TAPHONOMY OF VERTEBRATE MICROFOSSIL ASSEMBLAGES IN COASTAL ENVIRONMENTS: IN SEARCH OF A MODERN ANALOGOUS MODEL

Abstract

Coastal environments, located halfway between continental and marine realms, are peculiar settings that concentrate and preserve diverse assemblages of mixed autochthonous and allochthonous organisms (Fig. 1). Vertebrate microfossil assemblages are regularly described from Cretaceous coastal deposits, but taphonomic and stratinomic processes involved in the formation of such accumulations often remain unclear. Actuotaphonomic studies dealing with the composition, distribution, and preservation of a specific group (i.e., ecological fidelity) within a modern coastal thanatocoenosis mainly concern such invertebrates as mollusks (Bosence, 1979; Cumins et al., 1986; Henderson and Frey, 1986; Kidwell, 2008) and echinoderms (Greenstein, 1989). For vertebrates, burial experiments have been conducted using large carcasses of marine turtles (Meyer, 1991), but actuotaphonomic analyses have never been performed on microremains.⇓ Figure 1. From modern shallow marine settings to ancient coastal sediments: what about vertebrates microremains? A–F) Environments of the Bimini islands (Bahamas) where sediment samples were collected. Settings correspond to mangrove channels (A), mangrove shores (B), small beaches (C), shallow ponds (D), and lagoon channels (E). Sediments were also sampled in a holding pen used for several years for shark behavioral experiments in which juvenile lemon sharks were kept (F). Note three juvenile lemon sharks (red ellipses D) and three spotted eagle rays (E). G) Example of the calcareous bioclastic facies found in most of the sampled sites from Bimini. H–J) Cenomanian …