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Geological peculiarities from the Konin Lignite Mine, central Poland: An overview

Wachocki Robert, Chomiak Lilianna, Klęsk Jakub, Maciaszek Piotr, Urbański Paweł, Widera Marek, Zieliński Tomasz

Geologos

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2025

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Vol. 31, No. 1

31--43

EN

The 80th anniversary (1945–2025) of the Konin Lignite Mine (KLM) invites some summaries of the mine’s characteristics. Therefore, the current study is devoted to rocks/sediments and tectonic or sedimentary structures that were observed and examined in lignite opencasts in the vicinity of the town of Konin. Some of them can be considered wonders and/ or curiosities of nature, some are unique, and others are quite common. Hence, they were generally defined as geological peculiarities in this article. In stratigraphic order they are sandstones, cleats, crevasse splays, palaeochannels and palaeosols. They represent various lithostratigraphic units (formations and members) of the Neogene of central Poland, while their age ranges from the Early Miocene to the earliest Pliocene. Among the listed objects, quartzite sandstones (situated below and between the lignite beds) and palaeosols in the Poznań Clays are very common, known from other lignite opencasts in Poland. In the case of cleats and crevasse splays occurring within the lignite seam exploited by the KLM, they are among the most numerous and best developed of all lignite-bearing formations in the world. On the other hand, the presence of palaeochannels in fine-grained sediments, constituting the overburden of the exploited lignite seam, provides additional and convincing evidence for the fluvial origin of the Poznań Clays.

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„Rój” mioceńskich stożków krewasowych w Konińskim Zagłębiu Węgla Brunatnego, Polska środkowa – stan wiedzy

Chomiak Lilianna, Dziamara Mariusz, Klęsk Jakub, Wachocki Robert, Widera Marek

Przegląd Geologiczny

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2024

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Vol. 72, nr 5

215--224

EN

In the years 2015-2022, at least several relatively large lenses of inter-lignite sands were discovered and examined in lignite opencast mines near Konin in central Poland. They were interpreted as crevasse splays formed on the surface of Mid-Miocene mires (backswamps) during periodic floods. Due to the compaction of peat and the tectonic activity of the current lignite-rich deposit areas (grabens), the crevasse splays represent various genetic-facies types and subtypes. They may be single or numerous palaeoforms creating complexes of crevasse splays. Unfortunately, these inter-lignite sand bodies pose a significant obstacle to mining activities. Nevertheless, in relation to single fossil splays described in world literature, the abundance of such palaeoforms in the vicinity of Konin allows them to be jokingly called a “swarm” of Miocene crevasse splays.

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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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Architektura i geneza iłów w górnym poziomie węgli brunatnych formacji poznańskiej (środkowy miocen) : Odkrywka Tomisławice k. Konina w środkowej Polsce

Chomiak Lilianna, Urbański Paweł, Widera Marek

Przegląd Geologiczny

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2020

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Vol. 68, nr 6

526--534

EN

In the Tomisławice opencast mine, owned by the Konin Lignite Mine, a relatively widespread (>1.5 km2) and thick (up to 80 cm) layer of clay occurs within the first mid-Polish lignite seam. These fine-grained sediments are interpreted as deposited in a long-lasting lake that existed in the mid-Miocene backswamp area. Due to the exploitation of this seam forelectricity production, interbeddings of clastic sediments significantly reduce the quality of lignite. Currently, lignite is mined together with the clays in the Tomisławice opencast mine. Such procedure in extreme cases, where the maximum. thickness of the clay layer is up to 80cm, increases/may increase the ash content of the entire lignite seam almost twice. Therefore, selective lignite mining would be recommended, i.e. without clays, which unfortunately is not practiced due to technological and financial reasons.

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A comparative study of the oxide and elemental composition of ash from lignite burned at various temperatures – Konin Lignite Mine, Central Poland

Chomiak Lilianna, Widera Marek

Gospodarka Surowcami Mineralnymi

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2020

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T. 36, z. 4

145--160

EN

Lignite still plays a key role in the production of electricity in Poland. About one-third of domestic electric energy comes from lignite burned in large power plants that produce megatons (Mt) of bottom ash and fly ash annually. Nearly 11 wt% of the total ash generated by the lignite-fired power industry in Poland comes from lignite extracted from the Konin Lignite Mine. Part of the ash escapes into the atmosphere, and the rest is utilized, which is expensive and often harmful to the environment; hence, geochemical studies of these ashes are fully justified and increasingly carried out. The lignite samples examined in this paper represent the entire vertical section of the first Mid-Polish lignite seam (MPLS-1) mined in opencasts at Jóźwin IIB, Drzewce, and Tomisławice. First, the samples were oxidized (burnt) at one of three temperatures: 100, 850, and 950°C; then the chemical composition of oxides and trace elements was determined according to the ASTM D6349-13 standard. The ashes were rich in SiO2 and CaO; Ba, Sr, and Cu dominated the trace element content. Among the harmful elements found, Pb is of most concern. Only a few elements (Ba, Cu, Pb, Sb) reached values higher than their corresponding Clarke values. Based on the results obtained, it can be concluded that the examined ashes are approximately as harmful to the environment as ashes from other lignite used to generate electricity. Moreover, the increased amount of CaCO3 in the MPLS-1 is beneficial in the process of natural desulphurization.

PL

W ostatnich latach około jednej trzeciej polskiej energii elektrycznej pochodzi z węgla brunatnego, który jest spalany w wielkich elektrowniach. Powoduje to produkcję popiołów (żużla paleniskowego i popiołu lotnego) w łącznej ilości wyrażonej w milionach ton (Mt). Blisko 11% wag. popiołu produkowanego przez polską energetykę opartą na węglu brunatnym pochodzi z węgla wydobywanego przez Kopalnię Węgla Brunatnego Konin. Oczywiście, popiół jest składnikiem niepożądanym w węglu z wielu względów. Część popiołu może przedostać się do atmosfery, a pozostałą część należy poddać utylizacji, co jest kosztowne i często szkodliwe dla środowiska naturalnego. Stąd badania geochemiczne tych popiołów wydają się celowe i dlatego są coraz częściej przeprowadzane. Badane w tej pracy uśrednione próbki węgla reprezentują cały profil pierwszego środkowopolskiego pokładu węglowego (MPLS-1) eksploatowanego w odkrywkach: Jóźwin IIB, Drzewce i Tomisławice. Te próbki zostały najpierw utlenione/spalone w temperaturze: 100, 850 i 950°C. Następnie został określony ich skład chemiczny (tlenki i pierwiastki śladowe) według normy ASTM D6349-13. Badane popioły cechują się dominacją SiO2 i CaO, zaś w składzie pierwiastków śladowych przeważają: Ba, Sr i Cu. Natomiast wśród pierwiastków szkodliwych najważniejszy jest Pb. Wreszcie, tylko kilka z analizowanych pierwiastków (Ba, Cu, Pb, Sb) osiąga wartości wyższe niż wartości odpowiednich klarków. Na podstawie uzyskanych wyników można stwierdzić, że badane popioły są w przybliżeniu tak samo szkodliwe dla środowiska jak popioły z innych węgli brunatnych używanych do wytwarzania energii elektrycznej, a zwiększona ilość CaCO3 jest też korzystna w procesie naturalnego odsiarczania.

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Variation of lignite ash in vertical and horizontal sections of mining walls in the Konin Lignite Mine, central Poland

Chomiak Lilianna

Geology, Geophysics and Environment

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2020

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Vol. 46, no. 1

17--28

EN

This paper focuses on the variations of lignite ash along selected sections and mining walls from three lignite opencast mines in central Poland. They are owned by the Konin Lignite Mine, where the first Mid-Polish lignite seam is being mined to produce electricity. Ash content in lignite is important because ash lowers the calorific value of the lignite. The results obtained are based on 266 samples of lignite collected from the Drzewce, Tomisławice, and Jóźwin IIB opencasts. All samples were tested according to ISO 1171 standard procedures, that is, they were first burned at a temperature of 850°C, then the ash content was determined on a dry basis (Ad ), before the basic statistical parameters were calculated. The studied lignite seam is characterised by a variable distribution pattern of ash both along selected vertical sections and lignite walls, as well as between the three opencasts. The ash content of individual samples ranged from 6.5 to 69.8 wt%, while the average content in opencast mines varied from 9.7 to 17.6 wt%. The coefficient of variation is large (80.23–96.33%) in the case of the Drzewce and Tomisławice, and low to average (14.53–37.75%) in the case of Jóźwin IIB. Significant ash enrichment of some beds is interpreted in this article as a consequence of floods occurring in a Mid-Miocene mire (backswamp), but also of chemical precipitation. When lignite is burned to generate electricity, a relatively large amount of ash is produced. Therefore, recognition of ash content in lignite, in addition to the chemical composition and phase of ash, is recommended to better protect the environment. At the first stage of protection, it can be best achieved by analysing field samples for ash content.

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Crevasse splays within a lignite seam at the Tomisławice opencast mine near Konin, central Poland: architecture, sedimentology and depositional model

Chomiak Lilianna

Geologos

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2020

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Vol. 26, No. 1

25--37

EN

The present article focuses predominantly on sandy deposits that occur within the Middle Miocene lignite seam at the Tomisławice opencast mine, owned by the Konin Lignite Mine. As a result of mining activity, these siliciclastics were available for direct observation in 2015–2016. They are situated between two lignite benches over a distance of ~500 m in the lower part and ~200 m in the higher part of the exploitation levels. The maximum thickness of these sandy sediments, of a lenticular structure in a S–N cross section, is up to 1.8 m. With the exception of a thin lignite intercalation, these siliciclastics comprise mainly by fine-grained and well-sorted sands, and only their basal and top layers are enriched with silt particles and organic matter. Based on a detailed analysis of the sediments studied (i.e., their architecture and textural-structural features), I present a discussion of their genesis and then propose a model of their formation. These siliciclastics most likely formed during at least two flood events in the overbank area of a Middle Miocene meandering or anastomosing river. Following breaching of the natural river levee, the sandy particles (derived mainly from the main river channel and levees) were deposited on the mire (backswamp) surface in the form of crevasse splays. After each flooding event, vegetation developed on the top of these siliciclastics; hence, two crevasse-splay bodies (here referred to as the older and younger) came into existence. As a result, the first Mid-Polish lignite seam at the Tomisławice opencast mine is currently divided in two by relatively thick siliciclastics, which prevents a significant portion of this seam from being used for industrial purposes.

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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.

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Various genetic types of end moraines in the city of Poznań and its close vicinity, central-western Poland

Widera Marek, Chomiak Lilianna

Civil and Environmental Engineering Reports

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2019

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Vol. 29, no. 3

218--227

EN

The current research focuses on explaining the origin of end moraines running through the northernmost districts of the city of Poznań. The highest hills, that is, the Moraska Hill and the Dziewicza Hill, are a stagnation record of the Vistulian Glaciation of the Poznań Phase. These two hills represent terminal moraines of similar height and age, but the mechanism of their formation is diametrically opposed. The Dziewicza Hill is a typical accumulative end moraine, where Pleistocene deposits over 70 m thick are undisturbed. On the other hand, the Moraska Hill is a classic example of a push end moraine with a relatively thin cover of Pleistocene sediments and glaciotectonically elevated (up to 130 m a.s.l.) upper Neogene deposits. In the latter case, these strongly deformed sediments are the so-called "Poznań Clays" that underlie the Quaternary deposits in the vast area of the Polish Lowlands.