Diagenesis has been recognized for decades to significantly alter the trace elements biogenic signatures in fossil tooth enamel and bone that are routinely used for paleobiological and paleoenvironmental reconstructions. This signature is modified during diagenesis according to a complex continuum between two main processes, addition and substitution. For an additive-like, or early diagenesis, the trace elements biogenic profiles can be restored by leaching secondary minerals, but this technique is inefficient for a substitutive-like, or extensive diagenesis for which secondary trace elements are incorporated into the biogenic mineral. This scheme is however unclear for Ca, the major cation in tooth enamel and bone hydroxylapatite, whose stable isotope composition (δ44/42Ca) also conveys biological and environmental information. We present a suite of leaching experiments for monitoring δ44/42Ca values in artificial and natural fossil enamel and bone from different settings. The results show that enamel δ44/42Ca values are insensitive to an additive-like diagenesis that involves the formation of secondary Ca- carbonate mineral phases, while bone shows a consistent offset toward 44Ca-enriched values, that can be restored to the biogenic baseline by a leaching procedure. In the context of a substitutive-like diagenesis, bone exhibits constant δ44/42Ca values, insensitive to leaching, and shows a REE pattern symptomatic of extensive diagenesis. Such a REE pattern can be observed in fossil enamel for which δ44/42Ca values are still fluctuating and follow a trophic pattern. We conclude that Ca isotopes in fossil enamel are probably not prone to extensive diagenesis and argue that this immunity is due to the very low porosity of enamel that cannot accommodate enough secondary minerals to significantly modify the isotopic composition of the enamel Ca pool.
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RBINS Staff Publications 2023
Roof coverings are crucial elements in the architectural design of any building, from the most rudimentary to the most elaborate, because of the protection against weathering they offer to the buildings. Despite its important role, it remains many gaps or grey areas in our historical and technical knowledge of this stony materials used to make them. In north-western Europe, although roof tiles seem to have attracted the attention of researchers in France, Germany, the Netherlands and Great Britain, it must be said that slate did not benefit from the same interest. In Belgium as well roofing using slate has not been the subject of particular attention for periods r anging from the late medieval period to the 18th century. Situated at the crossroads of archaeology, archaeometry and history, this study aims to take stock of the use of this material in the southern part of the former Duchy of Brabant and more particularly in the Brussels Region. The available bibliography, archival sources and data from the geological analysis of samples from archaeological excavations will be mobilised to address several key questions: the goeographical origin of the roofing slates and, therefore, their transport – the Brussels Region is devoid of slate deposits and is dependent on import trade routes for its supply; the particular uses of slate (social groups, types of building); the question of the organisation of the slate roofers’ trade; the question of costs in relation to other raw material, tiles in particular; and finally, special attention will be paid to the various implementations observed in situ. This last approach will include a reflection on the diverted uses of this stony material in other types of structural work. In short, this contribution will seek to characterise the roofing slate in the history of construction in Brabant and Brussels and will resonate with a major ongoing research project dedicated to the evolution of the Brussels roof frames.
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