High-Resolution Late Devonian Magnetostratigraphy From the Canning Basin, Western Australia: A Re-Evaluation

Late Devonian time was a period of rapid upheaval in the Earth system, including climate change, sea level changes, widespread ocean anoxia, and the Frasnian-Famennian mass extinction; the cause(s) of these changes remain(s) uncertain. The Lennard Shelf of the Canning Basin in Western Australia contains carbonate reef sections spanning much of the Late Devonian Epoch and has been sampled for paleomagnetic analysis with studies by Hansma and colleagues in 2015 and Playton and colleagues in 2016. However, previous paleomagnetic directions were scattered and their use for magnetostratigraphy has been questioned. Here, rock magnetic data and magnetostratigraphy for a late Devonian drill-core from the Lennard Shelf were analyzed. Three magnetostratigraphic interpretations were made using different paleopoles that showed good correlation with each other and the earlier interpretations by Playton and colleagues in 2016. Additionally, the rock magnetic data revealed the samples contain various mixtures of detrital and diagenetic minerals, the former of which should be viable recorders of primary magnetic signatures. Even in samples with these detrital phases, paleomagnetic data were often noisy and produced ambiguous polarity assignments, likely due to the anomalously weak Devonian field. Because of this ambiguity and the absence of a robust paleopole, broader correlations for this critical time-period will be difficult without additional paleomagnetic data from the late Devonian Period. Expanded data for this interval could eventually shed light on the timing, causes, and rates of the Frasnian-Famennian mass extinction and other environmental shifts in the late Devonian Epoch

Linking Speleothem And Soil Magnetism In The Pau D'alho Cave (central South America)

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Mineral magnetism of Pau d'Alho cave sediments, soils outside the cave, and in the stalagmite #6 (ALHO6) in Midwest Brazil is presented. This high growth-rate speleothem (similar to 168 mm/ka) encompasses the past 1355 years. Oxygen and carbon isotope data from the same stalagmite allow for a direct comparison of the magnetic signal with changes in paleoprecipitation and soil dynamics at the surface. Magnetic experiments include isothermal remanent magnetization, anhysteretic remanent magnetization, hysteresis loops, first-order reversal curves, and low-temperature superconducting quantum interference device magnetometry. The main magnetic remanence carriers in ALHO6 are magnetite and goethite, with a nearly constant relative proportion. Remanent coercivities of magnetite in all our samples are within 14-17mT for an average grain-size of similar to 1-2 mu m, in the range of pedogenic magnetite, thus suggesting the detrital grains deposited in the stalagmite were produced in the soil above the cave. Magnetic remanence variations follow delta C-13 and delta O-18 data, suggesting a climatic control on the input of magnetic minerals into the Pau d'Alho cave system. The concentration of magnetic minerals in the stalagmite is governed by soil erosion above the cave, which by its turn is controlled by soil erosion and vegetation cover. Dry periods are associated with less stable soils and result in higher mineral fluxes carried into karst systems. Conversely, wetter periods are associated with soils topped by denser vegetation that retains micrometer-scale pedogenic minerals and thus reduces detrital fluxes into the cave.Mineral magnetism of Pau d'Alho cave sediments, soils outside the cave, and in the stalagmite #6 (ALHO6) in Midwest Brazil is presented. This high growth-rate speleothem (similar to 168 mm/ka) encompasses the past 1355 years. Oxygen and carbon isotope dat1211070247039CNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOCAPES - COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIORFAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOCoordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)304934/2014‐3, 454609/2014‐02043/20142012/03942‐4, 2012/01187‐

The response of a dune succession from Lencois Maranhenses, NE Brazil, to climate changes between MIS 3 and MIS 2

In tropical Southern Hemisphere South America, late Quaternary marine core and speleothem records provide different proxies and accurate chronologies correlating millennial-scale intervals of increased precipitation with southward shifts of the Intertropical Convergence Zone (ITCZ). However, the climatic effect of these intervals on coastal landforms is poorly understood. Here we investigated the response of abrupt and long-lasting climate events during the Marine Isotope Stages 3 and 2 in a 13.8-m thick sand succession located in a large-scale coastal eolian system, the Lencois Maranhenses Dunefield, NE Brazil, where winds and precipitation are anti-phased and controlled by the single action of the ITCZ. A chronology of the sediment overburden determined by optically stimulated luminescence (OSL) dating of 14 sediment samples obtained at 1-m intervals showed ages between 132.2 +/- 7.0 and 12.9 +/- 0.6 thousand years ago in stratigraphic order. A multi-proxy approach based on grain size, surface grain texture, heavy minerals, thermoluminescence (TL) sensitivity, inorganic geochemistry, reflectance, and magnetic parameters from 268 sediment samples collected at 5-cm intervals indicated periods of dune building and stabilization. Significant stabilization periods are synchronous with Heinrich Stadials 6, 4, 3, 2, and 1, and Greenland Stadial 4, within age model uncertainties. Heavy mineral analysis indicated a steady sand source to the dune succession, while TL sensitivity analysis of quartz grains showed the input allochthonous sediments during stadials. The preservation of peak dune activity during the Last Glacial Maximum is attributed to the enduring precipitation brought by the subsequent Heinrich Stadial 1 event