Évolution pléistocène de la Seine fluviatile préservée en Baie de Seine

New high-resolution seismic data complemented with bedrock samples allowed us to propose a revised geological map of the Bay of Seine and to better define the control by the geological substrate on the morphogenesis and evolution of the Seine River during Pleistocene times. The new data confirm previous works. The Bay of Seine can be divided into two geological parts: a Mesozoic monocline domain occupying most of the bay and a syncline domain, mostly Tertiary, in the north, at the transition with the Central English Channel area. The highlighting of Eocene synsedimentary deformations, marked by sliding blocks in the syncline domain, is one of the most original inputs of this new study in the Bay of Seine that underlines the significant role of the substrate on the formation of the Seine paleo-valley. In the monocline domain, three terraces, pre-Saalian, Saalian and Weischelian in age respectively, constitute the infill of the paleovalley, preferentially incised into the middle to upper Jurassic marl-dominated formations, and bounded to the north by the seaward extension of the Oxfordian cuesta. The three terraces are preserved only along the northern bank of the paleovalley, evidencing a NE-to-SW migration of the successive valleys during the Pleistocene. We assume this displacement results from the tectonic tilt of the Paris Basin western margin. In the North, the paleo-Seine is incised into the axis of the tertiary syncline, and comprises three fill terraces that are assumed to have similar ages than those of the terraces. The fill terrace pattern is associated to the subsiding character of this northern domain of the Bay of Seine.