Application of multi-seismic attributes analysis in the study of distributary channels     

《Marine and Petroleum Geology》2016

During the exploration of stratigraphic reservoirs, the key to locating these reservoirs is to identify the sandstone distribution. Seismic data can be used to recognize large-scale distributary-channel sedimentary bodies; however, depiction of sedimentary bodies in small distributary channels using traditional interpretation data from seismic profiles is extremely difficult. In the Upper Cretaceous first sandstone bed of the third member of the Nenjiang Formation (called the Nen 3 member for simplicity) in the XB area of the southern Songliao basin, distributary channels are the main sedimentary facies. The distributary channels migrate frequently; therefore, it is difficult to precisely depict the morphology of the channel and the distribution of sandstone. In this study, we investigated the deposition of distributary channels using equal-scale formation plane seismic attributes such as post-stack amplitude, instantaneous amplitude and seismic waveform classification, analyzed well logging data from target formations, and mapped the distribution of distributary channels. This study shows that seismic sedimentological study and stacking multiple attribute analysis can identify the distribution of distributary channels precisely and effectively. The attributes of equal-scale strata slices are evidently superior to those of time and horizon slices; Attribute extraction and selection of equal-scale formation slices is an essential step. The comprehensive selection of seismic attributes that show a good correlation to a single-well can be used to clearly depict channel bodies. The overlap of the 40-Hz single-frequency energy and the RMS amplitude depicts the sedimentary characteristics and shapes of sandstone bodies in main channels as well as small-scale distributary channels more clearly than a single attribute. These attributes show that the first sandstone bed of the Nen 3 member was from distributary channels with complex shapes. The distributary channels cut across each other vertically and laterally. It indicates that, during the deposition of the Nen 3 member in XB area, the direction of the main channel is from north to south, and the provenance could be from north and east. The method of this paper may provide some helpful suggestions to the geologist using seismic attributes to undertake research on sedimentary environment at other places in the world.  相似文献   

Beach tar accumulation, transport mechanisms, and sources of variability at Coal Oil Point, California     

Del Sontro TS  Leifer I  Luyendyk BP  Broitman BR 《Marine pollution bulletin》2007,54(9):1461-1471

A new field method for tar quantification was used at Coal Oil Point (COP), California to study the mechanisms transporting oil/tar from the nearby COP natural marine hydrocarbon seep field. This method segregates tar pieces into six size classes and assigns them an average mass based on laboratory or direct field measurements. Tar accumulation on the 19,927m(2) survey area was well resolved spatially by recording tar mass along twelve transects segmented into 4-m(2) blocks and then integrating over the survey area. A seasonal trend was apparent in total tar in which summer accumulations were an order of magnitude higher than winter accumulations. Based on multiple regression analyses between environmental data and tar accumulation, 34% of tar variability is explained by a combination of onshore advection via wind and low swell height inhibiting slick dispersion.  相似文献   

Mid–late Holocene hydrological changes in the Mahi River, arid western India   总被引：1，自引：0，他引：1  

Alpa Sridhar   《Geomorphology》2007,88(3-4):285-297

This paper attempts to quantify contemporary and palaeo-discharges and changes in the hydrologic regime through the mid–late Holocene in the alluvial reach of the arid Mahi River basin in western India. The occurrence of terraces and pointbars high above active river levels and change in the width/depth ratio can be regarded as geomorphic responses to changes in discharge. Discharge estimates are made based on the channel dimensions and established empirical relations for the three types of channels: mid–late Holocene, historic (the channel that deposited extensive pointbars above the present-day average flow level) and the present ones. The bankfull discharge of the mid–late Holocene channel was  55 000 m³ s^− 1 and that of the historic channel was  9500 m³ s^− 1, some  25 times and  5 times greater than that of the present river (2000 m³ s^− 1), respectively. Since the mid–late Holocene, the channel form has changed from wide, large-amplitude meanders to smaller meanders, and decreases in the width/depth ratio, unit stream power and the bed shear stresses have occurred. It can be inferred that there has been a trend of decreasing precipitation since the mid–late Holocene.  相似文献   

Channel geometry,bed material,and inferred flow conditions in ephemeral stream systems,barrier range,western N.S.W. Australia     

D. L. Dunkerley 《水文研究》1992,6(4):417-433

Streams draining the Barrier Range uplands in arid western N.S.W. are ephemeral and undergo rapid channel contraction away from the uplands as a consequence of transmission loss. These processes are documented on the basis of surveys of channel form and bed material at sequential sites located along the contracting lowland reaches of two representative streams. Channel width and depth display considerable fluctuation downstream, but cross-sectional area and maximum bed surface grain size decline in a very regular manner. Flood discharge, estimated from the channel capacity and predicted critical and mean flow velocities, also declines regularly. the trends are well fitted by log-linear models, and are reported in terms of a half-distance, the channel length in km over which the value of a morphometric parameter declines by 50 per cent. Rates of channel contraction and transmission loss are inferred to be inversely proportional to the volume of flow delivered from the upland section of the drainage basin. Unusual channel characteristics, including extensive tree growth in the bed, make application of ordinary flow equations difficult, because friction factors cannot be estimated with confidence. Systematic changes in the nature of the bed surface in contracting streams such as those studied here also have implications for the application of critical velocity equations, and highlight a need for further study of desert channels.  相似文献   

Experimental analysis of reservoir release wave routing in upland boulder bed rivers     

D. J. Gilvear 《水文研究》1989,3(3):261-276

Reservoir release wave routing during 33 controlled reservoir releases, along 15 upland boulder bed river channel reaches, on five different regulated rivers were monitored to assess the importance of river channel roughness and reservoir release magnitude on reservoir release wave speeds. Wave speeds varied between 0.52 and 3.01 m s^?1. Reservoir release wave translation, steepening, and attenuation occurred. With high channel roughness values reservoir release wave arrival speed is retarded in comparison to peak stage and wave steepening occurs, but with a reduction in channel roughness reservoir release wave front arrival is accelerated producing attentuation. The threshold between reservoir release wave front attenuation and steepening occurs at a pre-release discharge/channel width of approximately 0.1, an index of channel roughness. The paper also demonstrates, via comparison of observed and calculated reservoir release wave speeds on the River Washburn, Yorkshire, the difficulty of accurately predicting flood wave movement in upland boulder bed channels using existing prediction equations. The calculated values, however, revealed systematic error with pre-release discharge and reservoir release magnitude. Apparently the equations fail to account for the effects of high channel roughness together with pressure gradient forces, induced by rapid rates of stage change on the rising limb of reservoir releases. In order to accurately predict reservoir release wave movement in regulated rivers, this paper demonstrates that hydraulic studies need to be undertaken and pre-release discharges prescribed to determine desired reservoir release wave routing behaviour. Manipulation of the reservoir release pattern at the dam alone, cannot dictate reservoir release wave front form downstream or wave speed.  相似文献   

Sampling epifauna, a necessity for a better assessment of benthic ecosystem functioning: an example of the epibenthic aggregated species Ophiothrix fragilis from the Bay of Seine     

Lozach S  Dauvin JC  Méar Y  Murat A  Davoult D  Migné A 《Marine pollution bulletin》2011,62(12):2753-2760

Sampling the sea bottom surface remains difficult because of the surface hydraulic shock due to water flowing through the gear (i.e., the bow wave effect) and the loss of epifauna organisms due to the gear’s closing mechanism. Slow-moving mobile epifauna, such as the ophiuroid Ophiothrix fragilis, form high-density patches in the English Channel, not only on pebbles like in the Dover Strait or offshore Brittany but also on gravel in the Bay of Seine (>5000 ind m⁻²). Such populations form high biomasses and control the water transfer from the water column to the sediment. Estimating their real density and biomass is essential for the assessment of benthic ecosystem functioning using trophic web modelling. In this paper, we present and discuss the patch patterns and sampling efficiency of the different methods for collecting in the dense beds of O. fragilis in the Bay of Seine. The large Hamon grab (0.25 m⁻²) highly under-estimated the ophiuroid density, while the Smith McIntyre appeared adequate among the tested sampling grabs. Nowadays, diving sampling, underwater photography and videos with remote operated vehicle appear to be the recommended alternatives to estimate the real density of such dense slow-moving mobile epifauna.  相似文献   

Resonant period and Q of the Celtic Sea and Bristol Channel     

R.A. Heath 《Estuarine, Coastal and Shelf Science》1981,12(3):291-301

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长江中下游庐江-枞阳火山岩矿集区深部结构与成矿作用   总被引：32，自引：16，他引：16  

董树文  项怀顺  高锐  吕庆田  李建设  战双庆  卢占武  马立成 《岩石学报》2010,26(9):2529-2542

为探测长江中下游成矿带庐江-枞阳白垩纪火山岩盆地和铁、硫矿集区深部构造和地壳结构,探讨成矿深部控制条件,作者完成了穿越火山岩盆地的深反射地震剖面(150km,记录30s)和罗河铁矿区浅层高分辨反射地震剖面(20km),以及平行剖面的大地电磁、高精度重磁剖面,揭示了矿集区全地壳精细结构和电磁结构,同时开展区域构造测量和火山岩年代学研究,获得了新的认识。证实"耳状"的庐-枞火山岩盆地是一个沿北东向罗河断裂向东侧发育的非对称火山盆地,排除了另一半被断在西侧红层之下的判断;罗河断裂是一条切穿MOHO的深断裂,倾向南东,是引导地幔流体和岩浆上涌和喷发的通道,在中地壳形成岩浆房(反射亮斑);鉴别出多层界面,火山岩-侏罗系厚度约4～5km(其中火山岩厚度约3km),三叠系-震旦系变形层底界深度大致18～20km,变质基底组成中下地壳,MOHO平缓向北西倾,深度33～31km;追踪郯-庐断裂带的深部产状,陡立延伸到MOHO,宽约10km。从而揭示了早白垩系(132～127Ma)庐-枞火山岩矿集区深部过程与成矿、控矿作用。  相似文献   

Bedform morphology of salmon spawning areas in a large gravel-bed river     

Timothy P. Hanrahan   《Geomorphology》2007,86(3-4):529-536

While the importance of river channel morphology to salmon spawning habitat is increasingly recognized, quantitative measures of the relationships between channel morphology and habitat use are lacking. Such quantitative measures are necessary as management and regulatory agencies within the Pacific Northwest region of the USA, and elsewhere, seek to quantify potential spawning habitat and develop recovery goals for declining salmon populations. The objective of this study was to determine if fall Chinook salmon (Oncorhynchus tshawytscha) spawning areas in the Snake River, Idaho, USA, were correlated with specific bedform types at the pool–riffle scale. A bedform differencing technique was used to objectively quantify the longitudinal riverbed profile into four distinct pool–riffle units that were independent of discharge. The vertical location of thalweg points within these units was quantified with a riffle proximity index. Chinook salmon spawning areas were mapped and correlated with the pool–riffle units through the use of cross-tabulation tables. The results indicate that 84% of fall Chinook salmon spawning areas were correlated with riffles (χ² = 57.5, df = 3, p < 0.001), with 53% of those areas located on the upstream side of riffle crests. The majority of Snake River fall Chinook salmon spawning occurred at elevations greater than 80% of the difference in elevation between the nearest riffle crest and pool bottom. The analyses of bedform morphology will assist regional fish managers in quantifying existing and potential fall Chinook salmon spawning habitat, and will provide a quantitative framework for evaluating general ecological implications of channel morphology in large gravel-bed rivers.  相似文献   

The distribution of Potamothrix bavaricus (Oeschmann, 1913) (Oligochaeta) in anthropogenic freshwater habitats of an industrialised area (Upper Silesia, Poland)     

Mariola Krodkiewska   《Limnologica》2007,37(3):259-263

The studies have revealed that Potamothrix bavaricus (Oeschmann, 1913), generally rare in Poland, is a common species in the benthic oligochaete fauna of different anthropogenic freshwater habitats in a heavily industrialised area of Poland. It was often found in habitats with significant salinity, a high total hardness and a large content of nutrients. The evident resistance to various pollutants enables the settlement of P. bavaricus in such habitats, which are unsuitable for other oligochaete species.  相似文献