Fossil Woods from the Upper Carboniferous to Lower Jurassic Karoo Basin and Their Environmental Interpretation
Silicified fossil woods are scattered through the Karoo sequence and can be used to give an indication of the past vegetation and climate. It is not yet possible to relate the wood species directly to the leaf species, but having wood types that extend th
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Marion K. Bamford
Abstract
Silicified fossil woods are scattered through the Karoo sequence and can be used to give an indication of the past vegetation and climate. It is not yet possible to relate the wood species directly to the leaf species, but having wood types that extend through a long period of time is most useful for standardising the growth ring analyses. A relatively diverse flora has been recorded from the Carboniferous-Permian Dwyka and Ecca Groups of the western Kalahari Basin in north central Namibia. Lower Permian Ecca woods are widespread in southern Africa but of low diversity with only two genera, Australoxylon and Prototaxoxylon. Australoxylon continues into the Lower Beaufort (Upper Permian) and a new wood, Agathoxylon is present. The latter continues throughout the sequence and one species survives well after the end Permian extinction. Podocarpoxylon is present from the Upper Beaufort onwards. Although the Molteno (mid to Upper Triassic) has a very high diversity of plants and depositional environments there are only three wood genera, Agathoxylon, Podocarpoxylon and Rhexoxylon. Preliminary research on the growth rings of these gymnospermous woods is presented here and shows that there is some variation in climate over time, as expected, but also along the northeast–southwest axis. This axis is parallel to the lines of palaeolatitude so the variation in the climate signal may also be a result of local environmental conditions, or influenced by the distance from the seaway or hinterland. Keywords
Gymnosperms
16.1
Growth rings
Introduction
Although the Karoo Basin is better known for a rich fossil record of vertebrates from the Upper Carboniferous Dwyka Group to the Lower Jurassic Clarens Formation, there are also numerous well preserved pollen, leaf and wood floras (Anderson 1977; MacRae 1988; Aitken 1994; Barbolini 2014; Anderson and Anderson 1985; Prevec et al. 2009; Bamford 1999, 2004). To date, the emphasis has been on taxonomy and floral diversity, although application of M.K. Bamford (&) Evolutionary Studies Institute and School of Geosciences, University of the Witwatersrand, P Bag 3, Johannesburg, WITS 2050, South Africa e-mail: [email protected]
Permian
Agathoxylon
biostratigraphy to complement the vertebrate biozones has also been investigated (Bamford 1999; Barbolini 2014). The environment and climate of the Karoo Basin during the Upper Carboniferous to Lower Jurassic Periods in which the plants and animals lived are of great interest to palaeosciences because of the extensive and almost uninterrupted fossil record, including the progressive warming from the Carboniferous to the Triassic, and the end Permian mass extinction events. Various physical methods, therefore, have been used to attempt to reconstruct the palaeoenvironments, such as the sedimentology (Smith 1990), but as all of the animals and most of the plants are extinct, it is difficult to use many of the palaeoecological tools that are available. The Nearest Living Relative or Correspondence
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