Post-mid-Cretaceous eastern North Sea evolution inferred from 3D thermo-mechanical modelling   总被引：1，自引：0，他引：1  

Lykke Gemmer  Sren B. Nielsen  Mads Huuse  Holger Lykke-Andersen 《Tectonophysics》2002,350(4):105-342

The Late Cretaceous–Cenozoic evolution of the eastern North Sea region is investigated by 3D thermo-mechanical modelling. The model quantifies the integrated effects on basin evolution of large-scale lithospheric processes, rheology, strength heterogeneities, tectonics, eustasy, sedimentation and erosion.

The evolution of the area is influenced by a number of factors: (1) thermal subsidence centred in the central North Sea providing accommodation space for thick sediment deposits; (2) 250-m eustatic fall from the Late Cretaceous to present, which causes exhumation of the North Sea Basin margins; (3) varying sediment supply; (4) isostatic adjustments following erosion and sedimentation; (5) Late Cretaceous–early Cenozoic Alpine compressional phases causing tectonic inversion of the Sorgenfrei–Tornquist Zone (STZ) and other weak zones.

The stress field and the lateral variations in lithospheric strength control lithospheric deformation under compression. The lithosphere is relatively weak in areas where Moho is deep and the upper mantle warm and weak. In these areas the lithosphere is thickened during compression producing surface uplift and erosion (e.g., at the Ringkøbing–Fyn High and in the southern part of Sweden). Observed late Cretaceous–early Cenozoic shallow water depths at the Ringkøbing–Fyn High as well as Cenozoic surface uplift in southern Sweden (the South Swedish Dome (SSD)) are explained by this mechanism.

The STZ is a prominent crustal structural weakness zone. Under compression, this zone is inverted and its surface uplifted and eroded. Contemporaneously, marginal depositional troughs develop. Post-compressional relaxation causes a regional uplift of this zone.

The model predicts sediment distributions and paleo-water depths in accordance with observations. Sediment truncation and exhumation at the North Sea Basin margins are explained by fall in global sea level, isostatic adjustments to exhumation, and uplift of the inverted STZ. This underlines the importance of the mechanisms dealt with in this paper for the evolution of intra-cratonic sedimentary basins.  相似文献   

Small inflation sources producing seismic and infrasonic pulses during the 2000 eruptions of Miyake-jima, Japan     

Tomokazu Kobayashi  Yoshiaki Ida 《Earth and Planetary Science Letters》2005,240(2):291-301

During the 2000 activity of Miyake-jima volcano, Japan, we detected long period seismic signals with initial pulse widths of 1-2 s, accompanied by infrasonic pulses with almost the same pulse widths. The seismic signals were observed from 13 July 2000, a day before the second summit eruption. The occurrences of the seismic signals were intermittent with a gradual increase in their magnitudes and numbers building toward a significant explosive eruption on 18 August. After the eruption, the seismic and infrasonic events ceased. The results of a waveform inversion show that the initial motions were excited by an isotropic inflation source beneath the south edge of the caldera at a depth of 1.4 km. On the other hand, the sources of the infrasonic pulses were located in the summit caldera area. The times at which the infrasonic pulses were emitted at the surface were delayed by about 3 s from the origin times of the seismic events. It is suggested that small isotropic inflations excited seismic waves in the crust and simultaneously caused acoustic waves that traveled in the conduit and produced infrasonic pulses at the crater bottom. Considering the observed time differences and gas temperatures emitted from the vent, the conduit should have been filled with vapor mixed with SO₂ gas and volcanic ash. The change of the time differences between the seismic and infrasonic signals suggests that the seismic source became shallower within half a day before the August 18 explosive eruption. We interpret the source process as a fragmentation process of magma in which gas bubbles burst and quickly released part of the pressure that had been sustained by the tensional strength of magma.  相似文献   

Dynamic modelling of passive margin salt tectonics: effects of water loading, sediment properties and sedimentation patterns   总被引：1，自引：0，他引：1  

Lykke Gemmer  Christopher Beaumont  Steven J. Ings† 《Basin Research》2005,17(3):383-402

We investigate the evolution of passive continental margin sedimentary basins that contain salt through two‐dimensional (2D) analytical failure analysis and plane‐strain finite‐element modelling. We expand an earlier analytical failure analysis of a sedimentary basin/salt system at a passive continental margin to include the effects of submarine water loading and pore fluid pressure. Seaward thinning sediments above a weak salt layer produce a pressure gradient that induces Poiseuille flow in the viscous salt. We determine the circumstances under which failure at the head and toe of the frictional–plastic sediment wedge occurs, resulting in translation of the wedge, landward extension and seaward contraction, accompanied by Couette flow in the underlying salt. The effects of water: (i) increase solid and fluid pressures in the sediments; (ii) reduce the head to toe differential pressure in the salt and (iii) act as a buttress to oppose failure and translation of the sediment wedge. The magnitude of the translation velocity upon failure is reduced by the effects of water. The subsequent deformation is investigated using a 2D finite‐element model that includes the effects of the submarine setting and hydrostatic pore pressures. The model quantitatively simulates a 2D approximation of the evolution of natural sedimentary basins on continental margins that are formed above salt. Sediment progradation above a viscous salt layer results in formation of landward extensional basins and listric normal growth faults as well as seaward contraction. At a later stage, an allochthonous salt nappe overthrusts the autochthonous limit of the salt. The nature and distribution of major structures depends on the sediment properties and the sedimentation pattern. Strain weakening of sediment favours landward listric growth faults with formation of asymmetric extensional depocentres. Episodes of low sediment influx, with partial infill of depocentres, produce local pressure gradients in the salt that result in diapirism. Diapirs grow passively during sediment aggradation.  相似文献   

Sexual reproduction and early life‐history traits of the Mediterranean soft coral Alcyonium acaule          下载免费PDF全文

Núria Teixidó  Nathaniel Bensoussan  Andrea Gori  Ida Fiorillo  Núria Viladrich 《Marine Ecology》2016,37(1):134-144

Understanding processes that contribute to a better comprehension of the population dynamics of long‐lived species is critical for the maintenance and potential recovery of such species. Despite the abundance of soft corals in Mediterranean rocky reefs, little information exists on their life histories and reproductive patterns. In this study, we assessed the main reproductive characteristics and early life‐history traits of the long‐lived soft coral Alcyonium acaule. The sex ratio was 1:1; the smallest fertile colonies were one finger in size (2.1 ± 0.6 cm in height), and both colony and polyp fertility increased with colony size. Likewise, the number of eggs and spermary sacs per polyp increased significantly with colony size, whereas the diameter of the female and male sexual products did not. Over 6 years of observations (2007–2012), spawning occurred primarily in July, after the seawater reached 20 °C, in a single spawning episode per year. Approximately 80% of female colonies released eggs, which were retained on the surface of the mother colony by mucous strings for up to a few days. High fertilization rates were observed during spawning in 2008 and 2009 (94.9% and 87.0%, respectively). The timing of development was ~24 h for the blastulae, ~48–72 h for the planulae and 8–22 days for metamorphosis into primary polyps. Survivorship of planulae was relatively high (~50% at 45 days after release), but only 24% of larvae metamorphosed into primary polyps, and their survivorship was moderate after 2 months (65% in 2008 and 74% in 2009). Asexual reproduction was negligible, indicating that sexual reproduction is the main mechanism supporting the maintenance and recovery of populations.  相似文献   

Low Food Availability Narrows the Tolerance of the Copepod Eurytemora affinis to Salinity,but Not to Temperature     

Bruce G. Hammock  Sarah Lesmeister  Ida Flores  Gideon S. Bradburd  Frances H. Hammock  Swee J. Teh 《Estuaries and Coasts》2016,39(1):189-200

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Indonesian rainfall variability during Western North Pacific and Australian monsoon phase related to convectively coupled equatorial waves     

Ida Pramuwardani  Hartono  Sunarto  Ardhasena Sopaheluwakan 《Arabian Journal of Geosciences》2018,11(21):673

The Indonesian archipelago which has over 15,000 islands, lies in the tropics between Asia and Australia. This eventually alters the rainfall variability over the region, which was influenced by the Asian-Australian monsoon and controlled by intraseasonal variabilities such as convectively coupled equatorial waves (CCEW), i.e., Kelvin, n?=?1 equatorial Rossby (ER), mixed Rossby gravity (MRG), and n?=?1 Westward inertio gravity (WIG), including the Madden–Julian Oscillation (MJO). This study examines a 15-year 3B42 data for trapping CCEW and MJO in the region of Indonesia during both active and extreme Western North Pacific (WNP) and Australian (AU) monsoon phases, which are then compared with 30-year rainfall anomalies among 38 synoptic stations over Indonesia. The space–time spectral analysis is employed to filter each wave including the MJO in the equator, then proceeding with the empirical orthogonal function (EOF) method to seek each wave peak which then coincides with WNP and AU monsoon peaks over Indonesia. It is concluded that an extreme monsoon classification has proven to control rainfall activity related to the CCEW and MJO at 60.66% during December through February (DJF)-WNP for only the significant wave perturbation value. Meanwhile, the CCEW and MJO significantly increase/decrease precipitation at Day 0 for about 37.88% from the total of Day 1st to Day end. Although the contribution of the CCEW and MJO does not profoundly influence rainfall activity during monsoon phase over Indonesia, they still modulate weather condition for more than 50%. On the other hand, a complex topography with a number of land–sea complexities is capable of influencing the rainfall variability in the region as a negative relationship is associated with the CCEW and MJO either during DJF-WNP or July through August (JAS)-AU monsoon phase.  相似文献   

Eigen oscillation of a fluid sphere and source mechanism of harmonic volcanic tremor     

Eisuke Fujita  Yoshiaki Ida  Jun Oikawa 《Journal of Volcanology and Geothermal Research》1995,69(3-4)

The eigen oscillation of a fluid sphere embedded in an infinite elastic medium is analyzed to understand the source mechanism of volcanic tremor that vibrates nearly monotonically and attenuates slowly. The dimensionless eigen frequencies of the sinusoidal oscillation are calculated in a complex form with the attenuation factor in its imaginary part for various combinations of the three parameters: the contrasts of P-wave velocity, density and rigidity between the fluid and the country rock. Eigen oscillations consist of a high attenuation mode with a rapidly decaying pulsive wave at a low frequency and infinite number of regular modes with slowly decaying vibrations. For regular modes, the frequency of oscillation obtained from the real part of an eigen value is distributed in approximately regular intervals while the attenuation factor from the imaginary part is almost constant independent of the mode. Each eigen frequency of regular and high attenuation modes is degenerated with two independent eigen functions describing different distributions of displacement, velocity and stress. The theory is applied to harmonic volcanic tremor observed at Kusatsu-Shirane Volcano, central Japan. Observed spectral peaks of the tremor are explained by the eigen frequencies and attenuation factors of several lowest regular modes if the spherical fluid oscillator has a radius of dozens of meters and a P-wave velocity of about several hundred meters per second.  相似文献   

Latérite als Leithorizonte zur Rekonstruktion tektonischer Vorgänge auf den Festländern     

Prof. Dr. Ida Valeton 《International Journal of Earth Sciences》1973,62(1):153-161

A reconstruction is made of the relief which is probably developed through peneplanation and a contemporary deep kaolinisation during late Cretaceous time before the laterite formation and the relief at the time of the laterite formation in Eocene in the region of the present Guiana shield and its foreland. A characteristic plain with very shallow valleys and a thick Al-laterite on its surface was formed during Eocene time. The Al-laterite is used as a characteristic and reference horizon for the post Eocene tectonic which is characterized by a main bulge of the Guiana shield in Surinam, a weaker lift in Guyana and a submergence below sea level in the north.  相似文献   

Reply to Discussion of “Perceptual models of uncertainty for socio-hydrological systems: a flood risk change example”*     

Ida K. Westerberg  Giuliano Di Baldassarre  Keith J. Beven  Gemma Coxon  Tobias Krueger 《水文科学杂志》2020,65(Z2):2001-2003

ABSTRACT

Ertsen discusses the representation of reality and uncertainty in our paper, raising three critical points. In response to the first, we agree that discussion of different interpretations of the concept of uncertainty is important when developing perceptual models – making different uncertainty interpretations explicit was a key motivation behind our method. Secondly, we do not, as Ertsen suggests, deny anyone who is not a “certified” scientist to have relevant knowledge. The elicitation of diverse views by discussing perceptual models is a basis for open discussion and decision making. Thirdly, Ertsen suggests that it is not useful to treat socio-hydrological systems as if they exist. We argue that we act as “pragmatic realists” in most practical applications by treating socio-hydrological systems as an external reality that can be known. But the uncertainty that arises from our knowledge limitations needs to be recognized, as it may impact on practical decision making and associated costs.  相似文献   

Evolution of Planetesimal Velocities Based on Three-Body Orbital Integrations and Growth of Protoplanets     

Keiji OhtsukiGlen R. Stewart  Shigeru Ida 《Icarus》2002,155(2):436-453

We obtain the viscous stirring and dynamical friction rates of planetesimals with a Rayleigh distribution of eccentricities and inclinations, using three-body orbital integration and the procedure described by Ohtsuki (1999, Icarus137, 152), who evaluated these rates for ring particles. We find that these rates based on orbital integrations agree quite well with the analytic results of Stewart and Ida (2000, Icarus 143, 28) in high-velocity cases. In low-velocity cases where Kepler shear dominates the relative velocity, however, the three-body calculations show significant deviation from the formulas of Stewart and Ida, who did not investigate the rates for low velocities in detail but just presented a simple interpolation formula between their high-velocity formula and the numerical results for circular orbits. We calculate evolution of root mean square eccentricities and inclinations using the above stirring rates based on orbital integrations, and find excellent agreement with N-body simulations for both one- and two-component systems, even in the low-velocity cases. We derive semi-analytic formulas for the stirring and dynamical friction rates based on our numerical results, and confirm that they reproduce the results of N-body simulations with sufficient accuracy. Using these formulas, we calculate equilibrium velocities of planetesimals with given size distributions. At a stage before the onset of runaway growth of large bodies, the velocity distribution calculated by our new formulas are found to agree quite well with those obtained by using the formulas of Stewart and Ida or Wetherill and Stewart (1993, Icarus106, 190). However, at later stages, we find that the inclinations of small collisional fragments calculated by our new formulas can be much smaller than those calculated by the previously obtained formulas, so that they are more easily accreted by larger bodies in our case. The results essentially support the previous results such as runaway growth of protoplanets, but they could enhance their growth rate by 10-30% after early runaway growth, where those fragments with low random velocities can significantly contribute to rapid growth of runaway bodies.  相似文献