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Item Open Access A new perspective on the geohydrological and surface processes controlling the depositional environment at the Florisbad archaeozoological site(University of the Free State, 2009-04) Douglas, Rodney Malcolm; Tredoux, M.; Holmes, P. J.English: The Florisbad Quaternary Research Station and archaeozoological site is located 45 km north-west of Bloemfontein, Free State Province, South Africa (28° 46` 05.4”S, 26° 04` 10.7”E), and is sited around a series of highly saline, warm water spring vents. The site is partially covered by a large sand dune. The site is significant for three important reasons. Firstly, the discovery of the Florisbad skull (Homo helmei) in 1932 by Prof. T. Dreyer, secondly, a collection of faunal fossil remains representing at least 31 taxa, including extinct and extant species, and referred to as the Old Collection and, thirdly, a Middle Stone Age (MSA) human occupation horizon representing a temporary butchering site with evidence of a hearth, butchering tools, and faunal fossil remains. Spring- and excavation pit water samples were taken and analysed in 1988 during a high rainfall period, and in 1999 during an average rainfall period. In relation to the spring water, the results show that the total dissolved solids (TDS) of the excavation pit water were, in relation to the spring water, higher during the high rainfall period and lower during the average rainfall period. This was contrary to the norm, where it is expected that high rainfall periods should produce a decrease in TDS due to a dilution effect. The TDS of the spring-water remained stable throughout both high and average rainfall periods. Further analysis showed considerable TDS increases between the excavation pit waters, and between the pit waters and the spring-water. It is concluded that the pit waters were not directly related to the spring water and that the two water bodies were separate entities with the pit water being recognized as groundwater. An analysis of rainfall in relation to the TDS of the spring- and groundwater indicated that short-term rainfall affected the quality of the groundwater, but not the quality of the spring-water, while long-term rainfall had little effect on the quality of the spring-water. The question arose as to why the TDS of the groundwater was so much higher than that of the spring-water, and what factors were causing these differences? Organic-clay (peat) samples from the walls of the excavation pits as well as the walls of the open excavation area were analysed. The results of the analyses, and an examination of the stratigraphy, strongly suggested that minerals had accumulated in the organic-clay layers due to organic matter having a similar colloidal organization to that of clay, with the ability to adsorb large quantities of minerals on their outer surfaces. A comparison of the groundwater and organic-clay analyses results showed that the TDS of the decomposed Peat II organic-clay layer was considerably higher than that of the groundwater, with the same being true for the far less decomposed Peat IV organic-clay layer. By analysing and combing the water and organic-clay layer results with the many factors, mechanisms, and processes involved, it is concluded that the salinization of the organic-clay layers, and the flushing of ions from the organic-clay layers by percolating water during rainfall periods, is responsible for the increased mineralization of the groundwater. Other factors, mechanisms, and processes, such as rainfall, aeolian deposition, evaporation, capillarity, wind, temperature, matrix-suction, pH, Eh, PCO2, PO2, DOC, and biomineralization, all of which support the accumulation of free salts in a semi-arid environment such as Florisbad, were also investigated. Of primary importance was the question as to whether the spring-water was actually responsible for fossilization of the faunal remains, and could fossilization have taken place within the environs of the spring vents, or in the spring vents themselves? Previous research has suggested that the spring-water was calcium-carbonate rich, with evidence of calcium-carbonate deposition further suggesting that faunal remains of the Old Collection must have been in contact with the spring-water in spring vents for some time. An analysis of the spring-water analysed over the past 84 years indicated that there had never been sufficient Ca (under-saturation) in the spring-water for fossilization to occur, and this is confirmed by the current analyses. The contemporary lack of Ca in the springwater, combined with other environmental factors within the environs of spring vents, such as the lack of organic matter and clay, combined with a high Eh environment, also strongly indicated that, historically, fossilization could not have taken place within the environs of the springs. Contrary to earlier hypotheses, it is concluded that the spring water and spring flow would directly assist in the de-mineralization of faunal remains. A detailed investigation of the site, along with an analysis of the stratigraphy and sedimentation, revealed that previous theories on the formation of the site did not sufficiently accommodate the current stratigraphy in the context of the organic-clay layers, the salinization process, and fossilization. From this deduction all the existing and pre-existing evidence was revisited in an attempt to provide a hypothesis which would accommodate the existing morphology of the site, sedimentation, and fossilization. It is hypothesised that the spring site formed around a large drainage-impeded pan which was largely covered by a sand dune that had migrated from the area of the extensive salt pan to the north and north-west (Soutpan). The arms of the dune eventually came to rest up against the windward slope of a dune belt located just south of the spring site, and a dam began to form. High rainfall periods produced organic-clay layers, while sandy layers were produced during drier windy periods. This led to the formation of alternating horizontal layers of organic-clay and sand, eventually building up to almost the top of the sand dune on the leeward face. When the water level in the dam reached the top of the arms of the sand dune, it broke through the eastern arm. The dam water and sediments then evacuated the dam in a flash flood. This flash flood eroded the area to the east of the site to such an extent that the drainage was diverted, and a wide flat-bottomed vlei was formed where much of the dam sediments were deposited. This hypothesis provides an alternative for the formation of the spring site, accommodating all aspects of sedimentation, salinization, and fossilization. The dating of the Florisbad deposits and fossils has been subject to an ongoing debate since the first 14C dating was carried out in 1954. The ages and depths of recently published profiles did not appear to correspond to the assumption of greater compaction with depth and time. In an attempt to resolve this issue, linear, exponential, and logarithmic mathematical trend lines were then experimentally applied to the published profiles of electron spin resonance (ESR) and optical stimulated luminescence (OSL) dates in order to test the theory of compaction, and to validate the results. The hypothetical effect of manipulating ages on trend lines was also tested. A discussion on some possible shortfalls regarding the dating methods used is undertaken. A best logarithmic fit to data was obtained by holding the ESR Middle Stone Age Human Occupation Horizon (MSA) age at 127 ka, and advancing the lower deposit age from 250 ka to 420 ka. The next best fit to data occurred by regressing the ESR MSA age from 127 ka to 78 ka, and holding the lower deposit age at 250 ka. The application of exponential and linear trend lines produced poor fits to data. A suggested compaction trend line was also introduced which produced an ESR MSA age of 75 ka and a lower deposit age of 384 ka. In the final analysis, trend line results suggested an MSA age of 92 ±12 kyr and a basal deposit age of 400 ±20 ka. The logarithmic and suggested compaction trend line ages for the lower deposits both produced ages similar to the suggested Florisain – Cornelian faunal boundary of c. 400 ka. The exercise confirmed that the ages in the published profiles were disjunct and that this disjunction may be related to a number of different physical forces.