The acquisition of these two bathymetric boxes in the littoral zone made it possible to produce two unpublished Land-Sea DEMs and to usefully complete our vision of the Seine-Maritime's coastal rocky platforms. They confirmed the presence of subtidal steps, testifying to the past position of the chalk cliffs and to propose a model of erosive evolution of this rocky coastal sector since the Holocene (6500 years). This work proved the interest of a detailed cartography of the submerged portion of the littoral platforms (called subtidal rocky platforms), since they made it possible to show the existence of a continuous underwater relief marking the position of the past glacial cliff on the foreshore, dated at 6.5 ka (+/1 ka), end of the Holocene. The 4 coastal sectors analyzed, including two from the CROCO-CAUX campaign, show the remarkable homogeneity of this relief, which made it possible to calculate the average rate of retreat of the chalk cliffs over a period of 6500 years (cosmogenic dating). Compared to rates of erosion calculated on a contemporary scale (over 42 years). They show a clear acceleration of the erosion of the chalk cliffs, since the contemporary erosion rates are 43 to 67% higher than the long-term erosion rates. The rate of erosion in 40 years is therefore 2 to 3 times faster than during the last six millennia. These results were analyzed as part of Timothée Duguet's PhD thesis defended at Le Havre Normandy University in October 2019 and are the subject of a publication in Marine Geology, published in 2021.