Biostratigraphy of the Çeşmeler and Elmalι Dere formations: First records of upper Cretaceous planktonic foraminifera and radiolarians from the Eastern Pontides (Maçka,Trabzon, Turkey)

Upper Cretaceous pelagic deposits outcropping in the Maçka (Trabzon) region include radiolarians and pelagic foraminifera. The Çatak Group represented by the volcano-sedimentary successions consists of three formations having different properties. Two sections, ÇTK1 and ÇTK2, are selected from the Çe meler and Elmalι Dere formations, respectively, establishing the biostratigraphy of outcropping sedimentary units. A total of 17 species of Whiteinella, Helvetoglobotruncana, Marginotruncana, Dicarinella, Praeglobotruncana, Archaeoglobigerina and Hedbergella demonstrating the early Turonian–Coniacian are established in the ÇTK1 stratigraphic section. The early Turonian radiolarian fauna consisting of Halesium sexangulum Pessagno, 1971, Crucella cachensis Pessagno, 1971, Stichomitra communis Squinabol, 1903 is also defined in the same section. A total of 30 species of Crucella, Halesium, Pessagnobrachia, Patulibracchium, Alievium, Archaeospongoprunum, Dicyomitra, Stichomitra, Diacanthocapsa, Dactiyliodiscus, Amphipydax, Pseudoaulophocus, Acaeniotyle, Archaeodictyomitra, Actinomma, Xitus, Neosciadocapsidae characterizing the early and late Turonian, as well as the Coniacian–early Santonian are recognized from red-coloured pelagic limestones of the ÇTK2 section. Also, planktonic foraminifera species of Marginotruncana, Hedbergella, Heterohelix, Globotruncana, Globotruncanita, Archaeoglobigerina, Dicarinella characterizing the Coniacian–Santonian are described in the thin sections of the same samples. The age of red-coloured limestones is identified as the Coniacian–Santonian benefit from radiolarians and pelagic foraminifera. Consequently, radiolarians and pelagic foraminifera within sedimentary successions of the investigation area are distributed in two intervals that coincide with the early Turonian–Coniacian and Coniacian–Santonian intervals.     

Climate change and modelling of extreme temperatures in Switzerland

This study models maximum temperatures in Switzerland monitored in twelve locations using the generalised extreme value (GEV) distribution. The parameters of the GEV distribution are determined within a Bayesian framework. We find that the parameters of the underlying distribution underwent a substantial change in the beginning of the 1980s. This change is characterised by an increase both in the level and the variability. We assess the likelihood of the heat wave of the summer 2003 using the fitted GEV distribution by accounting for the presence of a structural break. The estimation results do suggest that the heat wave of 2003 is not that statistically improbable if an appropriate methodology is used for dealing with nonstationarity.     

The dispersion of surface waves and crustal structure in African continent

Summary In this study has been interpreted the Love- and Rayleigh-waves of Agadir earthquake on February 29, 1960 recorded at Lwiro and Skopje earthquake on July 26, 1963 recorded at Pretoria and Windhoek by long period Columbia type seismographs, and determined the crustal structure in Africa with dispersion of both Love- and Rayleigh-waves along the paths on two different directions. The obtained results are compared each other and with those founded recently by several investigators for Africa and Europe. Herewith has been showed that the average thickness of the crust in Africa is thinner than in Europe and the thickness in direction from Skopje to Pretoria is more than that from Agadir to Lwiro.

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Zusammenfassung In diesem Artikel wurden die Love- und Rayleigh-Wellen vom Erdbeben in Agadir vom 29. Februar 1960, aufgezeichnet in Lwiro, und vom Erdbeben in Skopje vom 26. Juli 1963, aufgezeichnet in Pretoria und Windhoek von langperiodischen Columbia-Seismographen, untersucht und somit mit Dispersion von beiden Love- und Rayleigh-Wellen der Aufbau der Erdkruste in Afrika bestimmt. Die erhaltenen Resultate wurden miteinander und mit anderen Werten, die bis heute von verschiedenen Autoren für Afrika und Europa bestimmt wurden, verglichen. Somit wurde vorgelegt, dass die Erdkruste in Afrika im allgemeinen dünner ist als in Europa und dass die Schicht in der Richtung von Skopje zu Pretoria dicker ist als in der Richtung von Agadir zu Lwiro.

     

Magnetic properties of monodomain aluminium-substituted titanomagnetite

A suite of synthetic titanomagnetites were prepared with compositions Fe_2.6?δTi_0.4Al_δO₄ and Fe_2.4?δTi_0.6Al_δO₄ (δ = 0, 0.1, 0.2 in both cases). Ball-milling of the synthesized samples produced material in the magnetic monodomain state as indicated by hysteresis loops and the Lowrie-Fuller test. The coercive force of the specimens depends on the Al concentration and lies in the range 1–2 kOe. The TRM induced in the samples is correspondingly “hard”. The low-field (0–1 Oe) TRM acquisition curve is linear. The higher field TRM-H curve is not in agreement with either monodomain or two-domain theoretical models.     

Role of carbonates in mitigation of metal release from mining waste. Evidence from humidity cells tests

 Leaching of two contrasting types of sulphidic tailings in humidity cells has been performed. The release of heavy metals and the oxidation rate have been studied. Tailings from the Laver mine contain a few percent sulphides and lack carbonates, whereas tailings from the Stekenjokk mine are both sulphide- and carbonate-rich. The results showed that in the leachates from the Laver samples, the metal concentrations increased and pH decreased with time, indicating an increased oxidation rate. In the Stekenjokk samples, pH remained high during the experiment, thereby keeping the metal concentrations low in the leachates. The oxidation rate also decreased with time, probably due to Fe-hydroxide coatings on sulphide surfaces. The results show that addition of carbonates and the maintenance of a high pH not only reduce the solubility of heavy metals, but also decrease the oxidation rate of sulphides. Received: 20 January 1998 · Accepted: 2 April 1998     

ON THE POSSIBLE CHANGES OF THE SOLAR DIFFERENTIAL ROTATION DURING THE ACTIVITY CYCLE DETERMINED USING MICROWAVE LOW-BRIGHTNESS-TEMPERATURE REGIONS AND Hα FILAMENTS AS TRACERS

The solar rotation rate obtained using the microwave Low-brightness-Temperature Regions (LTRs) as tracers in the heliographic range ± 55° from the years 1979–1980, 1981–1982, 1987–1988, and 1989–1991 varied from 3% to 4% in medium latitudes, and below 1% at the equator. Using H filaments as tracers at higher latitudes from the years 1979, 1980, 1982, 1984, and 1987, the solar rotation rate variation was between 2% and 8%. This represents an upper limit on the rotation rate variation during the solar activity cycle. Such changes could be caused by short-lived, large-scale velocity patterns on the solar surface. The Sun revealed a higher rotation rate on the average during the maxima of the solar activity cycles 21 and 22, i.e., in the periods 1979–1980 and 1989–1991, respectively, which differs from the rotation rates (lower on the average) in some years, 1981–1982 and 1987–1988, between the activity maximum and minimum (LTR data). Simultaneous comparison of rotation rates from LTRs and H filament tracings was possible in very limited time intervals and latitude bands only, and no systematic relationship was found, although the rotation rates determined by LTRs were mostly smaller than the rotation rates determined by H filaments. The errors obtained by applying different fitting procedures of the LTR data were analyzed, as well as the influence of the height correction. Finally, the north–south asymmetry in the rotation rate investigated by LTRs indicates that the southern solar hemisphere rotated slower in the periods under consideration, the difference being about 1%. The reliability of all obtained results is discussed and a comparison with other related studies was performed.     

Temporal variations in the fractal properties of seismicity in the North Anatolian Fault Zone between 31°E and 41°E

We investigate the nature of temporal variations in the statistical properties of seismicity associated with the North Anatolian Fault Zone between longitudes 31°–41°E during the instrumental period 1900–1992. Temporal variations in the seismicb value and the fractal (correlation) dimensionD _c of earthquake epicenters are examined for earthquakes of magnitudeM _S 4.5, using sliding windows of 100 consecutive events.b varies temporally between 0.6 and 1.0, andD _c between 0.6 and 1.4, both representing significant fluctuations above the errors in measurement technique. A strong negative correlation (r=–0.85) is observed betweenb andD _c , consistent with previous observation of seismicity in Japan and southern California. Major events early in this century (M _S 7) are associated with lowb and highD _c , respectively consistent with greater stress intensity and greater spatial clustering of epicenters—both implying a greater degree of stress concentration at this time.     

Late Quaternary palaeoenvironment of northern Guatemala: evidence from deep drill cores and seismic stratigraphy of Lake Petén Itzá

Long sediment cores were collected in spring 2006 from Lake Petén Itzá, northern Guatemala, in water depths ranging from 30 to 150 m, as part of an International Continental Scientific Drilling Program project. The sediment records from deep water consist mainly of alternating clay, gypsum and carbonate units and, in at least two drill sites, extend back >200 kyr. Most of the lithostratigraphic units are traceable throughout the basin along seismic reflections that serve as seismic stratigraphic boundaries and suggest that the lithostratigraphy can be used to infer regional palaeoenvironmental changes. A revised seismic stratigraphy was established on the basis of integrated lithological and seismic reflection data from the basin. From ca 200 to ca 85 ka, sediments are dominated by carbonate‐clay silt, often interbedded with sandy turbidites, indicating a sediment regime dominated by detrital sedimentation in a relatively humid climate. At ca 85 ka, an exposure horizon consisting of gravels, coarse sand and terrestrial gastropods marks a lake lowstand or partial basin desiccation, indicating dry climate conditions. From ca 85 to ca 48 ka, transgressive carbonate‐clay sediments, overlain by deep‐water clays, suggest a lake level rise and subsequent stabilization at high stage. From ca 48 ka to present, the lithology is characterized by alternating clay and gypsum units. Gypsum deposition correlates with Heinrich Events (i.e. dry climate), whereas clay units coincide with more humid interstadials.