Oil and Gas Accumulation in the Foreland Basins, Central and Western China

<正>Foreland basin represents one of the most important hydrocarbon habitats in central and western China.To distinguish these foreland basins regionally,and according to the need of petroleum exploration and favorable exploration areas,the foreland basins in central and western China can be divided into three structural types:superimposed,retrogressive and reformative foreland basin(or thrust belt),each with distinctive petroleum system characteristics in their petroleum system components(such as the source rock,reservoir rock,caprock,time of oil and gas accumulation,the remolding of oil/gas reservoir after accumulation,and the favorable exploration area,etc.).The superimposed type foreland basins,as exemplified by the Kuqa Depression of the Tarim Basin, characterized by two stages of early and late foreland basin development,typically contain at least two hydrocarbon source beds,one deposited in the early foreland development and another in the later fault-trough lake stage.Hydrocarbon accumulations in this type of foreland basin often occur in multiple stages of the basin development,though most of the highly productive pools were formed during the late stage of hydrocarbon migration and entrapment(Himalayan period).This is in sharp contrast to the retrogressive foreland basins(only developing foreland basin during the Permian to Triassic) such as the western Sichuan Basin,where prolific hydrocarbon source rocks are associated with sediments deposited during the early stages of the foreland basin development.As a result, hydrocarbon accumulations in retrogressive foreland basins occur mainly in the early stage of basin evolution.The reformative foreland basins(only developing foreland basin during the Himalayan period) such as the northern Qaidam Basin,in contrast,contain organic-rich,lacustrine so urce rocks deposited only in fault-trough lake basins occurring prior to the reformative foreland development during the late Cenozoic,with hydrocarbon accumulations taking place relatively late(Himalayan period).Therefore,the ultimate hydrocarbon potentials in the three types of foreland basins are largely determined by the extent of spatial and temporal matching among the thrust belts,hydrocarbon source kitchens,and regional and local caprocks.     

Sources and pathways of natural and anthropogenic hydrocarbons into the natural dump Arkona Basin (southern Baltic Sea)

 Surface sediments, suspended particulate matter and fluffy-layer material, collected in the Arkona Basin and the Pomeranian Bay during 1995–1997, as well as air particulate matter, collected on the island of Rügen during August 1995, were analysed for total organic carbon content, saturated and polycyclic aromatic hydrocarbons (PAH). The resulting concentrations and distributions of these compounds and molecular PAH ratios are discussed in terms of matrix, origin of the organic matter and seasonal variations. The data show that the Oder river can be identified as a major source for PAH transported into the southern part of the Arkona Basin. A strong atmospheric input of PAH is noted for the central and northern part of the basin. In general, anthropogenic and bacterially degraded hydrocarbons bound to organic carbon-rich and small particles are mainly deposited in the basin center, whereas their natural counterparts accumulate mainly on the basin flanks covered by coarser grained sediments. Received: 2 March 1999 · Accepted: 8 June 1999     

Environmental changes in Saginaw Bay,Lake Huron recorded by geolipid contents of sediments deposited since 1800

Changes in organic materials preserved within sediments of Saginaw Bay deposited over the past two centuries record corresponding periods in the environmental history of this part of Lake Huron and its watershed. Sediments deposited since 1940 show an increasingly greater input of aquatic organic matter in response to accelerating cultural eutrophication of Saginaw Bay. Concentrations of fatty acids, sterols, fatty alcohols, and aliphatic hydrocarbons are higher in these modern sediments than in deeper ones. Molecular distributions of these geolipids reflect less aquatic material deeper in the sediments. Prior to 1875, sediment organic matter appears to be diluted by mineral matter from enhanced erosion caused by clearing of the watershed for farming and settlement. During this period there is better preservation of carbonate minerals due to quicker burial. Since 1875, petroleum components comprise over 90% of the total aliphatic hydrocarbon content of these sediments, reflecting the advent and continued existence of chronic, low-level petroleum contamination of this part of the Great Lakes.     

Distribution and transport of hydrocarbons in surface sediments of the alaskan outer continental shelf

Surface sediments from the Outer Continental Shelf of Alaska were analyzed for hydrocarbons as part of an environmental survey sponsored by NOAA/BLM. Sediments were collected from the proposed oil lease areas of Beaufort Sea, southeastern Bering Sea, Norton Sound, Navarin Basin, Gulf of Alaska, Kodiak Shelf and lower Cook Inlet. Data on normal and branched alkanes and di- and triterpenoids from capillary gas chromatography (GC) and gas chromatography-mass spectrometry (GC/ MS) indicate that the area displays little evidence of petroleum hydrocarbons (i.e., seeps) except at a few isolated stations. Beaufort Sea sediments have the highest hydrocarbon budget, whereas Kodiak Shelf sediments have the lowest. The molecular markers of the hydrocarbons are of a mixed marine autochthonous and terrestrial allochthonous origin. Norton Sound and Cook Inlet sediments contain the highest levels of terrigenous lipids and Kodiak Shelf the lowest. The abundance of alkenes implies that relatively low oxidizing conditions exist in some of the depositional areas studied, suggesting that extraneous petroleum hydrocarbons introduced into these sediments would be expected to have a relatively long residence time. The distribution of polynuclear aromatic hydrocarbons (PAH) is complex and shows a pyrolytic origin. The data on perylene strongly favor the hypothesis that it is “performed” from terrigenous precursors and transported into the marine environment with no apparent in situ generation. Polynuclear aromatic hydrocarbons of diagenetic origin are probably dominant in Gulf of Alaska and Kodiak Shelf sediments.Two stations, north of Kalgin Island, in lower Cook Inlet and one in southeastern Bering Sea show typical weathered petroleum distribution of n-alkanes and triterpenoids. Probable pathways of transport and fate of petroleum hydrocarbons in case of an oil spill are also briefly discussed.     

Differential Hydrocarbon Enrichment and its Main Controlling Factors in Depressions of the Bohai Bay Basin Differential Hydrocarbon Enrichment and its Main Controlling Factors in Depressions of the Bohai Bay Basin

Significant differential hydrocarbon enrichment occurs in depressions in a petroliferous basin.There are multiple depressions in the Bohai Bay Basin, and each depression as a relatively independent unit of hydrocarbon generation, migration and accumulation, contains significantly different hydrocarbon generation conditions and enrichment degree. On the basis of previous documents and a large number of statistical data, this work comparatively analyzed the differential hydrocarbon enrichment and its major controlling factors in depressions of the Bohai Bay Basin. The results show that depressions in the Bohai Bay Basin have various hydrocarbon enrichment degrees, and can be categorized into four types, namely enormously oil-rich, oil-rich, oily and oil-poor depressions. In general, the enormously oil-rich and oil-rich depressions are distributed in the eastern part of the basin along the Tan-Lu and Lan-Liao faults, whereas depressions in the western part of the basin are poor in hydrocarbons. Moreover, the vertical distribution of hydrocarbons is also highly heterogeneous, with Pre-Paleogene strata rich in hydrocarbons in the northern and western depressions, Paleogene strata rich in hydrocarbons in the entire basin, and Neogene strata rich in hydrocarbons in the off-shore areas of the Bohai Bay Basin. From early depressions in onshore areas to the late depressions in offshore areas of the Bohai Bay Basin, the source rocks and source-reservoir-cap rock assemblages gradually become younger and shallower, and the hydrocarbon resource abundance gradually increases. Hydrocarbon supplying condition is the key factor constraining the hydrocarbon enrichment for different depressions,while the main source-reservoir-cap rock assemblage, sufficient hydrocarbons and the transportation capacity of faults control the vertical distribution of hydrocarbons. The main factors controlling hydrocarbon enrichment are different for different layers. The hydrocarbon supplying condition of source rocks is the key controlling factor, whereas the source-reservoir configuration, the main sourcereservoir-cap rock assemblages, and the fault transportation are the main factors of hydrocarbon enrichment in the Paleogene, Paleogene and Neogene, respectively.     

Differential Hydrocarbon Enrichment and its Main Controlling Factors in Depressions of the Bohai Bay Basin

Significant differential hydrocarbon enrichment occurs in depressions in a petroliferous basin. There are multiple depressions in the Bohai Bay Basin, and each depression as a relatively independent unit of hydrocarbon generation, migration and accumulation, contains significantly different hydrocarbon generation conditions and enrichment degree. On the basis of previous documents and a large number of statistical data, this work comparatively analyzed the differential hydrocarbon enrichment and its major controlling factors in depressions of the Bohai Bay Basin. The results show that depressions in the Bohai Bay Basin have various hydrocarbon enrichment degrees, and can be categorized into four types, namely enormously oil-rich, oil-rich, oily and oil-poor depressions. In general, the enormously oil-rich and oil-rich depressions are distributed in the eastern part of the basin along the Tan–Lu and Lan–Liao faults, whereas depressions in the western part of the basin are poor in hydrocarbons. Moreover, the vertical distribution of hydrocarbons is also highly heterogeneous, with Pre-Paleogene strata rich in hydrocarbons in the northern and western depressions, Paleogene strata rich in hydrocarbons in the entire basin, and Neogene strata rich in hydrocarbons in the off-shore areas of the Bohai Bay Basin. From early depressions in onshore areas to the late depressions in offshore areas of the Bohai Bay Basin, the source rocks and source-reservoir-cap rock assemblages gradually become younger and shallower, and the hydrocarbon resource abundance gradually increases. Hydrocarbon supplying condition is the key factor constraining the hydrocarbon enrichment for different depressions, while the main source-reservoir-cap rock assemblage, sufficient hydrocarbons and the transportation capacity of faults control the vertical distribution of hydrocarbons. The main factors controlling hydrocarbon enrichment are different for different layers. The hydrocarbon supplying condition of source rocks is the key controlling factor, whereas the source-reservoir configuration, the main source-reservoir-cap rock assemblages, and the fault transportation are the main factors of hydrocarbon enrichment in the Paleogene, Paleogene and Neogene, respectively.     

Relationship between Geological Structures and Hydrocarbon Enrichment of Different Depressions in the Bohai Bay Basin

The Bohai Bay Basin contains many depressions with varying degrees of hydrocarbon enrichment associated with the geological structures of different depressions. This study discussed the relationship between the geological structures and hydrocarbon enrichment of the depressions in the Bohai Bay Basin. Based on the Paleogene strata distribution and the length to width ratio of different depressions, their geological structures are divided into three types in plan-view: open(length/width 2), narrow(length/width 4) and transitional types(length/width 2–4). In cross section, the geological structures can be divided into dustpan I, dustpan II and double-faulted types. Based on tectonic evolution and sedimentary characteristics, the depressions are classified into early-formed, inherited and late-formed categories. Generally, narrow depressions are mainly located in the northeast and southwest of the Bohai Bay Basin, while open depressions are dominantly distributed in the central area of the basin; late-formed depressions are mainly around the Bohai sea area, and early-formed depressions are mostly located in the periphery of the basin. Geological structures of the depressions control the formation of the source, reservoir and cap rocks as well as hydrocarbon accumulation setting, and further influence the pay zones and oil-bearing sequence. In detail, dustpan II and doublefaulted depressions mainly have A-type sags, which often possess better hydrocarbon generation conditions than dustpan I ones; hydrocarbons in open dustpan II depressions tend to accumulate in the central uplift areas or buried hill, while those in narrow dustpan I depressions always accumulate in gentle slope belts. The oil-bearing sequence for different evolutional depressions corresponds well with the sedimentary strata of the main development stages of depressions. In early-formed depressions, hydrocarbons are mainly enriched in deeply buried reservoirs, while in late-formed depressions hydrocarbons are abundant in the relatively shallow traps. In summary, most inherited and late-formed dustpan II depressions are enriched in hydrocarbons due to their extensive source rocks and good source–reservoir–seal assemblages, whereas dustpan I and early-formed depressions are relatively poor in hydrocarbons.     

Modern sedimentology and hydrology of Lake Manitoba,Canada

Lake Manitoba, North America's thirteenth largest lake, occupies a glacier-scoured basin in south-central Manitoba. Despite its large size, the lake is extremely shallow with a mean depth of 4.5 m. The lake can be subdivided into two connected but distinctly different basins: a small, irregular-shaped North Basin and a much larger and smoother South Basin. Most of the water inflow is from the Waterhen River (42% of the inflow) and from precipitation directly on the lake's surface (40%), while nearly 60% of the outflow is by evaporation. Lake Manitoba water is alkaline and brackish with the salinity dominated by sodium and chloride ions. The surficial offshore deposits of the main South Basin of the lake consist mainly of silt and clay-sized sediments composed of detrital components (clay minerals, quartz, carbonates, and feldspars) and endogenic/authigenic components (carbonates, sulfides, and organic matter). In addition to these modern sediments, several areas of relict fluvial-shoreline sand and till deposits occur in the South Basin. The lacustrine processes presently operating in Lake Manitoba reflect the influence of (1) the extreme shallow depth of the lake, (2) the basin morphology, and (3) the water chemistry. In addition, land clearing and increased watershed drainage have resulted in substantially increased sedimentation rates in the South Basin during the past century.     

Past occurrences of hypoxia in the Baltic Sea and the role of climate variability,environmental change and human impact

The hypoxic zone in the Baltic Sea has increased in area about four times since 1960 and widespread oxygen deficiency has severely reduced macro benthic communities below the halocline in the Baltic Proper and the Gulf of Finland, which in turn has affected food chain dynamics, fish habitats and fisheries in the entire Baltic Sea. The cause of increased hypoxia is believed to be enhanced eutrophication through increased anthropogenic input of nutrients, such as nitrogen and phosphorus. However, the spatial variability of hypoxia on long time-scales is poorly known: and so are the driving mechanisms. We review the occurrence of hypoxia in modern time (last c. 50 years), modern historical time (AD 1950–1800) and during the more distant past (the last c. 10 000 years) and explore the role of climate variability, environmental change and human impact. We present a compilation of proxy records of hypoxia (laminated sediments) based on long sediment cores from the Baltic Sea. The cumulated results show that the deeper depressions of the Baltic Sea have experienced intermittent hypoxia during most of the Holocene and that regular laminations started to form c. 8500–7800 cal. yr BP ago, in association with the formation of a permanent halocline at the transition between the Early Littorina Sea and the Littorina Sea s. str. Laminated sediments were deposited during three main periods (i.e. between c. 8000–4000, 2000–800 cal. yr BP and subsequent to AD 1800) which overlap the Holocene Thermal Maximum (c. 9000–5000 cal. yr BP), the Medieval Warm Period (c. AD 750–1200) and the modern historical period (AD 1800 to present) and coincide with intervals of high surface salinity (at least during the Littorina s. str.) and high total organic carbon content. This study implies that there may be a correlation between climate variability in the past and the state of the marine environment, where milder and dryer periods with less freshwater run-off correspond to increased salinities and higher accumulation of organic carbon resulting in amplified hypoxia and enlarged distribution of laminated sediments. We suggest that hydrology changes in the drainage area on long time-scales have, as well as the inflow of saltier North Sea waters, controlled the deep oxic conditions in the Baltic Sea and that such changes have followed the general Holocene climate development in Northwest Europe. Increased hypoxia during the Medieval Warm Period also correlates with large-scale changes in land use that occurred in much of the Baltic Sea watershed during the early-medieval expansion. We suggest that hypoxia during this period in the Baltic Sea was not only caused by climate, but increased human impact was most likely an additional trigger. Large areas of the Baltic Sea have experienced intermittent hypoxic from at least AD 1900 with laminated sediments present in the Gotland Basin in the Baltic Proper since then and up to present time. This period coincides with the industrial revolution in Northwestern Europe which started around AD 1850, when population grew, cutting of drainage ditches intensified, and agricultural and forest industry expanded extensively.     

轻烃的稳态成因及其在油气勘探中的应用

对Mango的轻烃稳态成因理论进行了综述：基于大量实际分析资料,Mango发现轻烃的形成受一种化学过程控制,且有4个C,异构化合物的相对组成有显著的不变性,即轻烃稳态成因模式;基于该模式,Mango建立了轻烃参数与生油层最大埋深温度的关系,同时发现参数K1、1（2的不同来源于有机质类型不同。在该理论基础上,通过对苏北盆地湖相油和海相油气轻烃的分析,探讨了轻烃参数K1、K2在确定油气母质类型方面的应用,同时依据轻烃参数2,4．／2,3-DMP与最大埋深温度关系式计算了苏北湖相油与海相油气的生成温度,结果显示湖相油生成温度与甾烷C2920S／（S＋R）参数有较好的相关性,处于成熟阶段;海相油气生成温度显著高于湖相油,处于成熟晚期阶段。     

Lithology and formation conditions of paleogene rocks in the Dongying Depression (Bohai Bay Basin,China)

The Dongying Depression is one of the largest depressions in terms of hydrocarbon reserves not only within the Bohai Basin, but also in the whole Pacific region. This is related to the inherited pattern of geological evolution, as well as the optimal combination of oil source rocks, reservoirs, and caprocks, which alternate in both lateral and vertical directions. Diversity of the lithofacies composition of Eocene and Oligocene sediments in thick (proluvial, deltaic, fan deltaic, and deep-water) hemipelagic and gravitational deposits in the composition of various fans, predetermined the wide distribution of sandstone and gritstone beds with good filtration-capacity properties. The beds were filled with hydrocarbons that migrated from the adjacent layers of oil shales and clays. The role of the principal reservoirs was played by sandstones, which were deposited in distributary channels of Eocene deep-water fans. The detailed study of these underwater fans will make it possible to expand the reserves of hydrocarbons explored now in the Dongying Basin.     

Hydrocarbons in the surficial sediments of Lakes St. Clair,Erie, and Ontario

Although the long-term effects and the fate of petroleum hydrocarbons in marine and freshwater environments are not fully understood, it is generally recognized that much of the oil released by accidental spills or by various land sources ends up in the sediment where it may remain for at least several years The present study was undertaken to collect some initial data on the hydrocarbon concentrations in surficial sediments of lakes St Clair, Erie, and Ontario The distribution of hydrocarbons in these lakes followed the general patterns found for a number of contaminants, in that the distribution tended to coincide with the outlines of the sedimentary basins The highest concentrations were found in the Western Basin of Lake Erie and in the inshore zone around the west end of the lake, suggesting major inputs from the Detroit River Apart from some spots of high concentration around known dumping grounds, the concentrations gradually diminish toward the east The distribution pattern in Lake Ontario may be more readily ascribed to water circulation patterns than to any specific source around the lake The hydrocarbon levels were found to be significantly lower than those in Lake Erie in Lake St Clair only trace quantities of hydrocarbons were found, suggesting either low inputs or low sedimentation/accumulation rates due to its shallowness Although the present survey was limited to the top 3 cm of the sediments, the resulting distribution patterns indicate the western end of Lake Erie as the area with the heaviest hydrocarbon loadings The results may also facilitate the selection of specific areas where core sampling coupled with more complete analysis of the extracts could yield significant information on the long-term accumulation of anthropogenic hydrocarbons, and on their persistence and transformations in Great Lakes sediments     

Biogeochemical processes affecting the distribution and vertical transport of hydrocarbon residues in the coastal Mediterranean

Sediments, sediment trap material, dominant surface plankton and collected fecal material were sampled concurrently with surface seawater in a coastal Mediterranean ecosystem and analyzed for non-volatile hydrocarbons and chlorinated hydrocarbons. Results showed consistent partitioning of hydrocarbon classes between dissolved and particulate phases of surface waters which appeared to be related to component solubility and particle availability. Analysis of biological materials showed the biota were important not only in packaging residues into large, fast sinking particles, but also in modifying the composition of components through metabolism and selective incorporation into body tissues and feces. Apparent sedimentation rate was calculated by analysis of ²¹⁰Pb in sediment core samples and used to estimate average deposition rates of organics to the sea/sediment interface. The flux of particles through 100 m, as measured in the trap material in this sampling interval, was sufficient to balance most of the petroleum input to the sediments but accounted for only 17% of the average flux of PCBs to the sediments, and virtually none of the more soluble chlorinated hydrocarbon flux. Vertical transport via large fecal material compared to average background particles was seasonally low corresponding to a seasonal minimum in plankton biomass in late summer. Results show that hydrocarbon residues transported long distances away from input sources are highly modified, pointing to the geochemical significance of physical-chemical partitioning between seawater phases, incorporation into organisms and fecal material and biological/chemical degradation.     

Late Quaternary coastal and inner shelf stratigraphy, Apalachicola Delta region, Florida

Since the beginning of the Tertiary the sedimentology of the Gulf of Mexico Basin has been dominated by the depositional activity of the Mississippi River. The sedimentologic influence of the Mississippi diminishes with distance east or west of the Louisiana shelf, however. The Texas and northwest Florida shelf margins, for example, are characterized by a series of smaller deltas. In the inner and mid-shelf areas of these regions the near-surface sedimentary units include infilled stream channels and small deltas. Such features are commonly observed in sub-bottom seismic records from the middle and inner shelf of the northeastern Gulf, along the Apalachicola River coast of northwest Florida.

The Apalachicola River is the principal source of clastic sediment to the northeastern Gulf of Mexico. During the late Holocene virtually all of the river's sediment load has been deposited in the modern Apalachicola Delta and in the river's estuary, Apalachicola Bay, which has been filling rapidly. During late Quaternary lowstands, prior to the development of the modern estuary, the river traversed the present-day inner and mid-shelf, incising a network of channels. Based on seismic records, many of these buried shelf channels were considerably larger than their modern counterparts.

During lowstands the Apalachicola River also deposited coarse sediment on the shelf as deltaic and associated river-mouth sediments. These deposits comprise the modern near-surface sediments of the inner and middle shelf. An investigation of subsurface sedimentary features observed in seismic profiles provides details on the late Quaternary development of the northeastern Gulf of Mexico shelf. Seismic reflection profiles obtained on the inner and mid-shelf regions of northwest Florida reveal an approximately 50 m thickness of late Quaternary sediments, comprised of two and sometimes three discrete clastic sequences. Two lower fluvial sequences total as much as 40–50 m in thickness. A transgressive marine sand deposit overlies the older features in some places, varying in thickness from 0 to 5 m. Identification of seismic facies, combined with stratigraphic data from a suite of coastal boreholes, enables correlation of offshore seismic stratigraphic units with late Tertiary and Quaternary coastal stratigraphy.     

塔里木盆地东河砂岩沉积和储层特征及综合分析

东河砂岩是一套覆盖广泛的海侵初期的沉积产物,但不是一个等时沉积体,相当于晚泥盆世晚期至早石炭世早期沉积,具体沉积时间各地有差异。东河砂岩具有海侵初期填平补齐的特征,其沉积相决定于海侵的速度、沉积物的供给和海侵前的古地貌。塔北地区受塔北古隆起的阻挡,海水在古隆起周围滞留时间较长,又有较粗粒的物源供给,其沉积产物主要是滨岸海滩沉积;塔中地区由于地形复杂,沉积类型也比较复杂,底部砾岩段为河流相沉积,而块状砂岩段和砂砾岩段为河口湾和滨岸海滩沉积,不同段在成分、分选性和粒级上有较大的差异;塔里木盆地其他低平地区主要是海侵期快速的滨岸和陆架沉积。受沉积因素影响,东河砂岩有效储层的分布具有地域性,除沉积因素外,低的地温梯度和短期的深埋藏也是优质储层发育的重要控制因素。     

Hydrocarbons in western North Atlantic surface sediments

High concentrations of hydrocarbons (500–3000 μg/g dry weight) together with a complex and wide molecular weight range of composition, and low ¹⁴C activity of δ¹⁴C = ?833 ± 50%. strongly indicate that fossil fuel hydrocarbons make up the bulk of hydrocarbons in and near the New York Bight dump site areas. The composition and concentrations of hydrocarbons in Hudson Channel sediments suggest some transport of dump site hydrocarbons to areas in the channel midway to the edge of the continental shelf. Sediments at 16 stations in other areas of the continental shelf, continental slope and abyssal plain have hydrocarbon concentrations and compositions indicating that no more than 1 μg/g dry weight of fossil fuel hydrocarbons are present.N-alkanes from land sources were among the most predominant hydrocarbons in all samples except those in the New York Bight region. Their presence in abyssal plain surface sediments documents transport of some land derived organic matter to these deep ocean areas. Two 25-carbon cycloalkenes are among the more predominant hydrocarbons in continental shelf surface sediments except for the dump site areas. These two compounds are present in lower concentrations in slope sediments and are not detected in abyssal plain sediments.     

松辽盆地北部晚白垩系青一段源岩中芳基类异戊二烯烃的检出及意义

在松辽盆地晚白垩系青一段优质源岩中检测出了芳基类异戊二烯烃化合物,该类化合物以低碳数为主,主要分布在C13~C23之间,最高含量可占芳烃馏份的30%以上。该类化合物的检出以及根据饱和烃生物标志化合物特征分析,认为青一段源岩沉积时期水体具有盐度分层,湖底为微咸—半咸化、强还原的、富硫的环境,有机质除了以藻类贡献为主外,还有绿硫菌的贡献。芳基异戊二烯化合物检出和分布反映了古松辽湖在青一段沉积时期可能存在海侵,海侵方向从盆地东南向西北。     

Multiple sources of alkanes in Quaternary oceanic sediment of Antarctica

Normal alkanes (n-C₁₃n-C₃₆), isoprenoid hydrocarbons (i-C₁₅, i-C₁₆, i-C₁₈, i-C₁₉, and i-C₂₀) triterpanes (C₂₇C₃₂), and (C₂₇C₂₉) are present in low concentrations offshore Antarctica in near-surface, Quaternary sediment of the Wilkes Land continental margin and of the western Ross Sea. The distributions of these hydrocarbons are interpreted relative to possible sources and processes. The hydrocarbons appear to be mixtures of primary and recycled material from marine and terrigenous sources. The n-alkanes are most abundant and are characterized by two distinct populations, one of probable marine origin and the other likely from terrigenous, vascular plant sources. Because the continent of Antarctica today is devoid of higher plants, the plant-derived hydrocarbons in these offshore sediments probably came from wind-blown material and recycled Antarctic sediment that contains land-plant remains from an earlier period of time. Isoprenoid hydrocarbons are partially recycled and mainly of marine origin; the dominance of pristane over phytane suggests oxic paleoenvironmental conditions. Both modern and ancient triterpanes and steranes are present, and the distribution of these indicates a mixture of primary and recycled bacterial, algal, and possible higher-plant materials. Although the sampled sediments were deposited during the Quaternary, they apparently contain a significant component of hydrocarbons of pre-Quaternary age.     

Aliphatic hydrocarbons in coastal sediments of the Northern Cyprus (Eastern Mediterranean)

The sources and spatial distributions of aliphatic hydrocarbon concentrations were investigated in surficial sediments of the Northern Cyprus (Gemi Konagi, Girne and Gazi Magusa Areas). Aliphatic hydrocarbon levels were determined with a gas chromatography–mass spectrometer. Total aliphatic hydrocarbon (n-alkanes, Σ25; isoprenoids, Σ2) concentrations in the sediments were found in the range of 1107–6360 ng/g. Results indicated that the sediments were mainly dominated by odd numbered n-alkanes (n-C10–n-C34), maximizing at n-C17, n-C29 and n-C31. Statistical analyses and diagnostic ratios have been used to determine the possible sources and origins of aliphatic hydrocarbons. Aliphatic hydrocarbons were showed biogenic character at all sampling areas and were found mainly originated from terrestrial, marine and both terrestrial-marine plants at Gemi Konagi, Gazi Magusa and Girne, respectively.     

The early diagenesis of aliphatic hydrocarbons and organic matter in sedimentary particulates from Dabob Bay,Washington

Aliphatic hydrocarbon compositions were quantitatively characterized in plankton, sediment trap-collected particulate materials and sediments from Dabob Bay using high resolution glass capillary gas chromatography. The average net accumulation of individual hydrocarbons measured in a 1-yr series of sediment traps was compared with the net accumulation of corresponding compounds measured in three depth intervals of ²¹⁰Pb-dated bottom sediments. Systematic and rapid decreases in the net accumulation of individual hydrocarbons were observed from the sediment traps to the sediments. Most pronounced decreases were measured for planktonically derived hydrocarbon constituents (e.g. pristane and two unsaturated compounds) which are rapidly remineralized at or near the sediment-water interface. Consequently, the amount of each compound measured in deposited sediments is not necessarily a quantitative indication of its initial flux to the sediments. The n-alkanes (C_25,27,29,31). characteristic of terrestrial plant waxes, are the predominant hydrocarbons measured by 4–6 cm depth in these sediments and show reasonably constant net accumulation below this interval.Significant diagenetic alteration of the bulk organic matter contained in the average sediment trap particulate material is also noted through comparison with bottom sediments on the basis of organic C/N and δ¹³C measurements. Organic matter elementally similar to marine plankton is preferentially remineralized upon deposition of the sedimentary particulates. The residual organic matter remaining and buried in the bottom sediments closely resembles terrestrial organic matter.