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(2020) Deconvolving the Effects of Lithology, Sorting, and Chemical Weathering Using Compositional Analysis of Irrawaddy River Sediments

Baronas JJ, Lipp A, Stevenson E, Bickle M, Shorttle O & Tipper E


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10f: Room 3, Friday 26th June 05:39 - 05:42

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Submitted by Jotis Baronas on Tuesday 16th June 22:17
Author note, please find a direct link to the html presentation here: https://jbaronas.com/gs2020 (The pdf only links to the above, so no need to download.)

Submitted by Joel Scheingross on Thursday 25th June 20:35
Hi Jotis - Thanks for the interesting presentation (I enjoyed the webpage format!). Do you have any sense of what the transit time is for sediment to go from the Irrawaddy headwaters to the river outlet? I'm curious to what extent the differences between your data set and those from the Ganges (Lupker et al., 2012) and Amazon (Bouchez et al, 2012) stem from variation in lithology versus variation in floodplain storage time.
Thanks, Joel! To be blunt, no, we have no idea of the sediment transit time through the floodplain. I don't think this is well constrained even for such intensely-studied systems like the Amazon and the Ganges (point me to some papers, please, if I'm wrong!)... We did collect some sands for cosmogenic measurements, going downstream, but I don't expect the timescales to be long enough to show up in these (unless perhaps some fancy in-situ 14C measurements get done at some point). My guess would be that the timescales are shorter than the Ganges and the Amazon, based on the much smaller size of the Irrawaddy floodplain, as you can see from the basin shape on the map.

Submitted by Marisa Repasch on Friday 26th June 04:54
HI Jotis, thanks for sharing your cool data from the Irrawaddy. It's a super neat river system. I couldn't tell from the figures on your webpage, but what did you learn by making separate measurements of the oxyhydroxide phase? Do oxyhydroxide concentrations increase with distance downstream, or just with decreasing grain size?
Hi Marissa, thanks for the question! I've answered this during the live chat, which I assume will be available to watch as a recording soon. Just to repeat my answer briefly here... The oxides I discussed in this presentation refer to the nominal compositional oxides describing the bulk sediment chemistry (eg. SiO2, Al2O3, etc.). However, we do have some sequential leaching data, targeting specifically amorphous, easily reducible Fe-Mn-oxyhydroxides. These do generally increase downstream, however, there is still much work to do to determine whether they represent "modern" weathering, i.e. formed in soils and floodplains, or whether they are derived from sedimentary rocks.

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