Holocene Changes in the Douro Estuary (Northwestern Iberia).

Holocene changes are recorded by sedimentology and palynology on a 20 m long core retrieved in the mouth of the Douro estuary (northwestern Portugal). Results show that the early Holocene (10720-6530 calibrated/call YBP) was characterized by a warm and humid climate as testified by a well-established Pinus-Quercus-Alnus regional forest. Shelf and slope foraminifera assemblages as well as echinoderms gradually increased toward the end of this period, reflecting the sea-level rise that occurred between 11500 and 6000 cal yr BP. A gravel barrier developed in the southern part of the estuary as a result of sea-level rise attenuation and strong hydrodynamism of the river. A radical change from regional fluvially transported pollen assemblages (mainly composed of trees) to pollen spectra derived from local vegetation (mainly Ericaceae and Poaceae) occurred between 6530 and 1500 col yr BP, contemporaneously to the settlement of the gravel barrier. This suggests that the northward migration of the river main channel, already testified by the existence of a palaeovalley with its axis located southward of the present main channel, occurred as early as 6530 cal yr BP. [ABSTRACT FROM AUTHOR]