Guillermo F. Aceñolaza

Trace fossils and sedimentary facies from a Late Cambrian‐Early Ordovician tide‐dominated shelf (Santa Rosita Formation, northwest Argentina): Implications for ichnofacies models of shallow marine successions

The Santa Rosita Formation is one the most widely distributed lower Paleozoic units of northwest Argentina. At the Quebrada del Salto Alto section, east of Purmamarca, Jujuy Province, it is represented by four sedimentary facies: thick‐bedded planar cross‐stratified quartzose sandstones (A), thin‐bedded planar cross‐stratified quartzose sandstones and mudstones (B), wave‐rippled sandstones and bioturbated mudstones (C), and black and greenish gray shales (D). Paleocurrent data, sandstone architecture, and sedimentary structures from facies A and B indicate bipolar/bimodal paleoflows, suggesting the action of tidal currents. The succession is interpreted as that of a tide‐dominated shelf, with only secondary influence of wave processes. Trace fossils are restricted to facies B and C. The Cruziana ichnocoenosis is preserved on the soles of thin‐bedded planar cross‐stratified quartzose sandstones (facies B). This ichnocoenosis consists of Conostichus isp., Cruziana omanica, C. semiplicata, C. cf. tortworthi,...

The Cambrian System in Northwestern Argentina: stratigraphical and palaeontological framework

Cambrian sequences are widespread in the early Paleozoic of the Central Andean Basin. Siliciclastic sediments dominate these sequences although several minor occurrences of carbonates and volcanic rocks have been observed. The rocks assigned to the Cambrian System in NW Argentina are recognized in the Puna, Eastern Cordillera, Subandean Ranges and the Famatina System. This paper gives a general overview of the Cambrian formations outcropping in the northern provinces of Jujuy, Salta, Tucuman, Catamarca and La Rioja. Special emphasis has been given to the stratigraphical and biostratigraphical framework of the sequences. Late Precambrian-Early Cambrian thick sedimentary wackes dominate the basal Puncoviscana Formation (s.l.), characterized by a varied ichnofauna that includes the Precambrian-Cambrian transitional levels. Thick packages of sandstone facies characterize the overlying highly ichnofossiliferous Meson Group. A rich shelly fauna included in sandstones, shales and volcaniclastics, dominate in the Cambrian-Ordovician transitional levels of the overlying Cambro-Ordovician Santa Victoria and Cachiyuyo Groups. Palaeogeographic aspects dealing with the position and development of Cambrian basins are discussed. Several synthetic biostratigraphic tables are presented displaying the known record for the Cambrian System, including the transitional levels to the lowermost Ordovician in the above-mentioned regions.

El Ordovícico Medio del Anti-Atlas marroquí: paleobiodiversidad, actualización bioestratigráfica y correlación

Resumen Las formaciones del Ordovicico Medio del Anti-Atlas (sur de Marruecos) han librado un variado registro de trilobites, moluscos, equinodermos, braquiopodos, graptolitos, microfosiles e icnofosiles en alrededor de 180 localidades. Gran parte de ellas fueron descubiertas durante la realizacion de la cartografia geologica a escala 1:200.000 y la mayoria del material paleontologico permanece inedito. En este trabajo se revisa el marco geologico de todas las localidades fosiliferas conocidas (tanto las publicadas como las ineditas), poniendose en evidencia numerosas discrepancias litoestratigraficas en relacion con estudios precedentes. Ademas de la reevaluacion estratigrafica, se revisa el contenido paleontologico de cada formacion y localidad, actualizando la taxonomia de muchas de las formas identificadas. Desde el punto de vista cronoestratigrafico, el conjunto de la Formacion Tachilla y las cinco formaciones del Grupo Primer Bani se adscriben por vez primera a la escala regional mediterranea. Los limites Oretaniense-Dobrotiviense y Dobrotiviense-Berouniense se situan, respectivamente, en la Formacion de Bou-Zeroual y en el techo de la Formacion Izegguirene. El transito Oretaniense inferior-superior se emplaza provisionalmente en el tercio superior de la Formacion Tachilla, y el limite Dobrotiviense inferior-superior hacia la base o en la parte inferior de la Formacion Ouine-Inirne. Tambien se aporta la correlacion general de las unidades del Ordovicio Medio antiatlasico con respecto a la escala estandar o global del sistema Ordovicico. La base de la Serie Ordovicico Superior se situa probablemente en la parte inferior de la region como un centro importante de diversificacion para numerosas faunas mediterraneas, las cuales experimentan una amplia dispersion posterior en las plataformas marinas del norte de Gondwana.

El Alisal: a new locality with trace fossils of the Puncoviscana Formation (late Precambrian-early Cambrian) in Salta Province. Argentina

The Puncoviscana, Suncho and Las Aguaditas/Negro Peinado formations represent a thick siliciclastic folded succession that crops out on a strip about 800 km long and 150 km wide in northwestern Argentina (Jujuy, Salta, Tucuman, Catamarca and La Rioja provinces). These sequences are lithologically characterized by very lowgrade metamorphic sediments grading from slates to schists; turbidites, pelagic clays, limestones and volcanic rocks. On the basis of paleoichnological data, these units have been assigned to the late Precambrian-early Cambrian. A new locality bearing well preserved trace fossils from the Puncoviscana Formation is described herein. The outcrop is located about 45 km west of Salta city (Salta Province), displaying an alternation of colored differentiated grayish-bluish slates and fine sandstones. Ichnofossils include Cochlichnus anguineus HITCHCOCK, Helminthoidichnites tenuis FITCH, Helminthoida isp., Monomorphichnus lineatus CRIMES, LEGG and MARCOS ARBOLEYA, Planolites isp. and Torrowangea? isp., as well as some limb marks and a few slightly bended smooth trails (indet.). An Early Cambrian age for the succession at El Alisal as well as some environmental considerations are allowed by the ichnological association. In addition, the ichnogenus Planolites is mentioned for the first time from the “red shales and conglomerate type” facies at the neighbor locality of Chorrillos.

Chapter 9.3 Trace Fossils and the Agronomic Revolution at the Neoproterozoic-Cambrian Transition in Southwest Gondwana☆

Abstract The Ediacaran-Early Cambrian transition in the southwestern margin of Gondwana is represented in the Andean Margin of South America by the thick sequence of the Puncoviscana Basin. In southern Africa, the Nama and Vanrhynsdorp groups display partially equivalent successions. Trace fossil assemblages are well known from both regions, with relatively simple, low diversity forms in the lower stratigraphic levels. An increase in complexity is recorded in the upper sector of the Andean and African sequences, with a variety of Treptichnus -type traces that denotes a more gradual diversity increase towards the Cambrian than generally accepted. Trace fossil associations indicate that the fossiliferous levels of the Puncoviscana Basin may predate the uppermost lower Cambrian (pre-trilobite) successions of the Nama and Vanrhynsdorp groups, and lasted into the ‘trilobitic’ Cambrian. Intergradations between Treptichnus and different ichnogenera cast doubts on using related ichnospecies in Ediacaran-Early Cambrian biozonation.

Middle Ordovician (early Dapingian) conodonts in the Central Andean Basin of NW Argentina

Carlorosi, J., Heredia, S. & Aceñolaza, G, 2013. Middle Ordovician (early Dapingian) conodonts in the Central Andean Basin of NW Argentina. Alcheringa 37, 1–13. ISSN 0311-5518. This paper describes and analyzes the significance of a conodont fauna from the Alto del Cóndor Formation, exposed in the Los Colorados region of the Argentine Eastern Cordillera. Identified taxa are Baltoniodus triangularis, Baltoniodus sp. cf. B. triangularis, Drepanodus sp., Drepanoistodus basiovalis, Drepanoistodus sp. B., Erraticodon patu, Gothodus costulatus, Oistodus sp., Trapezognathus diprion, T. quadrangulum, Triangulodus sp. and Triangulodus? sp. The presence of Baltoniodus triangularis indicates the base of the Dapingian stage (Middle Ordovician). In addition, we report the coexistence of T. diprion and T. quadrangulum. The conodont association suggests a faunal affinity with Baltica and South China, both belonging to the Shallow-Sea Realm of the Temperate-Cold Domain. Josefina Carlorosi [josefinacarlorosi77@gmail]com], INSUGEO—Universidad Nacional de Tucumán—CONICET, Miguel Lillo 205, (4000) Tucumán, Argentina; Guillermo F. Aceñolaza [acecha@webmail.unt.edu.ar], Universidad Nacional de Tucumán—CONICET, Miguel Lillo 205, (4000) Tucumán, Argentina; Susana Heredia [sheredia@unsj.edu.ar], CONICET–CIGEOBIO and Instituto de Investigaciones Mineras, Facultad de Ingeniería, Universidad Nacional de San Juan, Urquiza y Libertador, (5400) San Juan, Argentina. Received 22.8.2012; revised 18.10.2012; accepted 24.10.12.

The worm Palaeoscolex from the Cambrian of NW Argentina: extending the biogeography of Cambrian priapulids to South America

Over one hundred years of palaeontological research in northwestern Argentina has provided extensive knowledge of Andean lower Palaeozoic fossil assemblages, with trilobites, graptolites, brachiopods and echinoderms being among the most prominent groups. This record is enriched by the recent discovery of soft-bodied worms in Cambrian outcrops of northwestern Argentina. Palaeoscolex sp. cf. P. ratcliffei from the Furongian Lampazar Formation in Jujuy is described, considerably expanding the biogeographical range of this genus and filling the distributional gap, between the well-known early–middle Cambrian occurrences of Palaeoscolex and those of its Ordovician species.

THE EYES OF THE EARLY TREMADOC OLENID TRILOBITE JUJUYASPIS KEIDELI KOBAYASHI, 1936

Abstract The morphology of the eyes of the olenid trilobite Jujuyaspis keideli Kobayashi, 1936, is described and illustrated. Studied specimens come from Early Tremadocian pyritiferous black shales of the Casa Colorada Formation (=Purmamarca shales) at Purmamarca, Jujuy Province, northwestern Argentina. The eyes are holochroal and proportionately large relative to the overall size of cephalon. They are always found attached to the librigena, showing no preserved lenses, only molds of their surfaces. Their molds demonstrate that lenses were numerous, biconvex, hexagonal in outline and arranged in an hexagonal close-packing system. The eye curvature and the disposition of the facets covering all the visual surface indicate that Jujuyaspis keideli Kobayashi had a visual field wider than that of most benthic olenids. The pattern of lens arrangement and the poorly developed peripheral zone support pelturine affinities for the species.

Integrated study of fauna and microflora from the Early Devonian (Pragian–Emsian) of northwestern Argentina

The Devonian System in northern Argentina has been broadly analysed, but details of its lithologies, biostratigraphy and fossil content have not been presented in a comprehensive study. We performed the first integrative analysis of the palynological and macrofossil content from the Pescado Formation at the Zenta Range, Argentina. We define a new species of cryptospore and extend the stratigraphic record of the ichnogenus Psammichnites isp. for South America. The stratigraphic ranges of the palynomorphs suggest a time span from the ?late Lochkovian to Pragian–earliest Emsian, but the co-occurrences of key invertebrates narrow the age of the beds to the late Pragian and early Emsian. Moreover, sedimentary analysis indicates a proximal shoreface–foreshore depocenter during this time range for the Zenta region. The contraction phase of the basin during the middle Pragian and Emsian is evidenced by the presence of sand bodies at the top of the column and the higher supply of terrigenous components. During this regression event, a low diversity Malvinokaffric Realm brachiopod assemblage occurs, with dominance of Australospirifer hawkinsi. The predominance of the latter species during this event is coeval with the first decline of the Malvinokaffric Realm in the neighbouring Paraná basin.

Basin evolution of the margin of Gondwana at the Neoproterozoic/ Cambrian transition: the Puncoviscana Formation of Northwest Argentina

The Puncoviscana Formation is an important stratigraphic sequence of sandstones and shales, with intercalated conglomerates, limestones and volcanic rocks. It was deposited at the Neo- proterozoic-Cambrian boundary in a shallow basin on the western margin of Gondwana. Trace fos- sils of the Puncoviscana Formation s.l. are represented by the Oldhamia and Nereites ichnoassocia- tions and the geographical distribution of assemblages are aligned as parallel belts, with a shallower eastern Nereites association and a deeper western Oldhamia association. They represent different temporal levels on the evolution of the basin. Detrital zircon spectra display a wide range of ages, which indicate their provenance from Neoproterozoic to Cambrian source areas as well as Meso- to Paleoproterozoic basement units, exhibiting typical Gondwanan ages. Thick limestone banks are interbedded in the Puncoviscana Formation s.l. that included the siliciclastic sequences, with very low- to medium-metamorphic grade. δ13C values for the limestones vary from -1.57 to +3.40/00 VPDB, while in the Sierras Pampeanas, δ13C values vary from +2.6 to +80/00 VPDB. Also, reported 87Sr/86Sr values allow a clear differentiation of two rock sets. The limestones interbedded with the Puncoviscana Formation yielded values typical for the Neoproterozoic-Cambrian transition, between 0.70868 and 0.70896; while the limestones of the Sierras Pampeanas display values between 0.70748 and 0.70756, common in the middle to late Ediacaran. Deformation and uplift of the Puncoviscana Formation is clearly represented in northern Argentina by the Tilcarian unconformity, which is over- lain by the Meson Group.