Chronostratigraphy and significance of the Rugosa Group (Cruziana, trace fossil) in the Ordovician strata of the South American Central Andean Basin

Abstract

Although most trace fossils display long temporal ranges, certain forms as the Paleozoic mostly trilobite trace Cruziana have particular biostratigraphic significance. The evolution and replacement of trilobite families during the Paleozoic are reflected by the morphological characteristics of trace fossils that have contributed to interpret ages in the “non-fossiliferous” shallow marine Gondwanan realm. The “Cruziana stratigraphy” concept is based on this scheme, where different sets of traces replace each other on the stratigraphical record. The Cruziana rugosa Group is part of this scheme, and has been classically mis-referred as an exclusively Lower Ordovician element in the Central Andean Basin of South America. This contribution reevaluates the presence of the C. rugosa Group in the Lower to Middle Ordovician strata of the Cordillera Oriental and Subandean ranges of Argentina and in the Lower to Upper Ordovician of the Cordillera Oriental and Subandean ranges of Bolivia, and highlights its original distribution on its type area. The current paper displays a biostratigraphically-supported analysis of its record, also contributing with little known data from the northern sector of the continent, in the Colombian Andes.