蒸气收集脉冲进样流动注射氢化物发生－原子荧光法测定痕量锑

研究了流动注射氢化物发生－原子荧光测定矿石中Ｓｂ的方法，提出用蒸气收集脉冲进样技术，较大地提高了氢化物发生法的灵敏度和检测能力。标准参考样品的分析结果与推荐值吻合，精密度（ＲＳＤ）和检出限分别为５．１％（８ｎｇ／ｍｌ，ｎ＝９）和０．１９ｎｇ／ｍｌ。测定速度为１２０样／ｈ。     

冲绳海槽的晚第四纪浊流沉积

冲绳海槽晚第四纪的浊流沉积发育在海底斜坡带和坡折处静水环境,属阵发性纵向浊流。物质来源于海槽中心斜坡区的滑塌沉积物、岛坡、陆坡和台湾宜兰浇滩的碎屑沉积物。受控于海底地形、滞流环境和构造岩浆活动以及伴生的浅源地震。 冲绳海槽海底表层浊流沉积物,形成在晚更新世末次冰期最盛期、末次冰期末和冰后期三个阶段,以末次冰期最盛期阵发频繁,浊积物最发育,与气候寒冷期有一定的相关性。     

The importance of breaching as a mechanism of subaqueous slope failure in fine sand

Large bank failures, comprising up to 10⁶ m³ of sediment, are common features along steep channel banks in estuaries and large rivers that consist of clean, fine sands, and are mostly assumed to be generated by sudden liquefaction of large masses of very loosely packed sand. Another less commonly recognized type of failure is manifested by the gradual retrogression of a very steep wall, steeper than the angle-of-repose. Instead of the voluminous surging plastic sediment-water flow, or hyperconcentrated density flow (sensu Mulder & Alexander, 2001 ) generated by liquefaction, this type of failure, known as breaching by dredging companies and hydraulic engineers, produces a sustained quasi-steady, turbidity current. To date, sedimentologists have not recognized the process of breaching as such. In this paper, it is suggested that breaching may be the origin of many thick, massive sand layers known from ancient deposits from various environments, notably in some turbidite successions. Possible differences in the sedimentary structure of the deposits produced by breach failures vs. liquefaction slope failures (=liquefaction flow slides) can be deduced from a knowledge of the sediment transport processes initiated by the failure. A field study is presented on some poorly structured beds in the Eocene Vlierzele Sands in Belgium, which are supposed to have originated from liquefaction failures, but are reinterpreted to be the products of breaching. It is postulated that the local steep slope disturbance required to initiate an active breach can be produced by a small liquefaction slope failure (=liquefaction flow slide failure) or local erosion by river or tidal channel flow at the initial stage of the failure event.     

Repeated cycles of submarine channel incision, infill and transition to sheet sandstone development in the Alpine Foreland Basin, SE France

The Grès de Champsaur turbidite system, deposited in a distal setting in the Alpine Foreland Basin of south‐eastern France, exhibits a repeated upsection alternation in sand body geometry between incised channels and sheet sands. The channels form symmetric lenticular erosional features, of width 900–1000 m (measured between the lateral limits of incision) and depth 65–115 m, and can be traced axially for up to 5 km. In each case, the channel fill is capped by a laterally persistent sandy sheet‐form interval, which lies upon a fine‐grained substrate beyond the channel margins. No intrachannel elements have been traced into the substrate sequence, suggesting that, before infill, the channels acted as open sea‐floor conduits of essentially the same dimensions as the preserved channel deposits. The channels are vertically stacked, although axial erosion juxtaposes younger channel axis deposits against the fill of older channels and their channel‐capping sheet sandstones to produce an apparently well‐connected composite sandstone body geometry. The predominant channel‐fill facies comprises coarse‐grained, amalgamated sandstones, which are commonly parallel‐ or cross‐stratified. Subsidiary facies of finer grained sandstone–mudstone couplets and clast‐bearing muddy debrites are commonly preserved as erosional remnants, suggesting a complex channel history of aggradation and erosion. The repeated cycles of channel incision, infill and transition to sheet sandstone development indicate repetitive incision and healing of the palaeo‐sea floor. A model is proposed that links incision to the development of relatively steep axial gradients (parallel to the mean dispersal direction) and the return to sheet‐form deposition to the re‐establishment of lower axial gradients, with the repetitive switch between incisional channels and sheet sandstones driven by changes in sediment input rate against a background of ongoing sea‐floor tilting.     

Sedimentary architecture beneath lakes subjected to storms: Control by turbidity current bypass and turbidite armouring,interpreted from ground‐penetrating radar images

Turbidites within Holocene lacustrine sediment cores occur worldwide and are valued deposits that record a history of earthquakes or storms. Without sedimentary architecture, however, interpretation of the cause, provenance and behaviour of their parent turbidity currents are speculative. Here, these interpretations are made from two‐dimensional ground‐penetrating radar images of ‘shore to shore’ architecture beneath three, previously cored lakes within the low seismicity New England (USA ) region. Shallow depths, low water and sediment conductivities, and signal sensitivity to density contrasts uniquely provided up to 30 m of sediment signal penetration. Core comparisons and signal analysis reveal that most horizons represent multidecimetre‐thick clusters of Holocene turbidites, which are denser than their organic‐rich silt matrix. Some horizons also represent erosional unconformities and sediment bypass interfaces. The key, common, architectural consequences of turbidity current activity include limited foreset progradation, conformably pinched or unconformable layers of organic‐rich sediment onlapped against slopes beneath 5 to 6 m of water, and mounded stratified sediments beneath rises. These features indicate that turbidity currents repeatedly bypassed the same slope without deposition and regardless of dip, and then simultaneously armoured and bypassed inter‐turbidite sediment along rises and basins to provide basinward, generally age‐conformable accumulation. The mounding precludes significant basinward focusing. Variable horizon amplitude suggests metre‐scale changes in armouring density. Unconformities localized near breaks in dip beneath slopes suggest erosive hydraulic jumps. One lake shows evidence of historically maintained channels associated with specific deltas. Shelf strata indicating inland current generation, similar key architecture in other, uncored lakes, countable, lake‐wide horizons, and absent slumps, slides and faults are consistent with storm‐driven turbidity currents, and with previous, core‐based conclusions that severe, Holocene storms were episodic throughout this region. The results generalize marine bypass and armouring to lacustrine settings, and so probably occur worldwide in lakes subject only to storms, including lakes where ground‐penetrating radar may locate core sites.     

Hummocky cross-stratification-like structures in deep-sea turbidites: Upper Cretaceous Basque basins (Western Pyrenees, France)

Hummocky cross-stratification is a sedimentary structure which is widely interpreted as the sedimentary record of an oscillatory current generated by energetic storm waves remobilizing surface sediment on the continental shelf. Sedimentary structures named hummocky cross-stratification-like structures, similar to true hummocky cross-stratification, have been observed in the Turonian–Senonian Basque Flysch Basin (south-west France). The bathymetry (1000 to 1500 m) suggests that the observed sedimentary structures do not result from a hydrodynamic process similar to those acting on a continental shelf. The morphology of these three-dimensional structures shares similarities with the morphology of hummocky cross-stratification despite a smaller size. The lateral extent of these structures ranges from a few decimetres to many decimetres; they consist of convex-up domes (hummock) and concave-up swales with a non-erosive base. Four types of hummocky cross-stratification-like geometries are described; they occur in association with structures such as climbing current ripple lamination and synsedimentary deformations. In the Basque Flysch, hummocky cross-stratification-like structures are only found in the Tc interval of the Bouma sequence. Hummocky cross-stratification-like structures are sporadic in the stratigraphic series and observed only in few turbidite beds or bed packages. This observation suggests that hummocky cross-stratification-like structures are linked genetically to the turbidity current but form under a very restricted range of parameters. These structures sometimes show an up-current (upslope) migration trend (antidunes). In the described examples, they could result from standing waves forming at the upper flow interface because of Kelvin–Helmholtz instability.     

自激振荡脉冲射流提高PDC钻头机械钻速实践

利用自激振荡脉冲射流原理,设计了脉冲射流喷嘴,应用于PDC石油钻头中,经过不同地域、不同地层、不同直径的实践应用表明,新型自激振荡脉冲射流PDC石油钻头与普通PDC钻头相比,机械钻速提高10%～30%;钻头寿命大幅度提高;破碎岩屑颗粒粒径增大2～4倍,扩大了勘探油井PDC钻头使用范围;有效地防止了钻头“泥包”等。     

‘Boninitic’ clasts from the Mesozoic olistostromes and turbidites of Angelokastron (Argolis,Greece)

The Lower Unit of the ophiolitic sequence of Northern Argolis comprises turbiditic sediments and olistostromes, both containing ophiolitic clasts, mainly crystal fragments (clinopyroxene, plagioclase, Cr-spinel, amphibole) in the turbidites and cumulitic intrusives (quartz noritic amphibole-bearing gabbros), subvolcanic rocks (dolerites) and various effusive lithologies (mainly Si-rich basalts to basaltic andesites) in the olistostromes. The volcanic rocks belong to three groups. In rare cases the lavas are mineralogically and chemically comparable with MORB; most of them, and the subvolcanic rocks, contain primary quartz and amphibole, orthopyroxene, Ca-rich plagioclase and clinopyroxene±Cr-spinels. All rocks are Si- and Mg-rich and have high concentrations of ‘compatible’ and very low concentrations of ‘incompatible’ elements. The REE profiles are characteristically U-shaped. Many of the observed features are comparable with those of subduction-related lavas and, in particular, with present day boninites and ophiolitic boninitic rocks. The gabbroic rocks have mineralogical and chemical analogies with the dolerites and lavas, thus it may be argued that the gabbros represent the intrusive counterparts of the ‘boninitic’ volcanic clasts. The mineral clasts occurring in the turbidites are chemically comparable with those analysed in the ophiolitic clasts of the overlying olistostrome. It may be concluded that the ophiolitic clasts of both olistostromes and turbidites were derived from a subduction-related sequence. An island arc–back-arc system might explain the occurrence of both boninitic and MORB-type lithologies in the olistostrome of Angelokastron. This may support the hypothesis of the onset of compressive tectonics along the Pindos Ocean during the Jurassic. © 1996 John Wiley & Sons, Ltd.     

Diachronisme des bassins turbiditiques d'avant-pays méso/néocrétacés du pays de Sault (Aude,Pyrénées françaises)

The cartographic, sedimentological and micropalaeontological analysis of remnants of Middle–Upper Cretaceous turbiditic basins from the ‘Pays de Sault’ (Aude, French Pyrenees) shows their diachronism (interpreted on a wider scale) and their sequence diversity. The ‘Gesse breccias’ are regarded as the proximal deposits of a Turonian narrow foreland basin, principally supplied by the erosion of the Jurassic–Lower Cretaceous cover of the High Primary Range to the south, induced by a strike-slip and overthrusting faulting within the en-échelon North-Pyrenean Fault Zone. More to the north, the North-Pyrenean ‘Axat Basin’ consists of two successive backstepping turbiditic wedges, respectively corresponding to an Upper Albian distal flysch and to a Middle–Upper Cenomanian more proximal flysch, all the series unconformably overlying structures that were folded then eroded before the Upper Albian. The previous concept of carbonate olistoliths included within the Axat Cenomanian flysch is also refuted: these large-size blocks are now interpreted as belonging to a tectonic slice destroyed and partly collapsed on the southern slope of the Rebenty Valley during the Quaternary. To cite this article: M.-J. Fondecave-Wallez, B. Peybernès, C. R. Geoscience 336 (2004).