Fossil wood from the Permian-Triassic Beaufort Group of South Africa’s Karoo Basin: Implications for palaeoclimate

Tree-growth rings act as high-resolution climate proxies because wood anatomy is directly related to water uptake and tree growth. 190 silicified wood samples representing three taxa from the main Karoo Basin of South Africa were analysed. These samples ( Agathoxylon africanum , Agathoxylon karooensis and Prototaxoxylon africanum ) are from two time zones, namely the late middle Permian (Capitanian) beds of the lower Beaufort Group, and the late Permian (Wuchiapingian-Changhsingian) beds of the upper Beaufort Group. The former lithostratigraphy is equivalent to the Tapinocephalus vertebrate Assemblage Zone while the latter is equivalent to the Daptocephalus Assemblage Zone. Although Karoo fossil woods are abundant, many of the growth rings exhibit shear zones or bands of crushed cells where the cells are too distorted to enable accurate measurement. The CSDM curves and average annual ring width from the undistorted growth rings of the lower Beaufort woods reflect a deciduous tree growth habit and average ring width of 3.57 mm, while the undistorted rings of the upper Beaufort woods reflect a deciduous tree growth habit and average ring width of 3.29 mm. Some within-season fluctuations are evident but there is very little difference between the two time periods, with possible slower growth for the upper Beaufort. The low species diversity and stable climate inferred from the woods do not support the proposed climate change interpreted from the faunal extinctions at the end-Guadalupian (Capitanian), however future studies will have to increase the number of measurable growth ring sequences to investigate possible climate and wood diversity correlations with the end-Guadalupian.