Biogenic barite as a proxy of paleoproductivity variations in the southern Peru-Chile Current.

Abstract

The aim of this dissertation was to reconstruct the Late Quatemary paleoproductivity in the Peru-Chile Current off northern and central Chile, using organic carbon and biogenic carbonate as mutually independent proxies of paleoproductivity, and to assess the suitability of biogenic barite as proxy of paleoproductivity. Since the terrigenous input to the Chilean continental slope is very high, the amount of biogenic barite in the sediment could not be determined by direct methods but had to be derived from normative calculations. The required terrigenous Ba/Al ratios were determined from stream sediments and from surface sediment sampIes from continental slope transects. Most of the measured ratios differ markedly from the 'crustal average' ratio that can be found in the literature. It was shown that the terrigenous Ba/Al ratio in sediments of the continental slope is determined by the geochemistry of the continental hinterland. A geochemical model was devised to calculate the terrigenous Ba/Al ratio from the Fe/Al ratio of the bulk sediment. The corrected biogenic barium accumulation rates were then compared with paleoproductivity reconstructions based upon organic carbon and biogenic carbonate.