DSpace Colección :
http://rid.unrn.edu.ar:80/handle/20.500.12049/8939
2024-02-15T15:45:31ZEstructuras sedimentarias inducidas por la actividad microbiana (ESIAM) en sistemas petroleros no convencionales (Los Molles-Lajas), cuenca Neuquina: implicancias para el análisis paleoambental.
http://rid.unrn.edu.ar:80/handle/20.500.12049/10872
Título: Estructuras sedimentarias inducidas por la actividad microbiana (ESIAM) en sistemas petroleros no convencionales (Los Molles-Lajas), cuenca Neuquina: implicancias para el análisis paleoambental.
Autor(es): Rodriguez, Maximiliano Nicolás
Abstract: This doctoral thesis was carried out in deposits of the Los Molles Formation (Toarcian - Lower Callovian) located in the Chacay Melehue, Arroyo Lapa and Picún Leufú Anticline localities within the Neuquén Basin. The Los Molles Formation is one of the oldest source rocks in the Neuquén Basin and constitutes an unconventional shale gas reservoir of great economic importance. In recent years, the presence of levels with microbial mats has been recognized in this unit, although their characteristics and implications have not yet been evaluated. For this reason, the main objective of this study was to analyze, characterize and document the presence of microbial mats in the Los Molles Formation, as well as to discuss their sedimentological and ichnological implications. Finally, the initial results obtained from the comparison between the microbial levels of the Los Molles Formation and those recognized in the Vaca Muerta Formation, are presented.
Field work consisted of detailed sedimentary sections and lithological profiling at the three localities, as well as level sampling with MISS. In the laboratory, the samples were analyzed by stereo microscope, petrographic microscope and scanning electron microscope.
Five facies associations were recognized and described for the Los Molles Formation: offshore, platform, deltaic front, prodelta, turbidite. Most of the levels assigned to microbial mats were found on deposits belonging to the offshore and platform facies associations and, to a lesser extent, on the turbidite facies associations.
The microbially induced sedimentary structures found in the Los Molles Formation comprised Kinneyia-type wrinkle structures, biolaminations, micro mat fabrics, possible dome constructions, reticulate patterns, small pinnacles and elephant skin. In the thin sections, textures and structures characteristics of microbial mats were recognized, such as anastomosing laminations, oriented grains, filaments and heavy minerals bound to the mat layers. Kinneyia-like wrinkled structures, biolaminations, mat microfabrics and pinnacles were also petrographically characterized. Scanning electron microscope images revealed the presence of structures resembling filaments and filament sheaths, spheroidal structures similar to coccoids, extracellular polymeric substances (EPS) and framboidal pyrite in isolation, in addition to EPS linked to filament-like structures and pyrite. Trace fossils assigned to Trichichnus isp., Chondrites intricatus,
Chondrites patulus, and Phycosiphon incertum were recognized at the Chacay Melehue and Arroyo Lapa localities.
These results reveal that the levels found and analyzed in the Los Molles Formation may have had a biological origin. The structures and textures identified may have originated from microbial mats located on the seafloor of the Neuquén Basin during the Toarcian – Lower Callovian. These communities were established in offshore and platform environments at depths between 200 and 400 m, in paleoecological and paleoenvironmental conditions that allowed their development, such as low oxygenation, low sedimentation rate, and low light. From the integration of ichnological and geobiological analyses, it was inferred that both Trichichnus isp. and the microbial mats could have a common origin from the biological activity of some genera of the Beggiaotoaceaea family. On the other hand, the microbial mats could have been a food source for benthic organisms, which would be reflected in trace fossils of undermat miners found in the organic levels. Comparison with microbial mats from the Vaca Muerta Formation indicates that the similarities in the thin section and the scanning electron microscope are unquestionable despite having formed in different environments. A very interesting aspect, which will be evaluated in the future, is to analyze the possibility that the biolaminated levels have been an important source of organic matter to the system, and thus may have contributed to the generation of hydrocarbons.2023-09-27T00:00:00ZEvidencia y análisis de cambios temporales en la zona del cerro Domuyo. Caracterización geofísica de su campo geotermal, y su microsismicidad asociada.
http://rid.unrn.edu.ar:80/handle/20.500.12049/10190
Título: Evidencia y análisis de cambios temporales en la zona del cerro Domuyo. Caracterización geofísica de su campo geotermal, y su microsismicidad asociada.
Autor(es): Godoy, Laura Beatriz
Abstract: No posee.2023-05-17T00:00:00ZAnálisis estructural y litológico del distrito la paloma. Metalogénesis de la veta sulfuro, macizo del deseado, Patagonia
http://rid.unrn.edu.ar:80/handle/20.500.12049/10189
Título: Análisis estructural y litológico del distrito la paloma. Metalogénesis de la veta sulfuro, macizo del deseado, Patagonia
Autor(es): Fernández, María Lis
Abstract: La Paloma, a vein-hosted Au-Ag and base metal epithermal district of the Don Nicolás Mine, is located in the northeast of the Deseado Massif, Patagonia, Argentina. The mineralization is hosted in the Middle Jurassic volcanic rocks of the Bajo Pobre Formation which comprises three main lithological groups: (1) lavas and intrusive rocks, (2) pyroclastic rocks, and (3) reworked volcaniclastic rocks. The first group, composed of andesite to basaltic-andesite coherent and autobrecciated flows as well as shallow subvolcanic (stocks and lacoliths) intrusions, is the most representative in the district. The second group, either intercalated between andesitic lava flows or intruded by basaltic-andesite stocks and lacoliths, is represented by pyroclastic surge, fall and flow deposits. Reworked volcaniclastic sequences comprise debris and hyperconcentrated flow deposits and reworked pyroclastic deposits scarcely preserved and restricted to topographic highs that overlie primary volcanic units or are intercalate between them.
The La Paloma district displays a complex vein network dominated by NNW to NW (with local N-S and NNE deflections) striking major veins (Sulfuro, Esperanza, Rocio, Princesa, Reyna and Verde), ENE to E-W (Duquesa) and NE (Arco Iris) striking structures. The NE-SW striking El Molino fault separates the Sulfuro Vein System (Sulfuro, Esperanza and Rocío veins) from the remaining veins located towards the north-northwest of the district. The normal to oblique- to strike-slip reactivation of pre-existing joints led to the hybrid extension-shear fractures hosting the mineralization of economic interest. Paleostress analysis unravels how all the resulting four sets of hybrid extension-shear fractures form two groups of structures that are kinematically compatible with a sub-vertical σ1 and either NNW (Group A) or ENE (Group B) trending σ3, within the framework of an extensional stress field characterized by multiple permutations between the σ3 and the σ2 axes. Such permutations are interpreted to have resulted from the reactivation of some of the NNW striking joints as normal faults in response to regional ENE stretching, and by orthogonal (i.e. NNW) extension in the hanging wall of such laterally-terminating normal faults associated with along-strike stretching produced by the differential downthrow of the hanging-wall block. Within this framework, further (i.e. NE and NW striking) joint sets were variably reactivated as oblique-slip dilational faults. The NNW trending hybrid extension-shear fractures (i.e. Sulfuro Vein System, Princesa–Reyna and Verde; Group B) were the most effective for hydrothermal fluid circulation and are characterized by the development of multi–episodic veins with exceptional width, strike continuity and ore grades whereas ENE to E-W striking structures (i.e. Duquesa; Group A) exhibit minor opening and filling events mainly represented by late stages. NE and NW striking oblique-slip dilational faults (i.e. Arco Iris Vein and El Molino fault; Group A and B, respectively) record no major vein opening history, and characterized by brecciated vein textures with minor silica cement and/or vein clasts within a fault gouge matrix.
Later fault reactivation appears to be associated with far a field propagation of
Andean stresses, probably related with the late Early Cretaceous shortening event known to have affected the studied sector of the Deseado Massif. This event is marked by superposed strike-slip and reverse fault slip components recording roughly E-W subhorizontal
compression (σ1). The subsequent tectonic evolution of the study area,
recorded by apatite fission track cooling ages, was characterized by steady-state
exhumation at a rate of c. 1 °C/Ma during the last 90 Ma.
The Au-Ag (Zn, Pb, Mo and Cu) Sulfuro Vein, the main ore body in the district
(174.251 Oz of gold and 525.985 Oz of silver and an average grade of 6.6 g/t Au and 20
g/t Ag), exhibits a sub-horizontal ore-shoot geometry, as are the areas of greater vein
thickness, consistent with dominant extensional faulting during mineralization except in
the northern sector where Au, Ag and Cu shoots and the thickest areas reflect a larger strike-slip component of motion and depletion of the fluid in these metals. This strikeslip component seems not to have exerted an important control in the distribution of Zn and Pb in this sector, where these metals continued to precipitate at lower temperatures favoured by the permeability of the volcaniclastic units. The highest values of Au, Ag, Cu, Mo, Pb, Zn and Sb are concentrated at depths between 50 and 100 m a.s.l. High Mo values occur also at greater depths in the southern sector of the vein and its distribution in shallower sectors is controlled by remobilization processes. The geochemical distribution of metals shows a slight vertical zonation and a distinct lateral zonation, which suggests upward hydrothermal fluid flow from deep zones in the southern termination of the vein where ore shoots exhibit steeper plunges, to the north through the NNW-NW striking fractures.
Three mineralizing stages contributed to the final metal endowment of the Sulfuro
Vein. The first, which corresponds to stage 3, introduced Mo ± Au (Ag) ± Cu
(molybdenite ± Au (electrum) ± chalcopyrite ± tennantite-tetraedrite) as millimetric dark sulfide-rich band at the beginning of the vein infill during the episode E1. The second and the third mineralizing stages, which correspond to stages 7 and 8, respectively, introduced Fe ± Au (Ag) and Fe ± Au (Ag) ± Cu ± Zn ± Pb ± As ± Sb, respectively, during the episode E2 and generated limited brecciation in the vein sealed by minerals of the E1 episode. Pyrite ± chalcopyrite ± tennantite-tetrahedrite ± sphalerite ± galena containing Au and/or electrum micro-inclusions, formed during this episode (E2) as breccia cement and filling veinlets. Based on the metal content and accompanying minerals, the Sulfuro Vein can be classified as a Au-Ag low sulfidation epithermal deposit enriched in Zn + Pb and unusually rich in Mo (up to 1.5 %). Quartz textures (colloform-crustriform banded, cockade, mosaic and brecciated) suggest several opening and subsequent vein filling events and the deposition of a silica gel from a boiling hydrothermal fluid which must have been responsible for the metal deposition.
Chlorite ± albite ± epidote formed distal (>20 - 30 m) to the Sulfuro Vein could
represent a regional propylitic alteration related to the magmatic heat source in the district prior to the onset of the Sulfuro Vein hydrothermal system. Host-rock interaction with boiling, neutral to slightly alkaline fluids formed chlorite ± albite ± adularia ± carbonates (dolomite, siderite and calcite) ± pyrite during the vein-related pre-ore stage. Syn-ore stage potassic dioctahedral phyllosilicates ± quartz ± pyrite overprint early formed minerals. Different grain size of dioctahedral potassic phyllosilicates were identified: – coarse-grained dioctahedral potassic phyllosilicates (>2 μm) or mica-like and – fine grained (<2 μm) potassic dioctahedral phyllosilicates represented by illite (or illite-richillite-smectite mixed layers) and by subordinated mixed-layers with variable amounts of illite. The composition and distribution of phyllosilicates near the vein (≤5 m) reflect paleotemperature gradients of the fluid with time, from >220°C (mica-like and illite-richillite-smectite mixed-layer) to <220°- 150° C (mixed-layer illite-smectite superimposed).
In the post-ore stage, Al-bearing silicates were partially dissolved and replaced by
widespread kaolinite. At shallow depths, above the central upflow zone, kaolinite ±
aluminum phosphate-sulfate ± dickite dominate and represent an advanced argillic
environment caused by steam-heated acid-sulfate waters. Smectite was the last mineral to form during the collapse of the hydrothermal activity.
The chemical compositions of some hydrothermal minerals are potential indicators
of paleo depths and proximity to the vein: - dolomite (Mg) was identified only at depth,
while calcite (Ca) and siderite (Fe) formed at intermediate and shallow zones,
respectively; - chlorites in the lower andesite shows more Fe than Mg near the vein and at greater depths; - secondary feldspars are scarce and relictic proximal to the vein compared to potassic dioctahedral phyllosilicates but are prominent alteration minerals with increasing distance from the vein. Relict adularia dominates in strongly altered rocks proximal to the vein whereas albite dominates in distal moderate to weakly altered rocks; and - the abundance and pervasiveness of potassic dioctahedral phyllosilicates + quartz + pyrite near the vein (≤5 m) constitute an excellent indicator of the mineralized structure as well as coarse-grained potassic dioctahedral phyllosilicate (>2 μm) confined to the contact with the vein and in deeper zones.
The isotopic composition of fluids in equilibrium with quartz (δ18Ofluid –5.8 to –1.5‰) and phyllosilicates (δ18Ofluid 0.1 to -2.4‰; δ2Hfluid –48 to –69.5) deposited in the vein during episodes E1 and E2, and fluids in equilibrium with phyllosilicates (δ18Ofluid –1‰; –2.3‰; δ2Hfluid –62 to –65) in the host rock, suggest their formation by mixture of meteoric Jurassic water with magmatic water and/or meteoric water that have isotopically exchanged with basement rocks. The carbon isotopic signatures (δ13C in solution as H2CO3: –7.5 and –7.1‰) and the sulfur isotopic composition of sulfides (δ34S ‰ –0.1 to 3.3‰) indicate a magmatic source. Cooling and the increase in the fO2 of the hydrothermal fluid through mixing with meteoric water in the northern sector and in shallow parts of the central sector, could have resulted in lower δ34S values of sphalerite, galena and chalcopyrite (δ34S ‰ –3.1, –5.3 and –11.1‰).
The Pb isotopic compositions of the galenas: 206Pb/204Pb (18.37 and 18.39), 207Pb/204Pb (15.61 and 15.62), 208Pb/204Pb (38.32 and 38.39) are similar to the isotopic composition of the volcanic rocks of the Bajo Pobre Formation and suggest a mixed sources of Pb, with contributions from the mantle and crust.
Ar–Ar ages (168.48 ± 1.21 Ma) obtained for illite-rich illite-smectite mixed layer and Re–Os molybdenite age (169.7 ± 0.9 Ma), indicate that the formation of the potassic dioctahedral phyllosilicates in the alteration halos of the Sulfuro Vein was coeval with Au-Mo mineralization in the vein. These radiometric ages are among the oldest ages known for Middle-Upper Jurassic epithermal deposits of the Deseado Massif.2023-05-17T00:00:00ZEvolución tectono-estratigráfica durante el triásico superior de la región de Los Menucos, macizo norpatagónico nor-occidental, provincia de Río Negro
http://rid.unrn.edu.ar:80/handle/20.500.12049/9075
Título: Evolución tectono-estratigráfica durante el triásico superior de la región de Los Menucos, macizo norpatagónico nor-occidental, provincia de Río Negro
Autor(es): Vera, Dario Ruben
Abstract: Two sets of volcano-sedimentary rocks of different ages, one of the Permian-Early Triassic age corresponding to the Los Menucos Complex and another of probable Late Triassic age, were identified in the Los Menucos region, in the northern sector of the North Patagonian Massif. The lithological, stratigraphical and sedimentological characteristics of the provisionally assigned to the Upper Triassic rocks that crop out
in the vicinity of Llancaqueo farm, 6 km towards the NE of Los Menucos, will be first presented. There is a volcanic and volcaniclastic succession with at least 368 m thick, which overlies an angular and erosive unconformity developed on the Los Menucos Complex. The lower section of the succession is characterized by deposits corresponding to alluvial fan systems, high-energy braided rivers and sinuous rivers
with floodplains, while the upper section is represented by a syn-sedimentary magmatism composed of mesosilicic to basic lava flows associated with subvolcanic bodies, and riodacitic ignimbrites. The informal denomination of sucesión volcanosedimentaria Llancaqueo was proposed to separate the volcano-sedimentary sequence of the Llancaqueo-type area from the rocks belonging to the Los Menucos Complex. In a regional context, the possible Upper Triassic age and the lithological characteristics of the sucesión volcano-sedimentaria Llancaqueo, suggest the search for correlations with the pyroclastic, volcanic and epiclastic sequences belonging to the Precuyano Cycle, or lateral equivalent within the Neuquén Basin.
Second, the main structures that affect the Llancaqueo volcano-sedimentary succession in the area surrounding the Llancaqueo farm and in the areas of La Laja and La Mina hills, in the vicinity of Los Menucos, were characterized. Three first and second-order fault domains were recognized, with strikes: 1) E-W with WNW-ESE and ENE-WSW variations, sub-vertical and mostly dextral or, to a lesser extent, leftlateral
kinematics; 2) NE-SW to N-S and dextral or dextral-normal or occasionally sinestral kinematics and 3) NW-SE to WNW-ESE, high angle and sinestral or sinestral-normal kinematics, or low angle and reverse motion. In addition, meso and megascopic folds trending NW-SE to WNW-ESE and NE-SW are developed both in
the rocks of the Los Menucos Complex and in the Llancaqueo volcano-sedimentary succession. The integration of the geometry of the faults and folds at their different scales and the kinematic analysis of the major faults from the study of minor faults, allowed establishing two successive deformation phases (D1 and D2). D1, of late triassic - early jurassic age, would be linked to a transtensive regime with NNE-SSO
to NE-SW extension directions and WNW-ESE to NW-SE shortening. Within the framework of this phase and actively controlled by the structure, the basin containing the Llancaqueo deposits would have been developed. On the other hand, D2, of possible Late Jurassic - Early Cretaceous age, would have a transpressive character related to a general NE-SW shortening and would have generated reactivations of
the previously generated faults. In the regional context, the stratigraphic and structural characteristics of the study area and the northwestern sector of the Northpatagonian Massif, in general, are very similar to the tectonics described in the Neuquén basin for Triassic-Cretaceous times. In this sense, both in the Neuquén basin and in the area of the north-western Northpatagonian Massif, a generalized crustal extension regime in a NE-SW direction would have dominated, in the first instance, during the Late Triassic – Early
Jurassic, equivalent to what is shown here is proposed as deformation phase D1. Then, during the Upper Jurassic – Lower Cretaceous, a transpressive deformation event would have occurred, comparable to the D2 deformation phase (proposed in this thesis) that generated the reactivation of the previously formed structures.2022-08-25T00:00:00ZTafonomía de los depósitos con vertebrados y leños fósiles en los niveles continentales de la Formación Mulichinco (Valanginiano) Cuenca Neuquina, Argentina
http://rid.unrn.edu.ar:80/handle/20.500.12049/9073
Título: Tafonomía de los depósitos con vertebrados y leños fósiles en los niveles continentales de la Formación Mulichinco (Valanginiano) Cuenca Neuquina, Argentina
Autor(es): Pino, Diego Alejandro
Abstract: no posee2022-08-29T00:00:00ZSEDIMENTOLOGÍA E ICNOLOGÍA DE LA FORMACIÓN LOS MOLLES EN LAS LOCALIDADES DE PICÚN LEUFÚ, SIERRA DE CHACAICÓ Y CORDILLERA DEL VIENTO, CUENCA NEUQUINA, ARGENTINA
http://rid.unrn.edu.ar:80/handle/20.500.12049/8978
Título: SEDIMENTOLOGÍA E ICNOLOGÍA DE LA FORMACIÓN LOS MOLLES EN LAS LOCALIDADES DE PICÚN LEUFÚ, SIERRA DE CHACAICÓ Y CORDILLERA DEL VIENTO, CUENCA NEUQUINA, ARGENTINA
Autor(es): Campetella, Débora Mical
Abstract: Sedimentological and ichnological studies in the Los Molles Formation (Toarcian- Aalenian), in Picún Leufú, Sierra de Chacaicó and Cordillera del Viento localities allowed to recognize six facies associations and six ichnoassemblages. These facies associations comprise shoreface, offshore, shelf, prodelta and delta front affected by turbidites and storms deposits. The six ichnoassemblages are characterized, in general, by low ichnodiversity and abundance. The most common ichnoassemblage is the one recognized in offshore-shelf environments, consisting of Chondrites intricatus, Trichichichnus appendicus, Trichichnus isp., Phycosiphon incertum. Subordinately, Phymatoderma isp, Cylindrichnus concentricus, Teichichnus rectus and Thalassinoides isp. also occur The ichnoassemblage developed in levee deposits of turbidite systems consist of Chondrites intricatus, Phycosiphon incertum, Trichichichnus isp, Chondrites patulus, and Nereites missouriensis, whereas the ichnoassemblage recognized in storm dominated – shelf deposits includes specimens of Chondrites intricatus, Phycosiphon incertum, Nereites isp., Skolithos linearis, Planolites isp., Arenicolites isp., Ophiomorpha isp., and Gyrochorte comosa. The shoreface, delta front and prodelta deposits were only recognized at Picún Leufú locality, where the transition between Los Molles and Lajas formations is well exposed. In this context, the ichnoassemblage recognized in the distal shoreface deposits consist of Skolithos linearis, Ophiomorpha isp. and Arenicolites isp., the ichnoassemblage developed in the prodelta deposits is composed of specimens assigned to Chondrites intricatus, Phycosiphon incertum and Planolites isp, while the ichnoassemblage recognized in the delta front deposits is characterized by the presence of Chondrites intricatus, Phycosiphon incertum, Nereites isp., Skolithos linearis and Ophiomorpha isp. Integration of the sedimentological and ichnological data, indicates that variations in salinity, turbidity and sedimentation rate were limiting factors that affected the development of benthic communities. However, oxygenation would have been the most important parameter controlling not only the diversity but also the abundance of biogenic structures in these substrates. Moreover, in this analysis it is important to take into account the regional context, since during most of the Jurassic and Cretaceous, the Neuquén basin behaved as a back-arc basin associated with a magmatic arc, which was connected to the proto-Pacific Ocean through narrow passages between
the volcanic island chain. This palaeogeographic situation produced an important regulation on the internal circulation of the basin, affecting the stratification of the water column, and its physical-chemical properties, and thus significantly affecting the development and establishment of benthic communities.2022-07-29T00:00:00ZLos Alvarezsauridae (Dinosauria, Theropoda, Coelurosauria) de América del Sur: anatomía y relaciones filogenética.
http://rid.unrn.edu.ar:80/handle/20.500.12049/8974
Título: Los Alvarezsauridae (Dinosauria, Theropoda, Coelurosauria) de América del Sur: anatomía y relaciones filogenética.
Autor(es): Meso, Jorge Gustavo
Abstract: This Doctoral Thesis presents an exhaustive review of the Patagonian alvarezsaurids (Dinosauria, Theropoda). It includes a detailed osteological description of specimens of Patagonykus puertai (Holotype, MCF-PVPH-37), cf. Patagonykus puertai (MCF-PVPH-38), Patagonykinae indet. (MCF-PVPH-102), Alvarezsaurus calvoi (Holotype, MUCPv-54), Achillesaurus manazzonei (Holotype, MACN-PV-RN 1116), Bonapartenykus ultimus (Holotype, MPCA 1290), and cf. Bonapartenykus ultimus (MPCN-PV 738). A phylogenetic analysis and a discussion about the taxonomic validity of the recognized species and the taxonomic assignment of the materials MCF-PVPH-38, MCF-PVPH-102 and MPCN-PV 738 are presented. Different evolutionary and paleobiological studies were carried out in order to elucidate functional and behavioral aspects.
Alvarezsaurus calvoi (MUCPv-54), Achillesaurus manazzonei (MACN-PV-RN 1116), Patagonykus puertai (MCF-PVPH-37) and Bonapartenykus ultimus (MPCA 1290) are valid species due to the presence of many autapomorphies. In this sense, the hypothesis proposed by P. Makovicky and collaborators that Achillesaurus manazzonei is a junior synonym of Alvarezsaurus calvoi is rejected. Likewise, certain morphological evidence allows hypothesizing that Alvarezsaurus calvoi represents a growth stage earlier than skeletal maturity. Specimen MCF-PVPH-38 is referable as cf. Patagonykus puertai, while MCF-PVPH-102 is considered an indeterminate Patagonykinae. In turn, MPCN-PV 738 is assigned as cf. Bonapartenykus ultimus based on the little overlapping material with the Bonapartenykus ultimus holotype.
The results obtained from the mineralogical characterization through the X-ray diffraction method of specimens MPCN-PV 738 and the holotype of Bonapartenykus ultimus (MPCA 1290), allow to suggest that both specimens come from the same geographical area and stratigraphic level.
The phylogenetic analysis, which is based upon the matrix of Gianechini and collaborators of 2018 with the inclusion of proper characters, and the database of Xu and collaborators of 2018, recovered the South American members of Alvarezsauria, such as Alnashetri cerropoliciensis (Candeleros Formation; Cenomanian), Patagonykus puertai (Portezuelo Formation, Turonian-Coniacian), Alvarezsaurus calvoi and Achillesaurus manazzonei (Bajo de La Carpa Formation, Coniacian-Santonian), and Bonapartenykus ultimus (Allen Formation, Campanian-Maastrichtian), nesting within the family Alvarezsauridae. In this sense, the forms that come from the Bajo de La Carpa Formation (Coniacian-Santonian) are recovered at the base of the Alvarezsauridae clade, while Alnashetri cerropoliciensis nests as a non-Patagonykinae alvarezsaurid. Regarding the type specimens of Patagonykus puertai and Bonapartenykus ultimus, they are recovered as members of the Patagonykinae subclade, a group that is recovered as a sister taxon of Parvicursorinae, both nested within the Alvarezsauridae. In addition, the topology obtained allows discerning the pattern, rhythm and time of evolution of the highly strange and derived alvarezsaurian skeleton, concluding in a gradual evolution. The Bremer and Bootstrap supports of the nodes (Haplocheirus + Aorun), [Bannykus + (Tugulusaurus + Xiyunykus)], and Patagonykinae, show indices that represent very robust values for these nodes. Likewise, these values suggest that two endemic clades originated early in Asia, while one endemic clade is observed in Patagonia, i.e., Patagonykinae.
The analysis of the directional trends of the Alvarezsauria clade, tested by means of a own database on body masses based on the Christiansen and Fariña method, subsequently calibrated with the group's phylogeny using the R software, shows two independent miniaturization events in the alvarezsaurid evolution, namely the former originating from the base of the Alvarezsauridae (sustained by Alvarezsaurus), and the latter within the Parvicursorinae. Analysis of the Alvarezsauria dentition reveals possible dental synapomorphies for the Alvarezsauria clade that should be tested in an integrative phylogenetic analysis. The general characterization of the forelimb and a partial reconstruction of the myology of alvarezsaurs demonstrate different configurations for Patagonykinae and Parvicursorinae. The multivariate analyzes carried out from the databases of Elissamburu and Vizcaíno, plus that of Cau and collaborators, show that the Patagonykinae would have had ranges of movements greater than those observed in Parvicursorinae, although the latter would have had a greater capacity to carry out more strenuous jobs. The morphometric analysis of the hindlimb and the use of the Snively and collaborators equations, show that the configuration of this element in Alvarezsauria is indicative of a highly cursorial lifestyle, as well as possible particular strategies for more efficient locomotion. The topology obtained in the phylogenetic analysis that was carried out in this Doctoral Thesis, allowed clarifying the ontogenetic changes observed in the ontogenetic series of the manual ungueal element II-2 within the clade Alvarezsauridae. In addition, the multivariate analysis carried out from the manual phalanx II-2 allows us to infer that alvarezsaurs could have performed functions such as hook-and-pull and piercing, where the arm would function as a single unit. The anatomy and myology of the alvarezsaurian tail show that the caudal vertebrae of alvarezsaurians exhibit a combination of derived osteological features that suggests functions unique among theropods, such as considerable dorsal and lateral movements, as well as exceptional abilities to support distal loading of their long tail without compromising stability and/or mobility.2022-07-07T00:00:00ZEl registro fósil de equinodermos en el Eoceno-Mioceno de Patagonia Argentina y Antártida
http://rid.unrn.edu.ar:80/handle/20.500.12049/8940
Título: El registro fósil de equinodermos en el Eoceno-Mioceno de Patagonia Argentina y Antártida
Autor(es): Palópolo, Evangelina Elizabeth
Abstract: This thesis includes a review and a compendium of the record of the phylum Echinodermata in Argentina, including Antarctica and the South Atlantic Islands, from Eocene to late Miocene. Echinoderms are bilaterial organisms, with secondary radial symmetry, mutable connective tissue, aquiferous vascular system and multielemental calcareous endoskeleton, composed by calcite with high magnesium content. They constitute an important part of the benthic marine ecosystems, as part of the trophic chain. They have low tolerance to changes in water temperature and salinity, and to the sediment and organic matter input, being good environmental indicators. The environmental conditions that improve the echinoderm preservation are: little to null transport, rapid burial or in life entombment, absence of subsequent reworking, anoxia or dysoxia, and deposit of fine to very fine sediments. The first studies on echinoderms in Latin America date back to the 19th century and laid the foundations for the rest of the studies on the subject. In Argentina, rocks from the Eocene-Miocene interval yielding echinoderm remains are assigned to the Man Aike (Middle-Late Eocene), San Julián (Late Oligocene), El Chacay (Early Miocene), Río Foyel (Early Miocene), Monte León (Early Miocene), Estancia 25 de Mayo (early Miocene), Chenque (early Miocene), Gran Bajo del Gualicho (early-middle Miocene) and Puerto Madryn (late Miocene) formations. These formations represent several transgressive-regressive pulses within the Patagonian territory in the Golfo San Jorge, Peninsula Valdés and Austral-Magallanes basins. In the Antarctic Peninsula, the echinoderm records come from the La Meseta (Middle Eocene), Submeseta (Late Eocene-Early Oligocene), Polonez Cove (Middle-Late Oligocene) and Cape Melville (Early Miocene) formations. Using high resolution imaging (SEM and microtomography), the species Zoroaster marambioensis was described from La Meseta Formation. Its preservation allowed identifying death and burial positions, inferring their possible life habits. It was interpreted that starfishes colonized the distal part of an estuary during a period when salinity was normal, died from a freshwater discharge through a hyperpychnic flow, and were immediately buried in fine sand, without further rework.
In the La Meseta and Submeseta formations (Seymour Island, Antarctica), the genera Abatus, Schizaster and Stigmatopygus were identified, using high contrast images and digital diagrams. These genera were previously recorded in Antarctica (Seymour and King George islands) and Patagonia (Santa Cruz and Chubut provinces, Argentina). These findings enabled making inferences about ancient marine connections between New Zealand, Australia, Antarctica, and Patagonia. In the Monte León Formation, a layer yelding spatangoid echinoids of the genus Brisaster preserved in situ, associated with their own traces and other ichnofossils that suggest a shallow marine environment. The depositional framework was interpreted as subtidal, affected by migration of large-scale bedforms, with important pyroclastic participation.
The compendium of the Eocene-Miocene record of echinoderms from Patagonia Argentina and Antarctica gathered more than 1,200 specimens, housed in 26 institutions, 9 of them located in Argentina. It includes 37 genera grouped into 13 orders, from all current classes, except the Class Holothuroidea. The Class Echinoidea is the best represented, with 19 genera (9 of them endemic from Patagonia). Irregular echinoids are recorded in the Eocene of Antarctica, the Oligocene of southern Santa Cruz, the early Miocene of northern Santa Cruz and southern Chubut, and the middle and late Miocene of northern Chubut, Río Negro, and Entre Ríos. A possible distribution pattern was proposed, running from south to north over time. The Cenozoic echinoderm global diversity is marked by a peak in the Eocene and another in the Miocene. In Antarctica, generic greatest diversity occurs in the middle Eocene, in La Meseta Formation, with 17 genera (5 of crinoids, 6 of asteroids, 5 of echinoids and 1 of ophiuroids). The observed communities are similar to those of the Mesozoic, indicating a shallower and warmer environment than the current one in Antarctica, with a scarcity of durophagous predators and abundant organic matter content. In Patagonia, the echinoderm diversity peak was documented during the early Miocene as in the rest of the world, in coincidence with the maximum flood of the second cycle from the Patagonian transgression (~ 20 Ma).
Descripción: Artículos publicados en el marco de esta tesis: Palópolo, E.E., Brezina, S., Casadío, S., y Santillana, S. (2017). A little window to Eocene:
exceptional preservaition of sea stars from La Meseta Fromation, Seymour Island, Antarctic
Penninsula. In Guaiquil, I., Leppe, M., Rojas, P., y Canales, R., (eds.). Visiones de Ciencia Antártica,
Libro de Resúmenes, IX Congreso Latinoamericano de Ciencias Antártica, Punta Arenas-Chile, 654-
657. Publicación del Instituo Antártico Chileno.
Palópolo, E.E., Brezina, S., Casadío, S., Santillana, S. y Griffin, M. (2018). A Thousand ways to die:
exceptional preservation of sea stars on a paleosurface from La MEseta Formation (Eocene, Antarctic
Peninsula). In Libro de resúmenes de la Reunión de comunicaciones de la Asociación Paleontológica
Argentina (RCAPA 2018). Publicación Electrónica de la Asociación Paleontológica
Argentina, 19:R21.
Palópolo, E.E., Casadío, S, Kroh, A., Harzhauser, M, y Griffin, M. (2019). Life and death in a
submarine volcanic ash dune: the case of a group of patagonian miocene echinoids. In Libro de
resúmenes de la Reunión de comunicaciones de la Asociación Paleontológica Argentina (RCAPA
2019): 137.
Palópolo, E.E., Kroh, A., Harzhauser, M., Griffin, M., Casadío, S., y Carmona, N. (2021a). An early
Miocene spatangoid assemblage on a submarine volcanic ash dune from Patagonia
(Argentina). Journal of South American Earth Sciences, 103214.
Palópolo, E.E., Brezina, S.S., Casadío, S., Griffin, M., y Santillana, S. (2021b). A new zoroasterid
asteroid from the Eocene of Seymour Island, Antarctica. Acta Palaeontologica Polonica 66.
https://doi.org/10.4202/app.00714.20192022-06-15T00:00:00Z