The past thermokarst activities in valleys of northern France and Belgium covered the Upper Weichselian and the Upper Saalian periods. To develop in western Europe, thermokarst first requires an accumulation of ground ice close to the surface progressively stored along the glacial-time permafrost aggradation: it is regionally uncommon during the early glacials, especially on the plateau, but frequent during the Upper Pleniglacials in valleys. These features mostly relate to various frost mounds created by injection and segregated ices. The role of ice wedges is really very limited in this zone of southern extent of the European palaeo-permafrost on plateau and terraces. Thermokarst events are mostly susceptible to occur during the coldest part of the glacial. With a more progressive warming or a retrogressive thermokarst triggered by erosion, as in Arctic today, deformations are more gradual, in direct relation with the rheological properties of the sediments and usually local drainage. They are in concurrence with the vegetation dynamic that will limit its expression. Thermokarst events are in first order orbitally forced under control of a maximum insolation and a minimum in precession, as well as during the Weichselian and the Saalian. They are moreover, associated with abrupt warming transmitted by Dansgaerd Oeschger events. Snowiness and mild winter temperatures are probably the main triggers for thermokarst activity as of today. Other events can be triggered by solar activity as at 20 ka or perhaps enhanced by major ash splay as during the MIS 6b Zeiffen interstadial. Thermokarst events are usually followed on the continent by a reorganization of the rivers from braided to meandering systems. Published in : Geomorphology (2019), vol. 327, pp. 613-628 DOI: 10.1016/j.geomorph.2018.08.036 Status : Postprint (Author’s version)

The past thermokarst activities in valleys of northern France and Belgium covered the Upper Weichselian and the Upper Saalian periods. To develop in western Europe, thermokarst first requires an accumulation of ground ice close to the surface progressively stored along the glacial-time permafrost aggradation: it is regionally uncommon during the early glacials, especially on the plateau, but frequent during the Upper Pleniglacials in valleys. These features mostly relate to various frost mounds created by injection and segregated ices. The role of ice wedges is really very limited in this zone of southern extent of the European palaeo-permafrost on plateau and terraces. Thermokarst events are mostly susceptible to occur during the coldest part of the glacial. With a more progressive warming or a retrogressive thermokarst triggered by erosion, as in Arctic today, deformations are more gradual, in direct relation with the rheological properties of the sediments and usually local drainage. They are in concurrence with the vegetation dynamic that will limit its expression. Thermokarst events are in first order orbitally forced under control of a maximum insolation and a minimum in precession, as well as during the Weichselian and the Saalian. They are moreover, associated with abrupt warming transmitted by Dansgaerd Oeschger events. Snowiness and mild winter temperatures are probably the main triggers for thermokarst activity as of today. Other events can be triggered by solar activity as at 20 ka or perhaps enhanced by major ash splay as during the MIS 6b Zeiffen interstadial. Thermokarst events are usually followed on the continent by a reorganization of the rivers from braided to meandering systems. (C) 2018 Elsevier B.V. All rights reserved.

This study presents the first application of the U/Pb dating method to highly Pb-depleted diagenetic geodic calcites of the Jurassic formations of the Paris Basin that leads to a reappraisal of the palaeohydrological history of this region. Composite U/Pb ages from multiple geodes, combined with delta O-18 analyses, reveal two main phases of diagenetic fluid circulations linked with major regional tectonic events. Dogger formations recorded a first diagenetic fluid episode at 147.8 +/- 3.8 Ma, i.e. at the very beginning of the emersion of the basin during the Tithonian period and 30 Ma earlier than previously assumed. delta O-18 results confirmed that most of the calcitic cement phases that closed the porosity of these formations precipitated at the beginning of the Cretaceous period. Oxfordian formations recorded another major meteoric fluid circulation at 33.5 +/- 2.8 Ma related to the initial stage of the European Cenozoic Rift System (ECRIS). Consequently, the porosity of the Mesozoic formations of the studied area may have been closed sooner than previously thought, before the main ECRIS rifting phase of Oligocene age. This study shows that U/Pb dating of secondary geodic calcite offers a new powerful way for reconstructing the coupled palaeohydrological and diagenetic history of sedimentary basins.

A thermokarst is a collapse feature resulting from the thawing of ice‐rich permafrost or of massive ice of various origins. Little attention has been paid to the sedimentary fabric resulting from this type of collapse, except for glaciotectonic features. In western Europe, two palaeo‐forms are commonly studied: lithalsas and ice‐wedge casts. Collapsed pingos are much rarer. Very few papers have compiled present‐day and fossil data. Here, field data collected from quarries in the eastern Paris Basin were analysed, providing useful records of thermokarst collapses in alluvial calcareous silts, sands, and gravels. These forms have a circular shape when viewed on satellite images. Permafrost is attested regionally by the recurrent occurrence of meter‐sized pattern grounds at the surface of the chalk and of ice‐wedge casts. Traces of segregation and reticulate ice are common. These features are primarily connected to a major interstadial, c . 150 ka BP , orbitally forced and commonly associated with a major glacial retreat. They occur both in drained and waterlogged situations, resulting in a specific pattern of deformation. They are controlled by the brittle and plastic behaviour of sediments and resemble passive glaciotectonism. Normal and reverse faults, with the offset decreasing downward, are common, and those with local shear are reported. Lithalsas, seasonal frost blisters, spring frost blisters and perhaps pingos seem to have formed. Most of these deformations correspond to thermokarst sinkholes bordered by gravitational collapse faults. The offset of these faults increases towards the surface, and the faults have been recurrently confused with neotectonism triggered by palaeo‐earthquakes. However, there are no faults beneath the observed deformation features, and the region lacks recorded seismic activity over the last century. Our data may be helpful in interpreting similar structures elsewhere.

Four stepped fluvial terraces along the Aube River Valley have been dated using the Electron Spin Resonance (ESR) method applied on optically bleached quartz. The obtained chronology indicates that the deposition of the terraces system was initiated during the Middle Pleistocene, i.e. later that in other valleys of Parisian Basin area (Cher, Creuse, Somme), in which the oldest fluvial sheets are coeval of Lower Pleistocene times. This pattern raises the question of the preservation of the alluvial sheets, of the Aube river course at that time or even of its existence. On the other hand, the evolution of the system follows the general model proposed for several rivers of the northern Parisian Basin (Seine, Somme, Yonne), each sheet corresponding to the depositional balance of a Glacial/Interglacial cycle.

Quatre nappes fluviatiles fossiles étagées sur les versants de la vallée de l'Aube ont fait l'objet de datations par la méthode de la résonance de spin électronique (ESR) appliquée aux grains de quartz optiquement blanchis. Les âges obtenus indiquent que la mise en place du système de terrasses alluviales s'est initiée pendant le Pléistocène moyen. Cette mise en place semble donc différer sensiblement de celles observées dans d'autres vallées du Bassin parisien (Cher, Creuse ou Somme), qui ont débuté dès le Pléistocène inférieur et pose la question pour l'Aube de la préservation des nappes alluviales, de l'existence ou de la position de son tracé au Pléistocène inférieur. La chronologie de ces nappes alluviales du Pléistocène moyen s'inscrit dans le modèle général de mise en place proposé pour plusieurs rivières du nord du Bassin de Paris (Seine, Somme, Yonne), chaque nappe représentant le bilan d'un cycle Glaciaire/Interglaciaire.

On earth, landscape morphology is mainly controlled by rivers evolutions and their interactions with hillslopes. But hydrographic network may be re-organized by stream capture and modify deeply the relief. This transition may be induced by several mechanisms (diversion, headward erosion, avulsion, or subterranean filling up). It has interested numerous scientists since a long time (Davis 1895, Blache 1943, Lesson-Quinif 2001 & Le Roux-Harmand 1997-2009...). Here we focus on stream piracies by headward erosion, when an actively eroding low level stream (called the captor) encroaches on the drainage of a nearby stream flowing at a higher level (called the diverter) and diverts part of the water of the higher stream. During the last decades, several landscapes evolution models (LEM) have been developed to quantify the topography evolution with diffusion and advection equations. These models play an important role in sharpening our thinking to better understand the interaction between landscape evolution processes. LEM were developed basically to simulate erosion, tectonic and climate at different scales of time and space. But, these models were not designed to describe specific mechanisms as the stream capture. It's one of the aims of this work to evaluate LEM for this purpose. In this paper, we develop a 1D model based on LEM equations to investigate the stream piracy by headward erosion responses to climatic or tectonic changes. This model incorporates the most common equations used in quantitative geomorphology; diffusion in hillslope, advection in river (detachment-limited mode) and an inequality based on slope and drainage area for the limit between these two domains (Montgomery and Dietrich, 1988). First, simulations on analytical cases highlight the stream head progression mechanism, and the results indicate that this progression rate is mainly controlled by the slope at the captor source. Consequently, the aggradation of the diverter or (and) the incision of the captor accelerate the process. Then, a predictive study with an improved version of GOLEM (software developed by Tucker & Slingerland in 1994) on the Meuse basin shows that several piracies may probably occur in the future. A comparison with the 1D model gives similar results. The simplicity and the flexibility of the 1D model allow complex simulations in the Meuse basin taking into account: lithological differences of outcropping layers, Meuse deposition tendency, etc. Once the 2D simulations or topography analysis locate potential captures, 1D simulation may intensively be used, as it presents many advantages; weak execution time, simple limits conditions setting, less time for data preparation, etc. Consequently, a sensitivity analysis to estimate piracies ages is realized with the developed 1D model.

Knowledge of Oxfordian karst in the area between Meuse and Marne : insights by hydrological analyses. In the Lorraine region, Oxfordian limestones have a thickness up to 250 meters, but despite of that, they appear poorly karstified, except in the the Meuse/Marne interfluvial area. On this plateau, named "Haut-Pays", karst is known since the Roman epoch at Grand, and from the 19th century onward also at Trampot. Since the 1960ies, the karst of this sector was subject of many scientific investigations, especially speleological, which led to an inventory of exo-and endokarstic forms where possible (Hadès network). Colorimetric tracer tests made it possible to establish models of underground water circulation in the limestones. Finally, the oxfordian karst of this sector already was the subject of many works. However, results were obtained only from specific measurements, either in time or in space. The investigation of this karstic system, starting with recent hydrometric data (2007-2008), being conducted over at least a hydrological year, brings a new light on this karst. On an annual scale, the hydrological balances make it possible to calculate the surfaces of the catchment areas to the discharge systems. The functional analysis, starting with the medium daily of hourly discharge, makes it possible to specify the nature of the oxfordian karst on the plateau, where this geological formation outcrops. It feeds the regional artesian aquifer flowing towards the center of the Paris basin.

Helium concentration measurements made on water and rock samples collected at various depths along a 2000 m depth borehole drilled in the eastern part of the Paris basin and reaching the Triassic conglomerates were used to establish a vertical profile of dissolved helium concentration throughout the entire Mesozoic sedimentary pile. Wireline logging tools were used to measure rock density, porosity and U and Th contents every 15 cm in the various formations. Samples from the deepest Muschelkalk and Buntsandstein show a very good agreement between measured and calculated 4He porewater contents. Shallower levels show lower and lower 4He concentrations compared to calculated values when going upwards. The data set obtained by wireline logging measurements was used as inputs for numerical simulations of 1D He production/diffusion throughout the 2000 m profile. Several assumptions regarding the transport properties in the various sedimentary layers were tested and all were found to yield fairly good agreement between modeled and measured He concentrations. There is no need to invoke either a transient regime or a deep crustal He flux in this “quiet” (seismically inactive) part of the Paris basin. Moreover, the modeling results suggest that the Keuper massive halite level associated with the upper Muschelkalk pre-evaporitic series efficiently isolates the overlying layers from any input from deeper formations in the Meuse/Haute Marne area.

A fully coupled three-dimensional groundwater flow and heat transport (convection–conduction) model has been developed, including permafrost. The model covers the entire Paris basin and is focused on the Meuse/Haute-Marne Sector area and the Bure investigation site. The model was calibrated on the basis of the present hydro-thermal situation. The studied time period corresponds to what is considered a typical climatic cycle of length 130,000 year. A build-up of a superficial glacial ice mass is not included in the model; it is assumed that accumulated snow will melt during the summer months. The temperature boundary condition on top of the model is specified as a time-varying surface temperature. The temperatures are derived from an estimate of the future climatic evolution. It is the changes with time of the prescribed temperatures along the topography that drives all changes in groundwater flow, temperature and permafrost inside the model. The simulations are transient, but the initial condition of the base case represents a steady state situation. The simulated time period, for reaching a steady state situation of groundwater flows and temperatures in the deep and highly permeable layers of the Dogger (in the Sector area) is considerable (in the range of 50,000 years), depending on perturbation studied (e.g. a change in surface temperature of 5°) and convergence criteria. The simulated depth of the permafrost varies in space and time during the studied glacial periods. Within the area studied (the Sector area), the simulated permafrost reaches a maximum depth of approx. 110 m. This is a median depth taking into account the spatial distribution of the permafrost. The lowest simulated temperature in the lower parts of the Callovo–Oxfordian clay stone, in the immediate vicinity of the Bure investigation site (in the Sector area), is approx. 14.5 °C, which is approx. 7.5 °C lower than the initial temperature (22 °C). A full reversion back to the initial temperatures will not occur during the studied climatic cycle. There are no dramatic changes in size and direction of the groundwater flow, when considering the climatic cycle studied and the deeper geological layers directly above and below the Callovo–Oxfordian clay stone, downstream of the Bure site. The largest change will occur during periods with large extension of permafrost; the flow is reduced with approximately 10% through 25%, in relation to the initial flow (considering median values of the spatially varying flow field). The changes in the Dogger units are smaller than the changes in the Oxfordian units. The groundwater flow at great depths has not fully reverted to the initial flow situation at the end of the studied climatic cycle. When considering near-surface layers and outcrops of highly permeable materials, the situation will be very different to that at greater depths. With extensive permafrost, hydraulic conductivity and recharge will be reduced to zero, the head values below the permafrost may fall as much as 50 m and the groundwater flow close to the outcrops will be reduced accordingly.

(1) IMEP, UMR 6116 du CNRS, Europole Mediterraneen de L’Arbois, Bâtiment Villemin, BP 80, 13545 Aix-en-Provence Cedex 04, France. valerie.andrieu@univ-cezanne.fr, (2) LSCE Orme, Bât. 709, Orme des Merisiers, 91191 Gif sur Yvette, France, (3) Department of Geology, Lund University, Solvegatan 13, SE-223 62 Lund, Sweden, (4) LPAP, Universite de Liege, Bat. B5C, 17 Allee du Six Aout, B-4000, Liege, Belgium, (5) Andra, Direction Scientifique, Milieu Geologique, 1-7 rue Jean Monnet, 92298 Châtenay-Malabry, France, (6) Institut des Sciences de la Terre d’Orleans (ISTO), UMR 6113 du CNRS, 45067 Orleans Cedex, France, (7) Lamont-Doherty Earth Observatory, Columbia University, Palisades, New York 10964, USA, (8) EDYTEM, Universite de Savoie, 73376 Le Bourget du Lac, France, (9) Universitat Bern, Institut fur Geologie, Baltzerstrasse 1-3, 3012 Bern, Switzerland, (10) Institute of Geology, Chinese Academy of Sciences, P.O. Box 9825, Beijing 100029, China