Contribution Of Marine Organic Matter Research Articles

Distribution and isotopic compositions of phenanthrene and methylphenanthrenes in crude oils: Implications for source input delineation and grouping oil families

This study aimed to identify the origins of crude oils by analyzing the δ13C values of phenanthrene (Phen) and methylphenanthrenes (9-MP and 1-MP) in some selected oils from the Tarim Basin (NW China), Termit Basin (Niger), Bongor Basin (Chad), and Fushan Depression (South China Sea). The study showed that oils with low 9-MP/1-MP ratios (<2.0), phenanthrene (Phen) δ13C values below −30.0‰, and Δ13C(9MP-Phen) and Δ13C(1MP-Phen) values above zero are marine-originated oils, while oils with high 9-MP/1-MP ratios (>2.0), phenanthrene (Phen) δ13C values above −20.0‰, and Δ13C(9MP-Phen) and Δ13C(1MP-Phen) values below zero are terrestrial-originated oils. Oil samples with high 9-MP/1-MP ratios (>2.0), phenanthrene (Phen) δ13C values ranging from −30.0‰ to −20.0‰, and Δ13C(9MP−Phen) and Δ13C(1MP-Phen) plots below zero are mixed-originated oils with higher terrestrial contribution. In contrast, oils with low 9-MP/1-MP ratios, phenanthrene (Phen) δ13C values ranging from −30.0‰ to −20.0‰, and plotting above and below Δ13C(9-MP−Phen) and Δ13C(1-MP−Phen) vice versa, are mixed-originated oils with higher contribution from marine sources.In combination with the geological settings, the results indicated that the oils from the Tarim Basin have three distinct origins. The majority of the oils are marine-sourced oils derived from the Lower-Paleozoic marine carbonate rocks. Oil samples *T2, *T3, and *T4 are mixed-originated oils with higher terrestrial contribution generated from the Mesozoic lacustrine shales/mudstones in the Tarim Basin. The oil samples *T1 (XH1) and *T9 (S94) are from a mixed origin with higher marine material, are derived from Upper-Paleozoic marine shale source rocks in the Tarim Basin. In Termit Basin, most of the selected oils are mixed oils with higher marine organism contribution from YSQ1 and YSQ2 source rocks from the Mesozoic Yogou Shale Formations, except for *T27 oil sample (Douwani-1), which is a mixed oil with higher terrestrial contribution from YSQ3 source rocks of the Mesozoic Yogou Shale Formations. As for the selected oils from Bongor Basin and Fushan Depression, they are mixed oils with higher contributions from aquatic organisms generated from the Mesozoic and Cenozoic lacustrine shale rocks, respectively.This approach allowed to identify for the first time the mixed origin with higher contribution of marine organic matter of the oil samples *T1 (XH1) and *T9 (S94) from the Tarim Basin, and the mixed origin with higher contribution of terrestrial organic matter of the oil sample *T27 (Douwani-1) from the Termit Basin.

Persistent increase in carbon burial in the Gulf of Mannar, during the Meghalayan Age: Influence of primary productivity and better preservation

AbstractThe oceans store a substantial fraction of carbon as calcium carbonate (CaCO3) and organic carbon (Corg) and constitute a significant component of the global carbon cycle. The Corgand CaCO3flux depends on productivity and is strongly modulated by the Asian monsoon in the tropics. Anthropogenic activities are likely to influence the monsoon and thus it is imperative to understand its implications on carbon burial in the oceans. We have reconstructed multi-decadal CaCO3and Corgburial changes and associated processes during the last 4.9 ky, including the Meghalayan Age, from the Gulf of Mannar. The influence of monsoon on carbon burial is reconstructed from the absolute abundance of planktic foraminifera and relative abundance ofGlobigerina bulloides. Both Corgand CaCO3increased throughout the Meghalayan Age, except between 3.0–3.5 ka and the last millennium. The increase in Corgburial during the Meghalayan Age was observed throughout the eastern Arabian Sea. The concomitant decrease in the Corgto nitrogen ratio suggests increased contribution of marine organic matter. Although the upwelling was intense until 1.5 ka, the lack of a definite increasing trend suggests that the persistent increase in Corgand CaCO3during the early Meghalayan Age was mainly driven by higher productivity during the winter season coupled with better preservation in the sediments. Both the intervals (3.0–3.5 ka and the last millennium) of nearly constant carbon burial coincide with a steady sea-level. The low carbon burial during the last millennium is attributed to the weaker-upwelling-induced lower productivity.

Assessment of terrigenous and marine sourced oils mixtures: Los Manueles field, Maracaibo basin Venezuela

Seven crude oil samples from Los Manueles field, Maracaibo Basin, Venezuela, were analyzed to evaluate oil mixtures associated with different oil charges into the reservoirs. Analyses of the bulk physicochemical parameters suggest variations in the API gravity, the concentration of saturated and aromatic hydrocarbons, NSO compounds + asphaltenes, sulfur, vanadium, nickel, and the biomarkers distribution. The oils were divided in two groups: G-I with high saturated hydrocarbons and low NSO compounds + asphaltenes, sulfur, vanadium and nickel, a bimodal distribution of n-alkanes, high Pr/Ph and oleanane index, low steranes index, low abundance of tricyclic terpanes and C35S/C34S &lt; 0.54 and G-II with low saturated hydrocarbons and high NSO compounds+ asphaltenes, sulfur, vanadium and nickel, an unimodal distribution of n-alkanes with low Pr/Ph and oleanane index, high steranes index, abundance of tricyclic terpanes and C35S/C34S &gt; 0.70. G-I has a higher contribution of terrigenous organic matter compared to G-II, characterized by a higher contribution of marine organic matter. Source rock lithology biomarker indicators suggest marine shale as the source rock for oils of terrigenous origin. The results indicate that oils were generated by two independent source rocks, La Luna Formation and a secondary source rock with terrigenous organic matter, probably represented by the Capacho Formation.

Origin, Depositional Environment and Thermal Maturity of some Source Rocks from Niger Delta Basin, Nigeria

Eleven (11) core samples from Agbada and Akata formations in the Niger Delta, Nigeria, were analyzed using gas chromatography-mass spectrometry to evaluate their paleodepositional conditions and source input as well as to determine their thermal maturity. The distribution of n-alkanes, isoprenoids, and biomarkers indicate a mixture (marine/terrigenous) organic matter source input for Agbada and Akata formation sediments deposited in marine environment. Low values of Phytane/nC18 (0.45 to 1.32) and Pristane/nC17 (0.37 to 1.8) indicates Marine organic matter contribution and anoxic-suboxic (Type II/III kerogens) depositional conditions of extract for Agbada and Akata Formations. The Carbon Preference Index (CPI) values for all analysed samples are slightly greater than 1.0 indicate a mixed input of marine and terrigenous organic matter deposited under relatively reducing (dysoxic) conditions. The high concentration of Oleanane in studied samples reveals that source rocks are tertiary age and belong to marine deltaic depositional environment. Moderate to higher Gammacerane index values ranging from 0.06 to 0.11, suggests water-column stratification, potentially due to hypersalinity for Isan oilfield well samples from Agbada formation. Biomarker maturity parameters suggest that the sediments have reached the early stages of hydrocarbon generation.

Carbon and nitrogen isotopic compositions of particulate organic matter in the upwelling zone off the east coast of Hainan Island, China

The isotopic compositions (δ13C and δ15N) and C/N ratios of suspended particulate organic matter (POM) were investigated off the east coast of Hainan Island in the South China Sea during summer. Coastal upwelling influenced the nearshore stations of transects S2 and S3, and higher δ13C and δ15N values suggested that coastal upwelling played a significant role in determining the POM sources. The POM at the nearshore area of transect S1 was controlled by the coastal current and freshwater discharge. Additionally, organic matter may be transported to the offshore area via tidal movements in transects S1 and S3. Based on the stable isotope analysis in an R model, the marine organic matter contribution in the upwelling area (19%) was higher than that in the other areas (transect S1 and the offshore area) (7%). The δ13C and δ15N values and C/N ratios reflect the carbon and nitrogen sources and their cycling in the upwelling zone off the east coast of Hainan Island.

Hydrocarbon Potential of the Middle–Late Jurassic Series of Northwestern Iraq: A Case Study in the Shaikhan Oil Field

The Middle–Late Jurassic Sargelu, Naokelekan, and Barsarin formations of northwestern Iraq have been investigated in the Shaikhan oilfield (well Shaikhan-8) to assess their potential for hydrocarbon generation.The results of total organic carbon analysis and rock-eval pyrolysis revealed a good-to-excellent hydrocarbon content and suggest that the depositional conditions were suitable for the production and preservation of organic matter. The thermal maturity proxy indicates that the studied formations were at the start of the hydrocarbon generation period. Most of the samples from the Sargelu and Barsarin formations belong to kerogen type II, whereas those of the Naokelekan Formation belong to kerogen type II/III. The Pr/Ph, Pr/n-C17, and Ph/n-C18 ratios of the extracted bitumen indicated that the organic matter originated from marine sources under reducing conditions. The stable carbon isotope composition of the saturated and aromatic hydrocarbon fractions ranged from –28.3 to –27.7 ‰ and –28.0 to –27.7 ‰, respectively. The biomarker results show a high contribution of marine organic matter that was preserved under relatively anoxic conditions. The profiles of the burial and thermal maturity history show that the simulated generation zones, based on the calculated vitrinite reflectance, indicate immature (0.44%–0.6%)-to-early oil generating (0.6%–0.75%) source rock. The low thermal maturity of the studied formations relative to the depth may be attributed to the low geothermal gradient and heat flow.

Carbon and nitrogen isotopic composition of particulate organic matter in the Pearl River Estuary and the adjacent shelf

The isotopic composition (δ13C and δ15N), organic carbon and nitrogen contents and C/N ratios of suspended particulate organic matter (POM) collected from the Pearl River Estuary and the adjacent shelf during spring and summer of 2017 were determined to understand the main controlling factors of spatiotemporal distribution and to elucidate the sources of particulate organic matter. Our study revealed considerable spatial variability of these parameters. In summer, δ13C in the Pearl River Estuary generally increased seawards, reflecting the increasing contribution of marine organic matter. Domestic sewage and industrial wastewater were responsible for relatively high δ15N in the Pearl River Estuary. In spring, δ13C on the adjacent shelf generally decreased from land to sea, with elevated δ13C occurred at the nearshore stations, suggesting that the eutrophic level, phytoplankton biomass and microbial activity played an important role in determining the sources of POM. Compared with δ13C, δ15N values displayed a complicated spatial distribution. Especially in the bottom water, enriched δ15N would be influenced by the degradation and mineralization of suspended matter. Given that isotopic values in summer can be applied in source apportionment, a Bayesian isotope mixing model was used to estimate that in summer the marine and terrestrial organic matter contributed 47% and 38% in the Pearl River Estuary, respectively. The greatest contribution from marine-derived POM (73%) was observed on the adjacent shelf.

Biomarkers stratigraphy of Irati Formation (Lower Permian) in the southern portion of Paraná Basin (Brazil)

This study covers the application of biomarkers as stratigraphic markers in a Lower Permian marine section from the Paraná Basin, southern Brazil. The biomarker variations reveal changes in sedimentary environment that were not detected by sedimentological and paleontological methods and will contribute to high resolution stratigraphy. The Irati Formation contains two lithostratigraphic units: (1) the lower unit (Taquaral Member) is composed of shales, deposited in a marine epicontinental to restricted environment and (2) the upper unit (Assistência Member) which consists of carbonates interbedded with shales and organic-rich shale intervals deposited in a restricted marine environment. The biomarker differences observed in the Taquaral Member can be explained by two different types of organic matter. The lower and upper parts are characterized by a high relative abundance of high molecular weight n-alkanes, C27 (17α) trisnorhopane, C31 αβR homohopane, high hopanes/steranes ratio, and low hydrogen index values. This facies contains greater relative amount of terrestrial organic matter. The low hopanes/steranes ratio, together with the high hydrogen index values and amorphous organic matter relative proportion observed in the middle part of the Taquaral Member indicate a more marine organic matter contribution. In the Assistência Member based on gammacerane/C30 αβ hopane ratio, C28ααα (20R) methylcholestane/C29ααα (20R) methylcholestane ratio, total organic carbon, hydrogen index values, palynofacies and sedimentary structures it was possible to distinguish changes in salinity and redox conditions. The bituminous shales intervals were deposited in an anoxic environment (high total organic carbon, high hydrogen index values, high preserved amorphous organic matter content) with lower salinity (lower gammacerane/C30 αβ hopane and C28ααα (20R) methylcholestane/C29ααα (20R) ethylcholestane ratios) on the other hand, the limestones intervals were deposited in an aerobic environment (low total organic carbon, low hydrogen index values, high oxidized organic matter content) with higher salinity (higher gammacerane/C30 αβ hopane and C28ααα (20R) methylcholestane/C29ααα (20R) methylcholestane ratios).

Bulk geochemical characteristics and carbon isotope composition of oils from the Sayhut sub-basin in the Gulf of Aden with emphasis on organic matter input, age and maturity

The Sayhut sub-basin is undergoing hydrocarbon exploration province in the Gulf of Aden, South Yemen. In this study, geochemical analyses were performed on three oil samples from two exploration wells in the Sayhut sub-basin. The results were used to describe the source organic matter input, age and maturity and to correlate between crude oils from different pay zones.The high saturated hydrocarbon values of more than 70% indicate that the analysed oils are normal crude oils and not degraded oils. This is supported by a complete suite of their normal alkanes and acyclic isoprenoids. The hydrocarbon distributions of normal alkane and isoprenoid with bulk carbon isotope data also suggest that the analysed oils are grouped into two genetic families and were generated from marine-source rock. The family A presents by one oil sample representing Harshiyat reservoir rock and characterized by relatively high Ph/Ph ratio>2 and δ13C values of their saturated and aromatic hydrocarbon fractions range from −26.1‰ to −24.8‰. This oil family was derived from mixed organic matter with high contribution of a terrigenous organic matter input. The family A was deposited under suboxic conditions during the Late Cretaceous age. The family B presents by two oil samples representing Ghaydah and Habshiyah reservoir rocks and characterized by relatively low Ph/Ph ratio<2 and carbon isotope less than −23 for their saturated and aromatic hydrocarbon fractions. These oils were generated from source rock containing high contributions of marine organic matter (e.g., algal and microbial) with minor amount of land plant source inputs that was deposited in more reducing conditions. The family B oils are consistent with those of the Paleogene Umm Er Radhuma source rock.The hydrocarbon distribution and oil composition data also indicate that the analysed oils were generated from mature source rocks with a peak oil-window maturity.

Geochemical characterization of the Jurassic Amran deposits from Sharab area (SW Yemen): Origin of organic matter, paleoenvironmental and paleoclimate conditions during deposition

Calcareous shales and black limestones of the Jurassic Amran Group, located in the Sharab area (SW Yemen), were analysed based on organic and inorganic geochemical methods. The results of this study were used to reconstruct the paleoenvironmental and paleoclimatic conditions during Jurassic time and their relevance to organic matter enrichment during deposition of the Amran calcareous shale and black limestone deposits. The analysed Amran samples have present-day TOC and Stotal content values in the range of 0.25–0.91 wt % and 0.59–4.96 wt %, respectively. The relationship between Stotal and TOC contents indicates that the Jurassic Amran deposits were deposited in a marine environment as supported by biomarker environmental indicators. Biomarker distributions also reflect that the analysed Amran deposits received high contributions of marine organic matter (e.g., algal and microbial) with minor amount of land plant source inputs. Low oxygen (reducing) conditions during deposition of the Jurassic Amran deposits are indicated from low Pr/Ph values and relatively high elemental ratios of V/Ni and V/(V + Ni). Enrichment in the pyrite grains and very high DOPT and high Fe/Al ratios further suggest reducing bottom waters. This paleo-redox (i.e., reducing) conditions contributed to preservation of organic matter during deposition of the Jurassic Amran deposits. Semi-arid to warm climatic conditions are also evidenced during deposition of the Amran sediments and consequently increased biological productivity within the photic zone of the water column during deposition. Therefore, the increased bio-productivity in combination with good preservation of organic matter identified as the major mechanisms that gave rise to organic matter enrichment. This contradicts with the low organic matter content of the present-day TOC values of less than 1%. The biomarker maturity data indicate that the analysed Amran samples are of high thermal maturity; therefore, the low present-day TOC is attributed to the thermal effect on the original organic matter. This high thermal maturity level is due to the presence of volcanic rocks, which have invaded the Jurassic rocks during Late Oligocene to Early Miocene.

Geochemical investigation of oils from Cretaceous to Eocene sedimentary sequences of the Abadan Plain, Southwest Iran

Oil samples from Lower Cretaceous to Eocene reservoirs in southwest Iran were analyzed using gas chromatography–mass spectrometry and gas chromatography–isotope ratio mass spectrometry for genetic classification of oil families and determining their maturity. The Studied oil samples are non-biodegraded and their gravity range from 18.3 to 37° API. The slight even/odd n-alkane predominance, coupled with low Pr/Ph values, suggests their likely source rocks with a predominance of algal organic matter, type IIS kerogen deposited under strongly reducing marine environments. The biomarker distribution of investigated oils is characterized by high concentration of both C29 and C30 hopanes and ratios of C29/C30H are generally greater than unity. There is a marked predominance of C29 regular sterane over C27 and C28 homologs in our studied oils. High sterane/hopane values and cross plot of the δ13C sat versus δ13C aro show contribution of marine organic matter. Medium value of gammacerane index and other salinity indices show water density stratification and high salinity conditions of the environment of deposition. It can be concluded that the studied reservoirs, due to their variable maturity have different API gravity and contain two oil families (types A and B) with latter being deeper and comprising more mature oils.

Seasonal variations of stable carbon isotopic composition of bulk aerosol carbon from Gosan site, Jeju Island in the East China Sea

This study explores the usefulness of stable isotopic composition (δ13C) along with other chemical tracers and air mass trajectory to identify the primary and secondary sources of carbonaceous aerosols. Aerosol samples (n = 84) were collected continuously from April 2003 to April 2004 at Gosan site in Jeju Island, South Korea. The concentrations of total carbon (TC), HCl fumed carbonate-free total carbon (fumed-TC) and their δ13C were measured online using elemental analyzer interfaced to isotope ratio mass spectrometer (EA-IRMS). Similar concentrations of TC and fumed-TC and their similar δ13C values suggest the insignificant contribution of inorganic carbon to Gosan aerosols. The monthly averaged δ13CTC showed the lowest in April/May (−24.2 to −24.4‰), which is related with the highest concentrations of oxalic acid (a secondary tracer). The result indicates an enhanced contribution of TC from secondary sources. The monthly averaged δ13CTC in July/August (−23.0 to −22.5‰) were similar to those in January/February (−23.1‰ to −22.7‰). However, chemical tracers and air mass transport pattern suggest that the pollution source regions in January/February are completely different from those in July/August. Higher δ13C values in July/August are aligned with higher concentration ratios of marine tracers (azelaic acid/TC and methanesulfonate/TC), suggesting an enhanced contribution of marine organic matter to the aerosol loading. Higher δ13C values in January/February are associated with higher concentrations of phthalic acid and K+/TC, indicating more contributions of carbonaceous aerosols from fossil fuel and C4-plant biomass combustion. This study demonstrates that δ13CTC, along with other chemical tracers and air mass trajectory, can be used as a tracer to understand the importance of primary versus secondary pollution sources of carbonaceous aerosols in the atmosphere.

Geochemistry and organic petrology study of Kimmeridgian organic-rich shales in the Marib-Shabowah Basin, Yemen: Origin and implication for depositional environments and oil-generation potential

Kimmeridgian organic-rich shales of the Madbi Formation from the Marib-Shabowah Basin in western Yemen were analysed to evaluate the type of organic matter, origin and depositional environments as well as their oil-generation potential. Results of the current study establishes the organic geochemical characteristics of the Kimmeridgian organic-rich shales and identifies the kerogen type based on their organic petrographic characteristics as observed under reflected white light and blue light excitation. Kerogen microscopy shows that the Kimmeridgian organic-rich shales contain a large amount of organic matter, consisting predominantly of yellow fluorescing alginite and amorphous organic matter with marine-microfossils (e.g., dinoflagellate cysts and micro-foraminiferal linings). Terrigenous organic matters (e.g., vitrinite, spores and pollen) are also present in low quantities. The high contributions of marine organic matter with minor terrigenous organic matter are also confirmed by carbon isotopic values. The organic richness of the Kimmeridgian shales is mainly due to good preservation under suboxic to relatively anoxic conditions, as indicated by the percent of numerous pyritized fragments associated with the organic matter. The biomarker parameters obtained from mass spectrometer data on m/z 191 and m/z 217 also indicate that these organic-rich shales contain mixed organic matter that were deposited in a marine environment and preserved under suboxic to relatively anoxic conditions.The Kimmeridgian organic-rich shales thus have high oil and low gas-generation potential due to oil window maturities and the nature of the organic matter, with high content of hydrogen-rich Type II and mixed Type II-III kerogens with minor contributions of Type III kerogen.

Environmental changes in the Pearl River Estuary (China) as reflected by light stable isotopes and organic contaminants

A dated surface sediment core and surface sediment samples from the Pearl River Estuary (PRE) were analyzed for the spatial distribution and the temporal evolution of light stable isotope (C, N, and S) signals, besides organic contaminants (PAHs, DDTs, HCHs and PCBs). The sediment core was recovered from about 6.5 m water depth and was deposited with a sedimentation rate of about 4.5 mm/a. The stable carbon ( 13C/ 12C) and nitrogen ( 15N/ 14N) isotope signatures of organic carbon and total nitrogen, and the sulfur ( 34S/ 32S) isotope signature of reduced inorganic sulfur (TRIS) have been analyzed by combustion stable isotope-ratio-monitoring mass spectrometry to follow changes in the sources of organic matter and changes in the corresponding sedimentary element cycles within the past about 120 years. Carbon and sulfur isotope signals are depleted in the heavier isotopes compared to surface water inorganic carbon and seawater sulfate, respectively. Nitrogen isotope ratios, on the other hand, display an enrichment of the heavier isotope when compared to atmospheric air. Both, the carbon and nitrogen isotope signals indicate a mixture of different organic matter sources. The downcore variations can be related to by changes in the relative mixing proportions of OM besides minor effects due to eutrophication. A conservative evaluation of carbon isotope signatures ( δ 13C between − 23.8 and − 25.7‰) considering a control by changing mixing proportions, yields a mixture of 20 to 49% marine organic matter as one end-member, with up to 80% derived from terrestrial sources. The relative enhancement of reactive organic matter starts before the sixties of the last century. Nitrogen isotope variations in the sediment core indicate that changes in the nitrogen cycle took place in the early seventies, likely due to enhanced eutrophication in the PRE. The highest values of pesticides and polychlorinated biphenyls (PCBs) were found in the sediment layer dated for 1980. The areal investigations of surface sediments indicate higher contributions of marine organic matter with enhanced distance from the coast line. Relatively heavy stable isotope data are only found in coarse-grained surface sediments, probably due to enhanced nitrate penetration and benthic denitrification, or local pollution. The sulfur isotopic composition of TRIS reflects the dissimilatory activity of bacteria upon early diagenetic oxidation of organic matter using dissolved sulfate as final electron acceptor. Before the sixties of the 20th century, the activity (metabolic rates) of sulfate-reducing bacteria seems to have been increased due to enhanced input of metabolizable organic matter, indicating changes in the depositional environment and the benthic sulfur cycle. The temporal variabilities of C and N isotope ratios and organic contaminants as reflected in the sediment core are compared to spatial changes in surface sediment samples, indicating an increasing contribution of marine organic matter with increasing distance from the coast. Application of a binary carbon isotope mixing model yields proportions between 35 and 77% contributions from non-marine organic matter. Due to the low organic carbon content the values of organic pollutants in surface sediments are relatively low in comparison the other investigations in the Pearl River Estuary area.

Humic substances in estuarine soils colonized by Spartina maritima

This study characterizes humic substances (HS) from two soils colonized by Spartina maritima at different physiographical positions in estuarine environments on the north-western coast of the Iberian Peninsula: the Villaviciosa site, a stand close to the main tidal channel, and the Ortigueira site, located in the low salt marsh. Humic and fulvic acids were extracted from the soils and characterized qualitatively by the following spectroscopic techniques: Fourier transform infrared spectroscopy, fluorescence spectroscopy and solid-state 13C nuclear magnetic resonance. The characterized HS showed a predominance of low humified compounds with a high proportion of aliphatic components and a low degree of aromaticity. The HS composition differed substantially between sites. In the Villaviciosa soil, the large amount of nonpolar aliphatic components and the very low degree of aromaticity may indicate a significant contribution of marine organic matter and/or microbial material to the HS. However, in the HS from the Ortigueira soil, the higher proportion of polysaccharides together with the presence of lignin-derived compounds may indicate greater inputs of vascular plant material. The δ 13C isotopic composition of the bulk soils highlights the large input of Spartina maritima debris to the Ortigueira site, whereas in the Villaviciosa site, organic contributions from this C4 vascular plant were not so evident. The results indicate that in these soils colonized by Spartina maritima, physiographical position has an important effect on the composition of soil HS and, therefore, must be considered in the study of organic matter characteristics in such estuarine environments.

Stable carbon isotopic ratios and ionic composition of the high‐Arctic aerosols: An increase in δ13C values from winter to spring

Atmospheric particles were collected in the high Arctic at Alert during winter (February) and spring (April–May) and were subjected to stable carbon isotopic (δ13C) measurements to better understand the source of carbonaceous aerosols. The mean δ13C values of aerosol total carbon (TC) were observed to increase from winter (−25.7 ± 0.7‰) to spring (−23.7 ± 0.8‰). A strong correlation (r2 = 0.92, p &lt; 0.001) was found between the δ13C values and Na+/TC ratios. The increased δ13C values were most likely explained by an enhanced sea‐to‐air emission of marine organic matter to the high Arctic and also by a decreased atmospheric transport of anthropogenic carbon from the midlatitudes. The backward trajectory analysis together with inorganic ion analysis indicated that spring aerosols were more affected by the Arctic Ocean than winter aerosols that were mainly derived from the primary pollutants emitted in the midlatitudes. On the basis of the δ13C values and Na+/TC ratios, contribution of marine organic matter to aerosol TC was estimated to be 45% in late spring. The enhanced sea‐to‐air emission of marine organic carbon is probably linked with a melting of sea ice, expansion of leads, and increased biological activity in the Arctic Ocean after the polar sunrise in spring.

基礎試錐「佐渡南西沖」の掘削結果に基づいた佐渡〜富山湾海域における石油システムの考察

The petroleum system in the deep water of the Toyama Trough to the southwest offshore of the Sado Island in the Japan Sea was considered based on the analytical results of METI Sado Nansei Oki S and D drillings and their preliminary surveys.The middle Miocene Lower Teradomari and Nanatani Formations indicate good source rock potential (0.90-2.98% TOC). The kerogen type is a mixture of Type II and III. The bitumens include organic matter from both marine and terrestrial sources, notably characterized by very abundant oleanane like the case of oils in the Kubiki area onshore Niigata.The oil sample collected from the Shiiya Formation of METI Sado Nansei Oki S is characterized by its high oleanane content. A seeped oil sample on the sea bottom, although heavily degraded, also indicates similar oleanane content and carbon isotope characteristics that can be correlated to the oil.The source rock of the oil is thought to be the mudstone of the Lower Teradomari and Nanatani Formations from the analytical results of the petroleum source potential, carbon isotopes and biomarker indices, especially the ratio of oleanane to norhopane content. The contribution of marine organic matter to the oil seems to be slightly higher than that to the mudstone in the Lower Teradomari and Nanatani Formations of the well. It suggests that the oil was derived from the source rocks of the same horizon that deposited in the basin center in comparison with the well location.The methane hydrate samples taken by preliminary sea bottom survey are referred to be thermogenic origin from the carbon isotope ratio. It can be isotopically correlated to headspace gas samples collected at 1900m and deeper zone of METI Sado Nansei Oki D well. This means that the deeper gas migrated to the surface very quickly without the appreciable input of shallow biogenic gas.Fluid inclusion analysis implies that the generated hydrocarbon was once trapped in the lower Teradomari Formation at METI Sado Nansei Oki D, then it migrated upward to the Shiiya sandstones through large faults and finally accumulated in the structural crest of the Shiiya horizon (METI Sado Nansei Oki S). Part of the hydrocarbons leaked from the Shiiya Formation through a number of minor faults to form methane hydrates and many Direct Hydrocarbon Indicators (DHI) that are observed with three dimensional (3D) seismic data.The kitchen area of the oil is estimated to be a syncline that locates west of the wells and is buried deeply along the Toyama Trough. It is suggested that the kitchen area provided hydrocarbons to deep water large structures and possibly to the onshore areas such as Kubiki Oil Field. The conditions required for oil accumulation in the Shiiya sandstone include the presence of deep faults for migration pathways and the absence of shallow fault that may leak hydrocarbons. Therefore 3D seismic is necessary to evaluate such geological condition.

Combined use of Δ 14C and δ 13C values to trace transportation and deposition processes of terrestrial particulate organic matter in coastal marine environments

Accelerator mass spectrometry was used to measure radiocarbons of riverine suspended particles and sediments from the estuary, continental shelf and slope off the coast of Tokachi River in Japan. The spatial distribution of Δ 14C and δ 13C values of sedimentary organic matter was divided into those of (1) estuary, (2) continental shelf, and (3) continental slope. For shelf sediments, respective maxima can be seen for Δ 14C value, C/N ratio and organic carbon content at a station near the river mouth. The mean grain size of surface sediments also exhibits a similar trend. The δ 13C values show a minimum near the river mouth. The shelf composition does not appear to be a simple mixture of terrestrial and marine origin. From the above data, it is considered that the spatial distribution of Δ 14C and δ 13C values may reflect variations in dispersion and deposition processes together with the size fractionation of riverine suspended particles, the resuspension of sediments, and differences in the contribution of marine organic matter.

Orbital forcing of organic carbon burial in the proto-North Atlantic during oceanic anoxic event 2

The Cenomanian/Turonian (C/T) intervals at DSDP Sites 105 and 603B from the northern part of the proto-North Atlantic show high amplitude, short-term cyclic variations in total organic carbon (TOC) content. The more pronounced changes in TOC are also reflected by changes in lithology from green claystones (TOC<1%) to black claystones (TOC>1%). Although their depositional history was different, the individual TOC cycles at Sites 105 and 603B can be correlated using stable carbon isotope stratigraphy. Sedimentation rates obtained from the isotope stratigraphy and spectral analyses indicate that these cycles were predominately precession controlled. The coinciding variations in HI, OI, δ 13C org and the abundance of marine relative to terrestrial biomarkers, as well as the low abundance of lignin pyrolysis products generated from the kerogen of the black claystones, indicate that these cyclic variations reflect changes in the contribution of marine organic matter (OM). The cooccurrence of lamination, enrichment of redox-sensitive trace metals and presence of molecular fossils of pigments from green sulfur bacteria indicate that the northern proto-North Atlantic Ocean water column was periodically euxinic from the bottom to at least the base of the photic zone (<150 m) during the deposition of the black claystones. In contrast, the green claystones are bioturbated, are enriched in Mn, do not show enrichments in redox-sensitive trace metals and show biomarker distributions indicative of long oxygen exposure times, indicating more oxic water conditions. At the same time, there is evidence (e.g., abundance of biogenic silica and significant 13C-enrichment for OC of phytoplanktic origin) for enhanced primary productivity during the deposition of the black claystones. We propose that increased primary productivity periodically overwhelmed the oxic OM remineralisation potential of the bottom waters resulting in the deposition of OM-rich black claystones. Because the amount of oxygen used for OM remineralisation exceeded the amount supplied by diffusion and deep-water circulation, the northern proto-North Atlantic became euxinic during these periods. Both Sites 105 and 603B show trends of continually increasing TOC contents and HI values of the black claystones up section, which most likely resulted from both enhanced preservation due to increased anoxia and increased production of marine OM during oceanic anoxic event 2 (OAE2).

有機地球化学的にみた新潟地域における原油とその根源岩の関係

The paleoenvironment and the distribution of source rocks in the Niigata oil and gas fields was detailed (Sato et al., 1995, this volume).We describe the organic geochemical characteristics of oils produced and probable source rocks, and oil-to-oil and oil-to-source rock correlation using aliphatic biomarkers.Petroleum potential evaluation based on the S1+S2 values on Rock Eval pyrolysis revealed that the argillaceous rocks in the Lower Teradomari LT2 and LT4 zones correspond to possible or potential source rocks (Hirai and Miyamoto, 1992).Triterpane and sterane compositions of the oils and bitumens extracted from argillaceous rocks were compared with each other. The results of the triterpane (m/z 191) and sterane (m/z 217) fragmentograms showed that these oils are matured, and two types of oils can be distinguished (Hirai et al., 1992), and their corresponding source rocks are suggested.(1) The Niitsu type oils produced mainly in the eastern oil and/or gas fields with low oleanane/norhopane ratios (lower than 1.0) and relatively low C29/C27 sterane ratios, suggesting that they were generated from the effective source rocks in the Lower Teradomari LT4 zone with larger contribution of marine organic matter. The Shintainai, Shiunji, Aga-Oki, Higashi-Niigata, Matsuzaki, Minami-Aga, Minami-Niitsu, Kuwayama, Yoshida and Mitsuke fields are classified in this type.(2) The Kubiki type oils are produced mainly in the western oil and/or gas fields with high oleanane/norhopane ratios (higher than 1.0) and relatively high C29/C27 sterane ratios, suggesting that they were generated from the effective source rocks in the Lower Teradomari LT2 zone with larger contribution of terrestrial organic matter. The Fujikawa, Minami-Nagaoka, Tamugiyama, Amaze, Nishiyama, Katamachi, Kuroi, Meiji and Gohtsu fields are classified in this type.