Late Quaternary palaeoenvironmental reconstruction of a Chobe Enclave landform (NW Botswana) based on pedological and geochemical indices

The importance of pedogenesis in understanding soil distribution patterns in current and past geologic periods is well
established, but feld identifcation of pedogenic features is always a big challenge in pedostratigraphic units because of post
burial alterations. An ~8 m landform presents a complete pedostratigraphic section at Chobe Enclave alluvial plain, northern Botswana. This study investigated pedological indices including morphological, physico-chemical, geochemical and
mineralogical properties of the landform, with the aim of reconstructing the palaeoenvironments and palaeoclimate during
the evolution of the landform. SiO2 is the dominant elemental oxide (40.6–98.9 wt%) followed by CaO (0.02–29.6 wt%),
Fe2O3 (0.48–2.64 wt%), MgO (0.14–1.81 wt%) and Al2O3 (0.29–0.93 wt%). The clay-sized minerals present are quartz,
calcite, sepiolite and kaolinite. The carbonates had strong positive correlation with Sr (R2=0.935), while Fe2O3 had weak
positive correlation with TiO2 (R2=0.0187). Gradual obliteration of the sedimentary layers and the formation of indurated
illuvial horizon indicate secondary recrystallisation of the palustrine carbonates. There is evidence of two cyclic intervals
that produced specifc two pedostratigraphic levels and two soil orders—Entisols and Calcisols, and therein pedofeatures
and geochemical variations suggest long-term climate change, i.e. from wet to dry in the Chobe Enclave in the late Quaternary. This study has presented a new calibration of the Chobe Enclave landform to include pedogenic horizons instead of
a sedimentary bed of palustrine carbonate deposit lying over fne sediments in a fuvial system, as previously documented.