Provenance and paleogeography of the Southern Paran? Basin : geochemistry and U\\Pb zircon geochronology of the Carboniferous-Permian transition.

The Carboniferous-Permian transition of the intracratonic Paran? Basin (S Brazil) includes important evidence of the climate change, tectonics, and paleogeographic configuration of SW Gondwana. During this period, the Late Paleozoic Ice Age (LPIA) was in its final phase in the Paran? Basin, producing a temperate-tropical climate through the transition to the Permian. UPb laser ablation ICP-MS detrital zircon dates and whole-rock geochemistry of rocks from the upper Itarar? Group (Carboniferous) and the lowermost Rio Bonito Formation (Early Permian) in the southern Paran? Basin are determined to characterize the sedimentary-dispersal patterns of the source area and glacial paleoflow. Geochemistry proxies suggest that the studied units experienced different degrees of weathering, with the Itarar? Group's units forming in an arid environment. The overlying Rio Bonito Formation's units were deposited under hotter and more humid climate conditions. The Late Carboniferous to Early Permian units showed similar zircon-age distribution patterns, with a Neoproterozoic main peak from the Uruguayan Sul-Riograndese Shield. A lack of Mesoproterozoic sources in the studied samples indicates that this area of the Paran? Basin probably did not receive sediments from the African side during the Late Carboniferous as previously described. This result suggests a more complex system in which ice caps and small ice sheets dominated the glacial environment during the Late Carboniferous in this segment of SW Gondwana

Granulite accretion to Rio de la Plata Craton, based on zircon U-Pb-Hf isotopes : tectonic implications for Columbia Supercontinent reconstruction.

The paleogeographic reconstruction of the Rio de la Plata involved either allocthonous or autochthonous process reflecting directly the Paleoproterozoic connection of the craton to Columbia Supercontinent. Santa Maria Chico Granulite Complex is a significant fragment of Rio de la Plata intensely affected by the Brasiliano Orogeny. Zircon U-Pb-Hf isotopes by LA-ICP-MS, mineral and whole-rock chemistry and a pseudo-section are presently interpreted. U-Pb-Hf isotopes characterize two main accretionary and metamorphic events: oceanic juvenile crustal accretion (i) 2430?2290?Ma (?Hf(t)?=??3.17 to +7.00), with arc related metamorphism (830?870??C, 6.7?7.2?kbar) at ~2.3?Ga; and continental arc accretion (ii) 2240?2120?Ma (?Hf(t)?=??4 to +2.4), with continental collision metamorphism (770?790??C, 8.7?9.1?kbar) at 2.1?2.0?Ga. Alkaline granitic dikes related to crustal extension at 1.8?Ga cut the granulitic rocks after the stabilization of this crustal segment. The present data point to formation of Paleoproterozoic granulitic rocks of the Santa Maria Chico Granulite Complex and adjacent Nico P?rez and Rivera terranes in multi-stage volcanic arcs to continental collision environment over 370?Ma (2430 to 2060?Ma). These terranes were amalgamated in the Paleoproterozoic to the core of the Rio de la Plata Craton as part of Columbia Supercontinent and intensely reworked during the amalgamation of Western Gondwana in the Neoproterozoic

Post-glacial permian debris flow deposits and their paleoclimatic implications (Mariana Pimentel paleovalley, southern Paran? Basin).

The end of the Late Paleozoic Ice Age was followed by a global warming climate. This climate transition is characterized by, beyond other aspects, a decrease in the intensity of physical weathering, characteristic of arid conditions, and an increase in the intensity of chemical weathering. In the southern Parana ? Basin, the post-glacial onset and intense record of ?Pedra-Areia? diamictite within the Mariana Pimentel paleovalley was likely controlled by warming climate conditions and mark a period of intense rainfall and slope instability. To test this hypothesis, we have performed facies and sequence stratigraphy analysis on cores located within the Mariana Pimentel paleovalley, and U?Pb-Hf investigations to acquire sediment provenance information. Diamictite deposits were produced by debris flow processes, which transported regolith from the valley wall to the bottom, eroding and incorporating mud and peat when reaching the bottom of the valley. The local source of sediment is explained by the sedimentological characteristics of the diamictite and zircon provenance studies. These deposits are preserved within the transgressive system tract and the abundant deposition was controlled by increasing temperature and humidity, and thus the increase in chemical weathering on the walls, forming the regolith. The development of more humid and warmer climatic conditions, contrasting with the cold and dry climate of the glacial period, was an important control over diamictite deposition

The oldest record of Ediacaran macrofossils in Gondwana (~563 Ma, Itajaí Basin, Brazil)

International audienceThe Avalon biota (Ediacaran Period, 570–559 Ma) marks the first appearance of macroscopic and complex benthic communities in the fossil record. This assemblage is known from a few localities worldwide, mainly in Canada and England. Here, we report for the first time the presence of Ediacaran macrofossils in deposits of similar age from Gondwana (Itajaí Basin, southern Brazil). Our new radiometric date (~563 Ma) indicates that the Itajaí Basin can be chronocorrelated with the classic Avalonian deposits and thus represents one of the oldest records of the Ediacaran biota in Gondwana. We describe the presence of the Ediacaran genus Palaeopascichnus, as well as discs (Aspidella and Nimbia), and other problematic forms. Contrary to the deep-marine macroorganisms of the Avalon Assemblage, the Itajaí fossils are associated with abundant and exceptionally preserved three-dimensional microbial mats and microbially induced sedimentary structures (MISS) in relatively shallow settings (upper slope and distal delta front deposits). In this sense, the Itajaí biota could represent early adaptations of benthic macrobiota to the shallower and more photic environments that characterize the later White Sea Assemblage