The fossil assemblage from the Tagatiya Guazu Formation (Ediacaran Itapucumi Group, Paraguay) represents a unique opportunity to investigate paleoecological parameters and contribute with taxonomic information regarding Cloudina associations in SW Gondwana.La asociación fósil de la Formación de Tagatiya Guazu (Grupo ediacárico de Itapucumi, Paraguay) representa una oportunidad única para investigar los parámetros paleoecológicos y contribuir con información taxonómica sobre las asociaciones de Cloudina en Gondwana SW

Inglez, L.

Okubo, J.

Simões, M. G.

Warren, L. V.

Estudios Geológicos

English

The fossil assemblage from the Tagatiya Guazu Formation (Ediacaran Itapucumi Group, Paraguay) represents a unique opportunity to investigate paleoecological parameters and contribute with taxonomic information regarding Cloudina associations in SW Gondwana.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Univ Estadual Paulista, Inst Geociencias & Ciencias Exatas, Dept Geol Aplicada, Ave 24A,1515, BR-13506900 Rio Claro, BrazilUniv Estadual Paulista, Inst Biociencias, Dept Zool, BR-18618000 Botucatu, SP, BrazilUniv Estadual Paulista, Inst Geociencias & Ciencias Exatas, Dept Geol Aplicada, Ave 24A,1515, BR-13506900 Rio Claro, BrazilUniv Estadual Paulista, Inst Biociencias, Dept Zool, BR-18618000 Botucatu, SP, BrazilFAPESP: 2018/26230-

Inglez, L. [UNESP]

Warren, L. V. [UNESP]

Okubo, J. [UNESP]

Simoes, M. G. [UNESP]

Repositório Institucional UNESP

Reassessing the taphonomy of in situ Cloudina assemblages from the Tagatiya Guazu Formation, Ediacaran Itapucumi Group, Paraguay

Estudios Geológicos (E-Journal)

Estudios Geológicosjulio-diciembre 2019, 75(2), e100ISSN-L: 0367-0449https://doi.org/10.3989/egeol.43595.555Recibido el 10 de mayo de 2019; Aceptado el 1 de julio de 2019; Publicado online el 19 de noviembre de 2019Citation / Cómo citar este artículo: Inglez, L. et al. (2019). Reassessing the taphonomy of in situ Cloudina assemblages from the Tagatiya Guazu Formation, Ediacaran Itapucumi Group, Paraguay. Estudios Geológicos 75(2): e100. https://doi.org/10.3989/egeol.43595.555.Copyright: © 2019 CSIC. This is an open-access article distributed under the terms of the Creative Commons Attribution-Non Commercial (by-nc) Spain 4.0 License.Reassessing the taphonomy of in situ Cloudina assemblages from the Tagatiya Guazu Formation, Ediacaran Itapucumi Group, ParaguayReevaluación de la tafonomía de las asociaciones conservadas in situ de Cloudina en la Formación de Tagatiya Guazu, Grupo ediacárico de Itapucumi, ParaguayL. Inglez1, L.V. Warren1, J. Okubo1, M.G. Simões21Departamento de Geologia Aplicada, Instituto de Geociências e Ciências Exatas, Universidade Estadual Paulista, Avenida 24A, 1515, Rio Claro 13506-900, Brazil. Email: lucas.inglez@hotmail.com; ORCID ID: http://orcid.org/0000-0002-2815-8788, http://orcid.org/0000-0002-2050-6514, http://orcid.org/0000-0001-9160-99942Departamento de Zoologia, Instituto de Biociências, Universidade Estadual Paulista, Distrito de Rubião Júnior, Botucatu 18618-000, Brazil. ORCID ID: http://orcid.org/0000-0002-8706-3199ABSTRACTThe fossil assemblage from the Tagatiya Guazu Formation (Ediacaran Itapucumi Group, Paraguay) represents a unique opportunity to investigate paleoecological parameters and contribute with taxonomic information  regarding Cloudina associations in SW Gondwana.Keywords: Cloudina; Tagatiya Guazu Formation; Ediacaran; Paraguay.RESUMENLa asociación fósil de la Formación de Tagatiya Guazu (Grupo ediacárico de Itapucumi, Paraguay) representa una oportunidad única para investigar los parámetros paleoecológicos y contribuir con información taxonómica sobre las asociaciones de Cloudina en Gondwana SW.Palabras clave: Cloudina; Formación de Tagatiya Guazu; Ediacárico; ParaguayIntroductionCloudina is one of the main index fossils of the Ediacaran Period commonly occurring in carbon-ate platform settings as in situ clusters or loosely packed parautochthonous bioclastic deposits in close association with microbial facies. However, despite these taphonomic and sedimentologic attri-butes found in almost all Cloudina accumulations worldwide, many doubts persist regarding the (a) phylogenetic affinity, (b) palaeoecology and(c) taphonomy of this biomineralized metazoan.2 L. Inglez et al.Estudios Geológicos, 75(2), julio-diciembre 2019, e100, ISSN-L: 0367-0449. https://doi.org/10.3989/egeol.43595.555One of the greatest issues concerning the interpre-tation of Cloudina palaeobiology is related to the preservational quality of the fossils, which varies according to distinct rock matrixes, in some cases precluding the precise interpretation of its tridi-mensional morphology. This also hampers the use of detailed morphometric parameters (i.e., oblique/transverse annulations at the exterior surface of fun-nels) that can be easily or better observed in those individuals preserved in phosphatized material (Cai et al., 2017). When the preservation occurs in carbonate rocks, the lack of compositional contrast between recrystallized shell walls and carbonate rock matrix that embeds them, hindering mechani-cal or chemical separation of individuals, or even the assessment through micro-CT scanning. On the other hand, size distribution of tubes in autochtho-nous Cloudina assemblages has demonstrated to be a useful, and sometimes the only approach possible to define taxonomic characters and assess informa-tion on the structure of palaeocommunities, modes of reproduction and ontogeny. Indeed, at the type locality of the Nama Group, taxonomic classifica-tion within two species of Cloudina (C. hartmanae and C. riemkeae) was mainly based on differences in tube diameter (Germs, 1972). Additionally, mor-phometry was also used to infer size variations in response to environmental changes, suggesting gen-eralist and adaptable growth strategies for this taxon (Wood et al., 2017).ResultsThe fossil-bearing Tagatiya Guazu Formation (Itapucumi Group), on northeastern Paraguay is characterized by an intercalation of grainstone, mudstone and microbial facies interpreted as depos-ited in a protected lagoonal environment. This unit is particularly rich in bioclastic concentrations of Corumbella, Namacalathus and Cloudina skeletal remains (Warren et al., 2017). When associated to microbialite facies, previous taphonomic analysis (Warren et al., 2013) has demonstrated that Cloudina occur as either vertically oriented tubes or as pros-trate carapaces with little or no taphonomic signa-tures (fragmentation, abrasion) indicating extensive lateral transport and prolonged residence time at the sediment-water interface (Fig. 1). These features strongly suggest that they possibly represent autoch-thonous individuals. Here we analyzed both types of occurrences in (i) naturally weathered surfaces, (ii) polished slabs and (iii) thin sections in order to identify faciologi-cal, taphonomical and morphological parameters. We have taken systematic measurement of the cara-pace diameters from distinct types of assemblages and use Shapiro-Wilk test to determine the normal-ity of their distribution. The Kolmogorov-Smirnov tests was employed to statistically compare the dis-tinct assemblages. Based on detailed observation and quantitative analysis we identified that autoch-thonous Cloudina assemblages can occur with two different patterns of carapace concentrations (subdi-visions of the Type 2 shell concentration proposed by Warren et al., 2013).The first accumulations (Pattern A) (Fig. 1A-D), is characterized by relatively sparse to dense aggre-gations of mainly large rectilinear to slightly curved Cloudina carapaces (between 0.25 and 2.77 mm in diameter). Sometimes diagnostic morphological fea-tures such as well-pronounced flaring apertural rims (Fig. 1B, D) and transverse annulations in funnels outer surface are preserved. Tubes generally possess constant diameters along its length, but few may present a slight enlargement in diameter towards the apertural end (modes of growth A and B after Wood et al., 2017). They either occur vertical, hori-zontal or obliquely oriented in massive to clotted (thrombolitic) carbonatic matrix. This association often preserves fragmentary and sparse remains of Corumbella and Namacalathus skeletal elements. The second type of accumulation (Pattern B) (Fig. 1E-J), is characterized by sparse to dense concen-trations of visibly smaller specimens of Cloudina than those observed in the Pattern A (between 0.12 and 0.90 mm in diameter). The specimens are highly recrystallized and mostly filled with sparry calcite cement, which precludes the observation of detailed external morphological features in the cara-paces. Tubes possess constant diameters (modes of growth B or C, after Wood et al., 2017) and have a high degree of sinuosity, with curves sometimes approaching 90º (Fig. 1H-J). They occur associated with thin-laminated grainstone and planar microbial-ites mostly horizontally to bedding, but also in verti-cally oriented.Reassessing the taphonomy of in situ Cloudina assemblages 3Estudios Geológicos, 75(2), julio-diciembre 2019, e100, ISSN-L: 0367-0449. https://doi.org/10.3989/egeol.43595.555ConclusionsOur preliminary data suggests a strong correlation between sedimentary facies, and distinct morphotypes and sizes of Cloudina carapaces from in situ assem-blages. In general, autochthonous accumulations dominated by small and highly sinuous specimens are preserved in laminated grainstone in contrast to Figure 1.—Distinct autochthonous assemblages from the Tagatiya Guazu Formation, Itapucumi Group. A-D. In situ assemblage of Pattern A, with large Cloudina specimens partially preserved in life-position (A and C). A. general view of naturally weathered surface with recrystallized Cloudina tubes. B. Well preserved specimen with pronounced apertural rims in funnels flaring outwards. C. Transverse section of vertically oriented tube. D. Idem B. E-J. Autochthonous assemblages dominated by small Cloudina carapaces showing high degree of sinuosity of the tubes. E. General view of carapace distribution in the bedding plan. F-G. Vertically (in situ?) oriented tubes interpreted as preserved in life position. H-J. Recrystallized specimens with pronounced sinuosity of tubes.4 L. Inglez et al.Estudios Geológicos, 75(2), julio-diciembre 2019, e100, ISSN-L: 0367-0449. https://doi.org/10.3989/egeol.43595.555assemblages of large and rectilinear carapaces that are usually found in thrombolitic facies. Further investigation is necessary in order to test whether these characteristics might represent paleoecologi-cal responses to different environmental contexts, or could be controlled by taphonomic processes.ACKNOWLEDGMENTSThis research is sponsored by FAPESP (grant 2018/26230-6).ReferencesCai, Y.; Cortijo, I.; Schiffbauer, J.D. & Hua, H. (2017). Taxonomy of late Ediacaran index fossil Cloudina and a new similar taxon from South China. Precambrian Research, 298: 146–156. https://doi.org/10.1016/j.precamres.2017.05.016Germs, G.J.; (1972). New shelly fossils from the Nama Group, South West Africa, American Journal of  Science, 272: 752–761. https://doi.org/10.2475/ajs. 272.8.752Warren, L.V.; Simões, M.G.; Fairchild, T.R.; Ricco-mini, C.; Gaucher, C.; Anelli, L.E.; Freitas, B.T.; Boggiani, P.C. & Quaglio, F. (2013). Origin and impact of the oldest metazoan bioclastic sediments. Geology, 41: 507–510. https://doi.org/10.1130/G33931.1Warren, L.V.; Quaglio, F.; Simões, M.G.; Gaucher, C.; Riccomini, C.; Poiré, D.G.; Freitas, B.T.;  Boggiani, P.C. & Sial, A.N. (2017). Cloudina-Corumbella-Namacalathus association from the Itapucumi Group, Paraguay: increasing ecosystem complexity and tiering at the end of the Ediacaran. Precambrian Research, 298: 79–87. https://doi.org/10.1016/j.precamres. 2017.05.003Wood, R.; Curtis, A.; Penny, A.; Zhuravlev, A.Y.; Curtis-Walcott, S.; Iipinge, S. & Bowyer, F. (2017). Flexible and responsive growth strategy of the Ediacaran skeletal Cloudina from the Nama Group, Namibia. Geology, 45: 1–4. https://doi.org/ 10.1130/G38807.1

Reevaluación de la tafonomía de las asociaciones conservadas in situ de Cloudina en la Formación de Tagatiya Guazu, Grupo ediacárico de Itapucumi, Paraguay

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Reevaluación de la tafonomía de las asociaciones conservadas in situ de Cloudina en la Formación de Tagatiya Guazu, Grupo ediacárico de Itapucumi, Paraguay

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