Testing deep-time fungi and algae as proxies in palaeoecological analysis: A case study of a Maastrichtian flora from Patagonia, Argentina

NUÑEZ OTAÑO, NOELIA B.; PEREZ PINCHEIRA EGLY; LLORENS, MAGDALENA

Manizales

Congreso; 54th AASP Meeting - Manizales 2022; 2022

The palynological society

Using form-taxa names in deep-time studies and modern taxa names in quaternary studies is a common practice, particularly for fungi. In recent discussions about how to designate NPP taxa, researchers are reaching a consensus to follow modern taxonomic schemes whenever possible. The main goal of this research work is to assign modern affinities to fossil fungi and algae from Puntudo Chico Formation (Campanian?-Maastrichtian) of basin Cañadón Asfalto, Chubut Province, Argentina. Also, testing how useful will be to assign modern taxa names, specially to these geologically old fossil fungi avoiding form-taxa designations when those species have no stratigraphic values but valuable paleoecological information. The studied samples (n = 6, NF 1-6) came from a small profile of grey-brown limestone and claystone, and those facies could represent a floodplain environment. These samples have micro and mesofossils, abundant palynomorphs like algae, fungi, spores of bryophytes, lycophytes, and Monilophyta, and pollen grains of conifers (Araucariaceae, Cheirolepidiaceae, and Podocarpaceae), cycads (Cycadopites sp.) and angiosperms (i.e., Arecaceae, Liliaceae, Proteaceae) typical of a continental association of an open forest with a clear dominance of angiosperms. After this study, algae were found in the 6 samples with a total of 12 taxa mainly from shallow nutrient-rich freshwater environments (Botryococcus, Lecaniella, Leiosphaeridia, Ovoidites spp., and Pediastrum). A total of 12 fungal taxa were identified in 4 out of the 6 samples (cf. Dyctiosporium, cf. Endophragmiella, cf. Monodyctis, cf. Sporidesmium, cf. Taeoniella, among others). Modern ecological requirements of the NPPs identified lead us to conclude this study site was a woody forest, with an understory of herbaceous angiosperm, and after the register of, for example cf. Endophragmiella and cf. Monodictys sp., indicate the presence of lichens as a fungal substrate. Also, the presence of the fungal genus cf. Entorrhiza could indicate the presence of marsh vegetation in one of the samples (NF 2). The level water fluctuation can be notice by the distribution of algae taxa, along with the presence of some fungal taxa found in a freshwater setting with temperate to tropical climate. This study highlights the importance of designate NPPs in deep time studies using modern taxonomic schemes and particularly for fossil fungi linking form-taxa names with modern fungal genera along with their ecological requirements (trophic mode, guild, substrate preferences, climatic range, etc) allowing us to test fungi as valuable proxies for paleoenvironmental reconstructions despite how old the sediments are.