This paper concerns a multiobjective optimization problem for an underwater ultrasonic transducer based on the porous piezoelectric ceramics. The number of the design variables was decreased using ...the obtained dependences for the effective characteristics of PZT material on porosity. The optimization problem based on the Pareto-frontier calculation has been solved using the live-link of finite-element (FE) package Comsol Multiphysics with MATLAB.
Newly collected Rhaetian plant compressions of the seed fern
Ptilozamites nilssonii Nathorst 1878 from Jameson Land, Eastern Greenland, revealed both simple and forked, unipinnate and bipinnate ...morphologies, indicating a closer relationship between the genera
Ptilozamites Nathorst 1878 and
Ctenozamites Nathorst 1886 than previously documented. Cuticle analysis revealed micromorphological traits typical of simply pinnate
P. nilssonii on bipinnate leaf forms, yet up until the discovery of this material
Ptilozamites has never been considered bipinnate. In 1886, the genus
Ctenozamites was erected for species similar in epidermal characters to
Ptilozamites, but presenting a typical bipinnate character, rarely or never unipinnate. As the new Greenland material collected from South Tancrediakløft and Astartekløft have shown, both genera are now very strongly related anatomically, and therefore identical from a systematic point of view. We therefore propose the use of the genus
Ptilozamites as
Ctenozamites Nathorst 1886 is a synonym of
Ptilozamites Nathorst 1878.
This paper critically appraises the evidence for a succession of ice-dammed lakes in the central Strait of Magellan (c. 53°S) c. 17 000-12 250 cal. yr BP. The topographic configuration of islands and ...channels in the southern Strait of Magellan means that the presence of lakes provides compelling constraints on the position of former ice margins. Lake shorelines and glacio-lacustrine sediments have been dated by their association with a key tephra layer from Volcan Reclús (c. 15 510-14 350 cal. years bp) and by
14
C-dated peats. The timing of glacial lake formation and associated glacier readvances is at odds with the rapid and widespread glacier retreat of the Patagonian ice fields further north after c. 17 000 cal. yr bp, suggesting rather that the lakes were coeval with the Antarctic Cold Reversal and persisted to the Late-glacial/Holocene transition. This apparent asymmetrical latitudinal response in glacier behaviour may reflect overlapping spheres of northern hemisphere and Antarctic climatic influence in the Magellan region.
Previously published platinum group element (PGE) and rare earth element data (REE) from a sample suite of the Palaeogene flood basalts of the East Greenland rifted margin are used to approximate ...primary magma compositions by numerical models of mantle melting. Both high-Ti and low-Ti basalts are found intercalated in the coastal section "the Sortebre Profile" in central East Greenland, and the apparent lack of mixing between the two series indicates coexistence of two geographically separated melting regions and plumbing systems during continental breakup above the Palaeogene Iceland plume. The lavas show little or no sign of crustal contamination and the limited variation in La/Sm and Cu/Pd ratios can be interpreted to reflect mantle source composition and melting processes. Numerical modelling indicate that the low-Ti series formed by F ~20% melting in a columnar melting regime from a slightly depleted upper mantle source with a relatively normal S-content (~180 ppm S). In contrast, the high-Ti series formed by much lower degrees of melting ( F ~6%) in a spreading-related, triangular melting regime from a relatively S-poor (~100 ppm S) source. The low-Ti suite was S-undersaturated at the stage of melt segregation from a shallow mantle source due to the high degree of melting. In contrast, the high-Ti suite probably formed from a S-poor source where some low degree melt batches were S-saturated at the stage of deep segregation in distal parts of the triangular melting regime. This suite shows a geochemical high pressure garnet-signature and adiabatic decompression could therefore have played a role in keeping the mantle-derived S in solution before Fe-enrichment related to fractional crystallisation also increased the S-capacity of these melts. PUBLICATION ABSTRACT
Integrated field structural studies and SHRIMP U–Pb zircon and monazite dating have been undertaken in Renland, west of Scoresby Sund district in the southern part of the East Greenland Caledonides. ...Southwest Renland is dominated by metasedimentary rocks correlated with the Krummedal supracrustal succession of East Greenland and which on Renland were intruded by augen granites. Krummedal psammite from Renland yielded a spectrum of Mesoproterozoic to Palaeoproterozoic detrital U–Pb zircon dates, the youngest of which indicate deposition of the psammite occurred c. 1000 Ma ago, thus post-dating Grenvillian continent–continent collision in North American Laurentia. These Krummedal metasediments were deformed into regional nappe-scale folds prior to metamorphism, crustal anatexis and genesis of augen granites; an example of the latter has been dated at 915±18 Ma (U–Pb zircon). This demonstrates early Neoproterozoic high-temperature tectono-metamorphism affecting rocks within the southern East Greenland Caledonides, broadly contemporaneous with similar rocks farther north in East Greenland and with Sveconorwegian events on Baltica. Still in southwestern Renland, a later thermal event led to development of uppermost amphibolite to granulite facies metamorphic assemblages, veins and patches of in situ garnetiferous melt-bearing neosome in both metasediments (432±6 Ma, U–Pb zircon) and in the augen granites, and contemporaneous biotite-bearing granite sheets in top-down-to-the-E extensional shear zones (434±5 Ma, U–Pb zircon). Monazites from southwestern Renland record Caledonian thermal events as late as 410−400 Ma. In contrast, southeastern Renland is dominated by quartzofeldspathic migmatites with a strongly Caledonian signature but enclosing relicts of augen granite and retrogressed granulite facies psammitic and pelitic metasediment. There is also a sequence of Caledonian granitoid intrusions. Two samples from a hypersthene monzonite intrusion yielded U–Pb zircon dates of 424±8 Ma and 424±6 Ma. This pluton shows the marginal effects of the regional migmatization and was intruded early in the sequence of granitoid emplacement. An amphibolite facies migmatite, textural evidence from which suggests that it had never hosted granulite facies assemblages, records zircon growth at 423±6 Ma, and closure of monazite by 402±10 Ma. High grade metamorphism, and the protracted sequence of granitoid emplacement and still younger thermal events which together span the period between 430 and 400 Ma may, in part, reflect complicated lithospheric dynamics associated with subduction outboard of the Laurentian margin. Crustal segments carrying the relict evidence of Neoproterozoic and early Caledonian events must then quickly have been thrust northwestwards in foreland-propagating, northwesterly directed thrusts over Cambro-Ordovician platformal sequences on the Laurentian margin. This records the final closure of Iapetus, encroachment of Baltica and continent–continent collision from late Llandovery times (425–430 Ma).
Laminated glacimarine sediments are observed in visual core logs and x‐radiographs from Scoresby Sund and Nansen Fjord, east Greenland. They are mostly underlain and overlain by massive or stratified ...glacimarine diamicton (Dmm or Dms), which is a product of iceberg delivery of heterogeneous debris and, in Scoresby Sund, reworking by deep‐drafted iceberg keels. The laminated sediments are AMS radiocarbon dated to two cold periods since the last, Late Weichselian deglaciation: the Younger Dryas stadial (Milne Land Stadial in east Greenland) and the Little Ice Age. During cold climatic events, multiyear shorefast sea ice (‘sikussak’) formed in these fjords and trapped the icebergs. Fine‐grained, laminated muds (Fl) were deposited in Scoresby Sund when the flux of icebergs was suppressed, but turbid meltwater continued to provide some sediment flux to the fjord systems, varying through time to produce laminations. In Nansen Fjord, thinner and often massive mud layers (Fm) resulted from shorter intervals of sea‐ice cover with no ice rafting. Stratified diamicton layers (Dms), which alternate with mud deposition to produce a laminated unit, probably represent intervening times of more open conditions with iceberg rafting. In Scoresby Sund, foraminifera are either absent from the laminated unit or begin to appear towards the end of its deposition. The absence of both benthic and planktonic foraminifera also suggests that multiyear sea ice was covering the core sites. There is no evidence of macrofaunal activity, and bioturbation is absent from the laminated sediments. Satellite data show that multiyear shorefast sea ice is present in several areas of the high Arctic today, and this traps icebergs calved from interior ice‐cap drainage basins. Thus, the process of laminated glacimarine sediment formation is likely to be applicable to a number of areas of the modern and Quaternary Arctic.
Ion chromatography data of Ca, Mg, Cl and Ca and Coulter® counter particle measurements are used to study the cycle of marine and continental primary aerosol reaching Greenland in relation to ...climatic changes over the last 150 kyr. A detailed comparison between Greenland (Dome Summit) and Antarctic (Vostok) records provides new insight on a potential link between northern and southern patterns. Ca is a good indicator of continental input and is mainly emitted as CaCO3. An attempt is made to estimate the contribution of aluminosilicates using the concentration of insoluble particles greater than 0.5 μm in diameter. The relative abundance of non‐sea‐salt Mg and Ca and of aluminosilicate shows that the calcium content of continental background aerosol over Greenland was much higher during the glacial age. The neutralization capacity of carbonaceous aerosol is estimated. The inverse relationship between δ18O and continental input as well as the response of this input to the rapid climatic variations that have occurred during the second part of the glacial age are discussed in terms of source and transport modification in relation to the presence and the extent of the great Laurentide ice cap. The corresponding Vostok profiles strongly suggest that some of the phenomena observed at high northern latitudes are of global concern. The marine component of Na (Nam) is a good tracer of sea‐salt aerosol. Similarly to continental input, it shows an inverse but more linear relationship with δ18O. The sensitivity of Greenland and Antarctic marine input to climate variations of small and large amplitude is compared, and a corresponding estimation is made for the aeolian contribution. The respective influence of atmospheric circulation and the water vapor cycle is discussed. The chlorine to marine sodium weight ratio increases with temperature from values very close to the bulk seawater ratio during the last glacial maximum (18–20 kyr B.P.) to values significantly higher during the Holocene and warm Eemian. The corresponding excess of chloride (HCl) is discussed in terms of atmospheric transport, taking into account the role of atmospheric acidity on sea‐salt fractionation processes. Owing to postdepositional phenomena, similar Vostok data must be considered cautiously. Nevertheless, aerosol fractionation seems to have been much more important over the Vostok site, except during glacial extrema.
Two Palaeoproterozoic volcanic successions, the Hekla Sund (HS) Formation and the Aage Berthelsen Gletscher (AaB) Gletscher Formation, occur within the Caledonian orogen of eastern North Greenland. ...They consist mainly of mafic pillow lavas, deformed and metamorphosed under greenschist-facies conditions during the Caledonian orogeny. Zircons from a rhyolitic ignimbrite in the HS Formation have yielded an age of 1740±6 Ma. In both formations the volcanic rocks are intercalated with immature sandstones and conglomerates that accumulated in the vicinity of active fault scarps; a shallow marine, rifted basin is implied. Relative concentrations of the more immobile minor and trace elements (Ti, Zr, Nb, Y and rare-earth elements) in both rock suites were unaffected by the metamorphism. Fractional crystallisation of olivine, clinopyroxene and, probably, plagioclase, as well as assimilation of crustal rocks was involved in the petrogenesis of the HS Formation. The AaB basalts have higher Mg, Ni and Cr and lower concentrations of incompatible elements than the rocks of the HS Formation, and they could be regarded as more primitive products of the same magmatic event. However, marked differences in incompatible trace element ratios in the two suites are unlikely to reflect either differences in fractionation histories or variable contamination, and suggest compositional differences in the mantle source rocks. Basalts from the two formations have distinct
ε
Nd values (−4.6 and −4.8 for the HS Formation, −5.9–−5.6 for the AaB Gletscher Formation), which is consistent with this interpretation. The volcanic rocks at HS and AaB Gletscher were erupted shortly after a long period of orogenic activity between 2000 and 1750 Ma ago. Following post-orogenic emplacement of granites at ca. 1750–1740 Ma, uplift and erosion took place, and accumulation of extensive immature sediments occurred simultaneously with formation of the volcanic rocks described in this paper. The magmatism that gave rise to the two formations may have been caused by melting during lithospheric extension.
The East Greenland record of glaciation and environmental change is based on a combination of onshore and offshore studies. Glaciological work on contemporary outlet glaciers provides background for ...interpreting the glaciation styles of the past. The Scoresby Sund fjord system, the single largest outlet of the Inland Ice in East Greenland, and the adjacent continental shelf and slope, were the main working areas. The regionality of these results was tested with onshore and offshore work on sites further to the north in the East Greenland fjord zone.
The record spans the period since Isotope Stage 7 (ca 240
ka). The most extensive glaciation phases were the Lollandselv and Scoresby Sund glaciations (Isotope Stages 7 and 6). The Langelandselv interglaciation (Isotope Substage 5e) comprises shallow marine sediments at more than 20 sites onshore, and
Cibicides wuellerstorfii carrying sediments on the continental slope. Summer temperatures were 2–3° warmer than the Holocene optimum, and there was vigorous advection of warm Atlantic water into the fjords. The warm period seems to be accompanied by a eustatic sea-level rise of ca 20
m. During the Weichselian there were three major glacier advances, the Aucellaelv, Jyllandselv, and Flakkerhuk stades (Isotope Substages 5d, ?5b, and Stages 3–2). All three advances mark a shift from one topographically determined stable position to another. In each phase the glaciers occupied almost the same space in the fjord basins and had their fronts on the inner shelf. But the glacial regime and duration was different. The Aucellaelv stade lasted ca 10
ka, and the regime resembled that of present day outlet glaciers 600
km further to the north. The Flakkerhuk stade lasted for ca 50
ka, but left only thin and sporadic till, as well as glaciolacustrine sediments in ice-dammed river valleys. The regime was polar, similar to present day glaciers in Antarctica. Its culmination, the last glacial maximum, in the period between 22 and 14
ka, is shown by a maximum in IRD deposition on the continental slope. After 12
ka, and before 10
ka, the outer fjord basins in the southern fjord zone had been abandoned by the glaciers, and at ca 9.5
ka the last resurgence, the Milne Land stade, had ended.
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