The association between bubble trails and folia: a morphological and sedimentary indicator of hypogenic speleogenesis by degassing, example from Adaouste Cave (Provence, France)

Bubble trails are subaqueous features in carbonate caves, which are made by the corrosion of ascending carbon dioxide bubbles.Folia are calcite deposits resembling inverted rimstone dams in saturated pools. Based on morphological studies in Adaouste Cave(Provence, France) and on studies elsewhere in the world, we propose a new genetic model for folia, close to the model of Green(1991). The association of bubble trails and folia, occurring on overhanging walls, is interpreted to be an indicator of hypogenicdegassing occurring just below the water table. The associatio

Quantifying Biogenic Versus Detrital Carbonates on Marine Shelf: An Isotopic Approach

International audienceThe terrigenous sedimentary budget of passive margins, records variations in past sedimentary fluxes, and thus can be used to infer past variations of Earth surface deformation processes or climate change. Accurate estimates of sediment fluxes over various times and spatial scales are therefore crucial. Traditionally, offshore sediment volume determination only considers siliciclastic accumulation, the carbonate fraction (i.e., CaCO 3) being considered only as in situ production. Here we propose a new geochemical methodology to decipher and quantify the number of detrital carbonates in comparison to in situ produced biogenic carbonates. This isotopic approach enables considering the export of detrital carbonates and investigating its effect on sediment budgets. This study, located in the Gulf of Lion, is based on a 300 m long sediment borehole located near the shelf break and covering the last 500 000 years (i.e., five glacial-interglacial periods). Strontium isotope (87 Sr/ 86 Sr) of carbonate fractions (0.70809 to 0.70858) are significantly less radiogenic than modern seawater (i.e., 0.7092) and show fluctuations in agreement with stratigraphic and climatic variations. These results suggest an unsuspected high export of detrital carbonates from the catchment area during both glacial (between 55 and 85% of the sedimentary carbonate fraction) and interglacial (between 30 and 50%) conditions. Thus, not only do detrital carbonate fluxes need to be factored into sediment flux calculations, but these results also suggest that detrital carbonate components could potentially have a strong influence on bulk carbonate 87 Sr/ 86 Sr ratios when not obtained from micro drilled biogenic carbonates, such as the entirety of the Precambrian Sr chemostratigraphic record

Découverte et étude de remplissages karstiques allochtones d’âge miocène dans l’Obiou (Dévoluy, Alpes françaises) Implications géomorphologiques et paléogéographiques

International audienceAt the mountainside of Obiou (2 789 m) located in the Dévoluy massif (Southwestern Alps) a fortunate discovery has revealed the presence of allochthonous crystalline pebbles excavated from marmot holes. Successive prospecting in the surrounding caves have permitted to identifycrystalline allochthonous sediments such as conglomerates, sands and clays, which formed endokarstic deposits. According to petrographic diversity with presence of granite, orthogneiss, varia gneiss, migmatites, amphibolic gneiss, volcanic basic rocks, sandstones and even limestone with nummulites, these alluvions originate from the SW of the Ecrins massif (Champsaur and Valgaudemar), the localities which are nowadays drained by the Drac River, situated some 1 600 m below the studied caves. These alluvions were analyzed using cosmogenic nuclides (10Be, 26Al, 21Ne), in order to determine their burial ages. However, the dating was compromised due to 26Al concentrations being bellow the limit of quantification (very old burial ages, probably more than 5 Ma). Nevertheless, one sample was analyzed for 10Be/21Ne indicating 15,6 ± 3,8 Ma burial age, which corresponds to Miocene. Even though, our burial dating is quite large due to analytical limitations, the caves in Obiou should be considered as important geomorphological marker of the ancient Drac River drainage (called “paleo-Drac”), during the middle Miocene. Furthercosmogenic nuclide analyses are conducted, in order to precise the burial age of the alluvions and thus frame the incision and uplift rates of this part of the French Alps.Sur les flancs de l’Obiou (2 789 m) dans le massif du Dévoluy (Hautes-Alpes et Isère, France), une découverte fortuite a été réalisée : celle de galets cristallins affleurant, depuis un terrier de marmottes, au beau milieu d’un éboulis calcaire. La prospection de plusieurs cavités environnantes a mis au jour la présence d’alluvions cristallins allochtones sous forme de conglomérats, sables et argiles constituant une série de remplissages endokarstiques. Du point de vue pétrographique, le spectre compte notamment des granites, orthogneiss, gneiss divers, migmatites, gneiss amphiboliques, roches volcaniques basiques, mais aussi des grès, et même des calcaires gréseux à nummulites. D’après cette pétrographie, laprovenance de ces alluvions se situe dans le S-O du massif des Écrins (Champsaur et Valgaudemar), une zone des massifs cristallins externes actuellement drainée par le Drac, lequel s’écoule à environ 1 600 m en contrebas des cavités étudiées. Nous avons tenté de déterminer la durée del’enfouissement de ces alluvions en utilisant des nucléides cosmogéniques produits in situ (10Be, 26Al, 21Ne). Du fait de la faible teneur en 26Al en deçà de la limite de détection, les âges d’enfouissement seraient supérieurs à 5 Ma. Pour un échantillon dont la teneur en 21Ne a été mesurée, le rapport 10Be/21Ne permet une estimation de la durée d’enfouissement aux alentours de 15,6 ± 3,8 Ma, donnant un âge miocène.Au regard de ces âges, les cavités de l’Obiou doivent être considérées comme un niveau repère traduisant la position d’un ancien réseau hydrographique du « paléo-Drac » au Miocène moyen. Des analyses complémentaires de 21Ne couplées au 10Be sont actuellement entreprises pour préciser l’âge d’enfouissement de ces alluvions afin de parvenir à mieux contraindre les taux d’incision et de soulèvement de ce secteur des Alpes françaises

Hydrogeological insights at Stromboli volcano (Italy) from geoelectrical, temperature, and CO2 soil degassing investigations

Finding the geometry of aquifers in an active volcano is important for evaluating the hazards associated with phreato-magmatic phenomena and incidentally to address the problem of water supply. A combination of electrical resistivity tomography (ERT), self-potential, CO2, and temperature measurements provides insights about the location and pattern of ground water flow at Stromboli volcano. The measurements were conducted along a NE-SW profile across the island from Scari to Ginostra, crossing the summit (Pizzo) area. ERT data (electrode spacing 20 m, depth of penetration of ~200 m) shows the shallow architecture through the distribution of the resistivities. The hydrothermal system is characterized by low values of the resistivity (2000 Ω m) except on the North-East flank of the volcano where a cold aquifer is detected at a depth of ~80 m (resistivity in the range 70?300 Ω m). CO2 and temperature measurements corroborate the delineation of the hydrothermal body in the summit part of the volcano while a negative self-potential anomaly underlines the position of the cold aquifer

Role of sediment in speleogenesis : sedimentation and paragenesis

Although the effects of sedimentation in caves have been recognised for many years, its role in speleogenesis is frequently overlooked. Influxes of sediment into a cave system fundamentally alter the way cave passages develop, either by alluviation in a vadose environment, forcing lateral corrosion and the development of notches, or by upwards dissolution in a phreatic environment through a process known as paragenesis. Sediment influxes affect the hydrological functioning of a karst aquifer by changing the way conduits behave and subsequently develop both in plan and long section. Here we give an overview of the mechanisms of cave sedimentation and describe how the process of alluviation and paragenesis affect speleogenesis. A characteristic suite of meso- and micro-scale dissolutional features can be used to recognise paragenetic development, which is reviewed here. In a vadose environment these include alluvial notches, whilst in a phreatic environment, half tubes, anastomoses and pendants, bedrock fins and paragenetic dissolution ramps result. Using these to identify phases of sedimentation and paragenesis is crucial for reconstructing denudation chronologies from cave deposits. We suggest that sedimentation and paragenesis are most likely to occur in certain geomorphological situations, such as ice marginal and periglacial environments, beneath thick residual soils and where rivers can transport fluvial sediment into a cave, either via stream sinks or back-flooding

Hydrogeological insights at Stromboli volcano (Italy) from geoelectrical, temperature, and CO2 soil degassing investigations

Finding the geometry of aquifers in an active volcano is important for evaluating the hazards associated with phreatomagmatic phenomena and incidentally to address the problem of water supply. A combination of electrical resistivity tomography (ERT), self-potential, CO2, and temperature measurements provides insights about the location and pattern of ground water flow at Stromboli volcano. The measurements were conducted along a NE-SW profile across the island from Scari to Ginostra, crossing the summit (Pizzo) area. ERT data (electrode spacing 20 m, depth of penetration of 200 m) shows the shallow architecture through the distribution of the resistivities. The hydrothermal system is characterized by low values of the resistivity (<50 W m) while the surrounding rocks are resistive (>2000 W m) except on the North-East flank of the volcano where a cold aquifer is detected at a depth of 80 m (resistivity in the range 70–300 W m). CO2 and temperature measurements corroborate the delineation of the hydrothermal body in the summit part of the volcano while a negative self-potential anomaly underlines the position of the cold aquifer. Citation: Finizola, A., A. Revil, E. Rizzo, S. Piscitelli, T. Ricci, J. Morin, B. Angeletti, L. Mocochain, and F. Sortino (2006), Hydrogeological insights at Stromboli volcano (Italy) from geoelectrical, temperature, and CO2 soil degassing investigations, Geophys. Res. Lett., 33, L17304, doi:10.1029/ 2006GL02684

Hydrogeological insights at Stromboli volcano (Italy) from geoelectrical, temperature and CO2 soil degassing investigations

Finding the geometry of aquifers in an active volcano is important for evaluating the hazards associated with phreatomagmatic phenomena and incidentally to address the problem of water supply. A combination of electrical resistivity tomography (ERT), self-potential, CO2, and temperature measurements provides insights about the location and pattern of ground water flow at Stromboli volcano. The measurements were conducted along a NE-SW profile across the island from Scari to Ginostra, crossing the summit (Pizzo) area. ERT data (electrode spacing 20 m, depth of penetration of 200 m) shows the shallow architecture through the distribution of the resistivities. The hydrothermal system is characterized by low values of the resistivity (<50 W m) while the surrounding rocks are resistive (>2000 W m) except on the North-East flank of the volcano where a cold aquifer is detected at a depth of 80 m (resistivity in the range 70–300 W m). CO2 and temperature measurements corroborate the delineation of the hydrothermal body in the summit part of the volcano while a negative self-potential anomaly underlines the position of the cold aquifer

Aléa et risque sismique en Provence: tectonique active et sismotectonique des Failles de la Moyenne Durance et de la Trévaresse

International audienceLe séisme de Lambesc de 1909 est une illustration du risque sismique auquel la Provence est exposée. L'approche de la tectonique active et de la paléosismologie appliquée aux failles de la Moyenne Durance et de la Trévaresse, complémentaire de la sismologie instrumentale, montre que ces accidents ont des taux de déplacement d'environ 0,1 mm/an. La première, qui constitue la bordure orientale du bassin du Sud-Est, est active depuis le Paléozoïque. Son activité actuelle est limitée à l'épaisse couverture sédimentaire qui paraît découplée mécaniquement du socle. Les déformations plio-quaternaires le long de cet accident indiquent un mouvement décrochant senestre à composante inverse. Cette activité peut s'expliquer, partiellement, par une poussée alpine vers le sud combinée à « l'effondrement » gravitaire de la chaîne. La faille de la Moyenne Durance comprend plusieurs segments. L'un de ces segments paraît être en connexion avec la faille de la Trévaresse. Celle-ci, très probablement responsable du séisme de 1909, a formé l'anticlinal de rampe de la Trévaresse. La question des effets de site est illustrée par les caractéristiques lithologiques et topographiques dans le secteur de Vernègues. On envisage également le rôle du remplissage sédimentaire des canyons messiniens dans l'apparition de dégâts à la surface du sol. Mots-clés : Failles actives, déformations récentes, couverture provençale, séisme de Lambesc, canyons messiniens, effets de site. Abstract:

A two-step process for the reflooding of the Mediterranean after the Messinian Salinity Crisis

The Messinian Salinity Crisis is well known to have resulted from a significant drop of the Mediterranean sea level. Considering both onshore and offshore observations, the subsequent reflooding is generally thought to have been very sudden. We present here offshore seismic evidence from the Gulf of Lions and re-visited onshore data from Italy and Turkey that lead to a new concept of a two-step reflooding of the Mediterranean Basin after the Messinian Salinity Crisis. The refilling was first moderate and relatively slow accompanied by transgressive ravinement, and later on very rapid, preserving the subaerial Messinian Erosional Surface. The amplitude of these two successive rises of sea level has been estimated at ≤500 m for the first rise and 600–900 m for the second rise. Evaporites from the central Mediterranean basins appear to have been deposited principally at the beginning of the first step of reflooding. After the second step, which preceeded the Zanclean Global Stratotype Section and Point, successive connections with the Paratethyan Dacic Basin, then the Adriatic foredeep, and finally the Euxinian Basin occurred, as a consequence of the continued global rise in sea level. A complex morphology with sills and sub-basins led to diachronous events such as the so-called ‘Lago Mare’.This study helps to distinguish events that were synchronous over the entire Mediterranean realm, such as the two-step reflooding, from those that were more local and diachronous. In addition, the shoreline that marks the transition between these two steps of reflooding in the Provence Basin provides a remarkable palaeogeographical marker for subsidence studies

A two-step process for the reflooding of the Mediterranean after the Messinian Salinity Crisis

The Messinian Salinity Crisis is well known to have resulted from a significant drop of the Mediterranean sea level. Considering both onshore and offshore observations, the subsequent reflooding is generally thought to have been very sudden. We present here offshore seismic evidence from the Gulf of Lions and re-visited onshore data from Italy and Turkey that lead to a new concept of a two-step reflooding of the Mediterranean Basin after the Messinian Salinity Crisis. The refilling was first moderate and relatively slow accompanied by transgressive ravinement, and later on very rapid, preserving the subaerial Messinian Erosional Surface. The amplitude of these two successive rises of sea level has been estimated at ≤500 m for the first rise and 600-900 m for the second rise. Evaporites from the central Mediterranean basins appear to have been deposited principally at the beginning of the first step of reflooding. After the second step, which preceeded the Zanclean Global Stratotype Section and Point, successive connections with the Paratethyan Dacic Basin, then the Adriatic foredeep, and finally the Euxinian Basin occurred, as a consequence of the continued global rise in sea level. A complex morphology with sills and sub-basins led to diachronous events such as the so-called 'Lago Mare'.This study helps to distinguish events that were synchronous over the entire Mediterranean realm, such as the two-step reflooding, from those that were more local and diachronous. In addition, the shoreline that marks the transition between these two steps of reflooding in the Provence Basin provides a remarkable palaeogeographical marker for subsidence studies. © 2011 Blackwell Publishing Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists