Determining the boundaries, structure and volume of buried shell matrix deposits using ground-penetrating radar: A case study from northern Australia

Ground-penetrating radar (GPR) is used in this study to delineate the extent and internal structure of a large late Holocene buried shell matrix site at Thundiy, Bentinck Island, northern Australia. Shell matrix sites comprise a key component of the coastal archaeological record. The extensive nature of many shell matrix sites presents challenges for archaeological sampling regimes. While large-scale excavation is undesirable and impractical, limited test pits often represent only a tiny fraction of large shell deposits and are rarely considered representative. This study transforms GPR data into three-dimensional models which form the basis of deposit volume estimates. Volume estimates are evaluated against excavation data to test their accuracy. Results demonstrate that this novel methodology can generate accurate three-dimensional representations of buried shell matrices and highly accurate volume estimations with error margins of 3.5% ± 7%. It is recommended, though, that more inclusive error margins of 19.5% ± 17% are used to account for potential error, especially where results cannot be verified. This greater understanding of the extent and structural variability of deposits can be utilised to create robust sampling strategies for excavation. The methodology could also be further employed to enhance comparative regional studies and to add to conservation and management practices of buried shell matrix sites. If applied more widely this methodology will not only benefit our understanding of shell matrix deposits but also the wider archaeological record of coastal regions worldwide.