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

Abstract

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.

Early warning signals of the termination of the African Humid Period(s)

“…The major control on K concentrations is the hydrochemistry of the paleolake and porewater. These exert a direct control on the degree of authigenic mineral formation in the sediment, such as low-temperature illitization of smectites and analcime formation during episodes of higher alkalinity and salinity in the closed-basin lake resulting from a drier climate [23][24][25][26] . The progressive authigenic K-fixation in smectites with increasing evaporative conditions was found to be further enhanced by the excess in the octahedral layer charge that is caused by Al-to-Mg substitutions in clay minerals with more alkaline and saline lake conditions 23,24 .…”

Scanning Hyperspectral Imaging for In Situ Biogeochemical Analysis of Lake Sediment Cores: Review of Recent Developments

“…In calcareous sediments of Lake Jaczno, calcite-rich lamina could be distinguished using a simple threshold applied to total reflectance; this method works because calcite lamina are more reflective than surrounding organic sediments [ 12 ]. Hyperspectral images (spectral range of 250–17,000 nm) of dried samples taken from sediment cores from Chew Bahir Basin, Ethiopia provided useful information on minerals (i.e., calcite, smectite, analcime) and sediment geochemistry that compared well with X-ray diffraction mineralogical analysis and X-ray fluorescence elemental analyses [ 72 ].…”

Exploring the Past Biosphere of Chew Bahir/Southern Ethiopia: Cross-Species Hybridization Capture of Ancient Sedimentary DNA from a Deep Drill Core

“…The duplicate cores were retrieved in close proximity to each other, core HSPDP-CHB12-2A at 4.7612°N, 36.7668°E and core HSPDP-CHB14-2B at 4.7613°N, 36.7670°E (Cohen et al, 2016;Campisano et al, 2017). They are 278.58 mbs ( meters below surface) (core HSPDP-CHB14-2A) and 266.38 mbs (core HSPDP-CHB14-2B) long and were merged into a composite core, ∼292.76 mcd ( meters composite depth, hereinafter written as ∼292.76 m for simplicity) long, after correlating the physical properties and imagery of the cores 2A and 2B (Arnold et al, 2021;Duesing et al, 2021;Roberts et al, 2021;Schaebitz et al, 2021;Trauth et al, 2021). Together they replenish missing data in each other and the composite core with ∼90% continuity will be referred to as one core in the following.…”