Colloque

Isotopic traces of lead from distinct sources in the Laurentian Trough sediments

Charles Goubill

W.K. Johnson

R.W. Macdonald

C.S. Wong

Membre a labase

Charles Goubill

Résumé du colloque

The difference in stable lead isotope composition (206Pb/207Pb, 206Pb/208Pb, 206Pb/204Pb) found in various leachable fractions of deep, pre-industrial sediments from the Laurentian Trough shows the existence of two natural lead sources for this environment. The lead from one source is extracted by successive leachings with pH 5 acetate buffer followed by hydroxylamine-acetic acid solution. The lead from the other source, which is much less radiogenic, is found in the residue of the previous extractions. From a careful examination of our data for sediments accumulated over the last century, we conclude there is one other lead source, most likely anthropogenic. Assuming that the isotopic composition of the anthropogenic source is identical to that found in the Eastern Canadian atmosphere (due to combined gasoline combustion and industrial activity) and choosing reasonable isotopic composition for the two natural sources, we can reconcile the total concentration and isotopic composition of all measurements with a simple 3-source model. This approach provides a way to determine the relative contribution of each lead type in each of the sedimentary fractions and to discuss their early diagenetic pathways.