Changes in the winter precipitation in Romania and its relation to the large-scale circulation   总被引：1，自引：0，他引：1  

ARISTITA BUSUIOC  HANS VON STORCH 《地球，A辑:动力气象学与海洋学》1996,48(4):538-552

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Ferroan calcite replacement indicates former magnesian calcite skeletons     

DETLEV K. RICHTER  HANS FÜCHTBAUER 《Sedimentology》1978,25(6):843-860

The replacement by ferroan calcite with preservation of the original structures can be used as a new criterion for identifying skeletons originally composed of high-magnesian calcite. This applies to bryozoa, rugose corals, echinoderms, many foraminifera, most ostracods, red algae, and serpulids. On the other hand, skeletons originally composed of low-magnesian calcite were never replaced by ferroan calcite, as shown by belemnites, brachiopods, and most of the pelecypods. Using this criterion, an original low-magnesian calcite composition is inferred for Tentaculites and some ostracods and foraminifera, whereas a previous high-magnesian calcite composition is inferred for trilobites, oligostegina and certain ooids. Chemical instability of high-magnesian calcite is suggested to be the driving force of the replacement by ferroan calcite. In most of the thirty-seven samples investigated, of Oligocene to Devonian age, the ferrous iron concentration of the interstitial fluid increased during diagenesis, as shown by well established sequences of cement A and B and fissure fill. This offers a relative time scale for diagenetic processes. Ferroan calcites contain up to 6 mol % FeCO₃ and up to 5 mol % MgCO₃. In this range of concentration, the distribution coefficients for Fe and Mg between calcite and solution at about 25°C are about 1 to 0-03, respectively, according to experiments. Possible sources of iron are iron oxides and hydroxides as well as clay minerals including glauconite. Though a submarine origin below the sediment surface is conceivable for ferroan calcite, there are serious limiting conditions such as low Eh and, at the same time, lack in sulphate-reducing bacteria. On the other hand, ferroan ‘dedolomite’, compositional zonality in individual ferroan calcite overgrowths, low δ¹⁸C and δ¹⁸O values, and low Mg concentrations point more to a meteoric-phreatic origin of many ferroan calcite occurrences.  相似文献   

SEDIMENT TRANSPORT, DELTA GROWTH AND SEDIMENTATION IN LAKE NIGARDSVATN, NORWAY     

GUNNAR ØSTREM  NILS HAAKENSEN  HANS CHR. OLSEN 《Geografiska Annaler: Series A, Physical Geography》2005,87(1):243-258

ABSTRACT. The retreat of Nigardsbreen, an outlet glacier from the ice-cap Jostedalsbreen in south-central Norway, from its largest extent during the Little Ice Age, uncovered a proglacial lake during 1936–1967. This lake, Nigardsvatn, has been studied since 1968 in order to obtain data on solid material carried by the meltwater stream from the glacier, both in suspension and as bottom load. Between 70 and 85% of the suspended sediment has been deposited on the lake bottom, forming annual varves. The coarse material has been deposited in a delta, the formation of which started in 1968. Its growth, and hence the volume of total annual bottom load, has been surveyed annually for the past 36 years. In 1969 the entire bottom load was collected by building a fence-like net across the river. Material >3 cm was caught by this net, and formed approximately half the amount of suspended sediment transport during the same three-week period. Annual average deposition on the delta was 11800×10³ kg for the period 1968–2003. This is almost the same amount as carried in suspension from the glacier on an annual mean basis for the 36-year period. If conditions remain constant, the lake will be completely filled in about 500 years. The glacier erosion is calculated to be 0.3 mm/a.  相似文献   

Poor fen succession over ombrotrophic peat related to late Holocene increased surface wetness in subarctic Quebec,Canada     

MICHELLE GARNEAU  ALEXANDRE LAMARRE  ÉLISABETH C. ROBERT  GABRIEL MAGNAN  HANS ASNONG  STEVE PRATTE 《第四纪科学杂志》2013,28(8):748-760

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Amino acid geochronology of selected interglacial sites in the North Sea area.   总被引：2，自引：0，他引：2  

KAREN LUISE KNUDSEN  HANS PETTER SEJRUP 《Boreas: An International Journal of Quaternary Research》1988,17(3):347-354

Isoleucine epimerization (alle/Ile) ratios have been measured on foraminiferal tests from interglaical sites in the southern North Sea region. In order to evaluate the possibilities of this amino acid method on benthic foraminifera, sites were chosen from areas where the stratigraphy was already well known. The study demonstrates that the isoleucine epimerization reaction in benthic foraminifera can be used for correlation and as a means of relative age estimation within a limited geographic area. Previous suggestions of a Holsteinian age for the Rugrd, Tornskov, and Wacken sites are supported for the Kås Hoved site. The age of most presumed Eemian sites is supported by the amino acid results; the Reighton site also seems to belong in this interglacial.  相似文献   

Late Weichselian glaciation history of the northern North Sea   总被引：8，自引：1，他引：8  

HANS PETTER SEJRUP  HAFLIDI HAFLIDASON  INGE AARSETH  EDWARD KING  CARL FREDRIK FORSBERG  DAVID LONG  KÅRE ROKOENGEN 《Boreas: An International Journal of Quaternary Research》1994,23(1):1-13

Based on new data from the Fladen, Sleipner and Troll areas, combined with earlier published results, a glaciation curve for the Late Weichselian in the northern North Sea is constructed. The youngest date on marine sedimentation prior to the late Weichselian maximum ice extent is 29.4 ka BP. At this time the North Sea and probably large parts of southern Norway were deglaciated (corresponding to the Alesund interstadial in western Norway). In a period between 29.4 and c. 22 ka BP, the northern North Sea experienced its maximum Weichselian glaciation with a coalescing British and Scandinavian ice sheet. The first recorded marine inundation is found in the Fladen area where marine sedimentation started close to 22 ka BP. After this the ice fronts receded both to the east and west. The North Sea Plateau, and possibly parts of the Norwegian Trench, were ice-free close to 19.0 ka, and after this a short readvance occurred in this area. This event is correlated with the advance recorded at Dimlington, Yorkshire, and the corresponding climatostratigraphic unit is denoted the Dimlington Stadial (18.5 ka to 15.1 ka). The Norwegian Trench was deglaciated at 15.1 ka in the Troll area. The data from the North Sea, together with the results from Andwa, northern Norway (Vorren et al . 1988; Møller et al . 1992), suggest that the maximum extent of the last glaciation along the NW-European seaboard from the British Isles to northern Norway was prior to c . 22 ka BP.  相似文献   

The late Proterozoic Zig-Zag Dal Basalt Formation of eastern North Greenland     

KALSBEEK  FEIKO; JEPSEN  HANS F. 《Journal of Petrology》1984,25(3):644-664

The late Proterozoic (c. 1230 Ma) Zig-Zag Dal Basalt Formationfound in the platform area of eastern North Greenland is a remnantof a sequence of tholeiitic flood basalts which once may havecovered a large part of North Greenland. The basalts can besubdivided into three main units, totalling up to 1350 m inthickness and erupted within a short interval of time. Someof the flows are more than 100 m thick and have volumes of hundredsof cubic kilometers. Most of the basalts are aphyric or containvery sparse phenocrysts of plagioclase and augite. The chemical composition of the basalts was strongly influencedby hydrothermal metasomatism (incipient spilitization) soonafter deposition. Study of less-mobile elements suggests thatthe basalts formed from increasingly depleted mantle sources.Chemical discontinuities occur between the three main unitsand are probably related to breaks in the volcanic activity.Chemical variation within each unit is mainly governed by lowpressure fractionation of olivine, augite and plagioclase, althoughsuccessive flows do not represent successively more fractionatedmagma batches. Assimilation of crustal material at depth doesnot seem to have greatly affected the basic magma.  相似文献   

A symposium on the genesis of till     

HANS G. JOHANSSON 《Boreas: An International Journal of Quaternary Research》1977,6(2):71-72

A symposium on the genesis of till entitled Till/Sweden-76 was held in Stockholm 16–18 August 1976. This issue of Boreas contains most of the papers presented at the symposium.  相似文献   

Diagenetic formation of gypsum and dolomite in a cold‐water coral mound in the Porcupine Seabight,off Ireland     

HANS PIRLET  LAURA M. WEHRMANN  BENJAMIN BRUNNER  NORBERT FRANK  JAN DEWANCKELE  DAVID VAN ROOIJ  ANNELEEN FOUBERT  RUDY SWENNEN  LIEVEN NAUDTS  MATTHIEU BOONE  VEERLE CNUDDE  JEAN‐PIERRE HENRIET 《Sedimentology》2010,57(3):786-805

Authigenic gypsum was found in a gravity core, retrieved from the top of Mound Perseverance, a giant cold‐water coral mound in the Porcupine Basin, off Ireland. The occurrence of gypsum in such an environment is intriguing, because gypsum, a classic evaporitic mineral, is undersaturated with respect to sea water. Sedimentological, petrographic and isotopic evidence point to diagenetic formation of the gypsum, tied to oxidation of sedimentary sulphide minerals (i.e. pyrite). This oxidation is attributed to a phase of increased bottom currents which caused erosion and enhanced inflow of oxidizing fluids into the mound sediments. The oxidation of pyrite produced acidity, causing carbonate dissolution and subsequently leading to pore‐water oversaturation with respect to gypsum and dolomite. Calculations based on the isotopic compositions of gypsum and pyrite reveal that between 21·6% and 28·6% of the sulphate incorporated into the gypsum derived from pyrite oxidation. The dissolution of carbonate increased the porosity in the affected sediment layer but promoted lithification of the sediments at the sediment‐water interface. Thus, authigenic gypsum can serve as a signature for diagenetic oxidation events in carbonate‐rich sediments. These observations demonstrate that fluid flow, steered by environmental factors, has an important effect on the diagenesis of coral mounds.  相似文献   

CO₂ measurements from polar ice cores: more data from different sites     

THOMAS STAFFELBACH  BERNHARD STAUFFER  REAS SIGG  HANS OESCHGER 《Tellus. Series B, Chemical and physical meteorology》1991,43(2):91-96

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