Sediment Source Areas Research Articles

Ion microprobe (SHRIMP) U–Pb dating of Upper Cretaceous volcanics from the northern Lord Howe Rise, Tasman Sea

Rock samples recovered during the Australian–French AUSFAIR MD153 Survey in 2006 from the northern Lord Howe Rise and the Fairway Ridge provide new constraints on the tectonostratigraphic evolution of the region and represent significant new information from a region in which few rocks have been dated. SHRIMP U–Pb dating of zircon from rocks from the Lord Howe Rise indicates alkali volcanism in the area at 97 Ma (trachyte) and 74 Ma (latite). The older volcanic activity is probably related to the widespread Late Cretaceous magmatism along the eastern Gondwana margin, whereas the younger activity may be related to the opening of the Tasman Sea or rifting in the New Caledonia Basin. The pebbly clasts and shell fossils in some of the associated volcaniclastic rocks provide evidence for the existence of landmasses as a sediment source area in the northern Lord Howe Rise region, and the initial marine incursion into the area around Campanian time.

Sediment and particulate phosphorus characteristics in grassed waterways from row crop corn and alfalfa fields collected by manual University of Exeter samplers and automatic sampling

AbstractPhosphorus (P) export from agricultural lands above known threshold levels can result in adverse impacts to receiving water quality. Phosphorus loss occurs in dissolved and sediment‐bound, or particulate phosphorous (PP), forms, with the latter often dominating losses from row‐cropped systems. To target practices, land managers need good computer models and model developers need good monitoring data. Sediment monitoring data (e.g. radiometric finger printing and sediment P sorption capacity) can help identify sediment source areas and improve models, but require more sediment mass than is typically obtained by automatic sampling. This study compares a simple suspended sediment sampler developed at the University of Exeter (UE) with automatic sampling in intermittent channels draining corn and alfalfa fields. The corn field had a greater runoff coefficient (27%) than alfalfa (11%). No differences were found in enrichment ratios (sediment constituent/soil constituent) in PP (PPER) or percent loss on ignition (LOIER) between paired UE samplers on corn. The median LOIER for the UE samplers (1·9%) did not differ significantly (p > 0·13) from the automatic sampler (2·0%). The PPER from the UE samplers was on average 20% lower than the automatic samplers. A correlation (r2 = 0·75) was found between sediment PP and % LOI from automatic samplers and UE samplers for particles < 50 µm, while for > 50 µm PP concentration did not change with changes in % LOI. Sediment ammonium‐oxalate extractable metals were similarly related to LOI, with the strongest correlation for iron (r2 = 0·71) and magnesium (r2 = 0·70). Copyright © 2011 John Wiley & Sons, Ltd.

Whiting-related sediment export along the Middle Miocene carbonate ramp of Great Bahama Bank

Modern aragonite needles are present all along the modern leeward margin of Great Bahama Bank (ODP Leg 166), while Middle Miocene sediments contain needles only in more distal areas (Sites 1006 and 1007). In contrast to the rimmed, flat-topped platform topography during the Plio-Pleistocene, the Miocene Great Bahama Bank morphology is a carbonate ramp profile. This might imply a different location and precipitation type for Miocene aragonite needles. In this study, aragonite needles in Miocene sediments were isolated using a granulometric separation method. Furthermore, the isolation of the various carbonate components enables the identification of primary versus diagenetic components. The Miocene aragonite needles are concentrated in the finest granulometric sediment fractions (<12 μm). The fraction-specific geochemical analyses (δ13C, δ18O and Sr elemental abundance) represent useful tools to assess the possible sources of the aragonite mud. The geochemical variation of the fractions, rich in pristine aragonite needles, and the characteristics of the needle morphology point to whiting phenomena as the main sediment source and algal fragmentation as a minor component. Both components indicate shallow-water environments as the main sediment source area. Ramp-top-related fine-grained particles now present at distal sites were likely exported as suspended material similar to present-day transport mechanisms. The scarcity of needles at proximal sites is probably linked to hydrodynamic processes but dissolution and recrystallization processes cannot be excluded. The granulometric separation approach applied here enables a better characterization of the finest carbonate particles representing an important step towards the discrimination between primary and diagenetic fine-grained components.

Chapter 37 U–Pb SIMS zircon geochronology of Triassic and Jurassic sandstones on northwestern Axel Heiberg Island, northern Sverdrup Basin, Arctic Canada

Abstract Detrital U–Pb zircon age data from five stratigraphically controlled Mesozoic sandstones collected from a relatively continuous section in northwestern Axel Heiberg Island are used to evaluate the sediment dispersal patterns and source areas of the northern Sverdrup Basin. Three distinctive provenance types are identified. Early Triassic, Late Triassic and Middle Jurassic samples are dominated by Permo-Triassic zircons and are inferred to be derived from the Taimyr Peninsula/Polar Urals, the New Siberian Islands or some unexposed source submerged beneath the Arctic Ocean. The presence of chrome spinel in these samples suggests a component of mafic–ultramafic material in the source. An Early Jurassic sample is dominated by late Neoproterozoic–early Silurian zircons, which correlate with the Caledonian and Timanian orogens of the Barents Shelf region. A Late Jurassic sample is dominated by Meso-, Palaeoproterozoic and Archaean zircons interpreted to be sourced from the Canada–Greenland shield. Supplementary material: Heavy mineral data (Table S1) and U–Th–Pb ion microprobe analytical data (Table S2) are available at http://www.geolsoc.org.uk/SUP18475 .

Determining Nutrient and Sediment Critical Source Areas with SWAT: Effect of Lumped Calibration

In many watershed modeling studies, due to limited data, model parameters for flow, sediment, and nutrients are calibrated and validated against observed data only at the watershed outlet. Model parameters are adjusted systematically for the entire watershed to obtain the closest match between the model-simulated and observed data at the watershed outlet (lumped calibration). It is hypothesized that the relative loadings of pollutants and/or sediments contributed by each computational unit are not affected by this calibration procedure. In other words, areas generating relatively higher pollutant loads with an uncalibrated model will still generate relatively higher loads after calibration. This study explored the effect of lumped calibration of the Soil and Water Assessment Tool (SWAT) on locations of sediment and nutrient critical source areas (CSAs). Two watersheds in Alabama with differing size, topography, hydrology, and land use/cover characteristics were used to study the variations in locations of sediment, total phosphorus (TP), and total nitrogen (TN) CSAs identified by calibrated and uncalibrated SWAT models. Identified CSAs for sediment, TP, and TN were mostly the same with and without the calibration of the model in both watersheds. This study thus concluded that lumped calibration of the SWAT model using data at the watershed outlet has little effect on the locations of CSAs. Based on the results from these two watersheds, it was further concluded that SWAT can be used without calibration for identification of CSAs in watersheds that lack sufficient data for model calibration, but not for all other modeling purposes. More studies are encouraged to support these findings.

Use of rare earth oxides as tracers to identify sediment source areas for agricultural hillslopes

Abstract. Understanding sediment sources is essential to enable more effective targeting of in-field mitigation approaches to reduce diffuse pollution from agricultural land. In this paper we report on the application of rare earth element oxides to arable soils at hillslope scale in order to determine sediment source areas and their relative importance, using a non-intrusive method of surface spraying. Runoff, sediments and rare earth elements lost from four arable hillslope lengths at a site in the UK with clay soils were monitored from three rainfall events after tracer application. Measured erosion rates were low, reflecting the typical event conditions occurring at the site, and less than 1% of the applied REO tracers were recovered, which is consistent with the results of comparable studies. Tracer recovery at the base of the hillslope was able to indicate the relative importance of different hillslope sediment source areas, which were found to be consistent between events. The principal source of eroded sediments was the upslope area, implying that the wheel tracks were principally conduits for sediment transport, and not highly active sites of erosion. Mitigation treatments for sediment losses from arable hillslopes should therefore focus on methodologies for trapping mobile sediments within wheel track areas through increasing surface roughness or reducing the connectivity of sediment transport processes.

Dynamics of the Barents-Kara ice sheet as revealed by quartz sand grain microtextures of the late Pleistocene Arctic Ocean sediments

During the entire Quaternary, ice sheets advanced and retreated across the circum-Arctic margins in a series of climate related glacial-interglacial cycles. It is critical to obtain evaluation of the nature of initiated glaciers at the Arctic margins after the pronounced interglacial periods. In this study this will be done by inferring from glacially generated quartz sand grain surface microtextures and related sedimentology extracted from the central Arctic Ocean sediments. These microtextures can be correlated with the generation and fluctuations in the extent of the late Pleistocene Eurasian Ice Sheet i.e. Barents-Kara Ice Sheet. The central Arctic Ocean sediments in the Lomonosov Ridge, having been deposited after the late Pleistocene interglaciations and having had no internal hiatuses, provide an excellent time window for usage of quartz sand grain surface textures for evaluating possible evolving glaciers and continental ice sheets. This is based on the fact that iceberg and sea-ice transported quartz sand grains and their mechanically formed surface textures, created under high cryostatic stress, are diagnostic for glacier thickness and dynamics having been existed in sediment source areas. Sand-sized quartz grains in deep marine sediments favour iceberg or sea-ice transportation with characteristic content of microtextures formed prior this transportation. The sand grain surface microtextures and their frequencies of the selected submarine Lomonosov Ridge sediments during Marine Isotope Stage (MIS) 5 to MIS 3 are analysed using a scanning electron microscope (SEM). Coring during the Arctic Ocean 96 expedition (core 96/12-1pc) provided alternating clay to silty clay sediments which are characterised by prominent silt to sand-size containing intervals. The specific glacial crushing and high cryostatic stress generated features, such as high angularity, conchoidal fractures, steps and sub-parallel linear fractures, were observed from quartz sand grain surfaces. Continental ice generation and extent are evident soon after the Eemian interglaciation and the following MIS 4 stage shows the highest frequencies of glacigenic microtextures. The microtexture generation under high cryostatic pressure underneath ice more than 1 km thick, can be taken as concurrent signal of the temporal expansion of the northernmost continental ice sheets, which could easily have reached the shelf break of the Barents, Kara and western Laptev seas during that time.

Submarine fans at all sea-level stands: Tectono-morphologic and climatic controls on terrigenous sediment delivery to the deep sea

Research Article| October 01, 2010 Submarine fans at all sea-level stands: Tectono-morphologic and climatic controls on terrigenous sediment delivery to the deep sea Jacob A. Covault; Jacob A. Covault 1Chevron Energy Technology Company, Clastic Stratigraphy R&D, San Ramon, California 94583, USA Search for other works by this author on: GSW Google Scholar Stephan A. Graham Stephan A. Graham 2Department of Geological and Environmental Sciences, Stanford University, Stanford, California 94305, USA Search for other works by this author on: GSW Google Scholar Geology (2010) 38 (10): 939–942. https://doi.org/10.1130/G31081.1 Article history received: 30 Jan 2010 rev-recd: 18 May 2010 accepted: 22 May 2010 first online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Jacob A. Covault, Stephan A. Graham; Submarine fans at all sea-level stands: Tectono-morphologic and climatic controls on terrigenous sediment delivery to the deep sea. Geology 2010;; 38 (10): 939–942. doi: https://doi.org/10.1130/G31081.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Early models of stratigraphic sequence development across continental margins predicted terrigenous sediment delivery to the deep sea principally during periods of sea-level fall and lowstand. However, subsequent models acknowledged caveats to these early predictions. We employ a global database of millennial-scale continental-margin deep-sea deposition rates, activities of canyon-channel systems, and episodes of submarine-fan growth since 35 ka to assess the timing of terrigenous sediment delivery to the deep sea. As predicted by the early models, the majority of continental-margin deep-sea deposition occurred during periods of marine transgression and lowstand of sea level. However, deep-sea deposition is shown to have occurred at all sea-level states, and some deep-sea fans predominantly grew during periods of sea-level highstand. Terrigenous sediment delivery to the deep sea depends on factors such as tectono-morphologic character of the margin (e.g., narrow shelves) and climatic forcings (e.g., subglacial meltwater and monsoonal pulses). A fundamental understanding of the tectonic and climatic forcings inherent to a continental margin and its terrestrial sediment source area is essential to accurately predict timing and magnitude of deep-sea deposition and place it in the context of sequence stratigraphy. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Effect of Soil Data Resolution on Identification of Critical Source Areas of Sediment

Identification of critical source areas (CSAs) of pollution in a watershed is important for effective implementation of best man- agement practices (BMPs). Process-based watershed models are often used for this purpose. One of the main inputs to these models is the spatially explicit soils data. The objective of this study was to evaluate whether the use of two commonly used soil data sets, the State Soil Geographic (STATSGO) and the Soil Survey Geographic (SSURGO) data, can lead to differences in location of CSAs of sediment. A watershed model, Soil and Water Assessment Tool (SWAT), in combination with the Tukey-Kramer test was used for locating CSAs in the Fish River watershed located in coastal Alabama. The model was calibrated and validated using flow data from a U.S. Geological Survey (USGS) gauging station located within the watershed. The locations of the CSAs of sediment were analyzed at subwatershed and hydrologic response unit (HRU) levels. Results show that the locations of the CSAs were different for the two soil data sets. The locations of the CSAs varied at both subwatershed and HRU levels. The use of STATSGO soil data resulted in higher soil erodibility factor and surface runoff. As a result, higher sediment yield was obtained from the use of the STATSGO data as compared with the sediment yield obtained from the use of the SSURGO data. Therefore, for accurate identification of CSAs of sediment (and potentially other pollutants) and for effective imple- mentation of economically feasible BMPs, it is important to use the most detailed spatial data set available. DOI: 10.1061/(ASCE)HE .1943-5584.0000318. © 2011 American Society of Civil Engineers.

Sources and depositional processes of tsunami deposits: Analysis using foraminiferal tests and hydrodynamic verification

AbstractForaminiferal tests are commonly found in tsunami deposits and provide evidence of transport of sea floor sediments, sometimes from source areas more than 100 m deep and several kilometers away. These data contribute to estimates of the physical properties of tsunami waves, such as their amplitude and period. The tractive force of tsunami waves is inversely proportional to the water depth at sediment source areas, whereas the horizontal sediment transport distance by tsunami waves is proportional to the wave period and amplitude. We derived formulas for the amplitudes and periods of tsunami waves as functions of water depth at the sediment source area and sediment transport distance based on foraminiferal assemblages in tsunami deposits. We applied these formulas to derive wave amplitudes and periods from data on tsunami deposits in previous studies. For some examples, estimated wave parameters were reasonable matches for the actual tsunamis, although other cases had improbably large values. Such inconsistencies probably reflect: (i) local amplification of tsunami waves by submarine topography, such as submarine canyons; and (ii) errors in estimated water depth at the sediment source area and sediment transport distance, which mainly derive from insufficient identification of foraminiferal tests.

Revised magnetostratigraphy and characteristics of the fluviolacustrine sedimentation of the Kashmir basin, India, during Pliocene‐Pleistocene

The Pliocene‐Pleistocene Karewa Group sediments of the Kashmir basin, India, provide an important continental archive for past climatic reconstruction. The present study reevaluates the magnetic polarity stratigraphy and the nature of the depositional environment at a 440‐m‐thick section along Romushi river near Pakharpur (33°48′50″N, 74°45′54″E). Magnetic remanences are predominantly carried by Ti‐rich titanomagnetite and magnetite. We identified eight normal and eight reversed‐polarity magnetozones in this succession, ranging between 4.40 and 0.77 Ma. The polarity sequence includes the new identification of the Cochiti and the Mammoth and their preceding and succeeding reversed/normal as well as the Jaramillo subchrons. Anisotropy of magnetic susceptibility data suggest the existence of northeast‐ and northwest‐flowing fluvial system before 4.18 Ma, indicating the Pir Panjal range at the southwest as the sediment source area. Following this, the valley was under the influence of fluviolacustrine environment between 4.18 and 0.77 Ma. Our results suggest relatively strong flow velocity toward the northeast during the upper Gilbert, Gauss, and lower and middle Matuyama chrons (4.18–1.07 Ma). In the upper Matuyama chron (&lt;1.07 Ma), the prevailing paleocurrent direction in the basin changed toward the northwest with a reduced flow velocity, indicating the emergence of the ancestral Jhelum river. On the basis of the magnetic polarity chronology, the sediment accumulation rate indicates a very low value of ∼4.6 cm kyr−1 before 1.95 Ma to ∼33 cm kyr−1 between 1.95 and 1.77 Ma and 23 cm kyr−1 after 1.77 Ma. We attribute temporal changes in sedimentation rate to the interplay between climate (predominantly westerlies) and tectonics (pulsating Pir Panjal uplift).

Temporal changes in suspended sediment transport in an Atlantic catchment, NW Spain

Catchment scale suspended sediment (SS) transport studies in northwest Spain are of special interest as little research at this scale has been done in this region. However, the role of sediments in the transfer of nutrients and contaminants to coastal areas in this region has been highlighted. Data were collected from the Corbeira catchment during a 3-year period and the variability in SS load at different temporal scales (within-events variability, monthly/seasonal, and annual) was analyzed. The statistical relationship between discharge and suspended sediment concentration (SSC) from samples obtained every 15 days as well as during runoff events in October 2004 to September 2007 showed a marked scatter of points. Hence, the rating curve method does not seem appropriate to estimate SSC in this catchment. The results also demonstrated that at the within-events scale, most of the SS peaks preceded the discharge peaks (70% of runoff events), implying that zones nearby or well connected to the stream are the dominant sediment source areas. In some cases, rills and ephemeral gullies developed in cropland were the main source of sediment delivered to the stream. Furthermore, a reduction in SSC was observed in sequences of events, which can be mainly linked to a phenomenon of sediment exhaustion. At the seasonal scale, most of the total annual SS load was transported during the autumn months, the period in which, generally, the largest number of events occurred, while in the summer, total annual SS load was very low (< 1%). At the annual scale, specific SS yield (SSY) ranged from 5.4 to 11.2 Mg km -2 y -1. The variability in SSY was correlated with the number and magnitude of runoff events recorded yearly, since runoff events dominated SS transport and yield. For instance, in the last hydrological year (2006/07), more than 80% of the SS load was exported in runoff events involving < 10% of the time.

Factors controlling hydro-sedimentary response during runoff events in a rural catchment in the humid Spanish zone

Abstract In Galicia (NW Spain) studies on the suspended sediment (SS) transported in river catchments are scarce. Using a dataset comprising three hydrological years (2004/05–2006/07) in the Corbeira catchment (NW Spain), the relationships between rainfall, runoff and SS are analysed at event scale. The catchment was instrumented to measure rainfall, water level and SS in the stream. Several event (rainfall, discharge and SS concentration and load) and pre-event (rainfall and discharge) variables were calculated for all the events analysed. Correlation matrices were developed using these data. Discharge characteristics and rainfall depth showed good correlations with SS concentration and load. Suspended sediment and discharge relationships were also examined. In most of the events, the SS peak preceded peak discharge (clockwise hysteresis), implying that zones near the stream are the main sediment source areas.

Regional scale modeling of hillslope sediment delivery: A case study in the Barasona Reservoir watershed (Spain) using WATEM/SEDEM

Soil erosion and sediment delivery to streams are important environmental problems and major concerns in sustainable development. In recent years several tools have been proposed for assessing the delivery of sediment from hillslopes to stream networks, but there are still few examples of their application to large basins, and studies include a discussion of calibration and validation issues. In this study a spatially distributed soil erosion and sediment delivery model (WATEM/SEDEM) was applied to the watershed of the Barasona Reservoir (1504 km 2 , Central Spanish Pyrenees), which is drained by the Ésera and Isábena Rivers. Model calibration and validation was based on the depositional history of the Barasona Reservoir and suspended sediment records over 3 years (May 2005–May 2008) at the outlet of the Isábena River. Despite interannual differences in precipitation and runoff, it was possible to establish an optimum value (7–23) for the ktc parameter. This enabled estimation of the long-term average annual sediment yield to the reservoir, as well as the relative contribution of each river. Large spatial variability in hillslope sediment delivery was found, and the major sediment sources were in the lower part of the watershed (agricultural fields) and in the badlands developed on Eocene marls in the middle part of the watershed (Pyrenean Inner Ranges). The relative importance of sediment source areas was assessed in relation to land use, and the relationship between the sediment delivery ratio and the catchment area was studied as a function of the geomorphological units. For the moment WATEM/SEDEM remains mainly as a researcher’s tool, until either the problem of the scarcity of soil erosion data or the need for calibration of the transport parameters will be solved.

Facies control on sandstone composition (and influence of statistical methods on interpretations) in the John Henry Member, Straight Cliffs Formation, Southern Utah, USA

The Upper Cretaceous John Henry Member of the Straight Cliffs Formation preserves regressive shoreface and channel facies, and transgressive lagoonal tidal inlet facies that suggest distinct modal sandstone compositions. Detrital modes from six sandstone facies (upper shoreface, lower shoreface, deflected mouth bars, fluvial channels, tidal inlets and washover fans), and their spatial and temporal variations, provide additional data regarding the depositional environments and setting of the John Henry Member. Three statistical methods were utilized: univariate standard deviation and confidence interval and multivariate logratio transformations to assess the compositional difference between facies using estimation of means. Both univariate statistical methods have some inherent problems. Standard deviation does not account for sample size, while the confidence interval method incorporates a t-test to account for only some of the uncertainty of small sample size. The results of the univariate methods differ slightly and both indicate statistically distinct sandstone compositions based on facies. Multivariate statistics are much more robust and suggest similar trends, yet display different compositional means and have inconclusive confidence fields as they incorporate all of the uncertainty associated with small sampling sizes. In general, sandstone compositions become more quartz-rich and compositionally mature as sediment is transported from proximal fluvial environments to distal upper shoreface environments. This trend reflects the degree of preferential reworking or winnowing of unstable grains prior to lithification. More complicated relationships are observed as facies distributions shift through space and time. Sandstone compositions support a deflected wave-dominated deltaic interpretation for the John Henry Member in this area. Sandstone compositions become more lithic-rich from north to south, corresponding to the facies distribution of upper shoreface and deflected mouth bars, respectively. Mouth bars occur at the intersection of the fluvial channel and the coastline where sand is deflected via longshore drift to the southern portion of the field area. Upper shoreface facies located further away from mouth bar facies are heavily reworked by wave processes and contain more mature quartz-rich modal compositions. Additionally, high feldspathic and lithic concentrations in tidal inlet facies suggest that this facies was sourced closer to mouth bars rather than updrift upper shoreface sediments. A shift in sandstone composition occurs at the end of the second transgressive–regressive cycle of the John Henry Member throughout the Rogers Canyon area. This compositional change is concurrent with a relatively large basinward shift in facies, which suggests that it reflects the transition from regressive to transgressive facies associated with the relative sea level fall rather than a change in the main sediment source area.

Cenozoic post-rift sedimentation off northwest Britain: Recording the detritus of episodic uplift on a passive continental margin

The Cenozoic sedimentary basins on the Atlantic margin of NW Britain contain a remarkable record of tectonically influenced post-breakup sedimentation. We have mapped the distribution and quantified the solid grain volume of four unconformity-bound successions in the region: the Eocene (~6–8 × 104 km3), Oligocene (~2 × 104 km3), MioceneLower Pliocene (~4–5 × 104 km3) and Lower PlioceneHolocene (~4–5 × 104 km3) complementing previous work on the Paleocene succession. Approximately 80% of the total Cenozoic sediment volume on the Atlantic margin of NW Britain was deposited in Eocene and later times. The relative volumes of the Cenozoic succession do not support previous claims that the Paleocene was the main period of Cenozoic uplift and erosion of sediment source areas. Rather, the Cenozoic sedimentary basins on the Atlantic margin of NW Britain record the detritus of four major episodes of Cenozoic uplift of the British Isles (Paleocene, Eocene–Oligocene, Miocene and Pliocene–Pleistocene).

OBSERVATION OF CURRENTS AND SUSPENDED SEDIMENT CONCENTRATION OFF NORTHERN JIANGSU COAST, CHINA

The abandoned Yellow River delta off Jiangsu coast is an important sediment source area,where erosion occurs and large amounts of suspended materials are carried seaward. In order to understand the hydrodynamic process here,a 3-vessel simultaneous measurement was conducted with ADP (acoustic Doppler profiler) and water samplers in autumn of 2006. The analyses of survey data show suspended sediment fluxes,the changes of currents and suspended sediment concentrations. The net suspended sediment fluxes of a tidal cycle range from 103 kg m-1 to 104 kg m-1,mainly to the south. First order estimation of yearly fluxes through the area is similar to a long-term average estimation. The investigation shows the currents are controlled by tides. The suspended sediment concentrations change within a tidal cycle. There are peaks of suspended sediments concentrations corresponding approximately to the time just after the maximum current velocity. Data show that velocity gradients become larger when velocity is bigger. High velocity gradients mean high bed shear stress. The high bed shear stress in turn causes the erosion and resuspension of seabed sediments,resulting in a high suspended sediment concentration in the water column.

Sediment transport off the Huanghe (Yellow River) delta and in the adjacent Bohai Sea in winter and seasonal comparison

Based on the data on the current velocity, water temperature, salinity, turbidity and concentration of suspended sediment collected in November 2006 along three survey transects at three time-series, ship-based stations off the Huanghe (Yellow River) delta, and at twenty-four grid survey stations in the adjacent Bohai Sea, sediment transport off the Huanghe delta and in the adjacent Bohai Sea under winter regime were studied and compared with those from the summer season. The homogeneous distribution of salinity, temperature and sediment in the water column indicated a well-mixed body of water. A zone of high suspended sediment concentrations (SSC) >100 mg l −1 with a width of 35 km was identified along the delta coast. Two highest SSC centers were found in the surface and middle water layers around the abandoned Diaokou Huanghe river mouth and the present Huanghe river mouth, and the third one in the bottom layer around the abandoned Qingshuigou Huanghe river mouth. These three highest SSC centers become major sediment source areas in winter. Based on the location of the high bottom shear stress zone, the prevailing wave directions and the protuberant topography of the river mouths, we identified the resuspension origin of the three highest SSC centers caused mostly by the winter storm waves, partially by tidal currents. Suspended sediment flux (SSF) along the three coastal transects indicated that the sediment in the northwest part of the delta was transported northeastward and southeastward along the coast of the recent delta lobe. The SSC and SSF were higher in winter than summer by 1.7–27.1 and 2–122.5 times, respectively, except around the present river mouth. This indicates that the intensity of sediment transport in winter is much stronger than in summer due to the powerful effect of winter storms although the river water and sediment discharges to the sea were much greater in summer. The massive Huanghe sediment to the sea was accumulated in a narrow coastal area due to weak hydrodynamics in summer, and then strongly resuspended mostly by storm waves in winter and transported to the offshore area. The coastal area off the Huanghe delta acts as a sediment sink in summer and converted to be a sediment source in winter in response to the seasonal variation of the East Asian monsoon in this region. The erosion–accumulation pattern of the Huanghe subaqueous delta from 1976 to 2003 illustrates that river-laden sediment is deposited mainly in the southern part off the coastal area and it is also the result of intensive southward sediment transport in winter.

Chemostratigraphy of upper Jurassic reservoir sandstones, Danish Central Graben, North Sea

A chemostratigraphic study of Upper Jurassic sandstones in the northern Danish Central Graben has been undertaken within the framework of a well-defined stratigraphic/sedimentological model based particularly on cored well sections. Two reservoir sandstone units are recognised, the transgressive marginal marine to shoreface sandstone of the Gert Member and the regressive to transgressive shoreface sandstone of the Ravn Member. Both members belong to the Heno Formation, which is equivalent to the Fulmar Formation (UK) and the Ula Formation (Norway). Multivariate analysis of geochemical data from 264 core samples from 8 wells reveals the distinction between the two reservoir sandstones (Gert and Ravn members) and the two offshore claystones (Farsund and Lola formations). Specific elements have proven to be important for this separation and these elements demonstrate differences even in 2-dimensional cross plots. The Farsund Formation is characterised by higher V, U and P 2O 5, and lower MgO and K 2O when compared with the Lola Formation. The Gert Member typically has higher maximum amounts of Cr and TiO 2 than the Ravn Member. The high Cr and TiO 2 content (probably from chrome spinel and Ti-minerals) might be related to a source of exposed Carboniferous sediments in the Gert Ridge area. The Ravn Member is characterised by higher Na 2O, P 2O 5 and Th contents than the Gert Member, which may reflect a higher content of plagioclase (Na 2O) and a changed heavy mineral assemblage. The Mid North Sea High is a likely source for the heavy mineral suite that characterises the Ravn Member. The Rita-1 well, situated closest to the Mid North Sea High, seems to have been more influenced by this source than the other wells. In the Hejre area, a volcanic source supplying K-feldspar may be responsible for the relatively high K 2O/Al 2O 3 observed in both the Gert and Ravn members. Hence in addition to differentiation between the two reservoir sands and between the two offshore claystones, this study also illustrates the use of geochemical data for evaluation of source characteristics and dominance of different sediment source areas.

Statistical distribution of soil loss and sediment yield at Sparacia experimental area, Sicily

An analysis of the statistical distribution of event soil loss was carried out using the data collected in the period 1999–2008 at the microplots and plots of the Sparacia experimental area (Sicily, Italy). For a given microplot size, the analysis allowed to establish that the soil loss frequency distribution was skewed. Using the soil loss normalized by the event mean value, the analysis also showed that the frequency distributions corresponding to different microplot and plot sizes were overlapping, i.e. all distributions were extracted by the same statistical population. The developed analysis allowed to suggest that the soil loss of a given return period can be estimated using a scale and a frequency factor. Finally the sediment yield data collected in two basins of the Sparacia area were used to compare the frequency distributions of normalized soil erosion data collected at different spatial scales (plot, basin). The overlapping of the two distributions was satisfactory, and the conclusion was that the mean value of the measured variable is expressive of the characteristics of the sediment source area.