Geologos, 2016, 22, 3


Recent Submissions

Now showing 1 - 6 of 6
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    Soft-sediment deformation structures in cores from lacustrine slurry deposits of the Late Triassic Yanchang Fm. (central China)
    (Instytut Geologii UAM, 2016-12) Yang, Renchao; van Loon, A.J. (Tom); Yin, Wei; Fan, Aiping; Han, Zuozhen
    The fine-grained autochthonous sedimentation in the deep part of a Late Triassic lake was frequently interrupted by gravity-induced mass flows. Some of these mass flows were so rich in water that they must have represented slurries. This can be deduced from the soft-sediment deformation structures that abound in cores from these lacustrine deposits which constitute the Yanchang Fm., which is present in the Ordos Basin (central China). The flows and the resulting SSDS were probably triggered by earthquakes, volcanic eruptions, shear stress of gravity flows, and/or the sudden release of overburden-induced excess pore-fluid pressure. The tectonically active setting, the depositional slope and the high sedimentation rate facilitated the development of soft-sediment deformations, which consist mainly of load casts and associated structures such as pseudonodules and flame structures. Sediments with such deformations were occasionally eroded by slurries and became embedded in their deposits.
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    Representatives of the family Actinostromatidae (Stromatoporoidea) in the Devonian of southern Poland and their ecological significance
    (Instytut Geologii UAM, 2016-12) Wolniewicz, Paweł
    Stromatoporoids of the family Actinostromatidae are common constituents of Givetian to Frasnian (Devonian) or- ganic buildups. The species-level structure of actinostromatid assemblages from the Devonian of southern Poland is described in the present paper, with special emphasis on ecological factors that influenced species composition of the communities. Nine species of the genera Actinostroma and Bifariostroma are distinguished. Members of the family Actinostromatidae predominated in stromatoporoid assemblages within lower Frasnian carbonate buildup margins. The most diverse actinostromatid faunas were found within the middle Givetian Stringocephalus Bank, in the upper Givetian–lower Frasnian biostromal complex and in the lower Frasnian organic buildups. Species-level biodiversi- ty was lowest within detrital facies which surrounded the Frasnian carbonate buildups. Species of Actinostroma with well-developed colliculi are commonest within the middle Givetian to early Frasnian coral-stromatoporoid biostromal complexes, whereas species with strongly reduced colliculi predominate early-middle Frasnian organic buildups. The skeletal structure of actinostromatids reflects environmental changes, documenting a transition from species with thin, close-set pillars and widely spaced laminae (common in the middle Givetian) to those with long, thick pillars and meg- apillars (in Bifariostroma), which were predominant during the early and middle Frasnian. The distribution of growth forms among species reveals a significant intraspecific variation. Species of Actinostroma can be either tabular or low domical, depending on the palaeoenvironmental setting. Thus, the present study confirms that stromatoporoid mor- phology was influenced by environmental conditions.
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    An overview of lithotype associations of Miocene lignite seams exploited in Poland
    (Instytut Geologii UAM, 2016-12) Widera, Marek
    Currently, three stratigraphically distinct lignite seams of Early to Middle Miocene age are exploited in Poland, namely the third Ścinawa lignite seam (ŚLS-3), the second Lusatian lignite seam (LLS-2) and the first Mid-Polish lignite seam (MPLS-1). All of these are composed of numerous macroscopically distinguishable layers defined as lignite lithotypes. In the present paper, the lithotypes of Polish lignites are grouped into seven major lithotype associations that originat- ed in various types of mire. Therefore, an approximate reconstruction of mire type can be based on lignite lithotypes. Within the Polish lignite seams examined, the commonest in order of importance are: xylodetritic (XDL), detroxylitic (DXL), detritic (DL) and xylitic (XL) lithotype associations, mostly with a massive (m) or horizontal (h) structure. They are particularly dominant in lignite opencasts belonging to the Konin and Adamów mines. However, in the lowermost seams at the Turów and Bełchatów mines, a substantial part of the seams comprises the bitumen-rich (BL) lithotype as- sociation. These seams also lignite lithotypes that in large quantities have a gelified (g) and/or nodular (n) structure. In contrast, lignites from the Sieniawa mine are characterised by an admixture of the best-developed lithotype associations of both fusitic (FL) and weathered (WL) lignites. Moreover, the vast majority of these lignites have a folded (fo) and/or faulted (fa) structure, because they were completely deformed by glaciotectonics.
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    Dating the Morasko meteorite fall by natural thermoluminescence of the fusion crust
    (Instytut Geologii UAM, 2016-12) Fedorowicz, Stanisław; Stankowski, Wojciech T.J.
    The date of fall of the Morasko iron meteorite was determined by means of thermoluminescence measurements of the fusion crust and related local materials. Three small pieces, commonly referred to as ‘shrapnel’, were used. The results obtained are 4.5–5.0 ka, which is in good agreement with previous estimates of 4–6 ka on the basis of radiometric, do- simetric and palynological methods.
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    Microstructural, modal and geochemical changes as a result of granodiorite mylonitisation – a case study from the Rolovská shear zone (Čierna hora Mts, Western Carpathians, Slovakia)
    (Instytut Geologii UAM, 2016-12) Farkašovský, Roman; Bónová, Katarína; Košuth, Marián
    Strong tectonic remobilisation and shear zone development are typical features of the easternmost part of the Vepori- cum tectonic unit in the Western Carpathians. The granodiorite mylonites in the area of the Rolovská shear zone (Čierna hora Mts) underwent a complex polystage evolution during the Hercynian and Alpine orogenies. Deformation during the latter reached greenschist facies under metamorphic conditions. Mylonites are macroscopically foliated rocks with a stretching lineation and shear bands. Structurally different mylonite types, ranging from protomylonites to ulramylo- nites with typical grainsize reduction from the margins towards the shear zone centre, have been assessed. The modal mineralogy of the different mylonite types changes considerably. Typical is a progressive decrease in feldspar content and simultaneously the quartz and white mica content increases from protomylonites towards the most strongly defor- med ultramylonites. The deformation had a brittle character in less deformed rocks and a ductile one in more deformed tectonites. Obvious chemical changes occur in mesomylonites and ultramylonites. During mylonitisation, the original biotite granodiorite was depleted of Mg, Fe, Na, Ca and Ba, while K, Rb and mainly Si increased considerably. Other (major and trace) elements reflect erratic behaviour due to lateral mobility. Chemical changes indicate the breakdown and subsequent recrystallisation of biotite and feldspars and, in turn, the crystallisation of albite and sericite. REE de- crease in ultramylonites due to the breakup of accessory minerals during deformation and alteration.
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    Sedimentology and ichnology of Neogene Coastal Swamp deposits in the Niger Delta Basin, Nigeria
    (Instytut Geologii UAM, 2016-12) Ezeh, Sunny C.; Mode, Wilfred A.; Ozumba, Berti M.; Yelwa, Nura A.
    Often analyses of depositional environments from sparse data result in poor interpretation, especially in multipartite depositional settings such as the Niger Delta. For instance, differentiating channel sandstones, heteroliths and mud- stones within proximal environments from those of distal facies is difficult if interpretations rely solely on well log sig- natures. Therefore, in order to achieve an effective and efficient interpretation of the depositional conditions of a given unit, integrated tools must be applied such as matching core descriptions with wireline log signature. In the present paper cores of three wells from the Coastal Swamp depositional belt of the Niger Delta are examined in order to achieve full understanding of the depositional environments. The well sections comprise cross-bedded sandstones, heteroliths (coastal and lower shoreface) and mudstones that were laid down in wave, river and tidal processes. Interpretations were made from each data set comprising gamma ray logs, described sedimentological cores showing sedimentary fea- tures and ichnological characteristics; these were integrated to define the depositional settings. Some portions from one of the well sections reveal a blocky gamma ray well log signature instead of a coarsening-upward trend that characteris- es a shoreface setting while in other wells the signatures for heteroliths at some sections are bell blocky in shaped rather than serrated. Besides, heteroliths and mudstones within the proximal facies and those of distal facies were difficult to distinguish solely on well log signatures. However, interpretation based on sedimentology and ichnology of cores from these facies was used to correct these inconsistencies. It follows that depositional environment interpretation (especially in multifarious depositional environments such as the Niger Delta) should ideally be made together with other raw data for accuracy and those based solely on well log signatures should be treated with caution.
Uniwersytet im. Adama Mickiewicza w Poznaniu
Biblioteka Uniwersytetu im. Adama Mickiewicza w Poznaniu
Ministerstwo Nauki i Szkolnictwa Wyższego