Rock magnetic properties across the Paleocene-Eocene Thermal Maximum in Marlborough, New Zealand

Rock magnetic properties have been investigated across the Paleocene-Eocene Thermal Maximum (PETM) in three uplifted sections of Paleogene marine sedimentary rocks in Marlborough, South Island, New Zealand. The sections are exposed along Mead Stream, Dee Stream and Muzzle Stream and represent a depth transect up a continental margin from an upper slope to an outer shelf. Sampling was focused on rock beds previously examined for their biostratigraphy and stable carbon isotope (d13C) composition, and where a prominent clay-rich interval referred to as Dee Marl marks the initial 80-100 kyr of the PETM. Measured magnetic properties include bulk magnetic susceptibility, hysteresis cycles and isothermal remanent magnetization (IRM) acquisition and back-demagnetization curves. A strong inverse correlation between magnetic susceptibility and bulk carbonate d13C is found across the PETM such that Dee Marl has low d13C and high magnetic susceptibility. At Mead Stream this interval also contains increased saturation-IRM, and thus ferromagnetic content. Rock magnetic behaviour across PETM is best explained by an increase in terrigenous discharge. This inference has been made previously for PETM intervals in New Zealand and elsewhere, although with different proxies. Increased terrigenous discharge probably signifies an acceleration of the hydrological and weathering cycles. Some changes in magnetic phases could also reflect a drop in redox conditions, which could represent higher sedimentation rates, greater input of organic carbon, dysoxic bottom waters, or a combination of all three. A drop in redox conditions has been inferred for other marine sections spanning the PETM

Unidad Técnica de Geodesia, Geofísica y Magnetismo de Rocas: Laboratorio de Paleomagnetismo, Magnetismo de Rocas y Modelado Geomagnético

Trabajo presentado en la I Reunión Científica del Instituto de Geociencias (CSIC-UCM), los días 15 y 16 de septiembre de 2011.Peer reviewe

Adventive hydrothermal circulation on Stromboli volcano (Aeolian Islands, Italy) revealed by geophysical and geochemical approaches: Implications for general fluid flow models on volcanoes

International audienceOn March 15th 2007 a paroxysmal explosion occurred at the Stromboli volcano. This event generated a large amount of products, mostly lithic blocks, some of which impacted the ground as far as down to 200 m a.s.l., about 1.5 km far away from the active vents. Two days after the explosion, a new vapour emission was discovered on the north-eastern flank of the volcanic edifice, at 560 m a.s.l., just above the area called "Nel Cannestrà". This new vapour emission was due to a block impact. In order to investigate the block impact area to understand the appearance of the vapour emission, we conducted on May 2008 a multidisciplinary study involving Electrical Resistivity Tomography (ERT), Ground Penetrating Radar (GPR), Self-Potential (SP), CO2 soil diffuse degassing and soil temperature surveys. This complementary data set revealed the presence of an anomalous conductive body, probably related to a shallow hydrothermal level, at about 10-15 m depth, more or less parallel to the topography. It is the first time that such a hydrothermal fluid flow, with a temperature close to the water boiling point (76 °C) has been evidenced at Stromboli at this low elevation on the flank of the edifice. The ERT results suggest a possible link between (1) the main central hydrothermal system of Stromboli, located just above the plumbing system feeding the active vents, with a maximum of subsurface soil temperature close to 90 °C and limited by the NeoStromboli summit crater boundary and (2) the investigated area of Nel Cannestrà, at ~ 500 m a.s.l., a buried eruptive fissure active 9 ka ago. In parallel, SP and CO2 soil diffuse degassing measurements suggest in this sector at slightly lower elevation from the block impact crater a magmatic and hydrothermal fluid rising system along the N41° regional fault. A complementary ERT profile, on May 2009, carried out from the NeoStromboli crater boundary down to the block impact crater displayed a flank fluid flow apparently connected to a deeper system. The concept of shallow hydrothermal level have been compared to similar ERT results recently obtained on Mount Etna and La Fossa cone of Vulcano. This information needs to be taken into account in general fluid flow models on volcanoes. In particular, peripheral thermal waters (as those bordering the north-eastern coast of Stromboli) could be contaminated by hydrothermal and magmatic fluids coming from regional faults but also from the summit

Paleomagnetic constraints on the age of Lomo Negro volcanic eruption (El Hierro, Canary Islands)

A paleomagnetic study has been carried out in 29 cores drilled at 6 different sites from the volcanic products of Lomo Negro eruption (El Hierro, Canary Islands, Spain). Systematic thermal and alternating field demagnetization of the samples’ NRM (Natural Remanent Magnetization) revealed a northward, stable paleomagnetic direction similar in all the samples. Rock magnetic experiments indicate that this paleomagnetic component is carried by a mixture of high-Ti and low-Ti titanomagnetite crystals typical of basaltic lithologies that have experienced a significant degree of oxyexsolution during subaerial cooling. The well constrained paleomagnetic direction of Lomo Negro lavas was used to perform a paleomagnetic dating of the volcanic event, using the SHA.DIF.14k global geomagnetic model restricted for the last three thousand years. It can be unambiguously concluded that Lomo Negro eruption occurred well before the previously proposed date of 1793 AD, with three different age ranges being statistically possible during the last 3 ka: 115 BC-7 AD, 410-626 AD, and 1499-1602 AD. The calibration of a previously published non-calibrated 14C dating suggests a XVI c. date for Lomo Negro eruption. This conclusion leaves open the possibility that the seismic crisis occurred at El Hierro in 1793 AD was related to an intrusive magmatic event that either did not reach the surface or either culminated in an unregistered submarine eruption similar to the one occurred in 2011-2012 at the southern off-shore ridge of the island.Published1497-15141A. Geomagnetismo e PaleomagnetismoJCR Journalrestricte

Paleomagnetic constraints on the age of Lomo Negro volcanic eruption (El Hierro, Canary Islands)

A paleomagnetic study has been carried out in 29 cores drilled at 6 different sites from the volcanic products of Lomo Negro eruption (El Hierro, Canary Islands, Spain). Systematic thermal and alternating field demagnetization of the samples’ NRM (Natural Remanent Magnetization) revealed a northward, stable paleomagnetic direction similar in all the samples. Rock magnetic experiments indicate that this paleomagnetic component is carried by a mixture of high-Ti and low-Ti titanomagnetite crystals typical of basaltic lithologies that have experienced a significant degree of oxyexsolution during subaerial cooling. The well constrained paleomagnetic direction of Lomo Negro lavas was used to perform a paleomagnetic dating of the volcanic event, using the SHA.DIF.14k global geomagnetic model restricted for the last three thousand years. It can be unambiguously concluded that Lomo Negro eruption occurred well before the previously proposed date of 1793 AD, with three different age ranges being statistically possible during the last 3 ka: 115 BC-7 AD, 410-626 AD, and 1499-1602 AD. The calibration of a previously published non-calibrated 14C dating suggests a XVI c. date for Lomo Negro eruption. This conclusion leaves open the possibility that the seismic crisis occurred at El Hierro in 1793 AD was related to an intrusive magmatic event that either did not reach the surface or either culminated in an unregistered submarine eruption similar to the one occurred in 2011-2012 at the southern off-shore ridge of the island

Magnetic characterization of cretaceous-tertiary boundary sediments

Rock magnetic properties across several K-T boundary sections have been investigated to reveal any possible magnetic signature associated with the remains of the impact event at the end of the Cretaceous. Studied sections' locations vary in distance to the Chicxulub structure from distal (Agost and Caravaca, Spain), through closer (ODP Hole 1049A, Blake Nose, North Atlantic), to proximal (El Mimbral and La Lajilla, Mexico). A clear magnetic signature is associated with the fireball layer in the most distal sections, consisting of a sharp increase in susceptibility and saturation isothermal remanent magnetization (SIRM), and a decrease in remanence coercivity. Magnetic properties in these sections point to a distinctive ferrimagnetic phase, probably corresponding to the reported Mg- and Ni-rich, highly oxidized spinels of meteoritic origin. At closer and proximal sections magnetic properties are different. Although there is an increase in susceptibility and SIRM associated with a rusty layer placed on top of the siliciclastic deposit in proximal sections, and with a similar limonitic layer on top of the spherule bed that defines the boundary at Blake Nose, the magnetic properties indicate a mixture of iron oxyhydroxides dominated by fine-grained goethite. Based on previous geochemical studies at Blake Nose and new geochemical and PGE abundance measurements performed in this work at El Mimbral, this goethite-rich layer can be interpreted as an effect of diagenetic remobilization and precipitation of Fe. There is not enough evidence to assert that this Fe concentration layer at proximal sections is directly related to deposition of fine meteoritic material. Magnetic, geochemical, and iridium data reject it as a primary meteoritic phase

Transformação ambiental de um estuário industrializado no século XIX: o registo sedimentar de Avilés (Asturias, N Espanha)

The Avilés estuary is one of the most important industrial ports in northern Spain, whose natural characteristics have been largely altered since the 1830s. Here, the environmental transformation of this estuary during the 19th century is explored using a multi-proxy approach including benthic foraminiferal content, sedimentology (grain-size), trace metals and short-lived radionuclides (210Pb and 137Cs) analysed from a 50-cm-long sediment core and a surface sample collected from the middle part of the estuary in the Pedro Menéndez Channel. The obtained results provide evidence that indicate an evolution from a naturally-driven environment with high a marine influence towards a more restricted setting under brackish conditions. The observed environmental change is interpreted as being mostly derived from physical modifications linked to the marsh reclamation and channelling starting in 1833 and intensified since 1860. This study provides a preindustrial environmental reference framework for future studies in coastal areas of the NW Atlantic Iberian margin.O estuário de Avilés é um dos portos industriais mais importantes do norte de Espanha, cujas características naturais foram bastante alteradas desde 1830. A transformação ambiental deste estuário durante o século XIX é estudada usando uma abordagem multi-proxy incluindo foraminíferos bentónicos, sedimentologia (dimensão do grão), metais traço e radionuclídeos de vida curta (210Pb e 137Cs) analisados a partir de sedimento de um testemunho de sondagem com 50 cm de comprimento e uma amostra recolhida à superfície na parte média do estuário do Canal de Pedro Menéndez. Os resultados obtidos fornecem evidências que indicam evolução de um ambiente com elevada influência marinha para um ambiente mais restrito em condições salobras. A alteração ambiental observada é interpretada como resultado de modificações físicas ligadas à recuperação e canalização de pântanos a partir de 1833, e intensificada desde 1860. Este estudo fornece um exemplo de referência ambiental pré-industrial para estudos futuros em áreas costeiras da margem NW Ibérica do Atlântico.Acknowledgements: This research was funded by the projects “ANTROPICOSTA-2: Anthropocene sedimentary record of the coastal and marine areas of Northern Atlantic Iberia” (RTI2018-095678-B-C21 (MCIU/AEI/FEDER, UE)) and Harea-Geología Litoral (IT976-16). Jon Gardoki was supported by a predoctoral grant from the Basque Government (PRE_2020_1_0035). Lígia Castro (Universidade Nova de Lisboa) and one anonymous reviewer improved the original manuscript with their comments and suggestions. It is contribution 55 of the Geo-Q Zentroa Research Unit (Joaquín Gómez de Llarena Laboratory)

Public diplomacy and Slovenian Embassy in Washington, D.C.

Re-examination of sediment cores from Deep Sea Drilling Project (DSDP) Site 277 on the western margin of the Campbell Plateau (paleolatitude of ∼65°S) has identified an intact Paleocene-Eocene (P-E) boundary overlain by a 34 cm thick record of the Paleocene-Eocene Thermal Maximum (PETM) within nannofossil chalk. The upper part of the PETM is truncated, either due to drilling disturbance or a sedimentary hiatus. An intact record of the onset of the PETM is indicated by a gradual decrease in δ13C values over 20 cm, followed by a 14 cm interval in which δ13C is 2‰ lighter than uppermost Paleocene values. After accounting for effects of diagenetic alteration, we use δ18O and Mg/Ca values from foraminiferal tests to determine that intermediate and surface waters warmed by ∼5-6° at the onset of the PETM prior to the full development of the negative δ13C excursion. After this initial warming, sea temperatures were relatively stable through the PETM but declined abruptly across the horizon that truncates the event at this site. Mg/Ca analysis of foraminiferal tests indicates peak intermediate and surface water temperatures of ∼19 and ∼32°C, respectively. These temperatures may be influenced by residual diagenetic factors and changes in ocean circulation, and surface water values may also be biased towards warm-season temperatures

Geophysical and geochemical survey across El Hierro (Canary Islands) during the 2011-2012 monogenetic eruption

7th International MAAR Conference, 21-25 Mayo (2018), Olot.Enhancing volcanic risk assessment and developing new methodologies for volcanic activity are among the main challenges in Geosciences. In the field of Volcanology, it depends directly on our understanding of when, where, and which type of volcanic eruptions will take place. In the case of polygenetic volcanoes the emphasis is usually on “when will the eruption take place? In the case of the monogenetic volcanism, while a certain monotony exists in the composition of magmas from an eruption and another, we can observe a huge diversity in the eruptive dynamics inside a volcanic field and sometimes for a single edifice (e.g. Smith and Nemeth, 2017), switching from low-energy lava flows to violent hydromagmatic explosions. As a consequence, understanding which type of eruption we can expect is crucial. Contrary to polygenetic volcanoes, for which the eruptive activity is mostly centered on the edifice, the magma can reach the surface almost anywhere in a monogenetic field, depending on tectonics, local geology, etc. Knowing where the next eruption will take place becomes a big challenge as well. In any case, some major issues consist in (1) understanding the local features affecting the triggering of eruptions and the volcano dynamics, (2) understanding which of the measurable parameters are relevant for the observation of monogenetic activity, and (3) implementing observation methods adapted to monogenetic fields.This research has been supported by IGN and CSIC, and funding by the European Commission (282759: “VUELCO”) and the MINECO grant CGL2011-16144-E. S. Barde-Cabusson was funded by JAE-Doc Program (JAEDoc_ 09_01319)Peer reviewe