Cecilia R. Amenábar

Middle Devonian microfloras and megafloras from western Argentina and southern Bolivia: their importance in the palaeobiogeographical and palaeoclimatic evolution of western Gondwana

Abstract The study of microfloras and megafloras from western Argentina and southern Bolivia presented here extends our knowledge of the biodiversity and succession of floristic events during the Middle Devonian, and hence improves the current biostratigraphy. Among floral remains, species attributable to ‘Haplostigma’ are mostly recorded from the same Grandispora pseudoreticulata and other palynomorph-bearing sections at Balapuca (southern Bolivia) and Del Chaco and La Cortadera creeks in the Precordillera of Argentina. The northernmost record of Grandispora pseudoreticulata is recorded from a third palynoassemblage from the Pando x-1 corehole of northern Bolivia. A great similarity among all these assemblages (notably abundant Grandispora pseudoreticulata) suggests the identification of terrestrial connections, or at least proximity, of these local areas and other regions in South America during the Givetian. Comparison with other contemporary Gondwanan palynofloras shows cosmopolitan species (e.g. Geminospora lemurata, Samarisporites triangulatus, Archaeozonotriletes variabilis, Chelinospora concinna) along with some others with more restricted distribution (e.g. Grandispora pseudoreticulata, Leiotriletes balapucensis, Acinosporites ledundae). This pattern defines an Afro-South American Subrealm, which most likely results from the effects of palaeolatitude and, in a lesser way, local palaeoenvironmental conditions. On the other hand, such a level of cosmopolitanism supports previous palaeogeographical reconstructions where a narrow Rheic Ocean was developed between Euramerica and the northern parts of Africa and South America.