THE SCLERACTINIAN GENUS ACTINACIS . SYSTEMATIC REVISION AND STRATIGRAPHIC RECORD OF THE TERTIARY SPECIES WITH SPECIAL REGARD TO ITALIAN OCCURRENCES

Twenty-seven Tertiary species belonging to the cosmopolitan reef-building scleractinian genus Actinacis, have been described in the literature. A detailed systematic revision has been  carried out for Italian and European species by thin section  measurements of material mostly sampled from several Italian localities by observation of some holotypes and topotypes and accurare examination of the available literature. A combination of several measured corallite morphologic characters and diagnostic features is proposed as a reliable tool for species recognition. Results indicate that only three species, of the twelve described for the Italian Tertiary sites, actually belong to the genus Actinacis. Moreover, a list of synonyms and a stratigraphic range chart of the established species are proposed. An approximate taxonomic identification and stratigraphic distribution are given for those species not included in the systematic revision. Preliminary examination of the stratigraphic and geographic distribution of Actinacis species suggests that:1) the Tertiary distribution of the genus ranges from the Late Paleocene to the Late Oligocene (from Late Cuisian to Middle Chattian as concerns ltaly); 2)the highest species diversity occurred during the Middle Eocene, when the genus consisted of a relatively large number of geographically restricted species; 3) only two widespread species survived the Eocene/Oligocene turnover and reached the Late Oligocene, when the genus became globally extinct

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.&nbsp

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

Impact of ocean acidification on crystallographic vital effect of the coral skeleton

Distinguishing between environmental and species-specific physiological signals, recorded in coral skeletons, is one of the fundamental challenges in their reliable use as (paleo)climate proxies. To date, characteristic biological bias in skeleton-recorded environmental signatures (vital effect) was shown in shifts in geochemical signatures. Herein, for the first time, we have assessed crystallographic parameters of bio-aragonite to study the response of the reefbuilding coral Stylophora pistillata to experimental seawater acidification (pH 8.2, 7.6 and 7.3). Skeletons formed under high pCO2 conditions show systematic crystallographic changes such as better constrained crystal orientation and anisotropic distortions of bio-aragonite lattice parameters due to increased amount of intracrystalline organic matrix and water content. These variations in crystallographic features that seem to reflect physiological adjustments of biomineralizing organisms to environmental change, are herein called crystallographic vital effect (CVE). CVE may register those changes in the biomineralization process that may not yet be perceived at the macromorphological skeletal level. https://doi.org/10.1038/s41467-019-10833-6 OPEN

Exceptional development of dissepimental coenosteum in the new Eocene scleractinian coral genus Nancygyra (Ypresian, Monte Postale, NE Italy)

In colonial corals, the polyps are interconnected with a common tissue called coenosarc. Polyps and coenosarc secrete distinct skeletal structures: corallites and coenosteum, respectively. Ratio of corallite to coenosteum development may vary resulting in two extreme architectural patterns of coral colonies: corallite-dominated (e.g., cerioid) and coenosteum-dominated (e.g., aphroid) colonies. A large suite of examples of these patterns can be identified among extant and fossil corals, including Paleozoic rugosan corals. Herein we describe the new early Eocene colonial scleractinian coral genus Nancygyra that forms exceptional coenosteum-dominated colonies. The colonies were found in Ypresian limestones at Monte Postale (Lessini Mountains, Veneto, NE Italy), very close to the Pesciara di Bolca Fossil-Lagerstätte, where coralgal buildups have been recently recognised and described. The corallum is massive and consists of corallites of variable size (typically few millimeters in lesser calicular diameter) dispersed and protruding from a very extensive and dense dissepimental coenosteum. The coenosteum forms ca. 60-80% of the corallum volume and is made of vesicular convex dissepiments. The new coral is tentatively assigned to Euphylliidae (known in the fossil record since the Paleocene) whose modern representatives develop similar extensive coenosteum with sticking-out corallites (Galaxea) and form coralla with well-developed walls and thickened axial margins of septa (Euphyllia). Among stratigraphically older scleractinian corals, similar extent of dissepimental coenosteum development is shown by some Mesozoic amphiastreids and rhipidogyriids

New paleoenvironmental insights on the Miocene condensed phosphatic layer of Salento (southern Italy) unlocked by the coral-mollusc fossil archive

From the Late Oligocene to the Late Miocene, the central Mediterranean area was characterized by the extensive deposition of phosphate-rich sediments. They are usually represented by 10 to 20-cm-thick hardgrounds made of phosphatic and glauconitic sediments containing a rich macrofossil association. This study represents the first thorough investigation of the biotic assemblage of Mediterranean phosphorites aimed at collecting new information on the environmental factors controlling their deposition. The Serravallian/Tortonian phosphatic deposits of the Salento Peninsula (“Aturia level”) have been selected for the abundance of fossil remains and special attention is given to the coral–mollusc association. Two different facies have been recognized: a basal coral rudstone that includes most of the macrofossils, superimposed by a detrital rudstone made of thin layers mainly composed of phosphatic fragments. These two facies are separated by a phosphatic crust several millimeters in thickness. The coral assemblage contains at least 17 azooxanthellate taxa belonging to four families, while the molluscs are represented by a rich gastropod fauna (26 species), associated with bivalves (18 species) and cephalopods (two species). Four distinct depositional phases have been recognized, with the coral rudstone representing the key-facies to reconstruct the onset of the “Aturia level” and the original environment of its fossil content. The composition of the coral–mollusc association has been reliably compared with present-day analog taxa, suggesting the occurrence of a heterogeneous seafloor formed by rocky substrates and accumulations of soft sediment, at around 100–350-m water depth, and under the influence of moderate-to-strong bottom currents rich in nutrients and resuspended organic matter

HIGH CORAL DIVERSITY IS COUPLED WITH REEF-BUILDING CAPACITY DURING THE LATE OLIGOCENE WARMING EVENT (CASTRO LIMESTONE, SALENTO PENINSULA, S ITALY)

The Oligocene, well known as the apex of Cenozoic reef growth, is a crucial period of time to investigate the mutual relationship between coral reef construction and coral diversity and their link with palaeoclimate and palaeoenvironmental changes. Here we provide a complete characterization of the Upper Oligocene reef complex of the Castro Limestone (Salento Peninsula, S Italy), which is one of the best-preserved Oligocene coral reefs of the Mediterranean region. By combining facies analysis with the first detailed characterization of its coral fauna, we show that the Castro Limestone has both a rich scleractinian coral fauna (25 genera and 41 species) and a large reef volume, and it represents a luxuriant fringing reef formed within the euphotic zone in clear water conditions facing the open sea. The coral fauna differs both in its composition and in its proportions among reef palaeoenvironments, ranging from the shallow back reef to the fore reef slope, and its stratigraphic and palaeogeographic distribution testifies to the persistence of a cosmopolitan Tethyan fauna in Oligocene time, with the Mediterranean and Indo-Pacific provinces being more closely connected than the Mediterranean and the Caribbean. The age of the Castro Limestone is here reassigned to the middle-late Chattian, which coincides with the Late Oligocene Warming Event (LOWE) when atmospheric CO2 values declined. We suggest that the strong reef-building capacity of the Castro Limestone, coupled with high coral diversity, was not hampered by warming conditions but most probably promoted by the reduced pCO2 and a suitable local/regional physiographic setting

High coral diversity is coupled with reef-building capacity during the Late Oligocene Warming Event (Castro Limestone, Salento Peninsula, S Italy)

The Oligocene, well known as the apex of Cenozoic reef growth, is a crucial period of time to investigate the mutual relationship between coral reef construction and coral diversity and their link with palaeoclimate and palaeoenvironmental changes. Here we provide a complete characterization of the upper Oligocene reef complex of the Castro Limestone (Salento Peninsula, S Italy), which is one of the best-preserved Oligocene coral reefs of the Mediterranean region. By combining facies analysis with the first detailed characterization of its coral fauna, we show that the Castro Limestone has both a rich scleractinian coral fauna (25 genera and 41 species) and a large reef volume, and it represents a luxuriant fringing reef formed within the euphotic zone in clear water conditions facing the open sea. The coral fauna differs both in its composition and in its proportions among reef palaeoenvironments, ranging from the shallow back reef to the fore reef slope, and its stratigraphic and palaeogeographic distribution testifies to the persistence of a cosmopolitan Tethyan fauna in Oligocene time, with the Mediterranean and Indo-Pacific provinces being more closely connected than the Mediterranean and the Caribbean. The age of the Castro Limestone is here reassigned to the middle-late Chattian, which coincides with the Late Oligocene Warming Event (LOWE) when atmospheric CO2 values declined. We suggest that the strong reef-building capacity of the Castro Limestone, coupled with high coral diversity, was not hampered by warming conditions but most probably promoted by the reduced pCO2 and a suitable local/regional physiographic setting

Revisiting reef models in the Oligocene of northern Italy (Venetian Southern Alps)

The lower Oligocene coral communities and reefs exposed in the Lessini Shelf of northern Italy may record one of the oldest well-developed barrier reef/lagoon systems of the Cenozoic. However, the rimmed-shelf interpretation has been repeatedly challenged in favour of a ramp model with scattered corals. Based upon a re-analysis of selected localities in the Lessini Shelf, we here provide support for the barrier reef model based on four key observations: 1) systematic changes of coral growth-forms from branching in the proximal areas to massive at the platform margin; 2) a progressive increase of the hydrodynamic energy from the proximal belt towards the more distal environments in the Berici Hills; 3) the occurrence of shallow-water, euphotic conditions throughout the whole depositional system; and 4) the presence of restricted circulation in the proximal environments during sea-level lowstands, with lack of coral colonies. These features, together with the evidence of coral frameworks located on the southeastern edge of the Lessini Shelf, substantiate the occurrence of a reef-rimmed margin. The reefal rim acted as an efficient barrier, with the formation of a landward, wide lagoon protected from the action of waves and currents