Oxygen isotope ratios of phenocrysts from alkali basalts of the Pannonian basin: Evidence for an O-isotopically homogeneous upper mantle beneath a subduction-influenced area   总被引：1，自引：0，他引：1  

G  bor Dobosi  Hilary Downes  David Mattey  Antal Embey-Isztin 《Lithos》1998,42(3-4):213-223

Oxygen isotope compositions of olivine and pyroxene phenocrysts and pyroxene and amphibole megacrysts from Neogene alkali basalts of the Pannonian basin (0.5–11 Ma) have been determined by laser fluorination. Measured δ¹⁸O values in olivine and clinopyroxene phenocrysts show rather restricted variations from 5.00 to 5.20‰ and from 5.07 to 5.34%., respectively, with cpx-ol fractionations Δ¹⁸O(cpx-ol) ranging from + 0.04 to + 0.29‰. These δ¹⁸O values are significantly lower than those of the corresponding whole rocks, suggesting that low temperature alteration has increased the ¹⁸O/¹⁶O ratios of the groundmass of host rocks, even in fresh looking samples, whereas their phenocrysts have retained original oxygen isotope compositions. The uniform oxygen isotope ratio in the phenocrysts suggests that the mantle source of the alkali basalts was also homogeneous with respect to its oxygen isotope composition, which is in contrast to the relatively wide variation of Sr, Nd and Pb isotope ratios in the source. Variations in radiogenic isotope compositions in the basalts have been explained by the interaction of subduction-related fluids with the mantle source of the basalts. If this is the case, then the fluids which caused significant changes in the Sr and Pb isotope ratios of the mantle source clearly did not noticeably modify its oxygen isotope composition. These data support the opinion that the upper mantle is more homogeneous with respect to its oxygen isotope composition than it was previously considered.  相似文献   

Late Quaternary palaeohydrology of the Konya Basin, Turkey, based on isotope studies of modern hydrology and lacustrine carbonates     

Melanie J. Leng  Neil Roberts  Jane M. Reed  Hilary J. Sloane 《Journal of Paleolimnology》1999,22(2):187-204

The Konya plain in south central Anatolia, Turkey, which is now largely dry, was occupied around the time of the Last Glacial Maximum by a fresh-oligosaline lake covering more than 4000 km². Sediment cores from three residual water bodies (Pinarbai, Akgöl and Süleymanhaci) within the larger Pleistocene lake basin, have been analysed using a multidisciplinary approach. The sediment sequences are dated as spanning the last 50 Ka years, although breaks in sedimentation mean that there is only partial chronological overlap between them. Carbon and oxygen isotope analyses on lacustrine carbonate from the three cores give contrasting isotope profiles which reflect the different ages and independent hydrological behaviour of different sub-basins through the late Quaternary. Distinguishing changes that are regional from local effects is aided by modern isotope hydrology studies and by comparing the carbonate ¹³C and ¹⁸O values to diatom and other analyses undertaken on the same cores.  相似文献   

Recent paleolimnology of three lakes in Northwestern Minnesota     

Hilary H. Birks  M.C. Whiteside  Donna M. Stark  R.C. Bright 《Quaternary Research》1976,6(2):249-IN11

A paleolimnological study was undertaken to investigate changes in three Minnesota lakes over the last 100 years and to demonstrate the stratigraphic effects of cultural eutrophication in two of them. The study combined the analysis of the lake sediment from short cores with stratigraphic analyses of pollen, plant macrofossils, mollusks, diatoms and certain other algae, chydorid Cladocera, and Daphnia ephippia.The rise of Ambrosia type pollen (ragweed) marks the onset of interference with the landscape by European man, which can be closely dated. Calculations of sedimentation rates from this base gave reasonable correlations of other stratigraphic events with historical events.Elk Lake is considered “unpolluted” today and was chosen as a control. Man's effects are limited to logging some of the surrounding forest and to the construction of a dam. Small changes in the lake's fauna and flora are demonstrated, showing the sensitivity of the lake to changes in its catchment area.Lake Sallie and St. Clair Lake, in the same watershed as the city of Detroit Lakes, have been affected not only by logging but also by addition of nutrients from agricultural runoff and sewage effluent. Considerable responses by the lake organisms are apparent. In Lake Sallie the changes were gradual, but in St. Clair Lake they were very abrupt because the lake was partially drained at the same time and the water volume was thereby reduced.The merits of such an integrated study, the types of information gained from the analyses of the various fossils, and the wider application of the results are discussed.  相似文献   

New age estimates and climatostratigraphic correlations for the Borrobol and Penifiler Tephras: evidence from Abernethy Forest,Scotland     

I. P. Matthews  Hilary H. Birks  A. J. Bourne  S. J. Brooks  J. J. Lowe  A. MacLeod  S. D. F. Pyne‐O'Donnell 《第四纪科学杂志》2011,26(3):247-252

The emerging tephrostratigraphy of NW Europe spanning the last termination (ca. 15–9 ka) provides the potential for synchronizing marine, ice‐core and terrestrial records, but is currently compromised by stratigraphic complications, geochemical ambiguity and imprecise age estimates for some layers. Here we present new tephrostratigraphic, radiocarbon and chironomid‐based palaeotemperature data from Abernethy Forest, Scotland, that refine the ages and stratigraphic positions of the Borrobol and Penifiler tephras. The Borrobol Tephra (14.14–13.95 cal ka BP) was deposited in a relatively warm period equated with Greenland Interstadial sub‐stage GI‐1e. The younger Penifiler Tephra (14.09–13.65 cal ka BP) is closely associated with a cold oscillation equated with GI‐1d. We also present evidence for a previously undescribed tephra layer that has a major‐element chemical signature identical to the Vedde Ash. It is associated with the warming trend at the end of the Younger Dryas, and dates between 11.79 and 11.20 cal ka BP. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Late-glacial and early-Holocene Trichoptera (Insecta) from Kråkenes Lake, western Norway     

John O. Solem  Hilary H. Birks 《Journal of Paleolimnology》2000,23(1):49-56

Fossil Trichoptera (caddisfly) remains have been identified and quantitatively recorded in the late-glacial and early-Holocene sediments from Kråkenes Lake, western Norway. The sediment sequence was deposited between 12,300 and 8850 ¹⁴C BP, covering the Allerød, Younger Dryas, and early-Holocene periods. The first Trichoptera were recorded at 12,000 ¹⁴C BP, and during the Allerod a diverse assemblage of Limnephilidae taxa developed in the lake. By about 11,400 ¹⁴C BP the relatively thermophilous Polycentropus flavomaculatus and Limnephilus rhombicus were present, suggesting that the summer water temperature was at least 17 °C. This temperature fell by 5-8 °C at the start of the Younger Dryas, and the thermophilous taxa were replaced within 20-40 ¹⁴C yrs by Apatania spp., including the arctic-alpine A. zonella, suggesting a maximum summer water temperature of 10-12 °C. The Trichoptera assemblage was impoverished in numbers and in diversity over the next 200 yrs as the severe conditions of the Younger Dryas developed. As soon as temperatures rose and glacial meltwater and silt input ended about 700 ¹⁴C yrs later, the resident Apatania assemblage expanded immediately, within 10 yrs. About 130 yrs later, thermophilous taxa replaced Apatania, and a much more diverse assemblage than in the Allerod occupied the varied habitats made available by the development of the Holocene lake ecosystem. The 130 yr delay may have been caused by a gradual temperature increase crossing a critical threshold, or by the time taken for thermophilous taxa to migrate from their Younger Dryas refugia.  相似文献   

Introduction to the reconstruction of the late-glacial and early-Holocene aquatic ecosystems at Kråkenes Lake, Norway     

Hilary H. Birks  Herbert E. Wright 《Journal of Paleolimnology》2000,23(1):1-5

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The development of the aquatic ecosystem at Kråkenes Lake, western Norway, during the late glacial and early Holocene - a synthesis   总被引：2，自引：0，他引：2  

Hilary H. Birks  R.W. Battarbee  H.J.B. Birks 《Journal of Paleolimnology》2000,23(1):91-114

This paper synthesises the palaeoecological reconstructions, including palaeoclimatic inferences, based on the available fossil record of plants (pollen, macrofossils, mosses, diatoms) and animals (chironomids, Cladocera, Coleoptera, Trichoptera, oribatid mites) in the late-glacial and early-Holocene sediments of Kråkenes Lake, western Norway, with special emphasis on changes in the aquatic ecosystem. New percentage and influx pollen diagrams for selected taxa provide insights into the terrestrial setting. The information from all the proxies is collated in a stratigraphical chart, and the inferred changes in the lake and its catchment are discussed. The individual fossil sequences are summarised by detrended correspondence analysis (DCA), and sample scores on the first DCA axes are plotted against an estimated calendar-year timescale for comparison of the timing and magnitude of changes in assemblage composition. The DCA plots show that the large late-glacial biotic changes were synchronous, and were driven by the overriding forcing factor of temperature. During the early Holocene, however, the changes in different groups were more gradual and were independent of each other, showing that other factors were important and interactive, such as the inwash of dissolved and particulate material from the catchment, the base and nutrient status of the lake-water, and the internal processes of ecosystem succession and sediment accumulation. This multi-disciplinary study, with proxies for changes in the lake and in the catchment, highlights the dependence of lake biota and processes not only on regional climatic changes but also on changes in the lake catchment and on internal processes within the lake. Rates of change for each group are also estimated and compared. The reaction times to the sharp temperature changes at the start and end of the Younger Dryas were very rapid and occurred within a decade of the temperature change. Aquatic organisms tracked the temperature and environmental changes very closely, and are probably the best recorders of late-glacial climatic change in the fossil record.  相似文献   

Recession,restructuring and workplace reform: unemployment and the underclass in Australia in the 1990s     

Hilary P. M. Winchester 《The Australian geographer》1991,22(2):112-116

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The effect of nitrogen loading on a brackish estuarine faunal community: A stable isotope approach     

Rachel?A.?Keats  Laurie?J.?OsherEmail author  Hilary?A.?Neckles 《Estuaries and Coasts》2004,27(3):460-471

Coastal ecosystems worldwide face increased nutrient enrichment from shoreline and watershed development and atmospheric pollution. We investigated the response of the faunal community of a small microtidal estuary dominated byRuppia maritima (widgeon grass) in Maine, United States, to increased nitrogen loading using an in situ mesocosm enrichment experiment. Community response was characterized by assessing quantitative shifts in macroinvertebrate community composition and identifying changes in food web structure using stable carbon and nitrogen isotope ratios of producers and consumers. The community was dominated by brackish water invertebrates including midge larvae, oligochaetes, damselfly larvae, amphipods, and ostracods. Experimental nutrient additions resulted in significantly lower densities of herbivorous chironomids and predatory damselflies and greater densities of deposit feeding oligochaetes. Grazing midge larvae (Chironomidae:Dicrotendipes, Cricotopus) consumed epiphytic algae under both natural and enriched conditions. Deposit feedingChironomus was dependent on allochthonous sources of detritus under natural conditions and exhibited a shift to autochthonous sources of detritus under enriched conditions. PredatoryEnallagma primarily consumed grazing chironomids under all but the highest loading conditions. Experimental nutrient loading resulted in an increase in generalist deposit feeders dependent on autochthonous sources of detritus.  相似文献   

Announcements     

H. J. B. Birks  Hilary H. Birks 《Journal of Paleolimnology》1988,1(2):161-161

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