Fig. 2.

Downcore variations of ²⁰⁸Pb/²⁰⁴Pb, ²⁰⁶Pb/²⁰⁴Pb, and ²⁰⁷Pb/²⁰⁴Pb in leachates, ²⁰⁸Pb/²⁰⁶Pb in residues, and Pb concentrations. The Young Group consists of all of the samples above layer N45, and the Old Group of all of the samples below. The different paleo-environmental units are also indicated (9, 12, 13). The dates supporting the Age Model of the section were provided by archaeological materials (9–13). The tephra unit of the AD 79 event is indicated by red shading. This latter is identified both geochemically (dark-red shading), by the cluster of the three samples constituting the upper end-member of the unpolluted water mixing line (component α; see Fig. 3); sedimentologically (light-red shading), by specific sedimentological features (pumice stones); and archaeologically, by consistent archaeological dates (i.e., the second and third date from the bottom of the section). The parallel drift of ²⁰⁸Pb/²⁰⁴Pb and ²⁰⁶Pb/²⁰⁴Pb through time toward geologically old Pb reflects an increasing influence of pollution by the Pb pipe network (fistulae) and is a measure of urban development.