Taphonomy in the light of intrinsic shell properties and life habits: Marine bivalves from the Eemian of northern Russia

A taphonomic analysis of the bivalves Arctica islandica (Arcticidae), Astarte borealis (Astartidae), Mytilus edulis (Mytilidae), and Spisula elliptica (Mactridae) from shallow-marine last interglacial sediments exposed along the Pyoza river, Arkhangelsk region, shows that they differ in preservation, probably because of differences in shell shape, shell structures, and life habits. The shells indicate that the temporal sequence of taphonomic processes was as follows: (1) pre-mortem bioerosion and dissolution; (2) post-mortem bioerosion; (3) abrasion, disarticulation, and fragmentation; and (4) dissolution. A new graphic illustration, the taphonomic constituent diagram (TCD), is proposed to illustrate the sequences of taphonomic processes. It is inspired by the ichnofabric constituent diagram used in ichnology and integrates the shell surface coverage of different taphonomic features by graphically plotting them against relative time. The taphonomic constituent diagram may display differences in the chronologic order of paleoenvironmental processes. Also, the diagram enables a combination of both microscopic and macroscopic taphonomic features, and eases comparative studies of fossil assemblages.