A 5000-Years History of Climate Change Based on Variations in the Composition of the Clay Fraction from Oceanic Sediments Off Galicia

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Clay mineralogical studies have been undertaken on the OMEX core KSGX40 (164cm long) recovered from the Galicia Muddy Deposit of the continental shelf off Ria de Vigo. The chronology for this work is supported by three AMS 14C datings based on mixed foraminifera. Datings were corrected for a marine reservoir effect of 400 years and converted to calendar ages. Mineralogical studies were carried out on the<2μm fraction of the sediments using X-ray diffraction. The studied core spans the past-5000 cal years BR This record show high detrital illite and kaolinite contents and low smectite and/or chlorite contents, compatible with expected mid-latitude temperate humid climate. Although significant quantitative variations in clay mineralogy is clearly expressed by the (kaolinite+smectite)/(illite+chlorite)(Kt+Sm/Il+Chl) ratio and by illite “crystallinity”. Higher values of Kt+Sm/Il+Chl ratio and illite “crystallinity”(indicating poor crystallinities) suggest the occurrence, during the last 5000-years, of several intervals of warmth, for instance the Roman Warm Period (-2500-1950 cal years BP) and the Medieval Warm Period (-1100 and 700 cal years BP), intercalating cyclic colder events, like the Ice Age Cold Epoch (-3300-2500 cal years BP) and the Little Ice Age (-500-150 cal years BP). This work shows the potential of clay minerals to identify weak-amplitude and short climatic changes in Galicia Muddy Deposit.

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