Xavier Boës

TL;DR: The discovery of Lomekwi 3 is reported, a 3.3-million-year-old archaeological site where in situ stone artefacts occur in spatiotemporal association with Pliocene hominin fossils in a wooded palaeoenvironment and the name ‘Lomekwian’ is proposed, which predates the Oldowan by 700,000 years and marks a new beginning to the known archaeological record.

Abstract: In lake sediment investigations of heavy metal pollution history, it has become a common approach to calculate enrichment factors (EFs) by normalizing elemental distributions to a reference lithogenic element. However, this approach requires that the reference element remains stable once it has been deposited to the sediment (it is not affected by diagenetic processes). This is rarely studied in well-controlled field experiments. Here, we test the commonly used reference elements titanium (Ti), zirconium (Zr), aluminum (Al), and rubidium (Rb). We use a unique series of freeze cores collected in different years since 1979 in Lake Nylandssjon in northern Sweden. This lake has sediment with distinct varves (annually laminated deposit). Element concentrations in individual varves were analyzed using X-ray fluorescence (XRF) spectroscopy. By tracking the newly formed surface varve from different cores across this core series, i.e., following the element concentration in a specific varve as it becomes progressively aged, it was possible to assess the potential impact of diagenetic processes on geochemical signatures. Results confirm the conservative character of the studied elements; there was neither an increasing nor a decreasing concentration trend with time during sediment ageing for any of these elements. Secondly, we addressed the question ‘which of them is the most appropriate for EFs estimates with the aim of distinguishing anthropogenic from geogenic inputs, for example in pollution studies’. To assess the reliability of the EFs we used lead (Pb) as an example, because anthropogenic Pb in the sediment could be independently calculated using stable Pb isotopes. When anthropogenic Pb concentrations calculated with Pb-EFs were compared to the anthropogenic Pb concentrations derived from stable Pb isotopes, the differences found were 20% for Ti, 10% for Zr, 11% for Al, and 27% for Rb when upper continental crust concentrations were used for the background ratio. Based on the results from Nylandssjon our suggestions are that (1) when using EFs on a single core, which is the normal case in paleolimnology, multiple reference elements should be used together and (2) the results from those should be critically evaluated.

TL;DR: The authors discussed paleoenvironmental evolution in the Baikal region during the Holocene using new records of aquatic (diatom) and terrestrial vegetation changes from Hovsgol, Mongolia's largest and deepest lake.

TL;DR: In this article, the authors used radionuclide profiles to date four short sediment cores taken from two Chilean lakes located in a highly active geodynamic setting, including Lake Puyehue and Lake Icalma.

TL;DR: In this paper, a 53 cm-long sedimentary sequence selected among eight short cores retrieved in Lago Puyehue (Chile, 40-S) contains a 600-yr-long undisturbed record of paleo-precipitation changes.