1997年电子出版物(英)

科学期刊的出版和发行技术正在迅速变化．主要对Ap.J.如何使用电子投稿方式及该杂志的网上版作了介绍．同时也叙述了较快的审稿及非常快速的出版等方面的进展。     

Industrialization affects heavy metal and carbon isotope concentrations in recent Baltic Sea sediments

Recent sediment cores of the western Baltic Sea were analyzed for heavy metal and carbon isotope contents. The sedimentation rate was determined from radiocarbon dates to be 1.4 mm/yr. The ‘recent age’ of the sediment was about 850 yr. Within the upper 20 cm of sediment, certain heavy metals became increasingly enriched towards the surface; Cd, Pb, Zn and Cu increased 7-, 4-, 3- and 2-fold, respectively, whereas Fe, Mn, Ni and Co remained unchanged. Simultaneously, the radiocarbon content decreased by about 14 per cent. The enrichment in heavy metals as well as the decrease in the ¹⁴C-concentration during the last 130 ± 30yr parallels industrial growth as reflected in European fossil fuel consumption within that same period of time. The near-surface sediments are affected by residues released from fossil fuels at the rate of about 30 g/m² yr for the past two decades. The residues have a pronounced effect on the heavy metal and carbon isotope composition of the most Recent sediments allowing estimates to be made for sedimentation, erosion and heavy metal pollution.     

The Bingham Distribution of Quaternions and Its Spherical Radon Transform in Texture Analysis

Spherical geometry of quaternions is employed to characterize the Bingham distribution on the 3-dimensional sphere as being uniquely composed of a bipolar, a circular and a spherical component. A new parametrization of its dispersion parameters provides a classification of patterns of crystallographic preferred orientations (CPO, or textures). It is shown that the Bingham distribution can represent most types of ideal CPO patterns; in particular single component, fiber and surface textures are represented by rotationally invariant bipolar, circular and spherical distributions, respectively. Pole figures of given crystal directions are derived by the spherical Radon transform of the Bingham probability density function of rotations, which are displayed for general and special cases.     

Beitrag zur Geochemie österreichischer Granitoide

Zusammenfassung Es wurden 122 Proben granitoider Gesteine, die größtenteils aus dem Bereiche der Alpen und der südlichen Böhmischen Masse stammen, mit Hilfe instrumenteller Methoden auf die Elemente Be, Ca, Co, Cr, Cu, Fe, Ga, K, Li, Ni, Pb, Rb, Sc, Sn, Sr, Ti, Tl, V, Y, Zn und Zr analysiert. Dabei fanden die Emissionsspektral-analyse und die Röntgenfluoreszenzanalyse Anwendung. Für die Bestimmung sehr geringer Konzentrationen der Elemente Pb, Sn, Tl und Zn in sauren Silikatgesteinen wurde eine spezielle Doppelbogenmethode ausgearbeitet.Aus den Analysendaten wurden die Durchschnittsgehalte der einzelnen Elemente errechnet und mit Literaturwerten über die Gehalte von seltenen Elementen in Granitoiden verglichen. Bei den meisten Daten wurde Übereinstimmung gefunden, bei einigen anderen (Be, Co, Ni, Rb, Sc) Korrekturvorschläge gemacht.Die Variationsbreiten der Konzentrationen der einzelnen Elemente wurden an Hand von Histogrammen beschrieben und kurz diskutiert.

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Summary 122 samples of granitoidic rocks from the Alps and the southern part of the Bohemian Massif were analysed for the elements Be, Ca, Co, Cr, Cu, Fe, Ga, K, Li, Ni, Pb, Rb, Sc, Sn, Sr, Ti, Tl, V, Y, Zn, and Zr by means of emission-spectrochemical analysis and X-ray fluorescence analysis. A special method employing a double arc was developped for determining very small concentrations of the elements Pb, Sn, Tl, and Zn in acid silicate rocks.The average contents of the individual elements were calculated from the data of analysis and compared with the data on the contents of rare elements in granitoidic rocks, as quoted in literature. In most cases the data were conformable, however, in some other cases (Be, Co, Ni, Rb, Sc) corrections were suggested.The ranges of the concentrations of the individual elements were described by means of histograms and were discussed briefly.

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Mit 4 Textabbildungen

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Herrn Professor Dr.F. Machatschki zum 70. Geburtstag gewidmet.     

Hardground formation in the Bannock Basin, Eastern Mediterranean

Twenty kilogrammes of crusts and slabs of indurated carbonate sediment, usually referred to as hardgrounds, were dredged along the eastern steep wall of the Bannock Basin during the 1984 cruise of R.V. Bannock.

The crusts range in thickness from one to a few centimetres and the fragments of these crusts are irregular in shape. Their surface is always uneven and their colour ranges from white to brownish dark grey. Some slabs are impregnated along one side by ferromanganese sesquioxides, and borings occur in several samples. Serpulid tubes have been observed in one instance. The borings and serpulids suggest formation of the hardgrounds at or close to the sediment/water interface and exposure at the seafloor.

The degree of lithification is generally different on the inferred upper and lower sides of the slabs. An upward increase of lithification across the slabs is reflected by mineralogy, ultrastructure and stable isotope composition of the carbonate. X-ray diffraction analyses indicate high-magnesian calcite as the predominant carbonate with minor amounts of low-magnesian calcite and dolomite. Occasionally, large gypsum crystals are attached to the hardgrounds and sometimes smaller ones are dispersed through the carbonate matrix.

An increase in diagenesis is reflected by the passage from friable, nodular nannofossil chalk to nannofossil limestone and hard xenotopic calcite micrite. Overgrowth of coccoliths and internal cementation of the tests of planktonic foraminifera by high-Mg calcite increase from chalk to limestone. In the hard, fully cemented micrites, coccoliths can no longer be recognised in the xenotopic fabric. Pteropods occur as dissolution moulds with aragonite preserved as only tiny relics.

Carbon and oxygen isotope analyses were performed on different samples. The progressive lithification to chalk and limestone is marked by a shift in the δ¹⁸O values from +1.2‰ to +5.4‰ (PDB). This change indicates that precipitation of high-Mg calcite and possibly also recrystallisation of the original biogenic carbonate took place within cold and hypersaline brines which were enriched in ¹⁸O. The oxygen isotope data suggest that lithification and gypsum precipitation occurred under identical conditions. The carbon isotope data show progressive diagenetic change from values near +1‰ to values of +3‰. This change may reflect a contribution of methanogenetic CO₂ to the hypersaline brine.     

Differential Late Paleozoic active margin evolution in South-Central Chile (37°S–40°S) – the Lanalhue Fault Zone

The N–S oriented Coastal Cordillera of South Central Chile shows marked lithological contrasts along strike at 38°S. Here, the sinistral NW–SE-striking Lanalhue Fault Zone (nomen novum) juxtaposes Permo-Carboniferous magmatic arc granitoids and associated, frontally accreted metasediments (Eastern Series) in the northeast with a Late Carboniferous to Triassic basal-accretionary forearc wedge complex (Western Series) in the southwest. The fault is interpreted as an initially ductile deformation zone with divergent character, located in the eastern flank of the basally growing, upwarping, and exhuming Western Series. It was later transformed and reactivated as a semiductile to brittle sinistral transform fault. Rb–Sr data and fluid inclusion studies of late-stage fault-related mineralizations revealed Early Permian ages between 280 and 270 Ma for fault activity, with subsequent minor erosion. Regionally, crystallization of arc intrusives and related metamorphism occurred between 306 and 286 Ma, preceded by early increments of convergence-related deformation. Basal Western Series accretion started at >290 Ma and lasted to 250 Ma. North of the Lanalhue fault, Late Paleozoic magmatic arc granitoids are nearly 100 km closer to the present day Andean trench than further south. We hypothesize that this marked difference in paleo-forearc width is due to an Early Permian period of subduction erosion north of 38°S, contrasting with ongoing accretion further south, which kinematically triggered the evolution of the Lanalhue Fault Zone. Permo-Triassic margin segmentation was due to differential forearc accretion and denudation characteristics, and is now expressed in contrasting lithologies and metamorphic signatures in todays Andean forearc region north and south of the Lanalhue Fault Zone.     

Mesozoic to Quaternary continental margin dynamics in South-Central Chile (36–42°S): the apatite and zircon fission track perspective

Zircon and apatite fission track data provide constraints on the exhumation history, fault activity, and thermal evolution of the South-Central Chilean active continental margin (36°S–42°S), which we use to assess the tectonic and geomorphic response of the margin to the Andean subduction regime. Several domains with different exhumation histories are identified. The Coastal Cordillera is characterized by uniform and coherent exhumation between Late Triassic (～200 Ma) and late Miocene times, with surprisingly slow average rates of 0.03–0.04 mm/a. Thermal anomalies, related to Late Cretaceous and early Miocene magmatism, have regionally modified fission track age patterns. The Upper Cretaceous thermal overprint is of previously unrecognized significance and extent in the Coastal Cordillera south of 39°S. With the exception of a local but distinct Pliocene to Recent exhumation period in the high-relief Cordillera Nahuelbuta segment between 37°S and 38°S, Cenozoic overall exhumation in the Coastal Cordillera was very slow. The sedimentary record shows that uplift and subsidence here was episodic, with low amplitudes and durations. This rules out large-scale, long-term, Cenozoic accretion, trench-parallel tilting, and tectonic erosion processes in the forearc. The Main Andean Cordillera shows markedly greater long-term exhumation rates than the Coastal Cordillera and, at ～39°S, a steep exhumation gradient. To the south, long-term average Pliocene to Recent exhumation rates of ～1 to ～2 mm/a in the Liquiñe area (39°45′S) are almost an order of magnitude more rapid than average Paleogene to Recent exhumation near Lonquimay (38°30′S) and farther north. While no imprint of the intra-arc Liquiñe-Ofqui Fault Zone on the exhumation pattern is evident, long-term exhumation rates decrease from the crest of the Andes toward the western foothills. Exhumation gradients correlate with climatic gradients, suggesting a causal link to the variable intensity of late Miocene to Pleistocene glacial erosion.