Overbank sediments from central Mexico: an evaluation of their use in regional geochemical mapping and in studies of contamination from modern and historical mining |
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| Institution: | 1. British Geological Survey, Environmental Science Centre, Keyworth, Nottingham NG12 5GG, UK;2. British Geological Survey, Murchison House, West Mains Road, Edinburgh EH9 3LA, UK;1. State Key Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002, China;2. Development and Research Center, China Geological Survey, Beijing 100037, China;3. Laboratory of Isotope Geology, Ministry of Land and Resources, State Key Laboratory of Continental Dynamics, Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China;4. Faculty of Land Resource and Engineering, Kunming University of Science and Technology, Kunming 650093, China;5. Department of Geology, Faculty of Sciences, University of Tehran, Tehran 14155-64155, Iran |
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| Abstract: | Overbank sediment sequences in central Mexico display vertical changes in chemistry which can be related to both anthropogenic contamination and natural geological sources and processes. They also show significant lateral chemical variation, at both local and regional levels, which makes the design of a sampling strategy for regional geochemical mapping or contamination studies difficult. This variation is particularly pronounced in drainage basins which have been contaminated by mining activity and limits the use of overbank sediment as a systematic regional geochemical mapping medium. To be used with confidence, overbank sediments require detailed studies of fluvial geomorphology and history, accompanied by accurate age dating. Active drainage sediments are a more viable alternative in areas of historical mining activity, but must be examined carefully in the light of the regional background where levels of contamination are low or the contaminants are buried within the river floodplain. |
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