Análise geoquímica da coluna de amostragem D (camadas A/B/C – Eb) da gruta do Caldeirão

Pag António João Cruz, "Análise geoquímica da coluna de amostragem D (camadas A/B/C – Eb) da gruta do Caldeirão", in João Zilhão (ed.), Gruta do Caldeirão. O Neolítico Antigo, Lisboa, Instituto Português do Património Arquitectónico e Arqueológico, 1992, ISBN 0-972-9374-00-07, pp. 203-215



Abstract The chemical, textural and adsortive properties determined for the 10 samples of sampling column D (corresponding to the upper part, including the Holocene levels, of the sedimentary filling of Gruta do Caldeirão) have made possible the discussion of stratigraphical and environmental problems. The concentration profile of the organic carbon and the classification of the samples (for the fraction extracted with hydrochloric acid) through a numerical taxonomy procedure, have shown that samples D5 and D6 belonged to layer Ea, and not to an upper, disturbed, part of layer Eb, as initially thought (Zilhão, chapter 3). The geochemical results also show the existence of mineralogical continuity throughout the sedimentary sequence sampled in column D, and, consequently, the absence of significant changes in the structure of the sediment catchment of the cave. There is also no evidence for significant climatic changes inside the cave, except for a slight increase in humidity at the top of the superficial layer. There is no evidence for leaching either. The classification of the properties suggests a twofold origin for the different components of the sediment: an endogenous one, for calcite, and an exogenous one, for quartz and the other materials. The accumulation of the latter inside the cave was conditioned by the action of maritime winds blowing from the west, as shown by the sodium/potassium ratio (Table 2), and by the development of the vegetation, while the variations in the concentration of the calcite may be due to mechanical processes connected with the human occupation. Figs. 3,5 and 6 are interpreted as indicating that vegetation was relatively dense at the end of the Paleolithic as well as during the Neolithic. However, extensive burning has partially destroyed it in post-Neolithic times, originating a significant increase in soil mobility.
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