Ancient DNA in smectites – microdiffraction and micromorphology

Ancient sedimentary DNA (sedaDNA) is transforming archaeology but its reliability hinges on its preservation within sediments. Smectite clays are crucial: they intercalate DNA in their interlayers, shielding it from degradation. Yet sedaDNA preservation varies with smectite type and its integrity depends on its microtextural appearance. In archaeological sediments, smectites can occur as coatings, aggregates or in the matrix. These contexts have distinct implications: coatings are post-depositional features hosting allochthonous DNA, whereas matrix smectites likely carry in situ signals. We propose to use microdiffraction mapping at ESRF ID13 on resin-impregnated sediment thin sections to identify smectites and pinpoint their spatial location at submicron resolution. This capability, beyond the reach of conventional petrography and laboratory microdiffraction, will directly link smectite type and context allowing us to assess the integrity and preservation of the sedaDNA signal.