FACIES
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Erlangen 2002
The Messinian Reef Complex of the Salento Peninsula (Southern Italy): Stratigraphy, Facies and Paleoenvironmental Interpretation Francesca R. Bosellini, Antonio Russo, Alessandro Vescogni, Modena
KEYWORDS:STRATIGRAPHY- FACIES - PALEOECOLOGY REI-,~FS- SOUTIIERN ITALY - LATE MI()CENE(MHSSINIAN)
Contents
Summary 1 Introduction 2 Geological background and stratigraphic setting 3 Facies analysis 3. I Methods 3.2 Depositional facies 3.2.1 Back reef and shelf facies association 3.2.2 Shelf-edge facies association 3.2.3 Reef slope facies association 3.2.4 Reef substrate facies 4 Paleoecology of reef-building organisms 4.1 Corals 4.2 Vennetids 4.3 Halbneda 4.4 Secondary reef builders 5 Conclusions References SUMMARY
An integrated study of the early Messinian reef complex cropping out along the eastern coast of the Salento Peninsula (southern Italy), including stratigraphy, facies analysis and paleoecological aspects, is here presented. Fourteen facies types belonging to tba'ee main facies associations (back reef and shelf, shelf-edge, slope) have been recognized. They document a wide spectrum of depositional environments, reef building organisms and growth fabrics, in response to depth and other environmental factors in different parts of the reel" complex. The biotic structure of the reef is also described and discussed in detail. It consists of different types of reel: building organisms and of their bioconstructions (mat n ly Petites coral reefs, Halimeda bioherms and vermetidmicrobial "trottoirs"), that differ in composition and structure according to their position on the shelf edge-toslope profile. Results indicate that the reef complex of the Salento Peninsula has strong similarities with the typical early Messinian reefs of the Mediterranean region. However, the recognition of some peculiar features, i.e. the remarkable occurrence of Halimeda bioherms and of ver-
metid-microbial "'trottoirs", gives new insights for better understanding reef patterns and de,eelopment o f the reel belt during the Late Miocene in the Mediterranean.
1 INTRODUCTION The Messinian carbonate plallbrms of the Mediterranean region constituIe a very special and welJ-known setting for understanding :he important geological, biological and climatic processes that governed the na|ure of their peculiar reef environments (Franseen el al., 1996). P,elatively large-scale recl'structurcs are in fact associated w'ilh an extremely low diversity of zooxantlnellate corals and with other lypical biotic characters such as the renmrkable abundance of Halimeda, red algae and stromatolites. Variations in salinity have been firstly invoked to explain such characteristics, but also il has been suggested that periodic incursions of cold Atlantic waters into the western Mediterranean stressed tl~e latest Mcssinian reefs and therefore also c(mtributed :o their low diversity and simplified guild structure (Esteban, 1979, 1996; Santisteban, 1981 : Rouchy et al., 1986). The most probable explanation fl)r this decrease is now believed to be a combination of global climatic cooling associated to a northward teclonic shift of the Mediterranean borderlands outside the tropical-subtropical beh, leading to the disappearance of the Mediterranean reef coral province (Esteban. 1996: Rosen, 1999). In general, due to the landmark revision and synthesis by Chevalier (1961) and to the nunlcrous studies of Spanish geologists and paleontologists, discussions on the nature of Mediterranean [,ate Miocene reefs started liom the western regions, whose reel's and corals are generally still much better studied Ihan Neogene faunas elsewhere in Eurupc and the Mediterranean. Within this framework, the Messinian reel: recently discovered along the eastern coast of the Salento Peninsula (southern Italy) is the first true reel: recorded for the "Adriatic region" for this period of time and provides new data for understanding reef patterns and development of the reef belt during the Late Miocene in the Mediterranean.
Addresses: Prof. F.R. Bosellini, Prof. A. Russo and Dr. A. Vescogni, I)ipartimento di Palcobiologia c dell'erie Bolartico. [.iniversi:'Adi Modena e Reggio Emilia, Via Universifft 4, 41100 Modena, Italy. Fax: (059) 218212; E-mail: fiabos| russo~:unimo.it,
[email protected],
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It is therefore the main goal of this report to provide a fairly complete picture of the entire Messinian reef complex, including stratigraphy, facies analysis and paleoecological aspects. The quite complex biotic structure of this reef, consisting of very different reef-building assemblages (Halimeda bioherms, Porites reels and vermetid-microbial bioconstructions) will be also described and discussed in detail. 2 G E O L O G I C A l . B A C K G R O U N D AND STRATIGRAPHIC SETTING
Fig. 1. Location map of the Salento Peninsula and of the study area (right).
In the last few years, the Messinian reef of the Salento Peninsula has been the object of several investigations and some preliminary results have been published (Bosellini et al., 1999; Vescogni, 2000; Bosellini et al., 2001), basically dealing with the geological setting of the reef complex or with the specific nature of its biotic components.
The Salento Peninsula can be considered the carapace of the much larger Apulia Platform, a carbonate bank bordering, during the Mesozoic, the northern margin of the African continent. Along the present-day eastern coast of the Salento Peninsula, from Capo d'Otranto to Capo S. Maria di Leuca (Fig. 1), there is a continuous and spectacular exposure of a Cretaceous to Quaternary succession, mostly constituted of carbonate rocks and including several reef tracts. A stratigraphic review and a new geological map of the area have been recently published (Bosellini A. et al., 1999); we refer to this paper for detailed description and interpretation of the entire stratigraphic succession and for complete list of references concerning local geological contributions. The stratigraphic and geological peculiarity of this area is the following: whereas on the platform top, i.e. the Salento peninsula proper, the succession is few to tens-of-metres thick and punctuated by large lacunae, on the margin, along the present-day eastern coast of the peninsula, several carbonate systems of late Cretaceous to Pleistocene age, separated by maior unconformities, are laterally disposed and grafted one upon the other (Fig. 2). Except for the Creta-
Fig. 2. Stratigraphic architecture of the eastern Salento Peninsula: 1 - Upper Cretaceous "substratum". 2 - Torre Tiggiano Limestone (Lutetian). 3 - Torte Specchialaguardia Limestone (Priabonian). 4- Castro Limestone (lower Chattian). 5 - Porto Badisco Calcarenite (upper Chattian). 6 - Aturia Level (upper Burdigalian/lower Messinian). 7 - Novaglie Formation (lower Messinian). 8 - Andrano Calcarenite (lower Messinian). 9 - Leuca Breccia (upper Messinian). 10 - Lower Pliocene. 11 - Salento Calcarenite (lower Pleistocene). (modified from Bosellini et al., 1999).
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Fig. 3. Representative stratigraphic sections of the Novaglic Formaliorl showing development of three superi reposed reel units separated by two clear erosional surfaces. Facies types are also indicated for each section.
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ceous, Middle Eocene and Quaternary deposits, all others are clinostratificd slope systems and include well developed reef tracts of Priabonian, early Chattian and early Messinian age (Bosellini and Russo, 1992; Bosellini et al., 2001). Bosellini et al. (1999) interpreted this stratigraphic architecture as the result of the relative tectonic stability of the platform carapace that, during the last 60 m.y., was constantly near sea level and sediments were mainly accommodated and preserved on the deep mat'gin and slope of the plattbrm. The Messinian reef complex described in this paper is exposed along the eastern coast of the Salento Peninsula from the locality of Tricase Porto to Capo S. Maria di Leuca, for a total length of about 17 kin (Fig. 1). It has been formally named Novaglie Formation and interpreted as a succession of fringing reefs accommodated in palaco-reentrances or palaeo-embayments of the original Messinian rocky shore and overlying discordantly Cretaceous to Oligocene units. The corresponding back-reef and shel fcarbonates are known as Andrano Calcarenite (Bosellini et al., 1999) (Fig. 2). The Novaglie Formation basically consists of three superimposed units, separated by two clear erosional surfaces (Fig. 2, Fig. 3; P1.18/1,2), which have been interpreted to be the result of relative sea level fluctuations (4thorder) comparable with those indicated by Esteban (1996) and Pedley (1996a) for the early Messinian of the Mediterranean. Both the two unconformities arc colonized by vermetid-microbial bioconstructions. Only during deposition of the first unit (unit I), when accomodation space was considerable, a quite complete reef tract and associated clinostratified forereef slope developed (PI. 18/3,4). Facies types and reef organisms of the three reef units will be described in detail in the following paragraphs together with illustrations of some (at least the most important) of the numerous stratigraphic sections that constitute the base for the construction of the depositional and paleoecological model that will be presented in the conclusive part of this paper. Finally, it is important to underline that, whereas a considerable number of Late Miocene reefs have been generically ascribed to theTortonian-Messinian interval, for the Salento reef complex a relatively precise dating (early Messinian) has been achieved using benthic foraminifera and ostracod associations (Bosellini et al., 1999; Bosellini et al., 200 l).
Plate Fig. I. Fig.2. Fig. 3. Fig. 4.
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4 FACIES ANALYSIS 4.1 Methods Facies analysis has been carried out through the study of numerous stratigraphic sections cropping out mainly in road-cuts located along the coast from Porto Tricase to Leuca. In particular, sixteen sections have been measured, sampled and studied with respect to their sedimentological and paleontological characters. Only the more representative are considered and illustrated in the present report (Fig. 3, 4). They include: Tricase section (roadcut 1 km south of Tricase, along the Tricase-Tiggiano road), Leuca 1 section (along the coastal road from km 48.6 to Capo S.Maria di Leuca), Leuca 2 section (along the roadcut between Capo S.Maria di Leuca and Leuca), Lighthouse section (along the cliffbelow the Leuca lighthouse), Novaglie section (Marina di Novaglie harbour and along the roadcut from the harbour up to the coastal road), Ciolo section (along the roadcut of the new road connecting the coast to Gagliano). Fourteen facies types have been identified on the base of macroscopic observations in the field and microfacies analysis. Moreover, those facies types that mostly characterize the Novaglie Formation reef complex and that also include the various reef-building assemblages have been investigated more in detail, providing data on the architecture and structure of bioconstructions (setting, shape, quantitative estimation of the framework density, growth fabric), biotic components (taxonomic composition and relative abundance of the main reef-builders, growth form, associated fauna), and intra-reef sediment (texture and fabric). Growth fabrics of the various "reefal" units have been identified and named according to the recent terminology proposed by lnsalaco (1998). As regards the quantitative estimation of the "framework" density (sensu Perrin et al., 1995) and of relative abundance of the main reef-building organisms, the line-intercept transect method has been adopted (Bosellini and Perrin, 1994; Pen-in et al., 1995; Bosellini, 1998). Several transect lines have been measured along wellexposed subvertical outcrop surfaces and intercept lengths of corals in growth position and sediment were measured continuously to the nearest millimetre. Corals were identified in the field at the generic level, growth form and size were also recorded and data are expressed as percentageabundance in relation to unit linear distance along sampling
Outcrop views of the Messinian reef complex (Novaglie Formation, lower Messinian, Salento Peninsula, Southern Italy). Front view of reef unit I. The lower massive cli ffis the clinostratified complex. The higher massive and smaller cliff underneath the contact with reef unit II is the reef front of unit I. Lateral view of reef unit II, showing progradation and clinoforms to the left. Unit III overlies unconformably unit II. The reef core at Ciolo cove, reef unit I. The clinostratified forereef slope, reef unit I.
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Plate Fig. 1. Fig. 2. Fig. 3. Fig. 4.
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Back reef and shelf facies association (Novaglie Formation, lower Messinian, Salento Peninsula, Southern Italy). Porites and Siderastrea bearing facies. Thickets of small branching Porites in growth position. Oolitic calcarenite. Bar scale: 0.5 mm. Porites and Siderastrea bearing facies. Moulds of subspherical-knobby Siderastrea crenulata (Goldfuss). Bar scale: 1 cm. Porites and Siderastrea bearing facies. Wackestone matrix. Bar scale: 0.5 mm
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plasticity and wide variability as regards calicular characters (Chevalier, 1961; Brakel, 1977; Veron and Pichon, 1982; Budd et al., 1994) has led to a complicated and unstable taxonomy of both extant and fossil species. Most recent approaches for recognition of modern Porites species, that are based on three-dimensional measurements of stable characters, cannot really be used for fossil material whose calicular surfaces are usually badly preserved. Although Riegl and Piller (1997) recently tried to find characters reliable for identification of fossil material, determination of fossil Porites species using thin-sections is still rather arbitrary and, in any case, very well preserved colonies are necessary. In this study, despite abundance and variety of Porites colonies, the badly preserved and highly recristallized material prevented any kind of identification at the species level. On the contrary, species have been identified for the few Siderastrea and very rare Solenastrea.
4.2 Depositional facies A total of fourteen facies types has been recognized in the measured stratigraphic sections. With exception of the facies that characterizes the very base of the Novaglie Formation (reef substrate facies), all others have been grouped into three main facies associations (back reef and shelf, shelf-edge, slope). The terms facies and facies association are used here according to their definitions given by Mutti (in Bosellini et al., 1989). Each facies association corresponds to a depositional environment in a broad sense (lagoon, tidal-flat, beach, sandy shoal, reef, slope, basin) and is usually composed of typical facies, i.e. groups of strata or lithologies which reflect specific subenvironments and/or particular sedimentary processes. A quite complete succession, showing the development of the three units that constitute the Novaglie Formation, crops out in the Leuca 1 section, Fig. 3). Other five stratigraphic sections, including facies types not represented in Leuca 1 section, will be considered and illustrated in Fig. 3. In order to better understand geometries and facies relationships, maps showing areal distribution of facies associations for unit I, 1I and III are also presented (Fig. 4).
Plate Fig. 1. Fig. 2. Fig. 3. Fig. 4. Fig. 5. Fig. 6.
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4.2.1 Back reef and shelf facies association This facies association, known as Andrano Calcarenite (Bosellini et al, 1999) and poorly developed within the Messinian reef complex proper, represents a shallow shoreward reef flat and associated lagoon environment s.s. Although occurring in both unit I and II, it is represented by few outcrops, normally present in the most internal areas (with respect to the present-day coastline) of the Novaglie Formation (Tricase section, Fig. 3, Fig. 4). The following three different lithofacies have been recognized. - Oolitic calcarenite
This facies, about 2.6 m thick, is represented in the upper part of the Tricase section (Fig. 3) and consists of a yellowish oolitic packstone, with oolites cemented by a mosaic fabric (PI. 19/2). Texture and the common occurrence of crossbedding and "hen'ingbone" structures indicate that this facies could probably represent tidal bars developed in a shoal area. - Porites and Sideras'trea-bearingJhcies
This facies consists of two distinct subfacies. The first one, about 2 in thick, occurs only in unit I (Tricase section, Fig. 3), and consists of poorly stratified and strongly bioturbated marly limestones (mudstone-wackestone). Corals are quite abundant and consist of Porites and Siderastrea crenulata. Their relative proportions (19% for Porites and 8% for S. crenulata) have been estimated along a transect line of 15 m together with the density of the "framework" (27%) (Fig. 5a). Porites is mainly represented by branching colonies in growth position with short and relative thin sticks (about 2.3 cm their average diameter), forming in places small dense thickets (PI. 19/1 ). Some small globous colonies also occur. Siderastrea crenulata, characteristic of this facies, appears as empty moulds of completely leached, small subspherical or knobby colonies (about 4 cm large) (PI. 19/ 3). Corals are commonly associated with benthic foraminifera, gastropods, ostracods, bivalves and echinoids. Coralline algae are relatively rare. According to the terminology of Insalaco (1998), growth fabric can be classified as a sparse pillarstone. Sediment is a mudstone-wackestone whose bio-
Shelf-edge facies association (Novaglie Formation, lower Messinian, Salento Peninsula, Southern Italy). Stromatolitic facies. Undulated stromatolitic laminae. Stromatolitic facies. Internal fabric of stromatotitic laminae showing alternation ofpeloidal micritic layers and thin bioclastic levels. Bar scale: 1 ram. Vermetid-microbial "trottoirs". Outcrop view. Vermetid-microbial "trottoirs". Polished surface showing the typical chaotic aggregation (V: vermetids, S: serpulids, B: bryozoans). Bar scale: 1 cm. Vermetid-microbial "trottoirs". Micritic crusts binding vermetid and serpulid tubes (V: vermetids, S: serpulids, M: micritic crust). Bar scale: 1 ram. Branched coralline algal facies. Fan-shaped growth morphology of Spongites.
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Fig. 5. a) Diagram representing a 15 m transect across the back reef and showing density of the framework and relative abundance of the reef-building coral genera, b) A 20 m transect measured across the reef core and showing the linear density of the framework. clastic component represents in situ fragmentation of the nearby reef biota (Pl. 19/4). The second subfacies (Leuca 2 section, Fig. 3) is represented only in unit II and is about 2 m thick. It is very similar in the composition of the coral fauna and growth fabric to the one described above. Linear measurements across a transect line of 10 m indicate a density of the "fi'amework" of about 25%. However, partly different are the associated fauna (vermetids are quite common together with crusts and fragments of coralline algae) and sediment type (bioclastic. strongly cemented wackestonepackstone),sug~estmg aless protected environment, much closer to the reef margin. - Bioturbated biocalcarenite This facies mainly consists of massive to poorly stratified biocalcarenites with alternating layers of laminated marly limestones and lumachella. Biocalcarenites are bioturbated and consist of packstone-grainstone rich in oolites, gastropods and bivalves (Cardium is abundant), associated with ostracods, benthic foraminifera (Elphidium and miliolids are quite abundant), echinoids, vermetids and some fi'agments of Halimeda, coralline algae and corals. Centimetric layers of marls and marly limestones also occur and are characterized by abundant ostracods (Aurila sp., Grinioneis minor, Xestoleberis sp., Cyprideis ruggierii, Cyprideis sp., Dorukella sp., HiItermannicytere sp., Pokornyella italica, Pokot77vella devians, Arutella saheliensis) that clearly indicate a shallow water environment. Moreover, abundance of Cyprideis with juvenile stages suggests episodes of brackish water influx.
Plate Fig. 1. Fig. 2. Fig. 3. Fig. 4. Fig. 5.
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4.2.2 Shelf-edge facies association During deposition of the three reefal units, the available accomodation space was considerably different according to different rates of relative sea level changes. Consequently, the shelf edge was colonized by a true coral reef only during deposition of unit I and II, whereas extremely shallow- water facies types characterize unit III, which was deposited during a very small relative sea-level rise. - Bivalve biocalcarenite This facies type constitutes the upper portion of the Novaglie Formation succession and, together with the stromatolitic facies and vermetid-microbial "trottoirs", characterizes mostly the third reef unit. It consists of bioturbated wackestone-packstone rich in fragments of bivalves, vermetids, benthic foraminifera and coralline algae, and its maximum thickness is on the order of 4 m (Leuca 1 and Leuca 2 sections, Fig. 3). The top of this facies is characterized by scattered accumulations of large bivalves and is, ill places, incised by erosion channels (probably tidal) infilled by a fining upward calcarenite, laminated in the upper part. - Stromatoliticfacies This facies crops out, with a maximum thickness of about 6 m, in the third unit and in particular in Leuca 1 and Leuca 2 sections (Fig. 3). It is basically characterized by irregularly laminated stromatolitic structures (1-2 cm to 1015 cm thick) (P1. 20/1) associated with some encrusting
Shelf-edge and slope facies associations (Novaglie Formation, lower Messinian, Salento Peninsula, Southern Italy). Porites boundstone. Massive colonies of Porites in growth position. Porites boundstone. Branching rod-like colony of Porites in growth position. Porites boundstone. Polygenic encrustations of coralline algae, encrusting foraminifera and thin micritic crusts on branching Porites. A boring of endolithic algae is also present. Bar scale: 1 mm. Porites boundstone. Lithophyllum pusmlatum Foslie encrusting Porites. Bar scale: 1 mm. Platy Porites facies. Platy colonies of Porites in growth position.
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- Vermetid-microbial "trottoirs"
Fig. 6. Interpreted environmental setting of the vermetid-microbial "trottoirs" along the margin of the Apulia Platform.
Fig. 7. Relative abundance of main components in the vermetidmicrobial "trottoirs".
colonies of Porites at the base and lumachella deposits (bivalves, gastropods, vermetids, serpulids, etc.). Stromatolitic laminae consist of alternating peloidal-micritic layers (submillimetric to 1.5 cm thick) and very thin bioclastic levels (P1.20/2). Polygenic encmstations made of alternations of sub-millimetric, discontinuous layers, mainly represented by encrusting foraminifera ( M i n i a c i n a sp., Nubecularia sp.) and crustose coralline algae, followed by encrusting bryozoans with some vermetids and serpulids, are also common. Vermetid-microbial "trottoirs", described below, are in places intercalated with this facies.
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The two erosion surfaces present at the top of unit I and unit II, and that characterize the base of both units II and III, are typically encrusted and colonized by relatively small vermetid bioconstructions that we call "trottoirs" according to the terminology adopted for similar examples of the present-day Mediterranean Sea (P6r~s and Picard, 1964). We refer to Bosellini et al. (2001) and Vescogni (2000) for a general overview of vermetid reefs and specific references. Size (width: 15-20 m; maximum measurable length: about 100 m; maximum thickness: about 70 cm) and shape of these bioconstructions are illustrated in Fig. 6. Their internal structure is characterized by a chaotic aggregation of vennetids and serpulids, binding organisms such as membraniporiform bryozoans and coralline algae and, most of all, by microbial crusts and micritic coatings (P1. 20/ 3,4,5). The relative abundance of these components is indicated by the diagrams of Fig. 7: vermetids (24%), serpulids (8%), bryozoans and coralline algae (7%), sediment, mainly represented by microbial and micritic crusts (61%). Vermetids of these structures are entirely represented by the genus Petaloconchus, with shells characterized by closely coiled early whorls and by terminal, unwound "feeding tubes" (1.5-2 cm long and about 1.6 mm large), and are commonly encrusted by serpulids, dominated by the genus Spirobranchus. Associated organisms are represented by small benthic foraminifera, echinoids, ostracods and rare gastropods. Millhnetric to sub-millimetric laminae of microbial crusts, mainly represented by peloidal and micritic aggregations, fill interskeletal spaces or bind directly vermetid and serpulid tubes thus playing a fundamental role in strengthening and "cementing" the entire structure. - Branched coralline algal facies
This facies, about 1 m thick, crops out in the upper part of the Lighthouse section, at the top of the Porites boundstone facies (Fig. 3). It consists of a wackestone-packstone rich in coralline algae. Other bioclasts are mainly represented by fragments of bivalves, benthic foraminifera, serpulids, echinoids, gastropods. Spongites is the dominant genus, characterized by small thickets (about 45 cm large, 30
Slope facies association and reef substrate facies (Novaglie Formation, lower Messinian, Salento Peninsula, Southern Italy).
Fig. 1. Fig. 2.
Halimeda packstones and biocalcarenites. Bioclastic packstone. Bar scale: 1 ram. Halimeda bioherms. Outcrop view showing chaotic aggregation of closely packed disarticulated seg-
Fig. 3.
Halimeda bioherms. Well-preserved Halimeda segments coated by isopachous marine cement. Bar scale: 1 ram.
Fig. 4. Fig. 5. Fig. 6.
Reel' substrate facies. Close-up of thin lenses showing small "thicket-like" vermetid aggregates. Reef substrate facies. Outcrop view of the "isooriented vermetid facies" Bar scale: 1 cm Reef substrate facies. Reworked barnacles associated with the "isooriented vermetid facies". Bar scale: 5 cm.
ments.
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cm high) and fan-shaped morphologies constituted by thin branches, usually 5-6 mm thick (rarely reaching 1.5 cm) (P1. 20/6). Together with coralline algae also some Porites colonies are present, showing a platy growth morphology with short vertical nodules on their npper surface, similar to those lk)und at the top of the reef slope (platy Porites facies). - Porites boundstone
This facies is represented in both unit I, with a thickness of about 30 m, and unit II, with a thickness of about 15 m (Fig. 3). Representative sections are for reef unit I: upper part of Ciolo section (P1. 18/3) and Lighthouse section, and for reef unit ll: Leuca I section: rocky hill near km 49.1 of the coastal road. The lower part of this facies is mainly represented by clinostratified and massive beds of wackestones and packstones. A dense growth of corals is observed, almost entirely represented by massive colonies of Porites (about 20-40 cm large) (Pl. 21/1 ), commonly bored by lithophagid bivalves, boring sponges and endolithic algae (PI. 2 I/3). Some columnar Porites morphotypes also occur, together with just a few colonies of Siderastrea. The density of the "framework", varying from 25 to 70%, has been estimated through the measurement of three transects of 10-15 m (Fig. 5b). Growth fabric consists of a quite dense domestone. Millimetric crusts of coralline algae followed by polygenic crusts are commonly developed on the upper surfaces of Porites colonies. Towards the upper part of this facies, massive Pm4tes are gradually replaced by columnar and rod-like Porites (colonies about 20-40 cm large and 30-50 cm high, diameter of sticks from 2.5 cm to 5 cm) (Pl. 21/2) that form a dense pillarstone. Polygenic encrustations, thicket with respect to those observed on massive colonies (about I cm), coralline algae, encrusting bryozoans and foraminifera (Miniacina sp., Nubecularia sp.) together with thin micritic crusts strongly bind Porites branches (PI. 21/3,4). This facies is also characterized by the association of corals with abundant coralline algae (crusts and rhodoliths) together with Halimeda, bryozoans, vermetids, serpulids, benthic foraminifera, ostracods, bivalves (including Lithophaga), gastropods and echinoids. The sediment consists of wackestone-packstone.
in places and especially towards the top, can form relatively dense sheetstones (sensu Insalaco, 1998). Platy Porites are defined according to Rosen et al. (in press) as thin, flat unifacial coral colonies, with broadly upward-facing calical surfaces, dominant orientation of plates more or less horizontal and lying parallel to bedding. Some may consist of complexes of plates (tiers). Platy Porites of the slope facies of the Novaglie Formation are about 20 cm large and 4-5 cm thick. These colonies may develop superstratal laminae, as documented by their undersides comlnonly colonized by cryptic encrusters (especially encrusting foraminifera such as miniacinids and haddonids), or rest directly on the substrate. Their upper surfaces are mainly encrusted by coralline algae, together with some foraminifera and serpulids, and show some vertical nodules or small columns (2-3 cm high) in the upper part of the facies. The associated fauna, generally similar to that of the Porites boundstone facies, is also characterized by the occurrence of more abundant Halimeda and some planktic foraminifera. Sediment is similar to that described for the following facies (Halimeda packstones and biocalcarenites), but quite fine sediment (wackestone) has been observed in some shelter cavities of the Porites sheetstones. In this facies, one colony o f Solenastrea desmouIinsi has been recognized. - Halimeda packstones and biocalcarenites
This facies association constitutes the largest part of the outcropping reef complex and is preserved for a total height of about 120-130 m. It is mainly represented in unit I and is characterized by clinostratified beds (P1. 18/4). Best outcrops include Ciolo section and Leuca 1 section (Fig. 3). Starting from the top of the slope, five distinct facies have been identified.
This facies constitutes an important part of the clinostratified deposits of the Novaglie Formation (Fig. 3). It consists of various kinds of bioclastic calcarenites (from fine-grained wackestone-packstone to coarse-grained packstone-grainstone), bioturbated in places, and often intercalated with Halimeda bioherms, breccias and megabreccias. Primary dips are generally about 20~ ~. Biotic grain types include benthic and planktic foraminifera, bivalves (whole shells and broken fragments), coralline algae and Halimeda plates, fi'agments of corals, echinoids, gastropods, bryozoans, vermetids, serpulids and ostracods (PI. 22/1). Nonskeletal carbonate grains include numerous peloids and intraclasts. Locally, several platy colonies of Porites in growth position and increasing upwards, have been observed. In some localities (Ciolo section), rhodolith-rich levels have been also found. These algal beds are 1-1.5 m thick and characterized by a great number of sparse rhodoliths (usually 5-6 cm in diameter) sometimes overgrown by discontinuous corallinc algal crusts, thus forming small algal pavements. The biocalcarenites of this facies are in places also associated with Halimeda-rich beds (up to 50 cm thick) that consist of graded layers of packstones with abundant reworked Halimeda plates, abraded, micritized and showing preferred orientation parallel to bedding.
- Platy Poritesfacies
- Halimeda bioherms
This facies is well developed in the base of the Leuca 1 section (Fig. 3), where it is exposed for about 60 m, along the prograding reef front. It is characterized by the occurrence of platy colonies of Porites in growth position (Pl. 21/5) that,
This facies is represented by massive, slightly lenticular structures (about 30 m long and 4-5 in thick) roughly placed at the base of the proximal slope (15~ ~ and smzounded by poorly stratified bioclastic calcarenites and breccias. One
4.2.3 Slope facies association
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of the best outcrops is located along the coastal road, 3 kin north of Cape S. Maria di Leuca (Leuca 1 section, Fig. 3). The core of these structures consists of a chaotic aggregation of closely packed disarticulated Halimeda segments, which constitute about 80-90% of the bioclastic component (Pl. 22/ 2). Halimeda segments are generally very well preserved and rarely broken, in places encrusted by bryozoans and coralline algae. Centimetric layers, where Halimeda segments show a subhorizontal orientation, ,are randomly distributed within the massive chaotic structure. The associated fauna is represented by benthic foraminifera, bivalves, bryozoans, echinoids, coralline algae, ostracods and rare vermetids. Halimeda segments, embedded in a dense micritie sediment (wackestone) with a few bioclasts and abundant peloids, are commonly coated by crusts of isopachous marine cement (PI. 22/'3). Shelter cavities and residual voids arc filled by sparry calcite. Sedimentary structures indicative of transport are poorly developed. - Breccias and megabreccias
This facies consists of clinostratified breccia and megabreccia layers and its maximum thickness can be observed in the Lighthouse and Ciolo sections (respectively about 20 m and 15 m). Megabreccia layers about 2-3 m thick are often intercalated with Halimeda packstones and biocalcarenites (Leuca 1 section), and lime mudstones. Clasts mainly consist of cemented shelf-margin blocks that can be larger than 1 m across and are rich in reworked colonies and fragments of Petites. Matrix is represented by bioclastic wackestonepackstone. Locally, several platy colonies of Porites in growth position have been observed. - Bioclastic limestones (with intercalated lime mudstones)
This facies crops out in the lower part of thc Ciolo section (Fig. 3) with an average thickness of about 5 m and can be interpreted as the distal and deeper part of the slope. It consists of fine grained bioclastic limestones (wackestone-mudstone) associated with several intercalations of pelagic lime mudstones (about 10-15 cm thick) rich in planktic and small benthic foraminifera associated with ostracods, small fragments of bivalves, echinoids, bryozoans and coralline algae. In places these lime mudstoncs appear as completely barren and can be intercalated with breccia and megabreccia layers. 4.2.4
Reefsubstrate facies
This facies typifies discontinuously the base o f the Novaglie Formation and lies unconformably on the ()ligocene Castro Limestone, its maximum thickness is about 2 m. Best outcrops occur at Marina di Novaglie and ahmg the roadcut from the harbour up to the coastal road (Novaglie section, Fig. 3), on the top of the plateau south of Marina Serra and along the coastal road south of the Ciolo cove (km 45 of the coastal road). Thin-lenticular banks (about 10 cm thick and 10 m hmg) mainly constituted of in situ growth of vermetids (Pl. 22/4), in places associated with barnacles, characterize the ,,'cry base of this facies. Vermetids are most probably totally.
represented by the only one gcnus Petalocopwhus but, with respect to the dense chaotic franmwork typical of the vermctid "lrotums" previously described, they form small, sparse "'thickel-like" aggregates (Pl. 22/4). Also growth morphology is different, with vcrmetid conchs shov,,ing a prevailing vertical growth and ver 3 long fcecling tubes (sometimes tip to 8 cm). Except some crusts and globousb anchln_ colollles el bryozoai/s, encrustin~ organisms such as serpulids and coralline algae, abundant in the "'trottoirs", are here cxtrcmely rare and mainly represented by some fragments. The sediment consists ofa fine mudstonc-wackestone rich in ostracods and planktic foraminifera. Towards the top, this facies is represented by clinostrati fled layers characterized by accumulations ofisooriented vennetids parallel to stratification (Pl. 22/5) and often associated with reworked barnacles (Pl. 22/6). Vermetids are mainly represented by intcrnal molds of long lizeding tubes (maximum length about 8 cm), whereas rests of coiled parts are relatively rare. Rare bryozoans crusts have been observed. Sedinlent and bioclasts arc similar to those of the underlaying thin vermetid banks. r
"
0
"
"
"
5 PALEOECOI~O(,Y OF REEF IIUILDIN(; ORGANISMS Rcef building organisms recognized in the early Messinian reef complex of the Salento Peninsula comprise a wide spectrum of taxa and growth fabrics in response to depth and to the various environmental factors that acted in different parts of the recf complex. Together with scleractinian corals, clearly dominated by thc genus Porites. other organisms, mainly represented by Halimeda, vermetids and coralline algae togethcr with rnicrobial crusts, contributed in different ways (primary and secondary reef builders) to the formation of the various types of bioconstructions that abundantly grew on both margin and slope of the Novaglic Formation recf complex. In the following paragraphs, the different rccf building organisms will be considered separately. Some general features as regards their paleoecology and their paleocnvironmental interpretation will bc underlined, also by con> parison with presenl-day analogues and with other studies carried out in coeval Mediterranean reef sites. 5.1 Corals The scleractinian genus Porites is the dominant reef builder of the early Messinian reef complex cropping out along tile southeastern coast of the Salento Peninsula. Porites reefs developed during deposition of units I and II and different types of growth fabrics and growth forms characterized back rccf, shelf-edge and slope facies associations. Zonation o f coral colonies according to their growth morpholog,v is illusu'ated in Fig. 8, together with main facies types developed during deposition of unit 1. Thcse features are in general very similar to those thal characterize many other Messinian reefs of the Mediterranean (Esteban, 1979, 1996: Pomar, 1991 ; Pomar et al., 1996) and the depositional
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model of Fig. 8 is very consistent with the "B"-type coral reefs of Esteban (1996). Platy colonies of PoHtes occur in the proximal slope facies of the Messinian Salento reef. Similar morphotypes have commonly been recognized in relative deep zones of both Recent and ancient reefs and recent studies (Insalaco, 1996; Bosellini, 1998; Rosen et al., in press) have suggested that they represent a photoadaptive response by photosymbiotic corals to reduced illumination in deeper and/or more turbid waters. Massive colonies of Porites colonized the deeper part of the Salento reef front, whereas its shallow seaward-facing portion is mainly characterized by branching Porites. Although, in general, branching Porites are deeper with respect to massive ones, the zonation pattern recognized in the Satento reef has been described for some other Messinian reef sites such as those of Spain, Almeria Province (Dabrio et al., 1981; Riding et al., 1991 ; Braga and Martin, 1996) and Fortuna Basin, (Santisteban, 198 I), Algeria (Saint Martin, 1990), Sicily and Pelagian Islands (Grasso and Pedley, 1989; Pedley, 1996b). Occurrence of branching Porites at very shallow depths has been explained as a last growth response to relatively rapid sea-level changes or to increasing cooler and high-nutrient levels, or as a morphological adaptation to withstand high levels of fine-grained elastic sedimentation. As regards the Salento reef, geological and sedimentological evidence indicates that the reel' was part of a carbonate platform (Apulia Platform) developed in a"clean" carbonate environment with no terrigenous influx. On the
base of these data and according to the depositional model of Fig. 8, we suggest that branching Porites, strongly reinforced by abundant crusts (coralline algae, encrusting foraminifera and micritic laminae), were most probably a growth response to relative fast sea-level rises. This hypothesis is also supported by the branched coralline algal facies abrubtly overlying the Petites boundstone facies (Lighthouse section). Most probably, the branched Porites framework was not able to keep up the growing sea level and has been replaced by delicate branching coralline algae and by platy Porites colonies, typical of deeper environments. 5.2 Vermetids
Vermetid "reefs" or "trottoirs" of the Salento Peninsula occur along the shallower seaward portion of the platform edge and their structure and shape, previously described, are generally similar to those of present-day examples (Fig. 6). In present-day marine environments, within the intertidal or shallow subtidal zone and under relatively high hydrodynamic conditions, vermetids are able to build up small bioconstructions in associations with coralline algae, serpulids and benthic foraminifera (P6r~s and Picard, 1964; Safriel, 1966, 1975; Hadfield et al., 1972; Ginsburg and Schroeder, 1973; Focke, 1977; Laborel, 1986; Jones and Hunter, 1995; Antonioli et al., 1998, 1999). We refer to Bosellini et al. (2001) and Vescogni (2000) for a general overview of vermetid reefs and for more specific references.
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Modern vermetid "reefs" mostly develop in subtropical conditions, close to tropical coral reels diffusion boundaries (with a minimum tolerable temperature of 14~ 16%, or in historically depauperate coral reef situations (i.e.. Bermuda, Cape Verde, Fernando de Noronha of Brasil, Mediterranean Sea) (Safriel, 1966, 1975; Hadfield et al., 1972: Jorles and Hunter, 1995), and within normal marine to slightly brackish salinity values (Shier, 1969; Wood, 1999). As regards ancient vennetid "reefs", these have been recorded mainly from the Miocene. Most occurrences refer to the Late Miocene of the Mediterranean (Montenat et al.. 1980; Grasso et al., 1982; Saint Martin, 1990: Saint Martin and Andrd, 1992; Pedley, 1996a,b; Pomar ct al., 1996: Keupp and Bellas, 2000) but have been poorly studied in detail. Only Pisera (1985) provided a careful palcoccological analysis of Middle Miocene (Badenian) algal-vermctid reefs of the Paratethys (Roztocze Hills, south-easlern Poland) and recognized, analogously to what observed in the Salento vermetid "reefs", the dominance of the genus Petaloconchus and the importance of coralline algae and bryozoans as secondary framebuilders. The analysis of specimens collected by D. Bosence from vennetid bioconslmctions at the top of Petites reefs in the Messinian of"La Molata", Cabo de Gata (Las Negras ), southern Spain (Bosence, pers. comm.), also underli ned some strong similarities with the vermetid "reefs" described in this paper. Both are placed at the top of Porites reel'.,; and consist of scattered patches, about 1 m thick at maxirnunl, developed along the shallow shelt'edge. The internal chaotic structure is very similar and biotic composition is clearly dominatcd by Petaloconchus (the only genus among vermetids) together with serpulids, bryozoans and coralline algae. These data, also compared with ecological features typical of present-day examples, provide some useful paleoecological indications as regards the Late Miocene of the Mediterranean. First of all, being restricted to the intertidal or shallow subtidal zone, fossil vermetid "trottoirs" can be used as reliable paleobathymetric indicators. Moreover, their pre ferential occurrence in the Messinian and in association with low-diversity coral reefs (paleotemperatures estimated by Rosen, 1999, as being below 18~ supports the climatic cooling broadly recognized for the Late Mioccnc. In the Messinian reef complex of the Salento Peninsula, vermetids occur not only within the "trottoirs" but also in different facies, as described for the reef substrate facies. Here they form thin lenticular banks where, most probably the same species of Petaloconchus that formed the "tmttoirs" (Schiapparelli pers. comm) developed a morphotype with much longer feeding tubes and prevailing vertical growth in response to different ecological conditions. Very similar structures, called "loose aggregates", have in fact described by Hughes (1979) as typical of protected or deeper environments and possibly associated with high sediment supply. Very interesting for its problematic paleoecologic and paleoenvironmental interpretation, is also the "isooriented vermetid" facies that characterizes the top of the reef
Fig. 9. Sequence of hypothetical stages leading to the formation of the "'isoorienled vermetid facies" (.d: depth ranging from 20 to 50 m). Explanation in the text. substratc facies. A similar facies has been described recently by Betzler et al. (2000) and interpreted as an in situ bioconstructed structure, where vermetids grow subhorizontally as a primary attitude at a depth below 20 mctres. The interpretation presented in this report is instead in favour of the resedimented nature of the isooriented vermetids accumulations. Observalions leading to this interpretation include: I) Vermetids usually need a considerable hydrodynamic energy (current. waves) For their nutrition and respiraticm and. in case of specimens living in low energy environments, they show vertical feeding tubes raising to the shell mouth away from accumulating sediment (Hughes, 1979). It is therefore difficult to explain their association with the fine mud in which they should horizontally live. 2) The rare individuals living "free" on muddy substrate are normally characterized by extremely irregular morphologies and smaller sizes (Savazzi. 1996).
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3) Fragments of feeding tubes arc extremely abundant with respect to the rare complete vermetid specimens. 4) The undersurfaces of feeding tubes, sometimes colonized by successive growths of vermetids, do not support an original horizontal mode of lifc within a muddy substrate. The problem, however, is to identify the provenance of both the vermetid shells and their fine matrix, which is totally different from the typical biocalcarenite of the Messinian slope. At this regard, it seems useful to point out other two typical characters of these deposits: 1) they are always placed at the base of the first unit, and lie directly on older lithologies; this implies necessarily that origin and deposition of this facies are associated with the initial phases of the first Messinian transgression; 2) locally, the thin lenticular vermelid banks (with upward oriented shells and matrix similar to the "isooriented facies") occur on the unconformity surface. These lenses are comparable with the loose aggregates previously mentioned and described by Hughes (1979). Summarizing the various data reported above, we suggest the following possible origin for the "isooriented vermetid facies" (Fig. 9). A first colonization by loose aggregates occur at a depth of about 20-50 m, at the beginning of the first Messinian transgression (Fig. 9a). This is also the paleodepth suggested by Baroncelli (2001) for a similar facies of Pliocene age found near Asti (northern Italy) and by Betzler et al. (2000) for the Late Miocene of Spain. With the growing sea-level, vermetids migrate upward to keep their depth compatible with their ecological demands being, in other words, a "time-transgressive facies" (Fig. 9b). Moreover, the thick shell aggregate traps the fine suspended mud, also preserving it from mechanical removal. Subsequently, due to overloading or other destabilizing processes (slumps, storm waves), the upward-oriented vermetid loose aggregates were disintegrated and, together with their fine matrix, redeposited downslope, locally burying older "in place" bioconstructions (Fig. 9c). The prevailing occurrence of feeding tubes in the isooriented accumulations should be related to their facility to be broken and gravity transported. One could argue that relatively few detrital carbonate grains occur in these peculiar isooriented vermetid bodies. It is possible to reply to this objection pointing out that the in situ upward growing vermetid reefs colonized an unconformity surface, a "polished" hardground practically devoid of any loose material: no sediment, except the vermctids, could be exported off-platform during this time. In spite of several problems still open, we believe this model is the hypothesis that better explains the various data and characters observed in outcrop.
"reef builder" (facies type: Halimeda bioherms) in the proximal slope subenvironment, forming scattered massive and slightly lenticular structures consisting of a chaotic aggregation of closely packed disarticulated segments. Modern analogs (Hine et al., 1988; Marshall and Davies, 1988; Roberts and Macintyre, 1988; Roberts et al., 1988), also referred in literature to as mounds, banks or bioherms, generally occur at depths of several tens-of-metres (commonly 20-50 m) and have been recently called "segment reefs" by Orme and Riding (1995) in order to point out their parautochthonous nature. The Halimeda bioherms of the Salento Peninsula are very similar to those known from some Messinian reefs of the Sorbas Basin in southeastern Spain and that represent, so far, the only other fossil example (Braga et al., 1996; Martin et al., 1997). Both characteristic of mid slope facies, they can be similarly interpreted as parautochthonous and early lithifled by marine cement encrustation together with, as regards bioherms of Spain, micritic and peloidal microbial crusts. According to modem examples, main factors controlling occurrence of Halimeda reefs include: light, sedimentation and nutrient supply (Martin et al., 1997). Moderate light intensity, generally corresponding to depths of 20-50 m, appears to favour Halimeda reef development. At shallower depths increased competition and higher hydrodynamic energy could most probably inhibit both rapid growth and synsedimentary lithification, whereas at greater depths reduced light levels become the most important limiting factor. Relatively pure carbonate settings, with reduced siliciclastic supply, may also favourHalimedareefdevelopmont. Nutrient supply related to upwelling of oceanic waters has been suggested to be a key factor controlling the luxuriant growth of both present day and fossil Halimeda reefs and accumulations (Mankievicz, 1988; Marshall and Davies, 1988; Phipps and Roberts, 1988). According to Martin and Braga (1994), also some typical features of Messinian reefs of the western Mediterannean, such the extensive development of microbial carbonates (stromatolites and thrombolites) and diatomite depositions in adjacent basins, may support the hypothesis that upwelling of nutrient-rich waters also favoured luxuriant Halimeda growth on the Messinian reef slopes. As regards the Halimeda bioherms of the Salento Peninsula, in support of the nutrient supply hypothesis we can not adduce the evidence of diatomitic deposits as no basinal facies are preserved and also micritic coatings and microbial sediments, although present, are not so much developed as in the western part of the Mediterranean.
5.3 Halimeda
5.4 Secondary reef builders
The codiacean alga Halimeda is an important biotic component of the Novaglie Formation reef complex, in particular during deposition of unit I when a consistent reef slope developed. In fact, although present in all facies associations, Halimeda was an important sediment producer (facies type: Halimeda packstones and biocalcarenites) and
Secondary reef builders associated with the coral framework are represented by encrusting organisms, coralline algae being the most frequent and abundant. Millimetric coralline algal crusts are often observed on corals in growth position or coating vermetids and serpulid tubes, or found as fragments in the matrix. Coralline algal
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crusts can be also considered as important components of the framework within some reef zones. In particular, in the upper part of the Petites boundstone facies they fornl warty protuberances (sensu Woelkerling et al., 1993) up to 1.5 cm thick, sometimes binding togettler adjacent coral sticks. In the Lighthouse section, about I in large areas of the coral l:ramework are almost entirely occupied by superimposed crusts that develop 2-3 cm thick warty, lumpy or ffuticose protuberances (sensu Woelkerling et al., 1993). Corailine algae crusts of the vermetids "trottoirs" are reduced in thickness with respect to those of the coral framework and show thin foliose and layered growth morphologies. Coralline algal also occur as rhodoliths in the reef slope (Halimeda packstones and biocalcarenites facies) showing adiscoidal-ellipsoidal shape with a colum nat structure (sensu Bosence, 1983), typical of medium to low energy environment. Rhodoliths associated with coralline algal crests sometimes form small, thin algal pavements (Ciolo section). The most common genera are Lithophylhun (the only genus recognized within vermetid "trottoirs") and Spong#es, with a lower amount of Lithothamnion and Sporolithon. Other im portan t secondary reef builders are re pre sen ted by the so-called micritic or microbial crusts that have been recognized in both vermetid and coral bioconstructions. As regard the coral framework, micritic crusts con> monly represent the last phase of a typical encrusting sequence (Perrin, 2000) that usually starts with an early millimetric coralline algal crust directly coating Petites colonies, often followed by alternations of sub-millimetric, discontinuous layers, mainly represented by encrusting foraminifera and finally by a micritic crust. Within vermctid "trottoirs", dense micritic coatings may be found also binding directly vermetid and serpulid tubes. The distribution of micritic crusts shows a preferential development in areas of shallow water and with a rclativclv high hydrodynamic energy (i.e., vermetid "trottoirs" and shallow reef front) where they played an important role in supporting and binding the framework. Bushy clotted and peloidal micrites fl'om Recent and fossil reefs have been commonly demonstrated or intreprctcd, although it is difficult to prove in ancient material, as due to microbial activity, either bacterial or cyanobacterial in ori.gin (Chafetz, 1986; Riding et a1.,1991; Reitner, 1993). The polygenic encrustations observed within the reef of the Salento Peninsula are similar to those described for other Miocene coral reefs of the Mediterranean region (Riding et al., 1991; Perrin, 2000) and it is suggested that deteriorating temperature conditions, maybe associated with an increase of nutrients, possibly provided "extra habitat" opportunities exploited by the microbial community and, among corals, only the tolerant genus Petites was able to Uow (Riding el al., 1991; Moissette and Saint Martin, 1992: Pedley and Grasso, 1994; Pedley, 1996b). Finally, other secondary reef builders of the Salento reef, although of minor importance, are represented by encrust i ng bryozoans, encrusting foraminifera such as miniacinids and haddonids, and serpulids.
6 CONC1,USIONS Our study of the lower Messinian fringing reef positioned along the Adriatic margin of the Apulia Platform (eastern coast of the Salcnto Peninsula) has led to the following conclusions: 1. Fourteen facies types belonging to three main facies associations (back reef and shel f, shel f-edge, slope) have been recognized. These facies document a wide spectrum of dcpositional environments, reel" building organisms and growth fabrics, in response to depth and other environmental factors in different paris of the reef c o n l plex. 2. Various types of organisms, including the coral genus Por#es, Halimedo, vermetids, coralline algae and microbial crusts arc iinportant reef contributors. Their reefs (Petites coral reefs, Italimeda bioherms and vermetid-microbial "'trottoirs") occur as discrete bioconstructions that differ in composition and structure according to their position on shell" edge-to-slol)c profile. 3. Facies types and the composition of the coral fauna, ahnost exclusively represented by the genus Porites, together with the occurrence of micritic crusts and abundance ol'ttalimedo in the slope facies, allow to include the reef complex of the Salcnto Peninsula within the typical early Messinian reefs of the Meditcrranean (B-type of Esteban. 1996). 4. According to Petites growth morphology, a depthrelated coral zonation tins been observed. Platy Petites characterize the proximal slope, massive colonies are typical of the reef wall, whereas branching colonies, that colonized the shallow reef front and back reef. are interpreted as a fasl growth response to relative sea-level rises. 5. Vermetids constitute a remarkable feature of the Salento reef. They lorn~ both scattered "trottoirs" along the shoreline (together with microbial crusts) and t h i n lenticular banks, the last ones associated, at major depths along the slope, with characteristic accumulations ofisooriented shells. Bricfly reported for other Late Miocene Mediterranean reefs, thcsc "reefs" are here described in detail and discussed in regard to their paleoecologic significance. Results indicate that "trotloirs'" can be used as reliable palcobathymetric and palcoclimatic tracers. 6. Halimeda bioherms, so far recorded only in the Sorbas Basin (Spain), characterize the Salento reef slope. This feature, recognized in two different dcpositional settings, suggests that the luxuriant growth of Halimeda during the Messinian was controlled by some ecological factors that affected an extensive area of the Mcditerranoah region.
ACKNOVr We thank Mateu Estehan and Werner Piller for their helpful reviews. Wc want to thank also D. Boscnce lor providing samples of veimetid bioconstructions from Niiar (Spain). Coralline algae have been classified by A.Vescogni during his stage ill Granada with help of J.C. Braga (grants A.
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Vescogni). This study has been supported by grants M U R S T (Colin 2000).
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