Distribution Of Surficial Sediments Research Articles

Distribution and composition of the surficial sediments of Georgian Bay and North Channel

Distribution and composition of the surficial sediments of Georgian Bay and North Channel

Sediment transport in the Bristol Channel: A review

Investigations into the physical oceanographic characteristics of the Bristol Channel and Severn Estuary are reviewed; these include the general pattern of water movement and the influence of high freshwater discharges on the salinity distribution. Various approaches to the problem of defining sediment transport paths in the macrotidal estuarine system, for fine grained and coarse grained material, are summarised. Transport patterns are examined, for example, through: the distribution of surficial sediments and their associated bedforms; seabed drifter studies; the analysis of tidal current and wave data, separately and in combination, because of their influence on bedload transport paths; satellite imagery, within the visible part of the spectrum; and on the basis of output from depth-averaged numerical models. Comparison between the interpretations shows that there are discrepancies and contradictions in the derived sediment transport paths. In particular, it is difficult to explain the up-channel movement of fine grained material against a background of inferred offshore movement, shown by the orientation of sandwaves and the direction of movement of the surface waters. An early model to overcome this contradiction incorporated ‘two-way differential transport’ throughout the water column. Localised contradictions in the transport paths for sand and ‘fine sediment’ occur in the inner part of the Bristol Channel. The most recent conjectural models for sediment movement incorporate an ebb- dominated zone along the central axis of the Channel, together with flood-dominated coastal zones. This lateral variation in transport paths, across the Channel, constrasts with the earlier proposition for vertical differentiation; it is suggested by seabed drifter recovery patterns and confirmed by the output from one of the numerical models. Transport towards the flood-dominated zones at the boundaries is enhanced under the superimposed influence of waves, which is demonstrated through the use of sediment transport formulae and sand tracer experiments. Although the annual contribution of the rivers to the overall sediment budget is shown to be small, the time of retention of waters and sediment within the system could result in fluviatile sediment inputs being retained for tens of years. In an attempt to extrapolate observations of transport processes into the ancient record, a preliminary facies model for the macrotidal Bristol Channel is presented. The model shows the availability of sand increasing in an onshore direction; progressing in this direction, the facies pass from scoured bedrock and lag deposits, through cross bedded megaripple foresets and the topset planar bedding of intertidal flats, to Holocene fill and supratidal deposits.

Sedimentation in an intermountain lake, Lake Okotanpe, Hokkaido. I. Sedimentary processes derived from the grain size distribution of surficial sediments.

In Lake Okotanpe, Hokkaido, surficial sediments were picked up at 59 points from the lake bottom, lake shore, and river bed and -bank. All the samples were analyzed for grain size and ignition loss. From the analytical results, the following conclusions can be drawn :1. The lake bottom sediments, as a whole, consist of more than 80% silt and clay in weight. Excessive sedimentation in the lake could take place during the torrential floods of influent rivers, carrying a large washload of much silt and clay.2. The lake sedimentary processes are represented by transportation and deposition of the fine suspended grains due to river induced turbidity currents and sediment dispersion.3. The turbidity currents have a hydrodynamic feature of being controlled considerably by the topography of the lake basin. Therefore, the 'threshold' and the 'constricted' wall characteristic of the basin shape of Lake Okotanpe, can induce the convergence and subsequent lateral spreading of turbidity currents. Consequently, they cause sediments to have a more fine-textured, poorly sorted and almost log-normal grain size distribution. 4. The flowing condition of sediment dispersion is controlled by convective currents induced in the inflow-outflow system of the lake. Its sedimentary region is limited to the southmost area of the lake. The flowing processes of suspension, controlled by turbidity currents and sediment dispersion, are consistent with the flowing conditions of river induced currents observed in October 1983.Ignition loss for the lake bottom sediments, as a whole, ranges from 5 to 20%. The organisms almost all originate in the terrestrial plants. In the northeast recess, however, the ignition loss reaches the maximum of 30%, where an artificial effect is added.

Assessing hydrography and man's influence on sediments in the northern Suez Canal

This study identifies the distribution of water masses and surficial sediment texture in the northern part of the Suez Canal after its reopening and just before completion of the widening and deepening project which took place in 1980. The investigation compares the results of a hydrographic-bottom sediment texture survey made in June 1979 with a comprehensive analysis of Canal mineralogical-sedimentological provinces made at about the same time, in April 1980. The two studies, conducted independently, provide a basis for assessing the role of hydrography versus that of dredging and ship traffic on the distribution of surficial sediments in this part of the Canal. Although Mediterranean water flowing into the Canal carries some sediment of Nile-Mediterranean derivation, it is a considerably less significant factor than anthropogenic influences on sediment dispersal.

Pollen distribution in the bottom sediments of the western North Atlantic Ocean

An extensive survey of pollen distribution in surficial sediments from the slope and rise between 29° and 72°N, shows patterns which reflect the distribution of vegetation in eastern North America and the effects of aeolian, fluvial, and marine sedimentation. The results of the analysis of 94 core tops show that pollen concentration ranges from 23,000 to 10 grains per gram, and decreases offshore with distance from vegetation sources and northward in relation to lower vegetation density. Maximum concentration occurs in organic-rich, fine-grained lutum deposited off rivers draining the southeastern United States. Low pollen concentrations are associated with high-energy environments, such as the Western Boundary Undercurrent and the Labrador Current. Percentages of dominant pollen types generally correspond with onshore distribution of pollen and vegetation. Oak and other deciduous pollen types are the most abundant in marine sediments off the deciduous forests of eastern United States. Hemlock pollen is essentially restricted to sediments off the hemlock-oak forests of northeastern U.S. and southeastern Canada, and spruce pollen is most abundant adjacent boreal forests and forest-tundra formations. The relative increase in pine pollen seaward reflects the selective effects of marine transport. Synthesis of pollen data by Q-mode factor analysis shows that major vegetation formations of eastern North America produce distinctive, regional marine pollen assemblages.

Discharge of elemental sulfur and its distribution in surficial sediments in the region of the buccaneer oil field

The concentration of elemental sulfur in the produced water effluent from production platforms in the Buccaneer oil field was determined. In 15 samples collected between June, 1977 and May, 1978 the mean sulfur content was 457 ppm (range: <100 to 1200 ppm). The concentration of elemental sulfur in surficial sediment samples collected from the immediate vicinity of the production platforms in October, 1977 ranged from 0.30 to 11.85 ppm. There was no correlation between alkane and sulfur concentrations either in the effluents or the sediments.

M2 tidal effects in greater Cook Strait, New Zealand

The application of an M2 nonlinear numerical tidal model to the shelf seas of central New Zealand (∼38,500 km2 area) is described. It has provided a preliminary assessment of tidal and residual currents, bottom stress, energy dissipation, and the stratification index. The existence of a permanent, tidally driven mesoscale eddy (∼75 km diameter) is predicted north of D'Urville Island. Large spatial gradients in bottom stress qualitatively agree with many features of the surficial sediment distribution. A comparison of all available bulk stratification data with the h/u3 stratification index clearly demonstrates the dominance of tidal versus wind mixing over the control of summer stratification. A potential application of the model to fisheries science is suggested through a comparison of the stratification index contour map and some observations of squid fishing vessel locations.

Distribution of surficial sediments of the central and southern Strait of Georgia, British Columbia

The Strait of Georgia is a long, narrow, semi-enclosed basin with a restricted circulation and a single sediment source, the Fraser River, providing practically all the sediment now being deposited in the Strait. This river is building a delta into the Strait from the east side near the south end. Ridges of Pleistocene deposits within the Strait and Pleistocene material around the margins, like bedrock exposures, provide local sources of sediment of only minor importance.Sandy sediments are concentrated in the vicinity of the delta, and in the southern and southeastern parts of the Strait. Mean grain size decreases from the delta toward the northwest along the axis of the Strait, and basinwards from the margins. Silts and clays are deposited in deep water west and north of the delta front. Bedrock or poorly sorted sediments containing gravel occur near tidal passes, on the Vancouver Island shelf area, on ridge tops within the Strait, and with sandy sediments at the southeastern end of the study area. The Pleistocene ridges are areas of nondeposition, having at most a thin veneer of modern mud on their crests and upper flanks.

Sedimentation in two Catalonian canyons, northwestern Mediterranean

The Cap Creus and Lacaze-Duthiers canyons, cut on the narrow subsiding margin off the eastern Pyrenees, play an important role in downslope sediment transport in the northwestern Mediterranean. This conclusion is based on an evaluation of the surficial sediment distribution patterns, cores, direct visual observations of the sea floor made in 24 submersible dives and tight-grid seismic survey data. Down-canyon sediment movement (mostly by slump and gravity flow mechanisms) since the end of the Pliocene has resulted in the formation of the Catalonia Fan at the base of the slope west of the Rhone Cone.

Sediments of the Continental Margin off the Eastern United States

The character and distribution of surficial sediments on the continental shelf and slope between northern Maine and southern Florida have been denned on the basis of more than 6,000 bottom samples. Most shelf sediments were deposited in shallow water (probably littoral depths) during the last lower stand of sea level. Modern sediments are accumulating only in estuaries, in certain nearshore areas and on the continental slope. A large portion of the shelf sediment north of lat 41° N. was deposited by Pleistocene glaciers that covered the area. Sediments on the middle Atlantic shelf consist of predominantly arkosic to subarkosic fluvial sands. The inner shelf off the southeastern United States is covered by suborthoquartzitic fluvial sands, derived mostly from Piedmont rivers; carbonate-rich sands occur over much of the outer shelf and upper slope. Residual detritus, reworked from underlying mid-Tertiary formations, is an important sedimentary component on Georges Bank and Nantucket Shoals, Onslow Bay, the Florida-Hatteras slope, and the Blake Plateau. Although most sediments are not in compositional equilibrium with the present-day shelf environment, there is considerable evidence to suggest that many may be in at least partial textural equilibrium. Holocene reworking has removed most fine-grained sediment, leaving only coarse to medium sand. Some fine-grained fluvial sediment escapes the estuaries and near-shore during floods and storms, but this influx is not sufficient to offset the effect of winnowing by currents and waves. A significant portion of the modern near-shore sediment, in fact, may be derived from landward transport of fine-grained sediment from the central and outer shelf. Despite the evidence of active sediment movement on the shelf, however, the net lateral transport of sand and gravel appears to be limited. Because of the lack of present-day terrigenous sedimentation, a primary source of modern shelf sediment is calcareous skeletal material. If the present-day surface were preserved in the geologic record, much of it probably would be a carbonate-rich layer, containing altered and reworked skeletal material representing a variety of depositional environments.

Interpretative studies of cladoceran microfossils in lake sediments

Cladoceran microfossils per unit weight of sediment have been found to be either randomly distributed or clumped in their distribution in surficial sediments of freshwater lakes. These results indi...