Taphonomy of mass mollusc shell accumulation at Amvrakikos Gulf lagoon complex sandy barriers (NW Greece)

•Massive shell depositions at lagoon sand strips are dominated by bivalves.•Cerastoderma glaucum and Polititapes aureus are the dominant bivalve species.•Taphonomic shell analysis reveals the supply/preservation state at the sand strips. The preservation status of the mollusc shell accumulation of sandy barriers at the Amvrakikos Gulf lagoon complex was studied. Taphonomic shell analysis of dead mollusc depositions was undertaken in the summer of 2016 at Amvrakikos lagoon complex within the Tsoukalio and Logarou sandy barriers, which showed significant differences among the major abundant bivalve species of Cerastoderma glaucum and Polititapes aureus. Both hydrodynamic transport and differential exposure to environmental conditions differ among the accumulated shells depositions of the lagoonal sandy barriers. The heavier and more durable shells of C. glaucum are frequently found concentrated at the Tsoukalio lagoon accumulations and show a higher intensity of fragmentation whereas at Logarou lagoon the bioerosion and abrasion is more intense. On the other hand, the lighter, thinner, and thus more fragile shells of P. aureus show higher concentration and intensity of fragmentation and bioerosion at Logarou lagoon sandy barriers. The continuous deposition of shells at Tsoukalio lagoonal sandy barriers, contrary to the long-term deposition at Logarou lagoon, explains the different types of accumulations among the lagoons which are attributed to the geomorphology of the sandy shores as well as the morphological characteristics of the different shells.