重庆老龙洞二叠系-三叠系界线地层微生物岩研究

The largest mass extinction in the Phanerozoic happened at the end of the Permian. The microbialites formed in the extreme environments after the mass extinction has become a hotspot for geologists and paleontologists throughout the world. The dendroid microbialites that were described for the first time in 1999 from the Permian-Triassic boundary section at Laolongdong, Chongqing, have been studied by many geologists from China and overseas. Two important viewpoints about their origin have been proposed. Some researchers believed that they resemble Quaternary travertine shrubs in form, and may belong to microbialites. Some other researchers proposed that the dendroid structure is composed of clots formed by coccoidal cynaobacteria, and is microbialite. Our detailed survey on the section reveals that: (1) there is an interval of speckled “microbialite” in the section, and it underlies the dendroid “microbialite”, (2) the dendroid “microbialite” does not always have dendroid appearance; they are dendroid only in very local places; they are not dendroid in most places; for this reason, they are not comparable to recent tufa; (3) the volume of the dendroid structure greatly increases toward the top of the dendroid microbialite interval: accounting to 70% of the whole rock in the top part. This distribution pattern implies that the formation of this structure may be related to downward migration of the diagenetic fluid. Examination of thin sections reveals that the dendroid structure or point-like structure in the “microbialite” look as lighter areas in the thin sections and are composed of large blocky clear calcites containing scattered yellow dirty small calcite rhombi and irregular “points” of relict lime mudstone or wackestone or packstone. Their formation is by any one of the following two processes: (1) dissolution → filling of large blocky calcite; (2) dolomitization → dedolomitization → dissolution by meteoric fresh water → filling by large blocky calcites. It has been found that there are at least two sea-level falls during the P-T transition. As the sea level fall, the carbonate deposits came into supratidal environment, and suffered dolomitization caused by evaporative fluid or mixing water of sea water and meteoric water. Since the fluid migrated downward from the top of the deposits and in random pathway, the dolomitization formed dendroid or speckled dolomitic areas. As the deposits came into subaerial environments, the meteoric fresh water migrated along the dendroid or speckled dolomitic area with higher porosity, and dissolution happened, which caused the rock became spongy or alveolate. In later time, after the strata came into phreatic zone, large clear blocky calcites grew in and filled the pores in the spongy areas. The dendroid and speckled structure were formed in this way, rather than composed of clots formed by coccoid cyanobecteria. The microbial fossils in Laolongdong section include two types. The first is the tube-like cyanobecteria in middle Bed 3, which are generally less than 1 mm in length, taper toward one end, and are internally filled by microspars. They are straight or sinuous, with micritic wall 0.005~0.01 mm thick. Since this kind of microbial fossils are abundant in middle Bed 3, this rock belongs to microbialite. The second type occurs in Bed 5 and lower and middle Bed 6. They are irregular globular in shape, generally 0.2 ~ 0.5 mm in size, with several outward progresses, and internally filled by one layer of needle-like calcite cements on the wall and the large blocky calcite in the inner space. According to their shape and preservation way, it is inferred that this kind of fossils were formed from some kind of bacterial colony. The bacterial colony may be cuticle in composition, since it has some hardness as it is indicated by its resistance to deposit loading. These organisms discomposed during diagenetic time, and formed good porosity. In later diagenetic time, these pores were firstly cemented by needle-like calcites and later filled by large blocky calcites. So, the bacterial colony promoted the formation of dendroid and speckled structures. However, they did not always form such structures. On the other hand, even though no bacterial colony or other microbes or any kind of fossils were present, dendroid or speckled structures can form. Bed 4 of Laolongdong section contains abundant gastropods but no microbial fossils, and is not microbialite, even though it is speckled. The top of Bed 6 is dendroid, but contain no microbial fossils, and is not micrbialite.

五台山区义兴寨岩体、车厂－北台岩体地球化学和变质作用及其大地构造意义

There are many Archean TTG grey suites in the Wutaishan area, northern Shanxi Province, China. In the past one hundred years, many geologists have done excellent research work in the Wutaishan and its adjacent regions. However, the TTG suites were almost neglected. Located in the northern slope of Mt. Hengshan-namely the Archean Hengshan Island Arc, intruded the Zhujiafang supercrustal rocks at almost 2.5Ga, the Yixingzhai TTG Suite is originated from partial melting of the ancient lower crust upper mantle by REE and trace elements, and the emplacement occurred in an Archean island arc. The rocks are mainly of tonalitic, I type, and calc-alkaline trends are found in the magmatic evolution. At almost 1.8 Ga, the suite was transformed to be dome-like schists in an arc-arc collision event, and the rocks were metamorphosed to an extent of amphibolitic to granulitic facies. The peak metamorphic condition is of 710-760 ℃/0.68-0.72GPa, and the subsequent cooling history is recorded as 560-620 ℃/0.46-0.60GPa. In the center of the Mt. Wutaishan-known as the Archean Wutaishan Island Arc, intruded the Archean Chechang-Beitai TTG Suite, which is of 2.5Ga old and of trondhjemitic and tonalitic, with coexisting I- and S-types and a trondhjemitic magmatic evolution trend. Through REE and trace elements, the suite is believed to be from the partial melting of the ancient lower crust or upper mantle. The 1.8 Ga collision event also made the suite gneissic and the it was metamorphosed to be amphibolitic facies, whose peak condition is approximately of 680 (±50) ℃/0.7Gpa, and the subsequent cooling process is recorded as 680 (±50) ℃、550(±50) ℃、420(±10) ℃. Crustal growth is fulfilled through magmatic intrusion as well as eruption at about 2.5Ga, arc-arc collision at about 1.8 Ga in the Wutaishan area and its environs. Additionally, the biotite-muscovite and muscovite-plagioclase geothermometers are refined, and the biotite-hornblende geothermometer is developed in this dissertation.

改造型盆地油气成藏机理与油气预测－以银根－额济纳旗盆地为例

Reformed basin is a basin that underwent multiple immense reformation after the sedimentary stage, the major geologic elements of the petroleum system in the prototyped basin are destroyed to a certain extent, and their petroleum system has been reconstructed. This type of basin is frequently found in the course of exploration both home and abroad. In China, especially in the western and southern part of China, the basins in which oil explorations have been conducted are mostly reformed basins. The reformed basins from Paleozoic, Late Mesozoic to Cenozoic are widely distributed in West and South China. They are, and moreover, will be a challenge for oil and gas exploration. The conventional investigation and exploration techniques used in the slightly reconstructed basin just don't work well when facing the reformed basin. Therefore, the study on the reformed basin, especially the study on the pool-forming mechanism and reservoir prediction becomes a focus and one of difficulties for the geologists overseas and domestic. Yingen-Ejinaqi Basin is a typical case of the Late Mesozoic and Cenozoic reformed basins in China. It locates in West China and is a exploration frontier with difficulties and no break through is made for years. A comprehensive research on it will be of significance for oil and gas exploration in similar basins of China. The late research for reformed basin in China now is mainly concentrated on basin classification, formation mechanism, geologic features, and survey technique, distribution regularity of oil accumulation and its dominating factors, assessment of oil exploration prospect and target zones, etc. On the other hand, the study on the pool-forming mechanism and reservoir prediction seems insufficient in systematization, and the research is deficient in methodology and combination of qualitative and quantitative studies, as well as the application of the new theory and techniques. The current efforts are mainly directed to structures (faults), sedimentation, the relationship between reservoir evolution and oil accumulation, and some other relevant fields. However, the application of the new theory and techniques seems to be insufficient such as petroleum system, pool-forming dynamics, fluid pressure compartment, and basin simulation, etc. So is the dynamic and integrated research. As a result, incomplete knowledge and understandings derived from the research on pool-forming mechanism and reservoir prediction often do not accord with rea-lity of the basin. The study and exploration under the guidance of this knowledge will inevitably lead to errors and failure. This paper, based on the previous study of the other geologists on reformed basins, with emphasis on "wholeness or systematic, dynamic and integrated" research, presents a reverse thinking of beginning from conserved units in the basin and the combination of qualitative and quantitative study with new theory and technique by building a geological model. The paper also puts forward a new thought for studying the oil & gas accumulation and reservoir prediction , and establishes a new research system for reformed basin. It is verified by the known reservoir and oil accumulation area in the basin and has a practical value for use and reference. The new ideas and achievements in this research are as following: 1.This is the first time that the system for studying the reformed basin and its pool-forming mechanism and reservoir prediction is presented. A reverse thinking and combination of qualitative & quantitative are applied here with emphasis on "wholeness or systematic, dynamic and integrated" research, new theory, techniques & methods comprehensive use and geologic models building. 2. Identifying criterion and methods, classifying schemes, and denominating principles for the conserved units of reformed basins are presented in this paper. The geologic model of conserved units of Yingen-Ejinaqi Basin has been built. It is a practical method when combined with the traditional way for basin survey and the conserved units study. 3.The dynamic sources of basin deformation are believed to be stress, gravity and thermodynamics. The stress and gravity are key factors in basin deformation and pool forming, especially stress. Scientific proof is provided by classifying the functional type, style and range of the stress, gravity and thermodynamics. 4.The pool forming and reservoir distribution of Yingen-Ejinaqi Basin are controlled by multiple factors or geologic conditions or/and co-controlled by both of them. The qualitative and quantitative research on petroleum system and basin modeling will help us understand and determine the pool-forming period of the conserved unit (timing), the oil migrating direction (orientation), the oil accumulating region (location), the oil distributing border (bordering) and the size of oil accumulation (quantification). Thus the pool-forming and distribution zones can be predicted. 5.Three generating modes (reform-succession type, reform-destroyed type and reform-regenerating type or reform-newborn type) of pool forming for reformed basins are presented here, together with the inner relationships between basin deformation type, overlapping style and pool-forming modes. The pool-forming modes are determined by deformation type and overlapping style. Reservoir distribution will be predicted based on the modes and other concrete pool-forming conditions. 6.The evaluation methods of the conserved units and zones and the parameter selection are reliable in optimal selecting of target zones. The technical terms, new ideas and methods for the study of reformed basins, the pool-forming mechanism and reservoir prediction are presented in this paper. The concepts and terms, the identifying criterion, the denominating principles, the generating modes for pool forming, the methods of reservoir prediction, and the evaluation techniques for conserved units and zones can be used for reference in studies on the petroleum exploration of reformed basins in China and abroad. It serves as a typical example for further research of the reformed basins and the geologic regulations of oil accumulation. It has a practical value of use and reference. The future research in the field of pool-forming mechanism of the reformed basins may well be on the process simulation of pool-forming dynamics of the reformed basins. Experimental work has been conducted to simulate the processes by using quantitative and qualitative methods combined. The further study in this field calls for more efforts.

西南天山托云盆地白垩-新生代古地磁结果及其构造意义

Western China is regarded as an assemblage of blocks or microplates. The India/Asia postcollisional kinematics of these blocks has attracted many geologists to pay attentions, especially on the geodynamics and intracontinental deformation of Tibetan and adjoining parts of central Asia. So far there are still many debates on the amount of continental shortening and extrusion within Western China blocks. Paleomagnetism plays a very important role in the paleogeographic reconstruction and depiction of kinematics of the blocks, however the unequilibrium of paleomagentic data obtained from Western China prevents paleomagnetists from studying the kinematics and intracontinental deformation on the Tibetan plateau and the central Asia. Moreover, shallower inclinations observed in the Cretaceous and Cenozoic terrestrial red sediments in central Asia makes it difficult to precisely estimate the northward convergence of Tibetan plateau and its adjacent areas since the onset of the Indian/Asian collision. In this thesis, detailed rock magnetic, chronological and paleomagnetic studies have been carried out on the Tuoyun Basin in the southwestern Tianshan to discuss the possible continental shortening and tectonic movements since the Cretaceous-Tertiary. Ar-Ar geochronological study has been conducted on the upper and lower basalt series from the Tuoyun Basin, yielding that the lower and upper basalt series were extruded during 115-113 Ma and 61.8-56.9 Ma, respectively. Both the age spectrum and inverse isochron show that the samples from the upper and lower basalt series have experienced no significant thermal events since extrusion of the baslts. Rock magnetic studies including temperature dependence of magnetization and susceptibility during a heating-cooling cycle from temperature up to 600 ℃ suggest that the baslt samples from the lower and upper basalt series are ferromagnetically predominant of magnetite and a subordinate hematite with a few sites of titanomagnetite. The predominant magnetic mineral of the intercalated red beds is magnetite and hematite. Anisotropy of magnetic susceptibility shows that both the baslts and the intercalated red beds are unlikely to have undergone significant strain due to compaction or tectonic stress since formation of the rocks. The stable characteristic remanent magnetization (ChRM) isolated from the most samples of the upper and lower basalt series and intercalated red beds, passes fold test at the 99% confidence level. Together with the geochronological results, we interpret the characteristic component as a primary magnetization acquired in the formation of rocks. Some sites from both the upper and lower basalts yielded shallower inclinations than the reference field computed from the Eurasia APW, we prefer to argue that these shallow inclinations might be related to geomagnetic secular variation, whereas the shallow inclination in the intercalated red beds is likely to be related to detrital remanent magnetization. Paleomagnetic results from the early Cretaceous-Paleogene basalts indicate that no significant N-S convergence has taken place between the Tuoyun Basin and the south margin of Siberia. Furthermore, the Cretaceous and Tertiary paleomagnetic results suggest that the Tuoyun Basin was subjected to a local clockwise rotation of 20°-30° with respect to Eurasia since the Paleocene time, which is probably subsequent to the Cenozoic northward compression of the Pamir arc.

中国东海陆架盆地构造-热演化研究

East China Sea Shelf Basin (ECSSB), as a basin with prospect of oil & gas resource and due to its special geological location on the west margin of the west Pacific, attracts a lot of attention from many geologists in the world.Based on systematic temperature measurements, bottom hole temperature (BHT) and the oil temperature data, the geothermal gradients in the ECS SB are calculated and vary from 25 to 43°C/km, with a mean of 32.7°C/km. The geothermal gradient in Fuzhou Sag has the higher value(40.6°C/km) in Taibei Depression than that in others. The lower value (27.2 °C/km) occurs in in Xihu Depression. The middle values occurs in Jiaojiang and Lishui sags in Taibei Depression with a mean value of 34.8 °C/km. Incorporated with the measured thermal conductivity, heat flow values show that the ECSSB is characterized by present-day heat flow around 70.6mW/m2, varying between 55 and 88 mW/m2. No significant difference in heat flow is observed between the Xihu and the Taibei Depressions. These heat flow data suggest that the ECSSB is geothermally not a modem back-arc basin.Applying the paleogeothermal gradient based method, thermal history is reconstructed using vitrinite reflectance (VR) and apatite fission track (AFT) data. The results suggest that the thermal history was different in the Taibei and the Xihu depressions. Paleo-heat flow values when the pre-Tertiary formations experienced their maximum temperature at the end of the Paleocene reached a mean of 81 mW/m2 in the Taibei Depression, much higher than the present-day value. The lower Tertiary sediments in the Xihu Depression experienced maximum temperatures at the end of Oligocene and reached a mean paleo-heat flow value of 83.4 mW/m2. The time, when the paleo-heat flow reached the maximum value, suggests that the ECSSB rifted eastward.Tectonic subsidence analysis shows that the timing of the major rifting episode was different across the ECSSB. The rifting occurred from the Late Cretaceous to the early Eocene in the Taibei Depression, followed by thermal subsidence from the late Eocene to the end of Miocene. In contrast, in the Xihu Depression the initial subsidence lasted until the early Miocene and thermal subsidence to the end of Miocene. From Pliocene to the present, an accelerated subsidence took place all along the West Pacific margin of the east Asia.The thermal lithosphere thickness is determined by temperature profile in the lithosphere, the mantle adiabat or the dry basalt solidus. It indicates that the thermal lithosphere reached the thinnest thickness at the end of Eocene in the Taibei Depression and the end of Oligocene in the Xihu Depression, respectively, corresponding with a value of 57-66km and 56-64km. In Taibei Depression, the lithosphere thickness decreased 16-22km from the end of Mesozoic to Paleocene. After Paleocene, the thickness increased 13-16km and reached 71-79 km at present-day. In Xihu Depression, From the end of Oligocene to present-day, the thickness increased 10-13km and reached 69-76km at present-day. The evolution of the lithosphere thickness is associated closely with the lithosphere stretching.Combining the reconstructed thermal history and the burial history, the maturation of the Jurassic oil-source rock shows that the main hydrocarbon generation phase was in the mid-Jurassic and a secondary hydrocarbon generation occurred at the end of Paleocene. The secondary generation was controlled mainly by the tectono-thermal background during the Paleocene.