ANOMALIES OF RARE ELEMENTS IN MANGANESE MICRONODULES FROM ETHMODISCUS OOZES IN THE BRAZIL BASIN OF THE ATLANTIC OCEAN

The composition of manganese micronodules from miopelagic clays and Ethmodiscus oozes of the central part of the Brazil Basin (station 1537, R/V Akademik Sergei Vavilov) is considered. Micronodules were recovered from >50 μm fraction of sediments from the depth intervals of 300 to 305, 405 to 410 and 442 to 452 cm below seafloor. The composition of micronodules was determined in separate size fractions of 50–100, 100–250 and 250–500 μm after dissolution in 0.5N NH2OH × HCl + 25% CH3COOH. The contents of Co, Ni, Cu, Ce, Pb, W, Th, and Bi in micronodules of miopеlagic clays were found to be higher than in micronodules from Ethmodiscus oozes. In the latter, the positive anomalies of Li, As, Mo, Cd, Tl, and U were revealed. The REE composition of micronodules in miopelagic clays is similar to the composition of hydrogenous crusts with a maximum in middle REE and a positive cerium anomaly. Micronodules of Ethmodiscus oozes have a positive Ce anomaly 2.8–3.8 and a deficiency of light lanthanides, similar to the composition of dissolved REEs in pore and bottom ocean waters. High accumulation of redox-sensitive elements in micronodules (As, Mo, V, and Cd) indicates an anaerobic stage in the post-sedimentary period in Ethmodiscus ooze caused by high biological productivity of waters. The formation of micronodules began during the period when the reducing conditions changed to oxidizing ones. Elements with low mobility (As, Mo, V, and Cd) accumulated in sediments and pore water during the anaerobic stage were then sorbed on Mn oxyhydroxides during the oxidation stage.

Redox conditions in the Late Cretaceous Chalk Sea: the possible use of cerium anomalies as palaeoredox indicators in the Cenomanian and Turonian Chalk of England

The cerium anomalies preserved in the Chalk have been investigated as possible palaeoredox indicators of the Late Cretaceous Sea and its sediment. This has been based upon over a hundred new rare earth element analyses of selected samples and grain size fractions from the Chalk. Particular attention has been given to the methodology of differentiating between the cerium anomalies preserved in the bioclastic calcite and those in carbonate-fluorapatite preserved in the acetic acid insoluble residues of chalks. Variations in the cerium anomaly of different particle size fractions of uncemented chalks suggest that fractionation of rare earth elements between the Chalk’s seawater and the various organisms that contributed skeletal material to the bioclastic calcite of the Chalk may have occurred. Post-depositional processes of calcite cementation and late diagenetic sulphidisation have had no apparent effect on the cerium anomaly of the acetic acid insoluble residues. The cerium anomalies associated with the acetic acid insoluble residues from (1) an alternating sequence of chalks and marls from Ballard Cliff (Dorset, UK) typical of Milankovitch cyclicity show a marked diagenetic pattern, whereas those from (2) non-volcanic and volcanic marls display a pattern that is best explained by the variations in the availability of phosphorus and the timing of argillisation of volcanic glass during diagenesis. The general conclusion is drawn that the cerium anomalies preserved in the Chalk can provide an insight into the changing palaeoredox conditions in the Late Cretaceous Sea as well as in the pore fluids of its sediments.

Rare earth elements in some bottled waters of Serbia

Twenty-one bottled mineral and spring waters from Serbia were analyzed for 16 inorganic chemical parameters, including lanthanides and yttrium which belong to the group of so-called rare earth elements (REE). REE concentrations in the bottled water samples varied over a broad range, from 5.39 to 1585.82 ng/L. Total concentrations in the bottled water samples were calculated taking into account the classification of lanthanides into heavy (HREE) and light (LREE), with yttrium added to the HREE group. The LREE concentrations ranged from 3.62 to 1449.63 ng/L, while those of the HREE were from 0 to 136.19 ng/L. Distinct REE signatures were observed in waters that drained specific rocks. The REE patterns in groundwater from granitic and related rocks showed LREE and HREE enrichment, while groundwater with mafic rock influence exhibited slightly LREE enrichment. Several bottled water samples featured naturally-occurring carbon dioxide, whose solutional capacity contributed to the highest REE concentrations in the analyzed samples. High REE concentrations are also a result of sudden changes in oxidation-reduction conditions, which particularly affect La, Ce and Eu. Aquifers developed in granitic and related rocks (methamorphic and sedimentary rocks) constitute favorable environments for HREE in groundwater, corroborated by the occurrence of HREE in bottled water samples. The bottled water samples largely exhibited a negative cerium anomaly and nearly all the samples showed a positive europium anomaly.