Environmental constraints on faunal patterns: an example in Early Ordovician (Arenig) trilobite assemblages from the Argentine Cordillera Oriental

WAISFELD, B.G.; ASTINI, R.A.

Congreso; 9th International Symposium on the Ordovician System; 2003

The Acoite Formation (basal Arenig - middle Arenig) yields two contrasting lower Ordovician trilobite assemblages: the Thysanopyge Fauna and the Famatinolithus Fauna. These assemblages display significant differences in composition, geographic distribution and diversity patterns throughout the Cordillera Oriental. Hence, they represent an interesting case study for analyzing major environmental controls on faunal distribution, turnover, and replacement. Most significant faunal events include (1) the radiation of the Thysanopyge Fauna with a high proportion of endemics, and (2) an important faunal turnover involving the extinction of major representatives of the Thysanopyge Fauna and the subsequent expansion of the Famatinolithus Fauna (local radiation + immigration of perigondwanan taxa). Thus, our aim is to interpret the distribution of the Thysanopyge and Famatinolithus faunas across the shelf profile, to constrain environmental controls on diversity patterns, and to understand the significant turnover that takes place between both assemblages. The development of the Thysanopyge Fauna and the shift to the Famatinolithus Fauna is best recorded in the northern part of the Cordillera Oriental (Santa Victoria region), whereas the Famatinolithus Fauna is well-developed in the western region (Los Colorados-Chamarra region) thus the analysis will be focused in faunal and environmental changes documented in these areas.