Strontium isoscapes in The Netherlands. Spatial variations in ⁸⁷Sr/⁸⁶Sr as a proxy for palaeomobility

Strontium isotope analysis has been successfully applied to archaeological questions of residential mobility and animal husbandry for over three decades. To obtain a full understanding of variations in archaeological samples, spatial variations in bioavailable strontium should be accurately mapped or inferred. This paper presents the first archaeological bioavailable strontium map of The Netherlands. The map is compiled solely from archaeological enamel samples of rodents and selected mammals as they are considered to provide the best proxy of bioavailable Sr. The diversity of the Dutch geological subsurface is directly reflected in the spatial distribution of ⁸⁷Sr/⁸⁶Sr ratios. Six isoscapes are defined: A) Lower terrace of the river Meuse (0.7074-0.7091, n = 2); B) Marine and river Rhine sediments (0.7088-0.7092; n = 85); C) Holland peat area, Kempen and northern sand areas (0.7091-0.7095, n = 14); D) Rur Graben (0.7095-0.7105, n = 11); E) Push moraines (0.7095-0.7110, n = 7) and F) Northern and southern loess areas (0.7104-0.7113, n = 15). Although individual isoscapes may show some overlap, the mean of each isoscape is statistically significant different, except for zones D and E. Five other geological environments yielded no archaeological data, mainly due to poor preservation in acidic soils. To fill this data gap, additional biosphere samples will be collected and analysed. This approach, however, will require validation of the extent to which specific floral are offset compared to the average archaeological bioavailable strontium. The base map presented here now allows such a detailed assessment of potential offsets in the ⁸⁷Sr/⁸⁶Sr recorded by different proxies at the regional scale.