Sound velocity and related properties of seafloor sediments in the Bering Sea and Chukchi Sea

The Bering Sea shelf and Chukchi Sea shelf are believed to hold enormous oil and gas reserves which have attracted a lot of geophysical surveys. For the interpretation of acoustic geophysical survey results, sediment sound velocity is one of the main parameters. On seven sediment cores collected from the Bering Sea and Chukchi Sea during the 5th Chinese National Arctic Research Expedition, sound velocity measurements were made at 35, 50, 100, 135, 150, 174, 200, and 250 k Hz using eight separate pairs of ultrasonic transducers. The measured sound velocities range from 1 425.1 m/s to 1 606.4 m/s and are dispersive with the degrees of dispersion from 2.2% to 4.0% over a frequency range of 35–250 k Hz. After the sound velocity measurements, the measurements of selected geotechnical properties and the Scanning Electron Microscopic observation of microstructure were also made on the sediment cores. The results show that the seafloor sediments are composed of silty sand, sandy silt, coarse silt, clayey silt, sand-silt-clay and silty clay. Aggregate and diatom debris is found in the seafloor sediments. Through comparative analysis of microphotographs and geotechnical properties, it is assumed that the large pore spaces between aggregates and the intraparticulate porosity of diatom debris increase the porosity of the seafloor sediments, and affect other geotechnical properties. The correlation analysis of sound velocity and geotechnical properties shows that the correlation of sound velocity with porosity and wet bulk density is extreme significant, while the correlation of sound velocity with clay content, mean grain size and organic content is not significant. The regression equations between porosity, wet bulk density and sound velocity based on best-fit polynomial are given.     

Physical properties of calcareous ooze: Control by dissolution at depth

Eighteen box cores of pelagic calcareous ooze from the Ontong Java Plateau in the western equatorial Pacific were subsampled and analyzed for the following physical properties: grain size, porosity, saturated density, mean grain density, compressional sound velocity and shear strength. In addition, weight percent CaCO₃ was determined, and micropaleontological analyses of the Foraminifera were performed to determine preservation and sedimentation rates. Mean grain size of the sediments decreases at deeper depositional sites, primarily because of dissolution and fragmentation of calcareous microfossils. This, in turn, results in the sediments in deeper water having lower sound velocities and less shear strength. The physical properties of calcareous ooze are not significantly affected by any reprecipitation or incipient cementation of calcite that may occur soon after deposition.     

Tracking historical storm records from high-barrier lagoon deposits on the southeastern coast of Hainan Island,China

The relationship between storm activity and global warming remains uncertain. To better understand storm–climate relationships, coastal lagoon deposits are increasingly being investigated because they could provide high-resolution storm records long enough to cover past climate changes. However, site-specific sediment dynamics and high barriers may bias storm reconstructions. Here, we aimed to investigate these factors through the reconstruction of five distinct storm records (XCL-01, XC-03, XC-06, XC-07, XC-08) from different water depths in a lagoon with a high barrier (i.e., Xincun Lagoon of Hainan Island). Sediment cores were characterized using high-resolution grain size and XRF measurements, to identify storm events. These data were coupled with a numerical simulation to obtain bed shear stress data with high-spatial resolution to better understand storm-induced sediment transport mechanisms. 210Pb dating and Pb pollution chronostratigraphic markers indicated that the chronology of the storm deposit sequences of the cores span the period between 117 a and 348 a. The grain size and XRF results indicated numerous, highly variable and short-duration fluctuations, suggesting that storm-induced coarse-grained sediments were deposited at these core sites. The inconsistent storm events recorded in these cores suggest that these sites have different preservation potentials for storm deposits. However, the consistence between storm sediment records and historical documents for Core XCL-01 indicates that high-barrier lagoons could provide long-term storm event records with high preservation potential.     

南沙海域深水区表层沉积物声速与孔隙度相关关系

采用同轴差距测量法对南沙海域海底沉积物取样进行甲板现场声学测量,并计算了声速,结合沉积物取样分析获得的孔隙度,研究了海底表层100 cm沉积物的声速和孔隙度之间的相互关系,分析获得了孔隙度与海底沉积物声速关系的经验公式,结果表明此海域沉积物声速的临界孔隙度为67.80%。将此公式与国内外其他学者建立的经验公式进行了对比,分析发现各预测方程之间存在着差异,说明不同海域的沉积物声学特性具有差异性,经验公式具有区域性,同时分析了其他影响声速的因素。此项工作对于建立和研究南海声场环境具有重要意义。     

High‐frequency subbottom reflection types and lithologic and physical properties of sediments

Abstract

Eight types of reflections are interpreted from 3,800 km of 3.5 kHz profiles taken over a 25,000 km² area of the upper continental slope and shelf in the northeastern Gulf of Mexico off Panama City, Florida. The corresponding sediments in five of the reflection types were sampled in 77 piston cores from which data were obtained on in situ acoustic velocities (V), bulk densities (gr), sediment texture (mean grain size = Mz), CaCO₃ content (C), sedimentary structures, and gross sediment composition. A distinct bottom echo with numerous subbottom reflectors (Type I) is observed in deeper areas where terrigenous clay or lutite (Mgi = 9.9 to, gr = 1.4 g/cc, porosity (P) = 74 percent, C = 28 percent, and V (upper 2 m) = 1,435 m/s) predominates. Type I reflection grades upslope into Type IV, which shows a distinct bottom echo with fewer subbottom reflectors, and the corresponding sediment is a foraminiferal silty clay (mz = 9.4 to, gr = 1.43 g/cc, P = 73 percent, V = 1,447 m/s, and C = 37 percent). The uppermost slope gives indistinct, semiprolonged bottom echoes with faint subbottoms (Type VI) where calcareous silt (Mz = 6.6 to, gr = 1.57 g/cc, P = 65 percent, C = 70 percent, and V = 1,482 m/s) is the main sediment type. The shelf sediments (gr = 1.66 g/cc, P = 58 percent, V = sl1,530 m/ s), varying from coarse silt (Mz = 5.3 to) to very coarse sand (Mz = ‐0.3 to) and 25 to 100 percent carbonate, show indistinct, semiprolonged bottom echoes with intermittent or mushy subbottoms (Type VII). Prolonged echoes with no subbottoms (Type VIII) are observed in areas where algal sands of variable grain size (Mz ‐ ‐0.9 to 2.7 to, gr = 1.66 g/cc, P = 59 percent, V = 1,530 to 1,690 m/s) occur.

The major trends in reflection types (loss in depth of penetration, loss in number of reflectors, and prolongation of initial bottom reflections) follow gradients of sedimentary and physical properties of the sediments, which are increases in mean grain size, bulk density, in situ acoustic velocity, CaCO₃ content, and decrease in porosity. Increases in the reflection coefficient and attenuation of the sound energy in the shelf sediments are probably important factors in the observed decrease in the depth of penetration of the sound energy in the shelf sediments.     

超声无损检测技术在海底沉积物调查中的应用

论文就超声波无损检测技术在海底沉积物声学特性测量上的应用,介绍了其所需的必要设备、样品采集和测量基本原理。探讨了沉积物超声无损测量的资料处理与分析方法及其内容,主要包括声速、声衰减、声阻抗和声速比等声学特性计算;声速与孔隙度、平均粒径和粘土含量等物理力学参数的统计相关性研究。     

Scale-dependent physical and geoacoustic property variability of shallow-water carbonate sediments from the Dry Tortugas, Florida

 Spatial variability of shallow-water carbonate sediments near Dry Tortugas, Florida, is scale-dependent. Wet bulk density, grain density, porosity, compressional wave velocity, and grain size variability generally increase down to 2.4 m vertically and 850 m laterally. Grain size is most variable, followed by porosity, wet bulk density, compressional wave velocity, and grain density bothvertically and laterally, consistent with Walther’s Law. Variability was empirically modeled by linear regression analysis to predict variability based on scale, characterize sediment property variability, and quantify sedimentisotropy.     

Variation of temperature-dependent sound velocity in unconsolidated marine sediments: Laboratory measurements

Laboratory measurements of sound velocity in unconsolidated marine sediment were performed to establish specific correction curves between temperature and sound velocity. Cores from the Hupo Basin and the southern sea of Geumo Island were cooled and sound velocity was measured while gradually increasing temperature (from 3 to 30°C). Sediment textural and physical properties (porosity, water content, and bulk density) were measured at the same depth. Sound velocity increases with temperature for clay, mud, silt, and sand sediment, resulting in values of approximately 2.65, 2.72, 2.78, and 3.10?m/s/°C, respectively. These results are similar to those of previous studies, and differences are likely due to density, porosity, and clay contents of the sediment. Using these results, we present correction curves for sound velocity temperature dependence for each sediment texture, which can be used to correct from laboratory to in situ values to develop accurate geoacoustic model.     

渤海湾西岸潮间带沉积物粒度分布特征

根据2003年12月在渤海湾西岸海河口南缘至歧口间岸段采集的4个柱状沉积物样品和6个表层样品的粒度分析结果,探讨了渤海湾西岸潮间带的粒度分布特征和沉积作用。结果表明,由北向南,表层沉积物逐渐变细,分选性变差。海河口南缘至独流减河之间的表层沉积物为分选良好的细砂,至歧口附近变为粉砂质粘土。在垂直方向上,表层以下一定深度内沉积物的平均粒径都存在一均匀层,层内沉积物为分选良好的细砂,此深度以下沉积物中的粘土含量增加。说明由于60年代之后的自然变化和人类活动,入海泥沙量减少,改变了潮间带沉积物原有的输沙与海滩发育模式,导致独流减河以北的砂质沉积物出现粗化现象。     

Correlations between sound velocity and related properties of glacio-marine sediments: Barents sea

Statistical analysis of laboratory-measured compressional wave (sound) velocity, porosity, wet bulk density, and selected textural parameters of surface sediments from the Barents Sea reveals that clay content and mean grain size are the best indices to sound velocity. These parameters are followed closely by porosity and wet bulk density, while sand content provides the weakest index. Although Barents Sea surface sediments are characterized by fairly high variability, the results of the present study are in general agreement with studies of similar sediment types in other continental shelf environments.     

含砂量变化影响海底沉积物压缩波速度的分析研究

本文通过对南海海底沉积物样品的声学物理参数和沉积粒度特征统计分析,发现了高、低含砂量沉积物的声学物理特征存在明显差异,建立了海底沉积物的含砂量与压缩波速度、孔隙度、含水量和密度等经验公式,分析了含砂量变化与沉积物的体积压缩模量和密度变化的关系,从声速理论基础上阐明了含砂量变化引起沉积物压缩波速度变化的内在原因是含砂量变化引起了体积压缩模量和密度发生了变化,说明了含砂量增大引起沉积物压缩波速度增大的内在原因是含砂量增大引起了体积压缩模量变化量大于密度变化量,从而在数据统计和理论分析结合基础上,论证了含砂量是影响海底沉积物压缩波速度的重要因素之一。这一研究对声学方法反演海底沉积物粒度参数和沉积物类型、地声参数转换模型的建立,以及对水声反演海底和海底资源勘探等方面都具有重要理论意义和应用价值。     

南海北部大陆架海底沉积物物理性质研究

用物理(声学的、工程地质的、扫描电子显微镜)等技术方法,综合分析了沉积物结构特征和工程力学性质,研究了颗粒接触、堆垒、孔隙等现象与物理性质之间的关系,得出了沉积物声学物理参数和应力一应变性质之间的关系。结果表明,南海北部大陆架海底沉积物有6种结构类型,其中混合接触结构类型的沉积物具有较高的抗压强度和声速,浅层海底存在着高、低声速分层的中尺度结构。     

Relationships between the sound speed ratio and physical properties of surface sediments in the South Yellow Sea

Building empirical equations is an effective way to link the acoustic and physical properties of sediments. These equations play an important role in the prediction of sediments sound speeds required in underwater acoustics.Although many empirical equations coupling acoustic and physical properties have been developed over the past few decades, further confirmation of their applicability by obtaining large amounts of data, especially for equations based on in situ acoustic measurement techniques, is required. A sediment acoustic survey in the South Yellow Sea from 2009 to 2010 revealed statistical relationships between the in situ sound speed and sediment physical properties. To improve the comparability of these relationships with existing empirical equations, the present study calculated the ratio of the in situ sediment sound speed to the bottom seawater sound speed, and established the relationships between the sound speed ratio and the mean grain size, density and porosity of the sediment. The sound speed of seawater at in situ measurement stations was calculated using a perennially averaged seawater sound speed map by an interpolation method. Moreover, empirical relations between the index of impedance and the sound speed and the physical properties were established. The results confirmed that the existing empirical equations between the in situ sound speed ratio and the density and porosity have general suitability for application. This study also considered that a multiple-parameter equation coupling the sound speed ratio to both the porosity and the mean grain size may be more useful for predicting the sound speed than an equation coupling the sound speed ratio to the mean grain size.     

南海南部海域岛礁区海底珊瑚砂声速影响因素的初步研究

通过对南海南部海域岛礁区科学考察数据资料的分析研究,得出了岛礁区海底珊瑚砂的纵波声速随孔隙度、含水量增大而减小,以及声速随中值粒径、湿密度增大而增大的统计结果,并在Biot和Wyllie的松散饱和水沉积物声速理论公式与模型基础上,解释了物理力学因素对海底珊瑚砂声速的影响机制,阐明了固相因素和液相因素的强弱变化引起声速增大或减小的理论原因,分析了各种声速经验公式在海底珊瑚砂声速估算上的精度差异,得出了有必要建立包括海底珊瑚砂在内的单一类型声速经验公式的初步结论。     

Discrimination of Seafloor Sediment Properties by VWA

Analytical results of sound velocity and spectrum for seafloor sediment ore obtained by VWA (velocity-wave-amplitude) discrimination technique. Based on velocity-wave-amplitude, an understanding is gained of the physical condition and structural characteristics of seafloor sediment, which is combined with other geological information of the sedimentary layer to synthetically discriminate the properties of seafloor sediment. Experimental results show that, by using the relationship between sound velocity, wave form envelope, amplitude shape and size, and such parameters as sedimentary structure, microstructure, bedding, grain composition, mineral composition, and physical-mechanics, etc., the basic properties of the shallow surface seafloor sediment in the experimental sea area can be discriminated and the burial depth of traces of ancient marine transgression and regression events in the borehole cores of seafloor sediment can be divided, thus making an attempt of and contribution to the practice of acoustically remote-sensing and telemetering seafloor sediment.     

Discrimination of Seafloor Sediment Properties by VWA

Analytical results of sound velocity and spectrum for seafloor sediment ore obtained by VWA (velocity-wave-amplitude) discrimination technique. Based on velocity-wave-amplitude, an understanding is gained of the physical condition and structural characteristics of seafloor sediment, which is combined with other geological information of the sedimentary layer to synthetically discriminate the properties of seafloor sediment. Experimental results show that, by using the relationship between sound velocity, wave form envelope, amplitude shape and size, and such parameters as sedimentary structure, microstructure, bedding, grain composition, mineral composition, and physical-mechanics, etc., the basic properties of the shallow surface seafloor sediment in the experimental sea area can be discriminated and the burial depth of traces of ancient marine transgression and regression events in the borehole cores of seafloor sediment can be divided, thus making an attempt of and contribution to the practice of acoustically remote-sensing and telemetering seafloor sediment.     

Grain size and depositional environment as predictors of permeability in coastal marine sands

More than half of the surface sediments covering the continental shelves are sandy, which may permit substantial sub-seafloor pore water advection. Knowledge of sediment permeability is required for quantifying advection and associated solute transport, but studies of marine sediments typically report grain size analyses rather than permeability. Here data from 23 studies were examined to determine the range in permeabilities reported for sublittoral marine sands and to assess the utility of permeability–grain size relationships in this setting. In the resulting database, the permeability of small (∼30 cm) undisturbed cores collected from the sea floor all fell between 2 × 10⁻¹² and 4 × 10⁻¹⁰ m², a range where advective transport induced by wave and current action should be pervasive. The range in grain size was very similar for near-shore (<10 m water depth) and continental shelf samples (>10 m water depth), but the permeability of the continental shelf samples was consistently lower for the same median grain size. Empirical permeability–grain size relationships generated a poor fit (r² = 0.35) for the aggregate data, but separate relationships for near-shore and continental shelf samples were significantly better, r² = 0.66 and 0.77, respectively. Permeability–grain size relationships thus may be useful for sublittoral sands, but a larger database needs to be accumulated before reliable fit parameters and variability can be predicted. Thus it is recommended that permeability be routinely determined when characterizing sedimentological properties of marine sand deposits. Concurrent determinations of sediment bulk density and porosity may further improve estimates of permeability.     

用声速Cp和Cs判别沉积物性质

本文应用声速Cp和Cs对沉积物特性进行判别研究，给出了理论根据和实践的结果，表明高声连（Cp＞Co）的沉积物大多数为粗颗粒、低含水量和孔隙度；低声连（Cp＜Co）的沉积物大多数为细颗粒、高含水量和孔隙度。岩心声速垂向变化亦可以结合沉积相和环境因素判别出古海洋和地质事件。     

Analysis of the influences of physical parameters on sediment sound speed

Based on the core samples collected in different geological tectonic units in the southern South China Sea, the double parameter equations between sediment sound speed and physical parameters were developed. According to the double parameter equations, the influences of physical parameters (porosity, mean grain size, wet bulk density, and clay content) on sediment sound speed were analyzed. To analyze the sensitivity of each parameter in the double parameter equations, the error norm method was introduced. The most influencing physical parameters with relative order were analyzed using the error norm method. These results show that porosity has a major influence on the sound speed, and the most influential physical parameters on sound speed are as follows: porosity > wet bulk density > clay content > mean grain size.