2015-07-032015-07-032013-12-271666-115Xhttp://hdl.handle.net/2133/4866Se reconocen dentro de la sucesión sedimentaria atribuida al “Loteniense” o “Formación Lotena” en el área del anticlinal de Picún Leufú, dos unidades litoestratigráficas cuya relación de contacto está delineada a través de una superficie de discontinuidad de gran extensión regional. Se propone el nombre de Formación Mutrucó (nov.) para identificar a los antiguamente denominados “conglomerados basales del loteniense”, caracterizados por el desarrollo de depósitos gravosos gruesos de origen aluvial-costero, con retrabajo bajo influencia marina. Se restringe el nombre de Fm. Lotena (emend.) para denominar a la sucesión clástica fina caracterizada por la presencia de depósitos marinos someros, desarrollados entre los sectores de anteplaya inferior a plataforma interna bajo la influencia de oleaje y ocasionales eventos de tormentas (tempestitas). La sucesión de amonites de la Fm. Lotena (emend.), por primera vez descripta en detalle incluyendo especies no registrados anteriormente, permite asignar esta unidad a una posición cronoestratigráfica fehaciente. La sucesión de amonites representa claramente los horizontes patagoniensis y Choffatia de la Zona (cronoestatigráfica estándar) Patagoniensis. Esta zona cronoestratigráfica se correlaciona con la Zona Athleta del Caloviano Superior de la clasificación cronoestratigráfica estándar primaria internacional. Sobre la base de la información bioestratigráfica se asigna la Fm. Lotena (emend.) al Caloviano Superior (y con dudas a la parte baja del Oxfordiano Inferior, Zona Pressulus), mientras que la Fm. Mutrucó (nov.) es atribuida en función de sus relaciones estratigráficas al Caloviano Medio.Stratigraphy and ammonite fauna of the “Lotenian” deposits (Middle Callovian-Lower Oxfordian?) at the Picún Leufú anticline, Neuquén Basin, Picún Leufú Sub-basin, Argentina. The study area is located near the bridge of the National Road 40 on the Arroyo Picún Leufú, about 45 km south of Zapala Town in the Neuquén Province. The studied outcrops are approximately aligned along the Picún Leufú Anticline in the southern part of the Neuqúen Basin. The objective of this paper is to present the results of a detailed stratigraphical and palaeontological study of the Lotena Formation (s.l.). The Neuquén Basin consisted of an ensialic depression in southwestern South America originated in the MiddleLate Triassic in the western margin of the Gondwana Continent. Through the tectonic evolution of this basin there was a topographically positive structure named Dorsal de Huincul or Huincul Arc which acted intermitently dividing the basin asymetrically. South of the Huincul Arc developed a depocenter named Picún Leufú Sub-basin (PLSB) to which the studied deposits of the Lotena Formarion belong. In the PLSB the Lotena Group includes the Lotena, Fortín 1° de Mayo and Barda Negra (subcrop) formations. The Lotena Fm was originally roughly defined including deposits very different genetically, thus producing different interpretations, especially considering its vertical extent and the relationships between the deposits south and north of the Huincul Arc. The current interpretation of the Lotena Fm is as a succesion of conglomerates at the base followed by a thicker succession of yellowish-gray siltstones and yellowish-green claystones with ammonites and ostreids. Along the Neuquén Basin, the “Lotenian” (Lotena Group) includes coarse epiclastic deposits presented as thin horizons of conglomerates and/or coarse sandstones which have been linked to the dynamics of the margins of the basin and, especially, to the Huincul Arc. The basal conglomerate horizon in the section of the Lotena Group at Picún Leufú is herein differentiated from the Lotena Formation as a new lilhostratigraphic unit named Mutrucó Formation (nov.). The pelitic deposits overlying the Mutrucó Fm (nov.) become to conform a restricted Lotena Fm (emend.). The type locality of the Mutrucó Fm (nov.) is the Cañadón Mutrucó (from the Mapuche: Mutrú, agrio; Co, agua). The characteristic lithology consists of 4-5 m of moderately consolidate, coarse, gray conglomerates in the form of tabular bodies with wide lateral extension. The palaeoenvironmental analyisis indicates that the sedimentary processes which produced the deposits of the Mutrucó Fm (nov.) were under marine-alluvial influence. In the Cerro Lotena area the unit may reach a thickness of 16 m. The pelitic deposits overlying the Mutrucó Fm (nov.) and underlying the Fortín 1° de Mayo Fm (conglomerates) conform the Lotena Fm. (emend.). The type locality of the Lotena Fm s.l. has remained undefined, roughly in the Cerro Lotena area, for it is herein designated formally at Cañadón Mutrucó. The Lotena Fm (emend.) is composed by poorly consolidated, pelitic and finely psamitic deposits with thin calcareous siltstone levels commonly fossiliferous. The predominance of fine, light colour sediments with isolated coarse intercalations, and the occurrence of a diverse fossil macrofauna indicate shallow marine conditions, a sedimentary environment in the lower shoreface or inner shelf. The ammonite fauna has been sampled bed-by-bed in order to obtain a succession adequate for a reliable timecorrelation of the Lotena Fm, which had been remained uncertain. The ammonites collected show a moderately diverse local fauna, composed by at least six species belonging to four subfamilies (Hecticoceratinae, Reineckeiinae, Pseudoperisphinctinae and Perisphinctinae). Most of the species have been classified in open nomenclature because of the persistent scarcity and poor preservation of the ammonites in the upper Callovian of the Neuquén Basin. The species indentified are: Hecticoceras cf. lairense (Waagen), Rehmannia patagoniensis (Weaver), transients  and , Rehmannia? sp., Choffatia cf. isabellae Bonnot et al., Alligaticeras? aff. raguini (Gerard & Contaut), and Bol. Inst. Fis. Geol. 83 (2013): 35-68 Rosario - Argentina. Copia impresa / Printed copy [€ 30+5] http://www.fceia.unr.edu.ar/fisiografia Boletín del Instituto de Fisiografía y Geología 83, 2013 Binatisphinctes sp. A. This same ammonite succession is known from better material already described from the patagoniensis Horizon and Choffatia Horizon of the Upper Callovian Patagoniensis (standard chronostratigraphic) Zone of Manzano Escondido, just north of the Huincul Arc. The later transient  of R. patagoniensis has no tubercles on the phragmocone and the bodychamber has a single row of the conical tubercles typical of the species. These specimens closely resemble Jaspeiceras covacevichi Gröschke & Kossler from the upper Callovian/lower Oxfordian of Chile, suggesting Jaspeiceras Gröschke & Kossler could have originated from R. patagoniensis during the Late Callovian. Based on the ammonite succession of the Lotena Fm (emend.), it is concluded confidently that the lower part of this unit is Late Callovian in age, mainly Athleta Zone of the Primary International Standard Chronostratigraphic scale. The upper part of the Lotena Fm (emend.), where no ammonites were found, could be latest Late Callovian to Early Oxfordian in age. The Mutrucó Fm. (nov.) has not yielded ammonites, thus its age is estimated approximately Middle Callovian on the basis of its stratigraphic relationships only.application/pdf35-68spaopenAccessSedimentologíaBioestratigrafíaFormación LotenaFormación Mutrucó (nov.)Cuenca Neuquinaarticle