The LOG corer – a new device for obtaining short cores in soft lacustrine sediments

A wide variety of scientific disciplines require representative samples of benthic sediment. As a result, a large range of sampling devices have been developed, each best suited to a particular set of conditions. However, all sediment sampling devices have inherent design problems that affect the degree to which samples represent the intact sediment. These issues are summarised, and a new corer design (the LOG corer) is presented and discussed. The LOG corer is a remotely-operated light-weight gravity corer suitable for obtaining relatively undisturbed short sediment cores in soft lacustrine sediments.     

Diatoms in sediments of perennially ice-covered Lake Hoare, and implications for interpreting lake history in the McMurdo Dry Valleys of Antarctica

Diatom assemblages in surficial sediments, sediment cores, sediment traps, and inflowing streams of perennially ice-covered Lake Hoare, South Victorialand, Antarctica were examined to determine the distribution of diatom taxa, and to ascertain if diatom species composition has changed over time. Lake Hoare is a closed-basin lake with an area of 1.8 km², maximum depth of 34 m, and mean depth of 14 m, although lake level has been rising at a rate of 0.09 m yr^-1 in recent decades. The lake has an unusual regime of sediment deposition: coarse grained sediments accumulate on the ice surface and are deposited episodically on the lake bottom. Benthic microbial mats are covered in situ by the coarse episodic deposits, and the new surfaces are recolonized. Ice cover prevents wind-induced mixing, creating the unique depositional environment in which sediment cores record the history of a particular site, rather than a lake-wide integration. Shallow-water (<1 m) diatom assemblages (Stauroneis anceps, Navicula molesta, Diadesmis contenta var. parallela, Navicula peraustralis) were distinct from mid-depth (4–16 m) assemblages (Diadesmis contenta, Luticola muticopsis fo. reducta, Stauroneis anceps, Diadesmis contenta var. parallela, Luticola murrayi) and deep-water (26–31 m) assemblages (Luticola murrayi, Luticola muticopsis fo. reducta, Navicula molesta). Analysis of a sediment core (30 cm long, from 11 m water depth) from Lake Hoare revealed two abrupt changes in diatom assemblages. The upper section of the sediment core contained the greatest biomass of benthic microbial mat, as well as the greatest total abundance and diversity of diatoms. Relative abundances of diatoms in this section are similar to the surficial samples from mid-depths. An intermediate zone contained less organic material and lower densities of diatoms. The bottom section of core contained the least amount of microbial mat and organic material, and the lowest density of diatoms. The dominant process influencing species composition and abundance of diatom assemblages in the benthic microbial mats is episodic deposition of coarse sediment from the ice surface.     

The lacustrine depression at Annecy (France), geological setting and Quaternary evolution

The Annecy lacustrine depression lies in a tectonic transverse valley of structural origin, linking the present day towns of Annecy and Ugine and bounded by the Bauges and Bornes massifs. Only the last two major glacial periods are represented in the stratigraphic and geomorphic evidence from the area, but its successive glaciations that have been largely responsible for the form of the valley within which the present day lake lies. Of particular importance were the lobes of the Arve glacier, one shaping the depression from the south-east; the other from the north. The retreat of the glaciers left behind a more extensive precursor of the present day Lac d'Annecy, which latter constitutes the residual body of open water after lake level lowering, partial infilling and drainage diversions within the catchment. The drainage basin of the extended lake formed shortly after the last glacial maximum (LGM) in the region. Its extent can be determined from field sampling and coring and its elevation can be established at 460 m above present day sea level. The present day lake is more isolated, since the Fier river, to the north, no longer drains into it. To the southeast, the course of the Chaise river has also been diverted, leaving the lake's drainage basin reduced to half its post-LGM size. The major paleogeographical events in the Late-Quaternary evolution of the basin are described in chronological sequence.     

火星风沙地貌研究进展

作为最活跃的地貌塑造外营力,风力作用在火星表面塑造了各种各样的地貌形态。对火星风沙活动及风沙地貌的认识是随着观测和探测技术的进步而逐渐明确的。火星沙丘在北极地区连绵成带状分布,在其他地区分布比较零散,且主要与撞击坑、河谷和山谷相伴分布。火星风沙地貌与地球上相应的地貌类型形态相似而规模更大,表明两个星球上塑造风沙地貌的动力系统具有一定的相似性。火星沙丘主要由玄武岩质（北极部分沙丘为石膏质）颗粒堆积而成,沉积物粒度比地球粗,主要是由中沙和粗纱组成。随着获取影像时空分辨率的提高和着陆器在火星近表面的观测,发现火星上部分区域的沙丘和沙波纹比较活跃。同地球一样,火星风沙地貌也可指示火星气候的变化。     

Transverse Aeolian Ridges (TARs) on Mars

Aeolian processes are probably the dominant ongoing surface process on Mars; Large Dark Dunes (LDDs), particularly common aeolian landforms, were first recognized in the early 1970s. Recent, higher resolution images have revealed another, morphologically distinct, large population of smaller, ripple-like aeolian bedforms that have been termed “Transverse Aeolian Ridges” (TARs) as it is unknown whether they formed as large ripples or small dunes. We have begun a new study of TARs that examines their distribution, orientation, and morphology using > 10,000 high-resolution Mars Orbiter Camera (1.5 to 8 m/pixel resolution) images in a 45° longitude wide, pole-to-pole survey. The aim of this study is to assess whether TARs are active, to identify possible sediment sources and pathways, and to determine the volumes of sediment that they comprise. We present results from the first half of this study, in which we examine the northern hemisphere, and describe a new three-part classification scheme used to aid the survey.Our results show that TARs are abundant but not ubiquitous: preferentially forming proximal to friable, layered terrains such as those found in Terra Meridiani — the location of the ongoing Mars Exploration Rover “Opportunity” mission. TAR distribution in the northern hemisphere shows a strong latitudinal dependence with very few TARs being found north of  30° N. We also find that in most cases TARs are less mobile than LDDs, a conclusion possibly explained by Mars Exploration Rover Opportunity observations that show TAR-like ripples to have a core of fine material armored by a monolayer of granule-sized particles. This could disallow significant bedform movement under the current wind regime. That TARs are essentially inactive is confirmed by superposition relations with slope streaks and LDDs and by observations of superposed impact craters. We suggest that observations made by the Opportunity Rover in Terra Meridiani indicate that the small aeolian bedforms common here are ripples and not small dunes. Farther south, these bedforms transition into larger features indistinguishable from TARs, suggesting that TARs (in the Meridiani area at least) are ripples and not dunes.     

Origin of the valley networks on Mars: a hydrological perspective

The geomorphology of the martian valley networks is examined from a hydrological perspective for the compatibility with an origin by rainfall, globally higher heat flow, and localized hydrothermal systems. Comparison of morphology and spatial distribution of valleys on geologic surfaces with terrestrial fluvial valleys suggests that most martian valleys are probably not indicative of a rainfall origin, nor are they indicative of formation by an early global uniformly higher heat flow. In general, valleys are not uniformly distributed within geologic surface materials as are terrestrial fluvial valleys. Valleys tend to form either as isolated systems or in clusters on a geologic surface unit leaving large expanses of the unit virtually untouched by erosion. With the exception of fluvial valleys on some volcanoes, most martian valleys exhibit a sapping morphology and do not appear to have formed along with those that exhibit runoff morphology. In contrast, terrestrial sapping valleys form from and along with runoff valleys. The isolated or clustered distribution of valleys suggests localized water sources were important in drainage development. Persistent groundwater outflow driven by localized, but vigorous hydrothermal circulation associated with magmatism, volcanism, impacts, or tectonism is, however, consistent with valley morphology and distribution. Snowfall from sublimating ice-covered lakes or seas may have provided an atmospheric source of water for the formation of some valleys in regions where the surface is easily eroded and where localized geothermal/hydrothermal activity is sufficient to melt accumulated snowpacks.     

青藏高原湖泊沉积研究及其进展

青藏高原湖泊沉积研究主要围绕青藏高原隆升和全球变化响应开展的。研究揭示了青藏高原隆升具有整体性、阶段性和后期加速性。中晚更新世以来和末次间冰期-冰期气候演化过程得到重建,并能够与冰芯和深海氧同位素记录对比;同时也存在M IS3阶段强烈暖湿和末次冰盛期冷湿等区域特征;新仙女木事件在湖泊沉积物也有明显记录。全新世研究表明青藏高原早期暖湿并经历冷事件,大暖期普遍出现高水位,后期气候向干冷化方向发展。湖泊沉积环境定量化重建也得到研究。青藏高原湖泊沉积应在高分辨率纹层沉积和环境指标定量分析基础理论方面加强研究。     

青藏高原湖泊沉积研究及其进展

青藏高原湖泊沉积研究主要围绕青藏高原隆升和全球变化响应开展的。研究揭示了青藏高原隆升具有整体性、阶段性和后期加速性。中晚更新世以来和末次间冰期一冰期气候演化过程得到重建,并能够与冰芯和深海氧同位素记录对比;同时也存在MIS3阶段强烈暖湿和末次冰盛期冷湿等区域特征;新仙女木事件在湖泊沉积物也有明显记录。全新世研究表明青藏高原早期暖湿并经历冷事件,大暖期普遍出现高水位,后期气候向于冷化方向发展。湖泊沉积环境定量化重建也得到研究。青藏高原湖泊沉积应在高分辨率纹层沉积和环境指标定量分析基础理论方面加强研究。     

LAKE-ICE BLISTERS, TERRA NOVA BAY AREA, NORTHERN VICTORIA LAND, ANTARCTICA

Ice blisters, typically 0.2–0.8 m high and 5–20 m long, develop annually on perennially frozen lakes in Northern Victoria Land. They are believed to be caused by hydrostatic pressures generated through progressive freezing of solute-rich water beneath the lake-ice cover during winter. Lake-ice blisters in the study area differfrom icing blisters described from the northern hemisphere. The latter are caused by hydraulic pressures and are found at locations such as river beds or spring sites on sloping terrain. The Antarctic lake-ice blisters reflect the occurrence of dry-based perennially frozen lakes with high salt contents in an extremely cold and arid environment.     

Mars landscape evolution: influence of stratigraphy on geomorphology in the north polar region

Lithology and physical properties of strata exposed at the Earth's surface have direct influence on the erosion and geomorphic expression of landforms. While this is well known on our planet, examples on Mars are just coming to light among the tens of thousands of airphoto-quality images (resolutions 1.5–12 m/pixel) acquired since 1997 by the Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC). Specific examples occur among martian north polar layered materials, which MOC images reveal are divided into two distinct stratigraphic units: a lower, dark-toned layered unit and a younger, upper, lighter-toned layered unit. The lower unit is less resistant to wind erosion than the upper unit. The upper unit most likely consists of stratified dust and ice, while the lower unit contains abundant, poorly cemented sand. Sand is more easily mobilized by wind than dust; the lower resistance to erosion of the lower unit results from the presence of sand. Where wind erosion in polar troughs has penetrated to the lower unit, geomorphic change has proceeded more rapidly: sand has been liberated from the lower unit, and arcuate scarps have formed as the upper unit has been undermined. Wind erosion of the lower unit thus influences the geomorphology of the north polar region; this result likely explains the genesis of the large polar trough, Chasma Boreale, and the relations between dunes and arcuate scarps that have puzzled investigators for nearly three decades. The properties of the stratigraphic units suggest that the upper limit for the amount of water contained in the north polar layered materials may be 30–50% less than previously estimated.     

沙漠倒置河床研究进展及其对火星类似物研究的启示北大核心CSCD

沙漠倒置河床是干旱区一种特殊的河流状正地貌,这种地形倒置现象蕴含着河床由负转正的重要环境变化信息。本文遵循地貌学思路,基于全球范围内对沙漠倒置河床的研究报道以及野外勘察工作,对该地貌的空间分布、形态特征、物质组成、沉积结构以及形成机制进行了详细梳理。总体而言,世界各大主要沙漠地区均发育该地貌类型,其表层多为岩石碎屑或胶结物硬层,下伏质地相对松软的砂、黏土物质,由于河床和河岸周边沉积物的差异化侵蚀,河床被相对抬高。基于此,对火星倒置河床的成因机制、物质组成和形成时间进行了讨论。尽管对地球上沙漠倒置河床的研究已经取得一定进展,但未来研究仍需对其形成年代及其代表的气候意义进行深入分析;同时还应更多地与不同类型的火星倒置河床进行类比研究,这将对揭示火星水文活动和环境变化等科学问题提供重要依据。     

The siliceous sediments of Lake Cantara South,a saline lake in South Australia

A textural analysis of the siliceous sediments component of a small saline lake in south-eastern South Australia (Lake Cantara South) was undertaken. The data indicated periods of marine incursion, lagoonal dominance and elevated freshwater inputs. Lake Cantara originated as a marine embayment; then followed periods of intermittent marine connection; finally, the lake became athalassic (mostly saline but with occasional freshwater inundations). This history accords well with that derived from an examination of mollusc fossils (marine, estuarine, athalassic saline, and freshwater forms) and with previously published mineralogical, geochemical and geomorphological evidence.     

A comparison of methods used to estimate the height of sand dunes on Mars

The collection of morphometric data on small-scale landforms from other planetary bodies is difficult. We assess four methods that can be used to estimate the height of aeolian dunes on Mars. These are (1) stereography, (2) slip face length, (3) profiling photoclinometry, and (4) Mars Orbiter Laser Altimeter (MOLA). Results show that there is good agreement among the methods when conditions are ideal. However, limitations inherent to each method inhibited their accurate application to all sites. Collectively, these techniques provide data on a range of morphometric parameters, some of which were not previously available for dunes on Mars. They include dune height, width, length, surface area, volume, and longitudinal and transverse profiles. The utilization of these methods will facilitate a more accurate analysis of aeolian dunes on Mars and enable comparison with dunes on other planetary surfaces.     

Environmental change in Northern Egyptian Delta lakes during the late Holocene,based on diatom analysis

Quantitative and qualitative diatom analyses from the north Nile Delta lakes sediments of Egypt were used to evaluate the paleoenvironmental development of the lakes and climatic changes during the late Holocene. We analyzed 565 samples taken from 19 cores from Manzala, Burullus and Edku lakes. A total of 263 diatom species and varieties were identified. Multivariate statistical analyses distinguished 17 ecological groups that reflect changes in water salinity, lake-level and trophic state of the lakes, which in turn are mainly related to climatic changes and anthropogenic impacts. Manzala and Burullus lakes experienced a series of alternation between fresh, brackish and marine episodes, which were associated with wet and dry climates. Edku Lake cores, however, contained only three ecological groups that are characteristic of brackish water conditions. The general depositional regime in the lakes indicated five environmental phases: (a) a deep freshwater phase when the Nile flood water reach the lakes during humid warm climate; (b) a shallow freshwater phase with some macrophytes during a dry climate; (c) a shallow brackish water phase when Nile floodwater ceased during a dry climate and the lakes shifted to brackish conditions; (d) a mixed environmental phase when the seawater mixed with freshwater from drains and canals (water salinity fluctuated widely from freshwater to estuarine and full marine conditions); (e) a fully marine phase when seawater entered the lakes at all stages of the tide.     

基于DEM的地球与火星格状沙丘对比分析

沙丘是柴达木盆地可类比火星的重要地貌类型,沙丘形态是类火星风沙地貌研究的重要内容。基于数字地形分析（DTA）的方法,采用高程、坡度、坡向及地表复杂程度4个地形计量学指标对火星（北极地区）和地球（柴达木盆地）格状沙丘的地貌形态特征进行定量对比分析。结果表明：（1）两个研究区的高程剖面、坡度、坡向的地理学空间分布格局具有较大相似性;（2）高程、高程梯度、坡度和坡向的直方图相似度指数均大于0.7;（3）不同尺度上的分形维数近似相等,即地表复杂程度相似。用数字地形分析与直方图相似度指数结合的方法,定量或半定量地分析两个研究区沙丘地貌形态的相似性,这对类火星风沙地貌研究中科学选择试验点是一种新的尝试,以期为反演火星风沙地貌的形成与演化提供科学依据。     

A rock magnetic record from Lama Lake, Taymyr Peninsula, northern Central Siberia

An 11 m long sediment core ftorn Lama Lake, Northern Siberia, has been subjected to intense sedimentological, geochemical and rock magnetic analyses. According to a palynologic investigation the recovered sediments cover the whole Holocene and the late Pleistocene reaching back to about 17 ka. IRM acquisition experiments, hysteresis loop and back field as well as thermomagnetic measurements revealed magnetite in the pseudo-single domain range as the only remanence carrier. Sharp rock magnetic boundaries occur at 20 and 745 cm sub-bottom depth that are clearly linked to shifts in the median grain size of the magnetite. These boundaries are close to the present boundaries that bracket an anoxic zone between the subrecent and a late Pleistocene oxic section of the sediments. Within the anoxic section, magnetites are characterized by significantly larger median grain sizes but within a very narrow grain size range. The shift from fine grained magnetite within the oxic sediments to coarse grained magnetite is interpreted as the result of dissolution of the finest magnetite grains within the anoxic sediments. A significant shift of the Ti/Fe-ratio of the bulk sediment at a sub-bottom depth of 735 cm does not correspond to thermomagnetic properties, i.e. Curie-temperatures do not follow the variable Ti-content of the sediment.     

Clustered streamlined forms in Athabasca Valles, Mars: Evidence for sediment deposition during floodwater ponding

A unique clustering of layered streamlined forms in Athabasca Valles is hypothesized to reflect a significant hydraulic event. The forms, interpreted as sedimentary, are attributed to extensive sediment deposition during ponding and then streamlining of this sediment behind flow obstacles during ponded water outflow. These streamlined forms are analogous to those found in depositional basins and other loci of ponding in terrestrial catastrophic flood landscapes. These terrestrial streamlined forms can provide the best opportunity for reconstructing the history of the terrestrial flooding. Likewise, the streamlined forms in Athabasca Valles may provide the best opportunity to reconstruct the recent geologic history of this young Martian outflow channel.     

火星和地球雅丹形态学类比分析——以埃律西昂平原和柴达木盆地为例

作为一种风蚀地貌,雅丹地貌是对环境长期适应的一种表现,其形态特征可以反映所受内外营力的作用。对火星埃律西昂平原和地球柴达木盆地雅丹体的形态参数进行对比分析。结果显示：（1）埃律西昂平原雅丹体的长宽比（3.49）与柴达木盆地雅丹体的长宽比（3.57）较为接近,同时也与理想状态下的长宽比（4）接近,它们都具有流线型的形态,且处于雅丹体发育的成熟期。（2）柴达木盆地雅丹体是鲸背状,埃律西昂平原雅丹体是椭圆状,原因是柴达木盆地雅丹体常年受盛行风的影响,埃律西昂平原雅丹体受两种反向风的影响。柴达木盆地雅丹体表面崩裂的痕迹不明显,埃律西昂平原雅丹体表面崩裂的痕迹比较明显,原因是形成雅丹体的物质基础和温差环境不同：柴达木盆地雅丹体的物质基础是湖相沉积物,雅丹体表面有减弱风化的盐壳;埃律西昂平原雅丹体的物质基础是火山熔岩流,而且火星的昼夜温差大于地球。