Green Clay Research Articles

Short communication. Collection and characterisation of a population of Triticum boeoticum Boiss., a wild wheat species not previously found in the Mediterranean western region

A population of wild wheat was collected in July 2010 in an abandoned area near Madrid, Spain. This zone possesses a high botanical biodiversity together to a particular type of soil termed “green clays”. A sample of wheat was collected, multiplied and characterised for several agro-morphological traits and glutenin subunits. The 2n chromosome number revealed that it was a diploid wheat species, and characterisation data indicated that the accession was Triticum boeoticum Boiss. This species probably arrived as a weed of the einkorn crop grown in the zone until at least the first half of s. XIX. The specific edaphic and climatic characteristics of the habitat and the fact that there were no references so far about this species in the Mediterranean western region make this acquisition very valuable for wheat improvement. The new accession is conserved at the National Plant Genetic Resources Centre and a herbarium sheet has been deposited in the Royal Botanic Garden in Madrid.

87Sr/ 86Sr and 18O/ 16O ratios of clays from a hydrothermal area near the Galapagos rift as records of origin, crystallization temperature and fluid composition

Strontium and O isotope compositions of green clay minerals from sediment cores of three boreholes drilled into (sites 424A and 509B) and close to a hydrothermal mound (site 424B) near the Galapagos Spreading Center (DSDP Legs 54 and 70) were determined. The green clays consist mostly of a transition from Fe-smectite (nontronite) to glauconite. 87Sr/ 86Sr ratios were measured on clay size-fractions after gentle acid leaching and on the recovered leachates from different samples. The 87Sr/ 86Sr ratios of the clay residues from both the 424A and B sites are well below the modern seawater value, which points consistently to precipitation from hydrothermal fluids that contained variable amounts of seawater, even away from mound. However, most of the clay residues from mound site 509B have 87Sr/ 86Sr ratios significantly above the seawater value, suggesting the occurrence of a detrital component together with the new authigenic particles. The clay minerals of the hydrothermal mound are mixed with detrital components, and that of the sample taken outside but near the mound as a reference for the surrounding oceanic environment, yields a hydrothermal signature. Crystallization temperatures of the clays range from 32 to 63 °C assuming a δ 18O value of + 2.2‰ for the mineralizing fluids. Hydrothermal fluids generated in the underlying oceanic crust, mixed in varied proportions with ambient seawater and migrated into beds of the mound in a sequence of recurrent processes that ultimately resulted in the formation of the observed clay minerals. No significant temperature differences were detected for crystallization of the K-rich glauconite and K-depleted nontronite. The 87Sr/ 86Sr ratios of the Sr leached off the clay particles are near the value of modern seawater, inferring a progressive replacement of the hydrothermal fluids by seawater in the pore space of the mound sediments.

ORGANOPHILIC CLAY FOR OIL/WATER SEPARATION PROCESS BY FINITE BATH TESTS

This study examines the inclusion of a quaternary ammonium salt, an alkyl-dimethyl-benzyl ammonium chloride (Dodigen), on a green clay to evaluate its performance as an organophilic adsorbent in the oil/water separation process. The samples were characterized by X-Ray Diffraction, Differential Thermal and Thermogravimetric Analyses, Infrared Spectroscopy, Cation Exchange Capacity, Adsorption Capacity and the Foster Swelling test. The results indicated that the quaternary ammonium salts were intercalated between the layers of clay. A 22-factorial design was conducted with three central points in finite bath tests to determine the rate and capacity of oil removal by the organophilic clays. Values as high as 94.54 % of removal efficiency and 37.57 mg/g of removal capacity were reached in the assays, thus indicating that the use of organophilic clay has great potential in the oil/water separation process.

THE GEOLOGY, PALAEONTOLOGY AND EVOLUTION OF THE ETOSHA PAN, NAMIBIA: IMPLICATIONS FOR TERMINAL KALAHARI DEPOSITION

Research Article| September 01, 2010 THE GEOLOGY, PALAEONTOLOGY AND EVOLUTION OF THE ETOSHA PAN, NAMIBIA: IMPLICATIONS FOR TERMINAL KALAHARI DEPOSITION R. McG. MILLER; R. McG. MILLER Consulting Geologist, PO Box 11222, Windhoek, Namibia; e-mail: rmmiller@mweb.com.na Search for other works by this author on: GSW Google Scholar M. PICKFORD; M. PICKFORD College de France, and UMR 7207 du CNRS, CR2P, Muséum National d’Histoire Naturelle, 8, rue Buffon, F-75005 Paris, France, e-mail: Pickford@mnhn.fr Search for other works by this author on: GSW Google Scholar B. SENUT B. SENUT UMR 7207 du CNRS, CR2P, Muséum National d’Histoire Naturelle, 8, rue Buffon, F-75005 Paris, France, e-mail: senut@mnhn.fr Search for other works by this author on: GSW Google Scholar South African Journal of Geology (2010) 113 (3): 307–334. https://doi.org/10.2113/gssajg.113.3.307 Article history first online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation R. McG. MILLER, M. PICKFORD, B. SENUT; THE GEOLOGY, PALAEONTOLOGY AND EVOLUTION OF THE ETOSHA PAN, NAMIBIA: IMPLICATIONS FOR TERMINAL KALAHARI DEPOSITION. South African Journal of Geology 2010;; 113 (3): 307–334. doi: https://doi.org/10.2113/gssajg.113.3.307 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietySouth African Journal of Geology Search Advanced Search Abstract A mid to late Tertiary lake, Palaeolake Etosha, was the single collective end point of three drainage systems feeding southwards off the central Angolan highlands, the Cubango and Kunene Megafans and the Cuvelai Drainage System. The lake beds consist of 50 m of saline, olive green clay, the Etosha Pan Clay Member, containing authigenic analcime, monoclinic K-feldspar and glauconite. Fossil suites in two local sandstones near or at the top of the clay, the Oshigambo and Ekuma Delta Sandstone Members, include various antelope, pig, zebra, quagga, rhinoceros, elephant, lion, spring hare, ostrich, flamingo, crocodile, hippopotamus, freshwater turtles, catfish, bivalves and trees, which have respective ages of 6 ± 1 Ma and 4 ± 1 Ma. An oolitic, pan-margin limestone of limited lateral extent, the Poacher’s Point Carbonate Member, was the last unit deposited in the palaeolake. Flooding and complete desiccation were common occurrences in Palaeolake Etosha before it dried up completely at about 4 Ma under conditions of progressively increasing aridity. Over the ensuing 2 Ma, a huge groundwater calcrete, the Etosha Calcrete Formation, advanced northwards over the dry lake deposits and the surface Kalahari sands were reworked to produce the regional Kalahari dune fields.Resumption of periodic flow in the Cuvelai system resulted in cycles of flooding and desiccation in an ephemeral Cuvelai endpoint lake atop the Etosha Calcrete Formation in the Etosha area. Fragmentation of the calcrete by salt enabled strong easterly winds to remove the calcrete fines from the Etosha depression. This initiated the ‘excavation’ of the present Etosha Pan by wind ablation. Lunette dunes on the western side of Etosha Pan contain an inverted pan stratigraphy. Flooding of the present pan occurs occasionally and has been as deep as 10 m in the past. White magadi-type chert nodules have formed locally on the pan floor in animal footprints. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Sintering behaviour of nanostructured glass-ceramic glazes

The thermal behaviour of a glass-ceramic glaze based on the system SiO 2–CaO–ZnO–Al 2O 3 has been evaluated. Frit and kaolin were ball milling using dispersants and binders, and deposited on a green clay based ceramic support. The evolution of the glaze during the sintering step was observed that consisted of a glassy matrix, particles from kaolin and particles from frit. Particles from frit formed a nanostructure of interconnected nanoparticles. Pyroxenes devitrified from the glassy matrix and at higher temperatures they were dissolved in the glassy matrix. Both successes contributed to the final observed nanostructure produced by a spinodal decomposition process in which the crystalline phase had a pyroxene composition.

Evaluation of the medicinal use of clay minerals as antibacterial agents

Natural clays have been used to heal skin infections since the earliest recorded history. Recently, our attention was drawn to a clinical use of French green clay (rich in Fe‐smectite) for healing Buruli ulcer, a necrotizing fasciitis (‘flesh-eating’ infection) caused by Mycobacterium ulcerans. These clays and others like them are interesting as they may reveal an antibacterial mechanism that could provide an inexpensive treatment for this and other skin infections, especially in global areas with limited hospitals and medical resources. Microbiological testing of two French green clays and other clays used traditionally for healing identified three samples that were effective at killing a broad spectrum of human pathogens. A clear distinction must be made between ‘healing clays’ and those we have identified as antibacterial clays. The highly adsorptive properties of many clays may contribute to healing a variety of ailments, although they are not antibacterial. The antibacterial process displayed by the three identified clays is unknown. Therefore, we have investigated the mineralogical and chemical compositions of the antibacterial clays for comparison with non-antibacterial clays in an attempt to elucidate differences that may lead to identification of the antibacterial mechanism(s). The two French green clays used to treat Buruli ulcer, while similar in mineralogy, crystal size, and major element chemistry, have opposite effects on the bacterial populations tested. One clay deposit promoted bacterial growth whereas another killed the bacteria. The reasons for the difference in antibacterial properties thus far show that the bactericidal mechanism is not physical (e.g. an attraction between clay and bacteria), but by a chemical transfer or reaction. The chemical variables are still under investigation. Cation exchange experiments showed that the antibacterial component of the clay can be removed, implicating exchangeable cations in the antibacterial process. Furthermore, aqueous leachates of the antibacterial clays effectively kill the bacteria. Progressively heating the clay leads first to dehydration (200°C), then dehydroxylation (550°C or more), and finally to destruction of the clay mineral structure (∼900°C). By identifying the elements lost after each heating step, and testing the bactericidal effect of the heated product, we eliminated many toxins from consideration (e.g. microbes, organic compounds, volatile elements) and identified several redox-sensitive refractory metals that are common among antibacterial clays. We conclude that the pH and oxidation state buffered by the clay mineral surfaces is key to controlling the solution chemistry and redox-related reactions occurring at the bacterial cell wall.

Efficiency of natural and acid-activated clays in the removal of Pb(II) from aqueous solutions

The adsorption of Pb(2+) ions onto Tunisian clay in aqueous solution was studied in a batch system. Four samples of clay (RGC, RRC, AGC, and ARC) were used. The raw RGC and RRC clays were sampled in jebel Tejera-Esghira in Medenine area (Southeast of Tunisia). AGC and ARC corresponds respectively to RGC and RRC activated by 6M sulphuric acid. The adsorbents employed were characterized by X-Ray Diffraction, chemical analysis, and the specific surface area was also estimated. The ability of clay samples to remove Pb(2+) ions from aqueous solutions has been studied at different operating conditions: temperature and pH. The optimum pH for lead ions retention was found 7.0 for the four clay samples. The effect of temperature on adsorption phenomenon was also investigated. The results indicated that adsorption is an exothermic process for lead ions removal. The equilibrium adsorption data were analysed using the Langmuir and Freundlich isotherms. The adsorption capacities (X(m)) for RRC, RGC, ARC and AGC were found 17.84, 25.44, 27.15 and 40.75 mg g(-1), respectively. The performance of the red clay after activation was compared to that of silica gel, which has maximum adsorption of 20 mg g(-1). On the other hand, although the performance of activated carbon (88.3 mg g(-1)) is by far higher than that of the green clay after activation, the latter seems to have better performance than that of the silica gel.

Assessment of efficience of purification of chromic waster water with application of spondyle green clay

Results of conducted experiments on spondyle green clay applying as a natural ecologically safe coagulant for waste water purification from Cr ions was presented. Optimal quantity of coagulant that provides the maximum level of purification was defined.

Potassic and Ferriferous Green Clays From the Ancient Submarine Hydrothermal Deposit, with Special Reference to the Occurrence and Chemical Composition of the Clays from the Nurukawa Kuroko Deposit

Potassic and Ferriferous Green Clays From the Ancient Submarine Hydrothermal Deposit, with Special Reference to the Occurrence and Chemical Composition of the Clays from the Nurukawa Kuroko Deposit

Palynology of Lower Palaeogene (Thanetian-Ypresian) coastal deposits from the Barmer Basin (Akli Formation, Western Rajasthan, India): Palaeoenvironmental and palaeoclimatic implications

The 32-m thick sedimentary succession of the Paleocene-Eocene Akli Formation (Barmer basin, Rajasthan, India), which is exposed in an open-cast lignite mine, interbed several lignite seams that alternate with fossiliferous carbonaceous clays, green clays and widespread siderite bands and chert nodules. The palynofloral assemblages consist of spore, pollen and marine dinoflagellate cysts that indicate a Thanetian to Ypresian age. The assemblage is dominated by angiospermic pollen and specimens showing affinity with the mangrove Palm Nypa are also very abundant. The Nypa-like pollen specimens exhibit a wide range of morphological variation, some of the recorded morphotypes being restricted to this Indian basin. Preponderance of these pollen taxa indicates that the sediments were deposited in a coastal swamp surrounded by thick, Nypa-dominated mangrove vegetation. The dispersed organic matter separated from macerated residues indicates the dominance of anoxic conditions throughout the succession, although a gradual transition to oxic conditions is recorded in the upper part.

CHEMICAL AND MINERALOGICAL CHARACTERISTICS OF FRENCH GREEN CLAYS USED FOR HEALING.

The worldwide emergence of infectious diseases, together with the increasing incidence of antibiotic-resistant bacteria, elevate the need to properly detect, prevent, and effectively treat these infections. The overuse and misuse of common antibiotics in recent decades stimulates the need to identify new inhibitory agents. Therefore, natural products like clays, that display antibacterial properties, are of particular interest.The absorptive properties of clay minerals are well documented for healing skin and gastrointestinal ailments. However, the antibacterial properties of clays have received less scientific attention. French green clays have recently been shown to heal Buruli ulcer, a necrotic or 'flesh-eating' infection caused by Mycobacterium ulcerans. Assessing the antibacterial properties of these clays could provide an inexpensive treatment for Buruli ulcer and other skin infections.Antimicrobial testing of the two clays on a broad-spectrum of bacterial pathogens showed that one clay promotes bacterial growth (possibly provoking a response from the natural immune system), while another kills bacteria or significantly inhibits bacterial growth. This paper compares the mineralogy and chemical composition of the two French green clays used in the treatment of Buruli ulcer.Mineralogically, the two clays are dominated by 1Md illite and Fe-smectite. Comparing the chemistry of the clay minerals and exchangeable ions, we conclude that the chemistry of the clay, and the surface properties that affect pH and oxidation state, control the chemistry of the water used to moisten the clay poultices and contribute the critical antibacterial agent(s) that ultimately debilitate the bacteria.

Chemical study of limestone and clay for cement manufacturing in Darukhula, Nizampur District, Nowshera, North West Frontier Province (N.W.F.P.), Pakistan

Limestone and clay samples were collected from Darukhula and adjoining areas of the Nizampur District, Nowshera, N.W.F.P., Pakistan, and analyzed for different parameters in order to search for new reserves of suitable material for the manufacture of different types of cements in N.W.F.P. It was found that the area under study contains three types of limestones, including high grade limestone, Darukhula limestone and siliceous limestone, which contain 53%, 49.03% and 45.19% CaO, respectively, and three types of clay, including maroon color, yellow to yellowish-green color and green color clay containing 57.76%, 65.47% and 61.24% SiO2, respectively. Chemical analysis of the limestone and clay samples collected from the deposits in the area under study showed that all the elements found in these samples are within the range of permissible limits for the production of high-strength Portland cement, sulphate resisting cement and white cement. This paper covers the detailed version of the potential raw material deposits at Darukhula and adjoining areas of the Nizampur District.

Naturally occurring arsenic in the Miocene Hawthorn Group, southwestern Florida: Potential implication for phosphate mining

To understand the mineralogical association, concentration, and distribution of arsenic (As) in the Hawthorn Group, the chemical and mineralogical composition of 362 samples that were collected from 16 cores in southwestern Florida were examined in detail. In the study area, the Hawthorn Group consisted primarily of a basal carbonate unit (the Arcadia Formation) and an upper siliciclastic unit (The Peace River Formation). The Peace River Formation contains appreciable amounts of phosphate and is currently being exploited for phosphate ore. Samples were taken from cores of each formation at intervals of 7.5 m. In addition, to the interval samples, sections likely to have high As concentrations, such as zones with pyrite crystals, hydrous ferric oxides, green clays, and organic material, were collected and analyzed. Bulk As concentrations were determined by hydride generation-atomic fluorescence spectrometry (HG-AFS) after digestion with aqua regia (3:1 HCl and HNO 3). The elements Fe, Al, Si, Mg, Ca, S, and P were measured on the same solutions by inductively coupled plasma optical emission spectrometry (ICP-OES). The identification of discrete minerals was aided by scanning electron microscopy (SEM) and chemical compositions within the sample matrix and in individual minerals were obtained by electron-probe microanalysis (EMPA). This detailed mineralogical and geochemical study demonstrated that: (1) As in the Hawthorn Group varied from formation to formation and was mostly concentrated in trace minerals, such as pyrite; (2) average As concentrations significantly changed from 8.8 mg/kg ( σ = 8.6 mg/kg) in the Peace River Formation to 3.0 mg/kg ( σ = 3.7 mg/kg) in the Tampa Member of the Arcadia Formation. Arsenic concentrations for all Hawthorn samples varied from 0.1 to 69.0 mg/kg; (3) pyrite, with one exception, occurred as framboids and was unevenly distributed throughout the Hawthorn Group; (4) pyrite framboids were located inside a francolite (carbonate fluorapatite) matrix with As concentrations as high as 3730 mg/kg and as a trace mineral in the sediment matrix concentrations varying from <1 to 8260 mg/kg; (5) hydrous ferric oxides (HFO) contained As concentrations as high as 540 mg/kg; (6) francolite, organic material, and clays contained substantially less As than pyrite; (7) thus, the release of As from pyrite could pose a potential problem for the phosphate industry.

Black Sea–Marmara Sea Quaternary connections: new data from the Bosphorus, İstanbul, Turkey

Previous studies concluded that the Bosphorus Strait was formed during the Quaternary by fluvial incision of a valley between the Black Sea, to the north, and the Marmara Sea in the south. Hitherto, however, few details of the evolution of this connection have been elucidated from the sediments deposited within the Bosphorus itself. We report here details of sedimentological and palaeontological evidence relating to this history, obtained from five boreholes drilled into the unconsolidated sediment fill in the north-central sector of the Bosphorus, together with nearby geophysical profiles. The Quaternary fill of this part of the Bosphorus comprises two major facies associations. Yellow arkosic sands dominate the lower Facies Association A: these are assigned a Middle to Late Pleistocene age and the contained faunas have a lagoonal to lacustrine character and a Black Sea provenance (Paratethyan affinities). The abruptly succeeding units of Facies Association B comprise fining and coarsening upwards units of coarse to fine shelly and clayey sands that alternate with shell-bearing green clays. These sediments were formed in a range of marine and coastal settings and biostratigraphic evidence and absolute dating demonstrate the Mid–Late Holocene age of this upper unit. Initially brackish faunal assemblages in this upper unit show an upward increase in marine and Mediterranean affinities. Integrating these new data with previously published observations from coeval deposits in the southern Bosphorus and İzmıt Bay (NE Marmara Sea) we conclude that during the Late Pleistocene and Early Holocene a topographic barrier existed in the south-central sector of the Bosphorus, on both sides of which estuarine and lagoonal sediments accumulated, with distinctive Black Sea and Mediterranean faunas. During a significant rise in sea level, between 7000 and 5300 years ago, this barrier was finally submerged, permitting interchange of marine waters between the Mediterranean and the Black Sea and creating the present oceanographic situation. This evolution conflicts with the cataclysmic role of the Bosphorus in the early Holocene as postulated in the ‘Catastrophic Flood’ hypothesis of Ryan et al. [Mar. Geol. 138 (1997) 119–126; Annu. Rev. Earth Planet. Sci. 31 (2003) 525–554]. It also contrasts with the history recorded from the Gulf of İzmıt, where intermittent connection between these two bodies of water throughout much of the Quaternary is evident.

Varying depositional environments of gypsum successions in the Upper Miocene Eskisehir-Sivrihisar lacustrine basin, NW Turkiye

The basement rocks of Eskisehir-Sivrihisar basin are made of Upper Paleozoic metamorphic rocks and Upper Cretaceous ophiolite complex. These rocks are overlain by Middle Miocene sedimentary rocks the base. Upper Miocene-Pliocene stratigraphic succession consists of basal conglomerates, sandstones, claystones, limestones, dolomites and tuffs are thinly interbedded with cyclic evaporites. The main clay mineral assemblage consists of smectite, illite and sepiolite that are enriched in different percentage in different horizons. The Upper Miocene-Pliocene stratigraphic succession consists of alterations of gypsum, clayey carbonates and unconsolidated very soft dolomite beds, which are conformably underlain by sepiolite-bearing clayey carbonates and disconformably overlain by alluvium and conglomerate series of Pleistocene age. The Upper Miocene unit includes three different facies, based on sedimentary properties of gypsum from the base to the top; (I) laminated gypsum beds are thinly interbedded with dolomites and green clays; (2) gypsum rosettes within thin reddish and greenish clays and carbonates; and (3) scattered gypsum mainly within carbonates. Gypsums had been deposited in somewhat different depositional conditions in the same basin where multi-periodic evaporative episodes, ranging from saline to schizohaline environments, had been involved. During these episodes, under high Eh-pH intervals and high salinity conditions, three different types of gypsum formations had been developed in a meromictic-type lake under the influence of varying paleoclimatologic conditions and pore water chemistry of brines. All these gypsum morphologies respectively reflect the different conditions of environments of deposition in a Miocene playa lake basin: (1) subaqueous environments in playa lakes with short evaporation episodes; (2) marginal swamps with cyclic fluctuation of lake level; and (3) extended closed-lake with evaporatic lake water. These different gypsum morphologies are associated with distinctive sedimentary subfacies, which are also primarily related to cyclic climatic changes, alternating semi-arid and evaporite conditions, fluctuation of lake water level and sulphate input in the chemistry of lake water from runoff and hydrothermal source adjacent to basin.

New light on the age of the White Nile

Landsat 5 Thematic Mapper and 7 Enhanced Thematic Mapper imagery reveal lake shorelines in the White Nile valley as far south as lat 10°N. The highest shoreline is at 386 m elevation and was eroded when the White Nile formed a lake as wide as 70 km and >500 km long. Finely laminated green clays laid down on the floor of this lake are overlain by alluvial sands and clays, dated by optically stimulated luminescence as 15 ka to older than 250 ka. The alluvium was deposited during interglacial episodes of stronger summer monsoons and very high White Nile floods. The White Nile paleolake is much older than marine oxygen isotope stage 7 and may have formed ca. 400 ka, during the exceptionally long stage 11 interglacial.

The source of raw materials for Roman pottery from Leptiminus, Tunisia

AbstractLeptiminus, a Roman port city on the west coast of Tunisia, North Africa, exported olive oil and a garum fish paste to Rome. Excavations have uncovered many facilities including kilns and a potter's workshop, indicating an extensive ceramic industry. The vessels, manufactured at Leptiminus, included African red‐slip fineware, coarseware, and amphorae. A petrographic study of pottery sherds showed them to contain very similar temper, rounded aeolian sand grains and limestone, but varying in proportions to produce different textures. An investigation of the source of raw materials for the pottery found three distinct types of clay within a 50 km radius of Leptiminus: grey Miocene, brown Pliocene, and green Late Pliocene clay. Statistical analysis of trace element compositions, using induced neutron activation, of clays and sherds showed that the Pliocene brown clay was used to create all types of pottery. The specific clay horizon, used in Roman times, has apparently been removed by quarrying. However, a lateral continuation of this bed was found 7 m beneath the Leptiminus site 290. © 2002 Wiley Periodicals, Inc.

Mineralogy and chemistry of bentonite (?) deposits at Minjingu, Lake Manyara, North Tanzania

Olive green clays likely to be bentonitic in composition have been mineralogically and chemically studied. They occur in association with other lacustrine sediments at Lake Manyara. Radiocarbon dates from four diatom horizons indicate ages ranging from 12 Ka to 135 Ka suggesting a Mid-Holocene age. Middle Pleistocene age have been assigned to the ridged oncolites of Lake Manyara. The olive green coloured clays in the Manyara basin are known to occur in association with other lake beds including phosphorite deposits, stromatolites, bioturbated silty clays, partly silicified marls, conglomerates and olive green coloured opal beds. The results presented herein are from the olive green coloured clays. The olive green clays (bentonite?) are a result of devitrification or alteration of volcanic ashes and/or pyroclasts. The green clays occur in different forms as they are separated from each other by other lacustrine sediments. The alteration might have taken place in slightly different environments in terms of salinity and alkalinity. One of the top layer is friable and shows conchoidal fractures when dry. The other beds below in the lacustrine sequence are cemented with calcite and some dolomite as well as zeolites. The lowermost layer in the sequence is friable and shows cracks filled with coarse crystalline calcite. Mineralogically the bentonite is composed of the clay minerals illite, illite-smectite mixed layer clays, and chlorite. Other authigenic minerals include various zeolites (analcime, clinoptilolite, erionite and some traces of mordenite), opal, and fluorapatite. The clays have magnesium contents varying from 3.01% to 7.43%. The calcium contents vary widely due to presence or absence of one of the two minerals calcite or apatite. Trace elements like Ba, Ce, Sr, Zr are equally attributed to the presence of calcite and apatite. The formation of the illite-smectite mixed layer clays in an alternating manner with other lake sediments depicts different episodes of volcanic eruptions in the area. The mineralogical composition of smectites, zeolites, and opal in the green clays suggests a deposition of pyroclasts and volcanic ashes in a closed lake system with fluctuating levels. Due to evaporation alkalinity and salinity levels were fluctuating. The clays might have been bentonite which have undergone illitisation, a phenomena noted in other neighbouring rift basins.

Experimental determination of scattering matrices of randomly oriented fly ash and clay particles at 442 and 633 nm

We present measurements of the scattering angle distribution of the whole scattering matrix for randomly oriented particles of three mineral samples: fly ash, green clay, and red clay at 442 and 633 nm. Fly ash consists of aggregates of nearly spherical particles while green clay and red clay particles represent irregular compact particles. We compare the measured results for fly ash with an experimentally determined average scattering matrix which is based on measurements for a broad selection of irregular mineral aerosol particles. We find that the scattering matrix of our polydisperse sample of aggregates of nearly spherical particles differs considerably from that of compact particles. In addition, the angular distribution of the elements of the scattering matrix (except F22(θ)/ F11(θ)) for fly ash particles seem to be dominated by the single monomers. The effects of small differences in composition on the scattering behavior have also been studied by comparing our experimental results for green clay particles with those obtained by Volten et al. [2001] for red clay particles at the same wavelengths.

Carbon and Oxygen Isotope Ratios in Rona Limestone, Romania

Carbon and Oxygen Isotope Ratios in Rona Limestone, Romania. The carbon and oxygen isotopic compositions of limestones provide criteria for the evaluation of the depositional environment. For Jurassic and younger samples, the best discrimination between marine and fresh-water limestones is given by Z parameter, calculated as a linear correlation between δ 13 C and δ 18 O (‰ PDB). Rona Limestone (Upper Paleocene - Lower Eocene), outcropping on a small area in NW Transylvania (Meses area) is a local lacustrine facies. There, it divides Jibou Formation into the Lower Red Member and the Upper Variegated Member, respectively. Recently, a sequence containing a marine nannoplankton assemblage was identified in the base of Rona deposits. The main goal of our study was to characterize, based on the isotopic record, the primary environment of formation of the deposit, as well as that in which some diagenetic processes (the formation of dolomite and of green clay around the siliceous chert nodules) took place. Ten samples representing limestones, dolomitic limestone, marls and the green carbonate-rich clay were studied from petrographical and mineralogical points of view, and the carbon and oxygen isotopic ratios from the carbonate (calcite) component were measured. In conclusion, it was found that the procedure of extraction of CO2 we used enabled the discrimination between the isotopic prints of calcite vs. dolomite. This pleads for considering our results as a primary isotopic pattern in the bulk rock. The oxygen and carbon isotope data indicate a fresh- water depositional environment with Z<120. The δ 13 C mean value (-4.96 ‰ PDB) is, generally, representative for fresh-water carbonates of the Tertiary period. The same environment characterized also the formation of carbonates within the green clay.