I am currently analysing the processes and sources of sediment in East-African rivers, lakes and floodplains using sediment tracing techniques. However, in all the soil plot samples and floodplain cores, we find a very distinct distribution of Cerium. My study site is located closely to the active carbonatite volcano 'Ol doinyo Lengai'. We are exploring the possibility of the redistribution of Cerium by the volcano, where besides traditional weathering processes (bottom-up from the mother material), the element is periodically infused from the atmosphere following volcanic eruptions giving rise to its peculiar surface distribution and floodplain peaks.
Is there anyone who has observed this behaviour of Cerium (or other elements) in East-Africa or other parts of the world? It would be a great help to me if you could share some of these findings.
With kind regards,
Maarten
I hope this article can help you.
https://www.researchgate.net/publication/277570653_Flood_variation_and_soil_nutrient_content_in_floodplain_vegetation_communities_in_the_Okavango_Delta
There are many carbonatites and alkaline igneous rocks which gave host to REE mineralization, e.g. Kangankunde. One of the major host of cerium is monazite (CePO4). The heavy mineral may be concentrated in rivers and floodplains and is quite common in the weathering zone and soils within the clastic apron of the afore-mentioned magmatic rocks.
H.G.Dill
Dear Harald,
Thank you for the answer. We find a very distinct vertical distribution in our floodplains (see picture). If the source of the Ce was weathering and subsequent downstream concentration of Monazite or Bastnäsite minerals in the catchment, wouldn't the deposit in the floodplains be more constantly high (The time period in the core is around 50yr)? Are these minerals in general evenly spread within the igneous rocks? Also would the Ce concentration then be accompanied with similar distributions of potential substituting elements (Th, La, Nd)? Is there a possibility, explosive eruptions of the volcano distributes mineral particles as ash to normally geographic isolated catchments and that way creates these peaks?
Regards,
Maarten
Dear Maarten,
what is the scale of the x-axis? Is it Ce in ppm ? Can you also show us the litholog alongside the y-axis so as to see whether there is a correlation between Ce and the grain size.
Harald
Dear Harald,
Yes, the Ce concentration is in ppm. The grain size analysis has not been completed yet.
Regards,
Maarten
Dear Maarten,
currently I cannot do anything else and I have to wait for the litholog to see which way the Ce contents correlate with the host rock lithology. Is it part of the suspended or bed load (?).
With kind regards
Harald
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