Gravelly spit deposits in a transgressive systems tract: the Pleistocene Higashikanbe Gravel, central Japan

The Pleistocene Higashikanbe Gravel, which crops out along the Pacific coast of the Atsumi Peninsula, central Japan, consists of well‐sorted, pebble‐ to cobble‐size gravel beds with minor sand beds. The gravel includes large‐scale foreset beds (5–10 m high) and overlying subhorizontal beds (0·5–3 m thick), showing foreset and topset structure, from which the gravel has previously been interpreted as deposits of a Gilbert‐type delta. However, (1) the gravel beds lack evidence of fluvial activity, such as channels in the subhorizontal beds; (2) the foresets incline palaeolandwards; (3) the gravels fill a fluvially incised valley; and (4) the gravels overlie low‐energy deposits of a restricted environment, such as a bay or an estuary. The foresets generally dip towards the inferred palaeoshoreline, indicating landward accretion of gravel. Reconstruction of the palaeogeography of the peninsula indicates that the Higashikanbe Gravel was deposited as a spit similar to that developed at the western tip of the present Atsumi Peninsula, rather than as a delta. According to the new interpretation, the large‐scale foreset beds are deposits on the slopes of spit platforms and accreted in part to the sides of small islets that are fragments of the submerging spit during relative sea‐level rise. The subhorizontal beds include nearshore deposits on the spit platform topsets and deposits of gravel shoals or bars, which are reworked sediments of the spit beach gravels during a transgression. The lack of spit beach facies in the subhorizontal beds results from truncation by shoreface erosion. Dome structure, which is a cross‐sectional profile of a recurved gravel spit at its extreme point, and sandy tidal channel deposits deposited between the small islets were also identified in the Higashikanbe Gravel. The Higashikanbe Gravel fills a fluvially incised valley and occupies a significant part of a transgressive systems tract, suggesting that gravelly spits are likely to be well developed during transgressions. The large‐scale foreset beds and subhorizontal beds of gravelly spits in transgressive systems tracts contrast with the foreset and topset beds of deltas, characteristic of highstand, lowstand and shelf‐margin systems tracts.     

Detached mud prism origin of highstand systems tracts from mid-Pleistocene sequences, Wanganui Basin, New Zealand

Marine siltstone successions, 1–20 m thick, form the upper part of sequences in the mid-Pleistocene Castlecliff section (≈ 0·98–0·35 Ma). The siltstones were deposited within a broad shelf embayment at and about glacioeustatic highstands and are interpreted as highstand systems tracts (HST). Shell-rich to relatively shell-poor contacts at the base of Castlecliff HST are interpreted as downlap surfaces, which mark the quenching of transgressive in situ biogenic accumulation (backlap shellbed). Nonetheless, the basal parts of Castlecliff HST successions are enriched in fossil content in the context of the highstand successions as a whole and represent downlap shellbeds. Castlecliff HST are truncated above by sequence-bounding ravinement surfaces, such that complete sandier-upward successions and subaerial exposure surfaces associated with sequence boundaries sensu stricto are never preserved. Modern highstand sedimentation in the Taranaki Bight offshore from Castlecliff is characterized by a mid-shelf mud depocentre and a coastal shore-connected sand prism, both of which are encroaching upon intervening shell-rich relict and palimpsest transgressive deposits. The mud depocentre is up to 9 m thick, and deposition is influenced by a gyre caused by bathymetric steering of storm-driven currents along the embayed coastline. Modern highstand deposition in the Taranaki Bight, in which the mud depocentre is in part detached from the contemporary shore-connected sand prism, is regarded as an analogue for the deposition of the preserved lower parts of Castlecliff HST. The inferred architecture of Castlecliff HST therefore need not refer to the shore-connected, progradational geometry predicted by traditional sequence models. The model proposed herein may have application to other shelf palaeo-embayments in which mid-shelf focusing of fine-grained sediment has resulted from coastal steering of currents.     

Stability of fictitious Trojan planets in extrasolar systems

Our work deals with the dynamical possibility that in extrasolar planetary systems a terrestrial planet may have stable orbits in a 1:1 mean motion resonance with a Jovian like planet. We studied the motion of fictitious Trojans around the Lagrangian points L₄/L₅ and checked the stability and/or chaoticity of their motion with the aid of the Lyapunov Indicators and the maximum eccentricity. The computations were carried out using the dynamical model of the elliptic restricted three‐body problem that consists of a central star, a gas giant moving in the habitable zone, and a massless terrestrial planet. We found 3 new systems where the gas giant lies in the habitable zone, namely HD99109, HD101930, and HD33564. Additionally we investigated all known extrasolar planetary systems where the giant planet lies partly or fully in the habitable zone. The results show that the orbits around the Lagrangian points L₄/L₅ of all investigated systems are stable for long times (10⁷ revolutions). (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

On the global stability of single‐planet systems

In this paper, we estimate the global stability properties of single‐planet systems by using a catalogue of stability maps. The data of the catalogue were used to generate probability values on the mass parameter–eccentricity plane for the occurrence of stable orbits. We showed that the probability data can be well approximated by a second order surface. Using the resulted formula the likelihood of finding Earth‐like planets in single‐planet systems can be easily estimated. As an example, we derived estimations for four known exoplanetary systems. Our formula can be useful in selecting target stars for future space missions. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Deglacial meltwater drainage and glaciodynamics: inferences from Laurentide eskers, Canada

This paper evaluates current knowledge of Laurentide eskers in Canada in the light of developments in glacier hydrology and glacial sedimentology. Questions regarding the morpho-sedimentary relations of eskers, the synchroneity and operation of R-channel systems, the role of supraglacial meltwater input and proglacial water bodies, the controls on esker pattern, and the glaciodynamic condition of the ice sheet at the time of esker formation are discussed. A morphologic classification of eskers is proposed. Five types of eskers are identified and investigated. Type I eskers likely formed in extensive, synchronous, dendritic R-channel networks under regionally stagnant ice that terminated in standing water. Type II eskers likely formed in short, subaqueously terminating R-channels or reentrants close to an ice front or grounding line that may have actively retreated during esker sedimentation. Type III eskers plausibly formed in short R-channels that drained either to interior lakes in, or tunnel channels under, regionally stagnant ice. Type IV eskers may have formed as time-transgressive segments in short, subaerially terminating R-channels (or reentrants) that developed close to the ice margin as the ice front underwent stagnation-zone retreat or downwasted and backwasted regionally (stagnant ice); however, formation in synchronous R-channels cannot be discounted on the basis of reported observations. Type V eskers may have formed in H-channels that terminated subaerially. The spatial distribution of these esker types is discussed. The factors that determined Laurentide R-channel pattern and operation were likely a complex combination of (i) supraglacial meltwater discharge, (ii) the number and location of sink holes, (iii) the ice surface slope, thickness and velocity, and (iv) the permeability, topography and rigidity of the bed. These factors cause and respond to changes in ice dynamics and thermal regime over the glacial cycle.     

中国南方二叠纪沉积体系

二叠系是中国南方重要的海相含油气层系,经历了两次大的海侵－海退沉积旋回,形成了以海相碳酸盐岩为主,海相、陆相及过渡相并存的沉积古地理格局。根据典型剖面分析和岩相古地理研究,识别出4类沉积体系,即陆地沉积体系、混合沉积体系、碳酸盐台地沉积体系和斜坡盆地沉积体系。总结出4类基本的沉积体系组合,指出海平面变化和构造运动是控制沉积体系变化及其空间展布的决定因素。最后对成油气地质条件进行了分析和讨论,认为二叠系具有多套生储盖组合,其中以碳酸盐台地体系－斜坡盆地体系组合和混合沉积体系－斜坡盆地体系组合最为理想。     

莱州湾夏季浮游桡足类的摄食研究

于１９９７年７月有（１９－２４日）和小湖（２６－３０日）期间在莱州湾对不同大小桡足类自然群体（大型：〉５００ｍｍ,小型：２００－５００ｍｍ）的分布及肠道色素含量进行了现场测定,并在一个４８ｈ连续观测站（Ａ４）进行了肠道排空率和摄食节律实验。结果表明,浮动物肠道色素含量随个体的增大而增加,大型桡足类存在着一定的昼夜摄食节律,摄食高峰出现在夜间,小型桡足类摄食切律不明显。Ａ４站测得的桡足类摄食结果表明     

Investigation of dynamical chaotization in stellar systems with double massive centers using the Ricci curvature criterion

The Ricci curvature criterion is used to investigate the relative instability of various configurations of N-body gravitational systems. Systems with double massive centers are shown to be less stable than homogeneous systems or systems with single massive centers. In general, this is a confirmation that the Ricci curvature criterion is efficient in studying N-body systems by means of relatively simple computations.     

Optical, infrared and millimetre-wave properties of Vega-like systems – IV. Observations of a new sample of candidate Vega-like sources

Photometric observations at optical and near-infrared wavelengths are presented for members of a new sample of candidate Vega-like systems, or main sequence stars with excess infrared emission due to circumstellar dust. The observations are combined with IRAS fluxes to define the spectral energy distributions of the sources. Most of the sources show only photospheric emission at near-IR wavelengths, indicating a lack of hot (∼1000 K) dust. Mid-infrared spectra are presented for four sources from the sample. One of them, HD 150193, shows strong silicate emission, while another, HD 176363, was not detected. The spectra of two stars from our previous sample of Vega-like sources both show UIR-band emission, attributed to hydrocarbon materials. Detailed comparisons of the optical and IRAS positions suggest that in some cases the IRAS source is not physically associated with the visible star. Alternative associations are suggested for several of these sources. Fractional excess luminosities are derived from the observed spectral energy distributions. The values found are comparable to those measured previously for other Vega-like sources.     

GX-1型多功能旋喷钻机及配套钻具

简介了GX-1型多功能旋喷钻机及配套钻具的结构特点和生产试验情况。结果表明,该钻机性能可靠,结构合理,适合于多种地层的成孔与旋喷施工工艺。