Taphonomy of Quaternary Pectinidae and a Comparison With Early Permian Shells

Abstract

Actuopaleontology has been widely developed to improve the interpretations of the fossil record. In the Paraná Basin, a pectinid-dominated fossil record marks the Late Paleozoic strata (Upper Carboniferous, Lower Permian), an opportunity to compare their taphonomic signatures with Quaternary valves through actualistic research. This research aims to improve the biostratinomic knowledge of pectinid fossil concentrations, leading to better environmental and ecological interpretations of the fossil record. Thus, the present study is based on the taphonomy of 173 valves of Aequipecten tehuelchus. The Quaternary valves were collected on the foreshore of the coastal plain of the Rio Grande do Sul state. Fragmentation degree, flat/convex valve rate, dissolution, bioerosion (i.e., borings and drill holes), and incrustation were quantified. Following, Quaternary pectinid data were compared with available information on the Lower Permian pectinids from the Rio Bonito Formation (Paraná Basin). Not all signatures imprinted in the Quaternary material were observed in Permian molds. However, physical and biological damages were preferentially observed in both Quaternary and Permian samples. Quaternary pectinids on the modern beach suggest the high transportability and durability of their hard skeletons. These taphonomical and sedimentary processes increase the time-averaging and spatial-averaging since Lower Permian pectinids storm-assemblage was registered in the estuarine setting. Furthermore, both deposits studied here were generated during an icehouse/greenhouse transition, and the spatial averaging may have been increased due to the sea-level oscillation and consequent erosion/reworking in marginal marine environments.