RESUMO
The fourth member of the Sinian Dengying Formation in northern Sichuan was reformed by multistage diagenetic fluids. It is beneficial to systematically analyze the diagenetic evolution of the area to clarify the sedimentary evolution of the dolomite in the fourth member of the Dengying Formation and the fluid characteristics at different diagenetic stages. In this study, the petrological characteristics, vertical sedimentary evolution, diagenetic fluid stages, and diagenetic environment of Dengsi dolomite were analyzed by using carbon-oxygen strontium isotopes, rare-earth elements, major and trace elements, combined with the supporting thin section identification and cathodoluminescence techniques, and the source and properties of diagenetic fluid of Dengsi dolomite in different diagenetic environments were determined. The results show that (1) during the deposition period of the fourth member of the Dengying Formation, the water body showed a trend from shallow to deep and then steadily to shallow, which was in a shallow freshwater reducing environment and had a warm and humid paleoclimate environment; (2) the dolomite of the fourth member of Dengying Formation in northern Sichuan is less affected by terrigenous materials. The C and O isotopes of dolomite are generally negative at the top of the fourth member of the Dengying Formation, and the top of the formation is obviously transformed into rock by atmospheric fresh water; rare-earth elements show that dolomitized fluid is dominated by primitive seawater, and the marine fluid from or flowing through the carbonaceous shale formation rich in feldspar minerals in the Qiongzhusi formation during burial period makes the rare earth elements show obvious positive EU anomalies. The high 87Sr/86Sr ratio of the surrounding rock and cement is caused by the 87Sr-rich marine fluid coming from the fault communication or along the unconformity zone; (3) since the deposition of the dolomite of the fourth member of Dengshan formation in northern Sichuan, it has experienced multistage diagenesis. The multistage cement and fillings in the pores have recorded at least seven stages of fluid activity history: during the quasi-contemporaneous period, fresh water was transformed to increase pores, and seawater was cemented to damage pores. During the supergene period, the pore size of atmospheric freshwater increased generally; during the middle deep burial period, the acid fluid was reformed to increase the porosity, the 87Sr-rich hydrocarbon-bearing fluid was used to fill the damaged pores, and the Eu2+-rich marine source fluid was used to fill the damaged pores. In the deep burial period, siliceous hydrothermal fluid filled the damaged hole.
RESUMO
The success of blockchain technology in cryptocurrencies reveals its potential in the data management field. Recently, there is a trend in the database community to integrate blockchains and traditional databases to obtain security, efficiency, and privacy from the two distinctive but related systems. In this survey, we discuss the use of blockchain technology in the data management field and focus on the fusion system of blockchains and databases. We first classify existing blockchain-related data management technologies by their locations on the blockchain-database spectrum. Based on the taxonomy, we discuss three types of fusion systems and analyze their design spaces and trade-offs. Then, by further investigating the typical systems and techniques of each type of fusion system and comparing the solutions, we provide insights of each fusion model. Finally, we outline the unsolved challenges and promising directions in this field and believe that fusion systems will take a more important role in data management tasks. We hope this survey can help both academia and industry to better understand the advantages and limitations of blockchain-related data management systems and develop fusion systems that meet various requirements in practice.
RESUMO
The relative contributions of decreased upstream sediment loads and local estuarine engineering activities to the estuarine channel geometry are poorly understood. In this study, we analyze the hydrological changes and identify the location, duration and intensity of the estuarine engineering activities based on the channel morphologic changes from 1965 to 2017 at the five stations in the Pearl River Estuary. Thereafter, the Mann-Kendall (M-K) statistical test, empirical orthogonal function (EOF) tests, and channel geometry reconstruction based on the hydrological coefficient were performed to quantitatively estimate the relative contributions from upstream dam construction and estuarine engineering activities. The results show that the geometric changes in the five transects over the last 50 years could be divided into three stages. Stage I extends over approximately 23-33 years at the different channel transects, during which the channel geometries were mainly influenced by natural factors, with a balance between erosion and deposition. Stage II occurred during the next 11-20 years and the changes in the cumulated water depth in comparison to the values in the previous adjacent years at this stage are approximately 5-25 times the values in stage I. The human activities (e.g., sand excavation) contribute to >70-90% of the extreme geometric changes. Stage III lasted for <3-11 years in the different transects with a slight depositional trend, and policies regulating sand excavation were implemented during this stage. The rapid increase in the channel area and water depth caused by sand excavation can cause the downcutting of the riverbed, a decrease in the water level, and redistribution of the water and sediment discharge. Therefore, the monitoring, simulation and analysis of the variation in the typical channel geometry over the long term provide important means to understand the human activities occurring and insights for future sustainable estuarine management.