Marl Formation Research Articles

On site measurements of the redox and carbonate system parameters in the low-permeability Opalinus Clay formation at the Mont Terri Rock Laboratory

An in situ water sampling experiment was performed in the Opalinus Clay formation (Switzerland), with the aim of obtaining undisturbed pore water samples for its characterization. The study was made from a dedicated borehole, named BDI-B1, drilled in March 2002 in the DI niche of the Mont Terri Rock Laboratory, located at the north-western part of the formation, a few meters away of the underlying Jurensis Marl formation. Five water sampling campaigns have been completed, and on site measurements of the key parameters of the water, such as pH, Eh, Fe(II), S 2− and alkalinity, were performed under controlled conditions inside an anoxic glove box. The chemical composition of the seepage waters obtained from the borehole is Na–Cl type, with an ionic strength of about 0.4 M. The Cl concentrations fit the concentration profile of the Opalinus Clay pore water obtained in previous experiments from boreholes and squeezed water samples. The highest salinity is found in this zone of the Opalinus Clay, with around 12 g/L of chloride. A perturbation of the rock system was produced during the first stages of the experiment due to a packer failure. As a consequence, the borehole was exposed to air during the first phase of the experiment. The main perturbations induced were: (1) pyrite oxidation that caused an increase of sulphate, calcium, magnesium and bicarbonate content in the waters; and (2) the inflow of 3H-bearing water vapour that could penetrate the EDZ. This fresh water infiltration could have mixed with the original formation water, and tritium contents of up to 3.8 TU were measured in the first water sampling campaigns. Nevertheless, after some time the hydrogeochemical conditions of the formation were recovered, and the long-term instrumentation and monitoring of the borehole made possible to obtain different parameters of the formation. Successive water sampling campaigns show a tendency to the stabilization of the main parameters of the water, such as sulphate and pH to values of 1600 mg/L and 7.6, respectively. The on site determination of the key parameters of the pore waters such as pH, Fe(II) and alkalinity has allowed to model the main water–rock interaction processes of the Opalinus Clay formation. A redox potential of −196 mV at pH 7.6 was obtained.

Pedogenesis and clay mineralogical investigation of soils formed on gypsiferous and calcareous materials, on a transect, southwestern Iran

This study examined pedogenesis, as well as the clay mineralogy of soil and rock samples obtained from a transect of gypsiferous and calcareous materials. The main objectives of this research were to study the relationship between clay minerals and physiographic units as well as the relative importance of key pedogenic processes in controlling clay mineralogy. Palygorskite, chlorite, illite, smectite, quartz and interstratified minerals were observed in both soil and rock samples, using XRD, TEM and EDX analyses. Illite, chlorite, and interstratified minerals are inherited largely from parent rocks. Most of the smectite is inherited from highly smectite marl formations, although some may be the product of palygorskite weathering and transformation of illite particularly at the surface horizons. Neoformation of palygorskite, as a result of calcite and gypsum precipitation, seems to be a major pathway for the occurrence of this mineral, especially on plateau physiographic units, although inheritance has less importance. Gypsiferous soils showed more pedogenic palygorskite as compared to calcareous soils. Three morphological forms of palygorskite, related to degree of weathering, were identified in the studied pedons. New great groups and subgroups of Ustepts (Aridic Gypsiustepts and Aridic–calcic Gypsiustepts) are suggested to be included in Soil Taxonomy based on the properties of some of the studied pedons. Dissolution and transport of anhydrite from outcrops, is considered the main source of pedogenic gypsum in these soils. Micromorphological studies, including thin section observations and SEM analyses indicated variable habits of gypsum crystals suggested a dynamic soil environment.

Runoff and erosion in the Black Marls of the French Alps: Observations and measurements at the plot scale

The experimental basins of Draix in the southern French Alps have been monitored since 1984 in order to quantify and analyse the incidence and patterns of erosion in the badlands developed on Black Marl formations. In order to analyse the rainfall-runoff behaviour of the mudstone slopes, rainfall simulations were conducted on small plots 1 m 2 in area. Four different local geomorphologic conditions were selected for the experiments: (a) steep slope parallel or (b) perpendicular to the bedding, (c) moderate slope and (d) gravel-covered surface, both parallel to the bedding. Rainfall simulations were performed at a moderate intensity (12–25 mm h − 1 ) for 30 min on three plots in each location. Different delays between simulations offered different initial soil wetnesses. A simulation during high-intensity rainfall (90–150 mm h − 1 ) for 30 min was made on one plot of each type. One plot of each type was selected for monitoring during the following summer and autumn. In dry conditions, runoff was low or negligible. A second simulation carried out 1 day later again produced very low runoff coefficients. Runoff increased slightly when the interval between rainfall simulations was reduced to 30 min. In this case, a few grams of sediment were eroded, whereas no erosion was observed in the first two cases. Under high-intensity conditions, runoff began quickly and the runoff coefficients were high (20–50%). Erosion was notable, but not significantly different from dry conditions. The behaviour was very different during natural rainfall events, in particular summer storms: even if the mean rainfall intensity was lower than 60 mm h − 1 in 30 min, short periods of high intensity (more than 100 mm h − 1 in 5 min) revealed substantial erosion activity: more than 700 g m − 2 on all the plots for a rainfall event of 54 mm in 3 h and more than 600 g m − 2 for an event producing 26 mm. However, the runoff coefficients were on the same order as those of the last experiment under high-intensity conditions (32–55%). The rainfall intensity over the short duration and the kinetic energy of the raindrops were the main factors influencing particle detachment and movement.

Sedimentology and taphonomy of sirenian remains from the Middle Eocene of the Pamplona Basin (Navarre, western Pyrenees)

Sirenian vertebrae and ribs have been recently discovered from two Middle Eocene localities of the Pamplona Basin, Navarre (western Pyrenees). These outcrops correspond to different lower Bartonian lithostratigraphic units: the lower part of the Pamplona Marl Formation (Uztarrotz site) and the upper part of the Ardanatz Sandstone (Ardanatz site). The former represents a deep and low-energy sea floor far away from a deltaic slope; the Ardanatz environment probably corresponds to a semi-closed deltaic bay periodically affected by catastrophic floods (i.e., fluvial hyperpycnal flows). The presence of epibiontic activity suggests that the bones were exposed for a while prior to the burial. The histological structures are well preserved except in the peripheral region, where tubular-like microstructures filled by pyrite and iron oxides probably correspond to microbial bioerosion. The major mineral component of the fossil bones is francolite (carbonate fluorapatite). In the Ardanatz samples there is evidence of secondary francolite due to the late replacement of original carbonate fluorapatite through internal fractures. The Ardanatz and Uztarrotz sirenian fossils do not show any evidence of reelaboration. They have similar sum of rare earth elements (REE) concentrations relative to the host rock, but comparatively lower than in other vertebrate fossil bones. This feature may be due to the dense compact structure of pachyosteosclerotic sirenian bones.

Sedimentology of the Late Quaternary Wadi Hasa Marl Formation of Central Jordan: a record of climate variability

The sedimentary features and fossils within the Wadi Hasa Marl Formation coupled with optical luminescence chronology indicate alternating wet and dry periods have occurred on the Jordanian plateau since the last interglacial. The Jurf Ed Darawish Member rests unconformably on the Maastrichtian Muwaqqar Chalk Marl Formation and is composed predominantly of poorly sorted, clast-supported conglomerate. Palaeocurrents and clast composition indicate provenance from Cretaceous sedimentary rocks and Tertiary basalts to the west and southwest of the study site and the facies suggest a flashy alluvial depositional environment probably similar to the modern wadis. The overlying Burma Member consists of bedded grey-green clayey silts and marls with calcrete profiles, up to 1.2 m thick, and isolated gravel lenses. The fine-grained sediments contain charophytes, ostracods, bivalves and various species of gastropod indicating normal freshwater lacustrine conditions. The calcretes contain a poorly preserved fauna suggesting lacustrine deposition followed by subaerial exposure and pedogenesis. Three optical luminescence ages have been obtained from the Burma Member which suggest that the member ranges in age from >111 ka through to <40 ka. The facies variations are indicative of climatic fluctuations in Jordan during this period and human artefacts are found embedded in the sediments. This preliminary study suggests that the Late Quaternary central Jordan sedimentary record may preserve valuable evidence of complex climatic variation which will supplement the data from the Jordan Valley where tectonic activity complicates the sedimentary record.

Marine and Transitional Middle/Upper Eocene Units of the Southeastern Pyrenean Foreland Basin (NE Spain)

The stratigraphic basis of this work has allowed the use of larger foraminifers in the biostratigraphic characterisation of the new Shallow Benthic Zones (SBZ). This part of the volume presents a description of the sedimentary cycles formed by the transgressive-regressive systems of the Lutetian and Bartonian in the southeastern sector of the Ebro Foreland Basin.Concerning the Lutetian deposits studied in the Amer-Vic and Emporda areas, four sedimentary cycles have been characterised. The first and second are found within the Tavertet/Girona Limestone Formation (Reguant,1967;Palli,1972), while the third and fourth cycles cover the Coll de Malla Marl Formation (Clavell et al.,1970), the Bracons Formation (Gich,1969,1972), the Banyoles Marl Formation (Almela and Rios,1943),and the Bellmunt Formation (Gich,1969,1972). In the Bartonian deposits studied in the Igualada area,two transgressive-regressive sedimentary cycles have been characterised in the Collbas Formation (Ferrer,1971),the Igualada Formation (Ferrer,1971),and the Tossa Formation (Ferrer,1971). The Shallow Benthic Zones (SBZs)recognised within the Lutetian are the following:SBZ 13, from the Early Lutetian, in the transgressive system of the first cycle;SBZ 14,from the Middle Lutetian, in the second cycle and the lower part of the transgressive system of the third cycle; SBZ 15,from the Middle Lutetian, in the remaining parts of the third system; SBZ 16, from the Late Lutetian,throughout the fourth cycle.The association of larger foraminifers in the first and second cycles of the Bartonian in the Igualada area has been used as the basis for the definition of SBZs 17 and 18 recognised in the Bartonian of the western Tethys.

Stratigraphie, nannofossiles calcaires et foraminifères de la coupe du ruisseau de lespontes à saint-lon-les-mines (eocène moyen et supérieur d'aquitaine, France)

Detailed analysis of a series of outcrop sections along the Lespontes River and its tributaries at Saint-Lon-les-Mines has led to the identification of three predominantly marly units within the Middle and Upper Eocene of the Bassecq Syncline. The lowermost unit consists of bathyal marls, attributable to the Miretrain Marl Formation, and is of Late Lutetian - Early Bartonian age (NP 15b, NP 15c, NP 16 and base NP 17 ; EPA 9 to EPA 11 (? EPA12) and middle P 11 to top P 12). It is overlain by circalittoral, glauconitic indurate marls unknown up to now. This marly, intensely fractured unit, called the Bagats Marl Member, is defined to represent a new member within the Côte des Basques Marl Formation. It encompasses the Bartonian/Priabonian boundary sensu Berggren et al., 1995 (top NP 17 and base NP 18 ; EPA 13 and middle P 14). The uppermost unit is made up of fine sandy marls, containing several limestone intercalations towards the top. These Brihande Marls are included in the lower part of the Priabonian (NP 18, probably up to the top of the section ; EPA 13, EPA 14 and part of EPA 15, top P 14 and in part P 15). The succession of the Lespontes River is interpreted in terms of sequence stratigraphy, allowing refining its relationship within the Adour Basin. The integration of the data indicates that in Aquitaine the appearance of Chiasmolithus oamaruensis (base of zone NP 18) is prior to the appearance of Globigerinatheka semiinvoluta (base of zone P 15) and that nannofossil interval NP 19 - NP 20 is very difficult to identify in this area, due to the scarcity of the marker species Isthmolithus recurvus.

Hydrochemical Characteristics of the Major Springs in the Maqarin Dam Site on the Yarmouk River (Northern Jordan)

Most water development schemes in Jordan have paid limited attention to the chemistry of water and its implication on water origin, movement, and evolution. Various aspects of water quality have also been ignored in recent projects. Chemical characteristics of groundwater in a major catchment area adjacent to the Maqarin dam in northern Jordan have been investigated. Because water from this area is an intended major source of water for Jordan, it is vital to understand the nature of the chemistry of the springs in the area, as well as the potential water-rock interaction. The study area is underlain by sedimentary rocks of Upper Cretaceous age. This study evaluates the water quality of 12 springs from aquifers within the bituminous marl formation and chalky limestone formation (aquifers B-3 and B-4, respectively) situated in the surrounding area of the Maqarin dam site on the Yarmouk river. Analyses show that the water of the springs are characterized as alkaline earth-biocarbonate chemical type, consistent with the calcareous lithology of the aquifers. Constituents contained in all water from springs sampled are within or below World Health Organization (WHO) standards set for domestic purposes.

Eocene siliceous sponges from the Ebro Basin (Catalonia, Spain)

The Eocene (Bartonian) marls of the La Guixa Member and Gurb Member, Vic Marls Formation (Ebro Basin, Catalonia, Spain), contain a very rich and diversified siliceous sponge fauna. The fauna is dominated by hexactinellids; lithistids and other demosponges are rare. It consists of 16 species representing 16 genera. Eleven new species and two new genera are proposed for these sponges: Reguantella cavernosa nov. gen. nov. sp., Regadrella concinna nov. sp. (both Hexactinellida, Lyssacinosa), Eurete clava nov. sp., Pleuroguettardia iberica nov. sp., Aphrocallistes almeriae nov. sp., Hexactinella informis nov. sp. (all Hexactinellida, Hexactinosa), Brachiolites munterensis nov. sp., Centrosia viquensis nov. sp., Callicylix eocenicus nov. sp., Rhizocheton robustus nov. sp. (all Hexactinellida, Lychniscosa), Propetrosia pristina nov. gen. nov. sp. (Demospongia, Haplosclerida). Some genera of sponges in this fauna are still extant, but, in general, the predominant ones are very close in morphology, and, without doubt, closely related to the Late Cretaceous sponges. This fauna also differs considerably, in terms of composition, from most other described faunas of Tertiary sponges from the Mediterranean region, which are dominated by lithistid sponges. Lithistid sponges are rare in this investigated assemblage, which seems most similar to an as yet undescribed Eocene fauna from Italy. There is ecological differentiation in the proportions of particular sponges in various outcrops and/or stratigraphical levels that is clearly associated with water-depth-related controlling factor(s): Munter, Tona and Sta. Cecilia represent the deepest facies, Gurb is intermediate, and St. Roc and Vespella are the most shallow. The exact bathymetric position of the sponge fauna is difficult to estimate, but it seems that 100 m (but probably 200 m and more in the case of the deepest parts) of water depth may be inferred for this facies.

Study of the pore water chemistry through an argillaceous formation: a paleohydrochemical approach

The spatial and temporal changes of the pore water along an argillaceous formation were studied on the basis of the chemistries of the fluids collected through the system. The study is based on chemical characterisation results of the pore water, which requires careful sampling and 4 years monitoring. The concept was applied to the water sampled from several boreholes drilled through the Opalinus Clay formation in the anticline at Mont Terri, Canton Jura, Switzerland. Asymmetrical gradients from the clay formation toward the limestone overburden are observed. In this upper formation, recharge with low mineralised water has caused the diffusion of species from the saline pore waters in the clay formation and their depletion. These species form concentration profiles from the underlying Jurensis Marl formation containing hydrophobic organic material toward the upper Lower Dogger Limestone formation. Non-sorbing species such as chlorides, bromides, iodides and sulphates as well as Na as a weakly sorbing cation form increasing concentration profiles from the Lower Dogger Limestone into the Opalinus Clay formation. Heavy water isotopes display similar profiles. The pH increases slightly downward through the system (from about 7 to 8) together with the total organic C (TOC) concentration, while the total inorganic C (TIC) concentration decreases from the Lower Dogger Limestone through the Opalinus Clay formation. A similar profile is observed for pe which decreases from the limestone groundwater (+2.5) toward the underlying marl water (−2.5). The water composition is discussed taking into account in-situ pore water dilution from recharge water by mean of a diffusion mechanism. Quantification of this transport process and of the consequent concentration profile is carried out through the 165 m thick Opalinus Clay layer, which was impregnated by fossil pore water derived from Tethys Ocean, considering a diffusion process that started about 10 Ma ago. The apparent diffusion coefficients estimated in the Opalinus Clay for Cl −, Br −, I – and Na +, on one hand, and, for 2H and 18O on the other are 2.6±0.8 and 5.2±1.5·10 −11 m 2 s −1, respectively. These values are compared with data gained from other argillaceous systems. The Opalinus Clay formation is likely to have acted as a geological nanoporous barrier for 10 Ma.

AGGLUTINATED FORAMINIFERA FROM THE EPILIGURIAN SUCCESSION (MIDDLE EOCENE/LOWER MIOCENE, NORTHERN APENNINES, ITALY): SCANNING ELECTRON MICROSCOPIC CHARACTERIZATION AND PALEOENVIRONMENTAL IMPLICATIONS

Two sections of Epiligurian sediments (Northern Apennines, Italy) covering the chronostratigraphic interval from the Middle Eocene to the Lower Miocene were analyzed for their foraminiferal content. Several specimens belonging to 25 selected species of agglutinated foraminifera were analyzed using the energy-dispersive x-ray spectrometry (EDS) method. The collected data show how these species are selective in composition, size, and shape of the agglutinated grains and cement composition. Test microstructures can be subdivided into four groups: A relationship between test microstructure and paleobathymetric conditions for the Monte Piano Marl, Ranzano Sandstone, and Antognola Marl Formations was observed. An almost exclusive presence of agglutinated taxa showing microstructures I and II characterized the “facies varicolori” of the Monte Piano Marls (lower-middle bathyal depths, from 2000 m to 1000 m). A sharp increase in species showing microstructures III and, subordinately, IV characterized the overlying lithostratigraphic units (“facies grigia” of the Monte Piano Marls, Ranzano Sandstones and Antognola Marls) whose paleobathymetry decreases upwards (middle-upper bathyal up to slope/shelf break from 1000 to 200 m).

Carbon and Oxygen Isotope Compositions of Some Upper Cretaceous–Paleocene Sequences in Argentina and Chile

The Cretaceous-Paleocene (K-T) transition has been recorded in sedimentary carbonate rocks in northwestern Argentina and southern Chile. In the Yacoraite Basin, Argentina, this transition has been preserved in a 2 m thick marly layer, at the base of the Tunal Formation, which overlies lacustrine/marine carbonates of the Yacoraite Formation (Cabra Corral dam). The K-T transition is also preserved at Maimara, where Tertiary sandstones overlie a 50 m thick limestone bed of the Yacoraite Formation. In the Magellan Basin, Chile, glauconitic sandstones with calcitic cement and limestone concretions of the Maastrichtian Punta Rocallosa Formation are overlain by sandstones, claystones, and limestones of the Chorillo Chico Formation. The K-T transition is preserved in the lower portion of the Chorillo Chico Formation. Carbonates of the Yacoraite Formation display bulk-rock δ13C values from +1 to +2‰ PDB, with a negative incursion (−4‰ PDB) at the K-T transition. δ13C values in the Tunal Formation marls vary from −3 to −1‰ PDB. At Rocallosa Point, δ13C values in limestone strata, calcite cement, and limestone concretions vary from −4 to −33 ‰ PDB, and the lowest value in the Chorillo Chico Formation apparently marks the K-T transition. The δ18O fluctuations in the Yacoraite and Magellan carbonate rocks suggest a temperature drop at the K-T transition, followed by a temperature rise. High 87Sr/86Sr ratios (0.7140-0.7156) characterize the studied profiles of the Yacoraite Formation, documenting an important 87Sr-enriched source of Sr to the water from which these carbonates precipitated. At the Magellan basin, 87Sr/86Sr ratios are closer to the expected values for the global Late Cretaceous-Paleocene ocean.

On the late Pleistocene‐Holocene sapropel record of climatic and oceanographic variability in the eastern Mediterranean

Sapropels and intercalated marls in a piston core from the eastern Mediterranean are chemically and mineralogical distinct: kaolinite, smectite, and total S contents, Fe/A1, Ba/A1, Co/A1, Mo/A1, and V/A1 are higher, whereas quartz, Mg calcite, illite contents, Si/A1, Ti/A1, K/A1, Rb/A1, and Zr/A1 are lower in the sapropels. Missing and “ghost” sapropels are identified by mineralogical and chemical properties that are not prone to diagenesis. Primary production was higher (Ba/A1) and bottom water and/or interstitial oxygenation was lower (Co/A1, Mo/A1, Ni/A1, and V/A1) during sapropel formation. Wind speeds (quartz/clay, Si/A1, and Zr/A1) and bottom water salinities (Mg calcite/calcite) were higher during periods of marl formation. Sapropels represent a fundamentally different sedimentary facies whose formation is linked to changes in the hydrological balance in the basin, driven by precessionally modulated changes in monsoon strength and subtropical precipitation changes, which altered circulation, production, and sediment source areas.

Slumping and a sandbar deposit at the Cretaceous-Tertiary boundary in the El Tecolote section (northeastern Mexico): An impact-induced sediment gravity flow

Slumps affecting uppermost Mendez Formation marls, as well as the spherulitic layer and basal part of the sandy deposits of the Cretaceous-Tertiary (K-T) boundary clastic unit, are described at the new K-T El Tecolote section (northeastern Mexico). These K-T clastic deposits represent sedimentation at middle-bathyal water depths in channel and nonchannel or levee areas of reworked materials coming from environments ranging from outer shelf to shallower slope via a unidirectional, high- to low-density turbidite flow. We emphasize the development and accretion of a lateral bar in a channel area from a surging low-density turbidity current and under a high-flow regime. The slumps discovered on land and the sedimentary processes of the K-T clastic unit reflect destabilization and collapse of the continental margin, support the mechanism of gravity flows in the deep sea, and represent important and extensive evidence for the impact effects in the Gulf of Mexico triggered by the Chicxulub event.

Foraminiferal biofacies and palaeoenvironmental evolution of an Oligo-Miocene cool-water carbonate succession in the Otway Basin, southeast Australia

Abstract. This multidisciplinary study integrates fades studies and foraminiferal analyses to assess the palaeoenvironmental evolution of an Oligocene to Miocene cool-water carbonate succession in the Otway Basin, southeastern Australia. The cool-water carbonate succession in the Otway Basin records signals relating to the evolution of the Southern Ocean throughout the Cenozoic. The strata are correlated with the relative coastal onlap curve of Haq et al. (1988) and several sequences can be identified in three formations. The Early Oligocene Narrawaturk Formation (TA 4.5) comprises near the base high-energy, inner shelf biofacies (lowstand systems tracts) and up-section to lower energy mid- to outer shelf marls (TST and maximum flooding surfaces) with storm events and/or minor shallowing intervals. Foraminiferal reworking and post-depositional dolomitization occurs at the top of this unit. The Late Oligocene Clifton Formation (TB 1.1 and TB 1.2.) was deposited in a relatively high-energy inner to mid-shelf environment. The base of this unit preserves evidence of a shift in biofacies that correlates to a major sea-level fall at the Mid/Late Oligocene boundary coincident with a major ice advance in Antarctica, and correlates with other Mid-Oligocene unconformities world-wide. The Late Oligocene Gellibrand Marl Formation (TB 1.2 and TB 1.3) began with low-energy outer shelf cherty marly biofacies (TST and MFS) followed by mid- to outer shelf calcisiltites (HST). High-energy mid- to outer shelf conditions were established after an hiatus in the Late Oligocene. A relative sea-level rise at the base of the Lower Miocene (TB 1.5 and TB2.1) led to the deposition of lower energy outer shelf cherty marls.Four biofacies with distinctive foraminiferal faunas are distinguished. (1) Grey mid- to outer shelf low-energy bryozoal marls with infaunal foraminifera and high plankton values. Two foraminiferal assemblages occur: lagenids and Uvigerina are common in the Narrawaturk marls, whereas bolivinids and Astrononion occur in the Gellibrand marls. The faunal variation in the marls may relate to changes in nutrient supply, anoxia, the presence or absence of organic material and/or changes in depth. (2) Chalky packstone facies with a high epifaunal content were deposited in oligotrophic inner to mid-shelf palaeoenvironments subject to intermittent reworking. (3) Bryozoan-poor inner to outer shelf foraminiferal packstones and grainstones facies enriched in epifaunal forms. (4) Well-sorted coarsegrained regular echinoid and bryozoan-rich packstones to grainstones. Infaunal taxa are absent in this facies, where most preserved foraminifera are robust spherical to discoidal forms. The facies were deposited in inner to mid-shelf palaeoenvironments where reworking by intense wave action (either above normal wavebase or by storms) winnowed out all smaller foraminifera.The stratigraphic and palaeoenvironmental utility of the Cenozoic foraminifera studied is improved greatly by facies analyses. Similar integrated studies will lead to better correlations and palaeoenvironmental interpretations of southeastern Australian sequences and equivalent successions in the southern hemisphere.

Evolution of gas and aqueous fluid in low-permeability argillaceous rocks during uplift and exhumation of the central Swiss Alps

Fluid chemistry and the hydraulic regime in a marl formation of the Swiss Alps were studied by a number of techniques. Fluid inclusions record the conditions of maximum burial and regional low-temperature metamorphism, whereas fluid samples and hydraulic tests derived from deep boreholes reflect present-day, near-surface conditions. The characterization of the different types of fluids places constraints on the geochemical and hydraulic evolution of low-permeability argillaceous rocks during uplift and exhumation. Fluid inclusions were studied by microthermometry and sampled directly by decrepitation techniques. They contain a two-phase system consisting of an aqueous fluid and a coexisting CH 4-rich gas ( T=190–250°C, P lith≈2500 bar). Bulk and isotopic compositions of aqueous fluid inclusions are consistent with a mixture of connate seawater and water derived from the dehydration of clay minerals. Methane was generated in situ by thermal cracking of kerogen. Textural evidence and stable isotopic signatures of carbonates in veins and in the rock matrix indicate local buffering of fluid compositions and very low water/rock ratios. Free fluids residing in the present-day fracture and matrix porosity consist of CH 4-saturated Na–Cl groundwater with minute amounts of free CH 4 gas which occurs in druses. Their chemical and isotopic compositions are very similar to those of the fluid inclusions, suggesting a common origin. Post-metamorphic admixtures of externally derived waters cannot be identified, and it is suggested that present-day Na–Cl groundwaters that occur in the central parts of the marl have resided in the formation since the time of metamorphism some 20 Ma b.p. The only major change in the fluid composition has been the outgassing of CH 4 from the formation, most probably by diffusion. The hydraulic regime during metamorphism was characterized by localized fluid underpressures in open veins because widely scattered, sub-hydrostatic pressures were often identified in fluid inclusions. The central part of the argillaceous rock body, approximately coinciding with the region where Na–Cl groundwaters occur, has sub-hydrostatic pressures today, as indicated by hydraulic tests in deep boreholes. Both the closed-system behavior derived from the chemical and isotopic characteristics of the fluids and the (recurrent or continuous) existence of hydraulic underpressures suggest very low permeabilities of argillaceous rocks during metamorphism and throughout subsequent uplift and exhumation. All fluids present in the central parts of the formation are either connate or produced in situ. Even though major events of brittle faulting and unloading due to uplift occurred since the peak of metamorphism, fluid flow through the formation has been negligible.

Derivation and application of a geologic dataset for flow modelling by discrete fracture networks in low-permeability argillaceous rocks

Argillaceous rock formations are targets of exploration for radioactive waste disposal sites in several countries. Groundwater flow in most indurated argillaceous rocks is very limited and occurs (if at all) mainly in brittle discontinuities, such as faults. On the basis of surface observations, core logging and hydraulic measurements in boreholes penetrating an argillaceous marl formation in the Swiss Alps, the relationships between internal fault architecture, larger-scale arrangement of the fault network and fault transmissivity are explored. Only a fraction of all faults observed in the cores correlates with water inflow points into the boreholes, and this is taken as evidence of variable transmissivity within each fault. Such flow channeling is also supported by geologic evidence. Stochastic discrete fracture network models are used for the upscaling of measured fault transmissivities, namely for the calculation of effective hydraulic conductivities ( K eff) of model cubes with lengths of side of 50–500 m. Input data to these models include size, spacing, orientation, heterogeneity (flow channeling) and transmissivity of the faults. Fault size is not well known, but a sensitivity analysis shows that even the extreme assumption of infinite size yields K eff only less than 1 order of magnitude higher when compared to the base case. The effect of different arrangements of flow channels within each fault is also explored but has no appreciable effect on K eff. It is concluded that calculated values for K eff are robust because those input parameters that are least adequately known have only limited effects on the model results.

Le Crétacé inférieur dans le Massif de lʼOuarsenis et les Monts de Tiaret (Algérie du Nord)

The Lower Cretaceous sediments in the Monts de Tiaret (Oranian High Plains) (Tlemcenian Palaeogeographic Domain) and the Western Ouarsenis (Tellian Palaeogeographic Domain) are subdivided in lithostratigraphic units which differ for the Tlemcenian and the Tellian Domains. In the first one, a specific feature is the development of shalow, and in the second – of deep water sediments. The following formal lithostratigraphic units are distinguished in the Tlemcenian Domain: (1) Remaïlia Carbonate Formation – limestones, marls and dolomites (Berriasian – Early Hauterivian (p.p.); (2) Berthelot Sandstone Formation (Early Hauterivien (p.p.) – Aptian); (3) Djebel Tenfeld Carbonate Formation – alternation of marls and limestones, rich in shallow water molluscs. Within the Tellian Atlas (Tell ian Domain) are distinguished: (l) Oued Fodda Carbonate Formation (Late Tithonian – Early Aptian); (2) El Melaab Turbiditic Formation (new unit of Aptian (p.p.) – Early Albian age) subdivided in 2 new Members: (a) Oued Sidi Mohamed Member (Aptian) – marls with turbiditic sandstones – distal flysch; (b) Oued Mezdar Member (Early Albian) – sandstones with intercalations of marls – proximal flysch; (3) Rhedadoua Marls Formation (Middle – Late (p.p.) Albian; (4) Hassi ben Ziane Carbonate Formation – marls and limestones (Late Albian (p.p.) – Early Cenomanian). In the Chouala region crop out the allochtonous sediments of the Sidi Seba Achir Limestones-Marls Formation (new unit of Berriasian-Middle Aptian Age) subdivided in 3 new members: (a) Oued el Ouakal Member – alternation of marls and limestones (Berriasian – Valanginian); (b) Oued Malah Member - marls (Hauterivian); (c) Sidi Ounes Member – marls and limestones (Barremian – Middle Aptian). The region of the High Plains (Monts de Tiaret) was uplifted at the end of the Jurassic, and the Berriasian sea transgressed over it. The subsidence of the Tellian Domain continued since the Late Jurassic and became an area of turbiditic sedimentation during the Aptian-Early Albian. The sedimentation in the Tlemcenian and Tellian Domains continued without interruption into the Cenomanian.

Conceptual model for early diagenetic chert and dolomite, Amuri Limestone Group, north‐eastern South Island, New Zealand

ABSTRACTThe Late Cretaceous to Early Eocene, dominantly micritic, Amuri Limestone Group (ALG) was deposited in an approximately NW trending trough, in eastern Marlborough, New Zealand. The ALG comprises: the Mead Hill Formation; the Teredo, Lower and Middle Limestone formations; and the Upper and Lower Marl formations. Chert and dolomite are concentrated in the Mead Hill Formation, which contains five of six recognized diagenetic zones: Zone I at the base of the ALG consists almost entirely of chert; Zone II consists solely of chert and dolomite; Zone III comprises chert and limestone; Zone IV is composed of chert plus dolomite; Zone V is a chertified mudstone; and the minor amounts of chert found in the Middle Limestone Formation comprise Zone VI. With the exception of Zones IV and V, chert decreases stratigraphically upwards and away from the basin centre. All the dolomites are composed of &lt;1 mm diameter rhombohedra in discontinuous beds and lenses. Generally Ca‐rich, and non‐ to slightly ferroan, the dolomite contains approximately 500–900 ppm Mn and 200–400 ppm Sr. δ13C values average 1–2%PDB with δ18O ratios of about ‐4%PDB. Mass balance calculations indicate that the Mg2+ for dolomitization was derived from sea water. Sr, Fe and Mn concentrations are interpreted as indicating dolomite formation in the marine environment, with no influence from meteoric waters. The intimate association with pyrite implies dolomite formation in association with sulphate reduction, in the upper sediment column. δ18O data show that the bulk of the dolomite formed at temperatures below 50°C. All chert samples contain in excess of 90 wt% SiO2, about 1 wt% Al2O3 and 1 wt% from losses on ignition. Generally all other major elements total less than 2 wt% oxide. δ18O values range from 26·8 to 29·0%SMOW. Chert chemistry is consistent with the replacement of host carbonate and expulsion of carbonate‐bound components from the site of chertification, and the effective dilution by SiO2 of non‐carbonate‐bound insoluble residues. δ18O data indicate that chert formed in fluids of similar composition and temperature as the dolomite. The abundance of disseminated pyrite in cherts implies an association with sulphate reduction. Silica for chertification is thought to have initially come from dissolution of siliceous organisms. However, there is insufficient biogenic silica available to form the volumes of chert observed. It is suggested that the bulk of the silica came from SiO2‐rich pore waters generated by clay mineral reactions in the thick underlying mudstones. The ALG compacted down through these pore waters. Chert and dolomite nucleation are considered to have been penecontemporaneous. Dolomitization was initially probably the faster process, continuing as long as sulphate reduction prevailed and there was an adequate supply of Mg2+. The nucleation of chert, although initially slower (probably due to a relatively lower initial SiO2 supply), continued after cessation of dolomitization to the extent of completely chertifying the dolomite intercrystalline matrix. The amount of chertification decreased progressively as SiO2 supplies diminished, both stratigraphically upwards and away from the basin centre.

Hydrocarbon-derived imprints in olistostromes of the Early Serravallian Marnoso-arenacea Formation, Romagna Apennines (northern Italy)

Evidence of hydrocarbon venting within slumped bodies associated with the siliciclastic, dominantly turbiditic, Marnoso-arenacea Formation (Umbria-Romagna structural domain, Romagna Apennine, northern Italy) is documented with sedimentological, faunal, and geochemical data. Specifically,13C-depleted carbonate concretions and limestones and clusters of chemosynthetic clams (Vesicomyidae) have been identified in the marls of the Le Caselle Olistostrome and other slumped bodies contained within the Early Serravallian section of the Marnoso-arenacea Fm. Most of the olistostrome marls and limestones are extrabasinal and must have slid from a source area located several kilometers southwest of their present position. Thus, they presumably pertain to the Vicchio Marls Formation of the northeastern (outer) Tuscan structural domain, with possible minor contributions from the epi-Ligurian Bismantova Fm. It is suggested that venting of methane in the source area of the olistostromes permitted the establishment of exotic chemosynthetic communities and promoted the precipitation of carbonate concretions and limestones. According to the field evidence, these materials were later subjected to multistep downslope remobilization and were eventually carried into the Marnoso-arenacea basin through gravity mass transport.