Cambrian and Ordovician palaeobiogeography of Andean margin of Gondwana and accreted terranes

BENEDETTO, J.L., VACCARI, N., WAISFELD, B., SANCHEZ, T. Y FOGLIA, R.D.

Early Palaeozoic Peri-Gondwanan Terranes

Geological Society, Special Publication 325

Lugar: Londres; Año: 2009; p. 199 - 230

Abstract. Three main geologic units were involved in the lower Palaeozoic history of South America: (1) autochthonous intracratonic and pericratonic basins developed on and around the Gondwana basement (e.g. the Central Andean basin, CAB); (2) volcano-sedimentary basins marginal to Gondwana (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. The occurrence of olenellid trilobites in the Lower Cambrian limestones of Precordillera accounts for strong biogeographical affinities with Laurentia. Associated rhynchonelliformean brachiopods (e.g. Nisusia, Wimanella) are typical of low latitude palaeocontinents. Trilobites from the Middle and Upper Cambrian limestones include some key genera indicating Laurentian affinities (Glossopleura, Prozacanthoides, Plethopeltis). Trilobites from upper Tremadocian-Floian from Precordillera match with the Bathyurid Fauna. Associated brachiopods also include typical Laurentian taxa. Bivalves, although scarce, include the earliest known ambonychiids, which became typical of Laurentian by mid-late Ordovician. 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. In contrast, Furongian-Tremadocian trilobite faunas from Famatina, western Puna, and CAB are mostly widely distributed (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 show links with Bohemia and North Africa. Floian trilobites from these regions show a complex array of endemic and peri-Gondwanan forms. Coeval brachiopods from Famatina and western Puna are linked with the Celtic Realm. Lower Ordovician bivalves from the Central Andean and Famatina basins show clear affinities with NW Gondwana and peri-Gondwana terranes (South Wales, Montagne Noire, Armorican Massif, Iberia). By the Sandbian, affinities of Precordilleran brachiopods shift to western Gondwana (N Africa, Armorica, Perunica, and CAB), probably reflecting the accretion of the Precordillera (Cuyania) terrane to the proto-Andean margin, although some mixed faunas persist. The low-rich CAB brachiopod and bivalve assemblages display stronger ‘Mediterranean’ affinities than those from the Precordillera.