The influence of thermal maturity on the stable isotope compositions and concentrations of molybdenum, zinc and cadmium in organic-rich marine mudrocks

The concentrations and isotopic compositions of molybdenum (Mo), zinc (Zn) and cadmium (Cd) in organic-rich marine mudrocks may be used to characterize ocean chemistry in the geological past. These approaches rely on the rarely tested assumption that the geochemical signatures of these metals are not affected by the thermal maturation of the organic matter with which they are associated. We have conducted a series of artificial maturation experiments on two well-known immature organic-rich mudrocks, the Kimmeridge Blackstone Band (Late Jurassic age), and the Posidonia Shale (Early Jurassic age). These pyrolysis experiments allow us to trace changes in the composition of organic matter through varying stages of maturation, and the concentration and isotopic compositions of metals in rock residues and evolved organic fluids. Our results indicate that the thermal maturation of organic matter does not result in significant alteration of the isotopic compositions of Mo, Zn and Cd in the rock residues, which thus retain primary palaeodepositional information. Systematic increases in the concentrations of Mo, Zn and Cd in rock residues with progressively higher thermal maturity are attributed to the loss of substrate mass in the form of fluids released during pyrolysis-induced cracking of kerogen, and to the relatively low concentrations of Mo, Zn and Cd in these fluids. The Mo-isotope compositions of fluids produced during pyrolysis are isotopically similar to the bulk rock; in contrast the isotopic composition of Zn in organic fluids is ∼0.4–0.6‰ lighter than the bulk rock. The progressive loss of organic matter from rock residues during maturation coupled with the increases in metal concentrations leads to an increase of metal/TOC ratios, which may be up to double their original (syn-depositional) value in thermally mature rocks. This observation must be taken into account when using metal/TOC ratios as proxies for oceanic metal inventories throughout geological time. Finally, calculations using the mass of asphaltenes recovered during the pyrolysis experiments suggest that organically bound Mo, Zn and Cd account for several percent of the total rock metal inventory

The development of a glucose prediction model in critically ill patients

Purpose: The aim of the current study is to develop a prediction model for glucose levels applicable for all patients admitted to the ICU with an expected ICU stay of at least 24 h. This model will be incorporated in a closed-loop glucose system to continuously and automatically control glucose values. Methods: Data from a previous single-center randomized controlled study was used. All patients received a FreeStyle Navigator II subcutaneous CGM system from Abbott during their ICU stay. The total dataset was randomly divided into a training set and a validation set. A glucose prediction model was developed based on historical glucose data. Accuracy of the prediction model was determined using the Mean Squared Difference (MSD), the Mean Absolute Difference (MAD) and a Clarke Error Grid (CEG). Results: The dataset included 94 ICU patients with a total of 134,673 glucose measurements points that were used for modelling. MSD was 0.410 +/- 0.495 for the model, the MAD was 5.19 +/- 2.63 and in the CEG 99.8% of the data points were in the clinically acceptable regions. Conclusion: In this study a glucose prediction model for ICU patients is developed. This study shows that it is possible to accurately predict a patient's glucose 30 min ahead based on historical glucose data. This is the first step in the development of a closed-loop glucose system. (C) 2021 Elsevier B.V. All rights reserved