Bioklimatische Verhältnisse im südwestafrikanischen Steppengebiet     

Dr. Helmut Mayer  Dipl-Met. Josef Abele 《Theoretical and Applied Climatology》1976,24(4):337-347

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Beitrag zur Geochemie österreichischer Granitoide     

Helmut Grohmann 《Mineralogy and Petrology》1965,10(1-4):436-474

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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Herrn Professor Dr.F. Machatschki zum 70. Geburtstag gewidmet.  相似文献   

Hardground formation in the Bannock Basin, Eastern Mediterranean     

Fulvia S. Aghib  Daniel Bernoulli  Helmut Weissert 《Marine Geology》1991,100(1-4):103-113

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.  相似文献   

Zusammenhang zwisehen Kristallgröße und Salbandabstand bei magmatisehen Gang-Intrusionen     

Helmut G. F. Winkler 《Contributions to Mineralogy and Petrology》1948,1(2-3):251-268

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Datum adjustement with special consideration of laplace and length conditions     

Helmut Wolf 《Journal of Geodesy》1951,25(3):307-329

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

Johannes Glodny  Helmut Echtler  Santiago Collao  Mary Ardiles  Pablo Burn  Oscar Figueroa 《Journal of South American Earth Sciences》2008,26(4):397-411

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.  相似文献   

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

Johannes Glodny  Kirsten Gräfe  Helmut Echtler  Matthias Rosenau 《International Journal of Earth Sciences》2008,97(6):1271-1291

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.  相似文献   

Geothermal evolution of the Astrakhan Arch region of the Pricaspian basin     

Alik Ismail-Zadeh  Helmut Wilhelm  Yuri Volozh 《International Journal of Earth Sciences》2008,97(5):1029-1043

The Astrakhan Arch region contains one of the largest sub-salt structures of the Pricaspian basin, where perspectives for hydrocarbon generation and accumulation in the Devonian to Carboniferous deposits are considered to be high. The paper addresses the problem of structural and geothermal evolution of the region deformed by salt movements. Initially, we developed a model of the regional structural evolution along a geological profile using the volume-balancing and back-stripping methods and geological constraints on the sedimentation, erosion, and paleo-water depths. Then we developed geothermal models (along the study profile) associated with the regional structural evolution. The models were constrained by the temperatures measured in four deep boreholes along the profile. We show that the present temperatures and heat flux are influenced by the presence of salt diapirs. Since the Early Carboniferous and till Middle Permian times, the temperatures predicted by the models vary significantly due to the regional transgression and the presence of seawater. The temperature of Devonian–Carboniferous carbonates increases since the Late Permian (time of post-salt deposition) and attains its maximum values in the SW-part of the profile. If the model assumptions concerning the constant vertical and zero lateral heat fluxes are valid, we can conclude that hydrocarbons are most likely to be generated in the SW-part of the region for the post-Early Permian time.  相似文献   

Coastal sediments from the Algarve: low-latitude climate archive for the Aptian-Albian     

Ulrich Heimhofer  Thierry Adatte  Peter A. Hochuli  Stefan Burla  Helmut Weissert 《International Journal of Earth Sciences》2008,97(4):785-797

The Late Aptian to Early Albian transition has previously been identified as a possible example of substantial climate cooling within the mid-Cretaceous greenhouse period. To study the response of continental weathering and terrestrial vegetation to this cooling episode at low- to mid-latitudes, marine nearshore deposits from the Algarve Basin (SW Portugal) have been investigated with a combined approach including palynology, clay mineralogy and bulk-rock geochemistry. In the Lower Aptian part of the succession, quartz-rich sandstone facies is accompanied by high abundances of early diagenetic kaolinite, which is interpreted to reflect episodes of enhanced humidity and high meteoric flow-through. In contrast, the Late Aptian to Early Albian deposits are characterized by high abundances of detrital clay minerals (mica and chlorite) indicating the dominance of physical weathering processes in the source area, most probably related to low precipitation rates in conjunction with tectonically enhanced erosion. Palynological data show a strong dominance of Classopollis pollen associated with low pteridophyte spore abundances, suggesting warm semi-arid to arid palaeoenvironments. Changes in sedimentation patterns from varicoloured lagoonal marls to thick-bedded shallow-water carbonates are neither expressed in the spore-pollen assemblages nor in the distributions of clay minerals which both remain essentially stable throughout the Late Aptian to Early Albian. These relatively stable patterns are in contrast with various lines of evidence, predominantly from high-latitude areas, that suggest a significant cooling during this time interval. Our study demonstrates that terrestrial environments of low- to mid-latitude regions were not significantly affected by the Late Aptian - Early Albian “cold snap”.  相似文献   

Ocean current intensification during the Cretaceous oceanic anoxic event 2 – evidence from the northern Tethys          下载免费PDF全文

Stephan Wohlwend  Malcolm Hart  Helmut Weissert 《地学学报》2015,27(2):147-155

Mesozoic Oceanic Anoxic Events (OAEs) are expressions of major physical oceanographic changes at times of perturbation of the global carbon cycle. A northern Tethyan record of OAE2 is preserved in expanded Cenomanian–Turonian pelagic limestone sections (Seewen Formation) in Eastern Switzerland. The new carbonate carbon‐isotope stratigraphy extracted from these limestones demonstrates that the OAE2 is condensed in all the studied successions and only the onset of the δ¹³C excursion (5.0‰) is present. The condensed interval is characterized by dissolution features, which are filled by a glauconite quartz sandstone. This bed is overlain by a well‐sorted sandstone with intercalated limestone pebbles (Götzis Member), which can be compared with palimpsest sands forming today along current‐swept shelves. The wide distribution of this thin sandstone layer within OAE2 indicates that an intense, erosive, east‐west trending shelf current was active during the highest sea level and most extreme carbon‐cycle perturbation of the OAE2.  相似文献