Lower Ordovician graptolite biozonation and lithofacies of southern Bolivia: relevance for palaeogeographic interpretations

Abstract

The interpretation of the lithofacies and basin evolution of the early Ordovician of southern Bolivia is based on a number of sections on an E–W transect. Lithostratigraphic units are extremely diachronous and only the available data on the graptolite biostratigraphy enabled an interpretation of the basin evolution. The newly proposed graptolite biozonation includes the biozones of Rhabdinopora flabelliformis, Adelograptus sp., Araneograptus murrayi, Hunnegraptus copiosus, Tetragraptus phyllograptoides, Expansograptus protobalticus, Expansograptus holmi, Baltograptus minutus, Azygograptus lapworthi and Isograptus victoriae. Isograptus victoriae is the first isograptid identified from Gondwanan South America. The early Ordovician succession of southern Bolivia is the most complete one documented from South America and can be used as a standard for this continent. The faunas are most easily correlated with the faunal succession of Scandinavia and without doubt belong to the Atlantic graptolite faunal province. They show distinct differences from coeval faunas of the Argentine Precordillera, referable to the Pacific faunal province.