Fluvial and eolian ichnofaunas from the Lower Permian of South America (Patquía Formation, Paganzo Basin)

The Lower Permian Patquía Formation is the youngest unit of the Paganzo Basin, western Argentina. The lower section consists of red mudstones, and fine- and coarse grained sandstones deposited in fluvial systems with extensive and thick floodplain deposits. These rocks contain a low-diversity and relatively abundant association of trace fossils suggesting the activity of a sub-superficial to superficial fauna. The association is characterized by Rusophycus carbonarius (Cubichnia), Cruziana problematica (Repichnia), and Palaeophycus tubularis (Domichnia) of the Scoyenia ichnofacies. Disarticulated fish remains are also present. The upper section is dominated by red, cross-bedded, medium- to fine-grained sandstones deposited in eolian systems that host a lowdiversity and low-abundance association of trace fossils that indicates the activity of a mainly superficial fauna. Tetrapod footprints (Chelichnus duncani, oval digit imprints, short parallel grooves, and sinusoidal grooves), horizontal to vertical burrows (Palaeophycus tubularis and Skolithos isp. respectively), and arthropod trackways are the typical components of these deposits. The association shows elements of the three presently proposed eolian ichnofacies (Chelichnus, Octopodichnus and Entradichnus ichnofacies) suggesting the necessity of revision and the possible integration of these separate ichnofacies into a single model. The record of fossil vertebrate tracks is uncommon in Lower Permian strata of South America. Therefore, the ichnologic record of the Patquía Formation is a significant contribution to the understanding of Lower Permian South American ichnofaunas

Negative and positive feedback from a supernova remnant with SHREC: a detailed study of the shocked gas in IC443

Interstellar matter and star formatio

Discovery ofpeperites on Marambio Island, Antarctica, with considerations of their emplacement

The finding of peperite breccias on Marambio Island allows to confirm the existence of at least two different pulses in the instrusion of basaltic dykes within the James Ross Island Volcanic Group. Two important bodies of peperites were recognized at Filo Negro and Geoantar hill. They were formed by the intrusion of basaltic dykes in the unconsolidated Paleogene sediments of Sobral Formation. The breccias are composed of vesicular glassy fragments, and volcanic and sedimentary lithic constituents in a sand matrix. The intrusions were probably emplaced at very shallow depth and are possibly related to a younger volcanic pulse, dated at 1.3 Ma. © 1997 Asociaciôn Geolôgica Argentina.Fil:Caselli, A.T. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil:Massaferro, G.L. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina

Vanadiniferous micaceous concretions in the Patquia Formation (Permian), Sierra de Maz, Province of La Rioja

These concretions form discrete spherical bodies 2 to 20 cm in sizes, within medium grained massive sandstone (arkosic arenite). Three concentric zones are recognized: a) dark green to black core composed of quartz and feldespar cemented by illite and roscoellite, b) an intermediate pale red zone of hematite-coated quartz, and c) a white, iron-leached outer zone. Edax and ICP analyses reveal high concentrations of vanadium mainly in zones a) and b) (60340 and 2582 ppm respectivily), uranium (237 and 163 ppm), rubidium (252ppm) and copper (178ppm). The concretions are interpreted as formed under eodiagenetic conditions before the development of haematite cement which gave the red colour to the host rock.Fil:Caselli, A.T. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil:Limarino, C.O. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil:Castro, L.N. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina

Discovery of tillite on the western flank of the Hedionda Water anticline (Province of San Juan): evidence of ice movement during the Gondwana glaciation in the Paganzo River Basin

Fil:Marenssi, S.A. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil:Tripaldi, A. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil:Caselli, A.T. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil:Limarino, C.O. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina

Seismic activity and an anomalous fumarolic chemical composition due to seal effect in the volcanic system of Deception Island (Antarctica)

In this communication, the genesis of great anomalous seismic activity registered during austral summer 2003/2004 on Deception Island (Antarctica) is discussed, and related with changes on the chemical composition of fumarolic gases and vent deposits. Here we present a comparative analysis performed to explain this activity. We propose a possible parcial seal of the microfracture system. This effect allows an increase on pressure follow by reopening of microfractures, resulting on a sequence of seismic events and changes on the chemical composition of fumarolic emissions.Fil:Caselli, A.T. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil:Bengoa, C.L. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil:Agusto, M.R. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina

Costa Recta beach, Deception Island, West Antarctica: A retreated scarp of a submarine fault?

Deception Island (South Shetlands, Antarctica) is one of the most active volcanoes in Antarctica, having erupted recently in 1967, 1969 and 1970, damaging scientific stations on the island. It is also seismically very active. The island has attracted the attention of many researchers as it constitutes an undisturbed natural laboratory to study seismo-volcanic events and how they affect landscape modelling and evolution. One of the most remarkable geological and geomorphological features on Deception Island is the linearity of its easternmost coastal landform, the origin of which remains unknown. Some answers, based on presence of strike-slip fault or on the ice cap and beach geomorphological dynamics, have been reported in the literature. Our new work provides several indications of the existence of a dip-slip submarine fault, parallel to the coast (NNW-SSE), which suggests a tectonic origin for this morphological feature. Uplifted marine terraces, incision of a fluvial network over the ice cap, normal faulting parallel to the coast in the north and south rock heads bounding the beach and sharp shelf-break with rather constant slope, constitute some of this evidence. Terrace uplift and fluvial channel incision decreasing southward from Macaroni Point, indicates possible tilt movement across this inferred fault plane. © Antarctic Science Ltd.Fil:Caselli, A.T. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina

Gas geochemistry of the magmatic-hydrothermal fluid reservoir in the Copahue-Caviahue Volcanic Complex (Argentina)

Copahue volcano is part of the Caviahue\u2013Copahue Volcanic Complex (CCVC), which is located in the southwestern sector of the Caviahue volcano-tectonic depression (Argentina\u2013Chile). This depression is a pull-apart basin accommodating stresses between the southern Liqui\uf1e\u2013Ofqui strike slip and the northern Copahue\u2013Anti\uf1ir compressive fault systems, in a back-arc setting with respect to the Southern Andean Volcanic Zone. In this study, we present chemical (inorganic and organic) and isotope compositions (\u3b413C-CO2, \u3b415N, 3He/4He, 40Ar/36Ar, \u3b413C-CH4, \u3b4D-CH4, and \u3b4D-H2O and \u3b418O-H2O) of fumaroles and bubbling gases of thermal springs located at the foot of Copahue volcano sampled in 2006, 2007 and 2012. Helium isotope ratios, the highest observed for a Southern American volcano (R/Ra up to 7.94), indicate a non-classic arc-like setting, but rather an extensional regime subdued to asthenospheric thinning. \u3b413C-CO2 values (from 12 8.8\u2030 to 12 6.8\u2030 vs. V-PDB), \u3b415N values (+ 5.3\u2030 to + 5.5\u2030 vs. Air) and CO2/3He ratios (from 1.4 to 8.8 7 109) suggest that the magmatic source is significantly affected by contamination of subducted sediments. Gases discharged from the northern sector of the CCVC show contribution of 3He-poor fluids likely permeating through local fault systems. Despite the clear mantle isotope signature in the CCVC gases, the acidic gas species have suffered scrubbing processes by a hydrothermal system mainly recharged by meteoric water. Gas geothermometry in the H2O-CO2-CH4-CO-H2 system suggests that CO and H2 re-equilibrate in a separated vapor phase at 200\ub0\u2013220 \ub0C. On the contrary, rock\u2013fluid interactions controlling CO2, CH4 production from Sabatier reaction and C3H8 dehydrogenation seem to occur within the hydrothermal reservoir at temperatures ranging from 250\ub0 to 300 \ub0C. Fumarole gases sampled in 2006\u20132007 show relatively low N2/He and N2/Ar ratios and high R/Ra values with respect to those measured in 2012. Such compositional and isotope variations were likely related to injection of mafic magma that likely triggered the 2000 eruption. Therefore, changes affecting the magmatic system had a delayed effect on the chemistry of the CCVC gases due to the presence of the hydrothermal reservoir. However, geochemical monitoring activities mainly focused on the behavior of inert gas compounds (N2 and He), should be increased to investigate the mechanism at the origin of the unrest started in 2011

SiO emission as a probe of cloud-cloud collisions in infrared dark clouds

Infrared dark clouds (IRDCs) are very dense and highly extincted regions that host the initial conditions of star and stellar cluster formation. It is crucial to study the kinematics and molecular content of IRDCs to test their formation mechanism and ultimately characterize these initial conditions. We have obtained high-sensitivity Silicon Monoxide, SiO(2-1), emission maps towards the six IRDCs, G018.82-00.28, G019.27+00.07, G028.53-00.25, G028.67+00.13, G038.95-00.47, and G053.11+00.05 (cloud A, B, D, E, I, and J, respectively), using the 30-m antenna at the Instituto de Radioastronomía Millimétrica (IRAM30m). We have investigated the SiO spatial distribution and kinematic structure across the six clouds to look for signatures of cloud-cloud collision events that may have formed the IRDCs and triggered star formation within them. Towards clouds A, B, D, I, and J, we detect spatially compact SiO emission with broad-line profiles that are spatially coincident with massive cores. Towards the IRDCs A and I, we report an additional SiO component that shows narrow-line profiles and that is widespread across quiescent regions. Finally, we do not detect any significant SiO emission towards cloud E. We suggest that the broad and compact SiO emission detected towards the clouds is likely associated with ongoing star formation activity within the IRDCs. However, the additional narrow and widespread SiO emission detected towards cloud A and I may have originated from the collision between the IRDCs and flows of molecular gas pushed towards the clouds by nearby H ii regions.With funding from the Spanish government through the "María de Maeztu Unit of Excellence" accreditation (MDM-2017-0737