at Bui", Chile (42 0 8)

Richard Fortey Paleontology Department, British Museum 01 Natural History, Cromwell Rd., London, U.K.

Robert J. Pankhurst British Antarctic Survey, C/O NERC Isotope Geosclences Laboratory, Keyworth, Nottingham, NG12 5 GG, U.K.

Francisco Hervé Departamento de Geologla, Universidad de Chile, Casilla 13518, Correo 21, Santiago, Chile

ABSTRAeT

A calmoniid (Calmoniidae gen. nov. alf. Baine/la Rennie, 1930), an undetermined phacopoid trilobite and a zaphrentid coral are described Irom slate boulders at Buill (42°24'S, 72"43'W) in the Andes 01 Chiloé. This launule is consistentwith eariy Devonian sedimentation 01 at least part 01 the rocks lorming the accretionary complex 01 southern Chile, which outcrops extensively west 01 Suill, and was alfected by metamorphism in Late Palaeozoic to Early Mesozoic times. The presence 01 a southern Gondwana launal assemblage, which can be compared with Devonian launas in Argentina, Bolivia, the Malvinas (Falkland) Islands and South Alrica, suggests that this area lies towards the edge 01 an extensive shallow water platform during Devonian times.

Key words: Devonian, Trilobites, Southern Chile, Malvinokaffric.

R ES U M E N

Trilobites devónicos de Buill, Chile (42°S). Se describe un trilobites calmoniido (Calmoniidae gen. nov. alf. Bainella Rennie, 1930) un trilobites lacopoide indeterminado y un coral zafréntido, recolectados en rodados de pizarras en Buill, Chile (42°24'S; 72°43'W), en los Andes de Chiloé. Esta fáunula es consistente con una edad de sedimentación devónica inlerior, para al menos parte del complejo acrecionario del su r de Chile, que aflora extensamente al oeste de Buill y que lue metamorlizado en el Paleozoico Superior a Mesozoico inlerior. La presencia de una asociación faunística de Gondwana meridional, que puede ser comparada con faunas devónicas de Argentina, Bolivia, Islas Malvinas (Falkland) y Sudálrica, sugiere que esta área formaba parte de una extensa platalorma somera durante el Devónico.

Palabras claves: DevónIco, Trilobites, Sur de Chile, 'Malvinokaffric'.

INTRODUCTION

The coastal regions of southern Chile, including formed along the 'Pacific' margin of Gondwana Isla Grande de Chiloé (text-Fig. 1), are largely (Forsythe, 1982; Hervé et al., 1981). A unique fossil composed of low-grade metamorphic rocks locality at Isla Potranca (Miller and Sprechmann, representing a Late Paleozoic accretionary complex 1977) and Rb-Sr isochron dating (Davidson et al.,

Revista Geológica de Chile, Vol. 19, No. 2, p. 133-144, 1 Piare, 3 Figs.• December 1992. ARGENTINA c.> , ... HORNO~REN ) ~ N 42°

\. " I

C> ." , " \-.J'--~/~ <>'" el , 'C> I

\I, <:) \, -0 C,¡ ') ~ + I 60· ~ I 60· (8 / .~ + ~ 14 ¡, C) , ~ ~w~ / C)" \ o ,, m v v v v ~ (j Z v v v v ) ;; v V(-+--.¡: z 1+ + -1 JJ v vI '-\ ¡: 43° vI'+- + + O v '" m=< en Quaternary sediments + + North Patagonian Batholith > C2J ~ -< te e v v Quaternary volcanlcs Palaeozoic metamorphics 1292 ±4 1 Rb-Sr age (Ma ± 2 al ¡: LZJ ~- - ; () Ayacara Formation I / Liquiñe·Ofqul Fault Zone ¡: ~ m Text-FIG. 1. Location of Buill within a simplified geological map of continental Chiloé, modified from Mapa Geológico de Chile (Servicio Nacional de ~ Geología y Minería, 1982). !!J R. Fortey, R.J. Pankhurst and F. Hervé 135

1987; Hervé et al., 1988) suggest deposition as early Fiordo Reñihue, a beach area of ca, 25x400 m, is as Devonian, with a subsequent history of deformation covered solely by thousands of boulders of black and reactivation extending through to Early slate. The size and lithological homogeneity of this Mesozoic times. occurrence is such that it clearly represents the The mainland opposite Isla Grande de Chiloé, is more-or-Iess in situ weathering of a nearby outcrop separated from the Coast Ranges by the Golfo de which is not otherwise exposed. Fuenzalida (1979) Ancud, a subsided block equivalent to the Central found true outcrops of similar, but unfossiliferous Valley of central Chile, here submerged. It is largely slates on the forested hillside aboye Buill. They are constituted bythe northern extremity ofthe Mesozoic­ referred to here as Buill slates. The slate boulders on Cenozoic Patagonian Batholith, but there are also the beach contain fossil remains, including trilobites sparse outcrops of stratified rocks with obscure contact described by Biese (1953) as 'Calymenidae von relationships. These include the marine Ayacara devonischen Habitus'. In Levi et al. (1966), E. Pérez Formation, which is probably Eocene-Miocene, and refers to unidentifiable deformed fragments of low-grade metasedimentary rocks at a few localities trilobites, together with Cyathocrinites (?) and such as Huinay and the western part of Fiordo Aulacophyllum. Fuenzalida (1979) also noted the Reñihue where Buill is located. The age of deposition presence of fossil crinoids and corals. The present ofthese metasedimentary rocks andtheirconsequent paper describes new fossil material collected from relationship to the Paleozoic accretionary complexto two beach boulders in February 1988. which the west are unknown, but a Late establishes its Devonian age beyond doubt. The metamorphic age has been obtained at Huinay paleoecological, paleogeographical and tectonic (Pankhurst et al., 1992). significance of this assignment is briefly considered. At Buill (42°24'S;72°43'W), on the north shore of

PALEONTOLOGICAL DESCRIPTION

TRILOBITES the loss of much detail, making interpretation difficult, but a latex cast shows the essential features (Plate 1, The trilobite~ were originally reported by Biese Fig. 1). In spite of the limitations of preservation, a (1953) and Levi, Aguilar and Fuenzalida (1966); they notable feature is the extremely stout spines are of particular interest as trilobites are otherwise originating on sorne of the thoracic axial rings. It is virtually unknown from Chile. Preliminary clearfromtheir distribution that spines do not originate determinations were inconclusive, but included sorne from all the segments, but apparently from every fragmentary specimens attributed to Calymenidae. second orthird segment. This is perhaps most clearly New material includes a calmoniid allied to Bainella shown at the front and back of the thorax. However, which indicates an Early to Middle Devonian age. there are several ambiguities in determining the number of thoracic segments on the specimen, depending on how the intersegmental boundaries Order Salter, 1864 are drawn, and where the front of the pygidium is Family Calmoniidae Delo, 1935 taken. It is possible to regard the anterior margin of Calmoniid gen. nov. aff. 8ainella Rennie,1930 the pygidium as Iyingjust behindthe posteriorthoracic (Plate 1, Fig. 1) spine (which would then be on the last thoracic segment). If this is the case, the thorax would be Repository: Colección Paleontológica, Departa­ complete, with 11 segments (like all calmoniids), and mento de Geología, Universidad de Chile, number each transverse ring on the thorax would correspond CPDG (UCH) T-321. with an axial ring; spines would be developed on the Description: The poorly preserved specimen consists third, sixth, ninth and eleventh thoracic segments; of an external mould of an incomplete thorax and nothing is seen of the articulating half-rings. In this pygidium. The manner of preservation has resulted in case the thoracic pleurae can also be simply 136 DEVONIAN TRILOBITES AT BUlll, CHilE (42°5) interpreted: each transverse furrow being an very sharply upwards into a posteriorspine of compa­ interpleural boundary and no pleurae preserving rable stoutness to those on the thoracic axis. It is not pleural furrows. Under this explanation the pygidium known how long these spines were: obviously they would occupy about 30% of the sagittallength of the are curtailed on the specimen, and may well have specimen. However, since calmoniids all have strong been a centimetre or more in length. No sculptural thoracic pleuralfurrows their absence would be rather details are preserved. surprising, even given the preservation of the Discussion: The extremely robust dorsal spines are specimen. This suggests that another interpretation distinctive, regardless ofthe poorstate of preservation. should be considered. This would suppose that a The pygidium is very much like that of certain species smaller number of thoracic segments are present, of Bainella, for example B. cristagalli (Woodward, with both interpleural furrows and pleural furrows 1873) from the Devonian Bokkeveld Group of South present on the thoracic pleurae; some of the axial Africa (see Cooper, 1982, Fig. 97, 1, J), especially 'rings' would be interpreted as articulating half rings. with regard to the development of the posterior spine. For example, the second spine would be developed Species of Baínella have dorsal spines arising from on the posterior half of its segment, with a well the axial rings of the thoracic segments, where they developed articulating half ring in front, and a strongly represent extensions of the midposterior margin of furrowed pleura showing up well on the left. Accepting each ring: those of B. cristagalli are robust (Cooper, an extra free segment behind the posterior spine, this 1982, Fig. 107); some species from Bolivia (e.g. B. would suggest that the spines were developed on (Belenops) insolíta (Eldredge and Branisa, 1980, Fig. alternate thoracic segments, and that nine thoracic 9B) are quite similar in this feature. However, no segments were present on the specimen. The first species of which we are aware has robust spines two segments behind the head would be regarded as developed on only a few of the thoracic segments. In missing; of these, the second segment should bear a fact, in the trilobites as a whole, dorsal thoracic spines median spine, the first segment lacks one, while the are rather common on al! thoracic segments, but we occipital ring would be anticipated to carry a spine (as know of no other example where such spines are it does in many calmoniids), thus maintaining the developed sporadically alongthe length ofthe thorax. alternating pattern along the whole axial length. This is unusual enough to suggest that this form Although this interpretation has some plausibility the belongs in a new genus allied to Bainella. However, presence of eleven thoracic segments is preferredfor it is not realistic to name this new genus on the basis several reasons. First, if pleuralfurrows were present, of the distorted material available, for which reason one would expect them to curve towards the open nomenclature is employed. There is no reason segmental boundaries as they approach the axis, to suppose any age other than Devonian (Emsian­ which they do not; second, the axiallength (sagittal) Eifelian), during which period the radiation of such of the posterior thoracic axial rings would be out of calmoniids occurred. proportion tothe undoubted axial rings ofthe pygidium, which on calmoniids grade into one another; thirdly, the nine segment theory requires that one ortwo half Undetermined Phacopoid rings be concealed by a precedingsegment (otherwise (Plate 1, Fig. 2) there are not enough annulations on the specimen to account for a half ring on each segment) and there is Repository: Colección Paleontológica, Departa­ no evidence forthis; fourthly, because of the waythey mento de Geología, Universidad de Chile, number moulted it is quite common to find complete thorax + CPDG (UCH) T-322. pygidium (thoracopygon) in Phacopida; they come Discussion: The specimen displays nine thoracic together as a unit. Hence we acceptthat 11 segments segments, and an incomplete pygidium. It is clearly are present, and that the proportions of the pygidium distinct from the form described above because the are about the same as they are in other species of pygidium lacks a posterior spine, and axial spines are Bainella, about twice as wide as long. The pygidial missing from the thorax. The pleurae show some axis is rather low, occupying about one-third of ante­ indications of adaxial fulera; the pygidium shows tour rior pygidial width. Up to eight narrow axial rings are axial rings. Both the torm ot the thoracic pleurae, and indicated. The posterior end of the pygidium is turned the structure of the pygidium suggest that this is a R. Fortey. R.J. Pankhurst and F. HeNé 137

• 1 Buill • 2 Sierra Grande • 3 Southern Alriea • 4 Malvinas (Falkland) Island. • 5 Precordillera • 6 Sierra Almeida • 7 Bolivia • 8 Southern Perú • 9 Salar de Navidad Devonian pole position

~ land

S Limit 01 Malvinokaffric realm

Text-FIG.2. Eariy-Middle Devonian (Emsian-Eifelian) paleo­ geographical map show­ ing distribution of the Malvinokaffric and East­ ern Americas faunal realms. Dots indicate occurrence of coeval marine fossils referredto in tex!. Slightly modified from Oliver (1980).

phaeopoid, butthe material is inadequateto draw any them as zaphrentids whieh give little information further eonclusions. about age. However, their oeeurrence is eonsistent with a high latitude fauna (see below) too cold for CORALS hermatypic corals (Oliver, 1980). This leads to some scepticism about the earlier report of Aulacophyllum Dr. WA Oliver (written eommunieation, 1990 to (Levi et al., 1966) from the same localíty. RF) examined the eorals found at Buíll, determining

GONDWANA DEVONIAN FAUNAS Al HIGH PALAEOLAlllUDES

Those shallow water faunas that inhabited the genera. The latter ineludes trilobite faunas from the flooded cratonic areas surrounding the earlier Precordillera, whieh are comparable to those of north Devonian South Pole (text-Fig. 2) are often referred west Argentina and Bolivia. Because the form from to as Malvinokaffrie (Richter and Richter, 1942), Chíloé is probably a new genus it is not yet possible comprising a largely endemic fauna whieh was to fit it into this more refined scheme. Calmoniid adapted to eool temperatures and clastic substrates. trilobites are among the most charaeteristie of high Baldis (1975, 1979) and Baldis et al. (1982) have latitude Gondwana endemic faunas (Eldredge and sought to differentiate eastern (elassieal Branisa, 1980). Henee the discovery of a peculiar Malvinokaffric) from western ('Austral Andean calmoniid from southern Chile, searee though the Provinee', Baldis, 1979, p. 209; 'Central Andean material is, does suggest that the Malvinokaffrie Provinee', Baldis et al., 1982) boreal Gondwana (sensu lato) fauna is present there. The simple coral trilobite faunas as being charaeterized by different fromthe same beds is not inconsistent with this, sinee 138 DEVONIAN TRILOBITES AT BUILL, CHILE (42°8)

800

Text-FIG. 3. Generalized late Eariy Devonian paleogeo­ graphy 01 80uth Ameriea, after Barrett and lsaaeson (1988). This model is basad on the present day distribution 01 the land masses, but has been sligthtly modified to inelude the " Patagonia suture zone .. marking the supposed eollision 01 the Patagonian al­ loehtonous terrane later in the Paleozoie (Ramos, 1989). r---1.• ~ Malvinokaffuc fauna l ~i:::~~:~:).~;!~~1 Land

high latitude Gondwana localities also yield (sensu lato)faunas are also reported to be present in depauperate coral faunas (Oliver, 1980). Apparently the Lake Titicaca region. However, Boucot et al. (1980) the Chilean calmoniid is most closely related to the recorded an 'Eastern American real m' brachiopod genus Bainella, which occurs in South Africa, Bolivia, fauna from the coastal area of southern Perú, and Argentina and the Malvinas (Falkland Islands) Isaacson et al. (1985) have implied that a fauna with (Cooper, 1982). Manceñido and Damborenea (1984) similar affinities may occur at Salar de Navidad, only mentioned the presence of Bainella sp. at Sierra about 200 km westwards of the fauna in Sierra Grande, on the Atlantic coast of Patagonia (42°S). Almeida. Usually, Eastern American (Appalachian) Isaacson et al. (1985) have discussed Devonian faunas are supposed to typify warmer climatic belts brachiopods from the Sierra Almeida, northern Chile. than do high latitude Gondwana faunas, and the These includetypical high latitude Gondwana genera, close juxtaposition of the two faunal province in Chile Tropidoleptus and Australocoelia. Malvinokaffric is remarkable.

TECTONIC CONSIDERATIONS

The following considerations are based on the To the authors, this is obvious beyond any reasonable assumption that the slate boulders with the Devonian doubt, and no alternative explanation has been trilobites are an integral part of the low grade produced. metasedimentary uníts which crop out around Buill. There ís clearly a general concordance between R. Fortey, R.J. Pankhurst and F. HeNé 139

the depositional age of the Buill slates at Chiloé and platform to other parts of South America and to South that of the accretionary complex rocks at Isla Potran­ Africa. Different configurations of these hypothetical ca, Aisén, as suggested by the brachiopod platforms have been given by Popp and Baldis (1989) identifications of Miller and Sprechmann (1977). and by Barrett and Isaacson (1989). A simplified Metamorphism of the sediments of the complex has version of the latter is shown in text-figure 3, where consistently given younger Late Paleozoic to Early the suggested Patagonia suture (Ramos, 1984) has Mesozoic Rb-Sr ages. been added. In their paleogeograph ic reconstruction, It is interesting to note that the Devonian Popp and Baldis (1989) show an ecological barrier in sedimentation of the rocks in Chiloé and Aisén took the area of marine sedimentation north of Sierra place at a time for which there is no indication of an Grande, which would isolate the Buill region from the active magmatic arc in the southwestern margin of Malvinas (Falkland) Islands and South Africa. This present day South America. It is possible to conclude does not seem to be in accordance with our that at least part of the turbidite sequence that was conclusions, unless an alternative marine connection later incorporated in the accretionary prism was between the two areas existed elsewhere for example depos~ed in a passive continental margin environment . farther south. The occurrence of a Calmoniid trilobite The occurrence of shallow water trilobites of aff. Bainella described here is relevant to this type of Malvinokaffric affinities at Buill suggests, but does reconstruction as well as to the assessment of Pata­ not prove, that this portio n of the continent could have gonia as an exotic terrane (Ramos, 1984). been connected via a continuous shallow water

ACKNOWLEDGEMENTS

Samples were collected during Operation Raleigh Africa), J. Corvalán (Servicio Nacional de Geología y Expedition 13B to southern Chile in 1988: the field Minería, Chile) and V. Ramos (Universidad de Bue­ assistance of O.R. group Foxtrot and of M. Brook and nos Aires) helped to improve the text. Project 1181 of C. Maureira is acknowledged. Dr. Carlos Cingolani FONDECYT partially funded the research. This is a (Universidad de La Plata, Argentina) gave valuable contribution to project ICGP 279 "Terranes in help in tracking down previous literature. Reviews by Latinamerica". M. Cooper (University of Durban-Westville, South

REFERENCES

Baldis, B.A.J. 1975. Valoración de elementos faunísticos Biese, W. 1953. Chile. Zentralblatt tür Geologie und para una zonación y datación de edades en el Devónico Palaeontologie, Vol. 1, p. 555-563. Stuttgart. inferior de la Precordillera Argentina. In Congreso Ar­ Boucot, A.J.; Isaacson, P.E.; Laubacher, G. 1980. An eariy gentino de Paleontología y Bioestratigrafía, No. 1, Devonian, Eastern American Realm faunule from the Resúmenes, Vol. 1, p. 219-240. Tucumán. coast of southern Perú. Journal of Paleontology, Vol. Baldis, BAJ. 1979. Paleozoogeografía de los trilobites 54, p. 359-365. devónicos en Sudamérica Austral. Ameghiniana, Vol. Cooper, M.R. 1982. A revision 01 the Devonian (Emsian­ 16, p. 209-216. Eilelian)Trilobita from the Bokkeveld Group of South Baldis, B.; Beresi, M.; Bordonaro, O.; Vaca, A. 1982. Sín• Africa. SouthAfricanMuseum, Anna/s, Vol. 89, p.1-74. tesis evolutiva de la precordillera argentina. In Con­ Davidson, J.; Mpodozis, C.; Godoy, E.; Hervé, F.; Pankhurst, greso Latinoamericano de Geología, No.5, Actas, Vol. R.J.; Brook, M. 1987. Late Paleozoic accretionary 4, p. 399-445. Buenos Aires. complexes in the Gondwana margin 01 southern Chile: Barrett, S.; Isaacson, P. 1988. Devonian Paleogeography evidence from the Chonos Archipielago. In Gondwana ofSouth America.ln Devonian ofthe World (McMillan, Six: structure, tectonics and geophysics (Mackenzie, N.J., Embry, A.F., Glass, D.J.; editors). Canadian Society G.D., editor). American Geophysica/Union, Geophysical ofPetroleum Geologists, Memoir, Vol. 3, No, 14, p. 655- Monograph, No.40, p.221-227. Washington. 667. Delo, D.M. 1935. A revision 01 the phacopid trilobites. 140 DEVONIAN TRILOBITES AT BUILL, CHILE (42°S)

Joumal of Pa/eontology, Vol. 9, p. 402-420. Miller, H.; Sprechmann, P. 1978. Eine devonische Faunula Eldredge, N.; Branisa, L. 1980. Calmoniid trilobites of the aus dem Chonos-Archipel Region Aisén, Chile, und Lower Devonian Scaphocoelia Zone of Bolivia with ihre stratigraphische Bedeutung. Geologisches Jahr­ remarks on related species. American Museum of Na­ buch, Reihe B, Vol. 28, p. 37-45. tural History, Bulletin,Vol. 165, p. 185-289. Oliver, W.A. 1980. Corals in the Malvinokaffric Realm. Forsythe, R 1982. The late Palaeozoic to eariy Mesozoic Münsterische Forschungen zur Geologie und Paliion­ evolution of southern South America: A plate tectonic tologie, Vol. 52, p. 13-27. interpretation. Geological SocietyofLondon, Journal, Vol Pankhurst, R.J.; Hervé, F.; Rojas, L.; Cembrano, J. 1992. 139, p. 671-682. Magmatism and tectonics in continental Chiloé, Chile Fuenzalida, J.L. 1979. Estudio Geológico preliminar de (42°-42°30'S). Tectonophysics, Vol. 205, p. 283-294. Península Huequi, X Región. Memoria de Título (Inédi­ Popp, M.T.B.; Baldis, B. 1989. Trilobites y comunidades to), Universidad de Chile, Departamento de Geología, faun ísticas del Devónico de la Formación Ponta Grossa 158 p. (Paraná, Brasil). Yacimientos Petrolíferos Fiscales Bo­ Hervé, F.; Davidson J.; Godoy, E.; Mpodozis, A.C. ; livianos, Revista Técnica, Vol. 10, No. 3-4, p. 219-225. Covacevich, V. 1981 . The late Palaeozoic in Chile, Buenos Aires. stratigraphy, structure and possible tectonic framework. Ramos, V. 1984. Patagonia: ¿un continente paleozoico a la Academia Brasileira de Ciencias, Anais, Vol. 53, No. 2, deriva? In Congreso Geológico Argentino No. 9, Actas, p.367-373. Vol. 2, p.311-325. San Carios de Bariloche. Hervé, F.; Godoy, E.; Garrido, l. ; Hormazábal, L.; Brook, M.; Ramos, V. 1989. Late Proterozoic-Eariy Paleozoicof South Pankhurst, RJ.; Vogel, S. 1988. Geocronología y con­ Ame rica-a collisional history. Episodes, Vol. 11, No.33, diciones de metamorfismo del complejo de subducción p. 168-174. del Archipiélago de los Chonos. In Congreso Geológico Rennie, J.V.L. 1930. Some Phacopidea from Ihe Bokkeveld Chileno, No. 5, Actas, Vol. 2, p. E157-E173. Series. The Royal Societyof South Africa, Transactions, lsaacson, P.E. ; Fisher, L.L. ; Davidson, J. 1985. Devonian Vol. 18, p. 327-360. and Carboniferous stratigraphy of Sierra Almeida, Richter, R ; Richter, E. 1942. Die Trilobiten der Weimes­ northem Chile. Preliminary results. Revista Geológica Schichten am Hohen Venn mit Bemerkungen über die de Chile, No. 25-26, p. 113-124. Malvinocaffrische Provinz. Senckenbergian, Vol. 25, No. Levi, B.; Aguilar, A.; Fuenzalida, R 1966. Reconocimiento 1-3, p. 156-179. Frankfurt. geológico en las provincias de L1anquihue y Chiloé. Salter, J.W. 1864. A Monograph of British Trilobites. Instituto de Investigaciones Geológicas, Boletín, No. 19, PalaeontographicalSocietyofLondon, Monograph, Vol. 45 p. Santiago de Chile. 16,224 p. Manceñido, M.; Damborenea, S. 1984. Megafauna de Servicio Nacional de Geología y Minerra. 1982. Mapa Invertebrados paleozoicos y mesozoicos. In Congreso Geológico de Chile, 1 :1.000.000 (Escobar, F.; editor). Geológico Argentino, No. 9, Relatorio, Vol. 2, No. 5, p. Instituto Geográfico Militar, 6 hojas, Santiago. 413-465. San Carlos de Bariloche.

Manuscripl received: Apri117, 1991 ; accepled: May 5, 1992. A. FOrt9Y, R J. Pankhurst aOO F. HeNá '"

PLATE 1 142 DEVONIAN TRILOBITES AT BUILL, CHILE (42°8)

PLATE 1

Figures

Calrnoniid gen. nov. alf. Bainella Rennie. xl.5. Latex cast frorn external rnould showing prorninent dorsal spines.

2 Undeterrnined phacopoid. xl.5. R. Fortey, R.J. Pankhurst and F. HeNé 143

PLATE 1