Continental ecosystems at high palaeolatitude before and after the Devonian?Carboniferous boundary: two examples from South Africa and Argentina

PRESTIANNI, C.; GESS. R.; RUSTÁN, J.J.; BALSEIRO, D.; VACCARI, N.E.; STERREN, A.F.

Conferencia; IGCP 596 - SDS Symposium (September 20-22, 2015, Brussels) Climate change and Biodiversity patterns in the Mid-Palaeozoic; 2015

The terrestrialization of living forms is by far one of the most important process that took place during thePalaeozoic. It deeply modified all ecosystems, both marine and continental. Characterized by anunprecedented increase of the biodiversity and of the biomass on emerged lands, it is also marked, at the endof the Devonian period by severe crisis in marine ecosystems as well as by climatic instability. We here reporttwo assemblages situated at both sides of the Devonian?Carboniferous boundary. The first has been collectedby R.G. in the Waterloo Farm locality (South Africa) and is latest Famennian in age. The second comes fromthe Tournaisian part of the Sierra de las Minitas (Argentina). The purpose of this communication is tocompare two particularly different environmental settings documenting the changes that occurred globally atthe Devonian?Carboniferous boundary.The Waterloo Farm locality represents a lagoonal system partially separated from the Agulhas Sea by abarrier island complex (Gess & Hiller, 1995). Fine black anaerobic muds deposited in still portions of thelagoon accumulated a huge mixed assemblage representing the life of marine and fresh water influenced partsof the lagoonal system, as well as that of adjacent terrestrial environments. Terrestrial remains largely consistof plant material comprising a minimum of fifteen taxa. These represent most major Late Devonian groupsincluding zosterophyllopsids, trimerophytes, sphenophytes, herbaceous and arborescent lycopdsids,iridopterids and progymnosperms. This locality provides a unique holistic picture of high latitude continentallife in Gondwana immediately predating the End Devonian Extinction event.The here reported Sierra de la Minitas deposits consist in fine to medium grained fossiliferous sandstonesdeposited in a marine environment (Prestianni et al., 2015). Fossils from this interval include brachiopods,bivalves, crinoids, orthoconic nautiloids, gastropods, scarce fish remains and plants. The plant assemblagereveal a low diversity flora dominated by herbaceous lycopsids but also present traces of ferns and seed plants.Tournaisian Gondwanan plant communities from high latitudes are interpreted as being more complex thanpreviously thought. Their discovery in a sedimentary environment associated with glacigenic deposits, showsthat this new record might be linked to the coeval glacial age widely recorded elsewhere in Gondwana.