Palynological and oxygen isotope investigations on Late-Glacial sediment cores from Swiss lakes   总被引：2，自引：0，他引：2  

ULRICH EICHER  ULRICH SIEGENTHALER 《Boreas: An International Journal of Quaternary Research》1976,5(2):109-117

Results from detailed pollen and ¹⁸O/¹⁶O studies on two sediment profiles from small Swiss lakes are reported. ¹⁸O/¹⁶O records in lacustrine carbonate contain paleoclimatic information because they reflect mainly the isotope ratio in rain and snow which is correlated to temperature. Several transitions between different climatic periods determined palyno-logically are also indicated by marked changes in the isotope ratios in both profiles, namely the transitions Oldest Dryas - Bøiling and Allerød - Younger Dryas - Preboreal. ¹⁸o/¹⁶O was 2 to 3 %0 lower during Younger Dryas than during the adjacent periods, corresponding to a temperature drop of a few degrees Centigrade according to a tentative estimate.  相似文献   

Origin of migmatites by deformation-enhanced melt infiltration of orthogneiss: a new model based on quantitative microstructural analysis   总被引：2，自引：1，他引：1  

P. HASALOVÁ  K. SCHULMANN  O. LEXA  P. &#;TÍPSKÁ  F. HROUDA  S. ULRICH  J. HALODA  P. TÝCOVÁ 《Journal of Metamorphic Geology》2008,26(1):29-53

A detailed field study reveals a gradual transition from high‐grade solid‐state banded orthogneiss via stromatic migmatite and schlieren migmatite to irregular, foliation‐parallel bodies of nebulitic migmatite within the eastern part of the Gföhl Unit (Moldanubian domain, Bohemian Massif). The orthogneiss to nebulitic migmatite sequence is characterized by progressive destruction of well‐equilibrated banded microstructure by crystallization of new interstitial phases (Kfs, Pl and Qtz) along feldspar boundaries and by resorption of relict feldspar and biotite. The grain size of all felsic phases decreases continuously, whereas the population density of new phases increases. The new phases preferentially nucleate along high‐energy like–like boundaries causing the development of a regular distribution of individual phases. This evolutionary trend is accompanied by a decrease in grain shape preferred orientation of all felsic phases. To explain these data, a new petrogenetic model is proposed for the origin of felsic migmatites by melt infiltration from an external source into banded orthogneiss during deformation. In this model, infiltrating melt passes pervasively along grain boundaries through the whole‐rock volume and changes completely its macro‐ and microscopic appearance. It is suggested that the individual migmatite types represent different degrees of equilibration between the host rock and migrating melt during exhumation. The melt topology mimicked by feldspar in banded orthogneiss forms elongate pockets oriented at a high angle to the compositional banding, indicating that the melt distribution was controlled by the deformation of the solid framework. The microstructure exhibits features compatible with a combination of dislocation creep and grain boundary sliding deformation mechanisms. The migmatite microstructures developed by granular flow accompanied by melt‐enhanced diffusion and/or melt flow. However, an AMS study and quartz microfabrics suggest that the amount of melt present did not exceed a critical threshold during the deformation to allow free movements of grains.  相似文献   

Lithological and biochemical properties in sediments of Lama Lake as indicators for the late Pleistocene and Holocene ecosystem development of the southern Taymyr Peninsula, Central Siberia     

STEFANIE HARWART  BIRGIT HAGEDORN  MARTIN MELLES  ULRICH WAND 《Boreas: An International Journal of Quaternary Research》1999,28(1):167-180

In order to evaluate the sensitivity of aquatic and terrestrial ecosystems to climatic changes, lithological (sediment structure and color, grain size, physical properties) and biochemical (TOC, TOC/TN, δ¹³C of TOC and carbonates) investigations were carried out on an 11.12 m-long sediment core from Lama Lake (Central Siberia, Putorana Plateau). According to the pollen data, the sequence represents the termination of the Pleistocene, and the entire Holocene. It is composed of highly terrigenous and stratified clays and silts. Sediment structure, grain-size distribution, carbonate contents and physical properties of the sediment indicate that glaciers were present in the catchment area of Lama Lake during the period Oldest Dryas to AllerØd. For the same time period, δ¹³C values of TOC give indications of a perennial ice cover. Since the AllerØd, organic matter accumulation has increased, caused by an increasing input of land vegetation and aquatic primary production as revealed by relations TOC contents, TOC/TN ratios and δ¹³C values of TOC. During the Holocene climatic optimum, in late Preboreal and Boreal times, biogenic primary production in Lama Lake reached its maximum and the vegetation in the catchment area changed from grassy tundra to a dense forest. From the Atlantic period to the present, small variations in δ¹³C values of TOC and TOC contents are probably related to the location of Lama Lake on the border between grass and wooded steppe, leading to responses of environmental conditions to even small changes in climate.  相似文献   

Presolar silicon carbide from the Indarch (EH4) meteorite: Comparison with silicon carbide populations from other meteorite classes     

SARA S. RUSSELL  ULRICH OTT  CONEL M. O'D. ALEXANDER  ERNST K. ZINNER  JOHN W. ARDEN  C. T. PILLINGER 《Meteoritics & planetary science》1997,32(5):719-732

Abstract— Presolar SiC from the Indarch (EH4) meteorite was studied by scanning electron microscopy (SEM), by ion probe analysis for C and Si isotopic compositions, and by static source mass spectrometry for noble gas and C isotopic compositions. The data obtained are compared to SiC data from other meteorites, especially from Murchison (CM2), for which there is the most information available. The isotopic compositions of the major elements in SiC from Indarch and Murchison are similar. Stepped combustion data suggest a mean δ¹³C for SiC from both meteorites of ～+1430%o. Silicon isotopes in Indarch and Murchison SiC also compare well. In some other important respects, however, SiC in the two meteorites are different. Morphologically, SiC from Indarch appears finer grained than SiC from Murchison and is entirely composed of submicron grains. The finer-grained nature of Indarch SiC is confirmed by its noble gas characteristics. The mean Ne-E/Xe-S ratio for bulk Indarch SiC is significantly lower than the same ratio in Murchison (625 ± 47 vs. ～3500) but is similar to that of the finest grain-size fractions (<1 μm) in Murchison. A comparison of noble gas data from SiC from several different meteorites suggests that it might be Murchison SiC, rather than Indarch SiC, that is unusual. The grain-size disparities in SiC between meteorites are difficult to explain by residue processing differences or differing parent body processing. Instead, we speculate that a grain-size sorting mechanism for SiC may have operated in the solar nebula.  相似文献