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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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

This paper focuses on subaerial- and subaqueous-type crevasse splays in the lignite-bearing Mid-Miocene succession near the town of Konin in central Poland. During the formation of these floodplain forms arose on the surface of highly compactable peat, then transformed into lignite, in territories of at least intermittently active tectonics. Hence, both of these major types of crevasse splays are consistently divided into deformed and undeformed subtypes in this paper. All these types and subtypes are found within the first mid-Polish lignite seam (MPLS-1), which is mined for electricity production in the study area. The numerous borehole data and ongoing exploitation of the MPLS-1 allow the geological mapping and detailed facies analyses of the crevasse-splay sediments to be conducted in most cases. The crevasse-splay sandbodies studied in the Tomisławice and Jóźwin IIB lignite opencasts are small as they cover an area of <0.075–0.63 km2. Their maximum length reaches up to 0.9 km, whilst their maximum thickness obtained from the borehole is 5.3 m, and ca. 1.4–3 m as observed in the field. These sandy deposits were accumulated during overbank flooding on the Mid-Miocene mire (backswamp) surface under subaerial and/or subaqueous conditions. In the latter case, 'prograding splay deposits' are typical of crevasse-splay microdeltas. Due to the tectonic activity and high compaction properties of peat/lignite, the interseam sands sometimes underwent both ductile and brittle deformation. This allowed subtypes of the crevasse splays that split the currently mined MPLS-1 to be distinguished. In addition to the cognitive value, a better knowledge of the crevasse-splay sediments, their spatial distribution, and deposition mechanisms can be of great use for lignite extraction planning and operations. • Crevasse-splay sands are common in the Miocene lignite mined in central Poland. • These crevasse splays are easily divided into subaerial and subaqueous types. • Subsequently, deformed and undeformed subtypes are distinguished among them. • These sands were deposited on the 'dry' mire and/or in shallow lakes as microdeltas. • Some of the studied crevasse-splay sediments were syn-depositionally deformed. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

We reconstruct palaeoenvironmental conditions during the formation of the first Mid-Polish Lignite Seam (MPLS-1) of the Konin Basin of central Poland, which is of mid-Miocene age. In terms of macropetrography, the MPLS-1 comprises different lithotype associations, predominantly xylodetritic lignite, and represents the peat deposits of mires most likely inhabited by Myricaceae-Cyrillaceae shrubs. Palynological assemblages obtained from the MPLS-1 at the Adamów Lignite Opencast Mine indicate the existence of wetland/palustrine and mesophytic vegetation during the accumulation of the peat. Applying the Coexistence Approach to the palynological assemblages, climate is inferred to have been warm temperate and humid with a mean annual temperature (MAT) of 15.7–18.0 °C with plant communities similar to modern pocosins developed on coastal plains in southeastern USA. The palynological assemblages from the MPLS-1 at Jóźwin IIB Lignite Opencast Mine show palaeofloristic cyclicality. In the studied section, five cycles were identified, dominated by swamp forests (Taxodium/Glyptostrobus–Nyssa) similar to modern forests in southeastern USA and China. The climate at that time was warm temperate and humid (MAT = 15.7–20.5 °C) based on CA application. This is consistent with the significant contribution of warm temperate plants, typical of mixed mesophilous forests, which grew in the vicinity of the swamp forests. The results of geochemical analyses are generally in agreement with palaeobotanical studies, indicating angiosperm dominated the peat-forming vegetation. However, the geochemically-derived average temperature ranges of ca. 24.2–25.0 °C, based on the carbon preference index (CPI), is significantly higher. These differences between palynologically- and geochemically-derived MATs can be explained by the influence of changes in vegetation on the CPI values. The periodic contribution of algae and microorganisms to the biomass while the water table was raised is indicated by elevated abundances of short-chain n -FAs. In contrast, under acidic conditions, bacterial activity was limited, as indicated by ββ/(ββ + αβ) hopane ratios and low sulfur content. Based on sedimentological data, the MPLS-1 was mainly formed either proximal (Jóźwin IIB, Tomisławice) or more distal (Adamów) to the river channels as evidenced by the presence or absence of siliciclastic partings within the MPLS-1. In summary, the MPLS-1 accumulated mostly as low-lying mires under freshwater conditions, corresponding to the last peak of the Mid-Miocene Climatic Optimum and to the period thereafter when the climate showed a cooling trend. Our findings are placed in the context of palaeotectonics and palaeoclimates at regional and global scales. [Display omitted] • The first Mid-Polish Lignite Seam (MPLS-1) is mined in opencasts of central Poland. • This seam was originally developed in the dominant part as a low-lying mire. • The MPLS-1 was formed at different distances from the mid-Miocene river channels. • Tectonic and climatic changes had a decisive impact on the creation of the MPLS-1. • Its formation commenced during the last peak of the Mid-Miocene Climatic Optimum. [ABSTRACT FROM AUTHOR]