Patricia L. Ciccioli | Universidad de Buenos Aires (original) (raw)
Papers by Patricia L. Ciccioli
The provenance of sandstones deposited in the late Paleozoic Tepuel-Genoa Basin is analyzed in th... more The provenance of sandstones deposited in the late Paleozoic Tepuel-Genoa Basin is analyzed in this paper. Five sections were sampled in Esquel, Sierra de Tepuel, Sierra de Tecka, El Molle, and Río Genoa areas for petrographic and geochemical studies. The sandstones in the Tepuel-Genoa Basin are dominated by feldspathic litharenites and litharenites, showing lithic fragments of volcanic and sedimentary rocks in the Valle Chico Formation and medium-to high-grade metamorphic rock clasts in the rest of the units.
Journal of South American Earth Sciences, 2020
The Mina del Carmen, Bajo Barreal and Cañadón Seco Formations bear the most important Cretaceous ... more The Mina del Carmen, Bajo Barreal and Cañadón Seco Formations bear the most important Cretaceous reservoirs in the southern flank of the Golfo de San Jorge Basin, in which the porosity is mainly secondary in origin. Primary porosity is about 4% in average and can be divided in intergranular and intercrystalline porosity, the former is better preserved where chlorite rim cement is abundant, and the second occurs among crystals of the clay cement (main kaolinite). Secondary porosity comprises dissolution of feldspar, ductile fragments, clay cements, lithic grains, and carbonate-zeolite cements. Dissolution of feldspar produces the formation of authigenic kaolinite and secondary porosity; this mechanism dominates in the western area of the southern flank due to sandstones show higher amounts of plagioclase grains, which were very reactive to diagenetic dissolution. Ductile fragments, composed of tuffaceous mudstones (probably of intrabasinal origin), were strongly deformed during the compaction reducing the primary porosity and closing the pore system. Nevertheless, in sandstones containing similar proportions of intrabasinal and extrabasinal clasts, some ductile grains suffered massive dissolution increasing the secondary porosity. Another source of secondary porosity comprises the dissolution of tuff fragments, and locally, carbonate and zeolite cements. The secondary porosity includes the types redistributional (RDS) and pervasive (PVS). This division can be related to previous diagenetic model for the Bajo Barreal Formation. In this way, redistributional secondary porosity is linked to the first and the second events of diagenetic dissolution, while the pervasive secondary porosity to the third dissolution event, which likely had a telogenetic origin.
A 2400 m-thick sedimentary column belonging to the Toro Negro Formation was recorded along the Qu... more A 2400 m-thick sedimentary column belonging to the Toro Negro Formation was recorded along the Quebrada del Yeso, Sierra de Los Colorados (Vinchina Basin), La Rioja province, NW Argentina. The Vinchina basin is a good example of a closed basin surrounded by the Precordillera fold and thrust belt to the west and basementcored
blocks to the north, south (Western Sierras Pampeanas) and east (Sierra de Famatina). Seven facies associations (FA) are described and interpreted to represent fluvial, lacustrine and alluvial environments developed in the southern part of the Vinchina basin from the Late Miocene until the earliest Pleistocene. The depositional evolution of the formation was divided in four phases. Phase I (∼7–6.6 Ma) represents sedimentation in medial (FA I) to distal (FA II) parts of a southward directed distributive fluvial system with a retrogradational pattern. During phase II (6.6–6.1Ma), the distributive fluvial system was replaced by a mixed clastic-evaporitic shallow lake (FA III) in a high aggradational basin. In phase III (∼6.1–5 Ma) the eastward progradation of a
fluvial system (FA IV) was recorded as a distal clastic wedge. Finally, phase IV (∼5-2.4Ma) records two depositional cycles of proximal clastic wedge progradation of fluvial-dominated piedmonts (FAV, FAVII) from the
southwest (Sierra de Umango) and/or the west (Precordillera) with an intervening playa lake (FA VI).
Two new U-Pb ages obtained from zircons in volcanic ash layers confirm the Late Miocene age of the lower member of the Toro Negro Formation and permit a tight correlation with the central part of the basin (Quebrada de La Troya section). The sedimentation rate calculated for the dated lacustrine-fluvial interval is higher than the corresponding one in La Troya area suggesting a higher subsidence in the southern part of the basin. During the Late Miocene (∼7-6.6Ma) the ephemeral drainage was controlled by an arid to semiarid climate and initially dissipated mostly internally as terminal fan/distributive fluvial systems descending from the north. A thick lacustrine interval developed in the southern part of the basin between ∼6.6 and 6.1 Ma during a period of high subsidence and closed drainage. Besides, this interval coincides with increased aridity recorded in other basins in the Northwest of Argentina. By ∼6.1 Ma the area started to receive the first coarse-grained sediments heralding the progradation of a clastic wedge from the southwest-west (Sierra de Umango and Precordillera) which fully developed during the rest of the Pliocene to the earliest Pleistocene (∼5–2.4 Ma). The 6.1–2.4 Ma interval records ameliorating climate conditions.
XX Congreso Geologico Argentino, 2017
The South American caviomorph ichnogenus Tracheria troyana is reevaluated here based on recently ... more The South American caviomorph ichnogenus Tracheria troyana is reevaluated here based on recently discovered specimens that allow a more thorough investigation of footprint taphonomy and ichnotaxonomy. The footprints include detailed autopodium morphology and more complete gait patterns than previously reported. The redefinition of T. troyana involves key aspects as digit impressions of the manus asymmetrically arranged and digit V being the shortest and at times do
not print. It generally lacks metacarpal pads, resulting in almost digitigrade impressions and regularly preserved as tridactyl footprints. In the pes imprints, digits have a symmetrical arrangement. Phalangeal and metapodial pad impressions are preserved, occasionally showing the
presence of two heel pads. Trackways denote a marked overstep in which the pes impressions are placed in front of the manus. New data about T. troyana environmental distribution shows that typically characterizes overbank facies of anastomosing and meandering fluvial systems, which may be reflecting a habitat preference the producer. Here, we also present new digitized 3D images of the original type material of T. troyana, in order to preserve these materials, which were previously only available for viewing in the field.
Although Earth’s climate history is best known through marine records, the corresponding continen... more Although Earth’s climate history is best known through marine
records, the corresponding continental climatic conditions drive
the evolution of terrestrial life. Continental conditions during the
latest Miocene are of particular interest because global faunal
turnover is roughly synchronous with a period of global glaciation
from ∼6.2–5.5 Ma and with the Messinian Salinity Crisis from
∼6.0–5.3 Ma. Despite the climatic and ecological significance of
this period, the continental climatic conditions associated with it
remain unclear. We address this question using erosion rates of
ancient watersheds to constrain Mio-Pliocene climatic conditions in
the south-central Andes near 30° S. Our results show two slowdowns
in erosion rate, one from ∼6.1–5.2 Ma and another from
3.6 to 3.3 Ma, which we attribute to periods of continental aridity.
This view is supported by synchrony with other regional proxies for
aridity and with the timing of glacial ‟cold” periods as recorded by
marine proxies, such as the M2 isotope excursion.We thus conclude
that aridity in the south-central Andes is associated with cold periods
at high southern latitudes, perhaps due to a northward migration
of the Southern Hemisphere westerlies, which disrupted the
South American Low Level Jet that delivers moisture to southeastern
South America. Colder glacial periods, and possibly associated
reductions in atmospheric CO2, thus seem to be an important driver
of Mio-Pliocene ecological transitions in the central Andes. Finally,
this study demonstrates that paleo-erosion rates can be a powerful
proxy for ancient continental climates that lie beyond the reach of
most lacustrine and glacial archives.
RESUMEN Se propone, por primera vez, un cuadro estratigráfico integrado para las unidades pospale... more RESUMEN Se propone, por primera vez, un cuadro estratigráfico integrado para las unidades pospaleozoicas en la Precordillera Septen-trional sobre la base de las exposiciones comprendidas entre las quebradas de Santo Domingo y El Peñón. Esta área resulta una región crítica, no sólo para la estratigrafía de la Precordillera Septentrional, sino también como sección de referencia para la co-rrelación entre las unidades aflorantes en las Sierras Pampeanas y en el norte de Chile. Se han reconocido 6 unidades compren-didas entre el Triásico Tardío y el Mioceno-Plioceno? La más antigua corresponde a la Formación Santo Domingo, unidad de bancos rojos datada en el Triásico Tardío-Jurásico Temprano sobre la base del estudio de la xiloflora y dataciones radimétricas. Esta unidad es cubierta en discordancia por la Formación Ciénaga del Río Huaco (Cretácico Tardío), en la que han sido repor-tados restos óseos de titanosaurios. La Formación Puesto La Flecha (Eoceno tardío-Oligoceno) inicia el registro cenozoico de la comarca, y corresponde a una sucesión preorogénica a los primeros movimientos andinos compuesta por areniscas y pelitas formadas en ambientes fluviales de baja energía y cuerpos lacustres someros. La orogenia andina en la región está representa-da en las areniscas eólicas de la Formación Vallecito (Oligoceno tardío-Mioceno temprano), la que fue sedimentada bajo con-diciones áridas en un contexto de cuenca de antepaís hambrienta. Estas rocas son sucedidas por la unidad de " conglomerados y areniscas Refugio del Peñón " , formada por la progradación de cuñas clásticas desde el arco magmático y de los cabalgamien-tos más occidentales de la orogenia andina en la Argentina. Finalmente, el " conglomerado La Falda " indica el desplazamiento hacia el este del orógeno andino y el ascenso y destechado del granito que forma el núcleo de la Sierra del Peñón. ABSTRACT Stratigraphy of the Neogene, Paleogene and Mesozoic successions of the Santo Domingo and El Peñón creeks (Northern Precordillera of La Rioja) Geological surveys carried out in the Santo Domingo and El Peñón creeks allow, for the first time, proposing an integrated stratigraphic model for the post-Paleozoic units outcropping in the Precordillera Septentrional. The area encompassing the Santo Domingo and El Peñón creeks is a key section not only for the stratigraphy of the Precordillera but also for regional correlations with units of similar age from the Sierras Pampeanas and north of Chile. Six stratigraphic units between the Late Triassic and the Miocene were recognized. The oldest corresponds to the Santo Domingo Formation, a red bed sequence composed of conglomerates, sandstones and mudstones wich was dated in the Late Triassic-Early Jurassic based on the study of the xyloflora and a radiometric age. This unit is unconformably covered by sandstones and mudstones belonging to the Ciénaga del Río Huaco Formation (Late Cretaceous) which provided some skeletal remains of Titanosaurios. The Puesto La Flecha Formation (late Eocene–Oligocene) comprises sandstones and mudstones deposited in ephemeral fluvial systems together with shallow water bodies (Lower Member) and eolian dunes (Upper Member). The onset of the Andean Orogeny in the studied region is represented in the eolian sandstones of the Vallecito Formation (late Oligocene – early Miocene) which was formed in arid conditions within an underfilled foreland basin. These rocks are succeeded by the informally called unit of " conglomerates and sandstones Refugio del Peñón " that represent the progradation of clastic wedges from the volcanic arc located to the west. Finally, the informal unit of " conglomerates La Falda " points out the displacement towards the west of the Andean orogenic front and the uplift and unroofing of the granitic rocks forming the core of the Sierra del Peñón.
Aeolian Research, Jan 1, 2010
Landscapes of western Argentina are dominated by aeolian sand of diverse composition, reflecting ... more Landscapes of western Argentina are dominated by aeolian sand of diverse composition, reflecting multiple sediment sources. This study focuses on determining the petrography and geochemical composition of sand from three western Argentina dune fields, Médanos Grandes, Médanos Negros and San Luis, to better constrain the provenance of aeolian sand and its relation to Pampean loess. Médanos Grandes sands are litharenites to feldspathic litharenites, with metamorphic and volcanic rock fragments and lesser amounts of quartz and feldspar. Trace elements (U, Th, Sc, V) indicate the dominance of felsic source. A mixed provenance, with contributions from Sierras Pampeanas metamorphic-igneous complex, pre-Quaternary volcanic rocks and direct input from Andean explosive volcanism, is assumed. Médanos Negros sands are lithic feldsarenites, with abundant feldspars and quartz and lesser amounts of rock fragments. Trace elements indicate a mafic source for these aeolian sands, geochemically and petrographically distinct likely due to the input of ultramafic-mafic lithologies of the Sierra Pampeanas. The San Luis sand has substantial petrographic variability with lithic feldsarenites, feldspathic litharenites and lithic arenite. Trace element composition indicates a felsic source. A diagnostic attribute is the dominance of fresh pumice and volcanic glass shards. Contributions from Andean volcanic sources and local metamorphic and igneous rocks are ascertained. Pampean loess and western Argentina dune field sand show broad petrographic and geochemical similarities indicating aeolian sand, silt particles and, eventually, far travelled dust may have a relatively common source. Another viable source for loess is associated with aeolian abrasion in the many dune fields in western Argentina.
Eolian deposits are common in the western Pampas of Argentina, and most are assumed to be associa... more Eolian deposits are common in the western Pampas of Argentina, and most are assumed to be associated with glacial conditions. Stratigraphic and sedimentologic studies coupled with OSL dating in San Luis Province document for the first time a nearly continuous sequence of eolian sand sheet deposits that span most of the Holocene. Petrology and geochemical analyses indicate that the source of the sand is from pre-existing Pleistocene eolian sediments. Sandsheet deposition between ca. 12 and 1 ka is associated with sparse, Monte-type vegetation that occurs with drier conditions (MAP 450-100 mm) than the late 20st century (~700 mm). This paleoenvironmental inference is consistent with nearby pollen and lake level records. A persistent semi-arid environment in western Argentina during the Holocene may reflect sustained warm SSTs in the western equatorial Atlantic Ocean, which may have suppressed the pressure gradient between the South Atlantic Anticyclone and Chaco Low and thus, the flux of summer moisture to western Argentina. There appears to be a paleoclimatic “dipole” response between a dry western Argentina and wet southeastern Brazil, which is consistent with increasing strength of the South American Monsoon through the Holocene. Sand sheet accretion appears to cease by 800 to 200 years ago with wetter conditions and succession to Espinal vegetation prior to European contact.
Palaeogeography, …, Jan 1, 2009
"Miocene deposits of the Toro Negro Formation in La Rioja province, Argentina, host a rich verteb... more "Miocene deposits of the Toro Negro Formation in La Rioja province, Argentina, host a rich vertebrate and invertebrate ichnofauna. Trace fossils are recorded from the lower part of the Lower Member of the Toro Negro
Formation at Quebrada de La Troya. This succession consists of sandstone, intraformational breccia, mudstone and fewconglomerate deposited insandy anastomosingfluvial systemsdeveloped under a semi-arid climate.The invertebrate ichnofauna is composed of meniscate trace fossils (Taenidium barretti, Scoyenia gracilis), dwelling structures (Palaeophycus tubularis) and grazing trails (Helminthopsis hieroglyphica). The vertebrate ichnofauna includes avian (Fuscinapeda sirin, incumbent footprint, slender anisodactyl footprint) andmammalian footprints (Macrauchenichnus rector, cf. Venatoripes riojanus, small heteropod footprint, kidney-like footprints, and oval impressions). Tetrapod footprints and rare Palaeophycus and Helminthopsis are preserved on the top of exposed sandbars. Crevasse splay deposits preserve abundant meniscate trace fossils and dwelling tubes (e.g. Taenidium, Scoyenia and Palaeophycus) ascribed to the Scoyenia ichnofacies. Two suites of invertebrate trace fossils can be
differentiated:meniscate backfill structures (T. barretti) and other burrows (P. tubularis)without ornamentation, developed in a soft substrate, and striated traces (S. gracilis), that crosscut the former, developed in a firmer
substrate. The Toro Negro depositional system displays a high preservation potential for tracks due to seasonal flooding events, which rapidly buried the footprints. The favorable preservational conditions and good exposure of the
track-bearing surface enable us to interpret the track assemblage of the Toro Negro Formation as a sample of the original tetrapod fauna that inhabited that region at central-western Argentina during the Miocene. The identification of possible trackmakers is utilized in this work as a useful tool that contributes to our understanding of the ancient environment. The paleoichnocommunity is characterized by the number of trackmakers and the relative abundance of each type of footprints. A newmethod tomeasure footprint abundance
is proposed; the relative bioturbed area (RBA). Thismeasurement provides numerical characterization of the degree of bioturbation of the whole tracking surface caused by each ichnotaxa.The tetrapod fauna indicated by the footprint record was compared with the body fossil record of the Toro Negro
Formation. These records overlap in some ways, and in other ways they are complementary. The presence of large and medium to small ground sloth, proterotheriid litopterns, caviid rodents, and birds is pointed out by both body
fossils and ichnofossils. Body fossils include remains attributed to dasypodids, glyptodontids, and abrocomid rodents. Ichnofossils indicate the presence of macraucheniid litopterns and three types of birds: shorebirds, perching birds, and large cursorial birds."
The Toro Negro Formation is a foreland sequence in western La Rioja province, Argentina, which re... more The Toro Negro Formation is a foreland sequence in western La Rioja province, Argentina, which records the late-stage tectonic evolution of the Vinchina Basin. Together with the underlying Vinchina Formation, these two units represent one of the thickest and longest continually exposed foreland sections in northwest Argentina. The Vinchina basin is uniquely situated between the Toro Negro and Umango blocks of the Western Sierra Pampeanas to the north and south, the Precordillera to the west, and the Sierra de Famatina to the east. New U-Pb dating of volcanic tephra provides improved age constraints on the pace of sedimentation, and U-Pb ages of detrital zircons serve to strengthen existing provenance interpretations. We show that deposition of the Toro Negro Formation spans roughly 6.9 to 2.3 Ma: Late Miocene to Early Pleistocene. A high-relief, erosional unconformity with the underlying Vinchina Formation developed sometime between 9.3 and 6.9 Ma, although stratigraphic considerations suggest it spanned only the later part of this time interval (perhaps 7.5e6.9 Ma). Above this unconformity, undecompacted sedimentation rates are remarkably high at ~1.2 mm/yr, slowing to ~0.3 mm/yr after ~6 Ma. An unconformity in the upper part of the section is constrained to occur sometime between 5.0 and 3.0 Ma, probably beginning not long after 5.0 Ma. The timing of both unconformities broadly Matches the timing of inferred tectonic events in the Sierra Famatina ~50 km to the east, the Fiambal a basin to the north, and the Bermejo basin to the south, suggesting they May record regional tectonism at these times. Provenance interpretations of detrital zircon spectra are consistent with previous interpretations based on sediment petrography. They show that provenance did not change significantly during the course of Toro Negro deposition, precluding major tectonically-induced drainage reorganization events. Sediments were derived primarily from the north (Toro Negro Block) and west (Precordillera). The data are consistent with a subtle increase in sediment supply from the Precordillera beginning around 6.5 Ma.
Aeolian Research, 2010
Landscapes of western Argentina are dominated by aeolian sand of diverse composition, reflecting ... more Landscapes of western Argentina are dominated by aeolian sand of diverse composition, reflecting multiple sediment sources. This study focuses on determining the petrography and geochemical composition of sand from three western Argentina dune fields, Médanos Grandes, Médanos Negros and San Luis, to better constrain the provenance of aeolian sand and its relation to Pampean loess. Médanos Grandes sands are litharenites to feldspathic litharenites, with metamorphic and volcanic rock fragments and lesser amounts of quartz and feldspar. Trace elements (U, Th, Sc, V) indicate the dominance of felsic source. A mixed provenance, with contributions from Sierras Pampeanas metamorphic-igneous complex, pre-Quaternary volcanic rocks and direct input from Andean explosive volcanism, is assumed. Médanos Negros sands are lithic feldsarenites, with abundant feldspars and quartz and lesser amounts of rock fragments. Trace elements indicate a mafic source for these aeolian sands, geochemically and petrographically distinct likely due to the input of ultramafic-mafic lithologies of the Sierra Pampeanas. The San Luis sand has substantial petrographic variability with lithic feldsarenites, feldspathic litharenites and lithic arenite. Trace element composition indicates a felsic source. A diagnostic attribute is the dominance of fresh pumice and volcanic glass shards. Contributions from Andean volcanic sources and local metamorphic and igneous rocks are ascertained. Pampean loess and western Argentina dune field sand show broad petrographic and geochemical similarities indicating aeolian sand, silt particles and, eventually, far travelled dust may have a relatively common source. Another viable source for loess is associated with aeolian abrasion in the many dune fields in western Argentina.
Eolian deposits are common in the western Pampas of Argentina, and most are assumed to be associa... more Eolian deposits are common in the western Pampas of Argentina, and most are assumed to be associated with glacial conditions. Stratigraphic and sedimentologic studies coupled with OSL dating in San Luis Province document for the first time a nearly continuous sequence of eolian sand sheet deposits that span most of the
Holocene. Petrology and geochemical analyses indicate that the source of the sand is from pre-existing Pleistocene eolian sediments. Sand sheet deposition between ca. 12 and 1 ka is associatedwith sparse,Monte-type vegetation that occurs with drier conditions (MAP 450–100 mm) than the late 20th century (~700 mm). This
paleoenvironmental inference is consistent with nearby pollen and lake level records. A persistent semi-arid environment in western Argentina during the Holocene may reflect sustained warm SSTs in the western equatorial Atlantic Ocean, which may have suppressed the pressure gradient between the South Atlantic Anticyclone and
Chaco Low and thus, the flux of summer moisture to western Argentina. There appears to be a paleoclimatic “dipole” response between a dry western Argentina and a wet southeastern Brazil, which is consistent with the increasing strength of the South American Monsoon through the Holocene. Sand sheet accretion appears to cease by 800 to 200 years ago with wetter conditions and succession to Espinal vegetation prior to European contact.
sernageomin.cl
RESUMEN La Formación Toro Negro (Neógeno) registra parte de la sedimentación de la cuenca de ante... more RESUMEN La Formación Toro Negro (Neógeno) registra parte de la sedimentación de la cuenca de antepaís fracturado de Vinchina (Orogenia Andina) en el noroeste argentino. Esta unidad está compuesta por conglomerados, areniscas y pelitas junto con algunos ...
Geologica acta, 2011
Paganzo Group exposures (Tupe Formation) in the Huaco area provide an excellent opportunity for a... more Paganzo Group exposures (Tupe Formation) in the Huaco area provide an excellent opportunity for assessing the role of sea level and climatic changes on the morphology and nature of coastal fluvial systems deposited in areas of limited tectonic activity. The paleogeographic position of Huaco, close to a coastal region within the Paganzo Basin, allows identification of the effects of sea level change on fluvial architecture. Despite the fact that the Huaco area was dominated by coastal fluvial systems, three marine incursions flooded this part of the basin during the Namurian, Early Pennsylvanian and Late Pennsylvanian respectively. During deposition of the Paganzo Group, climatic conditions evolved from glacial (Namurian) to hot and dry (Late Cisuralian). Five types of fluvial deposits were recognized on the basis of architectural element analysis, lithofacies distribution and type of fluvial bounding surfaces present. Fluvial system 1 (FS1) constitutes the lower part of the Tupe Formation and consists of stacked multi-storey channel-fill complexes formed on large braided alluvial plains dominated by channel-avulsion processes. FS2 consists of multi-storey channels alternating with floodplain deposits including coal beds and organic-rich mudstones. This fluvial system is interpreted as the deposit of an anastomosed network of sandy channels. FS3 occurs between the Early Pennsylvanian and Late Pennsylvanian marine transgressions and consists of sandstones and some conglomerates that form stacked channel complexes. Sporadically, very fine-grained sandstone and mudstone floodplain deposits appear as thin intercalations. FS3 likely formed on braided alluvial plains with channels dominated by transversal bars. FS 4 corresponds to an anastomosed fluvial system that was dominated by two types of braided channel belts that were separated by narrow floodplains. Finally, FS5 is composed of fining-upward cycles ranging from gravely sandstones at the bottom of channels to muddy floodplain deposits at the top. The whole FS5 succession was deposited by high-sinuosity meandering rivers. Detailed stratigraphic analyses clearly suggest that both, sea level and climate changes were first-order controls on fluvial system configurations. In this way, braided systems belonging to FS1 correspond to a low-accommodation system tract. Whereas, coal beds of FS2, which resulted from high water-tables, correspond to a high accommodation system tract that was likely associated with advanced stages of the Late Pennsylvanian transgression. A signif-A . T E D E S C O e t a l .
The Talampaya Formation is the basal unit of the Ischigualasto-Villa Union rift system and has b... more The Talampaya Formation is the basal unit of the Ischigualasto-Villa Union rift system and has been traditionally assigned to the Triassic based on stratigraphic relationships. A median UePb age of 252.38 (þ0.09/0.22) Ma was obtained from volcanic zircons collected from a tuff bed close to the top of this unit at the Bordo Atravesado locality in the Cuesta de Miranda area (La Rioja, Argentina). This radiometric age is very close to the accepted PermianeTriassic boundary indicating that, at least in this locality,
sedimentation occurred during the Late Permian but may have extended into the earliest Triassic. This new evidence indicates that the onset of the extensional event that gave rise to the rift basins in western Argentina started during the Permian. Detailed sedimentological studies of the 260 m thick Talampaya
Formation allowed subdividing the succession into seven facies associations grouped into three evolutionary stages indicating that sedimentary environments initially evolved from alluvial fans to a braided river system. Subsequent intrabasinal volcanism associated with sediment deposition by low-to moderate-sinuosity rivers is recorded in the lower third of the column. The middle and upper part of the unit captures the evolution from ephemeral fluvial systems with an eolian interval to an ephemeral clastic lake with intermittent volcanic ash deposits. These changes indicate a progressive lowering of the landscape and a transition towards arid or semiarid conditions.
Drought episodes during the early–mid 20th century were recognized and described in several place... more Drought episodes during the early–mid 20th century were recognized and described in several places around the world, with extreme dry conditions and widespread landscape denudation, like during the famous ‘Dust Bowl’ in North America. However, there is scant documentation of droughts in southern South America, particularly from the Pampas, and none based on the geological record. In this article, we provide clear evidence of aeolian reactivation
and sand deposition in some areas of La Pampa and San Luis provinces, western Pampas (Argentina), during early–mid 20th century in response to drier conditions, probably amplified, like historic droughts in North America, by anthropogenic factors (e.g. significant population increase and agriculture expansion into a fragile environment). Evidence includes widespread bare sand blowouts, extensive surfaces with active sand migration, steep dune lee
slopes, and sharp crests covered by weak soil development (A/C profile), accompanied by historical documents. Optically stimulated luminescence (OSL) ages on aeolian beds confirm mobilization and sedimentation by wind processes c. 95–60 yr BP. Considering the dominant (over 70%) austral spring–summer precipitation, it is possible the rainfall deficit in western Pampas was linked to positive sea surface temperature (SST) anomalies in the western subtropical South Atlantic Ocean (20–30°S and 30–50° W), according to significant canonical correlation between the precipitation field in subtropical South America and the Atlantic Ocean SST anomalies.
The provenance of sandstones deposited in the late Paleozoic Tepuel-Genoa Basin is analyzed in th... more The provenance of sandstones deposited in the late Paleozoic Tepuel-Genoa Basin is analyzed in this paper. Five sections were sampled in Esquel, Sierra de Tepuel, Sierra de Tecka, El Molle, and Río Genoa areas for petrographic and geochemical studies. The sandstones in the Tepuel-Genoa Basin are dominated by feldspathic litharenites and litharenites, showing lithic fragments of volcanic and sedimentary rocks in the Valle Chico Formation and medium-to high-grade metamorphic rock clasts in the rest of the units.
Journal of South American Earth Sciences, 2020
The Mina del Carmen, Bajo Barreal and Cañadón Seco Formations bear the most important Cretaceous ... more The Mina del Carmen, Bajo Barreal and Cañadón Seco Formations bear the most important Cretaceous reservoirs in the southern flank of the Golfo de San Jorge Basin, in which the porosity is mainly secondary in origin. Primary porosity is about 4% in average and can be divided in intergranular and intercrystalline porosity, the former is better preserved where chlorite rim cement is abundant, and the second occurs among crystals of the clay cement (main kaolinite). Secondary porosity comprises dissolution of feldspar, ductile fragments, clay cements, lithic grains, and carbonate-zeolite cements. Dissolution of feldspar produces the formation of authigenic kaolinite and secondary porosity; this mechanism dominates in the western area of the southern flank due to sandstones show higher amounts of plagioclase grains, which were very reactive to diagenetic dissolution. Ductile fragments, composed of tuffaceous mudstones (probably of intrabasinal origin), were strongly deformed during the compaction reducing the primary porosity and closing the pore system. Nevertheless, in sandstones containing similar proportions of intrabasinal and extrabasinal clasts, some ductile grains suffered massive dissolution increasing the secondary porosity. Another source of secondary porosity comprises the dissolution of tuff fragments, and locally, carbonate and zeolite cements. The secondary porosity includes the types redistributional (RDS) and pervasive (PVS). This division can be related to previous diagenetic model for the Bajo Barreal Formation. In this way, redistributional secondary porosity is linked to the first and the second events of diagenetic dissolution, while the pervasive secondary porosity to the third dissolution event, which likely had a telogenetic origin.
A 2400 m-thick sedimentary column belonging to the Toro Negro Formation was recorded along the Qu... more A 2400 m-thick sedimentary column belonging to the Toro Negro Formation was recorded along the Quebrada del Yeso, Sierra de Los Colorados (Vinchina Basin), La Rioja province, NW Argentina. The Vinchina basin is a good example of a closed basin surrounded by the Precordillera fold and thrust belt to the west and basementcored
blocks to the north, south (Western Sierras Pampeanas) and east (Sierra de Famatina). Seven facies associations (FA) are described and interpreted to represent fluvial, lacustrine and alluvial environments developed in the southern part of the Vinchina basin from the Late Miocene until the earliest Pleistocene. The depositional evolution of the formation was divided in four phases. Phase I (∼7–6.6 Ma) represents sedimentation in medial (FA I) to distal (FA II) parts of a southward directed distributive fluvial system with a retrogradational pattern. During phase II (6.6–6.1Ma), the distributive fluvial system was replaced by a mixed clastic-evaporitic shallow lake (FA III) in a high aggradational basin. In phase III (∼6.1–5 Ma) the eastward progradation of a
fluvial system (FA IV) was recorded as a distal clastic wedge. Finally, phase IV (∼5-2.4Ma) records two depositional cycles of proximal clastic wedge progradation of fluvial-dominated piedmonts (FAV, FAVII) from the
southwest (Sierra de Umango) and/or the west (Precordillera) with an intervening playa lake (FA VI).
Two new U-Pb ages obtained from zircons in volcanic ash layers confirm the Late Miocene age of the lower member of the Toro Negro Formation and permit a tight correlation with the central part of the basin (Quebrada de La Troya section). The sedimentation rate calculated for the dated lacustrine-fluvial interval is higher than the corresponding one in La Troya area suggesting a higher subsidence in the southern part of the basin. During the Late Miocene (∼7-6.6Ma) the ephemeral drainage was controlled by an arid to semiarid climate and initially dissipated mostly internally as terminal fan/distributive fluvial systems descending from the north. A thick lacustrine interval developed in the southern part of the basin between ∼6.6 and 6.1 Ma during a period of high subsidence and closed drainage. Besides, this interval coincides with increased aridity recorded in other basins in the Northwest of Argentina. By ∼6.1 Ma the area started to receive the first coarse-grained sediments heralding the progradation of a clastic wedge from the southwest-west (Sierra de Umango and Precordillera) which fully developed during the rest of the Pliocene to the earliest Pleistocene (∼5–2.4 Ma). The 6.1–2.4 Ma interval records ameliorating climate conditions.
XX Congreso Geologico Argentino, 2017
The South American caviomorph ichnogenus Tracheria troyana is reevaluated here based on recently ... more The South American caviomorph ichnogenus Tracheria troyana is reevaluated here based on recently discovered specimens that allow a more thorough investigation of footprint taphonomy and ichnotaxonomy. The footprints include detailed autopodium morphology and more complete gait patterns than previously reported. The redefinition of T. troyana involves key aspects as digit impressions of the manus asymmetrically arranged and digit V being the shortest and at times do
not print. It generally lacks metacarpal pads, resulting in almost digitigrade impressions and regularly preserved as tridactyl footprints. In the pes imprints, digits have a symmetrical arrangement. Phalangeal and metapodial pad impressions are preserved, occasionally showing the
presence of two heel pads. Trackways denote a marked overstep in which the pes impressions are placed in front of the manus. New data about T. troyana environmental distribution shows that typically characterizes overbank facies of anastomosing and meandering fluvial systems, which may be reflecting a habitat preference the producer. Here, we also present new digitized 3D images of the original type material of T. troyana, in order to preserve these materials, which were previously only available for viewing in the field.
Although Earth’s climate history is best known through marine records, the corresponding continen... more Although Earth’s climate history is best known through marine
records, the corresponding continental climatic conditions drive
the evolution of terrestrial life. Continental conditions during the
latest Miocene are of particular interest because global faunal
turnover is roughly synchronous with a period of global glaciation
from ∼6.2–5.5 Ma and with the Messinian Salinity Crisis from
∼6.0–5.3 Ma. Despite the climatic and ecological significance of
this period, the continental climatic conditions associated with it
remain unclear. We address this question using erosion rates of
ancient watersheds to constrain Mio-Pliocene climatic conditions in
the south-central Andes near 30° S. Our results show two slowdowns
in erosion rate, one from ∼6.1–5.2 Ma and another from
3.6 to 3.3 Ma, which we attribute to periods of continental aridity.
This view is supported by synchrony with other regional proxies for
aridity and with the timing of glacial ‟cold” periods as recorded by
marine proxies, such as the M2 isotope excursion.We thus conclude
that aridity in the south-central Andes is associated with cold periods
at high southern latitudes, perhaps due to a northward migration
of the Southern Hemisphere westerlies, which disrupted the
South American Low Level Jet that delivers moisture to southeastern
South America. Colder glacial periods, and possibly associated
reductions in atmospheric CO2, thus seem to be an important driver
of Mio-Pliocene ecological transitions in the central Andes. Finally,
this study demonstrates that paleo-erosion rates can be a powerful
proxy for ancient continental climates that lie beyond the reach of
most lacustrine and glacial archives.
RESUMEN Se propone, por primera vez, un cuadro estratigráfico integrado para las unidades pospale... more RESUMEN Se propone, por primera vez, un cuadro estratigráfico integrado para las unidades pospaleozoicas en la Precordillera Septen-trional sobre la base de las exposiciones comprendidas entre las quebradas de Santo Domingo y El Peñón. Esta área resulta una región crítica, no sólo para la estratigrafía de la Precordillera Septentrional, sino también como sección de referencia para la co-rrelación entre las unidades aflorantes en las Sierras Pampeanas y en el norte de Chile. Se han reconocido 6 unidades compren-didas entre el Triásico Tardío y el Mioceno-Plioceno? La más antigua corresponde a la Formación Santo Domingo, unidad de bancos rojos datada en el Triásico Tardío-Jurásico Temprano sobre la base del estudio de la xiloflora y dataciones radimétricas. Esta unidad es cubierta en discordancia por la Formación Ciénaga del Río Huaco (Cretácico Tardío), en la que han sido repor-tados restos óseos de titanosaurios. La Formación Puesto La Flecha (Eoceno tardío-Oligoceno) inicia el registro cenozoico de la comarca, y corresponde a una sucesión preorogénica a los primeros movimientos andinos compuesta por areniscas y pelitas formadas en ambientes fluviales de baja energía y cuerpos lacustres someros. La orogenia andina en la región está representa-da en las areniscas eólicas de la Formación Vallecito (Oligoceno tardío-Mioceno temprano), la que fue sedimentada bajo con-diciones áridas en un contexto de cuenca de antepaís hambrienta. Estas rocas son sucedidas por la unidad de " conglomerados y areniscas Refugio del Peñón " , formada por la progradación de cuñas clásticas desde el arco magmático y de los cabalgamien-tos más occidentales de la orogenia andina en la Argentina. Finalmente, el " conglomerado La Falda " indica el desplazamiento hacia el este del orógeno andino y el ascenso y destechado del granito que forma el núcleo de la Sierra del Peñón. ABSTRACT Stratigraphy of the Neogene, Paleogene and Mesozoic successions of the Santo Domingo and El Peñón creeks (Northern Precordillera of La Rioja) Geological surveys carried out in the Santo Domingo and El Peñón creeks allow, for the first time, proposing an integrated stratigraphic model for the post-Paleozoic units outcropping in the Precordillera Septentrional. The area encompassing the Santo Domingo and El Peñón creeks is a key section not only for the stratigraphy of the Precordillera but also for regional correlations with units of similar age from the Sierras Pampeanas and north of Chile. Six stratigraphic units between the Late Triassic and the Miocene were recognized. The oldest corresponds to the Santo Domingo Formation, a red bed sequence composed of conglomerates, sandstones and mudstones wich was dated in the Late Triassic-Early Jurassic based on the study of the xyloflora and a radiometric age. This unit is unconformably covered by sandstones and mudstones belonging to the Ciénaga del Río Huaco Formation (Late Cretaceous) which provided some skeletal remains of Titanosaurios. The Puesto La Flecha Formation (late Eocene–Oligocene) comprises sandstones and mudstones deposited in ephemeral fluvial systems together with shallow water bodies (Lower Member) and eolian dunes (Upper Member). The onset of the Andean Orogeny in the studied region is represented in the eolian sandstones of the Vallecito Formation (late Oligocene – early Miocene) which was formed in arid conditions within an underfilled foreland basin. These rocks are succeeded by the informally called unit of " conglomerates and sandstones Refugio del Peñón " that represent the progradation of clastic wedges from the volcanic arc located to the west. Finally, the informal unit of " conglomerates La Falda " points out the displacement towards the west of the Andean orogenic front and the uplift and unroofing of the granitic rocks forming the core of the Sierra del Peñón.
Aeolian Research, Jan 1, 2010
Landscapes of western Argentina are dominated by aeolian sand of diverse composition, reflecting ... more Landscapes of western Argentina are dominated by aeolian sand of diverse composition, reflecting multiple sediment sources. This study focuses on determining the petrography and geochemical composition of sand from three western Argentina dune fields, Médanos Grandes, Médanos Negros and San Luis, to better constrain the provenance of aeolian sand and its relation to Pampean loess. Médanos Grandes sands are litharenites to feldspathic litharenites, with metamorphic and volcanic rock fragments and lesser amounts of quartz and feldspar. Trace elements (U, Th, Sc, V) indicate the dominance of felsic source. A mixed provenance, with contributions from Sierras Pampeanas metamorphic-igneous complex, pre-Quaternary volcanic rocks and direct input from Andean explosive volcanism, is assumed. Médanos Negros sands are lithic feldsarenites, with abundant feldspars and quartz and lesser amounts of rock fragments. Trace elements indicate a mafic source for these aeolian sands, geochemically and petrographically distinct likely due to the input of ultramafic-mafic lithologies of the Sierra Pampeanas. The San Luis sand has substantial petrographic variability with lithic feldsarenites, feldspathic litharenites and lithic arenite. Trace element composition indicates a felsic source. A diagnostic attribute is the dominance of fresh pumice and volcanic glass shards. Contributions from Andean volcanic sources and local metamorphic and igneous rocks are ascertained. Pampean loess and western Argentina dune field sand show broad petrographic and geochemical similarities indicating aeolian sand, silt particles and, eventually, far travelled dust may have a relatively common source. Another viable source for loess is associated with aeolian abrasion in the many dune fields in western Argentina.
Eolian deposits are common in the western Pampas of Argentina, and most are assumed to be associa... more Eolian deposits are common in the western Pampas of Argentina, and most are assumed to be associated with glacial conditions. Stratigraphic and sedimentologic studies coupled with OSL dating in San Luis Province document for the first time a nearly continuous sequence of eolian sand sheet deposits that span most of the Holocene. Petrology and geochemical analyses indicate that the source of the sand is from pre-existing Pleistocene eolian sediments. Sandsheet deposition between ca. 12 and 1 ka is associated with sparse, Monte-type vegetation that occurs with drier conditions (MAP 450-100 mm) than the late 20st century (~700 mm). This paleoenvironmental inference is consistent with nearby pollen and lake level records. A persistent semi-arid environment in western Argentina during the Holocene may reflect sustained warm SSTs in the western equatorial Atlantic Ocean, which may have suppressed the pressure gradient between the South Atlantic Anticyclone and Chaco Low and thus, the flux of summer moisture to western Argentina. There appears to be a paleoclimatic “dipole” response between a dry western Argentina and wet southeastern Brazil, which is consistent with increasing strength of the South American Monsoon through the Holocene. Sand sheet accretion appears to cease by 800 to 200 years ago with wetter conditions and succession to Espinal vegetation prior to European contact.
Palaeogeography, …, Jan 1, 2009
"Miocene deposits of the Toro Negro Formation in La Rioja province, Argentina, host a rich verteb... more "Miocene deposits of the Toro Negro Formation in La Rioja province, Argentina, host a rich vertebrate and invertebrate ichnofauna. Trace fossils are recorded from the lower part of the Lower Member of the Toro Negro
Formation at Quebrada de La Troya. This succession consists of sandstone, intraformational breccia, mudstone and fewconglomerate deposited insandy anastomosingfluvial systemsdeveloped under a semi-arid climate.The invertebrate ichnofauna is composed of meniscate trace fossils (Taenidium barretti, Scoyenia gracilis), dwelling structures (Palaeophycus tubularis) and grazing trails (Helminthopsis hieroglyphica). The vertebrate ichnofauna includes avian (Fuscinapeda sirin, incumbent footprint, slender anisodactyl footprint) andmammalian footprints (Macrauchenichnus rector, cf. Venatoripes riojanus, small heteropod footprint, kidney-like footprints, and oval impressions). Tetrapod footprints and rare Palaeophycus and Helminthopsis are preserved on the top of exposed sandbars. Crevasse splay deposits preserve abundant meniscate trace fossils and dwelling tubes (e.g. Taenidium, Scoyenia and Palaeophycus) ascribed to the Scoyenia ichnofacies. Two suites of invertebrate trace fossils can be
differentiated:meniscate backfill structures (T. barretti) and other burrows (P. tubularis)without ornamentation, developed in a soft substrate, and striated traces (S. gracilis), that crosscut the former, developed in a firmer
substrate. The Toro Negro depositional system displays a high preservation potential for tracks due to seasonal flooding events, which rapidly buried the footprints. The favorable preservational conditions and good exposure of the
track-bearing surface enable us to interpret the track assemblage of the Toro Negro Formation as a sample of the original tetrapod fauna that inhabited that region at central-western Argentina during the Miocene. The identification of possible trackmakers is utilized in this work as a useful tool that contributes to our understanding of the ancient environment. The paleoichnocommunity is characterized by the number of trackmakers and the relative abundance of each type of footprints. A newmethod tomeasure footprint abundance
is proposed; the relative bioturbed area (RBA). Thismeasurement provides numerical characterization of the degree of bioturbation of the whole tracking surface caused by each ichnotaxa.The tetrapod fauna indicated by the footprint record was compared with the body fossil record of the Toro Negro
Formation. These records overlap in some ways, and in other ways they are complementary. The presence of large and medium to small ground sloth, proterotheriid litopterns, caviid rodents, and birds is pointed out by both body
fossils and ichnofossils. Body fossils include remains attributed to dasypodids, glyptodontids, and abrocomid rodents. Ichnofossils indicate the presence of macraucheniid litopterns and three types of birds: shorebirds, perching birds, and large cursorial birds."
The Toro Negro Formation is a foreland sequence in western La Rioja province, Argentina, which re... more The Toro Negro Formation is a foreland sequence in western La Rioja province, Argentina, which records the late-stage tectonic evolution of the Vinchina Basin. Together with the underlying Vinchina Formation, these two units represent one of the thickest and longest continually exposed foreland sections in northwest Argentina. The Vinchina basin is uniquely situated between the Toro Negro and Umango blocks of the Western Sierra Pampeanas to the north and south, the Precordillera to the west, and the Sierra de Famatina to the east. New U-Pb dating of volcanic tephra provides improved age constraints on the pace of sedimentation, and U-Pb ages of detrital zircons serve to strengthen existing provenance interpretations. We show that deposition of the Toro Negro Formation spans roughly 6.9 to 2.3 Ma: Late Miocene to Early Pleistocene. A high-relief, erosional unconformity with the underlying Vinchina Formation developed sometime between 9.3 and 6.9 Ma, although stratigraphic considerations suggest it spanned only the later part of this time interval (perhaps 7.5e6.9 Ma). Above this unconformity, undecompacted sedimentation rates are remarkably high at ~1.2 mm/yr, slowing to ~0.3 mm/yr after ~6 Ma. An unconformity in the upper part of the section is constrained to occur sometime between 5.0 and 3.0 Ma, probably beginning not long after 5.0 Ma. The timing of both unconformities broadly Matches the timing of inferred tectonic events in the Sierra Famatina ~50 km to the east, the Fiambal a basin to the north, and the Bermejo basin to the south, suggesting they May record regional tectonism at these times. Provenance interpretations of detrital zircon spectra are consistent with previous interpretations based on sediment petrography. They show that provenance did not change significantly during the course of Toro Negro deposition, precluding major tectonically-induced drainage reorganization events. Sediments were derived primarily from the north (Toro Negro Block) and west (Precordillera). The data are consistent with a subtle increase in sediment supply from the Precordillera beginning around 6.5 Ma.
Aeolian Research, 2010
Landscapes of western Argentina are dominated by aeolian sand of diverse composition, reflecting ... more Landscapes of western Argentina are dominated by aeolian sand of diverse composition, reflecting multiple sediment sources. This study focuses on determining the petrography and geochemical composition of sand from three western Argentina dune fields, Médanos Grandes, Médanos Negros and San Luis, to better constrain the provenance of aeolian sand and its relation to Pampean loess. Médanos Grandes sands are litharenites to feldspathic litharenites, with metamorphic and volcanic rock fragments and lesser amounts of quartz and feldspar. Trace elements (U, Th, Sc, V) indicate the dominance of felsic source. A mixed provenance, with contributions from Sierras Pampeanas metamorphic-igneous complex, pre-Quaternary volcanic rocks and direct input from Andean explosive volcanism, is assumed. Médanos Negros sands are lithic feldsarenites, with abundant feldspars and quartz and lesser amounts of rock fragments. Trace elements indicate a mafic source for these aeolian sands, geochemically and petrographically distinct likely due to the input of ultramafic-mafic lithologies of the Sierra Pampeanas. The San Luis sand has substantial petrographic variability with lithic feldsarenites, feldspathic litharenites and lithic arenite. Trace element composition indicates a felsic source. A diagnostic attribute is the dominance of fresh pumice and volcanic glass shards. Contributions from Andean volcanic sources and local metamorphic and igneous rocks are ascertained. Pampean loess and western Argentina dune field sand show broad petrographic and geochemical similarities indicating aeolian sand, silt particles and, eventually, far travelled dust may have a relatively common source. Another viable source for loess is associated with aeolian abrasion in the many dune fields in western Argentina.
Eolian deposits are common in the western Pampas of Argentina, and most are assumed to be associa... more Eolian deposits are common in the western Pampas of Argentina, and most are assumed to be associated with glacial conditions. Stratigraphic and sedimentologic studies coupled with OSL dating in San Luis Province document for the first time a nearly continuous sequence of eolian sand sheet deposits that span most of the
Holocene. Petrology and geochemical analyses indicate that the source of the sand is from pre-existing Pleistocene eolian sediments. Sand sheet deposition between ca. 12 and 1 ka is associatedwith sparse,Monte-type vegetation that occurs with drier conditions (MAP 450–100 mm) than the late 20th century (~700 mm). This
paleoenvironmental inference is consistent with nearby pollen and lake level records. A persistent semi-arid environment in western Argentina during the Holocene may reflect sustained warm SSTs in the western equatorial Atlantic Ocean, which may have suppressed the pressure gradient between the South Atlantic Anticyclone and
Chaco Low and thus, the flux of summer moisture to western Argentina. There appears to be a paleoclimatic “dipole” response between a dry western Argentina and a wet southeastern Brazil, which is consistent with the increasing strength of the South American Monsoon through the Holocene. Sand sheet accretion appears to cease by 800 to 200 years ago with wetter conditions and succession to Espinal vegetation prior to European contact.
sernageomin.cl
RESUMEN La Formación Toro Negro (Neógeno) registra parte de la sedimentación de la cuenca de ante... more RESUMEN La Formación Toro Negro (Neógeno) registra parte de la sedimentación de la cuenca de antepaís fracturado de Vinchina (Orogenia Andina) en el noroeste argentino. Esta unidad está compuesta por conglomerados, areniscas y pelitas junto con algunos ...
Geologica acta, 2011
Paganzo Group exposures (Tupe Formation) in the Huaco area provide an excellent opportunity for a... more Paganzo Group exposures (Tupe Formation) in the Huaco area provide an excellent opportunity for assessing the role of sea level and climatic changes on the morphology and nature of coastal fluvial systems deposited in areas of limited tectonic activity. The paleogeographic position of Huaco, close to a coastal region within the Paganzo Basin, allows identification of the effects of sea level change on fluvial architecture. Despite the fact that the Huaco area was dominated by coastal fluvial systems, three marine incursions flooded this part of the basin during the Namurian, Early Pennsylvanian and Late Pennsylvanian respectively. During deposition of the Paganzo Group, climatic conditions evolved from glacial (Namurian) to hot and dry (Late Cisuralian). Five types of fluvial deposits were recognized on the basis of architectural element analysis, lithofacies distribution and type of fluvial bounding surfaces present. Fluvial system 1 (FS1) constitutes the lower part of the Tupe Formation and consists of stacked multi-storey channel-fill complexes formed on large braided alluvial plains dominated by channel-avulsion processes. FS2 consists of multi-storey channels alternating with floodplain deposits including coal beds and organic-rich mudstones. This fluvial system is interpreted as the deposit of an anastomosed network of sandy channels. FS3 occurs between the Early Pennsylvanian and Late Pennsylvanian marine transgressions and consists of sandstones and some conglomerates that form stacked channel complexes. Sporadically, very fine-grained sandstone and mudstone floodplain deposits appear as thin intercalations. FS3 likely formed on braided alluvial plains with channels dominated by transversal bars. FS 4 corresponds to an anastomosed fluvial system that was dominated by two types of braided channel belts that were separated by narrow floodplains. Finally, FS5 is composed of fining-upward cycles ranging from gravely sandstones at the bottom of channels to muddy floodplain deposits at the top. The whole FS5 succession was deposited by high-sinuosity meandering rivers. Detailed stratigraphic analyses clearly suggest that both, sea level and climate changes were first-order controls on fluvial system configurations. In this way, braided systems belonging to FS1 correspond to a low-accommodation system tract. Whereas, coal beds of FS2, which resulted from high water-tables, correspond to a high accommodation system tract that was likely associated with advanced stages of the Late Pennsylvanian transgression. A signif-A . T E D E S C O e t a l .
The Talampaya Formation is the basal unit of the Ischigualasto-Villa Union rift system and has b... more The Talampaya Formation is the basal unit of the Ischigualasto-Villa Union rift system and has been traditionally assigned to the Triassic based on stratigraphic relationships. A median UePb age of 252.38 (þ0.09/0.22) Ma was obtained from volcanic zircons collected from a tuff bed close to the top of this unit at the Bordo Atravesado locality in the Cuesta de Miranda area (La Rioja, Argentina). This radiometric age is very close to the accepted PermianeTriassic boundary indicating that, at least in this locality,
sedimentation occurred during the Late Permian but may have extended into the earliest Triassic. This new evidence indicates that the onset of the extensional event that gave rise to the rift basins in western Argentina started during the Permian. Detailed sedimentological studies of the 260 m thick Talampaya
Formation allowed subdividing the succession into seven facies associations grouped into three evolutionary stages indicating that sedimentary environments initially evolved from alluvial fans to a braided river system. Subsequent intrabasinal volcanism associated with sediment deposition by low-to moderate-sinuosity rivers is recorded in the lower third of the column. The middle and upper part of the unit captures the evolution from ephemeral fluvial systems with an eolian interval to an ephemeral clastic lake with intermittent volcanic ash deposits. These changes indicate a progressive lowering of the landscape and a transition towards arid or semiarid conditions.
Drought episodes during the early–mid 20th century were recognized and described in several place... more Drought episodes during the early–mid 20th century were recognized and described in several places around the world, with extreme dry conditions and widespread landscape denudation, like during the famous ‘Dust Bowl’ in North America. However, there is scant documentation of droughts in southern South America, particularly from the Pampas, and none based on the geological record. In this article, we provide clear evidence of aeolian reactivation
and sand deposition in some areas of La Pampa and San Luis provinces, western Pampas (Argentina), during early–mid 20th century in response to drier conditions, probably amplified, like historic droughts in North America, by anthropogenic factors (e.g. significant population increase and agriculture expansion into a fragile environment). Evidence includes widespread bare sand blowouts, extensive surfaces with active sand migration, steep dune lee
slopes, and sharp crests covered by weak soil development (A/C profile), accompanied by historical documents. Optically stimulated luminescence (OSL) ages on aeolian beds confirm mobilization and sedimentation by wind processes c. 95–60 yr BP. Considering the dominant (over 70%) austral spring–summer precipitation, it is possible the rainfall deficit in western Pampas was linked to positive sea surface temperature (SST) anomalies in the western subtropical South Atlantic Ocean (20–30°S and 30–50° W), according to significant canonical correlation between the precipitation field in subtropical South America and the Atlantic Ocean SST anomalies.
RESUMEN Se efectúa una revisión y actualización de la estratigrafía de las secuencias paleógenas ... more RESUMEN Se efectúa una revisión y actualización de la estratigrafía de las secuencias paleógenas y neógenas expuestas en las Sierras Pampeanas Noroccidentales y Precordillera septentrional de La Rioja. Aquí se reconocen tres princi-pales áreas de afl oramientos: 1. Sierra de Los Colorados (depocentro Vinchina), 2. Sierras de Yanso y La Flecha (depocentro La Troya) y 3. Quebrada de Santo Domingo-sierra del Peñón. Las rocas cenozoicas más antiguas corresponden a los estratos rojos de la Formación Puesto La Flecha, compuesta mayormente por areniscas y fangolitas depositadas en ambientes fl uviales de baja energía y lacustres efímeros durante el intervalo Eoceno tardío-Oligoceno temprano. La unidad es sucedida por un espeso conjunto de areniscas correspondientes a la Formación Vallecito (Oligoceno tardío-Mioceno temprano), formada principalmente por el apilamiento de secuencias de dunas eólicas. La Formación Cerro Morado (Mioceno temprano a medio) incluye dos miembros, el inferior compuesto por areniscas y fangolitas, junto a escasos conglomerados, y el superior de naturaleza volcánica y volcaniclástica. El inicio de la sedimentación de la Formación Vinchina, ocurrido entre los 16-15 Ma, marcó el comienzo de la sedimentación en la antefosa de la cuenca de antepaís. La mayor parte de la Formación Vinchina está compuesta por areniscas y fangolitas, con proporción subordinada de conglomerados y escasas evaporitas, mayormente depositadas por sistemas fl uviales de baja energía, asociados a depósitos lacustres efí-meros y eólicos. En el depocentro La Troya estas rocas son sucedidas por conglomerados, areniscas y pelitas de la Formación Zapallar; mientras que en el depocentro de Vinchina, mediando una superfi cie de fuerte incisión, se depositaron areniscas, fangolitas y conglomerados de la Formación Toro Negro (Mioceno más tardío-Pleis-toceno temprano) que representa el progresivo avance hacia el este de los cabalgamientos precordilleranos. Finalmente, conglomerados gruesos, brechas y areniscas, registran la canibalización de las cuencas de antepaís. Este intervalo corresponde a la Formación El Corral (Plioceno tardío-Pleistoceno) y registra la sedimentación, en gran medida sintectónica, en abanicos aluviales y sistemas fl uviales multicanalizados de alta energía. ABSTRACT Cenozoic stratigraphy of the foreland basins of the Sierras Pampeanas Noroccidentales and Precordillera of La Rioja. A review and update of the Paleogene and Neogene sequences cropping out in the Sierras Pampeanas Norocciden-tales and Precordillera of La Rioja is presented. Three main depositional areas are recognized: 1. Sierra de Los Colorados (Vinchina depocenter), 2. Sierras de Yanso and La Flecha (La Troya depocenter) and, 3. Quebrada de Santo Domingo-sierra del Peñón. The oldest Cenozoic rocks are red-beds of the Puesto La Flecha Formation composed of sandstones and mudstones deposited in low-energy fl uvial and ephemeral lacustrine environments. Radiometric, magnetostratigraphic and paleontological information locates this unit in the Upper Eo-cene-Lower Oligocene interval. The former unit is succeeded by a thick set of eolian sandstones corresponding to the Vallecito Formation (Upper Oligocene-Lower Miocene), formed mainly by the stacking of dune deposits. The Cerro Morado Formation (Lower to Middle Miocene) includes two members, the lower one composed of sandstones and mudstones, along with few conglomerates, and the upper one of volcanic and volcaniclastic nature. The beginning of the sedimentation of the Vinchina Formation, which occurred between 16 and 15 Ma, marked the onset of sedimentation in a retroarc foreland basin. Most of the Vinchina Formation is composed of sandstones and mudstones, with a subordinate proportion of conglomerates and few evaporites, all of them deposited by low-energy river systems, associated with ephemeral lakes and eolian deposits. In the La Troya depocenter these rocks are succeeded by conglomerates, sandstones and mudstones belonging to the Zapallar
Cenozoic Geology of the Central Andes of Argentina, 2011
149 XVI REUNIÓN ARGENTINA DE SEDIMENTOLOGÍA, 2018
La Formación Tambería constituye el registro sedimentario mioceno de la cuenca de antepaís de Fia... more La Formación Tambería constituye el registro sedimentario mioceno de la cuenca de antepaís de Fiambalá. El perfil expuesto a lo largo de la RN60 permite diferenciar tres miembros informales. En esta contribución se presenta un análisis paleoambiental del miembro inferior caracterizado por el predominio de areniscas con menor proporción de conglomerados y pelitas. Dentro de este miembro se reconocieron tres asociaciones de facies (AF). La AFI está dominada por areniscas medianas bien seleccionadas, laminadas y entrecruzadas, con delgadas intercalaciones de pelitas y, en menor medida, de bancos conglomerádicos de hasta 2 m de espesor. Se interpreta como un campo de dunas éolicas con interdunas húmedas y ocasionales cursos fluviales. La AFII presenta intercalaciones centimétricas de pelitas y areniscas con grietas de desecación que alternan métricamente con areniscas medianas bien seleccionadas con entrecruzamientos, bancos mantiformes de areniscas masivas o laminadas, y frecuentes cuerpos de base erosiva lentiformes areno-conglomerádicos, de hasta 2 m de espesor, internamente masivos o laminados. Corresponden a un sistema fluvial poco canalizado dominado por flujos mantiformes con desarrollo de dunas eólicas en las áreas de intercanal areno-pelíticas. La AFIII es similar a la anterior, pero los niveles areno-conglomerádicos constituyen fajas más recurrentes y potentes (hasta 7,5 m), compuestas por cuerpos lenticulares amalgamados grano-decrecientes, que gradan desde conglomerados masivos a areniscas gruesas laminadas o entrecruzadas, asociadas con bancos lobulares de areniscas masivas y laminadas, en ocasiones amalgamados y definiendo arreglos estratocrecientes. Corresponde a un sistema fluvial multicanalizado de baja sinuosidad con canales multiepisódicos separados por planicies con dunas eólicas.
XVI REUNIÓN ARGENTINA DE SEDIMENTOLOGÍA , 2018
El análisis de las modas detríticas de areniscas pertenecientes a la Formación Valle Chico y al G... more El análisis de las modas detríticas de areniscas pertenecientes a la Formación Valle Chico y al Grupo Tepuel (formaciones Pampa de Tepuel, Mojón de Hierro y Río Genoa) permite establecer las probables áreas de proveniencia para la cuenca neopaleozoica. Desde el punto de vista composicional, las areniscas corresponden a litoarenitas y litoarenitas feldespáticas con menor participación de feldarenitas líticas. El componente modal principal es el cuarzo que fue dividido en 4 tipos: cuarzo monocristalino (ampliamente dominante), cuarzo policristalino de grano grueso, milonítico y de grano fino. Entre los feldespatos, en la mayoría de las muestras predominan la ortosa (junto a escasa contribución de microclino) sobre la plagioclasa. Los fragmentos líticos incluyen por orden de abundancia metamorfitas de bajo grado, de mediano y alto grado y, menor proporción, de volcanitas y sedimentitas. Se pueden reconocer dos petrofacies principales: la primera de composición lítica metamórfica, dominante en las sedimentitas del Grupo Tepuel, refleja el aporte principalmente desde un orógeno reciclado cuarzoso a transicional. La segunda, correspondiente a la Formación Valle Chico, es también de composición lítica, pero difiere en la mayor participación de volcanitas con respecto a las metamorfitas y feldespato potásico. Este último grupo correspondería al aporte desde un arco volcánico disectado a parcialmente disectado. De esta manera, la evolución de la cuenca incluye sedimentitas derivadas del arco volcánico en las sedimentitas de la Formación Valle Chico que pasan temporalmente a un aporte de orógeno reciclado cuarzoso a transicional, con una contribución subordinada de rocas de basamento (Grupo Tepuel).
XVI REUNIÓN ARGENTINA DE SEDIMENTOLOGÍA, 2018
En esta contribución se analiza el registro estratigráfico de las unidades carboníferas y pérmica... more En esta contribución se analiza el registro estratigráfico de las unidades
carboníferas y pérmicas tempranas de la Cuenca Calingasta-Uspallata,
incluyendo a las formaciones Agua de Jagüel, Hoyada Verde, Tres Saltos y Del Ratón en la Precordillera, junto con las formaciones San Ignacio y Agua Negra en la Cordillera Frontal. El análisis de estas unidades permite reconocer cuatro superficies estratigráficas de expresión regional, las que señalan discontinuidades en la sedimentación y pueden ser utilizadas como niveles guías para la correlación. La superficie inferior S1, corresponde a la que marca la base de la Formación El Paso y el techo de la Formación Del Ratón, su antigüedad es asignada al Viseano y correlacionada con la fase tectónica Río Blanco. La superficie S2, interpretada como producida por una regresión
forzada, es la que separa a las formaciones Hoyada Verde y Tres Saltos y ha sido motivo de considerable debate en cuanto a su origen. Esta superficie se prolonga hacia el sur como un plano de incisión intraformacional dentro de la Formación Agua de Jagüel. Hacia la Cordillera Frontal S2 pierde su carácter erosivo y se expresa como un marcado cambio de facies. La superficie S3 registra un nuevo evento de regresión forzada y produce niveles de incisión, dentro de las formaciones Tres Saltos y Agua de Jagüel. La superficie S4, de probable origen tectónico, separa las formaciones Agua de Jagüel y Cordón de
Jagüel en la Precordillera y es correlativa de la discordancia angular
interpuesta entre las formaciones Agua Negra y San Ignacio.
VII International Conference Aeolian Research, 2010
Landscapes of western Argentina present several dune fields, many of them partially enclosed by h... more Landscapes of western Argentina present several dune fields, many of them partially enclosed by high ranges of the Andean domain. Médanos Grandes (MG) dune field (San Juan province) is bounded by the Sierra de Pie de Palo to the north, a high massif of Precambrian-Lower Paleozoic metasedimentary and metavolcanic rocks. Colluvial and fluvial deposits occur along the east, west and southern margins (Bermejo and San Juan River plains). To the northeast there is the Sierra de Valle Fértil, mostly composed of Precambrian-Lower Paleozoic metasedimentary rocks, some non- to strongly metamorphosed, mafic to acid igneous rocks and a sedimentary cover. Other important sediment sources are the Andes (Upper Paleozoic granites and sedimentary and volcanic successions of very variable ages), and the Precordillera (Paleozoic and Cenozoic sedimentary rocks with minor Upper Paleozoic volcanites). Two sets of samples from MG were petrographically studied. The first is middle to late Holocene aeolian sand that corresponds to litharenites to feldspathic litharenites, with metamorphic and volcanic lithics and lesser amounts of quartz and feldspar. The second group (samples from less than 10 cm deep digs, non-dated but likely younger than 100 year old aeolian sand) includes lithic feldsarenites to feldspathic litharenites, with higher amounts of quartz and feldspars. Although the tectonic environment of the source areas has not varied in the Holocene, the two groups show compositional differences reflected, among others, in the QFL ratio. The Holocene sand portrays a provenance from undissected to transitional arc, whereas the present sand samples plot in the dissected arc field. This difference reflects a multiple and changing sediment sources due to the aeolian reworking of the Bermejo and San Juan River plains that collect volcanic-sedimentary and crystalline basement detritus.
La presencia de depósitos mesozoicos en la Precordillera septentrional ha sido reconocida recient... more La presencia de depósitos mesozoicos en la Precordillera septentrional ha sido reconocida recientemente (ver revisión en Limarino et al., 2005). Estos afloramientos, representados por las Formaciones Santo Domingo (Triásico Superior-Jurásico Inferior) y Ciénaga del Río Huaco (Cretácico Superior), afloran en fajas meridionales con orientación NNO-SSE a lo largo de las provincias de San Juan y La Rioja, generando interesantes perspectivas para los modelos paleogeográficos de las cuencas mesozoicas. La extensión generalizada debida al desmembramiento de Gondwana dio lugar a la depositación de estas unidades en cuencas extensionales probablemente tipo hemi-graben someras, con dominio de sedimentación continental.
Journal of South American Earth Sciences, 2020
We describe new avian remains from the lower levels of the Toro Negro Formation (~7-6 Ma, U–Pb), ... more We describe new avian remains from the lower levels of the Toro Negro Formation (~7-6 Ma, U–Pb), exposed in
Quebrada de la Troya between Vinchina and Jagü´e towns in La Rioja Province, Argentina. The Toro Negro
Formation is composed of a thick continental sequence (~2.4 km) of sandstones, conglomerates and mudstones
deposited in both fluvial and lacustrine systems at the base of the unit. The avifauna of Toro Negro is low in
diversity, and the majority of the remains are fragmentary and isolated. However, it is interesting in that it
includes carnivorous birds such as a new species of a large eagle (Vinchinavis paka gen. et sp. nov.), scavengers
(condors) and large herbivores (rheas). On the whole, the occurrences documented within the Toro Negro
Formation confirm the presence of taxa with strong temperate warm preferences that typically inhabits open areas with arboreal patches within an arid-semiarid zone. The palaeoenvironmental characteristics of the fauna are confirmed as fully compatible with the evidence previously obtained through sedimentology and facies analysis.