The Cambrian–Tremadocian units of the Santa Victoria Group (northwestern Argentina): a new correlation scheme

Abstract

Detailed studies were carried out in Cambrian–Tremadocian successions of the Santa Victoria Group (late Upper Cambrian – early Upper Ordovician) exposed in the Argentine Eastern Cordillera. The resulting stratigraphic columns permit to analize some geological events concerning the early evolution of the Ordovician basin (Moya, 2003). In this opportunity, we present a correlation scheme based on the stratigraphic distribution of trilobites and graptolites coming from six areas of the Argentine Eastern Cordillera (Figures 1a–b and 2a–b). These areas were part of a wide marine shelf during the lower Paleozoic (Chaco Shelf), which embraced the Eastern Cordillera, Subandean Ranges and Chaco Plain. The Lipán Swell was an emergent to sub–emergent structure which divided the Chaco Shelf into an eastern part and a western part (horizontal and inclined lines respectively, Figure 2b). The stratigraphic columns here presented are based on individual sections in the western part of the region (La Quesera, Pascha and Angosto del Moreno) and to the integration of several profiles of the eastern part (Lesser and Mojotoro Ranges, Tilcara–Huacalera area in the eastern flank of the Quebrada de Humahuaca) (Figures 2 and 3). We defined seven stratigraphic intervals characterized by distinct fossil assemblages. Four of these stratigraphic intervals correspond to transgression– regression cycles, which are limited at bottom and top by sedimentary discontinuities that we tentatively compared to regressive events recorded in other regions (Cooper, 1999: References and comentaries): LREE (Lange Range Eustatic Event), ARE 1 and ARE 2 (multiple event, Acerocare Regressive Event), BMEE (Black Mountain Eustatic Event). On the other hand, we recognized two aditional regressive events: KRE (Kainella Regressive Event) and NORE (Notopeltis Regressive Event), as they are recorded inside the Kainella meridionalis and Notopeltis orthometopa zones. The data used correspond to those obtained by the authors in field work, without having yet incorporated the valuable and abundant information from other sources.