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The western Gondwana margin underwent a complex geodynamic history during the early Paleozoic, and major uncertainties remain as to the role of tectonism in sedimentary dynamics. This study focuses on the lower part Santa Rosita Formation and the coeval Guayoc Chico Group (Cordillera Oriental; Northwest Argentina), ranging from the late Cambrian (Furongian; Age 10) to Early Ordovician (early Tremadocian; Tr1). This stratigraphic interval has been previously interpreted as deposited in an extensional basin to a retro-arc basin without major regional tectonic-induced deformation during its deposition, only recording long-term relative sea-level fluctuations. Four areas (Sierra de Cajas, Angosto del Moreno, Quebrada de Trancas, and Quebrada de Moya) were chosen because they host the most complete and temporally well-constrained stratigraphic sections of the Cordillera Oriental. Throughout the stratigraphic sections, four main facies zones are described and attributed to deposition in estuarine, foreshore-shoreface, delta-front, and offshore environments. Trilobite biozones are used as the biostratigraphic framework. By integrating sedimentary facies analysis, biostratigraphy, and sequence stratigraphy from the four selected sections, a new scenario showcasing the evolution of the basin is proposed. This scenario interprets a tectonically induced deformation during the deposition of the Santa Rosita Formation and the coeval Guayoc Chico Group. The newly acquired sedimentological data show that physiographical changes took place during the Cambrian-Ordovician transition and are expressed in various localities. This major change is recorded in the stratigraphic architecture, where extensive wave-ravinement surfaces and sedimentary hiatus are the result of local, syn-depositional basement uplifts. The initiation of the Puna-Famatinian volcanic arc during the Early Ordovician on the western margin was likely responsible for deformation in the retro-arc basin and the proposed scenario is consistent with the stratigraphic evolution in other areas of the Cordillera Oriental (e.g., Sierra de Mojotoro) and the Sierra de Famatina. Therefore, this study helps to constrain the evolution of the western Gondwana margin during the early Paleozoic, showing changes in the stratigraphic architecture and basin evolution from an extensional to a retro-arc style.

Trilobites, key components of early Palaeozoic communities, are considered to have been invariably fully marine. Through the integration of ichnological, palaeobiological, and sedimentological datasets within a sequence-stratigraphical framework, we challenge this assumption. Here, we report uncontroversial trace and body fossil evidence of their presence in brackish-water settings. Our approach allows tracking of some trilobite groups foraying into tide-dominated estuaries. These trilobites were tolerant to salinity stress and able to make use of the ecological advantages offered by marginal-marine environments migrating up-estuary, following salt wedges either reflecting amphidromy or as euryhaline marine wanderers. Our data indicate two attempts of landward exploration via brackish water: phase 1 in which the outer portion of estuaries were colonized by olenids (Furongian–early late Tremadocian) and phase 2 involving exploration of the inner to middle estuarine zones by asaphids (Dapingian–Darriwilian). This study indicates that tolerance to salinity stress arose independently among different trilobite groups.

Tremadocian–Floian siliciclastic successions in the Argentine Cordillera Oriental are of great interest for the study of early ostracod radiation. Four genera and five species of ostracods have so far been documented in the basin from the Early–Late Tremadocian (Tr2). This contrasts with occurrences from other palaeocontinental areas, where typically only one species is described. Patterns of environmental distribution and ecological approaches of ostracod assemblages were analysed on the basis of richness, Fisher's alpha diversity, relative abundance and occupancy. Ecological patterns remained stable throughout the studied interval, mostly with one genus notably dominant over the others. At the regional scale, dominant taxa occur at a relatively large number of sites, which display high occupancy. The literature data on carbonate successions from the Baltoscandian basin show a similar pattern, with a single taxon dominant over the others in local assemblages and wide regional distribution of these dominants. This ecological pattern would therefore have persisted at least until the Dapingian, independently of the sedimentary regime. Ostracods were already present along the onshore–offshore gradient during the initial stages of radiation, showing a strong preference for deep subtidal settings during Tr2 and then spreading to shallower environments in Tr3 and to deeper ones in the Floian (Fl2–Fl3). A compilation of ostracod diversity data from several regions shows a remarkable increase during the Darriwilian. Based on the regions studied herein, this rise in diversity is decoupled from the environmental expansion of ostracods, as they were already recorded along the onshore–offshore profile early in their history on both siliciclastic and carbonate shelves. The Argentine Cordillera Oriental could be considered as a cradle of diversity, with an important role in the subsequent radiation of the group. Fil: Salas, María José. 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; Argentina Fil: Waisfeld, Beatriz Graciela. 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; Argentina Fil: Muñoz, Diego Fernando. 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; Argentina

The lower Paleozoic marine siliciclastic succession of the Central Andean Basin, northwestern Argentina, provides a valuable record of the onset of the Great Ordovician Biodiversification Event in western Gondwana. A new ichnospecies of rosette trace fossil, Gyrophyllites cristinae, is documented from lower and upper Tremadocian (Tr1 and Tr2) deposits of this basin. It is characterized by five to six non-overlapping petaloid lobes and can be easily differentiated from the other four formally defined ichnospecies. Gyrophyllites cristinae occurs at the top of hummocky cross-stratified sandstone regularly interbedded with mudstone. These deposits are interpreted as reflecting the alternation of high-energy storm events and low-energy fair-weather conditions immediately below the fair-weather wave base, representing deposition in offshore transition environments. Gyrophyllites has been traditionally interpreted as the product of worms of uncertain taxonomic affinity that mined the sediment in search for food (fodinichnia). The occurrence of Gyrophyllites cristinae in these Ordovician deposits records post-storm colonization. Storms may have increased oxygenation and supplied fresh organic detritus that were exploited by worm-like, surface detritus- or shallow deposit-feeders exploring the uppermost silt-rich fine-grained sediments. Fil: Muñoz, Diego Fernando. 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; Argentina. University of Saskatchewan; Canadá Fil: Mangano, Maria Gabriela. 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; Argentina Fil: Buatois, Luis Alberto. University of Saskatchewan; Canadá

Although environmental variability generates differences in the preservation of shell assemblages, intrinsic variations in shell characteristics can confound the effects of environment on preservation. However, several studies proposed that the composition of shell supply only affects the intensity of alteration but not its preservation trend along the environmental gradient and that environmental variability represents a major driver of taphofacies preservation. Here, we examine whether taphonomic differences among four infaunal and aragonitic bivalve species differing in shell thickness affect the definition of beach taphofacies in tropical carbonate environments on San Salvador Island (Bahamas). We show that (1) taphofacies can be discriminated with respect to (a) wave and storm activity as a function of exposure to Trade Winds, and (b) sandy beaches versus beaches with a mixture of sands and beach rock (representing a source of exhumed and cemented shells), and (2) species-specific bivalve assemblages show similar gradients in preservation, documenting that differences in preservation between species have minor effects on taphonomic discrimination of beach environments. Environments with a mixture of sands and beach rock are characterized by higher frequency of external cementation and abrasion than sandy beaches. Shells from low-energy beaches are more fragmented and discolored than shells from high-energy beaches. Previous studies showed that shells from San Salvador sandy beaches are more time-averaged than shells from rocky beaches. Differences in preservation between these two environments indicate two pathways: (1) assemblages on sandy beaches are degraded at higher rate but are enriched by old exhumed and lithified shells, and (2) assemblages on rocky beaches are cemented at higher rate. Old and lithified shells on sandy beaches are probably derived from submerged or exposed beach rock patches, leading to the mixture of young, well-preserved shells with old, poorly preserved shells. Shells on sandy beaches thus experience a complex history of burial and exhumation before their final deposition. Therefore, shell assemblages in lower energy carbonate environments from San Salvador Island are highly time-averaged, with the presence of old, poorly preserved shells. The depositional environment is thus the dominant factor controlling the structure of San Salvador beach taphofacies. Fil: Bayer, María Sol. 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; Argentina Fil: Balseiro, Diego. 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; Argentina Fil: Muñoz, Diego Fernando. 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; Argentina Fil: Gordillo, Sandra. 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; Argentina

Fil: Benedetto, Juan Luis Arnaldo. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Cordoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Cordoba. Facultad de Ciencias Exactas Fisicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; Argentina

The Patagonian Continental Shelf (PCS) is a dynamic region characterized by the confluence of two western boundary currents (the Brazil and Malvinas currents) and the presence of several oceanographic fronts, giving rise to a large and rich biological area. In this study we analyze the distribution pattern of brachiopod assemblages along a latitudinal range between 39°S and 55°S, including the relationship with different physical factors of the benthic zone, either measured in situ (depth, sediment, water temperature, and salinity) or provided by the Bio-ORACLE database (water temperature, salinity, phosphate concentration, nitrate concentration, dissolved oxygen concentration, primary productivity, phytoplankton, and current velocity). Data show that articulate brachiopods were not homogeneous in terms of species composition, body size, relative abundance and taphonomic signatures along the latitudinal gradient, thus indicating environmental sensitivity. The brachiopod assemblages throughout the gradient are characterized by the dominance of Magellania venosa, especially in the internal sector of the platform, accompanied by Terebratella dorsata towards the slope, and Liothyrella uva in the southern sector. Based on all available information, it appears that the main physical factors that affect the distribution of articulate brachiopods from the PCS were sediment grain size and water flow velocities. Also, in M. venosa shells, sediment grain size is also associated with fragmentation, abrasion and encrusting by invertebrates. Finally, the larger sizes of M. venosa appear to be associated with higher productivity areas rich in phytoplankton and suitable environmental water energy. Fil: Gordillo, Sandra. 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; Argentina Fil: Muñoz, Diego Fernando. 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; Argentina Fil: Bayer, María Sol. 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; Argentina Fil: Malvé, Mariano Ezequiel. Universidad Nacional de la Patagonia "San Juan Bosco". Facultad de Ciencias Naturales - Sede Comodoro; Argentina

Fil: Benedetto, Juan Luis Arnaldo. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Cordoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Cordoba. Facultad de Ciencias Exactas Fisicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; Argentina

The re-study of species previously attributed to the genus Nanorthis from the Tremadocian of north-western Argentina has led to the recognition of the new genera Gondwanorthis (type species Nanorthis calderensis Benedetto), to which the Iranian species Nanorthis bastamensis Ghobadi Pour, Kebriaee-Zadeh & Popov is also referred, and Lampazarorthis (type species Eoorthis bifurcata Harrington), which includes Nanorthis brachymyaria Benedetto and Lampazarorthis alata sp. nov. New extensive collections from the Cordillera Oriental support reassignment of the upper Tremadocian species Nanorthis purmamarcaensis to the genus Tarfaya. The species Nanorthis carinata Laurie, from Tasmania, is reassigned here to Tarfaya. According to the present taxonomic revision, Nanorthis is not cosmopolitan but is a pan-tropical genus, confined to Laurentia, the Laurentian-derived Precordillera terrane, and probably to Baltica, Siberia and Kazakhstanian terranes, whereas Gondwanorthis and Tarfaya are Gondwanan and peri-Gondwanan endemic taxa. Cladistic analysis of early orthoids, plectorthoids and dalmanelloids, including those recorded from mid to high latitude Gondwana successions, portrays Gondwanorthis and Lampazarorthis as a sister group basal to the tarfayid C heterorthid clade, whereas the South American and North African Incorthis appears as a basal member of this clade. Morphological and stratigraphical evidence provided in this study, along with the results of the cladistic analysis, supports the view that heterorthids could have arisen from the tarfayids by the end of Floian. The enlargement and incipient bilobation of the cardinal process in Tarfaya grandis leaves this species as a potential ancestor of Tissintia, which occurs in Darriwilian beds of the Central Andean Basin (Bolivia), but could have been present in this basin since the late Floian. We speculate that punctae in the Heterorthidae evolved independently from a Tarfaya-like ancestor, and that the transition from an impunctate to a punctate shell may have occurred repeatedly through rhynchonelliform evolution. Fil: Benedetto, Juan Luis Arnaldo. 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; Argentina Fil: Muñoz, Diego Fernando. 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; Argentina

New graptolite-trilobite records provide relevant information for the biostratigraphic framework of the lower Paleozoic in western Gondwana. Aorograptus victoriae (T. S. Hall), together with Adelogratus cf. A. altus Williams and Stevens and Ancoragraptus bulmani (Spjeldnaes) are described for the first time in the Santa Victoria area. These species come from the upper beds of the Santa Rosita Formation, expanding the distribution of the A. victoriae Biozone. The complete succession of the Aorograptus victoriae, Araneograptus murrayi, Hunnegraptus copiosus, Tetragraptus phyllograptoides, T. akzharensis, Baltograptus cf. B. deflexus and Didymograptellus bifidus biozones is confirmed for the first time at a single locality in the Cordillera Oriental, indicating a late Tremadocian—late Floian age for the upper deposits of the Santa Rosita Formation and the Acoite Formation in the studied area. The co-occurrence of trilobites with the records of these graptolite biozones enables a better resolution of the upper boundary of the Notopeltis orthometopa Biozone and the definition of associations partially filling gaps in the succession of traditional trilobite biozones (Asaphellus cf. A. stenorhachis/Leptoplastides and Megistaspis (Ekeraspis) associations). It also contributes towards clarifying the distribution of some members of the well-known Thysanopyge Fauna (T. taurinus, T. victoriensis and T. clavijoi). Together with the proposed framework, we also discuss previous records of conodonts and key palynomorphs (particularly chitinozoans) related to graptolite occurrences. Additionally, we provide new insights on regional and intercontinental correlation with classic Early Ordovician sections in northwestern Argentina (e.g., Pascha-Incamayo, Los Colorados, Mojotoro range and Humahuaca area), southern Bolivia and Balto-Scandinavia. Nuevos registros de graptolitos y trilobites presentados en este trabajo, permiten ajustar el esquema bioestratigráfico del Paleozoico Inferior del oeste de Gondwana. Aorograptus victoriae (T. S. Hall), junto a Adelogratus cf. A. altus Williams y Stevens y Ancoragraptus bulmani (Spjeldnaes) se describen por primera vez en el área de Santa Victoria (niveles superiores de la Formación Santa Rosita), extendiendo la distribución de la Biozona de Aorograptus victoriae. Se confirma por primera vez la sucesión completa de las biozonas de Aorograptus victoriae, Araneograptus murrayi, Hunnegraptus copiosus, Tetragraptus phyllograptoides, T. akzharensis, Baltograptus cf. B. deflexus y Didymograptellus bifidus en una misma localidad en la Cordillera Oriental, que indica una edad tremadociana tardía—floiana tardía para los depósitos superiores de la Formación Santa Rosita y de la Formación Acoite. Los nuevos hallazgos, permiten precisar el límite superior de la Zona de Notopeltis orthometopa, la definición de asociaciones que completan vacíos de información bioestratigráfica en la sucesión de trilobites (e.g., asociación de Asaphellus cf. A. stenorhachis/Leptoplastides y de Megistaspis (Ekeraspis)), y los rangos estratigráficos de miembros clave de la conocida Fauna de Thysanopyge (T. taurinus, T. victoriensis y T. clavijoi). Se discuten también registros previos de conodontes y palinomorfos guías (particularmente quitinozoos) asociados con graptolitos. Se brindan además nuevas precisiones para la correlación regional e intercontinental con secuencias clásicas del Ordovícico Inferior de las provincias de Salta y Jujuy del noroeste de Argentina, como Pascha-Incamayo, Los Colorados, Sierra de Mojotoro y la Quebrada de Humahuaca, y del sur de Bolivia y Balto-Escandinavia. Fil: Toro, Blanca Azucena. 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; Argentina Fil: Meroi Arcerito, Facundo René. 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; Argentina Fil: Muñoz, Diego Fernando. 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; Argentina Fil: Waisfeld, Beatriz Graciela. 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; Argentina Fil: de la Puente, Graciela Susana. Universidad Nacional del Comahue; Argentina

The early late Tremadocian (Tr2) interval is exceptionally well-represented in eastern areas of the Argentine Cordillera Oriental. New field collections and detailed taxonomic reassessments, as well as a reevaluation of regional data, permit the development of a highly resolved trilobite-based biostratigraphic framework. The concept of the traditional Bienvillia tetragonalis biozone is emended and the new Asaphellus nazarenensis biozone is proposed. Hence, the Tr2 interval encompasses a succession of four trilobite biozones including in ascending order the Kainella teiichii, the Bienvillia tetragonalis, the Asaphellus nazarenensis, and the Notopeltis orthometopa biozones. This resolution is notably higher than that provided by biostratigraphically significant groups such as graptolites and conodonts, and allows a detailed basinwide correlation. New taxonomic information on A. nazarenensis Tortello and Esteban and N. orthometopa (Harrington), is provided and the new species Asaphellus albae sp. nov. is defined. Detailed correlation of the trilobite fauna from the Tr2 interval with that of other paleocontinents is difficult. Taxa are mostly endemic or display wide geographic distributions but with long stratigraphic ranges. Overall, both trilobite-based and indirect international correlations highlight that this interval is hardly recognized, incompletely preserved, or the trilobite fauna is poorly known in most areas of Gondwana. Consequently, due to the completeness of the stratigraphic and fossil records of the Tr2 in the Cordillera Oriental, this region represents a global reference site for the study of this interval. El intervalo Tremadociano temprano tardío (Tr2) está excepcionalmente representado en la Cordillera Oriental, en sus flancos oriental y central. Nuevas colecciones, una revisión taxonómica moderna y la reevaluación de datos regionales, permitieron desarrollar un esquema bioestratigráfico de alta resolución con trilobites. Se modifica el concepto de la clásica biozona de Bienvillia tetragonalis y se establece una nueva unidad, la biozona de Asaphellus nazarenensis. Por lo tanto, el intervalo Tr2 presenta una sucesión de cuatro biozonas de trilobites, en orden ascendente: Kainella teiichii, Bienvillia tetragonalis, Asaphellus nazarenensis y Notopeltis orthometopa. El grado de resolución de este esquema duplica aquél de otros grupos de importancia bioestratigráfica como graptolitos y conodontes, permitiendo de esta manera mayores precisiones en la correlación regional. Asimismo, se brinda nueva información sobre las especies A. nazarenensis Tortello y Esteban y N. orthometopa (Harrington), y se define una nueva especie de asáfido: Asaphellus albae sp. nov. La posibilidad de correlación con sucesiones de otros paleocontinentes para el Tr2 es limitada ya que la mayoría de los taxa son endémicos, o bien presentan una distribución geográfica amplia pero frecuentmente, extensos rangos. Finalmente, tanto las correlaciones basadas en trilobites como aquéllas indirectas sugieren que el intervalo Tr2 es difícil de reconocer, su registro es fragmentario y/ o la fauna de trilobites es pobremente conocida en gran parte de Gondwana. Por lo tanto, dado el completo registro estratigráfico y paleontológico del Tr2 en la Cordillera Oriental, ésta constituye un sitio de referencia a nivel mundial para el estudio de este intervalo. Fil: Meroi Arcerito, Facundo René. Instituto de Investigaciones en Biodiversidad y Biotecnología , Consejo Nacional de Investigaciones Científicas y Técnicas, Facultad de Ciencias Exactas, Físicas y Naturales, Universidad Nacional de Mar del Plata (Grupo de entomología edáfica bonaerense subooriental), Mar del Plata; Argentina Fil: Waisfeld, Beatriz Graciela. 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; Argentina. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones Paleobiológicas; Argentina Fil: Vaccari, Norberto Emilio. 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; Argentina. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones Paleobiológicas; Argentina Fil: Muñoz, Diego Fernando. 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; Argentina. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones Paleobiológicas; Argentina

Se presenta el desarrollo de un sistema de apoyo a la toma de decisiones para calcular medidas de desempeño de un proyecto, incorporando la incertidumbre asociada a la duración de las actividades, considerando además relaciones de precedencia de cuatro diferentes tipos. El sistema genera repeticiones del desempeño del proyecto, donde se simulan las duraciones de las actividades. A partir de ellas, se estiman la duración esperada del proyecto y la probabilidad de que cada actividad forme parte de la ruta crítica, así como medidas del error de las estimaciones. Se realizó una validación de la herramienta con datos simulados, calculando el cubrimiento empírico, valores promedios y desviaciones estándar de los anchos medios, error cuadrático medio y sesgo empírico de la duración esperada. Se observó que se obtienen cubrimientos y anchos medios aceptables para un número pequeño de repeticiones The development of a decision support system to compute performance measures of a project, including the uncertainty associated to the activities duration as well as four different types of precedence relationships is presented. The system generates replicates of the project performance, and in each replication activities’ durations are simulated, From them, the expected completion time and the probability that each activity be part of the critical path are estimated, as well as their corresponding measurements of error. A validation of the decision support system was performed by computing the empirical coverage, mean and standard deviation of halfwidths, mean square error and empirical bias for the expected completion time of a given project. It was observed that good coverage and halfwidth are obtained for a small number of replications.

Este artículo presenta el desarrollo y la aplicación de un modelo de simulación que fue utilizado para pronosticar la demanda de repuestos de automóviles a partir de información obtenida de un distribuidor de automóviles y repuestos en México, D. F. En particular, este trabajo ilustra, con un modelo sencillo, cómo se pueden combinar la simulación estocástica y la estadística bayesiana para modelar y resolver problemas complejos de pronóstico. El marco propuesto es suficientemente general para aplicarse a modelos muy detallados del fenómeno en estudio. Los resultados obtenidos demuestran cómo se puede incorporar la incertidumbre en los parámetros del modelo, y su aplicación usando datos reales, revela cómo la amplitud de la muestra produce una distribución posterior con poca influencia sobre la distribución a priori.This article presents the development and application of a simulation model that was used to forecast the demand of automobile parts using information from a car dealer in Mexico, D. F. In particular, this work illustrates, using a simple model, how stochastic simulation and Bayesian statistics can be combined to model and solve complex forecasting problems. The proposed framework is general enough to be applied to very detailed models of the system under study. The results obtained demonstrate how uncertainty on the parameters of the model can be incorporated, and the application using real data shows how a large sample size produces a posterior distribution that has little influence from the prior distribution. Este artículo presenta el desarrollo y la aplicación de un modelo de simulación que fue utilizado para pronosticar la demanda de repuestos de automóviles a partir de información obtenida de un distribuidor de automóviles y repuestos en México, D. F. En particular, este trabajo ilustra, con un modelo sencillo, cómo se pueden combinar la simulación estocástica y la estadística bayesiana para modelar y resolver problemas complejos de pronóstico. El marco propuesto es suficientemente general para aplicarse a modelos muy detallados del fenómeno en estudio. Los resultados obtenidos demuestran cómo se puede incorporar la incertidumbre en los parámetros del modelo, y su aplicación usando datos reales, revela cómo la amplitud de la muestra produce una distribución posterior con poca influencia sobre la distribución a priori.