Search

The increasing desertification in the continental interior of Pangaea during the Permian-Triassic transition was of fundamental importance in the Earth landscape and life evolution. In the west-central Pangaea, northern Brazil, acid-saline-lake systems were gradually succeeded by dry aeolian ergs due to intense continentalization in arid climate setting. Detailed facies and architectural analysis were applied in the Permian-Triassic succession of the Parnaiba Basin, and seven facies associations were recognized: (1) ephemeral lake, represented by greenish and reddish gray laminated mudstones interbedded with chert-rich fine-grained sandstones, (2) marginal dune field consisting of fine-to medium-grained sandstones with planar cross-bedding sets, (3) shallow perennial saline lake consisting dominantly of red laminated mudstones with discontinuous layers of sigmoidal sandstones, (4) playa lake/ dry mudflat represented by reddish laminated mudstones interbedded with limestone, marl and gypsum lenses, (5) sand sheet consisting of laterally continuous beds of fine-to medium-grained sandstones with convoluted lamination, synsedimentary faults/microfaults and adhesion structures, (6) dune field formed by fine-to medium-grained sandstones with large-scale cross-bedding sets, and (7) volcanic plain, consisting of basalts interbedded with aeolian sandstones. During middle Permian, the shallow to deep ephemeral lakes occurred in large plains in the tropical zone of western to central Pangaea. The cyclicity of wet and dry lacustrine phases was triggered by changes in the groundwater level, low subsidence rate, and low accommodation space. The prolonged dry stages were characterized by the advance of the marginal dune fields as well as the establishment of large desiccated areas. In the upper Permian, the continuous process of Pangaea amalgamation led to the uplift of central and equatorial regions resulting in the retreat of epicontinental seas. Thereafter, there was the appearance of large-scale closed basins and continental saline environments. The extreme aridity conditions favored the decline of these great lakes and the development of an extensive Triassic Erg. Sand sheets occurred in the marginal areas of the erg, containing abundant ephemeral ponds and dispersed aeolian dunes. Extensive dune fields advanced as a consequence of the sediment availability increase, whereas deflation surfaces were produced by the widespread output of sediments. The total interruption of sediment availability to the erg in the upper Triassic provided an extreme and regional deflation surface overlaid by eoJurassic volcanic rocks, associated with the Pangaea breakup.

The tectonic evolution of the western Gondwana margin during Pangaea amalgation is recorded in variations in the Permo-Carboniferous back-arc basin sedimentation of Peru. This study provides the first radiometric age constraints on the volcanic and sedimentary sequences of south-central eastern Peru up to the western-most tip of Bolivia, and now permits the correlation of lateral facies variations to the late Paleozoic pre-Andean orogenic cycle. The two phases of Gondwanide magmatism and metamorphism at c. 315 Ma and c. 260 Ma are reflected in two major changes in this sedimentary environment. Our detrital U-Pb zircon ages demonstrate that the timing of Ambo Formation deposition corroborates the Late Mississipian age estimates. The transition from the Ambo to the Tarma Formation around the Middle Pennsylvanian Early Gondwanide Orogeny (c. 315 Ma) represents a relative deepening of the basin. Throughout the shallow marine deposits of the Tarma Formation evidence for contemporaneous volcanism becomes gradually more pronounced and culminates around 312 - 309 Ma. Continuous basin subsidence resulted in a buildup of platform carbonates of the Copacabana Formation. Our data highlights the presence of a previously unrecognized phase of deposition of mainly fluvial sandstones and localized volcanism (281–270 Ma), which we named ´Oqoruro Formation'. This sedimentary succession was previously miss-assigned to the so-called Mitu Group, which has recently been dated to start deposition in the Middle Triassic (∼245–240 Ma). The emersion of this marine basin coincides with the onset of a major plutonic pulse related to the Late Gondwanide Orogeny (c. 260). Exhumation lead to the consequent retreat of the epeiric sea to the present-day sub-Andean region, and the coeval accumulation of the fluvial Oqoruro Formation in south eastern Peru. These late Paleozoic palaeoenvironmental changes in the back-arc basins along the western Gondwana margin of southern reflect changes in tectonic plate reorganization in a long-lived Paleozoic accretionary orogeny.

The Caribbean Mountain System in Venezuela contains rocks formed at high-pressure/low-temperature (HP/LT) conditions by the Cretaceous–Paleocene oblique collision occurred between the Caribbean and South American plates and involving Rodinian-related blocks. 40 Ar/ 39 Ar dating of rocks from the Cordillera de la Costa and Margarita Island has constrained key pre- and syntectonothermal events associated with the emplacement of this system. In a Rodinian marble, two phlogopite crystals of different grain sizes yield plateau ages of 888 ± 4 Ma and 874 ± 4 Ma. These results are interpreted as cooling ages after a major anorthosite-mangerite-charnockite-granite-suite intrusion at 920 Ma related to the break-up of Rodinia along the Amazonian–Baltica collisional zone – the Putumayo Orogen. Current plate reconstructions during the Neoproterozoic and previous age results indicate a correlation between the anorthositic complexes located in northwestern Venezuela (Yumare Complex) and southern Norway (Rogaland Complex), suggesting a similar tectonic setting during orogenic relaxation along the Amazonian and Baltica suture. A temperature–time path based on calculated Ar-closure temperatures of phlogopite indicates rapid cooling of 14 ± 4 °C Ma −1 from 920 Ma to 888 Ma, and a very slow to almost isothermal cooling of 4 ± 2 °C Ma −1 from 888 Ma to 874 Ma. On Margarita Island, magnesiohornblende and (alumino) barroisite from HP/LT rocks and muscovite from a leucocratic rock that was intruded before the HP/LT event yield identical ages within error at c. 54–47 Ma, consistent with previous dating results across the island utilizing different isotopic systems. The close association of these rocks and the Manzanillo Shear Zone indicates a main pathway for Ca-rich, 40 Ar-free and hot fluids that locally raised the ambient T of the already exhumed and juxtaposed rock units. These fluids crystallized new hornblende and muscovite and thermally reset barroisite. This fluid activity event is 5 Ma younger than the last magmatic activity in the Aves Arc (c. 59 Ma) along its southern edge and related to the opening of the Grenada Basin. In the Cordillera de la Costa, magnesiohornblende, phengite, magnesian siderophyllite, ferroan phlogopite and K-feldspar from rock units of the Carayaca and Avila terranes yield a wide range of ages (275–20 Ma). The oldest ages (275 Ma and 120 Ma) obtained from the Caruao Metatonalite suggest at least two thermal events at these times and are in agreement with the amalgamation of Pangaea and fluid infiltration, respectively. The remaining ages (35–20 Ma) are consistent with previous results and reflect short-lived fluid infiltrations related to tectonothermal events. A phengite age of 35 Ma from an omphacitite lens in the Antimano Marble of the Carayaca Terrane indicates a younger HP/LT event than previously stated. The preservation of this phengite age and constant Si-content profile indicate a short-lived HP/LT event followed by a very rapid exhumation. At 35–20 Ma rocks from the Avila Terrane remained at shallower crustal levels than the ones of the Carayaca Terrane, but were thermally affected by tectonism and the infiltration of relatively cold and 40 Ar-free fluids causing widespread chloritization of trioctahedral micas.

The oldest archosauromorphs (dinosaurs, birds, crocodiles, and their stem-taxa) arerecorded in middle−upper Permian rocks, but it was not after the Permo−Triassic massextinction that the group shows a substantially high taxonomic richness andecomorphological disparity. The early evolutionary history of the Archosauromorphaduring the Early and Middle Triassic is mainly based on fossils recovered from rocks insouthern Africa, Europe and Asia, whereas South America possesses a morecomplete fossil record of the group only in the Late Triassic. Here we revisit, discuss,and reanalyse the non-archosaurian archosauromorph fossil record of the current-daySouth America. The Early Triassic archosauromorph record in this continent is stillscarce, but it documents the early evolution of the group in western Pangaea and iscrucial to understand more globally the biotic recovery after the Permo−Triassic massextinction. The Middle Triassic record is extremely scarce, but the Late Triassicarchosauromorph assemblage of South America is among the most diverse andabundant worldwide. The last decade has witnessed a considerable improvement inour knowledge of the record, taxonomy, phylogeny, and macroevolution of the groupwith the input from the South American fossils. Nevertheless, a considerable amount ofresearch is needed and ideally should be focused on some particular aspects of theTriassic evolutionary radiation of Archosauromorpha. Among them, the Early Triassicrecord should be expanded, more numerous and more complete Middle Triassicarchosauromorph specimens are crucial to have a more complete picture of theevolution of the group, and the taxonomy of groups like proterochampsids andhyperodapedontine rhynchosaurs should be clarified through detailed anatomical work. Fil: Ezcurra, Martin Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Museo Argentino de Ciencias Naturales ‘Bernardino Rivadavia’; Argentina Fil: Montefeltro, Felipe C.. Universidade Estadual Paulista Julio de Mesquita Filho; Brasil Fil: Pinheiro, Felipe L.. Universidade Federal do Pampa; Brasil Fil: Trotteyn, Maria Jimena. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Centro de Investigaciones de la Geosfera y Biosfera. Universidad Nacional de San Juan. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones de la Geosfera y Biosfera; Argentina Fil: Gentil, Adriel Roberto. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Museo Argentino de Ciencias Naturales ‘Bernardino Rivadavia’; Argentina Fil: Lehmann, Oscar Emilio Rodrigo. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Museo Argentino de Ciencias Naturales ‘Bernardino Rivadavia’; Argentina Fil: Pradelli, Luciano Agustín. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Museo Argentino de Ciencias Naturales ‘Bernardino Rivadavia’; Argentina

Break-up of western Pangaea initiated a back-arc type tectonic setting along the northwestern margin of Gondwana, which resulted in the accumulation of sedimentary and volcanic deposits in extensional basins during the Middle-Late Triassic. The Sierra Nevada de Santa Marta massif, at the northwestern termination of the Andes, exposes Upper Triassic syn-rift successions beneath a voluminous Lower Jurassic volcanic cover. In this contribution, we present a sedimentological and stratigraphical analysis of the Upper Triassic Los Indios and Corual formations, by integrating whole-rock geochemistry, zircon U–Pb geochronology, and a biostratigraphic revaluation of the conchostracan fossil content. We divide the Los Indios Formation into two sandy to conglomeratic and two muddy members. First and third members were deposited in a coarse-grained delta environment. The second and fourth members are interpreted to represent offshore deposits resulting from the encroachment of gravity-flow lobes. Volcanoclastic and volcanic rocks interbedded with sedimentary deposits of the Los Indios and Corual formations record bimodal basic-acid volcanism with a variably alkaline tendency. Based on their alkaline and calc-alkaline signature, and rare earth and trace element patterns, volcanic rocks display a back-arc affinity. With respect to the age of the Los Indios Formation, we recovered conchostracans diagnostic of Upper Carnian and Lower Norian fauna, bearing similarity with faunal assemblages of other Upper Triassic deposits exposed in the northern Andes. The Los Indios and Corual formations are considered as syn-rift successions in a back-arc extension setting. The development of this back-arc basin coincided with the Late Triassic separation of the Oaxaquia, Acatlan, and Chortis terranes during Pangaea break-up. Finally, the Early to Middle Jurassic evolution of the NW Gondwana margin is marked by the inception of a magmatic arc, which characterizes the establishment of Andean-type subduction coeval to ignimbrite flare-up.

The breakup of the supercontinent Pangaea in the Middle Jurassic and the subsequent breakup of Gondwana with the formation of the South Atlantic Ocean, were two of the most prominent paleogeographic events of the Phanerozoic. Acting as a major obstacle for the Gondwanan rift propagation, the Congo-Sao Francisco Craton was an ancient and one of the most stable regions on the Eastern/Central South America and Africa. Based on paleontological and on paleogeographical data, the present manuscript discusses how the main drainage of the Sao Francisco Craton connected both northeastern marginal and the central intracratonic Brazilian regions as it does nowadays. It also deals with the history of one of the oldest and most resilient South American drainages during the transitional phase of the Gondwanan breakup. Based on the occurrence of fishes, ostracods, palynomorphs, and aquatic plants, the results presented herein suggest the existence of a previous drainage interconnecting the marginal and interior rift-related basins in a time anterior to the Aptian/Albian transgressions.

The Mesozoic was the time of the break-up of Pangaea, with profound consequences not only for the paleocontinental configuration, but also for paleoclimates and for the evolution of life. Cool greenhouse conditions alternated with warm greenhouse and even hothouse conditions, with global average temperatures around 6–9 °C warmer than the present ones. There are only sparse and controversial evidence for polar ice; meanwhile, extensive evaporitic and desertic deposits are well described. Global sea levels were mainly high, and the content of atmospheric O 2 was varying between 15 and 25%. These conditions make the Mesozoic Earth an alien world compared to present-day conditions. Degassing from volcanism linked to the rifting process of Pangaea and methane emissions from reptilian biotas were climate-controlling factors because they enhanced atmospheric CO 2 concentrations up to 16 times compared to present-day levels. The continental break-up modified paleopositions and shoreline configurations of the landmasses, generating huge epicontinental seas and altering profoundly the oceanic circulation. The Mesozoic was also a time of important impact events as probable triggers for “impact winters”; and for the Era at least nine huge (diameter > 20 km) impact structures are known. This paper presents an abridged but updated overview of the Mesozoic paleogeographic and paleoclimatic variations, characterizing each period and sub-period in terms of paleoclimatic state and main tectonic and climatic events, and provides a brief geologic, stratigraphic, paleoclimatic and taphonomic characterization of dinosaur occurrences as recorded in the Brazilian continental basins.

The Borborema Province of northeastern Brazil is a major Proterozoic crustal province that, until now, has never been explored using deep crustal seismic methods. Here are reported the first results obtained from a high-quality seismic refraction/wide-angle reflection profile that has defined the internal seismic velocity structure and thickness of the crust in this region. Almost 400 recording stations were deployed in the Deep Seismic Refraction (DSR) experiment through an NW–SE ca. 900 km linear array and 19 shots were exploded at every 50 km along the line. Data from the 10 southeastern most shots of the seismic profile were processed in this work. The main features and geological structures crossed by the studied portion of the profile belong to the so-called Central Sub-province of the Borborema tectonic province. The crustal model obtained is compatible with a typical structure of extended crust. The model was essentially divided into three layers: upper crust, lower crust, and a half-space represented by the shallower portion of the mantle. The Moho is an irregular interface with depth ranging between 31.7 and 34.5 km, and beneath the Central Sub-province it varies from 31.5 to 33 km depth, where its limits are related to major crustal discontinuities. The distribution of velocities within the crust is heterogeneous, varying vertically from 5.7 to 6.3 km/s in the upper crust and from 6.45 to 6.9 km/s in the lower crust. From the average crustal velocity distribution it is evident that the Central Sub-province has seismic characteristics different from neighboring domains. The crust is relatively thin and crustal thickness variations in the profile are subtle due to stretching that occurred in the Cretaceous, during the fragmentation of Pangaea, opening of the South Atlantic Ocean and separation of South America from Africa.

The contact between the Guerrero and Sierra Madre tectonostratigraphic terranes has been proposed to lie in the Mesa Central, east of the city of Zacatecas. Marine Triassic units have been assigned to the Guerrero Terrane. It is here proposed that this contact occurs to the west of the city of Zacatecas and the Triassic marine sequence assigned to the Sierra Madre Terrane. We analyzed the stratigraphic record and structural features of pre-Late Jurassic sequences at four localities in the Mesa Central. They contain a marine turbiditic Triassic unit, which includes La Bellena, Taray, and Zacatecas Formations, and a continental unit of probable Middle Jurassic age. Triassic sandstones were derived from a cratonic area, without the influence of arc volcanism. The sequences were affected by two phases of deformation. The Triassic formations are unconformably overlain by a continental volcano-sedimentary sequence that contains fragments of sandstones derived from the underlying unit. Sedimentologic characteristics of the Triassic unit fit a submarine fan model. The submarine fan developed at the continental margin of Pangaea during Triassic times. Turbidite associations in the San Rafael Area indicate a middle fan depositional environment, while in the Real de Catorce Area, they correspond to the distal part (basin plain facies). At La Ballena and Zacatecas the turbidite associations occur in the middle part and perhaps the external part of the fan.