Significance of high C/N ratios in organic-carbon-rich Neogene sediments under the Benguela Current upwelling system

摘要

C-organic/N-total values change from similar to5 in middle Miocene sediments deposited under the Benguela Current upwelling system to similar to15 in latest Miocene and Pliocene sediments. Although the change appears to record a larger proportion of land-derived material in younger sediments, bulk delta(13)C(org) values indicate a predominance of marine origin for organic matter throughout the sequence. Marine paleoproductivity, as represented by mass accumulation rates of CaCO3 and organic carbon, increased over this time interval. We postulate that the larger C-organic/N-total values record a shift towards greater recycling rates of nitrogen-rich, relative to carbon-rich, organic matter components as the flux of total organic matter to the seafloor increased. Furthermore, we propose that high C-organic/N-total values may record enhanced paleoproductivity in other sedimentary sequences dominated by marine organic matter. (C) 2002 Elsevier Science Ltd. All rights reserved. [References: 45]