Francesca R. Bosellini

STRATIGRAPHIC ARCHITECTURE OF THE SALENTO COAST FROM CAPO D'OTRANTO TO S.MARIA DI LEUCA (APULIA, SOUTHERN ITALY)

The Cretaceous to Quaternary succession of the Apulia Platform cropping out on the eastern coast of the Salento Peninsula shows a special stratigraphic architecture. Whereas on the platform top, i.e. on the Salento Peninsula proper, the succession is at most a few tens of metres thick and is punctuated by unconformities, on the margin and slope of the platform, along the present-day eastern coast of the peninsula, several carbonate systems are laterally disposed and grafted one upon the other. Three of these systems are clinostratified and include well developed reef tracts of Priabonian, early Chattian and early Messinian age. The geologic conclusion of our study is that, since the Late Cretaceous, the eastern coast of the Salento Peninsula grossly coincided with the margin of the Apulia Platform. This paleogeographic element acted as a foreland horst and registered important geodynamic events related to the growth of the adjacent Hellenide and Apennine thrust belts. During the last 60 m.y., the horst carapace was constantly near sea level and sediments were mainly accommodated and preserved on the deep margin and slope of the platform.

Messinian reef-building assemblages of the Salento Peninsula (southern Italy): palaeobathymetric and palaeoclimatic significance

Abstract This paper mainly addresses the description and interpretation of different reef-building assemblages recognised within an early Messinian reef complex recently discovered along the eastern margin of the Apulia Platform (Salento Peninsula, southern Italy). It is the first Late Miocene reef recorded for the ‘Adriatic region’ and its location partly changes boundaries of coral reef distribution during this time in the Mediterranean. The Messinian reef complex (Novaglie Formation) is interpreted as a succession of fringing reefs accommodated in palaeo-reentrances or palaeo-embayments of the original Messinian rocky shore and overlying discordantly the underlying Cretaceous to Oligocene units. It consists of a discontinuous reef tract and associated clinostratified fore-reef slope. Relatively precise dating of the reef complex has been achieved using benthic foraminifera and ostracods associations. Three main different reef-building assemblages have been recognised: (1) Halimeda bioherms (2) Porites reef and (3) vermetid–microbial ‘trottoirs’. Each assemblage is described in detail according to its architecture and structure (setting, shape, quantitative estimation of the framework density), biotic components (taxonomic composition and relative abundance of the reef-builders, growth form, associated fauna), and intra-reef sediment (texture and fabric). Palaeoecologic analysis, based on physical observation within the margin-slope of the reef complex and in comparison with present-day analogues and their ecological demands, indicates that distribution and vertical succession of the three different reef assemblages are strictly depth-related, suggesting an ecological replacement consequent on small relative sea-level changes (fourth order), closely comparable with those already indicated for the early Messinian. Special attention is given to the remarkable abundance of vermetids that, together with microbial crusts, formed scattered ‘trottoirs’ along the shoreline. Vermetid occurrences have been extensively cited in the literature for the Late Miocene of the Mediterranean but poorly studied in detail. Here, their palaeoecologic significance is emphasised, indicating that these organisms can be used as reliable palaeobathymetric and palaeoclimatic indicators. Regarding the Miocene of the Mediterranean, development of vermetid–microbial ‘reefs’, so far recorded for the Messinian, is preferentially associated with low-diversity coral reefs and is interpreted as being mainly controlled by climatic constraints.

The Messinian reef complex of the Salento Peninsula (southern Italy): Stratigraphy, facies and paleoenvironmental interpretation

SummaryAn 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 three 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 reef complex.The biotic structure of the reef is also described and discussed in detail. It consists of different types of reef building organisms and of their bioconstructions (mainlyPorites 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 ofHalimeda bioherms and of vermetid-microbial “trottoirs”, gives new insights for better understanding reef patterns and development of the reef belt during the Late Miocene in the Mediterranean.

Diversity, composition and structure of Late Eocene shelf-edge coral associations (Nago Limestone, Northern Italy)

SummaryDuring the Late Eocene, shelf-edge patch reefs developed on the western margin of the Lessini Shelf. The coral fauna, studied in the Nago Limestone type locality, is described and interpreted for the first time, and provides further data for better understanding of the generally poorly known Eocene reef communities.Facies analysis was carried out across the shallowing upward succession that characterizes the well exposed type-section of the Nago Limestone. Four distinct facies are identified and a detailed qualitative-quantitative investigation has been applied to the coral-bearing facies in particular, in order to describe and quantify the distribution and palaeoecological zonation of corals.By a comparison of sedimentological and palaeoecological data, it is possible to reconstruct a depositional model of the Nago Limestone at its type locality. In particular, the palaeoecological study clearly reveals that corals change with depth in taxonomic composition, in percentage and proportion within the framework and in growth form, allowing the definition of a relative depth coral zonation.Three coral associations are recognized from the base to the top of the shallowing upward sequence. These differ from each other in the relative abundance of main reefbuilders, in the growth form exhibited by corals in growth position and in the density of the reef framework. These variations are interpreted as responses to major environmental controls which prevailed during the deposition of the different facies (mainly light intensity and hydrodynamic energy).The coral speciesActinacis rolleiReuss is the most abundant and ubiquitous coral of the Nago Limestone. Its adaptation to low-light levels is described here for the first time, confirming the high plasticity of this important Paleogene reef-builder.The results of the present study are finally compared with data from other Middle-Late Eocene European reef sites and some common features are inferred.

Mediterranean Corals Through Time: From Miocene to Present

Stony corals, especially scleractinians, are a recurrent component of the benthic fauna of the Mediterranean basin and its Mesozoic-to-Cenozoic precursors. Both morphological and geochemical features of coral skeletons place these organisms among the most important natural paleoarchives of the Mediterranean geological history. The present day low diversity of the Mediterranean scleractinian fauna (25 genera and only 33 species) strikingly contrasts with its high diversity in the Early-Middle Miocene (over 80 genera and hundreds of species). The decline in coral richness has occurred since the late Middle Miocene onwards. This impoverishment trend was not linear, but abrupt in shallow-water environments during and immediately after the Late Miocene and more gradual since the Pliocene onwards. At the end of the Miocene, the Mediterranean coral fauna underwent a drastic modification that led to the disappearance of almost all zooxanthellate corals and the well-established shallow-water coral-reef province. However, the generic diversity of azooxanthellate and deep-water corals did not undergo significant modifications, that were instead much stronger at the end of the Pliocene and of the Pleistocene. Indeed, before the Calabrian stage, all remnant Indo-Pacific-like azooxanthellate genera disappeared and a clear NE Atlantic affinity was established, whereas at the Pleistocene – Holocene boundary, there was a clear reduction in psychrospheric deep-water taxa. The causes that led to the impoverishment of the Mediterranean coral fauna diversity are complex and not all fully understood. However, there is a clear link between the coral diversity decrease, the gradual northward shift outside the tropical belt of the Mediterranean region, and the major climate modifications on a global scale during the last 20 million years.

Rhodolith-rich lithofacies of the Porto Badisco Calcarenites(upper Chattian, Salento, southern Italy)

This study describes the rhodolith-rich lithofacies of the Porto Badisco Calcarenites, an upper Chattian rhodalgal/larger foraminiferaldominated unit exposed in the southern part of the Apulia Carbonate Platform (Salento Peninsula, Italy). The lensoid rhodolith-rich lithosome at the base of the studied section is made of rhodolith rudstone and floatstone which infill a channel-like depression inherited from the substrate. Changes in the texture of the rhodolith facies and in the inner structure of the rhodoliths reflect variations in submarine current velocity across the section of the channel. Inherited topography controlled both the locus and the mode of rhodolith accumulation. The rhodolith lithosome is bounded by a flat surface above which rhodoliths are notably absent and beds are tabular. This implies that rhodolith accumulation ended as soon as substrate topography was completely levelled off. The taxonomic composition of the red algal and larger foraminiferal assemblages suggests that the rhodolith-rich unit deposited in the oligophotic zone. The abundance of tropical genera among the coralline algae (Lithoporella and Sporolithon) and the high diversity of larger foraminiferal assemblages indicate that the deposition of the Porto Badisco Calcarenites took place in the warm waters of the tropical to subtropical zone

CORAL FACIES AND CYCLICITY IN THE CASTELGOMBERTO LIMESTONE (Early Oligocene, Eastern Lessini Mountains, Northern Italy)

The Castelgomberto Limestone is a 2OO m thick unit of Early Oligocene age (Rupelian) outcropping in the Eastern Lessini Mountains (Southern Alps of Northern ltaly). The internal cyclic organization of this Oligocene unit is described and analyzed on the basis of four selected sections; about thirteen well-bedded grainstone units alternate with marly horizons rich in corals. This peculiar cyclicity is here interpreted as a response to variations in platform hydrodynamics, i. e. to smaller eustatic fluctuations affecting the Lessini Shelf reef-lagoonal complex. During highstand periods, the shelf was open and relatively deep (20-50 m), and tidal currents and periodic storms were able to distribute bioclastic sands (bars, sand waves and spillovers). During lowstands the shelf was more protected by the occurrence of marginal reefs and was colonized by patches of poritid corals, mainly branching. Moreover, the largely exposed northern areas supplied fine detritus to the shelf itself.

Coralgal buildups associated with the Bolca Fossil-Lagerstätten: new evidence from the Ypresian of Monte Postale (NE Italy)

The Monte Postale and Pesciara di Bolca sites are well-known Eocene Fossil-Lagerstätten. The origin of these deposits has been previously related to a lagoon environment, protected from the open sea by a barrier formed by some kind of reef. However, no detailed description of a bioconstructed system has ever been reported in the area. This study provides the first detailed characterization of the upper Ypresian Monte Postale reef, made of in situ corals, calcareous algae, and encrusting foraminifera. Three main facies associations have been recognized: (1) a coralgal rim, roughly E/W oriented, (2) lagoon deposits in the south and (3) fore-reef sediments towards the north. The coralgal rim is represented by a wave-resistant framework made of heavily calcified organisms associated to Alveolina accumulations; the adaptation of most of these organisms to the euphotic zone promoted their growth in proximity to the sea level, allowing this structure to act as an effective barrier. In particular, during relative sea-level lowstands or highstands, the coralgal rim could have limited the water exchange between the lagoon and the open sea, reducing the oxygenation in the lagoon and allowing the formation of the Fossil-Lagerstätten. During relative sea-level transgressions, the water could have risen well above the margin, establishing normal oxygenation and hampering the fossils’ preservation. The Monte Postale succession represents one of the few examples of lower Eocene bioconstructions. The description of this biotic assemblage provides new data for the characterization of reef communities during a crucial climatic phase, near the end of the early Eocene climatic optimum global warming.

Microtaphofacies analysis of lower Oligocene turbid-water coral assemblages

ABSTRACT The presence, distribution, and preservation of coral-rich facies in the lower Oligocene Gornji Grad Beds of Slovenia are analyzed using a microtaphofacies approach. This method allows taphonomic signatures to be recognized in thin section along with the presence of coral specimens and growth forms within and between stratigraphic logs. Coral-dominated limestones within the Gornji Grad Beds are represented by rudstones in a packstone-wackestone matrix. The conditions are generally reconstructed as turbid water due to the prevalence of muddy carbonate matrix, which also leads to excellently preserved morphological features in thin section. These beds represent a reference area for the study of Paleogene corals, especially during the Oligocene, a key phase of reef development during the Cenozoic. This study also contributes to the characterization of fossil reefs in turbid-water environments. The evaluated coral fauna is dominated by delicate-branching Stylophora and Acropora, although thickly branching (Actinacis, Goniopora), phaceloid (Caulastrea), and massive forms (Alveopora, Astreopora, Antiguastrea) also occur. Assessed taphonomic signatures include fragmentation, abrasion, bioerosion, and encrustation. Three types of bioerosion traces are distinguished (Entobia, Gastrochoenolites, Trypanites). Encrustation incl udes both thin crusts and complex multi-taxon sequences dominated by coralline algae. Five microtaphofacies are distinguished based on variation of taphonomic signatures, taxonomic composition, and growth forms. Differences in microtaphofacies are interpreted with respect to turbidity, sediment accumulation, and water turbulence; both parautochthonous and allochthonous deposits are reconstructed. A depositional model based on the distribution of microtaphofacies in the studied sections shows a succession of coral communities with different colonization strategies reflecting generally high stress levels.

Are coral reefs victims of their own past success

Pleistocene sea-level change transformed staghorn corals into prolific reef builders that are sensitive to anthropogenic stressors. As one of the most prolific and widespread reef builders, the staghorn coral Acropora holds a disproportionately large role in how coral reefs will respond to accelerating anthropogenic change. We show that although Acropora has a diverse history extended over the past 50 million years, it was not a dominant reef builder until the onset of high-amplitude glacioeustatic sea-level fluctuations 1.8 million years ago. High growth rates and propagation by fragmentation have favored staghorn corals since this time. In contrast, staghorn corals are among the most vulnerable corals to anthropogenic stressors, with marked global loss of abundance worldwide. The continued decline in staghorn coral abundance and the mounting challenges from both local stress and climate change will limit the coral reefs’ ability to provide ecosystem services.