|关键词: 珊瑚礁 物质收支方程 形态假设 悬沙输运 重力流 碳酸盐沉积
|PROCESS-PRODUCT RELATIONSHIPS OF ATOLL DEPOSITION SYSTEMS: A PRELIMINARY TESTING OF EXPLORATORY MODELING
Key Laboratory of Coastal and Island Development, Ministry of Education, School of Geographic and Oceanographic Sciences, Nanjing University, Nanjing 210023, China
|The quantitative modeling of marine sedimentary system can be divided into simulation and exploratory approaches, and the latter aims at establishing a continuous spectrum of sedimentary pattern and identifying new scientific questions. In the present contribution, a methodological framework of exploratory modeling was proposed to determine the definition domain of the independent variables contained in the governing equations, and then to define the range of dependent variables. In combination with the sediment budgeting principle and an assumption for the atoll geometry, the sediment transport and accumulation pattern over the atoll proper and its submarine terrace are predicted. Atoll is a unique type of coral reef, and its top part provides almost all the source of materials for reef growth and accumulation on reef slope and over the terrace. Results show that the growth of atolls is controlled by bioclastic production, and the extent and deposition rate at the terraces are controlled by the suspended sediment flux off the atoll, which is in turn controlled by water depth outside the atoll and the circulation of the ocean basin. The process of suspended sediment transport and gravity flow forms the alternating deposits. The hypsometric curves predicted by the model can be compared with the actual curves, to reveal the various mechanisms of the atoll evolution. Furthermore, the modeling output implies a number of scientific questions for further research, e.g., the magnitude of atoll growth and its control mechanisms, the temporal scale associated with the cyclisity of the deposits, the differentiation between the sediment gravity flows due to the coral self-organization mechanism and those due to earthquakes and other extreme events, the diversity of atoll-terrace sedimentary records in relation to the information on atoll evolution and environmental changes, and the influence of sea level changes on the atoll living conditions.
|Key words: coral reef material budgeting geometric assumption suspended sediment transport gravity flow carbonate deposition