Discs and discord: The paleontological record of Ediacaran discoidal structures in the south American continent

Author(s)

Inglez, L. ^[1] ; Warren, L. V. ^[1] ; Okubo, J. ^[1] ; Simoes, M. G. ^[2] ; Quaglio, F. ^[3] ; Arrouy, M. J. ^[4] ; Netto, R. G. ^[5]

Affiliation

^[1] Univ Estadual Paulista, Inst Geociencias & Ciencias Exatas, Dept Geol Aplicada, Ave 24A, 1515, BR-13506900 Rio Claro - Brazil

^[2] Univ Estadual Paulista, Inst Biociencias, Dept Zool, BR-18618000 Botucatu, SP - Brazil

^[3] Univ Fed Sao Paulo, Dept Ecol & Biol Evolut, Rua Prof Artur Riedel, 275, BR-09972270 Diadema - Brazil

^[4] UNLP CONICET, Ctr Invest Geol, Calle 1, 644, RA-1900 La Plata, Buenos Aires - Argentina

^[5] Univ Vale Rio Sinos UNISINOS, Programa Posgrad Geol, Sao Leopoldo, RS - Brazil

• Document type: Journal article
• Source: Journal of South American Earth Sciences; v. 89, p. 319-336, JAN 2019.
• Web of Science Citations: 0

Abstract

Discoidal sedimentary structures are commonly described in Proterozoic strata, and even more common in Ediacaran to lower Cambrian sedimentary successions. Many abiotic processes are able to produce such circular or discoidal structures in bedding planes, however, their abundance in Ediacaran strata suggests a possible correlation with the evolution and preservation of epibenthic metazoans that emerged at the end of this period. In the South American paleontological record, studies regarding the Ediacaran soft-bodied organisms are meager and restricted to few reports in Brazil, Paraguay, and Argentina. In many cases, such ``fossils{''} were only tentatively characterized in terms of their general morphology and putative taxonomic affinity. Thus, considering the almost absence of work on these enigmatic structures in South America, this paper aims to make a critical analysis on the main occurrences of Ediacaran-Cambrian discoidal structures described in this continent. Based on a detailed review and unpublished data, it was possible to provide a general picture concerning the main paleoenvironmental and sedimentary significance of this structures, as well as on the most promising prospects in terms of the paleontological record of Ediacaran soft-bodied metazoans in South American. In this sense, it was settled that occurrences such as those in the Jaibaras and Itajai basins should be reassessed in order to establish reliable criteria of biogenicity. In the case of the material from the Sete Lagoas and Tagatiya Guazu formations, it is considered more parsimonious to interpret the discoidal features as resulting from microbial processes. Similarly, the discoidal structures of the Cerro Negro Formation presents a series of internal laminations and textures that resembles those developed by processes of microbial grain binding and trapping suggesting that, at least part of this material, can be related to microbially induced sedimentary structures. Finally, for the ichnologically diversified Puncoviscana and Camaqua basins, two different scenarios were identified. The first presents an ichnological assemblage strongly indicative of lower Paleozoic, and possibly Cambrian affinity. Thus, the discs in association with these traces, should be viewed with caution and interpretations made in light of a Paleozoic context. The second possesses an ichnological association typical of that expected for the Ediacaran-Cambrian transition, and the diversity of discoidal forms can potentially represent imprints of macroorganisms on a microbially bounded substrate, thus deserving a more detailed approach. (AU)

• FAPESP's process: 15/24608-3 - Multi-proxy analysis of the Cerro Negro formation, Argentina: bioestratigraphy and paleoenvironment of the first Ediacaran fossillagerstätte in South America
• Grantee: Lucas Verissimo Warren
• Support Opportunities: Regular Research Grants