ORCID Profile
0000-0001-9848-9550
Current Organisation
Universidade de São Paulo
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Publisher: Elsevier BV
Date: 09-2019
Publisher: Elsevier BV
Date: 2020
Publisher: Proceedings of the National Academy of Sciences
Date: 10-12-2018
Abstract: The diminishing strength of the Earth’s magnetic dipole over recent millennia is accompanied by the increasing prominence of the geomagnetic South Atlantic Anomaly (SAA), which spreads over the South Atlantic Ocean and South America. The longevity of this feature at millennial timescales is elusive because of the scarcity of continuous geomagnetic data for the region. Here, we report a unique geomagnetic record for the last ∼1500 y that combines the data of two well-dated stalagmites from Pau d’Alho cave, located close to the present-day minimum of the anomaly in central South America. Magnetic directions and relative paleointensity data for both stalagmites are generally consistent and agree with historical data from the last 500 y. Before 1500 CE, the data adhere to the geomagnetic model ARCH3K.1, which is derived solely from archeomagnetic data. Our observations indicate rapid directional variations ( .1°/y) from approximately 860 to 960 CE and approximately 1450 to 1750 CE. A similar pattern of rapid directional variation observed from South Africa precedes the South American record by 224 ± 50 y. These results confirm that fast geomagnetic field variations linked to the SAA are a recurrent feature in the region. We develop synthetic models of reversed magnetic flux patches at the core–mantle boundary and calculate their expression at the Earth’s surface. The models that qualitatively resemble the observational data involve westward (and southward) migration of midlatitude patches, combined with their expansion and intensification.
Publisher: Elsevier BV
Date: 02-2012
Publisher: Elsevier BV
Date: 2004
Publisher: Elsevier BV
Date: 05-2021
Publisher: Elsevier BV
Date: 2021
Publisher: University of Chicago Press
Date: 05-2013
DOI: 10.1086/669979
Publisher: Geological Society of America
Date: 30-07-2014
DOI: 10.1130/B30842.1
Publisher: Elsevier BV
Date: 2020
Publisher: Springer Science and Business Media LLC
Date: 15-03-2022
DOI: 10.1038/S41467-022-28972-8
Abstract: Speleothems can provide high-quality continuous records of the direction and relative paleointensity of the geomagnetic field, combining high precision dating (with U-Th method) and rapid lock-in of their detrital magnetic particles during calcite precipitation. Paleomagnetic results for a mid-to-late Holocene stalagmite from Dona Benedita Cave in central Brazil encompass ~1900 years (3410 BP to 5310 BP, constrained by 12 U-Th ages) of paleomagnetic record from 58 s les (resolution of ~33 years). This dataset reveals angular variations of less than 0.06° yr −1 and a relatively steady paleointensity record (after calibration with geomagnetic field model) contrasting with the fast variations observed in younger speleothems from the same region under influence of the South Atlantic Anomaly. These results point to a quiescent period of the geomagnetic field during the mid-to-late Holocene in the area now comprised by the South Atlantic Anomaly, suggesting an intermittent or an absent behavior at the multi-millennial timescale.
Publisher: Elsevier BV
Date: 03-2012
Publisher: Elsevier BV
Date: 09-2022
Publisher: Elsevier BV
Date: 12-2021
Publisher: Elsevier BV
Date: 02-2017
Publisher: Elsevier BV
Date: 02-2000
Publisher: Elsevier BV
Date: 03-2012
Publisher: Elsevier BV
Date: 09-2015
Publisher: Frontiers Media SA
Date: 03-08-2021
DOI: 10.3389/FEART.2021.692895
Abstract: The Ediacaran-Cambrian transition is marked by the ersification of metazoans in the marine realm. However, this is not recorded by the Ediacaran-Cambrian Bambuí Group of the São Francisco basin, Brazil. Containing the sedimentary record of a partially confined foreland basin system, the Bambuí strata bear rare metazoan remnants and a major carbon isotope positive excursion decoupled from the global record. This has been explained by changes in the paleogeography of the basin, which became a restricted epicontinental sea in the core of the Gondwana supercontinent, promoting episodes of shallow water anoxia. Here, we report new δ 15 N bulk data from the two lowermost second-order transgressive-regressive sequences of the Bambuí Group. The results show a rise of δ 15 N values from +2 to +5‰ in the transgressive system tract of the basal sequence, which was deposited when the basin was connected to other marginal seas. Such excursion is interpreted as an oxygenation event in the Bambuí sea. Above, in the regressive systems tract, δ 15 N values vary from +2 to +5‰, pointing to instabilities in the N-cyle that are concomitant with the onset of basin restrictions, higher sedimentary supply/accommodation ratios, and the episodic anoxia. In the transgressive systems tract, the δ 15 N values stabilise at ∼+3.5‰, pointing to the establishment of an appreciable nitrate pool in shallow waters in spite of the basin full restriction as marked by the onset of a positive carbon isotope excursion. In sum, our data show that the N-cycle and its fluctuations were associated with variations in sedimentary supply/accommodation ratios induced by tectonically-related paleogeographic changes. The instability of the N-cycle and redox conditions plus the scarcity of nitrate along regression episodes might have hindered the development of early benthic metazoans within the Bambuí seawater and probably within other epicontinental seas during the late Ediacaran-Cambrian transition.
Publisher: Elsevier BV
Date: 04-2018
Publisher: Elsevier BV
Date: 11-2014
Publisher: Elsevier BV
Date: 06-2012
Publisher: Elsevier BV
Date: 03-2012
Publisher: Wiley
Date: 03-10-2014
DOI: 10.1111/SED.12143
Publisher: Elsevier BV
Date: 03-2012
Publisher: Elsevier BV
Date: 10-2013
Publisher: Elsevier BV
Date: 04-2013
Publisher: Wiley
Date: 12-2007
No related grants have been discovered for Ricardo Trindade.