Observations on Gulf of Alaska seamount chains by multi-beam sonar

Geomorphic and age data are presented for the Dellwood, Denson, Dickins, Giacomini, and Ely seamounts, the Tsimshian Seachannel, and the southern Juan de Fuca Ridge with Brown Bear, Bear Cub, Grizzly Bear, and Cobb seamounts. Formational speculations extrapolated to a regional scale allow the strikes and outer limits of the seamount chains to be interpreted. Six of these chains are shown in the Gulf of Alaska, none of which conform to the Pratt-Welker or Kodiak-Bowie in the literature. Different strikes show the chains/plate to have rotated 23° about 17 m.y. ago. Morphology also shows that there are four less guyots in the Gulf than previously thought, and that, at least in the Gulf of Alaska, guyot heights do not necessarily reflect sealevel during erosion.     

Amino acids and hexosamines in the Hess Rise core during the past 220,000 years

Core sediment samples collected from the Hess Rise, North Pacific, were analyzed for 20 common amino acids (AA) and two hexosamines (HA) to understand the relation between glacial–interglacial variations and deposition/preservation of sedimentary organic matter (OM). The sediments are predominantly carbonaceous (carbonates 35–80%). AA-based parameters—aspartic acid/glycine ratio and serine+threonine relative mole content—suggest that calcareous plankton was the major source of OM in these sediments. This inference is supported by the similarity in distribution patterns of AA and HA contents with that of organic carbon. Low values of AA/HA and glucosamine/galactosamine ratios (average 4.4 and 1.1, respectively) imply that much of the planktonic OM was replaced by microbial OM. The relative molar concentration of two nonprotein AA (β-alanine and γ-aminobutyric acid) varied with age of sediments; i.e., they were less abundant in recent sediments and more abundant in the oldest sediments. This trend is an indicator of extremely slow but continuous enzymatic degradation of proteinaceous OM within the sediments. So far, bulk OM has been believed to be one of the best proxies for estimation of primary productivity. However, it may be an underestimate, even for the late Quaternary sediments. Comparison of AA and HA content variations with SPECMAP stack revealed their enhanced deposition and preservation during glacial periods relative to interglacial periods. This, in turn, affected not only the planktonic production in surface waters but also the benthic community, including bacteria on the seafloor.     

Geological Consequences of the Accretion of Benham Rise to Northern Luzon, Philippines

Benham Rise is a large igneous province that has been accreted to the eastern seaboard of northern Lu-zon since Early Miocene. It started forming during the Eocene at a hotspot/mantle plume in the vicinity of the Central basin Spreading Center in the West Philippine Basin (CBSC) of the Philippine Sea Plate. Seafloor spreading from the CBSC and Parece Vela pushed Benham Rise towards Luzon. Eventually Benham Rise jammed against Luzon at the end of the Oligocene, with consequences that impacted on the geology of the Philippines which have been similarly noted in colli-sions of large igneous provinces in other areas. These are manifested as follows:     

Correlations Between Biogenic Components and Dust Input and Their Change Mechanism on Hess Rise,Central North Pacific,During the Late Quaternary*

The study of marine export production is helpful to trace the changes of oceanic and global carbon reservoirs. Dust input is an important factor inspiring marine export production. Measurements of carbonate, Opal, TOC and C_org/N were performed on Core SO202-37-2, which was retrieved from Hess Rise, central North Pacific during the German SO202-INOPEX Expedition, for reconstructing variations of the local export production and dust input. The core age model is constructed via morphologically correlating its foraminifer oxygen isotope record with those of Core H3571 and the LR04 stack. XRF-Ti/Ca can be used as a proxy for dust input and its distribution pattern is consistent with that of Opal content, possibly indicating that dust input may have affected the local export production, i.e. the local export production increased (decreased) with enhancing (declining) dust input during interglacial (glacial) periods. Fluctuations in dust input might be due to southward/northward migration of the Westerly Jet over the dust source regions during interglacial and glacial periods. Although global dust output increased during glacial periods, meridional migration of the Westerly Jet in this area made the distribution pattern of the dust deposition in the study area different from that of other areas.     

鲁西隆起和济阳坳陷新生代隆坳耦合关系

为探讨鲁西隆起的抬升史,研究鲁西隆起和济阳坳陷之间的隆-坳演化关系,进一步揭示渤海湾盆地的演化特征,主要利用裂变径迹分析和裂变径迹t-T模拟方法建立了新生代鲁西隆起的抬升史和济阳坳陷的沉降史。鲁西隆起三期抬升史分别为62～53Ma、44～37Ma和23～20Ma,济阳坳陷在65～46Ma和46～38Ma期间为快速构造沉降期,构造沉降量大,23Ma左右坳陷抬升。对比研究表明,新生代鲁西隆起的抬升与济阳坳陷沉降之间存在隆-坳耦合关系。鲁西隆起的抬升控制了济阳坳陷烃源岩的形成、油气运移时间和油气分布由南向北迁移,并为济阳坳陷古潜山油藏提供了有效的储集空间。研究还认为,鲁西隆起与济阳坳陷的隆坳耦合关系是渤海湾盆地及周边山系盆山耦合事件的一个组成部分。     

Oxidation of chalcopyrite by extended milling

Chalcopyrite has been milled for up to 50 h in oxygen, air and argon atmospheres using a laboratory ball mill. No phase changes were evident in argon but the XRD peaks were weaker and broader indicating crystalline refinement. In oxygen, even after 1 h milling peaks for CuSO₄·5H₂O were present and these became predominant after 20 h milling where the chalcopyrite peaks were absent. In air, partial oxidation to CuSO₄·5H₂O was evident after 50 h. Leaching of the resultant powders with water showed 80% dissolution after 50 h milling in oxygen, significantly greater than the 20% and 6% dissolution after milling for 50 h in air and argon respectively. Solution analyses showed the Cu/Fe ratio increased with milling time in oxygen suggesting selectivity may be possible. The insoluble residue was found to consist of haematite, elemental sulphur and unreacted chalcopyrite.     

Image Filtering by Factorial Kriging—Sensitivity analysis and application to Gloria side-scan sonar images

Factorial Kriging (FK) is a data- dependent spatial filtering method that can be used to remove both independent and correlated noise on geological images as well as to enhance lineaments for subsequent geological interpretation. The spatial variability of signal, noise, and lineaments, characterized by a variogram model, have been used explicitly in calculating FK filter coefficients that are equivalent to the kriging weighting coefficients. This is in contrast to the conventional spatial filtering method by predefined, data-independent filters, such as Gaussian and Sobel filters. The geostatistically optimal FK filter coefficients, however, do not guarantee an optimal filtering effect, if filter geometry (size and shape) are not properly selected. The selection of filter geometry has been investigated by examining the sensitivity of the FK filter coefficients to changes in filter size as well as variogram characteristics, such as nugget effect, type, range of influence, and anisotropy. The efficiency of data-dependent FK filtering relative to data-independent spatial filters has been evaluated through simulated stochastic images by two examples. In the first example, both FK and data-independent filters are used to remove white noise in simulated images. FK filtering results in a less blurring effect than the data-independent fillers, even for a filter size as large as 9 × 9. In the second example, FK and data-independent filters are compared relative to the extraction of lineaments and components showing anisotropic variability. It was determined that square windows of the filter mask are effective only for removing Isotropie components or white noise. A nonsquare windows must be used if anisotropic components are to be filtered out. FK filtering for lineament enhancement is shown to be resistant to image noise, whereas data-independent filters are sensitive to the presence of noise. We also have applied the FK filtering to the GLORIA side-scan sonar image from the Gulf of Mexico, illustrating that FK is superior to the data-independent filters in removing noise and enhancing lineaments. The case study also demonstrate that variogram analysis and FK filtering can be used for large images if a spectral analysis and optimal filter design in the frequency domain is prohibitive because of a large memory requirement.     

渤海湾西部声纳探测发现全新世埋藏槽谷

声波探测具有很高的分辨率和信号发射频度,可以获得高品质浅地层剖面,显示出沉积地层的结构与构造细节、斜层理等三角洲沉积标志特征。展示了渤海湾西部浅地层声纳探测原始记录。探测发现,在大沽口以东27km处存在一个以前不为人知的埋藏槽谷,涉及地层的时代为晚更新世末期与全新世中期。宽达几百米到1km,深约30m,走向北北西,形成时代距今约5000～6000a,可能代表了某种重大地质事件,其成因有溺谷充填和构造断陷2种可能。     

研究人员通过历史数据估计未来海平面上升情况

波士顿大学的古气候学家们在2011年第4期Nature(地球科学版)杂志上发布了一项研究成果,通过对澳大利亚3 Ma前古海岸线的研究,得出该时期的海平面比现在高大约15~100英尺的结论。该结果将帮助     

Displacements under linearly distributed pressures by extended Mindlin’s equations

Analytical elasticity solutions provide an efficient means of performing a first approximate analysis in foundation engineering. One of the well-known solutions is Mindlin’s solution to the stress and displacement induced by a point load at an embedment depth in a half-space. This solution is more superior but less widely used than Boussinesq’s solution. To promote this situation, Mindlin’s displacement equations are integrated to obtain a complete set of explicit formulae for calculating the displacements at an arbitrary point. The displacements are induced by uniformly and triangularly distributed horizontal or vertical pressures, which are exerted over a horizontal or vertical rectangular area in the interior of a homogeneous, isotropic, elastic half-space. These formulae facilitate the future development of computer programs for the analysis of related practical problems in foundation engineering.     

扩展简化Bishop法的取矩中心对安全系数的影响

扩展简化Bishop法的提出,为非圆弧滑面安全系数的求解提供了一个简便的途径。然而,在建立滑体总体力矩平衡方程时选择不同的取矩中心会得到不同的计算结果,这在某种程度上限制了该法的应用推广。为此,针对不同类型的滑面（组合滑面、折线滑面）,较为系统地研究了取矩中心对安全系数的影响规律,并提出了确定取矩中心的原则。算例分析表明：无论哪种类型的滑面,只要选择合适的取矩中心扩展简化Bishop法便可得到与严格法（Morgenstern-price法）相当的计算精度,且该法数值计算简便,具有较高的实用价值。     

Inverse analysis of an embankment on soft clay by extended Bayesian method

A new type of indirect inverse analysis procedure is proposed to overcome the difficulties the geotechnical inverse analyses are encountering (such as unstability and non-uniqueness of the solutions as well as multicollinearity). These difficulties are eased by combining the objective information (i.e. the observation data) and the subjective information (i.e. the prior information) in an appropriate manner by so-called extended Bayesian method. The method is based on a new view on Bayesian model proposed by Akaike. The problem of model identification in the inverse analysis is also tackled by applying well-known AIC but of the Bayesian version. A case study on an embankment on soft clay is presented to illustrate the effectiveness of the new method. A rather thorough review on the geotechnical inverse analysis is also presented to indicate the necessity of the proposed procedure. An appendix is attached to summarize the statistical background of the new method.     

Timing and distribution of calciturbidites around a deeply submerged carbonate platform in a seismically active setting (Pedro Bank, Northern Nicaragua Rise, Caribbean Sea)

The sedimentological study of thirteen sediment cores from the periplatform setting surrounding Pedro Bank (Northern Nicaragua Rise, Caribbean Sea) shows that during the last 300 ka turbidite deposition is controlled by at least four factors: (1) late Quaternary sea level fluctuations, (2) prolific fine-grained sediment production and export resulting in oversteepening of the upper slope environment, (3) the proximity to the bank margin, and (4) local slope and seafloor morphology. The most intriguing finding of this study is the paucity of turbidites, with only 101 turbidites in 13 cores in this tectonically active setting near the Caribbean plate boundary. Throughout the last 300 ka, the frequency of turbidite input during interglacial stages is three times higher than during glacial stages. Also it is obvious that changes in sea level influence the timing of turbidite deposition. This is especially evident during the transgressions resulting in rapid renewed bank-top flooding, subsequent neritic sediment overproduction, and offbank export. The flooding event during each transgression is usually recorded by the onset of turbidite deposition at various sites along several platform-to-basin transects in down- and upcurrent slope settings. Overall, however, more turbidites are deposited during the regressive rather than the transgressive phases in sea level, probably as a result of sediment reorganisation on the slope resulting in slope failure. Five cores show "highstand bundling" of calciturbidites, i.e. higher number of turbidites during highstands than during lowstands in sea level.     

宇宙成因核素~(10)Be揭示的北祁连山侵蚀速率特征

山脉侵蚀速率的大小和时空分布信息是研究山脉构造—气候相互作用和地貌演化的关键切入点,其大小是受气候还是构造控制争论已久。宇宙成因核素10Be方法为从千年至万年尺度上定量研究流域平均侵蚀速率提供了一种先进和快捷的技术手段,为揭示侵蚀速率与现代气候和构造地貌因子的关系并进行相关分析提供了基础。利用该方法对北祁连山近现代侵蚀速率进行了研究。所采集的9个流域现代河沙样品,结合前人数据进行共同分析,结果显示该区侵蚀速率的变化范围为18.7~833 mm/ka,北祁连山中段的侵蚀速率约为323 mm/ka,该区侵蚀速率与降雨量没有明显的对应关系,但与流域平均坡度呈现很好的非线性关系,揭示坡度是该区侵蚀速率的最主要控制因素。通过对比北祁连山地表平均侵蚀速率和该区域的断层垂直滑动速率发现整体上该区域地表侵蚀速率要低于祁连山北缘断层的垂直滑动速率,反映了北祁连山正处于地形抬升和生长的过程之中。     

Contemporary Deposition and Long-Term Accumulation of Sediment and Nutrients by Tidal Freshwater Forested Wetlands Impacted by Sea Level Rise

Contemporary deposition (artificial marker horizon, 3.5 years) and long-term accumulation rates (²¹⁰Pb profiles, ~150 years) of sediment and associated carbon (C), nitrogen (N), and phosphorus (P) were measured in wetlands along the tidal Savannah and Waccamaw rivers in the southeastern USA. Four sites along each river spanned an upstream-to-downstream salinification gradient, from upriver tidal freshwater forested wetland (TFFW), through moderately and highly salt-impacted forested wetlands, to oligohaline marsh downriver. Contemporary deposition rates (sediment, C, N, and P) were greatest in oligohaline marsh and lowest in TFFW along both rivers. Greater rates of deposition in oligohaline and salt-stressed forested wetlands were associated with a shift to greater clay and metal content that is likely associated with a change from low availability of watershed-derived sediment to TFFW and to greater availability of a coastal sediment source to oligohaline wetlands. Long-term accumulation rates along the Waccamaw River had the opposite spatial pattern compared to contemporary deposition, with greater rates in TFFW that declined to oligohaline marsh. Long-term sediment and elemental mass accumulation rates also were 3–9× lower than contemporary deposition rates. In comparison to other studies, sediment and associated nutrient accumulation in TFFW are lower than downriver/estuarine freshwater, oligohaline, and salt marshes, suggesting a reduced capacity for surface sedimentation (short-term) as well as shallow soil processes (long-term sedimentation) to offset sea level rise in TFFW. Nonetheless, their potentially large spatial extent suggests that TFFW have a large impact on the transport and fate of sediment and nutrients in tidal rivers and estuaries.     

Deglaciation pattern indicated by the ice-margin formations in Northern Karelia, eastern Finland

A map has been reconstructed representing the large-scale glacial and glaciofluvial morphology of Northern Karelia and the adjacent area of Soviet Karelia. Observations have been made on the directions of glacial striae and on the distribution of sub-aquatic and supra-aquatic terrain in order to obtain a consistent picture of the course of deglaciation in the area and the factors affecting it. The map indicates that the behaviour of the glacier during the deglaciation was largely governed by the distribution of sub-aquatic and supra-aquatic areas. The marginal zone of the ice sheet was divided into two large lobes in this area. The Finnish Lake District Lobe terminated mostly in water, giving rise to massive glaciofluvial accumulations, while the North Karelian Lobe flowed on the land above the highest shore levels, pushing up several more or less discontinuous narrow end-moraine ridges. Relatively large glaciofluvial deposits were also formed in the supra-aquatic area in places where the ice margin terminated in a local ice-dammed lake. It is evident that the Salpausselkä I and II end-moraines extend as continuous formations only to the zone where the former ice margin rose onto dry land during the deglaciation phase. The spatial and temporal differences in the glacial dynamics and differing depositional environments gave rise to the complex glacial morphology of Northern Karelia.     

Frictional slip plane growth by localization detection and the extended finite element method (XFEM)

This paper is concerned with developing a numerical tool for detecting instabilities in elasto‐plastic solids (with an emphasis on soils) and inserting a discontinuity at these instabilities allowing the boundary value problem to proceed beyond these instabilities. This consists of implementing an algorithm for detection of strong discontinuities within a finite element (FE) framework. These discontinuities are then inserted into the FE problem through the use of a displacement field enrichment technique called the extended finite element method (XFEM). The newly formed discontinuities are governed by a Mohr–Coulomb frictional law that is enforced by a penalty method. This implementation within an FE framework is then tested on a compressive soil block and a soil slope where the discontinuity is inserted and grown according to the localization detection. Copyright © 2010 John Wiley & Sons, Ltd.     

Petrogenesis of Olivine-phyric Basalts from the Aphanasey Nikitin Rise: Evidence for Contamination by Cratonic Lower Continental Crust

In this work we investigate the olivine-phyric basalt suiteof the Aphanasey Nikitin Rise, an intraplate volcanic structureformed during the Late Cretaceous in the Indian Ocean. The parentalmelt of the basalt suite has a hypersthene-normative tholeiiticcomposition with low H₂O content (0·3–0·5wt %) and high SiO₂/Al₂O₃ (3·5). The basalt suite ischaracterized by Nb, Ta, Th and U depletion, and uniquely low²⁰⁶Pb/²⁰⁴Pb and ¹⁴³Nd/¹⁴⁴Nd among the Cretaceous tholeiiticbasalts of the Indian Ocean. Our modelling demonstrates thatfractional crystallization of depleted mantle-derived melt andlower continental crust assimilation is a suitable model forthe genesis of the parental magma of this suite. The continentalcrustal material involved is characterized by long-term Rb,U and Th depletion and probably remained isolated for >10⁹years in cratonic Gondwanan lithosphere. On a broader scale,two geochemical groups can be distinguished among tholeiitesformed in the Indian Ocean basin during the period 115–75Ma, from the Aphanasey Nikitin Rise, the southern Kerguelenand Naturaliste plateaux and the Broken Ridge. Both groups havea compositional range from hypersthene-normative basalt to basalticandesite and are characterized by Nb–Ta depletion, extremelylow     

Meso-Cenozoic Tectonic Events Recorded by Apatite Fission Track in the Northern Longmen-Micang Mountains Region

There is a cross-cutting relationship between the E-W trending structures and the NE-trending structures in the northern Longmen-Micang Mountains region,which reflects possible regional tectonic transi...