Silty Fine Sand Research Articles

Flandrian relative sea level changes in the Ythan Valley, Northeast Scotland

AbstractRelict Flandrian estuarine deposits in the Ythan valley are confined to an area in the lower valley around the present estuary. They rest upon a discontinuous layer of peat over an irregular surface of sand and gravel, and consist for the most part of a grey silty clay, or carse deposit, which forms terraces or small areas of carseland. At the seaward end of the estuary the grey silty clay contains a layer of grey, micaceous, silty fine sand, which tapers into the basal peat, whilst in places the surface of the grey silty clay is covered by peat and/or blown sand. The vegetational context and age of these deposits have been determined at Waterside, near the mouth of the present estuary. Here, the grey silty clay accumulated as the result of a marine transgression which began in the early Flandrian, and culminated between about 6189·95 and some time prior to 4000·80 radiocarbon years B.P. The carseland surface produced by this phase of accumulation is the highest Flandrian estuarine surface in the valley, at about 4·5 m O.D., and is correlated with the Main Postglacial Shoreline elsewhere in eastern Scotland. Withdrawal of the sea from this level may have been interrupted by the formation of a lower carseland surface before present levels were reached, though this is far from certain. The grey, micaceous, silty fine sand layer is dated at approximately 6850·140 radiocarbon years B.P., and is correlated with similar layers that may have been deposited following a storm surge. The paper concludes with some considerations on the age and distribution of the Main Postglacial Shoreline in eastern Scotland.

The Caesar's Camp Gravel—an early Pleistocene fluvial periglacial deposit in southern England

New information from shallow boreholes and from recent exposures has allowed reinterpretation of the age and origin of the Caesar's Camp Gravel, near Aldershot. The deposit comprises two main sedimentary facies: a cobble-gravel facies composed principally of nodular flints, and a sand-clay facies occurring as thinner interbedded units. The composition of the gravel and its heavy mineral content are distinct from those of the gravels seen on Netley Heath with which it was once correlated. The deposit is thought to represent fluvial periglacial aggradation related to an early Pleistocene cold phase, pre-dating the main terrace sequence in the area and post-dating the nearby high-level marine deposits of late Pliocence/early Pleistocene age. A well defined palaeosol occurs in the upper part of the gravelly deposits and is overlain by silty fine sands presumed to be of loessic origin.

The benthic macroinvertebrates of the Block Island Sound

The benthic invertebrates of Block Island Sound have not been adequately studied, in contrast to other adjacent southern New England sounds. This study examines the species composition, abundance and biomass of benthic macrofaunal invertebrates at nine locations within Block Island Sound. The sites sampled, represent a wide range of subtidal habitats within the Sound, and were visited in February and September. Some 224 species were identified, of which almost half (104) were polychaetes. The benthic assemblages at most stations were dominated numerically by tube dwelling, surface detritus or suspension feeding amphipods, e.g. Ampelisca agassizi and A. vadorum, as well as the protobranch bivalve, Nucula proxima. This dominant Ampelisca-Nucula assemblage was associated with silty fine sand sediments. The average macrofaunal biomass for all stations was 158 g (wet weight) m −2, two thirds the average benthic biomass of Georges Bank, an important fishery area. Based on the examination of the records of earlier surveys in Block Island Sound, there is evidence that this silty-sand, ampeliscid-dominated assemblage has persisted since at least the mid-1940s.

Discussion on ‘Large landslides in London Clay at Herne Bay, Kent’ by E.N. Bromhead

M. D unbaven writes: The geometrical forms of the slips described in the paper bear many similarities to failures in mining waste dumps reported by Blight (1969). The important feature of the slides is the coincidence of the lower parts of the slip surfaces with a weaker layer of soil; in this case the Oldhaven Beds of silty fine sand. The example chosen for discussion is the Mirmar landslide where the weak layer forms the base of a simple slope. A careful study of some similar landslides has shown that the graben block and the en masse movement of the lower slope are common characteristics. Recent research at James Cook University has reproduced such failures in a small physical model. A slope made from a well graded cohesionless silica sand was built over a layer of bentonite saturated to give low yield strength. Overall dimensions of the slope were: height 400 mm, width 750 mm, base length 1100 mm. The kinematics of the failure have been determined by photography which revealed basically a movement of two ‘rigid’ wedges. A computer study based on a wedge analysis was conducted using both force balance and energy balance equations, with the condition that one slip-plane pass through the base material. The situation which created the highest force or energy imbalance was calculated by numerical optimization. For both methods, the predicted slip-planes closely followed those observed in the laboratory, however, different answers would be expected for a material which exhibited significant dilatancy.

A herringbone bedform pattern of possible Taylor-Görtler type flow origin seen in sonographs

Side-scan sonar records collected in a shallow arctic lagoon (2–2.5 m depth) reveal a herringbone pattern of current-aligned linear reflectors with branching diagonals. The major longitudinal reflectors have no detectable relief (<20 cm), are spaced 5–10 m apart, and may represent current-aligned helical cell boundaries preserved in the silty fine sand of the lagoon floor. The pattern suggests a three-dimensional flow regime of the Taylor-Görtler type.

Fabric-Property Relationships in fine Granular Materials

AbstractIn this investigation fabric-property relationships were studied in a silty fine sand sized crushed basalt—an artificial ‘soil’ that has previously been used to simulate lunar soil. The fabric was characterized by measuring preferred orientations of grains, and pore size distribution was determined by mercury intrusion porosimetry. When deposited by pouring, the grains acquired strong preferred orientations in the horizontal direction and formed pores between 1 and 30 μm dia. Densification by static or dynamic compaction resulted in near random grain arrangement and pore sizes between 0·1 and 10 μm dia.Strength in direct shear and one-dimensional compressibility with the associated lateral stresses were measured. The strength was up to 30 per cent higher when the sample was sheared normal to the preferred orientation of grains than when the shearing was parallel to the orientation direction. This is to be expected, as shearing across the preferentially oriented grains should involve breakage or reorientation of many grains. At a given initial void ratio the compressibility of statically compacted specimens was larger (up to 30 per cent higher axial strain) than that of dynamically compacted specimens at very low stresses. At higher stresses both samples exhibited equal compressibility, suggesting that the grains become more randomly arranged at low void ratios (comparing samples of equal initial void ratios).

Usable Beach-to-Offshore Model for Tide-Dominated Shoreline; Sapelo Island, Georgia: ABSTRACT

This study represents a cooperative effort by sedimentologists, zoologists, paleontologists, and mineralogists to determine what facies characteristics exist in a present-day sedimentary record. The results show that geologically recognizable subfacies can be established by primary physical and biogenic sedimentary structures. Beach zone: The rather low energy of the Sapelo Island shoreline and the low dip of the beach surface, combined with a tidal range of 2.1 m, result in characteristic morphology, grain-size distribution, and types of sedimentary structures. Most beach features are controlled by wave activity, and obvious bioturbation is not abundant in the beach zone. The backshore and upper foreshore contain few species and few individuals. The lower foreshore has few species but numerous individuals. Nearshore zone: At 100 m offshore (water depth, 1.5 m) there is a marked increase in the fine fraction; at the same place, biogenic sedimentary structures increase. Dominant sedimentary structures are ripple-laminated sand. Species of infaunal organisms are more abundant than in the beach but few individuals are present. At a distance of 2,500 m offshore (water depth, 2.7 m) biogenic sedimentary structures become the dominant characteristic of the fine silty sand. The unreworked part of the substrate is characterized by parallel to subparallel laminated sand. These beds, referred to as laminated-to-burrowed are separated by erosional bedding planes. Farther seaward at a distance of 5,500 m (water depth, 6 m) the substrate is almost completely reworked due to increased biogenic activity. This is the most densely populated zone in the beach-to-offshore sequence. Offshore zone: At a distance of 10 km seaward (water depth, 10.5 m) the substrate consists of clean, medium- to coarse-grained sands. Megaripples are the dominant physical sedimentary structure in the offshore area and few species and few individuals are found, but biogenic reworking by heart urchins is abundant. End_of_Article - Last_Page 629------------

Field Study of a Cellular Bulkhead

A detailed experimental analysis is presented of the structural behavior of a segment of a steel sheet pile cellular bulkhead in Long Beach Harbor, California. The bulkhead consists of 62-ft diam circular cells with connecting arcs and retains a 55-ft height of fine silty sand hydraulic fill. Measurements were made, beginning during construction and extending more than 4 yr, of sheet pile strains and deflections, pore water pressures, and soil and bulkhead movements.