Mesoscale fluvial erosion parameters deduced from modeling the Mediterranean sea level drop during the Messinian (late Miocene)

International audienceAfter a base level drop, rivers are the first components of the landscape to respond by incising into topography. A base level drop results in a knickpoint in the downstream part of river longitudinal profiles. Whether knickpoints are preserved or erased during the upstream propagation of incision is still debated. Preservation and erasure of knickpoints are two end-member processes that work in natural systems at different timescales, different length scales, and different places. The huge (1500 m) and fast (tens of kiloyears) sea level drop in the Mediterranean during the Messinian resulted in the fast propagation of incision far inland. This is especially the case in the Rhone Valley (southern France) where the knickpoint is 300 km from the Mediterranean coast. Numerical modeling of this event has been performed using the ros model, which simulates both erosional and depositional processes in rivers. The best fit between numerical results and geological data is obtained for a nonlinear relation between incision and drainage area and for a small transport length of sediment. This small transport length, at least 2 orders of magnitude lower than the length of the Rhone, suggests that the longitudinal profile relaxed in a diffusive way, so that the initial knickpoint was not preserved. Finally, after a base level fall, the propagation of fluvial incision is very fast at geological timescales (hundreds of kiloyears). Despite this, the diffusive response implies that the time required for restoration of an equilibrium profile is very long

Extending the clinical spectrum of X-linked Tonne-Kalscheuer syndrome (TOKAS):new insights from the fetal perspective

INTRODUCTION: Tonne-Kalscheuer syndrome (TOKAS) is a recessive X-linked multiple congenital anomaly disorder caused by RLIM variations. Of the 41 patients reported, only 7 antenatal cases were described.METHOD: After the antenatal diagnosis of TOKAS by exome analysis in a family followed for over 35 years because of multiple congenital anomalies in five male fetuses, a call for collaboration was made, resulting in a cohort of 11 previously unpublished cases.RESULTS: We present a TOKAS antenatal cohort, describing 11 new cases in 6 French families. We report a high frequency of diaphragmatic hernia (9 of 11), differences in sex development (10 of 11) and various visceral malformations. We report some recurrent dysmorphic features, but also pontocerebellar hypoplasia, pre-auricular skin tags and olfactory bulb abnormalities previously unreported in the literature. Although no clear genotype-phenotype correlation has yet emerged, we show that a recurrent p.(Arg611Cys) variant accounts for 66% of fetal TOKAS cases. We also report two new likely pathogenic variants in RLIM, outside of the two previously known mutational hotspots.CONCLUSION: Overall, we present the first fetal cohort of TOKAS, describe the clinical features that made it a recognisable syndrome at fetopathological examination, and extend the phenotypical spectrum and the known genotype of this rare disorder.</p

Dynamique de l'érosion fluviatile consécutive à une chute du niveau de base. L'exemple de la Crise de Salinité Messinienne

Base-level variations involve a perturbation of the erosional dynamics of a continental system. A base-level drop results in the upstream propagation of an incision that rejuvenates the landscape. This work aims to show how this erosional stage will affect the evolution of a landscape, depending on the parameters of the preexisting morphological system. It is based on an example of preserved base-level drop of large amplitude, which occurred during the Mediterranean Messinian Salinity Crisis, 5.5 Ma ago. Morphological analysis combined with a numerical modeling show that there is a divergence between the network growth and its effects on the long-term evolution of a landscape due to the occurrence of a regional slope line. The absence of a regional slope line can result in a major change such as the capture of the Atlantic waters in the Gibraltar Strait area, inducing the end of the Messinian Salinity Crisis.Les variations du niveau de base entraînent une perturbation de la dynamique érosive d'un système continental. Une chute du niveau de base se traduit par la propagation d'une incision fluviatile vers l'amont entraînant un rajeunissement du paysage. Cette étude a pour but de montrer comment cette érosion affecte l'évolution d'un paysage, suivant les paramètres du système morphologique préexistant. Elle s'appuie sur un exemple préservé de chute du niveau de base de grande ampleur pendant la Crise de Salinité Messinienne en Méditerranée il y a 5.5 Ma. L'étude morphologique des incisions messiniennes couplée à une modélisation numérique montre qu'il existe une dichotomie entre la vitesse de croissance d'un réseau et ses effets sur l'évolution à long terme d'un paysage en présence d'une pente régionale préexistante. L'absence de pente régionale peut conduire à une modification drastique comme la capture de l'Atlantique au niveau de Gibraltar qui a entraîné la fin de la Crise Messinienne

Geomorphological map of the Tiwanaku River watershed in Bolivia: implications for past and present human occupation

International audienceThe Altiplano and more specifically the Titicaca circum-lake sector have recorded several major landscape transformations. In particular, changes in the lake water level lead to a significant vulnerability and contributed to the development of flexible and diverse agropastoral activities of the pre-Columbian and current populations to climate change. The Tiwanaku River, particularly because of the presence of the pre-Columbian Tiwanaku site, has been the subject of several research studies aimed at characterizing the environment of the archaeological site. Here we propose a new synthesis of the geomorphology of the Tiwanaku River watershed based on an interdisciplinary approach (Historical geography and remote sensing, cross combined with field survey). Our results show that the general organization of the drainage system is influenced by lake level and climatic changes. However several watercourses of the Tiwanaku River might be related to pre-Columbian agricultural or protourban structures. Our work allowed to estimate the regressive pattern of the coastline of Lake Titicaca and to identify major changes of the terminal and medium watercourse of the Tiwanaku River over the last 70 years

Wave train model for knickpoint migration

International audienceRivers respond to a drop in their base level by incising the topography. The upstream propagation of an incision, as usually depicted by a knickpoint migration, is thought to depend on several parameters such as the drainage area, lithology, and the amplitude of the base level drop. We first investigate the case of the Messinian Salinity Crisis that was characterized by the extreme base level fall (1500 m) of the Mediterranean Sea at the end of the Miocene. The response of drainage areas of three orders of magnitude (103 to 106 km2) highlights the dominant role of the drainage area (with a square root relationship) in controlling the knickpoint migration after a base level fall. A compilation of mean rates of knickpoint propagation for time durations ranging from 102 to 107 years displays a similar relationship indicating that successive wave trains of knickpoint can migrate in a river: first, wave trains linked to the release of the alluvial cover and then, wave trains related to the bedrock incision, which correspond to the real time response of rivers. Wave trains with very low retreat rates (long lived knickpoints > 1 My) rather correspond to the response time of regional landscape

On the origin of the Strait of Gibraltar

International audienceMost interpretations of the Early Pliocene opening of the Strait of Gibraltar involve a tectonic process. However, no tectonic structure of this age has been unequivocally documented that could account for such a hypothesis. On the other hand, the sea-level drop of the Mediterranean during the Messinian Salinity Crisis has dramatically enhanced continental erosion and in particular regressive fluvial erosion. We show that such erosional process inevitably developed in the Gibraltar area. We finally propose that regressive fluvial erosion was at the origin of the opening of the Strait of Gibraltar

Signification des retraits de knickpoint et évolution du relief : L'exemple messinien

International audienc

How did the Messinian Salinity Crisis end?

The cause of the desiccation of the Mediterranean Sea during the Messinian Salinity Crisis has been widely debated, but its re-flooding remains poorly investigated. Interpretations generally involve tectonic collapse of the Strait of Gibraltar or global sealevel rise, or even a combination of both. The dramatic sea-level fall in the Mediterranean has induced deep fluvial incision all around the desiccated basin. We investigate erosion dynamics related to this base level drop by using the numerical simulator EROS. We show that intense regressive erosion develops inevitably in the Gibraltar area eventually inducing the piracy of the Atlantic waters by an eastward-flowing stream and the subsequent re-flooding of the Mediterranean

Dynamique de l'érosion fluviatile consécutive à une chute du niveau de base (l'exemple de la crise de salinité messinienne)

Les variations du niveau de base entraînent une perturbation de la dynamique érosive d'un système continental. Une chute du niveau de base se traduit par la propagation d'une incision fluviatile vers l'amont entraînant un rajeunissement du paysage. Cette étude a pour but de montrer comment cette érosion affecte l'évolution d'un paysage, suivant les paramètres du système morphologique préexistant. Elle s'appuie sur un exemple préservé de chute du niveau de base de grande ampleur pendant la Crise de Salinité Messinienne en Méditerranée il y a 5.5 Ma. L'étude morphologique des incisions messiniennes couplée à une modélisation numérique montre qu'il existe une dichotomie entre la vitesse de croissance d'un réseau et ses effets sur l'évolution à long terme d'un paysage en présence d'une pente régionale préexistante. L'absence de pente régionale peut conduire à une modification drastique comme la capture de l'Atlantique au niveau de Gibraltar qui a entraîné la fin de la Crise Messinienne.RENNES1-BU Sciences Philo (352382102) / SudocPARIS-Museum-Bib. de géologie (751055215) / SudocSudocFranceF

Cretaceous folding in the Dévoluy mountains (Subalpine Chains, France): gravity-driven detachment at the European paleomargin versus compressional event

International audienceSituée dans les Chaînes subalpines méridionales, la région du Dévoluy-Bochaine offre une " discordance anté-sénonienne " interprétée classiquement comme le résultat d'une phase de compression d'âge turonien. Nous présentons des arguments conduisant au contraire à interpréter cette discordance comme le résultat d'un glissement synsédimentaire majeur sur la pente de la paléomarge européenne. Pendant l'intervalle Tithonique-Crétacé supérieur, le Dévoluy-Bochaine était situé sur la pente joignant la plate-forme du Vercors et le Bassin vocontien (partie profonde du bassin du Sud-Est), dans lequel s'accumulaient glissements en masse et dépôts resédimentés. Sous la discordance, le plissement du Dévoluy affecte les séries allant du Kimméridgien au Cénomanien, détachées en " méga-collapse " sur les " Terres Noires " du Jurassique moyen-supérieur. La troncature du toit de l'unité collapsée résulte de plusieurs facteurs, failles normales, fragmentation des couches encore peu consolidées et érosion par les courants de fond. On ne trouve dans l'interface de discordance ni dépôts continentaux ou paléosols, ni conglomérats de transgression, mais seulement des brèches de pied d'escarpement de faille sous-marine. Les couches sus-jacentes, d'âge essentiellement coniacien-maastrichtien, sont des calci-turbidites chenalisées où les slumpings sont encore fréquents. En conclusion, les massifs du Dévoluy-Bochaine offre le premier exemple, dans les Alpes externes, d'un collapse synsédimentaire majeur comparable aux cas décrits en offshore sur les marges du Niger ou d'Israël