14 research outputs found
Pockets of Proterozoic hydrocarbons and implications for the Archaean
Precambrian biomarkers convey invaluable information
about the early evolution of life, ancient ecosystems, redox
conditions, climate and depositional environment and
prospective petroleum systems. They are however thermally
unstable, easily obliterated by contamination and thus
extremely difficult to find. This is particularly true if
conditions favourable for biomarker preservation had to
prevail for more than 2.5 billion years – the prerequisite for
finding Archaean biomarkers. Many organic geochemists
abandoned this hope after original discoveries of Archaean
biomarkers proved to be of younger origin [1,2] but our study
of ca. 550-825 Ma old sediments from the Centralian
Superbasin now shows that biomarkers can be preserved in
distinctive pockets in seemingly barren areas, even if sections
are metamorphosed in parts. Most Centralian sections seem
empty. Yet, eventually we identified intervals with preserved
biomarkers in three drill cores. A detailed investigation of 825
Ma sediments in drill core Mt Charlotte-1 revealed maturity
variations that are most likely due to hydrothermal influence
and in turn control the hydrocarbon preservation. Sediments
might appear metamorphosed after localized, subtle alteration
by hydrothermal fluids but protected intervals can still contain
biomarkers. The same might be true for Archaean sediments
and we might still find those protected intervals with
indigenous biomarkers that allow us to glimpse the early life
on earth
Impact of drill core contamination on compound-specific carbon and hydrogen isotopic signatures
Compound-specific carbon and hydrogen isotope ratios are routinely measured on extractable organic matter to decipher biogeochemical processes and events in Earth history. To deliver accurate interpretations, it is paramount that isotopic values are derived from indigenous compounds and are not the result of contamination. However, distinguishing between compounds from these different provenances can be difficult, especially if a degree of mixing occurred. In this study, we assess the impact of hydrocarbon contamination on the carbon and hydrogen isotopic composition of n-alkanes from similar to 820 Ma Precambrian evaporitic drill core samples through exterior/interior (E/I) rock extraction experiments. In these experiments, exterior and interior portions of the same rock samples were separately crushed to powder, extracted and processed. Compound-specific isotope values of n-alkanes from the different rock portions were subsequently measured and compared. In most cases, n-alkanes from exterior rock portions had consistently more depleted delta C-13 and delta H-2 values than their interior counterparts with an E/I isotopic offset averaging 0.1-6.9%, for delta C-13 and 2-33%, for delta H-2. These diverging isotope patterns tend to correspond to E/I concentration differences of n-alkanes and are the result of contaminants overprinting on indigenous isotopic signals. Through the application of E/I experiments, the degree of isotopic overprinting can be investigated and mixed indigenous/contaminant signals identified. (C) 2019 Elsevier Ltd. All rights reserved
An anelastic spectroscopy, differential scanning calorimetry and X-ray diffraction study of the crystallization process of Mg-Ni-Fe alloys
Abstract
The effects of heating-induced crystallization on the structural and mechanical properties of Mg\u2013Ni\u2013Fe amorphous ribbons were studied by anelastic spectroscopy, differential scanning calorimetry (DSC) and X-ray diffraction. DSC results show that the crystallization occurs through several non-reversible steps, which correspond to significant changes in the Young's modulus and concomitant irreversible elastic energy loss peaks. Moreover, an anelastic peak is found at 215 K, which for the first time indicates the presence of some dynamical process related to the simultaneous presence of different phases. The formation of a metastable Mg6Ni phase is detected, which transforms into Mg and Mg2Ni stable phases. A quantitative analysis of the different phases present at the different steps was also carried out
Hydrothermal synthesis of nanostructured hybrids based on iron oxide and branched PEI polymers. Influence of high pressure on structure and morphology
Homogeneous hybrids in which iron oxide nanoparticles are entrapped within polymer structure are of interest for their potential applications in biomedical field, such as diagnostic, therapeutic and theranostic purposes. For this reason, hybrid nanomaterials based on branched polyethyleneimine (PEI) and iron oxide with different ratios were synthesized in a single step by hydrothermal procedure at high pressure and low temperature. Iron oxide is formed in the presence of branched PEI and the interaction between them takes place in the reaction medium. The influence of synthesis parameters on the hybrid formation, as well as chemical and structural properties was studied by means of FTIR, DSC-TG, HRTEM, electron paramagnetic resonance (EPR), magnetic measurements (SQUID) and 57Fe M€ossbauer analyses.It has been shown that synthesis parameters influence thermal stability and morphology of the hybrids. FeO(OH) crystallites of 2e5 nm are formed. Iron oxyhydroxide nanoparticles strongly entrapped in PEI structure are obtained. The low and distributed values of the specific spontaneous magnetisation in samples prepared under the same pressure conditions support the presence of very fine FeO(OH) nanoparticles, which formation and magnetic properties are depending on the mass ratio between iron oxide and PEI