Abstract

An investigation of bulk-rock and clay-fraction compositions of two sedimentary cores from southern Chile was performed to evaluate the record of temporal climatic changes during the late Quaternary (11 ky and 30 ky BP). The bulk mineralogy shows an abundance of feldspars, mica and quartz, with lesser chlorite, amphibole and pyroxene, and variable amounts of carbonates. The clay fraction consists of illite, chlorite and scarce smectite. Smectite shows platy morphology, an Al-Fe beidellite chemical composition, and is detrital. Smectite, together with biogenic carbonate, increases in levels diagnostic of warmer phases. Increases in smectite are attributed either to the beginning of chemical weathering, allowed by the glacial retreat, or to ice extension and sea-level variations. Warmer climates also favoured the increase of carbonate productivity. Levels diagnostic of colder phases show a large decrease in carbonate, small amounts of smectite and large amounts of chlorite and mica, as the abundance of glaciers reduced the productivity and prevented chemical weathering.

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