THE OLDEST FOSSILS FROM PARAGUAY: CLOUDINA - CORUMBELLA ASSEMBLAGE IN THE ITAPUCUMI GROUP, EDIACARAN LucasVerissimo Warren" ([email protected]), Marcello Guimaraes Simoes 2 ([email protected]), Thomas Rich Fairchild" ([email protected]), Claudio RiccominP ([email protected]), Fernanda Quaglio" ([email protected]), Paulo Cesar BoggianP ([email protected]) :Depart ament o de Geologia Sedimentar e Ambiental, Instituto de Geociencias, Universidade de Sao Paulo - USP; -Instituto de Biociencias, Universidade Estadual Paulista - UNESP ABSTRACT Hoffman& Schrag,2002).Theappearance ofsoft­ bodied metazoans and the advent of the earliest Molds,fragments, and complete specimens skeletal organisms significantly changed the of Cloudina lucianoi, as well as fragments of ecological dynamics of Ediacaran environments. Corumbe!la werneri, stratiform stromatolites and Within this context, Cloudina is considered the thrombolites were found in carbonate rocks ofthe most important guide fossil of Ediacaran time Itapucumi Group, in Paraguay. The assemblage as it delimits an interval biozone between 548 described here corresponds to the oldest fossil and 542 Ma at the very top of the Proterozoic record found in this country and figures as one record (Grotzinger et al., 1995; Amthor et of the most complete Ediacaran metazoan al., 2003). In the Itapucumi Group, Paraguay, occurrences in South America. The association Cloudina was first described in float samples is comparable to other latest Neoproterozoic by Boggiani & Gaucher (2004) . The discovery occurrences worldwide, and comprises an of new of outcrops containing this and other important discovery for elucidating the diversity fossils, such as Corumbella, allowed correlation of these occurrences with similar assemblages and distribution of shelled organisms in the late from Namibia, Brazil, Oman, Canada and China Ediacaran. (Germs, 1972; Zaine & Fairchild, 1985; Conway­ Keywords: Ediacaran, Metazoan, Morris et al., 1990; Hoffman & Mountjoy, Paraguay 2001). The occurrence of these archaic skeletal organisms and microbialites in Paraguay opens a new window for research on the paleobiology RESUMO and paleogeography of late Neoproterozoic Rochas carbonaticas do Grupo Itapucumi, successions in South America. Paraguai Oriental, contern fosseis de moldes, fragmentos e especimes completos de Cloudina lucianoi, fragmentos do organismo Corumbe!la GEOLOGICAL SETTING werneri,estrornatolitosestratiformese trombolitos. The Itapucumi Group crops out in A assembleia aqui descrita corresponde ao mais northeastern Paraguay as a marginal thrust-and­ antigo registro fossilifero encontrado neste pais e fold belt and a sedimentary cover of the Rio Apa figura como umas das mais completas ocorrencias Block(Fig.1.1).The RioApaBlockis delimited on de metazoarios ediacaranos na America do the east by the Paraguay Belt, a W-vergent thrust­ SuI. Esta associacao pode ser comparada com and-fold belt involving the Ediacaran successions outras ocorrencias neoproterozoicas ao redor do of the Corumba Group. The Itapucumi Group mundo e constitui importante descoberta para a is about 400 m thick and comprises siliciclastic compreensao da diversidade e distribuicao dos rocks of the Vallemi Formation at the base, organismos esqueletais do final do Ediacarano. followed by limestones and dolomites of the Palavras-chave: Ediacarano, Metazoarios, Camba ]hopo and Tagatiya Guazu Formations, Paraguai and marl s and mudstones of the Cerro Curuzu Formation at its top (Warren, 2011). Close to INTRODU~AO the Paraguay River, to the west, the Itapucumi Group is metamorphosed at the greenschist The end of the Neoproterozoic Era is facies and intensely deformed. This Western marked by important climatic, tectonic and Domain ofthe Itapucumi Group is characterized evolutionary events (Hoffman et al., 1998; by shelf successions of ooid-grainstones of --------------433 - --- ---------- the Camba ]hopo Formation, deposited as relatively rigid shells of Claudina and the more beach spits and proximal coastal facies. To the flexible ones in Corumbella. east, rocks of the Tagatiya Guazu Formation comprise inter- to supratidal facies associated with stratiform stromatolites and thrombolites CONCLUSION containing fossils of Claudina and CarumbelJ.a The discovery of Claudina and Corumbella (Fig. 1.2). This sedimentary succession is made fragments in the Itapucumi Group corroborates up ofcalcareous facies bearing massive,laminated finding s of similar associations around the and cross-stratified grainstones, followed by world and expands significantly our knowledge heterolithic (calcareous) mudstone/grainstone on the depositional setting and composition of facies, mudstones, laminated microbial mats, Edia caran-age shelly metazoan assemblages. domical thrombolites (Fig. 1.3) and subaerial desiccation breccias. This facies association The discovery also expands the geographic suggests deposition in a peritidal evaporitic range of Corumbella outside its type-area of lagoonal environment upon a protected carbonate Corumba, Brazil. Moreover, it bears important platform. paleogeographic implications for carbonate platforms in the very early history of western Gondwana.Thus,the Itapucumi Group represents EDIACARAN FOSSILS a potential landmark deposit in the paleontology Fossils of the Itapucumi Group include ofthe latest Neoproterozoic ofSouth America. abundant fragments and nearly complete specimens ofClaudina lucianoi and short segments of Corumbella werneri. The succession of nested, ACKNOWLEDGEMENTS eccentrically emplaced, ring-like wall segments The authors thank the "Viceministerio de observed in some specimens is typical of the Minas y Energia de Paraguay"for logistic support genus Cloudina Germs 1972. Cloudina shells may in the field; IGCP - 478 "Neoproterozoic-Early occur in thin accumulations (Fig. 1.4) in troughs Events in SW Gondwana"; CNPq, CAPES between low-amplitude, wave-generated ripples, and FAPESP (projects 2010/02677-0 and and surrounding thrombolitic domes. Claudina 2010/ 19584-4) for financial support. LWR is also occurs in very fine grainstone as fragments and as prostrate, relatively complete individuals a post-doctoral scholarship of FAPESP. FQis (Fig. 1.5), together with in-place basal portions doctorate student ofthe IGC-USP and is funded of shells between thrombolitic domes. Corumbella by CNPq. CR, MGS and PCB are researchers of is recorded as parautocthonous fragments and CNPq. disarticulated segments along with fragmentes of Cloudina shells, a preservational pattern recorded REFERENCES by previous authors (Zaine 1991), but very rare, in the Tamengo Formation, Corumba Group, AMTHOR, J.E. ; GROTZINGER, J.P.; Brazil. The specimens of Corumbella in the SCHRODER, S.; BOWRING, S.A.; Itapucumi Group occur as flattened fragments RAMEZANI, J.; MARTIN, M.W. & of tubes, consisting of articulated, probably MATTER, A. 2003. Extinction ofCloudina organic annular elements (Fig. 1.6). 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Anais da Academia Brasileira de Ciencias, HOFFMAN, P.F., & SCHRAG, D.P. 2002 The 57: 130. snowball Earth hypothesis: testing the limits ofglobal change.Terra Nova, 14(3):129-155. ZAINE, M.F. 1991. Analise dos f6sseis de parte da Faixa Paraguai (MS, MT) e seu contexto HOFFMAN, P.F.; KAUFMAN, A.].; temporal e paleoambiental. University of HALVERSON, G.P. & SCHRAG, D.P. Sao Paulo,Unpublished Ph.D.Thesis,Brazil, 1998. A Neoproterozoic Snowball Earth. 218p. Science,281:1342-1346. Legend Lithologies mGrainstone • Grainstone/mudstone • Mudstone • Siltstone Sedlmenlaoy structures • Helerolithiclamination ~W9veripPIeS ~ Planartaminaucn 22° o Massive bedding DThmmbofiles Fossns ~ CkJudin8 n Corumb&l/a Figure 1. Location, stratigraphy and fossils from the Ediacaran-ageItapucumi Group, northeastern Paraguay. 1.1, Location map.1.2, Stratigraphic sections.1.3, Shell concentration of Cloudinaluclanoi.La, Domical thrombolites. 1.5, Close-up view of Cloudina lucianoi showing cone-in-cone arrangement.1.6, Fragment of Corumbella werneri. ---------------435 ---------- -----.