Cenomanian oysters from the Sergipe Basin, Brazil     

Jens Seeling  Peter Bengtson 《Cretaceous Research》1999,20(6):747

Cenomanian (mid Cretaceous) oysters from the Sergipe Basin in northeastern Brazil are described, with revisions of previously described forms. Nine genera and subgenera, including eleven species, are distinguished: Rastellum diluvianum (Linné, 1767), Amphidonte (Ceratostreon) reticulata (Reuss, 1846), A. (Ceratostreon) flabellata (Goldfuss, 1833), Exogyra (Costagyra) olisiponensis Sharpe, 1850, Ilymatogyra (Afrogyra) africana (Lamarck, 1801), Rhynchostreon (Rhynchostreon)mermeti (Coquand, 1862), R. (Laevigyra) obliquatum (Pulteney, 1813), R. (Laevigyra) sp., Pycnodonte (Phygraea) vesiculosa (J. Sowerby, 1823), Curvostrea rouvillei (Coquand, 1862) and Ambigostrea sp. No undoubted Turonian oysters are known from Sergipe, althoughR. (R.) mermeti possibly straddles the Cenomanian–Turonian boundary. This is in sharp contrast with the situation in the more northerly Brazilian basins, from where several Turonian but no Cenomanian forms have been described. Well-preserved material from Sergipe confirms the close relationship between Exogyra (Costagyra) Vialov andVultogryphaea Vialov. The palaeobiogeographical affinity of the oyster fauna is typically Tethyan with many taxa that are known particularly from the southern Tethys. The inferred palaeoenvironment as implied by the oysters is that of a shallow shelf.  相似文献   

High resolution climate simulations over the Arctic   总被引：1，自引：0，他引：1  

Annette Rinke  Klaus Dethloff  Arne Spekat  Wolfgang Enke  Jens Hesselbjerg Christensen 《Polar research》1999,18(2):143-150

The regional atmospheric climate model HIRHAM has been applied to the Arctic. Simulations for the whole year 1990 and for an ensemble of winter months (January of 1985-1995) have been performed. The comparison of the simulations with observational data analyses shows that the general spatial patterns are in good agreement with the data, in both the vertical structure and the annual cycle. For an additional validation of the model results, a multivariate classification of large-scale circulation patterns has been applied to the January ensemble model simulations.  相似文献   

Satellite SAR observation of shallow bottom topography of the east Australia Sea   总被引：2，自引：2，他引：0  

Zhou Changbao  G. Cresswell  P. Tildesley  C. S. Nilsson 《海洋学报(英文版)》1999,(2):215-223

INTRODUCTIONOne of the interesting oceanographic features detected with SAR is the shallow bottom toPOgraphic feature and bathymetry nearshore. The knowledge on sea bottom toPOgraphy is of vitalimPOrtance not only for shipping, fishery and all kinds of offshore activities, but also for the calibration and validation of morphodynamic models which are currently under development. Traditional bathymetric surveys consume time and cost. SAR remote sensing of oceanography may offeran altern…  相似文献   

Upper Cretaceous bottom current deposits,north-east Greenland     

Jussi Hovikoski  Alfred Uchman  Rikke Weibel  Henrik Nøhr-Hansen  Emma Sheldon  Jon Ineson  Morten Bjerager  Jens Therkelsen  Mette Olivarius  Michael Larsen  Peter Alsen  Jørgen Bojesen-Koefoed 《Sedimentology》2020,67(7):3619-3654

Reported ancient bottom current deposits in deep marine settings are scarce and most of them remain contentious. This study describes sedimentological, ichnological and petrographical characteristics of a drill core that covers ca 10 Myr of Upper Cretaceous stratigraphy at Hold with Hope, north-east Greenland. The core is divided into four facies associations, which are interpreted to reflect deposition from bottom currents, turbidity flows and hemipelagic settling in slope and/or near slope environments. The evidence for bottom current influence is three-fold. Firstly, pervasive indications of winnowing such as marine bioclast-rich lags and outsized clasts on ‘mud on mud’ contacts are suggestive of low-sediment concentration flows capable of transporting up to pebble-sized clasts. Common Mn–Fe–Mg rich carbonate matrix cements and various types of hiatal chemogenic lag deposits showing glauconite, apatite and carbonate clasts also point to condensation, prolonged exposure at the sediment–water interface and recurrent phases of sea-floor erosion. Secondly, such deposits can show indicators for tidal processes such as double mud-drapes, tangential bottom sets in dune-scale cross-bedding and cyclic rhythmites. Thirdly, inverse to normal grading at various scales is common in fully marine, commonly seafloor-derived sediments. Ichnological data indicate considerable taxonomic variability in the bottom current deposits, but recurrent fabrics are characteristically dominated by morphologically simple burrows such as Thalassinoides and Planolites, with secondary Phycosiphon, Nereites, Zoophycos and/or Chondrites. In general, opportunistic taxa are common whereas mature composite ichnofabrics are rare. The omission surfaces are locally burrowed with stiffground to firmground trace fossil suites. The results contribute to establishing sedimentological, ichnological and mineralogical criteria for recognition of bottom current deposits as well as to the understanding of the Late Cretaceous palaeoenvironmental evolution of the Arctic region.  相似文献   

An alternative approach to overcome shortcomings with multiple testing of binary data in ecotoxicology     

René?LehmannEmail author  Jean?Bachmann  Bilgin?Karaoglan  Jens?Lacker  Christian?Polleichtner  Hans?Toni?Ratte  Monika?Ratte 《Stochastic Environmental Research and Risk Assessment (SERRA)》2018,32(1):213-222

Binary data such as survival, hatching and mortality are assumed to be best described by a binomial distribution. This article provides a simple and straight forward approach for derivation of a no/lowest observed effect level (NOEL/LOEL) in a one-to-many control versus treatments setup. Practically, NOEL and LOEL values can be derived by means of different procedures, e.g. using Fisher’s exact test in coherence with adjusted p values. However, using adjusted p values heavily decreases statistical power. Alternatively, multiple t tests (e.g. Dunnett test procedure) together with arcsin-square-root transformations can be applied in order to account for variance heterogeneity of binomial data. Arcsin-square-root transformation, however, violates normal distribution because transformed data are constrained, while normal distribution provides data in the range \((-\infty ,\infty )\). Furthermore, results of statistical tests relying on an approximate normal distribution are approximate too. When testing for trends in probabilities of success (probs), the step down Cochran–Armitage trend test (CA) can be applied. The test statistic used is approximately normal. However, if probs approach 0 or 1, normal approximation of the null-distribution is suboptimal. Thus, critical values and p values lack statistical accuracy. We propose applying the closure principle (CP) and Fisher–Freeman–Halton test (FISH). The resulting CPFISH can solve the problems mentioned above. CP is used to overcome \(\alpha\)-inflation while FISH is applied to test for differences in probs between the control and any subset of treatment groups. Its applicability is presented by means of real data sets. Additionally, we performed a simulation study of 81 different setups (differing numbers of control replicates, numbers of treatments etc.), and compared the results of CPFISH to CA allowing us to point out the advantages and disadvantages of the CPFISH.  相似文献   

Evaluating preprocessing methods of digital elevation models for hydrological modelling          下载免费PDF全文

William Lidberg  Mats Nilsson  Tomas Lundmark  Anneli M. Ågren 《水文研究》2017,31(26):4660-4668

With the introduction of high‐resolution digital elevation models, it is possible to use digital terrain analysis to extract small streams. In order to map streams correctly, it is necessary to remove errors and artificial sinks in the digital elevation models. This step is known as preprocessing and will allow water to move across a digital landscape. However, new challenges are introduced with increasing resolution because the effect of anthropogenic artefacts such as road embankments and bridges increases with increased resolution. These are problematic during the preprocessing step because they are elevated above the surrounding landscape and act as artificial dams. The aims of this study were to evaluate the effect of different preprocessing methods such as breaching and filling on digital elevation models with different resolutions (2, 4, 8, and 16 m) and to evaluate which preprocessing methods most accurately route water across road impoundments at actual culvert locations. A unique dataset with over 30,000 field‐mapped road culverts was used to assess the accuracy of stream networks derived from digital elevation models using different preprocessing methods. Our results showed that the accuracy of stream networks increases with increasing resolution. Breaching created the most accurate stream networks on all resolutions, whereas filling was the least accurate. Burning streams from the topographic map across roads from the topographic map increased the accuracy for all methods and resolutions. In addition, the impact in terms of change in area and absolute volume between original and preprocessed digital elevation models was smaller for breaching than for filling. With the appropriate methods, it is possible to extract accurate stream networks from high‐resolution digital elevation models with extensive road networks, thus providing forest managers with stream networks that can be used when planning operations in wet areas or areas near streams to prevent rutting, sediment transport, and mercury export.  相似文献   

Perfect partial reconstructions for multiple simultaneous sources     

Jens Wittsten  Fredrik Andersson  Johan Robertsson  Lasse Amundsen 《Geophysical Prospecting》2019,67(6):1486-1497

A major focus of research in the seismic industry of the past two decades has been the acquisition and subsequent separation of seismic data using multiple sources fired simultaneously. The recently introduced method of signal apparition provides a new take on the problem by replacing the random time-shifts usually employed to encode the different sources by fully deterministic periodic time-shifts. In this paper, we give a mathematical proof showing that the signal apparition method results in optimally large regions in the frequency–wavenumber space where exact separation of sources is achieved. These regions are diamond shaped and we prove that using any other method of source encoding results in strictly smaller regions of exact separation. The results are valid for arbitrary number of sources. Numerical examples for different number of sources (three, respectively, four sources) demonstrate the exact recovery of these diamond-shaped regions. The implementation of the theoretical proofs in the field is illustrated by the results of a conducted field test.  相似文献   

Acoustic and petrophysical properties of mechanically compacted overconsolidated sands: part 1 – experimental results     

Sirikarn Narongsirikul  Nazmul Haque Mondol  Jens Jahren 《Geophysical Prospecting》2019,67(4):804-824

This paper part one is set out to lay primary observations of experimental compaction measurements to form the basis for rock physics modelling in paper part two. P- and S-wave velocities and corresponding petrophysical (porosity and density) properties of seven unconsolidated natural sands with different mineralogical compositions and textures are reported. The samples were compacted in a uniaxial strain configuration from 0.5 up to 30 MPa effective stresses. Each sand sample was subjected to three loading cycles to study the influence of stress reduction on acoustic velocities and rock physical properties with the key focus on simulating a complex burial history with periods of uplift. Results show significant differences in rock physical properties between normal compaction and overconsolidation (unloaded and reloaded). The differences observed for total porosity, density, and P- and S-wave velocities are attributed to irrecoverable permanent deformation. Microtextural differences affect petrophysical, acoustic, elastic and mechanical properties, mostly during normal consolidation but are less significant during unloading and reloading. Different pre-consolidation stress magnitudes, stress conditions (isotropic or uniaxial) and mineral compositions do not significantly affect the change in porosity and velocities during unloading as a similar steep velocity–porosity gradient is observed. The magnitude of change in the total porosity is low compared to the associated change in P- and S-wave velocities during stress release. This can be explained by the different sensitivity of the porosity and acoustic properties (velocities) to the change in stress. Stress reduction during unloading yields maximum changes in the total porosity, P- and S-wave velocities of 5%, 25%, and 50%, respectively. These proportions constitute the basis for the following empirical (approximation) correlations: Δϕ ∼ ±5 ΔV_P and ΔV_P ∼ ±2ΔV_S. The patterns observed in the experiments are similar to well log data from the Barents Sea. Applications to rock physics modelling and reservoir monitoring are reported in a companion paper.  相似文献