Fan Deltas and Floodplains in Valencian Coastal Plains

Abstract

The Valencian coastal plains are formed at the end of two important mountain systems: the Iberian Mountain Range to the north and the Baetic Mountains to the south. As a result of tectonic and neotectonic activity, several graben have been formed at the foot of these reliefs, which have been filled with Plio-Quaternary deposits. In all the coastal plains a depositional sequence is repeated in which the river deposits -fan deltas and alluvial plains- alternate with lagoons/marshes. Basin dimensions, sediment input, tectonics and neotectonics in the study area all determine the size, style and characteristics of fluvial forms, which in turn, influence the characteristics of the coast. Ephemeral rivers form prograding fan deltas when there is little subsidence or tectonic stability dominates. Aggrading fan deltas appear when subsidence predominates. The former make the coast protrude, while the latter are associated with straight coasts. On the other hand, due to the runoff scarcity, ephemeral streams provide fewer sediment inputs to the coastal system than perennial rivers. In addition, during flooding, both ephemeral and perennial rivers provide water and sediment to the lagoons, which are filled and transformed into marshes.