Densely packed concentrations of sessile barnacles (Cirripedia : Sessilia) from the Early Pliocene of SE Spain

Sessile barnacle assemblages, dominated by Concavus concavus (Bronn) and Balanus perforatus Bruguiere, are very abundant in the Lower Pliocene deposits of the Almeria-Nijar and Carboneras basins (southeastern Spain). They occur in shallow-coastal siliciclastic and mixed siliciclastic-carbonate sediments, forming dense concentrations in two contexts: (1) sheltered shallow-marine depressions and (2) the mouth of distributary channels feeding a delta lobe. Extensive colonization took place during periods of quiescence with a high nutrient and food supply inducing the formation of hummocks. Crowding of high morphotypes was presumably triggered by a high larval supply and recruitment rate. The barnacles are exceptionally well preserved, often as in situ clusters, many with opercula, and include a range of ontogenetic stages with some specimens preserving original colouration. Good preservation is probably due to sudden burial without further reworking.