A glacial chronology for northern East Greenland   总被引：3，自引：1，他引：3  

CHRISTIAN HJORT 《Boreas: An International Journal of Quaternary Research》1981,10(3):259-274

In East Greenland between 75 and 76N three different glacial episodes can be identified: (1) An early period with more or less total ice cover and in which the ice reached out onto the continental shelf - the Kap Mackenzie stadial; (2) a period with glaciation of intermediate extent, when nunataks and a few ice-free lowland areas existed - the Muschelbjerg stadial; and (3) a final period with glacial advance, when the glaciers were mainly restricted to fjords and larger valleys - the Nanok stadial. Each of these stadials was followed by a period with general deglaciation, from which marine shell-bearing sediments have been found; the Hochstetter Forland interstadial, the Peters Bugt interstadial and the Flandrian interglacial, respectively. The marine limit sank with each of these ice-free periods; probably an isostatic effect of the decreasing amplitude of the glacial advances. The deglaciation after the Nanok stadial began about 9500 B.P. It is not known for certain when this glacial advance started, but 13,000 B.P. or earlier is suggested. According to ¹⁴C datings the Peters Bugt interstadial dates from at least 45,000 B.P. and the Hochstetter Forland interstadial from at least 49,000 B.P. However, amino acid analyses indicate a distinct age difference between these two interstadial, and Th/U datings give age estimates of 70,000–115,000 B.P. for the Hochstetter Forland interstadial, which therefore seems to be of Early Weichselian age although a pre-Weichselian age cannot be excluded. The same applies to the preceding Kap Mackenzie stadial. The correspondence between the present glacial chronology and similar tripartite ones on Bafffin Island, Ellesmere Island and Svalbard seems reasonably good  相似文献   

Crystallization Pressure and Cooling History of the Giles Layered Igneous Complex, Central Australia   总被引：1，自引：0，他引：1  

BALLHAUS  CHRISTIAN; BERRY  RON F. 《Journal of Petrology》1991,32(1):1-28

The Giles Complex, central Australia, consists of a series oflarge layered gabbroic/ultramafic intrusions emplaced in acidicand intermediate granulites of the Middle Proterozoic Musgraveblock. Lithologies range from well-layered dunite, wehrlite,and pyroxenite in the lower primitive series, to massive olivinegabbro, gabbronorite, and anorthosite in the main units, andferrodiorites, vanadife-rous magnetite layers, and granophyresin the upper, most fractionated parts. Unlike many layered intrusions,the Giles Complex is tectonically dismembered to an extent thata reconstruction of the original morphology is difficult. The Complex is believed to be a type example for medium- tohigh-pressure differentiation. (1) Chilled margin samples (wherepreserved) are orthopyroxene-phyric, and liquidus olivine isreplaced by liquidus orthopyroxene at an mg-number of 0.77,suggesting a pressure-related expansion of the orthopyroxenestability field (Goode & Moore, 1975). (2) Tschermaks substitutioninto pyroxene and plagioclase-orthoclase solid solution areextensive, indicating unusually high crystallization temperaturerelated to high pressure; antiperthites in the Giles Complexare amongst the most calcic reported for terrestrial rocks.(3) The lower primitive cumulate units of the Complex are coroniticand feature a variety of subsolidus high-pressure reaction textures;olivine and cumulus chromite have reacted with calcic plagioclaseto orthopyroxene-clinopyroxene-spinel, olivine-spinel, and clinopyroxene-spinelsymplectites. The principal reaction mechanism for the symplectites was continuousmass transfer of alumina from plagioclase toward spinel, asthe Complex passed from the olivine-plagioclase stability fieldinto the pyroxene-spinel field during cooling. Geothermometersapplicable to the cumulates record a wide range of equilibrationtemperatures from late-magmatic to granulite-metamorphic conditions.FeMg₁ exchange gives closure temperatures around 600–700?C,whereas Al₂Mg₁Si₁ net-transfer equilibria have preserved highertemperatures around 750–900 ?C. Defocused beam bulk analysesof exsolved cumulus clinopyroxenes and intercumulus plagioclasesrecover magmatic compositions; i. e., two-pyroxene solvus CaMg_-1temperatures plot around 1120?50?C, whereas two-feldspar thermometersgive 1200?C. Pressures are calculated from thermochemical data with the heterogeneousequilibria 2 fo + an = en + di + sp, fo + an = di + Mg-Ts, andfo + an = en + Ca-Ts, after correcting spinel activities forselective retrograde FeMg_-1 exchange during cooling. These equilibria,combined with orthopyroxene-spinel Al₂Mg_-1Si_-1 temperaturesfor metamorphic assemblages and two-pyroxene temperatures forcumulus phases define a medium-pressure cooling path extendingfrom 1150 ?C (at 6?5 kb) to 750 ?C (at 6?2 kb). The resultssuggest an isobaric cooling path for the Giles Complex, withno evidence for a post-intrusive metamorphic overprint. Themagmas intruded at lower to middle crustal levels after thepervasive deformation in the Musgrave block, and probably afterthe peak metamorphic event.  相似文献   

Airline networks and the international diffusion of severe acute respiratory syndrome (SARS)   总被引：2，自引：0，他引：2  

JOHN T BOWEN JR    CHRISTIAN LAROE† 《The Geographical journal》2006,172(2):130-144

In fewer than four months in 2003, severe acute respiratory syndrome (SARS) spread from China to 25 countries and Taiwan, becoming the first new, easily transmissible infectious disease of the twenty-first century. The role of air transport in the diffusion of the disease became obvious early in the crisis; to assess that role more carefully, this study relates the spatial-temporal pattern of the SARS outbreak to a measure of airline network accessibility. Specifically, the accessibility from those countries that were infected by SARS, beginning with China, to other countries was measured using airline schedules. The country-pair accessibility measure, along with other country-level factors relevant to the disease, were tested as determinants of the speed with which SARS arrived in infected countries as well as its failure to arrive in most countries. The analyses indicate that airline network accessibility was an especially influential variable but also that the importance of this variable diminished in the latter weeks of the outbreak. The latter finding is partly attributable to public health measures, particularly health screening in airports. The timing and geography of those measures are reviewed using data from media reports and interim World Health Organization (WHO) documents during the outbreak. The uneven effort to curtail the international diffusion of SARS suggests further planning is needed to develop a concerted response to contain future epidemics.  相似文献   

Aspects of the Weichselian chronology in central East Greenland     

SVEND FUNDER  CHRISTIAN HJORT 《Boreas: An International Journal of Quaternary Research》1973,2(2):69-84

From central East Greenland, C₁₄ ages between 19,500 > 40,000 years B.P. have been obtained for six samples of marine bivalve shells. The ages seem to be consistent with geological observations and form the basis for a tentative chronology for the Weichselian ice age in the region. It appears that the maximum glaciation during Weichselian times was attained more than 40,000 years ago, and that since then ice-free areas have existed. This assumption agrees with evidence of botanical refugia in the region, and the restricted glacier activity especially during the Upper Pleniglacial (ca. 30,000–15,000 years B.P.) is explained by a reduced supply of moisture. A comparison with evidence from other parts of Greenland indicates that different glacial histories can be expected for different sectors of the Greenland Inland Ice.  相似文献   

Radiocarbon dated common mussels Mytilus edulis from eastern Svalbard and the Holocene marine climatic optimum     

CHRISTIAN HJORT  JAN MANGERUD  LENA ADRIELSSON  STEIN BONDEVIK  JON Y. LANDVIK  OTTO SALVIGSEN 《Polar research》1995,14(2):239-243

The common mussel Mytilus edulis is an indicator of milder marine conditions in the Arctic, with stronger Atlantic Water influx, during the Holocene and earlier interglacials. Twelve Holocene radiocarbon dates of mytilus from eastern Svalbard fall between ca 8800 and 5000 BP and roughly delimit the marine climatic optimum period there. The beginning of this period in the east coincides with the immigration of boreal extralimital molluscs to western Svalbard, indicating the culmination of Holocene Atlantic influence.  相似文献   

Distinguishing fluvio‐deltaic facies by bulk geochemistry and heavy minerals: an example from the Miocene of Denmark     

METTE OLIVARIUS  ERIK S. RASMUSSEN  VOLKERT SIERSMA  CHRISTIAN KNUDSEN  GUNVER K. PEDERSEN 《Sedimentology》2011,58(5):1155-1179

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Relationship between Late Pleistocene sea‐level variations,carbonate platform morphology and aragonite production (Maldives,Indian Ocean)     

ANDREAS PAUL  JOHN J. G. REIJMER  JÖRN FÜRSTENAU  HANNO KINKEL  CHRISTIAN BETZLER 《Sedimentology》2012,59(5):1640-1658

A piston core from the Maldives carbonate platform was investigated for carbonate mineralogy, grain‐size distributions, calcium carbonate content and organic carbon. The sedimentary record was linked to Late Pleistocene sea‐level variations, using an age model based on oxygen isotopes obtained from planktonic foramanifera, nannofossil biostratigraphy and ¹⁴C age determinations. The correlation between the sedimentary record and Late Pleistocene sea‐level showed that variations in aragonite and mud during the past 150 000 years were clearly related to flooding and sea floor exposure of the main lagoons of the atolls of the Maldives carbonate platform. Platform flooding events were characterized by strongly increased deposition of aragonite and mud within the Inner Sea of the Maldives. Exposure events, in contrast, can be recognized by rapid decreases in the values of both proxy records. The results show that sediments on the Maldives carbonate platform contain a continuous record of Pleistocene sea‐level variations. These sediments may, therefore, contribute to a better understanding of regional and even global sea‐level changes, and yield new insights into the interplay between ocean currents and carbonate platform morphology.  相似文献   

Mineral chemistry of lava flows from Linga area of the Eastern Deccan Volcanic Province,India     

SOHINI?GANGULYEmail author  JYOTISANKAR?RAY  CHRISTIAN?KOEBERL  THEODOROS?NTAFLOS  MOUSUMI?BANERJEE 《Journal of Earth System Science》2012,121(1):91-108

Several basaltic lava flows have been identified in the study area in and around Linga, in the Eastern Deccan Volcanic Province (EDVP) on the basis of distinctly developed structural zones defined by primary volcanic structures such as columnar joints and vesicles. These basaltic lava flows are spatially distributed in four different sectors, viz., (i) Bargona–Gadarwara (BG) sector (ii) Shikarpur–Linga (SL) sector (iii) Arjunvari–Survir Hill (AS) sector and (iv) Kukrachiman–Morand Hill (KM) sector. A three-tier classification scheme has been adopted for the characterization and classification of individual lava flows. Each lava flow consists of a Lower Colonnade Zone (LCZ) overlain by the Entablature Zone (EZ) and Upper Colonnade Zone (UCZ). The LCZ and UCZ grade into a distinct/indistinct Lower Vesicular Zone (LVZ) and Upper Vesicular Zone (UVZ), respectively. The LCZ and UCZ of the flows are characterized by columnar joints while the EZ is marked by multi-directional hackly jointing. The geometry of different joint patterns corresponds to different styles of cooling during solidification of lava flows. Detailed petrographic studies of the investigated lava flows reveal inequigranular phenocrystal basalts characterized by development of phenocrystal phases including plagioclase, clinopyroxene and olivine, whereas groundmass composition is marked by tiny plagioclase, clinopyroxene, opaque mineral and glass. Electron microprobe analyses indicate that the olivine has a wide range ∼Fo₂₂ to Fo₆₆ revealing a wide spectrum of compositional variation. Pyroxene compositions are distinctly designated as Quad pyroxenes. Phenocrystal pyroxenes are mostly diopsidic, while the groundmass pyroxenes mainly correspond to augite with a minor pigeonite component. Pyroxene phenocrysts are characterized by a prominent Ti-enrichment. Phenocrystal plagioclase grains are calcic (An_52.7–An_72.9), whereas groundmass plagioclase are relatively sodic (An_39.2–An_61.6). Groundmass opaque minerals are characteristically found to be Ti–magnetite/ilmenite/pyrophanite. Pyroxene thermometry reveals a temperature span of 850°C to 1280°C for the studied lavas while olivine–clinopyroxene thermometry yields a temperature range from 1040°–1160°C. The variation of temperature for the lava flows is ascribed to their normal cooling history after eruption.  相似文献   

Recent and subrecent sedimentary conditions in the southern part of the North Sea–Baltic Sea transition     

CHRISTIAN CHRISTIANSEN  HELMAR KUNZENDORF  CHRISTIAN OTTO  JACOB SENSTIUS 《Boreas: An International Journal of Quaternary Research》1993,22(4):357-366

The recent rate of net sedimentation (0–5mm/yr) in the southern Kattegat is to a high degree governed by resuspension. In shallow areas (10–25 m) there is no or very little sedimentation. Sediments here are sandy lag sediments with a low content of organic matter (0.5–3.0%), nitrogen (0–0.1%) and phosphorus (0.01–0.05%). In deep water (30–60 m) the sediments are clays or fine silts and generally have high contents of organic matter (3.0–10.8%), nitrogen (0.1–0.34%) and phosphorus (0.05–0.10%). Shallow water sediments are relatively well sorted because of resuspension of fine material, which is transported to deeper water. Here the sorting becomes poor because relatively coarser material is supplied during exceptional storm events. Discrimination on erosion/transport bottoms and on depositional bottoms was based on resuspension calculations, grain-size parameters and Passegas (1964) CM diagrams. The IG/N ratio was an useful additional tool. From the sediment content of CaCO₃ it is suggested that recent sedimentation in the deeper parts of southern Kattegat is less influenced by contributions from the North Sea than it was during the early Holocene.  相似文献   

Aerosol number to volume ratios in Southwest Portugal during ACE-2     

ULRIKE DUSEK  DAVID S. COVERT  ALFRED WIEDENSOHLER  CHRISTIAN NEUSÜSS  DIANA WEISE 《Tellus. Series B, Chemical and physical meteorology》2004,56(5):477-491

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