Burnt clay or terra bruciata in coastal basins of Southern Lazio, Italy Evidence for prehistoric ignicoltura or resulting from drainage of Holocene pyritic sediments?

In the Agro Pontino and Fondi basin (Southern Lazio, Italy), burnt clay type material is common and was generally ascribed to the impact of ignicoltura. Based on the widespread occurrence of this material it was hypothesized that in these areas such ignicoltura was widely practiced in pre- and protohistoric times. However, direct evidence thereof, in the form of distinctly fired material, is extremely scarce. Earlier published and recent observations and analyses of a number of characteristic burnt clay sites together provide strong evidence for a pedogenetic origin of this material, i.e. by weathering of Holocene pyritic humic to peaty clays, brought about by their drainage. The process is well known from studies on acid sulphate soils and results in the accumulation of secondary iron concretions that resemble burnt clay but have a pedogenetic origin. Other products formed include jarosite and eventually gypsum, both regularly found in connection with burnt clay type material in these Holocene coastal basins. It is concluded that current hypotheses concerning the role and intensity of in both areas need to be seriously revised. Lastly, it seems likely that such pedogenetic burnt clay also occurs in other Mediterranean coastal basins where during the Holocene pyritic sediments formed and later on were drained for agriculture.