Early diagenesis in anaerobic lake sediments—II. Thermodynamic and kinetic factors controlling the formation of iron phosphate

The ion activity product of Fe and phosphate in interstitial waters from four sediment cores taken from Greifensee, Switzerland indicate the presence of vivianite [Fe₃(PO₄)₂ · 8 H₂O] in the solid phase. Analysis of the sediment using an electron microprobe and by electron microscopy revealed P-rich grains to be also enriched in Fe. The combined methods provide strong evidence that vivianite is forming authigenically in the sediments. Thermodynamic stability calculations demonstrate that the most stable Fe and phosphate minerals (pyrite, siderite and apatite) are not the ones controlling the pore water chemistry. The results emphasize the importance of rate processes of mineral formation in early diagenesis.Calculations based on the sediment phosphate concentration, and the degree of supersaturation of Fe and phosphate in the upper portion (0–15 cm) of the pore waters, indicate that the rate of vivianite mineral growth is controlled by a surface reaction rather than a diffusion mechanism. The response time of dissolved phosphate in the sediment pore waters with respect to mineral precipitation is on the order of 1–20 days. Less than 15% of the phosphate released by organic matter degradation at the sediment-water interface and below is retained in the sediments.     

Seltene Mineralparagenesen in den Kalksteineinsehlüssen der Lava des Ettringer Bellerberges bei Mayen (Eifel)

Zusammenfassung Sechs metamorph veränderte Kalksteineinschlüsse aus verschiedenen Teilen der Lavaströme des Ettringer Bellerberges bei Mayen (Eifel) wurden optisch, chemisch und röntgenographisch untersucht. Sie setzen sich aus seltenen, z. T. erstmals in der Natur gefundenen Mineralen zusammen. Der Mineralbestand der Einschlüsse wird beschrieben. Er weicht von Probe zu Probe z. T. erheblich ab. Je nachdem in welchen Mineralen Fe und Al enthalten sind, lassen sich die Einschlüsse in 2 Gruppen einteilen: eine mit Brownmillerit, Mayenit, Larnit und eine 2. mit Wollastonit, Gehlenit, Magnetkies, Spinell.Am Aufbau aller Gesteine sind stets kristallwasserhaltige Minerale (Ettringet, Portlandit, Hydrocalumit) in z. T. ziemlich großen Mengen beteiligt. Diese Minerale kommen gelegentlich auch in Hohlräumen frei gewachsen vor.Eine völlig andere Zusammensetzung hat nur ein Teil aus dem Inneren eines Einschlusses. Er besteht nur aus Diopsid und Grossular.Soweit es die vorliegenden (noch nicht vollständigen) Untersuchungsergebnisse zulassen, werden mögliche Reaktionen, die zur Bildung dieser ungewöhnlichen Paragenese geführt haben könnten, diskutiert. Als Vergleich dienten nicht nur andere natürliche Kalkkontakte, sondern es wurden auch Erfahrungen der Zementforschung herangezogen.Die wasserfreien Minerale sind wahrscheinlich bei hohen Temperaturen und ziemlich niedrigen Drucken entstanden. Erst später; nachdem die Lava schon weitgehend abgekühlt war, können sich die kristallwasserhaltigen Minerale gebildet haben.Der Deutschen Forschungsgemeinschaft danken wir für das Bereitstellen von Geräten.

---

Six metamorphic altered limestone inclusions from different parts of the lava flows of the Ettringer Bellerberg near Mayen (Eifel, Germany) have been investigated by optical, chemical, and X-ray methods. They are composed of rare minerals, two of them have been found the first time naturally. The mineral composition of the inclusions is not uniform. They may be divided into two groups, one with brownmillerite, mayenite, larnite, and another one with wollastonite, gehlenite, pyrrhotite, spinel. A small (inner) part of one inclusion consists only of diopside and grossularite.In all rocks there are minerals containing crystallized water (ettringite, portlandite, and hydrocalumite), sometimes in large amounts. These minerals are found occasionally well developed in cavities.Possible modes of formation of this unusual paragenesis are discussed as far as it is permitted by the results of this investigation.

---

---

Herrn Prof. Dr.Carl W. Correns zum 70. Geburtstag gewidmet.     

Der petrogenetische Werdegang der Klinopyroxene in den tertiären Vulkaniten der Hocheifel I. Die Klinopyroxene der Alkaliolivinbasalt-Trachyt-Assoziation

Zusammenfassung Von über 150 Eraptionspunkten in der Hocheifel werden. 14 Gesteine als Verwtreter der Entwicklungsreihe. Alkaliolivinbasalt-Trachyt nach petrochemischen, optischen und aufbereitungstechnischen Gesichtspunkten ausgewählt und phasen mechanisch in ihre gesteinsbildenden Minerals zerlegt. Neben verschiedenen Klinopyroxenphasen, die sowohl die Klinopyroxeneingprenglinge als each die Grundmasseklinopyroxene enthalten, können fast ells assoziierten Minerals mitgewonnen und chemisch, optisch and röntgenographisch untersucht werden.Im Verlauf der Petrogenese zeigen die Klinopyroxene sine kontinuierliche Entwicklung vonCr- überTi-reiche Augite als Einsprenglinge zuNa-reichen oilerNa-Augiten in der Grundmasse, ohne daß aber Ägirinaugite oiler Ägirine in den sauersten Differentiaten erreicht werden. Neben intratellurischen und subeffusiven bis effusiven Stadien in der Mineralentwicklung, die rich mineralfaziell belegen lassen, tritt reliktisch mitNi-reichem Olivin, Cr-reichem Augit, Bronzit undCr-Spinell eine Mineralparagenese auf, die mit der der ultrabasitischen Xenolithe aus Alkalibasalten identisch ist and sich bis in die Mugearite in verschiedenen Überprägungszuständen nachweisen. läßt. lhr Vorhandensein wird genetisch auf ein initiates Hochdruck-Hochtemperatur- Stadium zurükgeführt, ilea die alkalibasaltische Schmelze am Anfang ibrer Entwicklung durchlanfen hat and dessen mögliche Ursachen mineralfaziell diskutiert werden.     

Lithium isotope composition of ordinary and carbonaceous chondrites, and differentiated planetary bodies: Bulk solar system and solar reservoirs

In order to better constrain the Li isotope composition of the bulk solar system and Li isotope fractionation during accretion and parent body processes, Li isotope compositions and concentrations were determined on a number of meteorite falls and finds. This is the first comprehensive study that systematically investigates a representative set of samples from carbonaceous chondrites (CI, CM2, CO3, CV3, CK4 and one ungrouped member), enstatite chondrites (EH, EL), ordinary chondrites (H, L, LL), and achondrites (one eucrite, diogenites, one pallasite, and a silicate inclusion from a IAB iron).

Carbonaceous chondrites have an average isotope composition of δ⁷Li = + 3.2‰ ± 1.9 (2σ) which agrees with the average composition of relatively pristine olivines (representative for the bulk composition) from the Earth primitive upper mantle (PUM). This is lighter than the average δ⁷Li of the basaltic differentiates of the Earth, Moon and Mars and the achondrites. It is an important observation, however, that the lighter end of the isotopic range of the differentiates always coincides with the averages of the mantle olivines and the carbonaceous chondrites. From this we conclude that the bulk of the inner solar system consists mostly of material from carbonaceous chondrites and that the variation seen in the differentiates is due to planetary body processes. Ordinary chondrites are significantly lighter than carbonaceous chondrites. No significant differences in δ⁷Li exist between enstatite chondrites (n = 3) and carbonaceous or ordinary chondrites. The difference between carbonaceous and ordinary chondrites and the variability within the chondrites could indicate the existence of distinct Li isotope reservoirs in the early solar nebula.     

Reproductive characteristics of invasive gammarids in the Rhine-Main-Danube catchment, South Germany

The gammarid composition at 25 sites in the rivers Danube, Main and the southern reaches of the Rhine were studied during the years 2002–2004. Dikerogammarus villosus and Echinogammarus ischnus were the most frequent species prevailing at 17 sites. Sympatric occurrence of D. villosus and E. ischnus was observed at 12 sites. Dikerogammarus haemobaphes was recorded at 7 sites; this species prevailed in the Danube, west of the Weltenburger Enge and in the Isar mouth where it co-existed with native species (Gammarus pulex and/or G. roeseli) at 6 sites. Dikerogammarus bispinosus and E. berilloni were found at only 1 site, where they co-existed with D. villosus and E. ischnus, and with D. villosus and native species, respectively. Investigation of reproductive characteristics at 3 sites showed that females of D. villosus and D. haemobaphes produced the biggest clutches with more than 100 eggs. Females of E. ischnus produced much smaller clutches (10–35 eggs on an average), but very big eggs. Clutch sizes and egg volumes of D. bispinosus and E. berilloni resembled those of native species. Our results suggest that the most successful invaders (D. villosus, D. haemobaphes and E. ischnus) display reproductive traits that facilitate their success. Both Dikerogammarus sp. allocate energy into production of many but small eggs, thus maximizing offspring number, while E. ischnus allocates its energy into production of fewer but large eggs which could be beneficial at sites where food is scarce.     

Mars: simply red?

Ernst Hauber and Gerhard Neukum present a new perspective on the martian surface on the basis of two years of observations by the High resolution Stereo Camera, part of ESA's Mars Express mission.
All HRSC images shown are copyright ESA/DLR/FU Berlin (G Neukum).