Bedload transport of mud as pedogenic aggregates in modern and ancient rivers |
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| Authors: | BRIAN R RUST GERALD C NANSON† |
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| Institution: | Department of Geology, University of Ottawa and Ottawa-Carleton Geoscience Centre, Ottawa, Canada KIN 6N5;Department of Geography, Rivers and Estuarine Research Group, University of Wollongong, Wollongong, NSW 2500, Australia |
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| Abstract: | Abundant sand-sized mud aggregates in the Cooper and Diamantina Rivers, Lake Eyre Basin, Australia are attributed to bedload transport of aggregates formed in deeply-cracked floodplain soils. The conditions required for formation of pedogenic mud aggregates are: (i) abundant clay containing at least minor swelling clay, and (ii) a climate with at least seasonally hot dry periods. The worldwide distribution of these soils (Vertisols) suggests that a significant amount of mud is transported as pedogenic aggregates by modern rivers. Ancient analogues in which mud aggregates and Vertisol profiles have been recognized are the Jurassic East Berlin Formation (Connecticut, USA) and the Carboniferous Maringouin Formation (New Brunswick and Nova Scotia, Canada). The dominant red mudstones of these formations are interpreted as mainly bedload sediments deposited by sheet floods in semi-arid palaeoclimates. The Triassic Hawkesbury Sandstone (NSW, Australia) also contains sand-sized mudstone aggregates, thought to be pedogenic, but its paleosol and other facies point to formation in a wetter palaeoclimate. The indications are that bedload transport of mud as pedogenic aggregates was as significant a process in ancient rivers as it is at present. |
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