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The -Early Record in Southwest 20

Claudio Gaucher

Abstract 20.1 Introduction A review of the Ediacaran-Early Cambrian fossil record in SW Gondwana is presented. Organic-walled microfossils SW-Gondwana includes several sedimentary successions of (acritarchs) reported from the region can be assigned for predominantly Late Ediacaran age (Figs. 20.1 and 20.2), fl the most part to the Late Ediacaran Leiosphere Palyno ora which preserve a rich fossil record. Early studies of these (LELP), with only a few occurrences of lower Ediacaran include in southern Africa the reports by Gürich acritarchs. So far, complex acanthomorphs (ECAP assem- (1930, 1933) of vendobionts (, ), which blage) are absent in fossil-bearing units of lower to were some of the first descriptions of Ediacaran soft-bodied mid-Ediacaran age, which may be the result of an adverse fossils. paleoclimate. The Ediacara soft-bodied biota is best In South America, Beurlen and Sommer (1957) described recorded in the , with occurrences recently the first skeletal fossils from rocks, although reported in South America. Biostratigraphically, they were assigned a Cambrian age. Later, Germs (1972a, b) soft-bodied fossils are best assigned to the latest Ediacaran erected the Cloudina and accepted a Neoproterozoic Nama Association. Ediacaran shelly fossils are wide- age for the fossils, representing the first Precambrian skeletal spread in SW Gondwana, including biostratigraphically fossils to be described worldwide. relevant genera such as Cloudina, , Corum- This chapter deals with the latest advances in Ediacaran bella and Titanotheca. The only group with a record and in southwestern Gond- – across the Ediacaran Cambrian boundary are trace fossils. wana. Four main fossil groups will be dealt with: acritarchs, Whereas simple, mostly bedding-parallel burrows and the Ediacara soft-bodied biota, skeletonized metazoans and “ ” biomat structures occur in Ediacaran matgrounds, , and trace fossils. Ediacaran-Early Cambrian meta- diverse vertical bioturbations characterize Early Cambrian phytes (vendotaenids) also occur in SW Gondwana, but “ ” mixgrounds. Ediacaran fossils can be useful for bios- because of the paucity of their record the reader is directed to tratigraphy. The early and Mid-Ediacaran are best zoned the few studies dealing with these fossils (Grant et al. 1991; using acritarchs, the Late Ediacaran with shelly fossils and Gaucher et al. 2003; Cohen et al. 2009). the Ediacaran–Cambrian boundary can be determined using trace fossils. Biostratigraphy, in turn, enables the correlation of distant sedimentary successions, which may 20.2 Acritarchs have paleogeographic implications. Ediacaran paleobio- geography, on the other hand, is hampered by the Ediacaran acritarchs (i.e., organic-walled microfossils of cosmopolitan of most taxa found in SW Gondwana. uncertain affinity) were first described in SW Gondwana from the Nama Group in (Germs 1972b; Germs et al. Keywords 1986) and from the Sierras Bayas Group in (Pothe Acritarchs Á Shelly fossils Á Ediacara biota de Baldis et al. 1983; Cingolani et al. 1991; Fig. 20.2). Á Biostratigraphy Acritarchs were thereafter reported for other units in the region (Figs. 20.1 and 20.2), such as the Corumbá Group in C. Gaucher (&) í Facultad de Ciencias, Instituto de Ciencias Geológicas, SW Brazil (Zaine 1991; Gaucher et al. 2003), the Bambu Universidad de La República, Iguá 4225, 11400 Montevideo, Group in central Brazil (Fairchild et al. 1996;Sánchez, Uruguay 2010), the Arroyo del Soldado Group in Uruguay (Gaucher e-mail: [email protected]

© Springer International Publishing AG, part of Springer Nature 2018 543 S. Siegesmund et al. (eds.), Geology of Southwest Gondwana, Regional Geology Reviews, https://doi.org/10.1007/978-3-319-68920-3_20 544 C. Gaucher

Fig. 20.1 Fossiliferous Ediacaran units indicated on a pre-drift Belt. Ediacaran fossiliferous units are indicated in italics: ASG Arroyo reassembly of Gondwana, modified after Porada (1989). PP Parana- del Soldado Group (and Las Ventanas Formation); BG Bambuí Group; panema ; RPC Río de la Plata Craton; SFC São Francisco CCG Cango Caves and Gamtoos groups; CG Corumbá Group; IG Craton. Red areas: Neoproterozoic to Early belts. Itapucumí Group; MG Mulden Group; NG Nama Group; OG Otavi (1) Western , (2) Eastern Sierras Pampeanas, Group; PF ; SBG Sierras Bayas and La (3) Southern Paraguay Belt, (4) Northern Paraguay Belt, (5) Tandilia Providencia groups; U&JB Ubajara and Jaibaras groups. Rectangle: System, (6) Saldania Belt, (7) Gariep Belt, (8) Damara Belt, (9) Kaoko see detail in Fig. 20.2 Belt, (10) Ribeira Belt, (11) Aracuaí Belt, (12) Lufilian Belt, (13) Zambezi et al. 1996, 1998, 2003, 2004; Gaucher 2000, 2014; Gaucher Early Cambrian acritarchs have not been found in SW and Poiré 2009), the Eleutério-Pico de Itapeva and Pouso Gondwana because the sparse sedimentary record of that age Alegre basins (SE Brazil; Teixeira and Gaucher 2004), the is either continental or very shallow marine, such as the Holgat Formation in Namibia (Gaucher et al. 2005b) and the upper Nama Group (Germs 1995) and the upper Arroyo del Cango Caves and Gamtoos groups in the Saldania Belt, Soldado Group (Sprechmann et al. 2004). Early Cambrian South Africa (Gaucher and Germs 2006). of the Puncoviscana Formation in NW Argentina More recently, acritarchs were described for the Las were deposited in deeper settings, but so far no acritarchs Ventanas Formation in Uruguay (Blanco and Gaucher 2005; have been found in these strata. Gaucher et al. 2008a), the Otavi and Mulden groups in Biostratigraphically, almost all of the known occurrences Namibia (Germs et al. 2009), the Alicia Formation of the La belong to the “Kotlin-Rovno” assemblage of Vidal and Providencia Group in Argentina (Poiré et al. 2010; Arrouy Moczydłowska-Vidal (1997), synonymous with the Late et al. 2015) and the Frecheirinha Formation of the Ubajara Ediacaran Leiosphere Palynoflora (LELP) of Gaucher and Group, NE Brazil (Chiglino et al. 2015; Fig. 20.1). Sprechmann (2009). 20 The Ediacaran-Early Cambrian Fossil Record … 545

Fig. 20.2 Map showing the location of fossiliferous Ediacaran units dealt with in this work, modified after Gaucher et al. (2005b) 546 C. Gaucher

The low-diversity LELP assemblage is dominated by Interestingly, no occurrences of morphologically complex small (<150 lm) and predominantly thin-walled Leio- acanthomorphs belonging to the ECAP have been found so sphaeridia (Fig. 20.3c), Bavlinella faveolata (Fig. 20.3d, e), far in SW Gondwana. The ECAP is recorded in Australia colonial microfossils of the genus Soldadophycus (Grey 2005), Baltica (Vorob’eva et al. 2009), in the upper (Fig. 20.3f), small (<20 lm) acanthomorphs of the genus Doushantuo Formation in China (McFadden et al. 2008; Liu Asteridium (=Micrhystridium) and large sphaeromorphs of et al. 2013; Fig. 20.4) and in (Moczydłowska 2005), the genus Chuaria (Germs et al. 1986; Steiner 1994). and it probably represents a relatively short period, possibly The LELP represents a depauperate assemblage which between the Gaskiers Glaciation (580 Ma; Pu et al. 2016) characterizes the last 20 myr of the Neoproterozoic (c. 560– and c. 560 Ma. This entire period is characterized by posi- 541 Ma), just before the Cambrian Explosion. It follows an tive d13C values known in the as EP2 that wiped out the diverse acritarchs of the excursion (Liu et al. 2013; Fig. 20.4). Ediacaran Complex Acanthomorph Palynoflora (ECAP; Deposition of the succession of the Las Ventanas Grey et al. 2003; Grey 2005). Between 75 and 90% of Formation in Uruguay is radiometrically constrained by the species became extinct during this event (Vidal and U–Pb SHRIMP method between 590 ± 2 Ma for basalts at Moczydłowska-Vidal 1997; Knoll et al. 2006), which may its (Mallmann et al. 2007) and 573 ± 11 Ma for vol- have been caused by eutrophication and the exclusion canoclastics at its top (Oyhantçabal et al. 2009). Glaciogenic of eukaryotic plankton by massive cyanobacterial blooms diamictites occur near the base of the unit and were assigned (e.g., Bavlinella faveolata blooms; Gaucher and Sprechmann to the Gaskiers Glaciation (Gaucher et al. 2008a). Thus the 2009). Las Ventanas Formation encompasses the time period in

Fig. 20.3 Ediacaran acritarchs from SW Gondwana. a Leiosphaeridia Yerbal Formation, Arroyo del Soldado Group (Gaucher 2000). tenuissima, large specimen from the Villa Mónica Formation, Sierras e Bavlinella faveolata, Kombuis Member, Cango Caves Group Bayas Group (Gaucher et al. 2005a). b Leiosphaeridia tenuissima, Las (Gaucher and Germs 2006). f Soldadophycus bossii,a Ventanas Formation (Gaucher et al. 2008a). c Leiosphaeridia minutis- saucer-shaped attached to a smaller, sphaeroidal colony. sima, two attached carbonized specimens from the Alicia Formation, Yerbal Formation (Arroyo del Soldado Group; Gaucher et al. 2004). La Providencia Group. d Bavlinella faveolata, thin section from the White scale bars represent 10 lm and black scale bars 50 lm 20 The Ediacaran-Early Cambrian Fossil Record … 547

Fig. 20.4 Correlation chart between different Ediacaran-Cambrian Tandilia: C. Lar Cerro Largo; Olav. Olavarría; L. Negra Loma Negra. successions in SW Gonwdana with South China as a reference, Arroyo del Soldado Group: BN Barriga Negra; CSF Cerros San showing biostratigraphic, radiochronological and chemostrati- Francisco; CV Cerro Victoria. Namibia: P. Nolloth: Port Nolloth Group; graphic data (modified from Boggiani et al. 2010 and references Nu. Numees Formation; Ho. Holgat Formation. South China: Zhuiaq. therein). Recalculated U–Pb ages for the Nama Group (Smith et al. Zhujiaqing Formation; Zh. Zhongyicun Member; ECAP Ediacaran 2017 and references therein). Biostratigraphic data: see text. Complex Acanthomorph Palynoflora which the ECAP dominated. However, acritarchs reported from the upper third of the unit are mostly leiosphaerids 20.3 Ediacara Soft-Bodied Biota (Blanco and Gaucher 2005; Gaucher et al. 2008a; Gaucher and Poiré 2009; Fig. 20.3b), albeit significantly larger (up to Soft-bodied were first described from the Nama 400 lm) than those characteristic of Late Ediacaran assem- Group by Gürich (1930, 1933). Thereafter, a number of blages (LELP). Why complex acanthomorphs are missing researchers expanded our knowledge of these remarkable from the Las Ventanas Formation remains to be explained. fossils (e.g., Richter 1955;Pflug 1966, 1970, 1972; Germs Large leiosphaerids were also described from shales of 1973a, b, 1995). These studies and more recent work have the Villa Mónica and Cerro Largo formations (lower Sierras shown that the Nama Group hosts one of the most remark- Bayas Group, Argentina), including Leiosphaeridia tenus- able Ediacara biota Lagerstätten worldwide. For a compre- sima up to 450 lm in diameter (Gaucher et al. 2005a; hensive bibliographical review of the Ediacara biota in Fig. 20.3a). A diamictite (Colombo Diamictite) occurs Namibia, the reader is referred to McCall (2006). between both occurrences and has been interpreted as being The Nama Group hosts the youngest of the three correlative to the Las Ventanas Formation (Fig. 20.4), and assemblages (547–541 Ma; Grotzinger et al. 1995; Nar- thus Gaskiers in age (Rapalini et al. 2013; Gaucher 2014). It bonne et al. 1995; Smith et al. 2017) so far recognized in the could be argued in this case that the relatively short-lived Ediacara biota: the Avalon, White Sea and Nama Associa- ECAP assemblage may coincide with the basal erosional tions (Waggoner 2003;Laflamme et al. 2013). The Nama of the Cerro Largo Formation. Association occurs in both the Kuibis and Schwarzrand 548 C. Gaucher subgroups, three-dimensionally preserved within (Leonov 2007). Interestingly, Nemiana simplex also occurs beds (Fig. 20.5a), which for the most part represent tem- in the lower Nama Group, originally described as the species pestites (storm deposits). The best-known Lagerstätten are Hagenetta aarensis (Hahn and Pflug 1988) and later rein- in the -arenites of the Kliphoek Member, Dabis For- terpreted as Nemiana simplex (Grazhdankin and Seilacher mation (Kuibis Subgroup), such as the world-class Aar Farm 2005; Leonov 2007; Ivantsov et al. 2014). An Ediacaran age occurrence. for the Puncoviscana fossils is consistent with U–Pb detrital The preservation is unusual for soft-bodied organisms, zircon ages from the host (Adams et al. 2011). and it prompted Seilacher (1984) to propose the “quilted air Barroso et al. (2014) reported the occurrence of mattress” model, which means that the organisms had a soft-bodied Ediacaran macrofossils in sandstones of the relatively compact shape but a large surface area. The high Jaibaras Group in NE Brazil (Ceará State; Fig. 20.1). Both surface/volume ratio points to a metabolism dependent on discs and fronds were described, including Cyclomedusa, interactions across the tegument, such as respiration, nutrient Ediacaria, Medusinites and , most of them uptake and excretion (Seilacher 2007). Apart from a few represented by a single specimen each. Barroso et al. (2014) examples of fossils belonging to known metazoan phylla also figured one specimen of , which has been (e.g., the mollusk Kimberella Fedonkin and Waggoner 1997 interpreted as a mollusk (Fedonkin and Waggoner 1997). or the Palaeophragmodictya Gehling Barroso et al. (2014) assign the fossils to the White Sea and Rigby 1996), the Ediacara biota represents a failed Association of Waggoner (2003), which is in accordance experiment of evolution, or as Seilacher (2007) put it, with a Late Edaicaran age for the Jaibaras Group, as indi- “strange as life on another planet, but easier to reach.” Sei- cated by acritarchs and Sr isotope ratios of the underlying lacher (1992) proposed the (-level?) Vendo- carbonates (see Chiglino et al. 2015). bionta, which currently continues to encompass all Ediacara More recently, Arrouy et al. (2016) have reported the soft-bodied fossils that cannot be assigned to known phyla. occurrence of discoid fossils with radial grooves and circular In the Nama Group, two groups of vendobionts occur: structures at their center in the Cerro Negro Formation (La those that grew by serial quilting (addition of “segments”) Providencia Group), which they classify as Aspidella and the more remarkable fractal vendobionts. Among the sp. (Fig. 20.5e, f). The diameter of the discs is typically serial vendobionts, Pteridinium (Fig. 20.5a, b), , between 1 and 2.5 cm, but some “giant” specimens exceed Namalia and occur in the Nama Group (e.g., 15 cm. The fossils occur in the underside of fine-grained, Grazhdankin and Seilacher 2002). Rangea, on the other tempestitic sandstone beds intercalated with reddish silt- hand, grew by means of fractal quilting (Narbonne 2004; stones (Arrouy et al. 2016). Interestingly, the discs are Grazhdankin and Seilacher 2005), unlike any other known associated with wrinkle structures (microbially induced organism outside the Vendobionta. Discoidal soft-bodied ), a characteristic feature that has been fossils assigned to Aspidella sp. have been described from compared to a “microbial death mask” (Gehling 1999). The the Schwarzrand Subgroup in the Zaris sub-basin (Darroch age of the Cerro Negro Formation is considered latest Edi- et al. 2016). acaran on the basis of the occurrence of the LELP acritarch In South Africa (southern Cape Province), an assemblage and also because of Cloudina preserved in Ediacara-type soft-bodied fossil occurs in the Groenefontein underlying of the Loma Negra Formation (Gau- Formation of the Cango Caves Group (Praekelt et al. 2008) cher et al. 2005a; Fig. 20.4). but it is still under study (G.J.B. Germs, pers. comm. 2017). Other possible occurrences of Ediacaran soft-bodied Beltanelloides has been found in the Groenefontein and Huis macrofossils in South America are the Itajaí and Camaquã Rivier formations of the Cango Caves Group, and microbial basins in southern Brazil (Fig. 20.2). In the Itajaí Basin, mats and enigmatic discoidal fossils (Aspidella?) throughout Zucatti-da-Rosa (2006) described Cyclomedusa and the unit (G.J.B. Germs, pers. comm.). Charniodiscus, Aspidella sp. and Parvancorina sp. from the In South America the Ediacara soft-bodied biota was Itajaí Group (Fig. 20.2). The depositional age of the conspicuously absent until very recently. Aceñolaza and fossil-bearing beds has been constrained by U–Pb zircon Aceñolaza (2007) described discoidal to bulbous fossils ages between 563 ± 3 Ma and 549 ± 4 Ma (Guadagnin from the latest Ediacaran Puncoviscana Formation at Pur- et al. 2010), which is in agreement with the known range of mamarca () and assigned them to Beltanel- the Ediacara soft-bodied biota. However, the poor preser- loides sp. (Fig. 20.5c, d). Aceñolaza et al. (2009) and vation of the fossils and lack of more detailed studies Aceñolaza (2012) reassigned the material to Nemiana sim- demand more work to confirm this occurrence (Netto 2012). plex. The fossils are preserved as positive hyporelief, range The same can be said for Aspidella sp. described from the in diameter between 0.9 and 2.5 cm and often show a cir- Camaquã Supergroup (Netto 2012; Fig. 20.2). cular structure (opening?) near their center (Fig. 20.5d). The A different type of Ediacaran soft-bodied fossil are discs resemble the type material from Ukraine and Russia tubular (vermiform) fossils best known from the Dengying 20 The Ediacaran-Early Cambrian Fossil Record … 549

Fig. 20.5 Ediacaran soft-bodied fossils. a Pteridinium, Kliphoek Puncoviscana Formation at Purmamarca. Note circular structure Member, Kuibis Subgroup (Nama Group) at Farm Plateau. b Pteri- near the center in specimens in d, as well as the considerable relief. dinium carolinaense, youngest occurrence of the genus in the e, f Aspidella sp. from the Cerro Negro Formation (La Providencia Spitzkopf Member, upper Schwarzrand Subgroup at Farm Swart- Group) at El Polvorín Quarry, showing radial grooves and circular punt (see Narbonne et al. 1997). c, d Nemiana simplex from the structures at the center. Scale in b, e and f is 8 cm

Formation in South China (Fig. 20.4), such as Gaojiashania represent multiple phyla and even multiple kingdoms. They (Cai et al. 2013), Shaanxilithes (Meyer et al. 2012) and inhabit an important transition from the latest Ediacaran to Wutubus (Chen et al. 2014). Therefore these fossils form part the early Cambrian (Schiffbauer et al. 2016). Tubular of the latest Ediacaran Nama Assemblage, and probably organisms co-existed with erniettomorphs for at least the last 550 C. Gaucher

Fig. 20.6 Ediacaran fossils with a carbonate shell. a Namacalathus Formation, Corumbá Group (polished slab). f Cloudina riemkeae,Kuibis hermanastes, Omkyk Member, Nama Group at Farm Zwartmodder. Subgroup. Nama Group, both longitudinal and cross-sections (Germs b Namacalathus hermanastes, in thrombolitic carbonates of the et al. 2009). g Cloudina hartmannae, longitudinal sections, Nama Itapucumí Group, Paraguay. c Namacalathus hermanastes,Itapucumí Group. h, i Corumbella werneri, from marl of the Tamengo Formation, Group, two attached specimens. d Cloudina lucianoi,Itapucumí Corumbá Group. Note flexibility in h and considerable relief and Group. Note cone in cone structure. e Cloudina lucianoi,Tamengo longitudinal ridge in i Scale bars equal 1 cm, except for f (1 mm) 20 The Ediacaran-Early Cambrian Fossil Record … 551

6 Ma of the Ediacaran period from about 547 Ma until mineralized, reaching 1 m in size. rietoogensis 541 Ma (Smith et al. 2017). The disappearance of this cos- has been reported from Driedoornvlakte carbonates mopolitan assemblage may represent the first (Kuibis Subgroup, Omkyk Member), associated with Phanerozoic-style mass extinction (Smith et al. 2017). thrombolite and (Wood et al. 2002). The Soft-bodied tubular fossils assigned to Shaanxilithes have colonies are made up of tubules of polygonal or labyrinthine been reported from the Schwarzrand Subgroup of the Nama cross-section, and the outer habit of the colony is domal, Group (Darroch et al. 2016). Gaojiashania, in turn, has been columnar or sheet-like. A cnidarian affinity related to tabu- reported from the c. 547 Ma Hoogland Member of the late corals is probable (Wood et al. 2002; Gaucher and Kuibis Subgroup (Smith et al. 2017). The tubular fossil Germs 2009), which would make Namapoikia the oldest Archaeichnium occurs in the c. 545 Ma Nasep and Huns corals in the Earth’s history. Members of the Schwarzrand Subgroup (GJB Germs, pers. Also in southern Africa, Titanotheca has been reported by comm.). The Buchholzbrunnichnus (Germs Gaucher et al. (2005b) from the upper Port Nolloth Group 1973b) is now considered to represent a tubular fossil (Holgat Formation) of southern Namibia. As will be resembling Gaojiashania (GJB Germs, pers. comm.). In explained below, Titanotheca is characterized by an agglu- South America, Corumbella could be considered to be a tinated and has been assigned to the Foraminiferida tubular fossil but, as will be explained below, it has been (Gaucher and Sprechmann 1999). related to either the cloudinids or the conularids. The greatest diversity of Ediacaran skeletal fossils of SW-Gondwana—unlike other fossil groups—is found on the South American side. The genus Cloudina occurs in bio- 20.4 Skeletonized Metazoans and Protists clastic calcarenites of the Corumbá Group (Brazil). It is in fact another species, Cloudina lucianoi (Beurlen and Som- Ediacaran skeletonized metazoans are probably the most mer; Zaine and Fairchild 1985), which has a size-frequency promising group of fossils for late Neoproterozoic bios- distribution intermediate between C. hartmannae and C. tratigraphy. SW Gondwana has an unmatched diversity and riemkeae (Gaucher et al. 2003; Fig. 20.6e). Along with abundance of these fossils, which was first recognized by the Cloudina, the species Corumbella werneri (Hahn et al. pioneering work of Germs (1972a), who created the genus 1982) occurs in marls of the Tamengo Formation (Corumbá Cloudina and postulated a Late Neoproterozoic age for the Group; Fig. 20.6h, i). The fossils were long considered to be fossils. An earlier report by Beurlen and Sommer (1957) soft-bodied and possibly related to the . However, recognized the same fossils in the Corumbá Group in Brazil, more recent work has shown that they were lightly miner- but they were assigned to the Cambrian genus Aulophycus. alized with (Warren et al. 2012; Pacheco The Nama Group hosts abundant calcified fossils, which et al. 2015). Whereas a group of researchers has postulated a in some cases form real coquinas, the oldest in Earth history. conularian affinity for Corumbella (Babcock et al. 2005; Van Cloudina is represented by two species, which differ essen- Iten et al. 2014; Pacheco et al. 2015), another group cur- tially in their size: the larger C. hartmannae (Fig. 20.6g) and rently favors a cloudinid affinity (Walde et al. 2015). Finally, the smaller C. riemkeae (Germs 1972a; Fig. 20.6f). Cloudina Titanotheca coimbrae has also been described from phos- has since been reported from all continents, including phorites of the Bocaina Formation in the Corumbá Group, Antarctica. Grant (1990) recognized the biostratigraphic c. 150 m stratigraphically below the first Cloudina occur- importance of the genus as an index fossil, and Gaucher and rences (Gaucher et al. 2003; Fig. 20.4). Germs (2009) formally proposed the Cloudina Range Zone. So far the most abundant and well-preserved Ediacaran The biological affinities of Cloudina are still debated but its shelly fossils in South America have been described from the most likely that its modern analogs are , possibly Itapucumí Group, which represents the southward extension serpulids (Germs 1972a; Hua et al. 2005). of the Corumbá Group into Paraguay. Cloudina lucianoi was Another common metazoan in the Nama first reported by Boggiani and Gaucher (2004; Fig. 20.6d). Group is Namacalathus hermanastes (Grotzinger et al. An association of Cloudina lucianoi and Corumbella wer- 2000). The species occurs, along with Cloudina, associated neri occurs in thrombolitic facies, much like in the Nama with thrombolite reefs, and it accounts for more than 75% of Group (Warren et al. 2011). As in the latter unit, Namaca- specimens there (Grotzinger et al. 2000). Namacalathus is lathus hermanastes also occurs in the thrombolitic facies characterized by a hollow stem attached to a spheroidal cup (Warren et al. 2017; Fig. 20.6b, c), although it is relatively with openings, whose distribution exhibits radial symmetry less abundant than in the Nama Group. (Fig. 20.6a). This, along with its sessile mode of life, sug- The most diverse shelly fossils in the whole of SW gests phylogenetic affinities with anthozoan cnidarians. Gondwana possibly occur in the Arroyo del Soldado Group The last skeletonized fossil to be found in the Nama in Uruguay. An assemblage of skeletal fossils, the Yerbal Group is at the same time the largest and more heavily biota, occurs in the homonymous Yerbal Formation 552 C. Gaucher

(Gaucher and Sprechmann 1999) and also in the overlying (Brazil). (c) Titanotheca coimbrae has been reported from limestones of the Polanco Formation (Gaucher and Poiré the late Neoproterozoic Pico de Itapeva and Cajamar basins 2009). It includes Cloudina riemkeae, which occurs in life in SE Brazil, and Cloudina cf. C. riemkeae from the cor- position (perpendicular to bedding) in siltstones of the relative Eleutério basin (Teixeira and Gaucher 2004). Yerbal Formation, or disarticulated in limestones of the Polanco Formation (Gaucher and Sprechmann 1999; Gau- cher 2000, 2014; Gaucher and Poiré 2009). In both cases the 20.5 Trace Fossils shells are replaced by hematite or silica. Apart from Cloudina, the Yerbal biota also includes Trace fossils are the only fossils in SW Gondwana with a abundant Titanotheca coimbrae, a foraminifer with a record across the Ediacaran–Cambrian boundary. made up of agglutinated rutile grains (Gaucher and In the Nama Group, trace fossils occur throughout the Sprechmann 1999; Gaucher and Germs 2009; Fig. 20.7a–c), succession. Ediacaran trace fossils of the Kuibis and lower much like present-day Bathysiphon (Lowenstam and Weiner Schwarzrand subgroups are sparse, small, mostly 1989). The fossils show reproduction by budding and often bedding-parallel and of low diversity (Germs 1972c; Crimes occur in groups, denoting a gregarious life mode (Gaucher and Germs 1982; Aceñolaza et al. 2009; Germs et al. 2009; and Poiré 2009). The advantage of a rutile could Fig. 20.8c). Streptichnus narbonnei, a complex trace fossil be related to its impervious nature against predators, which similar to pedum (=Phycodes pedum), has been could penetrate Cloudina shells and were extant in the Late described by Jensen and Runnegar (2005) from the upper- Ediacaran (e.g., Hua et al. 2003). The species Waltheria most Urusis Formation (middle Schwarzrand Group). In the marburgensis is also abundant in siltstones of the upper Nomtsas Formation (uppermost Schwarzrand Subgroup) and Yerbal Formation, and possibly had a phosphatic shell in the River subgroup, the species Treptichnus pedum (Gaucher and Sprechmann 1999). It is characterized by a occurs (Germs 1972c; Crimes and Germs 1982; Geyer 2005; multilayered, septate, rigid skeleton, which often shows Germs et al. 2009 and references therein; Fig. 20.4), which branching and reaches 1 cm in length (Gaucher 2000, 2014; indicates an early Cambrian age (Brasier et al. 1994)in Gaucher and Poiré 2009; Fig. 20.7d, e). It occurs in life accordance with U–Pb ages of interbedded ash beds and position or reworked as thin shell beds (Gaucher and Germs detrital zircons (Grotzinger et al. 1995; Blanco et al. 2011). 2009). Vertical traces, such as , appear in these units, Two other genera of skeletal fossils were described from although they were also described with doubts from the the Yerbal Formation: Soldadotubulus, which resembles Ediacaran portion of the Nama Group (Germs et al. 2009). Waltheria, and the genus Palaeodiscus (Gaucher and Other ichnogenera occurring in the upper Nama Group Sprechmann 1999; Gaucher 2000). In both cases the fossils include Trichophycus, Paleophycus, Gordia and Enig- are preserved as steinkerns and nothing can be said about the matichnus (Crimes and Germs 1982; Geyer 2005; Aceñolaza original composition of the shell. et al. 2009 and references therein; Germs et al. 2009). A sixth, still unnamed, species of shelly fossil occurs in In the correlative Vanrhynsdorp Group in South Africa, a the middle Yerbal Formation, some 1100 m stratigraphically similar pattern is observed. Simple, horizontal traces such as below the first Cloudina occurrence (Gaucher and Poiré , Helminthopsis and Helminthoidichnites occur in 2009). It occurs in large numbers, current-reworked on the Kwanous and lower Knersvlakte subgroups (Fig. 20.8b), bedding planes, and reaches 3 cm in length. Its shape is lower Vanrhynsdorp Group (Aceñolaza et al. 2009 and conical to tubular and it exhibits deeply stacked cones but references therein). Oldhamia geniculata has been reported differs from Cloudina in that the cones share the same apex from the middle Knersvlakte Subgroup, marking the low- (Fig. 20.7f). It is solitary, branched and arranged in X- or ermost occurrence of Cambrian trace fossils in the Van- star-shaped clusters. The fossils show Burgess -type rhynsdorp Group (Gresse 1992; Aceñolaza et al. 2009). reservation of the shell walls, which are replaced by cha- Treptichnus pedum occurs in subtidal to intertidal facies of mosite and sericite (Fig. 20.7f). Ongoing work is attempting the upper Knersvlakte and Brandkop subgroups (Buatois to reconstruct the morphology by means of digital tomog- et al. 2012). raphy (Gaucher et al. 2016). At the South American side, the Puncoviscana Formation Other occurrences of Ediacaran shelly fossils in sedi- in NW Argentina is the Ediacaran-Cambrian unit with the mentary successions in SW Gondwana include the follow- most diverse trace fossil record. Two assemblages were ing: (1) Cloudina cf. C. riemkeae occurs in limestones of the recognized—the Oldhamia and ichnoassociations Loma Negra Formation of the Sierras Bayas Group, —but the relative age of each association is difficult to Argentina (Gaucher et al. 2005a). (b) Warren et al. (2014) determine owing to the complex, multiphase deformation described Cloudina sp. and fragments assigned to Corum- that affected the unit (Aceñolaza and Toselli 2009). Both bella from the Sete Lagoas Formation, lower Bambuí Group assemblages are Early Cambrian in age, as indicated by 20 The Ediacaran-Early Cambrian Fossil Record … 553

Fig. 20.7 Other Ediacaran shelly fossils from pelites of the Yerbal thin section of holotype showing (1) initial sphaerical chamber and Formation, Arroyo del Soldado Group (Uruguay). a Titanotheca coim- (2) small branch (Gaucher and Sprechmann 1999). e Waltheria brae, paratype, SEM image (Gaucher and Sprechmann 1999). b Titan- marburgensis on bedding plane, showing two larger, septated, hema- otheca coimbrae, bilocular specimen in thin section, showing tized specimens. f Thin section of branched, tubular fossils with deeply (1) septum and (2) pore between chambers (Gaucher and Sprechmann nested cones and walls replaced by chamosite (Gaucher 2014). White 1999). c Same as previous with cross nicols. d Waltheria marburgensis, scale bars represent 0.1 mm and black scale bars 1 mm 554 C. Gaucher

Fig. 20.8 Ediacaran and Early Cambrian trace fossils. a Biomat the collection of INSUGEO, Tucumán, Argentina). e Helminthoraphe desiccation structures, Las Aguilas Formation, Sierras Bayas Group at isp., Puncoviscana Formation (INSUGEO collection). f Cochlichnus Taglioretti Quarry. b Planolites isp. from the Besonderheid Forma- isp., Puncoviscana Formation (INSUGEO collection). g Nereites salt- tion, middle Vanrhynsdorp Group. c Planolites isp. in of ensis (holotype at INSUGEO collection), Puncoviscana Formation. the Spitzkopf Member, upper Schwarzrand Subgroup at Swartpunt h Thalassinoides isp. boxworks, Puncoviscana Formation near San Farm. d Oldhamia radiata, Puncoviscana Formation (specimen from Antonio de los Cobres. Except for a and h, the scale is 8 cm 20 The Ediacaran-Early Cambrian Fossil Record … 555 detrital zircon age data (Adams et al. 2011). The Oldhamia upper Camaquã Supergroup, on the other hand, hosts a more assemblage comprises six Oldhamia ichnospecies (O. alata, diverse trace fossil assemblage. Netto (2012) described O. antiqua, O. curvata, O. flabellata, O. geniculata and O. Arthraria antiquata, Bergaueria hemispherica, Cochlichnus, radiata; Fig. 20.8d), Monomorphichnus lineatus, Palaeophycus, Planolites and so far undetermined treptich- Monomorphichnus isp., Dimorphichnus, Cochlichnus nid burrows. Microbially induced sedimentary structures, anguineus (Fig. 20.8f), Nereites, Helmintoidichnites tenuis, such as and Kinneya-type structures, are also Didymaulichnus lyelli and Thalassinoides isp. (Fig. 20.8h; quite common (Netto 2012). Aceñolaza and Aceñolaza 2005, 2007; Aceñolaza et al. 2009). The more diverse Nereites association includes Nereites saltensis (Fig. 20.8g), meandering burrows 20.6 Biostratigraphy and Paleogeography assigned to Helminthopsis spp. and Helminthoraphe sp. (Fig. 20.8e), Treptichnus, Monomorphichnus, Cochlich- 20.6.1 Biostratigraphy nus, Didymaulichnus, , Glockerichnus, Dimor- phichnus, Asaphoidichnus and Tasmanadia (Aceñolaza and One interesting pattern observed in SW Gondwana is the Aceñolaza 2005, 2007; Aceñolaza et al. 2009 and references abundance of Ediacaran, and especially Late Ediacaran, therein). fossils. Apart from acritarchs of the Otavi Group (Germs The ichnoassociations of the Puncoviscana Formation et al. 2009), Early Ediacaran and Cryogenian fossils are occur as northeast-trending belts and have been used to almost absent in SW Gondwana. divide the otherwise lithologically monotonous unit. In the Maieberg Formation (lower Otavi Group), the Whereas the Oldhamia association occurs in the west in polygonomorph acritarch Octoedryxium truncatum occurs in deeper facies, the Nereites association occurs in the east in marls of the Maieberg Formation, 170 m stratigraphically shallower depositional environments. Thus it is not yet clear above the contact with glacial diamictites of the Ghaub if the different assemblages respond to different ages or Formation (Gaucher and Germs 2007; Germs et al. 2009), merely to facies/paleoenvironmental control (Aceñolaza and which has been dated at 635 ± 1 Ma by Hoffmann et al. Aceñolaza 2005; Aceñolaza et al. 2009). (2004). The Maieberg Formation is comparable in age to the In stromatolitic carbonates of the uppermost Arroyo del lower Doushantuo Formation in China, which yielded large Soldado Group (Cerro Victoria Formation, Fig. 20.4), large and complex acanthomorphs of the Tianzhushania spinosa Thalassinoides boxworks were described by Sprechmann assemblage (Liu et al. 2013; Fig. 20.4). More work is et al. (2004). Gyrolithes and Palaeophycus also occur, and required to establish whether this assemblage is also repre- all traces show concretionary growth by silica. Thalassi- sented in the upper Otavi Group. noides of the Cerro Victoria Formation is similar in its large Complex acanthomorphic acritarchs of the ECAP size to the same ichnogenus from the Puncoviscana For- assemblage are so far absent in SW Gondwana. This is quite mation, and also resembles large, carbonate-facies Tha- puzzling because microfossil-bearing rocks of the same age lassinoides from the late Cambrian La Flecha and La Silla (580–570 Ma) occur in the Las Ventanas Formation in formations (e.g., Sial et al. 2008; Gaucher and Poiré 2009). Uruguay (Fig. 20.4) but these yielded only large leiso- The Sierras Bayas and La Providencia groups in Argen- phaerids. Paleoenvironmental, including paleoclimatic, fac- tina, on the other hand, mainly preserve Ediacaran trace tors may have played a role. Whereas the environments fossils. Apart from well-preserved biomat desiccation represented in the Las Ventanas Formation are glacial to structures (Fig. 20.8a; Porada and Bouougri 2008), cold, as indicated by sedimentary structures and the Chem- Helminthopsis has been reported from the Loma Negra ical Index of Alteration (Gaucher et al. 2008a; Blanco and Formation (Gaucher and Poiré 2009 and references therein). Gaucher 2014), the classical localities of ECAP acritarchs Bilobed burrows assigned to Archaeonassa, and Arumberia (South China, Australia, Siberia) occur in successions biomat strucures were reported by Arrouy et al. (2016) from deposited in tropical settings (Li et al. 2013). the Cerro Negro Formation. A similar assemblage of Shelly fossils are the most promising group from a Archaeonassa and Palaeophycus was reported by Warren biostratigraphic point of view. Apart from the et al. (2014) from the Sete Lagoas Formation of the Bambuí well-established, latest Ediacaran Cloudina Range Zone and Group (Brazil). associated taxa (Namacalathus, Corumbella; Fig. 20.4), Finally, Ediacaran trace fossils also occur in the Itajaí other taxa may prove useful as index fossils. So far the first Group and Camaquã Supergroup in southern Brazil appearance of Titanotheca coimbrae always occurs well (Fig. 20.2). In the Itajaí Group, horizontal, meandering beneath the first appearance of Cloudina (Fig. 20.4; Gaucher burrows were described by Zucatti-da-Rosa (2006) and and Germs 2009), and both species overlap at least in the assigned to Helminthoidichnites isp. The late Ediacaran Arroyo del Soldado Group for a few hundred meters of the (568–549 Ma; de Oliveira et al. 2014) Santa Bárbara Group, section (Gaucher and Sprechmann 1999). 556 C. Gaucher

Biostratigraphically, the Ediacaran–Cambrian boundary and São Francisco in the west and in the Río has been established in SW Gondwana only with the use of Apa/Amazonia and Laurentian cratons in the east according trace fossils. The “agronomic revolution” that occurred at the to the proposed reconstructions (Warren et al. 2014; Arrouy boundary, owing to which the Precambrian matgrounds were et al. 2016). The discipline of Ediacaran paleobiogeography irreversibly succeeded by Phanerozoic mixgrounds (Sei- is clearly still in its infancy. lacher 1999), is well represented in several units in the region. Recently described vermiform fossils may prove Acknowledgements This contribution is dedicated to the memory of useful in establishing the Ediacaran–Cambrian boundary as the late Peter Sprechmann (1938–2017), a pioneer of Precambrian well (Schiffbauer et al. 2016). paleontology in South America, professor, colleague and long-time friend. An earlier draft of the chapter was significantly improved thanks In summary, it can be stated that—biostratigraphically— to comments and data provided by Gerard Germs, to whom I am deeply the Early and Mid-Ediacaran are best zonated using acri- indebted. Thanks go to the book editors, Siegfried Siegesmund, Miguel tarchs, the Late Ediacaran with shelly fossils and the Edi- Basei and Pedro Oyhantçabal, for inviting me to write this contribution acaran–Cambrian boundary can be identified using trace and for their patience. Support from the Polo de Desarrollo Universi- tario “Geología y Recursos Minerales” (CURE-Universidad de la fossils. República) is gratefully acknowledged.

20.6.2 Paleogeography References

The question arises as to whether the fossil record can aid Aceñolaza FG (2012) of the Ediacaran-early Cambrian the complex paleogeographic reconstructions of the assem- transition in northwestern Argentina and related areas. Revue de bly of SW Gondwana. Paléobiologie, 11:299–309 ñ ñ ó Biostratigraphy can surely contribute to our understand- Ace olaza G, Ace olaza FG (2005) La Formaci n Puncoviscana y unidades estratigráficas vinculadas en el Neoproterozoico-Cámbrico ing of regional paleogeography by enabling the correlation temprano del Noroeste Argentino. Lat Am J Basin Anal between different successions. As an example, the Sierras 12(2):65–87 Bayas, Arroyo del Soldado, Itapucumí and Corumbá groups Aceñolaza G, Aceñolaza FG (2007) Insights in the Neoproterozoic– (Figs. 20.1 and 20.2) have many genera and species in early Cambrian transition of NW Argentina: facies, environments and fossils in the proto-margin of western Gondwana. In: common, such as Cloudina and a low-diversity acritarch Vickers_Rich P, Komarower P (eds) The Rise and Fall of the palynoflora (LELP assemblage). Their lithostratigraphy is , vol 286. Geological Society of London Special very similar (Fig. 20.4), with interbedded carbonates and Publication, The Geological Society, London, pp 1–13 siliciclastics, which reflect their deposition in a passive Aceñolaza FG, Toselli A (2009) The Pampean Orogen: Ediacaran-lower Cambrian evolutionary history of Central and margin setting. Gaucher et al. (2003, 2005a, 2008b) Northwest region of Argentina. In: Gaucher C, Sial AN, Halver- proposed that all these units were deposited in the same son GP, Frimmel HE (eds) Neoproterozoic-Cambrian tectonics, platform, which opened to the east and southeast and which global change and evolution: a focus on southwestern Gondwana. they named the Corumbá-Arroyo del Soldado-Sierras Bayas Developments in Precambrian Geology, vol 16. Elsevier, Amster- dam, pp 239–254 shelf (Gaucher et al. 2008b, 2009). Closure of the shelf took Aceñolaza GF, Germs GJB, Aceñolaza FG (2009) Trace fossils and the place in the basal Cambrian around 540–530 Ma (e.g., Agronomic Revolution at the Neoproterozoic-Cambrian transition Gaucher et al. 2008b; McGee et al. 2015) at the end of the in southwest Gondwana. In: Gaucher C, Sial AN, Halverson GP, Brasiliano-Pan African Cycle. Frimmel HE (eds) Neoproterozoic-Cambrian tectonics, global change and evolution: a focus on southwestern Gondwana. A few studies have also suggested that Ediacaran fossils Developments in Precambrian Geology, vol 16. Elsevier, Amster- could be used for paleobiogeographic reconstructions in SW dam, pp 339–347 Gondwana, specifically in support of the existence of the Adams CJ, Miller H, Aceñolaza FG, Toselli AJ, Griffin WL (2011) The Clymene Ocean (e.g., Warren et al. 2014; Arrouy et al. Pacific Gondwana margin in the late Neoproterozoic–early Paleo- zoic: detrital zircon U–Pb ages from metasediments in northwest 2016). However, it seems premature to use the Ediacaran Argentina reveal their maximum age, provenance and tectonic fossil record in SW Gondwana for paleobiogeographic setting. Gondwana Res 19:71–83 reconstructions. Most of the taxa, such as Cloudina, are Arrouy MJ, Poiré DG, Gómez Peral LE, Canalicchio JM (2015) cosmopolitan and have a global distribution, which could be Sedimentología y estratigrafía del Grupo La Providencia (nom. nov.): cubierta superior neoproterozoica, Sistema de Tandilia, explained by these organisms having planktonic larvae. In Argentina. Lat Am J Sediment Basin Anal 22(2):171–189 other cases, such as acritarchs, the organisms themselves Arrouy MJ, Warren LV, Quaglio F, Poiré DG, Simões MG, Rosa MB, were planktonic. Thus their occurrence alone cannot be used Gómez Peral LE (2016) Ediacaran discs from South America: to delimitate different biogeographical provinces. It should probable soft-bodied macrofossils unlock the paleogeography of the Clymene Ocean. Sci Rep 6:30590 be asked why similar benthic assemblages, such as the Babcock LE, Grunow AM, Sadowski GR, Leslie SA (2005) Corum- Cloudina-Namacalathus-Corumbella skeletal assemblage, bella, an Ediacaran-grade organism from the late Neoproterozoic of occur on both sides of the Clymene Ocean, in the Kalahari Brazil. Palaeogeogr Palaeoclimatol Palaeoecol 220:7–18 20 The Ediacaran-Early Cambrian Fossil Record … 557

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