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Ancient Floodplain Evolution and Techniques for Analysis |
Department of Earth Sciences, Cardiff University, Cardiff CF1 3YE, UK; and BG Exploration and Production, 100 Thames Valley Park Drive, Reading RG6 1PT, UK
Existing approaches to studying ancient floodplain deposits involve integrating lithofacies and palaeopedological data to identify medium- to long-term controls on deposition. However, deciphering short-term, annual or even seasonal events such as flooding duration and hydroperiod is rarely attempted, yet it is these that control the ecology of floodplains. An approach is presented that provides insights into the patterns of flood duration in ancient floodplain successions. The ability to identify criteria indicating frequent wetting and drying is critical and this is most easily done in successions with carbonate-dominated sediments (palustrine, hard-water systems) or where Vertisol palaeosols are present. Some ancient floodplain deposits contain metre-scale units displaying drying-out trends that reflect aggradation of the floodplain surface. Evidence of hydromorphism and Fe reduction and translocation is also critical for identifying hydromorphism related to flooding, but recognizing such effects in pre-Devonian fluvial successions will be difficult because of the low levels of organic matter in soils of that interval.
