1,721,070 research outputs found
Effects of late pleistocene-holocene climatic changes on the planktonic foraminifera in the Gulf of Gaeta (Tyrrhenian sea, Italy).
No full textEffects of late pleistocene-holocene climatic changes on the planktonic foraminifera in the Gulf of Gaeta (Tyrrhenian sea, Italy).
No full textNew tools in Modern Analogue Techniques: the number of analogues
No full textFor estimating paleoenvironmental parameters from fossil assemblages starting from the knowledge of modern data sets, the Modern Analogue Techniques (MAT) is broadly applied. A key stone of MAT is the decision of the number of modern analogues to be used. Most studies have applied a threshold value based on a distance metric or a threshold value assessed from a Receiver Operating Characteristic (ROC) curve. In this work we introduce new tools for selecting the number of analogues. These tools must take into account when the modern data are a grouped or ungrouped data set. In both situations we propose to calculate numerical indices commonly used in multivariate scenarios: correlation matrix, STRESS, MSD, and misclassification rate. Since each modern data consists of percentages of different specimens all of these indices must be coherent with the compositional nature of the data. Therefore, recent advances of log-ratio analysis are properly incorporated to our study
Benthic foraminiferal assemblage turnover during intensification of the Northern Hemisphere glaciation in the Piacenzian Punta Piccola section (Southern Italy).
No full textWe present the results of a high-resolution analysis of the benthic foraminiferal assemblages at the Punta Piccola section (Stratotype for the Piacenzian Stage), which spans the gradual climate transition of the intensification of the Northern Hemisphere glaciation (3.6–2.6 Ma). This study highlighted a major benthic foraminiferal fauna turnover, which started at about 3.05 Ma with LO of Cibicidoides italicus, registered the gradual decline of Stilostomella spp. and culminated at about 2.7–2.75 Ma, when the dominant Siphonina reticulata was replaced by Cibicidoides pachyderma, costate Bulimine, spinose Bulimine, spinose Uvigerine and the Bolivina dilatata group. Four compositional zones, identified by constrained cluster analysis, are indicative of palaeoenvironmental changes and document the transition from stable and mainly oligotrophic conditions to unstable, mesotrophic and more fluctuating bottom conditions. Two intervals of deposition of sapropelite clusters coded as O and A, investigated using both benthic and planktic assemblages, reveal that anoxia conditions were never reached. Planktic foraminifera in the sapropelite layers of cluster O indicate deep mixing and benthic foraminifera suggest an increase in export productivity to the sea floor. By contrast, planktic foraminifera in the uppermost sapropelite layers of cluster A indicate oligotrophic surface water conditions, stratification and more eutrophic subsurface water conditions, without deep mixing. The benthic foraminifera indicate hypoxic and eutrophic bottom conditions, and evidence the first episode of down-slope transport, which testifies to a strengthening of runoff and stratification of superficial waters, but not true stagnation
Ricostruzione paleogeografia paleoambientale della città di Napoli: un'indagine geoarcheologica
No full textMediante un approccio integrato di analisi geologiche ed archeologiche viene ricostruita la successione stratigrafica e paleoambientale del bacino del porto antico di Neapolis, dal terzo secolo a.C. al quinto secolo d.C. La ricostruzione viene estesa all'area della costa napoletana fra Posillipo e la Piana del Sebeto mediante correlazione con dati di altri scavi e sondaggi ubicati lungo la fascia costiera della città proponendo la ricostruzione delle fasi di progradazione della costa con gli spostamenti della linea di riva nel corso degli ultimi due millenni
Carta Geologica d'Italia alla scala 1:50.000 -Foglio 450 Sant'Angelo dei Lombardi. ISPRA, Servizio Geologico d'Italia
No full textSize fraction effects on planktonic foraminifera assemblages: a compositional contribution to the golden sieve rush
No full textA comparative study of Last Glacial to Holocene planktonic foraminiferal
assemblages obtained from >150 to >106 μm size fractions of a Tyrrhenian sea core
was carried out by means of compositional data analysis methods. The results show a
major loss of small-sized species in the>150μmsize fraction, resulting in underdetection
limit values for several Holocene samples. Statistical tests, performed by means
of contrast and bootstrap, indicate that the assemblages obtained differ statistically.
Nevertheless, despite the drawbacks of the analysis based on the >150 μm fraction,
these differences do not imply, in the compositional data analysis approach, a significant
change in covariance structure. Under compositional data analysis, covariancebased
analysis should give similar results regardless of the size fraction adopted, while
distance-based ones may give partly different results. The >106 μm size fraction, in
which both large and small-sized species are sufficiently represented, is proposed for
adoption in future studies focussing on palaeoclimatic reconstruction
The Pliocene to lower Pleistocene succession of the Apricena-Lesina-Poggio Imperiale quarrying district (Western Gargano, S Italy)
No full textVegetation and climate changes during the OIS 9-8 from Compositional Data Analysis and Modern Analogues Technique of the high resolution pollen record of Acerno (southern Italy)
No full textThe Acerno lacustrine basin is a tectonic palaeolake formed during the Middle Pleistocene. Pollen analysis and tephrostratigraphy performed on the lacustrine succession (about 100 m thick) allowed the vegetation history to be reconstructed and correlated with OIS 9 and 8 on the basis of the presence of the Lower WTT (297 ka) marker level (Russo Ermolli, 2000; Munno et al., 2001). Compositional data analysis pointed out the vegetation dynamics during the different phases of the climatic cycle. Constrained cluster analysis (Grimm, 1987; Di Donato et al., 2008) allowed identification of four pollen zones corresponding to as many vegetation phases. Relative Variation Biplots (Aitchison and Greenacre, 2002) got insight on the compositional changes in the pollen assemblages and on the relationship among taxa. The main source of variability, accounting for 41% of total variance, relies on the opposition between arboreal and herbaceous taxa along the first axis of biplots. This means a relatively high standard deviation of corresponding logratios. A secondary source of variability is related to the opposition between Betula and Pinus. The first taxon characterising the phases of climate amelioration preceeding the interglacial conditions while Pinus closing the forest succession before entering the glacial period. The position within the biplots of samples corresponding to each of the four pollen zones, identified through CCA, pointed to the vegetation cover variation along the Acerno cycle. The MAT (Hutson, 1979) was applied to the Acerno pollen record by using a modern pollen database of 7664 spectra. The reconstructed temperatures pointed out a series of oscillations that can be correlated to the OIS 9 substages. Precipitation shows a drastic decrease towards the top of the sequence corresponding to the onset of the OIS 8 glacial period
CODAMAT: a Modern Analogue Technique for compositional data.
No full textThe quantitative estimation of Sea Surface Temperatures from fossils assemblages is a fundamental issue in palaeoclimatic and paleooceanographic investigations. The Modern Analogue Technique, a widely adopted method based on direct comparison of fossil assemblages with modern coretop samples, was revised with the aim of conforming it to compositional data analysis. The new CODAMAT method was developed by adopting the Aitchison metric as distance measure. Modern coretop datasets are characterised by a large amount of zeros. The zero replacement was carried out by adopting a Bayesian approach to the zero replacement, based on a posterior estimation of the parameter of the multinomial distribution. The number of modern analogues from which reconstructing the SST was determined by means of a multiple approach by considering the Proxies correlation matrix, Standardized Residual Sum of Squares and Mean Squared Distance. This new CODAMAT method was applied to the planktonic foraminiferal assemblages of a core recovered in the Tyrrhenian Sea
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