Sedimentary and biotic evidence of a warm-water enclave in the cooler oceans of the latest Ordovician glacial phase, Yangtze Platform, South China block

Abstract   During the Hirnantian period, the Yangtze Platform was situated in the western part of the South China block (SCB) before its later rotation, in the middle–low paleolatitudes of the southern hemisphere in the northeast side of peri-Gondwana. It is part of the Kosov faunal province as indicated by the Hirnantia fauna. Sedimentary evidence shows the domination of cool ventilated marine water from its offshore ramp and shelf. Hirnantian shallow-water carbonate facies (Kuanyinchiao Bed) overlie earlier Ashgill graptolitic black shales (Wufeng Formation) as a result of marine regression. In the Yangtze Platform, however, we have found local areas of intertidal to nearshore facies that lack the typical highly diverse Hirnantia fauna. Some warm-water features (radial oolites, peloids, diverse solitary rugose corals and other benthic shelly fauna) occur commonly in some limited shallow areas, forming grainstones and packstones. Although interglacial episodes within the Hirnantian glaciation could be responsible for these features, their limited occurrence within the interior of the platform leads us to interpret the deposits as indicating that cold-water currents from the southeastern high latitudes were partly excluded from the nearshore area of the Yangtze Platform. The landmass of the eastern SCB in the Hirnantian epoch prevented access to some areas of the cold marine water masses that flowed from higher latitudes of Gondwana; the result was a persistence of warm-water shallow marine facies in some areas.     

Quartz and polymineral luminescence dating of Japanese loess over the last 0.6 Ma: Comparison with an independent chronology

There are only a few luminescence dating studies of loess sediments in Japan, but interleaved with these deposits are many well-described tephras of known age based on ¹⁴C and fission track analysis; these independent age controls provide an opportunity to test the reliability of loess luminescence ages. This study provides such a comparison at two sites in central Honshu, the largest island in the Japanese archipelago. Samples were collected from sequences of interleaved volcanic tephra and loess deposited on a Middle Pleistocene river terrace in the Niigata Prefecture and on an Early to Middle Pleistocene dissected fluvial surface at in the Tochigi Prefecture, Honshu. Equivalent doses (D_e) were estimated from fine grains (4–11 μm) using both polymineral IR-OSL and (post-IR) blue-OSL, and quartz blue-OSL. The blue-stimulated luminescence signals could be represented by up to three exponentially decaying components; only the most light sensitive of these components was used in the final D_e estimation. Almost all the estimates of D_e from polymineral IR-OSL are smaller than those from polymineral (post-IR) blue-OSL and quartz blue-OSL, whereas the latter two are in good agreement. The blue-light stimulated luminescence ages using the most light sensitive component are shown to be in good agreement with the independent control, up to 500 ka. Although the IR-OSL signals underestimate the known age, a simple laboratory fading test is found empirically to correct for this underestimation. We conclude that the most rapidly blue-stimulated luminescence signals from quartz extracted from our loess samples give reliable ages, and that future loess dating studies should concentrate on these signals.     

Methane-derived authigenic carbonates from the northern Gulf of Mexico — MD02 Cruise

Authigenic carbonates were sampled in piston cores collected from both the Tunica Mound and the Mississippi Canyon area on the continental slope of the northern Gulf of Mexico during a Marion Dufresne cruise in July 2002. The carbonates are present as hardgrounds, porous crusts, concretions or nodules and shell fragments with or without carbonate cements. Carbonates occurred at gas venting sites which are likely to overlie gas hydrates bearing sediments. Electron microprobe, X-ray diffraction (XRD) and thinsection investigations show that these carbonates are high-Mg calcite (6–21 mol% MgCO₃), with significant presence of framboidal pyrite. All carbonates are depleted in ¹³C (δ¹³C = − 61.9 to − 31.5‰ PDB) indicating that the carbon is derived mainly from anaerobic methane oxidation (AMO). Age estimates based on ¹⁴C dating of shell fragments and on regional sedimentation rates indicate that these authigenic carbonates formed within the last 1000 yr in the Mississippi Canyon and within 5500 yr at the Tunica Mound. The oxygen isotopic composition of carbonates ranges from + 3.4 to + 5.9‰ PDB. Oxygen isotopic compositions and Mg²⁺ contents of carbonates, and present in-situ temperatures of bottom seawater/sediments, show that some of these carbonates, especially from a core associated with underlying massive gas hydrates precipitated in or near equilibrium with bottom-water. On the other hand, those carbonates more enriched in ¹⁸O are interpreted to have precipitated from ¹⁸O-rich fluids which are thought to have been derived from the dissociation of gas hydrates. The dissociation of gas hydrates in the northern Gulf of Mexico within the last 5500 yr may be caused by nearby salt movement and related brines.     

日本SELENE月球探测计划和卫星间多普勒跟踪的数学模型

日本月球探测计划（SELENE）定于2004年夏季利用HIIa火箭发射一组共3颗绕月人造卫星。他们是主卫星、跟踪中断卫星和空间VLBI电波源。其主要科学目标之一是利用对绕月卫星的多普勒跟踪数据精确测定月球重力场,研究月球的起源与演化。SELENE计划中实现这个科学目标的关键技术是引入中继卫星,目的在于当处于低轨道的主卫星飞行到月球背面地面观测站无法观测时,采用卫星间跟踪方法（SST）,建立地面站与主卫星之间的联系,以得到月球背面重力场的直接测量数据。介绍了几种典型的四程卫星间多普勒跟踪模式和相应的数学模型,并针对SELENE计划中采用的特殊四程多普勒跟踪模式建立了卫星相对观测站速度与跟踪信号多普勒频移之间的转换关系。提出了利用GEODYNⅡ定轨分析软件处理SELENE多普勒跟踪数据的流程。     

The 2011 Tohoku-oki Earthquake Tsunami: Similarities and Differences to the 869 Jogan Tsunami on the Sendai Plain

A post-tsunami field survey following the 2011 Tohoku-oki Earthquake Tsunami was carried out to asses inundated area in Sendai Plain, Northeast Japan. The type of inundation was classified into two categories (major and minor) according to the amount of accumulated debris, garbage and sediment. Major and minor inundations were identified up to 4 and 5 km from the coastline, respectively. Many artificial geomorphological features, such as roadway embankments and canals, were believed to have affected the run-up process of the tsunami. The inundation area of the 2011 tsunami on the Sendai Plain is compared with that of the 869 Jogan tsunami, which was reconstructed using numerical modeling based on available historical and geological records. The inundation area of the 2011 Tohoku-oki tsunami is comparable to that of the 869 Jogan tsunami, although a direct comparison is difficult due to differences in geomorphological contexts between the paleo period and the present.     

Effectiveness of superelastic bars for seismic rehabilitation of clay‐unit masonry walls

This paper presents the results on shaking table tests of half‐scale brick walls performed to investigate the effectiveness of newly developed Cu–Al–Mn superelastic alloy (SEA) bars in retrofitting of historical masonry constructions. Problems associated with conventional steel reinforcing bars lie in degradation of stiffness and strength, or pinching phenomena, under cyclic loading, and presence of large residual cracks in structures during and after intense earthquakes. This paper attempts to resolve the problems by applying newly developed Cu–Al–Mn SEA bars, characterized by large recovery strain, low material cost, and high machinability, as partial replacements for steel bars. Sets of unreinforced, steel reinforced, and SEA‐reinforced specimens are subjected to scaled earthquake excitations in out‐of‐plane direction. Whereas steel‐reinforced specimens showed large residual inclinations, SEA‐reinforced specimens resulted in stable rocking response with slight residual inclinations. Corresponding nonlinear finite element (FE) models are developed to simulate the experimental observations. The FE models are further used to examine the sensitivity of the response with respect to the variations in experimental conditions. Both the experimental and numerical results demonstrate the superiority of Cu–Al–Mn SEA bars to conventional steel reinforcing bars in avoiding pinching phenomena. Copyright © 2012 John Wiley & Sons, Ltd.     

Distribution and photo-physiological condition of phytoplankton in the tropical and subtropical North Pacific

To better understand the vertical distribution of phytoplankton in the tropical and subtropical North Pacific, we used fast repetition rate fluorometry to investigate the photo-physiological condition of the phytoplankton assemblage in this region between February and March 2007. Along 155°E, between the equator and 24°N, the peak of fluorescence (F _m), an indication of the deep chlorophyll maximum (DCM), was deeper than the top of the nitracline and occurred at the 2.4 ± 1.3 % (mean ± SD) light depth (relative to 0 m). The photochemical efficiency (F _v/F _m) and effective absorption cross-section of photosystem II (σ_PSII) were low at the surface but increased rapidly at depths between the top of the nitracline (40–138 m) and the DCM (70–158 m), an indication that the photo-physiological condition of the phytoplankton improved below the top of the nitracline. The depth of the maximal F _v/F _m [Z(F _v/F _{m max})] was 18–32 m deeper than the DCM and corresponded to the 0.8 ± 0.2 % light depth. The values of F _v/F _m at the Z(F _v/F _{m max}) were 20 % higher than those at the DCM and averaged 0.48 ± 0.01. These results suggest that the phytoplankton assemblage beneath the DCM had a high potential photosynthetic performance capacity and was growing by using the very low ambient light in this region.     

Degassing, crystallization and eruption dynamics at Stromboli: trace element and lithium isotopic evidence from 2003 ashes

During its 1800-year-long persistent activity the Stromboli volcano has erupted a highly porphyritic (HP) volatile-poor scoriaceous magma and a low porphyritic (LP) volatile-rich pumiceous magma. The HP magma is erupted during normal Strombolian explosions and lava effusions, while the LP one is related to more energetic paroxysms. During the March–April 2003 explosive activity, Stromboli ejected two typologies of juvenile glassy ashes, namely highly vesicular LP shards and volatile-poor HP shards. Their textural and in situ chemical characteristics are used to unravel mutual relationships between HP and LP magmas, as well as magma dynamics within the shallow plumbing system. The mantle-normalized trace element patterns of both ash types show the typical arc-lava pattern; however, HP glasses possess incompatible element concentrations higher than LP glasses, along with Sr and Eu negative anomalies. HP shards are generally characterized by higher Li contents (to ~20 ppm) and lower δ⁷Li values (+1.2 to −3.8‰) with respect to LP shards (Li contents of 7–14 ppm and δ⁷Li ranging between +4.6 and +0.9‰). Fractional crystallization models based on major and trace element compositions, combined with a degassing model based on open-system Rayleigh distillation and on the assumption that ^melt/fluidD_Li > 1, show that abundant (~30%) plagioclase precipitation and variable degrees of degassing can lead the more primitive LP magma to evolve toward a differentiated (isotopically lighter) HP magma ponding in the upper conduit and undergoing slow continuous degassing-induced crystallization. This study also evidences that in March 2003 Stromboli volcano poured out a small early volume of LP magma that traveled slower within the conduit with respect to later and larger volumes of fast ascending LP magma erupted during the April 5 paroxysm. The different ascent rates and cooling rates of the two LP magma batches (i.e., pre- and post-paroxysm) resulted in small, but detectable, differences in their chemical signatures. Finally, this study highlights the high potential of in situ investigations of juvenile glassy ashes in petrologic and geochemical monitoring the volcanic activity and of Li isotopes as tracers of degassing processes within the shallow plumbing system.