variations of natural gas carbon isotope type curves and their interpretation a case study natural gas is dominated by low molecular weight gaseous hydrocarbons c1 c5 whose genetic and diagenetic information is mainly obtained from stable carbon isotope compositions ordos basin is one of the largest natural gas provinces in china by means of examining the carbon isotope compositions of the ordos basin gases altered patterns of the isotopetype curves due to secondary cracking thermochemical sulphate reduction tsr and mixing of gases generated from different sources are recognized and discussed a typical carbon isotope type curve is nearly linear on the natural gas plot chung h m gormly j r squires r m 1988 origin of gaseous hydrocarbons in subsurface environments theoretical considerations of carbon isotope distribution chemical geology 71 97 103 our results show that the isotope type curve pattern of tsr and gas secondary cracking in coal is convex due to catalysis while the isotope type curve of gas secondary cracking in reservoirs is concave the natural gas of yulin suligemiao and wushenqi gas fields is coal derived gas both coal derived gas and mixed gas from oil and gas prone sources exist in the ordovician reservoirs of the jingbian gas field depending on the borehole locations in the ordovician carbonate reservoirs tsr is recorded but uncommon whereas secondary cracking in reservoirs is often observed 2007 elsevier ltd all rights reserved

diagenetic and catagenetic products of isorenieratene molecular indicators for photic zone anoxia a wide range of novel diagenetic and catagenetic products of the diaromatic carotenoid isorenieratene a pigment of the photosynthetic green sulphur bacteria chlorobiaceae has been identified in a number of sedimentary rocks ranging from ordovician to miocene compound identification is based on nmr mass spectrometry the presence of atropisomers and stable carbon isotopes atropisomers contain an axially chiral centre which in combination with other chiral centres results in two or more diastereomers that can be separated on a normal gc column chlorobiaceae use the reverse tca cycle to fix carbon so that their biomass is enriched in 13c high 13c contents of isorenieratene derivatives therefore support their inferred origins isorenieratene derivatives include c 40 c 33 and c 32 diaryl isoprenoids and short chain aryl isoprenoids with additional aromatic and or s containing rings c 33 and c 32 compounds are diagenetic products of c 33 and c 32 carotenoids formed from isorenieratene during early diagenesis through expulsion of toluene and m xylene respectively cyclisation of the polyene acyclic isoprenoid chain can proceed via an intramolecular diels alder reaction followed by aromatisation of the newly formed ring sulphurisation is also an important process during early diagenesis competing with expulsion and cyclisation sulphur bound isorenieratane is released during progressive diagenesis due to cleavage of relatively weak ss and cs bonds cleavage of c c bonds during aromatisation of newly formed rings and during catagenesis yields short chain compounds the inherent presence of a conjugated double bond system in carotenoids implies that similar diagenetic and catagenetic reactions can occur with all carotenoids chlorobiaceae live at or below the oxic anoxic boundary layer and require both light and h 2s the presence of isorenieratene or its diagenetic and catagenetic products in ancient sedimentary rocks and crude oils is therefore an excellent indication for photic zone anoxia in the depositional environment diagenetic and catagenetic products of isorenieratene are expected to find applications in reconstruction of palaeoenvironments and in oil oil and oil source rock correlation studies their presence in several petroleum source rocks suggests that anoxia is an important environmental parameter for the preservation of organic matter

shale gas shale oil potential of upper visean black shales in the dniepr donets basin ukraine abstract upper visean rudov beds v 23 are considered as one of the main source rocks within the northwestern dniepr donets basin ddb average toc values within the srebnen bay northwestern ddb exceed 4 thickness up to 100 m average toc contents north and northwest of the srebnen bay up to 60 m are significantly lower 2 4 but still sufficient for unconventional hydrocarbon production whereas wells along the northeastern basin margin do not hold a shale oil gas potential 5 5 km although hydrogen index hi values of the most immature samples are 300 mghc gtoc basinal rudov beds host a potential to generate paraffinic naphthenic aromatic p n a low wax oil according to pyrolysis experiments a basinward maturity trend is visible but the maturity cut offs for shale oil gas production 0 8 rr 1 2 rr are reached at great depths 4 5 km 5 5 km only furthermore results of kinetic experiments do not argue for presence of type iis kerogen potentially triggering earlier hydrocarbon generation the mineralogy of rudov beds varies strongly in lateral and vertical directions limiting the predictability of mechanical behaviour samples from the siliceous basinal facies partly contain more than 60 of brittle minerals quartz feldspar carbonates etc suggesting a good fraccability this value is rarely reached by samples from the transitional and lagoonal calcareous and clayey facies the clay mineral fraction within many investigated rudov samples is dominated by kaolinite which is suggested to diminish the fraccability of shales apart from that expandable clay minerals ecm are present in samples from more than 5 km depth a result of low mesozoic heat flow

relationship between rank and composition of aromatic hydrocarbons for coals of different origins distributions of di and tricyclic aromatics were determined for upper carboniferous to oligocene coals of various origins in addition to upper carboniferous ruhr coals wealden lower creataceous coals from north west germany lower cretaceous coals from western canada and tertiary coals from japan and colombia were studied the coals ranged from sub bituminous to anthracite in rank and showed vitrinite reflectance from 0 4 to 4 9 rm the previously established relationship between the rank of coal in terms of vitrinite reflectance and the distribution patterns of individual aromatic hydrocarbon isomers has been verified and refined it is demonstrated how the above relationships can be used to calculate vitrinite reflectance from the methylphenanthrene index mpi 1 the chemical rank levels of coals can now be defined in terms of the calculated vitrinite reflectance rc

style and timing of salt tectonics in the dniepr donets basin ukraine implications for triggering and driving mechanisms of salt movement in sedimentary basins abstract the ukrainian dniepr donets basin ddb is a late palaeozoic intracratonic rift basin with sedimentary thicknesses up to 19 km displaying the effects of salt tectonics during its entire history of formation from late devonian rifting to the tertiary hundreds of concordant and discordant salt structures formed during this time it is demonstrated in this paper that the variety of styles of salt structure formation in the ddb provide important constraints on understanding the triggering and driving mechanisms of salt kinematics in sedimentary basins in general salt movement in the ddb began during the devonian syn rift phase of basin development and exerted controls on the later distribution of salt structures though the geometry of basement faults is not directly responsible for the regular spacing of salt structures post rift salt movements in the ddb occurred episodically episodes of salt movement were triggered by tectonic events specifically two extensional events during the carboniferous an extensional reactivation at the end of carboniferous earliest permian and a compressional event at the end of the cretaceous extensional events that induced salt movement were thick skinned i e basement involved in deformation rather than thin skinned most overburden deformation related to salt movements is ductile regardless of sedimentary bulk lithology and degree of diagenesis while the deformation of sedimentary cover in areas where salt is absent is mainly brittle this implies that the presence of salt changes the predominant mode of deformation of overlying sedimentary rocks episodes of salt movement lasted longer than the periods of active tectonics that initiated them buoyancy erosion and differential loading all played a role in driving halokinesis once tectonic forces had pushed the salt overburden system into disequilibrium among these factors erosion of overburden above growing salt structures acted as a key self renewing force for development of salt diapirs very high sedimentation rates related to high post rift tectonic subsidence rates particularly during the carboniferous were able to bury diapirs and to load salt bodies such that buoyancy erosion and differential loading forces eventually became insufficient to continue driving diapirism until the system was perturbed by an ensuing tectonic event in contrast some salt anticlines and diapirs developed continuously during the entire mesozoic because of much reduced tectonic subsidence rates and sedimentation supply during this time however a lower permian salt series and overhangs of buried diapirs played an important role in preventing overburden piercing and fracturing during the mesozoic and specifically during the late cretaceous salt diapirism phase

basin evolution and coal geology of the donets basin ukraine russia an overview abstract the donets basin is a major coal mining district in eastern ukraine and adjacent portions of russia it comprises the donbas foldbelt which is the uplifted and compressionally deformed part of the pripyat dniepr donets pdd basin and the significantly less deformed western donbas region the pdd basin is a late devonian rift structure located within the east european craton thick coal measures formed during the post rift stage of the basin in serpukhovian to moscovian times when about 130 seams each with a thickness over 0 45 m have been deposited early serpukhovian coal accumulated in a relatively narrow shore zone it is rich in inertinite and liptinite and very low in ash bashkirian and moscovian coal have a significantly wider lateral extension and are generally rich in vitrinite bashkirian and moscovian coal seams usually have high ash yields 12 18 and high sulfur contents 2 5 3 5 but these data vary significantly depending on peat facies coal rank ranges from subbituminous to anthracite and is mainly controlled by the depth of the seams and the heat flow during maximum permian burial permo triassic thermal events locally overprinted the resulting coalification pattern coked coal occurs at the contact to presumed permian sills and dikes southwest of donetsk deep permian burial was followed by major permian and mesozoic uplift events the donets basin hosts proven reserves in the order of 60 gt at the exploitable depth the thickness of coal seams currently mined is in the range of 0 6 to 2 5 m production during 2009 was 68 7 mt in the ukrainian and 4 9 mt in the russian part of the basin coal mines in the donets basin are among the gassiest in the world the average methane content of coal is 14 7 m t but numerous seams have significantly higher gas content the high methane content presents a severe mine safety problem on the other hand it represents also a high potential for coal mine bed methane projects emissions of coal gas released by mining and related structurally induced underground hazards coal and gas outbursts are a major problem for safe and efficient coal exploitation in the basin

oil gas source rock correlations in the dniepr donets basin ukraine new insights into the petroleum system abstract the dniepr donets basin ddb hosts a multi source petroleum system with more than 200 oil and gas fields mainly in carboniferous clastic rocks main aim of the present study was to correlate accumulated hydrocarbons with the most important source rocks and to verify their potential to generate oil and gas therefore molecular and isotopic composition as well as biomarker data obtained from 12 oil and condensate samples and 48 source rock extracts was used together with usgs data for a geological interpretation of hydrocarbon charging history within the central ddb results point to a significant contribution from upper visean black shales highly oil prone as well as mixed oil and gas prone serpukhovian rocks and minor contribution from an additional tournaisian source devonian rocks an important hydrocarbon source within the pripyat trough have not been identified as a major source within the central ddb additional input from bashkirian to moscovian shebelinka field as well as tournaisian to lower visean rocks e g dovgal field with higher contents of terrestrial organic matter is indicated in the se and nw part respectively whereas oil source correlation contradicts major hydrocarbon migration in many cases for tournaisian to middle carboniferous reservoir horizons accumulations within upper carboniferous to permian reservoirs require vertical migration up to 4000 m along faults related to devonian salt domes 1 d thermal models indicate hydrocarbon generation during permo carboniferous time however generation in coal bearing middle carboniferous horizons in the se part of the basin may have occurred during the mesozoic

stratigraphic distribution of macerals and biomarkers in the donets basin implications for paleoecology paleoclimatology and eustacy abstract more than one hundred and thirty coal seams and coaly layers occur in the donets basin donbas twenty eight 52 samples of them ranging in age from serpukhovian late mississipian to gzhelian late pennsylvanian 33 clastics and three limestones were studied in terms of maceral composition sulphur contents and biomarker distribution diterpanes are used to estimate the contribution of different groups of plants and the height of the water table in the swamp hopanes are a measure of bacterial activity in the peat and steranes indicate the relative input of wood and algae stratigraphic trends in these parameters are discussed in relation to paleoenvironment climatic changes and eustacy a tropical climate prevailed in the donbas from serpukhovian to kasimovian times nevertheless periods with drier and wetter conditions can be distinguished based on maceral and biomarker data relatively dry conditions are observed during serpukhovian and vereian times whereas wetter climates with a maximum of coal deposition occurred during the late bashkirian most of the moscovian and the earliest kasimovian no economic coal seams are hosted in upper kasimovian and gzhelian deposits a result of a change to an arid climate our data also suggest climatic changes during sequences of different order for the second order third order and fourth order sequences relatively dry or wet conditions occurred during coal deposition in the lowstand systems tract an intermediate climate during the transgressive systems tract and the maximum flooding and a wet climate during the highstand systems tract the results for high frequency sequences support the cecil s paleoclimatic model an intermediate paleoclimate during lst sandstone and levee siltstone a wet climate during early tst coal and a dry climate during late tst limestone mfs claystone and hst deltaic siltstone coals deposited during maximum flooding periods are more enriched in c27 steranes derived from algae and contain lower proportions of c29 steranes derived from the wood of higher plants

biomarker and n alkane isotope profiles for tertiary oils relationship to source rock depositional setting abstract biomarker and n alkane isotope profiles have been measured for 29 late cretaceous tertiary oils from se asia china papua new guinea new zealand and the u s a the results are interpreted with respect to six kinds of source rock depositional setting fluvio deltaic fd freshwater transitional tr lacustrine lac saline lacustrine sal marine deltaic md and marine carbonate mc a comparison of biomarker and n alkane isotope results suggests that parameters such as the oleanane hopane ratio may overestimate the higher plant contribution to marine oils the abundance of bicadinanes is much more variable than that of oleanane probably because of a specific association with the highly resinous dipterocarp hardwoods of se asia however traces do occur in an oil from outside the paleogeographic range of the dipterocarp family confirming that there is also a more general angiosperm source the bicadinane isomeric distribution is shown to depend on maturity leading to new maturity parameters which are resistant to even very heavy biodegradation retention indices based on the regular hopane series are provided for the main bicadinane and methyl bicadinane isomers and for a group of oleanane related triterpanes of unknown structure the presence of the latter compounds may indicate locally deposited as opposed to transported higher plant matter in the source source rock depositional setting is the primary control on the shape of the n alkane isotope profile with negatively sloping curves being characteristic of fd and tr oils and flat or positively sloping curves typical of marine oils the difference is probably related to the bacterial reworking of higher plant matter in the fd environment a slight isotopic anomaly at n c 17 correlates with the abundance of algal derived steranes and may indicate a minor marine contribution to the source of an fd oil

magmatism and the geodynamics of rifting of the pripyat dnieper donets rift east european platform abstract the distribution of volcanism in the late devonian pripyat dnieper donets rift within the east european platform based upon the results of deep drilling indicates that pre existing basement structures and the major rift bounding faults played an important role in channelling the magmas towards the surface major and trace element and sr nd isotopic studies of the most primitive basic and ultrabasic magmas combined with estimates of the amount of extension 1 1 to 1 3 strongly suggest that magmatism was triggered by the upwelling of a thermally and geochemically anomalous mantle plume from the deep mantle during the late frasnian the peak of the magmatism occurred in the famennian coincident with the maximum amount of lithospheric extension magmatism rifting and domal basement uplife were contemporaneous at several localities within the eep suggesting that the thermal and geodynamic evolution of the platform could have been influenced by a cluster of mantle plumes during the late devonian

shallow water flow around model conical islands of small side slope part ii submerged experiments have been conducted to study the unsteady wakes of submerged conical islands the islands used in the tests have side slopes ranging from 8 0 to 33 1 experiments in a shallow water channel with a steady subcritical free stream showed vortex shedding to occur in the wake when the water depth above the island apex was relatively small flow separation from positions near the island apex was found to be important in producing this unsteady wake as the water depth was increased the shedding was observed to become less vigorous and eventually stop all islands tested produced similar results with the angle of the island side slope exerting relatively little influence on the process the results of wind tunnel visualization studies which used a rigid top plate to produce the effect of fluid depth support the results from the water channel pictures of the surface flow patterns produced on the islands by the wind action are presented two dimensional 2d and three dimensional 3d shallow wate

the ratios of dibenzothiophene to phenanthrene and pristane to phytane as indicators of depositional environment and lithology of petroleum source rocks abstract the ratio of dibenzothiophene to phenanthrene and the ratio of pristane to phytane when coupled together provide a novel and convenient way to infer crude oil source rock depositional environments and lithologies such knowledge can significantly assist in identifying the source formation s in a basin thereby providing valuable guidance for further exploration the ability to infer this information from analysis of a crude oil is especially valuable as frequently the earliest samples in a new area may be shows and or drill stem test samples from exploratory wells which are characteristically drilled on structural highs stratigraphically remote from the source formation s a cross plot of dibenzothiophene phenanthrene versus the pristane phytane ratios measured on seventy five crude oils from forty one known source rocks ranging in age from ordovician to miocene consistently classified the oils into the following environment lithology groups marine carbonate marine carbonate mixed and lacustrine sulfate rich lacustrine sulfate poor marine and lacustrine shale and fluvial deltaic carbonaceous shale and coal the dibenzothiophene phenanthrene ratio alone is an excellent indicator of source rock lithology with carbonates having ratios 1 and shales having ratios the dibenzothiophene to phenanthrene and the pristane to phytane ratios can also be used to classify source rock paleodepositional environments the classification scheme is based on the premise that these ratios reflect the different eh ph regimes resulting from the significant microbiological and chemical processes occurring during deposition and early diagenesis of sediments the dibenzothiophene phenanthrene ratio assesses the availability of reduced sulfur for incorporation into organic matter and the pristane phytane ratio assesses the redox conditions within the depositional environment interpretation of these ratios has been aided by quantitative biomarker analysis and by carbon isotope data for pristane and phytane obtained by gas chromatography isotope ratio mass spectrometry

changing snow cover and the net mass balance of storglaciaren northern sweden the spatial and temporal variability of seasonal snow cover in glacierized catchments has important implications for the net mass balance of alpine glaciers this study examines the relationship between changing snowpack volume the resulting winter balance and the net mass balance of storglaciaren northern sweden using a conceptual model the net seasonal snow input to the glacier is simulated daily for 16 years from 1990 from this the annual snow accumulation and winter balance are calculated the model outputs are compared with snowlines delineated from classified aerial photographs aster and landsat 7 etm satellite imagery and with measured storglaciaren winter balances the results of the model indicate variability in the winter balance over the study period though there is a slightly negative trend overall the highest winter balances and seasonal snow volumes occurred in the early 1990s and correspond with positive net mass balances however the slightly negative trend in winter balance and decreased net seasonal snow volumes suggested by the model combined with the measured increasing trend in mass lost due to ablation have resulted in decreasing glacier net mass balances and a corresponding rise in ela over the study period

hydrocarbon habitat of the dniepr donets depression abstract basin inversion depending on its intensity can enhance the trapping potential of a basin or causes destruction of major hydrocarbon resources post inversion subsidence depending on its magnitude and the amount of syn inversion erosion can induce a second phase of hydrocarbon generation and the charging of inversion structures however this mechanism which contributed for instance to the hydrocarbon habitat of inverted basins in the southern north sea was not effective in the dniepr donets basin the dniepr donets depression forms part of the pripyat dniepr donets donbass karpinsky aulacogen that evolved as a devonian rift the post rift subsidence of this basin was interrupted during the late early permian when its southeastern parts were partly inverted further inversion pulses straddle the jurassic cretaceous and the cretaceous tertiary boundaries the dniepr donets depression hosts the most important hydrocarbon province of the ukraine at the beginning of 1994 ultimate recoverable reserves in established accumulations past production and remaining reserves amounted to about 170 10 6 t of oil and gas condensate and 980 10 9 m 3 gas the bulk of oil and gas accumulations is contained in carboniferous to early permian postrift series source rocks occur in devonian syn rift and carboniferous post rift series these attained maturity prior to basin inversion hydrocarbon accumulations are characterized by multiple reservoir seal pairs the mature syn rift devonian and the immature post inversion series contain only minor hydrocarbon accumulations oil and gas accumulations are mainly trapped in syn rift salt induced and inversion related structures the latter received their hydrocarbon charge mainly due to inversion induced destruction of pre existing accumulations and ensuing re migration of hydrocarbons

numerical modelling of the thermal evolution of the northwestern dniepr donets basin ukraine abstract the dniepr donets basin ddb is a late devonian rift structure located within the east european craton numerical heat flow models for 13 wells calibrated with new maturity data were used to evaluate temporal and lateral heat flow variations in the northwestern part of the basin the numerical models suggest that heat flow was relatively high during late carboniferous and or permian times the relatively high heat flow is probably related to an early permian re activation of tectonic activity reconstructed early permian heat flow values along the axial zone of the rift are about 60 mw m2 and increase to 90 mw m2 along the northern basin margin these values are higher than those expected from tectonic models considering a single late devonian rifting phase the calibration data are not sensitive to variations in the devonian carboniferous heat flow therefore the models do not allow deciding whether heat flows remained high after the devonian rifting or whether the reconstructed permian heat flows represent a separate heating event analysis of the vitrinite reflectance data suggest that the northeastern dniepr donets basin is characterised by a low mesozoic heat flow 30 35 mw m2 whereas the present day heat flow is about 45 mw m2

natural and artificial maturation of biological markers in a toarcian shale from northern germany steroid and terpenoid biological marker evolution was studied in a maturity sequence of lias toarcian shales and adjacent strata from three shallow boreholes in the hils syncline northern germany excellent facies control within the study area ensures the comparability of the organic matter type among the stratigraphically equivalent samples of the natural maturation series in the early hydrocarbon generation stage 0 68 r0 a strong facies dependence of some sterane and hopane isomerisation values was found within the same borehole at only a few metres depth difference the extent of sterane isomerisation at c 14 and c 17 was close to 80 in the toarcian shale and between about 55 and 65 in the adjacent dogger and lias sediments similar differences were observed for the 17 h hopane moretane and 22 29 30 trisnor 18 h neohopane 22 29 30 trisnor 17 h hopane ratios whereas the 20s 20s 20r sterane isomerisation ratio did not show this difference the observed differences mostly disappear by the end of the main oil generation phase 0 88 ro where several reactions appear to have reached completion hydrous pyrolysis experiments by variations of time and temperature were used to simulate the natural evolution of the biological markers results for sterane isomerisation in the high temperature range were compared to those published by mackenzie and mckenzie geol mag 120 417 470 1983 for natural sediments kinetic data derived for this reaction from the hydrous pyrolysis results alone or from the combination of hydrous pyrolysis and natural data sets differ markedly from those determined by mackenzie and mckenzie 1983 the hydrous pyrolysis data alone yield an activation energy for sterane isomerisation at c 20 of 131 kj mol the combined data of 170 kj mol the frequency factors are in the 105 108 s 1 range the significance of the data is discussed in detail

controls on spatial variability in snow accumulation on glaciers in the southern alps new zealand as revealed by crevasse stratigraphy net accumulation measurements from two glaciers located on opposite sides of the new zealand southern alps were used to explore processes controlling spatial variability the degree of variability as measured by the spatial variogram differed in each of the three successive years but the lowest variance occurred on both glaciers in march 2008 after a hot and dry summer strong relationships between net accumulation and elevation within the accumulation area were only found on franz josef glacier fjg despite this being the primary control used in glacier mass balance modelling interaction between wind and topography was found to be important to the distribution of net accumulation on both glaciers the crevasse stratigraphy method is an ideal way to gain good spatial coverage of net accumulation and particularly suited to glaciers with high annual precipitation copyright 2010 john wiley sons ltd

stable carbon isotope compositions of crude oils application to source depositional environments and petroleum alteration the carbon isotopic composition of the c15 saturate and aromatic hydrocarbon fractions and the gas chromatographs of the c15 saturate fraction of 339 oils were geochemically and statistically evaluated results of this study show that the average isotopic compositions of the c15 aromatic hydrocarbon fractions of oils sourced from terrigenous or marine organic matter are identical the average isotopic composition of the c15 saturate fraction of oils derived from terrigenous organic sources is slightly more negative 0 9 pmil than the average for marine oils but this difference is insufficient to be used as a reliable source indicator reports in the literature stating that marine oils are isotopically more positive than te rigenous oils and that the difference can be utilized to distinguish between the two are therefore not supported by this study the isotopic differences between oils sourced from terrigenous and marine organic matter do not manifest themselves in the range of absolute values of one oil fraction but rather in the isotopic relationship between the saturate and aromatic hydrocarbon fractions the isotopic relationship is the following oils of terrigenous organic source dgr13caro 1 12 dgr13csat 5 45 oils of marine organic source dgr13caro 1 10 dgr13csat 3 75 the difference between the two equations was evaluated statistically and a statistical parameter cv the canonical variable cv 2 53 dgr13csat 2 22 dgr13caro 11 65 was used to distinguish between marine and terrigenous oils cv values larger than 0 47 indicate predominantly a terrigenous organic source for the oil whereas cv values smaller than 0 47 indicate mostly a marine organic source thermal maturity differences in oils and isotopic variations in the source beds can cause as much as 2 pmil variations in the isotopic composition of one family of oils finally stable carbon isotopes can in some situations help correlate biodegraded oils to their nondegraded counterparts

the diversification of paleozoic fire systems and fluctuations in atmospheric oxygen concentration by comparing silurian through end permian 250 million years myr charcoal abundance with contemporaneous macroecological changes in vegetation and climate we aim to demonstrate that long term variations in fire occurrence and fire system diversification are related to fluctuations in late paleozoic atmospheric oxygen concentration charcoal a proxy for fire occurs in the fossil record from the late silurian 420 myr to the present its presence at any interval in the fossil record is already taken to constrain atmospheric oxygen within the range of 13 to 35 the fire window herein we observe that as predicted atmospheric oxygen levels rise from 13 in the late devonian to 30 in the late permian so too fires progressively occur in an increasing diversity of ecosystems sequentially data of note include the occurrence of charcoal in the late silurian early devonian indicating the burning of a diminutive dominantly rhyniophytoid vegetation an apparent paucity of charcoal in the middle to late devonian that coincides with a predicted atmospheric oxygen low and the subsequent diversification of fire systems throughout the remainder of the late paleozoic first fires become widespread during the early mississippian they then become commonplace in mire systems in the middle mississippian in the pennsylvanian they are first recorded in upland settings and finally based on coal petrology become extremely important in many permian mire settings these trends conform well to changes in atmospheric oxygen concentration as predicted by modeling and indicate oxygen levels are a significant control on long term fire occurrence

sedimentary cycles and paleogeography of the dnieper donets basin during the late visean serpukhovian based on multiscale analysis of well logs abstract an integrated approach combining the available geological geophysical information was employed to construct a series of paleogeographic maps of the northwestern part of the dnieper donets basin ddb during the late visean serpukhovian early carboniferous the major source of information consists of well log data the basin fill shows a pattern of stacked transgressive regressive units of different order correlations on the scale of the basin are based on biostratigraphy seismics cyclostratigraphic subdivisions and correlations of the successions throughout the basin the cyclicity has a multifold character short shallowing upward transgressive regressive t r cycles characterized by the presence of hydrocarbons productive horizons cover a time span of the order of 500 ka long cycles include 4 to 6 short t r cycles they seem to be correlatable to western europe and probably to north america the long cycles form part of higher order stacking patterns indicative of still longer cycles considering the variable thickness of the cycles throughout the basin tectonics must have influenced the character of the series in addition to glacio eustatic sea level fluctuations the paleogeographical development of the basin shows axial deposition during the late visean likely related to late stage rifting related subsidence of a central graben followed by basin wide subsidence related to thermal subsidence during the serpukhovian