Current crescents formed by marine algae (Valonia sp.): a new record of obstacle marks lacking preservation of obstacles

Obstacle marks, formed around non-permanent tools, commonly occur on the beach faces of Lower Long Sand Island and Sagar Island, two tidal islands in the Ganga River estuary, India. The marine globose algae, Valonia sp., which bloom profusely in the waters of the Bay of Bengal during winter, are deposited on beach faces after being carried by wave swash, and then act as impermeable obstacles in the path of wave backwash. This creates around the globose algal bodies U-shaped or crescentic marks 2–3 cm in width with arms 1–3 cm in length. The globose vesicles are soon broken up by external forces or by forces of surface tension, leaving crescentic marks around a circular filamentous impression. The crescents always open toward the direction of wave backwash. These structures may prove useful not only for interpreting the palaeoslope and palaeocurrent directions but also for recognizing the palaeoecology.     

液压油污染控制

工程机械液压系统故障大约有70T是由液压油污染引起的，本文阐述了水电施工机械设备液压油的污染对液压系统的影响及如何控制液压油污染，保证其清洁度，从而预防液压系统故障。     

Erosional marks on consolidated banks and slump blocks in the Rupen River, north-west India

Erosional marks, including grooves, current crescents and flutes, are present on banks and slump blocks of the Rupen River on the semi-arid plains of north-west India. The channel has a width:depth ratio of 6, and is incised up to 8 m through well consolidated, fine-grained aeolian sediment dated at ～ 20–60 ka. Pedogenic carbonate nodules embedded in the channel walls have localized scour, and reworked carbonate particles probably promoted corrasion during strong seasonal flow. Similar erosional marks are apparently scarce on modern river banks, and a distinctive combination of conditions, including a consolidated substrate and strong flow in a confined channel, is probably required for their generation and preservation on channel walls and on slump blocks.     

Primary depositional and diagenetic features in the banded iron formation and associated iron-ore deposits of Noamundi,Singhbhum district,Bihar, India

The Banded Hematite Jasper (BHJ) Formation of Noamundi region in Bihar, belonging to the lower part of the Iron Ore Group of early Precambrian age (c. 2900–3200 Ma), exhibits numerous primary depositional and diagenetic features, both in BHJ as well as the associated iron ore deposits. Observed primary depositional features include banding and bedding of different geometric-types, surface-markings including interference ripple-marks, current crescents, linear markings, scour-and-fill structures, etc. and within-mass microstructures such as spherulites, granules, discs and maculose cylindrical bodies. Diagenetic features, such as fabric changes, micro-dessication structures, gravity-density features, etc. and motion-and-disruption features of various kinds are also seen. The significance of various features in terms of probable mode and environments of deposition of BHJ and the iron ore beds has been considered. In general, shallow water environment of deposition in a region proximal to the shoreline with a rather steep paleoslope of the shelf has been surmised.     

东辽河铁路大桥桩基础施工地质问题的处理

东辽河铁路大桥地基的第四系存在多原因形成的人为物质,构成桥桩基础施工的障碍,使桩孔钻探施工难以进行。经采用多种方法对不同问题进行处理,达到了施工目的。     

Spinning with the dinosaurs: the fossil record of spiders

When most people hear the word 'fossil' they tend to conjure up images of giant dinosaurs such as Tyrannosaurus rex or shelled marine invertebrates. Prior to the Hollywood blockbuster movie Jurassic Park , which was based on recreating dinosaurs through extracting their DNA from fossil mosquitoes preserved in amber, few non-palaeontologists would entertain the notion that small, soft-bodied organisms such as insects occur in the fossil record. However, insects and spiders are common as fossils in amber, where they are often preserved with life-like fidelity, and they also occur to a lesser degree in carbonate rocks.     

岩浆不混溶分异过程动力学分析

根据实验和具体实例,从岩浆不混溶分异过程分析了不混溶球体相随粒经大小而发展演化的阶段性。在早期,数十微米级以下细小的不混溶球体相互相碰撞合并作用剧烈,生长迅速,正因为如此,以及岩浆结晶作用影响,这种球体相一般难以保存下来。另一极端情况是不混溶相生长到米级以上粒径的球体相时,由于快速的重力分离作用,也难以呈球状保存下来,而形成较大规模的分异层状体。只有毫米级到厘米级的不混溶球体相,由于发展缓慢,容易保存,以致可以在火成岩中看到这种球颗（粒）结构。有时微米级球体可以在淬冷火山岩基质中得以保存。从力学角度看,岩浆不混溶相的发展过程是一种有效的岩浆分异演化机理。     

Morphology, internal structure and mechanics of small longitudinal (seif) dunes in an aeolian horizon of the Proterozoic Dhandraul Quartzite, India

The excellently preserved metre-scale, linear bedforms in an aeolian horizon of the Proterozoic Dhandraul Quartzite, India, show oppositely dipping strata arranged in a zigzag pattern. The strata are dominantly of translatent type, deposited by along-crest migrating ripples preserved on the flanks of dunes. The bedforms thus may be interpreted in a morphodynamic sense as longitudinal (seif) dunes. In order to determine the regional palaeoflow pattern, the migration directions of ripples preserved at the top of sheet sandstones that are associated with the dune cross-strata and internally show subhorizontal translatent strata were measured. A directionally varying flow with a mean direction nearly parallel to the mean axial trend of the dunes is indicated. The kinematics of the dunes were thus largely the result of alternate operation of two oblique flow components, each of which was deflected at a dune crest into an along-crest flow on the downwind flank of the dune. The deflected flow formed along-crest migrating ripples, which in turn deposited climbing ripple strata. Alternate deposition on the two opposite flanks resulted in near vertical accretion of the dunes, as is indicated by the zigzag pattern of stratal arrangement.     

非开挖铺管中定向钻进轨迹设计研究

对非开挖工程中水平定向钻进轨迹最优化设计进行了深入研究。应用最优化理论的动态规划思想,以钻进台时为优化指标,根据障碍物位置、大小和钻孔参数,建立了轨迹设计的最优化模型;并推导出绕过两个障碍物的局部轨迹最优化函数,通过坐标变换,简化了兰维空间轨迹设计问题;开发了相应的软件实现模型的求解。     

The first dinosaur tracksite from Abruzzi (Monte Cagno,Central Apennines,Italy)

A new Lower Cretaceous (lower Aptian) dinosaur tracksite, from the eastern side of Monte Cagno (Abruzzi, Italy), is described. Different styles of track formation are represented on the site surface. Most of the footprints are preserved as deep tracks, produced by trackmakers sinking into soft mud. Some tracks, better preserved than the others, are characterized by metatarsal impressions and were interpreted as the resting traces of a crouching theropod (based on their orientation and three-dimensional morphology). The 135 cm length of the track with metatarsal impressions indicates huge pedal proportions and represents the largest theropod trackmaker ever documented from the Mesozoic peri-Adriatic platforms of Italy.     

莱阳盆地莱阳群恐龙足迹化石的新发现

在山东莱阳盆地早白垩世莱阳群龙旺庄组发现15个足迹化石。化石产在灰绿色细砾粗砂岩(转石)的下层面,呈层底凸形(Convex hyporelief)保存。研究表明,足迹为二足行走、趾行式、三趾型,趾端具尖、长爪。足长约13 cm,长大于宽,近中趾对称。趾间角较大:平均值Ⅱ27°Ⅲ27.2°Ⅳ,Ⅱ、Ⅳ趾夹角平均54.2°。趾垫不清晰,无尾迹印痕。经研究,笔者认为这是一新的足迹类型,命名为Paragrallator ichnogen. nov.,并将其归入Coelurosauria Huene 1914次亚目,Anchisauripodidae(Lull 1904)足迹科。即该足迹系由小型兽脚类恐龙——虚骨龙类所形成。恐龙足迹形成于滨湖相—河流相环境中。     

Thermochemolysis of organic matter preserved in stalagmites: A preliminary study

The analysis of organic matter (OM) preserved in stalagmites is a growing field, but there have been few studies of biomarker compounds such as lignin phenols that are widely used in other palaeoenvironmental contexts. Here we present a preliminary qualitative study of the OM in six stalagmite samples from contrasting environments, using thermochemolysis in the presence of tetramethylammonium hydroxide (TMAH). The results indicate that a wide variety of products is preserved, including several potential lignin-derived compounds, but also that further research is needed to maximise compound recovery and allow the analysis of dissolved OM preserved in stalagmites to reach its full potential.     

Granularity and textural analysis as a proxy for extreme wave events in southeast coast of India

Extreme wave events of 1000 and 1500 years (radiocarbon ages) have been recently reported in Mahabalipuram region, southeast coast of India. Subsequently, we carried out extensive sedimenttological analysis in regions covering a total lateral coverage of 12 km with a new archeological site as the central portion of the study area. Twelve trenches in shore normal profiles exhibit landward thinning sequences as well as upward fining sequences confirming with the global signatures of extreme wave events. The sediment size ranges from fine-to-medium and moderately well sorted-to-well sorted, and exhibit positive skewness with platykurtic-to-leptokurtic nature. We now propose the abrupt winnowing or back and forth motion including unidirectional transport of these deposited sediments, which results in positive skewness. Textural analyses derived from scanning electron microscope studies (SEM) demonstrate the alteration produced, in the ilmenite mineral with vivid presence of pits and crescents with deformation observed on the surface due to extreme wave activities. This is further confirmed with the predominance of high-density mineral such as magnetite (5.2) and other heavy minerals in these deposits inferred the high-intensity of the reworking process of the beach shelf sediments.     

Late Neogene sequence stratigraphic evolution of the Foz do Amazonas Basin,Brazil

The margin of the Foz do Amazonas Basin saw a shift from predominantly carbonate to siliciclastic sedimentation in the early late Miocene. By this time, the Amazon shelf had also been incised by a canyon that allowed direct influx of sediment to the basin floor, thus confirming that the palaeo‐Amazon fan had already initiated by that time (9.5–8.3 Ma). Above this interval, during a prolonged lowstand, Messinian third‐order sequences are preserved only in the incised‐valley fills of the canyon with no equivalent strata on the shelf. Third‐ and fourth‐order sequences younger than Messinian are preserved on the shelf after sea‐level rise above the shelf by the early Pliocene. Sequences younger than 3.8 Ma often show fourth‐order cyclicity with an average duration of 400 ka (larger scale eccentricity cycles) often preserved in high‐sedimentation‐rate areas of river deltas. Mass wasting and transportation of slope sediments to the basin began to play an important role in sediment dispersal at least as far back as the mid‐Pliocene, after rapid progradation had produced steeper slopes more prone to failure.     

The anatomy of exhumed river-channel belts: Bedform to belt-scale river kinematics of the Ruby Ranch Member,Cretaceous Cedar Mountain Formation,Utah, USA

Many published interpretations of ancient fluvial systems have relied on observations of extensive outcrops of thick successions. This paper, in contrast, demonstrates that a regional understanding of palaeoriver kinematics, depositional setting and sedimentation rates can be interpreted from local sedimentological measurements of bedform and barform strata. Dune and bar strata, channel planform geometry and bed topography are measured within exhumed fluvial strata exposed as ridges in the Ruby Ranch Member of the Cretaceous Cedar Mountain Formation, Utah, USA. The ridges are composed of lithified stacked channel belts, representing at least five or six re-occupations of a single-strand channel. Lateral sections reveal well-preserved barforms constructed of subaqueous dune cross-sets. The topography of palaeobarforms is preserved along the top surface of the outcrops. Comparisons of the channel-belt centreline to local palaeotransport directions indicate that channel planform geometry was preserved through the re-occupations, rather than being obscured by lateral migration. Rapid avulsions preserved the state of the active channel bed and its individual bars at the time of abandonment. Inferred minimum sedimentation durations for the preserved elements, inferred from cross-set thickness distributions and assumed bedform migration rates, vary within a belt from one to ten days. Using only these local sedimentological measurements, the depositional setting is interpreted as a fluvial megafan, given the similarity in river kinematics. This paper provides a systematic methodology for the future synthesis of vertical and planview data, including the drone-equipped 2020 Mars Rover mission, to exhumed fluvial and deltaic strata.     

Statistical landslide susceptibility assessment of the Mansehra and Torghar districts,Khyber Pakhtunkhwa Province,Pakistan

This paper presents laboratory experiments and numerical simulations of effects of submerged obstacles on tsunami-like solitary wave and its run-up. This study was carried out for the breaking and non-breaking solitary waves on 1:19.85 uniform slope which contains a submerged obstacle. New laboratory experiments are performed to describe the mitigation of tsunami amplitude and run-up under the effect of submerged obstacles. We are based on experimental results obtained to validate the numerical model. The numerical modeling using COULWAVE aims essentially to show the effect of the obstacle on the shape of solitary wave and the limit of this effect. Using a multiple nonlinear regression, we have determined a model to estimate height of run-up according to the amplitude of the wave and the obstacle peak depth.     

A millennial-scale record of Holocene tsunamis on the Kronotskiy Bay coast, Kamchatka, Russia

Deposits from as many as 50 large tsunamis during the last 7000 years are preserved on the Pacific coast of the Kamchatka Peninsula near the mouth of the Zhupanova River, southern Kronotskiy Bay. These deposits are dated and correlated using Holocene marker tephra layers. The combined, preserved record of tsunami deposits and of numerous marker tephras on Kamchatka offers an unprecedented opportunity to study tsunami frequency. For example, from the stratigraphy along southern Kronotskiy Bay, we estimate frequency of large tsunamis (>5 m runup). In the last 3000 years, the minimum frequency is about one large tsunami per 100 years, and the maximum about one large tsunami per 30 years; the latter frequency occurred from about 0 to 1000 A.D. This time interval corresponds to a period of increased seismicity and volcanic activity that appears to be recorded in many places on the Kamchatka Peninsula.     

Seismic Imaging from a TBM

Summary Seismic monitoring from the head of a tunnel-boring machine (TBM) enables improved assessment of the risks associated with the tunnel-boring process. The monitoring system provides a live image of ground conditions along the trajectory followed by the TBM and detects local heterogeneities such as boulders, foundations, and other obstacles that commonly pass undetected using local geotechnical techniques. From a seismic perspective, the underground setting of tunnelling projects places limitations on imaging capability. The principal limiting factor is the size of the area upon which transducers can be installed. This limitation requires adjustments to traditional seismic imaging techniques in which a large area is assumed to be available for attaching the transducers. Recently developed short imaging operators take this limitation into account and are used in the examples described herein. The unique conditions of tunnelling yield two advantages over traditional settings in terms of imaging: rotation of the cutter wheel and the lateral progression of the TBM. Rotation of the cutter wheel, upon which the transducers are installed, provides the opportunity to illuminate obstacles from different angles in different recordings. Spatial progression of the TBM enables improvement in the illumination of obstacles and the signal-to-noise ratio by combining recordings from different lateral positions. In this paper, these specific aspects of seismic imaging during tunnelling are discussed via models that represent different cases encountered in actual tunnelling projects. These case studies demonstrate the way in which image quality along the trajectory of the TBM is improved over that in traditional settings. In this way, the risks associated with the tunnelling process can be more accurately assured.     

Diagenesis of aragonite from Upper Cretaceous ammonites: a geochemical case-study

Shell aragonite from ammonites collected in the Upper Cretaceous of West Greenland was investigated by means of macroscopic/microscopic visual evaluation, analyses of calcite/aragonite ratios, carbon and oxygen isotopic compositions and Sr and Mg concentrations of shell carbonate and of amino acid compositions of organic matrices. The results are: (1) Material visually classified as well preserved may have suffered diagenetic modifications of mineralogical and chemical composition. (2) Of the chemical and mineralogical parameters studied, amino acid composition, calcite/aragonite ratios and magnesium concentrations were found to be most sensitive to post-depositional modifications, while oxygen isotope composition and strontium concentrations showed detectable diagenetic modifications only after more pronounced alterations. (3) Based on the Mg/Ca ratios and calcite concentrations of the shell aragonite, a diagenetic classification has been proposed grouping the material into well preserved, moderately preserved and poorly preserved. (4) The chemical and mineralogical composition of the best preserved material suggests that the Upper Cretaceous ammonites had a shell composition similar to that of modern Nautilus and other aragonite-shelled molluscs.     

Understanding older adults’ social capital in place: Obstacles to and opportunities for social contacts in the neighbourhood

Social capital has been a popular concept used in research and policy to stress the value of social contacts for the health and well-being of older adults. However, not much is known about the obstacles to and the opportunities for local social contacts in older adults’ everyday lives. In this paper we provide a geographical account of older adults’ social capital, by taking the main context of their daily life, the neighbourhood, into consideration. We draw on semi-structured and walking interviews with 17 older adults living in an urban neighbourhood in the Northern Netherlands in order to illustrate the meanings of, the obstacles to and the opportunities for local social contacts. Our findings show that the neighbourhood is not an isotropic surface where opportunities for developing social capital are evenly distributed. The potential benefits of older adults’ local social contacts differ depending on the place of social interaction within the neighbourhood and expectations associated with these interactions. Furthermore, different time geographies of older and younger residents as well as ageist stereotypes of older adults’ body capital influence the development of social capital in the neighbourhood.