INCITAP   20787
INSTITUTO DE CIENCIAS DE LA TIERRA Y AMBIENTALES DE LA PAMPA
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
Taphonomy, testes habesne? Bioerosion as witness of taphonomic history: A study case from the early Miocene of southern Patagonia, Argentina
Autor/es:
GRIFFIN, MIGUEL; PARRAS, ANA; GABRIELA PINEDA SALGADO
Lugar:
Santa Marta
Reunión:
Simposio; IV Simposio Latinoamericano de Icnología; 2018
Institución organizadora:
Universidad de Caldas
Resumen:
In taphonomic analysis of fossil concentrations in marine environments, bioerosion is usually regarded as an attribute closely related with time exposure of shelly remains at the water-sediment interface. The detailed study of bioerosion traces in conjunction with other taphonomic attributes could be also an important tool to understand other sedimentary and biological process and to reconstruct the taphonomic history of fossil concentrations. Bioerosion traces in four shell concentrations from the Monte León Formation (Cabeza de León section, Santa Cruz Province), were studied in detail. Two samples of 1L were taken from each concentration, which were washed and wet sieved with different mesh sizes. The shelly material retained in the mesh size 31/2 (5.660 mm) was observed under a stereoscopic microscope to identify the sclerobionts present and the degree of bioerosion, fragmentation, and corrasion, as well edge modification.Based on morphologic criteria, 22 ichnotaxa were recognized at ichnogeneric and ichnospecific rank. In each of the four concentrations, the ichnodiversity ranged between 14 and 15 ichnotaxa, being the most ichnodiverse traces those attributed to polychaetes and bryozoans. Traces produced by bryozoans were also the most abundant in all the concentrations, especially those attributed to Pennatichnus. To analyze the distribution of the tracemakers on shells of each concentration, a Goodness-of-Fit Test was performed. The presence of the traces in just one side of the shells was statistically significant. In gastropod shells the traces were specially found on the external surface. This distribution could be related with the available area to colonize epifaunal and shallow infaunal gastropods, which could be easily exposed to the interface and used as a biosubstrate, both syn-vivo and post-mortem. In bivalves, traces occurred in similar proportions in internal and external surfaces. Life habits found for most of the bivalves ?infaunal and seminfaunal? suggest that shells were colonized post-mortem. The biology of the potential tracemarkers suggests that the remains were exposed in shallow low to moderate energy waters, with presence of nutrients and a low sedimentation rate.Bioerosion distribution together with the high to moderate fragmentation and corrasion degrees, and the rounded edges of most of specimens suggest that mollusks were reworked after dead, exposing them and thus allowing the use of those biosubstrates by sclerobionts. Incomplete traces and their development on fragmented edges suggest that several events of reworking and colonization occurred. Although each concentration shows particular taphonomic signatures, the study of bioerosion traces helped to reveal that shell concentrations of the Monte León Formation underwent different and complex histories before final burial, reflecting several episodes of exposure that favored a taphonomic feedback and the development of hard substrate communities.