O Instituto de Geociências receberá a vista do Dr. Eric Font , da Universidade de Coimbra, na semana de 05 a 09/12.
O Dr. Eric Font é geólogo-geofísico e trabalha atualmente como professor auxiliar no Departamento de Ciências da Terra da Faculdade de Ciências e Tecnologia da Universidade de Coimbra, Portugal. Tem experiência de pesquisa em paleomagnetismo e magnetismo ambiental integrado a uma série de outras ferramentas geológicas, incluindo mineralogia, processos ígneos, sedimentologia, estratigrafia e geoquímica de isótopos estáveis.
Sua pesquisa se concentra nos principais desafios das Ciências da Terra, como os efeitos ambientais de grandes províncias ígneas (Deccan, CAMP) e seu impacto na biosfera (por exemplo, acidificação ambiental); o magnetismo dos espeleotemas; Glaciações Neoproterozóicas (a chamada Hipótese da Terra Bola de Neve); e eventos generalizados de remagnetização ligados à tectônica, paleogeografia e placas tectônicas.
Como parte da visita, ele ministrará duas palestras no IG:
Palestra 1: Deccan volcanism and the Cretaceous-Paleogene mass extinction
Dia 06/12, terça-feira, às 14h
The contribution of the Deccan Traps volcanism in the Cretaceous-Palaeogene (KPg) crisis is still a matter of debate. The main limitation is the lack of mass extinction proxies within the Deccan lava flows, making hard the correlation of the onset of Deccan volcanism in India with the mass extinction recorded in the global marine record. Recent advances in U–Pb and Ar–Ar radiometric dating have improved constraints for the onset and duration of the entire Deccan Magmatic province. However, deciphering the global climate and environmental effects of Deccan volcanism and the contribution to the end-Cretaceous mass extinction remain challenging. Here we present a review of the sedimentary markers indicative of Deccan-induced global changes, including an interval of low magnetic susceptibility, mercury anomalies, akaganéite, and biologic markers of high-stress conditions (e.g., disaster opportunist species, test fragmentation). In Bidart (France), Zumaia (Spain) and Gubbio (Italy), a low magnetic susceptibility interval marks the uppermost 50 cm below the mass extinction, which corresponds to the loss of detrital and biogenic magnetite produced by magnetotactic bacteria, and to dwarfed disaster opportunistic foraminifera, marked by test dissolution and fragmentation. This is interpreted as the result of continental and oceanic acidification and change in seawater/sediment chemistry. The low MS interval is accompanied by mercury anomalies, which indicate input of volcanic origin as suggested by lack of total organic carbon. A chlorine-rich iron (oxyhydr)oxide in the mercury-rich low magnetic susceptibility interval indicates akaganéite, which is very rare on Earth because its precipitation requires hyper-chlorinated, acidic and oxidizing conditions compatible with a volcanic environment. We propose that the observed akaganéite formed at low temperature and high altitude in the Deccan volcanic plumes and via global atmospheric transport deposited at Bidart, Zumaia and Gubbio. The association of low magnetic susceptibility, mercury, akaganéite, and high-stress microfossil species and disaster opportunists thus provide new sedimentary markers of Deccan volcanism and environmental acidification leading up to the end-Cretaceous mass extinction.
Correlation of the age and eruption rates of the Deccan Traps with the marine and continental sedimentary records. (A) Eruption rate models based on U-Pb and 40Ar-39Ar data of Schoene et al. (2019) and Sprain et al. (2019), respectively (modified from Kasbohm et al. (2021); (B) Atlantic ocean paleotemperatures estimated based on d18O benthic from ODP 1262 (Barnet et al., 2018); (C) Mean annual temperature estimated based on leaves from continental deposits of North Dakota and floral species richness (Wilf et al., 2003); (D) Osmium isotopic record from bulk carbonate from ODP 1262 core (Ravizza and VonderHaar, 2012) and the Bottacione (Gubbio, Italy) outcrop (Robinson et al., 2009); the low magnetic susceptibility interval at (E) Gubbio (Ellwood et al., 2003) and (F) Bidart (France) (Font et al., 2011); mercury content (ppb) of the K-Pg transition at Bidart (Font et al., 2016).
Palestra 2: The magnetic and climate signature of speleothems
Dia 07/12, quarta-feira, às 9h
Speleothems are secondary mineral deposits formed in caves and are excellent recorders of variations in the Earth’s magnetic field and climate during the Quaternary. Their age can be determined precisely using U-Th disequilibrium series dating, and the magnetic, geochemical and mineralogical signatures preserved in their thin laminations provide high-resolution climate- and environmental proxy time series, from sub-annual to millennial time scales. Speleothems host magnetic minerals that originate from the soils and rocks above a cavern system. As these magnetic minerals are incorporated into actively growing stalagmites, the grains acquire a detrital remanent magnetization (DRM), which accurately records the direction of the Earth’s magnetic field and can be readily measured using standard SQUID-based rock magnetometers. Magnetic studies of speleothems provide two important forms of data: i) Continuous and high-resolution records of short-term variations of the Earth´s magnetic field (EMF), and conversely the use of paleomagnetism as a dating tool of speleothems; and ii) High-resolution records of climate variability by linking rock magnetic properties to climate and environmental forcing parameters acting on soils. Here, I present a review of the recent advances in the field of speleothem magnetism, as well as limitations and perspectives. I also present the results of the investigation of Portuguese stalagmites obtained in the frame of the ongoing research and development projects.
(a) Photographs of speleothem under study before cutting (top), after cutting and replacement in its original position (middle), and orientation of the vertical plane with a magnetic compass (bottom).
(b) Vertical face of the speleothem with location of the cylindrical SPAIV specimens (1.1 × ~2 cm) collected for subsequent paleomagnetic measurements. Ages Before Christ (B.C.) and associated errors have been determined by interpolation of corrected 230Th ages for dated layers using the StalAge algorithm [Scholz and Hoffmann, 2011].
(c) Cylindrical specimens and their respective orientation illustrated in Figure 1b.
(d) The dip of calcite laminae is calculated based on the mean of the angles measured on the front (α) and back sides (α0) of the specimen.
Magnetic declination and inclination curves of SPAIV (red lines correspond to the original site-based mean magnetic declination and inclination per line; orange line corresponds the same data corrected by the effect of the slope, see Ponte et al., 2017 for more details) compared to PSV models (SHA.DIF.14K, CALS10K.1b, and pfm9k.1a) and discrete data from archaeomagnetic objects (northern Spain), volcanic material (Canary Islands), and two flowstone cores (Italian Alps).