Papers by Beatriz Aguirre-Urreta
Horacio H. Camacho Mónica I. Longobucco *Museo Argentino de Ciencias Naturales
Facies variation in basal sequences of the Vaca Muerta Formation at its type locality (Sierra de ... more Facies variation in basal sequences of the Vaca Muerta Formation at its type locality (Sierra de la Vaca Muerta), Neuquén Basin The Vaca Muerta-Quintuco system (early Tithonian – early Valanginian) is a broad shallowing-upward sedimentary cycle consisting of dark bituminous shales, marls, limestones, and sandstones, cropping out in the Neuquén Basin, west-central Argentina. This paper analyzes five sections of the three first depositional sequences in Sierra de la Vaca Muerta, Neuquén province. Detailed facies analysis allows differentiating five facies associations, representing basinal to shoreface facies of a mixed carbonate/siliciclastic shelf system (Lower Vaca Muerta Formation), and basinal to inner ramp facies of a homoclinal carbonate ramp system (Los Catutos Member), prograding northwestward from the southeastern margin of the basin. These results are useful as analogs in nearby areas, since the projections of shelf breaks mapped by Mitchum and Uliana end perpendicular to t...
RESUMEN Se presenta una síntesis de los megainvertebrados fósiles cretácicos organizados en un es... more RESUMEN Se presenta una síntesis de los megainvertebrados fósiles cretácicos organizados en un esquema estratigráfico por pisos, actualizan-do la información brindada en 1978 en el Primer Relatorio de la Geología del Neuquén. Dada la actual incertidumbre sobre la ubicación del límite Jurásico-Cretácico en términos bioestratigráficos, se provee inicialmente de una breve discusión sobre el tema. Se describe la presencia y distribución de diversos grupos de invertebrados tanto en ambientes marinos como continentales. Entre ellos moluscos tales como amonoideos, nautiloideos, bivalvos y gastrópodos asi como crinoideos y equinoideos, corales, briozoos, anélidos poliquetos, esponjas y crustáceos decápodos. En el Cretácico más temprano (Berriasiano-Hauteriviano) las faunas de invertebrados fósiles son dominantemente marinas, y abundan formas nectónicas y bentónicas asociadas a la transgresión del Océano Pacífico. En el Barremiano la diversidad y abundancia decrecen dramáticamente y se registran unas pocas especies marinas y continentales. Durante el Aptiano-Albiano las faunas de invertebrados se reducen a unos pocos moluscos de agua dulce. En el lapso Cenomaniano-Campaniano Temprano persisten los ambientes continentales y las faunas de invertebrados están restringidas a escasos bivalvos dulceacuícolas. Finalmente en el Campaniano Tardío-Maastrichtiano las sedimentitas marinas asociadas a la transgresión atlántica portan abundantes faunas bentónicas de moluscos y otros invertebrados y escasos elementos nectónicos. ABSTRACT Cretaceous megainvertebrates and their biostratigraphic significance.-A synthesis of the Cretaceous megainvertebrates is presented by stage. This is an update of the information presented in the first version of the Geology and Natural Recourses of Neuquén published in 1978. A brief summary of the Jurassic-Cretaceous boundary is also provided due to the present uncertainties about its definition on biostratigraphic grounds. The text deals with the presence and distribution of several invertebrate groups, both in marine and continental settings. Among them mollusks such as ammonoids, nautiloids, bivalves, gastropods, as well as crinoids and echinoids, cnidarians, bryozoans, annelid polychaetes, sponges and decapod crustaceans. In the Early Cretaceous (Berriasian-Hauterivian) the fossil invertebrate fauna is mostly marine, with abundant nektonic and benthonic forms associated with the Pacific transgression. In the Barremian, the abundance and diversity decrease dramatically and only a few marine and continental species are recorded. During the Aptian-Albian the invertebrate fauna is reduced to few freshwater molluscs. The continental environments persist in the Cenomanian-Early Campanian and the invertebrates are restricted to scarce freshwater bivalves. Finally in the Late Campanian-Maastrichtian the marine sedimentites associated with the Atlantic transgression bear abundant benthonic molluscs and other invertebrates together with few nektonic elements.
Cretaceous Research, 2003
RESUMEN Se presenta una síntesis de los megainvertebrados fósiles cretácicos organizados en un es... more RESUMEN Se presenta una síntesis de los megainvertebrados fósiles cretácicos organizados en un esquema estratigráfico por pisos, actualizan-do la información brindada en 1978 en el Primer Relatorio de la Geología del Neuquén. Dada la actual incertidumbre sobre la ubicación del límite Jurásico-Cretácico en términos bioestratigráficos, se provee inicialmente de una breve discusión sobre el tema. Se describe la presencia y distribución de diversos grupos de invertebrados tanto en ambientes marinos como continentales. Entre ellos moluscos tales como amonoideos, nautiloideos, bivalvos y gastrópodos asi como crinoideos y equinoideos, corales, briozoos, anélidos poliquetos, esponjas y crustáceos decápodos. En el Cretácico más temprano (Berriasiano-Hauteriviano) las faunas de invertebrados fósiles son dominantemente marinas, y abundan formas nectónicas y bentónicas asociadas a la transgresión del Océano Pacífico. En el Barremiano la diversidad y abundancia decrecen dramáticamente y se registran unas pocas especies marinas y continentales. Durante el Aptiano-Albiano las faunas de invertebrados se reducen a unos pocos moluscos de agua dulce. En el lapso Cenomaniano-Campaniano Temprano persisten los ambientes continentales y las faunas de invertebrados están restringidas a escasos bivalvos dulceacuícolas. Finalmente en el Campaniano Tardío-Maastrichtiano las sedimentitas marinas asociadas a la transgresión atlántica portan abundantes faunas bentónicas de moluscos y otros invertebrados y escasos elementos nectónicos. ABSTRACT Cretaceous megainvertebrates and their biostratigraphic significance.-A synthesis of the Cretaceous megainvertebrates is presented by stage. This is an update of the information presented in the first version of the Geology and Natural Recourses of Neuquén published in 1978. A brief summary of the Jurassic-Cretaceous boundary is also provided due to the present uncertainties about its definition on biostratigraphic grounds. The text deals with the presence and distribution of several invertebrate groups, both in marine and continental settings. Among them mollusks such as ammonoids, nautiloids, bivalves, gastropods, as well as crinoids and echinoids, cnidarians, bryozoans, annelid polychaetes, sponges and decapod crustaceans. In the Early Cretaceous (Berriasian-Hauterivian) the fossil invertebrate fauna is mostly marine, with abundant nektonic and benthonic forms associated with the Pacific transgression. In the Barremian, the abundance and diversity decrease dramatically and only a few marine and continental species are recorded. During the Aptian-Albian the invertebrate fauna is reduced to few freshwater molluscs. The continental environments persist in the Cenomanian-Early Campanian and the invertebrates are restricted to scarce freshwater bivalves. Finally in the Late Campanian-Maastrichtian the marine sedimentites associated with the Atlantic transgression bear abundant benthonic molluscs and other invertebrates together with few nektonic elements.
Cretaceous megainvertebrates and their biostratigraphic significance.- A synthesis of the Cretace... more Cretaceous megainvertebrates and their biostratigraphic significance.- A synthesis of the Cretaceous megainvertebrates is presented by stage. This is an update of the information presented in the first version of the Geology and Natural Recourses of Neuquén published in 1978. A brief summary of the Jurassic-Cretaceous boundary is also provided due to the present uncertainties about its definition on biostratigraphic grounds. The text deals with the presence and distribution of several invertebrate groups, both in marine and continental settings. Among them mollusks such as ammonoids, nautiloids, bivalves, gastropods, as well as crinoids and echinoids, cnidarians, bryozoans, annelid polychaetes, sponges and decapod crustaceans. In the Early Cretaceous (Berriasian-Hauterivian) the fossil invertebrate fauna is mostly marine, with abundant nektonic and benthonic forms associated with the Pacific transgression. In the Barremian, the abundance and diversity decrease dramatically and only ...
La presente contribución describe el recorrido histórico del estudio de los invertebrados fósiles... more La presente contribución describe el recorrido histórico del estudio de los invertebrados fósiles del Miembro La Tosca (Formación
Huitrín), en base a una revisión bibliográfica y a nuevos datos paleontológicos de campañas recientes a la sierra de la
Cara Cura y Ranquil del Norte en Mendoza. Groeber visitó por primera vez dicha región entre 1914 y 1917 y es allí donde se
colectan los primeros gastrópodos fósiles. Estos materiales fueron legados a R. Wichmann y M. Doello Jurado para su estudio
taxonómico y por un error inicial en la procedencia comenzaron las controversias acerca de las afinidades marinas o continentales
de la fauna. Además hubo errores en la determinación de bivalvos, gastrópodos y serpúlidos que en parte fueron adjudicados
a taxones dulceacuícolas tales como conchóstracos, algas charáceas y bivalvos unionoideos. Charles Weaver marcó
también un hito importante dado que fue el primero en describir bivalvos tosquenses, pero no habiendo tenido en cuenta las
publicaciones previas de Groeber los asignó al tope de la Formación Agrio. Los nuevos datos paleontológicos aquí aportados
incluyen el primer registro de trigonias y briozoarios cyclostomados, lo cual reafirma la filiación marina de la fauna. Asimismo
se describen dos taxones de gastrópodos y pavimentos de serpúlidos. La asociación de invertebrados se caracteriza por tener
baja diversidad, baja equitatividad, pequeño tamaño y conchillas delgadas en comparación con las faunas de la subyacente
Formación Agrio lo cual indica un ambiente marino marginal con estrés ambiental posiblemente por cambios en la salinidad.
Ameghiniana, Dec 16, 2013
Geological Magazine
Two tuffs in the Lower Cretaceous Agrio Formation, Neuquén Basin, provided U–Pb zircon radioisoto... more Two tuffs in the Lower Cretaceous Agrio Formation, Neuquén Basin, provided U–Pb zircon radioisotopic ages of 129.09±0.16 Ma and 127.42±0.15 Ma. Both horizons are well constrained biostratigraphically by ammonites and nannofossils and can be correlated with the ‘standard’ sequence of the Mediterranean Province. The lower horizon is very close to the base of the Upper Hauterivian and the upper horizon to the Hauterivian/Barremian boundary, indicating that the former lies at c. 129.5 Ma and the latter at c. 127 Ma. These new radioisotopic ages fill a gap of over 8 million years in the numerical calibration of the current global Early Cretaceous geological time scale.
INTRODUCCIÓN La Formación Agrio se encuentra bien representada en casi la totalidad de la cuenca ... more INTRODUCCIÓN La Formación Agrio se encuentra bien representada en casi la totalidad de la cuenca Neuquina, completando la secuencia marina del subciclo Mendociano de Groeber (1946). Tiene una edad valanginiana tardía-barremiana temprana, con base diacrónica (Aguirre-Urreta y Rawson, 1997) y consiste en una alternancia de calizas, pelitas, margas y areniscas. Fue dividida en tres miembros, de base a techo, Pilmatué, Avilé y Agua de la Mula (Weaver, 1931; Leanza et al., 2001), y se interpreta como depositada en un ambiente de rampa marina somera dominada por tormentas (Lazo et al., 2005). El Miembro Pilmatué está compuesto por unos 600 m de lutitas y fangolitas marinas con intercalaciones delgadas de areniscas y calizas, que representan una serie de secuencias de somerización (Lazo et al., 2005). La fauna que contienen sus bancos es variada; se compone principalmente de invertebrados, aunque se han encontrado restos aislados de peces picnodontiformes y de reptiles marinos. En este tra...
Sedimentologic and sequence stratigraphic analysis of the Vaca Muerta and Quintuco Formations in ... more Sedimentologic and sequence stratigraphic analysis of the Vaca Muerta and Quintuco Formations in Chos Malal area, Neuquén Basin. The Vaca Muerta-Quintuco system (early Tithonian – early Valanginian) is a broad shallowingupward sedimentary cycle consisting of dark bituminous shales, marls, limestones, and sandstones, cropping out in the Neuquén Basin, west-central Argentina. This paper analyzes three sections in Chos Malal area, northern Neuquén province. Detailed facies analysis allows to differentiate six facies associations, representing basinal to middle ramp facies of a homoclinal carbonate ramp system (Vaca Muerta Formation), and basinal to shoreface facies of a mixed carbonate/siliciclastic shelf system (Quintuco Formation), prograding westward from the eastern margin of the basin. Two sequence hierarchies are recognized, including five composite depositional sequences and thirteen high-frequency sequences. These results are useful as analogs in nearby areas, since the shelf b...
A new ammonoid species of the Andean endemic genus Andiceras Krantz is here described from upper ... more A new ammonoid species of the Andean endemic genus Andiceras Krantz is here described from upper Tithonian-lower Berriasian levels of the Vaca Muerta and Chachao Formations of the Mendoza Group, in north-western Mendoza Province, Argentina. Andiceras planulatus sp. nov. lies between the last beds with representatives of the Substeueroceras koeneni Assemblage Zone of late Tithonian age and the first bed yielding elements of the Argentiniceras noduliferum Assemblage Zone of early Berriasian age, according to the traditional Andean ammonoid zonation scheme. The particular stratigraphic position of Andiceras planulatus, together with its easily recognizable morphology makes this species a good potential biostratigraphic marker for the Jurassic-Cretaceous boundary in the Andean region.
In this work new records of elasmosaurid plesiosaurs are described from the Lower Cretaceous Agri... more In this work new records of elasmosaurid plesiosaurs are described from the Lower Cretaceous Agrio
Formation of the Neuquen Basin (west-central Argentina) and their bearing facies and taphonomic
modes are analyzed. New records from both members of the upper ValanginianeHauterivian Agrio
Formation are described along with a careful revision of previous records from the Pilmatue Member.
These records include the first elasmosaurids reported from the upper Hauterivian of South America.
Even though the studied materials comprise solely fragmentary postcranial elements, they suggest the
presence of at least two different elasmosaurid taxa. Additionally, the rarity of cervical centra with a
ventral notch in the articular faces among pre-Cenomanian elasmosaurids is confirmed. In terms of
plesiosaur taphonomy and bearingfacies the studied plesiosaurs from the Agrio Formation were
recorded in two different taphonomic modes, 1) preservation of disarticulated but closely associated
postcranial elements within dark-grey shales, that probably resulted from bloating, drifting and eventually
sinking of carcasses to a muddy and calm seafloor under oxic to suboxic conditions, without
further transport or physical reworking; and 2) preservation of isolated plesiosaur bones in shell beds,
including mostly weathered and encrusted isolated vertebrae. These taphonomic modes are not
randomly distributed in the studied marine succession, but closely follow cycles of changes in the
relative sea level and can be linked to fourth-order high frequency cycles. Taphonomic mode 1 includes
better preserved specimens deposited in highstand systems tract intervals subjected to higher sedimentation
rate while taphonomic mode 2 is related to transgressive systems tract intervals subjected to
a reduced sedimentation rate and higher time of exposure of remains on the seafloor, resulting in poorly
preserved specimens.
The presence of an exceptional accumulation of nautilid shells in sediments belonging to the Agri... more The presence of an exceptional accumulation of nautilid shells in sediments belonging to the Agrio Formation has been previously reported. The objective of this work is to analyze the microfacies of the beds that contain the nautilids and to compare them with the deposits above and below the exceptional nautilid accumulation. The logged section was accomplished at El Salado locality, and was assigned to the middle-upper part of the Pil-matué Member of the Agrio Formation, belonging to the Holcoptychites agrioensis biosubzone (Early Hauterivi-an). The sediments located below the nautilid bearing beds are heterolithic deposits exhibiting a thickening and coarsening upward trend. They are composed of interstratifications of sandstones, siltstones and claystones. Overlying the heterolithic deposits, up to three amalgamated limestone beds with nautiloids were identified. They are covered by gray bioclastic limestones. The limestones with nautilids were interpreted as amalgamated storm de...
High Resolution Biostratigraphy and Geochronology of the Vaca Muerta Formation, Neuquén Basin In ... more High Resolution Biostratigraphy and Geochronology of the Vaca Muerta Formation, Neuquén Basin In this work we present new results from studies of ammonites and calcareous nannofossils in selected surface sections of the Vaca Muerta Formation that have yielded a precise biochronology on this unit. Furthermore, these studies have been correlated with the classical biozonations of the Tethys in the case of the ammonites and have also adjusted events of calcareous nannofossils recognized in the Neuquén Basin with those of the Tethys. Geochronological U-Pb dating performed at both the Vaca Muerta and the underlying Tordillo Formation has provided absolute ages of both lithostratigraphic units. These data contrast markedly with the currently accepted ages for this interval by the International Commission on Stratigraphy (ICS) and the Geological Time Scales (GTS 2012) and are about 5 million years younger. Finally, we stress the importance and need for detailed biostratigraphic studies tha...
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Papers by Beatriz Aguirre-Urreta
Huitrín), en base a una revisión bibliográfica y a nuevos datos paleontológicos de campañas recientes a la sierra de la
Cara Cura y Ranquil del Norte en Mendoza. Groeber visitó por primera vez dicha región entre 1914 y 1917 y es allí donde se
colectan los primeros gastrópodos fósiles. Estos materiales fueron legados a R. Wichmann y M. Doello Jurado para su estudio
taxonómico y por un error inicial en la procedencia comenzaron las controversias acerca de las afinidades marinas o continentales
de la fauna. Además hubo errores en la determinación de bivalvos, gastrópodos y serpúlidos que en parte fueron adjudicados
a taxones dulceacuícolas tales como conchóstracos, algas charáceas y bivalvos unionoideos. Charles Weaver marcó
también un hito importante dado que fue el primero en describir bivalvos tosquenses, pero no habiendo tenido en cuenta las
publicaciones previas de Groeber los asignó al tope de la Formación Agrio. Los nuevos datos paleontológicos aquí aportados
incluyen el primer registro de trigonias y briozoarios cyclostomados, lo cual reafirma la filiación marina de la fauna. Asimismo
se describen dos taxones de gastrópodos y pavimentos de serpúlidos. La asociación de invertebrados se caracteriza por tener
baja diversidad, baja equitatividad, pequeño tamaño y conchillas delgadas en comparación con las faunas de la subyacente
Formación Agrio lo cual indica un ambiente marino marginal con estrés ambiental posiblemente por cambios en la salinidad.
Formation of the Neuquen Basin (west-central Argentina) and their bearing facies and taphonomic
modes are analyzed. New records from both members of the upper ValanginianeHauterivian Agrio
Formation are described along with a careful revision of previous records from the Pilmatue Member.
These records include the first elasmosaurids reported from the upper Hauterivian of South America.
Even though the studied materials comprise solely fragmentary postcranial elements, they suggest the
presence of at least two different elasmosaurid taxa. Additionally, the rarity of cervical centra with a
ventral notch in the articular faces among pre-Cenomanian elasmosaurids is confirmed. In terms of
plesiosaur taphonomy and bearingfacies the studied plesiosaurs from the Agrio Formation were
recorded in two different taphonomic modes, 1) preservation of disarticulated but closely associated
postcranial elements within dark-grey shales, that probably resulted from bloating, drifting and eventually
sinking of carcasses to a muddy and calm seafloor under oxic to suboxic conditions, without
further transport or physical reworking; and 2) preservation of isolated plesiosaur bones in shell beds,
including mostly weathered and encrusted isolated vertebrae. These taphonomic modes are not
randomly distributed in the studied marine succession, but closely follow cycles of changes in the
relative sea level and can be linked to fourth-order high frequency cycles. Taphonomic mode 1 includes
better preserved specimens deposited in highstand systems tract intervals subjected to higher sedimentation
rate while taphonomic mode 2 is related to transgressive systems tract intervals subjected to
a reduced sedimentation rate and higher time of exposure of remains on the seafloor, resulting in poorly
preserved specimens.
Huitrín), en base a una revisión bibliográfica y a nuevos datos paleontológicos de campañas recientes a la sierra de la
Cara Cura y Ranquil del Norte en Mendoza. Groeber visitó por primera vez dicha región entre 1914 y 1917 y es allí donde se
colectan los primeros gastrópodos fósiles. Estos materiales fueron legados a R. Wichmann y M. Doello Jurado para su estudio
taxonómico y por un error inicial en la procedencia comenzaron las controversias acerca de las afinidades marinas o continentales
de la fauna. Además hubo errores en la determinación de bivalvos, gastrópodos y serpúlidos que en parte fueron adjudicados
a taxones dulceacuícolas tales como conchóstracos, algas charáceas y bivalvos unionoideos. Charles Weaver marcó
también un hito importante dado que fue el primero en describir bivalvos tosquenses, pero no habiendo tenido en cuenta las
publicaciones previas de Groeber los asignó al tope de la Formación Agrio. Los nuevos datos paleontológicos aquí aportados
incluyen el primer registro de trigonias y briozoarios cyclostomados, lo cual reafirma la filiación marina de la fauna. Asimismo
se describen dos taxones de gastrópodos y pavimentos de serpúlidos. La asociación de invertebrados se caracteriza por tener
baja diversidad, baja equitatividad, pequeño tamaño y conchillas delgadas en comparación con las faunas de la subyacente
Formación Agrio lo cual indica un ambiente marino marginal con estrés ambiental posiblemente por cambios en la salinidad.
Formation of the Neuquen Basin (west-central Argentina) and their bearing facies and taphonomic
modes are analyzed. New records from both members of the upper ValanginianeHauterivian Agrio
Formation are described along with a careful revision of previous records from the Pilmatue Member.
These records include the first elasmosaurids reported from the upper Hauterivian of South America.
Even though the studied materials comprise solely fragmentary postcranial elements, they suggest the
presence of at least two different elasmosaurid taxa. Additionally, the rarity of cervical centra with a
ventral notch in the articular faces among pre-Cenomanian elasmosaurids is confirmed. In terms of
plesiosaur taphonomy and bearingfacies the studied plesiosaurs from the Agrio Formation were
recorded in two different taphonomic modes, 1) preservation of disarticulated but closely associated
postcranial elements within dark-grey shales, that probably resulted from bloating, drifting and eventually
sinking of carcasses to a muddy and calm seafloor under oxic to suboxic conditions, without
further transport or physical reworking; and 2) preservation of isolated plesiosaur bones in shell beds,
including mostly weathered and encrusted isolated vertebrae. These taphonomic modes are not
randomly distributed in the studied marine succession, but closely follow cycles of changes in the
relative sea level and can be linked to fourth-order high frequency cycles. Taphonomic mode 1 includes
better preserved specimens deposited in highstand systems tract intervals subjected to higher sedimentation
rate while taphonomic mode 2 is related to transgressive systems tract intervals subjected to
a reduced sedimentation rate and higher time of exposure of remains on the seafloor, resulting in poorly
preserved specimens.