Lignite Formation Research Articles

Regulation of energy properties and thermal behavior of bio-coal from lignocellulosic biomass using torrefaction

The energy properties in bio-coal, such as proximate analysis, element composition, high heat value, colour, thermal behavior are detailed elaborated. The results show bio-coal production processes from biomass can be divided into three stages which is close to coalification through the data in energy properties. The first stage called mild torrefaction (≤220 °C) seen as biomass to peat phase during coalification in the result of unstable oxygenated functional groups in hemicellulose are decomposed and Maillard reaction induces the colour modification. Second stage called moderate torrefaction (220–260 °C) seen as lignite formation process during coalification leads to degradation of celluloses. Biomass colour from brown to sepia due to the chromophoric groups. The heating value of maple sawdust (MS) increases to 30.02 MJ/kg of MS-260. Third stage called severe torrefaction (260–300 °C) considered as metamorphic episode of lignite to bituminous coal results of covalent bond cleavage, oxygenation of lignin and condensation of aromatic carbons. As functional groups decomposition during bio-coal production, three characteristic temperatures increase with the torrefied temperature increasing read from TG and DTG curves. The MS with the highest cellulose and aliphatic C–C bonds, is effective raw materials for bio-coal production by torrefaction with the close energy properties, thermal behavior to bituminous coals.

Clasts derived from rhizocretions in shallow-marine Miocene clastic deposits of northern Hungary: an example of zombie structures

Disc- and cylindrical-shaped clasts of fine-grained calcareous and ferruginous rock, each with a central tunnel, occur in shallow marine brackish Miocene sandy deposits of the Egyházasgerge Formation in Hungary. Previously, these have been interpreted as enigmatic biogenic (?) structures. After field and laboratory examination and comparisons with sub-recent rhizoclasts in subsoils developed on Quaternary fine-grained deposits in SE Poland, they are re-interpreted as redeposited rhizocretions possibly washed out of the coeval continental deposits of the Salgótarján Lignite Formation. Most are fragmented and abraded. They are termed rhizoclasts and are presented as an example of zombie structures inherited from another environment where they played a different role. Such rhizoclasts can be considered as an indicator of the source of the clastic material transported from a vegetated landmass on which moderate or poorly drained soils develop and plant roots penetrate the fine-grained substrate. In such soils, iron was mobilized, then fixed by oxidation, as the water table and oxygen levels fluctuated.

Sedimentology and foraminiferal paleoecology of the exposed Oligocene–Miocene Ogwashi-Asaba Formation in Issele-Uku area, Anambra Basin, southern Nigeria: A paleoenvironmental reconstruction

Sedimentological and foraminiferal paleoecological studies were carried out for the Oligocene–Miocene Ogwashi-Asaba Formation of the Anambra Basin at the Issele-Uku area in southern Nigeria, to reconstruct paleoenvironments. The pattern of rock successions and textural characteristics suggest the prevalence of fluvio-deltaic setting during the formation of lignites and clastic rocks of Ogwashi-Asaba Formation. Agglutinated benthic foraminiferal species such as Ammotium sp., Textularia sp., Gavelinella sp., Milliamina sp., Reophax sp., Bolivina sp., Eponides sp., Pseudobolivina sp. and Lenticulina sp. dominate the shale units whereas the planktonic forms are absent. All these species have very low population and diversity in the shales, which could be due to the presence of harsh conditions such as low oxygen level and scarcity of food, leading to poor survival. The assessments of benthic foraminifera's habitat suggest middle-to-inner neritic marine environment for the shales. Granulometric results suggest fluvial environment for the sandstone and deltaic for the lignite. The Ogwashi-Asaba Formation in Issele-Uku area of Anambra Basin, southern Nigeria, therefore, have records of shallow marine, and fluvio-deltaic paleoenvironments.

Source rock properties and kerogen decomposition kinetics of Eocene shales from petroliferous Barmer basin, western Rajasthan, India

Hydrocarbon exploration and production are going on in Barmer basin (Rajasthan, India) for more than a decade. The potential source rocks are of Paleocene – Eocene age, and Mesozoic siltstones form the reservoirs. The western and central portions of the Rajasthan basin are characterised by extensive lignite formations, which can be promising for artificial transformation to oil and gas. We study the source rock properties, depositional environments and hydrocarbon generation potential of the Paleogene lignitic shales of the Giral lignite mine and the Cretaceous Sarnu siltstones for their source and reservoir rock potentiality. The total organic carbon content (TOC) of the Giral samples range between 0.76 and 49.83 wt% and the thermal maturity, as reflected by the pyrolysis Tmax, lies between 412 and 468 °C. Sarnoo siltstones, on the other hand, have a very low TOC ranging from 0.02 to 0.08 wt% and a Tmax of 320–608 °C. The higher TOC and a lower oxygen index (OI) of Giral lignites and shaly lignites indicate the prevalence of a reducing depositional environment. Bulk organic geochemical parameters involving kerogen pyrolysis and thermal degradation kinetics indicate a more promising hydrocarbon generation potential in the lignite than shales, which, however exhibits higher thermal maturity of organic matter. Giral lignites as well as shales show dominantly Type-III heterogeneous kerogen, which is sourced from terrestrial organic matter. This is also corroborated by a broader distribution of activation energy derived from the thermal decomposition of the kerogen. The kerogen transformation ratio (KTR) and the hydrocarbon generation rate (HGR) suggest a considerably earlier and quicker kerogen transformation. Samples from the Sarnoo area offer no significant information on the source rock characteristics, due to their lean organic nature. However, lignites and shaly lignites of the Giral mine are identified as excellent candidates for their suitability towards easy conversion into hydrocarbon products through artificial techniques.

Decline of Neogene lignite formation as a result of vegetation and climate changes reflected in the middle Miocene palynoflora from the Ruja lignite deposit, SW Poland

The paper presents results of a palaeobotanical investigation of the borehole core Komorniki 97/72 from the Ruja lignite deposit, Lower Silesia. In the deposit lignites of three (2nd Lusatian, 2nd A Lubin, and 1st mid-Polish) middle Miocene groups of seams are present. The lignites of the 1st and 2nd groups are important correlation horizons throughout much of the Polish Lowlands and eastern Germany. The results of the palynological studies (spore–pollen, algae and fungi) and plant macroremains studies show that during the mid-Miocene mires' development, the vegetation was characteristic of wetlands (i.e., swamp and riparian forests, shrub bogs, and reed marshes) as well as mesophytic forests. The results were also used for palaeoclimatic investigation. The mean annual temperature (MAT), for each of the three sections, based on the coexistence approach (CA) method, was estimated in the range of 15.7–17.8 °C. Nevertheless, the frequency of thermophilous (palaeotropical and palaeotropical/warm-temperate) taxa indicate climate changes during the formation of the studied sediments. Composition of the spore–pollen spectra from the 2nd Lusatian seam (i.e., the presence of Meliaceae and Sapotaceae, which currently have pantropical distribution) show that the climate was humid and warm, close to subtropical. Later, many palaeotropical taxa disappeared, and the composition of the spore–pollen spectra indicates a warm temperate climate with slight fluctuations. Above the 1st mid-Polish seam, the climatic conditions changed in a way that did not favor the further formation of lignite deposits. These results correspond with the current understanding of climate change in the middle Miocene in Europe.

Paleoenvironmental, paleovegetational, and paleoclimatic changes during Paleogene lignite formation in Rajasthan, India

Paleoenvironmental, paleovegetational, and paleoclimatic changes during Paleogene lignite formation in Rajasthan, India

Geologic and Geochemical Features of Cretaceous Ge-Bearing Lignites in the Yenisei Middle Reaches

Abstract —Integrated geological and geochemical studies were performed for lignite from the Yenisei middle reaches, represented by carbonized fragments of trees with high germanium contents. Geochemical characteristics of terrigenous sediments with Ge-bearing lignite are determined. The chemical and mineral compositions, textures, and structures of carbonized wood fragments were studied. Scanning of individual cross sections of lignite fragments has revealed a regular distribution of germanium and impurity elements. Consistent patterns of the formation of Ge-containing lignites have been established, as well as the processes of their posthydrothermal transformation, which led to the impoverishment of the primary contents of the valuable component and to the input of a number of impurity elements. The latter formed rims over the lignite fragments and microveinlets with sulfide mineralization. The hypothesis has been put forward that germanium mineralization formed in lignites of the Kas basin, in particular, the Serchanskoe deposit.

Lignite oxidation under the influence of glacially derived groundwater: The pyropissite deposits of Zeitz-Weißenfels (Germany)

The Middle Eocene lignites of the Zeitz-Weißenfels coal mining area in central Germany hosted one of the most economically successful lithotypes of lignite deposits utilised in the paraffin industry of the 19th century, i.e. the pyropissite deposits. However, due to their economic significance, these rare lithotypes were almost completely mined out, such that presently only a few remnant deposits are known. Apart from the Zeitz-Weißenfels coal mining district, other pyropissite deposits were also encountered in other lignite mines, for instance, in the Hessian and Subhercynian Basins.Pyropissite is a whitish and bitumen-rich variety of soft brown coal (lignite) lithotypes, dominated by a homogeneous matrix with loosely embedded organic and inorganic components. Fresh exposure of pyropissite at Grana was logged and studied petrographically and geochemically, along with samples obtained from archival collections. Results were compared with those from the 19th and 20th century to derive general conclusions regarding origin and formation of pyropissite.Microscopically, the main constituent of this special lignite lithotype is amorphous to detrital in appearance. According to W. Schneider the term xanthinite is applied to this component, which forms the groundmass of the pyropissite. It contains high proportions of liptinitic substances with contributions of formless huminitic material and minor amounts of mineral matter. Geochemically, pyropissite is characterised by an increased H/C atomic ratio and a very high content of bitumen (in terms of toluene-soluble components) as well as low-temperature carbonisation tar.The obtained data revealed that the extraordinarily high content of liptinite and the paucity of huminitic material of the pyropissite deposits of the Zeitz-Weißenfels coal mining area are not related to primary depositional processes but rather are the result of dissipation of high condensed huminites and the consequent enrichment of liptinitic substances. The mechanism involves oxidation by groundwater and is related to glaciation processes operating during the Pleistocence. Such glacially derived processes also account for both vertical and horizontal distributions of the pyropissite.Thus, recent research activities may also serve as an innovative inspiration to fundamental understanding of the formation of lignites with extremely high liptinite content.

Paleoenvironment of Eocene lignite bearing succession from Bikaner-Nagaur Basin, western India: Organic petrography, palynology, palynofacies and geochemistry

Lignite and associated shale samples from the Matasukh mine of western India have been studied by petrographic, palynofacies, palynological and organic geochemical parameters. The objective is to understand the floral (organic) composition, and palaeo depositional conditions (ecology and climate) of the lignite-bearing sequence. Petrographically, the low rank B lignites are dominantly composed of huminite macerals, followed by moderate liptinite and low inertinite macerals. The predominance of detrohuminite (attrinite+densinite) with respect to telohuminite (textinite+ulminite) suggests that the woody vegetation has undergone higher degree of degradation during the peat accumulation, as is also indicated by the frequent occurrence of funginite. The TPI, GI, GWI and VI indices point towards limno-telmatic condition of the palaeomire during the deposition of lignite-forming peat under mesotrophic to rheotrophic basin conditions. The reducing conditions in the depositional site are evident from the frequent pyrite content. The studied samples had a high organic matter yield, which showed a co-dominance of phytoclasts and AOM. This nexus is indicative of a marginal marine depositional environment, also evident from Tyson's APP diagram. The palynofloral assemblage is dominated by angiosperm pollen, especially those having affinity with the family Arecaceae. The presence of palynomorphs of the family Dipterocarpaceae indicates the existence of rain-forest vegetation in the vicinity of the depositional site. The degradation products of oleanane and 23-norlupane in the sediment extracts also suggest that the angiosperm dominant higher plants served as the source for the peat-forming biomass. The presence of hopanes indicates high microbial activity during the formation of lignites. The high CPI and TAR values also indicate the large input of terrigenous higher plant materials.

CONTRIBUTION OF LIGNITE IN THE GREEK ECONOMY

The objective of the present work is the assessment of the lignite contribution to the energy balance of Greece, according to the creation processes and the chronological classification. The lignite deposits known so far in Greece have been discovered and researched from the scientists of IGME in the course of evolution since 1948 (Greek Geological Survey), 1950 (Institute of Geology and Surface Research), 1973 (National Institute of Geological and Mineral Exploration) and finally in its current form in 1976 (Institute of Geology and Mineral Exploration) and are divided into (a) “productive”, (b) future “productive” and (c) no financial interest in power generation. A project, co-financed by the Greek Government and the European Union, is currently implemented, aiming at the recovery of the latter in non-electrical purposes with very good results in the first stage of research. According to the works carried out so far it has been observed that lignite formation started in Greece during Eocene and continued to date. From 1950 until today there is an upward trend in lignite reserves. Lignite generates electricity at a rate 63% today with higher rates 79.3%, during 1994. In Greece 41% of lignite deposits were created during Miocene. However, only 13% of these deposits that contribute to electricity generation derive from economically exploitable reserves. In Greece, due mainly to use of lignite for electricity production, the cost of Kw/h for both domestic use and for industrial is below the European Union average.

A sequence stratigraphic investigation of a Miocene formation supported by coal seam quality parameters – Central Paratethys, N-Hungary

A stratigraphic investigation of the coal-bearing Miocene siliciclastic succession in structurally dissected basins of Northern Hungary was performed based on log correlations and is supported by coal petrology and sulphur data. The succession represents the Karpatian lower order global eustatic cycle of the Paratethys and was dissected into six higher order sedimentary sequences (sq-1 – sq-6). The coal-bearing strata in the Nógrád Basin (sq-1 – sq3) represent a lowstand systems tract (LST) prior to the Karpatian relative sea level rise. The transgressive systems tract (TST) starts with the ‘Oncophora Beds’ (sq-4) accumulated above a regional unconformity and containing coal beds in the Borsod Basin. The TST is superimposed by tectonically-forced higher order lowstand systems tracts (sq-5, sq-6) containing coal beds only in the relatively elevated East Borsod Basin.To support the sequence stratigraphic model, the average maceral and sulphur content of coal seams was also interpreted. The low sulphur (0.47%) content in sq.-1 reflects the lowstand environment determined by continental derived freshwater input. Transitional sulphur contents (0.66%–1.02%) in the late lowstand (sq-2 and sq.-3) indicate occasional saline invasions related to relative sea level rises. High (2.3%–2.6%) sulphur contents in the TST (sq-4) were caused by regular seawater inundations into the lagoon, while decreasing sulphur contents in sq-5 and sq-6 (2.28%–2.09%) reflect the increasing rate of freshwater income in association with the stepwise basinward shifts of the shoreline and the lagoonal facies. Within the Lower to Middle Miocene Salgótarján Lignite Formation, the analysis of coal seams contributed to the interpretation of relative sea level changes, and the sequence stratigraphic context facilitated both the interpretation of sulphur content in coals and the reliable correlation of coal seams.

Characteristics of Naturally Grown Biofilms in Deep Groundwaters and Their Heavy Metal Sorption Property in a Deep Subsurface Environment

ABSTRACTTwo biofilm samples were collected from anaerobic groundwater in the depth range of 158.8–199.4 m in a borehole drilled in the Tono area, Japan, to understand their effects on the migration behavior of heavy metals in subsurface environments. The depth range is featured geologically by the lignite formation of sedimentary rocks that bear a uranium ore and the underlying granitic formation. Microbiomes of the derived biofilms, as well as of the ambient bacterioplankton, were characterized based on 16S rRNA gene sequences (clones) or phylotypes, and their heavy metal sorption properties were examined with reference to geochemical features of groundwaters. Phylotypic compositions of the four microbiomes, i.e., of biofilm vs. planktonic bacteria as well as in granitic vs. sedimentary rock groundwaters showed significant differences. In addition, each microbiome was dominated by one or two distinctive phylotypes. In bacterioplankton, the phylotype related to a betaproteobacterial environmental clone dominated 54% of the sequenced clones derived from sedimentary rock groundwater, whereas those related to Denitratisoma oestradiolicum and Clostridium sp. dominated 45% and 37%, respectively, of the clones derived from granitic groundwater. In biofilms, the phylotypes related to Methylobacillus flagellatus and Ignavibacterium album accounted for 77% and 78% of the clones of the biofilms derived from the sedimentary rock and granitic groundwaters, respectively. Chemical and mineralogical analyses demonstrated that high amounts of heavy metals such as Fe, Ni, Cu, Zn, As, Cd, Pb, Th and U accumulated in the biofilms; and their sorption properties varied between biofilms presumably with influences of co-occurring Fe-hydroxides and sulfide minerals under the redox conditions of approximately −360 to 0 mV in subsurface environments. The biofilm-mineral interaction provides an implication for possible retardation of radionuclide migration in subsurface hydrology, which is of practical interest in geological disposal systems for high-level radioactive waste.

Reprint of “The possibility of underground gasification of lignite from Polish deposits”

The paper focuses on the possibility of underground gasification of lignite from Polish deposits. Lignite deposits in Poland are part of the European Lignite Formation. The profile of coal bearing sediments in Poland is several hundred meters (Paleocene–Pliocene), but it is fragmented vertically and is not complete at any point. It includes marine and brackish sediments, as well as Paleogene and Neogene land sediments. Lignite deposits originated both in platform areas and sedimentary basins in orogenic belts. The coals form extensive seams or lenses ranging from few meters to several dozen meters in thickness. There are 90 documented lignite deposits in Poland.Currently, geological resources of lignite are about 26,132Mt. On the Polish Lowland, ten lignite (eight major and two accompanying) seams have been distinguished within the Paleogene and Neogene stratigraphic columns. Only three of them (1st Mid-Polish, 2nd Lusatia, 3rd Ścinawa), and locally-five (additionally 2ndA Lubin and 4th Dąbrowa) are important from the economic point of view.The annual production of lignite in Polish open cast mines amounts to 65.0Mt per year, while it is primarily used by power plants. However, chemical processing of lignite is not yet developed. It is planned that pilot plants are to be developedfor underground lignite gasification in the near future. The geological structure of the Tertiary coal-bearing formation in the Polish Lowland was the basis for the development of guidelines and parameters for criteria verification of resource base (ortho-lignite) for underground coal gasification (UCG) in Poland. Lignites from the Polish coal deposits havethe characteristics of low rank coal (mean Rr 0.2–0.35), an average carbon content at around 62–65% C, high moisture content (>50%) and net calorific value (NCV) 6–20MJ/kg (mean 8.0MJ/kg).Petrographic composition of lignite (>80% humic components) makes it a preferred material for chemical processing. The available resources and lignite deposits have been verified on the basis of the assumed geological and technological criteria. Since the geologic and reservoir conditions are accompanied by the requirements of environmental protection, protection of groundwater reservoirs of drinking water and distance requirements between the gasification plants and residential buildings, roads and transmission lines, a significant reduction in coal resources suitable for underground gasification in Poland occurred. The aforementioned criteria were applied to the initial verification of lignite resources in the Polish deposits. The deposits useful for underground gasification are mainly located in the area from Głogów up to Ściniawa and Legnica. Some individual deposits are scattered in different locations (e.g. Węglewice, residual part of the Turów deposit).

The possibility of underground gasification of lignite from Polish deposits

The paper focuses on the possibility of underground gasification of lignite from Polish deposits. Lignite deposits in Poland are part of the European Lignite Formation. The profile of coal bearing sediments in Poland is several hundred meters (Paleocene–Pliocene), but it is fragmented vertically and is not complete at any point. It includes marine and brackish sediments, as well as Paleogene and Neogene land sediments. Lignite deposits originated both in platform areas and sedimentary basins in orogenic belts. The coals form extensive seams or lenses ranging from few meters to several dozen meters in thickness. There are 90 documented lignite deposits in Poland.Currently, geological resources of lignite are about 26,132Mt. On the Polish Lowland, ten lignite (eight major and two accompanying) seams have been distinguished within the Paleogene and Neogene stratigraphic columns. Only three of them (1st Mid-Polish, 2nd Lusatia, 3rd Ścinawa), and locally-five (additionally 2ndA Lubin and 4th Dąbrowa) are important from the economic point of view.The annual production of lignite in Polish open cast mines amounts to 65.0Mt per year, while it is primarily used by power plants. However, chemical processing of lignite is not yet developed. It is planned that pilot plants are to be developedfor underground lignite gasification in the near future. The geological structure of the Tertiary coal-bearing formation in the Polish Lowland was the basis for the development of guidelines and parameters for criteria verification of resource base (ortho-lignite) for underground coal gasification (UCG) in Poland. Lignites from the Polish coal deposits havethe characteristics of low rank coal (mean Rr 0.2–0.35), an average carbon content at around 62–65% C, high moisture content (>50%) and net calorific value (NCV) 6–20MJ/kg (mean 8.0MJ/kg).Petrographic composition of lignite (>80% humic components) makes it a preferred material for chemical processing. The available resources and lignite deposits have been verified on the basis of the assumed geological and technological criteria. Since the geologic and reservoir conditions are accompanied by the requirements of environmental protection, protection of groundwater reservoirs of drinking water and distance requirements between the gasification plants and residential buildings, roads and transmission lines, a significant reduction in coal resources suitable for underground gasification in Poland occurred. The aforementioned criteria were applied to the initial verification of lignite resources in the Polish deposits. The deposits useful for underground gasification are mainly located in the area from Głogów up to Ściniawa and Legnica. Some individual deposits are scattered in different locations (e.g. Węglewice, residual part of the Turów deposit).

PRINCIPLES OF ALLOCATION AND SPACE-TIME LIMITS OF CENOZOIC BROWN COAL FORMATIONS IN SOUTH-WESTERN PART OF EAST EUROPEAN PLATFORM

The Paleogene-Neogene lignite formations were allocated substantiating the characteristics of their composition, structure, distribution, development, and relationships with adjacent no-coals formations Given the significant geological study materials Cenozoic industrial coal-bearing deposits within the coating megastructures southwestern part of the East-European platform.

Rudabànya: Taphonomic analysis of a fossil hominid site from Hungary

The late Miocene deposits at Rudabànya, Hungary, were laid down in a shallow valley sloping westwards from a range of hills and opening out into the Pannonian Lake. Rise and fall of lake level gave rise to varying conditions, from dry land with soil formation to swamp and lake. The stratigraphic and palaeontological succession has been investigated at one of the sites, Rudabànya 2, where two cycles of deposition and erosion are represented, with soil formation, swamp conditions with lignite formation, and periods of extended high lake level succeeding each other. Both mammal and plant fossils are present at several levels. Taphonomic modifications in the Rudabànya 2 vertebrate faunas include losses of skeletal elements through carnivore selection, fluvial sorting at some levels, and post-depositional destruction by leaching and/or acid soils. The lowest level, the lower lignite, has few fossils. The fossil mammals from the level above, the grey marl, are the least modified but they are mixed with abraded, probably allochthonous, bone fragments and more complete specimens resulting from near-lake deaths. Modifications of bones by carnivores are indicated, but the specimens were too broken post-depositionally for the impact of the carnivores to be assessed. Carnivore action is also indicated for the fauna of the black clay which formed on the surface of the grey marl. The fauna consists of relatively abundant small mammals and the primates Anapithecus hernyaki and Dryopithecus hungaricus, with the latter much less common. The predator accumulating the smaller species was probably a viverrid. The red marl fauna is a transported assemblage from higher up the valley with the fossils extremely fragmentary and abraded and few identifiable specimens, almost all of which are teeth. The black mud fauna is also probably a transported assemblage, lower energy than the red marl environment, and the bones are much modified subsequently by acid corrosion similar to that seen today in bone preserved in peat bogs. Dryopithecus is a major constituent of the fauna, with Anapithecus less common. D. hungaricus is thus associated more strongly with swamp forest and shallow riverine conditions with low energy movement of water, and A. hernyaki is associated with lake shore (probably forest) conditions, accumulating in lake sediments and lake-flat sediments. The palaeoecology of the area as a whole, based on the associated flora and fauna, is a combination of swamp forest, lake shore forest and open mud flats.

In situ preservation and paleoenvironmental assessment of Taxodiacea fossil trees in the Bükkalja Lignite Formation, Bükkábrány open cast mine, Hungary

In summer 2007 sixteen Taxodium tree trunks were found in situ standing position in the Bükkábrány open cast mine. The fossil trees were exposed during the excavation of the overburden layers of the Bükkalja Lignite Formation (BL). The Bükkábrány discovery is a global novum because the trees are very well preserved but not fossilized that makes the most detailed and direct analysis feasible. In spite of the 7–8 million years passed, the actual site and the host formation is rather intact, lacking tectonic deformations, deeper burial and/or dewatering during uplift. Organic petrology of tree trunks and sedimentology of the overburden sands are the subjects of this study. The extremely good preservation of fossil trunk tissues, presence of high amount of cellulose and moisture content along with the slightly gelified state of the wood and the lack of deformation indicate that there was only limited alteration during the early diagenesis. Chemical investigation of standing trunks fossil driftwood nearby the Late Miocene trees, and the fossil woods in the underlying lignite have revealed that their cellulose and total phenol concentrations were significantly lower than in intact recent trees, applied for reference. Yet their preservation levels were quite high, also proving that the chemical degradation of the fossil wood tissues had not been taken place extensively in the mire and the trees remained exceptionally well preserved. Sudden burial of the trees by strand plain sand beds indicates flooding by heavy storms or tsunamis, which interrupted and terminated the peat formation and preserved the trunks from later oxidation and biodegradation.

Truncated higher order sequences as responses to compressive intraplate tectonic events superimposed on eustatic sea-level rise

High resolution sequence stratigraphic analysis of the lignite-bearing Miocene siliciclastic sequence of the Salótarján Lignite Formation (SLF) has been performed by lithostratigraphic dissection of more than 1350 boreholes and by detailed analysis of well logs from more than 150 boreholes. Biostratigraphic data indicate that the SLF represents a single 3rd order eustatic sequence, namely the Bur-4 of Vakarcs et al. [Vakarcs, G., Hardenbol, J., Abreu, V.S., Vail, P.R., Várnai, P., Tari, G., 1998. Oligocene–Middle Miocene depositional sequences of the central paratethys and their correlation with regional stages. SEPM Special Publication vol. 60, 209–231]. As for facies conditions, facies models for sandy shorefaces and/or wave dominated deltas can be applied. Twenty-six parasequences have been identified and mapped in the adjacent sub-basins from well-log correlations. The sharp-based sand bodies of ps. 10 and 17 were interpreted as the falling stage systems tract (FSST) of higher order sequences. The subsequent transgressive systems tracts (TST) are represented by retrograding sets of 2–3 parasequences (ps. 11–13, 18–19). Based on the regional unconformity at the base, and the regionally extended sharp-based sand bodies, three sequence boundaries (SB) were determined that dissect the 3rd order sequence into three higher order sequences. One of the special features of the sequence is that the FSSTs interrupt the rapid relative sea-level rises (ps. 9 and 16) and lie directly on the silty material of nearshore environments, leading to the lack of the higher order highstand system tracts (HST) (‘truncated transgressive semi-cycles’). Another characteristic is the striking basinward fore-stepping of the sedimentary depocentres and that of the facies belts of the lignite seams. The rapid relative sea-level falls implied by the two FSSTs are unexpected in the context of an overall eustatic rise, thus the possibility of tectonic origin of shallowing was investigated. This verification was based primarily on the observations that (1) the basin was united when parasequences 1 to 13 were developed, whereas (2) by the end of the sequence development the Palaeozoic basement protruded to the surface, dividing the basin, reflecting intense tectonic events simultaneous with sequence development. The FSSTs with the SBs above and the formation of higher order sequences can thus be regarded as sedimentary responses to syn-sedimentary tectonic elevation and tilting of the basement. This elevation was induced by tectonic compression and associated imbrication along a regional reverse fault that was known as the Darnó Line. The imbrication could have controlled not only the repeated relative sea-level falls but also the striking fore-stepping of the sedimentary depocentres and facies belts of the associated lignite seams. Tectonic tilting influenced not only the FSSTs, but the subsequent early TSTs as well, thus lignite seams associated with the tectonically counteracted TSTs are characterized by multiple seams with several accessory seams (Va, IIIa, b and Ia), while those associated with tectonically quiescent periods are aerially extensive and solitary. Comparison with other coal bearing formations enhanced the importance of the FSST in the interpretation of stratigraphic truncations, coal seam geometry conditions, facies shiftings and stratal geometry, enabling a more accurate description of syn-sedimentary tectonic events.

A short-term establishment of forest fen habitat during Pliocene lignite formation in the Ptolemais Basin, NW Macedonia, Greece

The intermontane basin of Ptolemais is part of a major tectonic trench, located in NW Greece and includes around 65% of Greek coal reserves. The Upper Xylite Layer (UXL) is a distinct lignite layer, being 3–6 m thick and outcropping in the upper part of the Pliocene Lignite-bearing Sequence at the Notio Field and Tomeas Eksi Mines of Ptolemais. Compared with the xylite-rich lithotypes, the matrix lithotypes within UXL contain more ash. Micropetrographic studies suggest that the Upper Xylite Layer is rich in huminite (>90%). Textinite dominates in the xylite-rich lithotypes, while attrinite dominates in the matrix lithotypes. The liptinite content is <10%, while inertinite rarely occurs. Palaeobotanical determination revealed that the xylite-rich coal originated from Coniferous vegetation, specifically from Glyptostrobus europaeus. The occurrence of G. europaeus as a coal-forming element is significant because, though this kind of vegetation was common in many Greek coals of Miocene age, this is the first time it has been recorded from the Pliocene. This study suggests that the Upper Xylite Layer is autochthonous. According to coal-facies diagrammes, peat accumulated under pure telmatic conditions in a relatively wet forest fen. Both herbaceous and arboreal vegetation contributed to peat formation.

EARLY STAGES OF LIGNITE FORMATION IN PTOLEMAIS BASIN: A COAL-PETROGRAPHIC APPROACH

With the present study it is intended to assess the depositional palaeoenvironment of the lower part of the Lignite-bearing Sequence in the Ptolemais Basin, and more specifically in the areas of Notio-Field and Tomeas-6 open pits. The sediments under study represent the seam between the Volcanic Tephra Layer and the Basal Marl, which constitute the roof and the floor, respectively. Coal-petrographic results showed that Huminite is the main macerai group (84-96%), while macérais from Liptinite and Inertinite groups display low values (&lt;10%). In bulk lignite samples the main mineral phases are quartz, calcite, clay minerals and feldspars, while in the ashes the main phases are quartz, anhydrite and lime. The palaeoenvironment of the lignite formation was reconstructed using the lithological, coalpetrographic and mineralogical data, as well as coal-facies diagrammes. In Notio-Field Mine, at the early stages of lignite formation the conditions used to be limnotelmatic, while in Tomeas-6 Mine they were telmatic. Upwards the conditions turned to more telmatic in both mine areas. The vegetation was mainly herbaceous with some arboreal elements occurring mostly in Tomeas-6 area. The water influx was generally intense resulting in enhanced inorganic input