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Early mining and smelting lead anomalies in geological archives as potential stratigraphic markers for the base of an early Anthropocene

This article reviews possible lower boundaries for an early Anthropocene period. Although a noticeable environmental impact of humans, caused by hunting, the use of fire, forest clearance, animal domestication and agriculture had already occurred in the Neolithic, these early signals are strongly diachronous and localised. Here, we examine early significant, synchronous and regional stratigraphic signals indicating an anthropogenic influence as consequences of mining and smelting-related trace metal contamination. A first regional lead contamination event in the Northern Hemisphere is recognized during the (Eastern Mediterranean) Late Bronze Age to Early Iron Age, between 3500 and 2800 BP, with a peak at around 3000 BP. Another pronounced anthropogenic lead peak is recorded around 2000 BP, during the Roman period. These events, as defined by lead enrichment and changes in lead isotope ratios, accompanied by other trace metal enrichments, are found in several types of archives, such as Arctic ice-cores and European peat-bogs, speleothems as well as fluvial, lake and marine records. Potential stratigraphic correlations and secondary markers may be present using tephrochronology, climate events, and magnetostratigraphy. Such a definition of the base of a formally defined (early) Anthropocene stage/period allows the application of the GSSP (Global Stratotype Section and Point) concept by using a point in a physical archive, and, in contrast to the late Anthropocene, includes a significant quantity of anthropogenic strata as evidence for an Anthropocene chronostratigraphic unit.