335 research outputs found
Data for: Cosmic spherules from Widerøefjellet, Sør Rondane Mountains (East Antarctica)
No full textProcessed major, trace, oxygen isotopic data for Widerøefjellet cosmic spherules
Microstructures and sclerochronology of the Lithiotis Facies bivalves (Lower Jurassic): Paleobiological and paleoclimatic significance and their resilience to the early Toarcian extinction
No full textMesozoic bivalves show some evolutionary phases of proliferation of larger, aberrant, and gregarious shells with a high rock-forming potential. The most well-known are the Upper Triassic megalodontids, the Lower Jurassic lithiotids and the Cretaceous rudists. Their extinction occurred during global crisis of biocalcifiers. The strongest demise of megalodontids occurred at the end of Triassic, the lithiotid bivalves almost disappear during the early Toarcian, while the extinction of the rudists occurred at the end of Cretaceous. Here, we analyzed bivalves of the Lithiotis Facies, which contains the most aberrant, peculiar and large shells of Cochlearites, Lithioperna, and Lithiotis and other, less common, gregarious taxa represented by the pterioid Gervilleioperna and Pachygervillia, the myalinid Pseudopachymytilus, the carditid Opisoma, and the megalodontid Pachyrisma (Durga) and Protodiceras, in order to understand their response to the early Toarcian extinction. Specimens from the Pliensbachian Rotzo Formation (Trento Platform, northern Italy) are exquisitely preserved, with most of the shell made of pristine aragonite and calcite, allowing to describe in detail their shell microstructures and to discuss it in the framework of the early Toarcian biocalcifier crisis. Due to the excellent preservation of these specimens, it was possible to perform sclerochronological and sclerochemical analyses through microscopy, stable isotope analysis and micro-X-ray fluorescence scanning, allowing to investigate seasonal patterns and their functional and paleoenvironmental significance. This analysis results in the identification of different growth rates among the different taxa and adds new tentative evidence for the paleoclimatic evolution of the Rotzo Formation. The maximum growth rate in ventral direction ranges from 20 mm/year in Lithioperna to a few mm/year in most of the other genera which have thick but smaller shells. These latter taxa showed a greater resilience to the environmental perturbances of the early Toarcian and most of them survived this crisis. The survivors also include representatives of the Fam. Pachyrismatidae (e.g., Pachyrisma, Early-Late Jurassic in age) from which the rudists had origin. Instead, bivalves mostly affected by the extinction were those with thicker and larger shells and a high annual growth rate
Chromite in main group pallasite meteorites: Accessory mineral tracing planetesimal differentiation
No full textAbstract Main group pallasite meteorites (PMG) are samples of an early, highly differentiated magmatic planetesimal dominated by olivine and metal‐sulfide‐phosphide assemblages with accessory chromite among other phases. This mineralogy reflects mantle‐ and core‐related reservoirs, but the relative contributions of each and the overall petrogenesis are obscured by high degrees of protolith melting. Here, we present new data on the chemistry of chromite in these meteorites and review previous datasets. The purely lithophile elements Mg and Al partition into chromite via (Mg,Fe)(Al,Cr) 2 O 4 and mainly reflect interactions with olivine and basaltic melt, respectively. Chromite cores are virtually always more aluminous than rims, and while MgO contents were likely reset during slow cooling, their Al 2 O 3 contents are more robust and were largely set during the period of silicate magmatism. Main group pallasite chromites display bimodality in Al 2 O 3 contents, with peak concentrations at ~7.7 wt% and below 6 wt%, which is unlike any other achondrite chromite population. Some chromites have very low Al 2 O 3 contents (~0.01 wt%) due to formation in the absence of silicate melt, that is, via exsolution of Cr from cooling liquid metal. High‐, low‐, and very low‐Al 2 O 3 chromites in these meteorites broadly reflect relict, prograde, and retrograde periods of planetesimal heating followed by cooling. The Al 2 O 3 contents of the chromites in many other achondrites and equilibrated chondrites are similar to the higher values in pallasites, with most greater than 3 wt%. This suggests that meteoritic chromite is a significant sink for 26 Al during its life as a heat source for planetesimal differentiation. To first order, it may be responsible for ~25%–50% (i.e., about one third) of heating in partially depleted mantles.Fonds Wetenschappelijk Onderzoek https://doi.org/10.13039/501100003130Alexander von Humboldt-Stiftung https://doi.org/10.13039/100005156Vrije Universiteit Brussel https://doi.org/10.13039/501100004418Belgian Federal Science Policy Office https://doi.org/10.13039/50110000274
Petrogenesis of main group pallasite meteorites based on relationships among texture, mineralogy, and geochemistry
No full textAbstract Main group pallasite meteorites are samples of a single early magmatic planetesimal, dominated by metal and olivine but containing accessory chromite, sulfide, phosphide, phosphates, and rare phosphoran olivine. They represent mixtures of core and mantle materials, but the environment of formation is poorly understood, with a quiescent core–mantle boundary, violent core–mantle mixture, or surface mixture all recently suggested. Here, we review main group pallasite data sets and petrologic characteristics, and present new observations on the low‐MnO pallasite Brahin that contains abundant fragmental olivine, but also rounded and angular olivine and potential evidence of sulfide–phosphide liquid immiscibility. A reassessment of the literature shows that low‐MnO and high‐FeO subgroups preferentially host rounded olivine and low‐temperature P 2 O 5 ‐rich phases such as the Mg‐phosphate farringtonite and phosphoran olivine. These phases form after metal and silicate reservoirs back‐react during decreasing temperature after initial separation, resulting in oxidation of phosphorus and chromium. Farringtonite and phosphoran olivine have not been found in the common subgroup PMG , which are mechanical mixtures of olivine, chromite with moderate Al 2 O 3 contents, primitive solid metal, and evolved liquid metal. Lower concentrations of Mn in olivine of the low‐MnO PMG subgroup, and high concentrations of Mn in low‐Al 2 O 3 chromites, trace the development and escape of sulfide‐rich melt in pallasites and the partially chalcophile behavior for Mn in this environment. Pallasites with rounded olivine indicate that the core–mantle boundary of their planetesimal may not be a simple interface but rather a volume in which interactions between metal, silicate, and other components occur
The Effect of Monetary Policy on Exchange Rates during Currency Crises; The Role of Debt, Institutions and Financial Openness
No full textThis paper examines the effect of monetary policy on the exchange rate during currency crises. Using data for a number of crisis episodes between 1986 and 2004, we find strong evidence that raising the interest rate: (i) has larger adverse balance sheet effects and is therefore less effective in countries with high domestic corporate short-term debt; (ii) is more credible and therefore more effective in countries with high-quality institutions; iii) is more credible and therefore more effective in countries with high external debt; and (iv) is less effective in countries with high capital account openness. We predict that monetary policy would have had the conventional supportive effect on the exchange rate during five of the crisis episodes in our sample, while it would have had the perverse effect during seven other episodes. For four episodes, we predict a statistically insignificant effect. Our results support the idea that the effect of monetary policy depends on its impact on fundamentals, as well as its credibility, as suggested in the recent theoretical literature. They also provide an explanation for the mixed findings in the empirical literature.Institutions;Capital Account Openness;Currency Crises;External Debt;Monetary Policy;Short-Term Debt
The Effect of Monetary Policy on Exchange Rates During Currency Crises: The Role of Debt, Institutions and Financial Openness
No full textThis paper examines the effect of monetary policy on the exchange rate during currency crises. Using data for a number of crisis episodes between 1986 and 2004, we find strong evidence that raising the interest rate: (i) has larger adverse balance sheet effects and is therefore less effective in countries with high domestic corporate short-term debt; (ii) is more credible and therefore more effective in countries with high-quality institutions; iii) is more credible and therefore more effective in countries with high external debt; and (iv) is less effective in countries with high capital account openness. We predict that monetary policy would have had the conventional supportive effect on the exchange rate during five of the crisis episodes in our sample, while it would have had the perverse effect during seven other episodes. For four episodes, we predict a statistically insignificant effect. Our results support the idea that the effect of monetary policy depends on its impact on fundamentals, as well as its credibility, as suggested in the recent theoretical literature. They also provide an explanation for the mixed findings in the empirical literature.Currency Crises;Institutions;Monetary Policy;Short-Term Debt;External Debt;Capital Account Openness
Petrogenesis of main group pallasite meteorites based on relationships among texture, mineralogy, and geochemistry
No full textPetrography, geochemistry and mineralogy of the Stonehenge Sarsens: Digital data collection
No full textThis collection includes a suite of digital materials that, in combination, characterise the petrography, mineralogy and geochemistry of a sarsen upright (Stone 58) from the central trilithon horseshoe at Stonehenge. The collection arises from work undertaken during the British Academy/Leverhulme Trust project “Geochemical fingerprinting the sarsen stones at Stonehenge” (Small Research Grant SG-170610), led by the University of Brighton.
As part of the project, permission was granted by English Heritage to sample a section from one of three cores drilled through the full thickness of Stone 58 during conservation work in 1958. This core had been returned to the UK from Florida in 2018 by Mr Robert Phillips, an employee of Van Moppes (Diamond Tools) Ltd, Basingstoke, who had been at Stonehenge during the drilling work. Mr Phillips was granted permission by the Ministry of Works to retain the core on behalf of the company and was gifted it by Van Moppes on his retirement to the USA. This core – referred to as the Phillips’ Core – is now held in the English Heritage Collections Store at Temple Cloud (Bath, UK).
The Phillips’ Core is 108cm long, has a 2.5cm diameter and is broken into six pieces ranging in length from 7 to 29cm. The digital materials within this collection result from the analysis of section 2-3 of the core, from 29 to 36cm along its length. Full details of sampling, analytical approaches and interpretation are provided in Nash et al. (2021) (see Metadata).Data copyright © David Nash, Jake Ciborowski, Tobias Salge, Magret Damaschke, Steven Goderis unless otherwise stated This work is licensed under a Creative Commons Attribution 4.0 International License. The linked data page is the published version of the data.NHM Repositor
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