Departmental Bulletin Paper Exploring the use of weathering index in alluvial fan chronology

Hardenbicker, Ulrike  ,  Watanabe, Makiko  ,  Kotowich, Roberta

(51)  , pp.109 - 118 , 2016 , Department of Geography, Tokyo Metropolitan University
Alluvial fan sediments can act as an archive of local environmental history. Sedimentation on alluvial fans is controlled by fluvial erosional processes occurring in upland drainage basins and slopes, and the subsequent transport processes which deliver the sediments from the catchment area to the fan. Low sedimentation rates are marked by buried soils and in situ weathering of sediments, while pedogenically unmodified sediment between buried soils reflects times of rapid sedimentation of the alluvial fan. Two borehole cores (FN 350 cm and AG 850 cm) from Holocene alluvial fans located in the Qu’Appelle Valley in southern Saskatchewan, Canada were analyzed in order to establish a relative chronology by using weathering indices. We evaluated if weathering indexes (the CaO/ZrO2 molar ratio, the Product Index and the Parker Index) are suitable to assess sediment weathering within alluvial fan. To quantify the degree of weathering within the sediment samples the three indices of weathering were calculated using the proportions of elements measured by Energy Dispersive X-ray Spectroscopy. There was an inverse relationship between weathering index and sample age.

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