Karst Network Research Articles

Construction of Master Recession Curve Using Genetic Algorithms

Construction of Master Recession Curve Using Genetic Algorithms The article describes a new methodology of using genetic algorithms to assemble a natural time series of discharge recession, from which a master recession curve can be interpreted both for streams and for springs. Presented approach can avoid obstacles such as limited time-series datasets, incomplete recessions or too many recessionary segments in many recession series, different time intervals of observations (daily or weekly frequencies). Short time-series intervals, imprecise or mistaken measurements and different types of datasets (averaged or directly measured data) are taken into account as well. Even rough measurements of discharges with inaccurate sensing range can be analysed, if sufficiently long observation is available. Complicated hydrograph shapes in the case of e.g. karstic springs (often caused by combination of laminar and turbulent discharge sub-regimes due to karst network settings) can be processed as well. Subsequent construction of master recession curve is much easier an offers better conditions for its interpretation. Presented algorithm was already implemented to a programme solution, completed on the user form.

Determination of the conduit structure in a karst aquifer based on tracer data—Lurbach system, Austria

ABSTRACTA structure model was used to analyse solute‐transport parameter estimates based on tracer breakthrough curves. In the model system, groundwater flow is envisioned to be organised in a complex conduit network providing a variety of short circuits with relative small carrying capacities along different erosion levels. The discharge through the fully filled conduits is limited owing to void geometries and turbulent flow; thus, a hierarchic overflow system evolves where conduits are (re‐)activated or dried up depending on the flow condition.Exemplified on the Lurbach–Tanneben karst aquifer, the applicability of the model approach was tested. Information derived from multi‐tracer experiments performed at different volumetric flow rates enabled to develop a structural model of the karst network, under constraint of the geomorphological and hydrological evolution of the site. Depending on the flow rate, groundwater is divided into up to eight flow paths. The spatial hierarchy of flow paths controls the sequence of flow path activation. Conduits of the topmost level are strongly influenced by reversible alteration processes. Sedimentation or blocking causes an overflow of water to the next higher conduit. Flow path specific dissolutional denudation rates were estimated using the temporal development of the partial discharge. Copyright © 2012 John Wiley & Sons, Ltd.

Systematics, conservation and morphology of the spider genus Tayshaneta (Araneae, Leptonetidae) in Central Texas Caves

The spider genus Tayshaneta is revised based on results from a three gene phylogenetic analysis (Ledford et al. 2011) and a comprehensive morphological survey using scanning electron (SEM) and compound light microscopy. The morphology and relationships within Tayshaneta are discussed and five species-groups are supported by phylogenetic analyses: the anopica group, the coeca group, the myopica group, the microps group and the sandersi group. Short branch lengths within Tayshaneta contrast sharply with the remaining North American genera and are viewed as evidence for a relatively recent radiation of species. Variation in troglomorphic morphology is discussed and compared to patterns found in other Texas cave invertebrates. Several species previously known as single cave endemics have wider ranges than expected, suggesting that some caves are not isolated habitats but instead form part of interconnected karst networks. Distribution maps are compared with karst faunal regions (KFR’s) in Central Texas and the implications for the conservation and recovery of Tayshaneta species are discussed. Ten new species are described: Tayshaneta archambaulti sp. n., Tayshaneta emeraldae sp. n., Tayshaneta fawcetti sp. n., Tayshaneta grubbsi sp. n., Tayshaneta madla sp. n., Tayshaneta oconnorae sp. n., Tayshaneta sandersi sp. n., Tayshaneta sprousei sp. n., Tayshaneta vidrio sp. n. and Tayshaneta whitei sp. n. The males for three species, Tayshaneta anopica (Gertsch, 1974), Tayshaneta devia (Gertsch, 1974) and Tayshaneta microps (Gertsch, 1974) are described for the first time. Tayshaneta furtiva (Gertsch, 1974) and Tayshaneta uvaldea (Gertsch, 1974) are declared nomina dubia as the female holotypes are not diagnosable and efforts to locate specimens at the type localities were unsuccessful. All Tayshaneta species are thoroughly illustrated, diagnosed and keyed. Distribution maps are also provided highlighting areas of taxonomic ambiguity in need of additional sampling.

Characterization of karstic networks by automatic extraction of geometrical and topological parameters: comparison between observations and stochastic simulations

Abstract Although karstic networks may have a major impact on fluid flow in reservoir characterization, they exhibit great intrinsic heterogeneity that makes their characterization very complex. This work proposes an integrated workflow to study and stochastically simulate karstic networks. This approach is based on the study of outcropping caves. Topological and geometrical parameters are automatically extracted from cave surveys. The extracted geometrical parameters are used to determine the input parameters of the stochastic simulations. These simulations utilize a structure-based, pixel-based and geostatistical approach. To check for consistency, a procedure is proposed to compare the topological and geometrical parameters of observed and simulated karst networks using multivariate analyses. The proposed integrated workflow has been successfully applied to a real case study involving karsts in Jurassic limestone from the south of France. The obtained karstic networks reproduce observed topological and geometrical parameters even when the employed simulation approach relies solely on geometrical parameters.

An algorithm for 3D simulation of branchwork karst networks using Horton parameters and 𝒜★ Application to a synthetic case

Abstract This paper presents a method to stochastically simulate 3D karstic networks and more specifically branchwork pattern cave systems. Considering that they can be compared with 3D fluvial networks, the topological classification of Strahler and the corresponding ratios of Horton are used to define three morphometric parameters. These parameters are integrated in an algorithm that computes branches hierarchically to obtain a final network organized around the main observed inlet and outlet with a branching complexity controlled by the user. Each branch corresponds to a low-cost path between two points calculated with the 𝒜★ graph search algorithm. Speleogenetic information on inception horizons, palaeo-water tables and fractures is accounted for by adapted definitions of the searching functions of 𝒜★. The method is demonstrated on a 3D synthetic case with discrete fractures networks, inception horizons and a palaeo-water table. The simulated karsts have a realistic geometry and are geologically consistent.

TAPHONOMIC ANALYSIS OF THE LOWER PLEISTOCENE PIRRO NORD FOSSIL LOCALITY (PIRRO 10 SITE, PUGLIA, SOUTHERN ITALY): A DEPOSITIONAL MODEL FOR VERTEBRATE ASSEMBLAGES IN A KARSTIC ENVIRONMENT

Taphonomic analyses have been conducted on the macromammal remains found in Sedimentary Unit 7 of the lower Pleistocene Pirro 10 site of the Pirro Nord locality in Italy. Recent field research has concentrated on investigating the fossil content of this site and the genesis of the karst network and its related deposits. In the present study, we distinguish between preburial and synsedimentary (during burial) processes in order to group the vertebrate remains into different taphonomic categories according to their various states of preservation, thus introducing the concept of taphorecord—borrowed from invertebrate taphonomy—into macrovertebrate taphonomy for the first time. Element quantification, evaluation of transport effects, and state of preservation of the skeletal elements were studied and all elements separated into four taphorecords according to their relative chronology. The use of taphorecords also improves the accuracy of the data obtained from the various methods of element quantification. The analysis of bone sorting and orientation indicates that the fossiliferous deposits originated by water flows carrying both fossils and sediments, alternating with phases of carcass accumulation and reelaboration of bones from previously deposited layers. The study presented here serves as a proof of concept for the use of taphorecords in analyses of fossiliferous deposits in caves.

A pseudo-genetic stochastic model to generate karstic networks

Summary In this paper, we present a methodology for the stochastic simulation of 3D karstic conduits accounting for conceptual knowledge about the speleogenesis processes and accounting for a wide variety of field measurements. The methodology consists of four main steps. First, a 3D geological model of the region is built. The second step consists in the stochastic modeling of the internal heterogeneity of the karst formations (e.g. initial fracturation, bedding planes, inception horizons, etc.). Then a study of the regional hydrology/hydrogeology is conducted to identify the potential inlets and outlets of the system, the base levels and the possibility of having different phases of karstification. The last step consists in generating the conduits in an iterative manner using a fast marching algorithm. In most of these steps, a probabilistic model can be used to represent the degree of knowledge available and the remaining uncertainty depending on the data at hand. The conduits are assumed to follow minimum effort paths in a heterogeneous medium from sinkholes or dolines toward springs. The search of the shortest path is performed using a fast marching algorithm. This process can be iterative, allowing to account for the presence of already simulated conduits and to produce a hierarchical network. The final result is a stochastic ensemble of 3D karst reservoir models that are all constrained by the regional geology, the local heterogeneities and the regional flow conditions. These networks can then be used to simulate flow and transport. Several levels of uncertainty can be considered (large scale geological structures, local heterogeneity, position of possible inlets and outlets, phases of karstification). Compared to other techniques, this method is fast, to account for the main factors controlling the 3D geometry of the network, and to allow conditioning from available field observations.

Morphometric analysis of three-dimensional networks of karst conduits

The main idiosyncrasy of a typical karst system is the presence of a three-dimensional network of conduits behaving as drains in the system and being responsible of both the quick response of karst springs to rainfall events and the complex distribution of solutes in the system. A morphometric analysis of the three-dimensional geometry of conduits provides quantitative measures that can be used in a range of applications. These morphometric parameters can be used as descriptors of the underground geomorphology, they provide information on speleogenesis processes, they can be correlated with karst denudation ratios, they can be used to control the simulation of realistic stochastic karst networks of conduits, and they can be correlated with hydrogeologic behaviour of the karst system. The main purpose of this paper is to define, describe and illustrate a range of morphometric indexes and morphometric functions that can be calculated nowadays because the availability of three-dimensional topographies provided by speleological work and the availability of the computational and graphical power provided by modern computers. Some of the morphometric parameters describe the existence of preferential directions of karstification, others describe the kartification along the vertical and the possible presence of inception horizons. Other indexes describe the shape complexity of the karstic network, whilst other indexes describe spatial variability of the conduit geometry, and other parameters give account of the connectivity of the three-dimensional network. The morphometric analysis is illustrated with a three-dimensional karstic network in Southern France.

PaPRIKa: a method for estimating karst resource and source vulnerability—application to the Ouysse karst system (southwest France)

The intrinsic vulnerability mapping method, PaPRIKa, is proposed as a common basis for karst groundwater protection in France. PaPRIKa is a specialized method for studying karst aquifers, derived from updating the RISKE and EPIK methods. Both the structure and functioning of karst aquifers are considered in order to develop a resource and source-vulnerability mapping method. PaPRIKa means Protection of aquifers from the assessment of four criteria: P for protection (considering the most protective aspects among parameters related to soil cover, unsaturated zone and epikarst behavior), R for rock type, I for infiltration and Ka for karstification degree. The Ouysse karst system, located in the Causses area in southwest France, is one of the nine pilot sites where this method was tested and standardized. The specificities of the Ouysse system such as the size of the catchment area, the spatial variability of the karst network development, the thick infiltration zone and the system’s dual character (both karst and non-karst areas), have provided a valuable field of application. The vulnerability of the resource was assessed for the entire catchment area, while source-orientated cartography was attempted for the catchment areas of the three different capture works used for drinking water.

Stratigraphical and palaeontological data from the Early Pleistocene Pirro 10 site of Pirro Nord (Puglia, south eastern Italy)

The Pirro Nord palaeontological and archaeological locality has been the object of recent field research to investigate the fossil content of its Early Pleistocene vertebrate palaeocommunities, and to understand the genesis of the karst network and related deposits that delivered the lithic industry representing the earliest human occupation of Europe known so far, spanning 1.7–1.3Ma. The succession of the Pirro 10 site has been described in terms of facies and fossil vertebrate content of the 37 distinguished Sedimentary Units (SU). On the whole, the succession is made of chemical and clastic sediments that include debris fall and alluvial deposits. SU are distinguished according to lithology, colour, discontinuities, lamination, fossil concentration, and taphonomical parameters. Palaeomagnetic data and biochronological characteristics refer the Pirro 10 site to the latest Late Villafranchian Mammal Age of the Italian biochronological mammal scale.The fossil content is quite homogenous. Common taxa are Axis eurygonos, Hystrix refossa, Ursus etruscus, Canis mosbachensis together with small mammal remains mainly represented by Chiroptera and the arvicolid Microtus (Allophaiomys) ex gr. ruffoi. A significant change in the taxonomic record occurs in SU 22 and 108, where a clear increase of Equus altidens and Bison (Eobison) degiulii remains indicates shifting towards drier and more open environments and possibly deteriorating local climatic conditions. In general, for all phases, taphonomic evidence suggests that (1) bone accumulation results from carcass transport into the cave system by accident, (2) skeletons were decomposed and partially disarticulated near the cave entrance, (3) the cave environment caused corrosion, desquamation and pitting, and (4) bones were moved within the cave system by water flow, usually for short distances.Pirro 10, Pirro 13 and all karst structures of the Pirro Nord locality during Early Pleistocene were part of a complex interconnected karst system. Dissolution was more effective along the highly fractured core-zones of the Pliocene fault that bounded the “Apricena horst” to the south, where Pirro 10 gallery and Pirro 13 shaft are located. At that time, Pirro 10 was developed within the vadose zone whereas Pirro 13 represented a vertical structure connecting the surface to an underground karst floor. In general, the filling of Pirro 10 indicates fluctuations of the base level: water flow circulation in phreatic and epiphreatic conditions led to the deposition of clastic sediments, whereas flowstones reflect base level lowerings.

Volcanogenic origin of cenotes near Mt Gambier, southeastern Australia

The cenotes near Mt Gambier are circular, cliffed, collapse dolines containing water-table lakes up to 125 m deep, floored by large rubble cones. They lie in a flat, coastal plain composed of mid-Tertiary limestone. Most of the deepest cenotes are concentrated in two small areas located along trends sub-parallel to the main joint direction in the limestone. The cenotes do not connect to underwater phreatic passages, and water chemistry data confirm that they are not part of an interconnected karst network. They formed by collapse into large chambers (up to > 1 million m 3) that extended 125 m or more below the land surface. Several cenotes have actively growing stromatolites on the sub-vertical walls that started growing at ∼ 8000 years BP. The caves that collapsed to form the deep Mt Gambier cenotes are much larger than shallow and deep phreatic caves in the area, and do not connect into deep phreatic systems. They were not formed by freshwater/seawater mixing, responsible for many of the well-known Yucatan cenotes, because they are not associated with locations of the mixing zone during previous high sea levels, and are much larger than caves presently forming along the mixing zone near Mt Gambier. Instead dissolution was most likely due to a process whereby acidified groundwater containing large amounts of volcanogenic CO 2 ascended up fractures from the magma chambers that fed the Pleistocene–Holocene volcanic eruptions in the area; deep reservoirs of volcanogenic CO 2 occur nearby. Cave dissolution could have been due to release of CO 2 during the Mt Gambier eruption ∼ 28,000 years ago, followed by collapse to form cenotes during the low sea levels of the Last Glacial Maximum ∼ 20,000 years ago. The cenotes then flooded ∼ 8000 years ago as sea level rose, and stromatolites began to grow on the walls.

Geophysical characterisation of karstic networks – Application to the Ouysse system (Poumeyssen, France)

In the framework of the management of karstic aquifers, geophysical reconnaissance can be used to locate conduits and caves, and to characterise the surrounding limestone matrix. Suitable characterisation of heterogeneities in the karstic environment is, however, challenging for ground-based geophysical methods. The present article describes the results, and evaluates the response and accuracy of combined geophysical measurements carried out at the Poumeyssen test site in France, involving electrical resistivity imaging (ERI), magnetic resonance sounding (MRS), “ mise-à-la-masse” electrical mapping, and seismic tomography. This site provides the opportunity to study a relatively wide, shallow, water-filled conduit whose location and shape are known from topographic work carried out by cave divers. Seismic and MRS provided the exact location and width of the conduit, to within a few meters. The seismic and electrical data suggest that the limestone medium surrounding the conduit is not homogeneous.

Mise-à-la-masse and smoke tests for mapping vadose zone karst

Roughly 20% of the United States is underlain by limestone or dolomite. Shallow karst, riddled with cavities and fractures enlarged by dissolution, poses a costly problem for engineers and developers. Nearly every conceivable geophysical method—microgravity, ground-penetrating radar, electromagnetics, seismic reflection, refraction tomography, seismic surface waves, resistivity, spontaneous potential, and induced polarization—has been conscripted in the war against damage caused by subsidence. In this paper, we will discuss two unusual methods that we have tested for mapping the extent of shallow karst: smoke tests and mise-a-la-masse resistivity. Both methods presuppose at least one borehole intersecting a cavity. Given the highly irregular nature of karst networks, the discovery of a cavity though drilling is sufficient to alert engineers that the site poses a potential problem, but little else can be determined using just the driller's log from a single borehole. The two methods we discuss provided a s...

Steady water level and temperature in a karstic system: The case of the coral Lifou Island (SW Pacific)

Lifou is an atoll uplifted to a near 100 m height near the Vanuatu Trench. Extensive karstification is recorded in the outer coral rim and to a lesser extend in the lagoon type limestones of the inner island. The orientations found in the longest karstic networks correspond rather well to the main fracture directions, but near coasts, the galleries are controlled by the paleo-shoreline, suggesting that mixing corrosion might be involved during cave formation. The freshwater level and temperature, recorded during one year inside two caves present smooth variations, if tidal components near 12 and 24 h periods are removed, and are poorly correlated with rain. Comparison with data recorded in a continental karst (Baget, Pyrénées) and in the chalk of the Paris Basin indicates that Lifou lacks an organized channel network able to collect and transfer quickly rainwater toward the phreatic zone.

The Late Pleistocene Duoi U’Oi cave in northern Vietnam: palaeontology, sedimentology, taphonomy and palaeoenvironments

This paper describes new fossil materials recovered at the Duoi U’Oi site, in December 2003, by a Vietnamese-French-Japanese team. The Duoi U’Oi cave is located in Man Duc village, 25 km of Hoà Binh city in northern Vietnam. It belongs to a karstic network developed in a dark grey micritic marine limestone dated from the Lower to the Middle Triassic. The sedimentary fill produced a rich mammalian fauna, essentially composed of isolated teeth of middle- to large-sized mammals (Artiodactyla, Perissodactyla, Proboscidea, Carnivora, Rodentia, Primates), and characteristic of Late Pleistocene. The results of the Duoi U’Oi fieldwork are of great interest for the following reasons: (1) the biochronological age of the fauna is consistent with 230Th/ 234U/ 238U dating from the calcitic floors (66±3 ka). The Duoi U’Oi fauna is thus the oldest well-dated modern fauna known for the Southeast Asian mainland; (2) in terms of sedimentology, the analysis of the formation of the fossiliferous breccia and that of the processes of deposits shows a close relation between the karstic deposits inside the cave and the deposits in the alluvial terraces. The observation of three levels of alluvial terraces associated with three caves situated at 62, 10 and 3 m above the present alluvial plain suggests that exokarstic and endokarstic sediments evolved together; (3) in terms of palaeobiogeography, Duoi U’Oi is the continental fauna showing the strongest resemblance with the Late Pleistocene faunas from Indonesian islands (Punung, Gunung Dawung, Lida Ajer, Sibrambang and Djambu caves); this implies that, at the time of Duoi U’Oi, ca 70 ka, the Sundaland was mainly characterised by faunas of modern aspect; (4) the analysis of major taphonomic factors that led to the mammal assemblage reveals a combination of selective agents (selective role of predators and porcupines, selective destruction of age classes for some species, selective preservation of fossils due to the deposition processes in the karstic network), which contribute to the poor representation of the diversity of the fauna; no arguments show that humans, present at Duoi U’Oi, might have a possible role in the taphonomic process; (5) the palaeoenvironmental reconstruction based on the composition of the faunal assemblage suggests a forested area and some open habitats, under warm and humid conditions.

Note on rain-triggered earthquakes and their dependence on karst geology

SUMMARY Recently reported rain-triggered seismicity from three separate storms occurred exclusively in karst geology. In this paper, I discuss how the hydrogeology of karst controls rain-triggered seismicity by channeling of the watershed after intense rainfall directly into the karst network. Such channeling results in very large increases in hydraulic head, and more importantly, substantially increases the vertical stress acting on the underlying pore-elastic media. Rapid loading upon a pore-elastic media induces seismicity by increasing pore pressure at depth in a manner similar to that observed from reservoir impounding. Using a simple 1-D model of a pore-elastic medium, it is shown that the instantaneous fluid pressure increase at depth is a substantial fraction of the pressure step applied at the boundary, followed by time-dependent pore pressure increases associated with the typical linear diffusion problem. These results have implications for the change in fluid pressure necessary to trigger earthquakes, and leads to the following hypothesis to be tested: Unambiguous rain-triggered seismicity will only occur in karst regions.

Seismicity rate and wave-velocity variations as consequences of rainfall: the case of the catastrophic storm of September 2002 in the Nîmes Fault region (Gard, France)

The western Provence in southern France is an intraplate low deforming region, cut by large sinistral strike-slip faults as the Nimes Fault. The deformation rate of this fault was estimated at 0.1 mm yr−1 from geological and morphological observations. Nevertheless, some large earthquakes occurred in this area in historical times inducing well-documented partial destructions on the roman monument 'Pont-du-Gard'. In order to investigate if this area is seismically active, we installed a temporary seismological network of 14 stations between the cities of Nimes and Avignon for a 1-yr period (2002 July–2003 June). We recorded and located a total amount of 80 earthquakes of magnitude Ml smaller than 2.8, and of 153 quarry blasts. The seismic event locations are interpreted in terms of regional tectonics as well as of geometry at depth of the Nimes Fault and of possible seismic activity of the Roquemaure Fault. At the beginning of 2002 September, a catastrophic storm occurred in the same area with cumulated precipitations at 600 mm in 28 hr, causing casualties and major inundations and damages. We identified a clear and sudden increase of the seismic activity as an immediate consequence of this exceptional meteorological phenomenon. We interpret this rainfall triggering of earthquakes as the response of the crust to an abrupt vertical loading. The geological context of this zone is characterized by the presence of sedimentary basins and of an important karstic network in a calcareous environment allowing the retention of a third of the total rainwater volume during few weeks after the catastrophic storm. Month by month inversion of the seismic wave velocities for only the first 1-km thick layer of the crust allows investigating the influence of the stored water. A clear decrease of both P- and S-velocities, and an increase of the Vp/Vs ratio are evidenced. The variations obtained are at 2, 6 and 4.5 per cent for P-, S-velocities and Vp/Vs ratio, respectively. These variations are discussed in confront of previous studies and can be directly related to the known water volume.

Mineralogical and geochemical characterization of nonsulfide Zn–Pb mineralization at Silvermines and Galmoy (Irish Midlands)

The nonsulfide zinc–lead mineralization in the Irish Midlands represents an example of surface oxidation of primary sulfide mineralization, redeposition and preservation under glacial till. In this preliminary study, we report on the mineralogy and chemical composition of the nonsulfide zinc mineralization at Silvermines and Galmoy deposits. At Silvermines, the analyses were carried out on samples from two drill cores (drillholes 302/3 and 303/3) located in Knockanroe Townland, at the periphery of the main orebody. At Galmoy, the nonsulfides were sampled from the G-orebody between 77 and 93 m below the surface, in an area where oxidation is very strong. At both sites, the dominant mineral composition of oxidized ores is relatively simple with smithsonite–hemimorphite at Silvermines and smithsonite at Galmoy. Primary sulfides and secondary carbonates/silicates are generally associated at both localities. Whole rock chemical analysis, SEM and optical studies have revealed evidence for open space filling and replacement of both primary sulfides and Carboniferous dolomite host rock by nonsulfide minerals. Smithsonite at Silvermines shows an evolution of different forms from early encrustations and botryoidal aggregates to late “rice grain” shaped crystals and a systematic decrease of Fe content with time in the paragenetic sequence. Early smithsonite replacing dolomite host rocks can be Fe- and Mn-rich. This evolution points to slightly more reducing conditions during deposition of the early Zn carbonates, compared to late smithsonites, which coexist with Mn and Fe (oxy)hydroxides. A complex association of at least three different, often intergrown types of smithsonite aggregates were observed at Galmoy, where replacement of sulfides and vug-infilling are predominant. Early globular or crustiform Pb- and Ca-rich smithsonite is followed by tiny rounded (Fe-poor) to one-dimensional (Fe-rich) clusters of smithsonite and again by late “rice grain” shaped smithsonite. Hemimorphite is virtually absent. Thin encrustations of sulfates, such as gypsum, boyleite, rozenite, copiapite and jarosite, often coat both sulfide and nonsulfide minerals and testify to recent and/or ongoing alteration. The lack of rhombohedral smithsonite, which characterizes the upper phreatic zone in Sardinia and in Belgium, indicates the relative immaturity of the weathering profiles in Ireland, the absence of a well-developed karstic network and, in consequence, the uneconomic character of nonsulfide concentrations.

Genesis of Vanadium Ores in the Otavi Mountainland, Namibia

Zn-Cu-Pb vanadate ores (descloizite, mottramite, and vanadinite) in the Otavi Mountainland, Namibia, once were considered the greatest vanadium deposits in the world, with resources estimated at several million tons of vanadium ore. The deposits, now mostly exhausted, occurred in collapse breccias and solution cavities related to a karstic network associated with the post-Gondwana land surfaces in carbonate rocks of the Neoproterozoic Otavi Group, which already contained primary sulfide orebodies. Although a supergene, post-Damaran origin has been generally accepted, the timing and genesis of this mineralization style remains controversial. Mottramite and Cu descloizite are particularly abundant around Cu sulfide deposits (Tsumeb type), whereas descloizite occurs in the areas surrounding primary sphalerite-willemite orebodies (Berg Aukas type). The V deposits the Otavi Mountainland represent a special low-temperature, weathering-related, non-sulfide ore type, also fairly widespread in other areas of southern Africa (e.g., Zambia, Angola). Here we describe the geologic setting of the main V deposits and their ore mineralogy, present some comprehensive major and trace element data for the vanadate ore minerals and gangue carbonates, as well as fluid inclusion microthermometry, O, C, Sr, and Pb isotope analyses, and direct (U-Th)/He descloizite thermochronometry. The vanadates are considered to have formed during a late phase in the depositional history of the post-Damaran supergene ores. Calcite and dolomite gangue are paragenetically coeval with the vanadates, occurring with the vein- and breccia-related ores and as cement in the deeper parts of the recent karst infills. The acidic conditions of sulfide alteration, coupled with a low Eh caused by the influence of organic matter, could have been favorable for vanadate precipitation. Geochemical results and isotope data indicate that most vanadate deposits were formed at temperatures of ~40° to 50°C by meteoric waters interacting with Neo-proterozoic shales, carbonates, and related primary sulfide ores, which were subjected to multiple weathering events in a karst environment. The age of most deposits appears to be generally confined to the Tertiary, with a distinct period of descloizite formation dated at 24 to 33 Ma. The V ores are genetically related to post-Gondwanan erosional episodes, controlled by tectonomorphological evolution following rifting phases in the Atlantic realm and spanning the period from the end of the Cretaceous to Pleistocene.

Band-e-Amir Lakes and Dragon Valley (Bamiyan): myths and seismicity in Afghanistan

Abstract Located SW of the Hindu Kush range, the Band-e-Amir lakes and other continental bioherms around Bamiyan are famous for their ordering into terraces and their great variety of colours. Numerous legends, the earliest likely dating to the establishment of the Zoroastrian religion, refer to the topography, ecology, and colours of the lakes and seismic activity of the area. The lakes have been formed by the chemical and biologically-induced build-up of semicircular or successive linear travertine dams. The discovery of a highly truncated karstic network located at an elevation of around 4000 m. along the base of Maastrichtian carbonate cliffs surrounding the lakes, may explain the presence of this carbonate sedimentation which has fluctuated with time and was responsible for legendary floods. Localized at the eastern end of the Herat strike-slip fault, the timing and duration of the build-ups and lakes are under the influence of intense seismic activity, partially due to the seismic activity of the nearby Hindu Kush, in relation to the northern drift of the Afghan Gondwanian block towards the Eurasiatic plate. These bioherms and lakes occur in an area of high risk; a zone of floods, freezing temperatures, earthquakes and rock avalanches caused by the high altitude and location in the Himalayan alpine belt. These natural features have affected local populations beginning with the movement into the area of more or less sedentary people, apparently coming from the Bactrian province. Such a fragile biological and sedimentological environment should be maintained by organized governmental assistance, with a primary goal of protecting the local inhabitants, but also preserving this exceptional environment for others to enjoy.