Showing papers on "Silt published in 1970"

Sound velocity and related properties of marine sediments, North Pacific

Abstract: This is the first of a series of reports on sound velocity, elasticity, and related properties of marine sediments from sedimentary environments associated with three major physiographic provinces in the North Pacific and adjacent areas: the continental terrace (shelf and slope), the deep-water abyssal plain (turbidite), and the abyssal hill (pelagic). The following properties are listed in tables and illustrated in diagrams that interrelate various properties: grain size (mean diameter, percentages of sand, silt, and clay), bulk density, density of mineral grains, porosity, sound velocity, velocity ratio (velocity in sediment/velocity in sea water), impedance, and density × (velocity)2. Values are given for each sediment type within each environment. Significant differences in the density and porosity of the environments studied are caused by mineralogy, size and shape of grains, and sediment structure; presence of diatoms and clay mineralogy are particularly important. General equations and diagrams relating density and porosity to velocity should be abandoned in favor of entry into diagrams or equations for a single environment; velocity is then predictable within 1 to 2 per cent in most environments. Mean grain size has one of the best empirical relationships with velocity, which permits derivation of useful data from size analyses of dried cores. Porosity and density are excellent indices by which to determine values of impedance and density × (velocity)2. There is no usable, empirical relationship between sound velocity and shear strength (cohesion) as measured in soil mechanics tests. No anisotropic velocity relationships were measured in surficial sediments, and none is predicted for the upper few hundred meters in sea-floor sediments.

Review of collapsing soils

Abstract: Soils which collapse (undergo large consolidation) when unusual amounts of water are added to them exist in many places around the world. Contrary to the ideas of many observers these collapsing soils derive from many different soil forming processes. Although surface collapse of 15 ft has occurred, the usual amount is considerably less. These soils are of open structure and exist in nature at less than 100% saturation. The major soil materials are silt, sand, or gravel or any of their combinations. Water in tension is the general binding material. A small amount of clay is present in many cases. Other binding agents sometimes contribute. The amount and rate of collapse is a function of grain shape, grain size, existing moisture content, kinds and amounts of clay present, void ratio, adsorbed ions, etc. Maximum collapse occurs at optimum clay content (10% in one case) and moisture content (between 13% and 39%). Most of the collapse can occur before the soil reaches 100% saturation. Estimates of the magnitude of possible collapse derived from routine tests generally are compared to field results.

Reflection coefficients and bottom losses at normal incidence computed from pacific sediment properties

Abstract: Rayleigh reflection coefficients and bottom losses of compressional waves at normal incidence on the water‐sediment interface are computed with values of density and velocity measured in sea‐floor sediment samples; main sediment types in three major environments of the Pacific and adjacent areas are included. Some typical average computed values of acoustic bottom loss at normal incidence in db are (1) continental shelf: sands, 8; silty sand, 10; sandy silt, 14; silty clay, 16; (2) abyssal plain: clayey silt, 17; silty clay and clay, 21; and (3) abyssal hill: silty clay and clay, 17. Comparisons with actual measurements at sea by several investigators demonstrate the validity of the approach.

Frost Action in Rocks: Some Experimental Data

Abstract: This series of experiments investigates the varying rates of frost shattering of several rock types. Rock samples were subjected to freeze-thaw cycles under two contrasting temperature regimes, 'Icelandic' (range + 8?C to - 8?C in 24 hours) and 'Siberian' (range + I5?C to - 30?C in 96 hours). The moisture content of the rock samples was also varied from a free-water environment (rock half immersed in water) to a saturated environment (thin film of water on rock). The experiments proved that the number of oscillations across freezing point was of greater importance to the rate of shattering than the intensity of freezing. Generally, samples in the free-water environment had a higher rate of shattering. The lithology and grain size of the rock specimens are of fundamental importance in controlling the rate of frost shatter- ing. Rates of shattering were related to the density of planes or points of weakness in the individual specimens. Lithology and grain size also controlled the morphology and size of the weathered products. IN REGIONS of present-day cryonival activity the disintegration of rock material by freeze-thaw action produces distinctive deposits. On relatively flat surfaces, blockfields or felsenmeere may result, whereas on steep slopes with rock outcrops, extensive talus or stratified screes may develop. Often the individual fragments are highly angular and irregular in shape, but can range in size from silt to large boulders. Such deposits can be observed in fossil and active form over large areas of the British Isles. Although approximately 50 per cent of the earth's surface experiences temperatures

Arsenic ‐ phosphorus interactions on corn

Abstract: Samples of two widely divergent soils, a Waupun silt loam and a Plainfield sand, deficient in P, were treated with 0, 20 or 80 ppm As and 0, 50, 100 or 300 ppm P in all possible combinations and cropped twice for 40 days to corn in the greenhouse. Arsenic had a much more pronounced toxicity to corn in the sand than on the silt loam. At the 80 ppm As level, P had little effect on As toxicity with the silt loam but enhanced toxicity with the sand and increasing rates of P increased As uptake by corn. At the 20 ppm As level, P did not affect As toxicity or uptake. Soil As extracted by N NH4OAc (pH 7.0) decreased with time but increased with increasing levels of applied P. Bray Pl extractable As was not greatly affected by applied P or time, and appeared to be a more suitable “available”; soil As test. From the results obtained, it would appear that P applications are not the solution to an As toxicity problem.

Environmental Influences on Early Development and Year-Class Strength of Northern Pike in Lakes Oahe and Sharpe, South Dakota

Abstract: Survival of artificially-fertilized ova and larvae of northern pike, Esox lucius, was estimated from embryos held in natural spawning areas in Lake Oahe and Lake Sharpe, two main stem Missouri River reservoirs. Mortalities approaching 100% during early embryonic development were associated with sudden drops in water temperature below 10 C or prolonged temperatures near 5 C. Silt deposition of 1.0 mm per day was associated with mortality of 97% or above. Following hatching available food appeared to be a more important factor in survival than temperature change or silt deposition. Estimates of year-class strength of northern pike in the two reservoirs suggest that large year classes were associated with stable to rising water level and temperature, flooded vegetation, and calm weather during the spawning season. Small year classes have been associated with abrupt water temperature fluctuations, dropping water level, and high silt deposits.

Sediments and Sedimentary Processes of Eastern Mississippi Cone, Gulf of Mexico

Abstract: The upper 6-7 m of sediment of the eastern Mississippi cone consists of a repetitious vertical succession of gray silt and silty clay intercalated with a few layers of fine sand and topped by a 20-50-cm layer of yellowish-brown foraminiferal clay. Disequilibrium age determinations indicate that the lower silty layers, representing the deposits of latest low sea-level stand, were deposited more rapidly than the upper foraminiferal clay. These sedimentation rates, which depend primarily on the rate of the detrital influx and sea-level change, average about 30 cm/1,000 years. Sedimentary processes on the deep-sea fan are interpreted from sedimentary structures, textures, and compositions, as well as from bathymetry, bottom photographs, and continuous seismic profiles. The more than 20 varieties of minor sedimentary structures recognized from X-ray radiographs are grouped into five varieties that correlate closely with sediment type. None of the structures is typical of vertical "turbidity sequences." On the contrary, the evidence suggests that the primary mechanisms of sediment transport are differential pelagic settling and low-flow-regime bottom currents, with mass movements by sliding or slumping common in channel and slope areas. Statistical evaluation of the occurrence and distribution of minor structures indicates that (1) most of the structures asso iated with coarser materials are analogous to structures formed by traction transport or by ripple migration in shallow water, and (2) the distribution of both bottom-current intensity and internal waves that create small-scale ripples is local. Photographs of the present bottom support this conclusion. The importance of diagenetic solution of carbonate, mostly planktonic foraminifers and pteropods, as verified by laboratory experimentation, is related to the degradation of organic matter in the sediments. The most active solution occurs near the boundary between the upper foraminiferal clay and the lower silty layers and is partly responsible for (1) the abrupt decrease of carbonate downward in the cores, (2) the rearrangement of clay particles into secondary thin laminae, and (3) the shortening of the distance between noncarbonate silt and sand layers or laminae. These results, combined with compaction, accentuate the uniformity of layering. The upper cone is indented by digitate leveed valleys and canyons cut by transverse ridges, whereas the lower section is characteristically smooth. The bathymetry of the cone reflects its underlying structure. Continuous seismic profiles show that the lower cone is composed of relatively uniform flat-lying beds, representing at least five major depositional cycles since Plio-Miocene time and as many as 14 since Late Cretaceous time. In contrast, the upper cone has many internal irregularities, probably caused by gravity sliding, folding, and slumping contemporaneous with deposition, and by diapiric salt intrusion. The cone's depocenter has shifted continuously basinward as the Mississippi delta has prograded gulfward since Late Cretaceous time.

Apollo 11: Soil Mechanics Results

Abstract: Data were extracted from astronaut observations, television coverage of the moon walk, and returned photographs and samples. It has been determined that the upper few centimeters of the lunar soil in the vicinity of Tranquility Base are characterized by a brownish, medium-gray, slightly cohesive granular soil composed largely of bulky grains in the silt to fine sand size range, with angular to subrounded rock fragments ranging up to 1 m in size distributed throughout the area. The lunar surface at this site is soft to depths of 5 cm to 20 cm, below which the resistance to penetration increases considerably. Although the soil differs considerably in composition and range of particle shapes from a terrestrial soil of the same particle size distribution, it does not appear to differ significantly in its mechanical behavior. The soil, while basically frictional in behavior, exhibits a small amount of cohesion and strong adhesive properties. Preliminary estimates of the in situ soil density gave a value of 1.6 g per cu cm.

Quaternary deposits at oxbow opencast coal site in the aire valley, yorkshire

Abstract: Summary Silts, sands and gravels below the floodplain of the river Aire at Oxbow opencast coal site are described and interpreted. A Lower Sand and Gravel resting on Coal Measures is thought to have had a fluvial origin and to be probably of Weichselian age. The flora and insect fauna of the succeeding Lower Silt indicate a tundra environment and a mammoth tusk from this deposit has yielded a radiocarbon date of about 38,600 years B.P. The characteristics of the overlying Middle Sand and Gravel suggest glacio-fluvial deposition, and it is considered that this deposit and the local terrace deposits may be “outwash” from the Weichselian Aire valley glacier. The flora of the succeeding Middle Silt also suggests a tundra environment. A rockhead ridge associated with an anticline in the Coal Measures has affected the deposition and subsequent disposition of the deposits below the Middle Silt. This anticlinal ridge is considered to be a cryoturbation structure. The Upper Sand and Gravel rests unconformably on the Middle Silt and Middle Sand and Gravel. It is of Flandrian age on the basis of its flora, which includes assemblages correctable with zone VI (later Boreal) and with zone VIIb (Sub-Boreal) or zone VIII (Sub-Atlantic). The succeeding Upper Silt forms the present floodplain surface.

Soil Contamination in the White Mountains, Eastern California

Abstract: Mineralogical investigation of lithosols formed on dolomite in a semiarid, subalpine environment reveals up to 30 percent contamination of the very fine sand fraction by rhyolitic ash from a distant source and as much as 50 percent local contamination of the silt fraction, largely attributable to aeolian processes. Total extraneous particles range from 3 to 73 percent in sand or silt fractions of a given soil sample. Short-term dust-trap and snow-residue collections place minimum aeolian deposition at approximately 0.00014 grams sq cm −1 yr −1 , a rate sufficient to account for the amounts of observed contamination. The data emphasize the need for precaution in interpretation of soil mineralogy and chemistry, under many climatic and topographic influences and in areas subject to Pleistocene volcanism.

Sedimentary environment and sediments of Cook Inlet, Alaska

Abstract: The distinctive sedimentary environment of Cook Inlet, south-central Alaska, may be attributable in part to a unique combination of the gross morphologic and climatologic characteristics of the area. The sediments consist predominantly of cobbles, pebbles, and sand with minor admixtures of silt- and clay-size material. Three sedimentary facies are suggested on the basis of the detailed grain-size distributions. The boundaries of each facies are very well defined. During the summer months, large quantities of glacially derived sediment are added to the upper reaches of the inlet. Strong currents prevent early deposition of most of the silt and clay which are transported seaward toward the Forelands morphologic constriction. In this area intense tidal flushing removes almost all material of less than gravel size. The rate of sediment supply to the inlet is minimal during the extended winter season, and sediments are reworked predominantly by ice rafting. Much of the material probably is deposited initially in the area adjacent to the Forelands.

Relaxation of piles in sand and inorganic silt

Abstract: Many attempts have been made to modify the pile driving formulas to make them realistic in terms of modern driving practices and equipment None seems to have had a long-lasting impact on the engineering profession The driving impulse of a pile is always associated with a temporary remolding of surrounding soil, a zone of excessive pore water pressure and the dilatancy of dense fine sand For piles subjected to loading tests or under the load of a structure, there is no displacement in the soil; therefore, no remolding, no dilatancy and no excessive pore water pressure arise around the pile A review has been made of the basic mechanics relating to relaxation of pile resistance in dense fine sand or inorganic silt as well as the freeze of piles in soft clay or organic silt The pile resistance at the beginning of redriving can be used more effectively in representing the static capacity of a pile than that encountered in initial driving

Turbid Bottom Water on the Continental Shelf of the Northern Bering Sea

Abstract: In July, 1968, the bottom water on the continental shelf of the northern Bering Sea contained concentrations of suspended material in excess of 2 ppm, or 5 mg 1-1 Near the Alaska mainland, concentrations were as much as fivefold greater. The material is 85 percent mineral grains and has a modal particle size of 20µ. Because of the net northward movement of the water through Bering Strait into the Chukchi Sea, the bottom water with its high silt concentration appears to be an important transport mechanism for supplying modern silt to the shelf in the Chukchi Sea.

Clay Minerals in Arctic Ocean Sea-Floor Sediments

Abstract: Sediments of the sea floor of the Canada Basin and Alpha Rise, about 500 miles north of Point Barrow, Alaska, were cored to a depth of about 3 meters below the sea-sediment interface beneath Ice Island T-3 where the ocean depth varies from 3500 to 3700 meters at different locations. The sediments are lutites of average grain-size composition, 28 percent sand, 31 percent silt, and 41 percent clay. The sediments are either gray or brownish gray, the brown coloration being due in part to the oxidation of ferrus sulfide. Colloidal organic matter amounts to about 3 percent of the whole sediment. The clay fraction of the sediments consists of approximately 60 percent mica (muscovite and illite, with possibly a little biotite), 20 percent chlorite (11b polytype, and chamositic chlorite), 10 ercent mixed-layer (mica-chlorite- vermiculite), and 10 percent non-clay minerals (quartz, 1-5 percent; feldspar, <1 percent; dolomite, <5 percent). The composition of the clay is similar in all 65 samples examined, but some of the thinly bedded sediments contain a large percentage of amorphous clay. Quartz, feldspar, and clay minerals are detrital, but diagenesis has modified and increased the mixed-layering of micas, and apparently has caused the development of chlorite and vermiculite. Dolomite (mostly concentrated in the silt fraction) may be authigenic, but it could be detrital and derived from the glaciation of dolomites. The clay has been slowly deposited from mixed airborne and water (and ice) transported material in tee closed basin of the Arctic Ocean.

Abstract: Grand Isle - A Barrier Island in the Gulf of Mexico

Abstract: Grand Isle is part of a barrier island chain along the coast of southeastern Louisiana. It separates the estuarine environment of Barataria Bay from the marine environment of the Gulf of Mexico. The island is 7-1/2 miles long and about half a mile wide. Mechanical analyses of 102 surface samples indicate that the island is composed of fine-grained terrigenous sand, silt and clay, with a minor percentage of shell material. Median grain diameters range from 0.166 mm for beach sands downward to 0.005 mm for isolated clay pockets of the back-island area. Grain size isopleth maps demonstrate a parallelism of grain size characteristics to sedimentary features and environments such as the beach, dunes, ridges, and inter-ridges. They also demonstrate an increase in the size of beach sand to the southwest. Beach and dune sands are well sorted. Ridge and inter-ridge sediments contain a higher percentage of silt and clay and exhibit poorer sorting. Organic content of representative sediment samples ranges from 0.20 to 9.08 percent. The high oxidation environments of the beach and dunes generally have the lowest organic content. Carbonate content in the form of shell material ranges up to 4.20 percent with the smaller grain-size sediments generally having a higher carbonate content. The subsurface stratigraphy was studied using 127 soil boring logs. All strata encountered by the borings (to a maximum depth of 320 feet) were Holocene sands and clays. The oxidized Pleistocene contact is interpreted to be at a depth of 400 feet as determined by deeper borings on nearby islands. Four Holocene sands are recognized in this subsurface section. The deepest sand, interpreted to be a Holocene transgressive unit, is 120 to 170 feet thick. The maximum thickness of three shallower sands is 43 feet, and the average thickness is 10 to 20 feet. The three upper sands are fine-to very fine-grained. The deepest sand is fine to coarse-grained. Typical silty prodelta clays and highly plastic offshore clays are found between the sand beds. The Grand Isle beach has an average slope of 2 1/2°. A low dune ridge runs almost continuously behind the beach. Approximately 25 sets of relict beach and dune ridges can be identified behind the active dunes. These sets trend nearly parallel to one another and to the present beach. The ridges are 25 to 100 feet wide and are three feet or less in height. The sediments to a depth of 100 feet are interpreted to be related to deltaic progradation of the ancestral Mississippi River. This deltaic progradation began about 5600 years ago when sea level reached a stillstand. The Lafourche delta formed west of Grand Isle about 2000 years ago. As wave action attacked the delta front, sediment was carried north-eastward by littoral currents. A barrier spit was constructed into the mouth of Barataria Bay. The barrier spit was eventually breached by a tidal gut. Grand Isle has grown from this original nucleus island by beach and dune-ridge accretions. End_of_Record - Last_Page 274-------

Nature of carbonate minerals in two saskatchewan soils

Abstract: The nature and distribution of carbonate minerals in selected Chernozemic soils was investigated. Soil from the Bmk, Cca and Ck horizons of two profiles was fractionated into various size fractions. Total carbonates, calcite and dolomite were determined on each fraction. The silt fraction of both parent materials was high in carbonate minerals which were primarily dolomite. The clay and fine silt fractions of the carbonate accumulation layers were high in calcite. It was evident that secondary carbonate accumulates as calcite of clay and fine silt sizes. There appeared to be periodic removal and accumulation of carbonates in the Bmk horizon, as it was low in dolomite but relatively high in calcite.

Removing deep silt and muck deposits

Abstract: A method and apparatus for removing silt, muck and other deposits from a water covered basin whose bottom has been covered with a relatively thick deposit, involving the use of a submerged housing unit supported from the surface in a controlled relationship to the deposits on the bottom of the basin. The submerged unit is provided with a gate at its forward end so as only to permit the entry of silt into the housing at the forward end as it is moved along the bottom, with the arrangement being such that a pressurized jet can be injected into the entering material to enable a workable mixture of water and silt to be achieved. Means are provided for then drawing the mixture to the surface so that the silt can be disposed of at a location outside the basin. Other facets of the invention include the use of automatic means for maintaining the submerged housing unit in a desirable relationship to the silt deposits; the use of a selectively operable gate at each end of the device so as to enable operation in either direction; and automatic means for injecting additional jets of water as needed to maintain proper consistency of the material being discharged.

Origin of quartz silt; comments on a note by Ph. H. Kuenen [discussion]

Abstract: For reference to paper under discussion, see this Bibliography Vol. 34, No. 3, 17 E70-08620; see also Vol. 33, No. 4, 17 N69-07380

Collapse of Fargo Grain Elevator

Abstract: The rate of application of the load and its magnitude at failure at the Fargo grain elevator were known Distribution of the load on the foundation was known There were, however, some complicating factors The subsoil consisted of four distinct layers within the significant depth Three of the layers were clay or silty clay while the fourth was an interbedded sand, silt and clay In addition, it was shown that shear strength varied greatly depending upon the method of testing The observed bearing capacity was compared with various computed values depending upon the method of measuring shear strength The results indicated that Skempton's solution gave excellent results if shear strengths measured by vane tests were used and the concept of progressive failure was utilized