Southern Buenos Aires Province Research Articles

Understanding the burial history and the hydrocarbon potential of the late Paleozoic Claromecó foreland Basin (Southwestern Gondwana, Argentina) by combining organic geochemistry, organic petrology, and thermal modeling

The Claromecó foreland Basin (Carboniferous–Permian; southern Buenos Aires province, Argentina) is key to understanding the paleotectonic evolution of the southwestern Gondwana margin and is relevant to energy resource exploration. This study reconstructs the thermal and burial history of the Claromecó Basin by integrating geochemical data, organic petrology, and thermal modeling techniques. Cores samples of the Tunas Formation (Pillahuincó Group, Early Permian) were studied. A 1D thermal model was constructed, calibrated with vitrinite reflectance measurements (VRo %), and corroborated with fluid inclusion and apatite fission track data from previous studies. Rock-Eval pyrolysis results show TOC% values ranging from 0.13 to 60.35 wt%. The Hydrogen index (HI < 50 mg HC/g TOC) and Oxygen index (OI < 50 mg CO2/g TOC) indicate the dominance of Type III and Type IV kerogens, most likely resulting from the thermal maturation of an original Type III kerogen. Petrologic observations confirm the presence of macerals from the inertinite group, as well as minor amounts of vitrinite and liptinite. The Tmax displays a temperature range mostly from 460 to 610 °C. The VRo % values range from 1.5 to 2.0%. Geochemical data combined with VRo % measurements confirm a late catagenesis to metagenesis stage within the wet to dry gas window for coals and organic-rich strata.In order to constrain the thermal evolution of the basin infill, different scenarios were tested by varying the heat flow and the missing section thickness associated with the uplift and erosion of the basin (Permian–Cenozoic unconformity). The best calibration results were obtained with an erosion thickness of 3000 up to 4200 m and paleo heat flow peaks of either 60 or 80 mW/m2 during the Lower Permian–Lower Cretaceous. The Tunas Formation was deposited and buried during the Permian–Triassic (Gondwanides Orogeny phase), reaching a maximum temperature of 180 °C. The results obtained by combining geochemical analysis, organic petrology, and thermal modeling techniques indicate that the coal beds of the Tunas Formation could have a current potential as gas-prone source rocks. Despite that, the hydrocarbon generation capacity of coal levels is currently low due to the high percentage of residual (Type IV) kerogen. Further research could help clarify if the hydrocarbons potentially expelled by these source rocks have been lost due to migration or could be trapped somewhere in the basin.

First assessment of debris pollution in the gastrointestinal content of juvenile Magellanic penguins (Spheniscus magellanicus) stranded on the west south Atlantic coasts

This paper provides the first evidence of debris pollution, including plastic, in juvenile Magellanic penguins (Spheniscus magellanicus) found stranded on the Atlantic coast of southern Buenos Aires Province, Argentina. Macro-, meso- and microparticles of anthropogenic origin were observed in 100 % of the studied birds, with debris abundance ranging between 33 and 200 items/bird. Microparticles represented 91 % of the total debris and 97 % of them were fibers. Black particles were the most abundant (30 %), followed by transparent (26 %), blue (14 %), yellow (10.3 %), and red (10 %). Infrared and Raman spectroscopy identified 62.7 % of the total particles as plastics, with polypropylene (27.8 %) and polyester (21.6 %) being the most abundant polymers. Semi-synthetic cellulosic fibers, metallic particles, and pigments were also found. The presence of metallic microparticles was suggested for the first time in penguins. Stranded juvenile Magellanic penguins are proposed as promising bioindicators of plastic pollution in the South Atlantic.

Demographic model for Aleppo pine invading Argentinean grasslands

Biological invasions represent one of the most significant threats to the conservation of biological diversity. Understanding the population dynamics of an invasive species is essential to detecting key components that allow the development of an effective management strategy. South American Pampas are particularly vulnerable to the invasion by alien woody plants that threaten the last remnants of native biodiversity. Aleppo pine (Pinus halepensis) invades mountain grasslands in southern Buenos Aires province, Argentina, where it changes the structure and dynamics of the whole ecosystem. We combined information on the biology of the species in its native range with our data in the invaded area to develop a population model aimed at understanding the invasion process and detecting key parameters associated with its success. A 12 × 12 stage-structured matrix model was used to describe the dynamics of the species in the area, through deterministic and stochastic projections. Population growth rates were greater than one for both types of projections, in accordance with its invasive capacity in the area. Elasticity analysis highlights the contribution of survival at the first adult stage (seven to 14 years) to the population growth rate, and in this way, draws attention to this stage when developing a species control strategy. Aleppo pine shares key biological characteristics with other high-impact invasive pine species in Argentina and other countries in the Southern Hemisphere. These similarities include the presence of serotinous cones and an abundant seed bank in the canopy, recruitment conditioned by competition in the regeneration niche, and a relatively short juvenile period. In this way, the model developed in this work could be easily adjusted for similar situations involving invasive congeners in other grassland ecosystems.

The Northernmost record of the goose genus Chloephaga (Eyton, 1838) (Aves, Anatidae) and its biogeographical implications

The aim of the present contribution is to describe a partial coracoid (CTES-PZ 7797) coming from Upper Pleistocene Toropí/Yupoí Formation, in Corrientes province, Argentina. The comparative anatomical analysis indicates that it belongs to an indeterminate species of the goose genus Chloephaga, but sharing some characters with the living C. picta. Today, members of this genus breed in Southern Patagonia and migrate to southern Buenos Aires province during the winter season, being its northernmost record 700 km far south from the fossil specimen here reported. The presence of Chloephaga farther north from its current geographical distribution is congruent with the presence in Upper Pleistocene outcrops in the area of mammals that are adapted to arid environments. This constitutes another taxon recorded at Arroyo Toropí that currently presents a different geographic distribution, such as observed in Leopardus pardalis, Chaetophractus villosus, Boa constrictor, Dolichotis patagonica, among other, and shed light on the complex palaeobiogeographic scenario that could have developed during the MIS 5 in the Mesopotamian region of Argentina.

Fragmentation of Coastal Grasslands by Plantations and Spontaneous Spread of Invasive Pines in the Southern Pampa

Coastal dunes of the southern Buenos Aires province, in Argentina, are one of the last remnants of biodiversity in the southern Pampa unit, within the Rio de la Plata Grasslands. While the direct loss of grasslands due to the advance of cities and afforestation is conspicuous, the negative effects of the subdivision of the remaining environments on biodiversity and ecosystem dynamics are less considered. Our work aimed to analyze the combined effect of fires and subdivision of grasslands by invasive alien trees. Our results suggest that fragmentation affects the resilience of coastal grasslands after fire and affects the course of succession, promoting the establishment of invasive alien plants. We also suggest that fires favor the advance of pines and acacias towards the interior of grassland remnants, further reducing their area. The effective conservation of the components of Pampas biodiversity that still persist in these coastal ecosystems will depend on preventing, mitigating and compensating the insularization effects associated with forest plantations and the expansion of invasive trees, by means of adequate territorial planning that allows remnants to be maintained in a good state of conservation.

Oldest Record of the Pit-Viper Bothrops (Squamata, Viperidae), from the Lower Pliocene of Buenos Aires Province, Argentina

The fossil record of the genus Bothrops is still sparse in South America. Most records belong to extant species recovered in strata not older than the late Pleistocene. The genus was also tentatively reported from the early Pliocene and early–middle Pleistocene of Buenos Aires province, Argentina, based on fragmentary specimens. The aim of the present contribution is to report the partial vertebral column of a viperid snake discovered in the lower Pliocene layers of Farola de Monte Hermoso locality, southern Buenos Aires province. The specimen can be referred to the extant genus Bothrops, representing the oldest occurrence for this taxon. This finding supports the hypothesis sustained by previous authors that indicate a “stasis” in the evolution of the South American herpetofauna since the late Neogene, at least.

Fossil record of a Characiform in the Monte Hermoso Formation (lower Pliocene), Buenos Aires, Argentina. Palaeobiogeographical implications

The fossil record of fishes from the Farola de Monte Hermoso locality (lower Pliocene) in the southern Buenos Aires province, Argentina, shows an unusual composition. The locality at the southern boundary of the Brazilian Ichthyogeographic Realm. However, its fossil record is composed of fossil fishes that are not necessarily related to Brazilian lineages, namely indeterminate siluriforms, trichomycterid catfishes, and percomorphaceans. The aim of the present contribution is to describe and report for the first time isolated specimens belonging to Characidae fishes. In the Pampean region the fossil record of characids is restricted to Oligosarcus Günther, 1864 sp. from the late-middle Pleistocene. The present finding fills a temporal gap between the Paleogene and Quaternary reports and indicates that Brazilian fish lineages were present in the area by early Pliocene times, and may constitute an indirect evidence of the evolution of the basins in the southern Pampean Area.

Taphonomy of a skeleton of Arctocephalus australis (Carnivora: Pinnipeda: Otariidae) from the Holocene of Miramar locality (southern Buenos Aires, Argentina)

The taphonomy of a partial skeleton of the fur seal Arctocephalus australis from the mid-Holocene of Miramar (southern Buenos Aires province, Argentina) comprising most of both hindlimbs and some vertebral elements is herein described and discussed. The main axis of the long bones is oriented perpendicular to the coastline, flexed and slightly disarticulated, while the vertebrae are somewhat arched, possibly suggesting rigor mortis. The specimen was probably transported from a nearby coastal area, and possibly died from starvation with subsequent stranding. Short weathering times, fragmentation and possible rotation of the pelvic region are the main factors affecting the remains. The material corresponds to a subadult individual, determined by the pattern of fusion of the epiphysis and size of long bones. This study adds important information on the taphonomy of Holocene marine mammals and paleoenvironmental conditions influencing the preservation of these pelagic pinnipeds along the Atlantic Ocean compared with the populations of the Pacific Ocean.

Spatio-temporal interactions of carnivore species in a coastal ecosystem in Argentina

Land-sea interface is an ecotone where the intersection of marine and terrestrial ecosystems create unique ecological conditions for terrestrial mobile species and freshwater-adapted organisms to exploit marine-derived food resources. Mammalian carnivores play an important role in almost any ecosystem where they live due to their top-down (or trophic cascade) effects on prey species and primary producers, thus structuring ecosystems along varied food-web pathways. We use camera trapping to study the patterns of coexistence, habitat use and activity pattern of carnivores species in a coastal area in southern Buenos Aires province, Argentina. We were able to detect five of the seven species of Mammalian carnivores being the Pampas fox Lycalopex gymnocercus and Geoffroy's cat Leopardus geoffroyi the two most common. Geoffroy's cat seems to use more intensively those areas close to the shoreline, while we found little support of it for Pampas fox; which seems to use more inland areas. Congruently, we found evidence of a lack of spatial and, to a lower extent, temporal avoidance between the two most common carnivore species of our study area. Our findings support those previous studies indicating that the coastal dunes have an important role in the conservation of the biodiversity of Buenos Aires province. Wildlife conservation is compatible with carefully-designed ecotourism and limited infrastructure development and this may be a unique chance for the areas of Buenos Aires coast that have not been affected yet by poorly planned, conservation-unfriendly urbanization.

Assessment of Culex pipiens bioforms in the world's southernmost distribution limit.

The mosquito Culex pipiens s.s. L. occurs as two bioforms that differ in physiology and behaviour affecting virus transmission cycles. To assess the occurrence of Cx. pipiens bioforms in the southernmost limit of its distribution, specimens were collected aboveground in southern Buenos Aires Province and east Patagonia, Argentina. Ten larvae and 25 adults were individually processed and identified by polymerase chain reaction (PCR) amplification of Ace-2 and CQ11 loci. Culex quinquefasciatus Say (one larva, two adults), Cx. pipiens f. molestus (one larva, one adult) and one adult of hybrid origin were identified in Buenos Aires Province; only Cx. pipiens f. molestus was recorded in Patagonia (eight larvae, 21 adults). The potential absence of bioform pipiens and its implications in arbovirus enzootic cycles is discussed.

An integrative approach unveils speciation within the threatened spider Calathotarsus simoni (Araneae: Mygalomorphae: Migidae)

The mygalomorph trapdoor spider family Migidae displays a quintessential Gondwanan distribution, including species in Australia, Africa, Madagascar, New Zealand, New Caledonia, and the southern cone of South America. The Argentinean fauna consists of a single species, Calathotarsus simoni Schiapelli & Gerschman, 1975, with a highly localized distribution range restricted to two mountain ranges in the southern Buenos Aires province, central Argentina. The recent discovery of specimens from new localities including adult males and females revealed morphological differences. Similarly, a molecular phylogenetic analysis using mitochondrial and nuclear markers distinguished two main lineages within C. simoni, showing genetic divergence in the levels reported for other species within the family. The two lineages corresponded to each of the two main ranges inhabited by the species and matched the morphological differences observed. Finally, an ecological niche modelling analysis revealed significant ecological differences between the lineages inhabiting the two mountain ranges. Based on integration of all the evidence, the new species Calathotarsus fangioi sp. nov. is described. The new species is circumscribed to the easternmost mountain range of Tandilia, while the distribution C. simoni is re-delimited to include only the western range of Ventania. Both species are diagnosed, described, and illustrated. This new species description and the conservation status for these remarkable spiders are further discussed.

Validation of MODIS-Aqua bio-optical algorithms for phytoplankton absorption coefficient measurement in optically complex waters of El Rincón (Argentina)

El Rincón is a highly productive area in the inner-shelf of the Argentine Sea, southern Buenos Aires Province (39°S–62.5°W; 41.5°S–60°W), regarded as the habitat for commercially valuable fish species and important for local artisanal fisheries. The aims of this work were to characterize for the first time the in situ absorption coefficient of phytoplankton (aph(λ)) in relation to phytoplankton composition and chlorophyll-a (Chl-a) concentration, and to evaluate the satellite retrieval of aph(443) using two atmospheric correction algorithms and three bio-optical semi-analytical algorithms in order to define which is more suitable for the study area. A total of 28 oceanographic cruises were performed between November 2013 and March 2017 and the sampling included physical variables (temperature, salinity, suspended particulate matter, SPM), Chl-a, phytoplankton absorption and composition. The phytoplankton community was mainly dominated by chain-forming diatoms from the microplankton size class (40–80%), while a single coccolithophore, Gephyrocapsa oceanica (cell diameter <10 µm) was a key component (up to 40%) of the nanoplankon. In situ Chl-a (mean 1.8 mg m−3) and aph (443) (mean 0.052 m−1) generally covariated with no clear seasonality. Their correlation was rather low (R2 = 0.52) and with high scattering, in agreement with the high interannual variability of phytoplankton composition. Further, the relative low mean specific absorption coefficient of phytoplankton (aph*(443), 0.032 m2 (mg Chl-a)−1) and (aph*(676), 0.014 m2 (mg Chl-a)−1) denoted the presence of big cells and pigment packaging effect. Aside from the optical complexity of these waters, reasonable results were found using the Quasi Analytical Algorithm in retrieving aph coefficient (R2 = 0.55, Bias = 19%) and switching the atmospheric correction algorithm depending on the distance to the coast, the depth and turbidity. The results found in this paper present for the first time the phytoplankton composition and absorption of algal material characteristics and the derived implication on the performance of bio-optical algorithms in the optically complex waters of El Rincon.

Surface Soil Type Preference for Burrowing of the Endangered and Endemic Trapdoor SpiderCalathotarsus simoni(Araneae: Migidae)

Abstract Calathotarsus simoni Schiapelli & Gerschman, 1975 is an endemic and rare trapdoor spider that lives exclusively in the mountainous systems of southern Buenos Aires province, central Argentina. In previous studies, authors suggested the preference of this species to a particular soil surface type. Thus, we hypothesized that this species differs in its responses to the soil surface type for burrow construction. To test this, we placed 26 adult females in chambers providing two choices (soil with moss and without moss) and compared the proportions of observations in each to evaluate species preference. Calathotarsus simoni significantly preferred the soil with moss. We observed a remarkable behaviour before the construction of the burrow when spiders were at the soil with moss. Finally, we discuss the possible ecological significances of this preference.

Joint mode and port choice for soy production in Buenos Aires province, Argentina

This study analyses the decision of port and mode choice of soy consolidators and producers from southern Buenos Aires province, Argentina. Nested logit models were estimated combining stated and revealed preference data. Estimations for Willingness to pay for one-day reduction in inventory, travel time, elasticities, iso-utility curves and hinterland were made. FAS (Free Alongside Ship) price, typically not considered, proved to be a relevant parameter in the mode-port choice. Other variables included were Service headway, freight price and travel time. Simulation results showed that reducing the train’s service headway and freight price are effective measures to encourage train demand.

A Controversial Unit Within The Argentine Neogene: The “Irenean” Fauna

The “Irenean” is a controversial unit traditionally employed to embrace fossil vertebrates and bearing-sediments of late Neogene—roughly Pliocene—age in southern Buenos Aires Province, Argentina. Although originally intended as an intermediate unit between Montehermosan and Chapadmalalan faunas, almost a century after its description, the “Irenenean” is still poorly known. Based on fieldwork by our team during the last 25 years in its type area, the Quequen Salado River, we revisit the basic aspects of the “Irenean”. We describe the main paleontological localities and the correlations suggested by fossils and sediments and also discuss the chronology of these deposits. We conclude that the “Irenean” is a complex unit composed of at least two fossilife rous assemblages. An older assemblage is found in sediments exposed in localities downstream of the mouth of Indio Rico; a younger assemblage is contained in outcrops upstream of the mentioned point and includes the classic site of Cascada Grande. The older assemblage includes the cingulate Macrochorobates sp., the caenolestid Pliolestes tripotamicus, the tardigrade Proscelidodon cf. P. patrius and the rodent Xenodontomys ellipticus, and points to a sensu lato Huayquerian Stage/Age. The younger assemblage is typified by several taxa, including the rodents Actenomys sp. and Eumysops laeviplicatus, the argyrolagid Argyrolagus sp., the didelphid Hyperdidelphys inexpectata, the macraucheniid Promacrauchenia cf. P. chapadmalense, and the cingulate Ringueletia simpsoni, suggesting a Montehermosan Stage/Age.

Reprint of “Survey and first molecular characterization of Echinococcus granulosus sensu stricto (G1) in Pampas fox (Lycalopex gymnocercus) in Buenos Aires province, Argentina”

Echinococcosis is a zoonosis caused by tapeworms of the genus Echinococcus. Echinococcus granulosus sensu lato (s. l.) has a world-wide distribution and its transmission is primarily maintained in a synanthropic cycle with dogs as definitive hosts and livestock species as intermediate hosts. However, many wild canids also function as definitive hosts for E. granulosus s. l. Echinococcosis in humans is mainly caused by E. granulosus sensu stricto (s. s.) G1 genotype. In the present work, we expanded the epidemiological study on echinococcosis reported cases in Pampas fox (Lycalopex gymnocercus) to provide a prevalence estimate for rural areas of southern Buenos Aires province, Argentina. Ninety-five whole intestines were analyzed using the sedimentation and counting technique with a result of 83 foxes (87.37%) harboring at least one helminth species. E. granulosus s. l. adults were found in one Pampas fox (1.05%). These adult helminthes were E. granulosus s. s. (G1) according to the genotyping analysis of a 450-bp region of the mitochondrial cytochrome c oxidase subunit 1 (cox1) gene.

Ancylostoma (Ancylostoma) buckleyi (Nematoda: Ancylostomatidae): new wild host and distribution expansion.

Here we report the occurrence of Ancylostoma (Ancylostoma) buckleyi (Le Roux and Biocca, 1957) (Nematoda: Ancylostomatidae) in the small intestine of Pampas foxes (Lycalopex gymnocercus) (Mammalia: Canidae). This fox is the most abundant native carnivore in southern South America, where it inhabits grasslands, open woodlands and areas highly modified by extensive ranching and agricultural activities. Material from 80 foxes in rural areas of southern Buenos Aires province, Argentina was examined. The intestinal tracts were carefully removed from each carcass and subsequently isolated by ligatures (pylorus and rectum). Examination of the intestinal content was performed using the sedimentation and counting technique. Four foxes (5%) were found to be parasitized with adult specimens of A. buckleyi. This is the first report of Ancylostoma (A.) buckleyi in Argentina and adds L. gymnocercus as new host of this nematode species.

Survey and first molecular characterization of Echinococcus granulosus sensu stricto (G1) in Pampas fox (Lycalopex gymnocercus) in Buenos Aires province, Argentina

Echinococcosis is a zoonosis caused by tapeworms of the genus Echinococcus. Echinococcus granulosus sensu lato (s. l.) has a world-wide distribution and its transmission is primarily maintained in a synanthropic cycle with dogs as definitive hosts and livestock species as intermediate hosts. However, many wild canids also function as definitive hosts for E. granulosus s. l. Echinococcosis in humans is mainly caused by E. granulosus sensu stricto (s. s.) G1 genotype. In the present work, we expanded the epidemiological study on echinococcosis reported cases in Pampas fox (Lycalopex gymnocercus) to provide a prevalence estimate for rural areas of southern Buenos Aires province, Argentina. Ninety-five whole intestines were analyzed using the sedimentation and counting technique with a result of 83 foxes (87.37%) harboring at least one helminth species. E. granulosus s. l. adults were found in one Pampas fox (1.05%). These adult helminthes were E. granulosus s. s. (G1) according to the genotyping analysis of a 450-bp region of the mitochondrial cytochrome c oxidase subunit 1 (cox1) gene.

A new species of Losdolobus Platnick & Brescovit 1994 (Araneae: Orsolobidae) from Argentina with notes on its ecology and distribution.

A new species of Losdolobus, L. nelsoni sp. nov., is described based on females and males collected from grasslands in the mountains of southern Buenos Aires province, Argentina. Additionally, the phenology of this new species is presented and some aspects of the biogeography and distribution of the genus are discussed.

Insights into Pleistocene palaeoenvironments and biostratigraphy in southern Buenos Aires province (Argentina) from continental deposits

The coastal cliffs of the Buenos Aires province (Argentina) have been the subject of intense paleontological studies since the XIX century. Therefore, many of the type localities in which is based the late Cenozoic Pampean biostratigraphic/chronostratigraphic scheme are located in this area. In this context, the sedimentites that crop out near the mouth of the Chocorí Creek contain a set of palaeontological sites that, because of their richness and well-preserved fossil content, hold high national and international importance. The aims of the present contribution are: 1) to make a stratigraphic and sedimentological characterization of the study area; 2) to list the fauna outcropped at these palaeontological sites and establish a biostratigraphic framework; 3) to elaborate a palaeoenvironmental model for the area.The study interval was informally subdivided into a lower, middle and upper interval. Interpretation was based on the presence of a number of key features such as architectural elements; channel:overbank ratio and palaeosol occurrence. The first two intervals were interpreted as continental deposits of a fluvio-alluvial nature and are the focus of this paper. The upper interval was related to foreshore marine deposits and will be studied in a future contribution. The lower interval is characterized mainly by overbank architectural elements in which calcisols and argillic protosols were identified. Channel-fill deposits are isolated and surrounded by fine-grained overbank successions and sedimentary structures are suggestive of mixed-load transport. The contact between the lower and middle intervals is an irregular, highly erosive surface characterized by a significant vertical change in the facies. This surface defines the base of multistorey sandbodies which's internal arrangement alongside with the low participation of overbank deposits suggests deposition by a braided fluvial system.Palaeosols and vertebrate fossils were used as palaeoclimatic, palaeoenvironmental and biostratigraphical proxies. Calcisol profiles, displaying Stages II to V morphologies (Machette, 1985), can be interpreted as evidence of periods of geomorphological stability that occurred under semi-arid to sub-humid climatic conditions. The occurrence of argillic Protosols stacked amongst the Calcisols evidence periods of relatively less stability, higher sediment supply and aggradation rates in the system. The vertebrate fossil assemblage and the invertebrate trace fossils also indicate semi-open landscapes under a seasonal, semi-arid climate. The presence of Platygonus, Glyptodon and Tolypeutes fossil remains in the lower interval suggest an Ensenadan age (middle Pleistocene) while the presence of Arctotherium bonariense in the V1 layer indicates post-Ensenadan (late Pleistocene) times for the middle interval.It is concluded that during accumulation of the Chocorí succession, glacio-eustasy and/or climate controlled the balance between generation of accommodation space and sediment supply. Analysis of the architectural elements indicates a general reduction in accommodation space. The lower interval represents the unconfined reaches of a large distributive system, more specifically, a low hierarchy, secondary drainage system inset in a high accommodation alluvial environment. The erosive surface identified at the base of the middle interval can be interpreted as representative of a period of negative accommodation in the system, when general erosion took place. The gradual restoration of accommodation in the fluvial system was accompanied by a low sediment accumulation rate and the development of a braided fluvial system in the middle interval.