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Pyritization of tubes and burrows from Late Pleistocene continental shelf sediments off North Norway 总被引：1，自引：0，他引：1
Four different types of pyritized tubes and three types of pyritized burrow fillings are described from Pleistocene glaciomarine sediments in Andfjorden, northern Norway. The tubes and burrows probably originated from tubicolous and burrowing polychaetes respectively. The decomposition of the organic matter in the tubes and burrows created a reducing micro-environment favouring precipitation of pyrite. By comparison with Holocene tubes from marine sediments in Andfjorden and FugloSyfjorden, it is seen that pyritization commenced with isolated spherules. These spherules with incipient pyrite crystals and framboids were formed mainly on the inner wall of the tube. Presence of a monosulphide in the Holocene Fugløyfjorden material suggests that the pyritization process has reached a later phase; the final result would be a completely pyritized trace fossil. It is shown that single pyrite crystals (octahedra) generally attain greater size in the burrow fillings than in the tubes. The microstructure found in some of the pyritized tubes is interpreted as a reflection of the microstructure in the original wall. Finally, the implications for the depositional environment in Pleistocene in Andfjorden is investigated with reference to the benthic skeletal macrofaunal assemblage in the sequence. The pyritized trace fossils occur frequently in an opportunistic assemblage from a period (c. 14,000–13,000 yr BP) characterized by some oxygen deficiency. Later (13,000–10,000 yr BP) they play a minor role in an established assemblage under improved oxygen conditions. 相似文献
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The brachiopod Macandrevia cranium (Müller, 1776) occurs in Late Weichselian and Holocene sediments from the Norwegian continental shelf. It is particularly well known from the southern Barents Sea where it is a characteristic member of the Holocene macrofpssil assemblages. The Recent biogeography of the species is established. The general distribution is not random, but is almost completely confined to the continental shelves surrounding the North Atlantic and the Norwegian-Greenland Sea. The distribution pattern is compared with information on autecology and possible limiting environmental factors. It is concluded that there is substantial evidence that the distribution of Recent M. cranium is a function of dispersal by the Gulf Stream and its continuations, e.g. the Norwegian Current and the North Cape Current. Thus the stratigraphic occurrence of M . cranium in sediments on the Norwegian continental shelf may be used as an important marker for the presence of Atlantic water. Late Weichselian records of rare specimens of the species are related to incipient influx of Atlantic water following the deglaciation. Early Holocene records of abundant specimens are related to the final intrusion of the Norwegian Current. These records also suggest that the Holocene introduction of the species is time-transgressive in a south-north direction. 相似文献
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JAN-PIETER BUYLAERT GUNTHER GHYSELS REW S. MURRAY KRISTINA J. THOMSEN DIMITRI VANDENBERGHE FRANS DE CORTE IRENÉE HEYSE PETER VAN DEN HAUTE 《Boreas: An International Journal of Quaternary Research》2009,38(1):160-175
We report on quartz Optically Stimulated Luminescence (OSL) dating of the infill of 14 relict sand wedges and composite-wedge pseudomorphs at 5 different sites in Flanders, Belgium. A laboratory dose recovery test indicates that the single-aliquot regenerative-dose (SAR) procedure is suitable for our samples (measured to a given dose ratio 0.980 ± 0.005; n =139). Completeness of resetting of the wedge infill of two samples was confirmed by single-grain analyses. The suite of optical ages indicates that repeated thermal contraction cracking, degradation and infilling with wind-blown sediment appear to have been commonplace in Flanders during the Late Pleniglacial (Oxygen Isotope Stage 2; OIS2); more specifically, around the Last Glacial Maximum (LGM, ∼21 kyr ago) and the transition period between the LGM and the start of the Lateglacial (∼15 kyr ago). Optical dating at one site has revealed two significantly older wedge levels, the younger inset into the older; the younger wedge has an age of 36 ± 4 kyr (Middle Pleniglacial; OIS3), the older wedge 129 ± 11 kyr, which points to formation during the Late Saalian (OIS6). Our OSL ages of the wedges and host sediments bracket formation of the BGB (Beuningen Gravel Bed: a widespread deflation horizon in northwestern Europe) at between ∼15 and 18 kyr; this is in good agreement with previous OSL dating studies. We conclude that optical dating using quartz SAR OSL establishes an absolute chronology for these periglacial phenomena and allows secure palaeoenvironmental reconstructions to be made. 相似文献
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Depositional environment and development of Danian bryozoan biomicrite mounds (Karlby Klint, Denmark) 总被引：1，自引：0，他引：1
ERIK THOMSEN 《Sedimentology》1976,23(4):485-509
The lower Danian bryozoan mounds exposed in the cliff at Karlby are described. Analyses of some sixty samples taken from a single mound reveal that the limestone is composed of about 30% of bryozoan fragments in a fine grained matrix. The texture and the grain-size distribution show that two distinct sedimentary facies can be recognized: (1) the northwestern flank and the basins with fine bryozoan fragments, a relatively small amount of matrix, and grain-supported texture; (2) the southeastern flank and the summit with coarse bryozoans, a larger amount of matrix and partly mud-supported texture. It is shown that the differences in the size of the bryozoan fragments are due to adaptations to changes in the water-movement rather than a result of significant transport. Thus, currents were roughly from the southeast producing more agitated water on the southeast flank and the summit and more gentle water on the northwest flank and in the basins. The unusual relationship between the velocity of the water-movement and the sedimentary facies is caused by an influence of the bryozoans on the depositional environment. On the southeast flank the higher current velocity favoured the growth of bryozoans, resulting in a relatively dense cover that was able to trap and bind the matrix. On the northwest flank the currents were slower and less favourable for growth, and the ability of the bryozoans to bind the sediment was correspondingly smaller. 相似文献
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