INVESTIGADORES
ROMERO Maria Virginia
congresos y reuniones científicas
Título:
Late Miocene climatic and environmental change interpreted from a giant oyster reef of Patagonia (Argentina).
Autor/es:
ROMERO, M.V.; MACMILLAN, L.; BREZINA, S.S.; CASADÍO, S.; BRITO, C.
Reunión:
Congreso; Reunión de Comunicaciones de la Asociación Paleontológica (RCAPA 2019); 2019
Resumen:
The Late Miocene Crassostrea patagonica (d´Orbigny, 1842) reef at Puerto Pirámides (S42º 35΄, W64º15΄, Patagonia) is interpreted as a downlap shell-bed within a highstand systems tract. Oyster shell δ18O (-4.4 to -3.2?) and δ13C (-2.0 to -3.2?) values are low and show large seasonal isotopic ranges, with a large amount of variability. These results suggest a marginal marine setting that received extensive freshwater input and mixing. As bulk carbon and oxygen stable isotopes suggest, the C. patagonica reef developed in an environment with large variation in temperature and salinity across seasons and years. Crassotrea patagonica are large (up to 30 cm), thick (up to 7 cm) and heavy (up to 3 kg) shells that provided suitable substrates for a very diverse assemblage of sclerobionts (e.g., boring bivalves, polychaetes, algae, fungi, sponges and others). Non-random distribution of sclerobionts and preference for the external surface of shells suggests colonization in vivo. The environment of C. patagonica is comparable with modern Crassostrea gigas (Thunberg, 1793) reefs at San Blas, Patagonia. The C. patagonica reef occupied the low energy intertidal zone in < 10 m water depth. Oysters lived with their umbones pointing downwards and the right or left valve was sitting indistinctly in the soft-bottom. Seasonality, as recorded today in the Península Valdés region, is suggested also for the environment of C. patagonica. The reef was preserved like an instantaneous picture with articulated and well preserved specimens, probably due to low temperatures and anoxic conditions or rapid burial of the shell accumulation.