Extended hopanes and 8,14-secohopanes up to C_(40)in unbiodegraded marine oils from the Tarim Basin,NW China

Extended 17α(H),21β(H)-hopanes and three series of 8,14-secohopanes up to C_(40),including 8α(H),14α(H),17α(H),21β(H)-,8α(H),14α(H),17β(H),21α(H)-and 8α(H),14β(H),17β(H),21α(H)-,were detected by GC-MS-MS method in the branched/cyclic hydrocarbon fractions of some unbiodegraded marine oils from the Tazhong uplift in the Tarim Basin,NW China.The coexistence of extended hopanes and 8,14-secohopanes up to C_(40)in unbiodegraded oils suggests that they are primary and independent on biodegradation.The similarity of distribution and composition for extended hopanes and 8,14-secohopanes up to C_(40)in unbiodegraded oils proposes that they could be derived from a similar biological precursor.However,an abrupt decrease up to 3-5 times in the relative abundance from C_(35)to C_(36)in C_(31-40)extended hopanes and extended 8,14-secohopanes suggests that C_(31-35)and C_(36-40)extended hopanes and extended 8,14-secohopanes should have their own biological precursor.The known C35bacteriohopanetetrol should be biological precursor of C_(31-35)extended hopanes and 8,14-secohopanes,but an unknown C_(40)functionalized hopanoid could be biological precursor of C_(36-40)extended hopanes and 8,14-secohopanes.More attention should be paid to their potential roles in oil-source correlation for severely biodegraded oils based on their widespread occurrence in various source rocks,unbiodegraded and severely biodegraded oils.

Thermal Effects on Composition of Rearranged Hopanes in Hydrocarbon Source Rocks

Objective The distribution characteristics and formation mechanism of rearranged hopanes in hydrocarbon source rocks are affected by various geological conditions.Among these geological conditions,thermal action has an important influence on the formation of rearranged hopanes,which has been however little documented previously.

Characteristics of Rearranged Hopanes of Hydrocarbon Source Rocks in Saline Sedimentary Environment： A Case Study of the Songliao Basin

The Songliao Basin, one of the biggest continental petroliferous basins in eastern China, is a Mesozoic- Cenozoic fault-depressed and fault-subsided basin developed on the Hercynian fold basement. Generally, rearranged hopanes are considered to be formed by clay- mediated acidic catalysis under oxic or suboxic environment, whereas high abundance of rearranged hopanes were found in hydrocarbon source rocks and crude oils that are derived from salty environment in the Songliao Basin. This phenomenon rarely happens all over the world.

Genesis of Abnormally High Abundant Rearranged Hopanes in Condensates from the Kuqa Depression, Tarim Basin

Objective The Tarim Basin is China＇s largest ore-bearing interior basin, and contains mainly marine oils. The Kuqa depression, a secondary structural unit within the northem Tarim Basin, is composed of Mesozoic and Cenozoic clastic sedimentary rocks dominated by continental oil. Previous research suggests that the crude oils especially condensates in the Kuqa depression are rich in abnormally high abundant rearranged hopanes. On the basis of 41 condensate samples and five oil samples from the Kuqa depression, this work systematically discussed the relationship between biomarker parameters and rearranged hopanes and deeply investigated the influence of depositional environment, original source,

New Discoveries of the Influence of Sedimentary Environment on Rearranged Hopanes in Source Rocks

Objective The distribution of rearranged hopanes in hydrocarbon source rocks is influenced by thermal maturity and original source input, and is also controlled by depositional conditions. Through comparison of lacustrine and coal-bearing source rocks, this work attempted to analyze the composition and origin of rearranged hopanes in hydrocarbon source rocks. Taken the source rocks from the Songliao Basin, Ordos Basin and Kuqa Depression as examples, we aimed to investigate the effect of the redox conditions, water salinity and oxygen content of the source-rock depositional environment on the formation of rearranged hopanes to provide theoretical basis for the genesis of rearranged hopanes.

The Biomarkers in the Mesoproterozoic Organic-rich Rocks of North China Craton:Implication for the Precursor and Preservation of Organism in the Prokaryotic Realm

Mesoproterozoic marine organic-rich rocks are widely distributed in the North China Craton,include the Gaoyuzhuang(GYZ),the Hongshuizhuang(HSZ),and the Xiamaling(XML)formations.According to the T;value and isomerisation ratio of C;homohopanes,the XML,HSZ,and GYZ samples were in low mature,mature and high mature stage,respectively.Biomarker distribution in extractable organic matter(EOM)of three Mesoproterozoic organic-rock samples in different maturity were analysed to reveal the organic precursor and preservation pathway of in the Mesoproterozoic Combined with gold-tube pyrolysates of three Mesoproterozoic samples,it could further illuminate the chemical composition of Mesoproterozoic kerogen,given excluding.The results indicated that the three formations were all deposited under reducing condition and their organic precursors mainly were some aquatic organisms.High content of rearranged hopanes was detected in EOM of XML and HSZ samples,whereas they were relatively low in the high mature GYZ sample.Contrast to that in EOM,the relative concentration of rearranged hopanes sharply decreased in the gold-tube pyrolysates of the XML kerogen,then slightly increased but was still significantly lower than the EOM of XML sample,which indicated that catalysis of clay minerals in the early diagenesis only changed the chemical composition of the unstable functional groups of the kerogen during the preservation.Due to the thriving heterotrophic microbes and low sink rate of particulate organic matter during the Mesoproterozoic,primary producers suffered extensive degradation during sinking process,only some resistant biopolymers lacking of lipid compounds survived from heterotrophic degradation,while heterotrophic microbes contained more proportion of organic precursors.Abundant pristane(Pr)and phytane(Ph)were only released in high mature stage because of the protection of the macromolecular structure of resistant biopolymers which prevented biomarkers from being altered by the thermal stress.The absence of 13α(n-alkyl)-tricyclic terpanes in the high matured hydrocarbon products also indicated the different precursors between different parts of Mesoproterozoic kerogen.The evolution of the biomarker composition and content of Mesoproterozoic kerogen showed some special characteristics differing from those of Phanerozoic kerogen.The total concentrations of hopanes displayed with an order of low mature stage>high mature stage>mature stage.Relative content of rearranged hopanes in the hydrocarbon generated in high mature stage was significantly lower than that in the low maturity stage.The ratios of Pr/n-C_(17) and Ph/n-C_(18) increased with thermal maturity,and the ratio of nC_(21-)/nC_(22+) decreased in the high maturity stage,thus displaying another order of mature stage>high maturity stage>low maturity stage.The unique preservation pathway of Mesoproterozoic organisms was attributed to the special evolution characteristics of biomarker distributions,which should be considered in the Mesoproterozoic marine environment and biological studies.

Distribution Patterns of Pentacyclic TriterpenoidHydrocarbons in Low-Mature Source Rocksfrom Eastern China

Four typical distribution patterns of pentacyclic triterpenoid hydrocarbons (types A-D) are distinguished in the low-mature source rocks from eastern China. Type A has a relatively high content of pentacyclic triterpenes. It exists in immature sediments and the distribution and abundance of triterpenes vary with the maturity of the sediments. An unknown C30 triterpene (UCT2) has also been detected in very shallow sediments. This compound is very unstable and disappears rapidly with the increase of depth. Type B is characterized by a relatively high amount of 17α(H), 21β(H)-30-homohopane. This kind of distribution pattern is common in coals and terrestrial sediments of low maturity. Type C has a relatively high content of diahopane and neohopane series. The analysis shows that this distribution pattern may have an indirect relationship with the input of higher plants despite its microbial source. There are C30—unconfirmed triterpane (UCT2) and a relatively high content of C35 hopane in type D. The distribution patterns of pentacyclic triterpenoids are varied under influences of biological sources, diagentic and sedimentary environments, thermal maturity etc. Therefore, they can provide useful information about the source rocks. Based on geochemical characteristics of the source rocks, the authors postulated that the type B and type C patterns are mainly related to suboxic-anoxic environments. Type D indicates the reducing to anoxic environment, in which C30-UCT3 may be related to some specific biological source in saline environments. The precursors and thermal evolution of some triterpenoid hydrocarbons are also discussed herein.

A new hopane triterpenoid from Saxiglossum angustissimum

A new hopane triterpenoid, hopane 22, 29-diol-29-formate （1）, has been isolated from the whole herbs of Saxiglossum angustissimum （Cries.） Ching and its structure has been successfully determined on the basis of spectroscopic evidences.

The Biodegradation of Dispersed Oil Does Not Induce Toxicity at Environmentally-Relevant Concentrations

Applying dispersants to spilled crude oil results in an oil in water dispersion of microscopic oil droplets that soon dilutes to levels below 1 ppm oil. These levels are substantially below those known to induce acute toxicity in 96-hour tests. We show here that oil hydrocarbons are biodegraded very rapidly in such situations (50% loss in 4 days in this experiment), and that no increase in acute toxicity to mysids (Americamysis bahia) is seen during this biodegradation, or over the following 20 days as the oil is further degraded (78% loss of detectable hydrocarbons in this experiment).

GEOCHEMISTY OF BICYCLIC ALKANES IN SEDIMENTS, COAL AND CRUDE OILS

By using GC-MS to analyze the extracts of source rocks, coal and crude oil samplesformed in different sedimentary environments in China, New Zealand and Australia, twenty-two compounds of five types of bicyclic alkanes have been dis covered in the samples. Thispaper makes an exposition of stereochemical structure, abundance and distributive features ofthese compounds and their relation to sedimentary environments and thermal evolution. Furt-thermore, it demonstrates how the abundance ratios of bicyclic alkanes to steranes and ter-panes, drimane to homodramane and the relative abundance of C15,C16,C12-C14 series of bicyclic-alkane compounds can be used to judge and determine types of oil and gas forming environ-ments （the depositive environments of source rocks from which the oil and gas wereformed）, characteristics of source rocks and degree of maturation.

The effects of biodegradation on biomarker maturity indicators in sequentially biodegraded oils from Liaohe Basin,China

By aid of gas chromatogram/mass spectrometry(GC-MS) ,the distributions and the compositions of biomarkers in a set of sequentially biodegraded oils from Liaohe Basin,China,have been quantitatively analyzed,and it has been found that during the biodegradation process of crude oils,the molecular maturity parameters such as Ts/Tm,homohopane C31 22S/(22S+22R) and sterane C29 20S/(20S+20R) ratios will be affected to different extent. The results show that except homohopane C31 22S/(22S+22R) ratio,Ts/Tm ratio will decrease with increasing biodegradation,but for C29 20S/(20S+20R) ratio,it will almost remain constant in slightly and moderately biodegraded oils,and then will increase quickly in severely biodegraded oils. The main reason is that there are some differences in the ability of resistant biodegradation for different isomer of biomarkers with different stereo configuration,resulting in the fact that destroying rate by bacteria for those biomarkers with weak ability will be higher than those with strong ability in resistant biodegradation. For example,18α(H) -22,29,30-trisnorhopanes(Ts) will be destroyed more quickly than 17α(H) -22,29,30-trisnorshopanres(Tm) ,and 20R isomer is more quickly than 20S isomer for C29 sterane,resulting in the relative ratios changed with increasing biodegradation. Therefore,much more attention should be paid to the biodegradation extent of crude oils and the type of biomarker maturity indicators,when the distributions and the compositions of biomarkers in biodegraded oils are used to determine the maturity of biodegraded oils.

Distributional Patterns of Hopenoid Hydrocarbons in Mudstone and Crude Oil, Banqiao Sag

As triterpenoid biomarkers mainly derived from prokaryote （e.g. bacteria andcyanobacteria）, hopenoid hydrocarbons are ubiquitous in fossil fuels and sediments.Ensminger et al. （1974） reported a normal distributional pattern of C27-C35 (withoutC28) hopanes with an absolute predominance of C30 hopane. In 1980, Seifert