Hydrothermal communities on the deep seafloor live around black smoker sites. The primary producers of hydrothermal ecosystems are thermophiles and archaea. Bacteria convert chemicals (from the sulfur rich fluid spewed out of vents) to energy, in a process called chemosynthesis. The comparison in modern hot spring microbe and ancient hydrothermal systems indicates that they have similar structural characteristics. Studies in mechanism of mineralization, the process of bacterial fossilization and the biochemical microbial biosignatures in sediment not only has crucial implication for the further probe into the rules of the activities of hydrothermal fluid in deep sea and minerogenic mechanism but also hold importance for exploration of signatures of life or prebiotic chemistry on other bodies in the solar system, as well as providing more robust criteria for recognizing biogenic features in ancient terrestrial and extraterrestrial materials. In addition, it has important theoretical meaning for the understanding of astrobiology and the origin of life.
This study is trying to reconstruct the lake status and regional palaeoclimate character based on XRD data and Pediastrumalgae from the core JLT11-A of Jilantai Salt Lake during the Last Glaical Maximum(LGM).The result suggested that the main minerals of the sediments were clastics(~85%)dominated by Quartz and Albite and about 10% of carbonates(mainly calcite),and both of them could be transported from land by strong winds,thus indicated a cold-dry climate as other palaeoclimatic records suggested.Although the sum of Chloride and sulfate minerals were generally less than 5%,its continuous appearance of Chloride suggested a basically high salinity.Therefore,the Pediastrum was not possible from the lake,but was transported by rivers.Mineral assemblage of Jilantai Lake is more connected with terrestrial material input and it is difficult to directly trace the lake water salinity.By comparing to the other records from neighboring regions,the LGM summer precipitation was higher than deglaciation period,while,it was lower comparing to the late MIS3 stage.The pattern of Jilantai Salt Lake evolution from LGM to the Last Deglaciation suggested that the mineral assemblage variations and lake status were strongly affected by the summer insolation,global and regional temperature,and Asian summer monsoon intensity.
The study on deposition and structural development history of the basins in Andaman Sea involved tectonic patterns,tectonic stress field features,deposition sequence and source provenance analysis.Through building up the important cross-section and faults system,combining with the regional tectonic evolution and using the geological,geophysical and geochemistry data,this paper analyzed the tectonic evolution characteristics of the basins in Andaman Sea.The basins in Andaman Sea have experienced pre-rifting,syn-rifting and inherit compression-shear transformation since Late Miocene.The early-period normal faults which were formed during the early stage of the pre-rifting were developed in the basin.The regional fractures were greatly influenced by Sagaing fault.The developed faults and folds in the late period were related to the direction of Sagaing fault and Indian Plate subduction from NNE.The basins in Andaman Sea have many diapiric structures,including accretionary wedge mixing medium diaper,magmatic arc diapir and mud diapir caused by back-arc striking-slip fault.Among them,the accretionary wedge mixing medium diapir is a special diapiric structure in the convergent continental margin of Burma sea.Special geographic position decides its individual tectonic stress field and the geotectonic evolution of basin.Intensive study on the basins in Andaman Sea will be in favor of exploring the oil and gas of convergent continental margin and play an instructive role in the development of plate tectonics.
Marine phytoplanktons (marine “bio-pumps”) bear half of the photosynthesis in the earth and play an important role in modulating the CO_2 concentration and global carbon cycle. The transition from the “iron hypothesis” to “silica hypothesis” reflects the responds and feedbacks of the “bio-pumps”, especially different marine phytoplanktons to the past climate changes. Different biomarkers produced by different phytoplanktons can be used to reconstruct marine phytoplankton community set-ups.For examples,fucoxanthin and C_(28)-sterols are mainly from Bacillariophyceae, whereas 19′-Hexanoyloxyfucoxanthin and C_(37)-C_(39) alketones are mainly from Haptophyceae. Special pigments in the water and lipids in the sediments have been successfully used to reconstruct the phytoplankton biomass and communies. Although the relationship between the phytoplanktons and the biomarkers needs much improvement, it is still proved a fast and efficient method compared with other methods and will have an important prospect in the future marine detection and paleoclimate research.
surface sediment samples were collected from Yuehu during November- December 1998 and August-September 1999, respectively.These samples were analyzed using a Cilas940 L Laser Analyzer and by sieving (for particles with a diameter of 2 mm and 2 mm, respectively) to obtain grain size parameters. Three grain size parameters, i. e., mean grain size(μ), sorting coefficient(δ) and skewness(sk) are then calculated by a moment method.Five main sediment types are present in Yuehu according to the sediment classification scheme proposed by Shu Gao(1993, slight modification based on Folk(1980) classification scheme). The result shows the sediment appears annular distribution and is mainly composed of fine materials: From bank to center the sediment becomes finer gradually, i.e., from gravel sand, muddy sand, sandy mud to mud in turn. Sand is only distributed on ebb delta and north-east corner of the lake. There is a close relationship between mean grain size for sediment and sediment types in Yuehu where the mud area is mostly enclosed by 6 contour. The mean grain size for sandy mud is between 6 and 4 and muddy sand is between 4 and 2. In the sand and gravel sand distributed area the mean grain size is less than 2. Sorting coefficient and skewness value for sediment in Yuehu is 2.0～2.5 and 1～2 respectively. But the sediment located over flood delta is not well sorted with the sorting coefficient value between 3.0 and 3.5. At the same time the sediment near the mouth is negatively skewed with a value of 0.5 and the skewness is near 0 in a small area to the east of the center. The two dimensional model for grain size trend analysis proposed by Gao and Collins(1992 ) is adopted to identify sediment transport pathways in the study area. The net sediment transport pathways derived by using this model show that sediment is transported from bank towards the center, except the net sediment transport pathways are not obvious over ebb delta and main channel.At the same time the result shows that the north and west part of the top of the lake, flood delta and center are deposition centers. Such patterns are highly consistent with the sediment distribution pattern. Therefore this model is applicable for such a small area as Yuehu.
A comparative analysis of the geochemical characteristics of sediments from the Oligocene Zhuhai Formation(32-23.8 Ma),the Miocene Zhujiang Formation(23.8-16.5 Ma),and the Hanjiang Formation(16.5—10.5 Ma) and a comprehensive analysis of the geochemical characteristics of rocks surrounding the paleo-Pearl River drainage contribute to understanding the influences of the Tibetan Plateau uplift on provenance evolution of the paleo-Pearl River.The results show that the geochemical characteristics of sediments from the Oligocene Zhuhai Formation are very different from the geochemical characteristics of sediments from the Miocene Zhujiang and Hanjiang Formations.The ∑ rare earth elements(REE) of mudstone is relatively high in the Zhuhai Formation,204.07-293.88 ppm(average 240.46 ppm),and low in the Zhujiang and Hanjiang Formations,181.32-236.73 ppm(average 203.83 ppm) and 166.84-236.65 ppm(average199.04 ppm),respectively.The chemical index of alteration(CIA) for these samples has a similar trend to the∑ REE:the CIA of the Zhuhai Formation is relatively high and the CIA of the Zhujiang and Hanjiang Formations is relatively low.The uplift of the Tibetan Plateau is crucial to the westward expansion of the paleo-Pearl River drainage.
The mid-latitude Asian continent can be roughly divided into two distinct climatic regions:the humid eastern-southern part of Asia mainly controlled by monsoon circulation and inland arid Asia(including the cold-arid northern Tibetan Plateau)in the western part dominated by the mid-latitude westerlies.Based on the extensive review of recently published literatures,we found that a dry early Holocene,a wettest mid-Holocene,and a moderately wet late Holocene dominated in arid central Asia(ACA),while a strong summer monsoon and humid climate characterized the early Holocene,and a weakened summer monsoon and drier climate prevailed during the late Holocene.During the past millennium,ACA experienced a dry Medieval Warm Period(MWP)and a humid Little Ice Age(LIA).In contrast,it is indicated by a speleothem proxy record from Wanxiang Cave that the monsoon precipitation was generally high during the MWP and generally low during the LIA.Over the last 100 or 50 years,moisture has increased in arid NW China,while climate in monsoon-influenced semi-arid NW China and North China has become drier.In addition,anti-phase relationship in precipitation changes between the northern Tibetan Plateau(climatically controlled by westerlies)and southern Tibetan Plateau(mainly influenced by Indian monsoon circulation)exists on decadal to centennial timescale.In summary,moisture variability in ACA and northern Tibetan Plateau has showed major difference from monsoon evolution on various time-scales in the Holocene.It is thus proposed that there is a westerly-dominated climate model in mid-latitude Asia during the modern interglacial period.
Smart well technique as a new well completion technique was developed rapidly and widely since 1990.This paper introduced the development of smart well technology,and summarized the smart well optimization and application worldwide.The application of smart well technology in layered reservoirs,fractured reservoirs,high permeability heterogeneous reservoirs and fluvial reservoir were introduced.The successful applications of smart well in oilfields were presented.The simplification conditions and application range were pointed.The future studies of smart well were proposed.
The Hechi-Yizhou fault zone is an east-west structural belt in the southern Xuefeng Mountains of the Yangtze block. It is significantly different from the NE-trending tectonic framework in the Yangtze block. But the cause is not clear. Based on remote sensing image,abundant field data,geological structural sections,MT and seismic interpretation,this paper systematically analyzed the Hechi-Yizhou fault zone from the surface to the depth. This research shows that the structural pattern of the Hechi-Yizhou fault zone is a north-trending imbricate structure,which separates the southern Xuefeng structural system from the Guizhong depression. This fault zone has experienced polyphase activities. The E-W-trending structures shaped its initial geometry in the Caledonian. During the Hercynian,it began to rift,controlling the deposition of the Guizhong depression. During the Indosinian,the fault zone intensively reversed and thrusted towards southeast at the Hechi-Yizhou segment as a result of the collisions between the Indochina and Yangtze blocks. This structure was propagated to the east,and formed a southward arc-convex belt finally. Then,the east-west compressional stress field in the Yanshanian generated the arc-like west-trending imbricate structure. The Liucheng-Zhongdu segment of the fault zone is its northward-imbricated ramp. Due to the superimposition of two-stage arc-like structures,a triangle zone occurred near the Hechi-Yizhou segment. Meanwhile,the main faults were linked together and strongly activated. The current tectonic framework is mainly a result of the complex geodynamic evolution during the Indosinian orogeny and Yanshanian orogeny: The west segment is the south-trending arc-like imbricate structures in the Indosinian orogeny,and the east segment is the west-trending arc-like imbricate structures in the Yanshanian orogeny. The two arcs just linked at the vicinity of Yizhou City.
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