P–T–t evolution of the Cycladic Blueschist Unit in Western Anatolia/Turkey: Geodynamic implications for the Aegean region

Eclogite and blueschist facies rocks occurring as a tectonic unit between the underlying Menderes Massif (MM) and the overlying Afyon Zone/Lycian Nappes and the Bornova Flysch Zone in western Anatolia represent the eastward continuation of the Cycladic Blueschist Unit (CBU) in Turkey. This high-P unit is attributed to the closure of the Pindos Ocean and consists of (a) a Triassic to Upper Cretaceous coherent series derived from passive continental margin sediments and (b) the tectonically overlying Upper Cretaceous Selçuk mélange with eclogite blocks embedded in a pelitic epidote-blueschist matrix. The coherent series has experienced epidote-blueschist facies metamorphism (490 ± 25°C/11.5 ± 1.5 kbar; 38 km depth). ⁴⁰Ar/³⁹Ar white mica and ²⁰⁶Pb/²³⁸U monazite dating of quartz metaconglomerate from coherent series yielded middle Eocene ages of 44 ± 0.3 and 40.1 ± 3.1 Ma for epidote-blueschist facies metamorphism, respectively. The epidote-blueschist facies metamorphism of the matrix of the Selçuk mélange culminates at 520 ± 15°C/13 ± 1.5 kbar, 43 km depth, and is dated at 57.5 ± 0.3–54.5 ± 0.1 Ma (⁴⁰Ar/³⁹Ar phengite). Eclogite facies metamorphism of the blocks (570 ± 30°C/18 ± 2 kbar, 60 km depth) is early Eocene and dated at 56.2 ± 1.5 Ma by ²⁰⁶Pb/²³⁸U zircon. Eclogites experienced a nearly isothermal retrogression (490 ± 40°C/~6 to 7 kbar) during their incorporation into the Selçuk mélange. The retrograde overprints of the coherent series (410 ± 15°C/7 ± 1.5 kbar from Dilek Peninsula and 485 ± 33°C/~6 to 7 kbar from Selçuk–Tire area) and the Selçuk mélange (510 ± 15°C/6 ± 1 kbar) are dated at 35.8 ± 0.5–34.3 ± 0.1 Ma by ⁴⁰Ar/³⁹Ar white mica and 31.6 ± 6.6 Ma by ²⁰⁶Pb/²³⁸U allanite dating methods, respectively. Regional geological constrains reveal that the contact between the MM and the CBU originally formed a lithosphere-scale transform fault zone. ⁴⁰Ar/³⁹Ar white mica age from the contact indicates that the CBU and the MM were tectonically juxtaposed under greenschist facies conditions during late Eocene, 35.1 ± 0.3 Ma.     

325-MHz observations of the ELAIS-N1 field using the Giant Metrewave Radio Telescope

We present observations of the European Large-Area ISO Survey-North 1 (ELAIS-N1) at 325 MHz using the Giant Metrewave Radio Telescope (GMRT), with the ultimate objective of identifying active galactic nuclei and starburst galaxies and examining their evolution with cosmic epoch. After combining the data from two different days we have achieved a median rms noise of  ≈40 μJy  beam⁻¹, which is the lowest that has been achieved at this frequency. We detect 1286 sources with a total flux density above  ≈270 μJy  . In this paper, we use our deep radio image to examine the spectral indices of these sources by comparing our flux density estimates with those of Garn et al. at 610 MHz with the GMRT, and surveys with the Very Large Array at 1400 MHz. We attempt to identify very steep spectrum sources which are likely to be either relic sources or high-redshift objects as well as inverted-spectra objects which could be Giga-Hertz Peaked Spectrum objects. We present the source counts, and report the possibility of a flattening in the normalized differential counts at low flux densities which has so far been reported at higher radio frequencies.     

Urban malaria in Africa: an environmental and socio-economic modelling approach for Yaoundé, Cameroon

Most of the existing predictive malaria risks spatial models use very broad spatial scales, and they are usually built-up for continental or national outlines. These models usually do not account for the complexity of socio-economic variables intervening into the malaria transmission process as well malaria prevention strategies. These spatial and thematic shortcomings are particularly interesting when looking at urban environments. This paper explains why a focus on urban malaria overcomes these shortcomings. A set of environmental variables derived from remotely sensed and ground climate station sources was used to build-up an ecological model. An original data collection process based on GPS measurements and retrospective interviews was introduced for the creation of various geoepidemiological and geosocial variables. Multinomial logistic models were used to predict and evaluate the contribution of various thematically separated groups of variables to malaria risk. Finally, it was possible to statistically and spatially evaluate the contribution of ecologic, socio-ecologic, socio-economic and behavioural characteristics of these groups of variables to malaria risks.     

Joint determination of K decay constants and Ar∗/K for the Fish Canyon sanidine standard, and improved accuracy for Ar/Ar geochronology

⁴⁰Ar/³⁹Ar and K-Ar geochronology have long suffered from large systematic errors arising from imprecise K and Ar isotopic data for standards and imprecisely determined decay constants for the branched decay of ⁴⁰K by electron capture and β⁻ emission. This study presents a statistical optimization approach allowing constraints from ⁴⁰K activity data, K-Ar isotopic data, and pairs of ²³⁸U-²⁰⁶Pb and ⁴⁰Ar/³⁹Ar data for rigorously selected rocks to be used as inputs for estimating the partial decay constants (λ_ε and λ_β) of ⁴⁰K and the ⁴⁰Ar∗/⁴⁰K ratio (κ_FCs) of the widely used Fish Canyon sanidine (FCs) standard. This yields values of κ_FCs = (1.6418 ± 0.0045) × 10⁻³, λ_ε = (0.5755 ± 0.0016) × 10⁻¹⁰ a⁻¹ and λ_β = (4.9737 ± 0.0093) × 10⁻¹⁰ a⁻¹. These results improve uncertainties in the decay constants by a factor of >4 relative to values derived from activity data alone. Uncertainties in these variables determined by our approach are moderately to highly correlated (cov(κ_FCs, λ_ε) = 7.1889 × 10⁻¹⁹, cov(κ_FCs, λ_β) = −7.1390 × 10⁻¹⁹, cov(λ_ε, λ_β) = −3.4497 × 10⁻²⁶) and one must take account of the covariances in error propagation by either linear or Monte Carlo methods. ⁴⁰Ar/³⁹Ar age errors estimated from these results are significantly reduced relative to previous calibrations. Also, age errors are smaller for a comparable level of isotopic measurement precision than those produced by the ²³⁸U/²⁰⁶Pb system, because the ⁴⁰Ar/³⁹Ar system is now jointly calibrated by both the ⁴⁰K and ²³⁸U decay constants, and because λ_ε(⁴⁰K) < λ(²³⁸U). Based on this new calibration, the age of the widely used Fish Canyon sanidine standard is 28.305 ± 0.036 Ma. The increased accuracy of ⁴⁰Ar/³⁹Ar ages is now adequate to provide meaningful validation of high-precision U/Pb or astronomical tuning ages in cases where closed system behavior of K and Ar can be established.     

Stuart vortices on a beta-plane

We study an inviscid mixing layer in the beta-plane model of a rotating fluid. Using a weakly nonlinear expansion, we find two-dimensional finite-amplitude waves of permanent form; these solutions are similar to those found earlier for a non-rotating mixing layer, but lose their symmetry because of the rotation. These vortices may propagate with constant phase velocity, the propagation speed being chosen to make the expansion as regular as possible. Alternative solutions are produced using a nonlinear critical layer analysis to remedy potential singularities which appear in the weakly nonlinear expansion. These alternative solutions also lose their symmetry because of the rotation and may also propagate with constant phase velocity.     

Dispersive Particle Transport: Identification of Macroscale Behavior in Heterogeneous Stratified Subsurface Flows

Dispersive mass transport processes in naturally heterogeneous geological formations (porous media) are investigated based on a particle approach to mass transport and on its numerical implementation using LPT3D, a Lagrangian Particle Tracking 3D code. We are currently using this approach for studying microscale and macroscale space–time behavior (advection, diffusion, dispersion) of tracer plumes, solutes, or miscible fluids, in 1,2,3-dimensional heterogeneous and anisotropic subsurface formations (aquifers, petroleum reservoirs). Our analyses are based on a general advection-diffusion model and numerical scheme where concentrations and fluxes are discretized in terms of particles. The advection-diffusion theory is presented in a probabilistic framework, and in particular, a numerical analysis is developed for the case of advective transport and rotational flows (numerical stability of the explicit Euler scheme). The remainder of the paper is devoted to the behavior of concentration, mass flux density, and statistical moments of the transported tracer plume in the case of heterogeneous steady flow fields, where macroscale dispersion occurs due to geologic heterogeneity and stratification. We focus on the case of perfectly stratified or multilayered media, obtained by generating many horizontal layers with a purely random transverse distribution of permeability and horizontal velocity. In this case, we calculate explicitly the exact mass concentration field C(x, t), mass flux density field f(x, t), and moments. This includes spatial moments and dispersion variance ² _x (t) on a finite domain L, and temporal moments on a finite time scale T, e.g., the mass variance of arrival times ² _T (x). The moments are related to flux concentrations in a way that takes explicitly into account finite space–time scales of analysis (time-dependent tracer mass; spatially variable flow through mass). The multilayered model problem is then used in numerical experiments for testing different ways of recovering information on tracer plume migration, dispersion, concentration and flux fields. Our analyses rely on a probabilistic interpretation that emerges naturally from the particle approach; it is based on spatial moments (particle positions), temporal moments (mass weighted arrival times), and probability densities (both concentrations and fluxes). Finally, as an alternative to direct estimations of the flux and concentration fields, we formulate and study the Moment Inverse Problem. Solving the MIP yields an indirect method for estimating the space–time distribution of flux concentrations based on observed or estimated moments of the plume. The moments may be estimated from field measurements, or numerically computed by particle tracking as we do here.     

Chrysophyte cysts as paleolimnological indicators of environmental change due to cottage development and acidic deposition in the Muskoka-Haliburton region, Ontario, Canada

Chrysophyte cysts preserved in recent and pre-industrial lake sediment samples from 54 Muskoka-Haliburton (Ontario) lakes were used in a paleolimnological study to determine the impact of acidic precipitation and cottage development on water quality. A total of 246 cyst morphotypes were identified. Ecological preferences of cyst morphotypes were determined using multivariate statistical analysis, cluster analysis, and species-environment correlations. Recent cyst assemblages were related to water chemistry and lake morphometric variables using Redundancy Analysis (RDA). The distribution of morphotypes was related to a gradient of acid neutralising capacity (ANC), expressed through the association of variables related to buffering (i.e. longitude, watershed area, and ionic concentration) with the first axis (₁ = 0.29). Cyst assemblages were also defined, to a lesser extent (₂ = 0.06), by a trophic status gradient, created through the combination of total nitrogen (TN), total phosphorus (TP), volume-weighted cottage density, and lake depth variables. The identification of lakewater pH and trophic status as important determinants of cyst assemblage structure allowed for the reconstruction of acidification and eutrophication related water chemistry changes using fossil cyst assemblages. The reconstruction of pre-industrial (pre-1850) water quality conditions with fossil cyst assemblages indicated that pH significantly decreased in 24.1% of the study lakes and increased in 16.7% of the lakes. Increases in pH in more alkaline drainage basins are attributed to alkalinity generation processes induced by acidic precipitation as has been shown in other studies. Total phosphorus (TP) concentrations significantly declined in 12.9% of the lakes and increased in 16.6% of lakes. Increases in [TP] were linked to cottage development. Decreases in trophic status may be due to landuse changes, the result of the acidification occurring in the area, or warmer and drier climates. A comparison of chrysophyte cyst and diatom water quality inferences show similar trends in pH changes. There is a good agreement between diatom and chrysophyte bioindicators with respect to [TP] changes in oligotrophic lakes (< 10 g/L); however, diatom inferences suggest that lakes with current [TP] values greater than 10 g/L have decreased in trophic status over time, while chrysophyte reconstructions suggest that these same lakes have become more productive systems.     

Quaternary of Chile: The state of research

The aim of this paper is to present a summary of current knowledge about Quaternary climatic changes, sea level fluctuations, tectonic deformation, and volcanic activity in Chile. In the Andean highlands of the hyperarid desert, glaciers and lakes fluctuated repeatedly. Evidence of pluvial periods is not well documented in the marginal desert. On the contrary, pronounced climatic changes are recorded in semiarid Chile. In central Chile two or three major glacial advances have been identified, but they remained confined within the high Cordillera. In the longitudinal valley of the Lake Region geomorphic remnants of four glaciations have been described; ¹⁴C dates are available for the last glaciation. The glacial history of the Fjord Region is still obscure. Whether Pleistocene climatic changes in the northern and southern part of Chile were synchronous or not is a problem which requires further investigation. Sea level fluctuations along the Chilean coast are in part ascribed to glacio-eustatic effects. They left striking sets of step-like marine terraces in northern and central Chile. From a paleontologic point of view the Pleistocene corresponds to a pronounced move toward isolation and endemic development of the marine fauna. The Quaternary tectonic tendency seems to be toward extension and not compression expected as sea-floor spreading compensation. Normal faults limiting uplifted, downwarped, and tilted blocks are common. Folds are rarely found. Northern Chile is characterized by an imposing chain of about 600 stratovolcanoes. They rest on Tertiary ignimbrites which cover the altiplano. Quartz-bearing latite-andesites are predominant. Present volcanic activity is sporadic and weak. South of a conspicuous gap between 27 and 33°S, Quaternary volcanism reappears in the high Cordillera, and many volcanoes have erupted violently within historic times. Rocks are fundamentally andesite or basaltic andesite. Poorly sorted ashes including pumice clasts in the Central Valley south of Santiago are interpreted as volcanic mudflows of late Pleistocene age.     

Die tertiäre und quartäre Entwicklung im Bereich der Kufrah-Oasen (Zentrale Sahara) unter besonderer Berücksichtigung aktualistischer Vorgänge

Zusammenfassung Im Verlauf der Oberkreide und des Tertiärs bestand im Bereich der Kufrah-Oasen eine Einebnungstendenz, die mit der Bildung einer Peneplain ihre Vollendung fand. Die Umlagerungsprodukte, nur wenige Meter mächtige Sande und Feinkiese, wurden während einer warmfeuchten Klimaperiode lateritisiert und anschließend unter semiariden Bedingungen zur Eisenkruste I verhärtet. Auf den geringfügig höher gelegenen Iateritfreien Erosionsflächen kam es zur Ausbildung einer Silikatkruste. Ein Wechsel zu feuchterem Klima und eventuelle schwache epirogenetische Hebungen des Gebietes bewirkten eine teilweise Erosion der Silikat- und der Eisenkruste sowie der Sedimente der Nubischen Serie. Dabei entstanden teils brecciöse, teils fanglomeratartige Sedimente, die sowohl auf der Eisenkruste I als auch auf dem mesozoischen Untergrund abgelagert wurden. Erneute Klimaveränderungen führten jetzt zur Laterisierung und Verhärtung der vorliegenden maximal 10–12 m mächtigen Sedimente und zur Entstehung der Eisenkruste II.Eine Tiefenerosion setzte ein, die die bestehende Peneplain in Insel- und Tafelberge auflöste. Eine kurzzeitige Unterbrechung der Erosion im Altquartär begünstigte die Sedimentation von Kiesen und von Grobschutt auf einem ca. 50 m unterhalb der ehemaligen Peneplain gelegenen Niveau. Der Grobschutt wurde ebenfalls lateritisiert zur Eisenkruste III.Eine Analyse des fossilen aquatischen Systems zeigt ein stark verzweigtes Flußsystem, das das gesamte Gebiet der Kufrah-Oasen von SW nach NE entwässerte. Die Erosionsprodukte wurden zum größten Teil abtransportiert. Daher sind nur geringmächtige fluviatile Sedimente erhalten.Mit dem Ende des Pleistozän wurde die aquatische Erosionstätigkeit durch Wechsel von feuchtem zu trockenem Klima mit wenigen Ausnahmen beendet. Es kam zur Ablagerung feinklastischer limnischer Sedimente in lokalen Depressionen, denen äolische Sande zwischengeschaltet wurden. In dieser Übergangsphase bildeten sich Schwemmfächer am Fuße von Schichtstufen und Inselbergen, wobei zum Teil bereits existierende Sanddünen überlagert wurden. Es vollzog sich alternierend ein Wechsel von feuchtem zu trockenem Klima. Der Beginn einer ariden Klimaentwicklung kann in die Zeit um 6000 B. P. gesetzt werden.Die meteorologischen Daten der Station Kufrah seit 1933 zeigen nur noch eine äolische Aktivität als Wechselwirkung von Erosion und Sedimentation an. Reliktflächen sind die Hammada- und Serirflächen; überwiegend Sedimentation findet in der Ausbildung von Dünen und Sandtennen statt. Die Sandtennen sind in multimodale ebene und bimodale undulierende Tennen zu unterteilen. Die Bimodalität ist eine Funktion des selektiven Abtransportes mittlerer Korngrößen und deren Anreicherung als Sanddünen oder Sandanwehungen. Die undulierenden Sandtennen sind daher eine Weiterentwicklung ebener Sandtennen. Dünen existieren in Form von Seif- und Barchandünen oder als eine Kombination aus beiden.Die aktualistischen Vorgänge des vollariden Gebietes der Kufrah-Oasen zeigen eine Tendenz zum erneuten Reliefausgleich durch Deflation und Korrasion exponierter Areale und Sedimentation in Depressionen.

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During the Upper Cretaceous and Tertiary time a tendency of relief deplaning existed in the Kufrah-Oasis area which was completed by the development of a peneplain. The eroded material, sands and gravels of a thickness of only a few meters became lateritic during a period of warm and moist and was hardened to ironcrust I during a semiarid climat. On the slightly higher erosional planes without laterite a silicacrust was developed. A change to a more humid climat and possibly slight epirogenic lifting of the territory brought about an in part erosion of the silicacrust, the ironcrust I and the mesozoic rocks. Thereby breccious and fanglomeratic sediments were deposited and after laterization and hardening the ironcrust LI was formed. An indeep erosion began and disolved the existing peneplain into mesas and inselbergs. A short interruption in the erosional activity during Early Quarternary favoured the sedimentation of coarse grained material which was laterized to ironcrust III. An analysis of the fossil aquatic system shows an extensively branched river system which drained the whole territory of the Kufrah area from SW to NE. The eroded material was flushed away to a great extent, so that only some very thin beds of fluvial sediments still exist. At the close of the Pleistocene the aquatic erosional activity ended by a change from humid to arid climate. Only fine clastic limnic sediments were deposited in some local depressions often alternating with aeolian sands. In this transition period alluvial fans developed on the foot of mesas, in some locations sedimentated on top of already existing-sanddunes. The begin of an arid desert climat can be put at approximately 6 000 years before present.The data of the Kufrah meteorological station since 1933 show the possibility of only aeolic activity in form of mutual erosion and sedimentation. The relic planes are the hammada and serir planes. Sedimentation is responsible for the creation of dunes and sandflats. The sandflats can be differenciated into multimodal even flats and bimodal gently undulating flats. The bimodality is a function of the selective removal of sand grains with distinctive diameters and their accumulation as dunes or sand drifts. The undulating sandflats therefore are a further development of the even sandflats. Dunes exist in form of seifdunes or barchan dunes or as combinations of both types.The actualistic events in the fully arid area of the Kufrah-Oasis again show a tendency towards levelling out of the relief by deflation and corrasion of exposed areas and sedimentation in depressions.

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Résumé Au cours du Crétacé supérieur et du Tertiaire, dans la région des Oasis de Koufra eut lieu un aplanissement dont la phase finale a abouti à une pénéplaine. Les produits du remaniement, des sables et des graviers de faible puissance, ont été látéritisés pendant une période chaude et humide indurés sous un climat semi-aride en croute ferrugineuse I. Sur les surfaces d'érosion plus élevées sans latérite se développait une croûte siliceuse. Le changement vers un climat plus humide et de faibles soulèvements tectoniques provoquèrent une érosion partielle des croûtes ferrugineuses et siliceuses et des sédiments de la série nubienne. Par ce remaniement se formaient des brèches et des fanglomérats qui se sont sédimentées aussi bien sur la croûte ferrugineuse I que sur le substratum méozoique. Un nouveau changement de climat provoqua la latéritisation et le durcissement des sédiment bréchiques et fanglomératiques la formation de la croûte ferrugineuse II.A la limite Tertiaire/Quaternaire commenca une érosion intense qui façonna la pénéplaine existente en inselbergs et tafelbergs. Une interruption brève de l'érosion au Quaternaire inférieur favorisa la sédimentation de graviers et blocs à un niveau d'à peu près 50 m inférieur à l'ancienne pénéplaine. Les graviers et les blocs ont été latéritisés ensemble pour former la croûte ferrugineuse III.Une anlyse du système hydrographique du Pleistocéne montre que toute la région des oasis de Koufra était drainée vers le Nord, période durant laquelle aucune sédimentation n'a eu lieu. A la fin du Pleitocène le climat changea une nouvelle fois pour devenir plus sec et l'érosion fluviatile se termina. Dans la phase de transition se déposèrent, au pied des corniches et des inselbergs, des éventails alluviaux en alternance avec le sable éolien. Le changement à un climat plus aride peut être daté à peu près 6000 B. P.Les données météorologiques de la station de Koufra, depuis 1933, ne permettent qu'une activité éolienne soit comme sédimentation soit comme érosion. Les surfaces »Hammada« et »Serir« sont des surfaces d'érosion résiduelles. La sédimentation se manifeste sous la forme de dunes et de plaines de sable. Les dunes existent sous forme de barchanes et de seifs; les plaines de sable sont à subdiviser du point de vue de la granulométrie en aires multimodales et en aires ondulées bimodales. La bimodalité est und fonction du transport sélectif des grains moyens.Le processus exogène récent dans la région des oasis de Koufra montre la tendance à un nouvel aplainissement effectué par une déflation et corrasion des terrains en relief et une sédimentation dans les dépressions.

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Gekürzte Dissertation D 77.