Volume 30 1993

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Browsing Volume 30 1993 by Author "de Wit, Michiel C J"

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    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.
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    Taxonomic description of fossil wood from Cainozoic Sak River terraces, near Brandvlei, Bushmanland, South Africa
    (Bernard Price Institute for Palaeontological Research, 1993) Bamford, Marion K; de Wit, Michiel C J
    Seven pieces of silicified wood are described from two sites near the Sak River, Bushmanland. The Miocene deposit yielded five specimens which can be assigned to the Dipterocarpaceae, Fagaceae, Myrtaceae, Oleaceae and Rutaceae. Of the two logs recovered from the Plio-Pleistocene deposit, only one was well enough preserved to be assigned to the Polygalaceae. All the woods indicate that the palaeoenvironment in that region was tropical to subtropical based on the wood structure, growth rings and from their modem counterparts.