The Cenomanian/Turonian oceanic anoxic event in the Razzak Field, north Western Desert, Egypt: Source rock potential and paleoenvironmental association

The Western Desert of Egypt is one of the world’s most prolific Jurassic and Cretaceous hydrocarbon provinces. It is one of many basins that experienced organic-rich sedimentation during the late Cenomanian/early Turonian referred to as oceanic anoxic event 2 (OAE2). The Razzak #7 oil well in the Razzak Field in the northern part of the Western Desert encountered the Upper Cretaceous Abu Roash Formation. This study analyzed 23 samples from the upper “G”, “F”, and lower “E” members of the Abu Roash Formation for palynomorphs, particulate organic matter, total organic carbon (TOC) and δ¹³C_org in order to identify the OAE2, determine hydrocarbon source rock potential, and interpret the depositional environment. The studied samples are generally poor in palynomorphs, but show a marked biofacies change between the lower “E” member and the rest of the studied samples. Palynofacies analysis (kerogen quality and quantity) indicates the presence of oil- and gas-prone materials (kerogen types I and II/III, respectively), and implies reducing marine paleoenvironmental conditions. Detailed carbon stable isotopic and organic carbon analyses indicate that fluctuations in the δ¹³C_org profile across the Abu Roash upper “G”, “F”, and lower “E” members correspond well with changes in TOC values. A positive δ¹³C_org excursion (∼2.01‰) believed to mark the short-term global OAE2 was identified within the organic-rich shaly limestone in the basal part of the Abu Roash “F” member. This excursion also coincides with the peak TOC measurement (24.61 wt.%) in the samples.     

Hydrocarbon source rock potential in the southwestern Gulf of Suez graben: Insights from organic geochemistry and palynofacies studies on well samples from the Ras El Bahar Oilfield

Palynological and biomarker characteristics of organic facies recovered from Cretaceous–Miocene well samples in the Ras El Bahar Oilfield, southwest Gulf of Suez, and their correlation with lithologies, environments of deposition and thermal maturity have provided a sound basis for determining their source potential for hydrocarbons. In addition to palynofacies analysis, TOC/Rock-Eval pyrolysis, kerogen concentrates, bitumen extraction, carbon isotopes and saturated and aromatic biomarkers enable qualitative and quantitative assessments of sedimentary organic matter to be made. The results obtained from Rock-Eval pyrolysis and molecular biomarker data indicate that most of the samples come from horizons that have fair to good hydrocarbon generation potential in the study area. The Upper Cretaceous–Paleocene-Lower Eocene samples contain mostly Type-II to Type-III organic matter with the capability of generating oil and gas. The sediments concerned accumulated in dysoxic–anoxic marine environments. By contrast, the Miocene rocks yielded mainly Type-III and Type-II/III organic matter with mainly gas-generating potential. These rocks reflect deposition in a marine environment into which there was significant terrigenous input. Three palynofacies types have been recognized. The first (A) consists of Type-III gas-prone kerogen and is typical of the Early–Middle Miocene Belayim, Kareem and upper Rudeis formations. The second (B) has mixed oil and gas features and characterizes the remainder of the Rudeis Formation. The third association (C) is dominated by amorphous organic matter, classified as borderline Type-II oil-prone kerogen, and is typical of the Matulla (Turonian–Santonian) and Wata (Turonian) formations. Rock-Eval T_max, PI, hopane and sterane biomarkers consistently indicate an immature to early mature stage of thermal maturity for the whole of the studied succession.     

Stable Carbon and Nitrogen Isotopic Characterization of Organic Matter in a Mangrove Ecosystem on the Southwestern Coast of Thailand

Organic matter in a tropical mangrove ecosystem was characterized by stable carbon and nitrogen isotopic analyze, conducted on various organic samples, including land and mangrove plants, soils, particulate organic matter (POM), and sea and river sediments along the southwestern coast of Thailand. The δ¹³C values of land plants and POM in river water can be explained in terms of a greater influence of C₃ plants than C₄ plants in this area. The POM and sediments from the Trang River and Ko Talibong area showed systematically higher δ¹⁵N values than those from Ko Muk and other coastal areas. Organic matter in the Trang River might be influenced by nitrogen released from agricultural or human waste, which could affect the isotopic composition of POM and sediments in the Trang River estuary and along the coast near the river mouth. We used a stochastic method to estimate the contributions of four organic end-members, identifiable by their δ¹³C and δ¹⁵N values. The results implied that seagrasses were a major source of sedimentary organic matter, contributing 42 ± 5% in the Ko Muk area and 36 ± 5% in the Ko Talibong area. The contribution of coastal POM to sediments was estimated to be only 13% in Ko Muk and 19% in Ko Talibong. Mangrove plants contributed approximately 23% in both areas. It was concluded that seagrasses are an important source of sedimentary organic matter in this coastal region of southwestern Thailand. This revised version was published online in August 2006 with corrections to the Cover Date.     

A cross-system analysis of sedimentary organic carbon in the mangrove ecosystems of Xuan Thuy National Park, Vietnam

A cross-system analysis of bulk sediment composition, total organic carbon (TOC), atomic C/N ratio, and carbon isotope composition (δ¹³C) in 82 surface sediment samples from natural and planted mangrove forests, bank and bottom of tidal creeks, tidal flat, and the subtidal habitat was conducted to examine the roles of mangroves in sedimentation and organic carbon (OC) accumulation processes, and to characterize sources of sedimentary OC of the mangrove ecosystem of Xuan Thuy National Park, Vietnam. Sediment grain sizes varied widely from 5.4 to 170.2 μm (mean 71.5 μm), with the fine sediment grain size fraction (< 63 μm) ranging from 11 to 99.3% (mean 72.5%). Bulk sediment composition suggested that mangroves play an important role in trapping fine sediments from river outflows and tidal water by the mechanisms of tidal current attenuation by vegetation and the ability of fine roots to bind sediments. The TOC content ranged from 0.08 to 2.18% (mean 0.78%), and was higher within mangrove forests compared to those of banks and bottoms of tidal creeks, tidal flat, and subtidal sediments. The sedimentary δ¹³C ranged from − 27.7 to − 20.4‰ (mean − 24.1‰), and mirrored the trend observed in TOC variation. The TOC and δ¹³C relationship showed that the factors of microbial remineralization and OC sources controlled the TOC pool of mangrove sediments. The comparison of δ¹³C and C/N ratio of sedimentary OC with those of mangrove and marine phytoplankton sources indicated that the sedimentary OC within mangrove forests and the subtidal habitat was mainly composed of mangrove and marine phytoplankton sources, respectively. The application of a simple mixing model showed that the mangrove contribution to sedimentary OC decreased as follows: natural mangrove forest > planted mangrove forest > tidal flat > creek bank > creek bottom > subtidal habitat.     

Organic geochemistry and petroleum potential of Early Cretaceous Garau Formation in central part of Lurestan zone,northwest of Zagros,Iran

Deposition of organic rich black shales and dark gray limestones in the Berriasian-Turonian interval has been documented in many parts of the world. The Early Cretaceous Garau Formation is well exposed in Lurestan zone in Iran and is composed of organic-rich shales and argillaceous limestones. The present study focuses on organic matter characterization and source rock potential of the Garau Formations in central part of Lurestan zone. A total of 81 core samples from 12 exploratory wells were subjected to detailed geochemical analyses. These samples have been investigated to determine the type and origin of the organic matter as well as their petroleum-generation potential by using Rock-Eval/TOC pyrolysis, GC and GCMS techniques. The results showed that TOC content ranges from 0.5 to 4.95 percent, PI and Tmax values are in the range of 0.2 and 0.6, and 437 and 502 °C. Most organic matter is marine in origin with sub ordinary amounts of terrestrial input suggesting kerogen types II-III and III. Measured vitrinite reflectance (Rrandom%) values varying between 0.78 and 1.21% indicating that the Garau sediments are thermally mature and represent peak to late stage of hydrocarbon generation window. Hydrocarbon potentiality of this formation is assessed fair to very good capable of generating chiefly gas and some oil. Biomarker characteristics are used to provide information about source and maturity of organic matter input and depositional environment. The relevant data include normal alkane and acyclic isoprenoids, distribution of the terpane and sterane aliphatic biomarkers. The Garau Formation is characterized by low Pr/Ph ratio (<1.0), high concentrations of C27 regular steranes and the presence of tricyclic terpanes. These data indicated a carbonate/shale source rock containing a mixture of aquatic (algal and bacterial) organic matter with a minor terrigenous organic matter contribution that was deposited in a marine environment under reducing conditions. The results obtained from biomarker characteristics also suggest that the Garau Formation is thermally mature which is in agreement with the results of Rock-Eval pyrolysis.     

Source rock characteristics and biostratigraphy of the Lower Silurian (Telychian) organic-rich shales at Akyaka, central Taurus region, Turkey

The Akyaka section in the central Taurus region in the southern part of Turkey includes the organic matter and graptolite-rich black shales which were deposited under dysoxic to anoxic marine conditions in the Early Silurian. A biostratigraphical analysis, based on graptolite assemblages, indicates that the sediments studied may well be referable to the querichi Biozone and early Telychian, Llandovery. A total of 15 samples have been subjected to Leco and Rock-Eval pyrolysis and graptolite reflectance measurements for determination of their source rock characteristics and thermal maturity. The total organic carbon content of the graptolite-bearing shales varies from 1.75 to 3.52 wt% with an average value of 2.86 wt%. The present Rock-Eval pyrolytic yields and calculated values of hydrogen and oxygen indexes imply that the recent organic matter type is inert kerogen. The measured maximum graptolite reflectance (G_Rmax %) values are between 5.04% and 6.75% corresponding to thermally over maturity. This high maturity suggests a deep burial of the Lower Silurian sediments resulting from overburden rocks of Upper Paleozoic to Mesozoic Upper Cretaceous and Middle-Upper Eocene thrusts occurred in the region.     

δC and δN biogeographic trends in rocky intertidal communities along the coast of South Africa: Evidence of strong environmental signatures

Ecosystem dynamics driven by top-down controls have been well documented in rocky intertidal communities, while the effects of bottom-up influences are comparatively poorly understood. We hypothesized that large-scale signatures of the physical environment may be identifiable along the South African coastline as it is subject to two very different current systems (Benguela and Agulhas Currents) that profoundly influence primary production and thus both food type and availability. Through stable isotope analysis, we examined biogeographic patterns in multiple trophic levels at four sites along a 1400-km stretch of South African coastline and investigated the dietary role of macroalgal-derived organic carbon in rocky intertidal communities. The general positioning of trophic groups was comparable across all sites, with animals from the same trophic levels grouping together and with a δ¹⁵N fractionation of 1–2‰ between levels. The species found at all sites demonstrated east–west δ¹⁵N enrichment, presumably reflecting a biogeographic shift in nitrogen sources linked to upwelling on the west coast. Filter-feeders gave particularly clear results. Using discriminant analysis, mussels could be categorized into four geographic groups based on carbon and nitrogen signatures: east coast, southeast coast, south-west coast and west coast. Barnacles and polychaetes showed similar geographic groupings to mussels, but with shifts in actual values (1‰ depletion in δ¹³C and 3‰ enrichment in δ¹⁵N relative to mussels). This suggests that fractionation varies between species within a trophic level.     

Bulk organic δC and C/N as indicators for sediment sources in the Pearl River delta and estuary,southern China

Preservation of organic matter in estuarine and coastal areas is an important process in the global carbon cycle. This paper presents bulk δ¹³C and C/N of organic matter from source to sink in the Pearl River catchment, delta and estuary, and discusses the applicability of δ¹³C and C/N as indicators for sources of organic matter in deltaic and estuarine sediments. In addition to the 91 surface sediment samples, other materials collected in this study cover the main sources of organic material to estuarine sediment. These are: terrestrial organic matter (TOM), including plants and soil samples from the catchment; estuarine and marine suspended particulate organic carbon (POC) from both summer and winter. Results show that the average δ¹³C of estuarine surface sediment increases from −25.0 ± 1.3‰ in the freshwater environment to −21.0 ± 0.2‰ in the marine environment, with C/N decreasing from 15.2 ± 3.3 to 6.8 ± 0.2. In the source areas, C₃ plants have lower δ¹³C than C₄ plants (−29.0 ± 1.8‰ and −13.1 ± 0.5‰ respectively). δ¹³C increases from −28.3 ± 0.8‰ in the forest soil to around −24.1‰ in both riverbank soil and mangrove soil due to increasing proportion of C₄ grasses. The δ¹³C_POC increases from −27.6 ± 0.8‰ in the freshwater areas to −22.4 ± 0.5‰ in the marine-brackish-water areas in winter, and ranges between −24.0‰ in freshwater areas and −25.4‰ in brackish-water areas in summer. Comparison of the δ¹³C and C/N between the sources and sink indicates a weakening TOM and freshwater POC input in the surface sedimentary organic matter seawards, and a strengthening contribution from the marine organic matter. Thus we suggest that bulk organic δ¹³C and C/N analysis can be used to indicate sources of sedimentary organic matter in estuarine environments. Organic carbon in surface sediments derived from anthropogenic sources such as human waste and organic pollutants from industrial and agricultural activities accounts for less than 10% of the total organic carbon (TOC). Although results also indicate elevated δ¹³C of sedimentary organic matter due to some agricultural products such as sugarcane, C₃ plants are still the dominant vegetation type in this area, and the bulk organic δ¹³C and C/N is still an effective indicator for sources of organic matter in estuarine sediments.     

Characterizing the depositional settings for sedimentary organic matter distributions in the Lower Yangtze River-East China Sea Shelf System

Grain-size distributions, total organic carbon (TOC) and total nitrogen (TN) concentrations, and TOC/TN ratios (C/N) were analysed for surface sediments from the Lower Yangtze River-East China Sea (ECS) shelf system. Hierarchical cluster analysis of grain-size parameters (mode, mean, sorting, skewness and kurtosis) has been employed to characterize grain-size compositions. The results suggest there are five grain-size compositional types (type-I–V) that fingerprint distinct depositional conditions. In areas with high sedimentation rates, hydrological sorting preferentially enriches the fraction coarser than 6.4ø (12 μm) in shallow seafloor sediments (water depth<30 m) by transporting the finer fraction to the deeper seafloor (water depth>30 m), and thus forms grain-size compositional type-I (shallow) and type-II (deep). In the open shelf, where modern sediment supply is very limited, grain-size types-III–V are identified according to different winnowing intensity. Overall TOC contents significantly correlate with mud proportions, suggesting muddy sediments are the primary control on OM accumulation. However, de-association of terrestrial OM from fine sediments in the Estuary and the occurrence of presumably relict OM in the open shelf exert additional controls on OM dispersal and carbon cycling in the ECS. By considering geography, oceanography, sediment source, and the relation between sedimentation conditions and sedimentary OM distributions, we define six depositional settings: the lower river, the estuary, the coast, the offshore upwelling area, the erosional area, and the open shelf. These settings describe the sediment dispersal and associated organic matter cycling in the Lower Yangtze River-ECS shelf system.     

溢油污染物在海底沉积物中的识别与垂向迁移——大连湾海底沉积物研究

沉积物插管短柱样品于2013年4月采自大连湾2010年“7·16”溢油事故污染区,BQ050站与BQ007站分别位于生物分散剂和化学分散剂喷洒区。沉积物的可溶有机质含量(沥青A)、有机碳同位素组成(δ¹³C_org)和²¹⁰Pb比活度分析结果表明:喷洒生物分散剂的重污染区(BQ050站),沉积物中TOC含量为0.58%～1.51%,平均为1.15%;δ¹³C_org值为-22.2‰～-20.5‰PDB,平均为-21.74‰PDB;沥青A含量为0.061 5%～0.566 4%,平均为0.174 9%;沥青A/TOC比值为7.0%～34.8%,平均为14.13%;²¹⁰Pb_ex比活度存在异常峰值分布,垂向分布特征与沥青A相似;2～16 cm段沉积物的可溶有机质具有明显的外来输入特征。喷洒化学分散剂的较轻污染区(BQ007站),沉积物中TOC含量为0.61%～1.14%,平均为0.87%,除8～14 cm层段外,比BQ050站略低;但沥青A含量与沥青A/TOC比值明显低于前者;δ¹³C_org值较BQ050站轻;²¹⁰Pb_ex比活度随柱样深度呈指数衰减,对数相关;外来有机质输入量较低。截至2013年4月,BQ050站溢油污染物在海底下16 cm深度处有特征信号,溢油污染物沥青A 组分垂向迁移距离约为15 cm。     

台湾海峡西部沉积物中碳的来源及埋藏

根据2005年夏季航次观测的沉积物中总有机碳(TOC)、无机碳(CaCO3)、总氮(TN)、悬浮体颗粒有机碳(POC)、沉积物粒度数据得出,台湾海峡西部表层沉积物TOC质量分数的范围为0.01～1.79,平均值为0.37±0.24,略高于20多年前台湾海峡南部海区,而低于台湾海峡中、北部海区;TOC的质量分数湾内比湾外...     

环雷州半岛近海表层沉积物有机碳分布及其控制因素分析

对环雷州半岛近海43个海底表层沉积物的总有机碳(TOC)、总氮(TN)、沉积介质条件(包括沉积物粒度)进行了分析,探讨了沉积物TOC、TN的区域分布特征以及影响有机碳分布的主要因素。结果表明,环雷州半岛近海海域海底表层沉积物有机碳含量在0~0.79%之间,平均值为0.26%。与中国其它近海海域相比,环雷州半岛大部分近海区域海底表层沉积物有机碳含量明显偏低,为有机质贫乏区,仅雷州半岛西南部流沙湾近海海域为TOC相对高值区。总氮含量也不高,在0.011%到0.100%之间,TOC与TN存在较强的正相关性,且平面上TOC与TN分布高度重合,显示氮元素主要以有机化合物形式存在。TOC/TN比值在5.1~14.3之间,表明沉积有机质具有陆源输入和海洋自生来源的混合特征,但以雷州半岛西侧北部及东侧中部海域受陆源有机质输入影响更大。大多数站位海底沉积物粒度构成以粉砂为主、粘土次之,少数站位以砂质沉积为主。沉积物有机碳含量与粘土及粉砂含量呈弱正相关性,与沉积物pH值、Eh值及砂含量呈弱负相关性,这表明海底沉积物有机质丰度受有机质来源输入、海底氧化还原状态和沉积水动力条件(沉积物粒度)等因素综合控制。     

Variability of organic δC and C/N in the Mersey Estuary, U.K. and its implications for sea-level reconstruction studies

Microfossil analysis (e.g. diatoms, foraminifera and pollen) represents the cornerstone of Holocene relative sea-level (RSL) reconstruction because their distribution in the contemporary inter-tidal zone is principally controlled by ground elevation within the tidal frame. A combination of poor microfossil preservation and a limited range in the sediment record may severely restrict the accuracy of resulting RSL reconstructions. Organic δ¹³C and C/N analysis of inter-tidal sediments have shown some potential as coastal palaeoenvironmental proxies. Here we assess their viability for reconstructing RSL change by examining patterns of organic δ¹³C and C/N values in a modern estuarine environment. δ¹³C and C/N analysis of bulk organic inter-tidal sediments and vegetation, as well as suspended and bedload organic sediments of the Mersey Estuary, U.K., demonstrate that the two main sources of organic carbon to surface saltmarsh sediments (terrestrial vegetation and tidal-derived particulate organic matter) have distinctive δ¹³C and C/N signatures. The resulting relationship between ground elevation within the tidal frame and surface sediment δ¹³C and C/N is unaffected by decompositional changes. The potential of this technique for RSL reconstruction is demonstrated by the analysis of part of an early Holocene sediment core from the Mersey Estuary. Organic δ¹³C and C/N analysis is less time consuming than microfossil analysis and is likely to provide continuous records of RSL change.     

Lignin phenols used to infer organic matter sources to Sepetiba Bay – RJ,Brasil

Lignin phenols were measured in the sediments of Sepitiba Bay, Rio de Janeiro, Brazil and in bedload sediments and suspended sediments of the four major fluvial inputs to the bay; São Francisco and Guandu Channels and the Guarda and Cação Rivers. Fluvial suspended lignin yields (Σ8 3.5–14.6 mgC 10 g dw⁻¹) vary little between the wet and dry seasons and are poorly correlated with fluvial chlorophyll concentrations (0.8–50.2 μgC L⁻¹). Despite current land use practices that favor grassland agriculture or industrial uses, fluvial lignin compositions are dominated by a degraded leaf-sourced material. The exception is the Guarda River, which has a slight influence from grasses. The Lignin Phenol Vegetation Index, coupled with acid/aldehyde and 3.5 Db/V ratios, indicate that degraded leaf-derived phenols are also the primary preserved lignin component in the bay. The presence of fringe Typha sp. and Spartina sp. grass beds surrounding portions of the Bay are not reflected in the lignin signature. Instead, lignin entering the bay appears to reflect the erosion of soils containing a degraded signature from the former Atlantic rain forest that once dominated the watershed, instead of containing a significant signature derived from current agricultural uses. A three-component mixing model using the LPVI, atomic N:C ratios, and stable carbon isotopes (which range between –26.8 and –21.8‰) supports the hypothesis that fluvial inputs to the bay are dominated by planktonic matter (78% of the input), with lignin dominated by leaf (14% of the input) over grass (6%). Sediments are composed of a roughly 50–50 mixture of autochthonous material and terrigenous material, with lignin being primarily sourced from leaf.     

Paleoenvironment and sea-level change in the early Cretaceous Barents Sea—implications from near-shore marine sapropels

The late Volgian (early "Boreal" Berriasian) sapropels of the Hekkingen Formation of the central Barents Sea show total organic carbon (TOC) contents from 3 to 36 wt%. The relationship between TOC content and sedimentation rate (SR), and the high Mo/Al ratios indicate deposition under oxygen-free bottom-water conditions, and suggest that preservation under anoxic conditions has largely contributed to the high accumulation of organic carbon. Hydrogen index values obtained from Rock-Eval pyrolysis are exceptionally high, and the organic matter is characterized by well-preserved type II kerogen. However, the occurrence of spores, freshwater algae, coal fragments, and charred land-plant remains strongly suggests proximity to land. Short-term oscillations, probably reflecting Milankovitch-type cyclicity, are superimposed on the long-term trend of constantly changing depositional conditions during most of the late Volgian. Progressively smaller amounts of terrestrial organic matter and larger amounts of marine organic matter upwards in the core section may have been caused by a continuous sea-level rise.     

Organic carbon content in surface sediments—defining regional provinces

Approaches to quantify the organic carbon accumulation on a global scale generally do not consider the small-scale variability of sedimentary and oceanographic boundary conditions along continental margins. In this study, we present a new approach to regionalize the total organic carbon (TOC) content in surface sediments (<5 cm sediment depth). It is based on a compilation of more than 5500 single measurements from various sources. Global TOC distribution was determined by the application of a combined qualitative and quantitative-geostatistical method. Overall, 33 benthic TOC-based provinces were defined and used to process the global distribution pattern of the TOC content in surface sediments in a 1°×1° grid resolution. Regional dependencies of data points within each single province are expressed by modeled semi-variograms. Measured and estimated TOC values show good correlation, emphasizing the reasonable applicability of the method. The accumulation of organic carbon in marine surface sediments is a key parameter in the control of mineralization processes and the material exchange between the sediment and the ocean water. Our approach will help to improve global budgets of nutrient and carbon cycles.     

Sources and preservation of organic matter in Plum Island salt marsh sediments (MA, USA): long-chain n-alkanes and stable carbon isotope compositions

Elemental (TOC, TN, C/N) and stable carbon isotopic (δ¹³C) compositions and n-alkane (nC_16–38) concentrations were measured for Spartina alterniflora, a C₄ marsh grass, Typha latifolia, a C₃ marsh grass, and three sediment cores collected from middle and upper estuarine sites from the Plum Island salt marshes. Our results indicated that the organic matter preserved in the sediments was highly affected by the marsh plants that dominated the sampling sites. δ¹³C values of organic matter preserved in the upper fresh water site sediment were more negative (−23.0±0.3‰) as affected by the C₃ plants than the values of organic matter preserved in the sediments of middle (−18.9±0.8‰) and mud flat sites (−19.4±0.1‰) as influenced mainly by the C₄ marsh plants. The distribution of n-alkanes measured in all sediments showed similar patterns as those determined in the marsh grasses S. alterniflora and T. latifolia, and nC₂₁ to nC₃₃ long-chain n-alkanes were the major compounds determined in all sediment samples. The strong odd-to-even carbon numbered n-alkane predominance was found in all three sediments and nC₂₉ was the most abundant homologue in all samples measured. Both δ¹³C compositions of organic matter and n-alkane distributions in these sediments indicate that the marsh plants could contribute significant amount of organic matter preserved in Plum Island salt marsh sediments. This suggests that salt marshes play an important role in the cycling of nutrients and organic carbon in the estuary and adjacent coastal waters.     

Natural background and anthropogenic inputs of polycyclic aromatic hydrocarbons (PAH) in sediments of South-Western Barents Sea

Polycyclic aromatic hydrocarbons (PAH) were measured in sediment cores from 13 locations in South-Western Barents Sea as part of a detailed study of the Norwegian seabed under the MAREANO program. The generally low PAH levels found, an average around 200 ng g⁻¹ dry weight for sum PAH, indicate low inputs of petroleum hydrocarbons to the marine environment in the area. Differences in PAH composition and various PAH ratios indicate a natural, mostly petrogenic origin of PAH in sediments from the open sea locations, while the fjord locations show higher pyrogenic PAH contents with an increase towards upper sediment layers, indicating low inputs from human activities. Petrogenic PAH levels increase in deeper sediments at open sea locations, also when normalised to total organic carbon (TOC) contents, suggesting natural leakages of oil-related hydrocarbons in the area.     

Distribution of the organic matter in the channel-levees systems of the Congo mud-rich deep-sea fan (West Africa). Implication for deep offshore petroleum source rocks and global carbon cycle

The quantity and the source of organic matter preserved in the Recent turbiditic channel-levees systems around 4000 m-depth off the Congo River were determined using bulk geochemical approaches (Rock-Eval, elemental and isotopic analyses) as well as molecular and optical analyses on selected samples. These mud-rich sediments contain high amount of organic matter (3% Corg on average), the origin of which is a mixture of terrestrial higher-plant debris and deeply oxidized phytoplanktonic material. Although the relative contribution of continental source versus marine source of the organic matter cannot be precisely quantified, the continental fraction appears significant (at least 70–80%) especially for such depths and distances from the coast. The organic matter distribution appears very homogeneous at different scales, from the single turbiditic event to the entire levee, and changes in accumulation rates have a little impact on the quantity and quality of preserved organic matter.     

Soldier crab (Dotilla myctiroides) distribution,food resources and subsequent role in organic matter fate in Ao Tang Khen,Phuket, Thailand

This study aimed to elucidate Dotilla myctiroides (H. Milne-Edwards) food resources and how the soldier crab influences the organic matter composition on the intertidal flat. A preliminary assessment of D. myctiroides size, sex, and population distribution was conducted to clarify the characteristics of the inhabiting population. Overall, D. myctiroides size and abundance was normal across the tidal flat area. Comparison of different sediment types from the soldier crab habitat (surface sediments, igloos, burrow lining, burrow pellets, feeding pellets, and feces) using the fatty acid (FA) analysis technique revealed D. myctiroides removes organic matter via the significantly lower contributions of polyunsaturated FAs, essential FAs, and dinoflagellates in the feeding pellets. Dotilla myctiroides tissue analysis of the hepatopancreas and hindgut in individuals that had been starved for 24 h confirmed not only the consumption of dinoflagellates, but diatoms and macroalgae as well. In addition, the FA metabolism within the digestive system implied the ability of the soldier crab to synthesize highly unsaturated FAs (HUFAs) such as 20:4n–6, 20:5n–3 and 22:6n–3.