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.     

New devices for sediment and water sampling

Four new devices for sediment and water sampling are described, viz. (1) a large-volume water sampler; (2) a water sampler for thin water layers, (3) a bottom-water sampler, and (4) a gravity corer with exchangeable plastic tubes for use in a small boat.     

Two apparatuses for sampling benthic fauna in surf zones

A suction corer which has been used in the turbulent surf zone is described as well as a scoop dredge which proved effective in shallow water and on dry beaches. The former is also effective under calm conditions in water ranging from a few centimetres to depths in excess of 20 m. These apparatuses both allow the rapid collection of consistent quantitative samples which is of prime importance in the surf zone.     

溶解性石油烃在砂上的吸附和解吸研究

采用海滨浴场的沙为吸附剂,0号柴油为吸附质,研究了溶解性石油烃（DPHs）在砂上的吸附及解吸规律.研究发现,砂对DPHs的吸附和解吸均符合一级反应模式;油的解吸速率比吸附速率慢13倍,并且有约25%的油残存于砂上, 因而污染威胁会在较长时间内存在.砂对海水中DPHs的吸附等温线可以用Henry型等温式描述,温度越高,海水中的油向砂上转移的量越小.通过吸附热力学分析,得出该吸附属于物理吸附范畴.     

Particle size effect on the saturation of methane hydrate in sediments – Constrained from experimental results

Except for those occurring at seafloor, most of natural gas hydrate form in sediments and are subject to the influence of sediment. Among these factors, the particle size effect on hydrate saturation level in sediment have been studied with a series of silica sands with various sizes, and the results obtained clearly indicate that particle size does play an important role in affecting the saturation level of hydrate in sediments. The proton relaxation times of water confined in the same series of silica sands, which were determined with NMR measurement, show logarithmic relationship with particle size. By comprehensive consideration of the results of hydrate saturation and water proton relaxation times, the particle size effect observed is tentatively explained by the water availability for hydrate formation in sediments.     

Particle size effect on the saturation of methane hydrate in sediments – Constrained from experimental results

Except for those occurring at seafloor, most of natural gas hydrate form in sediments and are subject to the influence of sediment. Among these factors, the particle size effect on hydrate saturation level in sediment have been studied with a series of silica sands with various sizes, and the results obtained clearly indicate that particle size does play an important role in affecting the saturation level of hydrate in sediments. The proton relaxation times of water confined in the same series of silica sands, which were determined with NMR measurement, show logarithmic relationship with particle size. By comprehensive consideration of the results of hydrate saturation and water proton relaxation times, the particle size effect observed is tentatively explained by the water availability for hydrate formation in sediments.     

重力活塞取样器贯入深度研究

重力活塞取样器是一种重要的海底连续沉积物采集仪器,贯入深度和样品质量对海洋地质研究有着重要影响。通过对重力活塞取样器贯入过程建立能量守恒方程,得出贯入深度控制方程。已知取样器参数和土质类型条件,可计算取样管贯入深度,深度受取样器重量、体积、形状、取样管直径和沉积物类型等因素共同影响。已知取样器参数和贯入深度,可推测海底沉积物类型。     

Observation of corer penetration and sample entry during gravity coring

Gravity core samples provide the basic data source for a wide range of geological, geotechnical and geochemical studies. However, the length of the core recovered is often less than the penetration achieved by the corer, such cores being described as shortened. If the penetration of the corer has been measured, and it is assumed that no dropout of the core occurs as the barrel is withdrawn from the seabed, it is present practice to reconstruct in situ dimensions using an overall correction factor based on this penetration and the length of core recovered. However, measurements, reported here, have been made of corer penetration and sample entry and these show that the entry deficit (penetration minus sample entry) develops in some instances continuously, and in others intermittently. These results indicate that an overall correction factor is unlikely to be appropriate to any given section of the core.     

Effect of Moisture on Attraction Force in Beach Sand

Beach sands located above the sea water level exist in an unsaturated, rather than a fully saturated or dry state. Within the unsaturated zone, a steep excavated surface can be sustained for some unknown but finite time, and some slopes may remain stable for extended time periods due to capillary forces. These observations clearly indicate small but nonzero values for attraction strength (tensile strength and cohesion) in unsaturated beach sands, especially apparent but not confined to settings where there are low stress levels. Thus, experiments were carried out to quantify the magnitude of attraction strength in moist sands (D _r ?=?30%) and to examine the variation of these values as a function of moisture content and presence of a small amount of fines. Tensile strength, which is significantly different from zero, increases with increasing moisture content and fines. However, the influences of fines on the tensile strength are substantially dependent on the water content. Apparent cohesion strength is also identified in moist sands. A simple relationship between tensile strength and apparent cohesion is proposed using the obtained data. This study would help to further understand the phenomenon of stability of beach sands.     

Breaching-related turbidites in fluvial and estuarine channels: Examples from outcrop and core and implications to reservoir models

An understanding of the paleoenvironment and the main sedimentary processes behind preserved deposits is crucial to correctly interpret and represent lithofacies and facies associations in geomodels that are used in the hydrocarbon industry, particularly when a limited dataset of cores is available. In this paper a fairly common facies association is discussed containing massive sands - here defined as thick (>0.5 m) structureless sand beds devoid of primary sedimentary structures, or with some faint lamination - deposited by mass failures of channel banks in deep fluvial and estuarine channels. Amongst geologists it is generally accepted that liquefaction is the main trigger of large bank failures in sandy subaqueous slopes. However, evidence is mounting that for sand deposits a slow, retrogressive failure mechanism of a steep subaqueous slope, known as breaching, is the dominant process. A model of breaching-induced turbidity current erosion and sedimentation is presented that explains the presence of sheet-like massive sands and channel-like massive sands and the sedimentary structures of the related deposits. Sheet-like packages of spaced planar lamination that are found together with massive sand bodies in deposits of these environments are identified as proximal depositional elements of breach failure events. The model, acquired from sedimentary structures in deposits in the Eocene estuarine Vlierzele Sands, Belgium, is applied to outcrops of the Dinantian fluvial Fell Sandstone, England, and cores of the Tilje and Nansen fms (Lower Jurassic, Norwegian Continental Shelf). The possible breach failure origin of some other massive sands described in literature from various ancient shallow water environments is discussed. Breach failure generated massive sands possibly also form in deep marine settings. The potentially thick and homogeneous, well-sorted sand deposits bear good properties for hydrocarbon flow when found in such an environment. However, in case of deposition in an estuarine or fluvial channel, these sand bodies are spatially constricted and careful facies interpretation is key to identifying this. When constructing a static reservoir model, this needs to be considered both for in-place volume calculations as well as drainage strategies.     

A hydraulic hammer corer utilizing hydrostatic energy for hard seafloor sediment coring

The paper presents the design and preliminary test results of a corer used for hard seafloor sediments sampling.Generally the sediment cores are provided by either gravity-type coring or deep-ocean drilling for a range of studies.However,in consideration of the operability and available sample length in collecting hard sediments,these methods exhibit no advantages.In this paper,a new corer which can exploit both hydrostatic energy and gravity energy for hard sediments coring is presented.The hydrostatic energy is provided by pressure differential between ambient seawater pressure and air pressure in an empty cavity.During sampling process,the corer penetrates into the sediment like a gravity corer and then automatically shifts to the percussion mode.The experiments in the laboratory indicate that the corer can complete 40 cycles in the sea with a cycle time of 2.8 seconds in percussion mode and impact the sample tube with the velocity of 0.2 m/s during each cycle.Besides,its adjustable falling velocity can make the corer achieve the maximum efficiency in coring different sediments.     

新型全封闭刀口联合式管口封的设计及应用

重力活塞取样器是海洋地质调查不可缺少的调查设备，而管口封又是重力活塞取样器的重要部件。管口封的好坏不但影响到取样器的贯入深度和取芯丰，还影响到所取岩芯的质量．介绍了一种最近研制成功的新型全封闭刀口联合式管口封。海上实验在特定海区成功的获取了17．11m的长岩芯，取样率达91．3％，创造了我国海洋地质调查用重力活塞取样器获取岩心的最长记录。该设计已通过国家知识产权局批准授予实用新型专利。     

Benthic macroinvertebrates' vertical distribution in the Tagus estuary (Portugal): The influence of tidal cycle

In this work we evaluated the vertical distribution pattern of benthic infauna during the tidal cycle at one of the most important mudflats of the Tagus estuary. Samples were collected hourly during 24 h periods at four complete tidal cycles, using a corer specifically designed for the study purpose that allowed easy and effective separation of 15 different sediment layers. A particular case of general linear models, the hurdle model, was used to analyse data sets. We found that different species have different distribution and abundance according to sediment layers. Results showed that individuals tend to go deeper into sediment with a lower water column height and that these migrations are more visible during spring tides.     

Settling velocity of sediments at high concentrations

New data on the settling velocity of artificial sediments and natural sands at high concentrations are presented. The data are compared with a widely used semiempirical Richardson and Zaki equation (Trans. Inst. Chem. Eng. 32 (1954) 35), which gives an accurate measure of the reduction in velocity as a function of concentration and an experimentally determined empirical power n. Here, a simple method of determining n is presented using standard equations for the clear water settling velocity and the seepage flow within fixed sediment beds. The resulting values for n are compared against values derived from new and existing laboratory data for beach and filter sands. For sands, the appropriate values of n are found to differ significantly from those suggested by Richardson and Zaki for spheres, and are typically larger, corresponding to a greater reduction in settling velocity at high concentrations. For fine and medium sands at concentrations of order 0.4, the hindered settling velocity reduces to about 70% of that expected using values of n derived for spheres. At concentrations of order 0.15, the hindered settling velocity reduces to less than half of the settling velocity in clear water. These reduced settling velocities have important implications for sediment transport modelling close to, and within, sheet flow layers and in the swash zone.     

Effect of Moisture on Attraction Force in Beach Sand

Beach sands located above the sea water level exist in an unsaturated, rather than a fully saturated or dry state. Within the unsaturated zone, a steep excavated surface can be sustained for some unknown but finite time, and some slopes may remain stable for extended time periods due to capillary forces. These observations clearly indicate small but nonzero values for attraction strength (tensile strength and cohesion) in unsaturated beach sands, especially apparent but not confined to settings where there are low stress levels. Thus, experiments were carried out to quantify the magnitude of attraction strength in moist sands (D_r = 30%) and to examine the variation of these values as a function of moisture content and presence of a small amount of fines. Tensile strength, which is significantly different from zero, increases with increasing moisture content and fines. However, the influences of fines on the tensile strength are substantially dependent on the water content. Apparent cohesion strength is also identified in moist sands. A simple relationship between tensile strength and apparent cohesion is proposed using the obtained data. This study would help to further understand the phenomenon of stability of beach sands.     

茅家港突堤工程建造前后滩面沉积物粒度变化及其原因分析

为研究茅家港附近岸滩面沉积物粒度的变化,在对茅家港近岸滩面沉积物粒度研究的基础上,于1993年9月、1994年1月进行了两次野外采样调查,在室内进行了粒度测量.通过测得的一手资料,绘出不同时间的粒度空间分布图和不同位置的剖面图,对茅家港滩面沉积物粒度的空间分布、季节变化及其反映的水动力变化和原因进行了分析研究,论述了茅家港工程建造前后滩面沉积物粒度变化的规律和原因.研究发现：工程建成后,因突堤内水动力减弱,突堤内滩面沉积物的粒度变细,且比突堤外的细,航道不再淤积,使航道的位置和深度稳定,有效地保护了航道;随着离岸距离增加,因水动力逐渐增强,滩面沉积物的粒径逐渐变粗;因冬季的水动力比夏季的水动力强,冬季滩面沉积物粒度比夏季粗.     

Benthic photosynthesis in submerged Wadden Sea intertidal flats

In this study we compare benthic photosynthesis during inundation in coarse sand, fine sand, and mixed sediment (sand/mud) intertidal flats in the German Wadden Sea. In situ determinations of oxygen-, DIC- and nutrient fluxes in stirred benthic chamber incubations were combined with measurements of sedimentary chlorophyll, incident light intensity at the sediment surface and scalar irradiance within the sediment. During submergence, microphytobenthos was light limited at all study sites as indicated by rapid response of gross photosynthesis to increasing incident light at the sea floor. However, depth integrated scalar irradiance was 2 to 3 times higher in the sands than in the mud. Consequently, gross photosynthesis in the net autotrophic fine sand and coarse sand flats during inundation was on average 4 and 11 times higher than in the net heterotrophic mud flat, despite higher total chlorophyll concentration in mud. Benthic photosynthesis may be enhanced in intertidal sands during inundation due to: (1) higher light availability to the microphytobenthos in the sands compared to muds, (2) more efficient transport of photosynthesis-limiting solutes to the microalgae with pore water flows in the permeable sands, and (3) more active metabolic state and different life strategies of microphytobenthos inhabiting sands.     

Marine Sand Resources Offshore Israel

Abstract

The continental margin of northern Sinai and Israel, up to Haifa Bay, is the northeastern limb of the submarine Nile Delta Cone. It is made up predominantly of clastics from the Nile and its predecessors. The continental shelf and coastal plain of Israel are built of a series of shore-parallel ridges composed of carbonate-cemented quartz sandstone (locally named kurkar), a lithification product of windblown sands that were piled up into dunes during the Pleistocene. The drop in global sea level and regression during the last glacial period exposed the continental shelf to subaerial erosion and created a widespread regional erosional unconformity which is expressed as a prominent seismic reflector at the top of the kurkar layers. The subsequent Holocene transgression abraded much of the westernmost kurkar ridges, drowned their cores, and covered the previous lowstand deposits with marine sands, which were in turn covered by a sequence of sub-Recent clayey silts.

The Mediterranean coasts of Sinai and Israel are part of the Nile littoral cell. Since the building of the Aswan dams the sand supplied to Israel's coastal system is derived mainly from erosion of the Nile Delta and from sands offshore Egypt that are stirred up by storm waves. The sands are transported by longshore and offshore currents along the coasts of northern Sinai and Israel. Their volume gradually declines northward with distance from their Nile source. The longshore transport terminates in Haifa Bay where some sand is trapped, and the test escapes to deeper water by bottom currents and through submarine canyons, thus denying Nile-derived sand supply to the 40-km-long Akko-Rosh Haniqra shelf.

The sand balance along Israel's coastal zone is a product of natural processes and human intervention. Losses due to the outgoing longshore transport, seaward escape, and landward wind transport exceed the natural gains from the incoming longshore transport and the abrasion of the coastal cliffs. The deficit is aggravated by the construction of (1) seaward-projecting structures that trap sands on the upstream side and (2) offshore detached breakwaters that trap sands between themselves and the coast. The negative sand balance is manifested by the removal of sand from the seabed and the consequent exposure of archaeological remains that were hitherto protected by it.

The sediments that escape seaward from the longshore transport system form a 2.5- to 4-km-wide sandy apron adjacent to the shore that extends to where the water is 30–40 m deep. The apron's slope (0.5–0.8°) is steeper than the theoretical equilibrium slope for the median grain-size diameter in this zone (0.1–0.3 mm).

The beach sands and the apron's surficial sands are well sorted. Their grain size decreases with distance from shore, from 0.2–0.3 mm nearshore to 0.11–0.16 mm by the drowned ridge. The coarse-grained fraction consists of skeletal debris (commonly 5–12% carbonate matter) and wave-milled kurkar grains (locally named zifzif). In deeper water, the basal sands underlying the fine-grained sediment cover consist of 1- to 30-cm layers whose composition ranges from silty sands to various types of sands (fine, medium, coarse, and gravelly) to zifzif. For the most part, they contain large amounts of skeletal debris (20–60%) and small fragments of kurkar.

Two types of kurkar rock were encountered offshore: a well-sorted, fine- to medium-grained (0.074–0.300 mm) lithified dune sand with variable amounts of carbonate cement, ranging from hard rock of low permeability to loose sand; and a porous sandstone made up predominantly of algal grains and skeletal debris (calcarenite).     

Estimation of Residual Undrained Shear Strength from Gravity Corer Penetration Data

Residual undrained shear strength, s _{u_res} , is an important parameter for analyzing the response of structures buried within potentially unstable soil mass. A framework for estimating s _{u_res} of fine grained sediments from gravity corer penetration has been developed considering viscous drag during free fall of the corer through seawater and cohesive energy loss during sediment penetration. The procedure was used to estimate s _{u_res} using data from a submarine geotechnical investigation in western Canada. Comparison of the results with alternative estimates of s _{u_res} from miniature torvane tests on the gravity core samples and CPTs performed nearby reveals a reasonable agreement.     

An improved core catcher for the Kiel box corer (“Kastenlot”)

The optimum efficiency of the Kiel box corer (“Kastenlot”) is dependent upon certain mechanical properties of the sediments. To avoid this limitation, a new core catcher was constructed and has been tested for several years in both shallow and deep-water sediments. The essential part of this catcher is a reinforced canvas curtain which is pulled slantwise through the core before the corer is pulled out of the sediment.