Sedimentary architecture of the Loire River drowned valleys of the French Atlantic shelf

A thick and complex Pleistocene coastal wedge, preserved in a fossil valley network offshore the Loire River estuary, has been identified through high-resolution seismic profiling. This system comprises three main valleys, 30 km long and 40–60 m deep, incised into Eocene sedimentary rocks lying unconformably on the South Armorican Massif basement. The coastal wedge is organized into six seismic units, representing a succession of colluvial, braided river, estuarine, fluvial, floodout marine sediments, and open marine bioturbated mudstones. These units are arranged in two depositional sequences bounded by a regional unconformity, with ages estimated to be Saalian (130–200 Ka) for the lower sequence and Weischelian (110–12 Ka) for the upper one, correlating with global sea-level changes. This study provides insights into the sedimentary architecture of drowned valleys on the French Atlantic shelf, linking offshore and onshore records to reconstruct past river incision and paleoenvironments.

Proust, J.-N., Renault, M., Guennoc, P., & Thinon, I. (2010). Sedimentary architecture of the Loire River drowned valleys of the French Atlantic shelf. Bulletin de La Société Géologique de France, 181(2), 129–149. https://doi.org/10.2113/gssgfbull.181.2.129