Site occupation and electric field gradient in acentric neptunite-measurements and evaluations concerning powder- and single crystal – Mössbauer spectroscopy and x-ray diffractometry

Mössbauer measurements on neptunite (KNa₂Li(Fe,Mn,Mg)₂Ti₂Si₈O₂₄) at 400?K reveal the distribution of Fe-ions on the crystallographic sites in agreement with neutron diffraction results published elsewhere. Even the previously postulated small amount of Fe-ions on the Ti(2) site has been detected, combined with a charge transfer which is in agreement with optical absorption investigations by other authors. A qualitative site occupation model is able to explain the different features of our observations. Single crystal Mössbauer measurements with the k-vector of incident γ-rays parallel to the crystallographic b-axis (space group Cc) of neptunite at different temperatures yield the angle β between the main component of the electric field gradient (EFG), V _zz and b. This angle is in close accordance with a calculated value of β for the Fe(1) position from electron density maps. The latter also reveal an absolute value of V _zz which is in satisfactory agreement with V _zz derived from Mössbauer spectroscopy.     

Coastal erosion vs riverine sediment discharge in the Arctic Shelf seas

This article presents a comparison of sediment input by rivers and by coastal erosion into both the Laptev Sea and the Canadian Beaufort Sea (CBS). New data on coastal erosion in the Laptev Sea, which are based on field measurements and remote sensing information, and existing data on coastal erosion in the CBS as well as riverine sediment discharge into both the Laptev Sea and the CBS are included. Strong regional differences in the percentages of coastal erosion and riverine sediment supply are observed. The CBS is dominated by the riverine sediment discharge (64.45᎒⁶ t a^-1) mainly of the Mackenzie River, which is the largest single source of sediments in the Arctic. Riverine sediment discharge into the Laptev Sea amounts to 24.10᎒⁶ t a^-1, more than 70% of which are related to the Lena River. In comparison with the CBS, the Laptev Sea coast on average delivers approximately twice as much sediment mass per kilometer, a result of higher erosion rates due to higher cliffs and seasonal ice melting. In the Laptev Sea sediment input by coastal erosion (58.4᎒⁶ t a^-1) is therefore more important than in the CBS and the ratio between riverine and coastal sediment input amounts to 0.4. Coastal erosion supplying 5.6᎒⁶ t a^-1 is less significant for the sediment budget of the CBS where riverine sediment discharge exceeds coastal sediment input by a factor of ca. 10.     

Climate impacts of environmental degradation in Sudan

There exists an impressive amount of work for Sudan showing the anthropogenic degradation of natural vegetation cover. However, there are few examples of consequent climatic changes in literature. This work, thus, seeks to assess such effects of environmental forcing on various climatic patterns over the past few decades. Within the frame of the present analysis, the results are quite striking and are in concordance with scientific contentions that such land degradation could result in climatic modification. Higher temperature and less rainfall, sunshine duration and global radiation have been noticed. Evapotranspiration has responded more to the warming and drying conditions, thus showed signs of increasing rates, especially during the wet season. However, the extent of increase seems to have been suppressed by the decrease in sunshine duration and solar radiation as well as the inconsistent behaviour of wind speed. Changes in the variability of the within-year monthly observations have also occurred, thus suggesting an increase in the occurrence of extremes. The observed climatic modification in the country has exaggerated the insidious drought conditions. The present findings are hoped to contribute to our understanding of the effects of environmental problem and assist in considering policy responses. This revised version was published online in July 2006 with corrections to the Cover Date.     

Composition and origin of lithic fragments and glasses in apollo 11 samples

Approximately 100 glasses and 52 lithic fragments from Apollo 11 lunar fines and microbreccias were analyzed with the electron microprobe. Ranges in bulk composition of lithic fragments are considerably outside the precision (<±1%) and accuracy (±2–5%) of the broad electron beam technique. Results of this study may be summarized as follows: i) A large variety of rock types different from the hand specimens (basalt) were found among the lithic fragments, namely anorthosites, troctolitic and noritic anorthosites, troctolites, and norites (different from Apollo 12 norites). ii) In analogy to the hand specimens, the basaltic lithic fragments may be subdivided into low-K and high-K groups, both of which extend considerably in composition beyond the hand specimens. iii) Glasses were divided into 6 groups: Group 1 are the compositional analogs of the anorthositic-troctolitic lithic fragments and were apparently formed in single-stage impact events directly from parent anorthosites and troctolites. iv) Group 2 glasses are identical in composition to Apollo 12 KREEP glass and noritic lithic fragments, but have no counterparts in our Apollo 11 lithic fragment suite. Occurrence of KREEP in Apollo 11,12, and 14 samples is indicative of its relatively high abundance and suggests that the lunar crust is less depleted in elements that are common in KREEP (e.g. K, rare earths, P) than was originally thought on the basis of Apollo 11 basalt studies. v) Group 3 glasses are the compositional analogs of the basaltic lithic fragments, but low-K and high-K glasses cannot be distinguished because of loss of K (and Na, P) by volatilization in the vitrification process. vi) Group 4 glasses have no compositional analogs among the lithic fragments and were probably derived from as yet unknown Fe-rich, moderately Ti-rich, Mg-poor basalts. vii) Group 5 (low Ti-high Mg peridotite equivalent) and 6 (ilmenite peridotite equivalent) glasses have no counterparts among the Apollo 11 lithic fragments, but rock equivalents to group 5 glasses were found in Apollo 12 samples. Group 6 glasses are abundant, have narrow compositional ranges, and are thought to be the products of impact melting of an as yet unrecognized ultramafic rock type. iix) The great variety of igneous rocks (e.g. anorthosites, troctolites, norites, basalts, peridotites) suggests that large scale melting or partial melting to considerable depth must have occurred on the moon.     

Oxide minerals in lithic fragments from Luna 20 fines

One hundred and seventy-six oxide mineral grains in the Luna 20 samples were analyzed by electron microprobe. Spinel is the most abundant oxide, occurring in troctolite fragments. Next most abundant is ilmenite, which occurs in all rock types except those containing spinel. Chromite also occurs in all rock types except those containing spinel. Minor amounts of ulvöspinel, armalcolite, zirkelite, baddeleyite and an unidentified TiO₂-rich phase were also found.Spinel grains are predominantly spinel-hercynite solid solutions, commonly with very minor chromite. The $\text{Fe}\text{(Fe + Mg)}$ ratio is generally lower than in spinel from Apollo 14 rocks. Chromites in non-mare rocks are similar to those from mare rocks. Ilmenite of mare origin is Mg-poor and Zr-rich compared to non-mare ilmenite; these elements may therefore be useful in determining the origin of ilmenite grains.Phase equilibria considerations suggest that spinel troctolite crystallized from a melt high in alumina; a likely candidate is the high-alumina basalt of Prinzet al. (1973a).Sub-micron wide rods of metallic Fe occur in plagioclase grains and may have formed by sub-solidus reduction processes.     

Die Gneishornfelse um Steinach in der Oberpfalz

Zusammenfassung Bereits vor der Intrusion des Leuchtenberger Granits waren seine Rahmen-gesteine unter den Bedingungen der Amphibolit-Fazies regionalmetamorph eingeformt worden, wobei sich folgende Paragenesen bildeten: Muscovit + Biotit + Granat ± Sillimanit ± Staurolith (+ Quarz + Plagioklas) Muscovit + Biotit ± Kalifeldspat (+ Quarz + Plagioklas).Die Kontaktmetamorphose führt in den äußeren Bereichen der Aureole zur Paragenese Muscovit + Andalusit + Cordierit + Biotit (+ Quarz + Plagioklas), die der Hornblende-Hornfels-Fazies entspricht.In der inneren Kontaktzone werden die p-t-Bedingungen einer höhergradierten Hornfelsfazies erreicht, die sich in der Paragenese ± Kalifeldspat + Sillimanit + Cordierit ± Almandin + Biotit (+ Quarz + Plagioklas) dokumentiert.Die zonale Anordnung der Mineral-Paragenesen im Kontakthof läßt sich durch quantitative Verbreitungskarten anschaulich machen (150 Modalanalysen aus 59 Fundpunkten). Phasenbeziehungen und Mineralreaktionen werden anhand von AKF- und AFM-Diagrammen diskutiert, für deren Aufstellung 19 Mineralanalysen neu ausgeführt wurden.Durch den Vergleich mit derzeit verfügbaren experimentellen Unterlagen lassen sich die p-t-Bedingungen im Steinacher Kontakthof abschätzen. Danach ist ein Druckbereich von 1,5–3 kbar am wahrscheinlichsten. Mit der Bildung der höchst-gradierten Hornfelse waren 550° C sicher überschritten, während nach dem Jaeger-Modell 700° C als alleroberste Temperaturgrenze anzusehen ist. In der innersten Kontaktzone muß man mit geringen O₂-Partialdrucken rechnen.

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The gneiss-hornfelses of Steinach, Oberpfalz (Bavaria)

The southern margin of the Leuchtenberg granite massive is surrounded by a thermal aureole in which banded gneisses and mica schists have been transformed into hornfelses containing andalusite, sillimanite, cordierite, and almandine.Before the intrusion of the granite, the country rocks had undergone regional metamorphism to give mineral assemblages typical of the amphibolite facies: Muscovite + biotite ± K-feldspar + quartz + plagioclase in the banded gneisses and muscovite + biotite + garnet ± sillimanite ± staurolite + quartz + plagioclase in the mica schists.In the outer zone of the aureole, contact metamorphism produced the assemblage: Muscovite + andalusite + cordierite + biotite + quartz + plagioclase, corresponding to the hornblende-hornfels facies.In the inner zone of the aureole, increasing temperatures yielded the high grade assemblages: K-feldspar + sillimanite + cordierite ± almandine + biotite + quartz + plagioclase sillimanite + cordierite ± almandine + biotite + quartz + plagioclase.The zonal arrangement of the mineral assemblages within the Steinach aureole is shown in quantitative distribution maps of andalusite, contact-metamorphic sillimanite, cordierite, and contact-metamorphic garnet respectively, based on 150 modal analyses (from 59 points, Fig. 1). Andalusite (Fig. 10) reaches its maximum at about 200–400 m from the granite border and, toward it, is more and more substituted by sillimanite (Fig. 11). On the other hand, contact metamorphic sillimanite goes to the outer zone of the aureole almost as far as andalusite. This means that the sillimanite isograd passed across the andalusite zone during the contact metamorphism. Cordierite (Fig. 12) shows a constant increase from the margin to the innermost zone of the aureole, as does contact metamorphic garnet (Fig. 13). Phase relations and mineral reactions are discussed in terms of AKP- and APM-diagrams (Figs. 14, 15, 17, 18) based on 19 new mineral analyses (Tables 5–9).With respect to the experimental data so far available, possible P-T-conditions within the Steinach aureole have been discussed. The transition from the low to the high grade assemblages took place very near to the cross-over point of the andalusite/sillimanite equilibrium curve and the breakdown curve of muscovite + quartz in the P-T-diagram (Figs. 16, 19).This gives a minimum H₂O-pressure of 1 kbar. In the innermost contact zone, temperatures must have exceeded 550° C, which is in good agreement with recent oxygen-isotope data as well as with Jaeger's model. As is shown by the ore mineral assemblages, studied in polished sections (Table 10), the oxygen activity in the high grade hornfelses was low.

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Prof. S. Matthes (Würzburg) möchte ich für das lebhafte, fördernde Interesse an dieser Arbeit sowie für die Überlassung von Proben und von Geräten der DFG meinen herz-lichen Dank aussprechen. Wesentlichen Anteil am Gelingen dieser Untersuchung hat auch Prof. B. W. Evans, dem ich für die freundschaftliche Aufnahme in Berkeley, für die ständige Bereitschaft zur Diskussion und für wertvolle Anregungen zu großem Dank verpflichtet bin. Weiter danke ich Prof. W. Schreyer (Bochum) und Prof. F. J. Turner (Berkeley) für die kritische Durchsicht des Manuskripts sowie Mr. L. K. Burns (Berkeley), Dr. A. Peters und Dr. P. Richter (Würzburg) für wichtige Hinweise bei der Analytik. Die Untersuchungen an der Mikrosonde in Berkeley wurden durch ein Stipendium der Deutschen Forschungs-gemeinschaft ermöglicht; das Gerät stand durch die Unterstützung der National Science Foundation (grant GA 500) zur Verfügung. Beiden Organisationen sei für ihre Hilfe gedankt.

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Textlich gekürzte, aber um neue Untersuchungsergebnisse erweiterte Fassung einer Habilitationsschrift, angenommen im Januar 1968 von der Naturwissenschaftlichen Fakultät der Universität Würzburg.     

Nuclear and incommensurate magnetic structure of NaFeGe2O6 between 5?K and 298?K and new data on multiferroic NaFeSi2O6

The compound NaFeGe₂O₆ was grown synthetically as polycrystalline powder and as large single crystals suitable for X-ray and neutron-diffraction experiments to clarify the low temperature evolution of secondary structural parameters and to determine the low temperature magnetic spins structure. NaFeGe₂O₆ is isotypic to the clinopyroxene-type compound aegirine and adopts the typical HT-C2/c clinopyroxene structure down to 2.5?K. The Na-bearing M2 polyhedra were identified to show the largest volume expansion between 2.5?K and room temperature, while the GeO₄ tetrahedra behave as stiff units. Magnetic susceptibility measurements show a broad maximum around 33?K, which marks the onset of low-dimensional magnetic ordering. Below 12?K NaFeGe₂O₆ transforms to an incommensurately modulated magnetic spin state, with k?=?[0.323, 1.0, 0.080] and a helical order of spins within the M1-chains of FeO₆ octahedra. This is determined by neutron-diffraction experiments on a single crystal. Comparison of NaFeGe₂O₆ with NaFeSi₂O₆ is given and it is shown that the magnetic ordering in the latter compound, aegirine, also is complex and is best described by two different spin states, a commensurate one with C2??/c?? symmetry and an incommensurate one, best being described by a spin density wave, oriented within the (1 0 1) plane.     

Water release patterns of heated speleothem calcite and hydrogen isotope composition of fluid inclusions

Speleothem fluid inclusions are a potential paleo-precipitation proxy to reconstruct past rainwater isotopic composition (δ¹⁸O, δD). To get a better insight in the extraction of inclusion water from heated speleothem calcite, we monitored the water released from crushed and uncrushed speleothem calcite, heated to 900 °C at a rate of 300 °C/h, with a quadrupole mass spectrometer. Crushed calcite released water in three not well individualised peaks between 25 and 360 °C, 360 and 650 °C and between 650 and 800 °C while uncrushed calcite released water in two distinct temperature intervals: between 25 and 550 °C and between 550 and 900 °C.Water from two speleothems from the Han-sur-Lesse cave was recovered using three different techniques: i) the crushing and heating to 360 °C technique, ii) the decrepitation by heating to 550 °C and iii) the decomposition by heating to 900 °C technique. Measurements of the δD of water recovered by the decomposition of Han-sur-Lesse calcite heated to 900 °C did not show a 20 to 30‰ offset as found by previous authors. However a difference of 7‰ was observed between water released before and after decomposition of the calcite. Water recovery from the Han-sur-Lesse samples suggests that a simple heating technique (up to 550 °C) without crushing could both (a) recover water with δD representative of that of the drip water and (b) double the water yield as compared to the crushing and heating method.Our study warns for possible contamination of the recovered inclusion water with hydration water of lime, responsible for the recovery of water with very negative δD values.     

Facies of slurry-flow deposits, Britannia Formation (Lower Cretaceous), North Sea: implications for flow evolution and deposit geometry

ABSTRACT Mud‐rich sandstone beds in the Lower Cretaceous Britannia Formation, UK North Sea, were deposited by sediment flows transitional between debris flows and turbidity currents, termed slurry flows. Much of the mud in these flows was transported as sand‐ and silt‐sized grains that were approximately hydraulically equivalent to suspended quartz and feldspar. In the eastern Britannia Field, individual slurry beds are continuous over long distances, and abundant core makes it possible to document facies changes across the field. Most beds display regular areal grain‐size changes. In this study, fining trends, especially in the size of the largest grains, are used to estimate palaeoflow and palaeoslope directions. In the middle part of the Britannia Formation, stratigraphic zones 40 and 45, slurry flows moved from south‐west and south towards the north‐east and north. Most zone 45 beds lens out before reaching the northern edge of the field, apparently by wedging out against the northern basin slope. Zone 40 and 45 beds show downflow facies transitions from low‐mud‐content, dish‐structured and wispy‐laminated sandstone to high‐mud‐content banded units. In zone 50, at the top of the formation, flows moved from north to south or north‐west to south‐east, and their deposits show transitions from proximal mud‐rich banded and mixed slurried beds to more distal lower‐mud‐content banded and wispy‐laminated units. The contrasting facies trends in zones 40 and 45 and zone 50 may reflect differing grain‐size relationships between quartz and feldspar grains and mud particles in the depositing flows. In zones 40 and 45, quartz grains average 0·30–0·32 mm in diameter, ≈ 0·10 mm coarser than in zone 50. The medium‐grained quartz in zones 40 and 45 flows may have been slightly coarser than the associated mud grains, resulting in the preferential deposition of quartz in proximal areas and downslope enrichment of the flows in mud. In zone 50 flows, mud was probably slightly coarser than the associated fine‐grained quartz, resulting in early mud sedimentation and enrichment of the distal flows in fine‐grained quartz and feldspar. Mud particles in all flows may have had an effective grain size of ≈ 0·25 mm. Both mud content and suspended‐load fallout rate played key roles in the sedimentation of Britannia slurry flows and structuring of the resulting deposits. During deposition of zones 40 and 45, the area of the eastern Britannia Field in block 16/26 may have been a locally enclosed subbasin within which the depositing slurry flows were locally ponded. Slurry beds in the eastern Britannia Field are ‘lumpy’ sheet‐like bodies that show facies changes but little additional complexity. There is no thin‐bedded facies that might represent waning flows analogous to low‐density turbidity currents. The dominance of laminar, cohesion‐dominated shear layers during sedimentation prevented most bed erosion, and the deposystem lacked channel, levee and overbank facies that commonly make up turbidity current‐dominated systems. Britannia slurry flows, although turbulent and capable of size‐fractionating even fine‐grained sediments, left sand bodies with geometries and facies more like those deposited by poorly differentiated laminar debris flows.     

A protoceratopsid skeleton with an associated track from the Upper Cretaceous of Mongolia

The Djadokhta Formation of the Gobi Desert is known for the number and diversity of dinosaur and other vertebrate bones and skeletons found there, but only theropod, hadrosaur and supposed ankylosaurid footprints have been reported from this stratum. Dinosaur footprints are also noted from the Nemegt Formation, and occur as typical dinosaur track accumulations (tracksites). An articulated protoceratopsid skeleton - specimen ZPAL Mg D-II/3 - was collected by the Polish-Mongolian Expedition of 1965 from the Djadokhta Formation of Flaming Cliffs in Mongolia. Recently, the natural cast of a tetradactyl digitigrade footprint was found underneath the pelvic girdle while the skeleton and matrix were being prepared. This is possibly the first find of a dinosaur track in close association with an articulated skeleton. Although Protoceratops is an extremely common dinosaur in Mongolia, its footprints have never previously been reported from the Late Cretaceous of the Gobi Desert.