| Abstrakt: |
In this paper the radiocarbon dates available for the Saharan desert are analyzed by a statistical procedure developed by Geyh (1969). A climatic interpretation is attempted for the resulting frequency distribution diagram and conclusions are drawn about the probable course of climatic fluctuations in the Saharan desert during late pleistocene and holocene time. The conclusions are corroborated by the results of geomorphological field work in the Tibesti region, especially by the sedimentary record of a terrace accumulated in the near-shore waters of a lake which existed in late pleistocene and early holocene time. Time periods for which a larger number of radiocarbon dates is available are coincident with humid phases, others represented by only a few dates with arid or erosional phases, as the peaks of the diagram correspond to periods of clayey, and the gaps minima to those of predominantly sandy accumulation. The general course of climatic fluctuations presents itself as follows (cf. fig. 1 a-d): The late Pleistocene and early Holocene were determined by a humid period, followed by a relatively arid interval between 11,700 and 10,500 B. P. This was followed by a remarkably humid phase, which leveled off to a well-balanced humid climate with still good conditions for vegetational growth around 8,700 B. P. About 7,100 B. P. an arid phase began with another change to more humid conditions around 6,000 B. P., which lasted until ca. 4,700 B. P. The time between 4,700 and 3,700 was arid. Until 1,000 B. P. there was a quite regular alternation of humid and arid phases with a duration of 700 to 800 years each. It is also confirmed that 1. the number of incorrect 14-C-dates is small as a whole. Those dates therefore hardly effect the results of the statistical analysis; - 2. the hard-water effect is of as little importance for limestone deposits from shallow lakes of the Tibesti as it is for those of central Europe; - 3. that human settlement activities follow the pattern of climatic fluctuations with only a minor time-lag. The beginnings of the "neolithic revolution” in the Saharan desert have to be looked for at about 8,000 B. P. |
