Abstract:The composition and particle morphology of diagenetic mixed-layer illite-smectite (I-S) in the shallow buried Ordovician Kinnekulle K-bentonite were studied to understand the process of illitization in the Baltic Basin. The same K-bentonite bed from 12 different locations in the Basin was sampled and analysed by means of X-ray diffraction (XRD), atomic-force microscopy (AFM) and K-Ar dating. Illite-smectite in the samples was identified as a highly illitic R1 type illite-smectite vermiculite (high-charge smect… Show more
“…In Podolia, diagenetic ages of the Ediacaran sedimentary rocks match with the illite ages of overlying Silurian bentonites, 339–390 Ma (Środoń, Paszkowski, Drygant, Anczkiewicz, & Banaś, 2013) and the illite ages north of Volyn fall within a broad range of ages recorded for the Ordovician bentonites of the Baltic Basin (Estonia and N Poland), 296–420 Ma (Somelar, Kirsimäe, & Środoń, 2009; Środoń, Clauer, et al, 2009). In both areas, authigenic K‐feldspars were also documented (Somelar et al., 2009; Środoń, Clauer, et al, 2009). Clearly, diagenesis of the Ediacaran and the overlying lower Palaeozoic sediments in the EEC interior and on its margin was controlled by common Palaeozoic geological processes.…”
The diagenetic history of the Ediacaran sedimentary rocks in the East European Craton (EEC) over the area extending from Arkhangelsk (Russia) in the north to Podolia (Ukraine) in the south was revealed by means of the XRD characterization and K–Ar dating of clay fractions, mudstone porosity measurements and organic geochemistry investigations. Mudstone porosity measurements produced direct evidence of shallow maximum burial of the Ediacaran sediments on the craton (Russia, Lithuania, Belarus, Volyn), not exceeding 1.5 km, and much deeper burial at the cratonic margin, in Podolia and Poland. In general, illitization of smectite and biomarker indices indicates more advanced diagenesis at the cratonic margin.
K–Ar dating of authigenic illite–smectite and aluminoceladonite revealed the Palaeozoic age of mineral diagenesis (ca. 450–300 Ma) both on the craton and its margin, with older ages generally observed in the north. When the maximum palaeotemperatures were evaluated from illite–smectite and biomarkers, based on the calibrations from the conventional burial diagenetic sections, a major mismatch was detected for the cratonic area: 100°C–130°C from illite––smectite and tens of oC lower from the lipid biomarkers. This diagenetic pattern was interpreted as the result of short‐lasting (in ky scale) pulses of potassium‐bearing hot fluids migrating from the Caledonian and Variscan orogens deep in the craton interior, effectively promoting illitization in porous rocks without altering the organic matter. Analogous short pulses of fluids were responsible for numerous diagenetic phenomena, including Mississippi Valley‐Type ore deposits, in the American Midwest, in front of the Appalachians. K–Ar dating indicates that the entire Proterozoic sedimentary cover of the Great Unconformity on the EEC remained untouched by measureable post‐sedimentary changes until the early Palaeozoic, thus for over 1000 My, which is an unprecedented finding.
“…In Podolia, diagenetic ages of the Ediacaran sedimentary rocks match with the illite ages of overlying Silurian bentonites, 339–390 Ma (Środoń, Paszkowski, Drygant, Anczkiewicz, & Banaś, 2013) and the illite ages north of Volyn fall within a broad range of ages recorded for the Ordovician bentonites of the Baltic Basin (Estonia and N Poland), 296–420 Ma (Somelar, Kirsimäe, & Środoń, 2009; Środoń, Clauer, et al, 2009). In both areas, authigenic K‐feldspars were also documented (Somelar et al., 2009; Środoń, Clauer, et al, 2009). Clearly, diagenesis of the Ediacaran and the overlying lower Palaeozoic sediments in the EEC interior and on its margin was controlled by common Palaeozoic geological processes.…”
The diagenetic history of the Ediacaran sedimentary rocks in the East European Craton (EEC) over the area extending from Arkhangelsk (Russia) in the north to Podolia (Ukraine) in the south was revealed by means of the XRD characterization and K–Ar dating of clay fractions, mudstone porosity measurements and organic geochemistry investigations. Mudstone porosity measurements produced direct evidence of shallow maximum burial of the Ediacaran sediments on the craton (Russia, Lithuania, Belarus, Volyn), not exceeding 1.5 km, and much deeper burial at the cratonic margin, in Podolia and Poland. In general, illitization of smectite and biomarker indices indicates more advanced diagenesis at the cratonic margin.
K–Ar dating of authigenic illite–smectite and aluminoceladonite revealed the Palaeozoic age of mineral diagenesis (ca. 450–300 Ma) both on the craton and its margin, with older ages generally observed in the north. When the maximum palaeotemperatures were evaluated from illite–smectite and biomarkers, based on the calibrations from the conventional burial diagenetic sections, a major mismatch was detected for the cratonic area: 100°C–130°C from illite––smectite and tens of oC lower from the lipid biomarkers. This diagenetic pattern was interpreted as the result of short‐lasting (in ky scale) pulses of potassium‐bearing hot fluids migrating from the Caledonian and Variscan orogens deep in the craton interior, effectively promoting illitization in porous rocks without altering the organic matter. Analogous short pulses of fluids were responsible for numerous diagenetic phenomena, including Mississippi Valley‐Type ore deposits, in the American Midwest, in front of the Appalachians. K–Ar dating indicates that the entire Proterozoic sedimentary cover of the Great Unconformity on the EEC remained untouched by measureable post‐sedimentary changes until the early Palaeozoic, thus for over 1000 My, which is an unprecedented finding.
“…The age of calcite precipitation in the Kalana cave system cannot be assessed at the present state of knowledge. Still, the hydrothermal signature in the oxygen isotope composition in AOM calcite suggests that its formation could be tentatively tied to either late Palaeozoic – Triassic low-temperature hydrothermal overprinting on rock magnetization revealed in carbonate rocks in Kalana (Preeden et al 2008), or to far-field hydrothermal influences of the latest phase of Caledonian Orogeny (425–400 Ma), expressed in the Baltic Basin in late Silurian – Devonian K–Ar isotope ages of illite-smectite in K-bentonites (Somelar, Kirsimäe & Srodon, 2009; Somelar et al 2010). Figure 6. Oxygen isotope fractionation curves for authigenic calcite from the Kalana cave.…”
Section: Discussionmentioning
confidence: 99%
“…Nevertheless, the diagenetic grade of clay minerals and palaeomagnetic remagnetization of sediments hint at a series of basin-wide (hydrothermal) fluid intrusions/thermal perturbations during the evolution of the Baltic Basin (e.g. Plado et al 2008; Preeden et al 2008; Somelar, Kirsimäe & Srodon, 2009; Somelar et al 2010). The cave structures in Kalana developed along the fracture systems where hydrothermal fluids could have been capable of locally heating up the organic-rich sediments and thermogenic methane production.…”
Aeronian (Silurian Period) carbonate rocks in Kalana quarry in central Estonia contain cave and fracture structures filled with calcitic speleothem precipitates of atypical composition. Calcite crystals in dolomitized limestone cave walls have diverse shapes (equant-blocky, bladed and fibrous), but most of the cave walls and speleothems are covered with an up to 10 cm thick crust of microcrystalline botryoidal calcite. The morphology of precipitates suggests their formation in low hydrodynamic conditions in water supersaturated with calcite. Calcite in speleothems is associated with the mineralization of sulphur-bearing minerals, such as pyrite and abundant barite. Unlike that of speleothem calcite, the stable isotope composition of authigenic calcite shows extreme depletion in 13C and large variations in δ13CPDB from –11 to –56‰, whereas the δ18OPDB values range from –5 to –12‰, suggesting calcite precipitation from a 13C-depleted carbon source supplied by microbially mediated anaerobic oxidation of methane and/or other hydrocarbons at elevated temperatures (up to 70°C). Systematic variation in the δ13CPDB and δ18OPDB values of layered precipitates indicates a change from an initially biogenic methane source to an either thermogenic methane or hydrocarbon source in the low-temperature hydrothermal fluid. Calcite speleothems in Kalana possibly developed at the mixing front of sulphate-rich seawater or groundwater and low-temperature methane-bearing hydrothermal fluids in the phreatic zone of a hypogenic-hydrothermal (karst) system.
“…For example, the illite-smectite type illustrated by upper layers in Figure 3 could be regarded a K-bentonites, while the kaolin type in the lower layers shown in Figure 3 could be regarded as kaolinitic bentonites. Because they have a unique position within the Bazhenov Shale Formation in general then it is evident that they could be as useful in oilfield exploration as tonsteins and K-bentonites are in coalfield and other geological explorations ( rodo , 1972;Somelar et al, 2009;Warren, 2016;Dai et al, 2017).…”
Section: Significance Of the Luminescent Layersmentioning
Argillites that strongly luminesce under UV radiation were detected in the Bazhenov Shale Formation (BSF) of the West Siberian Basin during routine core examination and found to be persistent over a wide lateral area. The mineralogy and fabric of these luminescent layers were characterized by optical and fluorescence microscopy, SEM, TEM, XRD and IR methods. Optical and fluorescence microscopy showed that the luminescent layers were to a large extent derived from volcanic ash falls and could be described as meta-tuffites, although normal detrital sedimentation continued at the same time. The layers have a thickness of several mm to a maximum of 3-4cm and can be defined as a clay-rich regional horizons. XRD showed that two principal clay minerals were present, namely a kaolinite, possibly with some dickite stacking, (kaolin-rich) and a mixed-layer illite-smectite (I/S) with R1 to R2 ordering similar to that found in K-bentonite. Total organic matter in the luminescent layers is much lower than that in the enclosing BSF clayey-silty siliceous sediments above and below as shown by pyrolytic analyses. Evidence is presented that the luminescent characteristic of the argillites is related to their clay mineralogy, specifically to their content *Revised Manuscript (clean copy) Click here to view linked References 2 of kaolin minerals, although a contribution from nitrogenous organic matter cannot be entirely discounted. In some ways the luminescent argillites can be compared with bentonites associated with ash transformations or with tonsteins in coal beds, which are also derived from volcanic ash falls and contain highly crystalline kaolinite. However, tonsteins originate at or near land surface whereas the argillites were apparently formed in the deep ocean. But just as tonsteins can be used for detailed stratigraphic studies and are valuable in the context of coal exploration, so may the luminescent argillites prove to be significant both stratigraphically and in the search for economic hydrocarbon deposits, bearing in mind that their clay mineralogy may be sensitive to temperature and depth of burial and related to their placement in the oil and gas window.
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