CICTERRA   20351
CENTRO DE INVESTIGACIONES EN CIENCIAS DE LA TIERRA
Unidad Ejecutora - UE
artículos
Título:
Unusual trilobite biofacies from the Lower Ordovician of theArgentineCordillera Oriental: New insights into olenid palaeoecology
Autor/es:
BALSEIRO, D., B.G. WAISFELD Y L.A. BUATOIS
Revista:
LETHAIA
Editorial:
WILEY-BLACKWELL PUBLISHING, INC
Referencias:
Lugar: Copenague; Año: 2011 vol. 44 p. 58 - 75
ISSN:
0024-1164
Resumen:
The study of biofacies has shown to be relevant in the understanding of trilobite
palaeoecology, palaeobiogeography, and macroevolution. The widespread Olenid
biofacies is one of the best known and is usually interpreted to occur in dysoxic
environments. Tremadocian successions of the Argentinian Cordillera Oriental bear a
diverse and long-studied olenid-dominated fauna. Based on cluster analysis, five
distinct biofacies are defined for the middle Tremadocian (Tr2 stage slice), distributed
from shelf (below storm wave base) to lower shoreface settings (above fair-weather
wave base). Ordination shows biofacies along two gradients, a bathymetrical one and
another related to oxygen content. All of them are dominated both taxonomically and
ecologically by olenids. This detailed quantitative palaeoecological study challenges
current views suggesting instead that the Olenidae dominated a broad range of
environments, from oxygenated shallow-marine to dysoxic deep-marine. Comparisons
with largely coeval trilobite records from geodynamically and palaeobiogeographically
disparate sites suggest that siliciclastic sedimentation appears as the most influential
controlling environmental factor upon olenid distribution and dominance. Further
comparisons across different climatic belts show that siliciclastic input controlled
trilobite diversity gradients, even more than latitude. From an autoecological viewpoint
distribution of traditional olenid morphotypes shows no relation to depth or to oxygen
content, and at least some members of the group appear to have had the possibility of coping with
low oxygen content, rather than being restricted to oxygen-deficient
environments. The analysis performed herein, together with recent research on the
group, demonstrate that factors controlling olenid distribution are more complex than
previously envisaged.