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Tectonic-climatic interactions during changes of depositional environments in the Carpathian foreland: an example from the Neogene of central Poland

Widera Marek, Zieliński Tomasz, Chomiak Lilianna, Maciaszek Piotr, Wachocki Robert, Bechtel Achim, Słodkowska Barbara, Worobiec Elżbieta, Worobiec Grzegorz

Acta Geologica Polonica

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2021

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Vol. 71, no. 4

519--542

EN

Many geological problems have not been convincingly explained so far and are debatable, for instance the origin and changes of the Neogene depositional environments in central Poland. Therefore, these changes have been reconstructed in terms of global to local tectonic and climatic fluctuations. The examined Neogene deposits are divided into a sub-lignite unit (Koźmin Formation), a lignite-bearing unit (Grey Clays Member), and a supra-lignite unit (Wielkopolska Member). The two lithostratigraphic members constitute the Poznań Formation. The results of facies analysis show that the Koźmin Formation was deposited by relatively high-gradient and well-drained braided rivers. Most likely, they encompassed widespread alluvial plains. In the case of the Grey Clays Member, the type of river in close proximity to which the mid-Miocene low-lying mires existed and then were transformed into the first Mid-Miocene Lignite Seam (MPLS-1), has not been resolved. The obtained results confirm the formation of the Wielkopolska Member by low-gradient, but mostly well-drained anastomosing or anastomosing-to-meandering rivers. The depositional evolution of the examined successions depended on tectonic and climatic changes that may be closely related to the mid-Miocene great tectonic remodelling of the Alpine-Carpathian orogen. This resulted in palaeogeographic changes in its foreland in the form of limiting the flow of wet air and water masses from the south and vertical tectonic movements.

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New insights into the genesis of the “Poznań clays” – upper neogene of Poland

Maciaszek Piotr, Chomiak Lilianna, Urbański Paweł, Widera Marek

Civil and Environmental Engineering Reports

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2020

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Vol. 30, no. 1

18--32

EN

The present study focuses on the upper Neogene deposits, called the “Poznań Clays”, that cover more than 75,000 km2 of Poland. They are situated between the first midPolish lignite seam and the glaciogenic deposits of the Pleistocene age. Lithostratigraphically, the “Poznań Clays” belong to the uppermost portion of the lignite-bearing Grey Clays Member and the whole Wielkopolska Member (Poznań Formation). The examined fine-grained sediments include mud-rich floodplain deposits with palaeosol remnants and large sandy-muddy or muddy palaeochannel bodies. Therefore, taking into account facies analysis, cross-sectional geometry, and the planform of the palaeochannels, it can be stated that the “Poznań Clays” formed in the environment of a late Neogene anastomosing river.

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The interpretative significance of ripple-derived sedimentary structures within an upper Neogene fluvial succession of central Poland

Maciaszek Piotr, Chomiak Lilianna, Wachocki Robert, Widera Marek

Geologos

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2019

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Vol. 25, No. 1

1--13

EN

Sedimentary structures discussed in the present study are genetically linked to ripples that consist of pure sand or alternating sand and mud layers. All types of ripple-related structures, such as climbing-ripple cross-lamination and heterolithic bedding, i.e., flaser, wavy and lenticular (nodular), have been identified for the first time in fluvial strata that have been characterised previously as commonly massive. These small-scale bedforms, produced by migrating ripples, have been documented in a fluvial channel of late Neogene age in central Poland. The abundance and co-occurrence of the structures discussed and their spatial distribution provide evidence of their formation under very low-energy conditions, when flow velocity changed markedly, but was often significantly less than 0.5 m/s. Therefore, these ripple-derived sedimentary structures are here recognised as typical of channel fills of an anastomosing river.

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Seismically-induced soft-sediment deformation in crevasse-splay microdelta deposits (Middle Miocene, central Poland)

Chomiak Lilianna, Maciaszek Piotr, Wachocki Robert, Widera Marek, Zieliński Tomasz

Geological Quarterly

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2019

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Vol. 63, No. 1

162--177

EN

Crevasse-splay microdelta deposits and their soft-sediment deformation structures (SSDS) are described from a tectonically active lignite-bearing area. These strongly deformed siliciclastic deposits, situated between two lignite benches, are typical of a crevasse-splay microdelta. They accumulated in the overbank zone of a Middle Miocene river system (backswamp area) where shallow ponds or lakes occasionally existed. The deformation takes the form of deformed lamination and load (load casts and flame structures) structures as well as seismic breccias within the first Mid-Polish lignite seam. Ductile deformation structures were generated first by liquefaction and then the breccia was formed under brittle conditions. The brecciation followed a sudden tectonic collapse resulting in an increase in pore pressure related to upward water movement. The occurrence in a tectonic graben and characteristic morphological features suggest an origin of these deformational structures with seismic shocks; thus, they can be called seismites. Hence, we provide strong evidence for accumulation of crevasse-splay sediments in the standing water of a backswamp area, and for tectonic activity in central Poland as the Middle Miocene lignite accumulated.

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Seismically induced soft-sediment deformation in crevasse-splay microdelta deposits (Middle Miocene, central Poland) – reply

Chomiak Lilianna, Maciaszek Piotr, Wachocki Robert, Widera Marek, Zieliński Tomasz

Geological Quarterly

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2019

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Vol. 63, No. 2

429--433

EN

We expected that our paper on the crevasse-splay microdelta (Chomiak et al., 2019) would arouse the interest of other researchers for at least two reasons. First, this is the first such palaeoform discovered and described within the Mid-Miocene lignite seam in Poland. Second, the microdelta siliciclastic deposits are strongly deformed both ductile and brittle. Therefore, we would like to thank Tom van Loon for his effort to comment on our article, including his words of appreciation, and above all, for pointing out some of the terminological and interpretative shortcomings. Our reply will be in line with the issues discussed in his comment.