Trough Slope Research Articles

Holocene glacier fluctuations and climate changes in the southeastern part of the Russian Altai (South Siberia) based on a radiocarbon chronology

This study investigates glacier dynamic and climatic variations in the southeastern part of the Russian Altai (SE Altai) during the last 7000 years. Recent glacier retreats and ice melting in moraines has led to exhumation of organic material allowing the possibility of radiocarbon dating. We report here 57 new radiocarbon dates from wood remains buried by moraines and from proglacial forefields, from peat layers and lacustrine sediments that cover moraines, from dead trees at the upper tree limit, and from rock glaciers on trough slopes from six glacial valleys in the North Chuya Range, SE Altai. Such a numerous dataset for the vast but unified in neotectonic and climatic conditions area is presented for the first time the history of research in the Altai.Together with 62 previously published radiocarbon ages, mainly of fossil soils and peat layers in the foot of the ranges in SE Altai, they form the basis for understanding the relative magnitudes and timing of the most important glacial and climatic events of SE Altai. New data refute the traditional concept of the Russian Altai Holocene glaciations as a consecutive retreat of the late Würm glaciers and argue their complete degradation at the head of trough valleys at least 7000 cal. years BP. Moraine complexes of three Holocene glacial stages are morphologically expressed in trough valleys of the North Chuya range. They correlate with three identified periods of glacial advances: from 4900 to 4200 cal. years BP (Akkem stage), from 2300 to 1700 cal. years BP (Historical stage) and in the 13th–19th centuries (Little Ice Age (LIA) or Aktru stage). The coincident extremes of lowering temperature and increasing precipitation during the Akkem stage led to abrupt glacier advances and forming of the most remote moraine complexes downstream in the valleys. Following glacier advances had distinctly smaller magnitudes. In addition to the radiocarbon data, the time limits of the Historical stage were defined more precisely using dendrochronological and archaeological data from Scythian burials of Pazyryk culture in SE Altai. Repeated forest regrowth in the presently glaciatiated area indicates significant retreat or even complete glacier degradation during interstage warming. The decreases of glacier length in the following stages argues for intensification of aridity in the SE Altai during the second half of the Holocene. The thermal minimum in the middle of 19th century, the greatest in the last millennium, did not positively influence the mass balance of glaciers, which also supports this conclusion.

Wide distribution and glacial origin of polar gypsum on Mars

The North Polar Cap of Mars is associated with different kinds of superficial sediments, including the Circumpolar Dune Field, interior dune fields and sedimentary veneers scattered over the ice cap. In order to resolve the mineralogical composition and the regional distribution of these sediments, we processed OMEGA and CRISM hyperspectral data with an original method based on spectral derivation. We find that gypsum is present in all areas where undefined hydrated minerals had been previously detected, including superficial sedimentary veneers covering the North Polar Cap, interior dune fields and the whole Circumpolar Dune Field. Morphological and structural analyses reveal that these gypsum crystals derive directly from the interior of the ice cap. The source of superficial sedimentary veneers is the dust that was previously contained in the upper part of the ice cap, the ice-rich North Polar Layered Deposits (NPLD). This gypsum-bearing dust was released, on south-facing slopes of spiral troughs and arcuate scarps, by ice ablation controlled by katabatic winds. By the analysis of all associations of erosional scarps and dune fields over the North Polar Cap, we also demonstrate that the polar dunes are composed of sand-sized particles that were previously contained in the sediment-rich Basal Unit (BU), corresponding to the lower part of the ice cap. These particles contain gypsum and were released from the BU, by regressive ablation of ice at marginal scarps that border the North Polar Cap and by vertical ablation of ice on Olympia Planum. From a reconstruction of wind streamlines over and around the ice cap, we infer that katabatic winds descending from the polar high and rotating around the North Polar Cap control the release of these gypsum-bearing particles by ice ablation and the redistribution of these particles in the Circumpolar Dune Field.

Rainfall-related debris flows in Carhuacocha Valley, Cordillera Huayhuash, Peru

Continuous heavy rainfall hit northern Peru in the second half of the 2008/2009 summer season. From the end of January to the beginning of March, the Cordillera Huayhuash experienced abnormally high precipitations that exceeded 270 mm. The antecedent rainfall, aggravated with a severe rainstorm of 20 mm on March 7 triggered a large debris flow in the upper Carhuacocha Valley early in the morning on March 8. The debris flow interrupted drainage from the upper part of the valley damming a lake in the narrow depression between the trough slope and the lateral moraine. As a result of the drainage interruption, water percolated through the moraine dam of Cangrajanca Lake where a secondary mass movement occurred in its inner slope. In September 2009, we mapped the debris flow and related landforms and estimated the total area and volume of both mass movements using geodetic measurements. About 104,000 m3 of sediments was moved from the trough slope towards the moraine from which 534,000 m3 flowed to Cangrajanca Lake subsequently. We analysed the rainfall conditions that triggered the debris flow using rainfall data from the nearby stations. We also compared the precipitation preceding the event with the rainfall thresholds for debris flow initiation.

CORNER EFFECTS IN DEEP EXCAVATIONS-ESTABLISHMENT OF A FORECAST MODEL FOR TAIPEI BASIN T2 ZONE

This study attempts to establish a novel model for forecasting wall deformation and ground surface settlement of deep excavations. The model is developed by considering the corner effect and examining the data from relevant case histories. The study is specifically limited to the construction works in the T2 zone of the Taipei Basin. The following results were obtained: (1) The maximum wall deformation during each excavation step was approximately 0.2%-0.5% of the excavation depth, and was influenced by the corner effect. (2) The maximum ground surface settlement took place approximately at the center of the wall; and settlements at the corners were smaller due to the corner effect, they were generally 20%-60% of the maximum settlement. (3) The area within a distance of two times the excavation depth had a relatively large settlement or relatively steep slope of settlement trough, which can be defined as the primary influence settlement area. The area at a distance of 2-3 times the excavation depth had a gentler slope of settlement trough and can be defined as the secondary influence settlement area. (4) If the analysis is carried out with theoretical hydrostatic pressure or with measured water pressure, the same tendency ”the deeper the wall embedment depth, the greater the factor of safety for overall stability” is found. This study also makes two specific contributions. First, the corner effects in deep excavations are further confirmed through more case studies. Secondly, a simple hazard analysis for estimating settlements induced by deep excavations is presented.

Quantifying sediment storage in a high alpine valley (Turtmanntal, Switzerland)

AbstractThe determination of sediment storage is a critical parameter in sediment budget analyses. But, in many sediment budget studies the quantification of magnitude and time‐scale of sediment storage is still the weakest part and often relies on crude estimations only, especially in large drainage basins (>100 km2). We present a new approach to storage quantification in a meso‐scale alpine catchment of the Swiss Alps (Turtmann Valley, 110 km2).The quantification of depositional volumes was performed by combining geophysical surveys and geographic information system (GIS) modelling techniques. Mean thickness values of each landform type calculated from these data was used to estimate the sediment volume in the hanging valleys and the trough slopes. Sediment volume of the remaining subsystems was determined by modelling an assumed parabolic bedrock surface using digital elevation model (DEM) data.A total sediment volume of 781·3×106–1005·7×106 m3 is deposited in the Turtmann Valley. Over 60% of this volume is stored in the 13 hanging valleys. Moraine landforms contain over 60% of the deposits in the hanging valleys followed by sediment stored on slopes (20%) and rock glaciers (15%).For the first time, a detailed quantification of different storage types was achieved in a catchment of this size. Sediment volumes have been used to calculate mean denudation rates for the different processes ranging from 0·1 to 2·6 mm/a based on a time span of 10 ka.As the quantification approach includes a number of assumptions and various sources of error the values given represent the order of magnitude of sediment storage that has to be expected in a catchment of this size. Copyright © 2009 John Wiley & Sons, Ltd.

Oil and gas potential of continental margins of the Pacific Ocean

Oil and gas basins (OGB) of active and transform margins of the Pacific Ocean are discussed. Their western and eastern parts differ substantially in the evolution, tectonic pattern, and scope of resources. In the west, marginal seas incorporated into the Cenozoic geodynamic system of deep-water basins (marginal seas) and conjugate island arcs exhibit a greater oil and gas potential (hereafter, petroleum potential) as compared to the eastern margin bounded by a deep-water trench and transformed into the framing with OGBs only in separate sectors. The abundance of siliceous rocks influenced the formation and accumulation of oil and gas in the Pacific region. The most part of hydrocarbon accumulations is related to organogenic edifices and channels of shelf fans. Oil and gas fields confined to fans on slopes of deep-water troughs of active and transform margins are also known. Proceeding from the global practice, significant petroleum potential in Russia is associated with back-arc seas of the Pacific. The poorly studied deep-water basins on slopes are worthy of special attention.

Siliciclastic Sediment Across the North Queensland Margin (Australia): A Holocene Perspective on Reciprocal Versus Coeval Deposition in Tropical Mixed Siliciclastic-Carbonate Systems

Abstract According to conventional models of reciprocal sedimentation for tropical mixed siliciclastic–carbonate systems, shedding of carbonate material dominates slope and basin sedimentation during transgression and highstand while siliciclastic deposition dominates during lowstand. This understanding permeates the stratigraphic literature and is the accepted depositional model on the Great Barrier Reef (GBR) margin. The results of this study, however, document coeval carbonate and siliciclastic highstand deposition on the GBR slope and basin. Seafloor sediment from Queensland Trough slopes and basin floor east of the GBR contains 20% to 50% terrigenous siliciclastic material. One hundred and twenty-six sediment samples were obtained from core tops and sediments grabs previously retrieved from shelf, slope, and basin environments of the North Queensland Margin. These samples were analyzed for their carbonate content, mineralogy, and major-element composition. The amount of terrigenous siliciclastic material in sediment from the North Queensland Margin can be approximated by three independent methods: (1) the noncarbonate residual, (2) the sum of quartz, clays, and feldspars, and (3) the sum of SiO2, Al2O3, Fe2O3, and TiO2. All three tracers show a distinct distribution of siliciclastic sediment across the margin. Shelf siliciclastic content is highest on the inner shelf, decreasing eastward toward the GBR, with the exception of relatively high siliciclastic content in several interreef passages. Queensland Trough siliciclastic content is highest on the slope and basin between 15° and 17° S latitude, decreasing to the south and east. Although the relative abundances of quartz and clay minerals vary across the margin, the chemistry suggests a similar origin for the siliciclastic material. Moreover, the zone of high siliciclastic abundance in Queensland Trough reflects enhanced siliciclastic accumulation. Siliciclastic material escapes the outer shelf to Queensland Trough through interreef passages between 15° and 17° S latitude. It is then focused to the south by ocean currents. Siliciclastic sediment is likely sourced from a combination of rivers transporting Holocene sediment to the GBR shelf and late Pleistocene sediment eroded from the outer shelf and reworked to Queensland Trough. Siliciclastic material crosses the shelf, although the mechanisms (e.g., river plumes, nepheloid layers, tidal currents, cyclones, mushroom jets) remain poorly constrained. However, shelf width is clearly an important factor in allowing cross-shelf transport to occur. Mass-balance calculations indicate that up to 13% of the late Holocene annual riverine sediment output may be delivered to Queensland Trough. Modern and ancient mixed system depositional models must be reevaluated to allow for the possibility of coeval siliciclastic and carbonate deposition.

Palaeogeographic Variability and Depositional Environments of the Upper Jurassic Carbonate Rocks of Velika Kapela Mt. (Gorski Kotar Area, Adriatic Carbonate Platform, Croatia)

Synsedimentary tectonics caused significant differentiation of sedimentary environments of the Adriatic Carbonate Platform during the Kimmeridgian. The most important changes have been recorded in W and central Croatia: along the NW part in present day W Istria there was an emergence with bauxite deposits, while along the NE margin of the platform, in the Karlovac area, a former emerged area was submerged. Penecontemporaneously between these areas, in the wider area of Velika Kapela Mt., a shallow intraplatform trough was formed, characterised by deposition of dark mudstones with nodules and thin layers of cherts and thin interbeds of tuffs in the upper part of the succession. Occurrences of planktonic foraminifera, radiolarians, calcisphaeres and rare ammonites indicate the sporadic influence of the open sea. Along the margins of the trough, peri-reefal environments were established, with flourishing developments of different reef-building organisms – hydrozoans, stromatoporoids, corals and bryozoans.Reefs were continuously destroyed, and in this way derived material was reworked and transported towards the trough slopes. An enormous quantity of this material caused progradation towards the deeper central part of the area, which was gradually infilled and narrowed.In the final phase, the trough was completely infilled, and peri-reefal environments gradually disappeared, since they were covered by ooid bars, culminating in the establishment of shallow environments over the entire area. A similar situation was recorded in another contemporaneous, also tectonically formed environment – the Lemeš trough, stretching from the vicinity of Bihać in NW Bosnia towards the south into Croatia, into E Lika and N Dalmatia. This trough had direct communication with the open Tethys realm, and thin-bedded and platy limestones with chert and pelagic organisms, including common ammonites, were deposited within it. The Lemeš trough was also surrounded by coral–hydrozoan reefs, and it was infilled by the same depositional processes as the neighbouring trough in the area of Velika Kapela Mt., and finally covered by shallow-water deposits. Although both troughs were probably formed by the same tectonicact, and had approximately the same duration – during the Kimmeridgian and Early Tithonian – they differ according to their palaeogeographic and facies characteristics. The trough investigated in the Velika Kapela Mt. was isolated, surrounded by shallow-marine platform environments, and had only temporary, indirect contact with the open sea. The Lemeš trough had a continuous connection with the open sea, as indicated by the relatively rich assemblages of pelagic organisms, especially ammonites, and is characterised by abundant cherts. However, both troughs are characterised by similar depositional sequences: both are underlain and overlain by shallow-water carbonate deposits, and they represent a consequence of a specific depositional event caused by tectonic deformation (formation of pull-apart basins) within the inner part of the Adriatic Carbonate Platform.

Gravity torques for surface waves

The effects of the gravity torques acting on the angular momentum of surface gravity waves are calculated theoretically. For short crested waves the gravity torque is caused by the force of gravity on the orbiting fluid particles acting down the slopes of the crests and troughs and in the direction parallel to the crests and troughs. The gravity torque tries to rotate the angular momentum vectors, and thus the waves themselves, counterclockwise in the horizontal plane, as viewed from above, in both hemispheres. The amount of rotation per unit time is computed to be significant assuming reasonable values for the along-crest and trough slopes for waves in a storm area. The gravity torque has a frequency which is double the frequency of the waves. For long crested waves the gravity torque acts in the vertical plane of the orbit and tries to decelerate the particles when they rise and accelerate them when they fall. By disrupting the horizontal cyclostrophic balance of forces on the fluid particles (centrifugal force versus pressure force) the gravity torque accounts qualitatively for the three characteristics of breaking waves: that they break at the surface, that they break at the crest, and that the crest breaks in the direction of wave propagation.

Design of Efficient Side‐Channel Spillway

The paper describes a simplified method of designing an efficient side‐channel spillway, with particular reference to an L‐shaped weir. The method can be used with minor modifications for a straight weir or one U‐shaped in plan. The invert of the collecting trough slopes down from the crest of the end weir to the chute. The invert is designed to be as high as practicable so as to reduce construction costs. An additional benefit from this design method is that the spillway operates with little wave action. The usual momentum equation has been extended to include the downstream component of velocity of approach of lateral inflow. The spillway trough profile is designed directly by an iterative process which has been computerized. The design shape should be checked by hydraulic modeling, but, in the example given, was found to require very little alteration.

Late Quaternary calcareous clayey-silty muds in the Obock Trough (Gulf of Aden): hemipelagites or fine-grained turbidites?

Summary Three cores have allowed us to survey Holocene deposits in a trough of the Gulf of Aden ridge. Within this particular environment (steep slopes, tectonic and volcanic activity) sediments are fine-grained, apparently homogeneous calcareous muds, rich in clay and planktonic microfossils: these features suggest that they are hemipelagic deposits. However, high sedimentation rates (20 to 50 cm/1000 yrs), lateral variation, and the occurrence of dynamic sedimentary structures (visible on X-radiographs and in thin sections), suggest that they have been emplaced mainly by gravity currents. These reworked hemipelagic materials are deposited on the shelf edge and on the trough slopes. This is confirmed by the sequential arrangement of sedimentary characteristics, as shown by analysis of microstructures, microfacies, carbonates, clay minerals, grain-size and other components. Two types of sequences have been observed; the first we call the ‘type sequence’. This commonly overlies an erosional surface and comprises three divisions from bottom to the top: Division I (equivalent to Piper’s E1 division); mud with 8–10% sand fraction, rich in biogenic tests which occur as well-sorted horizontal laminae. Division II (equivalent to Piper’s E2 and E3 divisions); mud with low sand fraction (1%), very poor in biogenic material, no lamination, but horizontal orientation of silt-sized bioclasts. Division III (equivalent to Piper’s E2 and E3 divisions); mud with low sand fraction (1%), very poor in biogenic material, no lamination, but horizontal orientation of silt-sized bioclasts. Division III (equivalent to Piper’s F division); mud with low sandy fraction, poorly-sorted biogenic material, no dynamic sedimentary structures. The second type of sequence is less common and comprises two divisions: Division I’a ; very thin layer (millimetric), rich in terrigenous silt, which scours underlying sediment and shows horizontal, oblique and cross lamination. Division I’b ; mud with low biogenic sand content, showing horizontal more or less clear and irregularly-distributed lamination. These two sequences correspond to divisions E and F defined by Bouma (1962) and Piper (1978) in terrigenous turbidite sequences. The ‘type sequence’ is comparable to turbiditic sequences described in pelagic or hemipelagic material, deposited in similar morpho-tectonic environments (e.g. the eastern Mediterranean Sea or Mid Atlantic Ridge fracture zone).

The vertical slope of the monsoon trough and its association with distribution of rainfall over India

By evaluating the Margules' simplified equation for the slope of a surface of airmass discontinuity with relevant data and comparing the computed slope with observations, it has been suggested that, to a high degree of approximation, the monsoon trough over India may be regarded as a surface of airmass discontinuity separating the relatively warm easterly winds in the north from the cool westerly winds in the south and sloping southward with height. Rainfall associated with the normal southward slope of the trough appears to be distributed mainly to the south of the MSL position of the trough. However, both the slope of the trough as well as the distribution of rainfall associated with it are found to undergo major changes when synoptic disturbances such as the Bay of Bengal depressions or western disturbances affect India. Some main patterns of these changes are identified and discussed with reference to the possible role of the synoptic disturbances.

Principal features of the crustal structure of the south-caspian basin and the conditions of its formation

The Earth's crust within the South Caspian basin has a condensed thickness and lacks a granite layer. However at the margins the thickness reaches 50 km. The South Caspian uplift, surrounded by troughs, is recognized in the southern part of the basin. The thickness of a sedimentary cover in basins is up to 25 km and on the uplift only 12–15 km. The age of the sedimentary cover is Cenozoic and that of the underlying consolidated basement is Mesozoic and even older. The South Caspian uplift and surrounding troughs show latitudinal strike while complicating local folds are both latitudinal and longitudinal. The strike of local folds is apparently the result of horizontal displacement of sediments along steep slopes of troughs and complicating major structures. It is suggested that the South Caspian basin occupied the zone where the intersection of rift troughs, which differ in age and direction, took place.

Depositional Environments Within High-Energy Tidally Dominated Embayments Along Pacific Margin, United States: ABSTRACT

Geophysical and sedimentological studies within lower Cook Inlet, Alaska, have revealed acoustic facies relations and sedimentologic depositional environments typical of large, tidally dominated estuarine systems along the Pacific margin of the United States. Since 1976, detailed high resolution seismic and sidescan sonar surveys, underwater television, and photography, together with sediment sampling, in lower Cook Inlet, have delineated six major depositional environments: high-energy tidal flat; trough-edge platform; trough slope; tidal trough (channel); channel-mouth plateau; and seaward progradational ramp. Within these environments are found lithofacies ranging from sand patches, sand ribbons, and mixed cobble-sand hard bottom to sand-wave bodies of oth large- and small-scale and to sand-wave and shell-lag complexes. These facies appear to be primarily controlled by the modern hydrodynamic regime and the availability of sediment within lower Cook Inlet. In lower Cook Inlet at present, sands and gravels are being deposited while older glacial sediments are being winnowed. Marine transgression since glaciation has resulted in a more energetic tidal environment in the present than existed in the past. Geophysical (evidence shows that deposition has occurred over a preexisting glacial topography consisting of an irregular surface cut by numerous shallow channels. In other areas, banks of till lightly covered by recent sediments appear to nearly crop out on the seafloor. Throughout lower Cook Inlet, however, modern sediments average approximately 30 to 40 m in thickness. Four primary acoustic depositional facies are recognized in the shallow subsurface sediments. The upper two acoustic facies can be correlated with the modern lithofacies within lower Cook Inlet. Facies A, considered to represent unsorted tills, overlies the eroded glacial surface and is up to 75 m thick. It has a characteristically nearly transparent acoustic appearance on high resolution geophysical records. Overlying Facies A is Facies B which is characterized by a strong acoustic reflection. This facies is very thin and is thought to represent glacially derived outwash gravels and cobbles. Facies C overlies Facies B and it is acoustically identified by its pattern of multiple horizontal reflectors which is thought to represent a succession of alternating layers of silt and sand. Fa ies C is considered to have been deposited when lower Cook Inlet was a quiet bay. The uppermost acoustic facies, Facies D, appears limited to trough, plateau, or ramp environments and is composed of large-scale sand-wave complexes. Modern analogous sand-wave complexes can be presently found in parts of lower Cook Inlet. Willipa Bay, Oregon, and San Francisco Bay, California, exhibit modern sediment facies which are similar in some ways to those described for lower Cook Inlet. Comparison of these Pacific margin embayments in terms of hydrodynamics, sediments, constructional history, and topography has led to a general facies model for high-energy tidally dominated estuarine systems. End_of_Article - Last_Page 448------------

Observations in drying pulverized coal using an ultrasonically vibrating trough

The purpose of this investigation was to study the influence of applying ultrasonics directly to a heated inclined drying trough in drying of thermal degradable powders such as desulfurized pulverized coal. A frequency of 20-kHz was used with intensities up to 150 W. The variables studies included: Ultrasonic intensity, temperature and slope of trough. It was found possible to convert 40%–60% of the heat into the evaporation of the moisture from the coal; 10% to heat the coal and moisture to the evaporation temperature; the remaining heat was lost by radiation and convection into the environment. It is conjectured that the direct addition of ultrasound to the drying trough aided both the moisture flow and heat transfer to the evaporating surface.

Relationships Between Bottom Topography and Marine Sediment Properties in an Area of Submarine Gullies

ABSTRACT A precise bathymetric survey, including the collection of 21 cores, was accomplished by the submersible DEEP QUEST along a gullied section of the upper San Diego Trough slope off Del Mar, California. The primary purpose of the study was to investigate the relationship between topography and the mass physical properties of marine sediments. A secondary objective was to gain more information on the nature and origin of these submarine gullies. The cores were obtained along precisely controlled transects down the gully axes as well as on transects approximately perpendicular to the axes. Sediment samples from the cores were tested in the laboratory for shear strength, water content, bulk density, grain size distribution, and mineralogic composition. Submarine gullies within the area appear to begin at the edge of the shelf and trend almost directly westward. The lateral extent of these gullies is from 800 to 1200 meters. Width of the larger gullies varies from 203 to 274 meters. The gullies have a relief of 18 to 30 meters. The morphology of the gullies strongly suggests that they were originally formed by subaerial erosion. Within the submarine gullies the only sediment property which appears possibly to be related to the topography is the grain size distribution. The expected progressive decrease in the grain particle size occurs in the seaward direction. A trend was observed in the water content-sediment depth profiles, which is believed to be a result of the grain size distribution and not of the topographic changes. This trend indicates water content values decreasing as the size of the sediment particles increase. Water content values also indicate a non-linear decrease with sediment depth. X-ray diffraction and heavy mineral analysis indicate that the sediments are very homogeneous in mineralogic composition throughout the area studied. Quartz was usually identified as the major constituent of the entire sample. Illite and mixed layer micas were the predominate clay minerals in the clay size fraction. The principal heavy minerals were amphiboles, pyroxenes and opaques.