Adjacent Limestone Research Articles

Identification and prediction of mixed water sources in adjacent limestone aquifers based on conventional hydrochemistry and strontium isotopes

Identification and prediction of mixed water sources in adjacent limestone aquifers based on conventional hydrochemistry and strontium isotopes

Diagenetic Evolution of Upper Cretaceous Kawagarh Carbonates from Attock Hazara Fold and Thrust Belt, Pakistan

A recent hydrocarbons discovery in 2021 in the Kawagarh Formation has brought attention to the significance of sedimentology and specifically diagenesis for understanding and characterizing the reservoir properties. The diagenetic history and multiscale processes that contributed to diagenesis were vaguely known. This study aimed to reconstruct various diagenetic phases, paragenetic sequences, and the interrelationship of these phases in the Kawagarh Formation. The diagenetic processes were identified and characterized through an integrated methodology utilizing the outcrop, petrographic, and geochemical analyses. Early calcite cementation was found to occur in the early stages of marine burial diagenesis involving pore fluid originating from the dissolution of aragonite in interlayer marl/mudstone beds and reprecipitating as microspar in adjacent limestone beds. The absence of mechanical compaction in wackstone and mudstone facies and the presence of late compaction in lithified packstones clearly imply that early calcite cementation occurred prior to compaction. Dolomitization with stylolites coupled with significant negative oxygen (δ18O) isotope values implies a fault-related hydrothermal dolomitization model. Uplift introduced the fractures and low Mg fresh fluids to the system which caused calcitisation in shallow burial settings. The depleted δ13C and negative δ18O values indicate the mixing of surface-derived waters with hot burial fluids during the calcitization. This study offers valuable insights into several aspects related to the formation and the basin itself, including burial depths, fluid influx, and geochemical gradients. It also sheds light on the evolution of reservoir properties such as porosity and permeability in dolomitization fronts. Such insights can be used to gain a deeper understanding about the burial history, basin evaluation, and reservoir characterization for hydrocarbon exploration.

Role of overlying and underlying limestones in the natural hydraulic fracturing of shale sections: The case of marine–continental transitional facies in the Southern North China Basin

A few limestone layers usually underlie and/or overlie the shale layers/sections in marine facies, especially in marine–continental transitional facies (MCTF). The role of limestones in the natural hydraulic fracturing of shale sections will help in selecting the fracturing location, improving the stimulation power, and clarifying fracture propagation law to product more shale oil and gas. Taking an MCTF in the Southern North China Basin as an example, the differences in natural fractures and mechanical properties between limestones and shales were compared to examine the role of limestone in hydraulic fracturing. Our analyses show that shales developed more non-tectonic fractures than limestones, usually interconnected with tectonic fractures to form a fracture network. Limestones generally have a higher Young’s modulus, compressive strength, in situ stress, and fracturing pressure and a more difficult fracture initiation than shales and sandstones. Overlying and underlying limestones with less fractures and higher mechanical properties can act as an effective barrier bed, which prevents induced fractures originating from the shale sections from penetrating their mechanical interfaces into the adjacent limestone sections. This action maintains a high stimulation power in the shale sections to form a complicated induced fracture network.

The Fine Characterization and Potential Photocatalytic Effect of Semiconducting Metal Minerals in Danxia Landforms

The Danxia landform is representative of the Cretaceous continental red sediment. The careful identification and potential environmental effects of minerals in Danxia red beds have yet to be clearly reported. In this work, reddish sandstone samples were collected from Lang Mountain Danxia landform in Xinning, Hunan province, China, and their mineral phases, element distribution, microstructure, and the spatial relationship of different minerals were investigated using polarizing optical microscope, environmental scanning electron microscopy, energy-dispersive X-ray analysis, electron probe microanalysis, micro-Raman spectra, micro- X-ray diffraction, X-ray fluorescence spectroscopy, and high-resolution transmission electron microscopy. The results revealed that iron oxide (mainly hematite) and titanium oxide (mainly anatase) were the dominant minerals in Danxia red layers. Microcrystalline hematite was suggested as being the coloring mineral. Anatase, reported here for the first time in Danxia red beds, constituted the content of titanium in the red layer (0.17–0.57%) and was present in a significantly higher amount than the adjacent limestone formation (0.13%). Over 95% of Fe/Ti oxides served as a cementation agent along the framework of coarse-grain minerals (quartz and feldspar). The hematite and anatase were visible-light-responsive semiconductors, with a band gap of 2.01 eV and 3.05 eV, respectively. Photoelectrochemical experiments were performed on synthetic hematite, anatase, and their coupled material. The inactive hematite displayed an enhanced 23-fold photocurrent at 0.8 V (vs. Ag/AgCl) when coupled with anatase. Furthermore, in a photodegradation experiment using methyl orange dye under simulated sunlight, the coupled material showed decolorizing efficiency 2.4 times that of hematite. The anatase, therefore, prominently improved the photocatalytic activities of hematite. It is proposed that these semiconducting minerals in red beds produce oxygen reactive species and have significant environmental effects, which is of great importance.

Geochemical and multi-isotopic (87Sr/86Sr, 143Nd/144Nd, 238U/235U) perspectives of sediment sources, depositional conditions, and diagenesis of the Marcellus Shale, Appalachian Basin, USA

We investigate sediment sources, depositional conditions and diagenetic processes affecting the Middle Devonian Marcellus Shale in the Appalachian Basin, eastern USA, a major target of natural gas exploration. Multiple proxies, including trace metal contents, rare earth elements (REE), the Sm-Nd and Rb-Sr isotope systems, and U isotopes were applied to whole rock digestions and sequentially extracted fractions of the Marcellus shale and adjacent units from two locations in the Appalachian Basin. The narrow range of εNd values (from −7.8 to −6.4 at 390 Ma) is consistent with derivation of the clastic sedimentary component of the Marcellus Shale from a well-mixed source of fluvial and eolian material of the Grenville orogenic belt, and indicate minimal post-depositional alteration of the Sm-Nd system. While silicate minerals host >80% of the REE in the shale, data from sequentially extracted fractions reflect post-depositional modifications at the mineralogical scale, which is not observed in whole rock REE patterns.Limestone units thought to have formed under open ocean (oxic) conditions have δ238U values and REE patterns consistent with modern seawater. The δ238U values in whole rock shale and authigenic phases are greater than those of modern seawater and the upper crust. The δ238U values of reduced phases (the oxidizable fraction consisting of organics and sulfide minerals) are ∼0.6‰ greater than that of modern seawater. Bulk shale and carbonate cement extracted from the shale have similar δ238U values, and are greater than δ238U values of adjacent limestone units. We suggest these trends are due to the accumulation of chemically and, more likely, biologically reduced U from anoxic to euxinic bottom water as well as the influence of diagenetic reactions between pore fluids and surrounding sediment and organic matter during diagenesis and catagenesis.

Physical and Chemical Evolution of the Dabaoshan Porphyry Mo Deposit, South China: Insights from Fluid Inclusions, Cathodoluminescence, and Trace Elements in Quartz

The Dabaoshan polymetallic deposits in the Nanling Range, South China, consist of porphyry and skarn-type Mo mineralization genetically related to Jurassic porphyritic intrusions and adjacent strata-bound Cu-Pb-Zn mineralization hosted in mid-Devonian limestone. Porphyry Mo mineralization is characterized by the superposition of multiple generations of crosscutting quartz-bearing veins including: barren quartz veins (V1), quartz-molybdenite veins with K-feldspar alteration halos that host the bulk of the Mo mineralization (V2), quartz-pyrite veins with muscovite alteration (V3), and late base metal mineralization with argillic alteration (V4), as well as limestone-hosted strata-bound Cu-Pb-Zn mineralization (VS). Fluid inclusion petrography and microthermometry combined with cathodoluminescent textures and trace elements in quartz reveal changes in pressure and temperature of the hydrothermal system that formed the deposit. V1 and V2 veins are dominated by low-salinity (1–6 wt % NaCl equiv), CO 2 -bearing (4–10 mol %) two-phase inclusions with about 35 vol % bubble trapped in the one-phase field above the solvus of the fluid. V1 veins are dominated by CL-bright granular quartz mosaics with higher CL intensity than any other vein type. This quartz also contains more Ti than any other vein generation (24–89 ppm), while Al, Ge, and Li concentrations overlap with other vein generations. Molybdenum ore-hosting V2 veins are also dominated by CL-bright granular quartz mosaics, but V2 veins display slightly less CL intensity and correspondingly lower Ti concentrations (10–65 ppm). V3 veins have a broader spatial distribution than V1 and V2 veins, extending from inside the porphyries out into the adjacent limestone. These veins are also dominated by low-salinity (2–6 wt % NaCl equiv), CO 2 -bearing (4–7 mol %) two-phase inclusions, these containing about 45 vol % bubble trapped above their solvus. V3 veins are dominated by CL-dark quartz with euhedral growth zones of oscillating CL intensity and systematically lower Ti concentrations than previous vein generations (1.5–12 ppm). Minor V4 veins cut all the above vein generations and also occur as late infill in V3 veins. Low-salinity (4–7 wt % NaCl equiv), CO 2 -bearing (4–5 mol %) two-phase inclusions with about 20 vol % bubble prevail in V4 veins. V4 veins have the lowest CL-intensity quartz of all vein types, with euhedral growth zones of oscillating CL intensity and the lowest Ti concentration of all vein types (0.54–5.3 ppm). Intersections of fluid inclusion isochores with Ti-in-quartz isopleths indicate that the hydrothermal system evolved from near-magmatic pressures and temperatures of 2.7 ± 0.2 kbars and 650° ± 40°C for V1 veins to 1.9 ± 0.2 kbars and 530° ± 40°C for V2 veins to 0.65 ± 0.2 kbars and 400° ± 40°C for V3 veins. V4 veins, which lack rutile, formed as the system cooled to 250° to 300°C at maximum pressures of 0.40 to 0.65 kbar. Unlike nearly all other reported porphyry-type ore deposits, quartz-bearing veins from the Dabaoshan porphyry Mo deposit contain few halite-bearing or vapor-dominated fluid inclusions in any vein type. The dearth of such fluid inclusions, coupled with the abundance of two- and three-phase CO 2 -bearing low-salinity fluid inclusions in all vein types is evidence that the formation conditions of V1 to V4 veins remained above the V-L surface in the H 2 O-NaCl-CO 2 system, such that fluid unmixing rarely occurred in the Dabaoshan hydrothermal system. This is further supported by only rare evidence for quartz dissolution textures in all vein types, implying that pressures were dominantly higher than zone of retrograde quartz solubility. Taken together, the fluid inclusions, CL textures, and quartz trace element data indicate that the Dabaoshan porphyry Mo deposit is one of the deepest formed porphyry-type ore deposits, having formed at depths of 6 to 7 km below surface. The extreme depth and lack of fluid unmixing inhibited Cu precipitation in the porphyry system, and instead allowed Cu to remain in solution to precipitate with Pb and Zn upon interaction with the surrounding Devonian limestone.

Leucaena leucocephala and adjacent native limestone forest habitats contrast in soil properties on Tinian Island

ABSTRACTAn ex situ germplasm collection of the endangered Cycas micronesica was established in a transition zone between biodiverse native forest and mature stands of the invasive species Leucaena leucocephala. Soil chemical properties were determined for the 2 tree cover types to inform management decisions. Total carbon, total nitrogen, calcium, and net ammonification were greater in native forest cover than in L. leucocephala patches. Net nitrification and net mineralization were greater under L. leucocephala cover. Trace metals also differed between the 2 forest cover types, with chromium, cobalt, and nickel accumulating to greater concentration under L. leucocephala cover and zinc accumulating to greater concentration under native forest cover. The results indicated that L. leucocephala cover generated substantial changes in soil chemical properties when compared with native forest tree cover, illuminating one means by which understory vegetation may be affected by changes in invasive tree cover.

Paleo-watertable definition using cave ferromanganese stromatolites and associated cave-wall notches (Sierra de Arnero, Spain)

The steeply-dipping-dolostone-hosted caves of the Sierra de Arnero (N Spain) contain low-gradient relict canyons with up to ten mapped levels of ferromanganese stromatolites and associated wall notches over a vertical range of 85m, the highest occurring ~460m above base level. Despite a plausible speleogenetic contribution by pyrite oxidation, and the irregular cave-wall mesomorphologies suggestive of hypogenic speleogenesis, the Arnero relict caves are dominantly epigenic, as indicated by the conduit pattern and the abundant allogenic sediments. Allogenic input declined over time due to a piracy-related decrease in the drainage area of allogenic streams, explaining the large size of the relict Arnero caves relative to the limited present-day outcrop area of the karstified carbonates. Allogenic-sediment input also explains the observed change from watertable canyons to phreatic conduits in the paleo-downstream direction. Stromatolites and notches arguably formed in cave-stream passages at the watertable. The best-defined paleo-watertables show an overall slope of 1.7°, consistent with the present-day relief of the watertable, with higher-slope segments caused by barriers related to sulfide mineralization. The formation of watertable stromatolites favored wall notching by the combined effect of enhanced acidity by Mn–Fe oxidation and shielding of cave floors against erosion. Abrasive bedload further contributed to notch formation by promoting lateral mechanical erosion and protecting passage floors. The irregular wallrock erosional forms of Arnero caves are related partly to paragenesis and partly to the porous nature of the host dolostones, which favored irregular dissolution near passage walls, generating friable halos. Subsequent mechanical erosion contributed to generate spongework patterns. The dolostone porosity also contributes to explain the paradox that virtually all Arnero caves are developed in dolostone despite being less soluble than adjacent limestone. U-series dating of carbonate speleothems and paleomagnetic data from ferromanganese stromatolites and clastic sediments indicate that the paleo-watertables recorded ~320m above the present-day watertable formed during the Matuyama Chron but prior to ~1.5Ma, implying long-term base-level-lowering rates from ~125 to ~213m/Ma. To our knowledge, this is the first attempt of paleomagnetic dating of cave ferromanganese stromatolites. These deposits are excellent geomagnetic recorders and offer a direct way to delineate and date paleo-watertables, especially in caves developed in dolostone.

Fluid inclusion and geochemical evidence for the origin of sparry calcite cements in Upper Permian Changxing reefal limestones, eastern Sichuan Basin (SW China)

Gas reservoirs in the Upper Permian Changxing Formation in eastern Sichuan Basin are found mostly in dolostones, rather than the contemporaneous reefal limestones that had most of their porosity occluded by pervasive calcite cementation. The sparry calcite, which was the latest but most abundant type of cement, was responsible for major porosity loss. Hence, this study focuses attention on the origin of sparry calcite by employing petrography (e.g. microscope, cathodoluminescence), geochemistry (carbon, oxygen and strontium isotopes, trace elements, and clumped isotope thermometry) and fluid inclusion analysis. The sparry calcite cements are interpreted to be of burial origin as shown by their enclosement of radiaxial calcite and host rock fragments, the presence of two-phase (liquid and vapor) fluid inclusions with higher homogenization temperatures, and relatively lower oxygen isotopic values. Sparry calcites show none to very dull cathodoluminescence, preserve similar carbon and strontium isotopic signatures to other chemical components of host rocks, and have low concentrations of Fe and Mn. These facts indicate that the source for precipitation of sparry calcites was most probably derived from chemical compaction of host rocks and/or adjacent limestone strata. The contrast in porosity and sparry calcite abundance between the reefal limestones and dolostones imply that pervasive dolomitization of carbonates in the Changxing Formation probably occurred prior to chemical compaction, rather than deep-burial dolomitization proposed in previous studies. Early dolomitization enhanced preservation of porosity because the dolostones were more resistant to chemical compaction than the limestones. Reefal limestones in the Changxing Formation gradually lost their porosity during progressive burial because of chemical compaction and the resultant sparry calcite cementation. This study emphasizes the importance of chemical compaction in carbonate cement precipitation and the resultant porosity occlusion in deep burial carbonate successions.

Syndepositional Deformation Features In High-Relief Carbonate Platforms: Long-Lived Conduits for Diagenetic Fluids

Abstract Syndepositional faults and fractures are known to affect early fluid flow in carbonate platforms. Less clear is whether they are active fluid conduits throughout the entire history of the platform strata. Syndeformational fractures in Permian (late Guadalupian) carbonates exposed in Dark Canyon, Guadalupe Mountains, New Mexico, U.S.A., address this question. Transmitted-light and cathodoluminescent petrography, stable-isotope and fluid-inclusion analyses, and clumped-isotope thermometry show that there were multiple episodes of fracturing, dissolution, cementation, and replacement in the fractures. Dolomite cement or dolomitized marine cements line the walls of some fractures and indicate the syndepositional reflux of evaporated Permian seawaters through the fractures. Fine- to medium-crystalline, luminescently zoned calcite may overlie the dolomite and marine cements, line fracture walls where those phases are absent, or cement karst breccia on fracture walls. The δ18O values of this calcite (−8.8 to −14.0‰ VPDB) and clumped-isotope temperatures (16° to 32°C) indicate precipitation from meteoric fluids (δ18OSMOW of −6.2 to −10.5‰) associated with episodic sea-level lowstands during the development of high-frequency depositional sequences. The early calcites can themselves be fractured, rotated, and recemented, indicating recurrent deformation and meteoric influx. Evaporite cements were once the dominant pore-filling phase in the fractures, forming both before and after the early meteoric cements. The earliest evaporites formed during deposition of Tansill limestone, probably from the same brines that formed dolomites. Evaporites that postdate the early calcite probably did not form until Permo-Triassic burial, when geomechanical analysis indicates that the syndepositional fractures were likely reactivated and brines could have been sourced from overlying bedded evaporite. All evaporite cements subsequently were calcitized, mainly by coarse-crystalline, inclusion-rich calcites that formed from warm (59° to 96°C) fluids. Calculated fluid isotopic compositions (δ18OSMOW of −0.5 to −4.7‰) imply mixing of meteoric and oil-field brines. Carbon isotope values (+2 to −17‰) indicate microbial degradation of hydrocarbons in some of those fluids, but not all. Geomechanical analysis indicates the potential for syndepositional fractures to have failed (reactivated) during Basin and Range extension, and the warm basinal fluids are interpreted to have migrated upward through the fractures during that event. Platform-margin fractures (unassociated with faults) witnessed cooler fluids (59° to 65°C) than outer-shelf fractures (70° to 96°C) because outer-shelf faults tapped waters from greater depths. The most recent fluid flow through the fractures generated dissolution features and laminated speleogenetic calcites, which are interpreted to result from intrastratal karsting associated with exhumation and weathering. Diagenetic features in the syndepositional fractures are equivalent to those observed in the adjacent limestones, suggesting active fluid communication between matrix and fractures throughout the diagenetic history of the rocks. The complex fracture paragenesis also indicates that syndepositional fractures are not only conduits for early fluid-flow networks, but they can also impact a rock's entire diagenetic history if reactivated by changing stress fields.

Origin of terra rossa on Amdo North Mountain on the Tibetan plateau, China: Evidence from quartz

Terra rossa was found overlying limestone on a planar erosion surface at approximately 5100 m on the summit of Amdo North Mountain on the Tibetan Plateau. The present study examined the quartz content, size distribution of the quartz grains, mineral composition, oxygen isotope ratios in the quartz, surface microtexture and crystal morphology of the quartz in the terra rossa and its potential source rocks to determine the derivation of the terra rossa. The results indicated that the component of the terra rossa on Amdo North Mountain is a mixture of weathering products from the underlying limestone, the overlying red sandy limestone and the adjacent limestone breccia. These different parent materials can result from being introduced under gravity and other mass transport during geological epoch. Therefore, the terra rossa on Amdo North Mountain is primarily a transported sedimentary deposit, not an in situ weathering solum. The source of much of the terra rossa is likely to be weathering products on adjacent uplands under paleo-landform frame. Multiple sources appear responsible for the terra rossa on Amdo North Mountain. Eolian dust, however, does not appear to have provided a significant addition to the terra rossa formation on Amdo North Mountain.

Examples of weathering and deterioration of Tertiary building stones at St. Michaels Cathedral in Cluj-Napoca (Romania)

St. Michaels Cathedral is one of the oldest Gothic architectural monuments in Cluj. It is built predominantly of Cenozoic (Eocene) limestones which were deposited on a shallow carbonate platform. They are composed of different facies and microfacies types with varying amounts of particles, matrix and cement. Limestones from the Baci quarry (Cluj Limestone), which is situated about 3 km from the centre of Cluj, were commonly used. The weathering features correspond to the microfacies types, to the position of the stones in the walls and to the exposure (east, south, west, and north), which controls the moisture/dry cycles. This interrelationship is documented by macroscopic and microscopic examples of the decay of samples analyzed from the lower part of the walls. General parameters for a correct classification of carbonate rocks and their importance for weathering are discussed. The general mechanisms of weathering (thermal expansion, water uptake, freezing, chemical weathering) are described. The migration of moisture (capillarity) and the formation of crusts of varying mineralogy on the surface of building stones are documented. Macroscopic description of damage includes the decay into plates and flakes, the formation of crusts, the formation of fractures, and the growth of lichens and microorganisms. The microscopic analysis documents characteristic damage in detail: fractures parallel to the surface of the stone, internal cementation of fossil chambers (micro-nodules), repeated formation of crusts in varying generations, fracturing in intensively lithified, rigid limestones, and settling of lichens in different positions. Furthermore, different historical mortars and modern “concrete-mortars” and their behaviour in comparison to the adjacent limestones are briefly discussed. The possible conservation and restoration of weathered limestones in St. Michaels Cathedral are discussed with regard to the most recent conservation methods. The advantages and disadvantages of surface conservation by silica ester, hydrophobic substances as well as by epoxy resin are also dealt with. Special methods for conservation (acrylic total impregnation, lime slurry, biological lime slurry) and DIN-methods as well as analysis of the success of the methods used are presented in a short summary.

Coastal Cave Development in Puerto Rico

The goal of this study was to provide a comprehensive and updated inventory of the coastal caves of Puerto Rico in an effort to contribute to a better understanding of cave development in this island setting. A total of 63 coastal caves were surveyed and analyzed using detailed cartography, morphometric analysis, resource inventory, and photo documentation. Located along the northern, western, and southern coastlines of Puerto Rico, many of these features, because of their small size and relative obscurity, had not been thoroughly studied in the course of previous fieldwork. Prominent sea cave (littoral) development was noted in all coastal areas, but previously undocumented examples of flank margin speleogenesis were also identified within the Quaternary eolianite and adjacent limestone exposures along the northern coast. Morphometric analysis of all the completed cave maps revealed that the 10 flank margin caves could be graphically distinguished from the 53 sea caves by comparison of cave perimeter to total cave area. Furthermore, morphometric comparison of multiple spatial parameters was sufficient to differentiate intact from denuded flank margin caves as well as identify segments within some flank margin caves that had been modified by littoral breach and/or cliff retreat. This study revealed a surprising variety and abundance of cave resources along these dynamic and complex Atlantic and Caribbean shorelines, utilizing a methodology capable of differentiating between flank margin and littoral cave development that can be further used to determine the speleogenic origins of coastline cave resources in other carbonate island settings.

Investigation of Masonry Failure of a Granite and Limestone Clad Historic Church in Eastern Pennsylvania

Abstract The use of dimension stone was commonplace in turn of the century churches and St. George’s in Shenandoah, PA, is an example of granite and limestone construction set in the anthracite belt of Eastern Pennsylvania. The structure’s two towers, over 100 feet tall, have recently succumbed to age, the elements, and poor long-term repairs and maintenance that veiled shifting limestone and granite. Early detection did not occur due to the lack of periodic inspection following ASTM’s Standard E 2270 “Standard Practice for Periodic Inspection of Building Facades for Unsafe Conditions,” and the oldest Lithuanian Catholic Church in the United States has temporarily closed. Field observations have revealed a variety of failures. Limestone and the front entrance has outwardly displaced from the mass masonry brick backup nearly 1 in. at several locations. Granite masonry at the top of the towers has outwardly displaced 3/4 in. and has caused adjacent decorative limestone elements to displace up to 2 in. away from the wall. Spalled fragments of limestone of different sizes have fallen to the ground from varying heights at the rate of nearly one piece per month during recent years. A condition assessment examining the masonry deficiencies has been completed and the building now faces substantial repair options that may impact the building’s operational viability.

Abdalajis east railway tunnel (Spain) – double shield universal TBM cope with extremely poor and squeezing formations

For more than 30 years Double Shield TBMs were successfully utilised all around the world in a variety of geological formations. However, in some circumstances, Double Shield TBMs required the execution of by-pass tunnels and other special hand mining works to face special extremely poor conditions, and mainly: important and rapid squeezing phenomena, very unstable tunnel faces (flowing ground) and combinations of the two. To overcome these limitations, the new Double Shield Universal (DSU) TBM was designed and successfully tested in a first experimental application in the 18 km long Val Viola tunnel in the north of Italy. Following this first experimental application a DSU TBM has been specifically designed and manufactured for the 10 m diameter high speed railway tunnel of Abdalajis (Spain). This DSU TBM is characterized by extended facilities to treat the ground ahead of the face. In the first 2,5 km of tunnel, the encountered argillite formation was very unstable with rapid convergence of the tunnel walls and frequent face collapses. Large gas inflows with pressures up to 11 bars were measured in this section. In particular, for about 600 m at the contact with the adjacent limestone formation, the argillite rock was completely altered by the tectonic action and transformed into a kind of flowing gravel with very low friction angle and small cohesion. To advance the TBM under these conditions it was necessary to make large use of expanding foams to fill large voids in front and over the cutterhead. In addition, several patterns of chemically grouted micro-piles were executed from inside the TBM shield to improve the ground characteristics and stability ahead of the machine. Despite these extreme conditions and the restrictions to the tunnelling operations given by the gas presence, the TBM was able to advance without requiring any bypass or hand mining excavation and without the shields to get trapped. The article describes with details the technologies and the methods adopted to overcome these special geological conditions as well as the possible improvements to DSU technology that have been derived from the Abdalajis experience. (A) This paper was presented at Safety in the underground space - Proceedings of the ITA-AITES 2006 World Tunnel Congress and the 32nd ITA General Assembly, Seoul, Korea, 22-27 April 2006. For the covering abstract see ITRD E129148. Reprinted with permission from Elsevier.

The role of fluids in faulting deformation:a case study from the Dead Sea Transform (Jordan)

The geochemistry of carbonate fault rocks has been examined in two areas of the Arava Fault segment, which forms the major branch of the Dead Sea Transform between the Dead Sea and the Gulf of Aquaba. The role of fluids in faulting deformation in the selected fault segment is remarkably different from observations at other major fault zones. Our data suggest reduced fluid rock interactions in both areas and limited fluid flow. The fault did not act as an important fluid conduit. There are no indications that hydrothermal reactions (cementation, dissolution) did change the strength and behavior of the fault zone, although the two areas show considerable differences with respect to fluid sources and fluid flow. In one area, the investigated calcite mineralization reveals an open fluid system with fluids originating from a variety of sources. Stable isotopes (δ13C, δ18O), strontium isotopes, and trace elements indicate both infiltration of descending (meteoric and/or sea water) and ascending hydrothermal fluids. In the other area, all geochemical data indicate only local (small scale) fluid redistribution. These fluids were derived from the adjacent limestones under nearly closed-system conditions.

Widespread cementation induced by inflow of continental water in the eastern part of the Paris basin: O and C isotopic study of carbonate cements

Mesozoic limestones from the eastern part of the Paris Basin display, mostly in strata rich in bioherms, abundant macro-cavities (vugs) and some connected micro-fractures almost completely filled with euhedral calcite crystals (late calcite spar). The interparticle porosity of limestones is also filled with euhedral calcite spar cements similar to those observed in vugs and fractures, and rarely displays the preservation of the structures typical of early marine cements. These calcite spars (both from vugs/fractures infillings and from cemented porosity) were studied in drilled cores cross-cutting the Kimmeridgian to Bathonian series with the main objective of determining the nature and flow regime of the fluids responsible for the strong porosity reduction observed in that part of the Paris Basin Mesozoic limestones. The approach combined mineralogical and geochemical studies (O and C stable isotopic compositions measured by conventional and SIMS methods) with temperature estimates from fluid inclusion analyses. The δ 13C values of late calcite are close to those of the host limestones and correlate with the δ 13C changes in host rocks, indicating a local source of C. By contrast, late calcites from vugs, fractures and also in the cemented interparticle porosity of limestones have δ 18O values around +21‰/SMOW, values which are distinct from those of bulk host limestones (+25‰ to +27‰). The δ 18O value of the fluid is estimated to be −6.8 to −2.5‰ for a crystallisation temperature between 32 and 42 °C determined from fluid inclusion studies. Thus, the parent fluid of cemented interparticle porosity and vug- and fracture-infillings likely contained a component of meteoric water, in contrast to the previous belief that the reduction of porosity in those series was related to early marine diagenesis. Possible situations in which such meteoric fluid could have occurred are: (i) a stage when the limestone aquifers were directly connected to surface water, and/or (ii) channelling of water, from deeper zones in the basin, through regional fault systems. The O isotopic compositions of the calcite cements in the underlying 140 m – thick Callovo-Oxfordian argillites and those of the less recrystallised Bathonian to Kimmeridgian limestones are those expected for unmodified marine calcite: δ 18O=ca. +28‰ SMOW. Therefore, from the isotopic point of view, the Callovo-Oxfordian argillites remained essentially unaffected by the paleo-fluid circulation documented in the adjacent limestones series. This indicates the argillites acted as an efficient permeability barrier in the past.

Origin and petrophysics of dolostone pore space

Abstract The common claim that dolomitization creates 12% porosity is based on the mole-for-mole replacement equation. However, in the past 50 years, data have been collected demonstrating that dolomitization does not create porosity. Instead, dolostones inherit the porosity and fabric of the precursor limestone, and porosity is reduced by overdolomitization. The porosity of the precursor limestone depends on the diagenetic history up to the time of dolomitization. Data show that: (1) carbonates are born with high porosity and lose porosity gradually over a long period; and (2) mud-dominated fabrics compact more readily than grain-dominated fabrics. The problem of estimating the time of dolomitization is minimized by confining observations to young limestones and associated dolostones. Limited data from Holocene dolomitic sediments suggest no change in porosity with dolomitization. Study of Plio-Pleistocene carbonates in Bonaire, Netherlands Antilles, demonstrates that precursor limestones are more porous than dolostones. Limestones average 25% porosity, whereas dolostones average 11% porosity. Data from the Neogene of the Great Bahama Bank show that dolostones and adjacent limestones both have 40% porosity. Porosity studies of the Jurassic Arab D Formation show that dolostones and associated grain-dominated limestones have similar porosity ranges and that the decrease in porosity with increasing dolomitization results from compaction of the mud-dominated fabrics. These data suggest that porosity in dolostone is not created by a mole-for-mole replacement mechanism. Instead, dolostone porosity is: (1) inherited from the precursor limestone; and (2) occluded by the process of overdolomitization. Palaeozoic dolostones, however, are commonly more porous than juxtaposed limestones. The explanation for this observation is that limestones lose porosity through compaction and cementation, whereas dolostones resist compaction and retain much of their porosity. Permeability studies have demonstrated that dolomitization of grain-dominated limestones usually does not change porosity-permeability relationships. Instead, precursor limestone fabric controls pore-size distribution. The dolomite crystal size of a muddominated dolostone may, however, be larger than the carbonate mud size, improving the porosity-permeability relationship substantially. Hence, there is a predictable relationship between interparticle (grains or crystals) porosity, permeability, precursor grain size and dolomite crystal size.

Fracture-pattern variations around a major fold and their implications regarding fracture prediction using limited data: an example from the Bristol Channel Basin

Abstract This chapter focuses on the evolution of fractures during the inversion of the Bristol Channel Basin, and examines the lateral and vertical consistency of the resulting fracture network within the alternating Liassic limestones and shales. The study has two principal aims. The first is to determine the reliability of fracture systems deduced using more limited data from less well-exposed regions or unexposed regions sampled only by drilling, and the second is to assess whether the fractures are linked to a regional stress field or are the result of a local stress field controlled by the geometry and mechanism of formation of a fold. The joint patterns were studied using a combination of scanline and window sampling, and the results indicate that there are considerable variations in the fracture systems between adjacent limestone beds and also lateral variation within the same bed. Although there is little doubt that the independent development of fracture patterns in adjacent limestone beds is facilitated by the intervening shale horizons, which allow them to become mechanically decoupled, the reasons for these variations are still unclear.

A new Savignia from Cretan caves (Araneae: Linyphiidae)

Savignia naniplopi sp. nov. is described from one male and nine female specimens collected in two adjacent limestone caves in Crete. The taxonomy of the Savignia group of species and the relationships of the new species are discussed.