The Stormy Path from Life to Death Assemblages: The Formation and Preservation of Mass Accumulations of Fossil Sand Dollars
PALAIOS, 2002, V. 17, p. 378-393 Clypeasteroids can be very common in Recent, shallow water environments in a variety of biogeographic settings and represent important members of benthic invertebrate communities. Mass deposits of fossil clypeasteroids are also common and characteristic of many Cenozoic shallow water deposits. Their distribution and formation, however, has received much less attention than molluscan counterparts, although fossil examples are found within all three of the
... hree of the clypeasteroid suborders. A comparison of two mass deposits of scutellid clypeasteroids from the Miocene of the Mediterranean (Gebel Gharra section, Eastern Desert, Egypt; Alahan Section, Mut Basin, Turkey) shows common features, but also significant differences. Both were formed in high energy, coarse sandy, shoreface environments. The Gebel Gharra section consists of a thick, multi-event accumulation with numerous sedimentary features dominated by complete and fragmented skeletal remains of a single taxon (Parascutella). The accumulations in Alahan represents a single, thin, multi-taxon (Amphiope, Parascutella) deposit dominated by very well preserved, complete specimens. Both units are interpreted as proximal storm deposits based on the general sedimentary environment, clast relationships, and taphonomic features. Four factors contributing to mass deposits of clypeasteroid sea urchins in Cenozoic sediments include: (1) their gregarious nature with very high density populations; (2) their relatively robust skeletal morphology; (3) the high transport capacity of their flattened, low density skeletons; and (4) their habitat in shoreface environments which is conducive to physical concentrations of skeletal material. The presence of mass clypeasteroid accumulations is compared to other echinoderm deposits and discussed within the context of their rapid evolution in the Cenozoic.