Inertinite-rich Tertiary coals from the Zeya–Bureya Basin, Far Eastern Russia

Selected Tertiary coals from the Zeya–Buryea Basin, Far Eastern Russia, were investigated for aspects of their coal type, rank, depositional environment and post-depositional history. The coals have been examined in outcrop (lithotype logging), microscopically (maceral, reflectance and fluorescence), and geochemically (proximate analysis).Two laterally extensive coal-bearing horizons occur: one of Palaeocene age and the other of early Miocene age. The Palaeocene coals were investigated in active open-cut mines at Raichikhinsk and Yerkovtsi and the early Miocene deposit in an abandoned open-cut mine at Cergeyevka.Palaeocene coals at Raichikhinsk and Yerkovtsi were indistinguishable from each other macroscopically, microscopically, and geochemically. The deposits were sufficiently coalified that brightness logging could be undertaken. Dull coals, with numerous fusainous wisps, were dominant. Four dulling-up sequences, which represent stacked peat deposits, were observed at Raichikhinsk. At Yerkovtsi, only a small section of the middle of the seam, which was mostly dull and muddy coal, was investigated. Petrographically, these coals were dominated by inertinite group macerals, which is unusual in non-Gondwanan coals and rare in the Tertiary. Rank classification was problematic with volatile matter (VM) content of vitrain (daf), macroscopic appearance, and microscopic textures suggesting subbituminous B rank, but carbon content, moisture content and specific energy indicating a lignite rank.Notwithstanding complications of rank, estimates of the maximum-range burial depths were calculated. Taking the VM (daf) content of vitrain as 48%, burial depth estimates range from 900 m for a high geothermal gradient and long heating time to a maximum of 3300 m for a low geothermal gradient and short heating time. These estimates are maxima as the coal rank may be lower than implied by the VM.The Cergeyevka deposit is a soft brown coal. Limited sampling of the upper-most portion indicated a high moisture content (75% daf) and an unusual, hydrogen-rich geochemistry. Lack of identifiable liptinites using either reflected light or fluorescence microscopy suggested a significant bituminite component. Otherwise, the coals appear to be typical for the Tertiary. An estimate of 125 m maximum burial depth was obtained using the bed-moisture content of the coal, which is around the present burial depth.Comparison of present-day thicknesses with inferred burial depths suggests that at least 500 m of section is missing between the Palaeocene coals and the early Miocene coals.Palaeoenvironmental considerations suggest that fire played a significant role in the accumulation of the peats at Raichikhinsk and Yerkovtsi. At Cergeyevka, peat accumulation ended by drowning of the mire.Two tuff beds were recognised within the seam at Raichikhinsk and one in the seam at Yerkovtsi. Correlation of the tuff beds is uncertain but they should prove useful in regional coal seam correlation and interpreting coal depositional environments. Geochemical analysis by XRF was complicated by high loss-on-ignition (LOI) values. Despite extensive alteration, an acid igneous source is implied from the presence of free quartz and TiO₂/Al₂O₃ ratios of 0.02 to 0.05.     

A high-latitude Gondwanan lagerstätte: The Permian permineralised peat biota of the Prince Charles Mountains,Antarctica

The Toploje Member chert is a Roadian to Wordian autochthonous–parautochthonous silicified peat preserved within the Lambert Graben, East Antarctica. It preserves a remarkable sample of terrestrial life from high-latitude central Gondwana prior to the Capitanian mass extinction event from both mega- and microfossil evidence that includes cryptic components rarely seen in other fossil assemblages. The peat layer is dominated by glossopterid and cordaitalean gymnosperms and contains moderately common herbaceous lycophytes, together with a broad array of dispersed organs of ferns and other gymnosperms. Rare arthropod–plant and fungal–plant interactions are preserved in detail, together with a plethora of fungal morphotypes, Peronosporomycetes, arthropod remains and a diverse coprolite assemblage. Comparisons to other Palaeozoic ecosystems show that the macroflora is of low diversity. The fungal and invertebrate–plant associations demonstrate that a multitude of ecological interactions were well developed by the Middle Permian in high-latitude forest mires that contributed to the dominant coal deposits of the Southern Hemisphere. Quantitative analysis of the constituents of the silicified peat and of macerals within adjacent coal seams reveals that whilst silicified peats provide an unparalleled sample of the organisms forming Permian coals, they do not necessarily reflect the volumetric proportions of constituents within the derived coal. The Toploje Member chert Lagerstätte provides a snapshot of a rapidly entombed mire climax ecosystem in the closing stages of the Palaeozoic, but prior to the onset of the protracted crisis that engulfed and overthrew these ecosystems at the close of the Permian.     

Anomalous gold contents in brown coals and peat in the south-eastern region of the Western-Siberian platform

One hundred twenty-two samples of Jurassic and Paleogene brown coals and 1254 peat samples from the south-eastern region of the Western-Siberian platform were analyzed for gold by the neutron-activation method. Mean content of Au in Jurassic coals is 30 ± 8 ppb, in Paleogene coals is 10.6 ± 4.8 ppb, and in peat is 6 ± 1.4 ppb. Concentrations of gold as high as 4.4 ppm were found in coal ash and 0.48 ppm in the peat ash. Coal beds with anomalous gold contents were found at Western-Siberian platform for the first time.Negative correlation between gold and ash yield in coals and peat and highest gold concentrations were found in low-ash and ultra-low-ash coals and peat. Primarily this is due to gold's association with organic matter.For the investigation of mode of occurrence of Au in peat the bitumen, water-soluble and high-hydrolyzed substances, humic acids, cellulose and lignin were extracted from it. It was determined that in peat about 95% of gold is combined with organic matter. Forty to sixty percent of Au is contained in humic acids and the same content is in lignin. Bitumens, water-soluble and high-hydrolyzed substances contain no more than 1% of general gold quantity in peat.The conditions of accumulation of high gold concentrations were considered. The authors suggest that Au accumulation in peat and brown coals and the connection between anomalous gold concentrations and organic matter in low-ash coals and peat can explain a biogenic–sorption mechanism of Au accumulation. The sources of formation of Au high concentration were various Au–Sb, Au–Ag Au–As–Sb deposits that are abundant in the Southern and South-Eastern peripheries of the coal basin.     

Petrography and geochemistry of Carboniferous coal seams in the Donets Basin (Ukraine): implications for paleoecology

The Carboniferous succession in the Donets Basin hosts about 130 seams, each with a thickness over 0.45 m. Nine economically important seams from the (south)western Donets Basin are studied using organic petrographical, inorganic geochemical, and organic geochemical techniques. The main aim of the study is the reconstruction of peat facies of Serpukhovian (Mississippian) and Moscovian (Middle Pennsylvanian) coals.Formation of major coal seams commenced during Serpukhovian times. Early Serpukhovian coal accumulated in a relatively narrow shore-zone and is rich in inertinite and liptinite. Very low ash yields, low to moderate sulphur contents, and upward increasing inertinite contents suggest coal deposition in raised mires.Moscovian coal has a significantly wider lateral extension and is generally rich in vitrinite. Coal properties vary widely in response to different peat facies. Low-sulphur, low-ash k₇ coal was formed in a raised mire or in a low-lying mire without detrital input. l₁ and l₃ seams containing several fluvial partings were formed in low-lying mires. Both seams are more than 2 m thick. Seams m₂ and m₃ contain high-sulphur coal, a consequence of deposition in a peat with marine influence. In contrast, syngenetic sulphur content is low in the m₅^{1 upper} seam, which was formed in a lacustrine setting. The late Moscovian n₁ seam, up to 2.4 m thick, accumulated in a swamp with a vegetation rich in bryophytes and pteridophytes. The properties of the n₁ seam are transitional between those of Serpukhovian and other Moscovian seams. Differences in maceral composition between Serpukhovian and Moscovian coals probably reflect changes in climate and vegetation type.Tuff layers are observed in the l₁, l₃, and m₃ seams. The l₃ and m₃ seams contain abundant authigenic quartz. Trace element contents are high in many seams. As contents are especially high in seams c₁₀², k₇, l₃ and m₃. Ash in the l₃ seam contains up to 8000 ppm As. Co is enriched near the base of several seams. Maxima up to 2400 ppm occur in the ash of the k₇ and l₃ seams. Cd contents in ash are frequently as high as 30 or 40 ppm.     

Organic petrology of Paleocene Marcelina Formation coals, Paso Diablo mine, western Venezuela: Tectonic controls on coal type

About 7 Mt of high volatile bituminous coal are produced annually from the four coal zones of the Upper Paleocene Marcelina Formation at the Paso Diablo open-pit mine of western Venezuela. As part of an ongoing coal quality study, we have characterized twenty-two coal channel samples from the mine using organic petrology techniques. Samples also were analyzed for proximate–ultimate parameters, forms of sulfur, free swelling index, ash fusion temperatures, and calorific value.Six of the samples represent incremental benches across the 12–13 m thick No. 4 bed, the stratigraphically lowest mined coal, which is also mined at the 10 km distant Mina Norte open-pit. Organic content of the No. 4 bed indicates an upward increase of woody vegetation and/or greater preservation of organic material throughout the life of the original mire(s). An upward increase in telovitrinite and corresponding decrease in detrovitrinite and inertinite illustrate this trend. In contrast, stratigraphically higher coal groups generally exhibit a ‘dulling upward’ trend.The generally high inertinite content, and low ash yield and sulfur content, suggest that the Paso Diablo coals were deposited in rain-fed raised mires, protected from clastic input and subjected to frequent oxidation and/or moisture stress. However, the two thinnest coal beds (both 0.7 m thick) are each characterized by lower inertinite and higher telovitrinite content relative to the rest of Paso Diablo coal beds, indicative of less well-established raised mire environments prior to drowning.Foreland basin Paleocene coals of western Venezuela, including the Paso Diablo deposit and time-correlative coal deposits of the Táchira and Mérida Andes, are characterized by high inertinite and consistently lower ash and sulfur relative to Eocene and younger coals of the area. We interpret these age-delimited coal quality characteristics to be due to water availability as a function of the tectonic control of subsidence rate. It is postulated that slower subsidence rates dominated during the Paleocene while greater foreland basin subsidence rates during the Eocene–Miocene resulted from the loading of nappe thrust sheets as part of the main construction phases of the Andean orogen. South-southeastward advance and emplacement of the Lara nappes during the oblique transpressive collision of the Caribbean and South American tectonic plates in the Paleocene was further removed from the sites of peat deposition, resulting in slower subsidence rates. Slower subsidence in the Paleocene may have favored the growth of raised mires, generating higher inertinite concentrations through more frequent moisture stress. Consistently low ash yield and sulfur content would be due to the protection from clastic input in raised mires, in addition to the leaching of mineral matter by rainfall and the development of acidic conditions preventing fixation of sulfur. In contrast, peat mires of Eocene–Miocene age encountered rapid subsidence due to the proximity of nappe emplacement, resulting in lower inertinite content, higher and more variable sulfur content, and higher ash yield.     

Modes of Occurrence and Geological Origin of Beryllium in Coals from the Pu''''an Coalfield, Guizhou, Southwest China

The concentration, modes of occurrence and geological origin of beryllium in five workable coal beds from the Pu'an Coalfield of Guizhou were studied using the inductively coupled-plasma mass spectrometry (ICP-MS), floating and sinking experiments (FSE) and sequential chemical extraction procedures (SCEP). The results show that the average concentration of beryllium in coals from the Pu'an Coalfield is 1.54μg/g, much lower than that in most Chinese and worldwide coals. Beryllium in the Pu'an coals was not significantly enriched. However, it should be noted that the No. 8 coal bed from the study area has a high concentration of beryllium, 6.89μg/g, three times higher than the background value of beryllium in coal. Beryllium in coal mainly occurs as organic association and has predominantly originated from coal-forming plants when its concentration is relatively low. The concentration of beryllium occurring as organic association is close to that distributed in inorganic matter when beryllium concentration of coal is similar to its background value, and in addition to coal-forming plants, beryllium is mainly derived from detrital materials of terrigenous origin. When beryllium is anomalously enriched in coal, it mainly occurs as organic association and is derived from volcanic tonsteins leached for a long geological time and then adsorbed by organic matter in peat mire.     

煤中一种植物生殖器官残体及其地质研究的意义

本文报道了发现于我国晚三叠世，侏罗纪及第三纪煤中一种植物生殖器官残体，它们类似于蕨类植物的大孢子，壁的表面具网状纹饰，但无单缝或三缝构造，有证据表明它们是裸子植物种子内的大孢子，这也是国内首次报道煤中的这种残体，利用生物显微镜和扫描电镜对上述各时代煤中的裸子植物大孢子壁的显微及来显微构造进行了初步研究，并就其所具有的古植物学，煤岩学和石油地质学意义进行了讨论。     

Comparison of the Eastern and Western Kentucky coal fields (Pennsylvanian), USA—why are coal distribution patterns and sulfur contents so different in these coal fields?

More than 130 Mt of Pennsylvanian coal is produced annually from two coal fields in Kentucky. The Western Kentucky Coal Field occurs in part of the Illinois Basin, an intercratonic basin, and the Eastern Kentucky Coal Field occurs in the Central Appalachian Basin, a foreland basin. The basins are only separated by 140 km, but mined western Kentucky coal beds exhibit significantly higher sulfur values than eastern Kentucky coals. Higher-sulfur coal beds in western Kentucky have generally been inferred to be caused by more marine influences than for eastern Kentucky coals.Comparison of strata in the two coal fields shows that more strata and more coal beds accumulated in the Eastern than Western Kentucky Coal Field in the Early and Middle Pennsylvanian, inferred to represent greater generation of tectonic accommodation in the foreland basin. Eastern Kentucky coal beds exhibit a greater tendency toward splitting and occurring in zones than time-equivalent western Kentucky coal beds, which is also inferred to represent foreland accommodation influences, overprinted by autogenic sedimentation effects. Western Kentucky coal beds exhibit higher sulfur values than their eastern counterparts, but western Kentucky coals occurring in Langsettian through Bolsovian strata can be low in sulfur content. Eastern Kentucky coal beds may increase in sulfur content beneath marine zones, but generally are still lower in sulfur than mined Western Kentucky coal beds, indicating that controls other than purely marine influences must have influenced coal quality.The bulk of production in the Eastern Kentucky Coal Field is from Duckmantian and Bolsovian coal beds, whereas production in the Western Kentucky Coal Field is from Westphalian D coals. Langsettian through Bolsovian paleoclimates in eastern Kentucky were favorable for peat doming, so numerous low-sulfur coals accumulated. These coals tend to occur in zones and are prone to lateral splitting because of foreland tectonic and sedimentation influences. In contrast, Westphalian D coal beds of western Kentucky accumulated during low differential tectonic accommodation, and therefore tend to be widespread and uniform in characteristics, but exhibit higher sulfur values because they accumulated in seasonally drier paleoclimates that were unfavorable for peat doming. Hence, basin analyses indicate that many differences between the mined coals of Kentucky's two coal fields are related to temporal changes in paleoclimate and tectonic accommodation, rather than solely being a function of marine influences.     

Petrological evolution of the Paleogene coal deposits of Jammu, Jammu and Kashmir, India

A detailed macro- and micro-petrological investigation of 8 coal seam profiles of Eocene age from the sub-Himalayan zone of Jammu was undertaken in order to characterize them petrographically and to focus on their evolution. The quantitative data suggest that these coals are vitrinite rich, with low concentrations of inertinite and rare occurrences of liptinite. According to microlithotype concentration these coals may be characterized as vitrinite rich, with minor amounts of clarite, vitrinertite and trimacerite. The dominant minerals are clays, siderite and pyrite (occurring mostly as disseminations, cavity filling and in framboidal state). These coals are vitric in type, low volatile bituminous in rank and ashy in grade.The petrographic character and the presence of teleutospores suggest that, similar to other Tertiary coal deposits in the world, the angiosperm flora contributed chiefly to the development of coal facies in the area. The maceral and microlithotype composition shows that these coals originated from the low forest and undisturbed (in situ) peat in foreland basins under limno-telmatic depositional conditions. The water was brackish with regular influxes of fresh water.     

Reconstruction of floral changes during deposition of the Miocene Embalut coal from Kutai Basin,Mahakam Delta,East Kalimantan,Indonesia by use of aromatic hydrocarbon composition and stable carbon isotope ratios of organic matter

The distribution of aromatic hydrocarbons and stable carbon isotope ratios of organic matter in a series of nine Miocene Embalut coal samples obtained from nine coal seams of Kutai Basin, East Kalimantan, Indonesia were studied. The rank of the Embalut coals ranged from lignites to low rank sub-bituminous coals (0.36–0.50% Rr), based on measurements of huminite reflectance. The aromatic hydrocarbon fractions of all coal samples were dominated by cadalene in the lower boiling point range and picene derivatives in the higher boiling point range of the gas chromatograms. Cadalene can be attributed to the contribution of Dipterocarpaceae and various hydrated picenes to the contribution of additional angiosperms to the coal forming vegetation. The picenes originate from alpha- and beta-amyrin. However, in some coal samples minor amounts of simonellite and retene were also detected which argues for an additional contribution of gymnosperms (conifers) to coal forming vegetation preferentially in the Middle Miocene and at the beginning of the Late Miocene. The results of stable carbon isotope ratios (δ¹³C) in most of the coal samples are consistent with their origin from angiosperms (δ¹³C between ?27.0‰ and ?28.0‰). During the Miocene the climate of Mahakam Delta was not uniformly moist and cooler than the present day climate. This would have been favourable for the growth of conifers, especially in the montane forests. The contribution of conifers to the Embalut coals might be a result of the cool Middle/Late Miocene climate during peat accumulation in the Kutai Basin.     

Mineral matter in triassic and tertiary low-rank coals from South Australia

The minerals and non-mineral inorganic constituents in Triassic and Tertiary low-rank coals from various coal deposits in South Australia were studied using selective chemical leaching and oxygen-plasma ashing techniques. Although gypsum may be present in some samples, most of the sodium, calcium and magnesium, as well as part of the sulphur, appears to occur as a combination of dissolved ions in pore water and exchangeable ions attached to carboxylate groups. Significant concentrations of iron and aluminium occur in acid-soluble form, probably as organometallic complexes within the hydrocarbon structure.Quartz is the dominant mineral in the Tertiary coal samples. It appears to be mainly detrital, but doubly terminated euhedral crystals suggest an authigenic origin in one of the deposits. Well crystallized kaolinite is common in the Triassic coals, while poorly crystallized kaolinite occurs in the Tertiary samples. Siderite, calcite and possibly collophane occur in the Triassic coals; sparse pyrite is present in both the Tertiary and the Triassic samples.The differences in minerals and other inorganic constituents between the Tertiary and Triassic deposits can be explained partly by variations in the composition of the pore waters permeating the strata, and partly by mobility of silica and alumina from different sources within the peat deposit. The relative mobility of the different inorganic constituents is also significant in beneficiation of the coal for use in combustion processes.     

Coal facies in a Cenozoic paralic lignite bed, Krabi Basin, southern Thailand: Changing peat-forming conditions related to relative sea-level controlled watertable variations

The Cenozoic Krabi Basin in the southern part of peninsular Thailand contains about 112 million tons proven coal reserves. At present, coal is only produced from the Bang Mark mine located in the southern part of the basin, where the main lignite bed is 7-20 m thick. The lignite bed occurs in an overall paralic succession. The present paper investigates the depositional conditions of an approximately 8 m thick lignite bed (main seam) in the Bang Mark mine using organic petrography, including maceral ratios, and geochemistry. The results are further interpreted in a sequence stratigraphic context. The lignite is of low rank and is completely dominated by huminite indicating generally oxygen-deficient conditions in the precursor mire. Very low inertinite contents suggest rare occurrences of wildfires. The lower part of the lignite bed represents a topogenous fresh water peat mire with open water areas that in few cases may have experienced influx of saline water. The peat mire was subjected to periodic inundations and deposition of siliciclastics. Tissue preservation was relatively poor. The upper part of the lignite bed represents a slightly domed fresh water ombrogenous peat mire with a stable watertable and a balance between peat accumulation and accommodation space creation that favoured preservation of plant tissues. In general, the mire vegetation changed from less woody in the topogenous mire to more arborescent in the ombrogenous mire, where plants with suberinised wood cell walls also were more frequent. Decompacted, the lignite bed corresponds to a minimum ~ 11 m thick peat deposit that records from ~ 22,000 to 55,000 years of peat accumulation. Watertable rise in the peat mire was controlled overall by relative sea-level rise. In a sequence stratigraphic context, the lignite bed overlies a terrestrialisation surface (TeS; sensu Diessel, 2007) and the lowermost part records peat formation during a falling watertable and a decreasing accommodation/peat accumulation ratio (terrestrialisation). An accommodation reversal surface (ARS; sensu Diessel, 2007) indicates a change to paludification style of peat formation characterised by rising watertable and a high accommodation/peat accumulation ratio. Another ARS marks a gradual change to a situation with a balanced accommodation/peat accumulation ratio. The overall watertable rise throughout peat formation, but at a gradually slower rate from base to top, suggests that the lignite bed could be located in the late transgressive systems tract (TST).     

http://www.sciencedirect.com/science/article/pii/S1674987111000879

Multiple sets of thick coal beds characterized by simple structure and shallow burial depth were developed in the Early and Middle Jurassic strata of the Ordos Basin,northwestern China.The huge reserves of this high quality coal have a high commercial value.We studied the coal’s petrologic characteristics and its maceral distribution to determine the maceral’s contribution to generation of oil and gas.The results show that the Jurassic coals in the Ordos Basin have special penological features because of the Basin’s unique depositional environment which was mainly a series of high-stand swamps in the upper fluvial system.These petrographic features are a result of the development of typical inland lakes where some sand bodies were formed by migrating rivers.After burial,the peat continued to undergo oxidizing conditions,this process generated extensive higher inertinile contents in the coals and the vitrinite components were altered to semi-vitrinite.The macroscopic petrographic types of these Jurassic coals are mainly semi-dull coal,dull coal,semilustrous and lustrous coal.The proportions of semi-dull coal and dull coal are higher in the basin margins,especially in the area near the northern margin.The numbers of semilustrous and lustrous coals increase southwards and towards the central basin.This situation indicates that different coal-forming swamp environments have major controlling effects on the coal components.Another observation is that in the Ordos" coal sequences,especially in the lower part,some sandstone beds are thick,up to 20 m with a coarse grain size.The higher fusinite content in the macerals accompanies a higher semi-vitrinite content with more complete and regular plant cell structure.The fusinite structure is clear and well preserved.After burial,the lithology of the roof and floor rocks can continue to affect the evolution of coal petrology.The sand bodies in the roof and floor exhibit good physical conditions so that pore water can maintain a long-term state of oxidation,circulation and connection to the coal.So coal components remain in an oxidation environment for a long time.Conversely,in the basin center,lacustrine facies developed and peat was rapidly covered by mudstone after burial and subsequent coal beds rapidly entered a reducing environment.As a result,abundant gelatification occurred and the vitrinite content increased.Exinite often accumulated in a specific position in the coal bed.Although the average exinite content is not high on the whole,it does significantly contribute to the total hydrocarbon generation. The exinite content has been underestimated,especially the amorphous bituminous fluid and its importance is emphasized here.The reason is that the fluid flows easily into fusinite which has strong rigidity,or flows into some fissures,where it is commonly neglected.     

Petrology of oligocene coal, makum coalfield, assam, Northeast India

There are five workable coal beds in the Tikak Parbat Formation of the Barail Group in the Makum coalfield, Tinsukia District, Assam. Two of these beds, 18 and 6 m thick, are persistent across the field. The coal is high volatile bituminous B/C, has excellent coking properties, and is of great importance as a blending coal to improve the coking properties of the lower-quality Gondwanan coals.These coals are bimacerites as vitrinertite or trimacerites as duroclarite. Virtrinite predominates with minor amounts of other macerals and minerals. The high percentage of vitrinite indicates that the bark and woody tissues were the dominant contributors to the precursor peat. These peats were strongly decomposed under anaerobic conditions as indicated by the abundance of the collinite type of vitrinite.     

Place vs. time and vegetational persistence: a comparison of four tropical mires from the Illinois Basin during the height of the Pennsylvanian Ice Age

Coal balls were collected from four coal beds in the southeastern part of the Illinois Basin. Collections were made from the Springfield, Herrin, and Baker coals in western Kentucky, and from the Danville Coal in southwestern Indiana. These four coal beds are among the principal mineable coals of the Illinois Basin and belong to the Carbondale and Shelburn Formations of late Middle Pennsylvanian age. Vegetational composition was analyzed quantitatively. Coal-ball samples from the Springfield, Herrin, and Baker are dominated by the lycopsid tree Lepidophloios, with lesser numbers of Psaronius tree ferns, medullosan pteridosperms, and the lycopsid trees Synchysidendron and Diaphorodendron. This vegetation is similar to that found in the Springfield and Herrin coals elsewhere in the Illinois Basin, as reported in previous studies. The Danville coal sample, which is considerably smaller than the others, is dominated by Psaronius with the lycopsids Sigillaria and Synchysidendron as subdominants.Coal balls from the Springfield coal were collected in zones directly from the coal bed and their zone-by-zone composition indicates three to four distinct plant assemblages. The other coals were analyzed as whole-seam random samples, averaging the landscape composition of the parent mire environments. This analysis indicates that these coals, separated from each other by marine and terrestrial-clastic deposits, have essentially the same floristic composition and, thus, appear to represent a common species pool that persisted throughout the late Middle Pennsylvanian, despite changes in baselevel and climate attendant the glacial–interglacial cyclicity of the Pennsylvanian ice age. Patterns of species abundance and diversity are much the same for the Springfield, Herrin, and Baker, although each coal, both in the local area sampled, and regionally, has its own paleobotanical peculiarities. Despite minor differences, these coals indicate a high degree of recurrence of assemblage and landscape organization. The Danville departs dramatically from the dominance–diversity composition of the older coals, presaging patterns of tree–fern and Sigillaria dominance of Late Pennsylvanian coals of the eastern United States, but, nonetheless, built on a species pool shared with the older coals.     

Sequence stratigraphic interpretation of a Pennsylvanian (Upper Carboniferous) coal from the central Appalachian Basin,USA

Peat mires retain a sensitive record of water‐table (base‐level) fluctuations throughout their accumulation. On this basis, coals provide one of the best opportunities to interpret high‐resolution base‐level change in ancient non‐marine deposits. The petrographic composition of 275 samples collected from 11 localities along a 100 km south‐west to north‐east transect across the regionally extensive (>37 000 km²) Pennsylvanian (Upper Carboniferous) Fire Clay coal of the Central Appalachian Basin, USA was analysed to determine its internal stratigraphy. The coal is positioned within the late lowstand/early transgressive systems tract of a fourth‐order depositional sequence. The results of the petrographic analyses reveal a cyclicity in the composition of the Fire Clay coal, which defines six units that are correlated over more than 100 km. Each coal cycle is characterized by a gradual upward transition from vitrinite‐dominated to inertinite‐dominated coal, which represents a ‘drying‐up’ succession. Increased concentrations of resistant peat components at the top of the drying‐up successions indicate reduced peat accumulation rates associated with slowing rate of water‐table rise, and may represent a residue of peat remaining from a phase of exposure and erosion resulting from a falling water table. These drying‐up successions are bound by surfaces that display an abrupt coal facies shift from inertinite‐rich to vitrinite‐rich coal, representing a rapid water‐table rise. Each cycle represents markedly different mire conditions with different aerial distributions, which supports the notion of temporal disconnection between each unit of coal, and suggests that considerable time may be ‘locked‐up’ in unit bounding exposure surfaces. Recognition that the rate of peat accumulation in a mire may vary considerably through time, has important implications for studies which assume that peat and coal successions provide continuous and time‐invariant records of base‐level fluctuations or palaeoecological change.     

华北晚古生代陆表海盆地海侵事件微观沉积特征及成煤探讨

采用沉积学、煤地质学、古生物学、地层学及地球化学等多技术手段,结合比较分析法的思路,分析了事件型海侵的特点和海侵事件沉积组合特征,研究发现:海侵事件沉积组合为区域对比性强、具沉积时间连续性与相序间断性的暴露沉积-煤层-灰岩组合,其关键沉积学特征是煤层底板的暴露沉积.海侵事件组合灰岩的古生化石个体小、破碎强烈等特征表现为高能量水体运动等环境,孢粉表现为低含量的单缝孢和裸子植物及高含量的三缝孢.地球化学分析表明暴露沉积为陆相环境,煤层中的微量元素表现为海相主要原因是由于泥炭沼泽覆于深水后受海水影响所致.海侵事件成煤与海侵过程成煤差异体现在两个方面:第一,盆地属性差异,即海侵事件成煤形成于陆表海盆地之中,而海侵过程成煤则形成于具有缓坡的边缘海盆地,第二,成煤原理存在着差异,海侵事件成煤强调的是成煤前海侵未发生前的碎屑体系废弃而发育大量泥炭沼泽且被后期突发性海侵终止,而海侵过程成煤则强调的是泥炭沼泽发育于滨海的活动碎屑体系并终止于后期的缓慢海平面上升.     

Coal depositional models in some Tertiary and Cretaceous coal fields in the U.S. Western Interior

Detailed stratigraphic and sedimentological studies of the Tertiary Tongue River Member of the Fort Union Formation in the Powder River Basin, Wyoming, and the Cretaceous Blackhawk Formation and Star Point Sandstone in the Wasatch Plateau, Utah, indicate that the depositional environments of coal played a major role in controlling coal thickness, lateral continuity, potential minability, and type of floor and roof rocks.The potentially minable, thick coal beds of the Tongue River Member were primarily formed in long-lived floodbasin backswamps of upper alluvial plain environment. Avulsion of meandering fluvial channels contributed to the erratic lateral extent of coals in this environment. Laterally extensive coals formed in floodbasin backswamps of a lower alluvial plain environment; however, interruption by overbank and crevasse-splay sedimentation produced highly split and merging coal beds. Lacustrine sedimentation common to the lower alluvial plain, similar to the lake-covered lower alluvial valley of the Atchafalaya River Basin, is related to a high-constructive delta. In contrast to these alluvial coals are the deltaic coal deposits of the Blackhawk Formation. The formation consists of three coal populations: upper delta plain, lower delta plain, and ‘back-barrier’. Coals of the lower delta plain are thick and laterally extensive, in contrast to those of the upper delta plain and ‘back-barrier’, which contain abundant, very thin and laterally discontinuous carbonaceous shale partings. The reworking of the delta-front sediments of the Star Point Sandstone suggests that the Blackhawk-Star Point delta was a high-destructive system.     

Organic facies and depositional palaeoenvironment of lignites from Rio Maior Basin (Portugal)

The Rio Maior Basin (Portugal) is a tectonic depression, filled by a Pliocene sequence that comprises, from floor to roof: (i) kaoliniferous fine sands, (ii) diatomites and lignites, (iii) recent deposits of sandstone and clay. The diatomites and lignites form a small dissimetric syncline with alternating seams. Ten lignite seams were identified and named from floor to roof as F, E, D, C.2, C.1, C, B, A, a and a′. Seams A, D, E and F are considered to be the main seams.The organic fraction consists mainly of macerals of the huminite group, with small percentages of inertinite and liptinite groups. However, the petrographic composition of each seam is distinct, particularly with regards to macerals of the huminite and liptinite groups.Calculation of petrographic indices permitted to plot the coals in facies and palaeoenvironment diagrams. Five facies have been defined: (i) aquatic, (ii) herbaceous swamp, (iii) mixed swamp with forest and herbaceous vegetation, (vi) forest swamp (wetter) and (v) forest swamp (drier).These lignites are humic coals formed from organic matter of terrestrial origin. The peat biomass at the origin of these coals formed from a very diverse vegetation comprising gymnosperms and angiosperms. In seams F, and occasionally in seams E and D, Botryococcus algae have also contributed to the biomass. Peat deposition corresponded to a rheotrophic hydrological regime: the water level always remained above the topographic surface of the basin. Nevertheless, during the deposition of seam A in the northern part of the basin, the water level was slightly below the topographic surface. The organic matter was preserved in anaeorobic conditions.     

中国西南地区二叠纪乐平世陆生生物大灭绝期煤中砷和硒的演化及古环境意义

为了探讨中国西南地区二叠系乐平统(上二叠统)龙潭组中下部煤系不同煤组分中砷、硒的含量和演化及古环境意义,对近10年来采集于中国西南扬子地台的二叠系乐平统龙潭组主采煤层的原煤、亮煤、煤矸石、黄铁矿结核等样品中砷、硒元素含量进行了测定和分析,并与中国华北地台一些煤矿的上石炭统-下二叠统太原组、山西组的原煤、镜煤、亮煤、煤矸石、黄铁矿结核等样品中砷、硒含量进行对比分析。结果表明：西南地区乐平统龙潭组煤的砷、硒含量变化较大,但总体高于华北晚石炭世和早二叠世煤的砷、硒含量;西南二叠系乐平统龙潭组大多数的亮煤中砷、硒含量高于原煤全煤样(刻槽样)中的砷、硒含量,也远远高于同煤层煤矸石的含量,龙潭组部分亮煤的砷含量尤其高,为55～338 mg/kg,还发现砷含量为89 mg/kg的亮煤。但华北上石炭统-下二叠统的镜煤中的砷、硒含量与之相反,低于原煤全煤样的砷、硒含量,其中砷含量非常低,为063～129 mg/kg。说明西南地区上二叠统煤中的砷和硒与煤的有机质密切相关,可能主要来源于成煤古植物。在西南乐平世早、中期第Ⅰ幕陆生生物集群灭绝事件期间,陆生动物的食物--植物中有毒有害元素砷、硒含量明显增加,陆生环境或泥炭沼泽中可溶性砷、硒含量增加。