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151.
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
152.
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
153.
Ocean current intensification during the Cretaceous oceanic anoxic event 2 – evidence from the northern Tethys 下载免费PDF全文
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
154.
Sr-isotope measurements of unaltered oyster shell calcite using laser-ablation multi-collector ICPMS techniques represent a powerful tool capable of establishing a chronostratigraphic framework for fossil near-shore deposits. This approach is tested on two shoal-water successions from the Portuguese Algarve and Lusitanian basins covering Late Barremian to Albian strata. 87 Sr/86 Sr values derived from low-Mg calcite of oyster shells fluctuate between 0.70717 ± 0.00001 and 0.70746 ± 0.00002; absolute values as well as stratigraphic trends match well with the global open-marine seawater signal. The new Sr-isotope results in combination with existing bio- and chemostratigraphic records allow for identification of an Early Aptian biocalcification crisis at both studied localities and show that this event has severely affected coastal environments along the evolving Atlantic. Siliciclastic intervals in the Algarve section are interpreted as near-shore equivalents of enhanced detrital shedding into shelf and deep-sea environments as a consequence of increased chemical weathering rates during humid climate episodes. 相似文献
155.
Ute V. Möstl Nikolay V. Erkaev Michael Zellinger Helmut Lammer Hannes Gröller Helfried K. Biernat Daniil Korovinskiy 《Icarus》2011,216(2):476-484
The Kelvin–Helmholtz instability gained scientific attention after observations at Venus by the spacecraft Pioneer Venus Orbiter gave rise to speculations that the instability contributes to the loss of planetary ions through the formation of plasma clouds. Since then, a handful of studies were devoted to the Kelvin–Helmholtz instability at the ionopause and its implications for Venus. The aim of this study is to investigate the stability of the two instability-relevant boundary layers around Venus: the induced magnetopause and the ionopause. We solve the 2D magnetohydrodynamic equations with the total variation diminishing Lax–Friedrichs algorithm and perform simulation runs with different initial conditions representing the situation at the boundary layers around Venus. Our results show that the Kelvin–Helmholtz instability does not seem to be able to reach its nonlinear vortex phase at the ionopause due to the very effective stabilizing effect of a large density jump across this boundary layer. This seems also to be true for the induced magnetopause for low solar activity. During high solar activity, however, there could occur conditions at the induced magnetopause which are in favour of the nonlinear evolution of the instability. For this situation, we estimated roughly a growth rate for planetary oxygen ions of about 7.6 × 1025 s−1, which should be regarded as an upper limit for loss due to the Kelvin–Helmholtz instability. 相似文献
156.
Helmut Schaeben 《Mathematical Geosciences》2014,46(7):887-893
Despite a missing definition of equivalence of mathematical models or methods by Zhang et al. (Math Geosci, 2013), an “equivalence” (Zhang et al., Math Geosci, 2013, p. 6,7,8,14) of modified weights-of-evidence (Agterberg, Nat Resour Res 20:95–101, 2011) and logistic regression does not generally exist. Its alleged proof is based on a previously conjectured linear relationship between weights of evidence and logistic regression parameters (Deng, Nat Resour Res 18:249–258, 2009), which does not generally exist either (Schaeben and van den Boogaart, Nat Resour Res 20:401–406, 2011). In fact, an extremely simple linear relationship exists only if the predictor variables are conditionally independent given the target variable, in which case the contrasts, i.e., the differences of the weights, are equal to the logistic regression parameters. Thus, weights-of-evidence is the special case of logistic regression if the predictor variables are binary and conditionally independent given the target variable. 相似文献
157.
Helmut TISCHLINGER 《地球学报》2010,31(Z1):62-63
The first discoveries of pterosaur fossils were made at the end of the 18th century and during the first decades of the 19th century in Bavaria, southern Germany. They originate from limestone quarries in the vicinity of the village of Solnhofen and adjacent hamlets as well as from limestone pits close to the town of Eichst?tt. 相似文献
158.
159.
While crystallography conventionally presumes that a single crystal carries a unique crystallographic orientation, modern
experimental techniques reveal that a single crystal may exhibit an orientation distribution. However, this distribution is
largely concentrated; it is extremely concentrated when compared with orientation distributions of polycrystalline specimen.
A case study of a deformation experiment with a single hematite crystal is presented, where the experimental deformation induced
twining, which in turn changed a largely concentrated unimodal “parent” orientation distribution into a multimodal orientation
distribution with a major mode resembling the parent mode and three minor modes corresponding to the progressive twining.
The free and open source software MTEX for texture analysis was used to compute and visualize orientations density functions
from both integral orientation measurements, i.e. neutron diffraction pole intensity data, and individual orientation measurements,
i.e. electron back scatter diffraction data. Thus it is exemplified that MTEX is capable of analysing orientation data from
largely concentrated orientation distributions. 相似文献
160.
First GOCE gravity field models derived by three different approaches 总被引:28,自引:10,他引:18
Roland Pail Sean Bruinsma Federica Migliaccio Christoph F?rste Helmut Goiginger Wolf-Dieter Schuh Eduard H?ck Mirko Reguzzoni Jan Martin Brockmann Oleg Abrikosov Martin Veicherts Thomas Fecher Reinhard Mayrhofer Ina Krasbutter Fernando Sans�� Carl Christian Tscherning 《Journal of Geodesy》2011,85(11):819-843
Three gravity field models, parameterized in terms of spherical harmonic coefficients, have been computed from 71 days of GOCE (Gravity field and steady-state Ocean Circulation Explorer) orbit and gradiometer data by applying independent gravity field processing methods. These gravity models are one major output of the European Space Agency (ESA) project GOCE High-level Processing Facility (HPF). The processing philosophies and architectures of these three complementary methods are presented and discussed, emphasizing the specific features of the three approaches. The resulting GOCE gravity field models, representing the first models containing the novel measurement type of gravity gradiometry ever computed, are analysed and assessed in detail. Together with the coefficient estimates, full variance-covariance matrices provide error information about the coefficient solutions. A comparison with state-of-the-art GRACE and combined gravity field models reveals the additional contribution of GOCE based on only 71 days of data. Compared with combined gravity field models, large deviations appear in regions where the terrestrial gravity data are known to be of low accuracy. The GOCE performance, assessed against the GRACE-only model ITG-Grace2010s, becomes superior at degree 150, and beyond. GOCE provides significant additional information of the global Earth gravity field, with an accuracy of the 2-month GOCE gravity field models of 10?cm in terms of geoid heights, and 3?mGal in terms of gravity anomalies, globally at a resolution of 100?km (degree/order 200). 相似文献