Pablo Pazos
Universidad de Buenos Aires, Geological Sciences, Faculty Member
- I Obtained a Geology degree from Buenos Aires University as well as a Ph.D. for the same institution. Post-Doct studi... moreI Obtained a Geology degree from Buenos Aires University as well as a Ph.D. for the same institution. Post-Doct studies were at the University of Liverpool (UK). I am a Principal Researcher at CONICET and Associate Professor (UBA). I am the head of the GISS Group (Ichnology, Sedimentology, and Substrate Group) in the IDEAN. I am The Head of the Institute IDEAN and y correct research interest involve sedimentology, stratigraphy and ichnologyedit
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Abstract: The Agrio Formation (Valanginian to early Barremian) is a siliciclastic and carbonate unit of the Neuquén Basin in west central Argentina. A conspicuous 20 m thick dolomitized section near the top of the upper Agua de la Mula... more
Abstract: The Agrio Formation (Valanginian to early Barremian) is a siliciclastic and carbonate unit of the Neuquén Basin in west central Argentina. A conspicuous 20 m thick dolomitized section near the top of the upper Agua de la Mula Member of the Agrio Formation was identified ...
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ABSTRACT Ichnological synthesis of the marine units of the Neuquén Basin, new data and future perspectives. In this paper the ichnology of the marine intervals of the Neuquén Basin is reviewed, taking into account an stratigraphic... more
ABSTRACT Ichnological synthesis of the marine units of the Neuquén Basin, new data and future perspectives. In this paper the ichnology of the marine intervals of the Neuquén Basin is reviewed, taking into account an stratigraphic framework and discussing previous works on ichnology that contain some ichnogenera (Lapispira) that are firstly documented in South America in Jurassic of the Río Atuel area, and other ichnogenera that constitute well preserved records in the Jurassic tidal influenced deltas of the Lajas Formation. The trace fossil record includes Asterosoma, Asteriacites, Dactyloidites, Diplocraterion, Gyrochorte, Palaeophycus, Polykladichnus, Schaubcilindrichnus, Siphonichnus, Thalassinoides, Teichichnus and rare traces in shallow marine deposits like Helminthorhaphe and root traces indicative of a very complex facies scheme. A special mention deserves the traces from the carbonates of the La Manga Formation at Bardas Blancas, that contain ichnogenera like Dactyloidites, Gyrochorte, Jamerosonichnites and Thalassinoides recorded in tempestites. The Lower Cretaceous record documented in the Mulichinco and Agrio Formation is composed of Asteriacites, Gyrochorte, Lockeia, Ophiomorpha, and possibly Bergaueria, documented in the Mulichinco Formation at Vega de Escalone locality. Other traces described in the Agrio Formation are Gyrochorte, Ophiomorpha, Thalassinoides, Teichichnus among others of dubious assignation recorded at Bajada del Agrio and other areas of the basin. New material coming from both units includes subaqueous vertebrate scratchs (Characichnos?) both from Vega de Escalone and Puerta Curaco. Arthropod trackways include both some with differentiated (Diplichnites?) and other specimen with undifferentiated appendages. In the indicatives of subaerial exposure in sections expected to be fully marine. Complex traces assigned to Hillichnus produced by tellinacean bivalves are the only record of such bivalves in the basin. Those ichnogenera are good examples that precede body fossil records and along with the scratch marks suggest very unexpected according to paleogeographic maps. Finally a brief analysis of the further work in the turbidites of the Molles Formation or the exploration of bioerosion and meiofauna records suggest that the knowledge about the ichnology of the Neuquén Basin is in its infancy if it is compared with the stratigraphic, paleontologic (biostratigraphic) and sedimentologic studies and also remains unexplored related to changes in permeability of reservoirs of bioturbated deposits documented from cores.
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ABSTRACT Ichnological synthesis of the marine units of the Neuquén Basin, new data and future perspectives. In this paper the ichnology of the marine intervals of the Neuquén Basin is reviewed, taking into account an stratigraphic... more
ABSTRACT Ichnological synthesis of the marine units of the Neuquén Basin, new data and future perspectives. In this paper the ichnology of the marine intervals of the Neuquén Basin is reviewed, taking into account an stratigraphic framework and discussing previous works on ichnology that contain some ichnogenera (Lapispira) that are firstly documented in South America in Jurassic of the Río Atuel area, and other ichnogenera that constitute well preserved records in the Jurassic tidal influenced deltas of the Lajas Formation. The trace fossil record includes Asterosoma, Asteriacites, Dactyloidites, Diplocraterion, Gyrochorte, Palaeophycus, Polykladichnus, Schaubcilindrichnus, Siphonichnus, Thalassinoides, Teichichnus and rare traces in shallow marine deposits like Helminthorhaphe and root traces indicative of a very complex facies scheme. A special mention deserves the traces from the carbonates of the La Manga Formation at Bardas Blancas, that contain ichnogenera like Dactyloidites, Gyrochorte, Jamerosonichnites and Thalassinoides recorded in tempestites. The Lower Cretaceous record documented in the Mulichinco and Agrio Formation is composed of Asteriacites, Gyrochorte, Lockeia, Ophiomorpha, and possibly Bergaueria, documented in the Mulichinco Formation at Vega de Escalone locality. Other traces described in the Agrio Formation are Gyrochorte, Ophiomorpha, Thalassinoides, Teichichnus among others of dubious assignation recorded at Bajada del Agrio and other areas of the basin. New material coming from both units includes subaqueous vertebrate scratchs (Characichnos?) both from Vega de Escalone and Puerta Curaco. Arthropod trackways include both some with differentiated (Diplichnites?) and other specimen with undifferentiated appendages. In the indicatives of subaerial exposure in sections expected to be fully marine. Complex traces assigned to Hillichnus produced by tellinacean bivalves are the only record of such bivalves in the basin. Those ichnogenera are good examples that precede body fossil records and along with the scratch marks suggest very unexpected according to paleogeographic maps. Finally a brief analysis of the further work in the turbidites of the Molles Formation or the exploration of bioerosion and meiofauna records suggest that the knowledge about the ichnology of the Neuquén Basin is in its infancy if it is compared with the stratigraphic, paleontologic (biostratigraphic) and sedimentologic studies and also remains unexplored related to changes in permeability of reservoirs of bioturbated deposits documented from cores.
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Sitio de la Asociación Peleontológica Argentina.
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Sitio de la Asociación Peleontológica Argentina.
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The El Imperial Formation is the classic sedimentary unit of the upper Palaeozoic (Penssylvanian-Cisuralian) of the San Rafael Basin. It is one of the best known basins in the central-western of Argentina. The studied unit is not in... more
The El Imperial Formation is the classic sedimentary unit of the upper Palaeozoic (Penssylvanian-Cisuralian) of the San Rafael Basin. It is one of the best known basins in the central-western of Argentina. The studied unit is not in complete agreement with the rules of the Codigo Argentino de Estratigrafia, like the type section and area, and formal internal divisions. In this paper several stratigraphic aspects are sorted out, but also a hypostratotype for the Canon del Atuel locality is proposed. Two formal members are defined and characterized. Correlation with the type section is proposed and an analysis of this new stratigraphic proposal is discussed with previous ones. In other hand, the age and the relevance of the discovery of marine deposits in the upper member or Cabeceras del Canon Member, and the significance of such transgression in the evolution of the sedimentary infill is analyzed.
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Sedimentological analysis of outer ramp facies: The Agrio Formation (Lower Cretaceous) in the central sector of the Neuquén Basin, Argentina. Microfacies of distal marine deposits of the Lower Cretaceous Agrio Formation – Pilmatué and... more
Sedimentological analysis of outer ramp facies: The Agrio Formation (Lower Cretaceous) in the central sector of the Neuquén Basin, Argentina. Microfacies of distal marine deposits of the Lower Cretaceous Agrio Formation – Pilmatué and Agua de la Mula members – in the Neuquén basin has been analyzed taken into account field data, whole-rock phase-minerals and clay mineralogy with X-ray diffraction, organic components and optical and electron microscopy. Depositional and diagenetic fabrics are compared for the lowermost part of both members. Two facies associations were distinguished that correspond to two depositional settings: distal outer ramp (FA-1); and, proximal outer ramp (FA-2). FA-1 is composed of sediments mainly deposited by suspension settling with calcareous microfossils partially preserved as fecal pellets and organo-minerallic aggregates related to high bioproductivity in the water column. Conversely, FA-2 is dominated by extrabasinal components with illite-rich clayto ...
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En el último lustro, una de las novedades del sector energético que capturaron la atención de los medios y, por extensión, del público fue la constatación de que existen muy importantes reservorios no convencionales de petróleo y gas en... more
En el último lustro, una de las novedades del sector energético que capturaron la atención de los medios y, por extensión, del público fue la constatación de que existen muy importantes reservorios no convencionales de petróleo y gas en Neuquén, y más concretamente en la formación geológica Vaca Muerta. Esto llevó a un sinfín de especulaciones políticas y económicas sobre las consecuencias que se derivarían, no solo para el mercado interno de energía en el que la demanda supera la producción interna y desde 2006 el país es importador neto sino, también, para la región, para la economía nacional e incluso para el lugar que ocupa la Argentina entre los productores mundiales de petróleo y gas.Fil: Pazos, Pablo Jose. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios...
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Abstract The Lajas Formation of the Neuquen Basin (Argentina) was deposited mainly during the Middle Jurassic but with a highly diachronic pattern. The exact time elapsed in the deposition of this unit remains controversial and depends on... more
Abstract The Lajas Formation of the Neuquen Basin (Argentina) was deposited mainly during the Middle Jurassic but with a highly diachronic pattern. The exact time elapsed in the deposition of this unit remains controversial and depends on the location within the basin. Particularly in the Portada Covunco locality, north of the Huincul High, the debate on the age of the Lajas Formation persists. The age of the unit has been assigned by sequence stratigraphy, palynological, and magnetostratigraphic studies. Moreover, previous studies suggest that the Lajas Formation in this locality is composed of two depositional sequences (Sq1 and Sq2) with a change in the composition of the sandstone, indicating different areas of sedimentary supply. The new U–Pb data (LA-ICP-MS) in the detrital zircons allows us to define a maximum depositional age of approximately 163 Ma for Sq1 and 162 Ma for Sq2, suggesting a Callovian age for the Lajas Formation in the studied area. Furthermore, we propose that the provenance pattern in Sq1 was dominated by U–Pb ages of detrital zircons from the Permian–Triassic (peak at 264, 244 and 215 Ma), indicating derivation predominantly from the North Patagonian Massif magmatic units; while Sq2 shows a provenance pattern of detrital zircons associated with the uplift and exhumation of units located to the southwest margin of the basin during the end of the Middle Jurassic. Interestingly, it is not possible to rule out that the Huincul High may be related to the change in the sedimentary supply area; the probable uplift of the Huincul High has resulted in an effective physical barrier that limited sediment input from the extreme southeast during the deposition of Sq2.
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La Formación El Imperial es una unidad sedimentaria clásica de la estratigrafía del Paleozoico superior (Pennsylvaniano-Cisuraliano) de la cuenca San Rafael, una de las más conocidas del centro-oeste de Argentina. Esta unidad presenta una... more
La Formación El Imperial es una unidad sedimentaria clásica de la estratigrafía del Paleozoico superior (Pennsylvaniano-Cisuraliano) de la cuenca San Rafael, una de las más conocidas del centro-oeste de Argentina. Esta unidad presenta una falta de adecuación al Código Argentino de Estratigrafía, como la definición de localidad, sección tipo y divisiones internas. En este trabajo se resuelven estos aspectos y además, se propone un hipoestratotipo para la localidad de Cañón del Atuel, donde se definen formalmente dos miembros a los que se caracteriza. Se proponen correlaciones con la sección y localidad tipo y se discute esta propuesta estratigráfica con otras previas. Por otra parte, se analiza la edad de la unidad y la relevancia del hallazgo de facies marinas en el superior o Miembro Cabecera del Cañón, en lo referente a la evolución del relleno sedimentario.The El Imperial Formation is the classic sedimentary unit of the upper Palaeozoic (Pennsylvanian-Cisuralian) of the San Rafae...
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La composicion y textura de las epiclastitas y la micromorfologia de los paleosuelos de la Formacion Mercedes, aflorante en el oeste y sur de Uruguay, permitieron determinar areas de procedencia, marco tectonico de las zonas de aporte,... more
La composicion y textura de las epiclastitas y la micromorfologia de los paleosuelos de la Formacion Mercedes, aflorante en el oeste y sur de Uruguay, permitieron determinar areas de procedencia, marco tectonico de las zonas de aporte, procesos diageneticos y variaciones paleoclimaticas en el Cretacico Superior de la cuenca de Parana. La composicion de las epiclastitas define dos sectores de distinta procedencia, con limite transicional; en el norte dominan clastos de la Formacion Arapey (volcanitas), con menor aporte de la Formacion Guichon (areniscas) y del basamento precambrico (metamorfitas y plutonitas). En el centro-sur dominan los ultimos, son escasos los de la Formacion Arapey y no hay participacion de la Formacion Guichon. El marco tectonico del area de aporte es cratonico, variando entre interior cratonico y continental transicional. El predominio de granos estables sobre metaestables e inestables, indica que las epiclastitas se depositaron bajo un clima calido y humedo. E...
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The Rio Seco de los Castanos Formation (San Rafael Block) holds one of the few middle Palaeozoic (Silurian−Devonian) records worldwide of a Nereites-Dictyodora dominated ichnofauna with sedimentological features such as oscillatory and... more
The Rio Seco de los Castanos Formation (San Rafael Block) holds one of the few middle Palaeozoic (Silurian−Devonian) records worldwide of a Nereites-Dictyodora dominated ichnofauna with sedimentological features such as oscillatory and combined-flow deposits. This record is associated with microbial mats in fine-grained intervals between turbidite-like deposits documented above the storm wave base. In this work, a detailed sedimentological study permitted to divide the unit into two informal sections separated by an erosional unconformity attributed to a sea level fall. Prograding turbidite-like sand-grained deposits document gravitational turbulent flows. The tectonostratigraphic framework allowed to disregard a submarine fan, whereas the unconformity does not support an autocyclic deltaic evolution. Palaeocurrents and palaeoslope indicators to the SW suggest a high source area to the NE, that contrasts with the well-established E-W trend of most of the units of similar age in the ...
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Study of “The Upper Cabo Ladrillero Beds” in the homonym locality, Lower Miocene of the Austral Basin, Tierra del Fuego. In the cliffs of the Ladrillero cape, situated on the Atlantic coast of the Isla Grande de Tierra del Fuego, the... more
Study of “The Upper Cabo Ladrillero Beds” in the homonym locality, Lower Miocene of the Austral Basin, Tierra del Fuego. In the cliffs of the Ladrillero cape, situated on the Atlantic coast of the Isla Grande de Tierra del Fuego, the uppermost records of the Austral or Magallanes foreland basin infill crop out. This locality contains Lower Miocene deposits informally named “Cabo Ladrillero beds” and “Cabo San Pablo beds” being the “upper Cabo Ladrillero beds” analyzed in this paper. This locality is situated around ten kilometers to the north of the emerging orogenic front (Punta Gruesa locality) where four facies association have been defined from gravitationally-driven supra batial to prograding and shallowing upward deltaic wedges. Deformed and massive beds by liquefaction processes and resedimentation are connected with abundant clastic dykes and synsedimentary faults. The statistic study suggests they are associated tectonic activity related to a transtensive episode rather tha...
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Several dinosaur tridactyl tracks showing inter- and intra-trackways morphological variations from the Cenomanian Candeleros Formation of the Neuquen Basin, Argentina, have been documented. Footprints occur on three different... more
Several dinosaur tridactyl tracks showing inter- and intra-trackways morphological variations from the Cenomanian Candeleros Formation of the Neuquen Basin, Argentina, have been documented. Footprints occur on three different stratigraphic levels and are impressed on medium-grained sandstone of fluvial origin. Level 1 includes deep tridactyl tracks with metatarsal impressions (average length of 31 cm) preserved as true tracks and undertracks that could have been generated due to simply sinking of the pes into a soft substrate and also probably by a continuous walk in a squatting position. Level 2 shows the largest tridactyl tracks (average length of 58 cm) recognized in this work, situated a few meters close to an already studied sauropod trackway. The different preservation between these bipedal and quadrupedal tracks could be explained due to different substrate properties and dissimilarities of the pedal shape between trackmakers. Level 3 comprises small to large tridactyl tracks...
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The Agrio Formation (Valanginian to early Barremian) is a siliciclastic and carbonate unit of the Neuquen Basin in west central Argentina. A conspicuous 20 m thick dolomitized section near the top of the upper Agua de la Mula Member of... more
The Agrio Formation (Valanginian to early Barremian) is a siliciclastic and carbonate unit of the Neuquen Basin in west central Argentina. A conspicuous 20 m thick dolomitized section near the top of the upper Agua de la Mula Member of the Agrio Formation was identified for the first time in this unit. The analyzed section is composed of dolostones with scarce siliciclastic intercalations. A tidal flat environment with highfrequency cycles is suggested for the measured section. Petrography, SEM, X-Ray, EDAX and cathodoluminiscence analyses showed two different dolomitization processes. The first one comprises early mimetic and non mimetic dolomitization on ooids, bioclasts and early marine cements. The second one reveals precipitation of dolomite cement. The mimic dolomitization indicates that this process took place before the inversion from aragonite to calcite, or from low magnesium calcite to high magnesium calcite. The dolomitization should have been soon after the deposition. ...
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Ichnological synthesis of the marine units of the Neuquen Basin, new data and future perspectives. In this paper the ichnology of the marine intervals of the Neuquen Basin is reviewed, taking into account an stratigraphic framework and... more
Ichnological synthesis of the marine units of the Neuquen Basin, new data and future perspectives. In this paper the ichnology of the marine intervals of the Neuquen Basin is reviewed, taking into account an stratigraphic framework and discussing pre- vious works on ichnology that contain some ichnogenus (Lapispira) that are firstly documented in South America in Jurassic rocks of the Rio Atuel area, and other ichnogenera that constitute well preserved records in the Jurassic tidal influenced del- tas of the Lajas Formation. The trace fossil record includes Asterosoma, Asteriacites, Dactyloidites, Diplocraterion, Gyrochorte, Palaeophycus, Polykladichnus, Schaubcilindrichnus, Siphonichnus, Thalassinoides, Teichichnus and rare traces in shallow marine deposits like Helmin-thorhaphe and root traces indicative of a very complex facies scheme. A special mention deserves the traces from the carbonates of the La Manga Formation at Bardas Blancas, that contain ichnogenera like Dactyloidites...
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The ichnogenus Psammichnites herein restricted to Psammichnites gigas is based on comparison of morphology, feeding behaviour, contrast between the burrows and the host rock and possible producers. The record of siphonal activity as a... more
The ichnogenus Psammichnites herein restricted to Psammichnites gigas is based on comparison of morphology, feeding behaviour, contrast between the burrows and the host rock and possible producers. The record of siphonal activity as a “snorkel device” is discussed. The diagnosis of the ichnogenus Olivellites now is amended and includes all the records of Psammichnites in the post-Cambrian. Olivellites is now documented in successions other than the classical tidal flat deposits facies of the Carboniferous of the USA. We propose that the producer of Olivellites was an animal with capacity for displacement to different shallow infaunal levels for different feeding strategies. An interpretation of detritus feeding behavior with sediment displacement (pasichnia) is favoured here. The producer of Olivellites was likely to have been a bivalved mollusc that evolved after the Late Ordovician mass extinction. It was euryhaline and lived in a broad bathymetric range, and is recorded in temper...
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The southern part of the Nirihuau basin at the valley of the Cushamen River region, is deformed and uplifted forming a prominent Precordillera Patagonica fold and thrust belt, east of the Patagonian Andes. The Nirihuau Basin infill is... more
The southern part of the Nirihuau basin at the valley of the Cushamen River region, is deformed and uplifted forming a prominent Precordillera Patagonica fold and thrust belt, east of the Patagonian Andes. The Nirihuau Basin infill is represented by Oligocene to Miocene sedimentary to volcaniclastic rocks gathered in eleven lithotypes belonging to four members. These foreland sequences are exposed by a combination of thin-skinned deformation whose shortening is transferred to the basement in the west beneath the Cordon del Maiten. The entire Nirihuau section as well as the overlying Collon Cura Formation is characterized by the occurrence of progressive unconformities, fact that implies synorogenic sedimentation at the time of the Cordon del Maiten range uplift. This belt is formed by an east-verging basement wedge associated with a series of backthrusts. The reactivation of the deformation associated with growth strata, indicates that the basin has evolved in a wedge-top of a forel...
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Abstract. The Early Cretaceous marine deposits of the Agrio Formation are widely distributed in southern Mendoza and Neuquén provinces, Argentina. The stratigraphic distribution of upper Valanginian to upper Hauterivian organic-walled... more
Abstract. The Early Cretaceous marine deposits of the Agrio Formation are widely distributed in southern Mendoza and Neuquén provinces, Argentina. The stratigraphic distribution of upper Valanginian to upper Hauterivian organic-walled dinoflagellate cysts was evaluated at the Agrio Formation, at Bajada del Agrio locality. The assemblages exhibit a relatively moderate to low diversity and those with greater abundance are dominated by a small number of species such as Circulodinium distinctum, Cribroperidinium spp., Exochosphaeridium spp., Florentinia mantellii, Kiokansium unituberculatum, and Oligosphaeridium complex. Three diagnostic bioevents of lowest (LO) and highest (HO) stratigraphic occurrences of taxa calibrated with the local ammonoid zonation were identified for the Early Cretaceous of the Neuquén Basin: the LO of Callaiosphaeridium sp. (base of Holcoptychites neuquensis Zone, earliest Hauterivian), the LO of Cymososphaeridium validum (uppermost Hoplitocrioceras gentilii Zone, upper early Hauterivian) and the HO of Cymososphaeridium validum (lowermost Crioceratites diamantensis Zone, late Hauterivian). The studied assemblages are compared with Early Cretaceous assemblages from the Northern Hemisphere. In general, the association of dinoflagellate cysts together with the selected diagnostic species exhibit a clear affinity with those of the Mediterranean region.
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Abstract The outcrops of the Lajas Formation at the Covunco section expose a succession that contrasts with the classical localities for the unit, due to subaerial exposure confirmed by a vertebrate track documented in the basal section... more
Abstract The outcrops of the Lajas Formation at the Covunco section expose a succession that contrasts with the classical localities for the unit, due to subaerial exposure confirmed by a vertebrate track documented in the basal section of the unit. The stacking pattern, facies distribution, subaerial exposure in the previously interpreted prodelta facies and the documented unconformity in the middle part of the unit are incompatible with the continuous deltaic evolution suggested previously for the studied locality. Regardless of the absence of a precise age for the succession, the regional literature of subsurface data, the paleontological remains and the intra-Callovian unconformity at the top of the unit, suggest a Bathonian (late?) up to Early Callovian age for the unit in the area. It is younger than the classical deltaic deposits extensively studied in outcrops or subsurface to the north-east and south of the Huincul High and confirms the diachronism between the south and north of the high and it sheds light on the late evolution of the unit. The younger age in Covunco section is compatible with the suggested age differences. The sedimentary record in the logged section was divided in three parts: a lower section containing marginal-marine deposits with tidal features like sigmoidal structures and muddy and coaly drapes, marine trace fossils (Asteriacites quinquefolius) and bioclastic deposits that are transitionally overlying the Los Molles Formation and end with fluvial deposits containing the vertebrate track. It is documentedat the top of an interval with3D dunes. The track is tridactyl and assigned to cf. Deltapodus. It constitutes the oldest record in Gondwana of a track attributed to tyreophorans. Isaberrysaura (Neoornitischia/Tyreophora) is the candidate producer, taking into account the stratigraphic and geographical proximity of the underlying Los Molles Formation that contains the skeletal remains. The track has some morphological features that suggest a possible swimming-wading behaviour as was previously proposed for stegosaurs. Overlying the fluvial interval, the middle section is composed of transgressive deposits containing abundant bioclastic conglomerates and channels with trunks. The upper section was deposited after a facies dislocation overlying a previously interpreted unconformity that suggests an abrupt change in the sedimentary record, containing pebbly sandstones intercalated with sandstone beds with Skolithos resembling “pipe rocks”. They are replaced upward by fine-grained sandstones with HCS, suggesting open marine conditions over the storm wave base level and a deepening upward trend. Then, the succession becomes sandier and highly bioturbated with abundant Rhizocorallium specimens and some lenticular channels with lateral accretion and abundant symmetrical wave ripple levels developed during a regressive phase.
Research Interests: Geology and Geophysics
Abstract Detailed descriptions of Nereites are uncommon. In this work, Nereites are thoroughly described from tidally influenced and wave dominated deposits in the Cretaceous of the Neuquen Basin (northern Patagonia). These Nereites show... more
Abstract Detailed descriptions of Nereites are uncommon. In this work, Nereites are thoroughly described from tidally influenced and wave dominated deposits in the Cretaceous of the Neuquen Basin (northern Patagonia). These Nereites show a great morphological variety in bedding-plane view. The application of different possible tracemakers for this renowned ichnogenus is discussed. Besides the well known morphology consisting of median tunnel surrounded by a halo composed of reworked material, a tripartite burrow structure has been observed that comprises in addition a disturbed, but not reworked zone at the external side of the reworking halo. The studied material provides evidence that the producers of these Nereites were shallow infaunal deposit-feeding organisms, a feeding strategy mentioned in many studies of the ichnogenus as matching a worm-like tracemaker, while the subsurface characteristics, particularly the disturbed outer zone, support a burrowing arthropod as tracemaker. Consequently, for interpretation of the potential trace producer, basic feeding strategy and burrow construction method should be differentiated and neither should be automatically linked with one particular tracemaker. The different morphologies of these Nereites allow referral of part of this material to N. missouriensis, but some cases of transitional forms remain problematic. The ratio between the width of the median tunnel and the enveloping zone (used as an ichnotaxobase) is not always due to variation in the burrowing depth of the producer. The same individual was able to produce wider or narrower enveloping areas in the same level along its course. In such cases, the use of this ichnotaxobase even at the ichnospecific level seems questionable.
Research Interests: Geology and Cretaceous
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Acomplex trace fossil that requires a three-dimensional (3D) reconstruction is described and interpreted. The specimens studied are assigned to a new ichnospecies ( Hillichnus agrioensis ) of Hillichnus Bromley et al ., 2003.Most of them... more
Acomplex trace fossil that requires a three-dimensional (3D) reconstruction is described and interpreted. The specimens studied are assigned to a new ichnospecies ( Hillichnus agrioensis ) of Hillichnus Bromley et al ., 2003.Most of them are uncollectable and a compound iconotype was designed to characterise the new ichnospecies. The three-dimensional trace fossil has been recorded in marginal-marine deposits close to the top of the Agrio Formation (Lower Cretaceous of Neuquen Basin, Argentina). The new ichnospecies shows a different pattern of feeding than H. lobosensis Bromley et al ., 2003, and records defaecation downward in the deeper preservational level (level 4). Feather-like structures (level 2) that typify the ichnogenus also record the activity of an inhalant siphon and indicate a retractile movement. The vertical shafts (level 1) are scarcely recorded. Aligned double rings also document the infaunal habit of the tellinid bivalves that are considered the most likely produ...
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... It is divided in three geological domains: the eastern, central and western domain, separated by tectonic megafeatures (Rossello et al., 2007). During the rest of the Phanerozoic the sedimentary record formed part of the Paraná, Santa... more
... It is divided in three geological domains: the eastern, central and western domain, separated by tectonic megafeatures (Rossello et al., 2007). During the rest of the Phanerozoic the sedimentary record formed part of the Paraná, Santa Lucía and Merín basins (Fig. 1). ...