principles of early development of karst conduits under natural and man made conditions revealed by mathematical analysis of numerical models numerical models of the enlargement of primary fissures in limestone by calcite aggressive water show a complex behavior if the lengths of the fractures are large and hydraulic heads are low as is the case in nature dissolution rates at the exit of the channel determine its development by causing a slow increase of water flow which after a long gestation time by positive feedback accelerates dramatically within a short time span mathematical analysis of simplified approximations yields an analytical expression for the breakthrough time when this happens in excellent agreement with the results of a numerical model this expression quantifies the geometrical hydraulic and chemical parameters determining such karst processes if the lengths of the enlarging channels are small but hydraulic heads are high as is the case for artificial hydraulic structures such as dams it is the widening at the entrance of the flow path which determines the enlargement of the conduit within the lifetime of the dam this can cause serious water losses this can also be explained by mathematical analysis of simplified approximations which yield an analytical threshold condition from which the safety of a dam can be judged thus in both cases the dynamic processes of karstification are revealed to gain a deeper understanding of the early development of karst systems as a further important result one finds that minimum conditions below which karstification cannot develop do not exist

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

origin and morphology of limestone caves limestone caves form along ground water paths of greatest discharge and solutional aggressiveness flow routes that acquire increasing discharge accelerate in growth while others languish with negligible growth as discharge increases a maximum rate of wall retreat is approached typically about 0 01 0 1 cm yr determined by chemical kinetics but nearly unaffected by further increase in discharge the time required to reach the maximum rate is nearly independent of kinetics and varies directly with flow distance and temperature and inversely with initial fracture width discharge gradient and pco2 most caves require 104 105 yr to reach traversable size their patterns depend on the mode of ground water recharge sinkhole recharge forms branching caves with tributaries that join downstream as higher order passages maze caves form where 1 steep gradients and great undersaturation allow many alternate paths to enlarge at similar rates or 2 discharge or renewal of undersaturation is uniform along many alternate routes flood water can form angular networks in fractured rock anastomotic mazes along low angle partings or sponge work where intergranular pores are dominant diffuse recharge also forms networks and spongework often aided by mixing of chemically different waters ramiform caves with sequential outward branches are formed mainly by rising thermal or h2s rich water dissolution rates in cooling water increase with discharge co2 content temperature and thermal gradient but only at thermal gradients of more than 0 01 c m can normal ground water co2 form caves without the aid of hypogenic acids or mixing artesian flow has no inherent tendency to form maze caves geologic structure and stratigraphy influence cave orientation and extent but alone they do not determine branch work versus maze character

pollen and diatom inferred climatic and hydrological changes in sumxi co basin western tibet since 13 000 yr b p although the tibetan plateau greatly influences the atmospheric circulation of the nortbern hemisphere few continuous paleoclimatic records are available from the plateau a 13 000 yr pollen and diatom record from the sumxi longmu co basin in western tibet gives information on major changes both in regional vegetation and in local hydrology after the basin first filled ca 13 000 yr b p a dry spell occurred about 10 500 yr b p within the interval spanned by the european younger dryas chronozone a major environmental change occurred suddenly at 10 000 yr b p with the establishment of wet conditions and was followed by a long term trend toward maximum aridity which lasted approximately 6000 yr short term oscillations are superimposed on this general climatic change with a major reversal event about 8000 yr b p and a second wet pulse leading to a maximum lake volume ca 7500 6000 yr b p maximum aridity occurred 4300 yr b p the major environmental fluctuations recorded at sumxi longmu co appear in phase with climatic changes recognized in north tropical africa suggesting that the 8000 to 7000 yr b p event was caused by an abrupt disequilibrium in the climatic system as was the younger dryas and possibly the 4300 yr b p event

a 13 000 year climate record from western tibet although the tibetan plateau is important in influencing the atmospheric circulation of the northern hemisphere1 3 there are only a few continuous palaeoclimate records available and these are limited to the plateau s northeastern margin4 6 here we present a 13 000 yr record from sumxi co western tibet constructed from both lake core and shoreline studies which shows that conditions in the early middle holocene were warmer and wetter than at present these results confirm model predictions of an intensified monsoon over the region at 9 000 yr bp owing to an orbitally induced increase in summer insolation7 8 we also find evidence for warm humid pulses at 12 500 and 10 000 yr bp in phase with the steps of the last deglaciation and for a return to cold dry conditions at 11 10 000 yr bp none of which can be explained by orbital variations the existence of the cold episode confirms that the cooling associated with the younger dry as event occurred in continental china6 9 and provides further evidence of the global nature of this event10

numerical versus statistical modelling of natural response of a karst hydrogeological system abstract structural and hydrodynamic characteristics of karst aquifers are mostly deduced from studies of global responses of karst springs hydrographs chemical or isotopic composition in this case global response is often used to make inferences with respect to infiltration and ground water flow processes as well as on the hydrodynamic parameters obviously the direct verification of these inferences is very difficult we have used an indirect method of verification introducing well defined theoretical karst structures into a finite element model and then analysing the simulated global response according to the currently accepted interpretation schemes as we know what we are introducing into the numeric model the consistency of the interpretation may be checked immediately the results obtained in the hydrogeological study of two karst basins in the swiss jura and from 2 d and 3 d numerical simulations show the difficulty of finding structural parameters and hydrodynamic behaviour from statistical methods alone i e correlation analyses discharge discharge and precipitation discharge in effect our first results show that the form of the correlograms depends on several factors besides the structure of the karst aquifer i on the form of the floods in other words the contrast between quick flow and base flow ii on the frequency of hydrological events during the period analysed and iii on the type of infiltration processes in other words the ratio of diffuse infiltration to concentrated infiltration obviously the variability of a karst hydrograph is a result of a combination of these factors distinction between them is not always possible on hydrographs and therefore on correlations discharge discharge and precipitation discharge

the arid humid transition in the sahara and the sahel during the last deglaciation at the time of the last glacial maximum the sahara and sahel regions of north africa were extremely dry new records of rainfall show that during the subsequent deglaciation the transition from arid to humid conditions in these regions occurred synchronously in two main steps comparison with other records of palaeoclimate in europe and the north atlantic ocean shows that certain common factors controlled changes in ocean and atmosphere dynamics during the deglaciation

conduit evolution in deep seated settings conceptual and numerical models based on field observations 1 to examine the interrelation between hydrogeological environment and conduit development in deep seated settings a conceptual model is tested by numerical modeling based on field observations simplified model settings are designed and crucial parameters are varied a coupled continuum pipe flow model is employed for simulating conduit development within the soluble unit of a multilayer aquifer system in agreement with field observations the evolving cave patterns are characterized by pronounced horizontal passages and multiple vertical conduits at the bottom of the soluble unit but only few at the top the frequency distribution of conduit diameters is found to be bimodal if the permeability of the rock formation is sufficiently high to allow competitive conduit development governed by the feedback between increasing flow and dissolution rates this feedback however is suppressed in low permeability formations as a consequence conduit development is uniform rather than competitive

thermoluminescence chronology of sand profiles in the thar desert and their implications thermoluminescence chronology of three sand profiles in western rajasthan indicates a peak in sand accretion rate at ca 14 ka and a period of dormancy during 13 6 ka bp this observation shows a general correlation with pollen and geochemical records from lakes in thar and demonstrates the potential of desert sands in paleoclimatic reconstruction thermoluminescence ages of 36 ka and 40 ka on two samples suggest that the aeolian sand mobilization activity in this regions is at least as old

generation of complex karstic conduit networks with a hydrochemical model in this paper we present a hydro chemical model that can be used to generate plausible karstic conduit networks that honor what is known about geology hydrology and topography of a karst system to make the model applicable to a range of natural karst systems we introduce a flexible and physically realistic flow boundary condition along the land surface moreover whereas comparable existing speleogenesis models use an explicit reactive transport scheme we propose an implicit reactive transport scheme to permit a coarser spatial discretization of the conduit cells an application to a real karst system illustrates that the model can generate a realistic karstic network that reproduces observed hydrologic behavior in terms of current spring flow rates regional hydraulic head field as well as average groundwater residence times our model provides a useful tool to generate ensembles of possible karstic conduit networks that may be used within a stochastic framework to analyze flow and transport prediction uncertainty associated with a lack of knowledge about network geometry

can we infer the age of karst conduit from the profile of potentiometric surface abstract the floridan aquifer consists of a high presence of karst features that make the landscape prone to sinkholes karst conduits can conduct high amounts of water and affect processes such as groundwater transport a karst conduit evolution model based on dissolution chemistry is applied to the silver springs springshed in ocala florida the model is able to reproduce the observed potentiometric head profiles more accurately than the one dimensional groundwater flow model for confined aquifer with leaky conditions in addition based on the initial fracture geometry and dissolution chemistry the model predicts the age of the conduits from the analyzed head profiles to be approximately 9 60 myrs old the understanding of the karst conduit geometric evolution and mapping can improve conduit age prediction as well as better characterize conduit flow patterns and subsequent groundwater processes

modelling karst geomorphology on different time scales abstract the evolution and flow in a karst aquifer is studied with numerical simulations based on the karst model karst aquifer simulation tool the aquifer consists of a three dimensional interconnected network of conduits representing fractures in the rock and a porous rock matrix representing the finer fissured system in the rock flow through the aquifer can be driven by both diffuse recharge from precipitation and localised sinking streams and the aquifer drains towards a large karst resurgence representing the base level superimposed onto the karst aquifer is a landscape which can evolve with time by small scale diffusive processes large scale river erosion and karst denudation fractures in the aquifer are enlarged with time by chemical dissolution enhancing the secondary porosity of the karst aquifer the enlargement of fractures results in a dramatic increase of the aquifer conductivity over several orders of magnitude and a change of flow patterns from an initially pore controlled to a heterogeneous fracture controlled aquifer during the evolution the water table is falling from an initially high position close to the land surface to a lower level coinciding with the actual base level two model scenarios are studied to elucidate the karst aquifer evolution in three dimensions the evolution models are then complemented by event type spring discharge modelling which can be used as a predictive tool for karst spring discharge and contaminant transport

early development of karst aquifers on percolation networks of fractures in limestone we have modeled flow and dissolution processes within percolation networks representing stochastic primary fracture systems in limestone at the beginning of karstification flow is evenly distributed on all fractures available as the system develops by dissolutional widening of the fractures preferred flow pathways evolve which attract more and more flow until at breakthrough the total flow rate increases dramatically these breakthrough times have been investigated with regard to their dependence on the initial fracture aperture width the dimension of the evolving karst aquifer hydraulic gradients connectivity of the percolation network and the chemical parameters such as higher order rate constants and exponents and equilibrium concentration they exhibit a behavior similar to that of breakthrough times for one dimensional conduits dreybrodt 1996 our results show that the structure of the evolving karst aquifer is determined by the initial geological setting however the final conduits are selected from competing pathways with potential breakthrough times close to each other whereby the details of the distribution of undersaturation with respect to calcite play an important role

the significance of turbulent flow representation in single continuum models 1 karst aquifers exhibit highly conductive features caused from rock dissolution processes flow within these structures can become turbulent and therefore can be expressed by nonlinear gradient functions one way to account for these effects is by coupling a continuum model with a conduit network alternatively turbulent flow can be considered by adapting the hydraulic conductivity within the continuum model consequently the significance of turbulent flow on the dynamic behavior of karst springs is investigated by an enhanced single continuum model that results in conduit type flow in continuum cells ctfc the single continuum approach ctfc represents laminar and turbulent flow as well as more complex hybrid models that require additional programming and numerical efforts a parameter study is conducted to investigate the effects of turbulent flow on the response of karst springs to recharge events using the new ctfc approach existing hybrid models and modflow 2005 results reflect the importance of representing 1 turbulent flow in karst conduits and 2 the exchange between conduits and continuum cells more specifically laminar models overestimate maximum spring discharge and underestimate hydraulic gradients within the conduit it follows that aquifer properties inferred from spring hydrographs are potentially impaired by ignoring flow effects due to turbulence the exchange factor used for hybrid models is necessary to account for the scale dependency between hydraulic properties of the matrix continuum and conduits this functionality which is not included in ctfc can be mimicked by appropriate use of the horizontal flow barrier package for modflow

modeling the influence of epikarst evolution on karst aquifer genesis a time variant recharge boundary condition for joint karst epikarst development 1 the epikarst a zone of increased weathering near the land surface determines the distribution of recharge to a karst aquifer in both space and time it links climatic and near surface geological conditions with the karstification of a limestone aquifer defining both the hydraulic and the chemical boundary conditions for the development of the karst system realistic modeling of the epikarst is therefore a prerequisite for the simulation of karst aquifer genesis a conceptual model of the joint karst epikarst evolution is presented in this paper an epikarst module is developed and implemented in a numerical continuum discrete conduit flow model for karst genesis which accounts for the joint evolution of the epikarst and the main karstic conduit network under unconfined conditions the influence of epikarst genesis on the evolution of the underlying karst aquifer is investigated in four scenarios it is found that only the interaction of epikarst and initial heterogeneity in the underlying carbonate rock leads to the development of a dendritic cave system if no heterogeneity in the initial conduit network or in the recharge distribution is included maze type caves develop

modeling three dimensional karst aquifer evolution using different matrix flow contributions summary we have developed the program package karstaquifer which simulates flow and transport in a three dimensional transient karst aquifer consisting of fractures and matrix elements the fractures can be enlarged by chemical dissolution of calcite increasing the secondary permeability of the karst aquifer boundary conditions for our model setup are guided by published benchmark models for karst aquifer evolution in two dimensions length and width with a 100 m high hydraulic head difference across the model domain responsible for relatively fast evolution of the aquifer we are interested in the effect of the third dimension on the evolution of the karst aquifer especially the effect of matrix flow with a matrix defined either as porous medium or as fine fracture system or both we first discuss our model results using a pseudo 3d setup to be able to directly compare results to the 2d benchmark scenarios published we then discuss real 3d models with a prominent fault located in the central part of the aquifer connecting input and output regions finally we replace the prominent fault with a statistical fracture diameter distribution our results compare well with existing 2d scenarios and the additional third dimension offers new insights into the evolution of karst aquifers especially the role of matrix flow under fixed head boundary conditions in their early phases can be studied in more detail

environmental change during the holocene in western china on a millennial timescale recent data on the evolution of the inland lakes loess palaeosol sequences and glacier variations in western china are briefly reviewed the lake history shows three distinct stages in the holocene i e low water levels before 7500 bp a stage of expansion during the climatic optimum between 7500 and 3500 bp and contraction after 3500 bp three stages wooded grassland mixed woodland wooded grassland becoming steppe also appear indicated by the holocene loess palaeosol sequence in the lanzhou region the optimal period for soil development being between 7500 and 3500 bp there were seven periods of glacier advance the continental glaciers advanced at about 8300 5700 4000 and 400 bp in northwestern china and the maritime glaciers advanced at about 3000 2000 1000 and 200 bp it is suggested that the climatic changes show two periodicities during the holocene namely at intervals of about 2500 and 1000 years

an invasion percolation model of drainage network evolution stream networks evolve by headward growth and branching away from escarpments such as rift margins the structure of these networks and their topographic relief are known to be fractal1 3 but no model so far has been able to generate the observed scaling properties here i present a statistical model of network growth in which stream heads branch and propagate at a rate that depends only on the local strength of the substrate this model corresponds to the process of invasion percolation4 with the added requirement of self avoidance it is a self organized critical system5 with properties similar to those of standard percolation models6 a description based on self avoiding invasion percolation reproduces the known scaling behaviour of stream networks and may provide a valuable tool for delineation of drainage patterns from digital topographic data sets7 8

influence of aperture variability on dissolutional growth of fissures in karst formations the influence of aperture variability on dissolutional growth of fissures is investigated on the basis of two dimensional numerical simulations the logarithm of the fissure aperture before dissolution begins is modeled as a gaussian stationary isotropic random field the initial phase of dissolutional growth is studied up to the time when turbulent flow first occurs at a point within the fissure the breakthrough time the breakthrough time in variable aperture fissures is smaller than that in uniform fissures and decreases as the coefficient of variation of the aperture field increases in comparing uniform and variable aperture fissures in limestone the breakthrough time with 0 1 is about a factor of 2 smaller than that in a uniform fissure the breakthrough time is reduced by about an order of magnitude with 2 0 the mechanism leading to reduced breakthrough times is the focusing of flow into preferential flow channels which are enlarged at a faster rate than the surrounding regions of slower flow dissolution channels are narrower and more tortuous as increases investigations of the influence of reaction rate reveal that the influence of aperture variability is more pronounced in rapidly dissolving rock in uniform fissures in rapidly dissolving minerals breakthrough times are very long since water becomes saturated with respect to the mineral within a short distance of the entrance to the flow path however in variable aperture fissures breakthrough occurs rapidly because of selective growth along preferential flow channels which progressively capture larger fractions of the total flow these results partly explain why conduits develop rapidly in gypsum although previous one dimensional studies suggest that conduit growth will not occur

a model comparison of karst aquifer evolution for different matrix flow formulations the evolution of permeability and flow in a karst aquifer is studied by numerical simulations the aquifer considered consists of a large central fracture a network of finer fissures and a porous rock matrix enlargement of both the central fracture and the fissures by chemical dissolution is possible hence the conductivities in the fracture and the fissure system can increase with time no dissolution is allowed in the porous rock matrix which has a constant conductivity flow is driven by a simple fixed head boundary condition representative for the initial phase of karstification a systematic parameter study is carried out by varying the initial width of the fissure network and the conductivity of the rock matrix while keeping the initial width of the central fracture fixed key parameters such as flowrates breakthrough times and conductivities for the different models are compared if either the conductivity of the rock matrix is high enough or the initial width of the fissures is large enough to carry flow breakthrough times of the aquifer are significantly reduced when compared to a model with low matrix conductivity and small fissures however due to the dissolutional widening of fissures the evolution of the aquifer is distinctively different for models with rock matrix simulated by a porous medium or a fissure network

karstification in unconfined limestone aquifers by mixing of phreatic water with surface water from a local input a model summary when water from the surface of a limestone plain seeps down through the fractured rock to the water table of an unconfined aquifer with low hydraulic gradient containing water saturated with respect to calcite mixing of these waters causes renewed aggressivity a model is presented which describes the evolution of karstification by dissolutional widening of the fractures downgradient from the local input of surface water the model couples flow in the fractures with dissolution rates dissolution rates are given by f k 1 c x ceq 4 where c x is the calcium concentration at distance x from the entrance of the fracture ceq is the equilibrium calcium concentration of the h2o caco3 co2 solution in the fracture and k is a rate constant the model describes two domains of waters saturated with respect to calcite at different partial pressure of co2 at the borders of these domains the waters mix and create dissolutional widening of the fractures by mixing corrosion a channel evolves along the border in the downgradient direction by about 100 m in 100 ky below this channel a zone of fractures with aperture widths up to 1 cm has originated the change of the hydraulic conductivity in the mixing zone shifts the border of the domains allowing the channel to grow in the downgradient direction below it the zone of widened fractures is invaded by saturated phreatic water and dissolution stops this process continues at the downgradient part of the conduit in summary we find cave conduits evolving close to the water table leaving significant cavernous structures below them a variety of modelling scenarios with different choices of parameters show that this evolution is typical and changes only in details but not in its basic behaviour

late quaternary sediments minerals and inferred geochemical history of didwana lake thar desert india abstract variations in clastic sediment texture mineralogy of both evaporites formed at the surface and precipitates formed below the lake floor and the relative chemical activities of the major dissolved components of the chemical precipitates have allowed reconstruction of the history of salinity and water level changes in didwana lake thar desert india hypersaline conditions prevailed at about the last glacial maximum with little evidence of clastic sediments entering the lake between ca 13 000 and 6000 b p the lake level fluctuated widely the lake alternately hypersaline and fresh and clastic sediments were delivered to the lake at a low rate deep water conditions occurred ca 6000 b p and clastic influx increased abruptly the water level dropped towards 4000 b p when the lake dried briefly since 4000 b p the lake has been ephemeral with a lowered rate of sedimentation and mildly saline conditions rather like those of today this sequence of changes documented in the lake parallels changes in vegetation recorded in published pollen diagrams from both the thar and the arabian sea correlation of the various lines of evidence suggests that the climate of the last glacial maximum at didwana was dry and windy with a weak monsson circulation the monsson was re established between ca 13 000 and a little before 6000 b p and when winter rainfall increased ca 6000 b p the lake filled to its maximum depth

simulating long term nitrate n contamination processes in the woodville karst plain using cfpv2 with umt3d summary a research version of cfp conduit flow process code cfpv2 is applied with umt3d to simulate long term 1966 2018 nitrate n contamination transport processes in the woodville karst plain wkp northern florida where karst conduit networks are well developed groundwater flow in the wkp limestone porous matrix is simulated using darcy s law and non laminar flow within conduits is described by darcy weisbach equation nitrate n conduit transport and advective exchanges of groundwater and nitrate n between conduits and limestone matrix are calculated by cfpv2 and umt3d instead of modflow and mt3dms since reynolds numbers for flows in conduits are over the criteria of laminar flow the developed numerical model is calibrated by field observations and then applied to simulate nitrate n transport in the wkp the numerical simulations verify the theories that two sprayfields near the city of tallahassee and septic tanks in the rural area are major nitrate n point sources within the wkp high nitrate n concentrations occur near lost creek sink and conduits of wakulla spring and spring creek springs where aquifer discharge groundwater conduit networks control nitrate n transport and regional contaminant distributions in the wkp as nitrate n is transported through conduits rapidly and spread over large areas

post miocene subtropical karst evolution lower suwannee river basin florida morphometric characteristics of 25 000 karstic depressions suggest that the last phase of the post miocene karstic evolution within the lower suwannee river basin of florida has been controlled by the lower sea level stands of the pleistocene and the formation of the suwannee river during the pleistocene as interglacial seas retreated marine terraces formed by sequential sea level lowstands and the time period of subaerial exposure diminished toward the sea consequently geomorphologically younger karst landforms formed as the elevation of marine terraces decreased the evolutionary geomorphological development of this heavily karstified region produced more frequent and or larger and more complex depressions at higher elevations a geographic information system analysis of morphometric and spatial distribution parameters of the karstic depressions within the lower suwannee river basin reveals that the florida karst is represented by broad shallow depressions with an average density of 6 07 km 2 and an average pitting index of 14 5 morphometric and spatial distribution parameters of karstic depressions show a great variation within the lower suwannee river area and thus preclude a simple morphoclimatic classification of karst landforms the tertiary carbonate rocks of the subtropical florida karst have relatively less joint frequency and significant primary porosity and do not produce the extreme karst landforms observed in the massive limestones of the tropics

sedimentology stratigraphy and tectonics of evolving wedge top depozone ariano basin southern apennines italy the late zanclean wedge top ariano basin located in the external sector of the southern apennines was initially characterized by alluvial and fan delta environments and successively southward of the benevento buonalbergo fault by a gradual drowning with coastal and alluvial plains evolving to shelf and marine coastal settings respectively basin evolution continued with a synsedimentary uplift of different sectors resulting in variations in the drainage pattern and basin shape and ultimately leading to complete basin closure and transition to continental depositional environments early pliocene paleogeography prior to the ariano basin activity is due to regional subsidence and subsequent differential uplifts that resulted from geodynamic processes related to both the downgoing apulian slab and the allochthonous orogenic wedge slab break off and the migration of a tear in the southeastward apulian slab occurred producing a strong subsidence in the external sectors of the southern apennines recorded by the development of the ariano basin subsequently out of sequence synsedimentary thrusting related to thin skinned tectonics occurred in the allochthonous units and unconformably overlying wedge top basin deposits producing northeastward migration of the main depocenters in the ariano basin finally renewed thrusting related to the inversion of pre existing normal faults located in the buried apulian platform and enhanced by regional uplift affected the whole tectonic and sedimentary pile as recorded by deformation of the overlying pliocene deposits

a new model for simulating spring discharge recession and estimating effective porosity of karst aquifers abstract quantitative analysis of recession curves of karst spring hydrographs is a vital tool for understanding karst hydrology and inferring hydraulic properties of karst aquifers this paper presents a new model for simulating karst spring recession curves the new model has the following characteristics 1 the model considers two separate but hydraulically connected reservoirs matrix reservoir and conduit reservoir 2 the model separates karst spring hydrograph recession into three stages conduit drainage stage mixed drainage stage with both conduit drainage and matrix drainage and matrix drainage stage and 3 in the mixed drainage stage the model uses multiple conduit layers to present different levels of conduit development the new model outperforms the classical mangin model and the recently developed fiorillo model for simulating observed discharge at the madison blue spring located in northern florida this is attributed to the latter two characteristics of the new model based on the new model a method is developed for estimating effective porosity of the matrix and conduit reservoirs for the three drainage stages the estimated porosity values are consistent with measured matrix porosity at the study site and with estimated conduit porosity reported in literature the new model for simulating karst spring hydrograph recession is mathematically general and can be applied to a wide range of karst spring hydrographs to understand groundwater flow in karst aquifers the limitations of the model are discussed at the end of this paper

incipient karst formation in carbonate rocks influence of fracture network topology abstract karst features in limestone aquifers often exhibit highly heterogeneous patterns which are strongly governed by structural complexities such as the spatial distribution and organization of fractures in natural carbonate rocks however until now little is known about the impact of structural complexity on karstification processes in this paper we use numerical models to investigate how structural heterogeneity affects the generation of incipient karst in natural fractured systems we develop a numerical model which couples the processes of fluid flow mass transport and dissolution kinetics that govern the growth of fracture aperture based on discrete fracture networks we apply the model to simulate conduit evolution in a natural joint network that displays a distinctive topological pattern a wide range of hydraulic gradient and initial fracture aperture is considered our results show that the network topology may generate a significant impact on dissolution pattern depending on how flow is organized within the discrete network if a channelized structure occurs in the flow network the dissolution pattern depends highly on the initial hydrogeological settings while if the flow network consists of branched segments a similar dissolution pattern emerges for a broad range of initial hydrogeological settings when the flow direction is normal to the persisting fracture orientation intermittent interruptions to the positive feedback process between flow and dissolution occur therefore the breakthrough is delayed we discuss the link between our results of dissolution modeling in fracture networks to previous modelling efforts in the context of single rough fractures and fracture network formed by orthogonal fracture sets

modeling of karst aquifer genesis influence of exchange flow 1 this paper presents a numerical model study simulating the early karstification of a single conduit embedded in a fissured system a hybrid continuum discrete pipe flow model cave is used for the modeling the effects of coupling of the two flow systems on type and duration of early karstification are studied for different boundary conditions assuming fixed head boundaries at both ends of the conduit coupling of the two flow systems via exchange flow between the conduit and the fissured system leads to an enhanced evolution of the conduit this effect is valid over a wide range of initial conduit diameters and karstification is accelerated by a factor of about 100 as compared to the case of no exchange flow parameter studies reveal the influence of the exchange coefficient and of the hydraulic conductivity of the fissured system on the development time for the conduit in a second scenario the upstream fixed head boundary is switched to a fixed flow boundary at a specified flow rate during the evolution limiting the amount of water draining toward the evolving conduit depending on the flow rate specified conduit evolution may be slowed down or greatly impaired if exchange flow is considered

simulation of the development of karst aquifers using a coupled continuum pipe flow model 1 this paper is intended to provide insight into the controlling mechanisms of karst genesis based on an advanced modeling approach covering the characteristic hydraulics in karst systems the dissolution kinetics and the associated temporal decrease in flow resistance karst water hydraulics is strongly governed by the interaction between a highly conductive low storage conduit network and a low conductive high storage rock matrix under variable boundary conditions only if this coupling of flow mechanisms is considered can an appropriate representation of other relevant processes be achieved e g carbonate dissolution transport of dissolved solids and limited groundwater recharge here a parameter study performed with the numerical model carbonate aquifer void evolution cave is presented which allows the simulation of the genesis of karst aquifers during geologic time periods cave integrates several important features relevant for different scenarios of karst evolution 1 the complex hydraulic interplay between flow in the karst conduits and in the small fissures of the rock matrix 2 laminar as well as turbulent flow conditions 3 time dependent and nonuniform recharge to both flow systems 4 the widening of the conduits accounting for appropriate physicochemical relationships governing calcite dissolution kinetics this is achieved by predefining an initial network of karst conduits protoconduits which are allowed to grow according to the amount of aggressive water available due to hydraulic boundary conditions the increase in conduit transmissivity is associated with an increase in conduit diameters while the conductivity of the fissured system is assumed to be constant in time the importance of various parameters controlling karst genesis is demonstrated in a parameter study covering the recharge distribution the upgradient boundary conditions for the conduit system and the hydraulic coupling between the conduit network and the rock matrix in particular it is shown that conduit diameters increase in downgradient or upgradient direction depending on the spatial distribution local versus uniform of the recharge component which directly enters the conduit system

global nature of the younger dryas cooling event inferred from oxygen isotope data from sulu sea cores the younger dryas an approximately 1 000 year long return to near glacial conditions interrupted the glacial holocene climate transition during which most of the northern hemisphere ice sheets melted evidence for the younger dryas event has been found mainly in sediments from the north atlantic ocean and northwest europe and this has led to the idea that the event was caused by an injection of meltwater into the north atlantic ocean1 3 this model however has been recently questioned in the light of coral reef data on the rate of sea level changes during this transition4 here we present high resolution oxygen isotope records from benthic and planktonic foraminifera from two radiocarbon dated cores in the sulu sea showing that the younger dry as occurred synchronously in the surface and deep waters of the sulu sea and the northern atlantic ocean by combining our results with other palaeoclimate data we suggest that the younger dry as event was a global phenomenon and we believe it to have been caused by low atmospheric co2concentrations

holocene late pleistocene climatic ice core records from qinghai tibetan plateau three ice cores to bedrock from the dunde ice cap on the north central qinghai tibetan plateau of china provide a detailed record of holocene and wisconsin wurm late glacial stage lgs climate changes in the subtropics the records reveal that lgs conditions were apparently colder wetter and dustier than holocene conditions the lgs part of the cores is characterized by more negative 18 o ratios increased dust content decreased soluble aerosol concentrations and reduced ice crystal sizes than the holocene part these changes occurred rapidly 10 000 years ago in addition the last 60 years were apparently one of the warmest periods in the entire record equalling levels of the holocene maximum between 6000 and 8000 years ago

a model of the early evolution of karst aquifers in limestone in the dimensions of length and depth a new model of the early evolution of limestone karst aquifers in the dimensions of length and depth is presented in its initial state the aquifer consists of a rock massive with evenly spaced fractures of about 50 mm aperture widths with an hydraulic conductivity of 10 27 ms 21 in addition to this a coarser network of prominent fractures with aperture widths of several 100 mm is also present boundary conditions of constant recharge 450 mm year or constant head from the input of allogenic streams are imposed first the position of the water table in the aquifer is calculated then dissolutional widening during a time step in all the fractures below the water table is found by use of the well known nonlinear dissolution kinetics of limestone this is iterated and the position of the water table as well as the fracture widths are found as a function of time in the case of constant recharge to a karst plateau the water table in any case drops to base level and conduits there propagate from the spring headwards if constant head conditions are valid the position of the water table remains almost stable and conduits propagate along the water table from the input towards the spring there is competition between conduit evolution along prominent fractures and along tight fissures close to the water table in any case under constant head conditions one of these pathways wins and early karst evolution is terminated by a breakthrough event with an explosive increase of the flow through the aquifer until constant head conditions break down depending on the boundary conditions of constant head or constant recharge or a combination of both it is possible to describe models of cave genesis which have been derived from field evidence such as the water table models of swinnerton geol soc am bull 34 1932 662 and rhoades and sinacori j geol 49 1941 785 as well as the four state model by ford and ewers can j earth sci 15 1978 1783 q 2001 elsevier science b v all rights reserved

uplift of tibetan plateau a history of the elevation and crustal thickness of the tibetan plateau since the continental collision at 45 ma has been computed using a kinematic model based on plate tectonic reconstructions and conservation of crustal volume in our reconstructions the indochina block was attached to the southern margin of eurasia before being extruded to the southeast as evidenced by the opening of the south china sea this opening affected the mass input into tibet so that tibet did not uplift to an elevation higher than 1 km until early miocene when spreading of the south china sea ceased the model then gives a steady rise of tibet from middle miocene to its present elevation