Palaeontologia africana

Now showing 1 - 3 of 3

Carboniferous pycnoxylic woods from the Dwyka Group of southern Namibia
(Bernard Price Institute for Palaeontological Research, 2001) Bangert, Berthold; Bamford, Marion K
Glacial deposits of the Dwyka Group between Keetmanshoop and Mariental in southern Namibia have been reinvestigated for palaeontological remains and associated tuff horizons in an attempt to accurately date the deposits. SHRIMP-based dating of juvenile zircons from these tuff horizons provide ages which cumulate in the latest Carboniferous (Gzelian). The pycnoxylic woods Megaporoxylon scherziKrausel and Megaporoxylon kaokense Krausel are described in detail for the first time and are compared with similar permineralised woods from Gondwana. Based on previous fossil wood studies covering the rocks of the main Karoo Basin, these species occur only in the Dwyka and lower Ecca Groups in southern Africa and do not extend to the upper Ecca Group.
Sensitivity of xylem vessel size and frequency to rainfall and temperature: implications for palaeontology
(Bernard Price Institute for Palaeontological Research, 1993) February, Ed
Based on the xylem vessel size and frequency in fossil wood, a number of studies have developed theories on climate change through time. The basic premise of these studies is that xylem vessel size decreases while vessel frequency increases with intensifying aridity. In this paper the relationship between rainfall and xylem vessel size and frequency is examined in two extant tree species. The results indicate that rainfall is related positively to vessel diameter and negatively to vessel frequency in Combretum apiculatum and Protea caffra. Xylem vessel size of both species is between 50 and 100 µm. However, the two species exhibit different responses to rainfall in that P. caffra has much smaller diameter vessels than C. apiculatum in high rainfall areas. These differences indicate that the potential for using xylem anatomy as a palaeoclimatic indicator has not been fully utilised. A more precise picture of climate change through time is possible with a more refined statistical analysis of reliably identified fossil wood.
Fossil wood from the Brandvlei area, Bushmanland as an indication of palaeoenvironmental changes during the Cainozoic
(Bernard Price Institute for Palaeontological Research, 1993) de Wit, Michiel C J; Bamford, Marion K
Remnants of Cainozoic fluvial deposits occur along the northerly flowing Sak River in Bushmanland, between Brandvlei and Sak River Station. The terraces can be subdivided into older and younger deposits, and occur approximately 60m and between 20m and 30m above the present-day river respectively. The older deposits are found to the east of the Sak River in the Geelvloer palaeo-valley. Most of the older 'terraces' are either hill-slope deposits or fans, and represent reworked fluvial sediments. A rounded vertebrate bone and several pieces of sub-rounded fossil wood were found in these deposits, which indicate a mid Miocene age for the original older deposits. Some of the fossil-wood samples have been positively identified as extant angiospermous families. The occurrence of fagaceous wood in two samples is of great interest biogeographically. Both the vertebrate fossil and the wood suggest that the mid Miocene climate was subtropical. At the end of the Miocene the wet period changed to arid conditions, and mature calcretes developed. This dry period was interrupted by pluvials during which the younger gravels were deposited. These alluvial terraces are interpreted as an aggradational sequence of braid bars associated with a wandering river, deposited under semi-arid conditions. Two well-rounded fossil-wood clasts, presumably reworked from the older terraces, were found in these sediments. One of which is identified as Polygalaceae. Based on similarities of lithofacies and style of diagenesis with the Van Wyksvlei sequence to the east, the younger terraces are probably Plio-Pleistocene in age.

Palaeontologia africana

Browse

Filters

Settings

Sort By

Results per page

Search Results