The Ordovician System is superbly represented in the Precordillera of western Argentina, at the Andean foothills. During the Middle Ordovician, an important paleogeographical rearrangement of depocenters and source areas took place associated with the demise of the Eopaleozoic carbonate platform of the Precordillera. This critical interval is recorded in the basin through widespread deposition of black shales over the fossiliferous limestones of the San Juan Formation, punctuated by local deposition of olistostromes, debris flows, conglomerates, and turbidites (e.g., Astini et al., 1995; Keller, 1999). Fossil dating of the lowest black shales and equivalent units indicates a diachronous deposition from north to south in the Precordillera basin (Hünicken, 1985; Albanesi et al., 1998).Fil: Voldman, Gustavo Gabriel. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Museo de Paleontología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; ArgentinaFil: Ortega, Gladys del Carmen. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Museo de Paleontología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Albanesi, Guillermo Luis. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Museo de Paleontología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; Argentin

Albanesi, Guillermo Luis

Ortega, Gladys del Carmen

Voldman, Gustavo Gabriel

English

LAReferencia - Red Federada de Repositorios Institucionales de Publicaciones Científicas Latinoamericanas

Publicación Especial Nº 13BUENOS AIRES2013ASOCIACIÓN PALEONTOLÓGICA ARGENTINACONODONTS FROM THE ANDESProceedings of the 3rd International Conodont Symposium&Regional Field Meeting of the IGCP project 591Edited byGuillermo L. Albanesi and Gladys Ortega117MIDDLE ORDOVICIAN CONODONTS AND GRAPTOLITES AT LOS CAUQUENES RANGE, CENTRAL PRECORDILLERA OF SAN JUAN, ARGENTINAVOLDMAN, G. G.1, 2, ORTEGA, G 1 AND ALBANESI, G. L. 1, 21  CONICET-Museo de Paleontología, CIGEA, Facultad de Ciencias Exactas, Físicas y Naturales, Universidad Nacional de Córdoba, X5000JJC, Córdoba, Argentina;gvoldman@efn.uncor.edu, gcortega@arnet.com.ar, galbanes@com.uncor.edu2  CICTERRA-CONICET, Córdoba, Argentina.Keywords: Conodonts. Graptolites. Biostratigraphy. Middle Ordovician. Precordillera. Argentina.CONODONTS FROM THE ANDES - Publicación Especial Nº 13 - Julio 2013 - PALEONTOLOGICAL NOTETHE Ordovician System is superbly represented in the Pre-cordillera of western Argentina, at the Andean foothills. Duringthe Middle Ordovician, an important paleogeographical re-arrangement of depocenters and source areas took place asso-ciated with the demise of the Eopaleozoic carbonate platformof the Precordillera. This critical interval is recorded in the basinthrough widespread deposition of black shales over the fossil-iferous limestones of the San Juan Formation, punctuated bylocal deposition of olistostromes, debris flows, conglomerates,and turbidites (e.g., Astini et al., 1995; Keller, 1999). Fossil dat-ing of the lowest black shales and equivalent units indicates adiachronous deposition from north to south in the Precordillerabasin (Hünicken, 1985; Albanesi et al., 1998).The occurrence of Ordovician clastic rocks in the Jáchal areais known since the study of Borrello and Gareca (1951), whorecorded Nemagraptus gracilis (J. Hall) in the Ordovician uppershaly succession that is exposed in the western flank of the CerroViejo, a prominent mountain situated midway between Huacoand Jáchal city. Harrington (in Harrington and Leanza, 1957)distinguished two formations in the lower and upper parts ofthis succession, the Cerro Viejo Shales and Los Azules Shales,respectively. Furque (1979) referred all the Ordovician clasticsequence to the Los Azules Formation, equivalent to the Gual-camayo Formation elsewhere. Later, Ortega (1987) refined thebiostratigraphy of the Los Azules Formation by determining alower member, made up of dark claystones and siltstones in-terbedded with K-bentonites (lower Darriwilian), a middlemember that consists of black shales and siltstones (upperDarriwilian), and an upper member of yellowish calcareous silt-stones and calcarenites (upper Sandbian). A hiatus covering thehighest Darriwilian and the lowest Sandbian is recorded be-tween the middle and upper members. The Los Azules Formation is arranged in small isolated out-crops aligned in narrow elongated belts with meridian orienta-tion. The best exposures of the Los Azules Formation are locatedat the foothill of the Cerro Viejo, between 30º 11’ 40" and 30º15’ 30" S Latitude, and 68º 34’30" and 68º 35’20" W Longi-tude, uplifted by the Niquivil Thrust (e.g., Ortega et al., 2007).It also crops out along western thrusts in the less studied suc-cessions of the La Chilca, Mogotes Azules, and the Aguada deLos Azulejitos on the northernmost Talacasto Range.The purpose of this paper is to describe for the first time arestricted stratigraphic exposure that bear a significant con-odont and graptolite fauna of the upper section of the San JuanFormation and the overlying the Los Azules Formation (Fig.1), which is currently under study. The stratigraphic section islocated at the Los Cauquenes Range, a parallel thrust belt tothe Cerro Viejo de Huaco thrust. The latter thrust belt is 4 kmto the east, where the Los Azules Creek, the type section of thehomonymous formation, is located.At the Oculta Creek, the upper levels of the San Juan For-mation are characterized by nodular limestones, which arehighly fossiliferous. These are roofed by a hardground surface,rich in nautiloids at the contact with the Los Azules Formation,which is interpreted as a marine flodding surface (Astini,1994).The Los Azules Formation presents 226 m in thicknessat the Oculta Creek, with the lower, middle and upper memberswell developed. It is unconformably overlain through angulardiscordance by Holocene alluvial fan deposits. The Los AzulesFormation starts with dark-brown argillites with yellowish al-teration and concoidal fracture interbedded with K-bentonites.The middle member consists of black-grey shales and siltstones,and the upper member is made up of calcareous siltstones ofdark colour and yellow alterations, with scarce mudstones strataintercalated, some of them reaching up to 1 m.In order to define the age of aforementioned strata by con-odont dating, we took 3 rock samples from the uppermost levelsof the San Juan Formation (4.5 kg) and 2 rock samples fromthe base of the Los Azules Formation (3 kg).The samples arecondensed limestone deposits, which after digesting in 10%acetic acid following the conventional procedures, producedover 2200 conodont elements. The collected specimens are wellpreserved and exhibit a CAI 2 (Epstein et al., 1977). These arestored in the Museo de Paleontología, Universidad Nacional deCórdoba, under repository code CORD-MP.The conodont collection exhibits a high species diversity(Fig. 2), including Ansella jemtlandica (Löfgren), Baltoniodus sp.,CONODONTS FROM THE ANDES - Publicación Especial Nº 13 - Julio 2013 - PALEONTOLOGICAL NOTE118Figure 1. Geological map with the location of the Oculta Creek, Central Precordillera, San Juan Province, Argentina (modified from Furque, 1979,Furque et al., 1998).VOLDMAN ET AL.: ORDOVICIAN BIOSTRATIGRAPHY AT LOS CAUQUENES RANGE, PRECORDILLERA119Figure 2. Darriwilian (Yangtzeplacognathus crassus Zone, Da2) conodonts from the Oculta Creek, Central Precordillera, San Juan Province, Argentina.1, 7, Drepanodus arcuatus Pander. 1, Pb element, CORD-MP28039, 7, Sa element, CORD-MP28045; 2, Cornuodus longibasis (Lindström), Sd element,CORD-MP 28040; 3, Ansella jemtlandica (Löfgren), M element, CORD-MP 28041; 4, Protopanderodus calceatus Bagnoli and Stouge, P element, CORD-MP 28042; 5, 12, 15, Yangtzeplacognathus crassus (Chen and Zhang). 5, Pb element,antero-lateral view, CORD-MP28043, 12, Sa element, upper view,CORD-MP 28050, 15, Pa element, upper view, CORD-MP28053; 6, Parapaltodus simplicissimus Stouge, M element, CORD-MP 28044; 8–9. Periodonn. sp. 8, M element, CORD-MP 28046, 9, Pa element, CORD-MP 28047; 10, Semiacontiodus potrerillensis Albanesi, long based coniform, CORD-MP28048; 11, Paroistodus horridus (Barnes and Poplawski), Sc element, CORD-MP28049; 13, Microzarkodina hagetiana Stouge and Bagnoli, M element,CORD-MP28051; 14, Histiodella holodentata Ethington and Clark, Pa element, CORD-MP28052; 16, Gen. et sp. indet., CORD-MP28054; 17, Pteracon-tiodus cryptodens (Mound), M element, CORD-MP28055; 18, Periodon macrodentatus (Graves and Ellison), M element, CORD-MP28056; 19, Errati-codon alternans (Hadding), Pb element, CORD-MP28057; 20, Drepanoistodus bellburnensis Stouge, M element, CORD-MP28058; 21, Fahraesodusmarathonensis (Bradshaw), Sa element, CORD-MP 28059; 22, Drepanoistodus costatus (Abaimova), Sa element, CORD-MP 28060; 23, Costiconuscostatus (Dzik), Sb element, CORD-MP 28061; 24, “Bryantodina” aff. typicalis Stauffer, Pa element, CORD-MP 28062; 25, Drepanoistodus table-pointensis Stouge, M element, CORD-MP 28063. All illustrated specimens proceed from sample TFSJ1º hrdgrnd. All elements show inner-lateral viewsexcept where indicated. Scale bar: 0.1 mm.“Bryantodina” aff. typicalis Stauffer, Cornuodus longibasis (Lind-ström), Costiconus costatus (Dzik), Drepanodus arcuatus Pander,D. reclinatus (Lindström), Drepanoistodus bellburnensis Stouge,D.costatus (Abaimova), D.forceps (Lindström), D. tablepointensisStouge, Erraticodon alternans (Hadding), Fahraesodus maratho-nensis (Bradshaw), Histiodella holodentata Ethington and Clark,Microzarkodina hagetiana Stouge and Bagnoli, Parapaltodus sim-plicissimus Stouge, Paroistodus originalis (Sergeeva), Paroistodushorridus primus Albanesi, P. h. secundus Albanesi, P. horridus hor-ridus (Barnes and Poplawski), Periodon macrodentatus (Gravesand Ellison), Protopanderodus calceatus Bagnoli and Stouge,Pteracontiodus cryptodens (Mound), Scolopodus striatus Pander,Semiacontiodus potrerillensis Albanesi and the index speciesYangtzeplacognathus crassus (Chen and Zhang). It also includesa new species of Periodon and a Gen. et sp. indet. This conodontassociation allows constraining the uppermost levels of the SanJuan Formation and the lower levels of the Los Azules Forma-tion to the Yangtzeplacognathus crassus Zone of early middleDarriwilian age (Da2) (Fig. 3), following the Baltoscandic andChinese schemes (Zhang, 1998; Löfgren and Zhang, 2003).This is consistent with the timing of the drowning of the SanJuan Formation in the nearby Cerro Viejo de Huaco (Ortega etal., 2007), as well as Los Blanquitos and La Trampa ranges, cen-tral area of the Precordillera (Albanesi et al., in press). In Lau-rentia, this interval correlates with Histiodella holodentataSubzone of the Periodon macrodentatus Zone (Stouge, 2012).The studied conodont assemblage is accompanied by spongespicules, brachiopods, foraminifers and gastropods. On the other hand, the argillites of the lower member ofthe Los Azules Formation contain a rich graptolite associationreferable to the early middle Darriwilian Levisograptus dentatusZone. It is composed of Tetragraptus quadribrachiatus (J. Hall),Pseudotrigonograptus ensiformis (J. Hall), Xiphograptus lofuensisLee, Acrograptus sp., Holmograptus bovis Williams and Stevens,Isograptus cf. victoriae divergens Harris, Parisograptus caduceus(Salter), Arienigraptus sp., Paraglossograptus tentaulatus (J. Hall),Levisograptus austrodentatus (Harris and Keble), L. cf. dentatus(Brongniart), L. sinicus (Mu and Lee) and L. primus (Legg).The stratigraphic contact of the lower member with the black-grey shales and siltstones of the middle member is partiallysplintered and covered. The latter member hosts a significantgraptolite fauna corresponding to the Pterograptus elegans Zone,just above the deformed levels. The overlying levels are domi-nated by biserial graptolites that represent the Hustedograptusteretiusculus Zone, following Ortega (1987). This way, the mid-dle member is late Darriwilian in age, yet the temporal defini-tion of its lower limit is hampered by the pervasive deformationof the stratigraphic levels. The upper member of the Los AzulesFormation includes graptolites of the Climacograptus bicornisZone (late Sandbian) characterized by the presence of the nom-inal taxon associated with Nemagraptus gracilis, Cryptograptustricornis (Carruthers), Glossograptus ciliatus (Emmons) and avariety of dicranograptids, and biserial graptolites.CONODONTS FROM THE ANDES - Publicación Especial Nº 13 - Julio 2013 - PALEONTOLOGICAL NOTE120Figure 3. Biostratigraphic chart for conodonts and graptolites of the Argentine Precordillera and correlation with reference schemes [modified fromWebby et al. (2004), Ortega et al. (2007), and Maletz et al. (2009)].ACKNOWLEDGMENTSThis study was funded by CONICET (Resolution 4541-12) and SECyT, Universidad Nacional de Córdoba. The pres-ent paper is a contribution to the IGCP Project 591.REFERENCESAlbanesi, G.L., Hünicken, M.A. and Barnes, C.R. 1998. Bioestratigrafía deconodontes de las secuencias ordovícicas del Cerro Potrerillo, PrecordilleraCentral de San Juan, R. Argentina. Actas de la Academia Nacional de Cien-cias, Córdoba 12: 7–72.Albanesi, G.L., Bergström, S.M., Serra, F., Feltes, N.A., Voldman, G.G. andOrtega, G. (in press). Darriwilian (Middle Ordovician) 13C chemostrati-graphy in the Precordillera of Argentina: Documentation of the middleDarriwilian Isotope Carbon Excursion (MDICE) and its use for intercon-tinental correlation. Palaeogeography, Palaeoclimatology, Palaeoecology.Astini, R.A. 1994. Análisis secuencial y paleoambientes de las pelitas negras(aloformación Gualcamayo) que suprayacen a las sucesiones carbonáticaseo-ordovícicas en la Precordillera Argentina. Revista de la Asociación Geoló-gica Argentina 49: 71–84.Astini, R.A., Benedetto, J.L. and Vaccari, N.E. 1995. The early Paleozoic evo-lution of the Argentine Precordillera as a Laurentian rifted, drifted and col-lided terrane: A geodinamic model. Geological Society of America Bulletin107: 253–273.Borrello, A.V. and Gareca, P.G. 1951. Sobre la presencia de “Nemagraptus gra-cilis” (Hall) en el Ordovícico del norte de San Juan. Revista de la AsociaciónGeológica Argentina 6: 187–193.Epstein, A.G., Epstein, J.B. and Harris, L.D. 1977. Conodont color alteration- An index to organic metamorphism.Geological Survey Professional Paper995: 1–27.Furque, G. 1979. Descripción Geológica de la Hoja 16c Jáchal. Servicio Ge-ológico Nacional, Boletín 164: 1–79.Furque, G., González, P. and Caballé, M. 1998. Descripción de la Hoja Ge-ológica 3169-II, San José de Jáchal (Provincias de San Juan y La Rioja). Ser-vicio Geológico Minero Argentino, Boletín 259: 1–150.Harrington, H.J. and Leanza, A.A. 1957. Ordovician trilobites of Argentina.University of Kansas Press, Department of Geology, Special Publication 1,Lawrence, 276 p.Hünicken, M.A. 1985. Lower Ordovician conodont biostratigraphy in Ar-gentina. Boletín Academia Nacional de Ciencias, Córdoba 56: 309–321.Keller, M. 1999. Argentine Precordillera: sedimentary and plate tectonic his-tory of a Laurentian crustal fragment in South America. Geological Societyof America, Special Paper 341: 1–130.Löfgren, A. and Zhang, J. 2003. Element association and morphology in someMiddle Ordovician platform-equipped conodonts. Journal of Paleontology77: 721–737.Maletz, J., Albanesi, G.L. and Voldman, G.G., 2009. Lower Darriwilian radi-olarians from the Argentine Precordillera. Geobios 42: 53–61.Ortega, G. 1987. [Las graptofaunas y los conodontes de la Formación LosAzules, Cerro Viejo, zona de Huaco, Departamento Jáchal, San Juan. Doc-toral Thesis, Facultad de Ciencias Exactas, Físicas y Naturales, UniversidadNacional de Córdoba, Córdoba. Unpublished]: 1-210.Ortega, G., Albanesi, G.L. and Frigerio, S.E. 2007. Graptolite–conodont bios-tratigraphy and biofacies of the Middle Ordovician Cerro Viejo succession,San Juan Precordillera, Argentina. Palaeogeography, Palaeoclimatology, Palae-cology 245: 245–263.Stouge, S. 2012. Middle Ordovician (late Dapingian–Darriwilian) conodontsfrom the Cow Head Group and Lower Head Formation,western New-foundland, Canada. Canadian Journal of Earth Sciences 49: 59–90.Webby, B.D., Cooper, R.A., Bergström, S.M., and Paris, F. 2004. Stratigraphicframework and time slices. In: B.D Webby, F. Paris, M.L. Droser, and I.G.Percival (Eds.), The Great Ordovician Biodiversification Event. ColumbiaUniversity Press, New York, p. 41–47.Zhang, J. 1998. Conodonts from the Guniutan Formation (Llanvirnian) inHubei and Hunan Provinces, south-central China. Stockholm Contributionsin Geology 46: 1–161. VOLDMAN ET AL.: ORDOVICIAN BIOSTRATIGRAPHY AT LOS CAUQUENES RANGE, PRECORDILLERA121

Middle Ordovician conodonts and graptolites at Los Cauquenes range, central Precordillera of San Juan, Argentina

CONICET Digital

https://ri.conicet.gov.ar/bitstream/11336/25701/2/CONICET_Digital_Nro.ac10a69e-d5e1-400b-a961-e06eadbd8d67_A.pdf

Middle Ordovician conodonts and graptolites at Los Cauquenes range, central Precordillera of San Juan, Argentina

Abstract

Similar works

Full text

Available Versions

LAReferencia - Red Federada de Repositorios Institucionales de Publicaciones Científicas Latinoamericanas

CONICET Digital