Distribution and germination of viable diatom resting stage cells in sediments of the East China Sea

The abundance and temporal patterns of viable diatom resting stage cells in sediments of the East China Sea in 2006 have been investigated. The abundance of viable resting stages was enumerated with the most probable number (MPN) technique. Overall, 25 diatom species (including varieties) belonging to 16 genera were detected. Viable resting stage cells were common, on the order of 10³ to 10⁶ cells/g dry mass. The abundant taxa included Skeletonema marina, S. dohrnii, Chaetoceros curvisetus and Thalassiosira spp., with Skeletonema accounting for 83.3% of the cell. The effects of temperature (10, 15, 20, 25℃), salinity (20, 25, 30, 35 psu) and light intensity (0, 300, 4 000, 8 000 lux) on the germination of resting stages in sediment samples were also determined. The results showed that light intensity had a significant positive effect on the germination of diatom resting stage cells (p <0.01) and that diatoms could not germinate in darkness. Temperature and salinity had no noticeable effects on the germination. The present study suggests that there are abundant diatom resting cells in sediments of the East China Sea, which could serve as a "seed bank" in the phytoplankton population succession and contribute to the initiation of algal blooms.     

Structurally controlled hydrothermal dolomites in Albian carbonates of the Asón valley,Basque Cantabrian Basin,Northern Spain

Shallow marine carbonate sedimentation dominated during the Albian in the western part of the Basque Cantabrian Basin in Northern Spain, forming the large Ramales Platform. This platform originated on a less subsiding tectonic block facing deeper and more subsiding areas to the south and east, which were created by tectonic activity in the Basin. Fracture-related hydrothermal dolomites hosted in these Albian carbonates are well exposed in the Asón valley area. Mapping in the studied area revealed several dolomite bodies related to main faults that cut the stratification almost at right angles. The bodies show a vertical development along fault-strike up to 900 m thick from which kilometre-scale branches expand following the stratification. Dolomitization is pervasive and independent of the limestone facies. Main dolomite facies are fine replacive, sucrosic and saddle. Petrography, C, O and Sr isotopes and fluid-inclusion analysis support a polyphase hydrothermal dolomitization at fluid temperatures between 75 °C and 240 °C and highly variable salinity of up to 22 wt.% NaCl. Fine dolomite replaced limestone first and then, sucrosic and saddle dolomites replaced part of the first dolomite and cemented newly created fracture porosity together with different calcite cements. Zebra dolomites and hydroclastic breccias are products of this later stage. Burial analysis of the host rock supports maximum burial temperatures of 80 °C and intense tectonic activity from the Albian to Turonian with a latest Albian peak subsidence. Albian stretching of the crust and subsequent ascent of the isotherms in the area is suggested to have produced sufficient heat to the dolomitizing fluids. The structural analysis indicates a strong transtensional tectonic activity in the studied area during Albian to Turonian time with the creation of an overstep between W–E trending and N–S trending faults. Fluids moved from subsiding areas to fractured uplifted parts of the Ramales Platform, enhanced by diapiric activity.     

Thermal regime of the northwest Indian rifted margin – Comparison with predictions

We use a simple approach to estimate the present-day thermal regime along the northwestern part of the Western Indian Passive Margin, offshore Pakistan. A compilation of bottom borehole temperatures and geothermal gradients derived from new observations of bottom-simulating reflections (BSRs) allows us to constrain the relationship between the thermal regime and the known tectonic and sedimentary framework along this margin. Effects of basin and crustal structure on the estimation of thermal gradients and heat flow are discussed. A hydrate system is located within the sedimentary deep marine setting and compared to other provinces on other continental margins. We calculate the potential radiogenic contribution to the surface heat flow along a profile across the margin. Measurements across the continental shelf show intermediate thermal gradients of 38–44 °C/km. The onshore Indus Basin shows a lower range of values spanning 18–31 °C/km. The Indus Fan slope and continental rise show an increasing gradient from 37 to 55 °C/km, with higher values associated with the thick depocenter. The gradient drops to 33 °C/km along the Somnath Ridge, which is a syn-rift volcanic construct located in a landward position relative to the latest spreading center around the Cretaceous–Paleogene transition.     

皖浙赣断裂带的界定及其基本特征

以往文献中及众多研究者所指的“皖浙赣断裂带”实际上包括了不同时代形成的、方向有变化的多组规模巨大的区域性断裂带;最早的断裂带形成于新元古代,最晚的形成于晚中生代。在地壳演化过程中,随着构造应力场的变化,不同时代的断裂带方向变化较大,新元古代晋宁期为北东向,早古生代加里东期为近东西向—北东东向,晚中生代为北北东向;每一期断裂带都有它们自己的大地构造背景和指示意义。文中认为,不同阶段形成的断裂带不能混为一谈。新元古代晋宁期的北东向断裂带南段基本上以赣东北蛇绿混杂岩带为代表,向北东延至皖南伏川断裂带,具有板块(或地体)边界断裂的性质;加里东期以近东西向祁门—歙县断裂带为代表,其西段被后期牵引成北东向,造成两侧的变质基底特征明显不同;二者均不属于皖浙赣断裂带的组成部分。而通常意义上所指的具有区域控岩控矿作用的皖浙赣断裂带,是晚中生代北北东向的赣东北—五城—歙县—绩溪—宁国断裂带,控制了侏罗—白垩纪红色盆地及燕山期岩浆岩的形成和分布,是一条具有控矿作用的重要的构造岩浆岩带。     

泌阳凹陷下二门油田油气成藏机制探讨

为了弄清下二门油田的油气成藏机理,利用包裹体、平衡剖面和生烃史模拟等技术,详细分析了其油气充注成藏过程,结果表明,早期(古近纪核二末期至核一末期)油气小规模缓慢充注,形成早期小规模油气藏;中期(古近纪廖庄期末构造抬升期)受差异抬升构造运动影响,油气大规模快速充注,形成中期大规模原生背斜油气藏;晚期(新近纪上寺组沉积末期)断裂发育,早、中期原生油气藏遭受破坏,同时深凹区核三下、上段生成的高成熟油气沿砂体侧向运移补给,油气大规模沿断层向上运移,遇遮挡形成大量次生油气藏和气藏。     

用树木年轮重建伊犁南天山北坡西部的降水量序列

根据采自伊犁地区南天山北坡11个采点的树木年轮样本,建立了每个采点的3种年表。通过单相关普查发现,标准化树轮年表序列与当年1~5月的降水显著相关。分析表明该时段降水与树木年轮生长呈正相关具有明确的树木生理学意义。利用新源上限(XNAUt)、昭苏上限(ZUt、ZUt 2)和特克斯下限(TLt)4个标准化树轮年表序列可较好地重建该区域在该时段的降水量。经交叉检验,所得重建方程是稳定可靠的,重建的降水序列是可信的。通过分析发现:伊犁地区南天山北坡300年以来1~5月的降水大致经历了6个偏湿阶段和6个偏干阶段;有2.0~2.8年、24.8年、28.3年、33年、99年的变化准周期;在1909年发生由多向少的突变;1740年、1870年发生由少向多的突变,其中又以1870年前后的突变最为明显。     

Variability of temperature,salinity and tidally‐averaged density in the middle estuary of the St Lawrence

Abstract

Surveys in the Middle Estuary of the St Lawrence have yielded a data base consisting of more than 15,000 T‐S pairs distributed over 62 13‐h profiling stations. Although the T‐S curves at each station are remarkably linear, the variability of the slopes and intercepts of the lines is considerable. The means and standard deviations of the temperature and salinity at each individual station are not explicable in terms of linear combinations of the parameters for location in the Estuary, the upstream water properties, the phase of the spring‐neap cycle and the tidal energies.

It is shown that the tidally‐averaged density structure is separable into horizontal and vertical components and that its vertical variation over the whole Estuary may be explained by any one of three different functional forms. However, its horizontal variation is not explicable in terms of linear combinations of the parameters mentioned in the paragraph above.

Plots of the horizontal variations in temperature, salinity or density may only be meaningful if the data are collected synoptically, and even then cannot be considered to be accurate over time‐scales longer than one tidal cycle.     

大庙斜长岩同位素地质年龄、稀土地球化学及其地质意义

大庙斜长岩的⁴⁰Ar/³⁹Ar年龄测定呈现出一条典型的马鞍型年龄谱,在中温阶段有二个明显的坪年龄1656±15 Ma和1029±7 Ma,结合其构造位置和全球斜长岩分布来看,它们分别代表了侵位年龄和后期热扰动的时代。密云奥长环斑花岗岩中角闪石的⁴⁰Ar/³⁹Ar坪年龄为1716±21 Ma。两者时空上密切相关,代表了裂谷作用初期非造山环境中双模式岩浆作用产物。斜长岩类和苏长岩之间稀土配分模式的相似性表明,它们明显为同一成因的岩浆分异系列的产物。     

Transition of Quaternary glacial cyclicity in deep-sea records at Nansha, the South China Sea

High-resolution oxygen isotope records over the last 2249 ka (MIS 1–86) have been obtained from cores of the upper section (105.08 m) at ODP Site 1143 (water depth of 2772 m) drilled in the Nansha area, southern South China Sea. The sampling resolution is at about 2 ka intervals, resulting in one of the best oxygen isotope records over the global ocean. The oxygen isotope curves, displaying details in the Pleistocene glacial cycles, have revealed a nearly 300 ka long stage of transition from a predominant 40 ka to 100 ka periodicity. Therefore, the “Mid-Pleistocene Revolution” should be considered as a process of transition rather than an abrupt change. Within the 100 ka glacial cycles, the changes in tropical sea surface water were found to lead those in high-latitude ice sheet. Our comparisons show that the ice sheet expansion and the glacial stage extension in the Northern Hemisphere with the 100 ka cycles must have been driven not by ice sheet itself, but by processes outside the high latitudes of the Northern Hemisphere.