Philippe Audra

The effect of the Messinian Deep Stage on karst development around the Mediterranean Sea. Examples from Southern France

It is difficult to explain the position and behaviour of the main karst springs of southern France without calling on a drop in the water table below those encountered at the lowest levels of Pleistocene glacio-eustatic fluctuations. The principal karst features around the Mediterranean are probably inherited from the Messinian period (“Salinity crisis”) when sea level dropped dramatically due to the closing of the Straight of Gibraltar and desiccation of the Mediterranean Sea. Important deep karst systems were formed because the regional ground water dropped and the main valleys were entrenched as canyons. Sea level rise during the Pliocene caused sedimentation in the Messinian canyons and water, under a low hydraulic head, entered the upper cave levels. The powerful submarine spring of Port-Miou is located south of Marseille in a drowned canyon of the Calanques massif. The main water flow comes from a vertical shaft that extends to a depth of more than 147 m bsl. The close shelf margin comprises a submarine karst plateau cut by a deep canyon whose bottom reaches 1,000 m bsl. The canyon ends upstream in a pocket valley without relation to any important continental valley. This canyon was probably excavated by the underground paleoriver of Port-Miou during the Messinian Salinity Crisis. Currently, seawater mixes with karst water at depth. The crisis also affected inland karst aquifers. The famous spring of Fontaine de Vaucluse was explored by a ROV (remote observation vehicle) to a depth of 308 m, 224 m below current sea level. Flutes observed on the wall of the shaft indicate the spring was formerly an air-filled shaft connected to a deep underground river flowing towards a deep valley. Outcroppings and seismic data confirm the presence of deep paleo-valleys filled with Pliocene sediments in the current Rhône and Durance valleys. In the Ardèche, several vauclusian springs may also be related to the Messinian Rhône canyon, located at about 200 m below present sea level. A Pliocene base level rise resulted in horizontal dry cave levels. In the hinterland of Gulf of Lion, the Cévennes karst margin was drained toward the hydrologic window opened by the Messinian erosional surface on the continental shelf.

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

INTRODUCTION Bubble trails are small channels developed subaqueously in the walls of carbonate caves by corrosion by carbon dioxide bubbles. Folia are among the most curious and rarest calcite speleothems: these subaqueous calcite coatings cover overhanging walls and resemble inverted rimstone dams. Their origin is still debated and several hypotheses have been suggested, among which two main hypotheses are: deposits at the surface of water bodies (pools with oscillating water level) or subaqueous speleothems in thermal caves. In the Adaouste Cave, bubble trails and folia are intimately associated, which is a paradox involving both corrosion and deposition, respectively. This paper presents a detailed analysis of their morphology and spatial distribution that provides a better understanding of their origin and significance. Our observations of bubble trails and folia from

Hypogenic origin of Provalata Cave, Republic of Macedonia: a distinct case of successive thermal carbonic and sulfuric acid speleogenesis

temperature, which leads to a progressive increase in CaCO3 solubility, and also a drastic drop of solubility near the water table due to the loss of CO2. As a result a geochemical zone of carbonate dissolution and zone of carbonate precipitation appear (Dublyansky, 2000a). Where H2S rich waters mix with shallower oxygen rich waters, sulfuric acid forms at or near water table, which rapidly dissolves the carbonate rocks (Egemeier, 1981). This process is known as sulfuric INTRODUCTION

Hypogene Karst Regions and Caves of the World

Signs of hypogenic speleogenesis have been detected in a number of caves of the Murcia Region (SE Spain), in some cases revealing active speleogenetic mechanisms rarely observed in hypogene cavities elsewhere in the world. Here, we investigate the hypogenic morphologies and speleothems of four caves in this region, namely Sima de la Higuera, Sima Destapada, Cueva del Agua and Cueva del Puerto. Also, other ten caves showing evidence for hypogenic speleogenesis has been preliminary described. Processes related to ancient and current hydrothermal activity, the discordance of permeability structures in the adjacent beds and the spatial arrangement of the regional hydrogeology have given rise to maze patterns and typical subaqueous hypogenic morphologies. These include spongework mazes, rising wall channels and shafts, feeders, bubble trails, solution pockets, megascallops and rising of chains cupolas, among others. Carbonic acid speleogenesis is responsible for the formation of most of these cave features; however, evidence of sulfuric acid speleogenesis (SAS) has been observed in Cueva del Puerto and Sima del Pulpo, which host massive secondary gypsum deposits. Speleothems typically linked to hydrothermal water upwelling and CO2 degassing close to the water table are present in most of these cavities, including folia, calcite spar crystals, cave clouds, calcite rafts deposits and several types of cave raft cones. The wide variety of hypogenic speleogenesis indicators and speleothems whose genesis is unconnected to meteoric water seepage reveals that the hydrothermal field of the Murcia Region hosts one of the densest active hypogenic subterranean networks in the world.

An Overview of the Hypogene Caves of Sicily

Karst in Sicily develops in both Messinian gypsum and Mesozoic or Tertiary limestone rocks. Caves are also found in the basalts of Mount Etna. Except for some rare cases, until recently most caves developed in limestone were considered to be of epigenetic origin. The discovery of gypsum in some of these caves, and especially detailed morphological studies, have allowed defining a hypogenic origin for a dozen of caves up to now. In some of these, the hypogenic evidences are very clear, while others remain in doubt because of the widespread presence of well-developed condensation-corrosion morphologies not necessarily related to hydrothermal fluids. This paper reports the present knowledge of hypogenic caves in the Island of Sicily.

Hypogene Caves in France

Hypogene speleogenesis (HS) describes cave development by rising fluids independent of recharge from the overlying or adjacent areas. Dissolution includes deep-seated acidic sources (CO2/H2S), “hydrothermal” cooling, mixing corrosion, and Sulfuric Acid Speleogenesis (SAS) at and above the water table. HS localizes in basin at sites of upward flows and convergences, in deformed strata at structural highs and major faults. In disrupted basins, geothermal gradient “pumps” downward meteoric water. Volcanism and magmatism produce “hyperkarst” combining CO2, H2S, thermalism, and microbial activity. Hypogene caves in France are presented according to a conceptual model. Isolated geodes are lined by calcite spar. 3D multistory caves (Pigette, Adaouste) show CO2 degassing morphologies (bubble trails, folia, tower cones, coral towers) and “hydrothermal” minerals (Fe–Mn oxi-hydroxides, barite, celadonite), with condensation–corrosion cupolas above the water Table. 2D maze caves develop below less permeable strata. Giant ascending shafts (Salins shaft), collapse shafts, and breccia pipes (called “organs” in the N.-French coal basin) correspond to “hyperkarst” phenomena. Caves with ore deposits are associated with sulfurs (Fe, Pb, Zn) or oxidized Fe. They often record past positions of base level and harbor unique features (black tubes, ghost-rock) or rare minerals. Along the water table, thermal gradient and CO2 /H2S degassing make condensation–corrosion and HS above the water table. Chevalley Aven shows upward dendritic pattern. Eventually, cupolas expand to large isolated chamber. Water table sulfuric caves develop headward with typical morphologies (corrosion tables, condensation domes, sulfuric karrens). Vapor shafts form by warm air convections and condensation–corrosion.

Dam Break Simulation Using DHI-MIKE21 in the Eg Hydropower Plant, Mongolia

This chapter focuses on a dam break assumptions and assesses a flood risk in the downstream area of the Eg hydropower plant, Mongolia. Two-dimensional DHI-MIKE model was set up. The model presents the volume of water in a reservoir, a flood mapping, and flood risk zone in the downstream area of the hydropower station. The model has been supplied by the Eg-Hantai, Selenge-Khutag, and Selenge-Khylganat hydrological stations data from 1994 to 2006, which are a water level, inflow discharge, and precipitation, and it has been collected by the Mongolian Institute of Meteorology Hydrology and Environment. Terrain property of objects in schematic outline was determined on a digital elevation model (DEM), the elevation data were produced by digitizing topographic maps. The dam break has been simulated with Mike21 modeling software. The initial elevation is 887.8 m (water depth 59 m) at the reservoir. Before dam failure, the observed discharge and the simulated Mike21 model’s outflow were analyzed to make a reasonable assumption (the purpose of assumption is that a failure and the resulting flood wave would affect the downstream area of the dam planned site). After analyses and model simulation, an artificial reservoir was built on the model to release water to the downstream area. In the model, it has been assumed that the dam failed completely and instantaneously. It means it will approach the maximum peak of flood. As a result, the total amount of 262.106 m3 water has been collected behind the dam. After water is released, flood area was determined and the maximum affected area is 145.1 km2 and the maximum depth is 15.1 m. The Mike21 model simulation result was closest to the observed peak, and the correlation (R) was 93%. Therefore, a floodplain in Mike21 results is an efficient tool to make a flood mapping and to assess flood risk in the downstream area of the hydropower plant.

Hypogene Caves in North Africa (Morocco, Algeria, Tunisia, Libya, and Egypt)

This chapter aims to describe the hypogene caves of North Africa. A few hypogene caves are known in Morocco, Tunisia, Libya, and Egypt. Algeria hosts most of hypogene caves known in this region. This includes hydrothermal cave springs (Ain Ouarka, Hassi Dermam, Aidour), mazes related to CO2 degassing (Kef el Kaous), iron-ore related caves (Rouina) and sulfuric acid speleogenesis (SAS) caves especially in the Azerou massif. This last area displays numerous caves recording the geomorphic evolution that follows the gradual exhumation of the thermal aquifer. Preliminary analytical data (geomorphology, mineralogy, isotopes, and U/Th dating) are presented.

Bat urea-derived minerals in arid environment. First identification of allantoin, C4H6N4O3, in Kahf Kharrat Najem Cave, United Arab Emirates

*audra@unice.fr Citation: