A large amount of deep oil has been discovered in the Tazhong Uplift, Tarim Basin whereas the oil source is still controversial. An integrated geochemical approach was utilized to unravel the characteristics, origin and alteration of the deep oils. This study showed that the Lower Cambrian oil from well ZS1C (1x) was featured by small or trace amounts of biomarkers, unusually high concentration of dibenzothiophenes (DBTs), high δ34S of DBTs and high δ13C value of n-alkanes. These suggest a close genetic relationship with the Cambrian source rocks and TSR alteration. On the contrary, the Middle Cambrian oils from well ZS1 (2a) were characterized by low δ13C of n-alkanes and relatively high δ34S of individual sulfur compounds and a general “V” shape of steranes, indicating a good genetic affinity with the Middle–Upper Ordovician source rocks. The middle Cambrian salt rock separating the oils was suggested to be one of the factors responsible for the differentiation. It was suggested that most of the deep oils in the Tazhong Uplift were mixed source based on biomarkers and carbon isotope, which contain TSR altered oil in varied degree. The percentage of the oils contributed by the Cambrian–Lower Ordovician was in the range of 19–100% (average 57%) controlled by several geological and geochemical events. Significant variations in the δ34S values for individual compounds in the oils were observed suggesting a combination of different extent of TSR and thermal maturation alterations. The unusually high DBTs concentrations in the Tazhong-4 oilfield suggested as a result of mixing with the ZS1C oil (1x) and Lower Ordovician oils based on δ34S values of DBT. This study will enhance our understanding of both deep and shallow oil sources in the Tazhong Uplift and clarify the formation mechanisms of the unusually high DBTs oils in the region. 相似文献
Long-chain alkyl diols contain an alkyl chain with alcohol groups at C1 and at the middle position of carbon chain, which exist widely in seas, rivers and lakes. It has been proven that these compounds are relatively resistant to degradation and have an extended occurrence in the geological record. In addition, they are relatively easy to identify. Therefore, long-chain alkyl diols can be used as potential biomarkers to trace the past change in paleoenvironment and paleoclimate. Although the sources of long-chain alkyl diols are still uncertain, the studies indicate that 1, 13 and 1, 15-diols are mainly produced by eustigmatophytes, while 14-diols are mainly from diatom Proboscia. So far, some proxies based on long-chain alkyl diols have been established to indicate the change in diatom productivity, upwelling intensity, salinity, sea surface temperature, riverine organic matter input and surface seawater nutrient concentration, which are significant for paleoenvironmental reconstruction. Current research and application of long-chain alkyl diols proxies were summarized, which would be helpful for further studying the source of long-chain alkyl diols and the application of relevant proxies in China’s marginal sea. 相似文献
The withdrawing Arctic ice edge will facilitate future sea transport and exploration activities in the area, which calls for the establishment of relevant cold water monitoring species. The present study presents first results of field baseline levels for core oil pollution biomarkers in Polar cod (Boreogadussaida) sampled from pristine, Arctic waters. Furthermore, biomarker response levels were characterized in controlled laboratory exposure experiments running over 2 weeks. Fish exposed to a simulated petrogenic spill (1 ppm dispersed, crude oil) exhibited elevated hepatic EROD activity, bile PAH-metabolites, and hepatic DNA-adducts, whereas male individuals exposed to simulated produced water (30 ppb nonylphenol) exhibited a strong induction of plasma vitellogenin. In conclusion, the results demonstrated low and robust biomarker baseline levels that were clearly different from exposure responses. In combination with its high abundance and circumpolar distribution, the Polar cod seems well qualified for oil pollution monitoring in Arctic waters. 相似文献
Lamellidens marginalis (Molluska Bivalvia Eulamellibranchiata) is an important member of the freshwater ecosystem of India, which is sustained by filtering phytoplankton, bacteria and other particulate organic matter from the available water. Hemocytes, the circulating blood cells of bivalves, function as immunological effector cells under exposure to toxins and/or parasites. The hemocytes of Lamellidens marginalis have been identified morphologically and enumerated as being qualified for use as a biomarker to analyze the threat of freshwater contamination by sublethal concentrations of sodium arsenite, a natural pollutant of freshwater ecosystems. Diverse subpopulations of hemocytes were identified as blast‐like cells, granulocytes, agranulocytes, hyalinocytes and asterocytes. Supression in the total count of hemocytes and blast‐like cells was recorded under the exposure of all the concentrations of sodium arsenite tested. Sodium arsenite elevated the relative density of granulocytes, hyalinocytes, and asterocytes. Partial restoration of the total count of the hemocytes was recorded after the post‐treated animals were maintained in arsenic‐free water for periods of 15 and 30 days. The data predict a shift in the immunological parameters of this bivalve in arsenic contaminated environments. The present study is aimed at quantifying the arsenic induced stress in Lamellidens marginalis and establishing the hemocyte density as a biomarker of aquatic pollution in selected geographical regions of India. 相似文献
Increasing numbers of industrial, agricultural and natural chemicals are present in sewage effluent and are known to elicit toxic effects in laboratory exposures, but little is known of their combined sub-lethal effect in the field. In this study, a combination of esterase activity and ventilation rate assays was performed to determine the neurological and physiological function of the freshwater crustacean Asellus aquaticus (L.) at sites above and below a sewage treatment works (STW). Cholinesterase and carboxylesterase activities were significantly inhibited (n=8, P<0.05) and ventilation rates increased (n=8, P=0.0001) in A. aquaticus at STW sites compared to those from reference sites, indicating a decrease in neurological and physiological function. The ecological relevance of these findings for the population dynamics of the organisms in the field is discussed. 相似文献
Metallothionein has been assayed in a range of aquatic animal tissues as an indicator of metal exposure. We sequenced chub (Leuciscus cephalus) metallothionein cDNA which showed over 90% homology to common carp, goldfish and stone loach and 77% homology to rainbow trout sequences for metallothionein. We then used the extended primer method to develop an accurate quantitative competitive RT-PCR assay for metallothionein mRNA. RT-PCR was used to measure metallothionein mRNA in feral chub from a range of field sites, with different levels of heavy metal pollution, in the West Midlands, UK. Measurements were complemented by analysis of liver and gill metallothionein protein by capillary electrophoresis. There was no significant difference in the metallothionein protein levels between fish of different rivers and there was no evidence of elevation of mRNA at the sites of highest metal exposure. The level of metal exposure (e.g. zinc, nickel and cadmium each ranging between 15 and 28 microg/l ) at the pH (7.5-8.5) of these rivers appears insufficient to elevate hepatic or gill metallothionein in chub. A lack of elevation of hepatic metallothionein mRNA in chub exposed to zinc, copper and manganese for 24 h and 10 days in the laboratory also suggests a non-responsiveness of this species. 相似文献
Fluctuations in lacustrine sedimentary environments significantly affect distributions of organic matter (OM), uranium, and other elements in shales. In this study a high-resolution geochemical record of fluctuations in the paleo-depositional environment of a terrestrial lake basin is provided on the basis of extensive samples collected from the Member 3 of the Paleogene Shahejie Formation (Es3) of the Niu-38 well in the Dongying Depression, Eastern China. These samples were tested for total organic carbon (TOC), element concentrations, and biomarkers to study the evolution and fluctuation in the depositional environments of an ancient lake basin and associated geochemical response. The evolution and fluctuation of the sedimentary environment from a deep lake to a semi-deep lake and then to a shallow lake delta were indicated by geochemical response. During this evolution, the values of TOC, S1, S2, Sr, and Ts/(Ts + Tm) remarkably decreased, whereas those of Co, Ni, Rb, Na, Fe/Mn, Fe/(Ca + Mg), and C29 mortane/C29 hopane significantly increased. The deep lake basin shows depositional fluctuations, as indicated by rock lithofacies and their geochemical parameters. A close interrelationship was observed among U concentration, TOC content, and inorganic element content. Uranium concentrations are positively correlated with TOC contents, Ca and Sr concentrations, and Sr/Ba and Ca/Mg ratios but negatively with K, Na, Ba, and Rb contents and Fe/(Ca + Mg) and Fe/Mn ratios. The observed increase in U concentration in the lower Es3 section is closely related to surface adsorption by clay minerals and OM, together with some replacements of Ca and Sr by U in the shales. 相似文献
