Papers by Silvina de Valais
Geological Society, London, Special Publications
The ichnology between marine and non-marine environments is a key field of work concerning the un... more The ichnology between marine and non-marine environments is a key field of work concerning the understanding of the variation of environmental parameters in inland-to-offshore transitional environments. In order to understand the geological and palaeobiological processes at these locations, this Special Publication attempts to discuss records in shallow-marine and transitional environments throughout the Phanerozoic, including topics such as ichnotaxonomy, ichnofacies analysis, ichnofabric analysis for records from both shallow-marine and transitional environments, and neoichnological aspects. The volume includes 14 papers in total: one focused on aspects of neoichnology in rock iguanas in coastal settings, nine concerning various shallow-marine palaeoenvironment topics and four addressing issues about dinosaur tracks in transitional environments.
Brazilian Journal of Geology
The Yacoraite Formation (NW Argentina) displays important microbialitic deposits of varied featur... more The Yacoraite Formation (NW Argentina) displays important microbialitic deposits of varied features throughout its six sub-basins. With the discovery of important microbialitic hydrocarbon reservoirs and the interest in lacustrine systems due to recent hydrocarbon finds in the presalt Cretaceous series of the South Atlantic, the importance of these organo-sedimentary structures has increased considerably. Because of this, in the past decade, numerous works in Yacoraite Formation have focused on its microbialites. In this study, we provide an updated summary of the existing background and state of knowledge of the microbialites in the Yacoraite Formation, which occupy different stratigraphic positions in diverse sub-basins separated by several kilometers. Due to this, these structures have developed under diverse conditions, giving rise to a great variety of structures and morphologies, useful as reliable and high-resolution proxies for paleoenvironmental studies and to discuss important ecological paradigms. In addition, microbialites of Yacoraite Formation show promising petrophysical conditions to be evaluated as reservoir rocks. Based on the large number of deposits mentioned throughout this work, and the morphological and structural variety of their microbialites, we can highlight Yacoraite Formation as one of the most important microbialite-bearing units in Argentina and South America.
Diversity
The Campanian Anacleto Formation holds an abundant and diverse ichnofossil and body-fossil verteb... more The Campanian Anacleto Formation holds an abundant and diverse ichnofossil and body-fossil vertebrate record. Despite the striking diversity of this record, pterosaur fossils had never been described from the unit. Here, we report four pterosaur manus tracks from fluvial red beds cropping out in the Área Natural Protegida Municipal Paso Córdoba (Río Negro Province, northern Patagonia, Argentina). Tracks are longer than wide, tridactyl with digit impressions of different lengths (I < II < III), anteriorly directed and laterally asymmetrical. Being on loose slabs and lacking direct examination of pes morphology, the material is classified as undetermined pterosaur tracks. The new find represents the first occurrence of pterosaurs from the lower–middle Campanian of Argentina and one of the few evidences from South America for this time interval. In addition, it is one of the few ichnological pterosaur records from Gondwana, thus shedding light on the palaeobiogeography of this cl...
Oliveira, Jacqueline Freitas. Laboratorio de Paleontologia e Evolucao UFG, Instituto de Ciencias ... more Oliveira, Jacqueline Freitas. Laboratorio de Paleontologia e Evolucao UFG, Instituto de Ciencias Biologicas UFG; Brasil.
Journal of Vertebrate Paleontology, Mar 12, 2008
The ichnotaxobases previously used to classify avian-like footprints, at the ichnogeneric, ichnos... more The ichnotaxobases previously used to classify avian-like footprints, at the ichnogeneric, ichnospecific, and ichnofamily level, are varied and contrasting. Consequently, an agreement on the most adequate taxobases to use for classifying these vertebrate trace fossils is necessary. The authors follow an ichnotaxonomy treatment independent to the age, locality provenance, and possible tracemaker of the trace fossils. The ichnotaxobases used to classify tracks with avian affinities at ichnogeneric and ichnospecific levels are evaluated and a proposal is made for useful and appropriate ichnotaxonomic criteria, considering those currently in use. Previous criteria used to distinguish avian footprints from non-avian theropod or ornithischian tracks are discussed. These concepts are applied to the avian footprints from the upper part of the Late Triassic-Early Jurassic Santo Domingo Formation from La Rioja province, northwest Argentina, which has yielded a diverse assemblage of trace fossils. The most conspicuous avian footprint is Gruipeda dominguensis isp. nov. The ichnogenus Gruipeda Panin and Avram, 1962 is revised and an emendation of its diagnosis is suggested.
Palaeogeography, Palaeoclimatology, Palaeoecology, Feb 1, 2009
The purpose of this study is to apply neoichnological observations to the behavioural and taphono... more The purpose of this study is to apply neoichnological observations to the behavioural and taphonomic interpretation of a Late Triassic-Early Jurassic track surface from the Santo Domingo Formation (Argentina) containing hundreds of bird-like tracks and trackways. In addition, the factors affecting the formation and preservation of bird tracks in lacustrine settings are particularly addressed. The 5.5 m 2 fossil track surface contains different types of trace fossils: the avian ichnotaxa Gruipeda dominguensis (the most abundant), bird-like tracks with elongated hallux impressions, small epichnial rounded pits, and invertebrate traces (Skolithos, Taenidium). The modern environmental analogue chosen for the neoichnological studies was a coastal freshwater pond (the Bajo de los Huesos, Chubut, Argentina) seasonally occupied by sandpipers (Calidris bairdii and Calidris fuscicollis; Charadriiformes). The comparison between the fossil succession and the modern example suggests that they share lithology and sedimentary structures and that sedimentary processes and local palaeoenvironment were fairly similar and do not bias ichnological comparisons. Field observations allowed to distinguish twenty one behaviours that produced distinct traces and four modern footprint types (1 to 4) related to specific substrate conditions. In particular, the preferential formation of bird tracks parallel to the waterline, also confirmed by studies on droppings and invertebrate fauna of the pond, and other associated sedimentary features (ripple marks, wrinkle marks, mud drape thickness) and trace fossils were important for recognition of the shoreline in the fossil example. These observations also allowed us to distinguish the adjacent deeper and shallower parts of the fossil pond and can be applicable to other similar case studies. Contrasting sediment properties and footprint types, some relationships and constraints on the formation and preservation of modern footprints are proposed; although these are very complex processes that will require further studies. Five of the behaviours recognised in the modern pond were inferred from the sixteen trackways distinguished on the fossil track surface, including walking, walking with a zigzag path, short runs, probing, and landing with legs directed forward (possible trace of flight). The recognition of traces of flight (Volichnia), probing marks, and tracks showing morphology similar to modern shorebirds (G. dominguensis), strongly suggest an avian affinity for the producers of the fossil tracks and, in consequence, the Santo Domingo track site would be younger than supposed.
Palaeogeography, Palaeoclimatology, Palaeoecology, Sep 1, 2006
This paper discusses the lithofacies distribution and ichnotaxonomic assignment of invertebrate, ... more This paper discusses the lithofacies distribution and ichnotaxonomic assignment of invertebrate, vertebrate and plant trace fossils in an Early Mesozoic ephemeral fluvio-lacustrine system from northwest Argentina. The overall palaeoenvironment is envisaged as a distal, low-gradient fluvio-lacustrine setting under semi-arid climate, similar to a terminal fan. Depositional lobes (facies association A) are composed of distributary ribbon channels (facies A1), and associated pond and sheetflood deposits (facies A2). Lowlands between depositional lobes (facies association B) contained poorly drained floodplain zones similar to wetlands (facies B1) and shallow closed lakes (facies B2). Depositional lobes were fringed by playa-lake settings (facies association C), including mudflats (facies C1) that are partially eroded by ephemeral fluvial channels (facies C2). The ichnofauna of the Santo Domingo Formation displays high ichnodiversity (30 trace fossil types) and includes 5 trace fossil assemblages that are linked to sedimentary facies. These trace fossil assemblages are highly distinctive as half of the recognised trace fossil types are assigned to different assemblages. The ephemeral fluvial channel assemblage (facies A1 and C2) displays the lower ichnodiversity (n = 6) and includes Skolithos linearis, Diplichnites sp., Palaeophycus tubularis, Taenidium barretti, Dicynodontipus sp. and footprints in cross-section. The floodplain pond assemblage (facies A2) shows the higher ichnodiversity (n = 15) and is composed of Diplichnites sp., Helminthoidichnites tenuis, P. tubularis, Rusophycus carbonarius, S. linearis, Spongeliomorpha carlsbergi, T. barretti, appendage marks, burrows with brush-like features, epichnial bilobed traces, hypichnial bilobed ridges, bird-like footprint type A, tridactyl footprints, footprints preserved in cross-section, and small epichnial rounded pits. The poorly drained floodplain assemblage (facies B1) is of moderate ichnodiversity (n = 10) and consists of H. tenuis, S. carlsbergi, ?Spongeliomorpha sp., imbricated backfilled burrow fillings, root trace type A, Tetrasauropus sp., bird-like footprint type A, large pentadactyl footprints, tridactyl footprints, and footprints preserved in cross-section. The high ichnodiversity (n = 13) nearshore lacustrine assemblage (facies B2) is the only assemblage that lacks vertebrate traces, and is composed of Cochlichnus anguineus, Cruziana problematica, H. tenuis, Palaeophycus heberti, P. striatus, P. tubularis, Scoyenia gracilis, S. carlsbergi, T. barretti, epichnial bilobed traces, hypichnial bilobed ridges, root trace type B, and scratch marks. The intermediate ichnodiversity (n = 9) mudflat assemblage (facies C1) is typified by the largest ichnodiversity of vertebrate tracks and includes H. tenuis, P. tubularis, S. carlsbergi, Dicynodontipus sp., Tetrasauropus sp., bird-like footprints of types B and C, large pentadactyl footprints, and tridactyl footprints. The trace fossil assemblages from Santo Domingo Formation are typical representatives of the Scoyenia ichnofacies. The distinctiveness of the studied trace fossil assemblages suggests that a future division of the Scoyenia ichnofacies would be possible, provided that occurrences of invertebrate, vertebrate and plant trace fossils in definite sedimentary facies are considered. The
Palaeontology, Mar 1, 2006
This paper contains the first comprehensive ichnotaxonomic review of the Triassic tetrapod track ... more This paper contains the first comprehensive ichnotaxonomic review of the Triassic tetrapod track record in Argentina, including previous accounts and new material recently discovered, and an analysis of its composition and stratigraphic distribution. Triassic footprints have been recorded from three basins: the Ischigualasto-Villa Unió n and Cuyo basins in northwest Argentina, and the Los Menucos depocentre in northern Patagonia. Most are in successions of Middle Triassic age; a lower number are from the Late Triassic, and there are two records from Early Triassic rocks. The known track types include: Brachychirotherium isp., cf. Brachychirotherium isp., Chirotherium barthii, Dicynodontipus ispp., Grallator isp., Rhynchosauroides isp., Rigalites ischigualastianus, Rigalites isp., Tetrasauropus isp., and bird-like, chirotheriid and unidentified tridactyl footprints. The ichnogenera Gallegosichnus Casamiquela, 1964, Calibarichnus Casamiquela, 1964, Palaciosichnus Casamiquela, 1964 and Stipanicichnus Casamiquela, 1975 are considered to be synonyms of Dicynodontipus (Hornstein, 1876). In addition, the abandonment of the following ichnogenera (and single ichnospecies) that are based on poorly preserved material is suggested: Ingenierichnus sierrai Casamiquela, 1964, Rogerbaletichnus aguilerai Casamiquela, 1964 and Shimmelia chirotheroides Casamiquela, 1964. At least eight Triassic ichnofaunas can be recognized. The most peculiar is that of the Late Triassic Los Menucos depocentre, which is characterized by the dominance of therapsid footprints (Dicynodontipus ispp.). The track assemblages from the Cuyo Basin display the highest ichnodiversity, with five footprint types.
Nature, Jun 27, 2002
I thank S. Zaranek for the finite difference cooling calculations, S. Grand for the global shear-... more I thank S. Zaranek for the finite difference cooling calculations, S. Grand for the global shear-wave velocity model, G. Abers for his gravity code, and D. Forsyth, D. Scheirer and Y. Liang for discussions. This research was supported by the NSF Geophysics Program.
Cretaceous Research, Oct 1, 2023
Environmental Earth Sciences, 2019
The present study aimed at performing a quantitative evaluation to propose a geoconservation plan... more The present study aimed at performing a quantitative evaluation to propose a geoconservation plan to the São Domingos geosite, and, therefore, to contribute with feasible actions, to the preservation of this paleontological heritage. The study area is located in the district in the Itaguatins municipality, northern Tocantins state, Brazil. The studied geosite is characterized by the presence of track fossils. The tracks have been assigned to herbivorous dinosaurs, basal sauropods, which were living in the area during the first periods of the Cretaceous. The following aspects were quantitatively evaluated: risk of degradation and potential for the educational and touristic use of the area. All these aspects were quantitatively evaluated with the methodology described in the app web GEOSSIT, administered by the Companhia de Pesquisa de Recursos Minerais. The São Domingos geosite has a high scientific value, with a national relevance, a moderate potential of educational use, a low potential of tourist use, and a high risk of degradation. The site, with interest and paleontological value, has the potential to be used in all level educational activities at, and it is important it should be used for such activities. The elements of the geosite are currently in an advanced degree of degradation, and urgent measures are required to mitigate the erosive activities that affect the footprint-bearing surfaces and that gradually increase their erosion.
Publicación Electrónica de la Asociación Paleontológica Argentina: Vol. 20 Núm. 1, Jan 7, 2021
El proposito fundamental de esta investigacion fue el de realizar una valoracion sobre la percepc... more El proposito fundamental de esta investigacion fue el de realizar una valoracion sobre la percepcion de los estudiantes sobre la implementacion de actividades secuenciadas didacticamente sobre la ensenanza del contenido regla de tres simple directa e inversa y los resultados en funcion de sus aprendizajes significativos. Esta experiencia educativa se realizo con 33 estudiantes de septimo grado de educacion media regular del colegio San Sebastian, durante el segundo semestre del ano academico 2015 del municipio de Acoyapa-Chontales. Considerando que el proceso ensenanza aprendizaje es un tema de alto grado de interes, e implica un cuestionamiento acerca de las realidades educativas, resultando oportuno intervenir de manera directa en su estudio. Es una investigacion desarrollada en los salones de clase, donde existen diferentes dificultades por parte del estudiantado en cuanto al exito de su aprendizaje, lo que permite describir los fenomenos educativos relacionados al contexto en qu...
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Papers by Silvina de Valais