Transport of particulate organic carbon by the Mississippi River and its fate in the Gulf of Mexico

This study was designed to determine the amount of particulate organic carbon (POC) introduced to the Gulf of Mexico by the Mississippi River and assess the influence of POC inputs on the development of hypoxia and burial of organic carbon on the Louisiana continental shelf. Samples of suspended sediment and supporting hydrographic data were collected from the river and >50 sites on the adjacent shelf. Suspended particles collected in the river averaged 1.8±0.3% organic carbon. Because of this uniformity, POC values (in μmol l^?1) correlated well with concentrations of total suspended matter. Net transport of total organic carbon by the Mississippi-Atchafalaya River system averaged 0.48×10¹² moles y^?1 with 66% of the total organic carbon carried as POC. Concentrations of POC decreased from as high as 600 μmol l^?1 in the river to <0.8 μmol l^?1 in offshore waters. In contrast, the organic carbon fraction of the suspended matter increased from <2% of the total mass in the river to >35% along the shelf at ≥10 km from the river mouth. River flow was a dominant factor in controlling particle and POC distributions; however, time-series data showed that tides and weather fronts can influence particle movement and POC concentrations. Values for apparent oxygen utilization (AOU) increased from ～60 μmol l^?1 to >200 μmol l^?1 along the shelf on approach to the region of chronic hypoxia. Short-term increases in AOU were related to transport of more particle-rich waters. Sediments buried on the shelf contained less organic carbon than incoming river particles. Orgamic carbon and δ¹³C values for shelf sediments indicated 3 that large amounts of both terrigenous and marine organic carbon are being decomposed in shelf waters and sediments to fuel observed hypoxia.     

Accumulation of terrestrial organic carbon on an active continental margin offshore southwestern Taiwan: Source-to-sink pathways of river-borne organic particles

Sediment samples (213 sites) collected from the tectonic-active continental margin, offshore southwestern Taiwan were analyzed for grain sizes, organic carbon, nitrogen and carbon isotopic composition to obtain mass accumulation rate of terrestrial organic carbon and carbon budget to evaluate fate of terrestrial organic carbon from small mountainous rivers on the continental margin offshore southwestern Taiwan. Terrestrial organic carbon accumulation rates range from 0.29 to 45.6 g C m⁻² yr⁻¹ with a total accumulation budget of 0.063 Mt yr⁻¹, which accounts for less than 13% of total river particulate organic carbon loads exported from the adjacent rivers, the Gaoping (a.k.a., Kaoping), Erhjen and Tsengwen rivers. This low burial efficiency of terrestrial organic carbon demonstrated that a majority of river-borne particles together with organic materials was moved away from the study area.For the river-borne particles from the Gaoping river, a pair of depocenters in the upper slope flanking the Gaoping submarine canyon are the locations where the maximum TC_org accumulation rate were observed which hold up to 45% (0.016 Mt yr⁻¹) of the calculated accumulation found in the study region. On the other hand, the occurrence of higher-fraction terrestrial organic carbon in the upper and middle Gaoping submarine canyon suggests that a majority of particulate organic carbon of the Gaoping river was transported directly into the deep-sea basin through the Gaoping submarine canyon. Our results demonstrated that active margin with narrow shelf and slope is not an efficient sink for the large amount of terrigenous organic carbon supplied by the small rivers, but, a transient environment for these river derived particles.     

Biogeochemical cycling in an organic-rich coastal marine basin: 9. Sources and accumulation rates of vascular plant-derived organic material

The sources, degradation and burial of vascular plant debris deposited over the past several decades in the lagoonal sediments of Cape Lookout Bight, North Carolina, are quantified using alkaline cupric oxide lignin oxidation product (LOP) analysis. Non-woody angiosperms, accounting for 92 ± 32% of the recognizable sedimentary vascular plant debris, are calculated to contribute 23 ± 17% of the total organic carbon buried over the past decade (upper meter of sediment column). When combined with a previously established sedimentary organic carbon budget for this site (Martens and Klump, 1984; Martens et al., 1987, in preparation) a vascular plant derived carbon burial rate of 26 ± 20 mole C m⁻² yr⁻¹ is calculated for this same time interval. The refractory nature and invariant depth distributions of the lignin oxidation products (LOP), when coupled with evidence for constant degradation rates of metabolizable materials, indicate that sediment accumulation at this site has been a steady state process with respect to source and burial of organic carbon since its conversion from an inner-continental shelf to a lagoonal environment during the late 1960's. Thus systematic down-core decreases in labile organic matter result from early diagenetic processes rather than input rate variations.     

Influence of the Yangtze River and grain size on the spatial variations of heavy metals and organic carbon in the East China Sea continental shelf sediments

Bulk heavy metal (Fe, Mn, Zn, Cu, Pb, Cd), Al, organic carbon and carbonate concentrations, grain sizes, and δC¹³ of the organic carbon distributions were studied in sediments collected throughout the East China Sea continental shelf and the Yangtze River Delta. The results demonstrated that terrigenous sediments from the Yangtze River is a dominating factor controlling the spatial variations of heavy metals and organic carbon concentrations on the East China Sea continental shelf. In addition, grain size and recent anthropogenic influences are also major factors modifying the spatial and vertical variations of heavy metals.Large spatial variations with a band type distribution of heavy metals, grain size, organic carbon and carbonate were observed. Higher concentrations of heavy metal and light δC¹³ of the organic carbon were found primarily in the Deltaic and inner shelf sediments. The band type distribution generally followed the coastline with little variations in the north–south direction. Away from the Delta and inner shelf (west–east direction), most heavy metal concentrations decreased rapidly with the exception of Cd where high concentrations of Cd were also found in the carbonate-rich shelf break sediments. Coarse-grained relict sediments and biogenic carbonate are two primary diluting agents for the fine-grained aluminosilicate sediments from the Yangtze River with high concentrations of heavy metals.Unusually high concentrations of Cu, Pb, and Cd showed both spatially and vertically that more pollution prevention measures are needed in the Yangtze River drainage basin in order to prevent further heavy metal pollution of the East China Sea inner continental shelf.     

Electrochemical study of hydrothermal and sedimentary pyrite dissolution

The dissolution of pyrite is of interest in the formation of acid mine drainage and is a complex electrochemical process. Being able to measure the rate of dissolution of particular pyrite samples under particular conditions is important for describing and predicting rates of AMD generation. Electrochemical techniques offer the promise of performing such measurements rapidly and with small samples. The oxidation of pyrite and the reduction of Fe³⁺ ions and/or O₂ half reactions involved in the pyrite dissolution process were investigated by cyclic voltammetry and steady-state voltammetry using three pyrite materials formed in both sedimentary and hydrothermal environments. For each sample, two kinds of pyrite working electrodes (conventional constructed compact solid electrode, and carbon paste electrode constructed from fine-grained pyrite particles) were employed. Results indicated that for both the hydrothermal and sedimentary pyrite samples the oxidation and reduction half reactions involved in dissolution were governed by charge transfer processes, suggesting that hydrothermal and sedimentary pyrites obey the same dissolution mechanism despite their different formation mechanisms. In addition, the results showed that it is feasible to use a C paste electrode constructed from fine-grained or powdered pyrite to study the pyrite dissolution process electrochemically and to derive approximate rate expressions from the electrochemical data.     

Depositional processes on an ancient and modern muddy shelf, northern California

The modern Eel River shelf and analogous Pleistocene Rio Dell Formation in northern California provide an ideal opportunity to combine the advantages of studying a modern environment with those of studying an ancient sequence, and thereby enables further understanding of muddy-shelf processes. The modern shelf is the site of accumulation of a thick deposit of Holocene mud. Both large-scale sediment distribution patterns and small-scale stratigraphy on the shelf indicate that river floods play an important role in sediment accumulation, even on a high-energy, ‘storm-dominated’ coast. The major factors in preservation of this flood ‘signature’ are the cohesive behaviour of fine-grained sediments and episodically rapid rates of sediment input. The Rio Dell Formation includes approximately 400 m of mostly fine-grained shelf deposits that accumulated offshore from a palaeo-Eel River mouth. The shelf sediments comprise four depositional sequences. Sequence 1 records progradation from outer to inner shelf depths. Facies trends closely resemble across-shelf trends on the modern shelf, suggesting that processes were similar. Detailed examination of these deposits provides insight into the nature and role of various processes on both the ancient and modern shelf. Muddy facies of the Rio Dell sequence are characterized by bioturbated, clayey silts, interbedded with event layers of several types. Clay-rich silt layers are interpreted as flood deposits and physically stratified, coarse-silt layers are interpreted to record transport and deposition of coarse silt on the midshelf during storms. Sediment-transport calculations and consideration of grain-size distributions of bioturbated sediments, which form the bulk of the Rio Dell sequence, suggest that these sediments are the result of biological homogenization of the fine-grained flood deposits and of the coarser-grained storm deposits. The results of this study in general indicate that fine-grained shelf deposits do preserve a distinguishable, if subtle, record of depositional processes.     

渤海湾北部滦河三角洲晚更新世以来沉积环境划分及碳埋藏速率的评价

【研究目的】 开展渤海湾北部滦河三角洲晚更新世以来不同沉积环境的划分,计算分析碳埋藏速率的大小和控制因素,进一步评价区域碳储能力。【研究方法】 本文对BXZK03孔岩芯开展晚更新世以来的古沉积环境恢复,并取样分析了包括粒度、年代(AMS14C 和OSL)、含水量、有机碳、总碳和其他营养成分等在内的测试指标。【研究结果】 该孔晚更新世以来地层自下而上划分为泛滥平原、海滩沙脊、浅海、障壁沙坝(三角洲前缘)和潟湖的沉积环境单元,各沉积单元平均有机碳埋藏速率大小依次为：障壁沙坝51.47 g/(m²·a)>海滩沙脊32.59 g/(m²·a)>浅海7.82 g/(m²·a)>潟湖4.66 g/(m²·a)。总碳、有机碳与各营养元素具有显著(P< 0.01)线性相关关系,方差分析显示沉积速率和碳浓度分别是滦河三角洲碳埋藏速率的主要控制因素。【结论】 滦河三角洲沉积物中有机碳浓度相对较低,但是在全新世三角洲沉积速率较高,使得有机碳埋藏速率也相对较高,因此具有一定的碳储能力。     

陆棚海泥岩的岩相特征及沉积过程

传统的沉积模式认为大部分细粒沉积岩（泥岩或页岩）的沉积发生在相对深水、低能的环境中。作为地表上分布最为广泛的沉积岩类型,泥页岩包含了对重构地质历史时期古地理、古气候的重要信息。泥页岩除了可以作为有效的烃源岩,勘探开发技术的进展更发掘出泥岩作为非常规油气储层的巨大潜力。近十年来,国内外对细粒沉积物的水槽实验、泥岩沉积微相的精细分析、以及泥岩岩相组成特征的研究取得了长足的进展。这些研究对泥岩的沉积过程和沉积模式在不同角度上提供了新的认知。大部分泥岩（甚至包括众多有机质含量高的泥岩）都可能沉积在相对浅水以及水动力条件相对较高的环境中。不同的沉积过程（底部水流）形成不同的泥岩沉积微相,并对有机质在泥岩中的埋藏富集具有重要的控制作用。以晚白垩纪北美西部内陆海道为例,总结在陆棚浅海环境中（最大水深< 200 m）,位于从近岸到远岸（> 500 km）不同沉积环境（包括前三角洲/下邻滨、内陆棚、中陆棚、和外陆棚环境）中的泥岩的主要沉积过程、沉积微相特征、以及富集有机质的潜力。由于沉积过程和沉积环境是决定泥岩成分、沉积相、和岩石物理特征非均质性的首要因素,不同浅海环境中的泥岩相特征和沉积模式可有助于利用泥岩地层进行古地理、古气候的重构,并能够对预测不同陆棚浅海环境中沉积的泥岩作为有效烃源岩或有效储层的潜力提供指导。     

东海内陆架有机碳的源—汇过程及其沉积记录

大陆边缘海是不同来源、不同性质有机碳沉积和埋藏的主要场所,在全球碳的生物地球化学循环过程中具有重要地位.东海内陆架接收大量陆源有机碳,并且具有较高的海洋生产力,是研究沉积有机碳来源、输运和埋藏的理想场所,已取得大量研究成果.在对相关文献进行系统整理的基础上,以沉积学的视角对前人研究成果进行了梳理,旨在为后续相关研究提供...     

Linking lithology and land use to sources of dissolved and particulate organic matter in headwaters of a temperate, passive-margin river system

A number of rivers have been found to transport highly aged organic matter [OM]; however, the sources of this aged material remain a matter of debate. One potential source may be erosion and weathering of headwater lithologies rich in ancient sedimentary OM. In this study, waters, suspended particulates, streambed sediments, rocks and soils from fourteen small headwater watersheds of a mid-size, temperate, passive margin river were sampled and characterized by Δ¹⁴C, δ¹³C, and POC/TPN ratios to identify sources of particulate and dissolved OM delivered to the river mainstem. These headwater sites encompass a range in lithology (OM-rich shales, OM-lean carbonate/mudstone facies, and OM-free crystalline rocks) and land use types (forested and agricultural), and allow investigation of the influence of agriculture and bedrock types on stream OM characteristics. Streams draining large areas of both agricultural land use and OM-rich lithology contain particulate OM [POM] that is more ¹⁴C-depleted than streams draining forested, shale-free watersheds. However, this is not sufficient to account for the significantly lower Δ¹⁴C-POC measured in the river mainstem. Dissolved OM [DOM] Δ¹⁴C are in all cases enriched compared to POM from the same stream, but are otherwise highly variable and unrelated to either land use or lithology. POC/TPN ratios were likewise highly variable. POC and DOC δ¹³C signatures were similar across all watersheds. Based on isotope mass balance, ¹⁴C-free fossil OM sources contribute 0-12% of total stream POM. Although these results do not unequivocally separate the influences of land use and lithology, watershed coverage by shale and agriculture are both important controls on stream Δ¹⁴C-POC. Thus export of aged, particle-associated OM may be a feature of river systems along both passive and active continental margins.     

Organic Carbon Isotope Geochemistry of the Neoproterozoic Doushantuo Formation, South China

The Neoproterozoic Doushantuo Formation on the Yangtze Platform, South China, documents a sedimentary succession with different sedimentary facies from carbonate platform to slope and to deep sea basin, and hosts one of the world-class phosphorite deposits. In these strata, exquisitely preserved fossils have been discovered： the Weng＇an biota. This study presents carbon isotope geochemistry which is associated paired carbonate and organic matter from the Weng＇an section of a carbonate platform （shelf of the Yangtze Platform, Guizhou Province） from the Songtao section and Nanming section of a transition belt （slope of the Yangtze Platform, Guizhou Province） and from the Yanwutan section （basin area of the Yangtze Platform, Hunan Province）. Environmental variations and bio-events on the Yangtze Platform during the Late Neoproterozoic and their causal relationship are discussed. Negative carbon isotope values for carbonate and organic carbon （mean δ^13Corg = -35.0‰） from the uppermost Nantuo Formation are followed by an overall increase in δ^13C up-section. Carbon isotope values vary between -9.9‰ and 3.6‰ for carbonate and between -35.6‰ and -21.5‰ for organic carbon, respectively. Heavier δ^13Ccarb values suggest an increase in organic carbon burial, possibly related to increasing productivity （such as the Weng＇an biota）. The δ^13C values of the sediments from the Doushantuo Formation decreased from the platform via the slope to basin, reflecting a reduced environment with minor dissolved inorganic carbon possibly due to a lower primary productivity. It is deduced that the classical upwelling process, the stratification structure and the hydrothermal eruption are principally important mechanisms to interpret the carbon isotopic compositions of the sediments from the Doushantuo Formation.     

Spatial and temporal variation of organic carbon in the northern South China Sea revealed by sedimentary records

Three sediment cores were taken from the Pearl River estuary and adjacent northern South China Sea (SCS). These sediment cores span the time interval 1900–2000 AD. The stratigraphy of the concentration, the ratio of total organic carbon (TOC) to total nitrogen (TN) and stable isotope (δ¹³C_org) of organic carbon (OC) from three high-resolution sediment cores were analyzed. The stratigraphic profiles of OC concentration, TOC/TN ratios and δ¹³C_org for the near past 100 yrs indicate that terrestrial organic matter decreases from 68.3% to 27.4% of the TOC in the Pearl River estuary, while Dapeng Bay (offshore east of Hong Kong) apparently had throughout little terrestrial organic matter input. The highest deposited OC occurs at the Humen River mouth and the OC concentrations are higher in the outer estuary than in the inner shelf of the northern SCS. The deposited OC at the River mouth increased with time, which could be caused by the high precipitation of land-derived organic matter and the high input of terrestrial organic matter, which is likely related to the rapid urbanization and industrial development in the Pearl River Delta since the 1970s. The OC concentrations did not exhibit an obvious increase with time in most areas of the Pear River estuary and adjacent inner shelf of the SCS, but the algal-derived OC concentration inferred from the δ¹³C_org values increased with time especially from 1980 to 2000 in the outer Pearl River estuary and Dapeng Bay. This increase is presumably caused by enhanced primary marine productivity supported by higher anthropogenic nutrient inputs.     

The influence of particles recycling on the geochemistry of sediments in a large tropical dam lake in the Amazonian region,Brazil

As a result of over-erosion of soils, the fine particles, which contain the majority of nutrients, are easily washed away from soils, which become deficient in a host of components, accumulating in lakes. On one hand, the accumulation of nutrients-rich sediments are a problem, as they affect the quality of the overlying water and decrease the water storage capacity of the system; on the other hand, sediments may constitute an important resource, as they are often extremely rich in organic and inorganic nutrients in readily available forms. In the framework of an extensive work on the use of rock related materials to enhance the fertility of impoverish soils, this study aimed to evaluate the role on the nutrients cycle, of particles recycling processes from the watershed to the bottom of a large dam reservoir, at a wet tropical region under high weathering conditions. The study focus on the mineralogical transformations that clay particles undergo from the soils of the drainage basin to their final deposition within the reservoir and their influence in terms of the geochemical characteristics of sediments. We studied the bottom sediments that accumulate in two distinct seasonal periods in Tucuruí reservoir, located in the Amazonian Basin, Brazil, and soils from its drainage basin. The surface layers of sediments in twenty sampling points with variable depths, are representative of the different morphological sections of the reservoir. Nineteen soil samples, representing the main soil classes, were collected near the margins of the reservoir. Sediments and soils were subjected to the same array of physical, mineralogical and geochemical analyses: (1) texture, (2) characterization and semi-quantification of the clay fraction mineralogy and (3) geochemical analysis of the total concentration of major elements, organic compounds (organic C and nitrogen), soluble fractions of nutrients (P and K), exchangeable fractions (cation exchange capacity, exchangeable bases and acidity) and pH(H₂O).There is a remarkable homogeneity in the sedimentary distribution along the reservoir in terms of the texture and mineralogy of the clay fraction and of the chemistry of the total, soluble and exchangeable phases. These observations contrast with the physical, morphological and chemical heterogeneity of the soils and the setting lithology. Most of the sediments has a higher contribution of fine-grained material and the mineralogy of the clay fraction is dominated by kaolinite in soils and kaolinite and illite in sediments, followed by lesser amounts of gibbsite, goethite, and metahaloisite and by small/vestigial contents of chlorite and smectite. The sediments are mainly inherited from the watershed but there exist marked differences between the accumulated sediments and their parent materials. These differences mainly come from the selective erosion of fine-grained particles and the extreme climatic conditions which enhance complex transformations of mineralogical and chemical nature. Compared with the parental soils, the reservoir sediments show the following differences: (1) enrichment in fine-grained and less dense inorganic particles, (2) aggradative mineralogical transformations, including enrichment in clay minerals with higher cationic adsorption and exchange capacity, (3) degradation of the crystalline structure of Fe- and Al-oxides (goethite, gibbsite), (4) increase in easily leached elements (Mg, Ca, P, K, Na) and decrease in chemically less mobile elements (Si, Fe) and (5) higher contents of organic carbon, nitrogen, and soluble forms of P and K, mainly concentrated in the clay fraction. These transformations are extremely important in the nutrients cycle, denoting that sediments represent an efficient sink for nutrients from the over-erosion of soils. Mineral and organic compounds can permanently or temporarily sequester these nutrients, recycling them and enhancing their availability through the slow release of components from relatively loose crystal structures. These processes can easily explain the enrichment in soluble and exchangeable forms of elements such as P, K, Ca or Mg. This study conclude that the particles recycling in a large tropical dam reservoir which receives high fluxes of allochthonous nutrients, has an important role in the good quality of sediments for agricultural use and in the profitable use of this technology to recover depleted soils in remediation projects in regions near large hydroelectric plants.     

Temporal variation and fluxes of dissolved and particulate organic carbon in the Apure,Caura and Orinoco rivers,Venezuela

The concentrations of total suspended sediments (TSS), dissolved organic carbon (DOC) and particulate organic carbon (POC) were measured in water samples taken monthly in the Apure, Caura and Orinoco rivers during a hydrological cycle (between Sept. 2007 and Aug. 2008). The DOC concentration values ranged between 1.5 and 6.8 mgC l⁻¹ in the Apure River; 2.07 and 4.9 mgC l⁻¹ in the Caura River and 1.66 and 5.35 mgC l⁻¹ in the Orinoco River. The mean concentration of DOC was 3.9 mgC l⁻¹ in the Apure River, 3.24 mgC l⁻¹ in the Caura River and 2.92 mgC l⁻¹ in the Orinoco River at Puerto Ordaz. The three rivers showed a similar temporal pattern in the concentrations of DOC, with higher DOC values during the increasing branch of the hydrograph due to wash-out processes of the organic material stored in soils. The mean concentration values of POC were 1.33 mgC l⁻¹; 0.77 mgC l⁻¹ and 0.91 mgC l⁻¹ in the Apure, Caura and Orinoco rivers, respectively. The inverse relationship found between the percentage in weight of the POC and the concentrations of TSS in the three rivers fits a logarithmic model, as it has been previously reported for other worldwide rivers. The POC concentrations in the Orinoco River showed a positive relationship with the TSS, suggesting that the POC in the Orinoco is the result of terrestrially organic matter. Although the fluxes of organic carbon (OC) in the three studied rivers are dependent on the values of water discharge, the fluxes of DOC during the increasing branch of the hydrograph are higher than those found during the decreasing stage, due to the yield of organic material accumulated in soils during the preceding dry season. The mean annual flux of total organic carbon (TOC) of the Orinoco River at Puerto Ordaz was about 4.27 × 10⁶ TonC yr⁻¹. Of this, 3.28 × 10⁶ TonC yr⁻¹ (77%) represents the flux of DOC and about 0.99 TonC yr⁻¹ (23%) represents the flux of POC. The mean annual input of TOC from the Apure River to the Orinoco River was about 4.92 × 10⁵ TonC yr⁻¹ (11.5%), while the contribution of TOC from the Caura River to the Orinoco River was estimated at 3.05 × 10⁵ TonC yr⁻¹ (7.1%).The values of annual transport of TOC calculated for the Apure, Caura and Orinoco rivers were lower than those reported twenty years ago. This could be related to interannual variations of precipitation in the Orinoco Basin, due to runoff variations can have a strong effect on the fluxes of OC from land to rivers.     

Infrared estimates of aliphatic kerogen carbon in sedimentary rocks

An infrared routine has been developed to estimate the aliphatic portion of kerogen carbon in sedimentary rocks. The procedure does not require isolation of the organic matter and is based on a computer-assisted determination of global band areas in the region of the aliphatic carbon-hydrogen stretching vibrations around 2900cm⁻¹. From these integrated absorptions the amount of aliphatic carbon C_al (mg of aliphatic carbon per gram of solvent-extracted rock) is calculated by means of a calibration with model rocks. Carbonate overtones which interfere in the case of limestones are eliminated by comparison to a CaCO₃ standard.The method has been applied to rocks containing kerogens of different types and maturities at TOC levels of 0.5 to 12%. The aliphatic carbon concentrations range from 0.5 to 60mg·g⁻¹ and correlate reasonably well with the residual genetic potentials of the rocks as measured by S₂ values from Rock-Eval pyrolysis. The ratio S₂/C_al is found to decrease with burial depth reflecting a maturity enhanced conversion of aliphatic carbon to fixed aromatic carbon under Rock-Eval conditions.     

Chemical composition of the graphitic black carbon fraction in riverine and marine sediments at sub-micron scales using carbon X-ray spectromicroscopy

The chemical composition of the graphitic black carbon (GBC) fraction of marine organic matter was explored in several marine and freshwater sedimentary environments along the west coast of North America and the Pacific Ocean. Analysis by carbon X-ray absorption near-edge structure spectroscopy and scanning transmission X-ray microscopy shows the GBC fraction of Stillaguamish River surface sediments to be dominated by more highly ordered and impure forms of graphite, together forming about 80% of the GBC, with a smaller percent of an aliphatic carbon component. Eel River Margin surface sediments had very little highly ordered graphite, and were instead dominated by amorphous carbon and to a lesser extent, impure graphite. However, the GBC of surface sediments from the Washington State Slope and the Mexico Margin was composed almost solely of amorphous carbon. Pre-anthropogenic, highly oxidized deep-sea sediments from the open Equatorial Pacific Ocean contained over half their GBC in different forms of graphite as well as highly aliphatic carbon, low aromatic/highly acidic aliphatic carbon, low aromatic/highly aliphatic carbon, and amorphous forms of carbon. Our results clearly show the impact of graphite and amorphous C phases in the BC fraction in modern riverine sediments and nearby marine shelf deposits. The pre-anthropogenic Equatorial Pacific GBC fraction is remarkable in the existence of highly ordered graphite.     

黄河三角洲全新世以来沉积环境的划分及各环境中碳埋藏速率的评价

为了研究黄河三角洲全新世不同古环境中的碳埋藏速率,于2007年在研究区布设了一口30.3 m浅钻,以对其进行了沉积学观测以及含水量、有机碳、总碳和营养成分测试分析.通过地层分析,将其全新世地层划分为8种沉积环境.运用历史地理学和沉积地质学综合分析方法对现代黄河三角洲沉积环境中部分层位进行了精确的年代划分,其他层位也进行了年代推测.同时利用确定的年代计算了不同沉积环境碳的埋藏速率.结果表明:总碳和有机碳与各营养元素都呈很好的线性相关;沉积物的沉积速率是有机碳和总碳埋藏速率的主控因素;虽然沉积物C_org浓度相对较低,但由于其高沉积速率,C_org的平均埋藏速率达到1 331 g/(m2·a),远高于世界其他高C_org浓度的湿地,因此是很好的碳汇地质体.      

沉积相带对川南龙马溪组页岩气富集的影响

为查明沉积相带对川南龙马溪组页岩气富集的影响,结合地层分布、岩性特征、沉积构造、有机碳含量、矿物组成、储集空间类型等特征,对龙马溪组页岩沉积相类型进行划分,并探讨沉积相带对有效页岩发育的影响,以期为页岩气富集条件评价提供依据。通过研究区6口页岩气井的钻井岩心观察,结合测井响应、实验测试分析,将龙马溪组划分为浅水泥质陆棚亚相、半深水陆棚亚相和深水陆棚亚相3种沉积亚相类型。有机碳含量、有效页岩的发育和分布、矿物组成以及孔隙发育特征是影响页岩气富集的关键因素,而这些因素均受控于沉积相带:沉积水体越深TOC含量越高,距离沉积中心越近TOC含量越高;龙马溪组地层厚度较大,但有效页岩厚度并不大,深水陆棚亚相沉积层段为页岩气富集的有效层段,且有效页岩层向沉积中心方向逐渐增厚;深水陆棚亚相丰富的生物供应为有效页岩带来了更高的有机质含量以及更多的脆性矿物,提高了岩石脆性;龙马溪组页岩中的孔隙类型主要为黏土矿物层间孔与有机质孔,且TOC含量高的沉积相带中有机质孔越发育。综上,深水陆棚亚相页岩具备有机质含量丰富、岩石脆性高、有机质孔发育等特征,是页岩气富集的最有利相带。     

Sources of sedimentary humic substances: vascular plant debris

A modern Washington continental shelf sediment was fractionated densimetrically using either an organic solvent, CBrCl₃, or aqueous ZnCl₂. The resulting low density materials (<2.06 g/ml) account for only 1% of the sediment mass but contain 25% of the sedimentary organic carbon and 53% of the lignin. The C/N ratios (30–40) and lignin phenol yields ($\text{Λ = 8}$) and compositions indicate that the low density materials are essentially pure vascular plant debris which is slightly enriched in woody (versus nonwoody) tissues compared to the bulk sediment. The low density materials yield approximately one-third of their organic carbon as humic substances and contribute 23% and 14% of the total sedimentary humic and fulvic acids, respectively. Assuming that the lignin remaining in the sedimentary fraction is also contained in plant fragments that yield similar levels of humic substances, then 50% and 30% of the total humic and fulvic acids, respectively, arise directly from plant debris.Base-extraction of fresh and naturally degraded vascular plant materials reveals that significant levels of humic and fulvic acids are obtained using classical extraction techniques. Approximately 1–2% of the carbon from fresh woods and 10–25% from leaves and bark were isolated as humic acids and 2–4 times those levels as fulvic acids. A highly degraded hardwood yielded up to 44% of its carbon as humic and fulvic acids. The humic acids from fresh plants are generally enriched in lignin components relative to carbohydrates and recognizable biochemicals account for up to 50% of the total carbon. Humic and fulvic acids extracted directly from sedimentary plant debris could be responsible for a major fraction of the biochemical component of humic substances.     

Upstream control of river anastomosis by sediment overloading,upper Columbia River,British Columbia,Canada

Anastomosing rivers, systems of multiple interconnected channels that enclose floodbasins, constitute a major category of rivers for which various sedimentary facies models have been developed. While the sedimentary products of anastomosing rivers are relatively well‐known, their genesis is still debated. A rapidly growing number of ancient alluvial successions being interpreted as of anastomosing river origin, including important hydrocarbon reservoirs, urge the development of robust models for the genesis of anastomosis, to facilitate better interpretation of ancient depositional settings and controls. The upper Columbia River, British Columbia, Canada, is the most‐studied anastomosing river and has played a key role in the development of an anastomosing river facies model. Two hypotheses for the origin of upper Columbia River anastomosis include the following: (i) downstream control by aggrading cross‐valley alluvial fans; and (ii) upstream control by excessive bedload input from tributaries. Both upstream and downstream control may force aggradation and avulsions in the upper Columbia River. In order to test both hypotheses, long‐term (millennia‐scale) floodplain sedimentation rates and avulsion frequencies are calculated using ¹⁴C‐dated deeply buried organic floodplain material from cross‐valley borehole transects. The results indicate a downstream decrease in floodplain sedimentation rate and avulsion frequency along the anastomosed reach, which is consistent with dominant upstream control by sediment overloading. The data here link recent avulsion activity to increased sediment supply during the Little Ice Age (ca 1100 to 1950 ad ). This link is supported by data showing that sediment supply to the upper Columbia study reach fluctuated in response to Holocene glacial advances and retreats in the hinterland. Upstream control of anastomosis has considerable implications for the reconstruction of the setting of interpreted ancient anastomosing systems. The present research underscores that anastomosing systems typically occur in relatively proximal settings with abundant sediment supplied to low‐gradient floodplains, a situation commonly found in intermontane and foreland basins.