Autori: N.J. Drenzek, K.A. Hughen, D.B. Montluçon, J.R. Southon, G.M. dos Santos, E.R.M. Druffel, L. Giosan, and T.I. Eglinton
Editorial: Geology, 37, p.239-242, 2009.
Recent studies suggest that as much as half of the organic carbon (OC)undergoing burial in the sediments of tectonically active continental margins may be the product of fossil shale
weathering. These estimates rely on the assumption that vascular plant detritus spends little time sequestered in intermediate reservoirs such as soils, freshwater sediments, and river
deltas , and thus only minimally contributes to the extraneously old 14C ages of total organic matter often observed on adjacent shelves. Here we test this paradigm by measuring the delta14C and del13C values of individual higher plant wax fatty acids as well as the del13C values of extractable alkanes isolated from the Eel River margin (California). The isotopic signatures of the long chain fatty acids indicate that vascular plant material has been sequestered for several thousand years before deposition. A coupled molecular isotope mass balance used to reassess the sedimentary carbon budget indicates that the fossil component is less abundant than previously estimated, with pre-aged terrestrial material instead composing a considerable proportion of all organic matter. If these findings are characteristic of other continental margins proximal to small mountainous rivers, then the importance of petrogenic OC burial in marine sediments may need to be reevaluated.
Cuvinte cheie: river floods, floodplain sediment storage, XRF scanning