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Modern cover-collapse sinkhole development in the Brooksville Ridge of west-central Florida uncovered paleokarst solution features filled with Miocene Peace River Formation sediments. Sedimentary structures in this paleokarst fill included a 70 cm-thick package of sub-rounded and moderately well-sorted quartz sandstone, and indurated with poikilotopic calcite cement—confirmed using X-ray diffraction (XRD). The morphology of the sediment package includes mm-scale compositional banding inside cm-scale ‘plops’, akin to types of commercial aquarium stone. Scanning electron microscopy (SEM), energy-dispersive X-ray spectra (XEDS), and portable X-ray fluorescence (pXRF) measurements reveal that metal oxides create the compositional banding and that the grains are frosted with kaolinite–montmorillonite clay. The shape of this ‘plopstone’ deposit, the compositional banding, and structures associated with soft-sediment deformation indicate Stokes Law throughfall in a near-stagnant sub-aqueous setting, with ‘plops’ held together by the cohesion of clay—like kinetic sand. Following deposition, density separation occurred during extensional strain, and cementation progressed slowly in calcite-saturated waters. Collectively, this ‘plopstone’ represents a likely product of sand raveling common during the development of cover-subsidence sinkholes. [ABSTRACT FROM AUTHOR]

To further ascertain the origin of the Ordovician Majiagou Formation reservoirs in the Ordos Basin, the M54-M51 sub-members of the Ordovician Majiagou Formation in the eastern Sulige gasfield of Ordos Basin were taken as examples to analyze the vertical development characteristics of eogenetic karst and to discover the dissolution mechanism and its control on reservoirs through observation of a large number of cores and thin sections. According to detailed analysis of petrologic characteristics, the reservoir rock types include micritic dolomite, grain dolomite and microbialite which have mainly moldic pore, intergranular (dissolved) pore, and (dissolved) residual framework pore as main reservoir space respectively. The study area developed upward-shallowing sequences, with an exposure surface at the top of a single upward-shallowing sequence. The karst systems under the exposure surface had typical exposure characteristics of early dissolution and filling, indicating these reservoirs were related to the facies-controlled eogenetic karstification. With the increase of karstification intensity, the reservoirs became worse in physical properties.

Abstract The Miami Oolite of South Florida is representative of a grainstone‐rich carbonate unit that has been surficially karsted, and therefore may be considered as an analogue for subsurface reservoirs/aquifers with ‘high’ permeability extremes. The deposit can potentially serve to improve a conceptual understanding of heterogeneity as imparted by shallow‐marine facies changes and early meteoric diagenetic modification. Reviewed here are recent studies of the Miami Oolite with the intent to emphasize those key aspects of the facies and early diagenesis that most impact permeability and fluid flow. The Miami Oolite displays the preserved morphology of a fossilized ooid sandbody, even though it has been subaerially exposed in a tropical climate since its deposition approximately 120 kyr bp during the last interglacial highstand. The depositional motif is one of a dip‐oriented, tidal bar belt of shoals and shallow channels fronted by a strike‐oriented barrier bar. The barrier bar comprises cross‐stratified grainstones and locally burrowed grain/packstones, while the tidal shoals and channels are more commonly burrowed pack/grainstones. Surficial karst features (dolines and stratiform caves) have been added during the ca 120 kyr of subaerial exposure, but of more significance is the associated solution‐enhancement of the widespread burrowed facies. Since the Miami Oolite is the uppermost portion of the Biscayne Aquifer, there is also an understanding of fluid flow through the deposit that sheds valuable insight on the larger scale, shallow subsurface plumbing. The pore system comprises matrix pores (interparticle and separate vugs) and touching‐vug macropores that are commonly associated with burrowed [Ophiomorpha] intervals. Ground‐penetrating radar, well and flow test data indicate that matrix porosity provides most of the groundwater storage, whereas the touching vug macropores account for the majority of flow. The dolines and shallow caves seem to be sufficiently spaced as to generally not be in direct connection, with the result that they are less important in terms of regional flow than the prevailing pore system.

Copyright of Acta Sedimentologica Sinica is the property of Acta Sedimentologica Sinica Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The Miami Oolite of South Florida is representative of a grainstone‐rich carbonate unit that has been surficially karsted, and therefore may be considered as an analogue for subsurface reservoirs/aquifers with 'high' permeability extremes. The deposit can potentially serve to improve a conceptual understanding of heterogeneity as imparted by shallow‐marine facies changes and early meteoric diagenetic modification. Reviewed here are recent studies of the Miami Oolite with the intent to emphasize those key aspects of the facies and early diagenesis that most impact permeability and fluid flow. The Miami Oolite displays the preserved morphology of a fossilized ooid sandbody, even though it has been subaerially exposed in a tropical climate since its deposition approximately 120 kyr bp during the last interglacial highstand. The depositional motif is one of a dip‐oriented, tidal bar belt of shoals and shallow channels fronted by a strike‐oriented barrier bar. The barrier bar comprises cross‐stratified grainstones and locally burrowed grain/packstones, while the tidal shoals and channels are more commonly burrowed pack/grainstones. Surficial karst features (dolines and stratiform caves) have been added during the ca 120 kyr of subaerial exposure, but of more significance is the associated solution‐enhancement of the widespread burrowed facies. Since the Miami Oolite is the uppermost portion of the Biscayne Aquifer, there is also an understanding of fluid flow through the deposit that sheds valuable insight on the larger scale, shallow subsurface plumbing. The pore system comprises matrix pores (interparticle and separate vugs) and touching‐vug macropores that are commonly associated with burrowed [Ophiomorpha] intervals. Ground‐penetrating radar, well and flow test data indicate that matrix porosity provides most of the groundwater storage, whereas the touching vug macropores account for the majority of flow. The dolines and shallow caves seem to be sufficiently spaced as to generally not be in direct connection, with the result that they are less important in terms of regional flow than the prevailing pore system. [ABSTRACT FROM AUTHOR]

Sistema Muévelo Rico is a 1.2 km long cave in Quintana Roo, less than 2 km from the Caribbean Sea. We measured illuminance to a level of 0.1 lux, organic matter (weight loss on ignition), temperature, and relative humidity. The last two were measured at hourly intervals for nearly one year. Approximately one-third of the cave has illuminance values greater than 0.01 lux, and most of the rest of the cave has light as well. Temperature and relative humidity were relatively constant, but they showed a daily cycle at all stations, albeit with different strengths. Organic matter averaged 8%, intermediate in value between surface and aphotic zones. Both eyeless species and eyed predators occurred throughout the cave. Their occurrence can best be explained by their foraging for organic matter and incurring an increased risk of predation.

Karst porosity system is widely developed in the Fourth Member of Neoproterozoic Dengying Formation in Central Sichuan Basin of China. The result of the previous exploration in this area based on the theory of telogenetic karst, which mainly focused on the fracture/fault belt especially in the karst slope, leaves much to be desired. Though a systematically geological research in this study, it is found that the dissolution holes are mainly concentrated on the mud mound deposits and granular rocks. Both of them have a greater primitive porosity and permeability than the micrite that originally formed in low-energy environments, which is facies controlled. On the basis of the above and the fact that a tectonic movement has caused a massive subaerial exposure of the formation that only experienced a shallow burial, it is proposed that the paleokarst porosity system is the product of eogenetic karst. Two-stage eogenetic karsts have been interpreted: the syngenetic exposure caused by the short-term relative sea-level fluctuation and the exposure caused by the uplift of the second phase of Tongwan tectonic movement. The meteoric alteration in syngenetic period is commonly marked by the development of intergranular pores but on a small scale. It is believed to be important for providing a good pore-permeability foundation for the later eogenetic karst. The later exposure occurs immediately at the end of the deposition of the Fourth Member of Dengying Formation that only experienced a shallow burial. Since the effect of compaction and cementation in this shallow burial before uplift is relatively weak, only the micrite has been densified and retaining the majority of original pores in the carbonate mounds and grain shoals as paths for karst flow. Moreover, combined with the geological background and seismic profile, it can be ascertained that the karst occurs in a coastal environment. Twelve meteoric lenses have been interpreted after recovering the karst palaeogeomorphology. The scale of the meteoric lens and the reservoir performance have shown a decreasing tendency from the coastal to the inland area, which also confirms this view. The results of this research have put emphasis on the lithologic differentiation in eogenetic karst and the geographical location of karst development thus might provide a reference for further reservoir prediction in this area and other similar places. [ABSTRACT FROM AUTHOR]

To make a better understanding of the stratigraphic correlation and ocean processes during the transition from Series 2 to Series 3 in the Cambrian, this study investigated the characteristics and origin of the palaeokarst in the uppermost part of the Longwangmiao Formation (Toyonian) and established the carbon isotopic curves of the shallow‐water succession. Macroscopically, the palaeokarst features have been identified, including the exposed surface, karstic trough, discolouration, and breccia in the upper part of the Longwangmiao Formation. The exposed surface is divided into the bedrock, weakly weathering zone, intensely weathering zone, dissolved‐collapsed zone, and weathering clay layer at the Dingzhai section. The reddish aluminous oxide and the stratiform‐dissolved pore are recognized in the Gaodongmiao section. The clast‐support breccia and matrix‐support breccia develop in the palaeokarst zone. Microscopically, three dissolution‐filling zones in grainstone (the matrix zone, half‐dissociated zone, and mixed‐filling zone) dissolved fibrous cement in the early diagenetic stage, microspar cement in a bright homogeneous luminescence, and medium‐crystal calcite showing a zonation luminescence are identified indicating the facies‐controlled attributes. The δ13C values are characterized by a lower range (4.4‰ to −2.1‰) in the karst zone. The REE pattern shows enriched middle REE, negative Eu anomalies, and low Y/Ho ratio, which is different from the nature of seawater. It is proposed that the palaeokarst in the upper part of the Longwangmiao Formation is the eogenetic karst controlled by high‐frequency sea‐level fluctuations. Two negative δ13C excursions (values −4.4‰ in D2 and −3.6‰ in D1) are respectively recognized, the top boundary and middle part of the Longwangmiao Formation. Based on the regional and global correlations, the excursion of D2 is the diagenetic signal in the shallow‐water setting, which correlated to ROECE event (Redlichiid‐Olenellid Extinction Carbon isotope Excursion) that occurred around the boundary between Series 2 and Series 3 in the Cambrian. The local signal of D2 is attributed to the sea‐level falling. [ABSTRACT FROM AUTHOR]

Penecontemporaneous dissolution has been considered as the dominant origin of reservoir formation, whereas epigenetic dissolution has also played certain roles in the improvement of reservoir capacity in the Upper Cretaceous Mishrif Formation in the Middle East. Here, we report a possible new reservoir origin based on a case study in the Halfaya oilfield of Iraq, that is, facies‐controlled eogenetic karstification. The most representative evidence is that early selective dissolution is not only present in relative high‐energy categories of rocks but also in low‐energy ones in the cored intervals. Meanwhile, the occurrence frequency of karstification varies among different environments and associated lithologies. In grainstones and packstones, spongy‐like dissolution pores and irregular karst channels are widely developed, with fillings and massive plastic breccias. In contrast, in wackestones, lots of high‐angle karst channels are developed based on biological burrows, and the karst is more frequently observed in the shoal environment than in the low‐energy environments. These characteristics are indication of eogenetic karstification. The model of this karstification can be attributed to a multiple superimposition of short‐term exposure during the penecontemporaneous stage and the medium‐term exposure after the shallow burial stage. The karst has impact on reservoir capacity, according to which 3 areas are divided in the increasing order, namely, the tight bedrock area, spongy‐like dissolution pores area, and karst channels and vugs‐filled area, among which the karst channels and vugs‐filled area is the most favourable for oil accumulation. This understanding might be general to the Mishrif reservoirs in the entire Middle East. [ABSTRACT FROM AUTHOR]

Udin Boršt is an isolated conglomerate terrace in Gorenjska region, Slovenia. A number of surface karst features and caves developed here due to the predominance of carbonate gravel. It is one of the last contiguous areas of lowland forest in Gorenjska region, and a popular recreation location for the people living nearby. Due to its karst surface and the forest it offered shelter to the locals in turbulent times. Its role during the period when bandits (rokovnjači) was common and during the Second World War is still preserved in folk memory. Due to its natural and cultural heritage, the area was protected as a Memorial park in 1985, but the legislation has become outdated and needs to be amended and updated. This article presents new findings on the geomorphological and intangible cultural heritage that need to be incorporated in the amended legislation.

Coastal karst is characterized by special geomorphologic and hydrodynamic conditions as well as by peculiar sedimentary, geochemical, and biospeleological environments. Generally, the more distinctive karstic features produced near the coastline are strongly influenced by sea-level changes, which generate a broad set of interactions between littoral processes and karst development. The glacioeustatic rises and falls of sea level affected the littoral karst in different ways, namely: vertical and horizontal shifts in the shoreline position, changes in elevation of the local water table, and vertical displacements of the halocline. Most eogenetic karsts have been subjected over long time spans to repeated changes of a variety of vertically-zoned geochemical environments: vadose, phreatic meteoric-water, brackish mixing-waters and even marine water. Many coastal caves appear to be passively drowned by Holocene sea-level rise, and to contain glacioeustatic pools of varied size where the current water table intersects formerly air-filled chambers or passages. These coastal phreatic waters are controlled by sea level and fluctuate with tides. Significantly, features such as phreatic speleothems that are able to record ancient sea levels occur closely associated to the surface of the pools. The cave pools are brackish or even marine anchialine environments that contain remarkable communities of troglobitic stygofauna. All of these aspects can be studied in detail along the southern and eastern coast of Mallorca Island owing to the widespread outcrop of Upper Miocene calcarenites, in which the development of eogenetic karst features started approximately 6 Ma ago, at the end of Messinian times. Some outstanding coastal caves result and include the celebrated Coves del Drac (explored by E.A. Martel in 1896), the labyrinthine Cova des Pas de Vallgornera (more than 30 km in length) and the recently explored Cova de sa Gleda (whose submerged passages exceed 10 km, as shown by scuba-diving surveys). Careful observations and detailed mapping of caves in the Upper Miocene reef rocks of Mallorca permit a better understanding of the coastal speleogenetic processes involved in a typical eogenetic karst over time ranges greater than 1 Ma. The role played by recurrent glacioeustatic oscillations of sea level and the subsequent rises and falls of the water table are emphasized in our model. There are two associated mechanisms: the triggering of breakdown by the loss of buoyant support that follows each lowering of sea level (i.e., during glaciations or smaller cold events) and the later underwater solution of boulders and collapse debris (during high sea levels that correspond to interglacial events). Additionally, tidal fluctuations affecting groundwaters would enhance solutional enlargement of caves and vug-porosity connected to the sea, rather than conventional karstic flow through conduits that probably is not as important an agent in eogenetic speleogenesis.

Solution pipes are abundant in Late Pleistocene aeolian calcarenites at Cape Bridgewater in southwestern Victoria, and were studied using field work, morphometric analysis, thin sections, mineralogical and chemical analyses, and OSL dating. The solution pipes are vertical tubes formed in aeolian limestone with matrix porosity. They are typically 0.1–1 m wide and 1–5 m deep, with rounded terminations and cemented rims up to 10 cm thick. They are overlain by palaeosols and filled mostly with palaeosol material; rhizoliths are commonly present in the solution pipe fills and the surrounding calcarenite. The solution pipes have formed by focused dissolution of aeolianite, relatively quickly after the sand deposition, and concurrently filled with soil as they developed. They most likely formed beneath trees (as a result of focused infiltration due to stemflow) or due to fingered flow (unstable wetting front that breaks into fingers as it moves downwards). Solution pipe formation was strongly dependent on climate; periods of solution pipe formation followed the deposition of aeolianites at the end of interglacials MIS 7, 9 and 11, when the dunes were stabilised by vegetation and there was sufficient rainfall for substantial subsoil dissolution. The cemented rims formed in the following drier glacial climates. Solution pipes are most abundant in the youngest aeolianite, probably reflecting the wetter climate at the end of MIS 7 that allowed a dense forest to cover the dunes. From MIS 5 to MIS 2 no deposition of calcareous sand occurred on Cape Bridgewater, and combined with a very wet interglacial period MIS 5e, resulted in additional karstification, allowing the pipes in the MIS 7 aeolianite to extend deeper and drill down into the underlying member. A well-developed calcrete layer drapes over these solution pipes, and probably formed during the dry, windy climate of the Last Glacial Maximum. [ABSTRACT FROM AUTHOR]

Hermeneutics is the theory of interpretation. One of its major components is recognizing prejudgments, or forestructures, that we bring to our objects of study. In this paper, we construct a historical narrative of the evolution of thinking about the role of caves in relation to groundwater flow in limestone, and we tabulate forestructures as they appear in the story. This account consists of three overlapping time periods: the before and after of an incident that repelled hydrogeologists and students of karst from each other in the middle of the 20th century; a period, up to around the turn of this century, when karst science and mainstream hydrogeology were on different tracks; and a period of convergence, now intertwining, beginning roughly in the last quarter of the 20th century. Two influential players in our story are M.K. Hubbert, whose introduction of the Eulerian perspective of flow was a force for divergence, and R.M. Garrels, whose founding of the field of sedimentary geochemistry was a force for convergence. Other key players include F.T. Mackenzie, J.E. Mylroie, V.T. Stringfield, the U.S. Geological Survey, the Bermuda Biological Station, and the Gerace Research Center in the Bahamas, along with the historical accounts of W.B. White. Our narrative ends with the broader acceptance of the concept of multiple-permeability karst aquifers. We flag in our construction a total of 43 forestructures distributed amongst the categories of hermeneutic theory: 14 in the category of preconceptions; 9 in goals; 14 in tools such as skills; and 6 in tools such as institutions. These counts are an example of the concept of social construction of statistics, and we discuss the implications in terms of the huge number of potential combinations of forestructures that could shape alternative historical narratives of this subject over this time frame. [ABSTRACT FROM AUTHOR]

Much of what is known about groundwater circulation and geochemical evolution in carbonate platforms is based on platforms that are fully confined or unconfined. Much less is known about groundwater flow paths and geochemical evolution in partially confined platforms, particularly those supporting surface water. In north-central Florida, sea level rise and a transition to a wetter climate during the Holocene formed rivers in unconfined portions of the Florida carbonate platform. Focusing on data from the Santa Fe River basin, we show river formation has led to important differences in the hydrological and geochemical evolution of the Santa Fe River basin relative to fully confined or unconfined platforms. Runoff from the siliciclastic confining layer drove river incision and created topographic relief, reorienting the termination of local and regional groundwater flow paths from the coast to the rivers in unconfined portions of the platform. The most chemically evolved groundwater occurs at the end of the longest and deepest flow paths, which discharge near the center of the platform because of incision of the Santa Fe River at the edge of the confining unit. This pattern of discharge of mineralized water differs from fully confined or unconfined platforms where discharge of the most mineralized water occurs at the coast. Mineralized water flowing into the Santa Fe River is diluted by less evolved water derived from shorter, shallower flow paths that discharge to the river downstream. Formation of rivers shortens flow path lengths, thereby decreasing groundwater residence times and allowing freshwater to discharge more quickly to the oceans in the newly formed rivers than in platforms that lack rivers. Similar dynamic changes to groundwater systems should be expected to occur in the future as climate change and sea level rise develop surface water on other carbonate platforms and low lying coastal aquifer systems. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

ABSTRACT Formation of extensive phreatic caves in eogenetic karst aquifers is widely believed to require mixing of fresh and saltwater. Extensive phreatic caves also occur, however, in eogenetic karst aquifers where fresh and saltwater do not mix, for example in the upper Floridan aquifer. These caves are thought to have formed in their modern settings by dissolution from sinking streams or by convergence of groundwater flow paths on springs. Alternatively, these caves have been hypothesized to have formed at lower water tables during sea level low-stands. These hypotheses have not previously been tested against one another. Analyzing morphological data and water chemistry from caves in the Suwannee River Basin in north-central Florida and water chemistry from wells in the central Florida carbonate platform indicates that phreatic caves within the Suwannee River Basin most likely formed at lower water tables during lower sea levels. Consideration of the hydrological and geochemical constraints posed by the upper Floridan aquifer leads to the conclusion that cave formation was most likely driven by dissolution of vadose CO2 gas into the groundwater. Sea level rise and a wetter climate during the mid-Holocene lifted the water table above the elevation of the caves and placed the caves tens of meters below the modern water table. When rising water tables reached the land surface, surface streams formed. Incision of surface streams breached the pre-existing caves to form modern springs, which provide access to the phreatic caves. Phreatic caves in the Suwannee River Basin are thus relict and have no causal relationship with modern surficial drainage systems. Neither mixing dissolution nor sinking streams are necessary to form laterally extensive phreatic caves in eogenetic karst aquifers. Dissolution at water tables, potentially driven by vadose CO2 gas, offers an underappreciated mechanism to form cavernous porosity in eogenetic carbonate rocks. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Physicochemical parameters have been studied in the water column of Inkwell, Church, and Watling's Blue Holes (San Salvador Island, Bahamas). Water samples were collected from multiple depths at the three blue holes to identify and characterize changes of physical and chemical parameters. The values were compared to the average ocean concentrations in order to assess how connectivity to the ocean, evaporation, freshwater input, and bacterial activity influence water rock interactions. The salinity concentrations vary between the surface and ~ -4 m in each blue hole before stabilizing to rather similar values (~19.6‹). Mixing processes in the water column at Inkwell and Church blue holes are inferred from changes in the concentration of chloride. The degree of variation is a mixed signal resulting from changes of the precipitation/evaporation balance and tidal driven water-rock interaction. Inkwell is strongly influenced by tidal pumping, which causes ample value fluctuations, most notably salinity (1.01 to 21.8‹), chloride (Cl-) from 300 to 9591.8 mg/L, and total hardness (9 to 293 mg/L) within the mixing zone. This location is the only site that may have a true halocline. Watlings's geochemical parameters have the smallest range (i.e., salinity 30.19 - 34.30‹) due to a lack of mixing that suggests that this site has a direct conduit connection to the ocean. The furthest inland blue hole (Church) lacks significant geochemical fluctuations with the exception of Cl-, which changes from 19600 mg/L to 1800 mg/L between the depths of 1 and 2 m. The abrupt modification of Cl- values between surface and -2 m suggests mixing is occurring. The lack of other parameter variations within the water column suggests restricted flow via narrow conduits or more likely matrix flow. Salinity values decrease from the surface (21.47‹) to ~ -1 m (17.78‹) whereas, sulfate (SO42-) concentration at the same depth reach its maximum value (4009 mg/L). The high sulfate values throughout the column (2634 to 4009 mg/L) are characteristic of seawater (>2700 mg/L), thus indicating seawater seepage into the blue hole. We assume the elevated salinity values at the surface and -1 m are pointing towards evaporative processes. [ABSTRACT FROM AUTHOR]

Summary: Exchange of water between conduits and aquifers occurs in many continental karst settings because allogenic recharge from confined catchments causes hydraulic heads in conduits to increase faster than in the aquifer. Most modern carbonate platforms lack allogenic catchments, allowing rainfall to recharge the aquifer uniformly without sufficiently altering head gradients to drive exchange between conduits and aquifers. Some modern carbonate platforms experience tidal variations which could lead to head gradients that drive exchange. To determine the impact of tides on exchange, we measured water elevations at high temporal resolution in the ocean, blue holes and wells on San Salvador Island and Rum Cay, Bahamas. Dampened tidal amplitudes inland indicate diffusivity values (transmissivity/storativity) at wells were around 1.3×106 m2/day and at blue holes were around 76.9×106 m2/day, assuming dampening results only from head loss. These diffusivity values were used to estimate hydraulic conductivity values of around 4.0–294×104 m/day although they may be lower if the aquifer thickness is greater than the estimated 10m. We assume wells provide values representing greater influence of matrix permeability than values from blue holes, which represent a greater influence of conduit permeability. Differences in permeability drive exchange because hydraulic head in the aquifer lags the head in the conduits and blue hole through a tidal cycle. If negligible head loss occurs with flow through conduits, as reflected in lag times less than 10min, then differences in elevation at the blue holes and the ocean may represent exchange of water between the blue hole and matrix porosity. With this assumption, about 0.9m3 of water is exchanged per half tidal cycle, or about 1% of the complete change in volume of water in the blue hole per half tidal cycle. This volume represents an average penetration into the aquifer of 6–8mm although it could be further in zones with elevated permeability. Exchange is reflected in systematic changes in specific conductivity and pH between high and low tide and the pH changes reflect reaction with the surrounding aquifer material. Since exchange occurs twice daily, cumulative alteration of aquifer porosity could be large. Tidal exchange should decrease away from the coast on large carbonate platforms so that tidally driven alteration will be enhanced at the rims over interior of carbonate platforms. [ABSTRACT FROM AUTHOR]

Summary: Most concepts of conduit development have focused on telogenetic karst aquifers, where low matrix permeability focuses flow and dissolution along joints, fractures, and bedding planes. However, conduits also exist in eogenetic karst aquifers, despite high matrix permeability which accounts for a significant component of flow. This study investigates dissolution within a 6-km long conduit system in the eogenetic Upper Floridan aquifer of north-central Florida that begins with a continuous source of allogenic recharge at the Santa Fe River Sink and discharges from a first-magnitude spring at the Santa Fe River Rise. Three sources of water to the conduit include the allogenic recharge, diffuse recharge through epikarst, and mineralized water upwelling from depth. Results of sampling and inverse modeling using PHREEQC suggest that dissolution within the conduit is episodic, occurring only during 30% of 16 sampling times between March 2003 and April 2007. During low flow conditions, carbonate saturated water flows from the matrix to the conduit, restricting contact between undersaturated allogenic water with the conduit wall. When gradients reverse during high flow conditions, undersaturated allogenic recharge enters the matrix. During these limited periods, estimates of dissolution within the conduit suggest wall retreat averages about 4×10−6 m/day, in agreement with upper estimates of maximum wall retreat for telogenetic karst. Because dissolution is episodic, time-averaged dissolution rates in the sink-rise system results in a wall retreat rate of about 7×10−7 m/day, which is at the lower end of wall retreat for telogenetic karst. Because of the high permeability matrix, conduits in eogenetic karst thus enlarge not just at the walls of fractures or pre-existing conduits such as those in telogenetic karst, but also may produce a friable halo surrounding the conduits that may be removed by additional mechanical processes. These observations stress the importance of matrix permeability in eogenetic karst and suggest new concepts may be necessary to describe how conduits develop within these porous rocks. [Copyright &y& Elsevier]

An examination of eogenetic karst along supratidal coastal and tidally-influenced inland-lake shoreline sites was conducted on San Salvador Island, Bahamas in order to gain insight into the karst forming processes active along the land-marine interface. Based on proximity to marine aerosols and the spatial distribution patterns of surficial karst morphologies and biotic populations, four shore-parallel geomorphic zones are identified. Spatial affinities suggest haloclastic, bioerosional, and to a lesser degree, mixing dissolution/corrosion processes dominate the seaward-most region of the coastal platform, the region regularly wetted by sea spray and most deeply dissected. Further landward, where the platform remains largely free of marine aerosol, surficial karst development is more subdued and appears to be dominated by meteoric dissolution processes. The observed meso- and microkarst morphologies and associated geomorphic zoning patterns are the combined products of biological, chemical, and physical processes unique to the supratidal zone, and are largely controlled by position relative to the landmarine interface and sea level. [ABSTRACT FROM AUTHOR]

Coastal karst is characterized by special geomorphologic and hydrodynamic conditions as well as by peculiar sedimentary, geochemical, and biospeleological environments. Generally, the more distinctive karstic features produced near the coastline are strongly influenced by sea-level changes, which generate a broad set of interactions between littoral processes and karst development. The glacioeustatic rises and falls of sea level affected the littoral karst in different ways, namely: vertical and horizontal shifts in the shoreline position, changes in elevation of the local water table, and vertical displacements of the halocline. Most eogenetic karsts have been subjected over long time spans to repeated changes of a variety of vertically-zoned geochemical environments: vadose, phreatic meteoric-water, brackish mixing-waters and even marine water. Many coastal caves appear to be passively drowned by Holocene sea-level rise, and to contain glacioeustatic pools of varied size where the current water table intersects formerly air-filled chambers or passages. These coastal phreatic waters are controlled by sea level and fluctuate with tides. Significantly, features such as phreatic speleothems that are able to record ancient sea levels occur closely associated to the surface of the pools. The cave pools are brackish or even marine anchialine environments that contain remarkable communities of troglobitic stygofauna. All of these aspects can be studied in detail along the southern and eastern coast of Mallorca Island owing to the widespread outcrop of Upper Miocene calcarenites, in which the development of eogenetic karst features started approximately 6 Ma ago, at the end of Messinian times. Some outstanding coastal caves result and include the celebrated Coves del Drac (explored by E.A. Martel in 1896), the labyrinthine Cova des Pas de Vallgornera (more than 30 km in length) and he recently explored Cova de sa Gleda (whose submerged passages exceed 10 km, as shown by scuba-diving surveys). Careful observations and detailed mapping of caves in the Upper Miocene reef rocks of Mallorca permit a better understanding of the coastal speleogenetic processes involved in a typical eogenetic karst over time ranges greater than 1 Ma. The role played by recurrent glacioeustatic oscillations of sea level and the subsequent rises and falls of the water table are emphasized in our model. There are two associated mechanisms: the triggering of breakdown by the loss of buoyant support that follows each lowering of sea level (i.e., during glaciations or smaller cold events) and the later underwater solution of boulders and collapse debris (during high sea levels that correspond to interglacial events). Additionally, tidal fluctuations affecting groundwaters would enhance solutional enlargement of caves and vug-porosity connected to the sea, rather than conventional karstic flow through conduits that probably is not as important an agent in eogenetic speleogenesis. [ABSTRACT FROM AUTHOR]

Geochemical characterization and numerical modelling of surface water and ground water, combined with hydrological observations, provide quantitative estimates of meteoric diagenesis in Pleistocene carbonates of the northern Bahamas. Meteoric waters equilibrate with aragonite, but water-rather than mineral controlled reactions dominate. Dissolutional lowering of the undifferentiated bedrock surface is an order of magnitude slower than that within soil-filled topographic hollows, generating small-scale relief at a rate of 65-140 mm ka-1 and a distinctive pocketed topography. Oxidation of organic matter within the subsoil and vadose zones generates an average PCO2 of 4-0 x 10-3 atm, which drives dissolution during vadose percolation and/or at the water table. However, these dissolution processes together account for < 60% of the average rock-derived calcium in groundwaters pumped from the freshwater lens. The additional calcium may derive from oxidation of organic carbon within the lens. Accounting for the high PCO2 of the lens waters. Mixing between meteoric waters of differing chemistry is diagenetically insignificant, but evapotranspiration from the shallow water table is an important drive for subsurface cementation. Porosity generation in the shallow vadose zone averages 1.6- 3.2% ka -1 Phireatic meteoric diagenesis is focused near the water table, where dissolution generates porosity at 1.4-2.8% ka -1. Maximum dissolution rates, however, are similar to those of evaporation-driven precipitation, which occludes porosity of 4.0 ± 0.6% ka-1. This drives porosity inversion, from primary interparticle to secondary mouldic, vug and channel porosity. In the deeper freshwater lens, oxidation of residual organic carbon and reoxidation of reduced sulphur species from deeper anaerobic oxidation of organic carbon may generate porosity up to 0.06% ka -1. Meteoric diagenesis relies critically on hydrological routing and vadose thickness (controlled by sea level), as well as the geochemical processes active. A thin vadose zone permits direct evaporation from the water table and drives precipitation of meteoric phreatic cements even where mineral stabilization is complete. [ABSTRACT FROM AUTHOR]

Summary: Time series analysis was applied to the precipitation, spring discharge and piezometric head data of two representative karst systems of Greece in order to study the function, hydrodynamic behaviour and hydraulic properties of the aquifers. Results obtained through autocorrelation, spectral density, cross-correlation, cross-amplitude, gain, coherence and phase functions showed that the Trifilia karst system is slightly karstified and has a large storage capacity. Baseflow dominates while quickflow is absent due to the lack of a well-organized karst network, suggesting that, probably, Darcian conditions exist. On the other hand, unlike the Trifilia karst system, the karstification processes in the Almyros karst system are more enhanced producing a better developed karst network, but contrary to the typical karst systems, baseflow and quickflow coexist. This system can be classified as an intermediate case between the two extreme karst types. [Copyright &y& Elsevier]

Eogenetic karst has been regarded as a dominant origin of hydrocarbon reservoirs, whereas quantifying the fluid-rock interactions and their impacts on porosity evolution during the palaeokarst process remain persistent challenges that limit the accuracy of reservoir quality prediction. This study investigates the dissolution of carbonate rocks with potential controlling factors by reactive transport modeling that couples fluid flow, mineral reactions and porosity changes in a one-dimensional vadose meteoric water-rock system. Simulation results of base case scenario and sensitivity analyses show that the duration of subaerial exposure and recharge capacity of rainwater significantly determine the karst-affected depth and porosity increment. The amount of calcite dissolution is also affected by a downward decrease in calcite solubility (temperature-dependent) and the enrichment of Ca2+ and HCO 3 − in the lower part. The atmospheric carbon dioxide concentration has a minor impact on the vertical extent of karst, while it facilitates the dissolution rate under high pCO 2 conditions. The influence of atmospheric pCO 2 variation over geological time on the porosity increment was reconstructed under hydrogeological conditions of the base case scenario (exposure time = 130 ka; rainfall = 628 mm/a). The differences in the dissolution rates and extent of karst between limestone and dolostone can be interpreted as the results of different rate-determining reaction mechanisms, i.e., thermodynamically controlled calcite and kinetically controlled dolomite. • Key factors affecting eogenetic karst are semi-quantitatively evaluated using reactive transport modeling. • The influence of atmospheric pCO 2 variation over geological time on the porosity increment is reconstructed. • Different rate-determining reaction mechanisms result in higher dissolution rate of calcite than dolomite. [ABSTRACT FROM AUTHOR]

Research on eogenetic karsts has mostly focused on oceanic settings but rarely targeted lacustrine settings. This study describes an eogenetic karst formed in a saline lacustrine setting in the upper 4th member of the Shahejie Formation (Es4s), Dongying Depression, China. Limestones were deposited on a landmass-attached carbonate platform characterized by boundstones and grainstones interbedded with micrites. Tectonic uplift at the end of Es4s caused the karstification in a saline lake shore setting over approximately 2 Ma. During the exposure period, pervasive macroporosity developed in intervals within the top 20 m below the unconformity. Caves formed along the periphery of the platform, and they are mainly at 0.2–1.3 m in height and are filled with wackestone sediments without turbulent flow features. The caves are interpreted as the result of mixing dissolution on the margin of a mixing zone of saline lake-water and fresh-water. Sponge-like intervals occur in interior areas and range from 0.5 to 2.5 m in height, and they present a spongy porosity with pyrite crusts, pervasive pyrite framboid disseminations and occasional cements. The sponge-like dissolution pores are analogous to the Swiss-cheese texture forming in modern and fossil mixing zones and are probably caused by microbially-mediated dissolution in a mixing zone where mixing rate is limited because of reduced circulation in saline lake phreatic water. A small number of sub-vertical conduits (turbulent flow paths) and pervasive fissures are generated due to dissolution by meteoric water. The dissolution effects are strongly influenced by primary lithofacies. Spongy dissolution and caves develop almost in boundstone and grainstone layers, which is probably because they maintained a high permeability after shallow burial and thus become the preferential diffuse flow paths. According to this model, the boundstone and grainstone intervals that developed along the periphery of the platform could be favorable reservoirs for future petroleum exploration. • The paleokarst was an eogenetic karst forming in a saline lake shore setting. • Mixing corrosion and microbially-mediated dissolution are the main causes of caves and spongy pores. • Boundstone and grainstone layers maintained a high permeability after shallow burial and became favorable to form macro-pores. • High-quality karst reservoirs developed in both the highs and transition zones of the platform. [ABSTRACT FROM AUTHOR]