristina, M., Toccaceli, M., Badalamenti, F., Riggio, S., 1990. Distribuzione delle formazioni a Molluschi Vermetidi lungo le coste siciliane. Atti 538 Congresso UZI, Palermo, p. 60. De Quadrefages, A., 1854. Souvenirs d’un Naturaliste: I. Paris. Delongeville, R., Laborel, J., Pirazzoli, P., Sanlaville, P., Arnold, M., Bernier, P., Evin, J., Montaggioni, L., 1993. Les variations recentes de la ligne de rivage sur le littoral Syrien. Quaternaire 4, 45–53. Fevret, M., Picard, J., Sanlaville, P., 1967. Sur la possibilite´ de datation de niveaux marins quaternaires par les Vermets. C. R. Acad. Sci., Ser. D 264, 1407–1409. Focke, J.W., 1977. The effect of a potentially reef-building vermetid community on an eroding limestone coast, Curacao, Netherland Anthilles. Proceedings of the 3rd International Coral Reef Symposium, Miami, Vol. 1, pp. 239–245. Guilderson, T.P., Fairbanks, R., Rubenstone, J.L., 1994. Tropical Temperature variations since 20,000 years ago: modulating interhemispheric climate change. Science 263, 663–665. IPCC Climate Change, 1994. In: Houghton, J.T., Meira Filho, L.G., Bruce, J., Lee, Hoesung, Callander, B.A., Haites, E., Harris, N., Maskelleds, K. ŽEds.., Radiative Forcing on Climate Change and an Evaluation of the IPCC IS92 Emission Scenarios. Cambridge Univ. Press, 339 pp. Jones, B., Hunter, I., 1995. Vermetid buildups from Grand Cayman British West Indies. J. Coastal Res. 4, 973–983. Kallel, N., Paterne, M., Labeyrie, L., Duplessy, J.C., Arnold, M., 1997. Temperature and salinity in the Tyrrhenian sea during the last 18,000 years. Palaeogeogr., Palaeoclimatol., Palaeoecol. 135, 97–108. Keigwin, L.D., 1996. The Little Ice Age and Medieval Warm Period in the Sargasso Sea. Science 274, 1504–1507.

169

Kemp, M., Laborel, J., 1968. Formations de vermets et d’algues calcaires sur les cotes du Bresil. Rec. Trav. Stat. Mar. Endoume 43 Ž59., 9–23. Ku, T.L., Kimmel, M.A., Eastronu, W.H.U., O’Neilu, T.J., 1974. Eustatic sea level 120,000 years ago on Oahu, Hawaii. Science 183, 959–962. Laborel, J., 1986. Vermetids. In: Van de Plassche, O. ŽEd.., Sea-level Research, A Manual for the Collection and the Evaluation of Data. Norwich, Geo Books, pp. 281–310. Laborel, J., 1987. Marine biogenic constructions in the Mediterranean, a review. Sci. Rep. Port-Cros Natl. Park 13, 97–126. Laborel, J., Delibrias, G., 1976. Niveaux marins recents a vermetidae du littoral ouest Africain. Assoc. Senegal. Etude Quat. Afr. Bull. 47, 97–110. Laborel, J., Laborel, F., 1996. Biological indicators of Holocene sea level and climatic variations on rocky coasts of tropical and subtropical regions. Quat. Int. 31, 53–60. Laborel, J., Laborel Deguen, F., 1994. Biological indicators of relative sea level variations and of coseismic displacements in the Mediterranean region. J. Coastal Res. 10, 395–415. Laborel, J., Mohorange, R., Lafont, R., Le Campion, J., LaborelDeguen, F., 1994. Biological evidence of sea level rise during the last 4500 years on the rocky coasts of continental southwestern France and Corsica. Mar. Geol. 120, 203–223. Leoni, G., Dai Pra, G., 1996. Variazioni del livello del mare nel tardo olocene lungo la costa del Lazio in base ad indicatori geoarcheologici. ENEA Environmental Departmet, RTr AMBr97r8, p. 110. Molinier, R., Picard, J., 1953. Notes biologiques a propos d’un voyage d’etude sur les cotes de Sicile. Ann. Inst. Oceanogr. 28 Ž4., 163–188. Monterosato, M.T.A., 1892. Monografia dei vermeti del Mediterraneo. Bull. Soc. Malacol. Ital. 17, 7–48. Peres, ´ J.M., Picard, J., 1952. Les corniches calcaires d’origine biologique en Mediterrane occidentale. Rec. Trav. Stat. Mar. Endoume 4 Ž1., 2–34. Pirazzoli, P.A., 1993. Global sea-level changes and their measurement. Global Planet. Changes 8, 135–148. Pirazzoli, P.A., 1996. Sea-level Change. The Last 20,000 Years. Wiley, 211 pp. Pirazzoli, P.A., Montaggioni, L.F., 1989. Crustal block movements from Holocene shorelines: Rhodes Island ŽGreece.. Tectonophysics 170, 89–114. Pirazzoli, P.A., Thommeret, J., Thommeret, Y., Laborel, J., Montaggioni, L.F., 1982. Crustal block movements from Holocene shorelines: Crete and Antikythira ŽGreece.. Tectonophysics 86, 27–43. Pirazzoli, P.A., Laborel, J., Saliege, J.F., Kayan, I., Person, A., 1991. Holocene raised shorelines on the Hatay coast ŽTurkey.: palaeoecological and tectonic implications. Mar. Geol. 96, 295–311. Pirazzoli, P.A., Stiros, J., Laborel, F., Laborel Degue, F., Arnold, M., Papageogiu, S., Moorhange, C., 1994a. Late Holocene shoreline changes related to paleosismic events in the Ionian Islands ŽGreece.. Holocene 4, 397–405. Pirazzoli, P.A., Stiros, J., Arnold, M., Laborel, F., Laborel Deguen,

170

F. Antonioli et al.r Marine Geology 161 (1999) 155–170

F., Papageogiu, S., 1994b. Episodic uplift deduced from Holocene shorelines in the Perhacora peninsula ŽCorinth area, Greece.. Tectonophysics 229, 201–204. Pirazzoli, P.A., Laborel, J., Stiros, S.C., 1996. Earthquake clustering in the eastern Mediterranean during historical times. J. Geophys. Res. 101, 6083–6097. Prat, H., 1935. Les formes d’erosion littorale dans l’archpel des Bermudes et l’evolution des atolls et recifs corallienns. Rev. Geogr. Phys. Geol. Dyn. 8 Ž3., 257–282. Safriel, U., 1966. Recent vermetid formation on the Mediterranean shore of Israel. Proc. Malacol. Soc. London 37, 27–34. Safriel, U., 1974. Vermetid gastropods and intertidal reefs in Israel and Bermuda. Science 186, 1113–1115. Safriel, U., 1975. The role of vermetid gastropods in the formations of Mediterranean and Atlantic reefs. Oecologia 20, 85– 101.

Sanlaville, P., 1977. Etude Geomorphologique de la region littorale de Liban. Univ. de Liban Sect. Etudes Geogr. Beirut. Schmiedt, G., 1972. Il Livello Antico del mar Tirreno. Testimonianze dei Resti Archeologici. Ed Olschki, p. 197. Stephenson, T.A., Stephenson, A., 1954. The Bermuda Islands. Endeavour 50, 72–80. Stuiver, M., Reimer, P.J., 1993. Extended 14 C data base and revised Calib 3.0 14 C age calibration program. Radiocarbon 35, 25–230. Tzur, Y., Safriel, U., 1978. Vermetids platforms as indicators of coastal movements. Isr. J. Earth Sci. 27, 124–127. Van Andel, T., Laborel, J., 1964. Recent high relative sea level stand near Recife, Brazil. Science 145, 580–581. Verrill, A.E., 1906. The Bermuda Islands. Trans. Conn. Acad. Arts Sci., New Haven 12, 1–348.