Sedimentary metal pollution signatures adjacent to the ancient centre of copper metallurgy at Khirbet Faynan in the desert of southern Jordan.

The impacts and course of heavy-metal pollution from ancient copper metallurgy that used a variety of accessory metal-rich ores possible associated hydrological engineering, and concurrent as well as later biological, diagenetic and geomorphic processes are all examined in a small desertic wadi adjacent to the ancient centre of copper metallurgy of the Khirbet Faynan, in southern Jordan. This novel study describes a step-by-step, multi-faceted approach to a type and scale of problem and geomorphological situation that differ from those most commonly examined in studies of past heavy-metal pollution. Although at this remote and arduous location much key geoarchaeological information is unknown, this investigation remains rooted in existing geomorphological descriptions and re-examines earlier explanations. It also describes the concentrations of other metals judged to be unlikely to be notably influenced by past industrial activity at the site. The exploration begins with a visually-based qualitative stratigraphic description of all metals determined by ICPMS studies to be present at more than trace concentrations in a complex sedimentary sequence in an exposure of surficial deposits in the wadi-floor, a process that also suggests further anomalies and uncertainties in existing understanding. PCA was used in a descriptive and inductive manner to clarify if previously inferred relationships were actually present between the concentrations
of different metals, and between these concentrations and geomorphological properties of the six lithofacies recognised in the sedimentary sequence. This PCA did not seek to make statistical inference. Such relationships were previously explained in terms of interactions between the presence or absence in
the vicinity of active pollution from industrial scale copper metallurgy and local (bio)geomorphological and post-depositional processes e these views were significantly, but not fully, supported. The PCA showed “overall gradients” that implied different pathways of various metals, between ancient active industrial landscapes and the post industrial situation of today. Previously unknown types
of geochemical local trends were also detected consistently within the ordination space for some lithofacies, but not for others. These “local gradients” appear to distinguish consistently between those bodies of sediments that were accumulating adjacent to and contemporary with times of active copper smelting and exploitation, from those bodies of sediment that were accumulating after ca. 1350 calendar years ago, and in receipt of heavy-metals eroded and recycled in abandoned, post-industrial landscapes. The properties of both types of gradient appear real, consistent and meaningful. The end of industrial scale copper processing in Late ByzantineeEarly Arab times in the exposure has been defined by the statistical relationships of its heavy-metal pollution yield, and separated from the impacts of an immediately preceding alluvial event. The PCA clarified a major anomaly in the geomorphological, archaeometallurgical and geochemical data. This is hypothesised to be the result of the water-proofing of the (often) porous sediments of this wadi-floor by the ancient process of puddling, possibly in association with the use of a major barrage immediately down-wadi. The extensive heavy-metal pollution evident in the modern landscape at this particular site is suggested to derive primarily from heavy-metal pollutants emitted in Classical times.