Constraining the origin of clacretes in Letlhakeng valley Botswana: physico-chemical and stable isotopes (O, C) studies

Abstract

This paper details the mineralogical, chemical and stable isotope abundances of calcrete in the Letlhakeng fossil valley. The stable isotope abundances (O and C) of calcretes yielded some values which were tested against the nature of the calcretes – pedogenic or groundwater type. The Kgalagadi (Kalahari) is a vast terrain, mantled by duricrusts (in valleys, pans). This study assessed calcrete formation criteria in the Letlhakeng valley. The oxygen and carbon isotopic values point to calcretes in this valley as being of groundwater type. The vegetation that coincides with the calcrete formation is dominated by C4 vegetation. The mineralogy of the duricrusts is dominated by carbonate (calcite, dolomite) and quartz. The carbonate material has pH values of about 8, with TDS of 89 to 217mg/L.

Key words: calcrete; mineralogy; stable isotopes; Kalahari; palaeo-environment.