Advanced Hyperspectral Analysis of Sediment Core Samples from the Chew Bahir Basin, Ethiopian Rift, in the Spectral Range from 0.25 to 17 µm:Support for Climate Proxy Interpretation

Establishing robust environmental proxies at newly investigated terrestrial sedimentary archives is a challenge, because straightforward climate reconstructions can be hampered by the complex relationship between climate parameters and sediment composition, proxy preservation or (in)sufficient sample material. We present a minimally invasive hyperspectral bidirectional reflectance analysis on discrete samples in the wavelength range from 0.25 to 17 mu m on 35 lacustrine sediment core samples from the Chew Bahir Basin, southern Ethiopia for climate proxy studies. We identified and used absorption bands at 2.2 mu m (Al-OH), at 2.3 mu m (Mg-OH), at 1.16 mu m (analcime), and at 3.98 mu m (calcite) for quantitative spectral analysis. The band depth ratios at 2.3/2.2 mu m in the spectra correlate with variations in the potassium content of the sediment samples, which also reflect periods of increased Al-to-Mg substitution in clay minerals during drier climatic episodes. During these episodes of drier conditions, absorption bands diagnostic of the presence of analcime and calcite support this interpretation, with analcime indicating the driest conditions. These results could be compared to qualitative analysis of other characteristic spectral properties in the spectral range between 0.25 and 17 mu m. The results of the hyperspectral measurements complement previous sedimentological and geochemical analyses, allowing us in particular to resolve more finely the processes of weathering in the catchment and low-temperature authigenic processes in the sediment. This enables us to better understand environmental changes in the habitat of early humans

Advanced Hyperspectral Analysis of Sediment Core Samples from the Chew Bahir Basin, Ethiopian Rift, in the Spectral Range from 0.25 to 17 µm: Support for Climate Proxy Interpretation

Establishing robust environmental proxies at newly investigated terrestrial sedimentary archives is a challenge, because straightforward climate reconstructions can be hampered by the complex relationship between climate parameters and sediment composition, proxy preservation or (in)sufficient sample material. We present a minimally invasive hyperspectral bidirectional reflectance analysis on discrete samples in the wavelength range from 0.25 to 17 µm on 35 lacustrine sediment core samples from the Chew Bahir Basin, southern Ethiopia for climate proxy studies. We identified and used absorption bands at 2.2 μm (Al–OH), at 2.3 μm (Mg–OH), at 1.16 μm (analcime), and at 3.98 μm (calcite) for quantitative spectral analysis. The band depth ratios at 2.3/2.2 μm in the spectra correlate with variations in the potassium content of the sediment samples, which also reflect periods of increased Al-to-Mg substitution in clay minerals during drier climatic episodes. During these episodes of drier conditions, absorption bands diagnostic of the presence of analcime and calcite support this interpretation, with analcime indicating the driest conditions. These results could be compared to qualitative analysis of other characteristic spectral properties in the spectral range between 0.25 and 17 µm. The results of the hyperspectral measurements complement previous sedimentological and geochemical analyses, allowing us in particular to resolve more finely the processes of weathering in the catchment and low-temperature authigenic processes in the sediment. This enables us to better understand environmental changes in the habitat of early humans

Updated Ganymede Mosaic from Juno Perijove 34 Images

In preparation of the JUICE mission with the primary target Ganymede we generated a new controlled version of the global Ganymede image mosaic from Voyager 1 and 2, Galileo, and Juno images

Hyperspectral analysis of core samples from Chew Bahir, Ethiopia, as climate proxy -implications on surface composition of the ExoMars rover landing site

This work shows that hyperspectral reflection data analysis can be a suitable method for paleoclimatic reconstruction similar to chemical proxies. The link between the hominin development and climatic variations of the past is topic of the “Hominin Sites and Paleolake Drilling Project”. In this study two drilling cores were taken in the Chew Bahir basin in the Ethiopian Rift in 2014. The presented thesis is based on core data and their spectral reflectance in the wavelength range from 0.3 μm to 17 μm. The samples mostly consist out of weathered phyllosilicates with variable potassium content. An increase of potassium is a consequence of an increase of physical weathering and erosion from sparsely vegetated rift shoulders during arid phases. Therefore, potassium is a valid climate proxy. High potassium content indicates arid climatic phases. An analysis of the depths of specific signature absorption bands of magnesium- hydroxyl at 2.3 μm displays a correlation with the potassium marker. Instead, the absorption bands of aluminum-hydroxyl at 2.2 μm show an anti-correlation with potassium, that presents humid conditions. Therefore, the absorption bands are an evident climate proxy for dry and wet cycles in this region. The interpretation of hyperspectral data leads to similar results as the interpretation of the chemical proxies in previous studies in Chew Bahir. In the presented thesis, hyperspectral data are a valid tool complementary to chemical proxies for the reconstruction of paleoenvironmental conditions in East Africa. These results are implicated on the landing site of ExoMars2022 in the Noachian Mars. In this region on Mars, the Oxia Planum, the development of phyllosilicates also occurs under aqueous activity, such as in Chew Bahir. The implications show a correlation of minerals in layered stratigraphy. The phyllosilicates underwent a substitution of cations under the influence of the current climate phase. These parallels support the hypothesis of a changing climate in early Mars’ history. The alteration processes are similar to Chew Bahir. But the temporal sequence and formation processes remain divergent. The cores from Chew Bahir report sediments from 600ka. The sediments of the Noachian Mars display a time range from 4.7- 3.4 Ga

Advanced hyperspectral analysis of sediment core samples from the Chew Bahir Basin, Ethiopian Rift in the spectral range from 0.25 to 17 µm: support for climate proxy information.

This paper reports on the application of advanced hyperspectral analysis to support the nondestructive study of samples from long sediment cores (up to 280 m coring depth) collected under the Hominin Sites and Paleolake Drilling Program (HSPDP) in the Chew Bahir region of southern Ethiopia. For this purpose, the bidirectional reflectance of 35 core samples from different core depths in the wavelength range from 0.25 to 17 µm was measured. It can be directly compared with spectral remote sensing data of the corresponding land surface areas. We examined the relationship between the derived mineralogical and geochemical properties of the core samples to test for linkage to the hydroclimate history of the region. Using XRD and µXRD methods, it has been shown that an illitization of the smectites and an octahedral Al-to-Mg substitution occurs in the phyllosilicate materials present during phases that have been associated with increased salinity and alkalinity due to enhanced evaporation (Foerster et al., 2018). These processes are found to be accompanied by potassium fixation and they are associated with the increase of the layer charge due to the authigenic changes of the octahedral composition. Reflection spectroscopy is a suitable method for studying such mineralogical properties. We investigated the spectral properties over a wide spectral range from UV to MIR. This enables detection of absorption bands of crystal field transitions of transition metal ions in the UV/VIS range and to detect the characteristic bands of OH, H2O, M-OH lattice vibrations in the NIR. It also allows the study of the fundamental vibration bands as well as other typical MIR features like the Christiansen band or transparency features of silicates and thus helps to reconstruct weathering paths. The results show that the main mineralogical components are clays of the smectite group. The samples are rich in montmorillonite and show variable concentrations of calcite. The clays are composed of tetrahedral coordinated, corner-connected SiO4 for which Si is partially substituted by Al and of edge-linked Al (OH)6 octahedrons in which part of the Al is substituted by Mg and which are layered by OH and H2O groups. Thus all reflectance spectra show the characteristic absorption bands at 1.4 µm (OH), 1.9 µm (H2O), 2.2 µm (Al-OH), and 2.3 µm (Mg-OH). Their band depth ratios derived from continuum removed spectra have been used to characterize the clay structure within different climate periods. The results support the model of illitization and potassium fixation during dry climate intervals. In addition, the spectral indicators determined in the MIR can be used to specify the mineralogical properties of silicates and other materials in terms of their geochemical composition. In summary, the method is suitable for examining the main mineralogical components of Chew Bahir core samples and enables confirmation of climate driven wet and dry weathering processes in the formation of phyllosilicates