Paleobiogeography of Early Ordovician palynomorphs and graptolites in northwestern Argentina: relationship with Western Gondwana

RUBINSTEIN, C. V., TORO, B. A., DE LA PUENTE, G. S. & SERVAIS, T.

Zaragoza, España

Simposio; IGCP Project 503 "Ordovician paleogeography and Palaeoclimate". Regional Meeting and Field-trip Zaragoza, 2007; 2007

Universidad de Zaragoza, Facultad de Ciencias y IGCP Project 503 "Ordovician paleogeography and Palaeoclimate"

During Ordovician times, the large foreland basin developed within the upper plate across the western Gondwana active margin gave origin to the CentralAndean Basin, in north-western Argentina, Bolivia and Peru. Different palaeogeographical recontructions locate north-western Argentina in an intermediate latitudinal position between approximately 30° to 40° in the southern hemisphere, in the Early Ordovician.Profuse studies on different faunas as trilobites and brachiopods from the Cordillera Oriental representing the shelf settings, and from the Sierras Subandinas, that correspond to the most proximal environmental settings of the Central Andean Basin, support an intermediate to high latitude for this region, displaying cold- and warm-water taxa.Graptolites have demonstrated its usefulness to establish paleogeographic relationships in Ordovician rocks. Although the primary controls in graptolite distribution are still under discussion, planktic forms show considerable faunal provincialism, enabling the differentiation of a cold-water AtlanticProvince and a warm-water Pacific Province, based on the temperature tolerance of certain faunal elements (Cooper et al., 1991). As a result of a recent taxonomical review of the biostratigraphically important species from the Cordillera Oriental, north-western Argentina (Toro and Maletz, 2007), new insights about the palaeogeographic affinities and biogeography of the Floian (early to middle Arenig according to the British nomenclature) graptolite faunas were obtained.On the other hand, marine microplankton as acritarchs and chitinozoans are useful for biogeographical purposes and they provide additional evidences to other fossil group results. Acritarchs and related algal marine forms (i. e. prasinophytes) recorded from the Early Ordovician of the Cordillera Oriental and the Sierras Subandinas led to a high to intermediate latitude for this region.Although in a preliminary stage of knowledge, chitinozoans data from north-western Argentina seem to display different stratigraphic ranges, especially for index taxa of northern Gondwana chitinozoan biozonation.