Pecoits et al. (Reports, 29 June 2012, p. 1693) describe bilaterian trace fossils and assign them an Ediacaran age based on the age of a granite interpreted as intrusive. We argue that the granite is not intrusive but in fact represents the basement of the sedimentary succession. Moreover, we show that identical trace fossils occur in nearby Carboniferous-Permian glacigenic rocks.Centro de Investigaciones Geológica

Beri, Ángeles

Bossi, Jorge

Gaucher, Claudio

Poiré, Daniel Gustavo

Sánchez Bettucci, Leda

Science

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Comment on “BilaterianBurrows and Grazing Behaviorat >585 Million Years Ago”Claudio Gaucher,1* Daniel G. Poiré,2 Jorge Bossi,3 Leda Sánchez Bettucci,1 Ángeles Beri1Pecoits et al. (Reports, 29 June 2012, p. 1693) describe bilaterian trace fossils and assign theman Ediacaran age based on the age of a granite interpreted as intrusive. We argue that thegranite is not intrusive but in fact represents the basement of the sedimentary succession. Moreover,we show that identical trace fossils occur in nearby Carboniferous-Permian glacigenic rocks.Pecoits et al. (1) report the occurrence oftrace fossils from the Tacuarí Formation(Uruguay), which they claim represent theoldest bilaterian burrows so far described. Theirage assignment is based on a U-Pb zircon age of585 T 3 million years (My) for a granitoid sup-posedly intruding the fossil-bearing succession,which would provide a minimum mid-Ediacaranage constraint for the fossils. However, the out-crops assigned to the Tacuarí Formation weretraditionally assigned to the upper Carboniferous–early Permian San Gregorio Formation (Fig. 1A),which represents the Gondwanan Glaciationin Uruguay (2–4). Pollen and spores assigned tothe Cristatisporites inconstans–Vittatina saccataAssemblage Zone (3) have been described fromsimilar lithologies only 4 km to the southwest and14 km to the northeast of the outcrops studiedby Pecoits et al. (5, 6). Thus, the critical piece ofevidence is the stratigraphic relationship betweenthe granite and the fossil-bearing rocks, which isnot clear.The geological map and the figures Pecoits et al.present to illustrate the nature of the contact arenot convincing with respect to the granite beingintrusive. Their figure S8 militates against thisinterpretation, because the rhythmites do notshow recrystallization or metamorphism, anda small fault at the contact has reoriented clayminerals. It is not a “chilled margin” becausethe granite displays an abrupt, knife-sharp con-tact with the sedimentary rock. If the pluton isnot intrusive with respect to the fossil-bearingsuccession, the age assignment and evolutionaryconclusions of Pecoits et al. (1) are fundamen-tally flawed.The granite has been traditionally interpretedas the basement of the succession (2, 7). The con-tact near fossil site C (1) is through a thin, ferru-ginous basal sandstone layer (Fig. 1, B to E).About 1.5 km to the south (latitude 32.50945°S;longitude 54.11917°W), the same contact com-prises a 5-m-thick glacial diamictite, which passesup-section into trace-fossil–bearing rhythmites.First, the diamictites include weathered, kaolinizedgranite clasts texturally identical to the underly-ing granite. Second, hematitization is better ex-plained by low-temperature processes, becauseit is cryptocrystalline and stratabound or con-fined to joints (Fig. 1, C and E to F). Third, pe-trographic thin sections show no recrystallizationor neoformation of metamorphic minerals at thecontact (Fig. 1, D to F). On the contrary, thereis excellent preservation of primary sedimentarystructures (lamination, graded beds, and linsenstructures), and clays are not recrystallized (Fig.1F). Finally, the xenoliths in the granitoid wereinterpreted as derived from the Tacuarí Formation(1) but no evidence was presented to support this.In fact, the xenoliths shown in (1) look very dif-ferent from the characteristic Tacuarí rhythmitesand could instead be derived from nearby Neo-proterozoic supracrustal successions, such as thePaso del Dragón Formation (2, 7, 8).The interpretation of the granitoid as dykes(1) is not supported by previous observations(2, 7). The rock is an equigranular (crystal sizearound 2 mm), predominantly isotropic quartz-diorite, but high-strain shear bands crosscut-ting the quartz-diorite and parallel to the strikeof the Sierra Ballena Shear Zone (SBSZ) (Fig.1A) were also observed. The geometry is of arelatively large pluton, as demonstrated by sim-ilar rocks cropping out 40 km to the northeast,which yielded U-Pb zircon ages of 580 T 10 My(8), within error of the Tacuarí quartz-diorite.In the Tacuarí area, the granite is always kaolin-ized in its upper 10 m (paleoweathering surface),beneath the contact with overlying sedimentaryrocks.Other lines of evidence also show that thefossil-bearing strata are younger than the quartz-diorite. The nearby SBSZ (Fig. 1A), which ac-cording to our observations does not affect thesedimentary succession, remained active until 551to 537 million years ago (Ma) (9), suggesting aCambrian or younger age for the trace fossils.Cleavage developed by nearby faults and tiltingof the Tacuarí Formation (7) are clearly local-ized and brittle in nature—not widespread sinistralshearing and mylonitization at the SBSZ, whichreached amphibolite facies or ~500°C (9). Thisis precluded by the excellent preservation of sed-imentary structures and trace fossils.The glacigenic San Gregorio Formation(Paraná Basin) crops out as a continuous band(2), with the area studied by Pecoits et al. locatedright within it (Fig. 1A). Trace fossils have beendescribed from the unit and from its correlatesin southern Brazil (10–12), which closely resem-ble the material figured by Pecoits et al. (1). Theyoccur in dropstone-bearing shales indistinguish-able from those of the Tacuarí Formation. Exam-ples of trace fossils of the San Gregorio Formationin the Guazunambí-Cerro de las Cuentas area(site CCU 22; latitude 32.632484°S; longitude54.462456°W) (Fig. 1A) include Gordia isp.(Fig. 2F) and bilobate burrows bearing striationsoblique to the midline of the trace (Fig. 2, B and C)classified as Cruziana problematica (Schindewolf)in nearby outcrops in southern Brazil (11, 12).These ichnofossils are identical to the Tacuarímaterial (1), which is shown here in Fig. 2, A,D, and E. At site CCU 22, the succession isundeformed, flat-lying, and unconformably over-lies folded late Ediacaran carbonates and shalesof the Arroyo del Soldado Group (13, 14). It isin turn overlain by Early Permian sandstonesof the Tres Islas Formation (2). The combina-tion of the same taxa, the same preservation,and the same glacial environment suggests thattrace fossils of the Tacuarí Formation are in factCarboniferous-Permian and not Neoproterozoicin age.Several authors have pointed out that postgla-cial transgressive units related to the Gondwananglaciation were deposited in freshwater environ-ments strongly affected by meltwater discharge(6, 12, 15). The impoverished ichnocoenosisfound in the Tacuarí rhythmites, including Gordiaand Cruziana problematica, is characteristic ofthese deposits (12, 15). Freshwater conditionsprobably excluded marine macro- and micro-fossils, which occur higher up in the San GregorioFormation (4). Furthermore, the extensive glacialcover of the continent that existed during thisperiod may be responsible for the scarcity ofspores and pollen in the rhythmites (6), whichinclude reworked, older palynomorphs (6).References and Notes1. E. Pecoits et al., Science 336, 1693 (2012).2. J. Bossi, L. Ferrando, Carta Geológica del Uruguay aEscala 1/500.000, versión digital 2.0. (Geoeditores,Montevideo, 2001).3. Á. Beri, P. Gutiérrez, L. Balarino, Rev. Palaeobot. Palynol.167, 16 (2011).4. A. Braun, P. Sprechmann, C. Gaucher, Neues Jahrb. Geol.Palaontol. Monatsh. 2003, 739 (2003).5. Á. Beri, C. Goso, Rev. Esp. Micropaleontol. 28, 67 (1996).6. Á. Beri, X. Martínez-Blanco, D. Mourelle, Geol. Acta 8,419 (2010).TECHNICALCOMMENT1Departamento de Geología, Facultad de Ciencias, Universidadde la República Iguá 4225, 11400 Montevideo, Uruguay.2Centro de Investigaciones Geológicas, Universidad Nacional deLa Plata-CONICET, calle 1 Nr. 644, 1900 La Plata, Argentina.3Departamento de Suelos y Aguas, Facultad de Agronomía,Universidad de la República, Garzón 780, Montevideo, Uruguay.*To whom correspondence should be addressed. E-mail:gaucher@chasque.net22 FEBRUARY 2013 VOL 339 SCIENCE www.sciencemag.org906-bon August 27, 2019 http://science.sciencemag.org/Downloaded from 7. F. Preciozzi, J. Spoturno, W. Heinzen, P. Rossi, Carta Geo-Estructural del Uruguay, Escala 1:2.000.000 (DINAMIGE,Montevideo, 1985).8. J. Bossi, C. Gaucher, in VI Congreso Uruguayo de Geología(Sociedad Uruguaya de Geología, Minas, Uruguay, 2010).9. P. Oyhantcabal, S. Siegesmund, K. Wemmer,C. W. Passchier, Int. J. Earth Sci. 100, 379 (2011).10. P. Balistieri, R. G. Netto, M. Verde, C. Goso, in XICongreso Latinoamericano de Geología (SociedadUruguaya de Geología, Montevideo, 2001).11. R. G. Netto, P. Balistieri, E. L. C. Lavina, D. M. Silveira,Palaeogeogr. Palaeoclimatol. Palaeoecol. 272, 240 (2009).12. J. H. D. Lima, R. G. Netto, Rev. Bras. Paleontol. 15, 5(2012).13. C. Gaucher, A. N. Sial, G. Blanco, P. Sprechmann,Gondwana Res. 7, 715 (2004).14. R. Frei, C. Gaucher, L. N. Døssing, A. N. Sial, EarthPlanet. Sci. Lett. 312, 114 (2011).15. L. A. Buatois, R. G. Netto, M. G. Mángano, in Late PaleozoicGlacial Events and Postglacial Transgressions in GondwanaO. R. López-Gamundi, L. A. Buatois, Eds. (Geological Societyof America, 2010), vol. 468, pp. 149–173.Acknowledgments: We thank A. Cellio and S. Mármolfor invaluable help during fieldwork. Funding by theUniversidad de la República (Uruguay) to C.G., J.B., andL.S.B. is gratefully acknowledged.17 September 2012; accepted 20 December 201210.1126/science.1230339Fig. 1. (A) Geological map (2) of the areastudied by Pecoits et al. (1) (rectangle),right within the outcrop area of the SanGregorio Formation in the region. Locationof site CCU 22 (San Gregorio Formation) isalso shown. Both geographical (WorldGeodetic System 84) and plane coordinates(Yacaré Datum) are shown (2). (B to F) Con-tact between the Tacuarí Formation and asso-ciated quartz-diorite at site C (1). (B) Outcropshowing sandstones and shales resting atopkaolinized granitoid. Length of hammer,40 cm. (C) Detail of the contact. Note theferruginous cement restricted to basalsandstone and fissures. (D) Overview ofthin section [area shown in (C)]. Note thebasal sandstone in contact with thequartz-diorite. (E) Detail of area arrowedin (C). Note the normal grading, showingthat the granite is at the base of the bed.(F) Same as previous with crossed nicols.Note the extremely fine-grained clays (darkgray) and fine-grained, stratabound hematitecement. No metamorphic minerals occur atthe contact.www.sciencemag.org SCIENCE VOL 339 22 FEBRUARY 2013 906-bTECHNICAL COMMENTon August 27, 2019 http://science.sciencemag.org/Downloaded from Fig. 2. Trace fossils of the Carboniferous San Gregorio Formation at site CCU 22 and of the TacuaríFormation. (A) Bilobate trace fossils of the Tacuarí Formation from (1). (B) Bilobate burrows of the SanGregorio Formation, possibly poorly preserved Cruziana problematica. Note the X-shaped crossing. (C) Detailof previous specimen, showing crossing and poorly preserved striations. (D) Cruziana problematica from finesiltstones of the Tacuarí Formation at its type area (latitude 32.50087°S; longitude 54.12827°W) showingfine striations oblique to the midline of the trace. (E) Sinusoidal trace fossil (Gordia isp.) from the TacuaríFormation at site A of Pecoits et al. (1, 7), with scattered dropstones. (F) Identical Gordia isp. from the SanGregorio Formation, also with scattered dropstones.22 FEBRUARY 2013 VOL 339 SCIENCE www.sciencemag.org906-bTECHNICAL COMMENTon August 27, 2019 http://science.sciencemag.org/Downloaded from Comment on "Bilaterian Burrows and Grazing Behavior at >585 Million Years Ago"Claudio Gaucher, Daniel G. Poiré, Jorge Bossi, Leda Sánchez Bettucci and Ángeles BeriDOI: 10.1126/science.1230339 (6122), 906.339Science ARTICLE TOOLS http://science.sciencemag.org/content/339/6122/906.2CONTENTRELATED http://science.sciencemag.org/content/sci/336/6089/1693.fullhttp://science.sciencemag.org/content/sci/339/6122/906.3.fullREFERENCEShttp://science.sciencemag.org/content/339/6122/906.2#BIBLThis article cites 10 articles, 1 of which you can access for freePERMISSIONS http://www.sciencemag.org/help/reprints-and-permissionsTerms of ServiceUse of this article is subject to the  is a registered trademark of AAAS.Sciencelicensee American Association for the Advancement of Science. No claim to original U.S. Government Works. The title Science, 1200 New York Avenue NW, Washington, DC 20005. 2017 © The Authors, some rights reserved; exclusive (print ISSN 0036-8075; online ISSN 1095-9203) is published by the American Association for the Advancement ofScience on August 27, 2019 http://science.sciencemag.org/Downloaded from 

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