Resumen de Brachiopod Shells on the Beach: Taphonomic Overprinting in a Fair-Weather Shell Accumulation
Marcello Guimaraes Simoes, Sabrina Coelho Rodrigues, Juliana de Moraes Leme, Ricardo Angelim Pires-Domingues
This study documents the occurrence of brachiopod shells (Bouchardia rosea) in wrack-lines from backshore deposits of a tropical beach (Itamambuca beach), in the northern coast (Ubatuba County) of the state of São Paulo, Brazil. The main goals are: (a) to analyze the provenance and sorting of the brachiopod shells; (b) to provide the taphonomic signatures of the shells, which may favor the recognizance, description and diagnoses of similar shell concentrations in ancient rocks, and (c) to discuss the taphonomic meaning of these detrital accumulations. Sampling transects were done at the reflective and dissipative sectors of the Itamambuca beach. For this project, two thousand brachiopod shells were collected and examined. In general, shells are minute, pale in color, and extremely rounded with reduced shell micro-relieves. Abrasion is the main taphonomic signature recorded. Abraded shells are characterized by V-shaped scars on the external surface, exposing the secondary fibrous layer of the shell microstructure. In some cases, holes produced by abrasion (facets) are recorded in the most convex portion of the shells. A pronounced bias in favor of ventral valve is also noted, and the size frequency distribution of shells is shaped by taphonomy. Finally, shells show intense taphonomic overprinting, but the taphonomic signatures recorded on those shells are worth to provide valuable clues about the taphonomic pathways and spatial transportation of each bioclast.
