Resumo Ingles
This work presents results of the taxonomic study and the stratigraphic distribution of twenty-six species of Tamengo and Guaicurus formations in five sections in the Corumbá and Ladário regions: Corcal and Laginha quarries, Porto Sobramil, Porto Figueiras and Ecoparque Cacimba. In addition, paleoecological and paleoenvironmental inferences are presented based on the occurrence of this fossil assemblage and the updating of the lithostratigraphic description of the sections of upper Corumbá Group. Cloudina carinata Cortijo et al., 2010, had documented occurrences in Spain and Siberia, and now it is presented unprecedented occurrence in America continent, from siltstones of the Tamengo Formation at Porto Figueiras section, Brazil. The studied paelobiota is composed of three biomineralizing metazoan: Cloudina lucianoi (Beurlen & Sommer, 1957), Cloudina carinata, Corumbella werneri Hahn et al., 1982, poriferous spicules, putative sponge gemmule and sessile epibionts prokaryotic-colony Vendotaenia antiqua Gnilovskaya, 1971. The present work also deals with taxonomy and stratigraphic distribution of the four ichnospecies: Gordia marina Emmons, 1844, Pilichnus cf. P. dichotomus Uchman, 1999, Didymaulichnus lyelli (Rouault, 1850) and Multina minima Uchman, 2001 that integrate the updated benthic vagile ichnofauna for upper portion of Corumbá Group. Three vendotaenid species were identified: Vendotaenia antiqua in Tamengo Formation, and two species in Guaicurus Formation: Eoholynia corumbensis Gaucher et al., 2003 and Tawuia dalensis Hofmann, 1979 in (Hofmann & Aitken, 1979). The species diversity of the Tamengo Formation fossil assemblage was complemented by the occurrence of sixteen microfissil species that possibly represented marine planktic, characterized by the permineralized microfossil Chuaria circularis Walcott, 1899 and other fifteen species of small sphaeromorphs organic-walled microfossils: Arctacellularia januarensis Denezine, 2018 nomem nudum, Leiosphaeridia ternata (Timofeev, 1966), Leiosphaeridia crassa (Naumova, 1949), Leiosphaeridia jacutica (Timofeev, 1966), Leiosphaeridia minutissima (Naumova, 1949), Leiosphaeridia tenuissima Eisenack, 1958, Leiosphaeridia obsuleta (Naumova, 1949), Bavlinella faveolata Vidal, 1976, Bambuites erichsenii Sommer, 1971, Synsphaeridium sp., Jacutianema sp., Lophosphaeridium sp., Ostiama microcystis Hermann, 1976 in (Timofeev et al., 1976), Navifusa sp. and Gen. 1 sp. 1. A dramatic changed was identified in paleoenvironmental conditions for deposition of Tamengo and Guaicurus formations. It can be clearly seen that there is a possibility of these changes contributing to the elimination of almost 95% of the paleobiota, including the extinction of the epibenthic metazoan and the disappearance of planktic organic-walled microfossil. Among all twenty-two species restricted to Tamengo Formation, there was only one survivior, the ichnospecies Multina minima that occurs in both of these formations. This local disappearance could be attributed to the global Ediacaran-Cambrian mass extinction. In addition, samples were prepared and analyzed from sections of three countries where organic-walled microfossils were recovered: nine species from the Nomtsas Formation, Namibia; four species from the Tagatiya Guazu Formation, Paraguay; and six species from the Dengying Formation, China. These results increased the scarce record of organic-walled microfossils species from these additional uppermost Ediacaran selected sections. Based on the taxonomic results and the stratigraphic distribution of the species identified from the Tamengo Formation in the Corcal quarry, a biostratigraphic essay consisting of seven biozones was proposed. Based on the complementation of the micropaleontological data for the three additional studied sections, and based on the paleontological record present in the bibliography for other selected sections, the Tamengo Formation biozones could be extended covering fifteen uppermost Ediacaran sections from nine countries: Brazil (four sections), Paraguay (three sections), Uruguay, Argentina, Namibia, China, Russia, Canada, United States and Oman, one section each. The seven biozones proposed were named, from bottom to top: Cloudina Assemblage Superzone that is distributed in all 15 analyzed sections. Inserted in this superzone, there are three biozones: Cloudina lucianoi/Corumbella werneri Interval Zone; Corumbella werneri Range Zone; Corumbellla werneri/Cloudina lucianoi Interval Zone, these three biozones have geographic distribution until the present which is restricted to Brazil and Paraguay. Two subzones are proposed: Bavlinella faveolata-Leiosphaeridia minutissima Assemblage Subzone inserted in the base of Corumbella werneri Range Zone and Vendotaenia antiqua-Cloudina lucianoi Concurrent-Range Subzone at the upper portion of the Corumbella werneri/Cloudina lucianoi Interval Zone. The first subzone spans across Brazil, Argentina, Uruguay, Namibia and China, the second across Brazil, Namibia, China and Siberia. Finally, Eoholynia corumbensis Range Zone was proposed in the base of Guaicurus Formation at Laginha quarry, lowermost Cambrian, which is restricted to Laginha quarry locality so far.
