19 research outputs found

    Ordoviitsiumi ja Siluri bentoniitide varadiageneetiline areng Balti Basseinis

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    Mixed-layer illite-smectite is one of most common clays minerals that forms in different geological environments including burial diagenesis, hydrothermal, metasomatic and (contact-)metamorphic alteration. Illitization of smectite is considered to proceed through mixed-layer illite-smectite intermediates, which show a progressive mineralogical trend with an increase of illite at the expense of smectite. This trend termed “smectite illitization” has been used in different ways to provide information about thermal and tectonic history of sedimentary basins. The Ordovician and Silurian sedimentary successions of the Baltic Basin contain numerous altered volcanic ash beds – bentonites that are usually K-rich and can be referred to as K-bentonites. The bentonite clay matrix in the Baltic Basin is typically composed of mixed-layer illite-smectite-vermiculite what can occur with some amount of kaolinite. However, the Upper Ordovician Katian age bentonites are characterized by chlorite-smectite type mixed–layer minerals. The illitization in the Ordovician and Silurian K-bentonite beds in the Baltic Basin is evidently controlled by a combination of burial and fluid–driven processes. The burial process predominated in the deeply buried southern and south-western part of the Baltic Basin. The influence of the burial diagenesis decreases with the decreasing burial depth from the southern part of the basin towards the central part of the basin. We suggest that illitization in the northern and north-western part of the basin was triggered by the prolonged flushing of K-rich fluids in relation to the latest phase of the development of the Scandinavian Caledonides about 420–400 Ma. The K-rich fluids were probably derived by the leaching of the K-feldspar Svecofennian crystalline basement, which were uplifted in the forebulge area of the Caledonian foredeep just at the northern and northwestern margin of the Baltic Basin.Illiit-smektiit on looduses levinuim segakihiline savimineraal, mis esineb nii murenemiskoorikutes(muldades), merelistes kui ka kontinentaalsetes setetes ja hüdrotermaalsetes muutumistsoonides. Illiit-smektiit (kvaasistabiilne faas) kujutab endast muutuva koostisega üleminekulist vaheastet kahe levinud savimineraali smektiidi ja illiidi vahel. Seda üleminekulist protsessi nimetatakse illitiseerumiseks. Illitiseerumist kontrollib keskkonna temperatuur, settes liikuvate fluidide ja algse smektiidi koostis, orgaaniliste ühendite juuresolek ning (reaktsiooni) kestus. Seega peaks illitiseerumine peegeldama settebasseini tektoonilis-termaalset arengut, sealhulgas basseini eksisteerimise vältel esinenud soojusvoo lokaalseid muutusi. Balti Basseini Alam-Palesoikumi Siluri ja Ordoviitsiumi karbonaatsetes kivimites esineb arvukalt bentoniidi (ümberkristalliseerunud püroklastilise materjali) kihte. Neid kunagisi vulkaanilise tuha kihte klassifitseeritakse tavaliselt kui K-bentoniite, mis märgib nende kõrgenenud kaaliumi sisaldust. Balti Basseini K-bentoniitide savifraktsioon (<2 µm) koosneb enamjaolt segakihilisest kolmekomponendilisest illiit-smektiit-vermikuliidi tüüpi mineraalist ja kaoliniidist. Erandiks on Ülem-Ordoviitsiumi Katiani (Pirgu lade) bentoniidid mille savifraktsiooni domineerivaks mineraaliks on kloriit-smektiidi (korrensiidi) tüüpi savimineraal. Segakihiliste mineraalide koostise, morfoloogia ja isotoopvanuste ruumiline varieerumine näitab, et Balti Basseini Ordoviitsiumi ja Siluri K-bentoniitide savimineraalide diageneesi on kontrollinud mattumisdiageneesi ja fluidi-protsesside kombinatsioon. Mattumisdiageneesi (st temperatuuri) kontrollitud illitiseerumine on domineeriv sügavalt maetud basseini lõuna- ja edelaosas. Mattumisdiageneesi protsesside osatähtus väheneb liikudes basseini lõunaosast basseini keskosa suunas koos bentoniidikihtide sügavuse vähenemisega. Peamiseks illitiseerumist mõjutavaks protsessiks Balti Basseini põhja- ja loodeosas on pikaaajaline K-rikaste fluidide sissevool, mis on seotud Skandinaavia Kaledoniidide arenguga (~420-400 Ma tagasi). Fluid rikastus K-ga tõenäoliselt meteoorsete vete liikumisel läbi Svekofennia kristalliinse aluskorra K-päevakivi rikaste kivimite, mis paiknesid Kaledoniidide eelsügaviku eelkerke (forebulge) alal

    Illitization of early paleozoic k-bentonites in the baltic basin : Decoupling of burial- and fluid-driven processes

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    The mineralogical characteristics of Ordovician and Silurian K-bentonites in the Baltic Basin were investigated in order to understand better the diagenetic development of these sediments and to link illitization with the tectonothermal evolution of the Basin. The driving mechanisms of illitization in the Baltic Basin are still not fully understood. The organic material thermal alteration indices are in conflict with the illite content in mixed-layer minerals. The clay fraction of the bentonites is mainly characterized by mixed-layered illite-smectite and kaolinite except in the Upper Ordovician Katian K-bentonites where mixed-layer chlorite-smectite (corrensite) occurs. The variation in expandability plus other geological data suggest that the illitization of Ordovician and Silurian K-bentonites in the Baltic Basin was controlled by a combination of burial and fluid driven processes. The illitization in the south and southwest sectors of the basin was effected mainly by burial processes. The influence of the burial process decreases with decreasing maximum burial towards the central part of the basin. The advanced illitization of the shallowburied succession in the north and northwest sectors of the basin was enhanced by the prolonged flushing of K-rich fluids in relation to the latest phase of development of the Scandinavian Caledonides ~420-400 Ma

    Altered volcanic ash as an indicator of marine environment, reflecting pH and sedimentation rate - Example from the Ordovician Kinnekulle bed of Baltoscandia

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    The composition of altered volcanic ash of the Late Ordovician Kinnekulle bed was studied in geological sections of the Baltic Paleobasin. The composition of altered ash varies with paleosea depth from northern Estonia to Lithuania. The ash bed in shallow shelf limestones contains an association of illite-smectite (I-S) and K-feldspar, with the KO content ranging from 7.5 to 15.3%. The limestone in the transition zone between shallow- and deep-shelf environments contains I-S-dominated ash with KO content from 6.0 to 7.5%. In the deep-shelf marlstone and shale, the volcanic ash bed consists of I-S and kaolinite with a KO content ranging from 4.1 to 6.0%. This shows that authigenic silicates from volcanic ash were formed during the early sedimentary-diagenetic processes. The composition of the altered volcanic ash can be used as a paleoenvironmental indicator showing the pH of the seawater or porewater in sediments as well as the sedimentation rate

    Notes on magnetic susceptibility in the Guil Valley alluvial mire correlated with the Punic invasion of Italia in 218 BC

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    The enigma of Hannibal’s route across the Alps in 218 BC is one of the most enduring questions of antiquity. Many authorities, some of whom have never ventured into the mountains, have argued for various preferred crossings of the Alps. Earlier efforts to identify the route focused on the two-tier rockfall and regrouping area on the lee side of the Range, originally described by Polybius in his The Rise of the Roman Empire, by Livy in The War with Hannibal, and later by Sir Gavin de Beer who searched out the topography and stream dynamics in the area of several projected crossing routes. Recently, attention shifted to the alluvial mire in the upper Guil River after cores and sections (sites G5 and G5A, Mahaney et al., 2016a) revealed the presence of churned-up or bioturbated beds, called the Mass Animal Deposition (MAD) layer. At approximately 45 ±15 cm depth, the top of the MAD layer contains abundant bacteria belonging to the class Clostridia that are found in the mammalian gut and fecal deposits, all dated by AMS 14C to 2168 cal yr BP (i.e., 218 BC with a 95% confidence interval). Samples for magnetic susceptibility collected from three additional sections (G5B, G5C and G5D) carrying the churned-up beds reveal heightened magnetic intensity within these bioturbated sediments that is suggestive of high magnetite content, one form of iron that often was used to cast weapons in ancient times. Magnetic susceptibility levels are highest within the churned-up beds with minor exceptions in two of the three sections analyzed, possibly indicating the presence of weathered tools, implements or weapons lost or discarded. The available data is sufficient to suggest that a GPR survey of the entire mire might well lead to recovery of the first artifacts from the invasion that would shed enormous light on the culture of ancient Carthage

    Cosmic airburst on developing allerød substrates (Soils) in the western alps, mt. viso area

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    Although much has been written about a cosmic impact event in the Western Alps of the Mt. Viso area, the event closely tied with the Younger Dryas Boundary (YDB) of 12.8 ka and onset of the Younger Dryas (YD), the affected land surface is considered to contain a similar black mat suite of sediment found on three continents. While work elsewhere has focused on recovered sediment from lake and ice cores, buried lacustrine/alluvial records, and surface glacial and paraglacial records, no one has traced a mountain morphosequence of deposits with the objective of investigating initial weathering/ soil morphogenesis that occurred in ice recessional deposits up to the YDB when the surface was subjected to intense heat, presumably, as hypothesized by Mahaney et al. (2016a) from a cosmic airburst. With the land surface rapidly free of ice following glacial retreat during the Bølling-Allerød interstadial, weathering processes ~13.5 to 12.8 ka led to weathering and soil morphogenesis in a slow progression as the land surface became free of ice. To determine the exposed land character in the mid- to late-Allerød, it is possible to utilize an inverted stratigraphic soil morphogenesis working backward in time, from known post-Little Ice Age (LIA) (i.e. time-zero) through LIA (~0.45 to ~0.10 ka), to at least the middle Neoglacial (~2 ka), to answer several questions. What were the likely soil profile states in existence at the end of the Allerød just prior to the cosmic impact/airburst (YDB)? Assuming these immature weathered regolith sections of the Late Allerød approximated the <1 ka old profiles seen today, and assuming the land surface was subjected to a hypothesized instant temperature burst from ambient to ~2200oC at ~12.8 ka, what would be the expected effect on the resident sediment? To test the mid-LG (YDB) to YD relationship we analyzed the paleosols in both suites of deposits – mid-LG to YD – to test that the airburst grains are restricted to Late Allerød paleosols and using relative-age-determination criteria, that the overlapping YD to mid-LG moraines are closely related in time. These are some of the questions about the black mat that we seek to answer with reference to sites in the upper Guil and Po rivers of the Mt. Viso area

    Separating Si phases from diagenetically-modified sediments through sequential leaching.

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    Silicon (Si) phases such as biogenic silica, lithogenic silicate and authigenic silica/silicate in marine sediments provide valuable information about past Si cycling. Wet-chemical sequential leaching methods are often applied to extract different Si phases from marine sediments to study Si diagenetic processes in shallow subsurface. The potential of this method to separate Si phases from deeply-buried and diagenetically-modified sediments has not been systematically examined. We applied a sequential leaching protocol to drill core sediments retrieved from the Ulleung Basin, East/Japan Sea. We performed geochemical (elemental abundance and stable Si isotopes, δ30Si) and microscopic (X-ray diffraction and scanning electron microscope) analyses to monitor leaching efficiency in separating different Si phases. We show that, prior to alkaline leaching, applying weak acid is able to remove metal oxide and/or clay-like phases. The following Na2CO3 leaching, based on a commonly-adopted protocol, is able to dissolve some but not all diatoms. The results of elemental contents and δ30Si values of leachates suggest that, in diagenetically-modified sediments, either a longer digesting time or a harsher alkaline leaching is needed to dissolve all diatoms. This is attributed to increased resistance of diatoms to Na2CO3 leaching as a result of reduced surface area and/or improved SiO2 tetrahedron ordering during diagenetic processes over time and burial depths. Lithogenic silicate minerals can be dissolved by NaOH and potentially separated from diatoms if the latter is completely removed in the preceding leaching steps. Even if a trace amount of diatom is left undissolved in the NaOH leaching, it is still possible to separate the two through a mass balance calculation given the knowledge of composition for the two end-members. We conclude that a successful separation of Si phases in diagenetically modified sediments relies on the knowledge of elemental abundance and even δ30Si values of the leachates, as well as information such as species of Si-skeleton organisms, contents and maturation degree of biogenic silica