Geologos, 2014, 20, 3


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Now showing 1 - 5 of 5
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    Do the available data permit clarification of the possible dependence of Palaeozoic brachiopod generic diversity dynamics on global sea-level changes? A viewpoint
    (Instytut Geologii UAM, 2014-09) Ruban, Dmitry A.
    At a glance, progress in palaeontology and eustatic reconstructions in the past decade permits to prove or to disprove the possible dependence of Palaeozoic brachiopod generic diversity dynamics on global sea-level changes. However, the available diversity curve is of much lower resolution than the eustatic curve. This problem can be resolved by decreasing the resolution of the latter. The other restriction linked to the chronostratigraphical incompatibility of the available data allows to focus on the Middle Palaeozoic only. A series of mass extinctions and other biotic crises in the Silurian-Devonian does not allow to interpret correctly the results of direct comparison of the brachiopod generic diversity dynamics with global sea-level changes. With the available data, it is only possible to hypothesize that the eustatic control was not playing a major part in diversity dynamics of Middle Palaeozoic brachiopods. The resolution of the stratigraphic ranges of Palaeozoic brachiopods should be increased significantly, and these ranges should be plotted against the most up-to-date geologic time scale. Until this task will be achieved, it is impossible to judge about the existence of any dependence (either full or partial) of the Palaeozoic brachiopod diversity dynamics on global sea-level changes.
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    Geochemistry and fluid-inclusion microthermometry of the Farsesh barite deposit, Iran
    (Instytut Geologii UAM, 2014-09) Zarasvandi, Alireza; Zaheri, Nazanin; Pourkaseb, Houshang; Chrachi, Abbas; Bagheri, Hashem
    The Permian carbonate-hosted Farsesh barite deposit is located southeast of the City of Aligudarz in the prov -ince of Lorestan, Iran. Structurally, this deposit lies in the Zagros metallogenic belt and the Sanandaj-Sirjan Zone. Barite mineralisations occur as open-space filling veins, and as massive and replacement ores along fractures, faults and shear zones of the Permian carbonate host rocks. In order to determine the structure, in addition to pe -trographic and fluid-inclusions studies, an ICP-MS analysis was carried out in order to measure the major as well as the trace and rare earth elements. The Farsesh barite deposit has a simple mineralogy, of which barite is the main mineral, followed by calcite, dolomite, quartz, and opaque minerals such as Fe-oxides. Replacement of bar -ite by calcite is common and is more frequent than space-filling mineralisation. Sulphide minerals are minor and mainly consist of chalcopyrite and pyrite, which are altered by weathering to covellite, malachite and azurite. Petrographic analysis and micro-thermometry were carried out on the two-phase liquid/vapour inclu -sions in ellipsoidal or irregularly shaped minerals ranging in size from 5–10 µm. The measurements were conducted on fluid inclusions during the heating and subsequent homogenisation in the liquid phase. The low homogenisation temperatures (200–125°C) and low to moderate salinity (4.2–20 eq wt% NaCl) in -dicate that the barite had precipitated from hydrothermal basinal water with low to moderate salinity. It appears from the major and trace elements that geochemical features such as Ba and Sr enrichment in the barite samples was accompanied by depletion of Pb, Zn, Hg, Cu and Sb. The geochemistry of the rare earth elements, such as low ΣREE concentrations, LREE-enrichment chondrite-normalised REE patterns, the negative Ce and positive Eu anomalies, the low Ce/La ratio and the positive La and Gd anomalies, suggest that the Farsesh barite was deposited from hydrothermally influenced sea water. The Farsesh deposit contains low-temperature hydrothermal barite. The scatter plots of the barite (close to sea water) in different areas on the CeN/SmN versus CeN/YbN diagram support the possibility that the barite was formed from seawater-bearing hydrothermal fluids.
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    Petrographical analysis of  Warthian fluvioglacial gravels as a tool to trace the source area – a case study from central Poland
    (Instytut Geologii UAM, 2014-09) Górska-Zabielska, Maria; Wachecka-Kotkowska, Lucyna
    The petrographical features of the medium- and coarse-grained gravels (4-10 mm and 20-60 mm, respectively) of weathered and fresh (unweathered) deposits indicate, in combination with so-called indicator and statistical erratics, that two glacial lobes joined in the borderland of the Polish Lowlands and Uplands. Lower Palaeozoic limestones become less frequent in the finer gravel fraction, whereas crystalline rocks and flints become more frequent. The petrographical analysis of the coarser gravel fraction indicates that the ice sheet advanced from the NE to NNW (the Widawka lobe) and from the NE to ENE (the Rawka, Pilica and Luciąża lobes). The source areas of the gravel deposited by the Warthian ice sheet were magmatic and sedimentary areas of both the Baltic and the SE Sweden basins.
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    Kame or moraine? A sedimentological study of a glaciomarginal landform at  Niedźwiedziny (Great  Polish  Lowland)
    (Instytut Geologii UAM, 2014-09) Ewert–Krzemieniewska, Aleksandra
    A sedimentary succession in a gravel pit at Niedźwiedziny was investigated in order to determine its origin: kame or moraine. The gravel pit is located in an isolated hill of approx. 600 m long and 250–400 m wide. The succession is built of glaciofluvial deposits: a sandy/gravelly unit in the lower and middle parts, overlain by diamicton. Five lithofacies have been distinguished, which represent two facies associations: (1) a fluvial association evolving from a high-energy to a transitional to a shallow braided river on an alluvial fan, and (2) an association of cohesive deposits representing a glacigenic mass flow. The interpretation is based mainly on palaeocurrent data and differs from conclusions by earlier investigators. The ice-marginal zone is characterised by a large variety of glaciomarginal forms. Their sedimentology, morphology and palaeogeography are determined by successive phases of deglaciation. The re -sults of the present study show that the character of the deglaciation in the study area changed with time from frontal to areal deglaciation.
Uniwersytet im. Adama Mickiewicza w Poznaniu
Biblioteka Uniwersytetu im. Adama Mickiewicza w Poznaniu
Ministerstwo Nauki i Szkolnictwa Wyższego