Near-surface pedosediments of Takatokwane saline pan, southern Botswana: Properties, pedogenic processes, and inferences of environmental change

• Published in: Geoderma Regional 2023-09, Vol.34, p.e00696, Article e00696
• Main Authors: Matshameko, Yvette, Okolo, Chukwuebuka C., Eze, Peter N.
• Format: Article
• Language: English
• Subjects: Arenosols; atomic absorption spectrometry; basins; Botswana; chemical precipitation; clay; color; Dryland; electrical conductivity; elemental composition; evolution; hydrolysis; illuviation; Kalahari Basin; Landscape evolution; mineralogy; organic matter; particle size distribution; sand; sandstone; soil formation; Soil salinity; X-ray diffraction
• ISSN: 2352-0094; 2352-0094
• DOI: 10.1016/j.geodrs.2023.e00696

Natural pans are an important feature of dry landscapes worldwide. The purpose of this study was to characterize, for the first time, the near-surface pedosediments of the prominent Takatokwane pan in southern Botswana using their physical, geochemical, and mineralogical properties, to explore past and active pedogenic processes, and to interpret the properties of the pedosediments in light of environmental change. Pedogenic parameters including particle size distribution, reaction, electrical conductivity, and organic matter content were determined using routine laboratory procedures. The total elemental composition was analyzed using inductively coupled plasma optical emission spectroscopy and inductively coupled plasma mass spectrometry. The clay mineralogical compositions of the pedosediments were determined using a Bruker D8 Advance X-ray diffractometer. A suite of geochemical coefficients was used to quantify the weathering and pedogenic processes. Granulometric analysis showed that the pedosediments were dominated by fine sand (380 – 890 g/kg). The two pedons were greenish-gray in color at a depth of 140 cm. The elemental abundances followed the order of SiO2 > Al2O3 > Fe2O3 > TiO2. The TiO2/Al2O3 coupled with mineralogy indicated a uniform origin of the parent materials and feldspathic sandstone components, which were redeposited in the pan environment. The geochemical weathering coefficient indicates incipient weathering. Smectite-enriched clay deposits in the basin paved the way for the formation of the vertical layers. At the meso-morphological scale, reworked pedofeatures indicative of clay illuviation and gleisation processes were observed. The dominant pedogenic processes in soils include hydrolysis, lessivage, illuviation, and gleisation. This set of processes indicates the cycles of humid pedogenesis. This study confirmed three cycles of deposition, chemical precipitation, and post-depositional alteration under changing environmental conditions. Evidence from this study points to the seasonality of the environment, which could be explored for an improved understanding of the evolution of the Takatokwane pan and the Kalahari Basin. •Takatokwane pan is extremely saline and have stagnic property.•Particle size distribution confirms the homogeneity of Kalahari sand in the region.•Illite dominate the clay fractions of the pan.•Hydrolysis, lessivage, and gleization are the active pedogenic processes.•The Pan preserved a record of sedimentation, p