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Rare earth elements in Oligo-Miocenic pelitic sediments from lagonegro basin, Southern Apennines, Italy: implication for provenance and source area weathering.
No full textThe Lagonegro Units are a part of the southern
Apennines orogenic wedge. The age of the Lagonegro
successions ranges from lower–middle Triassic to Oligo-
Miocene. During late Cretaceous and Oligocene the deposition
of calcareous-clastic sediments occurred interbedded
with shales (Flysch Rosso Fm). During Oligocene
and early Miocene, in the Mediterranean area, an
important variation of the tectonic regime occurred, and
siliciclastic sediments of the Numidian Basin unconformably
lay on the Meso-Cenozoic units of the Lagonegro
Basin. In the Lucanian Apennine, the Aquitanian–
Langhian Numidian Flysch Fm overlies the Flysch rosso
Fm. The shales of the Flysch rosso Fm have a peculiar
geochemical fingerprint relative to typical shales of post-
Archean age. The abundance of Ni and Cr is significantly
higher and the HREE chondrite-normalized patterns are
steep with a (Gd/Yb)ch>2. A supply of material from the
African Archean terranes could be the cause. The palaeoweathering
indices record changes at the source, reflecting
variations in the tectonic regime. The oldest samples are
derived from an environment in which steady-state weathering
conditions prevailed, whereas the youngest samples
are related to non-steady-state weathering conditions. This
difference could record deformational events that affected
the Mediterranean area during the Oligocene and early
Miocene. The sample at the top of the studied log has very
high silica content and an abundant coarse grain-sized
fraction. This suggests that this sample belongs to the
Numidian Flysch Fm. The geochemical proxies of this
sample are different from those associated with samples
from the Flysch rosso Fm, indicating that the source-area
of the Numidian Flysch Fm did not include the Archean
terranes
BOOK REVIEW: "Geochemistry", by Francis Albarède, 2003. Cambridge University Press, Shaftesbury Road, Cambridge CB2 2RU, United Kingdom
No full textPUBBLICATA SU:
JOURNAL OF SEDIMENTARY RESEARCH
AN INTERNATIONAL JOURNAL OF SEPM,
COLIN P. NORTH AND KITTY L. MILLIKEN, EDITORS
A.J. (TOM) VAN LOON AND LESLIE A. MELIM, ASSOCIATE EDITORS FOR BOOK REVIEWS
REVIEW ACCEPTED 12 OCTOBER 200
Geochemistry of shales from the southern Apennines (Italy): source-area weathering, sorting, provenance, and tectonic setting.
No full textThe southern Apennines orogenic wedge is a fold-and-thrust belt mainly derived from the deformation of the African-Apulian passive margin. Several wide belts have been recognised in the chain area including shallow-water, basinal and shelf-margin facies successions (middle Triassic-Miocene) and deep-water ophiolite-bearing successions (Jurassic-Miocene). In these successions the occurrence of fine-grained siliciclastic sediments is the rule and a thorough geochemical analysis, including lanthanides, actinides and transition metals is especially helpful as other signatures of source-area weathering, sorting, provenance and tectonic environment are not preserved. In the current paper the geochemistry of 164 shales is inspected to decipher the influence of the above cited factors on their composition.
Relative to the UCC, the shales are depleted in Si, Ca, Na, K, and LILE, enriched in transition elements and REEs, whereas HFSE contents are close to those of the UCC. Chondrite-normalised REE diagrams are PAAS- like.
The geochemical proxies point toward an upper continental source(s) affected by moderate, non-steady state, weathering. The weathering trends depart from micaceous-rich protoliths evolving toward illite and illite-smectite compositions. Volcaniclastic contribution and hydrothermal supply are not observed at all. In some cases an additional biogenic siliceous supply is observed. The sorting effect appears negligible.
The shales mainly record the tectonic setting of the source(s) and not those of the basins where deposition occurred. The source area, a former continental arc, can be envisaged in the Paleotethys suture zone, consistent with recent palinspastic restorations
REE and other trace elements in a granitic weathering profile from "Serre", southern Italy
No full textREE, V, Cr, Ni, Rb, Sr, Y, Zr and Nb behaviour in a granitic weathering profile in southern Italy is studied.
In the saprolites of the considered profile, depletion of V, Cr, Ni, Rb, Sr, Zr and Nb is observed. This is quite remarkable for Sr and Cr whereas REE and Y are enriched in the more altered portion of the profile and especially in its <2-mum fraction. Such enrichment is associated with the LREE-HREE fractionation and the positive Ce anomaly. The former results from an increased solubility of HREE in a non-acid environment as well as from the removal of the HREE-rich phases from the residual component. The latter is related to the redox chemistry of Ce which, as CeO2, is less soluble than the other REE. No analogy is observed between the behaviour of Ce and Fe, Mn and Cr. Saprolites also exhibit a negative Eu anomaly which is mostly inherited from the parental material.
Finally, the influence of accessory minerals in the REE distribution of weathering products and in sediments calls for a careful evaluation of preferential settling phenomena of heavy minerals during transportation and deposition processes. This is especially true in the parent material-sediment relationships
Trace elements distribution and mineralogical composition in the
No full textMineralogical composition and trace elements distribution in the < 2-mu m size fraction of Late Cretaceous-Oligocene shales from the southern Apennines (Italy) are presented.
The clay mineral assemblage consists of illite, smectite, kaolinite and minor chlorite. Analytical evidence points to a detrital micaceous precursor for illite and smectite. Accessory phases were also found. Chemical data, normalized with respect to the Post-Archean Australian Shales (PAAS), indicate depletion of Ba, Rb, Y, Zr and enrichment of Nb. PAAS-normalized REE-patterns exhibit a positive Eu anomaly and HREE depletion. A kaolinite-rich sample has high Sigma REE contents in contrast to smectite-rich fractions. A REE-pattern without appreciable Eu anomaly is displayed by the illite-rich sample.
Statistical data processing indicates a link between Ti, P, Y, Zr, Nb and Yb, suggesting that accessory phases may play a role in controlling HREE and that the observed LREE/HREE fractionation may also be due to hydraulic sorting of these phases. An important La-kaolinite relationship accounts for the capability of this phase to host LREE. Smectite and, thus, adsorption mechanisms, appear to exert a limited role in distributing REE. The Eu anomaly is a source inherited feature, probably not determined solely by clay minerals
Growth of hematite and boehmite in concretions from ancient karst bauxite: clue for past climate
No full textIn the Peri-Adriatic Apulia Carbonate Platform (southern ltaly), late Cretaceous karst bauxites
mark an emergence period during a wet tropical climate. Bauxite formed through clay accumulation
in the karst, ‘‘in situ’’ bauxitization and late formation of iron-rich concretions in a water-unsaturated
pedogenic environment. The concretions, which are geochemical recorders of the environment of
formation, have a large core of Al-hematite surrounded by a cortex of alternating Al-hematite and
boehmite. Boehmite forms instead of Al-hematite at lower water activity values. Using a model of
molecular diffusion and assuming the fluid flow negligible, the time necessary for growth of the
concretions has been calculated. The average-sized core grew in f180 ka. The Al-hematite
accretionary band grew in f8 ka whereas the boehmite accretionary band grew in f4.5 ka. The
average bulk concretions possibly formed in 300–400 ka. The growth of the concretions is assumed
to be a two-stage process. In the first stage, the core grew in a relatively long period of wet tropical
climate. In the second stage, drier conditions favouring boehmite stability alternated to a wetter
climate favouring Al-hematite stability. The growth of the bulk concretions is consistent with the
Earth’s long eccentricity cycle
Ce-anomaly in the textural component of Upper Cretaceous karst bauxites from the Apulian carbonate platform (southern Italy).
No full textThe chemical and mineralogical composition of Upper Cretaceous Apulian karat bauxites (southern Italy) and their textural components, i.e. ooids and matrix, has been studied. The bulk samples are composed of boehmite, hematite, anatase and kaolinite. The samples collected along a vertical profile show a downward enrichment for the elements Rb, Sr, Ba, Ni and Cr. A similar distribution is observed in deposits bauxitized in situ at the expense of matrix-like material collected in the karst zone.
The ooids consist mainly of hematite with minor boehmite and anatase, whereas in the matrix boehmite prevails on hematite, kaolinite and anatase. In the void fillings in the matrix there is a Ca-fluorocarbonate having a Ce/Ce* of 5.8. The ooids, with the exception of Ce, are enriched in REE and show a higher (La/Yb)(ch) ratio relative to the matrix. The matrix exhibits a large positive Ce-anomaly whereas the ooids have negative Ce-anomaly.
The Ce fractionation between the textural components can be explained assuming: (1) Ce oxidation and cerianite precipitation in the uppermost part of the deposits; (2) scavenging of REE from Ce-depleted percolating solutions by the iron oxide, inducing both REE-enrichment and Ce-negative anomalies in ooids; (3) remobilization of cerium as fluoride complex, as a consequence of more acidic conditions in the uppermost part of the deposit, and precipitation of Ce3+ as fluorocarbonate mineral toward the carbonate bedrock barrier, at alkaline pH. Alternatively, the cerium remobilization, possibly as a carbonate-fluoride complex, could be due to an Eh decrease, favoured by a rise of the groundwater level
Ferrouginous concretions in a Late Cretaceous karst bauxite: composition and conditions of formation
No full textThe karst bauxites from the Apulian carbonate platform southern Italy. have an ooidic texture. The concretions, which
are formed at the expense of the kaolinitic matrix, are composed of Al-hematite in the core and of Al-hematite and boehmite
in the banded cortex. The Al-hematite in the core has an average formula Al0.12Fe0.88.2O3 and the Al is within the range of
values observed in hematite formed through in situ epigenetic replacement of kaolinite. The Al substitution in hematite
involves a water-unsaturated environment, possibly promoted by fluctuations of the groundwater table followed by intense
drainage and evaporation. In the banded cortex, boehmite may form instead of Al-hematite at lower water activity values.
Further, the boehmite stability increases for high values of the a 3qra3
Al Hq ratio, which is mostly controlled by the pH of the
solution. The stability of the Al-hydroxide decreases with increasing pH
Hypothesis on the genesis of clay minerals in the fine fraction of "Argille Varicolori" from Andretta (southern Apennines)
No full textI depositi pelitici di età cretacico superiore-oligocene dell'Irpinia e della Lucania: nuovi dati di composizione mineralogica
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