How to cut a sediment core for <Superscript>210</Superscript>Pb geochronology: a supplement     

Xueqiang?LuEmail author  Eiji?Matsumoto 《Environmental Geology》2005,49(2):251-252

To obtain the profile of excess ²¹⁰Pb in sediment column, it is necessary to section the collected core to date. Sectioning thickness is generally not explicit. An approach when sedimentation rate is constant has been suggested by Lu and Matsumoto (Environ Geol 47:804–810, 2005). This paper addresses the case when sedimentation rate is variable. Actually, it is possible to assume that sedimentation rate is constant within the sectioning thickness and based on this concept, a tentative approach for determining reasonable sectioning thickness is proposed.  相似文献   

Core made of geotextile sand containers for rubble mound breakwaters and seawalls: Effect on armour stability and hydraulic performance     

Hocine Oumeraci 《Ocean Engineering》2011,38(1):159-170

A systematic armour stability and the hydraulic performance, including wave reflection, wave transmission, experimental study in the twin-wave flumes of Leichtweiss-Institute (LWI) is performed on a geocore breakwater and a conventional rubble mound breakwater in order to comparatively determine the wave run-up and wave overtopping. The geocore breakwater consists of a core made of sand-filled geotextile containers (GSC) covered by an armour made of rock. The geocore is more than an order of magnitude less permeable than the quarry run core of a conventional breakwater. As expected, the core permeability substantially affects the armour stability on the seaside slope, the wave transmission and the wave overtopping performance. Surprisingly, however, wave reflection and hydraulic stability of the rear slope are less affected. Formulae for the armour stability and hydraulic performance of the geocore breakwater are proposed, including wave reflection, transmission, run-up and overtopping.  相似文献   

Downhole well log and core montages from the Mount Elbert Gas Hydrate Stratigraphic Test Well, Alaska North Slope     

T.S. Collett  R.E. LewisW.J. Winters  M.W. LeeK.K. Rose  R.M. Boswell 《Marine and Petroleum Geology》2011,28(2):561-577

The BPXA-DOE-USGS Mount Elbert Gas Hydrate Stratigraphic Test Well was an integral part of an ongoing project to determine the future energy resource potential of gas hydrates on the Alaska North Slope. As part of this effort, the Mount Elbert well included an advanced downhole geophysical logging program. Because gas hydrate is unstable at ground surface pressure and temperature conditions, a major emphasis was placed on the downhole-logging program to determine the occurrence of gas hydrates and the in-situ physical properties of the sediments. In support of this effort, well-log and core data montages have been compiled which include downhole log and core-data obtained from the gas-hydrate-bearing sedimentary section in the Mount Elbert well. Also shown are numerous reservoir parameters, including gas-hydrate saturation and sediment porosity log traces calculated from available downhole well log and core data.  相似文献   

Holocene Sea Levels and Coastal Change,South-west Viti Levu Island,Fiji     

Kirti K. Lal 《The Australian geographer》2011,42(1):41-51

For the first time, a sediment core spanning the entire Holocene has been analysed from Fiji. The 6 m core was obtained from the floor of an ancient coastal lagoon (palaeolagoon) adjacent to Bourewa, the site of the earliest known human settlement in this island group. The basal sediments, just above bedrock, date from 11 470 cal bp. A major transition occurs around 8000 cal bp where marine influences on palaeolagoon sedimentation increase sharply. Full shallow-water marine conditions are attained around 4630 cal bp and last until 3480 cal bp after which there is a regressive phase. The results agree with the area-specific predictions of sea level in the ICE-4G model, particularly in the timing of the highstand. In addition, the results support the ideas (a) that early human colonisation of Fiji occurred during the late Holocene regression, (b) that the first inhabitants of Bourewa utilised both nearshore marine (reefal) and brackish lagoon food sources, and (c) that the abrupt human abandonment of the area around 2500 cal bp could have been prompted by a reduction in these resources driven largely by sea-level fall.  相似文献   

略论美国小都市区     

曹升生 《世界地理研究》2011,(4):84-90

在美国预算与管理总署于2000年推出的核心基础统计区（CBSA）里,首次出现了小都市统计区概念,成为与大都市统计区概念并列的的一个新城市化发展衡量标尺。小都市区概念能够扩充人们对非大都市区内在多样性的认识,增强对美国整体城市化水平的了解,其应用到实际,就是美国本土都市区地域面积首次超过农村地区,标志着美国城市化已进入全方位发展阶段。  相似文献   

用岩芯模拟测试参数做模型正演预测储层油、气、水边界          下载免费PDF全文

黄凯  徐群洲  杨晓海  赖仲康  张露菲 《地球物理学报》1998,41(Z1):414-421

利用地震资料进行AVO油气检测,需要提供准确的储层岩石物性参数．通过对准噶尔盆地西部储层岩样实验室测定,得出合不同流体岩石在不同温度、压力下纵横波速度、速度比、泊松比的变化规律及差异．根据其差异性,用Zoeppritz方程做模型正演,以确定目的层有无AVO响应,以便对地震剖面做针对性的特殊处理．实际应用结果表明,用实验室测试的岩石物性参数做模型正演,可提高AVO检测的准确性,为用地震资料结合实验室岩芯测试参数预测地层油、气、水边界提供了有效手段．  相似文献   

Magnetic instabilities in rapidly rotating spherical geometries I. from cylinders to spheres     

David R. Fearn  Werner S. Weiglhofer 《地球物理与天体物理流体动力学》2013,107(1-4):159-181

Abstract

The solution of the full nonlinear hydromagnetic dynamo problem is a major numerical undertaking. While efforts continue, supplementary studies into various aspects of the dynamo process can greatly improve our understanding of the mechanisms involved. In the present study, the linear stability of an electrically conducting fluid in a rigid, electrically insulating spherical container in the presence of a toroidal magnetic field B_o(r,θ)lø and toroidal velocity field U_o(r,θ)lø, [where (r,θ,ø) are polar coordinates] is investigated. The system, a model for the Earth's fluid core, is rapidly rotating, the magnetostrophic approximation is used and thermal effects are excluded. Earlier studies have adopted a cylindrical geometry in order to simplify the numerical analysis. Although the cylindrical geometry retains the fundamental physics, a spherical geometry is a more appropriate model for the Earth. Here, we use the results which have been found for cylindrical systems as guidelines for the more realistic spherical case. This is achieved by restricting attention to basic states depending only on the distance from the rotation axis and by concentrating on the field gradient instability. We then find that our calculations for the sphere are in very good qualitative agreement both with a local analysis and with the predictions from the results of the cylindrical geometry. We have thus established the existence of field gradient modes in a realistic (spherical) model and found a sound basis for the study of various other, more complicated, classes of magnetically driven instabilities which will be comprehensively investigated in future work.  相似文献   

Evidence for r-Mode Oscillations in Super-Kamiokande Solar Neutrino Data     

P. A. Sturrock 《Solar physics》2008,252(2):221-233

There has for some time been evidence of variability in radiochemical solar neutrino measurements, but this evidence has seemed suspect since the Cerenkov experiments have not shown similar evidence of variability. The present reanalysis of Super-Kamiokande data shows strong evidence of r-mode oscillations. The frequencies of these oscillations correspond to a region with a sidereal rotation rate of 13.97 year⁻¹. This estimate is incompatible with the rotation rate in the convection zone but is compatible with current estimates of the rotation rate in the radiative zone. The excitation of r modes in the radiative zone may be due to a velocity field originating in or related to the nuclear-burning core.  相似文献   

Penetration of molten iron alloy into the lower mantle phase     

Takashi Yoshino 《Comptes Rendus Geoscience》2019,351(2-3):171-181

The core–mantle boundary is the only interface where the metallic core and the silicate mantle interact physically and chemically. Many geophysical anomalies such as low shear velocity and high electrical conductivity have been observed at the bottom of the mantle. Perturbations in the Earth's rotation rate at decadal time periods require the existence of a thin conductive layer with a conductance of 10⁸ S. Substantial additions of molten iron from the outer core into the mantle may produce these geophysical anomalies. Although iron enrichment by penetration has only been observed in (Mg,Fe)O, the second dominant mineral in the lower mantle, the penetration process leading to iron enrichment in the silicate mantle has not been experimentally confirmed. In this study, high-pressure and high-temperature experiments were conducted to investigate the penetration of molten iron alloy into lower mantle phases; postspinel, polycrystalline bridgmanite and polycrystalline (Mg,Fe)O. At the interface between (Mg,Fe)O aggregate and molten iron alloy, liquid metal penetrated the (Mg,Fe)O aggregate along grain boundaries and formed a thin layer containing metal-rich blobs. In contrast, no penetration of molten iron alloy was observed at the interface between molten iron alloy and silicate phases. Penetration of liquid iron alloy into the (Mg,Fe)O aggregate is caused by the capillarity phenomenon or Mullins–Sekerka instability. Neither mechanism occurs at the boundary of pure polycrystalline MgO, indicating that the FeO in (Mg,Fe)O plays an essential role in this phenomenon. Infiltration of molten iron alloy along grain boundaries (capillarity phenomenon) is the dominant process and precedes penetration due to the Mullins–Sekerka instability. The capillarity phenomenon is governed by the balance of forces between surface tension and gravity. In the case where the ultralow velocity zone (ULVZ) with a low shear velocity is composed of Fe-rich (Mg,Fe)O, the maximum penetration distance of molten iron alloy by capillary rise is limited to 20 m. The addition of iron-rich melt to the base of the mantle is therefore unlikely to be the main cause of the high conductance of the CMB region predicted from decadal variation of the length of day. Furthermore, the absence of molten iron alloy penetration into silicate phases does not allow an extensive modification of the chemical composition of the mantle by core–mantle interaction.  相似文献   

On the implications of the coupled evolution of the deep planetary interior and the presence of surface ocean water in hydrous mantle convection     

《Comptes Rendus Geoscience》2019,351(2-3):197-208

We investigate the influence of the deep mantle water cycle incorporating dehydration reactions with subduction fluxes and degassing events on the thermal evolution of the Earth as a consequence of core–mantle thermal coupling. Since, in our numerical modeling, the mantle can have ocean masses ∼12 times larger than the present-day surface ocean, it seems that more than 13 ocean masses of water are at the maximum required within the planetary system overall to partition one ocean mass at the surface of the present-day Earth. This is caused by effects of water-dependent viscosity, which works at cooling down the mantle temperature significantly so that the water can be absorbed into the mantle transition zone and the uppermost lower mantle. This is a result similar to that without the effects of the thermal evolution of the Earth's core (Nakagawa et al., 2018). For the core's evolution, it seems to be expected for a partially molten state in the deep mantle over 2 billion years. Hence, the metal–silicate partitioning of hydrogen might have occurred at least 2 billion years ago. This suggests that the hydrogen generated from the phase transformation of hydrous-silicate-hosted water may have contributed to the partitioning of hydrogen into the metallic core, but it is still quite uncertain because the partitioning mechanism of hydrogen in metal–silicate partitioning is still controversial. In spite of many uncertainties for water circulation in the deep mantle, through this modeling investigation, it is possible to integrate the co-evolution of the deep planetary interior within that of the surface environment.  相似文献