Burial Of Sediments Research Articles

Effect of imposed anaerobic conditions on metals release from acid-mine drainage contaminated streambed sediments

Remediation of streams influenced by mine-drainage may require removal and burial of metal-containing bed sediments. Burial of aerobic sediments into an anaerobic environment may release metals, such as through reductive dissolution of metal oxyhydroxides. Mining-impacted aerobic streambed sediments collected from North Fork Clear Creek, Colorado were held under anaerobic conditions for four months. Eh, pH, and concentrations of Cd, Cu, Fe, Mn, and Zn (filtered at 1.5 μm, 0.45 μm, and 0.2 μm), sulfate, and dissolved organic carbon (DOC) were monitored in stream water/sediment slurries. Two sediment size fractions were examined (2 mm–63 μm and <63 μm). Sequential extractions evaluated the mineral phase with which metals were associated in the aerobic sediment. Released Cu was re-sequestered within 5 weeks, while Fe and Mn still were present at 16 weeks. Mn concentration was lower than in the initial stream water at and beyond 14 weeks for the smaller sized sediment. Cd was not released from either sediment size fraction. Zn was released at early times, but concentrations never exceeded those present in the initial stream water and all was re-sequestered over time. The greatest concentrations of Cu, Fe, Mn, and Zn were associated with the Fe/Mn reducible fraction. Sulfate and Fe were strongly correlated ( r = 0.90), seeming to indicate anaerobic dissolution of iron oxy-hydroxy-sulfate minerals. DOC and sulfate were strongly correlated ( r = 0.81), with iron having a moderately strong correlation with DOC ( r = 0.71). Overall concentrations of DOC, sulfate, Cu, Fe, and Zn and pH were significantly higher ( p < 0.05) in the water overlying the small sized sediment samples, while the concentrations of Mn released from the larger sized sediment samples were greater.

Biogenic silica in intertidal marsh plants and associated sediments of the Yangtze Estuary

Biogenic silica (BSi) contents in the marsh plants ( Phragmites australis, Scirpus mariqueter and Spartina alterniflora) and associated sediments in Chongming Island eastern intertidal flat of the Yangtze Estuary were determined. The BSi contents in P. australis, S. mariqueter and S. alterniflora varied from 25.78–42.74 mg/g, 5.71–19.53 mg/g and 6.71–8.92 mg/g, respectively. Over the entire growth season, P. australis and S. mariqueter were characterized by linear accumulation patterns of BSi. The aboveground biomass (leaves and culms) of the marsh plants generally contained more BSi than underground biomass (roots). BSi contents were relatively higher in dead plant tissues than in live tissues which was probably due to the decomposition and the leaching of labile components of plant tissues such as organic carbon and nitrogen. Comparing with the habitats of S. mariqueter and S. alterniflora, the highest BSi content was recorded in sediments inhabited by P. australis, with an annual average of 15.69 mg/g. Overall, the intertidal marshes in the Yangtze Estuary may act as a net sink of BSi via plant uptake and sedimentary burial.

Assessment of the oil source-rock potential of the Pedregoso Formation (Early Miocene) in the Falcón Basin of northwestern Venezuela

The early Miocene Pedregoso Formation is one of the numerous formations rich in organic matter within the stratigraphic record of the Urumaco Trough, in the central area of the Falcón Basin. Due to its lithological characteristics and stratigraphic position, this formation is of great interest regarding the basin's petroliferous systems. The evaluation of various inorganic and organic geochemical parameters indicates that the organic matter is primarily of marine origin, deposited in a marine carbonate environment typical of reefal systems, under oxic-to-dysoxic conditions. The low variability in the TOC concentrations and in the distributions of the biomarkers extracted from the samples suggests that the paleoenvironmental conditions and the organic-matter supply remained approximately constant throughout the sedimentation of this unit. The Pedregoso type-II organic matter (marine origin) and initial organic richness value (∼1.8%) suggest that this unit has probably generated hydrocarbons within the Urumaco Trough. However, present-day thermal maturity parameters reveal that the Pedregoso organic matter is overmature (dry gas window), indicating that this unit is only capable to generate gas. In addition, the geothermal gradient, maturity parameters, and the maximum paleotemperature estimated in this study suggest that the Pedregoso Formation reached a maximum burial depth the ∼6.5 km, consistent with the value obtained from data of stratigraphic thickness in the Urumaco Trough. This implies that the thermal anomaly that affected the basin during the Late Eocene–Early Miocene did not reach the central part of the basin, and therefore, the organic matter maturation in this unit is due to the sedimentary burial.

Phosphorus Burial in Sediments Along the Salinity Gradient of the Patuxent River, a Subestuary of the Chesapeake Bay (USA)

We used a sequential extraction technique and 210Pb dating to determine the chemical form and amount of particulate phosphorus (PP) that is retained during burial in 1-m-long sediment cores collected along a salinity gradient from tidal freshwater to the mesohaline waters of the Patuxent River, a subestuary of the Chesapeake Bay. PP buried in the study sites with salinity values ≤3 was similar in concentration and form to PP entering the Patuxent from the watershed, suggesting efficient sequestration by the sediments at these low-salinity sites. PP extracted with citrate–dithionite–bicarbonate was the dominant form of PP at all salinities and all depths, and organic-P was the second most abundant fraction. We estimated that 81% of PP entering from the watershed is trapped in the sediments of the upper Patuxent subestuary and that the subtidal sediments retain three times as much PP as the marshes adjacent to the study sites.

Application of low-temperature thermochronology to hydrothermal ore deposits: Formation, preservation and exhumation of epithermal gold systems from the Eastern Rhodopes, Bulgaria

New low-temperature thermochronological data have been used to quantify the protracted, Eocene–Miocene cooling histories of upper and lower plate rocks of the Kesebir–Kardamos extensional dome, Eastern Rhodopes, Bulgaria. 40Ar/ 39Ar and apatite fission-track data reveal that the lower plate has experienced continuous cooling and exhumation, since the Late Eocene. Muscovite 40Ar/ 39Ar plateau ages of 36.90 ± 0.16 Ma and 37.28 ± 0.19 Ma (2 σ) from metamorphic rocks of the footwall reveal the approximate time span during which they cooled below ∼ 350 °C during exhumation caused by detachment faulting. The sedimentary rock-hosted gold mineralization, which represents a thermal event at ∼ 250–220 °C, developed during the early stage of basin formation between 34.71 ± 0.16 Ma and 35.36 ± 0.21 Ma (adularia 40Ar/ 39Ar plateau ages; 2 σ). The termination of hydrothermal mineral deposition at Ada Tepe occurred contemporaneously with the earliest phase of calc–alkaline type magmatism at Iran Tepe (33.97 ± 0.36 Ma to 34.62 ± 0.46 Ma, hornblende and biotite 40Ar/ 39Ar plateau ages, 2 σ). Thermal history modelling of apatite fission-track data shows that the lower plate rocks cooled through ∼ 120 °C at ∼ 18.3 ± 1.9 Ma (1 σ). A time–temperature model obtained from zircon and apatite fission-track data from the upper plate reveals that it was being buried during the late Eocene. At ∼ 33–30 Ma, a dramatic change of the time–temperature path was caused by the initiation of horst–graben structures, resulting in rapid exhumation of the upper plate. Our new thermochronological data reveal many aspects of the mechanisms of formation of sedimentary rock-hosted gold deposits. The heat accumulated during sedimentary burial of the upper plate is a plausible heat source to drive hydrothermal fluid circulation and ore formation. The development of large half-graben basins in the hanging walls of detachment faults, accompanied by a favourable climate, may have created a situation that was adequate to capture a primary meteoric water supply that subsequently underwent hydrothermal convection. Our new 40Ar/ 39Ar age data indicate that magmatic activity was contemporaneous with gold deposition and must be considered as a source of heat, sulphur and/or a metal for the ore-forming hydrothermal system. The preservation and exhumation of sedimentary rock-hosted ore deposits is largely controlled by the exhumation history of the upper plate, which has been quantitatively constrained by low-temperature thermochronological methods, and commences with rapid exhumation at ∼ 33–30 Ma.

Modeling phosphorus cycling and carbon burial during Cretaceous Oceanic Anoxic Events

In the greenhouse world of the Cretaceous, there were episodes of oxygen depletion in the deep ocean associated with enhanced organic carbon burial in sediments (black shale formation). In this study, we use a box model of the oceanic phosphorus (P), organic carbon (orgC) and oxygen cycles to explore the hypothesis that variations in marine P availability control deep ocean oxygen depletion (anoxia) and the formation of black shales under Cretaceous ocean conditions. We find that, for the Cretaceous ocean, with large continental shelves, slow oceanic overturning and high sea surface temperatures, Oceanic Anoxic Events (OAEs) can be triggered by enhanced P supply from land, and that the system is particularly sensitive to oceanic mixing. In our baseline scenario, the deep sea becomes completely anoxic, while the shelves attain only partial anoxia. Sedimentary burial differs between the shelves and open ocean: while organic carbon burial is enhanced in both regions, deep sea reactive P burial decreases dramatically under anoxia, but not on the shelves, where oxygen depletion is not complete. Furthermore, our model results imply that OAEs can be sustained by P recycling from sediments under low-oxygen conditions. Ultimately, however, the feedbacks which result in the accumulation of atmospheric oxygen terminate the anoxic event. Atmospheric oxygen is modulated by land processes such as forest fires and oxidative weathering, which limit the rise of atmospheric O 2. Our model findings are corroborated by P burial data from the geological record for OAE2 (approximately 94 Myr BP). Through a sensitivity analysis we identify two necessary criteria for OAEs: low mixing of surface and deep waters (poor ocean ventilation) and enhanced sedimentary P recycling under low oxygen conditions. When these criteria are met, ocean anoxia is a robust result to a mild increase of continental supply of phosphorus, under a wide range of environmental conditions.

Traces of brine and hydrocarbon migration in carbon, oxygen, and sulfur isotopic compositions of reservoir rocks in the Talakan petroleum field, Southwestern Yakutia

Dolomites from the productive Osa horizon (upper subformation of the Lower Cambrian Bilir Formation) in the Talakan petroleum field show a prominent 1–2‰ decrease in δ18O (from 23–24 to 21–22‰), which presumably marks a zone of relatively high water/rock ratios. Productive boreholes are characterized by moderate δ34S values (from 25.1 to 30.6‰) and negative correlation between δ34S in anhydrite and δ18O in associated dolomite, which points to a partial sulfate reduction during catagenesis. In nonproductive borehole, δ34S values increase significantly (from 31.4 to 35.6‰) and show positive correlation with δ18O in dolomite. Rocks recovered by nonproductive borehole possibly recrystallized during early diagenesis, and, correspondingly lost their permeability and capacity to form pores. Limestones and dolomites of the Osa horizon have a carbon isotopic composition within the range of normal marine carbonates (δ13C = 0 ± 1 ‰), which does not indicate a significant role of organic matter in postsedimentary recrystallization of carbonate sediments. A positive δ13C excursion up to 4.5‰ recorded in the lower subformation of the Bilir Formation presumably occurred at the sedimentation stage under conditions of high rates of bioproductivity and organic matter burial in sediments.

A new look at old carbon in active margin sediments

Recent studies suggest that as much as half of the organic carbon (OC) undergoing burial in the sediments of tectonically active continental margins may be the product of fossil shale weathering. These estimates rely on the assumption that vascular plant detritus spends little time sequestered in intermediate reservoirs such as soils, freshwater sediments, and river deltas, and thus only minimally contributes to the extraneously old 14C ages of total organic matter often observed on adjacent shelves. Here we test this paradigm by measuring the Δ14C and δ13C values of individual higher plant wax fatty acids as well as the δ13C values of extractable alkanes isolated from the Eel River margin (California). The isotopic signatures of the long chain fatty acids indicate that vascular plant material has been sequestered for several thousand years before deposition. A coupled molecular isotope mass balance used to reassess the sedimentary carbon budget indicates that the fossil component is less abundant than previously estimated, with pre-aged terrestrial material instead composing a considerable proportion of all organic matter. If these findings are characteristic of other continental margins proximal to small mountainous rivers, then the importance of petrogenic OC burial in marine sediments may need to be reevaluated. © 2009 The Geological Society of America.

Thermal impact of the break-up of Pangea on the Iberian Peninsula, assessed by thermochronological dating and numerical modelling

Thermochronological studies of Variscan basement in Iberia yield cooling ages typically younger than ~ 200 Ma. In this paper, we explore the regional implications of this recurrent age maximum by examination of low and high temperature thermochronological datasets from all over Iberia. Based on these results, we show that in general the lack of cooling ages older than 200 Ma is the result of several important regional periods of thermal resetting. Resetting took place in areas of extension and burial during the Mesozoic break-up of Pangea. Evidence for large scale magmatism and mineralisation is found in Iberia during the Mesozoic, since at that time Iberia formed part of the Central Atlantic Magmatic Province and a large mineralization province extending from North Africa to Western Europe. Numerical modelling allows us to assess the conditions under which rocks in the upper crust may have been thermally reset and the mechanisms likely involved. Results show that active rifting combined with shallow magmatism, and to a lesser extent deep sedimentary burial, could have led to an increase of the geothermal gradient up to ~ 73 °C/km and the reset of thermochronometers with closure temperatures up to 200 °C. Yet, we suggest that also hydrothermal activity, associated to extensional basins, played an important role to the increase of temperatures of some basement rocks above 300 °C.

Role of Oxide Surface Chemistry and Phospholipid Phase on Adsorption and Self-Assembly: Isotherms and Atomic Force Microscopy

We have examined the effects of metal oxide surface chemistry and lipid phase on phospholipid adsorption affinity and self-assembly. Adsorption isotherms of ditridecanoylphosphocholine (DTPC) at 40 °C and pH 7.2 on quartz (α-SiO2), rutile (α-TiO2), and corundum (α-Al2O3) particle suspensions indicated oxide-dependent adsorption affinity that decreased as rutile > corundum ≅ quartz at low concentrations and corundum > rutile ≅ quartz at higher concentrations. Significantly, atomic force microscopy of DTPC and dipalmitoylphosphocholine (DPPC) at high concentration on planar oxide surfaces at 25 °C in liquid-crystal and gel phases, respectively, also showed oxide-specific adsorption. Multiple bilayers formed on corundum (100), indicating greater coverage compared to single bilayers, bilayer patches, or supported vesicle layers on the negatively charged surfaces of mica (001), rutile (100), and amorphous silica glass (fused quartz plate). Thus, the amount and self-assembly of adsorbed phospholipid was found to be oxide-dependent regardless of the lipid phase. Significantly, both experimental methods show multiple bilayer formation as a unique feature of the positively charged alumina surface. The observed oxide affinity sequences are interpreted as controlled by van der Waals and electrostatic forces between the oxide surface and the negatively charged (−R(PO4−)R′−) portion of the phosphocholine headgroup. Our results have implications for the interactions of amphiphilic molecules with mineral surfaces in diverse biogeochemical, biomedical, and industrial processes, including membrane-bound biomineralization, cell membrane stability during early evolution of life, organic matter burial in ocean sediments, the design of supported lipid bilayers and biomimetic cell membranes for medical implant devices, enhanced oil recovery, and ore extraction by froth flotation.

Diversity dynamics of marine planktonic diatoms across the Cenozoic

Diatoms are the dominant group of phytoplankton in the modern ocean. They account for approximately 40% of oceanic primary productivity and over 50% of organic carbon burial in marine sediments. Owing to their role as a biological carbon pump and effects on atmospheric CO(2) levels, there is great interest in elucidating factors that influenced the rapid rise in diatom diversity during the past 40 million years. Two biotic controls on diversification have been proposed to explain this diversity increase: (1) geochemical coupling between terrestrial grasslands and marine ecosystems through the global silicon cycle; and (2) competitive displacement of other phytoplankton lineages. However, these hypotheses have not been tested using sampling-standardized fossil data. Here we show that reconstructions of species diversity in marine phytoplankton reject these proposed controls and suggest a new pattern for oceanic diatom diversity across the Cenozoic. Peak species diversity in marine planktonic diatoms occurred at the Eocene-Oligocene boundary and was followed by a pronounced decline, from which diversity has not recovered. Although the roles of abiotic and biotic drivers of diversification remain unclear, major features of oceanic diatom evolution are decoupled from both grassland expansion and competition among phytoplankton groups.

The regional and global significance of nitrogen removal in lakes and reservoirs

Human activities have greatly increased the transport of biologically available nitrogen (N) through watersheds to potentially sensitive coastal ecosystems. Lentic water bodies (lakes and reservoirs) have the potential to act as important sinks for this reactive N as it is transported across the landscape because they offer ideal conditions for N burial in sediments or permanent loss via denitrification. However, the patterns and controls on lentic N removal have not been explored in great detail at large regional to global scales. In this paper we describe, evaluate, and apply a new, spatially explicit, annual-scale, global model of lentic N removal called NiRReLa (Nitrogen Retention in Reservoirs and Lakes). The NiRReLa model incorporates small lakes and reservoirs than have been included in previous global analyses, and also allows for separate treatment and analysis of reservoirs and natural lakes. Model runs for the mid-1990s indicate that lentic systems are indeed important sinks for N and are conservatively estimated to remove 19.7 Tg N year−1 from watersheds globally. Small lakes (<50 km2) were critical in the analysis, retaining almost half (9.3 Tg N year−1) of the global total. In model runs, capacity of lakes and reservoirs to remove watershed N varied substantially at the half-degree scale (0–100%) both as a function of climate and the density of lentic systems. Although reservoirs occupy just 6% of the global lentic surface area, we estimate they retain ~33% of the total N removed by lentic systems, due to a combination of higher drainage ratios (catchment surface area:lake or reservoir surface area), higher apparent settling velocities for N, and greater average N loading rates in reservoirs than in lakes. Finally, a sensitivity analysis of NiRReLa suggests that, on-average, N removal within lentic systems will respond more strongly to changes in land use and N loading than to changes in climate at the global scale.

Burial of organic carbon and carbonate on inner shelf of the northern South China Sea during the postglacial period

Two vibrocores from the inner shelf off Hong Kong are investigated to compare the contents of organic and inorganic carbon in postglacial sediments. The compositions of organic elements and carbonate are highly variable in the core sediments, but overall drop within the compositional ranges of modern seabed sediments in the Zhujiang estuarine and its shelf area. The Holocene sediments in the inner shelf have never been subject to subaerial exposure and the organic matter and carbonate can be preserved well. The burial of carbon in river-dominated shelf environments is highly dependent on the river flux with time. Nevertheless, it is difficult to establish a simple relationship between carbon burial in sediments in relation to climatic changes of basin-wide scale due to complex controls of production, transport and deposition of organic matter and carbonate. Our study suggests that the organic carbon to nitrogen ratio can not reliably identify the sources of depositional organic matters because of selective decomposition of organic matter components during humification and sedimentation. Caution is therefore needed in using organic elemental compositions as indicators of organic matter sources and paleoenvironmental changes in the East Asian continental shelves where intense river-sea interaction and variable carbon flux in geologic record occur.

CLEAR LAKE SEDIMENTS: ANTHROPOGENIC CHANGES IN PHYSICAL SEDIMENTOLOGY AND MAGNETIC RESPONSE

We analyzed the sedimentological characteristics and magnetic properties of cores from the three basins of Clear Lake, California, USA, to assess the depositional response to a series of land use changes that occurred in the watershed over the 20th century. Results indicate that distinct and abrupt shifts in particle size, magnetic concentration/mineralogy, and redox conditions occur concurrently with a variety of ecological and chemical changes in lake bed sediments. This coincidence of events occurred around 1927, a datum determined by an abrupt increase in total mercury (Hg) in Clear Lake cores and the known initiation of open-pit Hg mining at the Sulphur Bank Mercury Mine, confirmed by 210Pb dating. Ages below the 1927 horizon were determined by accelerator mass spectrometry on 14C of coarse organic debris. Calculated sedimentation rates below the 1927 datum are approximately 1 mm/yr, whereas rates from 1927 to 2000 are up to an order of magnitude higher, with averages of approximately 3.5-19 mm/yr. In both the Oaks and Upper Arms, the post-1927 co-occurrence of abrupt shifts in magnetic signatures with color differences indicative of changing redox conditions is interpreted to reflect a more oxygenated diagenetic regime and rapid burial of sediment below the depth of sulfate diffusion. Post-1927 in the Oaks Arm, grain size exhibits a gradual coarsening-upward pattern that we attribute to the input of mechanically deposited waste rock related to open-pit mining activities at the mine. In contrast, grain size in the Upper Arm exhibits a gradational fining-upward after 1927 that we interpret as human-induced erosion of fine-grained soils and chemically weathered rocks of the Franciscan Assemblage by heavy earthmoving equipment associated with a road- and home-building boom, exacerbated by stream channel mining and wetlands destruction. The flux of fine-grained sediment into the Upper Arm increased the nutrient load to the lake, and that in turn catalyzed profuse cyanobacterial blooms through the 20th century. The resulting organic biomass, in combination with the increased inorganic sediment supply, contributed to the abrupt increase in sedimentation rate after 1927.

Graphitization of organic matter and fluid‐deposited graphite in Palaeoproterozoic (Birimian) black shales of the Kaya‐Goren greenstone belt (Burkina Faso, West Africa)

AbstractPalaeoproterozoic black shales form an essential part of the Birimian volcanosedimentary belt in Burkina Faso, West Africa. The mean Rmax values and the atomic H/C values of the bulk carbonaceous matter (BCM), together with rock structures and mineral assemblages, indicate that these carbon‐rich rocks were metamorphosed to sub‐greenschist and low‐grade greenschist facies. X‐ray diffraction reveals that the (002) ‘graphite’ peak width in half maximum (FWHM) ranges from 0.43 to 0.71 °2θ in sub‐greenschist facies and from 0.27 to 0.41 °2θ in greenschist facies rocks, but the d(002) values in both groups of rocks are approximately the same (∼3.35 Å). The BCM of individual samples is composed of particles with very variable shape, reflectance and Raman spectra. Type I particles that predominate in sub‐greenschist facies are fine‐grained, irregular or elongate bodies 1 to 3 μm in size. Their maximum reflectance (Rmax) ranges between 2.5% and 8.2%, and Raman parameters R1 and R2 range from 0.5 to 1.4 and 0.5 to 0.8, respectively. Type II particles are lath‐shaped, up to 40 μm large bodies, commonly arranged parallel to white mica flakes. The number of these particles increases from sub‐greenschist to greenschist facies. Maximum reflectance varies between 6% and 11.2% and R1 and R2 Raman parameters range from 0.05 to 0.7 and from 0.1 to 0.5, respectively. Type III particles occur in hydrothermally altered and sheared rocks; these are nodular aggregates composed of grains up to 10 μm in size. This type of particles has very high reflectance (Rmax = 11–15%) and its Raman spectra indicate a very high degree of structural ordering corresponding to well‐ordered graphite. Type I particles represent original organic matter in the metasediments. Type II particles are believed to have been formed either in situ by solid‐state transformation of Type I particles or by crystallization from metamorphic fluids. Gradual graphitization of the Type I organic particles and the growth of lath‐shaped Type II particles from a fluid phase is assumed to have taken place under the peak metamorphic conditions associated with the burial of Birimian sediments during thrust tectonism, progressive tectonic accretion and crustal thickening during the D1 event of the Eburnean orogeny. The growth of equant, high‐reflectance postkinematic nodular aggregates of Type III particles is ascribed to the reduction of CO2‐rich fluids during a hydrothermal event associated with Late Eburnean D2 exhumation and strike–slip movements. Type I carbonaceous particles were only slightly affected by high‐temperature, low‐pressure contact metamorphism during intrusion of Late Eburnean magmatic bodies, whereas formation of Type II or III particles was not recorded in contact‐metamorphosed rocks at all.

Presentation, calibration and validation of the low-order, DCESS Earth System Model (Version 1)

Abstract. A new, low-order Earth System Model is described, calibrated and tested against Earth system data. The model features modules for the atmosphere, ocean, ocean sediment, land biosphere and lithosphere and has been designed to simulate global change on time scales of years to millions of years. The atmosphere module considers radiation balance, meridional transport of heat and water vapor between low-mid latitude and high latitude zones, heat and gas exchange with the ocean and sea ice and snow cover. Gases considered are carbon dioxide and methane for all three carbon isotopes, nitrous oxide and oxygen. The ocean module has 100 m vertical resolution, carbonate chemistry and prescribed circulation and mixing. Ocean biogeochemical tracers are phosphate, dissolved oxygen, dissolved inorganic carbon for all three carbon isotopes and alkalinity. Biogenic production of particulate organic matter in the ocean surface layer depends on phosphate availability but with lower efficiency in the high latitude zone, as determined by model fit to ocean data. The calcite to organic carbon rain ratio depends on surface layer temperature. The semi-analytical, ocean sediment module considers calcium carbonate dissolution and oxic and anoxic organic matter remineralisation. The sediment is composed of calcite, non-calcite mineral and reactive organic matter. Sediment porosity profiles are related to sediment composition and a bioturbated layer of 0.1 m thickness is assumed. A sediment segment is ascribed to each ocean layer and segment area stems from observed ocean depth distributions. Sediment burial is calculated from sedimentation velocities at the base of the bioturbated layer. Bioturbation rates and oxic and anoxic remineralisation rates depend on organic carbon rain rates and dissolved oxygen concentrations. The land biosphere module considers leaves, wood, litter and soil. Net primary production depends on atmospheric carbon dioxide concentration and remineralization rates in the litter and soil are related to mean atmospheric temperatures. Methane production is a small fraction of the soil remineralization. The lithosphere module considers outgassing, weathering of carbonate and silicate rocks and weathering of rocks containing old organic carbon and phosphorus. Weathering rates are related to mean atmospheric temperatures. A pre-industrial, steady state calibration to Earth system data is carried out. Ocean observations of temperature, carbon 14, phosphate, dissolved oxygen, dissolved inorganic carbon and alkalinity constrain air-sea exchange and ocean circulation, mixing and biogeochemical parameters. Observed calcite and organic carbon distributions and inventories in the ocean sediment help constrain sediment module parameters. Carbon isotopic data and carbonate vs. silicate weathering fractions are used to estimate initial lithosphere outgassing and rock weathering rates. Model performance is tested by simulating atmospheric greenhouse gas increases, global warming and model tracer evolution for the period 1765 to 2000, as forced by prescribed anthropogenic greenhouse gas inputs and other anthropogenic and natural forcing. Long term, transient model behavior is studied with a set of 100 000 year simulations, forced by a slow, 5000 Gt C input of CO2 to the atmosphere, and with a 1.5 million year simulation, forced by a doubling of lithosphere CO2 outgassing.

Assessment on Redox Conditions and Organic Burial of Siliciferous Sediments at the Latest Permian Dalong Formation in Shangsi, Sichuan, South China

The redox sensitive elements, molybdenum (Mo) and uranium (U), in marine sediments from the latest Permian Dalong Formation at the Shangsi Section, Northeast Sichuan, South China, were analyzed by inductively coupled plasma mass spectrometry (ICP-MS) to determine their response to a range of redox conditions, and to estimate the organic carbon burial rate. On the basis of the correlation between authigenic Mo abundance and organic carbon content in modern oceans, the organic carbon burial rates were calculated for the rocks at Dalong Formation, ranging from 0.48–125.83 mmol/(m 2 ·d), which shows a larger range than the mineralization rate of organic carbon at the continental margins (1.6–4.23 mmol/(m 2 ·d)). The Zr-normalized Mo and U abundances show large fluctuations in the entire section. The maxima of Zr-normalized Mo abundance and thus the maxima of the organic carbon burial rates were observed at the interval between the 155th and 156th beds (404–407 m above the base of Middle Permian). A decrease (the minimum) in U/Mo ratios is present in this interval. It is speculated that the oxygen-limited conditions and ultimately anoxia or euxinia may develop within this depth interval. In contrast, an enhanced enrichment of Zr-normalized U abundance is found, in association with less enrichment in Zr-normalized Mo abundance in the interval from the 151st to 154th beds (395–404 m above the base of Middle Permian), inferring the dominance of a suboxic/anoxic depositional condition (denitrifying condition), or without free H 2 S. The presence of small quantities of dissolved oxygen may have caused the solubilization and loss of Mo from sediments. It is proposed that the multiple cycles of abrupt oxidation and reduction due to the upwelling at this interval lead to the enhanced accumulation of authigenic U, but less enrichment of Mo. A decrease in the contents of U, Mo, and TOC is found above the 157th bed (407 m above the base of Middle Permian), in association with the enhanced U/Mo ratio, suggesting the overall oxic conditions at the end of the Dalong Formation.

Modeling of Mud Accumulation and Bed Characteristics in Tokyo Bay

This paper presents the modeling of mud accumulation in Tokyo Bay. The model consists of hydrodynamic, wave hindcasting, bed shear stress and multi-class sediment sub-models in order to simulate the sediment associated processes both in the water body and bed layer. The present model accounts for sediment transport, settling, deposition, resuspension, accumulation and burial sedimentation processes, and it is capable to reproduce the accumulation of muddy sediments. Following the concept of multi-class particle model, the bed characteristics, i.e. the spatial distributions of particle size and the water content ratio in bed materials, were computed and qualitatively verified with field investigation data. The computed spatial variation in mud accumulation rate, particle size distribution and water content ratio were consistent with field data. Some discrepancies were identified and discussed.

Lower Aptian Subbetic organic-rich facies, radiolarites, and associated deposits: the local expression of Oceanic Anoxic Event 1a (Carbonero Formation, southern Spain)

The Carbonero Formation represents a scarce, well documented example of Aptian anoxic facies in the Betic Cordillera. Generally, the Aptian record in the pelagic Subbetic basin is both very discontinuous and affected by frequent hiatuses, but in some subsident areas controlled by extensional faults (as in the Carbonero trough) an interesting record is preserved. The Carbonero Formation is characterised by a thick pelagic succession composed of marls with intercalations of calcareous turbidites and a thick interval of anoxic facies. This interval, dated as early Aptian, most likely represents the local expression of Ocean Anoxic Event 1a in the Subbetic basin. A multidisciplinary study including lithostratigraphy, biostratigraphy, and sedimentology has been carried out in the Carbonero Formation, with special attention to the anoxic interval. A collection of facies and sedimentary features has been characterised and interpreted, including barite concretions, calcareous concretions, black shales, siliceous marls and radiolarites, and calcareous turbidites. All these facies seem to have been deposited under oxygen-depleted conditions on a fault-bounded depression with a high subsidence rate. The accumulation and burial of sediments and the preservation of organic matter were controlled by both local and regional factors, such as the physiography of the basin and tectonic setting, as well as by global factors, such as palaeoceanographic and climatic changes.

Thorium-234 derived information on particle residence times and sediment deposition in shallow waters of the south-western Baltic Sea

Activities of the naturally occurring, short-lived and highly particle-reactive radionuclide tracer 234Th in the dissolved and particulate phase were measured at three shallow-water stations (maximum water depths: 15.6, 22.7 and 30.1 m) in Mecklenburg Bay (south-western Baltic Sea) to constrain the time scales of the dynamics and the depositional fate of particulate matter. Activities of particle-associated (> 0.4 μm) and total (particulate + dissolved) 234Th were in the range of 0.08–0.11 dpm L − 1 and 0.11–0.20 dpm L − 1 , respectively. The activity ratio of total 234Th and its long-lived and conservative parent nuclide 238U was well below unity (range: 0.09–0.19) indicating substantial radioactive disequilibria throughout the water column, very dynamic trace-metal scavenging and particle export from the water column at all three stations. For the discussion the 234Th data of this study were combined with previously published water-column 234Th and particulate-matter data from Mecklenburg Bay ( Kersten et al., 1998. Applied Geochemistry 13, 339–347). The resulting average vertical distribution of total 234Th/ 238U disequilibria was used to estimate the depositional 234Th flux to the sediment. There was a virtually constant net downward flux of 234Th of about 28 dpm m − 2 d − 1 leaving each water layer of one meter thickness. Thorium-234-derived net residence times of particulate material regarding settling from a given layer in the water column were typically on the order of days, but with maximum values of up to a couple of weeks. Based on an average ratio of particulate matter (PM) to particle-associated 234Th a net flux of about 145 mg PM m − 2 d − 1 was estimated to leave each water layer of one meter thickness. The estimated cumulative water-column-derived particulate-matter fluxes at the seafloor are higher by a factor of about 2 than previously published sediment-derived estimates for Mecklenburg Bay. This suggests that about half of the settling particulate material is exported from the study area and/or subject to processes such as mechanical breakdown, remineralisation and dissolution. Lateral particulate-matter redistribution and particle breakdown in the water column (as opposed to the sediment) seem to be favoured by (repeated) particle resuspension from and resettling to the seafloor before ultimate sedimentary burial. The importance of net lateral redistribution of particulate material seems to increase towards the seafloor and be particularly high within the bottommost few meters of the water column.