Abstract The aim of this study is to understand the water and contaminant (nitrate and atrazine) transfer in the unsaturated zone (UZ) of Chalk. For this, the underground quarry of Saint-Martin-le-Nœud is an exceptional site because it permits entry to the aquifer at the limit between the UZ and the saturated zone (SZ). It provides direct access to the water table: underground lakes and the output of the UZ (percolation water at the ceiling). The thicknesses of the UZ and the clay-with-flints (CwF) layer that overlie the Chalk, vary along the 1200 m length of the quarry. From 2012, the chemical evolution and the flow variability of groundwater are characterized for 16 sites with different UZ properties. Chalk groundwater has highly spatially variable hydrodynamic behaviour and geochemical properties. A peak of contaminants is observed in the UZ around 15–20 m depth, with differing behaviours of nitrate and atrazine. The downward matrix water velocity is estimated to be from 0.3 to over 0.72 m a −1 , and the water table is mainly composed of ‘old’ water resulting from transfer through the matrix. A thick CwF layer modifies (1) the transfer processes: surface water is stored in a sort of ‘near-surface perched groundwater’, the infiltration is concentrated by preferential pathways; and (2) water quality: pesticides degradation processes occur in the perched groundwater.

ABSTRACT The concept of biostratigraphy was a significant step in the evolution of geoscience. Alexandre Brongniart (1770–1847) and Georges Cuvier (1769–1832) were key contributors to developing the subdiscipline as they worked to decode the stratigraphy of the Paris Basin in the first decades of the nineteenth century. Their illustrations of fossils, local geologic columns, and a regional geologic map played a decisive role in furthering an understanding of the value of paleontology in the service of illuminating Earth history.

Abstract The Toarcian Oceanic Anoxic Event (T-OAE) is marked by major palaeoenvironmental and palaeoceanographical changes on a global scale, associated with a severe disturbance of the global carbon cycle and organic-rich facies deposition. Here, a multiproxy approach (petrographic and geochemical techniques) was applied to the study of the organic content of the T-OAE of the Paris Basin, whose phytoplanktonic origin has been previously inferred by its geochemical signature. The top of the tenuicostatum Zone is characterized by palynomorphs and marine phytoplankton-derived amorphous organic matter (AOM), representing a proximal marine environment with emplacement of euxinic conditions at the top (total organic carbon/sulfur content and increase in AOM). At the base of the serpentinum Zone the proliferation of bacterial biomass begins, with phytoplankton playing a secondary role. This indicates the development of stagnant and restrictive conditions in a proximal environment, with water column stratification (neohop-13(18)-ene). The majority of the serpentinum Zone is dominated by bacterial biomass, suggesting a marine environment with bottom-water stagnation, possibly related to basin palaeogeomorphology and circulation patterns, with episodic euxinia. This therefore suggests that the T-OAE organic fraction is dominated by bacterial biomass, not phytoplankton, showing the importance of an integrated approach to the determination of the organic facies.

Abstract: The properties of sandstones are strongly affected by formation of minerals in the pore space during diagenesis. In many sandstones, quartz overgrowths are the most important pore-filling cements and show a characteristic trace element composition. The most important impurities are Al, Li, H and Ge. The Al concentration of quartz may reach up to several 1000 µmol mol −1 and is assumed to reflect the composition of the porewater. Geochemical modelling of the activity ratio of Al and Si revealed a minimum at nearly neutral to slightly acid conditions. This minimum shifts to lower pH with increasing temperatures. Due to complexing, organic acids may strongly affect the Al solubility especially in acidic water at low temperatures. There is a linear correlation between Al and Li, indicating their incorporation in a combined [AlO 4 |Li] centre. Since Li only accounts for 10–30% of the Al concentration, the remaining Al needs to be balanced by H. The ratio of Li/H-compensated Al centres seems to depend on the Li activity and the pH in the aqueous solution. Germanium concentrations in quartz cements are slightly higher than the crustal average and they show a weak correlation with Al. The excess of Ge in authigenic quartz requires pre-enrichment, probably by formation of kaolinite. Possible applications of trace element analyses of authigenic quartz include discrimination of different sources that contribute to the supply of silica, enhanced understanding of inhomogeneities that are related to cementation and possible tracking of fluid migration.