内蒙古巴彦塔拉盆地砂岩型铀矿地质特征与主沉积物体系归属

从盆地沉积体系研究入手，以沉积微相研究为基础，划分了盆地含矿主岩的沉积体系和成因相带，明确了找矿目标层及其分布范围。腾格尔组上段为扇三角洲沉积体系，其中扇三角洲前缘砂体中发育潜水—层间氧化带型铀矿化。赛汉塔拉组为河流沉积体系，可按沉积微相及古气候特征分为上、下两段。下段为辫状河沉积，发育良好的砂体、富含有机质，它是本区重要的找矿目标层，产底河道型砂岩铀矿化。通过对后生蚀变和矿化特征的分析，认为早期为潜水氧化蚀变成矿；晚期为潜水—层间氧化蚀变成矿，同时还有来自天窗补给的含铀、含氧地下水被沿断裂上升的含H2S的油气还原叠加改造成矿。     

The infill of a supradetachment(?) basin: the continental to shallow-marine Upper Permian succession in the Dolomites and Carnia (Italy)

In the Dolomites and Carnia (eastern Southern Alps), the Upper Permian succession is represented by red beds of Val Gardena Sandstone, grading upwards and eastwards into the evaporitic and carbonate deposits of the Bellerophon Formation.

An overall transgressive pattern is shown by the general trend of the depositional setting, which evolved from flashy alluvial fans, through multiple-channel bedload rivers, mixed-load sinuous rivers, terminal fans, coastal sabkha and evaporitic lagoon, to a shallow, low-gradient marine ramp. The inferred fluvial regime was subject to rapid and erratic fluctuations in discharge. Palaeosols are represented by calcic soils, and suggest a warm to hot, semi-arid or dry subhumid climate with strongly seasonal rainfall. Vertic features are associated with more inland alluvial complexes: they are missing in the terminal-fan deposits, suggesting greater aridity in lowland (coastal) areas.

The Bellerophon Fm. consists of two units: a lower evaportte-bearing unit, deposited in a barred basin, and an upper shallow-marine carbonate unit, laid down on a very low-energy, low-gradient ramp.

Five third-order sequences and the lower part of a sixth sequence, collectively showing a backstepping pattern, have been identified in the succession. Due to the presence of a very low-gradient ramp margin, and the consequent ineffectiveness of relative sea-level falls in producing large-scale erosion in coastal areas, it is suggested that, rather than eustatic changes, degradational episodes marking sequence boundaries in the red-bed succession reflect changes in the climate-modulated intrinsic variables of discharge and sediment supply, and/or tectonic uplift.

Base level rises in, red-bed sequences are recorded by upward change from thick channel-belt sandstone bodies with an often high connectedness ratio, to progressively thinner channel deposits, ranging from isolated ribbons to channel-belt sandstone bodies potentially reaching high width/thickness ratios, encased in a comparably greater volume of overbank fines. This trend is thought to reflect the change from a confined geomorphic setting, with a limited area of potential avulsion, to an unrestricted setting with rivers free to move extensively; in addition, it documents the transition from an inland fluvial system with laterally migrating perennial or semi-perennial channels, to an ephemeral network of randomly migrating and frequently avulsing small terminal-fan distributaries, through a drastic downstream decrease in channel depth and discharge.

Identification of key sequence-stratigraphic relationships within the red-bed succession was mostly aided by the presence of easily recognizable and regionally correlated marine and marginal marine bed packages, traceable landwards into alluvial deposits showing faint traces of tidal activity, interpreted as the equivalent of marine maximum-flooding sediments. They may grade upwards into progradational fluvial packages showing basinward increase in thickness.

The Upper Permian deposits of the Southern Alps are considered part of an Upper Permian-Lower Triassic, second-order, structurally controlled sequence. The location of the basin on a thickened, previously active crust, affected by thermal perturbance after the last stages of the Variscan orogeny, the relatively reduced thickness of the basin fill, and predominantly long, transverse drainage networks, mostly derived from the denuded Insubric footwall, all suggest that sedimentation took place in a supradetachment basin, with a major detachment fault located in the palaeo-Insubric belt.     

A stability criterion inherent in laws governing alluvial channel flow

The stability criterion of maximum flow efficiency (MFE) has previously been found inherent in typical alluvial channel flow relationships, and this study investigates the general nature of this criterion using a wider range of flow resistance and bedload transport formulae. For straight alluvial channels, in which the effect of sediment sorting is insignificant, our detailed mathematical analysis demonstrates that a flow efficiency factor ε occurs generally as the ratio of sediment (bedload) discharge Q_s to stream power Ω (γQS) in the form of . When ε is maximized (i.e. Q_s is maximized or Ω is minimized), maximally efficient straight channel geometries derived from most flow resistance and bedload transport formulae are found compatible with observed bankfull hydraulic geometry relations. This study provides support for the use of the criteria of MFE, maximum sediment transporting capacity and minimum stream power for understanding the operation of alluvial rivers, and also addresses limitations to the direct application of its findings. Copyright © 2002 John Wiley & Sons, Ltd.     

Geomorphological and sedimentological analysis of a catastrophic flash flood in the Arás drainage basin (Central Pyrenees, Spain)

On August 7th, 1996, an intense and short-duration convective storm occurred over the 18.6-km² Arás drainage basin (Central Pyrenees, Spain). This high relief basin is composed of three subbasins, Aso, Betés and La Selva, and feeds the Arás alluvial fan, in the Gállego river valley. This alluvial fan had been drained by an artificial channel (about 125 m³/s at bank-full capacity). More than 30 check dams in its feeder channel, the Arás barranco, had been previously filled by earlier sediments. The heaviest rain was over the Betés subbasin (total rainfall 178.4 mm; maximum rainfall intensity of 153 mm/h for a 10-min time interval was estimated). Most of the rainfall fell in a 70-min period. This storm resulted in high runoff, causing catastrophic damage and significant geomorphic changes in the drainage basin, especially in the Betés subbasin. The high discharge, concentrated in the Arás barranco, destroyed most of the check dams, flushing out a great amount of debris. Major channel trenching and widening occurred in this barranco. When the confined sediment-laden flash flood reached the basin mouth, it sheet-flooded the southern sector of the Arás fan depositing a massive amount of debris. On this fan 87 people lost their lives and the direct physical damage has been estimated at 55 million dollars. Two stages in the development of the flood have been differentiated from the sedimentological and morphological analysis of the flooded fan lobe. A first stage (peak discharge) of sheet-flooding deposited a coarse boulder lobe, burying the artificial channel at the fan head and causing a darnming effect on the water flood. During the second stage (discharge decline) the flood made its way through the fan head, incising the previous debris accumulation and splitting into two main flow paths.     

若尔盖下包座地区三叠系沉积特征

若尔盖东部下包座地区广泛发育的三叠系西康群,大量沉积构造表现为一套近源相滨浅海→斜坡浊积扇→半深海盆地复理石→浅海陆棚相沉积。岩石地层格架属Ⅰ型层序     

High-resolution Echo-sounding and Detection of Embedded Archaeological Objects with Nonlinear Sub-bottom Profilers

Sub-bottom profilers based on nonlinear acoustics offer many advantages especially for detecting and locating embedded objects in shallow waters. They have a narrow beam in spite of small transducers and virtually no side lobes. It is possible to realize mobile low-frequent sub-bottom profilers, which transmit very short sound pulses. Excellent vertical as well as horizontal resolutions at reasonable penetrations are proven benefits of using this technique. In this paper some technical aspects are discussed and a new experimental nonlinear scanning sub-bottom profiler system is described. Results from a field trial in archaeological prospection are shown to illustrate the successful application in practice.     

Conglomeratic reservoir characterization in the Caiyu field of the Langgu sag, North China

Several subaqueous alluvial fans are developed along the footwall of the northern boundary fault zone—the Daxing fault of the Langgu sag, Bohai Bay Basin, North China. A distinct feature is the significant difference in hydrocarbon enrichment between neighboring wells drilled in the same sedimentary facies. This paper analyses the controlling factors for hydrocarbon accumulation of subaqueous alluvial fan in the Caiyu field, north of the Langgu sag. Based on reprocessed seismic data and using Jason inversion method, the contrast of cross-well correlation panel was established and a reservoir type model was build-up; reservoir heterogeneity was interpreted from inversion impedance data. The result shows six conglomeratic bodies in this fan, which are stacked vertically and laterally. The lithofacies is the key controlling factor for the hydrocarbon accumulation, and diagenesis and tectonic stresses also play important roles in the hydrocarbon enrichment.     

Morphodynamics of the barrier-inlet system, west-central Florida

The barrier-inlet system along the Gulf Coast of peninsular Florida has one of the most diverse morphologies of any barrier system in the world. The delicate balance between tidal- and wave-generated processes on this low-energy coast permits only slight changes in either of these processes to result in significant and rapidly developing morphologic responses. Some of these responses are the result of natural phenomena such as hurricanes opening tidal inlets, closure of inlets due to longshore transport of sediment, and changes in the availability of sediment. Tidal prism is the primary factor in controlling inlet morphology and is greatly influenced by anthropogenic activities in the backbarrier area. Human activity has also modified the coast in many ways over the past several decades, beginning with the construction of the first causeways in the 1920s. The various modifications by development have resulted in important morphodynamic changes in the barrier-inlet system. These include hardening the coast on the beach and at inlets, dredging and filling in backbarrier environments, and construction of fill-type causeways connecting the islands to the mainland. Construction of seawalls and jetties has inhibited normal coastal processes. Examples include the downdrift erosion at Blind Pass and Big Sarasota Pass. Construction of fill-type causeways between the barriers and the mainland has created artificial tidal divides that reduce the tidal prism at some inlets, thereby resulting in instability or closure such as Blind Pass and Dunedin Pass. This is further exacerbated by dredge and fill construction that reduces tidal prism by reducing the area of open water in the backbarrier. Dredging of the Intracoastal Waterway also results in a negative impact on selected inlets by channeling tidal flux away from some inlets. Impacts of these changes inhibit the barrier/inlet environments from responding to open coast processes.     

胜坨地区沙河街组沙四上亚段砂砾岩体沉积相与油气分布

摘 要 胜坨地区沙四上亚段发育了以砂砾岩扇体为主的沉积体系,在深水区存在各种浊积砂砾岩体。本文在岩心观察和描述的基础上,结合测井等资料,对胜坨地区沙四上亚段砂砾岩体的沉积特征进行了研究,并分析了其油气分布特征。结果表明胜坨地区沙四上亚段在同生断层的下降盘主要发育水进型扇三角洲沉积体系,同时还广泛发育了重力流水道和滑塌浊积扇等浊积砂砾岩体。该区各类砂砾岩油藏在平面上由洼陷中心向边缘相带依次分布岩性油气藏—构造油气藏—地层油气藏,油气分布明显受沉积相控制,不同的相带储层物性差异明显。扇三角洲扇中部位储集物性较好,为油气聚集有利相带;滑塌浊积扇和重力流水道等浊积岩体次之;扇三角洲扇根、扇端则因储集物性较差,含油气性较差。此外,继承性深洼陷与岩性的分区性对油气分布有较大的影响。