Platform-induced clay-mineral fractionation along a northern Tethyan basin-platform transect: implications for the interpretation of Early Cretaceous climate change (Late Hauterivian-Early Aptian)

High-resolution clay-mineral analyses were performed on upper Hauterivian to lower Aptian sediments along a platform-to-basin transect through the northern Tethyan margin from the Neuchâtel area (Switzerland), to the Vocontian Trough (France) in order to investigate links between climate change, carbonate platform evolution, and fractionation patterns in clay minerals during their transport.During the Hauterivian, the northern Tethyan carbonate platform developed in a heterozoan mode, and the associated ramp-like topography facilitated the export of detrital material into the adjacent basin, where clay-mineral assemblages are dominated by smectite and kaolinite is almost absent, thereby suggesting dry-seasonal conditions. During the Late Hauterivian Balearites balearis ammonite zone, a change to a more humid climate is documented by the appearance of kaolinite, which reaches up to 30% of the clay fraction in sediments in the Vocontian Trough. This prominent change just preceded the Faraoni Oceanic Anoxic Event and the onset of the demise of the Helvetic Carbonate Platform, which lasted to the late early Barremian.From the Late Barremian onwards, the renewed growth of the northern Tethyan carbonate platform in a photozoan mode and the associated development of a marginally confined platform topography fractionated the clay-mineral assemblages exported into hemipelagic settings: kaolinite particles were preferentially retained in proximal, platform settings, due to their size and their relatively high specific weight. In the inner platform environment preserved in the Swiss Jura, an average of 32% of kaolinite in the clay fraction is observed during the latest Barremian–earliest Aptian, whereas clay-mineral assemblages of coeval sediments from deeper depositional settings are dominated by smectite and show only minor amounts of kaolinite.This signifies that besides palaeoclimate conditions, the morphology and ecology of the carbonate platform had a significant effect on the distribution and composition of clay assemblages during the Late Hauterivian–Early Aptian along the northern Tethyan margin.     

Land use/cover change in central Tibet, c. 1830–1990: devising a GIS methodology to study a historical Tibetan land decree

In this study, historical Tibetan tax-related data pertaining to cultivated land in central Tibet are studied by means of GIS and compared with contemporary patterns. A Tibetan land decree from 1830 contains aggregated data on the amount of land-based tax units for estates in 57 districts of central Tibet. The purpose of this study is to devise a GIS methodology to study the potential utility of these data for historical geographical research, and to determine the approximate changes in cultivated land areas between 1830 and 1990. Traditional Tibetan tax data are significant for current efforts to construct historical land cover databases of the Tibetan Plateau region for the study of the human dimensions of global change.     

Die Verteilung des Yttriums und der Lanthaniden in einem Olivin-Alkali-Basalt mit Peridotit-Einschlüssen

Zusammenfassung In zwei Peridotit-Einschlüssen und dem sie umgebenden Olivin-Alkali-Basalt des Hirzsteins (Nordhessen) wurde die Verteilung des Yttriums und der Lanthaniden quantitativ bestimmt. Die Summe der Lanthaniden (La-Lu, einschließlich Y) beträgt für die Peridotit-Einschlüsse 10–20 ppm, für den Olivin-Alkali-Basalt 280–360 ppm. Die relative Verteilung der Lanthaniden in den Peridotit-Knollen, bezogen auf Chondrite, gibt keinen Hinweis auf große Unterschiede zwischen den leichteren (La-Sm) und schwereren (Eu-Lu) Elementen. Dagegen sind in dem Olivin-Alkali-Basalt die Lanthaniden La-Sm deutlich stärker angereichert gegenüber den Elementen Eu-Lu. Dieser Befund steht in Einklang mit der Vorstellung, daß die chemisch stärker fraktionierten Olivin-Alkali-Basalte eventuell aus weniger stark differenzierten primären Gesteinen (Eklogit, Granat-Peridotit, tholeiitischer Basalt) entstanden sind. In Übereinstimmung mit anderen Beobachtungen handelt es sich bei den Peridotit-Einschlüssen des untersuchten Vorkommens wahrscheinlich um Gesteinsstücke, die in keiner unmittelbaren genetischen Beziehung zu dem umgebenden Basalt stehen.

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The patterns of the relative distributions of the lanthanides have been determined in two lherzolite inclusions and their surrounding alkaline olivine basalt from a locality in Northern Hessia (Hirzstein), Germany. The total contents of Y, La-Lu in the lherzolite inclusions are 10–20 ppm and in the alkaline olivine basalt 280–360 ppm. There is no great difference in the ratios ppm Y, La-Lu in rocks/ppm Y, La-Lu in chondrites if we compare the light (La-Sm) and the heavier lanthanides (Eu-Lu) in the lherzolite inclusions. In the case of the alkaline olivine basalt however the related ratios increase from Sm to La to a maximum of about 250. These results correspond to an assumption that the alkaline olivine basalts with their higher degree of chemical fractionation are formed from less differentiated primary rocks (eclogite, garnet-peridotite, tholeiitic basalt). The lherzolite inclusions of the investigated locality have probably no direct genetic relation to the surrounding basalt.

     

Das Gondwana-Inlandeis in Südbrasilien

Zusammenfassung Entgegen den früheren Annahmen wird gezeigt, daß das südbrasilianische Gondwana-Inlandeis vom Süden (Riograndensischer Schild) stammt. Die mächtige, weder durch Glazialstauchungen noch durch glaziale oder interglaziale Erosion gestörte und unterbrochene Ablagerungsfolge, die damit ein vom europäischen Glazialdiluvium völlig abweichendes Verhalten zeigt, ist dadurch bedingt, daß das Eis in ein weiträumiges, fortschreitende epirogene Absenkung zeigendes Becken hineinfloß.Mit Unterstützung des Conselho Nacional d. Pesquisas, Rio de Janeiro.     

The transient oasis: Nutrient-phytoplankton dynamics and particle export in Hawaiian lee cyclones

Macronutrients, photosynthetic pigments, and particle export were assessed in two eddies during the E-Flux I and III cruises to investigate linkages between biogeochemical properties and export flux in Hawaiian lee cyclonic eddies. Cyclone Noah (E-Flux I), speculated to be in the ‘decay’ stage, exhibited modest increases in macronutrients and photosynthetic pigments at the eddy center compared to ambient waters. Cyclone Opal (E-Flux III) also exhibited modest increases in macronutrient concentrations, but a 2-fold enhancement in total chlorophyll a (TChl a) concentration within the eddy center. As indicated by fucoxanthin concentrations, the phytoplankton community in the deep chlorophyll maximum (DCM) of Opal was comprised mainly of diatoms. During an 8-day time series in the center of Opal, TChl a concentration and fucoxanthin in the DCM decreased by 50%, which was potentially triggered by silicic acid limitation. Despite the presence of a substantial diatom bloom, Opal did not deliver the expected export of particulate carbon and nitrogen, but rather a large biogenic silica export (4-fold increase relative to export in surrounding waters). Results suggest that controls on the life cycle of a Hawaiian lee cyclone are likely a combination of physical (eddy dynamics), chemical (nutrient limitation), and biological (growth and grazing imbalance) processes. Comparisons between Noah and Opal and previously studied cyclones in the region point to a relationship between the spin-up duration of a cyclone and the resulting biological response. Nonetheless, Hawaiian lee cyclones, which strongly influence the biogeochemistry of areas 100's of km in scale in the subtropical North Pacific Ocean, still remain an enigma.     

A time-series study of particulate matter export in the North Pacific Subtropical Gyre based on Th : U disequilibrium

Depth profiles of total ²³⁴Th (dissolved+particulate) were collected at Station ALOHA (22°45N, 158°00W) in the North Pacific Subtropical Gyre during 9 cruises from April 1999 to March 2000. Samples were collected and processed by a new 2 L technique that enables more detailed depth resolution then previous ²³⁴Th studies. Significant zones of particle export (²³⁴Th deficiency) and particle remineralization (²³⁴Th excess) were measured both temporally and with depth. ²³⁴Th derived particulate carbon (PC) and nitrogen (PN) fluxes were determined with steady-state and non-steady-state models and PC/²³⁴Th and PN/²³⁴Th ratios measured with both in situ pumps and free-drifting particle interceptor traps deployed at 150 m. ²³⁴Th based export estimates of 4.0±2.3 mmol C m⁻² d⁻¹ and 0.53±0.19 mmol N m⁻² d⁻¹, were approximately 60% higher than those measured in PIT style sediment traps from the same time period, 2.4±0.2 mmol C m⁻² d⁻¹ and 0.32±0.08 mmol N m⁻² d⁻¹. Most of this difference is attributable to two large export events that occurred during October and December 1999, when traps undercollected for ²³⁴Th by a factor of 2 to 4. ²³⁴Th export (ThE) ratios based on ²³⁴Th derived PC flux/¹⁴C based primary production ranged from 4% to 22% (average=8.8%). Our results confirm the recent estimates of C export by Emerson et al. (Nature 389 (1997) 951) and Sonnerup et al. (Deep-Sea Research I 46 (1999) 777) and indicate that C export from the oligotrophic ocean must be considered when discussing C sequestration in global climate change.     

Improved normalization of time‐lapse seismic data using normalized root mean square repeatability data to improve automatic production and seismic history matching in the Nelson field

Updating of reservoir models by history matching of 4D seismic data along with production data gives us a better understanding of changes to the reservoir, reduces risk in forecasting and leads to better management decisions. This process of seismic history matching requires an accurate representation of predicted and observed data so that they can be compared quantitatively when using automated inversion. Observed seismic data is often obtained as a relative measure of the reservoir state or its change, however. The data, usually attribute maps, need to be calibrated to be compared to predictions. In this paper we describe an alternative approach where we normalize the data by scaling to the model data in regions where predictions are good. To remove measurements of high uncertainty and make normalization more effective, we use a measure of repeatability of the monitor surveys to filter the observed time‐lapse data. We apply this approach to the Nelson field. We normalize the 4D signature based on deriving a least squares regression equation between the observed and synthetic data which consist of attributes representing measured acoustic impedances and predictions from the model. Two regression equations are derived as part of the analysis. For one, the whole 4D signature map of the reservoir is used while in the second, 4D seismic data is used from the vicinity of wells with a good production match. The repeatability of time‐lapse seismic data is assessed using the normalized root mean square of measurements outside of the reservoir. Where normalized root mean square is high, observations and predictions are ignored. Net: gross and permeability are modified to improve the match. The best results are obtained by using the normalized root mean square filtered maps of the 4D signature which better constrain normalization. The misfit of the first six years of history data is reduced by 55 per cent while the forecast of the following three years is reduced by 29 per cent. The well based normalization uses fewer data when repeatability is used as a filter and the result is poorer. The value of seismic data is demonstrated from production matching only where the history and forecast misfit reductions are 45% and 20% respectively while the seismic misfit increases by 5%. In the best case using seismic data, it dropped by 6%. We conclude that normalization with repeatability based filtering is a useful approach in the absence of full calibration and improves the reliability of seismic data.     

Lo strato base dell'atmosfera come determinante il clima delle Alpi

Zusammenfassung Die gewöhnlichen klimatologischen Betrachtungen insbesondere diejenigen mit Hilfe von Klimakarten beziehen sich auf das Makroklima der Erde. Als Extrem steht das Mikroklima in der üblichen Definition gegenüber. Die von beiden Betrachtungen behandelten Räume sind grössenordnungsmässig so verschieden, dass es zweckmässig ist, zwischen die genannten Klimabereiche noch das Mesoklima einzuschalten. Der Gültigkeitsbereich für die vorgenennten Begriffe wird für das Klima der Hochgebirge besprochen. Die Gebirgsatmosphäre wird als Gegenstand des Makroklimas anzusehen sein. Die Atmosphären der Berghänge und der Täler sind dagegen als Gegenstand des Mesoklimas anzusehen. 1) Die Schneedecke in den Hochgebirgen ist von besonderer Empfindlichkeit gegenüber der vertikalen Verteilung der Temperatur, daher ist die durchschnittliche Lage der Peplopause von entscheidender Bedeutung für die Andauer der Schneedecke in Hochgebirgen. 2) Die Peplopause ist entscheidend für die Vertikalgliederung der unteren Schichten der freien Atmosphäre, sie ist in ähnlicher Weise entscheidend für die Verteikalgliederung im Makroklima der Hochgebirge. Dies lässt sich durch die vertikale Verteilung der relativen Feuchtigkeit besonders deutlich zeigen. 3) Der Charakter der Grundschicht im Bereich der Gebirgsatmosphäre ist beispielsweise entscheidend für die Ausbildung der Gewitter in Hochgebirgen. 4) Die tiefsten Minimatemperaturen in Mitteleuropa wurden auf der Gestettneralm bei Lunz in Niederösterreich beobachtet. Neben den besonderen lokalen Verhältnissen war die Lage der Station oberhalb der Peplopause massgebend. 5) Der Temperaturgegensatz zwischen freier Atmosphäre und Berggipfeln ist verschieden für die Grundschicht einerseits und für die Peplopause und die darüberliegenden Schichten andrerseit. 6) Der Einfluss der Massenerhebungen auf die Gebirgsatmosphäre ist nach neueren Untersuchungen nicht mehr in einer thermischen Begünstigung zu sehen. Dass im Innern des Alpenmassivs Waldgrenze und alpine Schneegrenze höher liegen als in den Randzonen muss auf besondere Verhältnisse im Makroklima des Gebirges zurückgeführt werden und hier wird wiederum die durchschnittliche Lage der Peplopause von Einfluss sein.