Silty Deposits Research Articles

Settlement predictions in the Anatolian Motorway, Turkey

The Anatolian Motorway through the Asarsuyu Valley passes across the landslides which have been extensively disturbed by past fault movements. The Asarsuyu Valley is the most important crossing of the motorway between Istanbul and Ankara route. Along the Asarsuyu Valley, about 7 km of the roadway is still under construction. In this study, the magnitude and the rate of the settlement over consolidated clays in lacustrine deposits within the Asarsuyu Valley were compared with each other. On the basis of field observations and laboratory test results, it was determined that the lacustrine deposits were eroded up to 15 m by the river in the valley bottom. As results of unloading and desiccation process, the clay layers are overconsolidated. Settlement calculations indicate that the amount of clay layers has caused the intolerable consolidation settlement under the concrete structures and motorway embankment. In this respect, preloading embankment on clay and silty clay deposits was projected and constructed. On the basis of evaluations, estimated values of settlement are lower than those realized. However, the predicted settlement quantities are found reliable and comparable to field measurements. On the other hand, significant differences were observed between calculated and measured rate of the settlement. The high rate of the settlement, which was measured during preloading, was caused by the viscoelastic strain due to the relatively high load and sandy pockets available in the clay layers, but was not detected by the drilling and the micro/macro texture of the clay layers.

The marine Eemian of the Baltic: new pollen and diatom data from Peski, Russia, and Põhja‐Uhtju, Estonia

AbstractSeveral relatively well‐preserved last interglacial (Eemian, marine oxygen isotope substage 5e; ca. 130–116 ka) deposits containing marine diatom flora have been found in Finland. In addition to these Finnish sites, more numerous Eemian (Mikulino) marine deposits are known from the northwestern part of Russia and from Estonia.Two new clayey and silty deposits covered by till, one at Peski, Russia, and the other Põhja‐Uhtju, Estonia, were studied for pollen and diatom content. At Peski, the deposit representing the Eemian interglacial is 3.8 m thick. The polyhalobous diatom flora in the Corylus and Carpinus zones indicates the maximum of the marine transgression during the climatic optimum. Later, the increasing proportion of brackish water diatom flora indicates a lowering in the relative sea‐level, and finally, during a very late phase of the Eemian, the sharply increasing proportion of freshwater species indicates the isolation of the sedimentary basin from the Eemian Sea.At Põhja‐Uhtju, according to the pollen, the Eemian deposit is 3.5 m thick. Diatoms occur only in a layer 1.6 m thick, which represents the period of Corylus and Carpinus zones, and thus the period of the climatic optimum. The brackish–marine diatom flora consists mainly of littoral, shallow‐water species.Although Peski is situated at a higher altitude than Põhja‐Uhtju at present, the diatom stratigraphy at Peski indicates deeper and more saline conditions than at Põhja‐Uhtju during the Eemian. This probably is the result of variations in glacio‐isostatic rebound between these sites, which can be accounted for by differences of the ice load during the final phase of the Saalian glaciation. Copyright © 2002 John Wiley & Sons, Ltd.

Applicability of piezocone and dilatometer to characterize the soils of the Venice Lagoon

The effectiveness of two geotechnical investigation tools—the piezocone and the dilatometer—to characterize the soils forming the shallowest deposits of the upper quaternary basin of the Venice lagoon soil is examined in this study. For this purpose, the results of a comprehensive site and laboratory investigation carried out recently over a small lagoon area—the Malamocco Test Site—are used to evaluate the applicability of the most widely used charts or correlative equations to characterize soil profile and estimate the main geotechnical properties of these soils, when applied to the interpretation of CPTU and DMT results. The particular interest of this site—apart from its unquestionable historical relevance—is the presence, apparently without any regular pattern in depth and site, of a predominantly silty fraction combined with clay and/or sand, thus forming an erratic interbedding of various types of sediments. This case represents therefore the opposite condition of that which has been normally utilized in the past to calibrate the two devices, namely the presence of particularly homogeneous natural deposits or artificially sedimented homogeneous layers of sand or clay. The Malamocco Test Site may therefore be considered as test benchmark for the applicability of the two devices to characterize highly heterogeneous silty deposits.

Permeability evaluation and its implications for consolidation analysis of an Italian soft clay deposit

The present research concerns a comparative analysis of the possible methods for estimating soft silty clay permeability to be used in the analysis of consolidation. For this purpose the consolidation response of a thick and homogeneous, instrumented soft silty clay deposit, on which an embankment was constructed, is back-analyzed using the finite-element method. To model the consolidation process, permeability data are carefully determined both from laboratory and in situ piezocone tests. One-dimensional and triaxial permeability test data are compared with the results of piezocone dissipation tests, the latter interpreted using four different solutions. The effects of anisotropy on permeability characteristics influencing the consolidation rate are also discussed.Key words: consolidation, embankment, finite-element analyses, permeability, piezocone, soft silty clay.

Dust and loessic alluvial deposits in Northwestern Namibia (Damaraland, Kaokoveld): sedimentology and palaeoclimatic evidence based on luminescence data

In northwestern Namibia, silty deposits are widespread. The silts consist of two major components: locally produced weathering detritus and allochthonous dust blown in from the western Kalahari to the eastern margin of the Namib Desert. Sedimentological analysis and luminescence age estimations allow identification of distinct sedimentological and geomorphological processes associated with two different climatic periods. Between about 30 and 8 ka loessic alluvial deposits several metres in thickness accumulated in valleys and basins. The deposition was generated by weak slope wash and/or endoreic drainage of the ephemeral rivers. The dust input and the accumulation of silt in the valleys indicate semi-arid climatic conditions with weak summer rains and long dry seasons. Since about 9–8 ka, silt terraces caused by fluvial incision and erosion have been formed. These indicate more humid conditions than had occurred before. The change from a dry to a moister semi-arid climate at about 9–8 ka is confirmed by proxy data from drill cores off the Namibian coast and by dune studies in the south western Kalahari.

Late Holocene loess deposits and dust accumulation in the alpine meadow belt of the Wutai Shan, China

Greyish-yellow to light-brownish silty deposits in the alpine meadow belt of the Wutai Shan (Central China) were originally transported by wind, but are modified to some degree by local reworking and syn-depositional weathering. However, they are generally defined as loess deposits. Radiocarbon dates of wood fragments and charcoal prove that the loessic surficial sediment cover accumulated in the late Holocene. A lowering of the timberline, caused by a climatic deterioration since the Holocene Optimum, as well as the formation and maintainance of the dense alpine meadow vegetation, has probably favoured the accumulation of dust. Additional factors might have been the alternation between possible dust source areas in the deserts of northwestern China and the downwind accumulation area in the topographic mountain barrier of the Wutai Shan.

Recent gully erosion in the El Cautivo badlands (Tabernas, SE Spain)

Detailed geomorphic observations in El Cautivo badland area, in the semiarid SE of Spain, show a recent renewal of linear channel erosion following a period of aggradation. Prior to this renewal, the landscape was characterized by smooth colluvial pediments on the north-east facing aspects and relatively steep crusted microhillslopes on south-west facing aspects. First-order valleys within the badland landscape were smooth-floored and filled with silty deposits connected with pediment colluvial deposits. The conditions under which valley bottom deposition was replaced by channel incision were analyzed by a study of flow hydraulics (magnitude–frequency of eroding events vs. resistance of valley floor to water flow) and the pollen sequence in the recently cut deposits. Changes in the vegetation-carpeting the valley bottom seem to be responsible for the deposition–erosion alternation rather than changes in the magnitude–frequency of major runoff events, given the high sensitivity of flow hydraulics to changes in roughness. Present rainfall rates would not, on their own, be able to erode a well-vegetated valley bottom. Yet, the pollen sequence in the valley fills demonstrates a progressive deterioration in climatic conditions with the eventual disappearance of groups that require a constant level of soil moisture ( Alnus, Corylus, Cyperaceae). An increase in yearly rainfall or a change in temporal patterns would increase infiltration leading to permanent denser vegetation on footslopes and valley floors, helped by the natural water harvesting system. This vegetation cover would reduce the flow velocity and induce the deposition of the colluvium and valley fills, whereas erosion on headslopes would have been active enough to supply the sediments that were deposited downslope or on the valley bottoms. The reactivation of linear erosion would seem, therefore, to be a consequence of the decay of this permanent vegetation, induced by an increase in the duration or severity of drought periods, which meant that the water storage capacity of the valley fillings was insufficient to support it.

The Site of Ain Hanech Revisited: New Investigations at this Lower Pleistocene Site in Northern Algeria

New archaeological investigations have been carried out at the Oldowan site of Ain Hanech in northeast Algeria. The archaeological horizons are delineated and positioned relative to the regional stratigraphy. Preliminary palaeomagnetic analysis reveals normal polarity for the Oldowan occurrences that may be correlated with the Olduvai subchron on the indication of the vertebrate faunal biozonation. Broken up bones associated with stone artefacts and contained in a silty deposit mixed with sand and gravels were excavated from two archaeological sites. The bone assemblage includes equids, bovids, elephant, and rhinoceros, and dominated byEquus tabeti. Taphonomic patterns indicate that bones were buried rapidly over a period of years and while the site was occupied. The lithic artefacts are fresh and represent a coherent assemblage, including small debitage. The artefacts, made of limestone and flint, include flaked cobbles, whole flakes, various fragments, and retouched pieces. A microwear study, undertaken on pieces made of flint, indicates the use of two simple flakes and of one denticulate for meat processing. The stone artefact assemblage may be considered as a North African variant of the Oldowan.

Changements dans les circulations atmosphérique et océanique à la latitude des Canaries et du Maroc entre les stades isotopiques 2 et 1 [ Change in atmospheric and oceanic circulations at the latitude of the Canaries and Morocco between isotopic stages 2 and 1

During the Last Glacial Maximum (stade 2) geological and palynogical studies on deep sea drillings between North 24° and 36° had previously inferred to the northern shift of the tropical high pressures, of the marine trade-wind and associated up-welling and of a desert broadly spreaded on the Moghreb. But, according to the field discrimination between surficial mobile sands related to present trade-winds and lower weakly hardened sands related to paleowesterlies, recent inland studies in Fuerteventura (eastern Canary Islands) and south-western Morocco show that the Upper Pleistocene dry paleoclimate was geographically restricted to the Moroccan coasts and off-shore islands, in relation with a cold marine current supplied by ice melting waters which precisely stopped the rain formation in spite of prevailing westerlies. In Fuerteventura, a detailed field work and a critical study of numerous isotopic data relates to the repeatedly emplacement of hardened dune sands deposited between interlayered grey to brown thin paleosoils during the Stages 2 and 3. Good lithostratigraphical and isotopic correlations with these Canarian observations occur from the field data studied in various Moroccan coastal regions (Tiznit, Safi.Rabat). Finally, a chronology supported by more than very coherent 30 l4C datations infers a relation between the sand dunes spreading and intervening maxima of icebergs in Northern Atlantic; and between the interlayered paleosoils and intercalated wanning periods. At the end of the Lateglacial period, simultaneous climatic and environmental changes occur in eastern Canary Islands and coastal Morocco: a sand remobilization then an erosive crisis between 14000 and 10000 y. BP are consequential to important changes leading to interglacial conditions in the Holocene. In the both countries, morphological observations on mobile sands, supported by mineralogical and isotopic data, show that the trade-wind and associated up-welling replaced, in the Holocene, the westerlies and ice melting current; moreover major Saharan dust deposition causes upper light to brown silty deposits into the Canary Islands.

The geochemical paradox of ice‐complex sediments in north Siberia

AbstractIcy silty deposits in northern Siberia, here termed ‘ice‐complex sediments’ (ICS), have a higher salinization than other continental deposits of Neogene‐Pleistocene age. Data for salinity (%) and the ratio of Ca ion content to Cl ion content for samples from the Yana‐Indigirskaya and Kolymskaya lowlands indicate that the salinization of Pleistocene permafrost is lowest, that icy silts have salinities between 0.1% and 1.0%, and that recent floodplain, coastal and alas deposits have salinities greater than 1%. These differences are thought to reflect the phase change in gas‐liquid inclusions in crystals and rocks when they break and their contents (solutions) are released during freezing. This process is termed cryocryptogenesis. It is concluded that ICS deposits were formed under less humid and colder conditions than exist today in northern Yakutia, but more humid than central Yakutia.

High Resolution Sequence Stratigraphy and Reservoir Architecture of Proximal Alluvial Deposits: The Buntsandstein Facies of Central Spain: ABSTRACT

The Buntsandstein facies outcrops along a 12 km long, 150 m thick cuesta near Ayllon (Central Spain). The outcrop study is based on vertical sedimentological sections and continuous photo paneling, and demonstrates the presence of two depositional systems: an alluvial fan system in the lower half of the outcrop, and a straight and braided river system in the upper part of the outcrop. This overall evolution is probably related to base-level fall to base-level rise cycle, in which the reservoir architecture is linked to genetic units stacking pattern: during the base-level fall, the alluvial fan is prograding over sand flat and sandy alluvial plain deposits. Coarse and pebbly proximal sandsheets are interbedded with finer reddish distal deposits. Reservoirs units are laterally continuous, but silty alluvial plain deposits constitute vertical permeability barriers, during base-level stillstand, erosive channels and sandsheets are vertically amalgamated. Reservoirs units are laterally continuous and vertically connected, during the base-level rise, alluvial fan deposits are overlapped by straight river deposits. Reservoirs units are laterally connected but silty argillaceous alluvial plain horizons are preserved, at the end of the base-level rise, braided and straight river deposits are amalgamated. Fully connected, these reservoirs units have a very large lateral extension.more » A lithofacies database is compiled on this outcrop, and variograms, horizontal and vertical proportion curves are completed. Each stage of the base-level cycle is then quantitatively characterized by a specific heterogeneity pattern. The outcrop study will improve the prediction of reservoir extension and architecture in subsurface gas storage of the Paris basin.« less

Geotextile French drains in Indian rural roads — A case study

This paper presents a case study of the application of geotextile French drains to unsurfaced Indian rural roads. These roads are usually in a deplorable state owing to the accumulation of rainwater and household sewage on the surface. Such accumulations not only make the road surface impassable and environmentally hazardous but also affect the integrity and performance of the road. Conventional solutions, such as open ditches and gravel-filled trenches, do not work satisfactorily. A trial project was undertaken and a geotextile-wrapped French drain was used to drain the surface runoff, intercept ground-water inflows, and prevent weakening of the subgrade. The trial is located in an alluvial silty deposit, and suitable geotextiles have been tested and evaluated for their short-term and long-term hydraulic characteristics to meet the AASHTO-ARTBA specification. The drain, 300 mm wide, was filled with gravel and constructed over a length of nearly 100 m together with suitable catchpit and observation manholes. Installed in January 1991, the drain was found to give a satisfactory initial performance. Monitoring is still in progress.

A Mazama tephra marker bed in the Fraser Lowland, British Columbia

Drill cores from the Fraser River delta and western Fraser River floodplain, British Columbia, reveal a widespread tephra marker bed within silty floodplain deposits. Isolated tephra layers have been noted in previous studies in the Fraser Lowland and have been assumed to be Mazama tephra (ca. 6800 BP). This note presents the results of the first attempt to systematically identify a number of tephra samples from this area, based on X-ray energy spectroscopic analysis of their chemical compositions and bracketing radiocarbon ages. The results confirm that the tephra bed is Mazama, a finding of considerable utility to future studies in this area.

Interdune deposits of the Namib Sand Sea

The Namib Sand Sea of southwestern Africa is dominated by large north-south trending linear dunes. Interdune areas, however, comprise about 50% of the area of the Sand Sea and may consist of exposures of the pre-dune surface or sediments deposited between the dunes. Four major types of interdune deposits are identified and described: 1. (1) coarse poorly sorted aeolian sands 2. (2) localized calcareous lacustrine deposits 3. (3) silty deposits of ephemeral rivers that have flooded into the Sand Sea margins 4. (4) sabkhas and salt marshes near the coast. The preservation potential of these sediments is poor, except where they are buried and protected by dunes or stabilised by high groundwater levels in coastal areas.

Silty Deposits of a Low, Pleistocene‐age Terrace in Eastern Arkansas

AbstractA segment of Terrace Qtb3 of the Western Lowlands of Arkansas was transected to determine if the silty material capping the terrace is loess or silty alluvium. Four sites along an east‐west transect were sampled to test the hypothesis that the material is loess with its source area immediately east of the terrace segment. Three deposits dominated by silts were identified at each site by morphology, fine‐earth and clay‐free particle size distribution, and by distribution of total Ca and K in the coarse silt fraction. The lowest of the silty deposits was identified as alluvium by its sand contents and stratification in the lower part. The morphology of the upper two deposits was similar to that of loess on other terraces in the area. However, relationships between clay‐free particle size distribution and log distance from the proposed source area were not those expected for loess. Thus, these two deposits are also interpreted as silty alluvium. Geomorphic relationships indicate that the terrace is younger than Illinoian, but no minimum age can be deduced from current data.

The biostratigraphic position of the Kap København Formation based upon its foraminifera

Two lithological units are distinguished in the Kap Kebenhavn Formation (Funder & Hjort 1980; Funder et al. 1984; Funder et al. 1985): a lower member A composed mainly of clay, and an upper member B composed mainly of sand. An upper subunit of the latter. 82, comprises silty deposits. These sediments are in many places deformed and disturbed, partly squeezed and overthrusted. most probably by subsequent overriding glaciers. This blurs the stratigraphic picture at many places.

Genesis and Classification of Some Paleborolls and Cryoboralfs in Northern Utah

AbstractThree soil series in northern Utah were studied to determine if the apparent surface mantle is a depositional discontinuity. Field descriptions show a dark gray silty deposit overlying thick E horizons and reddish brown, clayey skeletal B horizons. Laboratory results show an abrupt change in texture and mineralogy with amphiboles and Ca‐feldspar and zeolites in the surface deposit or upper sequum and quartz, chlorite, mica, and kaolinite in the lower sequum. The fine clay in the upper sequum of all three soils is dominated by amorphous material suggesting an early stage of weathering. Results of these studies suggest that the older soils (lower sequum) were Alfisols. Recent additions of eolian material from Lake Bonneville sediments and Snake River plain have covered the Alfisols and mollic epipedons have developed in the eolian material. These soils are now classified as Paleborolls. We suggest that Thapto extragrade classification would help identify more of the characteristics of these soils than the present classification.

Outdoor natural background radiation in the Netherlands

As part of the SAWORA-project the outdoor natural background radiation was investigated by the National Institute of Public Health and Environmental Hygiene and by the Netherlands Energy Research Foundation. Measurements wer carried out with an ionization detector at more than 1000 locations evenly distributed throughout the country. After correction for the contribution of the cosmic radiation, the exposure rates were plotted on a map. Results show that the gamma radiation originating from the soil in The Netherlands varies between 1.1 and 7.2 μR/h (79 and 516 fC/(kg.s)). Comparison of the radiation map with a geological one indicates that “high” values of the exposure rates correspond to areas with silty deposits. The “low” exposure rates correspond to areas with sandy deposits. Gamma spectrometric analysis of the radiation at some locations shows that the terrestrial radiation is mainly caused by natural radionuclides.

Loess Deposits on a Pleistocene Age Terrace in Eastern Arkansas

AbstractThe area of eastern Arkansas between Crowley's Ridge and the Ozark Plateau, known as the Western Lowlands of Arkansas, was shaped by the ancestor of the Mississippi River. As this river responded to changes in glaciers upstream, a series of five braided stream terraces was formed within the lowlands. The second highest of these terraces was transected normal to its long axis to determine whether the silty materials capping this terrace were loess or silty alluvium and to determine the source area for any loess deposit(s). Two silty deposits were identified on the terrace by morphology, fine‐earth and clay‐free particle size distribution, and total Ca and K distribution. Relationships between clay‐free silt fractions and distance from a loess source, which are similar to relationships developed for other loess deposits, were utilized to locate source areas and to demonstrate the loessial nature of both deposits. The surface deposit, Peoria Loess, was correlated as a continuation of the Peoria Loess on Crowley's Ridge which had its source area in the lowlands east of Crowley's Ridge. The lower deposit, correlated as Loveland Silt, had a well‐developed paleosol in its upper part. The main source area for this loess was the lowlands west of the study terrace.

Measurement of sound-speed gradients in deep-ocean sediments using<tex>l_{1}</tex>deconvolution techniques

A method is described for measuring the sound speed and the sound-speed gradient of surficial sea floor sediment from bottom-reflected signals recorded in marine seismic experiments. The technique makes use of the ocean-bottom impulse responses that are deconvolved from the data by means of a novel curve-fitting algorithm based on the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">l_{1}</tex> norm (least absolute value) criterion. The algorithm constructs the impulse response by extracting spikes one at a time in a manner that causes the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">l_{1}</tex> error to decrease by the maximum amount possible as each spike is chosen. The <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">l_{1}</tex> curve-fitting approach is a completely general strategy for deconvolution, and our algorithm can be used with data obtained from any type of marine seismic source. Since our experiments have been carried out with small explosive charges, we have also developed a method for estimating the bubble-pulse wavelet directly from the recorded bottom-reflected signal. In this paper, the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">l_{1}</tex> algorithm is used to deconvolve impulse responses for data obtained in an experiment in the Alaskan Abyssal Plain. The sediment-sound-speed gradient determined from these results is typical of other values reported for turbidite abyssal plains where the surficial sediments are composed of unconsolidated silty deposits.