Sediment Source Areas Research Articles

Enhanced sea-ice export from the Arctic during the Younger Dryas

The Younger Dryas cold spell of the last deglaciation and related slowing of the Atlantic meridional overturning circulation have been linked to a large array of processes, notably an influx of fresh water into the North Atlantic related to partial drainage of glacial Lake Agassiz. Here we observe a major drainage event, in marine sediment cores raised from the Lomonosov Ridge, in the central Arctic Ocean marked by a pulse in detrital dolomitic-limestones. This points to an Arctic-Canadian sediment source area with about fivefold higher Younger Dryas ice-rafting deposition rate, in comparison with the Holocene. Our findings thus support the hypothesis of a glacial drainage event in the Canadian Arctic area, at the onset of the Younger Dryas, enhancing sea-ice production and drifting through the Arctic, then export through Fram Strait, towards Atlantic meridional overturning circulation sites of the northern North Atlantic.

Links between composition and provenance of Mesozoic siliciclastic sediments from western Calabria (southern Italy)

Mesozoic siliciclastic mudrocks (‘continental redbeds') at the base of the Stilo Unit of the northern sector of the Calabria-Peloritani Arc (southern Italy) are mainly composed of quartz, phyllosilicates (illite, illite/smectite mixed layers, kaolinite, chlorite), Fe-oxide (hematite) and feldspars. The <2 μm grain-size fraction shows high percent of I/S mixed layers, characterized by R value ranging from R0 to R3. The Kubler Index values indicate temperatures ranging from 130 °C to 160 °C. The source areas of the studied sediments were mainly characterized by metasediments of the Paleozoic basement with plutonic bodies. The limited importance of a mafic supply is confirmed by the La/Sc, Th/Sc, Th/Co, Th/Cr and Cr/Th ratios, that suggest a provenance from source areas fairly felsic rather than basic in composition. The CIA index indicates moderate weathering in the sediment source areas. The Al-Ti-Zr diagram and the Th/Sc vs. Zr/Sc plot indicate sedimentary sorting and recycling effects for the studied sediments. Preliminary geological and compositional data of these siliciclastic deposits suggest close similarities with the well studied Mesozoic continental redbed successions of the Internal domains of the circum-Mediterranean orogenic belts.

LA-ICPMS U–Pb zircon age constraints on the provenance of Cretaceous sediments in the Yichang area of the Jianghan Basin, central China

Detrital zircon U–Pb ages have been shown to be a powerful tool for provenance analysis and determining the exhumation of sediment source areas. This paper presents the results of detrital zircon LA-ICPMS U–Pb ages for Cretaceous sediments from the Yichang area of the Jianghan Basin, central China. The results provide new information on the provenance of these sediments and the detailed exhumation process of the Huangling Dome. Zircons with different age populations have been derived from the strata of the Huangling Dome. The Liantuo, Gucheng and Nantuo formations and the Kongling complex were exhumed, leading to deposition of the early Cretaceous Wulong Formation, which provides the sources of zircons with age peaks at 3.1–3.0, 2.5 and 1.8 Ga. Exhumation of the Huangling granitoid and contemporary volcanics provided the source of the late Cretaceous Luojingtan Formation, which contains zircons with age peaks at 1.1–0.95 and 0.83–0.74 Ga. The Qinling-Dabie orogeny supplied zircons with an age cluster of 0.27 to 0.18 Ga. These results indicate the timing of initial exhumation for the Huangling granite. They also show how overlying strata was first uplifted and eroded, followed by exposure of underlying strata at the surface during continued exhumation.

Geochemistry of Quaternary sediments of the Jeongokri archaeological site, Korea: implications for provenance and palaeoenvironments during the Late Pleistocene

AbstractThe geochemical characteristics of an approximately 6‐m‐long sediment core collected from the Jeongokri archaeological site (Hantan River, Korea) were examined to determine the provenance of the sediments and to reconstruct the palaeoenvironment of the study area during the Late Pleistocene (200–127 ka). The core sediments were subdivided into two parts based on grain size: an upper (0–380 cm depth) and lower part (&gt;380 cm depth). The lower part was deposited primarily by fluvial processes during an interglacial period [marine isotope stage (MIS) 7] with warm and humid conditions. Conversely, the upper part was mainly deposited by aeolian processes during a cold and dry glacial period (MIS 6). Geochemical characteristics, represented by major, trace and rare earth element (REE) compositions, and textures of the Jeongokri core sediments show distinct differences between the upper and lower parts. The mineralogy and major, trace and REE compositions indicate that the influence of felsic source rocks (e.g. granite) was dominant in the lower sediments, which were derived from the Hantan River. In contrast, increased quartz content and the very fine and homogeneous grain size in the upper sediments indicate an aeolian origin. REE ratios and distribution patterns, and geochemical signatures indicate that these sediments were derived predominantly from Chinese loess deposits and partially from local sediments from the Korean Peninsula; the possible source area of the upper sediments is the northern part of the Yellow Sea basin. The Yellow Sea basin, having mixed geochemical signatures between Chinese loess and Korean‐derived sediments, was exposed because of low sea levels during MIS 6. The exposed Yellow Sea basin was located in the path of winter‐monsoon winds, which may have carried a great deal of airborne sediments from the basin to the Jeongokri area. Copyright © 2011 John Wiley &amp; Sons, Ltd.

Clastic deposition, provenance, and sequence of Andean thrusting in the frontal Eastern Cordillera and Llanos foreland basin of Colombia

Sedimentological, provenance, and detrital thermochronological results for basin fill at the modern deformation front of the northern Andes (6°N latitude) provide a long-term, Eocene to Pliocene record of foreland-basin sedimentation along the Eastern Cordillera–Llanos basin boundary in Colombia. Lithofacies assemblages and paleocurrent orientations in the upward-coarsening, ~5-km-thick succession of the Nunchia syncline reveal a systematic shift from craton-derived, shallow-marine distal foreland (back-bulge) accumulation in the Mirador Formation, to orogen-sourced, deltaic, and coastal-influenced sedimentation of the distal to medial foreland (foredeep) in the Carbonera and Leon Formations, to anastomosing fluvial and distributive braided fluvial megafan systems of the proximal foreland (foredeep to wedge-top) basin in the lower and upper Guayabo Formation. These changes in depositional processes and sediment dispersal are supported by up-section variations in detrital zircon U-Pb and (U-Th)/He ages that record exhumation of evolving, compartmentalized sediment source areas in the Eastern Cordillera. The data are interpreted in terms of a progressive eastward advance in fold-and-thrust deformation, with late Eocene–Oligocene deformation in the axial zone of the Eastern Cordillera along the western edge of Floresta basin (Soapaga thrust), early Miocene reactivation (inversion) of the eastern margin of the Mesozoic rift system (Pajarito and Guaicaramo thrusts), and middle–late Miocene propagation of a footwall shortcut fault (Yopal thrust) that created the Nunchia syncline in a wedge-top (piggyback) setting of the eastern foothills along the transition from the Eastern Cordillera to Llanos foreland basin. Collectively, the data presented here for the frontal Eastern Cordillera define a general in-sequence pattern of eastward-advancing fold-and-thrust deformation during Cenozoic east-west shortening in the Colombian Andes.

Modelling Sediment Input to Surface Waters for German States with MEPhos: Methodology, Sensitivity and Uncertainty

Soil erosion on arable land and on steep vineyards is a major problem in the state of Hesse (21,115 km²) in central Germany. The aim of a joint study between the Research Centre Julich, the Hessian Agency for the Environment and Geology and the Hessian Ministry for the Environment, Energy, Agriculture and Consumer Protection was to delineate parcels which are severely affected by erosion and to identify sediment source areas. For this purpose, the ABAG, an adaptation of the USLE approach to German conditions, has been employed with the best available data sets on K-, C-, R- and LS-factor. Model results at the field scale show that soil losses in Hesse vary between 15 tonnes/hectare/year. The mean loss amounts to ca. 4.3 tonnes/hectare/year. The sediment delivery ratios for 450 sub-catchments range between 0.5 and 78% with a mean of 18%. Further analysis showed that LS- and C-factor are of highest sensitivity for the model output. Therefore, the effects of alternative algorithms or sources for LS- and C-factor on the results were assessed. An uncertainty analysis based on Gaussian error propagation and Monte Carlo simulation showed that the uncertainty of model results induced by input parameters is 1.7 tonnes/hectare/year or 34% of the mean annual soil loss. The model results are a good basis for further works concerning a soil erosion atlas and internet-based soil data viewer.

Meso-Archaean and Palaeo-Proterozoic sedimentary sequence stratigraphy of the Kaapvaal Craton

The Kaapvaal Craton hosts a number of Precambrian sedimentary successions which were deposited between 3105 Ma (Dominion Group) and 1700 Ma (Waterberg Group) Although younger Precambrian sedimentary sequences outcrop within southern Africa, they are restricted either to the margins of the Kaapvaal Craton, or are underlain by orogenic belts off the edge of the craton. The basins considered in this work are those which host the Witwatersrand and Pongola, Ventersdorp, Transvaal and Waterberg strata. Many of these basins can be considered to have formed as a response to reactivation along lineaments, which had initially formed by accretion processes during the amalgamation of the craton during the Mid-Archaean. Faulting along these lineaments controlled sedimentation either directly by controlling the basin margins, or indirectly by controlling the sediment source areas. Other basins are likely to be more controlled by thermal affects associated with mantle plumes. Accommodation in all these basins may have been generated primarily by flexural tectonics, in the case of the Witwatersrand, or by a combination of extensional and thermal subsidence in the case of the Ventersdorp, Transvaal and Waterberg. Wheeler diagrams are constructed to demonstrate stratigraphic relationships within these basins at the first- and second-order levels of cyclicity, and can be used to demonstrate the development of accommodation space on the craton through the Precambrian.

Assessing the potential effect of different land cover management practices on sediment yield from an abandoned farmland catchment in the Spanish Pyrenees

PurposeSediment delivery from headwater catchments to reservoirs is a serious threat to reservoir sustainability and is a critical issue in Mediterranean environments where water resources are scarce. In this study we assessed the consequences of two landscape management scenarios (natural vegetation recovery and scrub clearance) on soil erosion and sediment yield. The results were analyzed in relation to predicted and measured rates of soil erosion and sediment yield, with the aim of promoting better management practices.Materials and methodsThe study area was the Arnás River catchment (284 ha), which is located in the central Spanish Pyrenees; the area includes abandoned and poorly managed fields. The combination of the RUSLE and SEDD models of soil erosion and sediment delivery was evaluated in terms of its ability to predict annual rates of sediment yield, using field measurement data for seven water years at the gauging station. The consequences of natural plant succession in other areas of the Spanish Pyrenees and scrub clearance practices implemented by certain regional governments to increase grazing meadow areas and reduce the incidence of wildfires were spatially analyzed using GIS. The main sediment source areas were identified, and their specific and total sediment yields were calculated.Results and discussionThe predicted soil loss under existing conditions was 2.6 Mg ha−1 year−1, with 5% of the surface area affected by rates greater than 2 Mg. The measured sediment yield range was 69–534 Mg year−1. The maximum sediment yield detected was associated with an extraordinary debris flow. The predicted rates were strongly correlated to measured rates (Nash–Sutcliffe coefficient = 0.72). The main sources were alluvial deposits [specific sediment yield (SSY) = 51 Mg ha−1 year−1], bare soil (SSY = 12), unpaved trails (SSY = 11), lots (SSY = 4), and pastures (SSY = 1). Under a scenario of vegetation recovery, decreases of 3%, 17%, and 16% in soil loss and sediment delivery and yield (respectively) are predicted, whereas increases of 15%, 5%, and 2% are predicted following scrub clearance practices.ConclusionsCoupling the RUSLE and SEDD models enabled estimation of annual values of soil erosion and sediment delivery in monitored and unmonitored catchments of small and medium size, making this approach a useful tool for risk analysis. Management practices that combine fire-risk control, by the implementation of scrub clearance practices, with the effects of plant succession on sediment production are suggested as the best management strategy.

Pennsylvanian paleodepositional evolution of the greater Permian Basin, Texas and New Mexico: Depositional systems and hydrocarbon reservoir analysis

The Permian Basin of west Texas and New Mexico is the largest petroleum-producing basin in the United States. In this area, multiple episodes of Paleozoic faulting, uplift, and erosion occurred, including those events related to the Marathon-Ouachita orogeny (Hercynian orogenic cycle 350–250 Ma). Within Paleozoic rocks in the Permian Basin, the Pennsylvanian succession is the second most oil-productive system, next to the Permian. This succession has been viewed historically as sedimentologically and stratigraphically complex because of the interplay of deposition, coinciding with icehouse climatic conditions during a second-order global transgression, and presumed active tectonism.New paleodepositional systems maps for the Morrowan, Atokan, Desmoinesian, Missourian, and Virgilian stages of the greater Permian Basin are presented. This study integrates varied data, including outcrop, drill core, geophysical (seismic and gravity), wireline log, biostratigraphic, and reservoir quality. Systems maps depict the spatial and temporal distribution of sediment source areas, shallow-water to basinal carbonates, alluvial to open-marine siliciclastics, shales, and areas of uplift.A Pennsylvanian reservoir architecture and facies evolution diagram combines data on key reservoir facies and targets, including their dimensions; the relative location of the facies tracts within each depositional system; the overall system architecture; and each stage's potential for diagenetic modification. A unified depositional system model provides continuity between the paleodepositional systems maps and summarizes the entire Pennsylvanian facies proportion evolution within eight provinces of the Permian Basin. The depositional systems information is referenced to second- to fourth-order eustasy curves and tectonic input. The reservoir evolution diagram and paleodepositional maps used in conjunction with the unified systems model provide the reader with the most current and extensive integration of data on the Pennsylvanian geologic history in the greater Permian Basin from a sedimentologic and petroleum reservoir systems perspective. Insights into facies distribution, the overall development of the basin and its subbasins, tectonic episodes, identification of potential new play types and exploration targets, and new depositional and sequence-stratigraphic architectural models are presented in this article.

The coupling status of alluvial fans and debris cones: a review and synthesis

ABSTRACTAlluvial fans and debris cones link two zones of the fluvial system (e.g. hillslope gully systems to stream channels; mountain catchment sediment source areas to main river systems or to sedimentary basins) and therefore have important coupling or buffering roles. These roles may be both functional and preservational. The functional role includes debris‐cone coupling, which controls sediment supply from hillslope gully systems to stream channels, influencing channel morphology. Coupling through larger alluvial fans, expressed by fanhead trenching, causes a distal shift in sedimentation zones, or when expressed by through‐fan trenching, causes complete sediment by‐pass. The preservational role stems from the fact that fans and cones are temporary sediment storage zones, and may preserve a record of source–area environmental change more sensitively than would sediments preserved further downsystem. Fan coupling mechanisms include distally‐induced coupling (basal scour, ‘toe cutting’, marginal incision) and proximally‐induced coupling (fanhead and midfan trenching). These mechanisms lead initially to partial coupling, either extending the immediate sediment source area to the stream system or shifting the focus of sedimentation distally. Complete coupling involves transmission of sediment from the feeder catchment through the fan environment into the downstream drainage or a sedimentary basin. The implications of coupling relate to downstream channel response, fan morphology, sedimentation patterns and vertical sedimentary sequences. Temporal and spatial scales of coupling are related, and with increasing scales the dominant controls shift from storm events to land cover to climatic and base‐level change and ultimately to the relationships between tectonics and accommodation space. Finally, future research challenges are identified. Modern dating techniques and sophisticated analysis of remotely sensed data can greatly improve our understanding of fan dynamics, and should lead to better cross‐scale integration between short‐term process‐based approaches and long‐term sedimentological applications, while maintaining high quality field‐based observations. Copyright © 2011 John Wiley &amp; Sons, Ltd.

Rare earth elements tracing the soil erosion processes on slope surface under natural rainfall

A field experiment using rare earth elements (REEs) as tracers was conducted to investigate soil erosion processes on slope surfaces during rainfall events. A plot of 10 m × 2 m × 0.16 m with a gradient of 20° (36.4%) was established and the plot was divided into two layers and four segments. Various REE tracers were applied to the different layers and segments to determine sediment dynamics under natural rainfall. Results indicated that sheet erosion accounted for more than 90% of total erosion when the rainfall amount and density was not large enough to generate concentrated flows. Sediment source changed in different sections on the slope surface, and the primary sediment source area tended to move upslope as erosion progressed. In rill erosion, sediment discharge mainly originated from the toe-slope and moved upwards as erosion intensified. The results obtained from this study suggest that multi-REE tracer technique is valuable in understanding the erosion processes and determining sediment sources.

Characterisation and sediment–source linkages of intertidal sediment of the UK’s north Sefton Coast using magnetic and textural properties: findings and limitations

Sediment pathways and links to offshore processes are considered in the textural and magnetic characteristics of sediments of the intertidal flats and salt marshes of the north Sefton Coast, UK. In addition, sediment from a range of intertidal, marine and fluvial locations within the northwest region has similarly been characterised. Subsequently, the characteristics of these regional sediments, using a multivariate statistical approach of R- and Q-mode factor analyses, have been used to investigate the sediment transport pathways of the north Sefton Coast sediment. The benefits of fractionating sediment samples have been observed, and by using combinations of textural and isothermal remanent magnetic measurements, specific environments within the research have been successfully differentiated and characterised. Linkages between potential sediment source areas have also been established on a particle size-related basis.

Petrology, mineralogy, and geochemistry of submarine coals and petrified forest in the Sozopol Bay, Bulgaria

Abstract The mineralogy, petrology, and geochemistry of submarine coals and petrified tree trunks from the Sozopol Bay were investigated. The coals are lignites of Lower–Middle Miocene age. The petrified trunks are 40 cm up to 2 m high, some of which are in growth position and others are fallen. The main minerals in the coal are silicates of detrital origin (clay minerals) and authigenic pyrite. Authigenic sulfur and amber are present as well. In the Sozopol coals stored for 30 years, a neoformed mineral assemblage comprising mainly of gypsum, iron sulfates, sulfates of varying Fe, Na, Al, K, and Mg content, and halite has been observed. The formation of the sulfates was induced by bacterial activity as well. Germanium, Li, Rb, Ti, V, Mo, Cr, Mn, Co, and Ni are enriched in the coals as compared with the Clarke values of the world brown coals. In most of the samples studied, the contents of Ga, B, Y, W, Cu, Zn, Pb, P, and Zr are elevated as well. The element distribution is influenced by the lithotype composition. Most elements have a mixed mode of occurrence. Germanium, V, Ti, Cr, B, Na, and Ni (and to a lesser extent Sr and Cu) are organically associated, while K, Li, Rb, and Fe have a distinct inorganic mode of occurrence. Molybdenum follows strictly the Fe distribution. It is suggested that the main sources of the trace elements were the volcanic rocks in the sediment source area, from which the elements were leached in the peat bog.

Depositional and provenance record of the Paleogene transition from foreland to hinterland basin evolution during Andean orogenesis, northern Middle Magdalena Valley Basin, Colombia

Abstract The Central Cordillera and Eastern Cordillera of the northern Andes form the topographic flanks of the north-trending Magdalena Valley Basin. Constraining the growth of these ranges and intervening basin has implications for Andean shortening and the transformation from a foreland to hinterland basin configuration. We present sedimentological, paleocurrent, and sandstone petrographic results from Cenozoic type localities to provide insights into the tectonic history of the northern Middle Magdalena Valley Basin of Colombia. In the Nuevo Mundo Syncline, the mid-Paleocene transition from marine to nonmarine deposystems of the Lisama Formation corresponds with a paleocurrent shift from northward to eastward transport. These changes match detrital geochronological evidence for a contemporaneous shift from cratonic (Amazonian) to orogenic (Andean) provenance, suggesting initial shortening-related uplift of the Central Cordillera and foreland basin generation in the Magdalena Valley by mid-Paleocene time. Subsequent establishment of a meandering fluvial system is recorded in lower–middle Eocene strata of the lower La Paz Formation. Eastward paleocurrents in mid-Paleocene through uppermost Eocene fluvial deposits indicate a continuous influence of western sediment source areas. However, at the upper middle Eocene (∼40 Ma) boundary between the lower and upper La Paz Formation, sandstone compositions show a drastic decrease in lithic content, particularly lithic volcanic fragments. This change is accompanied by a facies shift from mixed channel and overbank facies to thick, amalgamated braided fluvial deposits of possible fluvial megafans, reflecting changes in both the composition and proximity of western sediment sources. We attribute these modifications to the growing influence of exhumed La Cira-Infantas paleohighs in the axial Magdalena Valley, features presently buried beneath upper Eocene–Quaternary basin fill along the western flank of the Nuevo Mundo Syncline. In uppermost Eocene strata of the lower Esmeraldas Formation, paleocurrents show a sharp reversal from eastward to dominantly westward transport that persisted into the Neogene. The Esmeraldas also records a change to more-distal, floodplain-dominated deposition of finer sediments. These adjustments are interpreted to reflect burial of the La Cira-Infantas highs and onset of Eastern Cordillera exhumation, resulting in a transition from foreland to hinterland basin conditions in the Magdalena Valley. The lack of significant variation in sandstone compositions suggests a bulk-rock compositional similarity between the La Cira-Infantas paleohighs (subsurface Magdalena Valley) and the Eastern Cordillera. Collectively, the data presented here refine previous thermochronologic and provenance studies and suggest that major uplift-induced exhumation in the Central Cordillera and Eastern Cordillera commenced by the mid-Paleocene and latest Eocene, respectively.

Middle slope contourite deposits and associated sedimentary facies off NE Argentina

The Argentine continental margin is characterised by a large contourite depositional system driven by southern-sourced water masses flowing at different water depths. Interest in contourite deposits is increasing in geoscience and related fields, though knowledge of the Argentine contourite system is still limited. In particular, studies based on core data providing detailed descriptions of sedimentary facies are lacking, as are investigations of principal sediment source areas and of key factors controlling sedimentary processes. This study combines visual core description and downcore grain-size analyses as well as petrographic thin-section and magnetic susceptibility analyses of 14 cores from intermediate water depths of 616–1,208 m to characterise contourite deposits on the north-eastern Argentinean slope. Gravel-rich, sandy–silty and muddy contourites as well as hemipelagic facies were identified. The deposition of these contourites was presumably controlled by sea level, the depth range of the Antarctic water mass, climate conditions and windborne terrigenous supply. It is proposed that, during glacial lowstands, muddy contourites were deposited at depths <900 m, whereas sandy–silty sequences dominated at deeper depths. During the late Pleistocene–Holocene transition, sandy–silty contourites covered the entire middle slope. Hemipelagic facies draped limited sectors of the middle slope when the sea level reached the present-day position and gravel-rich contourites became restricted to contouritic channels and moats. Northern Patagonia and the southern Pampa are the most plausible sources for sediments deposited via along-slope processes, whereas the Tandilia Range is the best candidate for sediments deposited via down-slope processes.

Reconstructing the Late Cretaceous inversion of the Roer Valley Graben (southern Netherlands) using a new model that integrates burial and provenance history with fission track thermochronology

[1] Apatite fission track thermochronology is a powerful tool for the reconstruction of the thermal and geological evolution of sedimentary basins. However, reconstructing basin evolution using thermochronological data is complicated by the fact that sediments also record the thermal history of their source areas. Moreover, samples frequently contain grains from multiple source areas. We have constructed a new numerical model that integrates sediment burial and thermal history with provenance history scenarios and that uses the derived thermal history to calculate synthetic apatite fission track data. We have applied this model to study the evolution of the Roer Valley Graben and to explore the dependency of fission track data on provenance and basin thermal history. Samples that are buried at shallow depths (<1400 m) preserve a mix of late Paleozoic and early Mesozoic provenance ages that correspond to the Caledonian and Variscan orogenic events of the sediment source areas, the London-Brabant and Ardenno-Rhenish massifs, respectively, with varying degrees of subsequent exhumation. Using this knowledge about the inherited thermal history, fission track data of Mesozoic sediments could be used to constrain the Late Cretaceous inversion of the basin with an accuracy of ±250 to ±500 m. These results show that inversion-related exhumation was localized, reaching a maximum of 750 to 1250 m in the eastern part of the basin, while not exceeding 500 m in the western half of the basin. These results are in agreement with the distribution of preserved preinversion sediments and syninversion sediment accumulations that flank the northeastern part of the basin.

An exploratory study on the use of enzyme activities as sediment tracers: biochemical fingerprints?

Little information exists on the potential of soil enzyme activities, which are sensitive to soil properties and management, for the characterization of sediment sources at the catchment scale. The objective of this study is to explore and evaluate enzyme activity as tracer for sediment fingerprinting in the Hiv catchment (55 km 2), Iran. Therefore, four enzymes were measured from 42 different sampling sites, covering three sediment source areas (rangeland/surface erosion, orchard/surface erosion, and streambank erosion), as well as from 12 sediment samples from reservoir check dams (sediment sinks). The results indicate that, based upon backward mode discriminant analysis, β-glucosidase and dehydrogenase, allowed more than 95% of the samples to be correctly assigned to their source areas. These enzymes were selected as input data for a mixing-model to determine the relative contribution of the sampled sediment sources. The mean contributions from rangeland, orchard and streambank sources in the study area were estimated as 11.3%, 15.1% and 73.7%, respectively. Using geochemical tracers, the mean contribution from rangeland, orchard and streambank sources was estimated as 14.1%, 9.5% and 74.8%, respectively. Combined biochemical and geochemical tracers, similar values were obtained (18.7%, 10.7% and 70.7%, respectively). Our results indicate that soil enzyme activity allows for a good characterization of sediment sources, and can provide a complementary tool to currently existing sediment fingerprinting approaches. However, the method should be also tested in other regions.

ASSESSING THE PERFORMANCE OF A SPATIALLY DISTRIBUTED SOIL EROSION AND SEDIMENT DELIVERY MODEL (WATEM/SEDEM) IN NORTHERN ETHIOPIA

ABSTRACTMost regional‐scale soil erosion models are spatially lumped and hence have limited application to practical problems such as the evaluation of the spatial variability of soil erosion and sediment delivery within a catchment. Therefore, the objectives of this study were as follows: (i) to calibrate and assess the performance of a spatially distributed WATEM/SEDEM model in predicting absolute sediment yield and specific sediment yield from 12 catchments in Tigray (Ethiopia) by using two different sediment transport capacity equations (original and modified) and (ii) to assess the performance of WATEM/SEDEM for the identification of critical sediment source areas needed for targeting catchment management.The performance of the two model versions for sediment yield was found promising for the 12 catchments. For both versions, model performance for the nine catchments with limited gully erosion was clearly better than the performance obtained when including the three catchments with significant gully erosion. Moreover, there is no significant difference (alpha 5 per cent) between the performances of the two model versions.Cultivated lands were found to be on average five times more prone to erosion than bush–shrub lands. The predicted soil loss values in most parts of Gindae catchment are generally high as compared with the soil formation rates. This emphasises the importance of implementing appropriate soil and water conservation measures in critical sediment source areas prioritising the steepest part of the catchment (i.e. areas with slope &gt;50 per cent).The applicability of the WATEM/SEDEM model to environments where gully erosion is important requires the incorporation of permanent gully and bank gully erosion in the model structure. Copyright © 2011 John Wiley &amp; Sons, Ltd.

Diagenetic sensitivity of paleoenvironmental proxies: A rock magnetic study of Australian continental margin sediments

A rock magnetic study of the upper 40 m of the Ocean Drilling Program Site 133‐820A recovered at the outer edge of the northeastern Australian continental margin shows that downcore variations in magnetic parameters are diagenetically driven and correlate with the changes in global sea level. We identified intervals enriched in single‐domain (SD) magnetite in the studied section. Unlike previous studies that postulated a detrital source, we show that the bulk of the SD fraction is biologically produced and is likely to be authigenic. The abundance of SD magnetite thus cannot be used as an indicator for provenance or sediment transport mechanisms. The biogenic magnetite was preserved during the high sedimentation rate periods, likely due to a short residence time in the corrosive zone of active iron reduction. The presence of the biogenic magnetite thus can be used as an indicator for a low degree of reductive dissolution. More advanced dissolution during the periods of slow sedimentation, coincident with sea level highstands, resulted in significant changes in the composition of the detrital assemblage, particularly in relative abundances of different mineral phases. The overall stability of the detrital magnetic minerals toward dissolution varies in the studied section as hematite &gt; magnetite &gt; goethite. Due to the higher stability of hematite, reductive diagenesis in general will lead to the lowering of the goethite/hematite (G/H) ratio, which can be mistaken for an increased aridity in the sedimentary source areas in the conventional interpretation for this proxy. The sensitivity of the G/H proxy to diagenesis should be taken into account in paleoenvironmental studies.

Geospatial and visual modeling for exploring sediment source areas across the Sele river landscape, Italy

This study uses the revised universal soil loss equation (RUSLE) and Geographic Information System technology to map erosion-prone areas in the Sele basin (Campania-Basilicata regions, southern Italy). Current land use/cover, soil erodibility and climate factors were evaluated to determine their effects on average annual soil loss. Geospatial technologies were applied to generate RUSLE factors and erosion map. Long-term soil losses were 53 Mg ha-1 per year averaged over an area of 2500 km2 and more than 30% of the Sele basin was subjected to soil losses higher than 20 Mg ha-1 per year. Data available in the study area allowed to estimate soil losses, but the absence of direct sediment measurements prevents an accurate evaluation of the model performance. Nevertheless, the results are similar to the ones from other studies, and provide useful preliminary information for landscape management and restoration.