Trace elements (REE) and isotopes (O,C, Sr) to characterize the metasomatic fluid sources: evidence from the skarn deposit (Fe,W, Cu) of Traversella (Ivrea,Italy)

The skarn complex of Traversella was formed at the expense of various rock types (calcic hornfels, gneiss, dolomitic marble) occurring in the contact aureole of the dioritic intrusion of Traversella (30±5 Ma). Application of phase equilibria has fixed the temperature of the primary stage of skarn formation between 550° C to 625° C. Similar applications indicate a larger range of temperature (525° C to 300° C) for the secondary stage. The different types of skarn (primary stage) are enriched in REE relative to the corresponding precursor rock (T.R.=126 ppm (protolith) to 228 ppm (inner zone) for the skarn on gneisses; T.R.=14 ppm to 71 ppm for the skarn on calcic hornfelses; T.R.=12 ppm to 200 ppm for the skarn on dolomitic marbles), but all the inner zones of these different types of skarn show a similar REE distribution with a slight LREE fractionation and no Eu anomaly. It is inferred that the primary metasomatic fluid has a parallel REE pattern. The oxygen isotope composition of water in equilibrium with the early stage of skarn at T=600° C ranges from 8.3 per mil to 8.9 per mil. At the beginning of the first hydroxylation stage (secondary stage), the fluid σ ¹⁸O remains in the range observed in the primary stage but within it, there is a sharp decrease from 8.0 per mil to 5.0 per mil. During the sulphidation stage, the fluid σ ¹⁸O decreases more gradually from 5.0 per mil to 3.0 per mil. The I _Sr of the early skarn silicates ranges from the values observed in the dolomitic marbles (0.70874 to 0.70971) to the I _Sr of the intrusion (0.70947 to 0.71064). During the secondary stage, there is a progressive increase of the minerals I _Sr up to 0.71372. The REE pattern of the primary metasomatic fluid does not put any precise constraint on the primary fluid source. On the other hand, both stable and radiogenic isotopes suggest that the early high-temperature metasomatic fluid was isotopically equilibrated with the dioritic intrusion. This implies that this early fluid is either exsolved from the crystallizing intrusion or a metamorphic water previously equilibrated with the intrusion. During the secondary stage, the replacement of the early anhydrous phases by hydrated parageneses is accompanied by the mixing with meteoric fluid as indicated by stable (σ ¹⁸O) and radiogenic (⁸⁷Sr/⁸⁶Sr) isotopes.     

Chemical and isotopic (C, O, Sr, Nd) characteristics of the Xiluvo carbonatite (central-western Mozambique)

Summary The Xiluvo complex of central Mozambique is made up of coarse- to fine-grained calciocarbonatites (sövites and alvikites), heavily altered lamprophyres and syenitic rocks that intruded the Precambrian basement ca. 120Ma ago. The carbonatites have fractionated rare earth element patterns (chondrite-normalized La/Yb=30–80) and markedly negative Rb, K, P, Zr and Ti anomalies in mantle-normalized incompatible element diagrams. The ¹⁸O (+7 to +8), ¹³C (–5), and the age-corrected ⁸⁷Sr/⁸⁶Sr (0.7032–0.7033) and ¹⁴³Nd/¹⁴⁴Nd (0.51263–0.51262) indicate an origin in the mantle. A few carbonatitic samples have higher ¹⁸O (+13), indicating interaction with high-¹⁸O crust or late-stage fluids. The chemical and isotopic compositions of the Xiluvo carbonatites and nearby carbonatites of similar age in Malawi indicate very similar sources, characterized by time-integrated depletion of Rb with respect to Sr and of Sm with respect to Nd. These characteristics point to a source similar in many respects to those of other East African carbonatites and to those of some ocean island basalts, with the additional influx of components possibly located in the African lithospheric mantle.     

Differentiating tower karst (fenglin) and cockpit karst (fengcong) using DEM contour,slope, and centroid

The complex geometry of tropical karst landforms poses particular challenges for morphometric analysis, morphological classification and evolutionary assessment. Detailed geomorphological studies of the two most spectacular forms—tower karst (fenglin) and cockpit karst (fengcong)—have employed time consuming and labor intensive field surveys, which have yielded inconclusive and ambiguous results. This paper tests a novel discriminatory approach utilizing contour, slope and centroid derived from the ASTER Global Digital Elevation Model to differentiate between cockpit and tower karst in the Guilin area of southern China. Morphological indices are calculated to compare and contrast geomorphic variations using Object-Based Image Analysis (OBIA). The results suggest that the method provides a feasible means of differentiating between tower and cockpit landforms, and that OBIA offers a fast and semi-automatic way to extract morphological parameters.     

Vinciennite and Cu-excess tennantite from the Layo (Cu,Sn, As,Au) epithermal deposit (Southern Peru)

Summary The Layo epithermal deposit, cutting Miocene-Pliocene calc-alkaline volcanites of the Tacaza group, includes a well-developed eastern zone (Vetas 7 and 8) in which brecciated and banded textures are associated with a large, intensely argillized zone containing diaspore and alunite. The vetas contain a typical Cu-As mineralogy of the acid-sulfate type (pyrite, enargite, Cu-excess tennantite, chalcopyrite, covellite) with an associated original stanniferous paragenesis including vinciennite and mawsonite. The vinciennite is close to the ideal end-member (Cu₁₀Fe₄SnAsS₁₆) and the Cu-excess tennantite (Cu₁₁FeAs₄S₁₃) shows a total absence of Zn and Ag; its very specific chemical composition suggests that all the iron is Fe³⁺, equilibrated by Cu⁺ and probably minor Cu²⁺.This particular mineralogical association implies deposition at relatively low temperature (300°C) and high aS₂ (10^–6.5 decreasing to 10^–8.5), from a Cu-S-rich and Fe-Zn-poor fluid. The acid-sulfate epithermal mineralization of the eastern vetas of Layo appears to have preceded an adularia-sericite epithermal mineralization expressed in the western vetas of Layo and also in the nearby large epithermal veins at Orcopampa and Shila. It also supports the genetic relationship that is commonly evoked between porphyry copper and epithermal deposits.

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Le minéralogie originale à vinciente et tennantite riche du gisement épithermal (Cu, Sn, As, Au) de Layo (Sud Péru)

Résumé Le gîte épithermal de Layo est encaissé dans les volcanites calco-alcalines Miocène-Pliocène du groupe de Tacaza. Sa zone orientale renferme des corps minéralisés (Vetas 7 et 8) bien développés, à textures bréchiques et rubanées associées à une large zone intensément argilisée contenant diaspore et alunite.Les vetas présentent une association minéralogique à As-Cu typique des gisements acide-sulfate (pyrite, énargite, tennantite riche en cuivre, chalcopyrite, covellite) et une paragenèse stannifère originale renfermant vinciennite et mawsonite. La vinciennite est proche du pôle théorique (Cu₁₀Fe₄SnAsS₁₆) et la tennantite riche en Cu (Cu₁₁FeAs₄S₁₃) est dépourvue de Zn et de Ag; sa composition chimique suggère que tout le fer se présente sous la forme Fe³⁺, en équilibre avec Cu⁺, avec probablement une participation mineure de Cu²⁺.Cette association minéralogique particulière implique une mise en place sous forte fugacité en soufre (aS₂ = 10^–6.5 décroissant jusqu'à 10^–8.5) à une température relativement basse de l'ordre de 300°C à partir d'un fluide riche en Cu et S et pauvre en Fe et Zn. La minéralisation de type acide-sulfate des vetas orientales de Layo précéderait celles de type adulaire-sericite des vetas occidentales de Layo et des gisements voisins de Orcopampa et Shila. Elle contribue à renforcer le lien fréquemment évoqué entre les porphyres cuprifères et les gisements épithermaux.

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With 10 Figures     

Relationships Between Geochemical Parameters (pH, DOC, SPM, EDTA Concentrations) and Trace Metal (Cd, Co, Cu, Fe, Mn, Ni, Pb, Zn) Concentrations in River Waters of Texas (USA)

Water samples from eight major Texas rivers were collected at different times during 1997–1998 to determine the dissolved and particulate trace metal concentrations, expected to show differences in climate patterns, river discharge and other hydrochemical conditions, and human activities along the different rivers. Specifically, two eastern Texas rivers (Sabine, Neches) lie in a region with high vegetation, flat topography, and high rainfall rates, while four Central Texas rivers (Trinity, Brazos, Colorado, and San Antonio) flow through large population centers. Relatively high dissolved organic carbon (DOC) concentrations in the eastern Texas rivers and lower pH led to higher Fe and Mn concentrations in river waters. The rivers that flow through large population centers showed elevated trace metal (e.g., Cd, Pb, Zn) concentrations partly due to anthropogenically produced organic ligands such as ethylenediaminetetraacetic acid (EDTA) present in these rivers. Trace metal levels were reduced below dams/reservoirs along several Texas rivers. Statistical analysis revealed four major factors (suspended particulate matter [SPM], EDTA, pH, and DOC) that can explain most of the observed variability of trace metal concentrations in these rivers. SPM concentrations directly controlled particulate metal contents. Variation in pH correlated with changes of dissolved Co, Fe, Mn, and Ni, and particulate Mn concentrations, while DOC concentrations were significantly related to dissolved Fe concentrations. Most importantly, it was found that, more than pH, EDTA concentrations exerted a major control on dissolved concentrations of Cd and Zn, and, to a lesser extent, Cu, Ni, and Pb.     

Isotope geochemistry (S,C, O,Sr, Pb) of the Chaudfontaine mineralization (Belgium)

Investigations on S, C, O, Sr, and Pb isotopes in ores, gangue, and country rocks of the Chaudfontaine ore deposit confirm that interbedded barite and white sparry calcites are cogenetic. They emphasize the marine origin of S and the nonmarine origin of the metals. They underline the important role played by the bacterial reduction at the site of deposition. Hypotheses concerning the source of the metals and the nature of the brines involved in their transportation are briefly discussed.     

Structural and compositional characterization of synthetic (Ca,Sr)-tremolite and (Ca,Sr)-diopside solid solutions

Tremolite (Ca_xSr_1–x)₂Mg₅[Si₈O₂₂/(OH)₂] and diopside (Ca_xSr_1–x)Mg[Si₂O₆] solid solutions have been synthesized hydrothermally in equilibrium with a 1 molar (Ca,Sr)Cl₂ aqueous solution at 750°C and 200 MPa. The solid run products have been investigated by optical, electron scanning and high resolution transmission electron microscopy, electron microprobe, X-ray-powder diffraction and Fourier-transform infrared spectroscopy. The synthesized (Ca,Sr)-tremolites are up to 2000 µm long and 30 µm wide, the (Ca,Sr)-diopsides are up to 150 µm long and 20 µm wide. In most runs the tremolites and diopsides are well ordered and chain multiplicity faults are rare. Nearly pure Sr-tremolite (tr_0.02Sr-tr_0.98) and Sr-diopside (di_0.01Sr-di_0.99) have been synthesized. A continuous solid solution series, i.e. complete substitution of Sr²⁺ for Ca²⁺ on M₄-sites exists for (Ca,Sr)-tremolite. Total substitution of Sr²⁺ for Ca²⁺ on M₂-sites can be assumed for (Ca,Sr)-diopsides. For (Ca,Sr)-tremolites the lattice parameters a, b and β are linear functions of composition and increase with Sr-content whereas c is constant. For the diopside series all 4 lattice parameters are a linear function of composition; a, b, c increase and β decreases with rising Sr-content. The unit cell volume for tremolite increases 3.47% from 906.68 ų for tremolite to 938.21 ų for Sr-tremolite. For diopside the unit cell volume increases 4.87 % from 439.91 ų for diopside to 461.30 ų for Sr-diopside. The observed splitting of the OH stretching band in tremolite is caused by different configurations of the next nearest neighbors (multi mode behavior). Resolved single bands can be attributed to the following configurations on the M₄-sites: SrSr, SrCa, CaCa and CaMg. The peak positions of these 4 absorption bands are a linear function of composition. They are shifted to lower wavenumbers with increasing Sr-content. No absorption band due to the SrMg configuration on the M₄-site is observed. This indicates a very low or negligible cummingtonite component in Sr-rich tremolites, which is also supported by electron microprobe analysis.     

Anomiid (bivalve) bioerosion on Pleistocene pectinid (bivalve) shells,Rhodes, Greece

A trace fossil, Centrichnus eccentricus, was found beneath a saddle oyster (Anomia ephippium) that was preserved undisturbed on its substratum (a shell of Pecten jacobaeus), at the site of attachment of the calcified byssus.     

Phyllosilicates (glauconite, illite, and chlorite) in terrigenous sediments of the Arymas Formation (Olenek High)

It is shown that globular phyllosilicates subjected to deep categenesis are abundant in Middle Riphean sandstones and siltstones (lower subformation of the Arymas Formation) of the Olenek High. Their detailed structural-crystallochemical characteristics are given. Secondary alterations of globules and the associated pelletal minerals at different stages of lithogenesis (illitization, chloritization, ferrugination, disintegration, and so on) are considered. Structural-crystallochemical characteristics of Fe-illite and Fe²⁺-Mg-chlorite in globules, pellets, separate clayey strata among glauconite-bearing sandstones and siltstones (hereafter, sandy-silty rocks), and mudstone interlayers are also presented. Possible mechanisms of the formation of these minerals are discussed.     

Early Devonian volcanics of southeastern Gorny Altai: Geochemistry,isotope (Sr,Nd, and O) composition,and petrogenesis (Aksai complex)

Geological, geochemical, and isotope (Sr, Nd, and O) parameters of Early Devonian (405 Ma) volcanics of southeastern Gorny Altai (Aksai and Kalguty volcanotectonic structures) are discussed. The studied igneous rock association comprises magnesian andesitoids, Nb-enriched andesite basalts, and A-type peraluminous silicic rocks (dacites, rhyolites, granites, and leucogranites). Magnesian andesitoids (mg# > 50) are characterized by a predominance of Na among alkalies (K₂O/Na₂O ≈ 0.1-0.7), medium contents of TiO₂ (~ 0.8-1.3 wt.%) and Al₂O₃ (~ 12-15 wt.%), enrichment in Cr (up to 216 ppm), and low Sr/Y ratios (4-15). The Nb-enriched (Nb = 10-17 ppm) andesite basalts have high contents of TiO₂ (1.7-2.7 wt.%) and P₂O₅ (0.4-1.4 wt.%). The A-type granitoids are characterized by high contents of K(K₂O/Na₂O ≤ 60) and alumina (ASI ≤ 2.9) and depletion in Ba, Sr, P, and Ti. The magnesian andesitoids and Nb-enriched andesite basalts are products of melts generated in the metasomatized lithospheric mantle; silicic magmas were formed through the melting of Cambrian-Ordovician metaturbidites of the Gorny Altai Group and, partly, Early-Middle Cambrian island-arc metabasites. The above rock association might have resulted from a plume impact on the lithospheric substrates of the continental paleomargin during the evolution of the Altai-Sayan rift system.     

Kimmeridgian (Late Jurassic) ostracods from Highway A16 (NW Switzerland): taxonomy, stratigraphy, ecology, and biogeography

Ostracods are a common microfaunal element of the Kimmeridgian of the Jura Mountains in NW Switzerland. The stratigraphical subdivision within the Kimmeridgian can as clearly be inferred from ostracods as it is the case from the ammonite biozonation. This proves the utiliy of the ostracod biozonation, especially where ammonites are not available or rare. The ostracod-bearing layers of the sequence under study (middle part of the Reuchenette Formation = Banné Member, Courtedoux Member and Lower Virgula Marls) have been deposited in waters with highly brackish to marine salinities (high in the pliohaline range to—predominanttly—brachyhaline according to the Venice System, Oertli 1964). From the base of the section (base of the Banné Member, high brachyhaline in average), salinities slowly decreased, with lowest salinities in the lower dinosaur track levels of Courtedoux Member (high pliohaline on average). They then increased again to higher salinities (high brachyhaline on average) above the upper dinosaur track levels of the Courtedoux Member and the Lower Virgula Marls (lowermost A. eudoxus Zone). These trends perfectly correlate with the increased occurence of ammonites above the upper dinosaur track levels. In terms of Kimmeridgian ostracod palaeobiogeography, the fauna of the NW Swiss Jura Mountains described in this work is most similar to the Aquitan and Paris Basins, a little less to Northern Germany, and even less (with not even half of the species in common) to Southern Germany. The NW Swiss Jura Mountains still belong to a largely boreally influenced “Western and Central European subprovince”, whereas Southern Germany (though located more to the north) was subjected to an enhanced tethyan influence.     

西藏阿里门士的真马化石

描述了2009年采自西藏阿里地区门士乡附近的2件真马化石,标本包括1件完整的右前第2指节骨和1件左第3蹠骨近端,均采自门士河右岸河湖相砂砾岩堆积中.标本粗壮,第3蹠骨近端关节面圆隆、对各跗骨关节面宽大,第2指节骨横宽.大小形态上与邻近的札达盆地上新世地层中的札达近三趾马Hipparion(Plesiohipparion...     

Fossil-Winged Fruits of Fraxinus(Oleaceae) and Liriodendron(Magnoliaceae) from the Duho Formation,Pohang Basin,Korea

Abstract: A total of 16 specimens of fossil-winged fruits were found from the Middle Miocene marine deposits, Duho Formation, Pohang Basin, Korea. They were identified into two structurally different groups: 15 specimens into a winged fruit of Fraxinus, and one specimen of Liriodendron. The most samaras (13 specimens) were identified as Fraxinus oishii, which is characterized by narrowly ovate or ovate–elliptic shapes that are 2.7–3.6 cm in length and 0.7–1 cm in width (l/w ratio=3.4–4). The apexes of the Fraxinus oishii samara are round or slightly emarginated, and a seed of the samara is always located at the base, of which the general shape is narrow rhombic-ellipsoidal. The seed is 1.2–2 cm long and 0.5–0.7 cm wide. Two specimens are different from the samara of Fraxinus oishii. They have a 6.6 length/width ratio (3.3 cm long and 0.5 cm wide), and thus, are temporarily classified into the Fraxinus sp. One specimen was recognized as a winged seed of Liriodendron meisenense. The wing is broadly lanceolate to elliptic in shape, has a smooth, acute apex, and is approximately 3 cm long and 0.7 cm wide. Samaras of Fraxinus oishii and Liriodendron meisenense were early reported from the Middle Miocene deposits from North Korea, but these specimens are the first discovery in South Korea. Further study of the Duho Formation may connect flora relationships between North and South Korea.     

Hydrochemistry of groundwater (GW) and surface water (SW) for assessment of fluoride in Chinnaeru river basin,Nalgonda district, (AP) India

Hydrochemical studies were conducted in Chinnaeru river basin of Nalgonda district, Andhra Pradesh, India, to explore the causes of high fluorides in groundwater and surface water causing a widespread incidence of fluorosis in local population. The concentration of fluoride in groundwater ranges from 0.4 to 2.9 and 0.6 to 3.6 mg/l, stream water ranges from 0.9 to 3.5 and 1.4 to 3.2 mg/l, tank water ranges from 0.4 to 2.8 and 0.9 to 2.3 mg/l, for pre- and post-monsoon periods, respectively. The modified Piper diagram reflects that the water belongs to Ca²⁺–Mg²⁺–HCO₃ ^? to Na⁺–HCO₃ ^? facies. Negative chloroalkali indices in both the seasons prove that ion exchange between Na⁺ and K⁺ in aquatic solution took place with Ca²⁺ and Mg²⁺ of host rock. The interpretation of plots for different major ions and molar ratios suggest that weathering of silicate rocks and water–rock interaction is responsible for major ion chemistry of groundwater/surface water. High fluoride content in groundwater was attributed to continuous water–rock interaction during the process of percolation with fluorite bearing country rocks under arid, low precipitation, and high evaporation conditions. The low calcium content in rocks and soils, and the presence of high levels of sodium bicarbonate are important factors favouring high levels of fluoride in waters. The basement rocks provide abundant mineral sources of fluoride in the form of amphibole, biotite, fluorite, mica and apatite.     

Effect of phosphate, silicate, and Ca on the morphology, structure and elemental composition of Fe(III)-precipitates formed in aerated Fe(II) and As(III) containing water

We investigated Fe(III)-precipitates formed from Fe(II) oxidation in water at pH 7 as a function of dissolved Fe(II), As(III), phosphate, and silicate in the absence and presence of Ca. We used transmission electron microscopy (TEM), including selected area electron diffraction (SAED) and energy dispersive X-ray spectroscopy (EDX) to characterize the morphology, structure and elemental composition of the precipitates. Results from our companion X-ray absorption spectroscopy (XAS) study suggested that the oxidation of Fe(II) leads to the sequential formation of distinct polymeric units in the following order: Fe(III)-phosphate oligomers in the presence of phosphate, silicate-rich hydrous ferric oxide (HFO-Si) at high Si/Fe (>0.5) or 2-line ferrihydrite (2L-Fh) at lower Si/Fe (∼0.1-0.5), and lepidocrocite (Lp) in the absence of phosphate at low Si/Fe (<0.1). Results from this study show that the size of the polymeric units increased along the same sequence and that the aggregation of these polymeric units resulted in spherical particles with characteristic surface textures changing from smooth to coarse. The diameter of the spherical particles increased from 15 to 380 nm as the molar ratio (P + Si + As)/Fe(II) in the starting solution decreased and larger spherical particles precipitated from Ca-containing than from Ca-free solutions. These trends suggested that the size of the spherical particles was controlled by the charge of the polymeric units. Spherical particles coagulated into flocs whose size was larger in the presence than in the absence of Ca. Further observations pointed to the importance of Fe(II) oxidation and polymerization versus polymer aggregation and floc formation kinetics in controlling the spatial arrangement of the different polymeric units within Fe(III)-precipitates. The resulting structural and compositional heterogeneity of short-range-ordered Fe(III)-precipitates likely affects their colloidal stability and their chemical reactivity and needs to be considered when addressing the fate of co-transformed trace elements such as arsenic.     

Proterozoic (pre-Ediacaran) glaciation and the high obliquity,low-latitude ice,strong seasonality (HOLIST) hypothesis: Principles and tests

Sedimentological observations and palaeomagnetic data for Cryogenian glacial deposits present the climatic paradox of grounded glaciers and in situ cold climate near sea-level, glaciomarine deposition, and accompanying large (up to 40 °C) seasonal changes of temperature, all in low to near-equatorial (< 10°) palaeolatitudes (equated with geographic latitudes). Neither the “snowball Earth” nor the “slushball Earth” hypothesis can account for such strong seasonality near the palaeoequator, which together with findings from sedimentology, chemostratigraphy, biogeochemistry, micropalaeontology, geochronology and climate modelling argue against those scenarios. An alternative explanation of glaciation and strong seasonality in low palaeolatitudes is offered by a high (> 54°) obliquity of the ecliptic, which would render the equator cooler than the poles, on average, and amplify global seasonality. A high obliquity per se would not have been a primary trigger for glaciation, but would have strongly influenced the latitudinal distribution of glaciers. The principle of low-latitude glaciation on a terrestrial planet with high obliquity is validated by theoretical studies and observations of Mars. A high obliquity for the early Earth is a likely outcome of a single giant impact at 4.5 Ga, the widely favoured mechanism for lunar origin. This implies that a high obliquity could have prevailed during most of the Precambrian, controlling the low palaeolatitude of glaciations in the early and late Palaeoproterozoic and Cryogenian. It is postulated that the obliquity changed to < 54° between the termination of the last Cryogenian low-palaeolatitude glaciation at ≤ 635 Ma and the initiation of Late Ordovician–Early Silurian circum-polar glaciation at 445 Ma.The High Obliquity, Low-latitude Ice, STrong seasonality (HOLIST) hypothesis for pre-Ediacaran glaciation emerges favourably from numerous glacial and non-glacial tests. The hypothesis is in accord with such established or implied features of Cryogenian glaciogenic successions as extensive and long-lived open seas, an active hydrological cycle, aridity and palaeowesterly (reversed zonal) winds in low palaeolatitudes, and the apparent diachronism or non-correlation of some low-palaeolatitude glaciations. A pre-Ediacaran high obliquity also offers a viable solution of the faint young Sun paradox of a warm Archaean Earth. Furthermore, reduction of obliquity during the Ediacaran–early Palaeozoic would have yielded a more habitable globe with much reduced seasonal stresses and may have been an important factor influencing the unique evolutionary events of the Ediacaran and Cambrian. The palaeolatitudinal distribution of evaporites cannot discriminate unambiguously between high- and low-obliquity states for the pre-Ediacaran Earth. Intervals of true polar wander such as postulated by others for the Ediacaran and Early Cambrian imply major mass-redistributions within the Earth at those times, which may provide a potential mechanism for reducing the obliquity during the Ediacaran–early Palaeozoic.     

Early life history and biology of the common fish parasite,Lironeca ovalis (Say) (Isopoda,Cymothoidae)

The first post-marsupial stage of the common fish parasite, Lironeca ovalis, is described and found to be identical to Aegathoa medialis Richardson. It is suggested that A. oculata (Say) may also be a young stage of L. ovalis. The juvenile isopods were observed to attach readily to potential host fish, juvenile striped bass and white perch, in the laboratory. However, the parasites could be dislodged easily, and there was no indication that they were actually feeding on the host fish. The isopods also did not feed on newly hatched Artemia nauplii or unicellular algae (Monochrysis lutheri and Phaeodactylum tricornutum) in culture trials. It appears that the young isopods can survive free-swimming for only 1–2 weeks without a host, but the animals may be able to maintain a more-or-less free existence for an extended period by moving from host to host via plankton.     

Crustal thickness estimate at AAE (Addis-Ababa, Ethiopia) and NAI (Nairobi, Kenya) using teleseismic P-wave conversions

Long-period teleseismic P waves recorded at AAE (Addis Ababa, Ethiopia) and NAI (Nairobi, Kenya) show comparable P_s conversions on the radial component of ground motion. The timing and amplitude of the P_s conversions are modeled with synthetic seismograms to get an estimate of crustal thickness under both stations. Instrument response and effective source time function are removed from the data using a P-wave equalization procedure. The timing of the P_s conversions, relative to direct P, suggests that both stations have similar crustal thickness. Using constraints on crustal velocities determined by previous surface wave dispersion and travel-time studies, the P_s-P timing suggests a crust of 41 km thickness. This agrees reasonably well with previous crustal estimates. Tangential wave forms exhibit large amplitudes and are consistent at most backazimuths. However, these wave forms could not be explained with models containing simple planar dipping interfaces. The crustal thickness of 41 km taken in conjunction with the close proximity of the stations to the rift zone suggests that crustal thinning is localized to the rift itself.     

Biogeochemistry of trace metals (Mn, Sr, Rb, Ba, Cu, Zn, Pb and Cd) in a river-wetland-lake system (Balaton Region, Hungary)

Mn, Sr, Ba, Rb, Cu, Zn, Pb and Cd concentrations have been measured seasonally in the water and deposited sediments of the system comprising: Zala river (main input) — Lakes Kis-Balaton 1 and 2 (small artificial lakes created in a former bay of Lake Balaton) — Keszthely bay (hypertrophic part of Lake Balaton). The concentrations of the trace elements together with pH, alkalinity, dissolved cations (Ca²⁺, Mg²⁺, Na⁺, and K⁺), dissolved inorganic ligands (Cl^–, SO₄ ^2–), particulate Al, Ca, inorganic and organic carbon are used to assess the contamination of the study area and biogeochemical processes controlling trace element concentrations. Thermodynamic speciation calculations have also been utilized to enhance our understanding of the system. In the sediments Rb, Ba, Cu and Zn concentrations were mainly controlled by the abundance of the aluminosilicate fraction. Strontium was mainly associated with the calcium carbonate fraction. The aluminosilicate fraction constitutes a major sink for Mn and Cd but the concentration of these elements are also strongly related to calcite precipitation. The main processes that control the dissolved distribution of trace elements in the Balaton system were: solid phase formation (carbonate) for Mn; coprecipitation with calcite for Sr, Ba, Rb and possibly Mn and Cd; adsorption/desorption processes (pH dependent) for Zn and Pb; solubilization of Mn and precipitation of Cd and Cu in reed covered wetland areas where anoxic conditions were probably existing during the warm season. A preliminary budget of atmospheric and river input to Lake Balaton has also been outlined. Although Lake Balaton, is subjected to anthropogenic inputs mainly from agricultural and domestic activities, their impact on trace element concentrations in the Balaton system is very limited due to the efficiency of removal processes (i.e. adsorption and co-precipitation) and to high sedimentation rates and strong sediment re-suspension. Anthropogenic inputs are only detected for Pb.