The sedimentary dynamics of fine-grained rivers: a novel application of marine geophysics to develop new fluvial facies models

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A lot is known about how rivers with sandy or gravelly beds operate and how these processes lead to characteristic depositional features such as point bars. By comparison, those dominated by finer-grained sediments are much less well understood. This is especially the case for their deposits, for example, as a result of this basic lack of knowledge it has been suggested that within channel fine-grained river sediments may have been incorrectly interpreted to be environments of overbank floodplain sedimentation. Thus very little is known about how the different building blocks of a fine-grained river are put together and what factors may control these building blocks. In short, the science of fine-grained rivers lags that of sandy/gravelly ones. This can be attributed in large part to the fact that the geophysical techniques that have revolutionised the study of sand and gravel bed rivers simply do not work in fine-grained ones. For example, for one of the most popular techniques, ground penetrating radar, the nature of the signal is so severely affected in fine grained environments that no data can be collected. This proposal seeks to address this shortcoming through the application of a geophysical technique more normally used in marine and deltaic settings. The parametric echosounder has proven capability to generate high-resolution data from fine-grained sediments. By application of a novel cross-over of technology the aim of this proposal is to use this technique in a river environment to generate the first large-scale, 3-D quantification of fine-grained river sedimentology. This is important because fines in ancient rocks will severely impact the ability of water and oil/gas to move. There are thus significant social (drinking water supply from aquifers) and economic (successful recovery of hydrocarbons) benefits from being able to understand fine-grained sediments fully so that they can be properly taken in to account in reservoir models.