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1.
Summary ?The rare earth, major and trace element geochemistry of Jurassic deep marine manganese shales allow insight into their environment
of deposition. We present data of 24 samples from the Northern Calcareous Alps (Eastern Alps), collected from Late Jurassic
strata of the Tennengebirge and from Early Jurassic strata of the Karwendel Mts. Whereas major and trace element geochemistry
is controlled by the detrital input, rare earth element data and the relationship between total organic carbon and (pyritic)
sulfur can be used to constrain the origin of the manganese accumulation. The data of this study are compatible with a hydrogenous
precipitation of manganese by strongly varying redox-conditions at the sediment–water interface of a slope basin.
Received December 21, 2001; revised version accepted February 18, 2002 相似文献
2.
M. El Ghorfi F. Melcher T. Oberthür A. E. Boukhari L. Maacha A. Maddi M. Mhaili 《Mineralogy and Petrology》2008,92(1-2):59-80
Summary The Neoproterozoic Bou Azzer ophiolite complex hosts numerous, small lenticular bodies of massive and disseminated chromite.
Metallurgical-grade high-Mg and high-Cr spinels (cores with 48–62 wt% Cr2O3) reveal complex alteration patterns of successive Cr and Mn enrichment and loss of Al towards the rims, while the Mg# ratios
[(Mg/(Mg + Fe2+)] remain almost constant. Concentration patterns of platinum-group elements are typical for ophiolitic chromitite poor in
sulfides, with predominance of the IPGE, variable Rh, and low Pt and Pd. The most abundant platinum-group mineral is Rh-bearing
laurite that occurs either included in spinel or in silicate matrix, whereas Os-Ir-Ru alloy is always included in spinel.
Laurite inclusions reveal complex intergrowth textures with Rh-Ru-Pt rich alloy, and with Rh-rich sulfide. Most laurites display
trends to sulfur-poor compositions leading to local formation of very fine-grained Ru-Os-Ir alloy phases. Ni-Co-Fe sulfides,
arsenides and sulfarsenides devoid of PGE are associated with the alteration of chromite. Textural position and chemical composition
of the base metal inclusions, as well as comparison of alteration features between chromite and accessory chromian spinel
in the Co-Ni-As ores of the Bou Azzer ophiolite indicate a close connection. It is suggested that hydrothermal fluids percolated
through the marginal zones of the ophiolite belt during greenschist facies metamorphism and deposited Ni-Co-Fe arsenides,
sulfarsenides and minor sulfides as accessories within altered chromitites, and also in structurally favourable zones as Ni-Co-As
ores.
Author’s address: Dr. Frank Melcher, Federal Institute for Geosciences and Natural Resources, Stilleweg 2, 30655 Hannover, Germany 相似文献
3.
ME Alexander CA Simon CL Griffiths K Peters S Sibanda S Miza 《African Journal of Marine Science》2016,38(1):141-144
Biological invasions continue to increase around the world, with impacts on many coastal marine systems. Here we review the South African marine invasion literature which, despite the field being relatively new, has grown to have significant presence in both the local and international arenas. Of the 79 papers reviewed, 70% focused on the establishment and spread of alien species, with modes of transport and introduction largely overlooked. An emphasis was also apparent towards field studies, in particular survey work, with few experimental studies. The overwhelming majority of papers focused on a single species, the Mediterranean mussel Mytilus galloprovincialis, reflecting the scale of this invasion and the tractable nature of rocky shores as study systems. With the exception of this one species, the impacts of marine alien species have rarely been quantified. We suggest that future research extends the taxonomic coverage of present work and develops a better understanding of the mechanisms of introduction, establishment and spread of marine alien species. Through an experimental approach, the drivers of altered ecological patterns and processes resulting from invasions should be addressed, providing insight into associated impacts. This approach will maintain the local applicability and international relevance of South African marine invasion research. 相似文献
4.
5.
The South African coastline has been invaded by numerous alien species. Rare pre-invasion (1980) and post-invasion datasets (2001 and 2012) exist for Marcus Island, a small land-tied island in Saldanha Bay, South Africa. These snapshot datasets of the island’s intertidal invertebrate community were complemented with monitoring across seasons, from 2014 to 2016. Invertebrate communities were compared among the summers of 1980, 2001, 2012, 2014, 2015 and 2016 to assess interannual differences, while invertebrates and algae were monitored quarter-annually to assess seasonal changes. In addition, the population dynamics of the alien mussel Mytilus galloprovincialis were monitored. Differences in invertebrate communities between consecutive summers were significant but much smaller than changes induced by the arrival of alien species. Invertebrate and seaweed communities differed among years and shore zones but not among seasons, whereas species diversity differed among years, seasons and shore zones, with zones having the strongest influence. The invasion by M. galloprovincialis, and ensuing spatial and temporal variability in its recruitment, emerged as the most important factor influencing community composition, overshadowing interannual and seasonal changes. This work highlights that the impacts of alien species can be distinguished from natural variability by combining long-term monitoring with surveys at finer temporal scales. This is an important step in extending our understanding of the impacts of marine alien species. 相似文献
6.
C.L. Melcher 《Geochimica et cosmochimica acta》1982,46(10):1999-2000
The usefulness of an “effective” trap depth to approximate the group of closely spaced trap depths responsible for the low temperature thermoluminescence in meteorites is evaluated on the basis of its success when used with the TL equivalent dose method to determine terrestrial ages of Antarctic meteorites. The ages determined in this way agree in every instance with terrestrial age determinations based on 14C, 26Al, 36Cl, and 53Mn. The application of an “effective” trap depth in this TL dating technique in no way implies that the TL signal actually arises from a single trap depth. 相似文献
7.
Thermoluminescence sensitivity measurements have been made on 18 unequilibrated ordinary chondrites; 12 finds from Antarctica, 5 non-Antarctic finds and 1 fall. The TL sensitivities of these meteorites, normalized to Dhajala, range from 0.034 (St. Mary's County) to 2.3 (Allan Hills A78084), and, based primarily on these data, petrologic type assignments range from 3.3 (St. Mary's County) to 3.9 (Allan Hills A78084). Although the very low levels of metamorphism experienced by types 3.0 to ~3.4 evidently cause large changes in TL sensitivity, the new data demonstrate that they are unable to cause any appreciable homogenization of silicate compositions. We have therefore slightly revised the silicate heterogeneity ranges corresponding to the lower petrologic types.We have discovered that the temperature of maximum TL emission and the broadness of the major TL peak, vary systematically with TL sensitivity; as TL increases these parameters first decrease and then increase. Several mechanisms which could account, partially or completely, for the relationship between TL sensitivity and metamorphism are discussed. Those which involve the formation of feldspar—the TL phosphor in equilibrated meteorites—seem to be consistent with the trends in peak temperature and peak width since experiments on terrestrial albite show that the TL peak broadens and moves to higher temperatures as the stable form changes from the low (ordered) state to the high (disordered) state. (The post-metamorphism equilibration temperature of type ~3.5 meteorites would then correspond to the transformation temperature for the high to low form of meteorite feldspar.) Other factors which may be involved are obscuration of the TL by carbonaceous material, changes in the composition of the phosphor and changes in the identity of the phosphor. 相似文献
8.
9.
CL de Moor SJ Johnston A Brandão RA Rademeyer JP Glazer LB Furman 《African Journal of Marine Science》2015,37(3):285-311
The waters off South Africa's coastline boast a rich mix of commercially fished species. Quantitative assessments of these marine resources have developed from simple methods first applied in the 1970s, to models that encompass a wide range of methodologies. The more valuable resources have undergone regular assessments in recent decades, with frequencies closely related to the management approach employed for each fishery. Many of these assessments form the operating models used to simulation-test candidate management procedures. This paper provides a comprehensive review of the assessments of 11 of the most important fisheries resources in South Africa. Some assessments use simple biomass dynamics models, whereas others are a hybrid of age- and length-based models, each designed to model the specific characteristics of the resource and fishery concerned. Many of the assessments have been disaggregated by species/stock and/or area as related multispecies/stock/ distribution hypotheses have arisen. This paper explores the similarities and differences in the data available and the methods applied. The review indicates that, whereas the status of three of these resources cannot be estimated reliably at present, the status of six resources is considered to be reasonable to good, whereas that of abalone Haliotis midae and West Coast rock lobster Jasus lalandii remains poor. 相似文献
10.