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F u n 2 d 6 la serena octubre 2015 ada en 19 Ammonite palaeontology and biostratigraphy from the Baños del Flaco Formation (Tithonian – Berriasian), central Chile

Christian Salazara * and Wolfgang Stinnesbeckb a Área Paleontología, Museo Nacional de Historia Natural, Parque Quinta Normal s/n, Casilla 787, Santiago, Chile b Institut für Geowissenschaften, Universität Heidelberg, INF 234, Im Neuenheimer Feld 234, 69120 Heidelberg, Germany

*email: [email protected]

Abstract. Invertebrate fossils are abundant in the Baños 1976, Salazar 2012, Salazar and Stinnesbeck 2015). The del Flaco Formation in the Tithonian (Late Jurassic) part of type locality of the Baños del Flaco Formation is located the section and are scare in the Berriasian (Lower in the homonymous area, in the valley of Río Tinguiririca, Cretaceous). The systematic palaeontology of ammonites central Chile. Four main sections are refered to this unit: from the Rio Maitenes locality (Baños del Flaco Formation) was recently documented and discussed by the authors. Rio Maitenes, Cajón el Fierro, Baños del Flaco south (type New records include Aulacosphinctes proximus, locality) and Baños del Flaco north. During the 1960ies Micracanthoceras spinulosum and Corongoceras Lajos Biro collected the fossils from Rio Maitenes bed-by- evolutum. First registers for Chile include bed. His field book was available to us and allowed us to Pseudolissoceras cf. zitteli, Lithacoceras malarguense, reconstruct the section; additional information was Choicensisphinctes windhauseni, Catutosphinctes cf. gathered through field work by us in the locality (Salazar americanensis, Virgatosphinctes scythicus and and Stinnesbeck 2015). Micracanthoceras microcanthum. Virgatosphinctes scythicus is a morphologically variable species and 2 Methodology synonymous with the South American taxa Virgatosphinctes andesensis, V. mendozanus, V. The Rio Maitenes ammonite assemblage is based on 243 mexicanus and V. leñaensis. Tithonian index fossils for well-preserved specimens. They are all internal moulds. Chile and Argentina are represented by Windhauseniceras Preservation is in three dimensions and deformation is internispinosum and Corongoceras alternans. Tithonian minor. Systematic nomenclature follows the ‘Treatise of index fossils include Virgatosphinctes scythicus previously known from the Russian platform and Micracanthoceras Invertebrate Paleontology’ (Wright et al. 1996; Arkell et microcanthum previously recorded from the Tethys. The al. 1957) to the genus level, and Fossilium catalogus I: record of Substeueroceras koeneni demonstrates that the Animalia, Lower Cretaceous Ammonites I (Klein 2005). uppermost strata of the Baños del Flaco Formation should Lithological descriptions are based on Wright (1992); be referred to the Lower Cretaceous (Berriasian). sedimentology and stratigraphy follow the concept and terminology of Coe et al. (2003), Catuneanu 2006, and Key words: Andes; Jurassic; Cretaceous; ammonites; Nichols (2009). biostratigraphy; palaeobiogeography. 3 Palaeontology and Biostratigraphy 1 Introduction The Baños del Flaco Formation is 369 m thick in the type Upper Jurassic to Lower Cretaceous succession are well locality and 536 m thick at Rio Maitenes; lithologies exposed in the High Andean Mountains of central Chile. consist of conglomerate, limestone, sandy limestone, Particularly, the Tithonian sedimentary rocks are known calcareous sandstone, calcareous siltstone and siltstone (Figure 1). A lower and an upper member are as the Lo Valdés and the Baños del Flaco formations (e.g. distinguished by their lithological composition. Corvalán 1956, Klohn 1960, Biro 1964, Covacevich et al.

601 ST 14 BIOESTRATIGRAFÍA Y PALEONTOLOGÍA ANDINA

Figure 1. Stratigraphical log and ranges of ammonites in the Baños del Flaco Formation at Rio Maitenes. The description of sections and the levels of collection of fossils are based on Biro`s field book and new own observations in the field (Salazar and Stinnesbeck 2015).

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The ammonite assemblage of the Baños del Flaco Substeueroceras koeneni Zone. The index fossil for the Formation is referred to 12 species and 10 genera. zone is S. koeneni, but the taxon is rare; the S. koeneni zone Aulacosphinctes proximus, Micracanthoceras spinulosum is recorded in the upper part of the upper Member of the and Corongoceras evolutum are new records for this Baños del Flaco Formation (Figure 1). formation. Pseudolissoceras cf. zitteli, Euvirgalithacoceras malarguense, Choicensisphinctes We assign the Baños del Flaco Formation to the middle windhauseni, Catutosphinctes cf. americanensis, Tithonian–early Berriasian (Figure 1). The Virgatosphinctes scythicus and Micracanthoceras Virgatosphinctes scythicus-Pseudolissoceras zitteli Zone microcanthum are registered for the first time in Chile. corresponds to the lower part of the middle Tithonian Micracanthoceras spinulosum shows strong ontogenetic based on the presence of V. scythicus, which is the index changes not recorded previously. Virgatosphinctes fossil of the lower middle Volgian (= middle Tithonian). scythicus is here considered a morphologically variable The Windhauseniceras internispinosum Zone is referred species and considered synonymous with classical South to the upper middle Tithonian. The Micracanthoceras American taxa such as Virgatosphinctes andesensis, V. microcanthum - Corongoceras alternans Zone mendozanus, V. mexicanus and V. leñaensis. corresponds to the upper Tithonian Stage, based on the fact Virgatosphinctes aff. pseudolictor, V. cf. raja and V. that M. microcanthum is the zonal index fossil of the upper guadalupensis are considered synonymous with E. Tithonian in the Tethys. The Substeueroceras koeneni malarguense, while V. tenuilineatus is synonymous with Zone is referred to the lower Berriasian Stage (Lower C. windhauseni and Aulacosphinctes chilensis with A. Cretaceous). proximus. Other synonymies include Micracanthoceras Acknowledgements lamberti and M. tapiai, with M. microcanthum, and Corongoceras rigali with C. alternans. We acknowledge the late Lajos Biro (formerly at the Ammonites presented here from the Baños del Flaco Universidad de Concepción), Gerardo Flores, Dr. Luis Formation at Rio Maitenes were collected in situ and bed- Arturo Quinzio–Sinn and Prof. Abraham Gonzalez by-bed. The distribution of the species is summarized in (Universidad de Concepción, Chile). Natalia Varela and Figure 2, and the boundaries of the biozones are tentative Patricio Zambrano (former Universidad de Concepción, at the moment using the lithological control. Chile). Tobias Gerwig and Bolko Janssen (former Universität Heidelberg, Germany). Dr. Georg Heumann Windhauseniceras internispinosum, Aulacosphinctes (STIPB, Bonn, Germany) and Dr. Mike Reich (GZG, proximus, Micracanthoceras microcanthum, M. Göttingen, Germany) are acknowledged for providing spinulosum and Corongoceras evolutum are the most access to material in their care. Dr. Ernesto Pérez abundant taxa. D`Angelo (former SNGM, Chile), Dr. Alfonso Rubilar (SNGM, Chile), Dr. Amaro Mourgues (former SNGM, Hallam et al. (1986) distinguished three biozones based on Chile), Dr. Christina Ifrim (Universität Heidelberg, ammonites collected at Rio Maitenes. Salazar and Germany) and Dr. Mikhail Rogov (Geological Institute of Stinnebeck (2015) re-define this zonation (Figure 1) and RAS Moscow, Russia), Dr. Horacio Parent (Universidad propose the following zonation: Nacional de Rosario, Argentina), Dr. István Főzy (Hungarian Natural History Museum, Hungary – Virgatosphinctes scythicus - Pseudolissoceras zitteli Őslénytani és Földtani Tár) for the supply of information Zone. This zone is characterized by the presence of V. and many helpful comments. Financial support to this scythicus and P. zitteli and also contains Lithacoceras project was given by BMBF CHL13WTZ-22 and malarguense and Choicensisphinctes windhauseni. It is Fondecyt de Iniciación 11140176. present in the lower part of the lower member of the Baños

del Flaco Formation (Fig. 2). Windhauseniceras internispinosum Zone. This zone is References defined by the occurrence of W. internispinosum. Catutosphinctes cf. americanensis and Aulacosphinctes Arkell, W.; Furnish W.; Kummel, B.; Miller, A.; Moore, R.; proximus are also present (Fig. 2). The zone is recorded in Schindewolf, O.; Sylvester–Bradley, P.; Wright, W. 1957. Introduction to Mesozoic Ammonoidea, part L. In Moore, R. C. the upper part of the lower member of the Baños del Flaco (ed.). Treatise on Invertebrate Paleontology, Part L, Mollusca 4, Formation. Cephalopoda–Ammonoidea. Geological Society of America, Boulder, Colorado and University of Kansas Press, Lawrence, Micracanthoceras microcanthum - Corongoceras Kansas. L490 pp. alternans Zone. M. microcanthum and C. alternans are index fossils for this unit, in the lower part of the upper Biro, L. 1964. Estudio sobre el límite Titoniano y el Neocomiano en member of the Baños del Flaco Formation. la Formación Lo Valdés, Provincia de Santiago, principamente en base a Ammonoideos. Memoria de Título (Inédito), Micracanthoceras spinulosum and Corongoceras Universidad de Chile, Departamento de Geología: 118 p. evolutum are also present. Catuneanu, O. 2006. Principles of Sequence Stratigraphy. Elsevier Publishing Co. 375 p., Amsterdam, Boston, Heidelberg. 603 ST 14 BIOESTRATIGRAFÍA Y PALEONTOLOGÍA ANDINA

Coe, A.; Bosence, D.; Church, K.; Flint, S.; Howell, J.; Wilson, R. 2003. The Sedimentary Record of Sea-Level Change. Cambridge University Press. 287 p. Cambridge.

Corvalán, J. 1956. Über marine Sedimente des Tithon und Neocom der Gegend von Santiago. Geologische Rundschau, 43: 919– 926.

Covacevich, V.; Varela, J.; Vergara, M. 1976. Estratigrafía y Sedimentación de la Formación Baños del Flaco al sur del Río Tinguiririca, Cordillera de los Andes. Provincia de Curicó, Chile. Actas I Congreso Geológico Chileno, A, 191–211.

Hallam, A., Biro-Bagoczki, L.; Pérez, E. 1986 Facies analysis of the Lo Valdés Formation (Tithonian-Hauterivian) of the High Cordillera of central Chile, and the palaeogeographic evolution of the Andean Basin. Geological Magazine 123 (4): 425-435.

Klein, J. 2005. Lower Cretaceous Ammonites I, Perisphinctaceae 1: Himalayitidae, Olcostephanidae, Holcodiscidae, Neocomitidae, Oosterellidae. 484 pp. In Riegraf, W. (ed.). Fossilium Catalogus I: Animalia. Backhuys Publishers, Leiden, 139.

Klohn, G. 1960. Geología de Santiago, O’Higgins, Colchagua y Curicó. Instituto de Investigaciones Geológicas Chile. 8. 95 pp.

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Salazar, C. 2012. The Jurassic-Cretaceous Boundary (Tithonian- Hauterivian) in the Andean Basin, Central Chile: Ammonite fauna, Bio- and Sequence Stratigraphy and Palaeobiogeography. Inaugural Dissertation. Universität Heidelberg. Germany. 388 p.

Salazar, C.; Stinnesbeck, W. 2015. Tithonian-Berriasian ammonites from the Baños del Flaco Formation, central Chile. Journal of Systematic Palaeontology,doi:10.1080/14772019.2015.1027310.

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Wright, C.; Callomon, J.; Howarth, M. 1996. Cretaceous Ammonoidea. Treatise on Invertebrate Paleontology, Part L, Mollusca 4. Geological Society of America, Boulder, Colorado and University of Kansas, Lawrence, Kansas. xx + 362 pp.

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