This item is non-discoverable
Late quaternary geomorphic palaeoenvironments of some central and marginal Great Karoo uplands, South Africa
Thesis / Dissertation
1998
Permanent link to this Item
Authors
Supervisors
Journal Title
Link to Journal
Journal ISSN
Volume Title
Publisher
Publisher
University of Cape Town
Faculty
Series
Abstract
Central Great Karoo uplands and their easterly margins have preserved within their landscapes sedimentary sequences which attest to deposition under a variety of geomorphic conditions. Fluvial and aeolian action, and slope and pedogenic processes hove influenced these environments. Most of the depositional sequences ore not intact but have been altered by erosion. This study concentrated on a suite of high altitude volley fills and other depositional landforms situated above the Great Escarpment along on east-west transect spanning some 500 km at approximately 32° south latitude. Field logging of depositional sequences combined with morphometric and geochemical laboratory analyses were utilised in an attempt to elucidate the environmental circumstances under which the sediments were deposited. Results from this investigation were then compared to work undertaken by other researchers in an effort to compile a broad brush picture of subregional environmental change in the central Great Karoo and its eastern margins during the late Quaternary. The findings dote bock approximately 20 000 years and comprise a fragmented depositional history attesting to changing geomorphic conditions during the late Pleistocene and the Holocene. The evidence from the semi-arid interior of South Africa reflects a shorter time span than do depositional environments in Lesotho and to the east of the Great Escarpment. Within central Great Karoo uplands, little evidence predating the Holocene has remained preserved. The exceptions are isolated aeolian deposits dating back to the Lost Glacial Maximum. The onset of the last cycle of sediment accumulation within Great Karoo volley headwaters appears to have been synchronous with the commencement of the Holocene. Any previous evidence was removed prior to 10 000 years BP (before present). A catastrophic model is postulated for the flushing out of these valleys. The lithology of sediments derived from the Mesozoic sedimentary rocks of the Karoo and the vegetation of the region may have exacerbated the impact of this late Pleistocene event or sequence of events. Subsequently, inorganic sediment infilled upland valleys from about 10 000 BP to 5000 BP, at which time there was a marked change to relatively organic rich accumulation. A gradualist model is proposed for this deposition, with moister conditions prevailing subsequent to the mid Holocene. The east-west rainfall gradient has also influenced the accumulation and preservation of valley sediments. Currently, Karoo uplands are vulnerable to erosion. with a major cycle of incision responsible for the present level of land degradation at many places within the Karoo. An anthropogenic trigger associated with the impact of European colonisation of the interior of southern Africa is suggested for this. The older, isolated aeolian deposits in the eastern margins of the study area support regional evidence for a dry Last Glacial Maximum over the southern African interior. There is also tentative evidence of greater aridity during a Younger Dryas (approximately 11 000 BP) cool phase. The harsh appearance of the Karoo landscape belies a biophysical system which is sensitive to both climatic and anthropogenic impacts. There is a need to understand the dynamics of Karoo geomorphic systems if this potentially fragile and unique environment is not to be degraded further.
Description
Reference:
Holmes, P.J. 1998. Late quaternary geomorphic palaeoenvironments of some central and marginal Great Karoo uplands, South Africa. . University of Cape Town ,Faculty of Science ,Department of Environmental and Geographical Science. http://hdl.handle.net/11427/41418