Cambrian and Ordovician biogeography of the South American margin of Gondwana and accreted terranes

BENEDETTO, J.L., VACCARI, N.E., WAISFELD, B.G. SÁNCHEZ, T.M. Y FOGLIA, R.D

Early Paleozoico peri-Gondwanan terranes: new insights from tectonics and biogeography

Geological Society of London

Lugar: Londres; Año: 2009; p. 201 - 232

Three main geologic units were involved in the lower Palaeozoic history of SouthAmerica: (1) autochthonous intracratonic and pericratonic basins developed around theGondwana basement (e.g. the Central Andean basin, CAB); (2) volcano-sedimentary basinsmarginal to Gondwana (e.g. Famatina and Puna volcanic belts); and (3) crustal fragmentsaccreted to the Andean margin through the Palaeozoic (e.g. Precordillera terrane). Knowledgeof brachiopods, trilobites, and bivalves substantially increased over the last years leading toassembly a more complete dataset. Furongian-Tremadocian trilobites from Famatina, westernPuna, and CAB are mostly widespread forms (Olenid Fauna); however, the record ofAmzasskiella and Onychopyge suggests a connection with East Gondwana, Siberia andKazhakstan. At that time, the Central Andean brachiopods and bivalves show links withIberia, Bohemia and North Africa. Floian trilobites from these regions show a complex arrayof endemic and peri-Gondwanan forms which indicates relatively free migration for sometaxa around Gondwana. Coeval brachiopods from Famatina and western Puna volcaniclasticrocks are of Celtic type, having some taxa in common with coeval faunas from south Perú,which would support the existence of a long and nearly continuous volcanic arc marginal tothe Iapetus Ocean. Cambrian to Middle Ordovician platform carbonate rocks are confined tothe Precordillera basin. Trilobites from the Lower and Upper Cambrian limestones of thePrecordillera include key genera indicating Laurentian affinities (Arcuolenellus,Madarocephalus, Plethopeltis). Associated rhynchonelliformean brachiopods (e.g. Nisusia,Wimanella) are also typical of low latitude palaeocontinents. Trilobites from upperTremadocian-Floian from Precordillera match with the Bathyurid Fauna, whereas associatedbrachiopods include a high percentage of Laurentian taxa. Since the Floian, a biotic exchangewith Gondwana and Baltica becomes evident in the Precordilleran trilobite faunas. ByDarriwilian times, Precordilleran brachiopods form a well-defined Low-latitude Realm, but2numerous Celtic and Baltic taxa immigrated into the basin. By the Sandbian, affinities ofPrecordilleran brachiopods shift to western Gondwana (N Africa, Armorica, Perunica, andcentral Andes), probably reflecting the accretion of the Precordillera (Cuyania) terrane to theproto-Andean margin, although some mixed faunas persist. The low-rich CAB brachiopod,bivalve and trilobite assemblages display stronger ‘Mediterranean’ affinities than those fromthe Precordillera. In summary, there is abundant palaeontologic data supporting that thePrecordillera is a Laurentian-derived far-travelled microcontinent accreted to Gondwanaduring the Lower Palaeozoic. We provide here a new early Middle Ordovician reconstructionof the southern and central proto-Andean margin based on recently published geologic data aswell as the new palaeontological evidence summarized in this paper.