ANTHROPOGENIC METALS AS NOVEL TRACERS OF COASTAL PROCESSES IN NORMANDY, FRANCE – THE GEOLOGY OF OPERATION OVERLORD AND THE ALLIED INVASION 80 YEARS LATER

Sediment accumulation rates and recycling efficiency are notoriously difficult to measure over geomorphic timescales in coastal systems. Anthropogenic detritus, if provenance can be constrained, can help build an understanding of these processes on decadal/centurial timescales. The coast of Normandy, France has been the subject of intense study due to its significance as the site of the largest naval invasion in history (Operation Overlord, 1944). Literature attributes much of the anthropogenic metal found on Normandy beaches to these battles and related events.

This research presents a detailed sedimentological analysis across the five main military landing sites. Over 300 samples collected from 16 surface transects and 21 sediment cores show consistent anthropogenic metals across the study area. All surface transects show an abrupt decrease in grain size from samples taken above the normal high-tide mark to samples taken within the daily tidal zone. This clear break in mean sediment size/sorting is mimicked by distribution of anthropogenic metals, with a pronounced increase in concentration below the high-tide mark. Cores also show changes in mean sediment size and metal abundance, but these shifts are decoupled with increasing grain size at 15 cm and a decrease in metals concentration at a greater depth of 45 cm. This decoupling of grain size and metals concentration at depth suggests that metal concentration in the cores is likely a function of time rather than depositional energy/processes.

If metallic material is attributed to the D-Day invasions of 1944, this suggests an upper limit to net sediment accumulation rates at ~ 0.6 cm/year. If metals are partially attributed to earlier industrialization, (e.g., opening of Société Métallurgique de Normandie, 1912), net annual sediment gain is slightly lower. The efficiency of natural beach scouring through major storm events is also potentially bracketed by this study – if offshore migration and re-accumulation of beach sands is responsible for mixing anthropogenic metals deeper into the sediment column, scour depth may not efficiently reach past 45 cm. Ongoing work will better constrain sedimentary processes along the Normandy coast and analogous coastlines in the present-day and ancient geologic record.