Precambrian Research 182 (2010) 382–401

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Precambrian Research

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Chemostratigraphy of the Tamengo Formation (Corumbá Group, Brazil): A contribution to the calibration of the Ediacaran carbon-isotope curve

Paulo C. Boggiani a,∗, Claudio Gaucher b,c, Alcides N. Sial d, Marly Babinski a, Cynthia M. Simon a, Claudio Riccomini a, Valderez P. Ferreira d, Thomas R. Fairchild a a Instituto de Geociências, Universidade de São Paulo, Rua do lago 562, São Paulo, SP, Brazil b Departamento de Geología, Facultad de Ciencias, Iguá 4225,11400 Montevideo, Uruguay c Institute of Geography and Geology, University of Copenhagen, Øster Voldgade 10, 1350 Copenhagen, Denmark d NEG-LABISE, Department of Geology, Federal University of Pernambuco, Recife, PE, Brazil article info abstract

Article history: The Corumbá Group, cropping out in the southern Paraguay Belt in Brazil, is one of the most complete Received 31 July 2009 Ediacaran sedimentary archives of palaeogeographic, climatic, biogeochemical and biotic evolution in Received in revised form 19 April 2010 southwestern Gondwana. The unit hosts a rich fossil record, including acritarchs, vendotaenids (Vendo- Accepted 2 June 2010 taenia, Eoholynia), soft-bodied metazoans (Corumbella) and skeletal fossils (Cloudina, Titanotheca). The Tamengo Formation, made up mainly of limestones and marls, provides a rich bio- and chemostrati- graphic record. Several outcrops, formerly assigned to the Cuiabá Group, are here included in the Tamengo Keywords: Formation on the basis of lithological and chemostratigraphical criteria. High-resolution carbon isotopic Neoproterozoic ı13 Cloudina analyses are reported for the Tamengo Formation, showing (from base to top): (1) a positive C excur- − Chemostratigraphy sion to +4‰ PDB above post-glacial negative values, (2) a negative excursion to 3.5‰ associated with Paraguay Belt a marked regression and subsequent transgression, (3) a positive excursion to +5.5‰, and (4) a plateau Brazil characterized by ı13C around +3‰. A U-Pb SHRIMP zircon age of an ash bed interbedded in the upper part of the ı13C positive plateau yielded 543 ± 3 Ma, which is considered as the depositional age (Babinski et al., 2008a). The positive plateau in the upper Tamengo Formation and the preceding positive excur- sion are ubiquitous features in several successions worldwide, including the Nama Group (Namibia), the Dengying Formation (South China) and the Nafun and Ara groups (Oman). This plateau is constrained between 542 and 551 Ma, thus consistent with the age of the upper Tamengo Formation. The negative excursion of the lower Tamengo Formation may be correlated to the Shuram–Wonoka negative anomaly, although ı13C values do not fall beyond −3.5‰ in the Brazilian sections. Sedimentary breccias occur just beneath this negative excursion in the lower Tamengo Formation. One possible interpretation of the ori- gin of these breccias is a glacioeustatic sea-level fall, but a tectonic interpretation cannot be completely ruled out. Published by Elsevier B.V.

1. Introduction Asia (Chumakov, 2009). A severe perturbation of the carbon cycle during both glacial events is evidenced by negative ı13C excur- The Neoproterozoic Era, and the Ediacaran Period (Knoll et al., sions, much like in the older Cryogenian glaciations (Halverson et 2004) in particular, were characterized by severe biogeochemical al., 2005, 2009; Kaufman et al., 2009). One of the most dramatic and climatic oscillations (e.g. Gaucher et al., 2009a). Several ice negative ı13C anomalies (Shuram–Wonoka anomaly) is recorded ages occurred in the Neoproterozoic (e.g. Hoffman, 2009), which in middle Ediacaran carbonates of Oman, Australia, southern China, were characterized by coeval positive to negative ı13C excursions Namibia, Norway and Siberia (Brasier et al., 2000; Walter et al., in marine carbonates. 2000; Amthor et al., 2003; Halverson et al., 2005; Fike et al., 2006; In the Ediacaran, the glacial record comprises the ca. 582 Ma Le Guerroué et al., 2006; McFadden et al., 2008; Melezhik et al., Gaskiers glaciation (Bowring et al., 2003) and the ca. 547 Ma Vinger- 2008). The Shuram–Wonoka anomaly ended just before 551 ± 1Ma breek glacial event (Germs, 1995; Kaufman et al., 2009), the latter and reached its nadir before 555 ± 6 Ma in south China (Condon et being possibly correlative to the Baykonurian glaciation in Central al., 2005; Zhang et al., 2005). The anomaly may be associated to the Gaskiers glaciation (Halverson et al., 2005, 2009), or post-date it (Sawaki et al., 2010), and is still a matter of debate regarding ∗ ı13 − Corresponding author. Tel.: +55 11 3091 4202; fax: +55 11 3091 4207. the meaning of extremely negative C values down to 12‰ E-mail address: [email protected] (P.C. Boggiani). VPDB (e.g. Le Guerroué et al., 2006; Bristow and Kennedy, 2008;

0301-9268/$ – see front matter. Published by Elsevier B.V. doi:10.1016/j.precamres.2010.06.003 P.C. Boggiani et al. / Precambrian Research 182 (2010) 382–401 383

Le Guerroué and Cozzi, 2010). Precise documentation of the secu- Group, is especially rich and thus central to our understanding lar variations of marine ı13C in the Ediacaran is thus important for of the overall environmental evolution in the Paraguay Belt and understanding the causes of paleoclimatic perturbations, evolution associated cratonic cover. In this work, we revisit the geographi- and extinction of organisms in general and the advent of the Meta- cal distribution of the Corumbá Group and associated units in the zoa in particular. Especially interesting are carbonate-dominated, Paraguay Belt, and report new carbon-isotope analyses of carbon- fossiliferous sedimentary successions with radiochronometric age ates. Emphasis is given to the correlation of the isotopic excursions constraints, such as the Nama Group in Namibia (e.g. Germs et al., recorded in the Corumbá Group, as well as their environmental 2009, and references therein). significance. In South America, one of the units providing the most complete record of Ediacaran climatic, biogeochemical and biotic evolution 2. Geological setting and age: Paraguay Belt and Corumbá is the Corumbá Group and the older Jacadigo Group and Puga For- Group mation, which crop out in the southern Paraguay Belt (Boggiani, 1998; Gaucher et al., 2003; Fig. 1). The most salient features of 2.1. Geological setting these units are the occurrence of probable glacial deposits asso- ciated to Rapitan-type banded iron formation (Puga Formation and The Paraguay Belt, a late Pan-African-Brasiliano age fold belt in Jacadigo Group, e.g. Urban et al., 1992; Alvarenga et al., 2009), thick southwestern Gondwana, is characterized by its convex, arc shape carbonates (Bocaina and Tamengo formations), abundant micro- (Fig. 1). It comprises a southern and a northern branch with distinc- and megafossils and phosphorites. The bio- and chemostratigraphic tively different lithostratigraphy. The main lithological similarity record of the Tamengo Formation, in the middle-upper Corumbá between the southern and northern Paraguay Belt is the presence

Fig. 1. Simplified geological map of the Paraguay Belt showing the location of the studied sections. 384 P.C. Boggiani et al. / Precambrian Research 182 (2010) 382–401 of extensive diamictite exposures at the base, generally assigned to the Tamengo Formation and acritarch assemblages similar to other the Puga Formation and interpreted as of glacial origin (Alvarenga late Ediacaran occurrences (Boggiani, 1998; Gaucher et al., 2003). and Trompette, 1992). Overlying carbonate units in the southern During the rift to drift evolution, widespread carbonate deposition (Corumbá Group) and northern (Araras Group) Paraguay Belt are of the Tamengo Formation represents an important transgression lithologically and biostratigraphically different, and probably of over the Apa River Block, which is also observed in Paraguayan ter- different age, as will be explained below. ritory (Itapucumí Group), where Cloudina fossils were also found The most expressive diamictite exposures have been described (Boggiani and Gaucher, 2004). No foreland basin deposits overlie in the northern Paraguay Belt, and initially defined as Jangada For- the Corumbá Group, highlighting the different basin evolution com- mation (Almeida, 1964a,b; Rocha Campos and Hasui, 1981) and pared to the northern Paraguay Belt, as suggested by Alvarenga et al. later correlated to the Puga Formation in the southern part of (in press). Gaucher et al. (2003, 2009b) suggested that this may be the belt (Corrêa et al., 1979; Araújo et al., 1982; Alvarenga and explained if the southern Paraguay Belt marks the eastern boundary Trompette, 1992). In the northern part, the Puga Formation exhibits of the Río de la Plata Craton, as opposed to the northern Paraguay evidence of glacially influenced sedimentation, such as faceted and Belt, which is clearly associated with the Amazonian Craton. striated pebbles and blocks. The unit is interpreted as deposited in a glaciomarine environment, with turbiditic flows occurring in 2.2. Age of the Corumbá Group and associated units eastern, more distal portions (Alvarenga and Trompette, 1992). Diamictites in the northern Paraguay Belt are overlain by well- Despite the absence of more accurate geochronological data, characterized cap carbonates belonging to the Araras Group, which diamictites of the Puga Formation in both the northern and south- present typical sedimentary features observed in other cap carbon- ern Paraguay Belt were interpreted as late Cryogenian (“Marinoan”; ates worldwide (Nogueira et al., 2003, 2007; Nogueira & Riccomini, Alvarenga and Trompette, 1992; Alvarenga et al., 2004; Babinski 2006; Alvarenga et al., 2004; Riccomini et al., 2007). Glaciogenic et al., 2006; Nogueira et al., 2007; Riccomini et al., 2007). This diamictites of the Serra Azul Formation overlie the Araras Group, interpretation is based only on the fact that diamictites are over- and were probably deposited during the Gaskiers glacial event lain by Cloudina-bearing carbonates. However, this relationship is (Figueiredo, 2006; Alvarenga et al., 2007, 2009; Figueiredo et al., observed only in the southern Paraguay Belt (Beurlen and Sommer, 2008). The Serra Azul Formation is in turn overlain by the Alto 1957; Zaine and Fairchild, 1985; Gaucher et al., 2003), and not in Paraguai Group, interpreted as a molasse succession (Almeida, its northern part. In the latter, the best available age constraint is a 1968, 1984; Alvarenga et al., 2000), possibly deposited in a fore- Pb-Pb isochron of 633 ± 25 Ma for cap carbonates at the base of the land basin related to the Paraguay Belt (Dantas et al., 2009; Gaucher Araras Group (Alvarenga et al., 2009), which is in good agreement et al., 2009b). with an end-Cryogenian age for the underlying diamictites. In the The lithostratigraphy of the southern Paraguay Belt differs southern Paraguay Belt, the youngest detrital zircon in the Puga markedly from that of the northern part (Fig. 1; for a detailed com- Formation yielded U-Pb SHRIMP zircon ages of 706 Ma, providing parison see Alvarenga et al., 2009). At the base, diamictites of the a maximum age constraint for the unit (Babinski et al., 2008b). Puga Formation interpreted as of glacial origin occur in the Morro In the Puerto Suárez region (Bolivia), a quartz-porphyry occur- do Puga hill, where the unit was first described (Maciel, 1959). In ring at the basis of the Jacadigo/Boqui Group yielded a K-Ar age of the same section red, laminated limestones of the lower Bocaina 623 ± 15 Ma (Shaw and O’Connor, 1986 in Berrangé and Litherland, Formation overlie the diamictites (Boggiani and Coimbra, 1996; 1982; Avila Salinas, 1992). The mentioned age favors an Edi- 13 Boggiani et al., 2003), yielding homogeneous ı CPDB values around acaran age for the Puga Formation. However, subsequent surveys −5‰. Stromatolitic “tubestones” occur in carbonates in the vicin- conducted in Bolivia failed to identify the mentioned volcanic ity of this occurrence (Porto Morrinhos; Fig. 10), which are identical rocks. Metabasites were mentioned by Almeida (1965), and, subse- to other examples of cap dolostones worldwide (e.g. Hegenberger, quently, reported from the northern Paraguay Belt (Cuiabá Group). 1987, 1993; Corsetti and Grotzinger, 2005). According to their iso- Nogueira et al. (1978) described metabasites and possible volcanic topic and sedimentological features, these carbonates have been ashes in the eastern Serra da Bodoquena. Metabasite samples were interpreted as a cap carbonate (Boggiani et al., 2003). The Puga For- collected in the Serra da Bodoquena but no zircons could be sepa- mation is interpreted as glacial, although typical glacial features rated, and the strong weathering precluded other geochronological such as facetted or striated clasts, have not been properly docu- studies. Finally, in the Nova Xavantina region, in the eastern portion mented. However, Rapitan-type BIF with granitic dropstones are of the northern Paraguay Belt, a metavolcanosedimentary succes- associated to the Puga Formation (Piacentini et al., 2007), rendering sion was described as the Araés sequence (Dantas and Martinelli, support for a glaciogenic origin of the diamictites. 2003). This sequence is considered part of the Cuiabá Group, which The predominantly terrigenous Cadiueus and Cerradinho for- in turn is interpreted as the distal equivalent of the glaciogenic mations were deposited at an early stage, in a context of Puga Formation (Alvarenga and Trompette, 1992). An alternative rift initiation and climax (Prosser, 1993), before the onset of interpretation of the volcanic rocks would be that they represent widespread carbonate deposition (Gaucher et al., 2003). The a separate, basal unit. Volcanic tuffs interbedded with Cloudina- Bocaina Formation comprises stromatolitic dolostones and sub- bearing carbonates of the upper Tamengo Formation at Corcal Mine ordinate, bedded phosphorite occurrences (Boggiani, 1998). The (Boggiani et al., 2005; Fig. 6) yielded an U-Pb SHRIMP zircon age of dolostones are overlain by the Tamengo Formation, comprising 543 ± 3Ma(Babinski et al., 2008a), which is within 1 Myr of the Edi- black limestones, marls and shales (Almeida, 1965, 1984; Boggiani, acaran – Cambrian boundary (Amthor et al., 2003). However, the 1998; Trompette et al., 1998; Alvarenga et al., 2000; Gaucher et al., whole Tamengo Formation and at least the lower Guaicurus Forma- 2003). Thick siltstones and shales of the Guaicurus Formation over- tion is Ediacaran in age, as shown by their fossil content (Gaucher lie the Tamengo Formation, representing the youngest unit of the et al., 2003 and references therein). Corumbá Group (Fig. 1). Within the rich fossil record of the Tamengo Formation the fol- Whereas the Puga, Cadiueus and Cerradinho formations are lowing groups are biostratigraphically significant: associated with the rift stage of basin evolution, the Bocaina, Tamengo, and Guaicurus formations represent the post-rift to (a) Cloudina lucianoi occurs as event-accumulations in grainstone drift stage. The evolution to open shelf sedimentation is strongly of the Tamengo Formation (Zaine and Fairchild, 1985; Hahn and suggested by phosphorite deposition at the top of the Bocaina For- Pflug, 1985; Gaucher et al., 2003). Cloudina is an index fossil of mation and the presence of the cosmopolitan fossil Cloudina in the late Ediacaran (e.g. Grant, 1990), and defines the Cloudina P.C. Boggiani et al. / Precambrian Research 182 (2010) 382–401 385

Range Zone between ca. 560 and 542 Ma (Gaucher and Germs, Carbon and oxygen isotope analyses on limestones from the 2009) Corcal and Horii Mines were carried out at the Stable Isotope Lab- (b) Corumbella werneri co-occurs with Cloudina in the Tamengo For- oratory of the Geochronological Research Center, University of São mation, and has been interpreted as a cnidarian, possibly related Paulo. Powders were recovered from rock slabs using a carbide den- to the Scyphozoa (Hahn et al., 1982; Walde et al., 1982; Babcock tal burr. Analyses were performed after CO2 gas extraction from the et al., 2005). carbonates in a high vacuum line after reaction with 100% H3PO4 (c) Titanotheca coimbrae occurs in phosphorites of the Bocaina For- at room temperature for 24 h. Following cryogenic cleaning, the mation (Gaucher et al., 2003). Titanotheca has been interpreted released CO2 was analyzed in a EUROPA GEO 20–20 mass spec- as an agglutinated foraminifer, occurring in late Ediacaran trometer, using IAEA standards as well as a secondary standard. (ca. 570–550 Ma) successions from South America and south- Results are reported in the conventional notation in per mil (‰) ern Africa (Gaucher and Sprechmann, 1999; Gaucher, 2000; relative to VPDB standard. Uncertainties are 0.1‰ for both carbon Teixeira and Gaucher, 2004; Gaucher et al., 2005; Gaucher and and oxygen isotope results. Germs, 2009; Fig. 11). Whole-rock chemical analyses were carried out on fused beads (d) A low-diversity acritarch assemblage dominated by Bavlinella by X-ray Fluorescence at the LABISE (UFPE), in a RIX 3000 RIGAKU faveolata occurs in the Tamengo Formation (Zaine and Fairchild, unit that is equipped with Rh tube (Laginha section) and at the 1987; Zaine, 1991; Gaucher et al., 2003), similar to other late X-ray fluorescence at IGC-USP (Corcal, Horii and Calbon sections). Ediacaran successions worldwide (Vidal and Moczydłowska- Vidal, 1997; Gaucher and Sprechmann, 2009). 4. Lithostratigraphy and facies of the Tamengo Formation (e) Vendotaenid algae including Vendotaenia antiqua, Tawuia sp. and Eoholynia corumbensis occur in the upper Corumbá Group The Tamengo Formation is characterized by black limestones (Gaucher et al., 2003), the latter species occurring only in and marls 100–200 m in thickness. The unit overlies the Bocaina siltstones of the lower Guaicurus Formation (Gaucher et al., Formation with erosional unconformity. This is best shown by the 2003). An algoflora characterized by Eoholynia occurs in the basal breccia of the Tamengo Formation (Boggiani, 1998), which Redkino Horizon of the East European Platform, and is con- comprises clasts of stromatolitic dolostone and phosphorite from strained between 558 and 555 Ma by U-Pb zircon ages of ash the Bocaina Formation, as well as granite, rhyolite, chert and schist beds (Fedonkin et al., 2007 and references therein). clasts. The matrix of the typically unstratified (chaotic) breccia is mainly composed of dolomite, apatite and occasional fluorite, the Thus, both biostratigraphic and radiometric data support a late latter possibly late diagenetic/hydrothermal in origin. At Laginha Ediacaran age for the Tamengo Formation. Mine, the breccia exceeds 30 m in thickness, and is concordantly overlain by mudstone and grainstone (Figs. 3 and 10). A package 3. Materials and methods of black, organic-rich marls 20 m in thickness occurs up section, representing a marker horizon (Fig. 3). The latter are overlain in Carbon and oxygen isotope analyses of carbonate samples from turn by ooid grainstones and intercalated rudstones, up to 75 m the Laginha, Saladeiro, Calbon and Baía das Garc¸ as Farm sections in thickness (Figs. 3 and 4). Grainstones of the Tamengo Formation were performed at the Stable Isotope Laboratory (LABISE) of the often show cross bedding, including hummocky cross bedding, and Federal University of Pernambuco (UFPE) at Recife, Brazil. Only least wavy structures (Boggiani, 1998). Cloudina-shell beds (event accu- altered portions of samples were micro-drilled with a 1 mm diam- mulations) mostly occur within this interval, as can be observed eter drill bit. CO2 was extracted from these carbonate samples on a at Corcal Quarry nearby Corumbá (Boggiani, 1998; Gaucher et al., high vacuum line after reaction with phosphoric acid at 25 ◦C dur- 2003). Grey siltstones of the Guaicurus Formation conformably ing three days, and cryogenically cleaned, according to the method overlie the Tamengo Formation. The contact displays low-relief described by Craig (1957). Released CO2 gas was analyzed for O and irregularities that may be related to exposure and karstification of C isotopes in a double inlet, triple collector mass spectrometer (VG the shelf prior to deposition of the Guaicurus Formation. Diamic- Isotech SIRA II), using the BSC reference gas (Borborema skarn cal- tites with limestone clasts up to 2 m in diameter derived from the cite) that was calibrated against NBS-18, NBS-19 and NBS-20, and Tamengo Formation occur in the lower Guaicurus Formation (Lag- has the ı18O value of −11.3‰PDB and ı13C = 8.6‰PDB. The exter- inha diamictite), 5–15 m above the top of the former unit (Boggiani nal precision based on multiple standard measurements of NBS-19 et al., 2004; Gaucher and Poiré, 2009; Fig. 10). This also shows was better than 0.1‰ for carbon and oxygen. Isotope analyses are that shallow-water carbonates were eroded prior or concomitant expressed in the ı-notation in parts per thousand in relation to the to deposition of the lower Guaicurus Formation. Clasts in the Lag- VPDB scale. inha diamictite often deform the underlying siltstones, allowing

Fig. 2. Idealized cross section of the Corumbá shelf, showing the Tamengo and Guaicurus Formations and the location of the studied profiles. 386 P.C. Boggiani et al. / Precambrian Research 182 (2010) 382–401

Table 1 Isotopic and geochemical data of studied samples of the Tamengo Formation.

Sample ıC13PDB ıO18PDB

Laginha western TMG 4 −0.11 −7.96 TMG 5 −0.43 −3.48 TMG 8 −3.32 −9.32 TMG 11 +0.27 −7.53 TMG 12 +0.42 −7.88 TMG 13 +4.59 −7.15 TMG 15 +1.30 −7.32 TMG 16 +1.87 −8.83 TMG 17 +2.60 −7.01 TMG 18 +3.15 −7.91 TMG 19 +3.11 −6.67 TMG 20 +1.39 −10.74 TMG 21 +2.75 −9.33

Laginha western base 05.LG. 2A −3.64 −5.58 05.LG. 2B −3.23 −6.58 05.LG. 2C −0.71 −8.87 05.LG. 2D −0.56 −8.98 05.LG. 2E −1.12 −11.48 05.LG. 2F −0.31 −9.84 05.LG. 2G −0.29 −9.77 05.LG. 2H −0.40 −4.68 05.LG. 2I −1.38 −6.03 05.LG. 2J −0.95 −4.82 05.LG. 2K −1.46 −5.31 05.LG. 2L −1.13 −5.71 05.LG. 2M −1.07 −6.16 05.LG. 2N −1.10 −6.91 05.LG. 2O −1.28 −6.51 05.LG. 2P −1.34 −5.43 05.LG. 2Q −1.35 −5.35 05.LG. 2R −1.51 −5.97 05.LG. 2S −1.89 −8.34 05.LG. 2T −1.10 −8.56 05.LG. 2U −0.36 −10.03 05.LG. 2V +0.45 −8.83 05.LG. 2X +0.13 −9.55 05.LG. 2Y +0.97 −6.39 05.LG. 2Z −0.56 −8.10 05.LG. 2A1 +0.34 −9.37 05.LG. 2B1 +0.56 −7.61 05.LG. 2C1 +0.54 −7.95 05.LG. 2D1 +3.18 −7.40

Sample ıC13PDB ıO18PDB Sr (ppm) Mn (ppm) Fe (ppm) Mn/Sr Fe/Sr

Laginha eastern LAG 01 −0.21 −6.37 1610 79 874 0.049 0.54 LAG 02 +0.26 −8.24 LAG 03 +4.04 −5.91 LAG 04 +3.94 −7.04 LAG 05 +2.70 −7.05 2232 172 7010 0.077 3.14 LAG 06 +4.03 −7.01 LAG 07 +5.32 −7.12 LAG 08 +5.29 −7.25 LAG 09 +4.19 −6.10 LAG 10 +5.43 −7.69 5453 91 4615 0.017 0.85 LAG 11 +5.53 −4.48 LAG 12 +1.62 −7.02 LAG 13 +2.18 −6.68 LAG 14 +3.06 −5.74 LAG 15 +3.12 −6.71 1864 23 773 0.012 0.41 LAG 16 +3.10 −6.17 LAG 17 +3.32 −6.14 LAG 18 +3.30 −6.06 LAG 19 +3.35 −6.18 LAG 20 +3.38 −6.38 2024 25 917 0.012 0.45 LAG 21 +3.33 −5.74 LAG 22 +3.24 −6.18 LAG 23 +2.84 −6.46 LAG 24 +2.60 −6.40 LAG 25 +2.83 −6.99 1610 25 749 0.015 0.46 LAG 26 +2.76 −7.10 LAG 27 +2.19 −7.66 P.C. Boggiani et al. / Precambrian Research 182 (2010) 382–401 387

Table 1 (Continued )

Sample ıC13PDB ıO18PDB Sr (ppm) Mn (ppm) Fe (ppm) Mn/Sr Fe/Sr

LAG 28 +2.90 −7.05 LAG 29 +3.02 −6.81 LAG 30 +2.70 −6.99 1392 27 934 0.019 0.67 LAG 31 +2.48 −7.30 LAG 32 +2.71 −7.18 LAG 33 +2.51 −7.20 LAG 34 +2.21 −6.80 LAG 35 +3.08 −5.94 2334 29 850 0.012 0.36 LAG 36 +3.09 −6.34 LAG 37 +3.03 −6.29 LAG 38 +2.90 −6.00 LAG 39 +2.56 −6.67 LAG 40 +2.56 −6.25 1543 29 829 0.019 0.54 LAG 41 +2.83 −7.07 LAG 42 +2.46 −6.40 LAG 43 +3.07 −6.42 LAG 44 +3.12 −6.49 LAG 45 +3.07 −6.78 1775 17 1112 0.009 0.63 LAG 46 +2.58 −6.49 LAG 47 +2.48 −7.23 LAG 48 +2.43 −7.69 LAG 49 +2.54 −7.29 LAG 50 +2.61 −6.51 1560 14 890 0.009 0.57 LAG 51 +2.82 −7.24 LAG 52 +3.14 −7.15 LAG 53 +3.23 −6.15 LAG 54 +3.33 −6.02 LAG 55 +3.20 −6.60 2161 10 1143 0.005 0.53 LAG 56 +3.29 6.51 LAG 57 +3.19 −5.96 LAG 58 LAG 59 +3.27 −5.99 LAG 60 +3.16 −5.53 2787 10 1016 0.004 0.36 LAG 61 +3.18 −7.01 LAG 62 +3.19 −6.44 LAG 63 +3.23 −5.34 LAG 64 +3.21 −6.64 LAG 65 +3.23 −6.40 2686 17 1304 0.006 0.48 LAG 66 +3.26 −6.28 LAG 67 +3.16 −6.40 LAG 68 +3.03 −7.17 LAG 69 +2.70 −7.21 LAG 70 +2.88 −6.33 2605 23 1000 0.009 0.38 LAG 71 +3.06 −7.69 LAG 72 +2.56 −7.90 LAG 73 +2.82 −6.61 LAG 74 +2.90 −7.78 LAG 75 +2.72 −7.92 1537 55 1063 0.03 0.69 LAG 76 +2.39 −8.14 LAG 77 +2.52 −7.59 LAG 78 +5.76 −7.07 LAG 79 +2.15 −7.98 LAG 80 +1.78 −8.51 LAG 81 +1.80 −8.41 LAG 82 +1.71 −10.02 LAG 83 +1.55 −9.07 LAG 84 +2.15 −9.26 LAG 85 +2.15 −9.25 LAG 86 +1.85 −9.58

Sample ıC13PDB ıO18PDB

Saladeiro CO 46 C +2.87 −10.30 CO 46 D +4.59 −7.18 CO 46 E +4.38 −7.93 CO 46 F +4.47 −7.97 CO 46 G +4.61 −7.90 CO 46 I +5.10 −6.53 CO 46 J +3.93 −8.38 CO 46 K +4.35 −6.29 CO 46 L +2.02 −9.84 CO 46 M +3.66 −7.07 388 P.C. Boggiani et al. / Precambrian Research 182 (2010) 382–401

Table 1 (Continued )

Sample ıC13PDB ıO18PDB Sr (ppm) Mn (%) Fe (%) Mn/Sr Fe/Sr

Corcal Y-A 4.4 −6.8 2381 0.013 0.077 0.55 0.32 Y-B 2394 Y-C 3.8 −5.9 2525 0.004 0.045 0.15 0.18 Y-D 4.1 −7 2067 0.010 0.189 0.49 0.91 Y-E 3.2 −5 2625 0.005 0.042 0.21 0.16 Y-F 5.5 −4.2 2845 0.005 0.031 0.16 0.11 Y-G 5.2 −4.1 2409 0.004 0.049 0.16 0.20 Y-H 4.8 −7.3 2480 0.004 0.028 0.16 0.11 Y-I 2417 Y-J 5.6 −7.5 2151 0.004 0.028 0.18 0.13 Y-Ia 1859 Y-Jb 5.4 −6.4 2171 0.003 0.045 0.14 0.21 Y-Kc 2056 Y-L 2173 Y-M 5.1 −7.7 2668 0.005 0.042 0.17 0.16 Y-P 5.6 −5.8 3161 0.005 0.021 0.15 0.07 Y-Q 5.2 −8.3 2241 Y-R 5.1 −8.3 2464 Y-S 5.2 −9.2 1944 Y-T 1698 0.005 0.049 0.27 0.29 Y-U 5 −9.3 1749 0.005 0.059 0.27 0.34 Y-V 4.8 −9.6 1862 0.004 0.052 0.21 0.28 Y-Xa -0.3 −10.1 1777 0.131 0.496 7.37 2.79 Y-Z 685 Z-B 4.9 −8.8 1827 0.005 0.056 0.28 0.31 Z-C 4.4 −8.4 1557 Z-E 4.3 −4.4 2055 0.005 0.045 0.26 0.22 Z-G 3.8 −7.8 1421 Z-H 1705 Z-I 2210 Z-K 4.1 −7.6 2671 0.009 0.080 0.32 0.30 Z-L 4.6 −7.4 2510 Z-M 5.2 −6.7 2962 0.008 0.056 0.26 0.19 Z-O 5.3 −5.6 2632 Z-R 5.3 −7.1 2895 0.007 0.035 0.24 0.12 Z-S 3272 Z-T 4.6 −6.3 2421 Z-V 5 −6.9 2505 0.004 0.066 0.15 0.27 Z-X 2866 Z-Y 3.5 −6.3 2063 0.006 0.063 0.30 0.31

Sample ıC13PDB ıO18PDB

Baía das Garc¸ as Farm BG-01 +2.77 −6.67 BG-02 +3.31 −6.05 BG-03 +1.57 −3.64 BG-04 +3.21 −5.51 BG-05 BG-06 +3.64 −4.68 BG-07 +2.99 −5.86 BG-08 +3.37 −5.70 BG-09 +2.48 −6.52 BG-10 +1.50 −5.84 BG-11 +3.98 −5.13

Sample ıC13PDB ıO18PDB Sr (ppm) Mn (%) Fe (%) Mn/Sr Fe/Sr

Horii MH-04 2.5 −5 3792 0.002 0.017 0.04 0.05 MH-07 3.0 −4.6 2536 0.002 0.003 0.09 0.01 MH-12 1.9 −6.2 3669 0.002 0.007 0.04 0.02 MH-15 3.0 −3.9 4321 0.002 0.003 0.04 0.01 MH-17 2.8 −3.4 3067 MH-20 2.7 −3.9 2772 0.002 0.003 0.07 0.01 MH-32 3.0 −4.6 7383 0.003 0.017 0.04 0.02 MH-45 2.7 −4.3 3119 MH-49 3365 0.002 0.003 0.07 0.01 MH-50 2.8 −4.2 3286 MH-51 3.0 −4 3261 0.004 0.017 0.12 0.05 MH-52 3.0 −6.2 2603 MH-54 2.9 −4.2 2934 MH-58 3.0 −4.3 3524 0.002 0.003 0.04 0.01 MH-59 2.8 −3.9 3604 MH-65 2.9 −4.5 4110 0.002 0.003 0.05 0.01 MH-74 3.1 −3.4 3583 0.002 0.003 0.04 0.01 P.C. Boggiani et al. / Precambrian Research 182 (2010) 382–401 389

Table 1 (Continued )

Sample ıC13PDB ıO18PDB Sr (ppm) Mn (%) Fe (%) Mn/Sr Fe/Sr

MH-79 10,289 0.005 0.122 0.05 0.12 MH-86 3.0 −4.2 3180 0.002 0.014 0.07 0.04 MH-92 3.1 −4.5 2553 0.002 0.003 0.06 0.01

13 18 Sample ıC PDB ıO PDB SiO2 MnO Fe2O3 Calbon CALB-02 3.98 −1.93 CALB-03 3.65 −1.83 4.61 0.009 0.37 CALB-04 4.59 −2.36 CALB 5s 4.95 −3.24 3.16 0.017 0.29 CALB 5inf 4.88 −2.79 3.16 0.017 0.29 CALB-06 5.22 −3.65 CALB-07 4.32 −1.95 28.48 0.009 0.34 CALB-08 4.14 −1.03 CALB-11 3.65 −4.12 2.32 0.017 0.45 CALB-12 4.44 −1.54 CALB-15a −0.15 0.79 0.027 0.57 CALB-15b 5.06 −0.12 0.79 0.027 0.57 CALB-18 5.28 −0.62

an interpretation as dropstones (Gaucher and Poiré, 2009). How- Bocaina Formation (dolomite, chert, phosphorite), and granite- ever, slumped, convoluted siltstone beds were observed at the same gneiss basement blocks showing that before deposition of the level, and an origin related to gravitational processes cannot be Tamengo Formation, erosion of the Bocaina Formation and its base- ruled out (Boggiani et al., 2004). ment must have occurred, possibly related to a significant eustatic The Tamengo Formation is best exposed at active and aban- debasement. doned mines around Corumbá. However its greatest expression is In the western part of the mine, polymictic breccias are found in the Serra da Bodoquena, occurring either as cover on the covered by 43 m of wackestone and mudstone-marl rhythmites 13 Apa River Block in the west, or part of the thrust-and fold belt to (Figs. 3 and 10). Negative ı CVPDB values down to −3.5‰ were the east. found only in this package (20–30 m thick), which is not exposed in In previous works, deformed carbonates in the eastern por- the eastern part of the mine due to fault truncation. We could docu- tion of the Paraguay Belt, considered in this work as belonging to ment the upper part of this negative excursion especially well in the the Tamengo Formation, were assigned to the older Cuiabá Group “western Laginha base” section, showing a gradual increase from (Corrêa et al., 1979; Nogueira et al., 1978; Araújo et al., 1982), solely −3.5‰ to positive values (Table 1; Fig. 3, right column). Velásquez et because they are more deformed. al. (2008) report several negative ı13C values between −2 and −1‰ In the Corumbá region, stratigraphic sections were measured in from this interval as well. Up section, a marked black mudstone- the Laginha, Saladeiro and Corcal Mines. In the Serra da Bodoquena marl rhythmite package occurs, in which a crossover from negative sections were studied at Horii and Calbon mines and at Baía das to positive ı13C values of up to +5.5‰ is recorded (Fig. 3). At the top Garc¸ as Farm (Fig. 2). of the Tamengo Formation in the western Laginha section, a thick Sections around Corumbá (Laginha, Saladeiro, and Corcal Mines) and homogeneous package of wackstones with intercalated rud- present sedimentary facies typical of a moderately-deep shelf stones occurs, showing rather homogeneous ı13C values around between storm and fair-weather wave base. The sections in the +3‰ (Fig. 3). A gently declining trend between +3 and +2‰ is Serra da Bodoquena (Horii and Calbon Mines) were deposited in observed in this interval (Fig. 3; Velásquez et al., 2008), and is also deeper environments (Fig. 2). Cloudina and Corumbella were found evident in the high-resolution ı13C curve obtained in the eastern only in the Saladeiro and Corcal Mines in Corumbá, and not in the Laginha Mine (Fig. 4). deeper sections. Cloudina was probably associated with stroma- 87Sr/86Sr values of 0.7086 were obtained for limestones of the tolitic and thrombolitic reefs (cf. Grotzinger et al., 2000), which middle and upper Tamengo Formation at Laginha Mine (Boggiani, agrees well with the bathymetric distribution of these fossils in the 1998; Babinski et al., 2008a; Fig. 3). Corumbá Group, where they occur in the shallower sections and The contact of the Tamengo Formation with siltstones and shales are current-reworked. of the overlying Guaicurus Formation is conformable and irreg- ular. As mentioned above, diamictites comprising large blocks of 5. Carbon-isotope chemostratigraphy Tamengo limestones occur at the base of the Guaicurus Formation (Fig. 10), and were interpreted as originated by gravitational flows 5.1. Laginha Mine section (Boggiani et al., 2004) or as a result of glacioeustatic sea-level fall (Gaucher and Poiré, 2009). At Laginha Mine, located 16 km to the south of Corumbá city The occurrence of rare Cloudina and Corumbella fragments along the Campo Grande-Corumbá highway (BR-262), the entire has been mentioned for the Tamengo Formation at Laginha Tamengo Formation is exposed. The unit occurs there in the flank Mine in the package of rhythmite (mudstone-carbonaceous marl: of a syncline, bedding dipping 50–60◦ to the southeast (Fig. 10). Zaine, 1991) above the negative C-isotope excursion. Furthermore With the advance of mining operations, the presence of low- to E. corumbensis occurs at the base of the Guaicurus Formation high-angle reverse faults and duplex structures could be observed. (Gaucher, 2000; Gaucher et al., 2003). A Bavlinella-dominated The faults likely promoted layer duplication in the western side of acritarch assemblage characterizes the carbonaceous marls (Zaine, the mine (Fig. 4). Despite these faults, it is possible to reconstruct 1991; Gaucher et al., 2003), and is possibly related to high- the original stratigraphy, which shows at the base polymic- bioproductivity intervals (Gaucher, 2000; Velásquez et al., 2008). tic, carbonatic breccias. They are composed of centimeter- to A Leiosphaeridia–Soldadophycus acritarch assemblage, similar to decimeter-sized clasts of typical lithological types of the subjacent other late Ediacaran successions in SW Gondwana (Gaucher and 390 P.C. Boggiani et al. / Precambrian Research 182 (2010) 382–401

Fig. 3. Stratigraphic column and chemostratigraphic data of the Tamengo Formation in the western part of Laginha Mine. Left: whole section. Right: parallel, more detailed section showing mainly the base of the Tamengo Formation.

Sprechmann, 2009), occurs in the lower Guaicurus Formation The Corcal and Saladeiro sections are interpreted as deposited in (Gaucher et al., 2003). relatively shallow water, probably at storm wave level, and clearly shallower than the section at Laginha Mine. As mentioned above, 5.2. Saladeiro and Corcal Mine sections this explains the rarity of metazoan fossils in the latter section. At Saladeiro Mine ı13C values vary between +4 and +5‰ for most 87 86 The Saladeiro and Corcal Mines are located in the Corumbá of the section, decreasing to +2‰ at the top (Fig. 5). Sr/ Sr ratios escarpment, on the shore of the Rio Paraguay (Tamengo channel). of 0.7085 were reported from these outcrops by Boggiani (1998). At both sections the Tamengo Formation is less deformed, except The Corcal Mine section was surveyed in more detail. The values 13 for the presence of folds and flexures at Corcal Mine. The Saladeiro of ı C are remarkably invariant for most of the section, hovering 13 Mine is located to the east of Corcal Mine, nearby the Cimento around +5‰ (Fig. 6). Slightly lighter ı C values between +3 and Itaú plant. These exposures provided the best preserved and most +4‰ occur both at the base and top of the section (Fig. 6). Mea- 87 86 abundant Cloudina and Corumbella (e.g. Beurlen and Sommer, 1957; sured Sr/ Sr ratios range between 0.7084 and 0.7085 (Babinski Hahn et al., 1982; Hahn and Pflug, 1985; Zaine and Fairchild, 1987; et al., 2008a; Table 1). Although no diagnostic textures have Zaine, 1991; Gaucher et al., 2003). been observed in thin section, distinct fine-grained layers interca- Grainstones predominate at both sections, and are interbedded lated with the grainstones and marls were identified as volcanic with black mudstone and marls. The latter show a characteristic tuffs. These layers are calcretized, and euhedral zircons yielded 238 206 decoloration if weathered. Decimetric grainstone beds often dis- a weighted mean U/ Pb SHRIMP age of 543 ± 3Ma (n = 17; play low-angle cross-lamination, and at least in some cases they 95% confidence), which is interpreted as the depositional age of represent hummocky cross-stratification. Symmetrical (wave) rip- the upper Tamengo Formation (Babinski et al., 2008a). These beds, ples are common. Concentrations of Cloudina shells often show although they are not typical pyroclastic rocks, are probably the hummocky cross-stratification, especially at Corcal Mine, thus rep- result of volcanic ash deposition and local reworking by currents. resenting bioclastic storm deposits (tempestites; Gaucher et al., 2003). Corumbellla occurs in marls, with concentrations of whole 5.3. Baía das Garc¸ as Farm section specimens restricted to cm-thick beds. At Corcal Mine, the contact between the Tamengo Formation and the overlying Guaicurus For- In Serra da Bodoquena, to the west of Bonito town, a 100 m thick, mation (siltstones and shales) is well exposed, showing that the key stratigraphic section is exposed at Baía das Garc¸ as Farm. There, section corresponds to the top of the Tamengo Formation. basement gneisses and granites are overlain by gently-dipping, P.C. Boggiani et al. / Precambrian Research 182 (2010) 382–401 391

Fig. 4. Stratigraphic column and high-resolution chemostratigraphic data of the Tamengo Formation in the eastern part of Laginha Mine. The contact between the basal breccias and overlying carbonates is faulted, the lower Tamengo Formation is missing.

well-sorted, graded subarkoses of the Cerradinho Formation. A the Tamengo Formation and should be included in that unit. The fining- and thinning-, deepening-upward succession follows, com- values of ı13C obtained in this study for carbonates at the Baía das prising siltstones and intercalated sandstones (Boggiani, 1998; Garc¸ as section are all positive and mostly around +3‰ (n = 9), reach- Gaucher, 2000). Near the top of the Cerradinho Formation, green ing +4‰ (Fig. 7), thus reinforcing an assignment to the Tamengo siltstones are interbedded with marls and limestone beds. They Formation. Moreover, thrombolites have been recently identified pass up section into black grainstone showing hummocky cross- in these carbonates (Fig. 10), similar to other occurrences in the stratification (Fig. 10) and mudstones, previously assigned to the southern Paraguay Belt (Itapucumí Group). Cerradinho Formation (Boggiani, 1998). Gaucher (2000) argued A Bavlinella–Soldadophycus acritarch assemblage and the vendo- that these carbonates are lithologically identical to limestones of taenid V. antiqua were reported from green siltstones of the upper 392 P.C. Boggiani et al. / Precambrian Research 182 (2010) 382–401

Fig. 5. Stratigraphic column, chemo- and biostratigraphic data of the upper Tamengo Formation at Saladeiro Mine.

Cerradinho Formation (Gaucher et al., 2003). The microfossils occur then limestones at the Baía das Garc¸ as section actually repre- just at the boundary between the Cerradinho and Tamengo forma- sent the base of the latter unit, being older than the breccias tions. at the base of the Laginha Mine section (Fig. 3). This in turn An important question is whether the positive ı13C values means that a positive ı13C excursion to at least +4‰ separates obtained from the lower Tamengo Formation at Baía das Garc¸as the post-glacial negative excursion above the Puga Formation and Farm correlate with the positive peak in the middle Tamengo the negative excursion above the breccias of the lower Tamengo Formation at Laginha Mine and elsewhere (e.g. Fig. 3), or if Formation. The alternative would be to assign the positive ı13C they pre-date the negative excursion in the lower Tamengo For- values at the Baía das Garc¸ as section to the middle Tamengo mation. Gaucher (2000) argued that the contact between the positive excursion, implying that there is a hiatus between the Cerradinho and Tamengo formations is transitional, which is sup- Cerradinho and Tamengo Formations, because negative ı13C are ported by their similar acritarch assemblages (Gaucher et al., missing at that section. Interbedded siltstones and limestones sug- 2003). If a lateral equivalence between the Bocaina and part of gest, however, that the contact between both units is transitional. the Tamengo Formation is assumed (e.g. Gaucher et al., 2003), Pending future confirmation, we mantain as a working hypoth- P.C. Boggiani et al. / Precambrian Research 182 (2010) 382–401 393

Fig. 6. Stratigraphic column, bio- and chemostratigraphic data of the upper Tamengo Formation at Corcal Mine. The contact with shales of the overlying Guaicurus Formation is not shown. U-Pb SHRIMP zircon age from Babinski et al. (2008b). esis a concordant contact between the Cerradinho and Tamengo as normal. The structure is an open fold with axis striking N45E and formations. axis plunge 30◦ to the NE. Carbonates at the Horii Mine section are characterized by 5.4. Horii Mine section decimeter-to-metric layers of ooid grainstones, with sporadic cm- thick intercalations of gray to black marls and massive mudstones. In the fold-and-thrust belt domain of the southern Paraguay The contact with shales of the Guaicurus Formation is not exposed Belt, the Tamengo Formation is exposed at Horii Mine, in the north- in the mine, and no metazoan fossils were found in this section. ern part of the Serra da Bodoquena (Figs. 1 and 2), nearby the town C-isotope values are very homogeneous and around +3‰ for the of Bodoquena. Although the succession there is affected by a thrust whole section (Fig. 8). 87Sr/86Sr ratios are fairly constant between fault, deformation is low and the polarity of the strata is interpreted 0.7083 and 0.7085 (Babinski et al., 2008a, Table 1).

Fig. 7. Stratigraphic column and chemostratigraphic data of the lower Tamengo Formation at Baía das Garc¸ as Farm. 394 P.C. Boggiani et al. / Precambrian Research 182 (2010) 382–401

Fig. 8. Stratigraphic column and chemostratigraphic data of the upper Tamengo Formation at Horii Mine, previously considered part of the Cuiabá Group and here assigned to the Corumbá Group. The contact with shales of the overlying Guaicurus Formation is not shown. P.C. Boggiani et al. / Precambrian Research 182 (2010) 382–401 395

Fig. 9. Stratigraphic column and chemostratigraphic data of the upper Tamengo Formation at Calbon Mine, where carbonates were previously assigned to the Cuiabá Group.

In the available geological maps of the area (Corrêa et al., 1979; Samples are recrystallized and partly silicified, but cathodolu- Araújo et al., 1982), these limestones are assigned to the Cuiabá minescence and petrographic analyses allowed extracting the least Group. However, the petrographic, faciological and – especially – altered portions with a millimetric drill for C and O isotope analysis. the chemostratigraphic features allow interpreting them as distal The values of ı13C are quite homogeneous, ranging between +3.7 facies of the Tamengo Formation, possibly of its upper part. As we and +5.3‰, thus similar to part of the Tamengo Formation. Cor- 18 will show below, carbonates exposed at Calbon Mine, further to the responding ı OVPDB values are quite heavy, between −0.12 and east, probably represent even a deeper water environment. −4.1‰. This may be interpreted as due to alteration, but because MnO values are less than 0.050%, the possibility of alteration is 5.5. Calbon Mine section rendered unlikely. Dolostones usually exhibit heavier ı18O ratios due to the fractionation factor between dolomite and co-existing In the more deformed part of the southern Paraguay Belt, meta- calcite, which has been determined as 2.6‰ (Vasconcelos et al., dolostones crop out which were mapped as part of the Cuiabá 2005). This factor largely explains the offset of ı18O values between Group, but their sedimentological and isotopic features allow limestones and dolostones of the Tamengo Formation. assigning them to the Tamengo Formation (i.e. Corumbá Group). Thus, on the basis of litho- and chemostratigraphy, we assign Representative exposures of these carbonates occur at Calbon carbonates exposed at Calbon Mine to the Tamengo Formation, Mine, nearby Miranda (Fig. 1). In this location, bedding strikes N20E representing a distal, deep-water setting. and dip 20◦ to the SE. A 23 m section was surveyed with sample collection at intervals of 1m (Fig. 9). 6. Discussion In the lower part, dolomitic mudstone and grainstone intercala- tions occur, passing up section into graphitic-phyllites. Dolomites 6.1. Nature of isotopic signals exhibit plane-parallel lamination, and sedimentary structures indicative of shallow water were not observed. Under the pet- The primary nature of ␦13C and 87Sr/86Sr values presented here rographic microscope, carbonates appear strongly deformed and is supported by the following facts: recrystallized, as observed in the field. Despite recrystallization, the original lamination is preserved, in spite of some tectonic stretch- (1) Mn/Sr values vary between 0.04 and 0.55 for limestones of ing. Besides deformation, a high amount of quartz and organic the Tamengo Formation (Table 1), thus within the “unaltered” matter in some samples was verified. Quartz has been remobilized field (Marshall, 1992; Jacobsen and Kaufman, 1999). Dolostones and precipitated as lenses concordant with foliation. yielded higher Mn/Sr ratios, of up to 7.4 (Table 1), but this is due 396 P.C. Boggiani et al. / Precambrian Research 182 (2010) 382–401

Fig. 10. Photographs of representative lithologic types and sedimentary structures of the Corumbá Group.(a) Columnar stromatolites of the Bocaina Formation at Porto Morrinhos, in the vicinity of cap carbonates of the Morro do Puga (length of pen: 10 cm). (b) Stromatolitic “tubestones” at the same locality as the previous; (c) Carbonate breccia with abundant phosphate clasts (black) at the base of the Tamengo Formation at Laginha Mine. (d) Contact between the basal breccias (left) and overlying rhythmites (carbonaceous marl-calcisiltite) of the lower Tamengo Formation, Laginha Mine. (e) Ash bed intercalated with limestones of the upper Tamengo Formation at Cor- cal Mine (length of pen: 10 cm). (f) Laginha diamictite at the base of the Guaicurus Formation, with limestone lonestones derived from the Tamengo Formation. (g) Hummocky P.C. Boggiani et al. / Precambrian Research 182 (2010) 382–401 397

to dolomite accepting more Mn and less Sr in the lattice, and graphic context of the upper Tamengo ash bed is consistent with a does not imply higher post-depositional alteration (Kah et al., 543 ± 3 Ma depositional age. In the Nama Group, U-Pb TIMS zircon 1999; Gaucher et al., 2007). ages of 543 ± 1 Ma and 545 ± 1 Ma for ash beds occurring within (2) Sr concentrations in limestones are high, between 685 and the upper part of the latest Ediacaran positive ı13C plateau were 10,300 ppm (Table 1), suggesting an aragonitic precursor. reported (Fig. 11; Grotzinger et al., 1995, 2000). Two negative (3) The values of ı18O in limestones are higher than −10‰ for the excursions in the Nama Group are, respectively, immediately above great majority of samples (all except 5 samples, Table 1), which and considerably below an ash bed dated U-Pb TIMS on zircon at is generally considered as the boundary between altered and 549 ± 1Ma(Fig. 11), showing that at least 6 Myr separated the neg- unaltered limestones (Marshall, 1992; Jacobsen and Kaufman, ative ı13C excursion from the upper part of the positive plateau 1999). (543 ± 1 Ma). Likewise, in southern China, the end of the last Edi- (4) Biomarker (hopanes, steranes, gammacerane) and Rock Eval acaran negative excursion is constrained by a U-Pb TIMS zircon age pyrolysis data from the Tamengo Formation (Velásquez et al., of 551 ± 0.7 Ma (Fig. 11; Condon et al., 2005; Zhou and Xiao, 2007). 2008), suggest that the degree of thermal alteration is low. Therefore, the time elapsed between the lower Tamengo negative excursion and the Tamengo-Guaicurus boundary can be estimated Thus, the C-isotope curves from the Tamengo Formation likely between 6 and 8 Myr, which implies reasonable sedimentation represent secular variations of coeval seawater values, and can be rates of 17–13 m/Myr, comparable to other ancient carbonate plat- compared to other successions worldwide. forms (Tucker and Wright, 1990). In the following we attempt to correlate the Corumbá Group, 6.2. Chemostratigraphic correlation and the global ı13C curve and the Tamengo Formation in particular, to other successions worldwide. Maybe the most ubiquitous chemostratigraphic feature Chemostratigraphic data support the hypothesis that many car- ocurring in the measured sections of the Tamengo Formation is the 13 bonate occurrences in the more deformed Paraguay Belt are in fact positive ı C plateau at the top of the unit. It is geochronologi- distal, deeper water carbonates belonging to the Tamengo Forma- cally constrained by both the occurrence of Cloudina and a U-Pb tion and not to the Cuiabá Group. SHRIMP zircon age of 543 ± 3 Ma at its top (Fig. 11). Exactly the C-isotope secular variations in the different sections of the same relationships are observed in the Schwarzrand Subgroup of Corumbá Group allow identifying the following chemostrati- the Nama Group (Namibia, Grotzinger et al., 1995; Germs et al., graphic features (Fig. 11): 2009), the upper Nafun and lower Ara groups in Oman (Amthor et al., 2003) and the Dengying Formation in southern China (Zhou and (1) A ubiquitous feature in the upper Tamengo Formation is rep- Xiao, 2007). According to the data from southern China, the plateau ı13 ± resented by a positive ı13C plateau around +3 to +5‰, gently starts with a positive C excursion at 551.1 0.7 Ma (Condon et decreasing toward the contact with the overlying Guaicurus al., 2005; Zhou and Xiao, 2007; Sawaki et al., 2010), located at Formation. This positive interval is associated with all known the boundary between the Doushantuo and overlying Dengying ı13 occurrences of Cloudina and Corumbella (e.g. Figs. 5 and 6). formations (Fig. 11). The high-resolution C curve obtained for (2) Below the previous plateau, a sharp ı13C positive excursion the eastern Laginha Mine (Fig. 4) is almost identical to the curve to >+5‰ is recorded at both sections in the Laginha Mine reported for the Dengying Formation. (Figs. 3 and 4). The curve at the eastern Laginha Mine is punctuated by lower ı13 (3) Also at Laginha Mine, a negative ı13C excursion to −3.5‰ char- C values (+1‰) separating the lower positive excursion (>+5‰) acterizes carbonates at the base of the Tamengo Formation from the overlying plateau (Fig. 4). This feature, which is not appar- overlying polymictic breccias and related to a regression fol- ent in the Chinese sections, is well recorded both in the Nama Group lowed by a subsequent transgression (Fig. 3). This feature was (Kuibis-Schwarzrand boundary) and at the boundary between the not found in the other sections studied, but the latter are incom- Nafun and Ara groups in Oman (Grotzinger et al., 1995, 2000; plete and do not show the base of the Tamengo Formation. Amthor et al., 2003; Fig. 11). In the Nama Group, this minor nega- (4) Boggiani (1998) reported positive ı13C values for dolostones tive excursion is associated to evidence of at least local glaciation of the Bocaina Formation immediately beneath the breccias of (Germs, 1995; Germs et al., 2009), and has been recently correlated the lower Tamengo Formation (Boggiani, 1998). Limestones of to karstification in coeval carbonates in the Saldania Belt (Praekelt the lower Tamengo Formation at Baía das Garc¸ as section also et al., 2008). yielded positive values (Fig. 7). We envisage that this positive A positive excursion to >+5‰ is recorded in the middle Tamengo ı13C excursion (up to +4‰) pre-dates the breccias and its asso- Formation. A similar positive excursion to ca. +5‰ is well con- ciated negative anomaly of the lower Tamengo Formation. strained in the Nama Group by an ash bed in its upper section dated ± (5) Negative ı13C values down to −5‰ characterize cap carbonates U-Pb TIMS on zircon at 549 1Ma(Grotzinger et al., 1995; Fig. 11). overlying the arguably glaciogenic Puga Formation in its type In Oman, an age of ca. 547 Ma has been reported for the positive area (Boggiani et al., 2003; Fig. 11). excursion of the Buah Group (Bowring et al., 2007), thus within error of the ages from the Nama Group. In China, a positive excur- sion to +5‰ in the lower Dengying Formation (EP3: Fig. 11) begins The reported U-Pb SHRIMP age of 543 Ma for an ash bed at the level of an ash bed dated U-Pb at 551.1 ± 0.7 Ma (Condon et al., occurring at the top of the positive ı13C plateau in the Tamengo 2005; Zhou and Xiao, 2007; Sawaki et al., 2010). Therefore, we sug- Formation, near the contact to the overlying Guaicurus Formation gest that the positive excursion of the middle Tamengo Formation (Babinski et al., 2008a; Fig. 11), deserves some consideration here. reflect a global event between 551 and ca. 548 Ma. In Oman, ash beds dated by U-Pb TIMS at 542 ± 0.3 Ma occur within Bearing the above correlations in mind, it follows that the neg- the negative ı13C Ediacaran–Cambrian boundary anomaly, which ative excursion in the lower Tamengo Formation matches (a) the immediately overlies a ı13C positive plateau and Cloudina-bearing negative excursion EN3 in the upper Doushantuo Formation (Zhou carbonates (Fig. 11; Amthor et al., 2003; Bowring et al., 2007). The and Xiao, 2007; Sawaki et al., 2010), (b) the negative excursion at most parsimonious explanation is that the bio- and chemostrati-

cross-stratification in calcarenites of the lower Tamengo Formation, Baía das Garc¸ as Farm. (h) Sheet-like thrombolites interbedded with calcarenites, lower Tamengo Formation, Baía das Garc¸ as Farm. Note clotted fabric. Length of scale: 8 cm. 398 P.C. Boggiani et al. / Precambrian Research 182 (2010) 382–401

Fig. 11. Composite ı13C curve of the Corumbá Group and corresponding 87Sr/86Sr, biostratigraphic and radiochronological data, and comparison to other coeval successions worldwide. Sources of data: (1) Gaucher et al. (2004, 2009c and references therein), Blanco et al. (2009), Oyhantc¸ abal et al. (2009), (2) Grotzinger et al. (1995, 2000), Fölling and Frimmel (2002), (3) this work, Gaucher et al. (2003); (4) Zhou and Xiao (2007), Condon et al. (2005); (5) Brasier et al. (2000), Amthor et al. (2003), Bowring et al., 2007. Abbreviations: (1) BN: Barriga Negra, CSF: Cerros San Francisco, CV: Cerro Victoria; (2) P.Nolloth: Port Nolloth Group, Nu.: Numees Formation, Ho.: Holgat Formation; (4) Zhuiaq.: Zhujiaqing Formation, Zh.: Zhongyicun Member.

the base of the Kuibis Subgroup (Saylor et al., 1998; Grotzinger et al., mation (unit B: Gaucher et al., 2004, 2009c) matches the negative 2000), and (c) the Shuram negative excursion of the Nafun Group excursion associated with carbonates overlying the breccias in in Oman (Brasier et al., 2000; Le Guerroué and Cozzi, 2010; Fig. 11). the lower Tamengo Formation. In both cases, a sea-level fall The Shuram negative anomaly, however, is more pronounced than and reworking of shelf sediments followed by renewed flood- the lower Tamengo negative excursion, the former reaching ı13C ing is evidenced, which has been related to glacioeustasy during values as low as −12‰ (e.g. Brasier et al., 2000; Le Guerroué et al., a non-global glaciation (Gaucher et al., 2004, 2009c; Gaucher 2006). However, this has been interpreted by Bristow and Kennedy and Poiré, 2009). Above this negative excursion, a positive ı13C (2008) as a local or diagenetic signal. Isotopic and geochemical data interval characterizes the upper Polanco Formation (Fig. 11), reported by Le Guerroué and Cozzi (2010) may be interpreted as and could be related to the positive ı13C values characteristic suggesting that ı13C values below −6‰ are diagenetically altered. of the upper Tamengo Formation. Interestingly, Cloudina occurs In the lower Nama Group, ı13C values do not drop below −5‰ beneath and within the negative excursion that characterizes unit (Grotzinger et al., 2000), similar to the lower Tamengo Formation B of the Polanco Formation (Gaucher and Sprechmann, 1999; (Fig. 11). Gaucher et al., 2003, 2009c; Gaucher and Germs, 2009), thus strati- The positive excursion recorded at the Baía das Garc¸ as section graphically lower than in the Tamengo Formation. This may be (Fig. 7), here assigned to the lower Tamengo Formation and thought more related to preservational factors rather than to evolutionary to pre-date the negative excursion found at Laginha Mine, matches trends. similar values in member III of the Doushantuo Formation (Zhou It is worth noting that, despite their geographical proximity, and Xiao, 2007; Sawaki et al., 2010; Fig. 11). ı13C curves obtained in the northern Paraguay Belt (Araras Group; The ı13C curve obtained for the Corumbá Group can be com- Alvarenga et al., 2004, 2009; Nogueira et al., 2007; Riccomini et pared to other Ediacaran successions in South America. The Arroyo al., 2007) differ markedly from that of the southern Paraguay Belt. del Soldado Group, deposited on the eastern margin of the Río de The Araras Group is possibly older than the Corumbá Group, as sug- la Plata Craton, shows a similar ı13C curve (Gaucher et al., 2004, gested by a Pb-Pb carbonate age of 633 ± 25 Ma for the lower Araras 2009c; Fig. 11), as already noted by Gaucher et al. (2003). The pos- Group (Alvarenga et al., 2009). itive ı13C excursion that characterizes the transition between the As mentioned above, a marked sea-level fall followed by siliciclastic Yerbal Formation and carbonates of the Polanco For- renewed transgression associated with a ı13C negative excursion mation parallels the lower Tamengo positive excursion (Fig. 11). is evidenced in the lower Tamengo Formation. The occurrence of The significant ı13C negative excursion in the lower Polanco For- clasts from the subjacent Bocaina Formation, and even granite- P.C. Boggiani et al. / Precambrian Research 182 (2010) 382–401 399 gneiss basement clasts, may be associated with considerable Alvarenga, C.J.S.de, Trompette, R., 1992. Glacially influenced sedimentation in the eustatic sea-level fall (e.g. Gaucher and Poiré, 2009). An alternative later Proterozoic of the Paraguay Belt (Mato Grosso, Brazil). Palaeogeography, Palaeoclimatology, Palaeoecology 92, 85–105. explanation can be related to the transition from rift to drift, which Alvarenga, C.J.S.de, Moura, C.A.V., Gorayeb, P.S.S., Abreu, F.A.M., 2000. Paraguay would make this regression-transgression a local phenomenon. and Araguaia Belts. In: Cordani, U.G., Milani, E.J., Thomaz Filho, A., Campos, However, the fact that the same regression is recorded in the Arroyo D.A. (Eds.), Tectonic Evolution of South America, 31st International Geological Congress. Rio de Janeiro, pp. 183–193. del Soldado and Sierras Bayas groups (Gaucher and Poiré, 2009), Alvarenga, C.J.S.de, Santos, R.V., Dantas, E.L., 2004. C–O–Sr isotopic stratigraphy of presently 2000–3000 km to the south, suggests that it is not just a cap carbonates overlying Marinoan-age glacial diamictites in the Paraguay Belt, local feature. Brazil. Precambrian Research 131, 1–21. Alvarenga, C.J.S.de, Figueiredo, M.F., Babinski, M., Pinho, F.E.C., 2007. Glacial diamic- tites of Serra Azul Formation (Ediacaran, Paraguay Belt): evidence of the Gaskiers 7. Conclusions glacial event in Brazil. Journal of South American Earth Science 23, 236–241. Alvarenga, C.J.S.de, Boggiani, P.C., Babinski, M., Dardenne, M.A., Figueiredo, M.F., The Tamengo Formation, and consequently the Corumbá Group, Santos, R.V., Dantas, E.L., 2009. The Amazonian Palaeocontinent. In: Gaucher, C., Sial, A.N., Halverson, G.P., Frimmel, H.E. (Eds.), Neoproterozoic–Cambrian crops out over an area larger than previously accepted. Several car- Tectonics, Global Change and Evolution: A Focus on Southwestern Gondwana. bonate occurrences, formerly assigned to the Cuiabá Group, are Developments in Precambrian Geology, vol. 16. Elsevier, pp. 15–28. here considered distal facies of the Tamengo Formation. Two exam- Alvarenga, C.J.S.de, Boggiani, P.C., Babinski, M., Dardenne, M.A., Figueiredo, M.F., San- ı13 tos, R.V., Sial, A.N., in press. Carbonates of the Araras and Corumbá groups in the ples are the Calbon and Horii Mines, which yielded C values Paraguay belt, Brazil. In: Arnaud, E., Shields, G., Halverson, G.P. (Eds.), Geolog- 87 86 between +2 and +5‰ VPDB and Sr/ Sr ratios between 0.7083 ical Record of Neoproterozoic Glaciations. Journal of the Geological Society of and 0.7085, typical for the upper Tamengo Formation. Limestones London, Memoir. Amthor, J.E., Grotzinger, J.P., Schröder, S., Bowring, S.A., Ramezani, J., Martin, overlying the Cerradinho Formation at Baía das Garc¸ as Farm are M.W., Matter, A., 2003. Extinction of Cloudina and Namacalathus at the assigned to the base of the Tamengo Formation, recording a posi- Precambrian–Cambrian boundary in Oman. Geology 31, 431–434. tive ı13C excursion to +4‰ VPDB. Up section, breccias in the lower Araújo, H.J.T.de, Santos Neto, A.dos, Trindade, C.A.H., Pinto, J.C.deA., Montalvão, Tamengo Formation record a significant regression followed by R.M.G.de, Dourado, T.D.deC., Palmeira, R.C.deB., Tassinari, C.C.G., 1982. Folha SF- 21 – Campo Grande, 1 – Geologia. Projeto RADAMBRASIL, Rio de Janeiro 28, 13 subsequent transgression, associated with negative ı C values 9–124. down to −3.5‰. The upper Tamengo Formation is characterized Avila Salinas, W.A., 1992. El magmatismo Cámbrico-Ordovícico en Bolivia. In: by a positive ı13C excursion to +5‰ VPDB, followed by a plateau Gutierrez-Marco, J.G., Saavedra, J., Rabano, I. (Eds.), Paleozoico Inferior de Iberoamérica. Universidad de Extremadura, Mérida, pp. 241–253. 87 86 at +3‰. Corresponding Sr/ Sr ratios vary between 0.7084 and Babcock, L.E., Grunow, A.M., Sadowski, G.R., Leslie, S.A., 2005. Corumbella,an 0.7086. An ash bed near the top of the positive plateau yielded a U- Ediacaran-grade organism from the Late Neoproterozoic of Brazil. Palaeogeog- Pb zircon age of 543 ± 3 Ma, which is consistent with similar ages raphy, Palaeoclimatology, Palaeoecology 220, 7–18. Babinski, M., Boggiani, P.C., Fanning, C.M., Fairchild, T.R., Simon, C.M., Sial, A.N., from Namibia and Oman for this interval. 2008a. U-PB SHRIMP geochronology and isotope chemostratigraphy (C, O, Sr) of The integrated calibration of the Ediacaran carbon-isotope the Tamengo Formation, Southern Paraguay Belt, Brazil. In: VI South American curve allows identifying a more complex scenario than previously Symposium on Isotope Geology, Book of Abstracts, San Carlos de Bariloche, p. 160. accepted by most compilations. Following the Gaskiers glaciation at Babinski, M., Fanning, C.M., Trindade, R.I.F., Boggiani, P.C., 2008b. U-Pb SHRIMP ages 583 Ma, three negative excursions have been identified, one ending from the Neoproterozoic southern Paraguay Belt: constraining the depositional at ca. 551 Ma (Shuram–Wonoka anomaly), a second at ca. 547 Ma age and sediment provenance of glaciogenic deposits. In: 4th SHRIMP Workshop, Abstract Volume, Saint Petersburg, pp. 19–21. separating the Kuibis and Schwarzrand subgroups in the Nama Babinski, M., Trindade, R.I.F., Alvarenga, C.J.S., Boggiani, P.C., Liu, D., Santos, R.V., Brito Group and the third at the Ediacaran–Cambrian boundary. The two Neves, B.B., 2006. Chronology of Neoproterozoic ice ages in Central Brazil. In: V. older negative excursions are probably recorded in the Tamengo South American Symposium on Isotope Geology, Short Papers, Punta del Este, Formation. These negative excursions are–at least in part- related pp. 223–226. Berrangé, J.P., Litherland, M., 1982. Sinopsis de la geología y potencial de minerales to glacial events, possibly of high-latitude and not global nature. el área del Proyecto Precámbrico – Proyeto de Exploracion Mineral del Oriente The most parsimonious interpretation for sedimentary breccias Boliviano. Fase I e II: 1976–1983, Informe no 21, 120 pp. occurring in the lower Tamengo Formation is a glacioeustatic sea- Beurlen, K., Sommer, F.W., 1957. Observac¸ ões estratigráficas e paleontológicas sobre o calcário Corumbá. Boletim Divisão Geologia e Mineralogia – DNPM 168, 1–47. level fall, as also postulated for correlative strata in the Arroyo del Blanco, G., Rajesh, H.M., Gaucher, C., Germs, G.J.B., Chemale Jr., F., 2009. Provenance Soldado Group (Uruguay), but a tectonic interpretation cannot be of the Arroyo del Soldado Group (Ediacaran to Cambrian, Uruguay): implications completely ruled out. for the paleogeographic evolution of southwestern Gondwana. Precambrian Research 171, 57–73. Boggiani, P.C., 1998. Análise estratigráfica da Bacia Corumbá (Neoproterozoico)- Acknowledgements Mato Grosso do Sul. Ph.D. Thesis, Universidade de São Paulo, Brazil, pp. 1–181. Boggiani, P.C., Coimbra, A.M., 1996. The Corumbá Group (Central South America) in the context of Late Neoproterozoic global changes. Anais da Academia Brasileira This work was supported by FAPESP (Proc. 04/01233-0 granted de Ciências. Resumo das Comunicac¸ ões 68 (4), 595–596. to PCB and Proc. 06/58688-1 to MB), by VITAE (B11487/10B003) Boggiani, P.C., Gaucher, C., 2004. Cloudina from the Itapucumi Group (Vendian, granted to VPF, and by PROSUL/CNPq (AC-38) granted to ANS. This is Paraguay): age and correlations. 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