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.; FOGLIA, R.D.

Early Palaeozoic peri-Gondwana terranes: new insights from tectonics and biogeography

Geological Society of London

Lugar: Londres; Año: 2008;

Three main geologic units were involved in the lower Palaeozoic history of South America: (1) autochthonous intracratonic and pericratonic basins developed around the Gondwana basement (e.g. the Central Andean basin, CAB); (2) volcano-sedimentary basins marginal to Gondwana (e.g. Famatina and Puna volcanic belts); and (3) crustal fragments accreted to the Andean margin through the Palaeozoic (e.g. Precordillera terrane). Knowledge of brachiopods, trilobites, and bivalves substantially increased over the last years leading to assembly a more complete dataset. Furongian-Tremadocian trilobites from Famatina, western Puna, and CAB are mostly widespread forms (Olenid Fauna); however, the record of Amzasskiella and Onychopyge suggests a connection with East Gondwana, Siberia and Kazhakstan. At that time, the Central Andean brachiopods and bivalves show links with Iberia, Bohemia and North Africa. Floian trilobites from these regions show a complex array of endemic and peri-Gondwanan forms which indicates relatively free migration for some taxa around Gondwana. Coeval brachiopods from Famatina and western Puna volcaniclastic rocks 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 to the Iapetus Ocean. Cambrian to Middle Ordovician platform carbonate rocks are confined to the Precordillera basin. Trilobites from the Lower and Upper Cambrian limestones of the Precordillera 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 upper Tremadocian-Floian from Precordillera match with the Bathyurid Fauna, whereas associated brachiopods include a high percentage of Laurentian taxa. Since the Floian, a biotic exchange with Gondwana and Baltica becomes evident in the Precordilleran trilobite faunas. By Darriwilian times, Precordilleran brachiopods form a well-defined Low-latitude Realm, but numerous Celtic and Baltic taxa immigrated into the basin. By the Sandbian, affinities of Precordilleran brachiopods shift to western Gondwana (N Africa, Armorica, Perunica, and central Andes), probably reflecting the accretion of the Precordillera (Cuyania) terrane to the proto-Andean margin, although some mixed faunas persist. The low-rich CAB brachiopod, bivalve and trilobite assemblages display stronger ‘Mediterranean’ affinities than those from the Precordillera. In summary, there is abundant palaeontologic data supporting that the Precordillera is a Laurentian-derived far-travelled microcontinent accreted to Gondwana during the Lower Palaeozoic. We provide here a new early Middle Ordovician reconstruction of the southern and central proto-Andean margin based on recently published geologic data as well as the new palaeontological evidence summarized in this paper.