LATE QUATERNARY PRECESSIONAL CYCLES OF TERRIGENOUS SEDIMENT INPUT OFFTHE NORTE-CHICO, CHILE (27.5-DEGREES-S) AND PALEOCLIMATIC IMPLICATIONS

The palaeoclimatic conditions during the Last Glacial Maximum (LGM) of southern South America and especially latitudinal shifts of the south ern westerly wind belt are still discussed controversially. Longer pal aeoclimatic records covering the Late Quaternary are rare. A particula rly sensitive area to Late Quaternary climatic changes is the Norte Ch ico, northern Chile, because of its extreme climatic gradients. Small shifts of the present climatic zonation could cause significant variat ions of the terrestrial sedimentary environment which would be recorde d in marine terrigenous sediments. To unveil the history of shifting c limatic zones in northern Chile, we present a sedimentological study o f a marine sediment core (GeoB 3375-1) from the continental slope off the Norte Chico (27.5 degrees S). Sedimentological investigations incl ude bulk- and silt grain-size determinations by sieving, Atterberg sep aration, and detailed SediGraph analyses. Additionally, clay mineralog ical parameters were obtained by X-ray diffraction methods. The C-14-d ated core, covering the time span from approximately 10,000 to 120,000 cal. yr B.P., consists of hemipelagic sediments. Terrigenous sediment ological parameters reveal a strong cyclicity, which is interpreted in terms of variations of sediment provenance, modifications of the terr estrial weathering regimes, and modes of sediment input to the ocean. These interpretations imply cyclic variations between comparatively ar id climates and more humid conditions with seasonal precipitation for northern Chile (27.5 degrees S) through the Late Quaternary. The cycli city of the terrigenous sediment parameters is strongly dominated by p recessional cycles. For the palaeoclimatic signal, this means that mor e humid conditions coincide with maxima of the precession index, as e. g. during the LGM. Higher seasonal precipitation for this part of Chil e is most likely derived from frontal winter rain of the Southern West erlies. Thus, the data presented here favour not only an equatorward s hift of this atmospheric circulation system during the LGM, but also p recession-controlled latitudinal movements throughout the Late Quatern ary. Precessional forcing of latitudinal movements of the westerly atm ospheric circulation system may be conceivable through teleconnections to the Northern Hemisphere monsoonal system in the Atlantic Ocean reg ion. (C) 1998 Elsevier Science B.V. All rights reserved.