Insights into preservation of fossil plant cuticles using thermally assisted hydrolysis methylation

The chemical composition of Cretaceous leaf remains showing exceptionally well preserved cuticles was investigated using pyrolysis gas chromatography–mass spectrometry (Py-GC–MS) and thermally assisted hydrolysis methylation (THM)-GC–MS. Samples of Coniferales (Frenelopsis) and Ginkgoales (Nehvizdya penalveri) leaf remains were collected from freshwater and coastal marine depositional environments. Material for pyrolysis included (i) untreated leaves and cuticles obtained after extraction from mineral rock matrix and bleaching, (ii) kerogen fraction from both materials, (iii) non-hydrolysable fraction from kerogen. The THM-GC–MS data from untreated leaves and bleached cuticles show that the fossil cuticle geopolymer essentially released aliphatic components upon thermal treatment, with a dominance of fatty acids (FAs) and n-alkanes/n-alkenes. The FAs are essentially resistant to bleaching and remain after solvent extraction. They occur mainly as short chain compounds ranging from C₆ to C₁₆ and with maximum abundance at C₈–C₉. The n-alkanes/n-alkenes from kerogen and the non-hydrolysable residue occur mainly as short chain compounds in the range C₁₀–C₁₆, with the highest abundance at C₉–C₁₂. The THM-GC–MS pyrograms of the fossil cuticles differ from those of cutan from fresh living plants. They support the preservation model via polymerization of monomers derived from cutin or from unsaturated cell FAs.     

Paleoproterozoic metamorphism in the northern Fennoscandian Shield: age constraints revealed by monazite

ABSTRACT

We have identified two contrasting styles of Paleoproterozoic metamorphism in the northern part of the Fennoscandian Shield. The Karelia and Lapland-Kola Provinces, comprising Archean and overlying Paleoproterozoic supracrustal rocks, show a typical medium pressure Barrovian-style metamorphism with commonly found kyanite-bearing mineral assemblages and ITD (isothermal decompression) PT paths. In the juxtaposed Svecofennia Province metamorphism represents low pressure-high temperature Buchan style with garnet-cordierite migmatites and intercalated andalusite-cordierite and andalusite-staurolite schists and sillimanite-muscovite gneisses. The retrograde PT paths show only a moderate uplift during cooling.

U-Pb age determinations on monazite were made using the LA-ICP-MS from more than 80 samples from metasedimentary rocks. The sampling covered most parts of the Paleoproterozoic bedrock in Finland. The analyses reveal three peaks at c. 1.91 Ga, 1.86–1.88 Ga and at 1.79–1.81 Ga. The oldest, c. 1.91 Ga monazites are mostly found in the Lapland-Kola Province which is located in the northernmost Finland. In the Karelia Province where the Paleoproterozoic is underlain by Archean bedrock monazite yielded ages of 1.76?1.81 Ga with only a few older exceptions in samples showing a spread of ²⁰⁷Pb/²⁰⁶Pb ages from c. 1.92–1.81 Ga. The Karelia Province underwent tectonic thickening, where monazite ages of around 1.80 Ga mostly represent exhumation near the temperature maximum.

In the Svecofennia Province monazite ages vary from c. 1.89 to 1.78 Ga. In the Western Finland Subprovince the monazite ages in high-grade migmatites are mostly 1.86?1.88 Ga but within the older migmatite areas there are lower grade zones where monazite yields ages of c. 1.80 Ga. Some samples also show a spread of ²⁰⁷Pb/²⁰⁶Pb ages from 1.89?1.86 Ga to c. 1.78 Ga. In the Southern Finland Subprovince most ages are either 1.80?1.78 Ga, especially in the andalusite grade schists, or the sample shows a spread of ²⁰⁷Pb/²⁰⁶Pb ages from c. 1.88 to 1.78 Ga. Only in the eastern part of the Southern Finland Subprovince there are rocks which yield merely 1.86?1.89 Ga ages. Low pressure-high temperature metamorphism and lack of high or medium P/T rocks in the Svecofennia Province refers rather to accretionary than collisional processes.     

Mapping ethnic diversity in highland Northern Vietnam

In this paper we initially present a critical review of a range of ethnological maps produced over the last 130 years for highland northern Vietnam. In particular we illustrate the many difficulties faced when trying to represent mosaics of ethnic highland minority groups on two dimensional maps. Such historical maps included no attempts to bring topographic details into the picture, an idea that would have been virtually impossible anyway, given the cartographic technologies at the time. Yet by not including such details or not representing them clearly, a partial image of these populations has been created that, over time, has become a standardised representation. Therefore, as a more systematic approach to the analysis of these highland minority groups, we present recent attempts to create more functional maps and models for the northern Vietnam province of Lao Cai, using modern cartographic techniques and geographic information systems. Utilising tools such as digital cartography and digital elevation models a wealth of information can be gained which has the potential, amongst other possible uses, to allow for a greater understanding and sensitivity regarding ethnic minority groups in Northern Vietnam, and their use of the local environment. This revised version was published online in July 2006 with corrections to the Cover Date.     

Sur l'assimilation variationnelle de données par un modèle d'écosystème marin de type NPZ

A variational data assimilation method is applied to a simplified marine ecosystem model of NPZ (Nutrient Phytoplankton Zooplankton) type, which implies five parameters. The method allows us to optimise these parameters by an iterative process of minimisation of a cost function which quantifies the quadratic discrepancy between observations and simulation results. The first part of this note describes how to obtain the adjoint model of the NPZ model allowing us to compute the gradient of the cost function relative to the parameters. Two experiments of artificial data assimilation then show the efficiency of this method, but also its limitations because of non-linearities and sensitivity problems of the model relative to the parameters. To cite this article: Y. Leredde et al., C. R. Geoscience 337 (2005).     

Hydrodynamics in the Gulf of Aigues-Mortes,NW Mediterranean Sea: In situ and modelling data

The Gulf of Aigues-Mortes (NW Mediterranean Sea) is a midshelf zone whose scale is an intermediate between the nearshore scale (0–10 m depth) and the coastal scale (including the whole continental shelf). Its hydrodynamics is investigated for the first time. ADCP, CTD and thermosalinograph data were collected during three short cruises (HYGAM; March 6–7, 20–21, April 5–6, 2005). They were scheduled approximately every 15 days to sample the gulf circulation under different weather conditions. Moreover, the cruise data were used to validate the Symphonie model, a 3D primitive equations circulation model. The circulation features displayed by in situ data were well reproduced by Symphonie. A downscaling modelling approach was implemented, the largest scale being obtained by the replay of the MFSTEP regional model of the North-Western Mediterranean Sea.     

Multibody approach for reactive transport modeling in discontinuous-heterogeneous porous media

Computational Geosciences - In the context of long-term degradation of porous media, the coupling between fracture mechanics and reactive transport is investigated. A reactive transport model in a...