Geochemical characteristics and families of the Paleozoic oil seepage and solid bitumen in the Southern Guizhou Depression,SW China

Fifteen oil seepage and solid bitumen samples in the Southern Guizhou Depression were analyzed with GC–MS. Characteristics of molecular markers and carbon isotopes are discussed systemically. The results showed that the oil seepage and solid bitumen samples in the Southern Guizhou Depression could be divided into two families: Ordovician and Siluric samples, and Permian samples. The two families are different in alkanes distribution, biomarkers, aromatic hydrocarbon composition,and stable carbon isotopes; differences mainly caused by source rock variation.

Paleo-oil reservoir pyrolysis and gas release in the Yangtze Block imply an alternative mechanism for the Late Permian Crisis

The causes of the global mass extinction that occurred around the Permian-Triassic boundary have been widely studied through the geological record and in various locations.The results show that volcanic activity was a key factor in initiating the crisis during the Late Permian.Compared to other thermal events triggered by volcanic activity,pyrolysis of petroleum in Pre-Permian reservoirs has rarely been suggested as a significant source of the greenhouse gases that caused the mass extinction.In this study,geochemical analysis is carried out of a huge paleo-oil reservoir in the Yangtze Block(YB),South China.The detection of mineral inclusions and pyrobitumens is evidence of rapid pyrolysis of accumulated oil in the Ediacaran reservoir.New evidence from hydrothermal minerals and the presence of domain mesophase in the pyrobitumen suggest that the pyrolysis process occurred abruptly and that greenhouse gases were rapidly released through venting pipes.The dating of such a complex geological event in this old and deeply buried reservoir is inevitably difficult and potentially unreliable.However,cross-validation of the multiple evidence sources,including hydrothermal minerals and domain mesophase,indicates that the rapid oil pyrolysis must have been driven by a major thermal event.Reconstruction of burial and thermal histories suggests that the thermal event was most likely to have been triggered by the Emeishan Large Igneous Province(ELIP),which was in a period of significant volcanic activity during the Late Permian.Massive volumes of gases,including methane,carbon dioxide,and possibly hydrogen sulfide,were released,causing a significant increase in greenhouse gases that may have contributed to global warming and the resulting mass extinction during the Late Permian Crisis(LPC).

Discovery of cutinitic liptobiolith in northwestern China and a comparative study with Luquan Devonian coal

Devonian cutinitic liptobiolith is a special cuticle-rich coal formed during the early stage of land plant evolution. In China, this special coal has previously only been reported in the Yangtze area, with the Luquan Devonian cutinitic liptobiolith of Yunnan Province being the most well-known. Recently, this type of coal was first discovered in the Bulonggoer Sag, to the northwest of the Junggar Basin, NW Xinjiang. Its geological age is regarded as the Givetian period of the late Middle Devonian,which is equivalent to the age of the Luquan Devonian coal. The cutinitic liptobiolith from NW Xinjiang has a distinct sheet-like texture resembling a stack of paper or leaf sheets in appearance, and so it is commonly called "paper coal" or "leaf coal". Ribbonlike cutinite(thick-walled type) is the most abundant maceral in the coal(>60% and up to 80%, on a mineral-free basis), followed by ribbon-like collotelinite. The NW Xinjiang and Luquan cutinitic liptobioliths share similar maceral compositions;while their coal-forming plants and depositional conditions are distinct. The NW Xinjiang cutinitic liptobiolith was deposited in a regional fluvial or flood plain condition, with lycopsids as the dominant coal-forming plants. In contrast, the Luquan cutinitic liptobiolith formed in a coastal-lagoon environment, with primitive ferns as the predominant coal-forming plants, followed by lycopsids. The saturated fractions of the NW Xinjiang and Luquan liptobioliths are mainly composed of tetracyclic diterpanes. However, the tetracyclic diterpane compositions in the NW Xinjiang cutinitic liptobiolith are distinct from those in the Luquan Devonian coal:The former is dominated by atisanes and the latter is mainly composed of phyllocladanes. Different coal-forming plants may have contributed to the distinct tetracyclic diterpane compositions.

Simulation experiment of immature oil genetic mechanism in lake facies of semi-salt water

The immature calcareous shale in the south slope of Dongying sag, Jiyang depression, plays a significant role in immature oil genesis, and is sampled to make simulation experiment. The geochemical characters of the products of soluble organic matter and kerogen are researched respectively. The yields of the two components and their relations are made out. The contribution ratio between soluble organic matter and kerogen undergoing early degradation in lake facies of semi-salt water is figured out for the first time, so the research into the genetic mechanism of immature oil is developed.

Carbon isotopic study of individual n-alkanes in certain modern organisms

Simulation experiment was carried out on all kinds of modern organisms significant to oil-gas generation and the C-isotopic values of n-alkanes in different organisms. The distribution characteristics of individual n-alkane isotopes are studied. The experimental results supply important clues in biological provenance of n-alkanes in sedimentary organisms.

Petrology and geochemistry of the Carboniferous cutinite-rich coals from the Hequ area of Shanxi Province, China

Coal samples taken from the Taiyuan Formation in the Hequ area, China, for this study are typical cutinite-rich coals.The petrology and geochemistry of the samples were analyzed using microscopic examination, proximate and ultimate analysis,rock pyrolysis, and gas chromatography-mass spectrometry(GC-MS). The cutinites in Haochuan(HC) coals are predominantly of the thin-walled type, whereas those in the Jingzigou(JZG) coals are predominantly thick-walled. The variable thickness of cutinites in different coals is related to the environment in which the coal-forming plants grew. Compared with typical Ⅲ kerogens, HC and JZG bituminous coals are characterized by high volatile matter yields and hydrogen contents due to the elevated hydrogen-rich cutinite content. Pyrolysis data indicate that these cutinite-rich coals can be expected to generate commercial liquid and gaseous hydrocarbons. Pristane(Pr) and phytane(Ph) are both abundant in the samples, with the Pr/Ph ratios for both the HC and JZG coals being >3.0, indicating moderate maturity and oxic peat depositional conditions. The C>>C>Cnormalized relative abundance of regular steranes is consistent with a dominant contribution from higher plants.Abundant hopanes in the coals also suggest a substantial organic matter input from bacteria, which are common inhabitants of peat and coal. Palynology studies indicate that pteridophytes are likely to be the most common coal-forming plants. A gymnosperm contribution is also indicated by the presence of tetracyclic diterpenes. Massive accumulations of cuticles as cutinite in coal are rare and account for only a small proportion of coals worldwide. However, cutinite-rich coals are found in the northern margin of the North China Craton, in the Taiyuan Formation. The accumulation of cutinite in this area is the result of distinctive peat deposition conditions. Frequent marine transgression was an important contributing factor.