Phreatic Zone Research Articles

Multiphase of the meteoric diagenetic environment of carbonates and its relationship with reservoir: a case study of the Jingxi Area in the Ordos Basin, China

The meteoric diagenetic environment has multiphase characteristic, but the scales of the reservoirs in different meteoric diagenetic environments have been rarely considered. On the basis of geological and well-logging analyses, three distinct phases of the meteoric diagenetic process were observed in the Ordovician of the Jingxi area in Ordos Basin, China. The phreatic zone formed in the first phase is partially preserved, whereas those formed in the second and third phases are completely retained. Strata in the western (close to the Central Uplift Belt) and eastern parts underwent bedding-parallel meteoric dissolution and cross-layer meteoric dissolution, respectively. The distributions of the dissolution formation thicknesses in two successive phases of the meteoric diagenetic process exhibit complementarity at the same positions in the plane. The favorable reservoirs at the top of the Ordovician are mainly distributed in the western parts. The second phase of the meteoric diagenetic process is most conducive to the formation of carbonate reservoirs. By dividing and comparing the multiphases of the meteoric diagenetic environment of carbonates, the favorable karst reservoirs can be predicted in each phase.

Speleogenesis, geometry, and topology of caves: A quantitative study of 3D karst conduits

Karst systems are hierarchically spatially organized three-dimensional (3D) networks of conduits behaving as drains for groundwater flow. Recently, geostatistical approaches proposed to generate karst networks from data and parameters stemming from analogous observed karst features. Other studies have qualitatively highlighted relationships between speleogenetic processes and cave patterns. However, few studies have been performed to quantitatively define these relationships. This paper reports a quantitative study of cave geometries and topologies that takes the underlying speleogenetic processes into account. In order to study the spatial organization of caves, a 3D numerical database was built from 26 caves, corresponding to 621km of cumulative cave passages representative of the variety of karst network patterns. The database includes 3D speleological surveys for which the speleogenetic context is known, allowing the polygenic karst networks to be divided into 48 monogenic cave samples and classified into four cave patterns: vadose branchwork (VB), water-table cave (WTC), looping cave (LC), and angular maze (AM). Eight morphometric cave descriptors were calculated, four geometrical parameters (width-height ratio, tortuosity, curvature, and vertical index) and four topological ones (degree of node connectivity, α and γ graph indices, and ramification index) respectively. The results were validated by statistical analyses (Kruskal-Wallis test and PCA). The VB patterns are clearly distinct from AM ones and from a third group including WTC and LC. A quantitative database of cave morphology characteristics is provided, depending on their speleogenetic processes. These characteristics can be used to constrain and/or validate 3D geostatistical simulations. This study shows how important it is to relate the geometry and connectivity of cave networks to recharge and flow processes. Conversely, the approach developed here provides proxies to estimate the evolution of the vadose zone to epiphreatic and phreatic zones in limestones from the quantitative analysis of existing cave patterns.

Discovery of a shoal-controlled karst dolomite reservoir in the Middle Permian Qixia Formation, northwestern Sichuan Basin, Southwest China

The dolomites of the Middle Permian Qixia Formation have been important targets of natural gas exploration in the Sichuan Basin for decades. However, more and more exploration and research indicate that the formation of the reservoir might be related to karstification. To testify this hypothesis, we conduct comprehensive outcrop, core, and logging analyses based on a case study in the representative northwestern Sichuan Basin, which has obtained exploration breakthroughs recently. Results show that the Qixia dolomite reservoirs are mainly developed within fine-crystalline dolomites formed by a series of diagenetic modifications, which can be further divided into three types according to the macro- and micro-occurrences of dolomites: euhedral-subhedral crystalline dolomites in the quasi-stratiform karst system (mean porosity and permeability is 3.51% and 3.11 mD, respectively), euhedral-subhedral crystalline dolomites in the leopard porphyritic karst system (mean porosity and permeability is 3.36% and 1.22 mD, respectively), and allotriomorphic mosaic crystalline dolomites with residual parent rock fabrics (mean porosity and permeability is 0.94% and 0.92 mD, respectively). Their reservoir qualities decrease along the order. The formation mechanism of the reservoir is shoal-controlled karst. The preservation of residual intergranular pores within the thin-layer grainstones of shoal facies provides favorable channels for karst water. In the vadose zone, the heterogeneous dissolution within grainstones leads to the formation of leopard porphyritic dissolution features. In the phreatic zone, the karst water flowing along the stratiform grainstones results in the formation of quasi-stratiform dissolution features. The karst system is filled with loose carbonate sands and gravels, whose reservoir properties are far superior to parent rocks, and they can provide migration channels for the hydrothermal fluids with rich Mg2+ in the burial stage. The replacement of hydrothermal fluid results in the redistribution of pores and vugs of inter-fillings within karst system and the formation of intercrystalline pores and residual vugs, but the reservoir space of parent rocks keeps the same as the original condition. Therefore, the exploration of the Qixia dolomite reservoir should be changed to shoal-controlled karst.

Nitrates and phosphates in cave waters of Krak\xf3w-Cz\u0119stochowa Upland, southern Poland

The paper presents the varied presence of nitrates and phosphates in water from caves located in Częstochowa and Kraków, in urban, strongly anthropogenic conditions, representing the vadose zone of the fissure-karstic-porous massif of Upper Jurassic limestones. Hydrochemical research was carried out by the authors in the Cave on the Stone in Częstochowa in 2012–2015, in caves of the Zakrzówek horst from 1996 to 2002, and in the Dragon’s Cave by the research team of J. Motyka in 1995–1998. A number of NO3 and PO4 measurements were performed in waters sampled at these research sites: 20 measurements each of NO3 and PO4 at the Cave on the Stone, 228 of NO3 and 422 of PO4 at Zakrzówek, and 19 each of NO3 and PO4 at the Dragon’s Cave. To assess the quality aspect of N and P compounds in waters from the Cave on the Stone, the results of geochemical modelling were processed using PHREEQC software. In cave waters, the oxidised form of nitrogen NO3− predominates; in surface waters in the vicinity, unoxidised forms prevail: NH4+, NH3, and NH4SO4−. Among phosphorus speciations, dissolved forms are dominant: HPO42−, H2PO4−, and the insoluble form CaHPO4; in surface waters, these forms are practically absent. Transformations of water chemistry in ‘urban’ caves, often centuries old, manifest themselves in, inter alia, the occurrence of multi-ionic waters, including seasonal variations and extremely diversified concentrations, with very high concentrations in subpopulations of NO3 (0.2–485 mg dm−3) and P (0.02–6.87 mg dm−3). The common presence of NO3 in waters of the phreatic zone of the Częstochowa Upland, an area developed in an agricultural direction, is documented by, inter alia, the exploitation of intakes supplying the city of Częstochowa (10–57 mg dm−3, 2011) and crenological studies from 2008 to 2015 (NO3, 2–58 mg dm−3), at simultaneously low phosphate concentrations (PO4, 0.02–0.24 mg dm−3).

Interaction between karst terrain and bauxites: evidence from Quaternary orebody distribution in Guangxi, SW China

Most bauxite in China is located upon the karst surface, yet the relation between karstification process and bauxite formation is barely known. Here we discuss how the relation affects the karst and bauxite evolution through analyzing distributions of orebody parameters from 9,007 exploration wells (434 orebodies) in western Guangxi, South China block. In high-elevation karst terrain dominated by peaks, orebodies have greater average thickness, lower Al2O3 and higher Fe2O3T than those in low-elevation region dominated by depressions. Principal component and multifractal analyses show that the Al2O3, Fe2O3T and LOI and the orebody thickness, determined by depression geometry, have more even distributions in high-elevation terrain. This explains that the interaction between the oxidized, alkaline water in karst surface and the ferrous clay minerals that released H+ during bauxite secondary weathering was more intensive in high-elevation terrain than in low-elevation one. The interaction with self-organized nature is considered responsible for the even development of karstic depressions and bauxite orebody thicknesses in high-elevation terrain. In comparison, SiO2 distribution is more even in low-elevation terrain, where connected depressions near the phreatic zone facilitated SiO2 mobilization and even distribution.

Paleogeomorphology restoration and the controlling effects of paleogeomorphology on karst reservoirs: a case study of an ordovician-aged section in Tahe oilfield, Tarim Basin, China

The Tarim Basin is the largest petroliferous basin in northwestern China and contains the Tahe oilfield, the highest hydrocarbon enrichment in the entire basin. Paleogeomorphology has important controlling effects on carbonate reservoir development. Using core data, thin sections and drilling, logging and seismic data, paleokarst was identified and analyzed. The paleogeomorphology of the top low-middle Ordovician was recovered following a comprehensive utilization of the impression and residual thickness methods in combination with unconformity identification. Based on the filling thickness and residual thickness, the karst paleogeomorphic units were classified, and their controlling effects on reservoirs analyzed. The second-order paleogeomorphic units primarily include four types: karst highland, karst gentle⁃slope, karst steep⁃slope and karst basin. The karst gentle⁃slope and karst steep⁃slope are further classified quantitatively into third-order paleogeomorphic units (monadnock, tableland, karst terrace and trench). The results show that the development of the karst reservoir differed in different geomorphic units. In the karst gentle slope, the favorable areas for karst reservoir development are the karst terrace, tableland, monadnock, and the ends and flanks of trench. In the karst steep⁃slope, the karst terrace and tableland are favorable areas. In the vertical vadose and phreatic zones of the gentle-slope region, a large number of caves and underground river systems developed, but in the steep-slope region, only a small number of shafts and isolated caves are observed. This study plays an important role in oil and gas exploration and development.

BEACHROCKS CEMENT CHARACTERISTICS AND CONDITIONS OF FORMATION. CASE STUDY PLATANIAS BEACH, CHANIA, GREECE

Beachrocks represents a coastal deposition in the intertidal area, and studying their properties may lead to create a model which identifies the conditions of their formation (paleo-environment). This paper focuses most intently on the cement material which is able to recover the paleo-environment conditions during diagenesis of such coastal sediment. We used optical microscopy, secondary electron microscopy and Raman Spectroscopy to characterize the cement texture, mineralogy and chemistry in the beachrocks. The existence of pure calcite primarily controlled by the meteorite water, while Mg-calcite appears between the lowermeteoric and the upper marine phreatic zone. Finally, the presence of aragonite associated with the marine phreatic to lower marine vadose environment.

Soil as a Basic Nexus Tool: Soils at the Center of the Food–Energy–Water Nexus

Soil is the medium for plant growth and the substrate for all biogeochemical and biogeophysical processes. Soil’s unique natural organization forms the foundation of any food–water–energy nexus system. It forms a habitat for billions of diverse micro, meso, and macrofauna and flora and is the basis of numerous ecosystem services essential to human well-being and nature conservancy. It moderates soil hydrological processes within the entire vadose zone: which is part of the earth between the soil surface and the phreatic zone. Soil structure also supports numerous ecosystem services including nutrient transformation and availability, water quality and renewability, denaturing and transport of pollutants, and groundwater table fluctuations. It also moderates the soil–water–plant-energy nexus with the replenishement of green-water supply (from precipitation) for plants and soil biota, which in turn enables the production of biomass as a source of food, feed, fiber, and biofuel feedstock. Indeed, soil is a very large reservoir for water and carbon with strong influences on local, regional, and global climate. Also, the energy factor is connected with the climate change through soil–water–food–energy nexus because of numerous interlinked pathways including gaseous emissions, energy and food production, and recycling of nutrients and water at regional, national, and global scales. Through provisioning of numerous ecosystem services, the soil–water–food–energy–climate nexus is interwoven with the ecosystem security and functioning of planet’s four ecospheres (i.e., atmosphere, hydrosphere, lithosphere, and the biosphere). Therefore, the health of soil, plants, animals, people, and ecosystems is one and indivisible. This interconnectivity is also the basis of the “4 per Thousand” initiative adopted by the COP21, the Climate Summit of 2015 in Paris, and “Adapting African Agriculture” (AAA) by COP22 in Morocco. Consequently, soil is not only a foundation for securing the natural resources: food, water and energy, but it is under desperate need to be integrated and appreciated in understanding the complex interconnectedness of any food, energy, water and soil system. Concentration and stock of soil organic carbon are the key soil properties that determine the physical, chemical, biological, and ecological properties and processes, and are major control of all nexuses described herein. This chapter presents a conceptual model and the role of soil as a naturally organized medium to protect global food, water, energy securities. Moreover, it elaborates on using soil as a basic nexus tool and proposes a paradigm shift in integrating soil and creating the food–energy–water–soil nexus.

Identification of runoff formation with two dyes in a mid-latitude mountain headwater

Abstract. Subsurface flow in peat bog areas and its role in the hydrologic cycle has garnered increased attention as water scarcity and floods have increased due to a changing climate. In order to further probe the mechanisms in peat bog areas and contextualize them at the catchment scale, this experimental study identifies runoff formation at two opposite hillslopes in a peaty mountain headwater; a slope with organic peat soils and a shallow phreatic zone (0.5 m below surface), and a slope with mineral Podzol soils and no detectable groundwater (> 2 m below surface). Similarities and differences in infiltration, percolation and preferential flow paths between both hillslopes could be identified by sprinkling experiments with Brilliant Blue and Fluorescein sodium. To our knowledge, this is the first time these two dyes have been compared in their ability to stain preferential flow paths in soils. Dye-stained soil profiles within and downstream of the sprinkling areas were excavated parallel (lateral profiles) and perpendicular (frontal profiles) to the slopes' gradients. That way preferential flow patterns in the soil could be clearly identified. The results show that biomat flow, shallow subsurface flow in the organic topsoil layer, occurred at both hillslopes; however, at the peat bog hillslope it was significantly more prominent. The dye solutions infiltrated into the soil and continued either as lateral subsurface pipe flow in the case of the peat bog, or percolated vertically towards the bedrock in the case of the Podzol. This study provides evidence that subsurface pipe flow, lateral preferential flow along decomposed tree roots or logs in the unsaturated zone, is a major runoff formation process at the peat bog hillslope and in the adjacent riparian zone.

Origin and influence of the superficial structure on the morphogenesis (Eocene plateaux of the eastern Paris Basin)

The concept of superficial structure relates to surficial deformations that are determined neither by tectonic deformation nor by surface geomorphic processes sensu stricto. This work addresses two mechanisms leading to structural surface disturbances in the Lutetian strata of the Eocene plateaux of the eastern Paris Basin. Firstly, mechanical release which is associated with stress-relief during Quaternary valley downcutting. It results in lateral spreading of the middle Lutetian limestone, and subsequent sub-erosion of underlying sands may cause valley-side cambering. Secondly, ghost-rock karstification in the phreatic zone which is leading to surficial collapse of the upper Lutetian cover. Geological structure (thickness and porosity of the middle Lutetian limestone) and valley-side slopes stratigraphy (position of the upper Ypresian sand) control the spatial distribution of these processes. Ghost-rock karstification, conditioned by tectonic joints is confined to the west; to the east, cambering processes occur where upper Ypresian sand aquifer and alluvial aquifer are connected. During the Quaternary, periglacial conditions account for cambering processes and also for a second phase of karstification within an aquifer perched in the active layer, and from mechanical release joints. Resultant morphological features are then inherited and cambering is even a fossil process where upper Ypresian sand crops out above the valley floor. Consequently, large-scale landforms, derived from the superficial structure, are essentially inactive.

Study on characteristics and genesis of botryoidal dolostone of the Upper Sinian Dengying Formation: a case study from Hanyuan region, Sichuan, China

Botryoidal dolostone (BD) developed extensively within the Neoproterozoic Upper Sinian Dengying Formation in the Hanyuan region, which is an important gas reservoir. Based on literature review, a study of their outcrop characteristics, petrology, microfabric, degree of order, and genesis reveal that BD mainly comprises botryoidal lumps (BL) originated from depositional-penecontemporaneous seawater and botryoidal and ctenoid cements or fillings. BL occurred in parallel beds during the depositional-syngenetic stage, including core and coating. The core consists of grapestone and thrombolite, which is dominated by muddy and microcrystalline high-magnesium calcite (HMC) resulting from marine deposition and micro-organism capturing and binding effects. The coating, classified as either thin or thick, is mainly isopachous fibrous aragonite (IFA) that formed during the depositional-syngenetic stage. Thin coatings formed in the turbulent sea bottom, while thicker ones formed in a relatively quiet sea bottom. Botryoidal and ctenoid cements and fillings compose IFA and HMC. IFA that includes marine phreatic zone deposition from the syngenetic-penecontemporaneous stage mainly occurs in the spaces between grains of BL and intraclast or on the top of them. The HMC that is the product from meteoric leaching in the penecontemporaneous stage and marine deposition occurs in the dissolved pores and fractures. During the process when BL and the botryoidal, ctenoid cements, or fillings formed, either abiogenetic or microbiogenic aragonite and HMC were mimetically dolomitized and preserved the primary texture and structure. BD was also reworked by the meteoric leaching in the penecontemporaneous and supergenous stages.

Paleokarst of the Lianglitage Formation related to tectonic unconformity at the top of the Ordovician in the eastern Tazhong Uplift, Tarim Basin, NW China

The Lianglitage Formation (also named Lianglitag Formation) is an important hydrocarbon reservoir in the Tarim Basin; the reef and shoal facies of this formation have previously been extensively investigated. The paleokarst of the formation related to a tectonic unconformity at the top of the Ordovician (Tg5) has, however, not been widely investigated. In this paper, we undertake a comprehensive study of the paleokarst by an integrated analysis of seismic data, well‐logging data, and core data. Several geomorphologic units that formed at the end of the Ordovician period are identified, including a fault‐thrust uplift high, inter‐uplifts sag, uplift platform, and fault‐thrust anticline; these units are controlled by west–east and northwest–southeast striking faults. The thickness of erosion is estimated to be 200 to 700 meters. The paleokarst is characterized by large and small caves, dense vugs, and dissolution fractures. Large caves predominantly developed in exposed areas and on the slopes. Dense vugs and small caves, features that contribute to premium hydrocarbon reservoirs, are generally tens of meters away from the unconformity, whereas dissolution fractures, predominantly filled by mud and silts, are situated in close proximity to the unconformity and faults. Four karst zones can be identified from vertical profiles: weathered crust (1–2 m thick), vertical infiltration zone (tens of meters thick), phreatic zone (tens to hundreds of meters thick), and a bottom zone that is largely unaffected by karstification. The karst of the Lianglitage Formation at the end of the Ordovician was mainly controlled by tectonic movement, paleogeomorphology, lithofacies, faults, and fractures. The karstification process is summarized in a karst model.

Nitrogen loss by anaerobic ammonium oxidation in unconfined aquifer soils

Anaerobic ammonium oxidation (anammox) is recognized as an important process for nitrogen cycling, yet little is known about its role in the subsurface biosphere. In this study, we investigated the presence, abundance, and role of anammox bacteria in upland soil cores from Tianjin, China (20 m depth) and Basel, Switzerland (10 m depth), using isotope-tracing techniques, (q)PCR assays, and 16 S rRNA & hzsB gene clone libraries, along with nutrient profiles of soil core samples. Anammox in the phreatic (water-saturated) zone contributed to 37.5–67.6% of the N-loss (up to 0.675 gN m−2d−1), with anammox activities of 0.005–0.74 nmolN g−1soil h−1, which were even higher than the denitrification rates. By contrast, no significant anammox was measured in the vadose zone. Higher anammox bacterial cell densities were observed (0.75–1.4 × 107copies g−1soil) in the phreatic zone, where ammonia-oxidizing bacteria (AOB) maybe the major source of nitrite for anammox bacteria. The anammox bacterial cells in soils of the vadose zone were all <103copies g−1soil. We suggest that the subsurface provides a favorable niche for anammox bacteria whose contribution to N cycling and groundwater nitrate removal seems considerably larger than previously known.

Groundwater Potential and Vulnerability Assessment from Integrated Geophysical Methods, Borehole Logging, and Hydrogeological Measurement

Geophysical investigations and hydrogeological measurements were carried out in Akoko area of Ondo State, Nigeria which are characterized by rugged hills of Precambrian Basement Complex of Southwestern Nigeria comprising mainly of the Migmatite-Gneiss-Quartzite Complex of Archean-Proterozoic age. The study was aimed at evaluating the groundwater potential of the area and assess the vulnerability of the aquifers/water bearing units within the phreatic zone to contamination especially from surface activities/anthropogenetic sources. Seventy soundings were carried out along fifteen traverses where the VLF-EM measurement was also conducted. The hydrogeological measurement involved determination of static water level/vadose zone thickness from 138 wells. Also four borehole were drilled after thorough geophysical investigations in order to constrain the interpretation of the geophysical investigation. Findings show that the major water bearing units/aquifer in the area are the weathered layer (clayey in nature) and fractured basement as delinated on the geoelectric sections, borehole sections, and very low frequency electromagnetic. The combination of these aquifer units are common in Ikare and Akungba parts of the study area. The visible depth of groundwater exploitation in the area is between 10 – 40 m. The static water level is generally less than 5 m. The map of the overburden shows that Akoko area is generally made up of thin overburden thickness except at Irun, Ogbagi, Arigidi, and Oke Agbe that showed moderate overburden thickness (10 m – 20 m). The static water level measured in the study area ranged from0.75 m – 16 m, with a modal range of 1.1 – 3.0 m as they constituted for about 78 % of the area. This generally showed that the static water level was shallow across the study area, thus suggesting that the surficial aquifers/water bearing units would be highly vulnerable to anthropogenetic/surface activities which are the major sources of groundwater contamination. Clay or silt, characterized by low resistivity (1 – 100 Ω-m) and very low permeability, and impervious or semi-impervious topsoil materials (laterite and lateritic sand), characterized by high resistivity values (&gt;400 Ω-m) constitutedthe protective layers that cappedthe vadose zones in the area. The topsoil can provide protection to a reasonable extent, but limited due to its thin thickness across the area.

Occurrences and genesis of palygorskite/sepiolite and associated minerals in the Barzaman formation, United Arab Emirates

AbstractThe Barzaman Formation exposed in the United Arab Emirates was deposited as a series of fluvial sediment sequences lying along the western margin of the Hajar Mountains, part of the Oman–UAE ophiolite. This formation consists of a sequence of rocks dominated by variably cemented and altered conglomerates comprising calcareous siltstones and calcareous clays deposited during the Miocene to Pliocene under a humid climate. The conglomerates are composed largely of ultramafic and lesser-mafic clasts. The present study was undertaken in order to understand the occurrence and genesis of palygorskite and sepiolite in relation to the environmental changes including evaporitic and sabkha environments.Sediments were collected from two trenches and a drill hole of ∼22 m depth. Samples were analysed by optical petrograpy, X-ray diffraction and scanning electron microscopy. Pedogenesis occurred at the deeper level in well cemented conglomerate which constitutes the hard crust. Post-depositional erosion started in marine phreatic or vadose zones as shown by the neoformation of serpentine from the weathering of olivine as well as of calcite and dolomite. Neoformation of palygorskite, sepiolite, dolomite and halite occurred under evaporitic conditions on calcareous silty clay facies. Relatively hot, vadose and oxidizing environmental conditions affected the calcareous siltstone facies leading to the genesis of dolomite and palygorskite by direct precipitation from solution rich in Ca, Mg, Al, Fe and Si ions.

The Geologic Context of Wonderstone: A Complex, Outcrop-Scaled Pattern of Iron-Oxide Cement

Abstract Although siderite is a widespread early diagenetic mineral in fluvial systems, it is unstable in oxidizing environments and destroyed in permeable rocks that experience uplift and exhumation. The products of siderite oxidation, however, (mm- to cm-scale rhombs, concretions, and complex bands of iron-oxide cement) are widespread in the rock record of fluvial systems. The fluvial channels of the Shinarump Member of the Chinle Formation in southern Utah and northern Arizona, U.S.A., provide an excellent suite of examples of diagenetic features produced by Triassic and Neogene oxidation of early diagenetic siderite. These diagenetic features also provide direct evidence of the level of the water table during deposition of the Shinarump member. Large, in situ, discoidal concretions containing preserved siderite are present in Shinarump floodplain siltstones. Rip-up clasts derived from the siltstones developed iron-oxide rinds during late-stage, near-surface oxidation. These two structures show that floodplain silts contained abundant organic matter and methanic pore water. Groundwater recharging through these silts carried reducing water through underlying sand bodies and discharged into active channels. Degassing of CO2 and methanogenesis caused rhombic crystals of siderite to precipitate in channel sands during these wet intervals. Some of this siderite may have been oxidized during dry intervals when groundwater circulation reversed, but most siderite in the channel sands was preserved until the Shinarump was exhumed during the Neogene. As oxygenated near-surface water entered joints in the lithified Shinarump, colonies of iron-oxidizing microbes living in the phreatic zone occupied redox boundaries and used the rhombic crystals of siderite in the sandstone and the spherulitic siderite in transported siltstone intraclasts as their sources of energy and carbon. The ferrous iron released from dissolving siderite within the intraclasts was oxidized at the siltstone–sandstone contact, generating rinded concretions similar to those in the Cretaceous Dakota Formation. Complex banding known as wonderstone was produced in the channel sandstones from oxidation of the rhombic siderite; the pattern is a combination of Liesegang bands and microbially mediated cements. The preserved rhombs are pseudomorphs after siderite crystals that were either oxidized during Triassic dry intervals, or escaped Neogene microbial oxidation in the phreatic zone, only to be oxidized abiotically in the vadose zone. Microbes are likely oxidizing Shinarump siderite a few kilometers down dip of outcrops with exposed wonderstone. At such locations, the Shinarump is in contact with overlying water-saturated Quaternary alluvium.

Sub‐annual variability in historical water source use by Mediterranean riparian trees

AbstractThe seasonal availability of water within a tree's rooting zone may be an important determinant for individual tree growth and overall forest health, particularly in riparian corridors of Mediterranean climate zones that are vulnerable to water stress. Here, we present a new method that combines dendro‐isotopes and isotope modelling for determining how water source use varies over 10 consecutive growing seasons (2000–2010) for co‐occurring species Populus nigra and Fraxinus excelsior, along the Rhône River, south‐eastern France. We conducted highly resolved δ18O analysis of cellulose micro‐slices within tree‐rings and back‐calculated the δ18O signature of source water available at the time of growth using a biochemical fractionation model. We related these patterns to inferred seasonal hydrological partitioning through comparison with δ18O of waters from the vadose and phreatic zones, precipitation and streamflow. The shallowly rooted Fraxinus displayed greater sub‐annual source water variability, as well as greater isotopic enrichment, reflecting use of precipitation‐derived vadose moisture. Its earlywood was formed mainly from winter rainfall (δ18O depleted) whilst the latewood was composed from growing season precipitation (δ18O enriched). In Populus, the sub‐annual source water use was relatively depleted, suggesting use of hyporheic water and regional groundwater. From 2007, both species converged in their pattern of water source uptake which was attributed to a decline in phreatic water access for Populus. These results demonstrate that the seasonal variability in source water use can be identified retrospectively, a method which may prove important for anticipating the future consequences of climate‐driven changes to the hydrological cycle. © 2016 The Authors. Ecohydrology published by John Wiley &amp; Sons, Ltd.

Differences between groundwater fauna in shallow and in deep intergranular aquifers as an indication of different characteristics of habitats and hydraulic connections

&lt;p&gt;The fauna in the hyporheic zones of rivers has been relatively well studied but that from the phreatic zone remains comparatively unknown and there are few investigations into deeper intergranular aquifers (over 30 m in depth) due to technical difficulties. Two shallow boreholes of 29 m depth and two deep boreholes of 100 m depth, both near Ljubljana (Slovenia), were sampled more than 30 times between 14 January 2008 and 3 March 2009. On each occasion 14.4 to 18.0 m&lt;sup&gt;3&lt;/sup&gt; of water were abstracted using a high-capacity pump, then filtered by means of a plankton net with a mesh size of 60 µm. Organisms larger than 2 mm were damaged by the pump rotors, but their identification was still possible, while smaller representatives of the Copepoda (Crustacea) passed the rotors without damage. A near-by artesian borehole was sampled on 6 occasions. Water chemistry, physical properties and faunal composition analyses were carried out for each borehole. A total of 32 taxa, 24 of which were stygobites, were identified. Copepoda alone were represented by 16 species, 15 of which were stygobites. The shallow boreholes differ from the deep boreholes in their higher temperatures and higher concentrations of K&lt;sup&gt;+&lt;/sup&gt;, Na&lt;sup&gt;+&lt;/sup&gt;, Ca&lt;sup&gt;2+&lt;/sup&gt;, Mg&lt;sup&gt;2+&lt;/sup&gt; and SO&lt;sub&gt;4&lt;/sub&gt;&lt;sup&gt;2-&lt;/sup&gt; ions. The copepod communities in samples from the shallow boreholes differ sharply from those from the deep boreholes. There were also clear differences between shallow boreholes in two aquifers located a few kilometres apart, in physical and chemical characteristics as well as in fauna composition. Taxa with different ecological affinities, collected from groundwater, are indicators of hydraulic connections between different parts of an aquifer as well as of communication between surface and subsurface water bodies. The present study suggests that subterranean fauna, as well as epigean fauna, can provide effective support for classical dye/salt tracing experiments.&lt;/p&gt;

An analytical solution for predicting the transient seepage from a subsurface drainage system

Subsurface drainage systems have been widely used to deal with soil salinization and waterlogging problems around the world. In this paper, a mathematical model was introduced to quantify the transient behavior of the groundwater table and the seepage from a subsurface drainage system. Based on the assumption of a hydrostatic pressure distribution, the model considered the pore-water flow in both the phreatic and vadose soil zones. An approximate analytical solution for the model was derived to quantify the drainage of soils which were initially water-saturated. The analytical solution was validated against laboratory experiments and a 2-D Richards equation-based model, and found to predict well the transient water seepage from the subsurface drainage system. A saturated flow-based model was also tested and found to over-predict the time required for drainage and the total water seepage by nearly one order of magnitude, in comparison with the experimental results and the present analytical solution. During drainage, a vadose zone with a significant water storage capacity developed above the phreatic surface. A considerable amount of water still remained in the vadose zone at the steady state with the water table situated at the drain bottom. Sensitivity analyses demonstrated that effects of the vadose zone were intensified with an increased thickness of capillary fringe, capillary rise and/or burying depth of drains, in terms of the required drainage time and total water seepage. The analytical solution provides guidance for assessing the capillary effects on the effectiveness and efficiency of subsurface drainage systems for combating soil salinization and waterlogging problems.

Geologic features and genesis of the barriers and intercalations in carbonates: A case study of the Cretaceous Mishrif Formation, West Qurna oil field, Iraq

Abstract The type, poroperm relationship, log response characteristics and identification criteria of the barriers and intercalations in the carbonates of the Cretaceous Mishrif Formation in the West Qurna oil field of Iraq are studied through comprehensive analysis of cores, thin sections and well logs. The genesis and distribution of the barriers and intercalations are analyzed from the perspectives of sequence stratigraphy, depositional facies and diagenesis. The barriers and intercalations can be classified into three types: grainstone, packstone and wackestone. The barriers and intercalations generally exist in restricted platform facies and evaporative platform facies, some in open platform. They are common in transgressive cycles and early regressive cycles, forming continuously, extensive barriers and intercalations near the sequence boundaries. Penecontemporaneous cementation, burial compaction, and burial cementation led to the decrease of the porosity, damaged the space of the reservoir pores and became the important factors for the genesis of the barriers and intercalations. In the epidiagenetic phase, a large number of CaCO3 precipitated in the phreatic water zone below free-water table, leading to the formation of packstone and grainstone barriers and intercalations in a large scale. Through comprehensive log analysis, log identification criteria and the distribution of the barriers and intercalations are determined. The barriers are mainly distributed in the sections of CRI and CRII, and the intercalations are concentrated in the section of mB1. For different types of barriers and intercalations, packstones are the most in quantity, followed by grainstones and wackestones.