New Evidence for the Age and Palaeoecology of the Knysna Formation, South Africa

Abstract

The existence of lignitic deposits (Knysna Formation) on the South African south coast, near to the town of Knysna has been recognised for more than a century. However, a combination of limited study and few natural exposures has meant that the age and stratigraphie position of the Knysna Formation are unclear, despite its potential as a palaeoenvironmental archive. We pre.sent a new suite of chronological, geochemical and palynological data obtained from a recently identified lignite exposure in this area. The lignite pollen assemblage is dominated by palms CArecaceae), which are now locally extinct, and contains additional palynomorphs of tropical affinity, along with (moist-temperate) Podocarpus-type pollen, grasses, and herbaceous pollen types (e.g. Clijfortia-type, Asteraceae). Overall, the assemblage shows some commonalities with the Miocene Elandsfontein Formation in the Western Cape. The lignites are dominated by a diverse range of higher plant biomarkers, including abundant leaf wax lipids, as well as Iignin monomers and leaf cuticle-derived macromolecular organic matter. All strongly indicate a terrestrial depositional setting, perhaps akin to contemporary palm swamps. A number of sesquiterpenoids imply the presence of gymnosperms, supporting observations from the pollen data and previously reported macro-fossil finds.The application of isothermal thermoluminescence techniques to coversands overlying the lignite produced a minimum age of -1.7 Ma. Additional clues as to the likely age of the lignite are provided by compound-specific stable carbon isotope analyses of the leaf wax lipids. These are approximately 8%o enriched relative to typical C, vegetation leaf waxes, and imply a potential contribution from C^ vegetation. From this, an age post-dating the Oligocène may be inferred, and in conjunction with the site's geomorphic setting, an age post dating the middle Miocene is considered plausible. This is markedly younger than previous (Eocene) age estimates for the Knynsa Formation.

Fires in the Cenozoic: a late flowering of flammable ecosystems

“…Fossil evidence suggests lowland vegetation along the coastal regions was forest and woodland or at least a mosaic of forest and fynbos until the mid-Miocene ( Coetzee and Rogers, 1982 ; Coetzee and Muller, 1984 ; Carr et al, 2010 ; Roberts et al, 2011 , 2013 ). The lowland forests retreated and were replaced by flammable shrublands though dates are uncertain (see e.g., Carr et al, 2010 ; Roberts et al, 2013 ). The change from lowland forests and woodlands to pyrophytic fynbos shrublands is usually attributed to climate change and especially the appearance of winter-wet/summer-dry Mediterranean climate (e.g., Goldblatt and Manning, 2002 ).…”

Sediment provenance of the Wilderness barrier dunes, southern Cape coast, South Africa

“…OSL dating has demonstrated that the coversands are significantly older than the barrier dunes, and their major‐element concentrations suggest that they are more weathered (Holmes et al. , 2007 ; Carr et al. , 2010a), but it remains unknown whether they represent an older, more weathered generation of dunes of similar origin to the barriers, and/or whether recycling of the coversands has provided a significant source of material for the younger dunes.…”

Palaeoenvironments during a terminal Oligocene or early Miocene transgression in a fluvial system at the southwestern tip of Africa

“…For the 3D models produced in this work, contours indicating the depth to granite were 216 digitised in ArcGis from onshore boreholes (Rogers, 1980 pyroprobe, interfaced with a Perkin Elmer Clarus 500 GC/MS system (Carr et al, 2010b).…”