Meteoric Water Flow Research Articles

Geology, geochemistry, fluid inclusion microthermometry and depositional environment of the Early Cretaceous Meymeh sub-seafloor replacement sideritic-ankeritic iron deposit, Malayer-Esfahan Metallogenic Belt, Iran

Meymeh sideritic-ankeritic iron deposit in the eastern part of Malayer-Esfahan Metallogenic Belt (MEMB) is formed in the sedimentary-volcanic rocks of the Early Cretaceous sequence. Ore mineralization in the study area based on stratigraphic location and type of host rocks divided in two ore horizons. Lower ore horizon located in the dolomitic-sandy limestone (Kc3) unit, which upper ore horizon is formed in thin-bedded limestone (Km) rocks. Petrographic studies indicates that mineralization comprises three ore facies: stockwork, bedded and massive ore facies. The most important primary minerals are siderite, ankerite, ferroan-dolomite, pyrite, pyrolusite, barite and minor chalcopyrite. The most frequent textures in the ore zones include laminae, replacement, vein-veinlet, massive and banded. Dolomitization and silicification are the main wall rock alteration styles; alteration intensity increases towards the ore zones. Based on relationships between ore minerals and rock forming minerals, ore mineralization (hypogene and supergene) in the Meymeh deposit formed during three main stages: fine-grained Fe-carbonate bands are intricately interlayered with dolomite beds. Sideritic-ankeritic bands exhibit classic sedimentary textures, such as laminations and bedding, indicative of a syn-sedimentary to early diagenesis origin. Coarser-grained stage two siderites and ankerites show breccia and vein-veinlet textures, and are considered to have formed by replacement during burial diagenetic sub-seafloor fluid flow. In stage three, siderite and ankerite were converted to secondary iron oxides such as oxide/hydroxide Fe minerals during meteoric water flow through the inverted normal and thrust faults and uplift. The primary two-phase fluid inclusions in the quartz-2 and ankerite-2 minerals that have been investigated from the ore mineralization section of the Meymeh deposit are homogenized at temperatures between 110.3 to 226.9 °C. Salinities of the primary fluid inclusions range from 3.39 wt.% to 14.77 % NaCl eq. This finding suggests that hydrothermal brine fluid mixing with seawater could be the primary mechanism that prompted ore formation. The similarity of REE patterns between siderite and ankerite in different ore facies and host rock carbonates indicates their derivation from the same ore fluids. The Meymeh deposit is considered a typical case of sedimentary hydrothermal diagenetic sideritic-ankeritic mineralization, in which minerals deposited when hydrothermal fluid was released from anoxic to suboxic water columns.

A Multiple Interactive Continua Model (MINC) to Simulate Reactive Mass Transport in a Post-Mining Coal Zone: A Case Study of the Ibbenbüren Westfield

We tested the suitability of the multiple interactive continua approach (MINC) to simulate reactive mass transport in a disturbed post-mining coal zone. To the authors’ knowledge, this approach has not been employed in such mining settings despite its relative success in other environmental fields. To this end, TOUGHREACT software was used to set up a MINC model of the unsaturated overburden of the Ibbenbüren Westfield. With it, we examined and evaluated water–rock interactions in both the fractured and porous continua as the main driver of elevated hydrogen, iron, sulfate, and chloride concentrations in the coal mine groundwater. Long and seasonal geochemical signatures were obtained by formulating and applying a five-stage modelling process that depicts the mining history of the area. The simulation results agree well with the concentrations and discharge trends measured in the mine drainage. Oxygen and meteoric water flow through the fractured continuum, leading to a high and steady release of hydrogen, iron, and sulfate ions derived from pyrite oxidation in the matrix continua closest to the fractures. Likewise, high chloride concentrations resulted from the mixing and gradual release of relatively immobile solutes in the matrix as they interacted with percolating water in the fracture. In both cases, the use of a multiple continua approach was essential to resolve sharp gradients for advection and faster kinetic reactions, while reducing the model’s dependence on block size for diffusive transport at the fracture–matrix interface. The model further allows for the calculation and analysis of solute exchange and transport in the unsaturated overburden resulting from rebound and imbibition processes, something pioneering when compared to other models in the field.

Clay mineral formation and transformation in non-marine environments and implications for Early Cretaceous palaeoclimatic evolution: The Weald Basin, Southeast England

Analyses of clay minerals within the Early Cretaceous Weald Basin, Southeast England reveal kaolinite, illite and chlorite as the main detrital clay minerals while glauconite and smectite are subordinates. A kaolinite-rich assemblage which characterized the sand-dominated Ashdown and Tunbridge Wells Sand formations and an illite-dominated assemblage associated mostly with the Wadhurst Clay and Weald Clay formations are recognized. Kaolinite was enriched in the Ashdown and Tunbridge Wells Sand formations during warm and humid climate with high precipitation that encouraged chemical weathering and leaching, while cold and dry conditions favoured the concentration of illite in the Wadhurst Clay and Weald Clay formations. Rainfall patterns associated with warm climate were drastically reduced during the drier climatic conditions. Most clay minerals are detrital in origin, with chlorite being more prominent than previously recognized. Contrary to previous studies and assumptions, this study revealed that authigenic clay minerals are present in the Hastings Beds, with vermiform and mica-replacive kaolinite being the most common, consistent with humid depositional environments. Isolated authigenic illite is also present, along with a chloritized grain, providing evidence for mesodiagenesis. The absence of dickite and occurrence of kaolinite, suggest that authigenic illite formed in relatively shallow burial conditions, indicating a maximum burial depth of 2500 m–3000 m, about 1000 m deeper than previous estimates of 1500 m–2000 m. Authigenic clay minerals are absent in the Weald Clay Formation possibly because of hindered flow of meteoric water and limited growth space for authigenic minerals. This study is significant in: 1) reinforcing multiple methods to facilitate a robust and balanced knowledge of formation and transformation of clay minerals; 2) investigating detrital and authigenic clay mineral assemblages when assessing the palaeoenvironments of sedimentary basins.

Effect of Glacial/Interglacial Recharge Conditions on Flow of Meteoric Water Through Deep Orogenic Faults: Insights Into the Geothermal System at Grimsel Pass, Switzerland

AbstractMany meteoric‐recharged, fault‐hosted geothermal systems in amagmatic orogenic belts have been active through the Pleistocene glacial/interglacial climate fluctuations. The effects of climate‐induced recharge variations on fluid flow patterns and residence times of the thermal waters are complex and may influence how the geothermal and mineralization potential of the systems are evaluated. We report systematic thermal‐hydraulic simulations designed to reveal the effects of recharge variations, using a model patterned on the orogenic geothermal system at Grimsel Pass in the Swiss Alps. Previous studies have shown that fault‐bounded circulation of meteoric water is driven to depths of ∼10 km by the high alpine topography. Simulations suggest that the current single‐pass flow is typical of interglacial periods, during which (a) meteoric recharge into the fault is high (above tens of centimeters per year), (b) conditions are at or somewhat below the critical Rayleigh number, and (c) hydraulic connectivity along the fault plane is extensive (an extent of at least 10 km into increasingly higher terrain is required to explain the 10 km penetration depth). The subcritical condition constrains the bulk fault permeability to <1e‐14 m2. In contrast, the limited recharge during the numerous Pleistocene glaciation events likely induced a layered flow system, with single‐pass flow confined to shallow depths while non‐Rayleigh convection occurred deeper in the fault. The same layering can be observed at low aspect ratios (length/depth) of the fault plane, when the available recharge area limits flux through the fault.

Fault-controlled geothermal fluids of the northern Trans-Mexican Volcanic Belt: A geochemical and isotopic study of the Los Geysers field (Valley of Queretaro, Mexico)

This study focuses on the geochemical and isotopic composition of natural spring waters and gases discharging at Los Geysers thermal area (northern Trans-Mexican Volcanic Belt, TMVB) and its relations to the regional tectonic framework. Water is of Na-HCO3 type and samples were collected at temperatures ranging from 48°C to 98°C and pH from 6.8 to 9.3. Stable isotope compositions (−10.0 to −8.0‰ for δ18O and −75.6 to −69.7‰ for δD) deviate from the global and local meteoric lines suggesting fractionation by steam loss The 87Sr/86Sr values of the thermal waters range from 0.70664 to 0.70698 indicating that most of the strontium comes from the dissolution of carbonate belonging to the late Berriasian to early Valanginian in the Guanajuato conglomerate group and a minor component of less radiogenic Sr from Paleogene–Neogene volcano-sedimentary and volcanic rocks. Solute geothermometers reveal a reservoir temperature around 164°C. A mixture between air and hydrothermal CO2 composes the bubbling gases. Helium isotopes data (R/Ra=0.96–1.71) and 4He/20Ne ratios (0.53–9.41) reveal that helium is dominated by a radiogenic component with a considerable mantle-He contribution (up to 20.8%). Since there is no active volcanism at the northern TMVB, mantle-He is best explained by transport of volatiles along active faults reaching the crust-mantle boundary. The conceptual hydrogeochemical model involves a thermal aquifer at ∼1000m depth which is recharged by regional meteoric water flow, a high thermal gradient (∼153°C/km) and fast fluid upflow to the surface along discontinuities related to regional horst and graben tectonics.

Stranded landscapes in the humid tropics: Earth's oldest land surfaces

Defying common expectations, some of the oldest landscapes on Earth are found in the humid tropics. 40Ar/39Ar dating shows that Fe-rich regolith that armors the ∼700–1000 m elevation banded iron-formation plateaus at Urucum, Mato Grosso do Sul, Brazil, results from chemical weathering that began at least 70 million years ago. Cosmogenic 3He concentrations in residual hematite clasts and the underlying saprolite on one plateau imply an extraordinarily slow surface lowering rate of 0.07–0.10 mMa−1 maintained over the last ∼17–70 Ma. Cosmogenic 10Be and 26Al concentrations in a quartz vein in the same plateau suggest a similarly low surface erosion rate of ∼0.11–0.18 mMa−1 over the past few million years. Cosmogenic 3He concentrations in goethite cementing a ∼200 m elevation indurated pediment ∼3 km northwest of the plateau escarpment yields a minimum exposure age of ∼2.6 Ma, revealing that some of the low-lying areas had already been incised and locally stabilized by goethite cementation by then. In contrast, 36Cl measurements on limestone outcrops at ∼170 m elevation and ∼6.5 km northwest of the Urucum plateau reveal short-term erosion rates of 7.1 ± 0.4 and 10.1 ± 0.5 mMa−1, showing that areas not stabilized by goethite cementation are undergoing erosion at a relatively fast pace. The ∼700 m of relief at Urucum is consistent with differential denudation over ∼70 Ma controlled by lithological differences in chemical and physical rates of weathering and erosion. Effective chemical weathering and protracted low rates of erosion for the high-elevation surface result in armoring by a resilient residue of hematite blocks that are relatively insoluble and too heavy to transport. Armoring by the surface lag of large chemically resilient hematite blocks and bedded hematite saprolite focuses meteoric water flow into the subsurface and along faults. Preferential subsurface flow along the permeable pathways between insoluble hematite blocks, combined with segmentation of the Urucum Surface into isolated catchments too small to host active drainage systems, brings physical erosion to a stand-still. The only effective erosive processes on the Urucum plateau are subsurface chemical erosion and scarp retreat. Non-steady-state landscapes in which elevation differences result from prolonged differential denudation are a common feature of Earth's southern hemisphere cratons, and they inherit their present form from underlying lithologies coupled with geomorphic processes active since the Mesozoic.

Green altered sandstone related to hydrocarbon migration from the uranium deposits in the northern Ordos Basin, China

The formation of sandstone-hosted uranium deposits has been linked to upward migration of hydrocarbons in many sedimentary basins. However, hydrocarbon-induced diagenetic alterations associated with uranium mineralization and preservation are rarely discussed. Here, we report the bleaching of red sandstone to green in the Middle Jurassic Zhiluo Formation from the uranium deposits in the northern Ordos Basin, China. The original gray sandstone underwent oxidation and was reddened by the downward flow of meteoric water from the northern margin of the basin during the Late Cretaceous–Cenozoic uplift. This process resulted in the leaching of preore-stage uranium concentration and oxidation of preore pyrite in the organic matter-rich sandstone. Uranyl and sulfate ions were carried downward through the host sandstone by oxygenated groundwater. Meanwhile, hydrocarbons migrated upward and reacted with the downward flowing oxidizing fluids, which induced uranium mineralization at the redox interface between the red and gray sandstone where iron was reduced to Fe2+ and incorporated into pyrite cement. The highly negative 34S values (−58.0‰ to −33.4‰ V-CDT) of the pyrite indicate that it originated from bacterial sulfate reduction during hydrocarbon biodegradation. Abundant organic acids and CO2 were generated from hydrocarbon oxidation, resulting in the dissolution of feldspars and the precipitation of kaolinite in the mineralized sandstone. With the formation of the Cenozoic Hetao graben to the north, the gravity-driven flow of meteoric water was limited, resulting in progressive halting of epigenetic uranium mineralization. Then, the upward hydrocarbons dominated the fluid system throughout the northern slope of the basin and bleached the previous red sandstone updip, which set up a strong reducing environment and protected the early formed uranium deposits at the paleo-redox front from oxidation and remobilization. Due to the oxygen and sulfur supply absence, the iron released from hematite during bleaching was immobilized and incorporated into Fe-rich chlorite that imparts the green color, rather than into pyrite or reprecipitation as hematite. This study provides insights for the processes of hydrocarbon-water-rock interactions associated with uranium mineralization and preservation, which can serve as exploration guides for sandstone-hosted uranium deposits.

Outcrop fracture network characterization for unraveling deformation sequence, geomechanical properties distribution, and slope stability in a flysch sequence (Monte Venere Formation, Northern Apennines, Italy)

A detailed characterization of outcrop fracture networks in the turbiditic flysch sequence of the Monte Venere Formation (Northern Apennines) together with in situ measurements of rock strength using the Schmidt hammer provided important insights into the sequence of deformation and the slope stability conditions. The inferred sequence of structure formation from oldest to youngest is bedding-parallel cleavage, veins and normal faults, joints, and strike-slip faults (sheared joints). Alteration halos around fractures (joints, splay joints, strike-slip faults, and some normal faults) point out that these structures were conductive to meteoric water during uplift and erosion in the Holocene. Calcite-filled veins without alteration halos are considered local barriers to fluid flow and diffusion. Bedding thickness controls rock fracturing characterization parameters in the Monte Venere Formation. Reactivation in shear of pre-existing structures, however, causes the formation of splay joint clusters that locally increase fracture density contributing to degrade the mechanical strength of the rock. These localized clusters are apparent in detailed outcrop maps but they are usually not detected by the rock fracturing characterization parameters. Our data also imply that the presence of bedding-parallel cleavage is more important than layer thickness in controlling the rock compressive strength and ultimately the peak shear strength along a potentially sliding surface. This study takes closer look at landslide formation in a sloped flysch sequence under Mediterranean climate conditions and allowed to consider a conceptual model for landslide occurrence in which structural discontinuities and meteoric water flow through fracture networks are main triggering factors.

Meteoric Water and Salt-Dome-Related Diagenesis in Tertiary Turbidite Reservoirs from the EspÍrito Santo Basin, Brazil

Abstract Quantitative petrography and stable-isotope and fluid-inclusion analysis revealed that the diagenetic evolution of two Tertiary turbidite sandstone reservoirs from the offshore part of the Espirito Santo Basin, eastern Brazil, was influenced by the flow of meteoric water and salt-dome-related fluids, which had different impacts on their quality. Influx of meteoric water during early burial, in response to relative sea-level fall, resulted in extensive kaolinization and dissolution of framework silicate grains. Mesogenetic compactional fluids were progressively modified by the proximity of salt domes, which led to ubiquitous feldspar albitization and localized quartz, calcite, and saddle-dolomite precipitation. Fluid inclusions in quartz overgrowths indicate that the precipitating fluids had salinities predominantly in the range 8–13 wt% NaCl equivalent and temperatures largely in the 100–155°C range (higher than present-day formation temperatures—105° up to 115°C). The distribution of feldspar albitization suggests that the fracture systems along the margins of the salt domes acted as preferential pathways for such hot brines. However, the influence of the salt domes on the diagenetic processes of the reservoirs was relatively mild, despite their proximity, because pore-filling neoformed illite is absent, and occurrence of quartz cement is limited in the sandstones, which may be related to the late burial of the reservoirs and the intermittent behavior of the salt-dome-associated fracture systems as effective conduits for reactive fluids. We expect that this paper may contribute to the understanding and prediction of diagenesis and reservoir properties of turbidite sandstones influenced by meteoric and salt-dome-related fluids in offshore Espirito Santo Basin and in other similar areas.

Self-potential characteristics of the dormant period of Izu-Oshima volcano

Continuous self-potential (SP) monitoring has been conducted at Izu-Oshima volcano to detect signals resulting from volcanic activity since the installation of an SP monitoring network in March 2006. Since the installation, annual variations of up to 100 mV have been recorded. If we exclude these annual variations, temporal variations in SP do not show notable changes. This is consistent with the volcano being in a state of quiescence during the measurement period. The annual variations have the different amplitudes and mean levels between stations. To investigate the causes of these annual variations, we carried out numerical simulations of SP generation associated with downward meteoric water flow through electrokinetic coupling in a ~ 550 m thick unsaturated layer. The results show that the vertical electric potential gradient varies with changes in liquid-phase saturation in the unsaturated layer. These changes are caused by variations in the rate of meteoric water percolation. This, in turn, correlates with fluctuations in daily precipitation, thus explaining the annual SP variation recorded at the ground surface. Differences in the amplitude and mean level of SP variation are shown to be associated with different rock properties, especially permeability, porosity, and electrical conductivity. Our results indicate that observable SP changes will appear at stations near the summit if the distributions of liquid-phase saturation and/or pertinent parameters controlling the electrokinetic coupling in the thick unsaturated layer are modified the upward flow of volcanic gas.

Calcite raft geochemistry as a hydrological proxy for Holocene aquifer conditions in Hoyo Negro and Ich Balam (Sac Actun Cave System), Quintana Roo, Mexico

Two cores from calcite rafts deposits located in Cenote Ich Balam and Hoyo Negro were dated and analyzed for 87Sr/86Sr, δ18O, δ13C, Sr/Ca and Cl/Ca. The geochemical records show changing aquifer salinity spanning the last ∼ 8.5 cal kyrs BP and interrelationships with Holocene climate trends (wet and dry periods). During the wet mid-Holocene, the salinity of the meteoric Water Mass (WM; at 7.8–8.3 cal kyrs BP) was relatively high at 1.5–2.7 ppt and then became less saline (1.0–1.5 ppt) during the last ∼ 7000 yrs as climate became progressively drier. High salinity of the meteoric WM during the wet mid-Holocene is attributed to increased turbulent mixing between the meteoric and underlying marine WM. Increased precipitation, in terms of amount, frequency, and intensity (e.g. hurricanes) causes higher flow of meteoric water towards the coast and mixing at the halocline, a phenomenon recorded with recent instrumental monitoring of the aquifer. Conversely, during dry periods reduced precipitation and flow in the meteoric WM would result in lower salinity. Karst properties and Holocene sea-level rise also seem to have an effect on the aquifer. When the regionally extensive network of shallow cave passages (∼ 10–12 m water depth) are flooded at ∼ 8000 cal yrs BP, there is a rapid shift in salinity. This study demonstrates that calcite raft deposits can be used as paleo-environmental recorders documenting the effects of sea level and climate change on aquifer condition.

The role played by carbonate cementation in controlling reservoir quality of the Triassic Skagerrak Formation, Norway

Anomalously high porosities up to 30% at burial depth of >3000 m along with varying amounts and types of carbonate cements occur in the fluvial channel sandstone facies of the Triassic Skagerrak Formation, Central Graben, Norway. However, porosities of the Skagerrak Formation are lower in the Norwegian sector than in the UK sector. In this study, petrographic analysis, core examination, scanning electron microscopy, elemental mapping, carbon and oxygen isotope, fluid inclusion and microgeometry analysis are performed to determine the diagenesis and direct influence on reservoir quality, with particular focus on the role played by carbonate cementation. The sandstones are mainly fine-grained lithic-arkosic to sub-arkosic arenites and display a wide range of intergranular volumes (2.3%–43.7% with an average of 23.6%). Porosity loss is mainly due to compaction (av. 26.6%) with minor contribution from cementation (av. 12.1%). The carbonate cements are patchy in distribution (from trace to 20.7%) and appear as various types e.g. calcretes (i.e. calcareous concreted gravels), poikilitic sparite and sparry ferroan dolomite, and euhedral or/and aggregated ankerite/ferroan dolomite crystals. This study highlights the association of carbonate precipitation with the remobilisation of carbonate from intra-Skagerrak calcretes during early burial stage i.e. <500 m. During deeper burial, compaction is inhibited by carbonate cements, resulting high intergranular volume of up to 32% and 29% for fine- and medium-grained sandstones, respectively. Carbonate cement dissolution probably results from both meteoric water flow with CO2 during shallow burial, and organic CO2 and carboxylic acid during deep burial. The maximum intergranular volume enhanced by dissolution of early carbonate cements is calculated to 8% and 5% for fine- and medium-grained sandstones, respectively. Compaction continues to exert influence after dissolution of carbonate cements, which results in a loss of ∼6% intergranular volume for fine- and medium-grained sandstones. Reservoir quality of the Norwegian sector is poorer than that of the UK sector due to a lower coverage of clay mineral coats e.g. chlorite, later and deeper onset of pore fluid overpressure, lower solubility of carbonate compared to halite, and a higher matrix content.

Light Hydrocarbon Geochemistry of Oils in the Alpine Foreland Basin: Impact of Geothermal Fluids on the Petroleum System

Oil is produced in the Austrian sector of the Alpine Foreland Basin from Eocene and Cenomanian reservoirs. Apart from petroleum, the basin hosts a significant geothermal potential, which is based on the regional flow of meteoric water through Malmian (Upper Jurassic) carbonate rocks. Oils are predominantly composed of n-alkanes, while some samples are progressively depleted in light aromatic components. The depletion in aromatic components relative to abundant n-alkanes is an effect of water washing. Waters coproduced with oils that are affected by water washing show a progressive reduction in salinity and depletion in 2H and 18O isotopes, indicating that the degree of water washing is mainly controlled by the inflow of meteoric water from the Malmian aquifer. In some fields with Cenomanian reservoir rocks, a hydraulic connectivity with the Malmian aquifer is evident. However, water washing is also recognized in Eocene reservoirs and in areas where the Malmian aquifer is missing. This shows that existing flow models for the regional Malmian aquifer have to be modified. Therefore, the results emphasize the importance of combining data from the petroleum and geothermal industry, which are often handled separately.

Coal seam gas distribution and hydrodynamics of the Sydney Basin, NSW, Australia

This paper reviews various coal seam gas (CSG) models that have been developed for the Sydney Basin, and provides an alternative interpretation for gas composition layering and deep-seated CO2 origins. Open file CSG wells, supplemented by mine-scale information, were used to examine trends in gas content and composition at locations from the margin to the centre of the basin. Regionally available hydrochemistry data and interpretations of hydrodynamics were incorporated with conventional petroleum well data on porosity and permeability. The synthesised gas and groundwater model presented in this paper suggests that meteoric water flow under hydrostatic pressure transports methanogenic consortia into the subsurface and that water chemistry evolves during migration from calcium-rich freshwaters in inland recharge areas towards sodium-rich brackish water down-gradient and with depth. Groundwater chemistry changes result in the dissolution and precipitation of minerals as well as affecting the behaviour of dissolved gases such as CO2. Mixing of carbonate-rich waters with waters of significantly different chemistries at depth causes the liberation of CO2 gas from the solution that is adsorbed into the coal matrix in hydrodynamically closed terrains. In more open systems, excess CO2 in the groundwater (carried as bicarbonate) may lead to precipitation of calcite in the host strata. As a result, areas in the central and eastern parts of the basin do not host spatially extensive CO2 gas accumulations but experience more widespread calcite mineralisation, with gas compositions dominated by hydrocarbons, including wet gases. Basin boundary areas (commonly topographic and/or structural highs) in the northern, western and southern parts of the basin commonly contain CO2-rich gases at depth. This deep-seated CO2-rich gas is generally thought to derive from local to continental scale magmatic intrusions, but could also be the product of carbonate dissolution or acetate fermentation.

Shear-enhanced compaction bands formed at shallow burial conditions; implications for fluid flow (Provence, France)

Field observations of highly porous and permeable sandstone in the Orange area (S-E Basin, France) show that networks of shear-enhanced compaction bands can form in a contractional regime at burial depths of about 400 m ± 100 m. These bands show equal compaction and shear displacements, are organized in conjugate and densely distributed networks, and are restricted to the coarse-grained (mean grain diameter of 0.6 ± 0.1 mm) and less porous (porosity of 26 ± 2%) sand layers. The bands are crush microbreccia with limited grain comminution and high grain microfracture density. They show reductions of permeability (mD) ranging from 0 to little more than 1 order of magnitude. They show no control on the alteration products related to meteoric water flow, which suggests that these shear-enhanced compaction bands have no or only negligible influence on subsurface fluid flow. Their selective occurrence and small (20%) reduction in transmissibility in densely populated layers prevented them from compartmentalizing the sandstone reservoirs. A comparison with compaction-band populations in the Navajo and Aztec sandtsones (western U.S.) emphasizes the role of burial depth and the presence of chemical compaction processes for the sealing potential of deformation bands.

Authigenesis of Titania Minerals and the Mobility of Ti: New Evidence From Pro-Deltaic Sandstones, Cretaceous Scotian Basin, Canada

Titania (TiO2) minerals are minor diagenetic phases in many sandstone–shale successions, but the conditions of Ti mobility and titania authigenesis are poorly known. Here, new modes of occurrence of authigenic titania minerals, filling pores and replacing phytodetritus, are documented from Lower Cretaceous prodeltaic sandstones in the offshore Scotian Basin of southeastern Canada. Textural relationships suggest that titania minerals formed at the same time as kaolinite, most commonly below lowstand sequence boundaries, related to flux of meteoric water. Such authigenic titania is most abundant in thin-bedded sandstones interbedded with thick prodeltaic mudstone in which fine-grained detrital Ti-rich minerals are concentrated. Textures in titania that has replaced uncompacted phytodetritus suggest microbial mediation in near-surface eodiagenesis. Eogenetic titania is enriched in phosphorus (∼ 0.6% P2O5) and may co-occur with authigenic fluorapatite and crandallite crystals. Such titania resulted from prolonged flow of meteoric water that dissolved P from apatite and feldspar, thereby enhancing Ti solubility. In basins with supply of immature sediment from granitic terranes and important diagenesis by meteoric water, the assumption that Ti is an immobile element and that rutile or other titania minerals are exclusively of detrital origin may not be valid. Probable mesodiagenetic titania has low P content, suggesting that Ti mobility under these conditions was facilitated by some other agent, probably organic acids. The results of this study illustrate that even in cases where titania minerals are volumetrically insignificant, their microtextures and trace-element chemistry can provide important insights into the character of fluid flow during diagenesis of siliciclastic rocks.

Migration of geothermal fluids in extensional terrains: the ore deposits of the Boccheggiano-Montieri area (southern Tuscany, Italy)

An integrated study based on fluid inclusion, δ18O composition and structural analyses was carried out on a Pliocene fossil hydrothermal system, located to the South of the present active Larderello geothermal field, in the Boccheggiano-Montieri area. The study area is typified by mineralized cataclastic levels related to Late Oligocene–Early Miocene thrust surfaces, and to the following two generations of normal faults of Miocene and Pliocene ages, respectively. Within the damage zone of the Pliocene Boccheggiano fault, the mineralization is mainly made up of quartz and pyrite. Quartz + Pb–Zn sulfides, or quartz + Pb–Zn sulfides + fluorite + carbonates assemblages occur instead in the older cataclastic levels. Two generations of liquid-rich fluid inclusions were recognized in quartz and fluorite: the first one, with homogenization temperatures ranging between 172 and 331°C and salinity between 0.0 and 8.8 wt.% NaClequiv., records the early stage of hydrothermal activity. The second generation of fluid inclusions documents a later stage, with homogenization temperature from 124 to 288°C and salinity from 0.2 to 1.9 wt.% NaClequiv.. Fluid inclusions analyses also indicate that mixing of fluid with distinct salinities and/or temperatures was a widespread process during the early stage, and that fluid temperatures decreased moving from the Boccheggiano fault toward the more distal and older cataclastic levels. The δ18O values of water in equilibrium with hydrothermal quartz, which range from −5.7 to −0.1‰, are related to the circulation of meteoric water mixed with saline water that leached the evaporite level and enriched in δ18O through water–rock interaction, and/or with magmatically derived fluids. Results indicate that the damage zone of the Pliocene Boccheggiano fault represented the main channel for the flow of meteoric water, which was heated at depth, then mixed with high salinity fluids, and finally ascend to infiltrate along the older cataclastic levels. Our results, based on fluid inclusions, oxygen isotopic compositions and structural analyses indicate that a single fluid flow path run through the damage zone of the Boccheggiano fault and the older cataclasites, which were thus hydraulically connected.

Genetic Model and Exploration Guidelines for Kaolin Beneath Unconformities in the Lower Cretaceous Fluvial Chaswood Formation, Nova Scotia

Potentially commercial deposits of kaolin are found in the fluvial Lower Cretaceous Chaswood Formation, the sedimentologically proximal equivalent of deltaic sediments of the offshore Scotian basin. The geological setting of the kaolin deposits has been interpreted from high-resolution seismic-reflection profiles and boreholes, and mineralogical studies on one reference borehole. The kaolin is a product of early diagenesis involving meteoric water below the water table. The distribution of kaolin is controlled by the presence of intraformational unconformities that were sites of ground water recharge, and are marked by the development of oxisols above the water table. Such diagenesis was facilitated by interbedded, loosely consolidated, permeable sandstone. The highest-grade kaolin deposits are found in areas close to river belts, where overbank muds were not sufficiently drained to develop paleosols, but where later uplift created intraformational unconformities. In the sandstone, meteoric water flow altered feldspars to kaolin, thus yielding commercial silica sand deposits. It also altered ilmenite to rutile, which is concentrated as secondary placers in modern rivers that have eroded the Chaswood Formation and tills derived therefrom.

The heat transfer in the region of the Mauna Kea (Hawaii)—constraints from borehole temperature measurements and coupled thermo-hydraulic modeling

The objectives of this paper are an understanding of the thermal and hydraulic field because of a negative temperature gradient and cold temperatures in the 1-km-deep borehole of the Hawaiian Scientific Drilling Project (HSDP), located near the coast line. The temperature pattern is attributed to a superposition of thermal and hydraulic processes. In the deeper borehole (HSDP-2, depth 3.1 km) detailed temperature monitoring was performed. Temperature measurements reveal two different thermal regimes. The upper part is characterised by cold temperatures and a negative temperature gradient similar to those observed in the shallow pilot borehole. Below 1100 m, increasing temperatures are observed. Different processes, such as topographically driven groundwater flow, ingress of salt water and conductive heat flow are investigated by numerical modeling. A pure conductive scenario fails to match the temperature measurements, implying that both borehole sections are overprinted by advective conditions. Coupled fluid and heat flow modeling with solute transport yield results that agree with observed temperatures. The results of these simulations suggest that meteoric water flow from the mountain range controls the thermal conditions in the upper part of the borehole. Below this level, the thermal regime is additionally affected by circulation of salt water from the nearby ocean. Each of these flow systems has been observed at other locations: topographically driven fresh water at locations with pronounced topography and ingress of salt water is typical for islands or coastal areas. At Hawaii, they coincide and influence each other, resulting in a salt water interface occurring at greater depth than expected.

The evolution of fluid flow systems prior to, during, and post MVT mineralization in the Givetian-Frasnian carbonates of the Emanuel Range, Western Australia

The Emanuel Range is part of the extensive Devonian Reef complex, which overlies the Lennard Shelf, a section of shallowbasement at the northern end of the Canning Basin in Western Australia. The reef complexes formed in an extensional tectonic environment and host numerous Mississippi Valley-type (MVT) Zn Pb accumulations. The distribution, relative timing, and origin of calcite, dolomite, and MVT sulphide generations in the southeastern Emanuel Range indicate that the fluid flow systems operating during Middle Devonian to Middle Carboniferous burial changed significantly through time. The topographic flow of meteoric water from north to south, driven through alluvial fans shed from the highlands of the Precambrian Kimberley block to the north of the Emanuel Range, was the longest-lived fluid flow system. The topographic flow system operated intermittently during periods of lowstand in the Givetian and early Frasnian and continued throughout subsequent burial and uplift in the Middle Carboniferous. During early to intermediate burial depths (< 500 m), stratigraphically focused compactionally driven fluids of predominantly modified marine origin entered the reefs from a depocentre to the south of the Emanuel Range. During later burial (1–1.5 km) in the Late Devonian and Early Carboniferous, more deeply sourced fluids were driven laterally into the Emanuel Range from the Fitzroy Trough to the south. The introduction of compactionally driven, hot metalliferous hydrocarbon-bearing brines into the sequence occurred episodically, precipitating MVT sulphides. Between hydrothermal pulses, formation waters decreased in temperature and salinity, due to mixing with cooler surface waters. Hydrothermal brines flowed laterally from south to north until encounter with the Cadjebut Fault, which impeded brine flow. Further brine movement was focused through dilatant faults with a NNE orientation (thought to be related to transfer zones; Veamcombe, J.R., Dentith, M., Doerling, S., Reed, A., Cooper, R., Hart, J., Muhling, P., Windrim, D., Woad, G., 1995. Structural controls on Mississippi Valley-type mineralization, the southeastern Lennard Shelf, Western Australia. In: Sangster, D.E. (Ed.), Carbonate-Hosted Lead-Zinc Deposits. Society of Economic Geologists, Special Publication, vol. 4. 1995, pp. 74–94.) and near-vertical hydraulic fractures related to high fluid pressures. Through time, hydrothermal pulses became both less frequent and less intense, and topographically driven flow again dominated.