Early Ordovician palynomorphs of the Orcomato Formation at La Candelaria Range (Salta): Chronological and environmental considerations of a remarkable locality in NW Argentina

ARÁOZ, L., ACEÑOLAZA, G., VERGEL, MM. AND HEREDIA, S.

COMPTES RENDUS PALEVOL

ELSEVIER FRANCE-EDITIONS SCIENTIFIQUES MEDICALES ELSEVIER

Lugar: Paris; Año: 2020

1631-0683

An acritarch assemblage is reported for the first time from the Ordovician strata of the southern part of the Santa Barbara System of NW Argentina. This region is an area highlighted as an outstanding marginal sector of the early Paleozoic Central Andean Basin. The assemblage is described from the Tremadocian shales of the Orcomato Formation cropping out on the western flank of La Candelaria Range, a unit that have yielded trilobites, brachiopods and sponges. The identified assemblage is characterized by the absence of typical Furongian taxa (late Cambrian), and the relative diversification and abundance of diachromorphs acritarchs, data that restricts its age to the early Tremadocian (earliest Ordovician). These include Vulcanisphaera africana (and abundant transitional forms between V. africana and other unidentified species), Acanthodiacrodium angustum, Cymatiogalea velifera, Saharidia fragilis as the most remarkable forms. The microfloras can be directly compared to those recorded from the northern sequences of Jujuy province (Argentina) and southern Bolivian. Also, whith those of northern Africa (Algerian Sahara, Tunisia, Libya). Important morphological innovations in the Cambro-Ordovician transition have been described in different fossil groups, associated to and increasing acritarch diversity that is also recorded in the Central Andean Basin as a part of the western margin of Gondwana. Data herein presented provides firm biostratigraphic foundations to date the fossiliferous strata of the Orcomato Formation, offering additional elements for a better understanding of a marginal and environmentally restricted area in the southern sector of the early Paleozoic strata that is included within the greater South American Subandean System.