Systematic study of Gondwanan trilete spores from Middle Jurassic rocks of Northern Patagonia, Argentina

Abstract

Abundant and well-preserved bryophyte and fern spores recovered from the Lajas Formation (Cuyo Group) were studied in detail. This spore assemblage comprises a complete and diverse group, composed by 6 genera and 17 species, including Marchantiophyta spores that are atypical in the Middle Jurassic, both in Argentina and worldwide. In addition, the large number of specimens belonging to Converrucosisporites and Concavissimisporites fossil-genera enabled us to make a revision of both genera, and emend their generic diagnoses to avoid their superposition. The presence of Converrucosisporites pricei and Concavissimisporites verrucosus enables us to refine the previously interpreted age for the Lajas Formation at the Portada Covunco area (late Bathonian–Callovian) to middle–late Callovian. The development of an unexpected palaeoecosystem rich in humid-demanding species was interpreted for the studied area during the Middle Jurassic, based on the recorded spore assemblage.