Holocene evolution of the Cávado estuary (NW Portugal)

Abstract

This paper aims to contribute to the understanding of the Holocene evolution of the Cávado estuarine coastal system (Portugal) and the adjacent terrestrial areas, using a multidisciplinary approach, which includes geomorphology, sedimentology, palynology, radiocarbon and history. During the Early Holocene, the Cávado environment was characterized by the dominance of coarse sediments especially in the most westward areas, corresponding to fluvial energetic dynamics. During the Middle Holocene, the presence of wetlands dominated especially in the most sheltered areas. The pollen data reflect the predominance of forests during the initial phases of the introduction of agriculture, with a significant presence of humid forests. Between 4240 and 3980 cal BP, a sudden marine flooding took place over the peat. During the Late Holocene, there was a succession of low, high and again low energy fluvial environments in the eastward sheltered areas, while high energy dominated in the Fão channel entrance, with marine influence on the uppermost units. The pollen content reflects a situation of high human influence, with a poor representation of natural forests and a predominance of agrosystems, related to the rise of the Cávado estuary as a port during the heyday of the city of Braga during the Roman and Suevian periods, as described in historical texts and archaeological research. In connection with this growth, the pollen data show the existence of local Pinus plantations related to shipbuilding and repair in the port. During these times, the estuary was larger and open to the sea at Fão. After the 15th century, with the general silting of coastal areas, the inlet closed and the river mouth was displaced to the North.