The Chiriguelo carbonatitic complex crops out in northeastern Paraguay at the central western fri... more The Chiriguelo carbonatitic complex crops out in northeastern Paraguay at the central western fringe of the stratoid volcanic rock-types of the Serra Geral Formation. At least three stages of emplacement of carbonatitic rocks can be distinguished: a C1 main savite, a C2 alvikite and a C3 ferrocarbonatite. A C4 stage may be inferred from the diffusion of late quartz, barite, and uranpyrochlore. The geologic, petrographic, and geochemical traits show environmental conditions similar to volcanic ones, and point to a vertical zonation in the fenitization processes versus a K-enrichment near the surl~tce. The C-O isotopic data suggest a loss of isotopically light water, along with a loss of St, following the hydrothermal recrystallization process(esl of the main s0vite. Such losses may be related to low-temperature (e.g. down to 25°C) weathering processes.
Bellanca, A., Calvo, J., Censi, P., Neri, R. and Pozo, M., 1992. Recognition of lake-level change... more Bellanca, A., Calvo, J., Censi, P., Neri, R. and Pozo, M., 1992. Recognition of lake-level changes in Miocene lacustrine units, Madrid Basin, Spain. Evidence from facies analysis, isotope geochemistry and clay mineralogy. Sediment. Geol., 76: 135-153.
. Oxygen isotope composition and rate of growth of Patella coerulea, Monodonta turbinata and M. a... more . Oxygen isotope composition and rate of growth of Patella coerulea, Monodonta turbinata and M. articulata shells from the western coast of Sicily. Palaeogeogr., Palaeoclimatol., Palaeoecol., 42: 305--311. The oxygen-isotope composition of carbonate from the outermost portions of Patella coerulea, Monodonta turbinata and M. articulata shells has been measured from April 1979 to July 1981, with an interval during the summer of 1980, and correlated with the ambient temperature. Carbonate from M. turbinata has yielded values that, on the whole, reproduce the environmental temperature range acceptably; P. coerulea and M. articulata ir, dicate precipitation taking place at temperatures lower than those measured in seawater; this is particularly accentuated in summer. This pattern does not necessarily exclude shell carbonate from precipitating under equilibrium conditions with seawater; rather it indicates a higher calcification rate in medium--warm periods for M. turbinata (with slower precipitation in winter), and in medium--cold periods for P. coerulea and M. articulata (with slow calcification, and even short interruptions during the warmest spells in summer).
Schifano, G. and Censi, P., 1986. Oxygen and carbon isotope composition, magnesium and strontium ... more Schifano, G. and Censi, P., 1986. Oxygen and carbon isotope composition, magnesium and strontium contents of calcite from a subtidal Patella coerulea shell. Chem. Geol. (Isot. Geosci. Sect.), 58: 325-331.
Potassic dyke swarm in the Sapucai Graben, eastern. Paragaay: petrographical, mineralogical and g... more Potassic dyke swarm in the Sapucai Graben, eastern. Paragaay: petrographical, mineralogical and geochemical outlines. In: A. Peccerillo and S. Foley (Editors), Potassic and Ultrapotassic Magmas and their Origin. Lithos, 28: 283-301.
garnet peridotite is favoured as a possible mantle source for the spread potassic magmatism and S... more garnet peridotite is favoured as a possible mantle source for the spread potassic magmatism and SGF tholeiites (Early Cretaceous); investigated rocks. The close association of potassic and sodic rock (2) Asunción sodic magmatism (Late Cretaceous-Oligocene). The suites in the ASU demands that their parental magmas derived potassic rocks form a compositional continuum from moderately to from a heterogeneous subcontinental mantle, variously enriched in strongly potassic. Two potassic suites are proposed, i.e. basanite to incompatible elements. Significant H 2 O, CO 2 and F are expected phonolite and alkali basalt to trachyte and their intrusive analogues. in the mantle source(s) for the occurrence of coeval carbonatites. The sodic rocks include ankaratrites, nephelinites and phonolites. Two similar but distinct parental magmas have been inferred for Any genetic hypothesis based on a 'mantle plume' system is constrained by strong lithospheric mantle characteristics. This does the potassic suites, both characterized by strongly fractionated REE * Corresponding author. Fax: 0039 40 569 823.
Explosive volcanic eruptions eject large volumes of high surface area, metal-rich dust and ash in... more Explosive volcanic eruptions eject large volumes of high surface area, metal-rich dust and ash into the atmosphere. In areas near major volcanic eruptions, humans often interact with these materials and may bioaccumulate heavy and toxic metals. To evaluate these interactions, we examine bronchoalveolar lavage samples (BAL) collected from people exposed to the paroxysmal 2001 Etna eruption. BAL samples reveal a strong enrichment of many toxic heavy metals and the capacity for trace elements released from inhaled particles to induce crystallisation of phosphatic microcryst biominerals in intraaveolar spaces. BAL rare earth element (REE) concentration patterns normalised to shale reveal a 'V-shaped' feature caused by the depletion of elements from Nd to Tb (mid-REEs) as compared to the variable enrichments of heavy lanthanides, Y, La and Ce. This pattern is consistent with P. Censi ( ) 1 2 P. Censi et al.
Rare earth elements (REE) were investigated in siliceous stromatolites forming in the Specchio di... more Rare earth elements (REE) were investigated in siliceous stromatolites forming in the Specchio di Venere Lake on Pantelleria Island. Chondrite-normalised patterns show significant La enrichments and Eu depletions suggesting that fluids involved in stromatolite growth experienced strong rock-water interactions under hydrothermal conditions. At the same time, enrichments in heavy REE (HREE) with respect to intermediate REE (MREE) suggest that hydrothermal fluids interacted with microbial mats during deposition of the stromatolites. The above-mentioned features suggest that rock-water interactions and bacterial activity were simultaneously recorded in the REE patterns of stromatolites, and can be discriminated in terms of amplitudes of the La anomaly, and the HREE/MREE ratio.
A sedimentary sequence spanning Marine Isotope Stage (MIS) 6 to MIS 2 in core LC07, recovered in ... more A sedimentary sequence spanning Marine Isotope Stage (MIS) 6 to MIS 2 in core LC07, recovered in the central Mediterranean, has been investigated in order to produce a highresolution paleoceanographic reconstruction. The changes in productivity deduced from calcareous plankton relative abundances and independently confirmed by the Ba XS fluctuations are linked to the stability of the water column which is mainly controlled by the water mass temperature. During glacial intervals, productivity was generally enhanced. Oligotrophic and warmer water masses with a deepened seasonal thermocline can be inferred for most of MIS5. The magnetic properties of the sediment show increased occurrences of North Africa dust in the central Mediterranean during cold phases, likely as a consequence of a more efficient erosive process triggered by southward displacement of the intertropical convergence zone. Although increases in both productivity and Saharan dust occurred during cold periods, the atmospheric inputs do not seem to contribute significantly to the fertilization of primary producers. A Shannon Index curve has been used to tentatively synthesize the variations of calcareous nannofossil assemblages through the last 150 kyr. The assemblage diversity sharply increased coincident with the transition from the penultimate glacial to the last interglacial, subsequently low diversity was gradually reached again in the last glacial.
Quantitative analysis of 67 calcareous nannofossil assemblages from surface sediments recovered i... more Quantitative analysis of 67 calcareous nannofossil assemblages from surface sediments recovered in a wide area across the Sicily Channel has been carried out in order to improve the interpretation of palaeontological data based on this planktonic group in a key area for Mediterranean palaeoceanographic studies. The investigation focused on three case studies that demonstrate the high potentiality of such a combined approach, taking into account the recent distribution of taxa or groups of taxa on the sea floor and the palaeontological record. The distribution of reworked specimens over the northern Sicily Channel sea floor validates the role of southern Sicily as a source region for reworked nannofossils and the role of rivers as their carrier. Eustatic sea-level fluctuations can be considered to be the main factor that influenced the abundance variations in sedimentary sequences of this area. The distribution of Florisphaera profunda can be explained in terms of topography (positive correlation) and mesoscale oceanographic circulation. In particular, its significant anti-correlation to the amount of chlorophyll-A deduced by satellite imagery validates the use of this species as a proxy for palaeoproductivity reconstructions. Finally, high abundance values of G. oceanica are confined to the westernmost part of the Sicily Channel, coinciding with a water mass salinity minimum. In particular, abundances of up to about 10% were observed in the westernmost part of the African Margin, suggesting the importance of the Atlantic Tunisian Current, whose activity is more pronounced in winter. The comparison of data of this species between 135 and 110 kyr BP, inside and outside the Channel, led us to deduce that the physical transport in almost unmodified waters of Atlantic origin might be the most important factor for its significant occurrence.
Geochemical characteristics were systematically determined for Early Cretaceous samples of carbon... more Geochemical characteristics were systematically determined for Early Cretaceous samples of carbonatitic rocks from Eastern Paraguay (Rio Apa, Amambay and Central Provinces). The data show that all the occurrences have an enriched isotopic signature and that the carbonatites have negligible or absent crustal signature. A petrogenetic model (parent liquids, fractional crystallization, hydrothermal interactions and weathering) is proposed as a function of incompatible trace element, stable (O-C) and radiogenic (Sr-Nd) isotope variations with the aim to test the significance of carbonatitic complexes as a marker of the metasomatized subcontinental lithospheric mantle. The results indicate that the carbonatites and primary carbonates from eastern Paraguay, and those from the north eastern Paran~ Basin (SE Brazil), were affected by metasomatic events distinct in time and composition. 238 F. Castorina et al. Zusammenfassung Karbonatite aus Ost-Paraguay und ihre genetische Beziehung zu Kalium-Magmatismus: C, O, Sr und Nd Isotope Die geochemischen Charakteristika von friihkretazischen Karbonatitproben aus Ostparaguay (Rio Alpa, Amambay und Zentrale Provinzen) wurden untersucht. Die Daten belegen, dal~ alle Vorkommen eine isotopische Anreicherungssignatur zeigen und dab ihnen eine entsprechende Krustensignatur fehlt. Ein Petrologisches Modell (Ausgangsschmelze, fraktionierte Kristallisation, hydrothermale Interaktion und Verwitterung) wird auf Grund der Verteilung der inkompatiblen Spurenelemente, der stabilen (C-O) und radiogenen (Sr-Nd) Isotope vorgeschlagen. Es versucht die Bedeutung der Karbonatitkomplexe als ,,Markerhorizonte" des metasomatischen subkontinentalen Mantels zu tiberpriifen. Die Ergebnisse zeigen, daf5 die Karbonatite und die prim[iren Karbonate in Ostparaguay, und jene aus dem Paran~i Becken SiJdost-Brasiliens dutch zeitlich und zusammensetzungsm~Big unterschiedliche metasomatische Prozesse erfaBt wurden.
The Early Cretaceous (138-130 Ma) carbonatites and associated alkaline rocks of Angola belong to ... more The Early Cretaceous (138-130 Ma) carbonatites and associated alkaline rocks of Angola belong to the Parand-Angola-Etendeka Province and occur as ring complexes and other central-type intrusions along northeast trending tectonic lineaments, parallel to the trend of coeval Namibian alkaline complexes. Most of the Angolan carbonatite-alkaline bodies are located along the apical part of the Mo~:amedes Arch, a structure representing the African counterpart of the Ponta Grossa Arch in southern Brazil, where several alkaline-carbonatite complexes were also emplaced in the Early Cretaceous. Geochemical and isotopic (C, O, Sr and Nd) characteristics determined for five carbonatitic occurrences indicate that: (1) the overall geochemical composition, including the O-C isotopes, is within the range of the Early and Late Cretaceous Brazilian occurrences from the Paran& Basin; (2) the La versus La/Yb relationships are consistent with the exsolution of C02-rich melts from trachyphonolitic magmas; and (3) the l"3Nd/l~Nd and 87Sr/SBSr initial ratios are similar to the initial isotopic ratios (129 Ma) of alkaline complexes in northwest Namibia. In contrast, the Lupongola carbonatites have a distinctly different 143Nd/~Nd initial ratio, suggesting a different source. The Angolan carbonatites have Sr-Nd isotopic compositions ranging from bulk earth to timeintegrated depleted sources. Since those from eastern Paraguay (at the western fringe of the Parand-Angola-Etendeka Province) and Brazil appear to be related to mantle-derived melts with time-integrated enriched or B.E. isotopic characteristics, it is concluded that the carbonatites of the Paran&-Angola-Etendeka Province have compositionally distinct mantle sources. Such mantle heterogeneity is attributed to 'metasomatic processes', which would have occurred at ca 0.6-0.7 Ga (Angola, northwest Namibia and Brazil) and ca 1.8 Ga (eastern Paraguay), as suggested by Nd-model ages.
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