Yu. I. Pikovskii

The composition and the source of hydrocarbons in sediments taken from the tectonically active Andaman Backarc Basin, Indian Ocean

Abstract Concentrations of total hydrocarbons in sediments of the tectonically active part of the Andaman Basin ranged from 130–720 (with an average of 349) mg/kg in the most active Spreading zone (the Rift Valley) to 43–180 (with an average of 113) mg/kg in the less active Fault zone of the Deep Basin. Average concentrations of total aromatic hydrocarbons ranged from 215 mg/kg in the Spreading zone to 49 mg/kg in the Deep Basin. Compound distributions were dominated by short-chain n -alkanes n -C 13 – n -C 24 (on the average, 77% in the Spreading zone and 64% in the Deep Basin, correspondingly). Distribution of n -alkanes in this region is characterized by a carbon predominance index (CPI 13–35 ) being mainly either below or about 1,0. Substituted homologues of biphenyl, fluorene, naphthalene, phenanthrene, benzofluorenes, chrysene (6-methylchrysene), pyrene and perylene (3-methylperylene) as well as unsubstituted individual polycyclic aromatic hydrocarbon (PAH): pyrene, benzo( a )pyrene, perylene, benzo( g , h , i )perylene, were identified in all samples. Concentrations of substituted homologues of PAH ranged, on the average, from 27 μg/kg in the Spreading zone to 16 μg/kg in the Deep Basin. Concentrations of unsubstituted individual PAH ranged, on the average, from 25 μg/kg in Spreading zone to17 μg/kg in the Deep Basin. A composition of both aliphatic hydrocarbons and PAH in the sediments of the region studied is identical to the composition of non-biological compounds: petroleum products or hydrothermal organic matter. Anthropogenic sources in region studied are of minor importance. From the results obtained, it may be deduced that the hydrocarbons in the sediments of the tectonically active part of the Andaman Basin are mainly due to an alteration of sediment organic matter by emanation processes (hydrothermal and thermal fluxes, Earths outgassing, petroleum show, etc.).

The maps of soil tolerance toward pollution with oil products and polycyclic aromatic hydrocarbons: Methodological aspects

Natural factors ensuring soil tolerance toward pollution with technogenic hydrocarbons, particularly, oil products and polycyclic aromatic hydrocarbons, are considered. The maps of the self-purification capacity of the soils of Russia and its particular humid and arid regions with respect to their contamination with technogenic hydrocarbons are analyzed. The principles lying in the basis of these maps are discussed. It is argued that the cartographic assessment of soil tolerance toward pollution with technogenic hydrocarbons is necessary for setting the values of maximum permissible concentrations of hydrocarbons in soils, for the choice of adequate soil rehabilitation procedures, and for the organization of soil monitoring.

Hydrocarbons in the Bay of Bengal and Central Indian Basin bottom sediments: Indicators of geochemical processes in the lithosphere

Abstract A study on the bulk distributions and molecular structures of n -alkanes and polycyclic aromatic hydrocarbons (PAH) in organic matter of the sediments from the Bay of Bengal and the Eastern and Central Indian Basins was undertaken. The former two regions represent areas characterised by “normal” sedimentation while the third one mainly represents a region of “active tectonism”. Content of the hydrocarbons in the sediments of “normal” sedimentation ranges between 4.6 and 10.5 μg/g and aromatic hydrocarbons ranges between 0 and 0.38 μg/g. n -Alkanes in the sediments of the northern deep part of the Bay of Bengal consist mostly of long-chain structures (total C 25 –C 33 up to 70%) with a high carbon preference index (CPI=3.01–3.43), indicating a large contribution of organic matter from terrigenous sources. The sediments from the Eastern Indian Basin have n -alkane distributions in which the long-chain components did not exceed 52.5% and the CPI was 1.7–1.90, indicating that the hydrocarbons are mostly derived from marine sources. Sharp increases of hydrocarbons are found in the vicinity of the tectonically active region of the Central Indian Basin, particularly in the sediments collected from the fracture zone. The total concentration of hydrocarbons increase to 170 μg/g and the aromatic hydrocarbons fraction to 156.3 μg/g. The proportion of short-chain n -alkanes increases up to 70%, CPI decreases to 0.76–1.12, and high concentrations of n -C 16 (16–40%) occur, all of which are absent in the other samples. The molecular content of PAH includes the unsubstituted individual structures: biphenyl, fluorene, pyrene, perylene, benzo( ghi )perylene, and the groups of homologues of naphthalene, benzofluorene, phenanthrene and chrysene. The association of the PAH and composition of paraffin hydrocarbons in the surficial sediments of deformation zone indicate that these are the resultant products of hydrothermal processes. It is, therefore, suggested that the association and composition of the hydrocarbons in sediments can be utilised as a paleoceanographic parameter to decipher the history of tectonism of an area.

Hydrocarbons in Soils: Origin, Composition, and Behavior (Review)

It has been shown that a large body of evidence on the sources, transformation, and migration of hydrocarbons in soils has been acquired by different researchers. Available data about the origin and behavior of hydrocarbon gases, total petroleum hydrocarbons, polycyclic aromatic hydrocarbons, alkanes, and other compounds have been considered successively. A wide range of natural and anthropogenic factors affecting the transformation and migration of hydrocarbons in soils have been analyzed. The indicative value of these compounds has been explained. At the same time, many problems related to hydrocarbons in soils are still insufficiently understood. Sparse and fragmentary data are available in the literature on the interaction of different hydrocarbon groups in the soil. Few data refer to the features of hydrocarbons in background zonal soils; there are almost no interzonal comparisons. The behavior of hydrocarbons in soils of different landscape-geographical positions is characterized in isolated publications. The hydrocarbon status of soils as an integral complex of interrelated hydrocarbons is almost not analyzed. Hydrocarbons of a single class (polycyclic aromatic hydrocarbons, hydrocarbon gases, n-alkanes, etc.) are usually characterized in each publication.

Factors and features of the hydrocarbon status of soils

The hydrocarbon status (HCS) of soils has been characterized using a set of quantitative parameters, which can be obtained in the routine laboratory studies of soil samples. This is a general quantitative and qualitative characterization of hexane bitumoids and individual polycyclic aromatic hydrocarbons prevailing in natural objects. Field survey of soil air has been performed in order to determine the composition and content of gaseous hydrocarbons. The features and factors of soil HCS formation have been studied in soils of eight key sites in forest, steppe, and dry-steppe landscapes of European Russia. Along with zonal diversity, the presence of any local anomalous natural or technogenic factor capable of affecting the soil HCS (gas emanations from the deep lithosphere, specific parent rocks, pollutant fallout from the atmosphere, confinement to an oil field, etc.) has been used as the criterion of their selection. It has been shown that, just as the humus and salt statuses of soils have become their important integrated characteristics, so the study of soil HCS allows reaching a new level of knowledge of the nature of soils and their processes. The parameters of soil HCS adequately reflect the features of bioclimatic and topolithological factors of pedogenesis, the properties of soils, and the level of technogenic impact on the soil cover. Accumulation of new factual data and refinement of soil-geographical studies are necessary for more thorough study of soil HCS.

Hydrocarbon status of soils in an oil-producing region with karst relief

Features and factors of the hydrocarbon status of soils developed in oil-producing karst regions were considered using an oilfield as an example. The notion of the hydrocarbon status of soils involves the proportions of the gas, bitumen, and polyarene components of the total hydrocarbons and their radial and lateral variations. The following types of soil hydrocarbon status were identified: (1) the background (reference) type; (2) the first kind of emanation type related to soil degassing (most probably, in an oilfield); (3) the technogenic type developed in the areas of oil spills, contaminated surface runoff, and industrial waste storage; and (4) the emanation type of the second kind related to the degassing and evaporation of spilled oil and other substances in underground karst caves. It was shown that the data on the hydrocarbon status of the soils can be used for the identification of hydrocarbon areas in the soil cover and the indication of the sources of pollutants deteriorating the environmental conditions in the landscape.

Exothermic and endothermic soils of Iceland

This paper is based on the results of the study of soils and soil-forming rocks on five key sites in Iceland, including the coastal plain (the Hvammur key site), piedmont plain (the Hveragerði key site), the Holocene lava plateau (the Reykjanes key site), and the zone of modern hydrothermal activity in the north of the rift zone of Iceland (the Theistareykir and Námafjall key sites). The studied soils are subdivided by us into the groups of exothermic and endothermic soils. Exothermic soils are the soils that develop from the congealed volcanic deposits. These soils are specified by the homogeneous dark gray color and sandy texture. Their mineral components are weakly transformed. Exothermic soils developed under good drainage conditions have the low content of organic matter (about 1.5% Corg). The soil reaction is neutral within the entire profile. Under impeded drainage conditions, the organic carbon content in the exothermic soils reaches its maximum of about 7%, and the soil reaction varies from acid to neutral values. Endothermic soils are the soils that are subjected at present or were subjected in the past to the high-temperature hydrothermal metamorphism. They have mottled color patterns with sharp color contrast in the soil profile; their texture is loamy or clayey. These soils are rich in secondary minerals with a predominance of smectite; kaolinite, pyrite, anatase, gypsum, and other secondary minerals can also be found in them. The properties of endothermic soils are largely controlled by the provincial features of the hydrothermal activity, including the chemical composition of hydrothermal water, the soil temperature, the duration of hydrothermal activity, etc.

Polycyclic Aromatic Hydrocarbons in Holocene Sediments and Tephra of Iceland (Composition and Distribution Features)

This work considers results of the study of Holocene cover sediments of Iceland largely composed of wind-transported palagonitized hyaloclastite particles and coeval horizons of acid and basic tephra. It is established that polyciclic aromatic hydrocarbons (PAH) are released from the basaltic glass in natural environments only in the case of intense physicochemical alteration and destruction of its structure. This process does not influence the composition of polycyclic aromatic hydrocarbons and their quantitative proportions. No new polyclic aromatic hydrocarbons formed during several thousands of years of the Holocene section accumulation. Hydrocarbons are transferred from fixed the state in basaltic glass into the free state in palagonites practically without any changes. Polyciclic aromatic hydrocarbons were mainly redeposited by winds, derived together with palagonite from weathered hyaloclastites, and precipitated from atmosphere with tephra during eruptions.

Hydrocarbon status of soils under atmospheric pollution from a local industrial source

Contents and compositions of bitumoids, polycyclic aromatic hydrocarbons (PAHs), and free and retained hydrocarbon gases in soils along a transect at different distances from the local industrial source of atmospheric pollution with soot emissions have been studied. The reserves of PAHs progressively decrease when the distance from the source increases. Among the individual PAHs, the most significant decrease is observed for benzo[a]pyrene, tetraphene, pyrene, chrysene, and anthracene. On plowlands, the share of heavy PAHs—benzo[ghi]perylene, benzo[a]pyrene, perylene, etc.—is lower than in the forest soils. In automorphic soils of the park zone adjacent to the industrial zone, the penetration depth of four-, five-, and sixring PAHs from the atmosphere is no more than 25 cm. In soils under natural forest vegetation, heavy PAHs do not penetrate deeper than 5 cm; in tilled soils, their penetration depth coincides with the lower boundary of plow horizons. Analysis of free gases in the soil air revealed hydrocarbons only under forest. From the quantitative and qualitative parameters of the content, reserves, and compositions of different hydrocarbons, the following modification types of hydrocarbon status in the studied soils were revealed: injection, atmosedimentation–injection, atmosedimentation–impact, atmosedimentation–distant, and biogeochemical types.

Mineralized Microbiota: A Possible Indicator of Hydrocarbon Flows in the Rift Zone of Iceland

Relationships of mineralized microbiota with the content of polycyclic aromatic hydrocarbons in hydrothermal systems are considered. It has been established that the mineralized microbiota can serve as an indicator of hydrothermal hydrocarbon flows in present-day and ancient deposits.