Towards an understanding of climate proxy formation in the Chew Bahir basin, southern Ethiopian Rift

Checklist for the use of potassium concentrations in siliciclastic sediments as paleoenvironmental archives

“…If the K/Rb ratio is not stable and tends to be larger than that in the UCC, post-sedimentary enrichment by K (metasomatism) could have acted (van den Kamp, 2016). The impact of metasomatism was also evaluated using A-CN-K plots (Fedo et al, 1995, also used by Zhao et al, 2018, microscopic examination of clay mineral particles to distinguish their detrital and autochthonous origin (Martínez-Braceras et al, 2017;Wang et al, 2017), and mineral (micro)analysis (Kříbek et al, 2017;Foerster et al, 2018) to…”

“…The concentration of the less mobile K, usually in geochemically normalised form such as the K/Al ratio, could thus provide the most straightforward weathering proxy under temperate to warm climates, as it was demonstrated for marine sediments deposited close to river estuaries (Clift et al, 2014;Zhao et al, 2018), continental foreland basins (Vögeli et al, 2017), continental basins in semiarid climates (Foerster et al, 2015(Foerster et al, , 2018, and freshwater lakes (Matys Grygar et al, 2014, 2017a, 2017b. The K concentrations in sediment profiles, covering sufficiently long time interval, may exhibit orbital signatures, which prove their climatic control (Colin et al, 2014;Foerster et al, 2015Foerster et al, , 2018Matys Grygar et al, 2014, 2017a, 2017b, 2019.…”

“…Their correct handling is not trivial and needs further research and testing. (2) In hydrologically closed lacustrine or palustrine environments, the main mechanism controlling K concentrations may be the neo-formation of K-carriers in sediments in contact with pore waters mineralised during prolonged droughts (Foerster et al, 2015), in particular formation of analcime, illite, and feldspars from dissolved K + , kaolinite and other clay minerals (Larsen, 2008;Kříbek et al, 2017;Foerster et al, 2018). This mechanism is thermodynamically analogous to "retrograde" clay mineral formation in the marine environment (Cuadros et al, 2017) and basinal brines (van den Kamp, 2016).…”

Classifying past climate change in the Chew Bahir basin, southern Ethiopia, using recurrence quantification analysis

“…1) (Cohen et al, 2016;Campisano et al, 2017) and the Collaborative Research Center CRC-806 at the University of Cologne, and were described in detail in earlier publications (e.g., Foerster et al, 2012Foerster et al, , 2015Trauth et al, 2015). We used the potassium (K) concentrations of the sediment, determined by micro X-ray fluorescence (μXRF) scanning, as a proxy of aridity (Foerster et al, 2012;Trauth et al, 2015;Foerster et al, 2018). Dynamic time warping (DTW) was employed for aligning the K records from the six cores CB01-06 (Trauth et al, 2018).…”

“…We first used the method on prototypical data in order to assess its performance with typical palaeoclimate transitions. We then performed an RQA on the Late Quaternary climate record from Chew Bahir cores CB01-06 because it provides one of the most detailed records of climate change available from the vicinity of important sites for modern human fossil (Foerster et al, 2012(Foerster et al, , 2015(Foerster et al, , 2018Trauth et al, 2015Trauth et al, , 2018.…”