Neogene coralline-algal growth-forms and their palaeoenvironments in the Almanzora river valley (Almeria, S.E. Spain)

Abstract

The Almanzora river valley is an elongate E-W depression containing mainly Neogene sediments. During the Late Tortonian several horizons of crustose coralline algae developed in three distinct sedimentary contexts: (a) on coastal platforms and talus slopes, (b) on fan deltas and (c) associated with corals in patch-reefs growing at the furthermost extremes of coastal fan deltas. In the former two cases the predominant growths are as rhodoliths associated with mobile substrates. In the coastal systems an increase in depth results in a change in both the morphology and the composition of the rhodoliths. With depth there is a significant increase in the diversity of algal species and a concomitant increase in the size of the algal covering compared to the nucleus and thus the morphology of the rhodolith depends less and less on the shape of the nucleus itself. The massive crusts and columns, which mark the limit of development of the shallow-water rhodoliths, in the deeper examples are covered by branching and thin, leafy (laminar) growths. In the fan deltas the development of the rhodoliths is similar to that of the deeper coastal zones. In the patch-reefs the specific composition of the algal associations changes somewhat and the growths, developed on a stable substrate under low-energy conditions, are mainly vertical branches arising from thin crusts.