Microfósseis em forma de vaso (VSMs) do Ediacarano Inferior do sul do Cráton Amazônico : implicações para amebas testáceas (Arcellinida)

Abstract

Vasiform microfossils is an informal group that hosts different biological identities asforaminifera, ciliates, chitinozoans and vase-shaped microfossils (VSMs). In the last case, they were widely recognized as Tonian index fossils, until being recently reportedinCryogenian deposits of the Urucum Formation in Brazil. In this study, we report the first occurrences of early ediacaran vasiform microfossils that share similarities with VSMs, widely accepted as testate amoebae fossils. They are found in subsurface rocks of theParecis Basin reaching Marinoan glacial deposits of the Puga Formation and Ediacaranrocks of Guia and Nobres formations in Brazil. These Neoproterozoic sedimentarysequences cover the Amazonian Craton and can be observed progressively deformedtothe SE of the Parecis Basin. In the Puga Formation, mineralized tests resemble the VSMPalaeoamphora urucumense. Organic tests share similarities with the VSMLimetalageniformis in the Guia Formation whereas in the Nobres Formation they are morediverse and similar to Bonniea dacruchares, Bonniea sp., Cycliocyrilliumsimplex, Cycliocyrillium torquata, P. urucumense, and L. lageniformis. The similarities betweenfossils reported here with Tonian index-fossils motivates the review of VSMs temporal distribution attributed to amoebozoa, once this record may extend the known occurrencesof VSMs to the interval between 1100 and 557 Ma. The fossil species L. lageniformis, P. urucumense, Bonniea pytinaia, B. dacruchares, C. simplex, and C. torquataoccur throughout Tonian and rarely in Ediacaran deposits. If comproved, the newtemporal distribution revealed here points that only Obelix rootsii, Hemisphaeriella ornata, Trachycyrillium pudens, Bonniea makrocurtos, and Melanocyrilliumhexodiademaappear restricted to the Tonian. In contrast, Taruma rata is limited to the Cryogenian. Although VSMs occur in Tonian, Cryogenian and Ediacaran deposits, their highest diversity is observed in the Tonian followed by a continuous decline towards theEdiacaran. The Puga Formation and Araras Group assemblages demonstrate that thediversity of vasiform microfossils recorded during the Ediacaran is higher than previouslythought, which increases the number of known organisms that survived the Cryogenianglobal glaciations.