1,721,066 research outputs found
Diversity, composition and structure of Late Eocene shelf-edge coral associations (Nago Limestone, Northern Italy)
No full textDuring 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 reef-builders, 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 species Actinacis rollei REUSS 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
Biotic changes and their control on Oligocene-Miocene reefs: A case study from the Apulia Platforrn margin (southern Italy)
No full textThe Oligocene-Miocene represents, for the Cenozoic, a period of extensive reef development and is characterized by a number of important changes influencing both carbonate-producing biota and architecture of reefs and carbonate platforms. The Mediterranean region, in particular, was characterized during this time by a complex palaeogeographic and climatic history with stepwise transition towards cooler conditions, biotic turnovers and the complete disappearance of zooxanthellate corals and reefs at the very end of the Miocene. A comparative study of two reef complexes that in different times (Chattian and Messinian) grew in the same physiographic and depositional setting, i.e. the stable, undeformed eastern margin of the Apulia Platform (eastern coast of the Salento Peninsula, southern Italy), highlights evolutionary, ecological and climatic changes that differentiate Oligocene and Late Miocene reef biota of the region. In particular, the study illustrates how different reef biotic assemblages can produce different reef types, frameworks and growth fabrics along reef tracts and reef slopes. The Chattian reef is characterized by a homogeneous reef-building biota, being largely dominated by a high diversity and abundant coral fauna associated with a moderate presence of coralline algae, and thus forming a single reef type. In contrast, the Messinian reef shows a very low coral diversity but several other reef-building components with abundant and varied secondary reef builders (coralline algae, Halimeda, encrusting foraminifera, bryozoans, serpulids and microbial associations). The reef, therefore, is characterized by a heterogeneous reef-building biota that forms different frameworks and growth fabrics. The feedback to the environment of this different biotic composition is very evident in the two reefs and especially in the slope. During the Chattian a slope, mainly consisting of gravity-displaced debris, resulted from the abundant production of reef rubble, associated with a relatively poor framebuilding capacity. Conversely, during the Messinian, a biologically stabilized slope resulted from proliferation of a variety of binding organisms that strongly colonized the substrate. The climatic cooling which occurred during the Miocene may be considered the main controlling factor of the diversity turnovers and changes that affected the coral fauna, but other environmental factors, such as changes in nutrient regimes and in hydrodynamic conditions of the sea associated with the emerging Apennine chain, may have played a role in determining differences in the reef biota and in the reef facies. (c) 2006 Elsevier B.V. All rights reserved
Oligocene corals from Monte Bastia (Vicentin Lessini Mountains, N.Italy)
No full textThis study describes and illustrates 20 species of Oligocene corals from a new excavation near the top of Monte Bastia, close to the town of Montecchio Maggiore (Vicenza). As described by Bosellini & Russo (1988), 3 different Oligocene coral communities can be recognized in the Lessini Shelf. The coral fauna here presented belongs to the high species diversity community, typical of the Late Rupelian, or at least to the top of the average species diversity communit
Coral facies and cyclicity in the Castelgomberto Limestone (Early Oligocene, Eastern Lessini Mountains, Northern Italy).
Full text linkThe Castelgomberto Limestone is a 200 m thick unit of Early Oligocene age (Rupelian) outcropping in the eastern Lessini Mountains (Southern Alps of Northern Italy). The internal cyclic organization of this Oligocene unit is described and analyzed on the basis of four selected sections; about 13 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 (20-50m), and tidal currents and periodic storms were able to distribute bioclastic sands. 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
The Oligocene Actinacis coral community of the Southern Alps (Italy): temperature vs. terrigenous control.
No full textExamination of the classic Oligocene coral reefs of the Vicentin (Southern Alps, Northern Italy), reveals a low specific diversity community dominated by Actinacis rollei Reuss. In the lower part of the Oligocene succession, above the Eocene-Oligocene boundary, A. rollei can be sporadically associated with few other species. Increasing species diversity occurs at the end of the Rupelian, where the succession is terminated. As a dramatic lowering of sea-water temperature is documented at the Eocene-Oligocene boundary, we interpret the Actinacis "explosion" in the Early Oligocene mainly as a hypothermic effect. The increasing coral species diversity during the Rupelian may then be a response to ameliorating sea-water temperature
REEFCORAL: an efficient tool for evaluating the taxonomic and palaeoecological evolution of z-coral communities in the Cenozoic Mediterranean realm
No full textCon lo scopo di valutare ed interpretare l’evoluzione delle comunità a coralli della regione mediterranea durante il Cenozoico, è stato recentemente messo a punto il REEFCORAL database. Attualmente il database contiene più di 3000 presenze di generi di coralli ottenuti da 285 località oligo-miocenichedi regioni circum-mediterranee (incluso l’attuale Bacino del Mediterraneo, la Paratetide, e alcune aree del Medio-Oriente ed europee affacciate sull’Atlantico). Attraverso i dati ottenuti dal database è stato possibile ricostruire le variazioni nella ricchezza dei generi per l’intera regione mediterranea durante l’Oligo-Miocene. Inoltre, applicando la relazione quantitativa che lega la ricchezza tassonomica dei coralli di scogliera attuali alla temperatura media annuale dell’acqua (evidenziata dalla cosiddetta “Energy Hypothesis”), i dati relativi a 102 località selezionate sono stati testati come strumento per la stima di paleotemperature
Estimating sea-surface palaeotemperatures from shallow-water carbonates: the example of Mediterranean Oligocene-Miocene corals.
No full textThe coral fauna of Vitigliano: qualitative and quantitative analysis in a back reef environment (Castro Limestone, Late Oligocene, Salento Peninsula, Southern Italy)
No full textThe Castro Limestone, Middle Chattian in age, consists of various reef facies and has been described as a fringing reef complex. The reef facies outcropping near Vitigliano and the associated coral fauna, which have been previously interpreted to be part of a back-reef subenvironment, are here defined both qualitatively and quantitatively. Three main quantitative methods have been used for the characterization of the back reef facies: 1) counts of coral colonies on a subvertical measured surface, 2) line-transects, 3) quadrats. The results obtained from the various quantitative methods are compared and discussed. Moreover the coral density has been quantified from both linear and areal measurements and has been evaluated to be around 20%. However, corals occur as scattered colonies and do not form a true framework
The Scleractinian genus Actinacis. Systematic revision and stratigraphic record of the Tertiary species with special regard to Italian occurrences.
Full text linkTwenty-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. A combination of several measured corallite morphologic characters and diagnostic features is proposed as a realiable tool for species recognition. 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; 2) the highest species diversity occrred 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
Organismi costruttori e ambiente di scogliera
No full textSi tratta di una introduzione alla paleoecologia dell'ambiente di scogliera con definizioni ed aspetti caratteristici delle scogliere coralline attuali, con una finestra sull scogliere del record geologico
- …
