Imp.Iannace UU//TTHH DDAATTIINNGG AANNDD GGEEOOCCHHEEMMIISSTTRRYY OOFF CCAARRBBOONNAATTEE CCOONNCCRREETTIIOONNSS AASSSSOOCCIIAATTEEDD WWIITTHH UUPPPPEERR PPLLEEIISSTTOOCCEENNEE FFOOSSSSIILL SSHHOORREELLIINNEESS OOFF TTHHEE SSOORRRREENNTTOO PPEENNIINNSSUULLAA ((CCOONNCCAA DDEEII MMAARRIINNII,, SSOOUUTTHHEERRNN IITTAALLYY)) AAlleessssaannddrroo IIaannnnaaccee11,, PPaaoollaa RRoommaannoo11 && PPaaoollaa TTuucccciimmeeii22 1Dipartimento di Scienze della Terra, Università di Napoli Federico II, Napoli, Italia, aleianna@unina.it, paromano@unina.it; 2Dipartimento di Scienze Geologiche, Università "Roma Tre", Roma, Italia, tuccimei@uniroma3.it ABSTRACT U-series dating and geochemical analyses were performed on carbonate concretions in order to put chronological constraints on the associated fossil shorelines. In particular, samples were taken from concretions found at Conca dei Marini Cape where former shoreli- nes ascribed to the Upper Pleistocene are present. From the chronological data the height of sea level during highstands of Late Pleistocene is inferred; moreover, due to the tectonic stability of the area the estimated height could be taken as a close approximation of eustatic sea level position. A +3.5 m a.s.l. sea level highstand which occurred during the end of Oxygen Isotopic Stage (OIS) 5e was recognised by the U/Th age and elevation of the concretion covering a wave-cut platform. Furthermore, new interpretations for more recent sea level highstands were obtained by analyses performed on two calcitic concretions associated with a marine biocalcarenite. They indicate that the sea level at the end of OIS 3 was close to the present day one; such a conclusion disagrees with the generally accepted sea levl position derived from proxy data taken from oceanic cores while it agrees with recent chronological data obtained from marine deposits in the Gulf of Taranto (Southern Italy). RIASSUNTO In due siti della Penisola Sorrentina , presso il Capo di Conca dei Marini, sono state rinvenute alcune concrezioni carbonatiche in asso- ciazione con depositi e forme marine ascritte in letteratura agli stazionamenti alti del livello marino correlati con lo Stadio 5 della strati- grafia basata sugli isotopi dell'ossigeno. Su queste concrezioni sono state eseguite datazioni U/Th al fine di ottenere ulteriori vincoli cro- nologici (limiti ante quem o post quem) per la genesi delle linee di riva, ed analisi sedimentologiche e geochimiche indirizzate alla deter- minazione del loro ambiente diagenetico. Le condizioni di stabilità tettonica tardo quaternaria caratterizzanti l'area in studio hanno con- sentito, inoltre, di porre in relazione la posizione altimetrica dei depositi e delle forme cronologicamente inquadrati ad altrettante posi- zioni eustatiche del livello marino durante gli Stadi Isotopici 5 e 3 del Pleistocene superiore. Fra i risultati più interessanti si segnalano quelli ottenuti da una concrezione laminare datata al sottostadio 5d che ricopre una piattaforma di abrasione posta a +3,5 m s.l.m., la cui genesi va così inquadrata nella parte finale del sottostadio 5e, e le datazioni di due concrezioni calcitiche che si intercalano ad una biocalcarenite marina a + 4 m s.l.m. Queste ultime, datate allo Stadio3, suggeriscono una posizione del livello marino per quel periodo prossima al livello marino odierno; tale conclusione da un lato contrasta con quanto sinora proposto in letteratura sulla base di dati indi- retti ottenuti da carote oceaniche, d'altra parte è in accordo con recenti dati ottenuti su depositi marini affioranti sulle coste del Golfo di Taranto. Key words: emerged shorelines, calcareous concretions, geochemistry, U-series data, Upper Pleistocene, southern Italy. Parole chiave: linee di riva, concrezioni calcaree, geochimica, datazioni U/Th, Pleistocene superiore, Italia meridionale. Il Quaternario Italian Journal of Quaternary Sciences 1166(1Bis), 2003, 49-54 11.. IINNTTRROODDUUCCTTIIOONN The Sorrento promontory is a NE-SW trending horst facing Capri island along the coast of the Campania region (Fig.1). Highly resistant rocks – carbo- nates of Meso-Cenozoic age – displaced by normal faults in structural blocks constitute the promontory. As such, the Peninsula is characterised by a structure-con- trolled type of coast with high and rectilinear sea cliffs interrupted by angular plan-shaped bays and pocket beaches. Offshore, plunging cliffs alternating with nar- row coastal benches are generally present. Similarly, the Quaternary fossil shorelines of the Peninsula are represented by scattered and small rem- nants of marine terraces and by scarce outcrops of coarse-textured beach deposits patched onto the bedrock and usually barren. There are a very few sites where fossiliferous Pleistocene marine deposits are pre- sent such as the well known Ieranto and Conca dei Marini bays, where Eutyrrhenian marine deposits were pointed out (Brancaccio et al., 1978). In this paper we present new chronological data on the Upper Pleistocene fossil shorelines of the Sorrento Peninsula. They have been obtained by U- series data performed on carbonate concretions which we have found closely or directly associated with some sea level stand indicators, both of erosional and deposi- tional origin, in Conca dei Marini area. 22.. GGEEOOMMOORRPPHHOOLLOOGGYY,, SSTTRRAATTIIGGRRAAPPHHYY AANNDD SSEEDDIIMMEENNTTOOLLOOGGYY Two Sites of Conca dei Marini promontory (Site I and Site II in fig.1) have been studied in detail in this paper. The Upper Pleistocene shorelines are represen- ted by patches of marine deposits and by bioerosive notches and emerged platforms, located at elevation 50 A. Iannace, P. Romano & P. Tuccimei between +8 and +1.5 m. They were studied in Brancaccio et al. (1978), Cinque & Romano (1990), Riccio et al. (2001). In Site I several carbonate concretions associated with a + 8 m high notch have been found (Fig.2). The concretions are finely laminated and fill bowl-like cavi- ties present all along the notch concavity. Microscopically, the concretions consist of alternation of microsparitic laminae. XRD analyses revealed the pre- sence of some aragonite together with calcite. The ori- gin of the cavities and carbonated infilling appears very problematic. Possibly, the cavities originated as Lithophaga sp. burrows and were subsequently enlar- ged by chemical weathering. The former studies carried Fig. 1 - Geological scheme of the Sorrento Peninsula with the locations of the Conca dei Marini promontory and of the Site I and Site II bays (after Riccio et al., 2001 modified). Fig. 2 - Geological section of Site I bay (after Riccio et al., 2001 modified). The photographs show a detailed and a complete view of the concretions present all along the + 8 m high notch. 51U/Th dating and Geochemistry ... Fig. 3 - Geological section of Site II bay. For details of the concretions see fig. 4. Fig. 4 - Details of the calcareous concretions asso- ciated with marine deposits or erosional morpholo- gies at Site II bay. A) the concretion lying onto the +3.5/4 emerged bench, 2/4 cm thick. B) the concre- tions cementing the upper part of a marine calcare- nite, 1/2 cm thick. 52 out in the area (Brancaccio et al., 1978; Riccio et al., 2001) indicated an Euthyrrenian age of the + 8 m notch because it is closely associated with a marine deposit with Cladocora coespitosa. In Site II different generations of calcareous con- cretions were found closely or directly associated with emerged shorelines (Fig. 3). Some platy, laminated cal- citic concretions (Fig.4A) lie onto a +3.5/4 m high wave- cut platform which was tentatively ascribed to a late OI substage 5e sea level stand by Riccio et al. (2001). Other generations of concretions intercalated in the upper part of a marine calcarenite at +4 m a.s.l. (Fig. 3 and Fig. 4B) were observed. The marine deposit covers the +3.5/4 m high emerged platform and there it is only some 60 cm thick; laterally, instead, the deposit thickens to some 100 cm because it fills a sheltered niche whose bottom is 1 m lower than the terrace and is cut directly into the Mesozoic carbonates of the substra- te. The deposits are distinctly clinostratified and dip landward with a fan-shaped bedding which progressi- vely compensates the difference in accomodation space between the terrace and the niche. This demonstrates that the protected niche was filled gravitationally by sediments coming from the sea-ward side and washed over the threshold represented by the bench. The sediments, as reported in Riccio et al. (2001), consist of a matrix-free coarse calcarenite to calcirudite. The part of deposits closer to the sea is distinctly coar- ser, with single grains reaching some cm in diameter. Grains are subrounded and show a good sorting within each layer. They consist mainly of bioclasts and lithocla- sts of coarse-crystalline dolomites. Only one layer, at 80 cm, consist mostly of more angular and reddened litho- clasts. The bioclasts are represented mainly by frag- ments of articulate and inarticulate bivalvs, gastropods, bryozoan and echinoderms and of red algae. Frequent are also micritic grains of unknown origin. The deposit is generally highly porous and crumbly because of a very low degree of cementation. In fact, in the thin section, only an irregular, discontinuous rim of limpid, equant calcite cement is present showing frequently meniscus textures. Only a few layers in the upper part of the depo- sits are heavily cemented by several laminated carbona- te concrections. The concretions are represented by several mm thick laminated layers consisting exclusively of precipita- ted carbonate which interrupt the sedimentary layering (Fig 4B and 5). However, there are also calcarenite layers made harder by the presence of the same carbo- nate precipitate covering the sigle grains. The geometric relations between cement and sediment layers demon- strate that most of the cementation took place during deposition. Moreover, it is clear from field relations that for the latest concrections, downward, stalactitic growth on cavity floor was contemporaneous with upward growth on the sediment surface, probably as a flowsto- ne. The microstructures are characterised by alternating laminae of spar and microspar often showing the pre- sence of fibrous structures due to the crystallographic continuity of single crystals of each superposed lamina. This especially occurs when the laminae are not planar but form domes and arches. In the case of upward growth on the sediment surface these structures are comparable to those of stromatolites according to the definition of De Micco & Hardie (1994). Otherwise, they are typical of coconut calcite in stalactitic growth. These concrections are morphologically comparable to many spleothems but also to some carbonates formed in spe- cial conditions in supersaturated marine waters, as sug- gested by Riccio et al. (2001). 33.. GGEEOOCCHHEEMMIISSTTRRYY The several carbonate concrections at Conca dei Marini are the only available material to constrain cronolo- gically the associated sediments and erosional features. To this aim, several samples have been collected from: - the concrections cementing the upper part of the bio- calcarenite at Site II, both in the stalactitic (samples CM5) and stalagmitic (sample CM4) portions; - the problematic circular concrections partly covering the +8 m notch at Site I (sample CM1); - the concrection covering the coastal bench at 3.5-4 m at Site II (samples CM6); From the collected material, four samples have been analysed by U-series disequilibria, nine for O and C stable isotopes. The list of samples and results are shown in Tables 1 and 2. For U-series disequilibria measurements, samples were crushed into several-millimetre-diameter pieces with a stainless-steel chisel. These fragments were exa- mined under a binocular microscope and any piece that A. Iannace, P. Romano & P. Tuccimei Fig 5 - Details of the stalactitic (CM4) and the stalagmitic (CM5) portions of the concrections cementing the marine calcarenite at Site II. 53 showed signs of secondary alteration was discarded. The remaining portion was ultrasonically cleaned in distilled water twice. The analytical procedure used for U and Th separation was that reported by Bischoff et al. (1988). Three to six gram samples were spiked with a 228Th + 232U tracer (in secular equilibrium) and activity ratios were counted in an EG&G ORTEC 920-8 alpha spectrometer system. The ages and the initial 234U/238U activity ratios were calculated by means of ISOPLOT, a plotting and regression program designed by Ludwig (1994) for radiogenic-isotope data. The uranium con- tents, the activity ratios and the calculated 230Th ages are listed in Table 1; all errors are reported as 1 sigma. For O and C isotope ratios measurements, a few mg of powder have been obtained with a dental drill from areas which are exclusively formed of precipitated carbonates. Carbonate powders were reacted with 100% phosphoric acid at 75 °C and analysed in a carbo- nate preparation line connected to a Finnigan Mat 252 mass spectrometer. The analyses have been carried out at the Stable Isotope Laboratory of Erlangen University (Germany). Results are shown in Table 2. All the subsamples extracted from CM4 and CM5 samples have δ13C and δ18O isotope values ranging from -3,7 to -8,1 and from -2,2 to -3,5 (PDB) respectively. These values, especially the C-isotope ratios, indicate precipitation from meteoric waters. The relatively marked variation within the sample set cannot be explai- ned precisely and has to be attributed to temperature and compositional variation in the parent fluid, both pos- sibly linked to seasonal or climatic factors. The initial 234U/238U activity ratios calculated from two samples of the same concretions are 1.05 and 1.07, both not consi- stent with the average uranium composition of the oceans (about 1.15). The only isotopically different carbonate is repre- sented by the cavity-filling concretions found at +8 m at Site I (CM1). In fact, a single measurement performed on this material gave δ18O and δ13C values of -0.1 and -0.8 (PDB) respectively, distinctly heavier than the other samples. Part of this difference can be attributed to the presence of aragonite in these concretions, which has a slightly higher fractionation factor with respect to calci- te, both for carbon (1.8 per mil) and oxygen (0.6 per mil). However, the measured value implies at least a partial contribution of marine waters during precipitation. A simple evaporation effect on meteoric waters can be excluded because this would have raised the measured O-isotopes ratios but not the C-isotopes ones. This interpretation is further strengthened by U-geochemi- stry. In fact, both U-content and 234U/238U activity ratios are higher than in the CM 4 and 5 samples, this again suggesting a marine contribution in the precipitation of these concrections. For CM6, sample U-data suggest a meteoric ori- gin and a single δ18O and δ13C measurement seems to confirm this. 44.. DDIISSCCUUSSSSIIOONN The chronological data obtained at Conca dei Marini (Table 1) permit to infer the height of sea-level during high-stands of the Late Pleistocene. The estima- ted height can be taken as a close approximation of eustatic sea level positions. In fact, as pointed out in Brancaccio et al. (1978) and Riccio et al. (2001), the Conca dei Marini sites have suffered a maximum uplift of 1.5 m since the Eutyrrhenian, corresponding to a mean rate of 10-2 mm/a. The calculated age for the concrection covering the +3.5 m bench (CM6) is 109.1 ka (Table 1), which falls within OI substage 5d (Martinson et al. 1987). This only represents an upper limit for the age of the bench. The lower one is the Eutyrrhenian because the bench can be correlated to a +3.5 notch cutting the Cladocora deposit (see Fig. 2), as discussed in Riccio et al. (2001). Thus, the geochronological data confirm the hypothesis that this highstand occurred during late substage 5e. However, the ages of the other concrections provi- U/Th dating and Geochemistry ... Table 1 - U-series data, mineralogy and inferred isotope stage of samples from Conca dei Marini (Italy). Quoted ratios are activity ratios and errors are expressed as 1 sigma. (234U/238U)init. represents the initial uranium ratio. Sample Mineralogy U ppm (230Th/232Th) (234U/238U) (230Th/234U) (234U/238U)init. Age (ka) Stage CM1 aragonite+ 3.439 ± 0.098 25 ± 1 1.126 ± 0.014 0.387 ± 0,015 1.146 ± 0.016 52.7 ± 2.6 3 Mg calcite CM4 calcite 1.878 ± 0.035 75 ± 10 1.059 ± 0.017 0.424 ± 0.012 1.07 ± 0.02 59.6 ± 2.2 3 -- 4 CM5 calcite 1.211 ± 0.022 34 ± 3 1.043 ± 0.017 0.397 ± 0.011 1.050 ± 0.020 54.8 ± 2 3 CM6 calcite 0.514 ± 0.016 856 ± 792 1.057 ± 0.034 0.638 ± 0.025 1.078 ± 0.046 109.1 ± 7.3 5d Table 2 - C and O isotope ratios measured on Conca dei Marini concretions. Sample δ13c std.dev. δ18O std.dev CM1 -0.8 0.02 -0.2 0.02 CM 4a -7.2 0.03 -3.0 0.03 CM 4b -8.1 0.02 -3.5 0.02 CM 4c -5.5 0.02 -3.2 0.04 CM 4d -5.5 0.03 -3.3 0.06 CM 5a -5.7 0.02 -2.5 0.03 CM 5b -6.1 0.02 -2.4 0.05 CM 5c -3.7 0.02 -2.2 0.06 CM 5d -5.5 0.01 -2.6 0.02 CM 6 -6.5 0.04 -4.1 0.04 54 de new interpretations for more recent sea level high- stands. In fact, U-series data indicate an age of approxi- mately 54-59 ka for the CM 5 and CM 4 concrections respectively (table 1), which can be considered as an estimate of the age of the bioclastic deposits. These ages correspond to the beginning of OIS 3. The sedi- mentological evidence indicates clearly that the deposits formed as a backshore deposit washed over the bench into a sheltered niche on the rocky coast during storms. Considering the height of the marine calcarenite, this would indicate that the contemporaneous sea level was not so far from the present day one. Such a conclusion disagrees with the largely accepted assumption that the sea level during the whole OIS 3 was some tens of meter below the present one. This conclusion is gene- rally derived from proxy data, specifically by assuming a more or less direct relationship between O-isotope values in oceanic foraminifers and ice-volume (Chappel & Shakcleton, 1986). However, recent research in the Mediterranean area has found a little sedimentological evidence, supported by geochronological data, of a highstand above the present sea level during OIS 3 (Belluomini et al., 2002). Our data provide further sup- port to these findings. The U- and O-C isotope geochemistry of the pro- blematic concrections of + 7/8 m at Site 1 represents a further possible evidence that sea level was close to the present one during OIS 3. In fact, the calculated age is 52 ka and U content and O and C isotope ratios indicate a precipitation by a fluid with a partial marine contribu- tion. A possible explanation is that sea water came from marine spray over the rocky cliffs. We think that the data of Conca dei Marini and those reported by Belluomini et al (2002) impose further research in other areas, coupled with a critical review of published data concerned with recent sea level high- stands, in order to definitively verify the validity of the generally accepted Late Pleistocene sea level curves. AACCKKNNOOWWLLEEDDGGEEMMEENNTTSS This paper was financially supported by CNR n.99.00646 ct05 Grant: "Ricostruzione delle principali variazioni indotte sui sistemi geomorfici dalle flutuazioni climatiche tardo quaternarie e storiche", local chief scientist Prof. A. Cinque. RREEFFEERREENNCCEESS Belluomini G., Caldara M., Casini C., Cerasoli M., Mandra L., Mastronuzzi G., Palmentola G., Sansò P., Tuccimei P. & Vesica P.L. (2002) - The age of late Pleistocene shorelines and tectonic activity of Taranto area, Southern Italy. Quaternary Science Reviews, 2211, 525-547. Bishoff J.L., Rosenbauer R.J., Tavoso A. & Lumley H. (1988). 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