Paleoenvironment and sea-level change in the early Cretaceous Barents Sea—implications from near-shore marine sapropels     

Uwe?LangrockEmail author  Ruediger?Stein  Marcus?Lipinski  Hans-Jürgen?Brumsack 《Geo-Marine Letters》2003,23(1):34-42

The late Volgian (early "Boreal" Berriasian) sapropels of the Hekkingen Formation of the central Barents Sea show total organic carbon (TOC) contents from 3 to 36 wt%. The relationship between TOC content and sedimentation rate (SR), and the high Mo/Al ratios indicate deposition under oxygen-free bottom-water conditions, and suggest that preservation under anoxic conditions has largely contributed to the high accumulation of organic carbon. Hydrogen index values obtained from Rock-Eval pyrolysis are exceptionally high, and the organic matter is characterized by well-preserved type II kerogen. However, the occurrence of spores, freshwater algae, coal fragments, and charred land-plant remains strongly suggests proximity to land. Short-term oscillations, probably reflecting Milankovitch-type cyclicity, are superimposed on the long-term trend of constantly changing depositional conditions during most of the late Volgian. Progressively smaller amounts of terrestrial organic matter and larger amounts of marine organic matter upwards in the core section may have been caused by a continuous sea-level rise.  相似文献   

Paleoenvironmental reconstruction of the Early to Middle Miocene Central Paratethys using stable isotopes from bryozoan skeletons     

Marcus M. Key Jr.  Kamil Zágoršek  William P. Patterson 《International Journal of Earth Sciences》2013,102(1):305-318

Stable carbon and oxygen isotope values from single bryozoan colonies were used to reconstruct the paleoenvironments of the Early to Middle Miocene (Ottnangian to Badenian) sediments of the Central Paratethys. This approach utilizes a locally abundant allochem while avoiding matrix and multiple allochem contamination from bulk rock samples. Bryozoan colonies (and a few foraminifera and rock matrix samples) from 14 localities yielded 399 carbon and oxygen isotope values. Data from six of the localities (15 % of the total number of samples) were interpreted as having been diagenetically altered and were rejected. The remaining data indicate a primarily localized upwelling signal with lesser variation caused by global climatic and regional tectonic forcing of sea level, salinity, and temperature. Paleotemperatures were calculated to range from 12 to 21 °C. Despite potential taxonomic and diagenetic problems, bryozoan colonies are a powerful, underutilized source of paleoenvironmental carbon and oxygen isotope data.  相似文献   

Jupiter’s shrinking Great Red Spot and steady Oval BA: Velocity measurements with the ‘Advection Corrected Correlation Image Velocimetry’ automated cloud-tracking method     

Xylar S. Asay-Davis  Philip S. Marcus  Imke de Pater 《Icarus》2009,203(1):164-188

We show that between 1996 and 2006, the area circumscribed by the high-speed collar of the Great Red Spot (GRS) shrunk by 15%, while the peak velocities within its collar remained constant. This shrinkage indicates a dynamical change in the GRS because the region circumscribed by the collar is nearly coincident with the location of the potential vorticity anomaly of the GRS. It was previously observed that the area of the clouds associated with the GRS has been shrinking. However, the cloud cover of the GRS is not coincident with the location of its potential vorticity anomaly or any other of its known dynamical features. We show that the peak velocities of the Oval BA were nearly the same in 2000, when the Oval was white, and in 2006, when it was red, as were all of the other features of the two velocities fields. To measure temporal changes in the GRS and Oval, we extracted velocities from images taken with Galileo, Cassini, and the Hubble Space Telescope using a new iterative method called Advection Corrected Correlation Image Velocimetry (ACCIV). ACCIV finds correlations over image pairs with 10-h time separations when other automated velocity-extraction methods are limited to time separations of 2 h or less. Typically, ACCIV velocities produced from images separated by 10 h had errors that are 3-6 times smaller than similar velocities extracted from images separated by 2 h or less. ACCIV produces velocity fields containing hundreds of thousands of independent correlation vectors (tie-points). Dense velocity fields are needed to locate the loci of peak velocities and other features.  相似文献   

The Commonwealth, ‘development’ and post-colonial responsibility     

Marcus Power 《Geoforum》2009,40(1):14-24

One important (though often neglected) part of the ‘development business’ committed to principles of partnership is the Commonwealth, a voluntary association of 54 independent countries, almost all of which were formerly under British rule. This paper focuses on the Commonwealth’s contemporary sense of ‘responsibility’ for shaping African development through ‘partnership’ and by promoting ‘good governance’ and examines the particular example of Mozambique, which joined the Commonwealth in 1995. In exploring exactly what membership of this post-colonial ‘family’ has meant for Mozambique the paper explores the neocolonial paternalism and sense of trusteeship that the Commonwealth has articulated in its often very apolitical vision of African development which seems to lock the continent into a permanent stage of tutelage and to repetitively reduce Africa to a set of core deficiencies for which externally generated ‘solutions’ must be devised. More generally, the paper also examines the wider context of the Commonwealth’s involvement in Africa by looking at the connections it has made to British industry, British charities and the British Department for International Development (DFID). The paper concludes with an assessment of the ‘showcase’ potential of Mozambique and its importance to Commonwealth and DFID narrations of an African ‘success’ story of peace, stability and growth since the end of the country’s devastating civil war in 1992.  相似文献   

Latest Pleistocene and Holocene glacier variations in the European Alps   总被引：1，自引：0，他引：1  

Susan Ivy-Ochs  Hanns Kerschner  Max Maisch  Marcus Christl  Peter W. Kubik  Christian Schlüchter 《Quaternary Science Reviews》2009,28(21-22):2137-2149

In the Alps, climatic conditions reflected in glacier and rock glacier activity in the earliest Holocene show a strong affinity to conditions in the latest Pleistocene (Younger Dryas). Glacier advances in the Alps related to Younger Dryas cooling led to the deposition of Egesen stadial moraines. Egesen stadial moraines can be divided into three or in some cases even more phases (sub-stadials). Moraines of the earliest and most extended advance, the Egesen maximum, stabilized at 12.2 ± 1.0 ka based on ¹⁰Be exposure dating at the Schönferwall (Tyrol, Austria) and the Julier Pass-outer moraine (Switzerland). Final stabilization of moraines at the end of the Egesen stadial was at 11.3 ± 0.9 ka as shown by ¹⁰Be data from four sites across the Alps. From west to east the sites are Piano del Praiet (northwestern Italy), Grosser Aletschgletscher (central Switzerland), Julier Pass-inner moraine (eastern Switzerland), and Val Viola (northeastern Italy). There is excellent agreement of the ¹⁰Be ages from the four sites. In the earliest Holocene, glaciers in the northernmost mountain ranges advanced at around 10.8 ± 1.1 ka as shown by ¹⁰Be data from the Kartell site (northern Tyrol, Austria). In more sheltered, drier regions rock glacier activity dominated as shown, for example, at Julier Pass and Larstig valley (Tyrol, Austria). New ¹⁰Be dates presented here for two rock glaciers in Larstig valley indicate final stabilization no later than 10.5 ± 0.8 ka. Based on this data, we conclude the earliest Holocene (between 11.6 and about 10.5 ka) was still strongly affected by the cold climatic conditions of the Younger Dryas and the Preboreal oscillation, with the intervening warming phase having had the effect of rapid downwasting of Egesen glaciers. At or slightly before 10.5 ka rapid shrinkage of glaciers to a size smaller than their late 20th century size reflects markedly warmer and possibly also drier climate. Between about 10.5 ka and 3.3 ka conditions in the Alps were not conducive to significant glacier expansion except possibly during rare brief intervals. Past tree-line data from Kaunertal (Tyrol, Austria) in concert with radiocarbon and dendrochronologically dated wood fragments found recently in the glacier forefields in both the Swiss and Austrian Alps points to long periods during the Holocene when glaciers were smaller than they were during the late 20th century. Equilibrium line altitudes (ELA) were about 200 m higher than they are today and about 300 m higher in comparison to Little Ice Age (LIA) ELAs. The Larstig rock glacier site we dated with ¹⁰Be is the type area for a postulated mid-Holocene cold period called the Larstig oscillation (presumed age about 7.0 ka). Our data point to final stabilization of those rock glaciers in the earliest Holocene and not in the middle Holocene. The combined data indicate there was no time window in the middle Holocene long enough for rock glaciers of the size and at the elevation of the Larstig site to have formed. During the short infrequent cold oscillations between 10.5 and 3.3 ka small glaciers (less than several km²) may have advanced to close to their LIA dimensions. Overall, the cold periods were just too short for large glaciers to advance. After 3.3 ka, climate conditions became generally colder and warm periods were brief and less frequent. Large glaciers (for example Grosser Aletschgletscher) advanced markedly at 3.0–2.6 ka, around 600 AD and during the LIA. Glaciers in the Alps attained their LIA maximum extents in the 14th, 17th, and 19th centuries, with most reaching their greatest LIA extent in the final 1850/1860 AD advance.  相似文献   

The activities of potassium chloride and of water in Dead Sea brine     

Y Marcus 《Geochimica et cosmochimica acta》1977,41(12):1739-1744

The activities of KCl and of H₂O in Dead Sea water were estimated according to several approaches dealing with multicomponent electrolyte solutions. The activity of H₂O, both measured directly via its vapor pressure and calculated theoretically, is 0.754 ± 0.004 for brine of density 1.207 ± 0.003gcm^?3 at 25°C. The mean ionic activity of KCl in this brine ranges from 0.876 to 1.199 according to various treatments. These correspond to binary aqueous solutions 8.6–12.1 times richer than the brine. The brine cannot be simultaneously in equilibrium with respect to both H₂O and KCl with such binary solutions, so a hypothetically perfect semipermeable membrane cannot lead to a state of equilibrium between the brine and aqueous KCl of any concentration.  相似文献   

Public Participation in Planning: an intellectual history     

Marcus B. Lane 《The Australian geographer》2005,36(3):283-299

This paper tracks the changing role of public participation in planning thought. In doing so, the paper shows that the role of public participation in planning is largely determined by the nature of the planning enterprise being undertaken. The definition of the planning problem, the kinds of knowledge used in planning practice, and the conceptualisation of the planning and decision-making context are the important determinants of the extent of participation offered to the public. The paper therefore contributes to thinking about how to evaluate public participation by showing that it can only be understood in terms of the decision-making context in which it is embedded. Specifically, it makes little sense to evaluate public participation in terms that are not shared by the planning model itself  相似文献   

Exposure assessment using high spatial resolution hyperspectral (HSRH) imagery     

G.M. Jacquez  W. Andrew Marcus  Richard J. Aspinall  Dunrie A. Greiling 《Journal of Geographical Systems》2002,4(1):1-14

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A rifted inside corner massif on the Mid-Atlantic Ridge at 5°S     

T. J. Reston  W. Weinrebe  I. Grevemeyer  E. R. Flueh  N. C. Mitchell  L. Kirstein  C. Kopp  H. Kopp  participants of Meteor / 《Earth and Planetary Science Letters》2002,200(3-4):255-269

The structure of the Mid-Atlantic Ridge at 5°S was investigated during a recent cruise with the FS Meteor. A major dextral transform fault (hereafter the 5°S FZ) offsets the ridge left-laterally by 80 km. Just south of the transform and to the west of the median valley, the inside corner (IC – the region bounded by the ridge and the active transform) is marked by a major massif, characterized by a corrugated upper surface. Fossil IC massifs can also be identified further to the west. Unusually, a massif almost as high as the IC massif also characterizes the outside corner (OC) south of the inactive fracture zone and to the east of the median valley. This OC massif has axis-parallel dimensions identical to the IC massif and both are bounded on their sides closest to the spreading axis by abrupt, steep slopes. An axial volcanic ridge is well developed in the median valley both south of the IC/OC massifs and in an abandoned rift valley to the east of the OC massif, but is absent along the new ridge-axis segment between the IC and OC massifs. Wide-angle seismic data show that between the massifs, the crust of the median valley thins markedly towards the FZ. These observations are consistent with the formation of the OC massif by the rifting of an IC core complex and the development of a new spreading centre between the IC and OC massifs. The split IC massif presents an opportunity to study the internal structure of the footwall of a detachment fault, from the corrugated fault surface to deeper beneath the fault, without recourse to drilling. Preliminary dredging recovered gabbros from the scarp slope of the rifted IC massif, and serpentinites and gabbros from the intersection of this scarp with the corrugated surface. This is compatible with a concentration of serpentinites along the detachment surface, even where the massif internally is largely plutonic in nature.  相似文献   

The S reflector west of Galicia: the seismic signature of a detachment fault     

T. J. Reston 《Geophysical Journal International》1996,127(1):230-244

The so-called S reflector is a group of bright, continuous reflections underlying the landward-tilted fault blocks of the west Galicia rifted margin, S has been interpreted as the brittle-ductile transition, the lop of an intrusion, a detachment fault, and the crust-mantle boundary. To constrain the internal structure of the reflector, we have carried out detailed analyses of these reflections. We compare the waveforms of the seafloor reflection and its first multiple, both to determine the amplitude of the seafloor reflection and to show (hat the seafloor is in effect a spike in the reflectivity series so that the seafloor reflection can be used as the far-field wavelet, including both source and receiver ghosts. We compare (he waveform of the seafloor and 5 and show that, within the resolution of our data, S is a reflection from a step increase in acoustic impedance. This result is confirmed through complex trace analysis, and in particular the determination of the apparent polarity of S, and the examination of the instantaneous frequency function: S is consistently positive polarity, and shows no significant frequency anomaly. Simple modelling shows that S is very unlikely to be a reflection from a thin layer. We thus conclude that S is probably a single steplike interface. From the varying frequency content of the data, we determine a value for the effective Q between S and the seafloor, and use this to assess the amplitude loss due to attenuation and scattering. We use a comparison between the seafloor and the S reflection to constrain the amplitude of S, and estimate a reflection coefficient for S of at least 0.2 in places, decreasing landwards. By analogy with structures developed in the highly extended regions of the western United States, we consider that the most likely interpretation of S is as a sharp west-dipping detachment fault separating a 'granitic' upper plate from a higher-velocity lower plate, locally probably serpentinized mantle.  相似文献