Magnetostratigraphy and Carbon isotopes of Ediacaran Avellaneda Formation, Rio de La Plata Craton, Argentina

The Ediacaran Period (635-542 Ma) witnessed a series of extraordinary events. It arises with the end of the Marinoan Glaciation and deposition of worldwide enigmatic cap carbonate deposits. This abrupt shift in paleoclimatic conditions coincides with major fluctuations in the isotope ratios of carbon and sulfur, and with significant changes in the concentration of redox-sensitive elements in marine sediments. The Ediacaran is also a period marked by rapid changes in geomagnetic polarity. Magnetostratigraphy may therefore provide high-resolution correlation between Ediacaran successions worldwide. Here, we combine stratigraphy logs, carbon isotopes and magnetostratigraphy on the Avellaneda Formation (590-560 Ma) which at the Rio La Plata Craton, eastern Argentina. We investigated two drill cores (TSE-34 and TSE-7) with a 0.3-0.7 m resolution covering the entire Avellaneda Formation, corresponding to 98 standard specimens (25 mm in diameter). The basal contact of the Avellaneda Formation with the underlying mudstone rocks from Loma Negra Formation (~ 590 Ma) is present in both cores. The upper contact with the Alicia Formation, only observed in TSE-34 core, is transitional. The TSE-7 displays an erosional contact between Avellenda and Cerro Negro Formations (~ 560 Ma). After stepwise thermal demagnetization up to 600°C, almost all samples provided a characteristic magnetization between 350°C and 600°C, therefore Ti-poor magnetite or titanohematite is likely the main carrier of the stable remanence in these rocks. A high-temperature, dual-polarity component is persistent and coherent in the two drill cores. The base of the unit is marked by normal polarity, followed by a reverse interval, followed by persistent normal polarity across to the upper part of the Avellaneda Formation. This magnetostratigraphic framework, together with the carbon isotope signal, will be compared with results recently obtained for potentially coeval successions in China, Canada and United States.Fil: Afonso, Jhon. Universidade de Sao Paulo; BrasilFil: Ferreira Da Trindade, Ricardo Ivan. Universidade de Sao Paulo; BrasilFil: Franceschinis, Pablo Reinaldo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; ArgentinaFil: Arrouy, Maria Julia. Universidad Nacional del Centro de la Provincia de Buenos Aires. Rectorado. Instituto de Hidrología de Llanuras - Sede Azul. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Instituto de Hidrología de Llanuras - Sede Azul; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; ArgentinaEGU General Assembly 2020AustriaEuropean Geosciences Unio

Age and provenance of the Cryogenian to Cambrian passive margin to foreland basin sequence of the northern Paraguay Belt, Brazil

The Paraguay Belt in central South America\ud developed in response to the collision of\ud the Amazonian craton, the São Francisco\ud craton, and the Paranapanema block. The\ud alleged “Brasiliano” age (ca. 620 Ma) of\ud orogenesis has recently been questioned by\ud paleo magnetic and radioisotopic ages that\ud indicate the closing stages of orogenesis occurred\ud well into the Cambrian. We investigated\ud the timing of deposition and source\ud areas for these sedimentary rocks overlying\ud the Amazonian craton using integrated\ud U-Pb and Hf isotope data of detrital zircons\ud from within this sequence. In total, 742 detrital\ud zircon U-Pb ages were analyzed from\ud samples taken from the base to the top of this\ud sedimentary succession. Maximum depositional\ud ages from the uppermost part of this\ud sequence of rocks, the Diamantino Formation,\ud indicate that fi nal deposition began no\ud earlier than 560 ± 13 Ma and possibly as\ud young as the Cambrian. Given that zircon\ud inheritance in these rocks continues up until\ud this age and that known Amazonian craton\ud ages are older than ca. 950 Ma, we considered\ud other potential sources for these sediments.\ud This was achieved by integrating the\ud U-Pb detrital zircon data with Hf isotopic\ud data from these zircons that have εHf values\ud ranging from –18 to 12. The εHf signature is\ud consistent, with a predominantly Amazonian\ud source until the early Neoproterozoic, at\ud which point the signal becomes signifi cantly\ud more evolved. These data, when combined\ud with other evidence discussed here, are\ud consistent with an ocean to the east of the\ud present-day Amazonian craton that did not\ud close until the latest Ediacaran–Cambrian

Aeromagnetic and physical-chemical properties of some complexes from Goiás\ud Alkaline Province

The Goiás Alkaline Province (GAP), located on the\ud north edge of the Paraná Basin, has alkaline complexes with strong\ud magnetic signatures. The 3D inversion of magnetic signal was performed\ud on the aeromagnetic data. Since the intrusions present a\ud strong remnant magnetization, as measured in the laboratory, a careful\ud analysis of this component was also realized. The sum vector of\ud the remnant and induced components were used as a virtual induced\ud magnetic field during the 3D inversion process. The geometric parameters\ud were obtained from the quantitative analysis of magnetic\ud data, using Total Gradient Direction and Analytical Signal Phase,\ud performed over magnetic signal reduced to the pole. Magnetic susceptibility\ud and density were measured in laboratory. All this information\ud were used as the initial model in the inversion. The results\ud of 3D inversion show that the alkaline intrusions have roots up to\ud 10-12 km depth. The magnetic susceptibility is distributed in almost\ud spherical and cylindrical shapes. The possibility of spherical shapes\ud arise the hypothesis that the GAP intrusions at the northern part of\ud the province represent magmatic chambers. The alkaline magma ascends\ud from the lithosphere, and used two main fault systems as space\ud for emplacement. These faults systems appear in the magnetic signal\ud analysis as linear magnetic features. Chemical analysis confirmed the\ud alkaline and subalkaline character of the magmas. The high MgO\ud content shows the primitive character of these intrusions but the Ba\ud anomaly indicates a possible crustal contamination.FAPESP - 2006/00201-2 e 2007/53179-

Shrimp zircon geochronology constrains on Permian pyroclastic levels, Claromecó Basin, South West margin of Gondwana, Argentina

Pyroclastic levels are descripted in Sierras Australes outcrops and Claromeco Basin sub-surface records, interbedded with mudrocks and coal beds in the base of the Tunas Formation sequence that correspond to the Permian South West margin of Gondwana. The pyroclastic levels classify as fine tuff. SHRIMP zircon ages obtained are 291.7 ± 2.9 Ma in the outcrop and 295.5 ± 8.0 Ma in the subsurface. These ages are consistent with other zircon SHRIMP ages of other outcrops tuff of the Tunas Formation, with Permian flora, and with tuff ages of correlated Gondwana areas, in the Paraná, Karoo and Paganzo basins. These data, in addition with other geological evidences, support a tectonically active and changing environment during the Permian of Gondwana. The ages allowed calculating a northward latitudinal speed of 2.7 cm/year for Gondwana during the Permian. This latitudinal movement is explained as the consequence of the final coupling of several continental microplates, gradually amalgamated from the southern margins of Gondwana and from the northern of Laurentia to configure the final Pangea during the Triassic. Since the main accretions in the southwestern margin of Gondwana could have started during the Devonian - Carboniferous, this Permian orogeny (San Rafael Orogenic Phase in Argentina) would be representing the post - collisional deformation, with a peak of compression in the Early Permian that was attenuating towards the foreland during the Late Permian - Early Triassic. With these results, it is also possible to constraint the age of the upper Paleozoic glaciation up to 295, previous to the deposition of the Tunas Formation in the Sauce Grande Formation.Fil: Arzadún, Guadalupe. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. La.Te. Andes; ArgentinaFil: Tomezzoli, Renata Nela. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; ArgentinaFil: Ferreira Da Trindade, Ricardo Ivan. Universidade de Sao Paulo; BrasilFil: Gallo, Leandro César. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; ArgentinaFil: Cesaretti, Nora Noemi. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; Argentina. Universidad Nacional del Sur. Departamento de Geología; ArgentinaFil: Calvagno, Juan Martín. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; Argentin

New Ediacaran Paleomagnetic Pole for the Rio de la Plata Craton: Paleogeographic Restrictions in the Assembly of Western Gondwana

Preliminary paleomagnetic data obtained in marls of the Avellaneda Formation (La Providencia Group) of Ediacarian age outcropping in the Río de la Plata craton (RPC) are presented. Sampling was carried out in quarry and in a bore-core. Standard stepwise demagnetization showed a directional consistency among both sets of samples yielding a preliminary paleomagnetic pole located at 0.8° N, 308.4° E, (A95: 5.7°, n: 68) for the Avellaneda Formation. This indicates very high latitudes for the craton and suggests that the most accepted Ediacarian apparent polar wander path (APWP) for the 600-500 Ma period for RPC must be reconsidered.Fil: Franceschinis, Pablo Reinaldo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; ArgentinaFil: Alfonso, Jhon. Universidade do Sao Paulo. Instituto de Astronomia, Geofísica e Ciências Atmosféricas; BrasilFil: Rapalini, Augusto Ernesto. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; ArgentinaFil: Arrouy, Maria Julia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigaciones Geológicas. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Centro de Investigaciones Geológicas; Argentina. Comisión de Investigaciones Científicas de la Provincia de Buenos Aires. Instituto de Hidrología de Llanuras "Dr. Eduardo Jorge Usunoff". - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tandil. Instituto de Hidrología de Llanuras "Dr. Eduardo Jorge Usunoff". - Universidad Nacional del Centro de la Provincia de Buenos Aires. Instituto de Hidrología de Llanuras "Dr. Eduardo Jorge Usunoff"; ArgentinaFil: Ferreira Da Trindade, Ricardo Ivan. Universidade do Sao Paulo. Instituto de Astronomia, Geofísica e Ciências Atmosféricas; BrasilFil: Poire, Daniel Gustavo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigaciones Geológicas. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Centro de Investigaciones Geológicas; ArgentinaSixth Biennial Meeting of Latin American Association of Paleomagnetism and GeomagnetismRancaguaChileLatin American Association of Paleomagnetism and Geomagnetis

New paleomagnetic and AMS study of mafic sills from the Rio Branco region - MT (SE of Amazonian Craton)

We present a paleomagnetic and AMS study on mafic sills cutting sedimentary rocks from the Rio \ud Branco region, Mato Grosso state (Amazonian Craton). U-Pb (zircons) dating on a gabbro and a \ud granophyre from the mafic-felsic Rio Branco Suite yielded ages of 1471 ± 8 Ma and 1427 ± 10 \ud Ma, respectively. 108 samples from 11 sites were sampled, from which 3 sites are represented by \ud sedimentary rocks collected close to three sills for a baked contact test AMS measurements yielded \ud planar fabric for analyzed rocks, which is expected for unmetamorphosed and undeformed sills and \ud sedimentary rocks. Afler AF and thermal demagnetization southwestern, steep positive inclination \ud characteristic remanent magnetization (ChRM) directions were isolated for the sills Dm=208.2', \ud Im=68.5' (n =8, A95=6.4'), which yielded the paleomagnetic pole at 46.4'S; 277.00E (A95=10.2°). \ud These directions are very close to those found previously on mafic sills in the same region. \ud Consequently, a new mean direction was calculated encompassing 18 sites (Dm=197.4', Im=62.9', \ud A95=5.7") which defined the paleomagnetic pole at 56.00S; 278.5'E (A95=7.9°). Magnetic mineralogy \ud study indicates PSD-magnetite grains as the main magnetic carrier of ChRM directions. Although the \ud baked contact test was not conclusive, paleomagnetic poles from other contemporary basic intrusions \ud from the same region suggest that the Rio Branco sills' ChRM directions represent a thermoremanent \ud magnetization (TRM) acquired during the emplacement, at about 1430 Ma

Hydrothermally-induced changes in mineralogy and magnetic properties of oxidized A-type granites

The changes in magnetic mineralogy due to the hydrothermal alteration of A-type granitic rocks have been thoroughly\ud investigated in samples fromthe granite of Tana (Corsica, France), and compared with other A-type granites:\ud Meruoca (NE Brazil), Bushveld (South Africa), Mount Scott (Wichita Mountains, Oklahoma, USA) and the\ud stratoid hypersolvus granites of Madagascar. The altered red-colored samples and their non-altered equivalents\ud were magnetically characterized by means of magnetic susceptibility measurements, hysteresis loops, remanent\ud coercivity spectra, and Lowrie test. It is shown that hydrothermalization in magnetite-bearing granites is related\ud to the formation of fine-grained magnetite and hematite, and to coeval depletion in the content of primary lowcoercive\ud coarse-grained magnetite. These mineralogical changes give typical rock magnetic signatures, namely\ud lower susceptibilitymagnitudes and anisotropy degrees, prolateAMS (anisotropy ofmagnetic susceptibility) fabrics\ud and increased coercivities. Optical microscopy and SEM (scanning electronic microscopy) images suggest\ud that the orientation of the secondary magnetic minerals is related to fluid-pathways and micro-fractures formed\ud during the hydrothermal event and therefore may be unrelated to magma emplacement and crystallization fabrics.\ud Changes inmagnetic mineralogy and grain-size distribution have also to be considered for any paleomagnetic\ud and iron isotope studies in granites.INSU-3F (Failles, fractures, flux) 2008 projec

Umbria-Marche Basin, Central Italy: A Reference Section for the Aptian-Albian Interval at Low Latitudes

Within the Cretaceous Period, the Aptian-Albian interval (125–99.6 Ma, Ogg et al., 2008) was a critical time on a global scale. This is evident from 1) changes in the nature of the ocean-climate system brought about by increased ocean crust production coupled with active midplate and plate margin volcanism in a shifting paleogeography (Skelton et al., 2003); 2) cyclic deposition and preservation of common “black shales”, some of them termed Oceanic Anoxic Events(OAE1a to OAE1d) (Schlanger and Jenkyns, 1976; Arthur et al., 1990); 3) periodic changes in redox conditions at the ocean bottom (Oceanic Red Beds, ORBs) (Wang et al., 2009); and 4) rapid biotic radiations and turnovers (Leckie et al., 2002). The Aptian-Albian time is also of interest for one of the most noteworthy geomagnetic events, namely the post-M0r “Cretaceous Quiet Zone”. This long and constant normal polarity superchron without any convincing true reversal to date (Satolli et al., 2008) precludes usage of reversals magnetostratigraphy from the Aptian through the Santonian. The Poggio le Guaine core was designed to provide a high-resolution age model and a high-resolution relative magnetic paleointensity reference curve for the Aptian-Albian interval of the long normal Cretaceous superchron; it was also designed to understand the causal linkages among geological, biogeochemical, oceanographic and climatic eventsas well as their consequences. The core was drilled at Poggio le Guaine, where the most continuous, complete, and best preserved Aptian-Albian succession is exposed throughout the Umbria-Marche Basin (UMB) of the northern Apennines of central Italy (Fig. 1). It represents a continuous record of fossiliferous pelagic rocks extending from the Albian-Cenomanian boundary down to the uppermost Barremian (99.6–126 Ma). In this progress report we present the first preliminary findings of this ongoing project

The hydrological response of Northeastern Brazil during \ud last deglaciation

Paleociimate proxy and numerical modelling data suggest prominent change in precipitation over lowland tropical South America during last deglaciation. The hydrography of Northeastem Brazil under such change in precipitation, however, remains poorly investigated. Unresolved issues relate to the possible change in sources and amounls of terrigenous input delivered to the continental slope off Northeastern Brazil. Here we analyzed a set of marine sediment cores retrieved from off the Parnaíba River Delta during research cruise MSM20/3 that provide an excellent opportunity to \ud address these issues. Detailed radiocarbon-based age models indicate that the sedimentation rates at our core sites increased significantly from ~ 20 cm/kyr during the Last Glacial Maximum to ~70 cm/kyr during Heinrich Stadial1, and then back to ~ 20 cm/kyr during the Bolling-Allerod. One possibility for this extreme rise in sedimentation rate is the simulated reversal of the North Brazil Current and lhe supposed input of Amazonian sediment to the continental slope off the Parnaiba River Delta. Here \ud our Nd isotopic data will help to disentangle the different sedimentary sources since the terrigenous supply from the Parnaíba and the Amazon Rivers have considerably different signatures. The ENd(O) measurement of modern sediment samples (i.e., soil, river suspended sediment load), to be collecled over Northeastem Brazil and already available marine surface and downcore results will greatly contribute to clarify possible change in the terrigenous sources. Our data shed new light into our knowledge of the coupled hydrological process (i.e., fluvial erosion and weathering) over Northeastem \ud Brazil and its relationship with the Atlantic Meridional Oceanic Circulatio