F. Lamy et al., LATE QUATERNARY PRECESSIONAL CYCLES OF TERRIGENOUS SEDIMENT INPUT OFFTHE NORTE-CHICO, CHILE (27.5-DEGREES-S) AND PALEOCLIMATIC IMPLICATIONS, Palaeogeography, palaeoclimatology, palaeoecology, 141(3-4), 1998, pp. 233-251
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.