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

Abstract

Three main geological units were involved in the Early 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); (3) crustal fragments accreted to the Andean margin through the Palaeozoic (e.g. Precordillera terrane). Knowledge of brachiopods, trilobites and bivalves has increased substantially over recent years, leading to the assembly of a more complete dataset. Furongian–Tremadocian trilobites from Famatina, western Puna and the CAB are mostly widespread forms (Olenid Fauna); however, the record of Amzasskiella and Onychopyge suggests a connection with East Gondwana, Siberia and Kazakhstan. 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, indicative of 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 Peru, 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 the upper Tremadocian–Floian sequences of the Precordillera match those of the Bathyurid Fauna, whereas associated brachiopods include a high percentage of Laurentian taxa. From 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 West Gondwanan (North 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-richness CAB brachiopod, bivalve and trilobite assemblages display stronger ‘Mediterranean’ affinities than those from the Precordillera. In summary, there are abundant palaeontological data supporting the view that the Precordillera is a Laurentian-derived far-travelled microcontinent accreted to Gondwana during the Early Palaeozoic. A new early Middle Ordovician reconstruction of the southern and central proto-Andean margin is based on recently published geological data as well as the new palaeontological evidence summarized in this paper.

Linguloidean brachiopods from the Lower Ordovician (Tremadocian) of northwestern Argentina

“…The record of Leptembolon and Libecoviella in the high-to temperate-latitude Central Andean region attests to a peri-Gondwanan distribution of these genera. However, the presence of the new genus Torobolus suggests a certain degree of isolation of the Central Andean Basin from other Gondwanan regions during the Lower Ordovician, in accordance with the evidence from rhynchonelliform brachiopods (Benedetto et al 2009, and references therein), trilobites (Waisfeld & Vaccari 2003, 2008b, and bivalves (Sánchez 2005(Sánchez , 2008. Mergl (1997a) and Bednarzcyk (1999) suggested that the Thysanotos-Leptembolon Fauna had a peri-Gondwanan origin.…”

“…The record of Kvania and the Bohemian-like obolids described herein suggest a migratory route linking the Central Andean Basin with north Gondwana and Perunica along the clastic platforms fringing the Brazilian and North African cratons. Since the late Dapingian-Sandbian the Central Andean brachiopods and bivalves display unambiguous affinities with the Mediterranean faunas, as has been demonstrated in numerous papers (Havlíček & Branisa 1980;Babin 1993;Sánchez & Babin 1993;Benedetto & Sánchez 2003;Benedetto et al 2009;Benedetto , 1014.…”

“…10.3) for the Middle Ordovician linguliforms, and by Benedetto et al (2009, fig. 7) for the Floian-lower Dapingian rhynchonelliforms.…”

“…This is supported by the finding of Libecoviella and Leptembolon in strata slightly older (Tr2) than those yielding these genera in the Perunica terrane, together with the occurrence of Thysanotos in the Late Cambrian of Central Iran (Bassett et al 1999, Popov et al 2013. The role of the Central Andean Basin as site of origination of some rhynchonelliform brachiopod lineages, however, is documented by the occurrence in the lower Tremadocian of NW Argentina of the billingselloid brachiopod Chaniella Benedetto (2009), which has been considered a basal form of the entire polytoechoid clade (Benedetto 2009, Topper et al 2013. Another example is the record of Protorthisina simplex Benedetto -the earliest rhynchonelliform brachiopod so far discovered from the Central Andean Basin -in strata of Furongian age (Lampazar Formation).…”

Conodont biostratigraphy and global correlation of the middle Darriwilian-lower Sandbian (Ordovician) Las Aguaditas Formation, Precordillera of San Juan, Argentina

“…The study of Cambrian and Ordovician faunas is crucial to understand the origin, migration and accretion to its present position. Some authors suggest an allochthonous origin for this terrane, with rifting from Laurentia, beginning drift across the Iapetus Ocean in the Cambrian and accretion to the western margin of Gondwana by the Mid or mid-Late Ordovician (Benedetto, 1993;Benedetto et al, 2009;Astini et al, 1995;Bordonaro and Banchig, 1995;Albanesi et al, 1995a;Albanesi and Bergström, 2010). An alternative hypothesis considers the Precordillera a para-autochthonous Gondwanan block, which drifted along the Gondwana margin from its original position close to Antarctica and South Africa (Aceñolaza et al, 2002;Finney, 2007).…”