Navegando por Autor "ROMERO BARRERA, Ivan Alfredo"

Agora exibindo 1 - 2 de 2

Acesso aberto (Open Access)
Paleoambiente do Grupo Serra Grande, borda Leste da Bacia do Parnaíba, localidade de Ipueiras, Estado do Ceará
(Universidade Federal do Pará, 2020-04-25) ROMERO BARRERA, Ivan Alfredo; NOGUEIRA, Afonso César Rodrigues; http://lattes.cnpq.br/8867836268820998
The transition between the Ordovician and Silurian periods in the western portion of the Gondwana supercontinent was marked by a long glacial period, which had its peak in the Hirnantian (~ 445 Ma). This event occurred during a long greenhouse climatic period, in which the CO2 content in the atmosphere was five times greater than the current one. The supercontinent Gondwana migration towards the South Pole was concomitant with astronomical factors such as changes in the rotation of the earth and decreased solar radiation that favoured the ice-sheets growth. The end of the glaciation was marked by the most substantial increase in the eustatic sea-level recorded in the earth history, generating significant marine transgressions, which started at Llandovery (~ 443 Ma) and ended at Ludlow (~ 423 Ma). One of the best records of these events within the West Gondwana context is the Serra Grande Group, which represents an Ordovician-Devonian siliciclastic succession present in the Parnaíba Basin, northeastern Brazil. This sequence outcropping on the eastern edge of the basin is divided into three formations: Ipu, Tianguá, and Jaicós. Previously work of this Group has a strictly regional and lithostratigraphic character, which has not allowed determining the depositional environments and systems based on a precise stratigraphic framework. This work presents new interpretations of depositional systems present in the Serra Grande Group record, based on sedimentological and stratigraphic analyses of the outcrops located in the Ipueiras region, Ceará State, Northeast Brazil. The detailed faciological description of this siliciclastic succession had as main objective to propose a depositional and evolutionary model for these deposits. Outcrop-based facies and stratigraphical analysis of this siliciclastic succession indicated fluvial, glacial, and coastal depositional systems grouped on seven facies associations (FA). Deposits of sheet braided plains (AF1), consisting of coarse and conglomerate sandstones with cross-stratification. Glacial deposits (AF2 and AF3) corresponding to massive conglomerate, thick sandstone with cross-stratification and massive diamictites. Stratified diamictite with drop clasts were deposited in a glacial-marine environment (AF4). Laminated black shales (AF5) are interpreted as deposited in offshore settings during post-glacial stages. Deltaic deposits (AF6) consist of laminated siltite and sandstone with sigmoidal cross-stratification and occurrences of the ichnogenus Arthrophycus. This fluvial-glacial-deltaic succession is erosively overlaid by sandstones with trough cross-stratification, deposited within a channelled braided plain (AF7). This proposal confirms partially the previous paleoenvironmental interpretation discarding the presence of subaerial alluvial fan and outwash plain deposits for this unit. The sequence stratigraphy of Serra Grande Group was refined using mainly the coherent interpretation of the key surfaces and comparing the system tracts with the global sea-level curve providing a more robust third-order sequential evolutive model that includes three depositional sequences. The development of an extensive fluvial system (AF1, Ipu Formation) directly over the basin basement, with thicknesses of hundreds of meters, suggests a perennial river probably supplied by mountainous regions to the west of Gondwana. These deposits of middle Ordovician age were generated under low sea conditions belonging to sequence 1, and are truncated by a significant unconformity that possibly removed the transgressive and highstand strata. This unconformity produced by the glacial dynamics removed approximately 25 Ma from the sedimentary record of the basin. The second sequence started with the advance of the ice-sheets in the early Silurian, with the installation of an ice-contact fan (AF2 and AF3, Ipu Formation), in lowstand conditions. During the icesheet retreat, large amounts of water and debris were released, allowing the deposition of stratified diamictites with the presence of dropstones (AF4, Ipu Formation). The transgressive phase culminated in an increase in sea level and subsequent deposition of black shales from AF5 (Tianguá Formation), during the middle to late Silurian period. The highstand phase in the late Silurian is marked by the installation of a delta system (AF6, Tianguá Formation). In the early Devonian, an expressive new stage of sea-level fall produced an unconformity on the continental shelf concomitant with the progradation of a braided river system (AF7, Jaicós Formation), under lowstand phase of sequence 3. The Serra Grande Group paleoenvironmental and paleoclimatic reconstruction provided important sedimentological and stratigraphic elements for understanding the pre- and post-glacial transgressive and regressive phases, as well as assisting in the paleogeographic reconstruction of West Gondwana ice-sheets during the Silurian.
Acesso aberto (Open Access)
As sucessões cambriana-siluriana da Bacia do Parnaíba e da Província Mineral de Carajás: paleoambiente, proveniência e extensão da glaciação siluriana no Gondwana Oeste.
(Universidade Federal do Pará, 2024-01-12) ROMERO BARRERA, Ivan Alfredo; NOGUEIRA, Afonso Cesar Rodrigues; http://lattes.cnpq.br/8867836268820998
The Lower Paleozoic sedimentary record corresponding to the northern and northeastern Brazilian sedimentary basins is well exposed in outcrops within the Parnaíba Basin and locally in the Carajás Mineral Province (CMP). These deposits, considered Cambrian/OrdovicianSilurian age, based on the Silurian glacial strata identification maximum depositional age (UPb in detrital zircon), represent a unique opportunity to understand the paleoenvironmental and paleogeographic evolution of Western Gondwana. The records analyzed in this study include siliciclastic sequences with thicknesses ranging between 300–400m and lateral continuity that exceeds 300,000 km², representing alluvial, glacio-marine, and deltaic deposits unconformably overlying crystalline basement rocks. The basal succession comprises coarse-grained lithoarenites and fluvial conglomerates exposed in intracratonic basins and isolated grabens in northeastern Brazil and central Africa. In Brazil, these units correspond to the Ipu, Cariri, and Tacaratu formations, while in Africa, they are represented by the Inkisi, Banalia, and Biano groups. The conglomerates and sandstones of the Ipu Formation, at the base of the Serra Grande Group in the Parnaíba Basin, are here correlated with the corresponding alluvial deposits of the Gorotire Formation in the Paredão Group within isolated grabens in the CMP. These deposits are sharply overlain by massive to stratified diamictites, carbonaceous shales with dumpstone and dropstone structures, and sandstones with sigmoidal cross-stratification belonging to the upper member of the Paredão Group in CMP and the Tianguá Formation in Parnaíba Basin. During the amalgamation of the Gondwana supercontinent in the Neoproterozoic-Cambrian periods transition, the coalescence of continental masses was controlled by the development of major orogenic systems, accompanied by the deposition of the first sedimentary sequences in rift-type basins. These extensive subsiding geotectonic compartments coincided with the reorganization of regional drainage patterns and the generation of large sediment volumes transported by transcontinental fluvial systems. At the Cambrian-Ordovician period boundary, these “Big Rivers” extended across vast peneplains for hundreds of kilometers, overcoming the current intracratonic basin limits along the northwestern margin of the supercontinent and fed by diverse source areas. The fluvial architecture of these successions consists of massive to stratified tabular beds of conglomerates and sandstones, laterally continuous over kilometers and sometimes filling concave-channel geometries. These deposits are arranged in metric-scale fining-upward cycles, reflecting the dominance of sheet flow processes with sporadic channel incisions filled by small- to large-scale two- and three-dimensional bedforms. Alluvial fan facies for the Ipu Formation were not observed, suggesting basinal edges erosion. In addition, unidirectional paleocurrent data predominantly oriented NNW extend beyond the Parnaíba Basin current limits, indicating that the depositional area was more extensive than presently preserved. During the transition between the Ordovician and Silurian periods, the western portion of the Gondwana Supercontinent experienced an extensive glacial period, climaxing in the Hirnantian (~445 Ma), as recorded in rocks from northern African basins. Thus, the glacial event that began in the Middle Ordovician likely froze continental areas representing the headboard of large alluvial systems in Africa and Brazil, initiating the decline of these transcontinental drainages. The migration of the supercontinent toward the South Pole coincided with astronomical factors such as Earth rotational changes and decreased solar radiation, promoting ice sheet growth. The end of the glacial event was marked by the largest eustatic sea-level rise in Earth history, triggering significant marine transgressions starting in the Llandovery (~443 Ma) and ending in the Ludlow (~423 Ma). The melting phase promotes the development of proglacial glacio-marine systems with widespread icebergs, ablation processes, and an expansion of anoxic zones in seas, allowing extensive global organic matter preservation. The ice-melt deltaic systems progradation marks the end of the post-glacial sequence deposition. These events records are well represented in Paredão Group upper member and Tianguá Formation successions. Through the investigation of Ordovician sedimentary records from northeastern Brazil and central Africa, complemented with detailed analyses of fluvial architecture and U-Pb detrital zircon ages, a compelling narrative emerges of immense transcontinental drainage systems that shaped the landscape after the Gondwana Supercontinent amalgamation. Additionally, Paleozoic records are described for the first time in the CMP, providing a critical key for improved stratigraphic understanding and enhancing paleoenvironmental, paleogeographic, and paleoclimatic reconstructions of the Gondwana supercontinent during the Lower Paleozoic.