Taphonomy and taphofacies models of the Pliocene deposits of Vejer de la Frontera (Cádiz, SW Spain)

A quantitative taphonomic analysis of the fossil assemblages, together with a sedimentary study of the Pliocene deposits of the Vejer Basin (Cádiz, Spain), has been carried out. This multidisciplinary analysis has allowed us to establish with great precision the palaeoenvironmental conditions under which these materials were formed. The Pliocene deposits can be divided into three units, named from bottom to top: Unit 1, Unit 2 and Unit 3. Unit 1 is formed of medium-to-coarse-grained sands at the base, corresponding to subtidal bar deposits. At the top, the sands become coarser, and beach and littoral dunes were formed. Within these sedimentological contexts, the fossil remains exhibit a strong degree of taphonomic destruction due to high hydrodynamic energy. Unit 2, consisting of clays, corresponds to deposits formed in a protected coastal bay. A low-energy environment allowed the fossils to maintain a good state of conservation and even thin-shelled bivalves with a delicate ornamentation are preserved. Unit 3 comprises highly bioclastic sands and calcarenites-calcirudites. This unit displays a shallowing upwards trend, passing from deposits generated under shallow subtidal conditions in the lower part to materials deposited on beaches and coastal dunes in the upper part. Under these conditions, the fossil remains show a high degree of taphonomic destruction. In Units 1 and 3, the fossils are mainly accumulated in horizontal beds, with extensive lateral continuity and with erosive bottoms and graded tops. These accumulations of fossils are interpreted as tempestites. As compared with the fossils preserved in surrounding sediments, the taphonomic attributes of these bioclasts suggest a superposition of the background and event processes. During normal conditions, the high energy of the littoral environments produced a strong degree of taphonomic destruction. During storm events, a mixture of taphonomic attributes was produced: high fragmentation and disarticulation and little abrasion and edge rounding of the fragments. This mixture was a consequence of sudden burial after storms, which prevented long periods of exposure of the bioclasts in the taphonomically active zone. Three taphofacies models are proposed, based on taphonomic attributes of fossils contained in the different units: inner-shelf taphofacies, protected shallow-lagoon taphofacies and storm bed taphofacies.