The timing of the postglacial marine transgression in the Ría de Ferrol (NW Iberia): A new multiproxy approach from its sedimentary infill

The Ría de Ferrol is a confined tide-dominated incised valley in the mesotidal passive Atlantic margin of NW Iberia. A new multidisciplinary approach enables a high-resolution reconstruction of the main environmental changes affecting this area during the Lateglacial and the Holocene. We defined the main seismic and sedimentary facies in the infill and selected different key points to be cored. A number of multiproxy analyses were performed on four sections of sediment (sedimentology, X-ray fluorescence, radiocarbon dating and palynological analyses). Physiography exerted a strong control on the evolution of the basin, as a rock-bounded narrow channel in the middle of the basin influenced the flooding of the ria during the postglacial marine transgression. Depositional environments shifted towards the east as the sea level rose and fluvial facies at the base were covered by facies from a tide-dominated estuary, which were predominant during most of the Holocene. Several layers of sediments from stagnant freshwater areas dominated by Juncus sp. were recovered at ca. −20.5 to −21, ca. −13.1 to −13.5, −12.5 to −12.8 and −12.1 to −13.5 m NMMA along the central axis of the embayment, and dated to be older than 10190–10290; 10790–10970; 7510–8220 and 7130–7830 cal yr BP. They may respectively represent a local stage of lowering sea-level dated at the end of the Lateglacial (i.e. the Younger Dryas), and different episodes of deceleration/stabilization of sea-level rise occurred during the early Holocene (i.e. the 11.4, 10.5, 9.3, 8.2 kyr Henrich events). Thus, for the first time in this region, we were able to generate a high-resolution spatial–temporal interpretation of environmental changes linked to the relative sea-level variations using subtidal sediments from the same sub-basin (and thus free of substantial/differential post-depositional deformations) that describes in detail the flooding of the ancient coastal plains of this region at the beginning of the Holocene.