crustal velocity structure of the omineca belt southeastern canadian cordillera travel time inversion and amplitude modeling of a 350 km lithoprobe seismic refraction wide angle reflection profile determined the velocity structure of the crust and upper mantle along strike in the omineca belt of the canadian cordillera the upper crust to 12 18 km depth has velocities from 5 6 to 6 2 km s 1 and two shear zones the monashee decollement and gwillim creek shear zone are imaged by the wide angle reflections and velocity trends minor velocity differences on either side of the monashee decollement may be related to separate rock origins prominent reflections define the boundaries of a low velocity midcrustal layer from 10 15 km to 20 25 km depth with velocities less than 6 1 km s 1 the low velocities of the midcrust associated with high electrical conductivities and high heat flow may be considered as support for the hypothesis of fluids in the cordilleran crust though other possibilities such as the effect of high temperatures on rock velocities are possible in the lower crust velocities range from 6 4 6 5 km s 1 at the top of the lower crust to 6 6 6 8 km s 1 at its base the moho is very clearly defined by the refraction wide angle reflection data and has a gentle southerly dip crustal thicknesses are 35 37 km a thin crust mantle transition zone of 1 2 km thickness in which velocities vary between 7 6 and 7 7 km s 1 is consistent with coincident reflection data upper mantle velocities range from 7 9 to 8 1 km s 1 with indications from the data of upper mantle layering in comparison with neighboring regions the omineca belt has an anomalously thin crust low crustal velocities and a low velocity upper mantle similar only to the basin and range province the velocity structure may partly mirror the temperature profile which has overprinted the geological signature of the region as measured by the seismic refraction method the characteristics of a thin crust and lithosphere along with low velocities from midcrust to mantle suggests that both the basin and range and the southern canadian cordillera are currently being heated from a source within the mantle

the selection of sites for paleovegetational studies the judicious selection of sites for paleovegetational and paleoclimatic studies permits paleoecologists to answer specific research questions that go beyond primary descriptions of past vegetation we present a model that describes the relationship between basin size and pollen source area and predicts the proportions of local extralocal and regional pollen sampled by lake basins of different size the distinctive sampling properties of lakes peats and small hollows can be exploited to provide details of pattern in paleovegetation so long as attention is given to the limitations and problems of these types of sites combinations of site types in a single study most fully exploit the information contained in sediments

crustal thickness beneath the queen charlotte basin canada results of a seismically constrained gravity inversion a gravity inversion routine was used to calculate crustal thickness variations in the queen charlotte basin western canada first a crustal bouguer anomaly was derived using a digital well constrained depth to basement map and densities determined from well logs and rock samples this anomaly was subsequently inverted for crustal thickness assuming a single density contrast at depth and an average crustal thickness provided by seismic refraction data the results restricted to that portion of the basin for which there are good quality data show crustal thickness variations of the order of 12 km regions of thin crust are located off northern vancouver island 20 km along the axis of hecate strait and in northern queen charlotte sound 24 km thicker crust is associated with central queen charlotte ridge and northeastern hecate strait tests show these trends in crustal thickness prevail for all reasonable ranges of input parameters calculated residual gravity anomalies contain information useful for mapping the distribution of volcanics interbedded with sediments in subbasins and for refining estimates of depth to basement derived from seismic data alone our results are for the most part in excellent agreement with seismically derived estimates of moho depth they show minimum crustal thickness beneath regions of maximum sediment accumulation supporting an extensional origin for the basin they indicate that this extension was quite heterogeneous and yield minimum estimates which vary from 13 in some parts of the basin to as much as 65 in others the results can be used to discriminate between models on the tertiary evolution of the basin the observed trends are not predicted by the lithospheric flexure or simple margin perpendicular extension models but are consistent with a model of crustal thinning by distributed shear in a transtensional regime

bioassay for estimating the biogenic methane generating potential of coal samples abstract generation of secondary biogenic methane in coal beds is likely controlled by a combination of factors such as the bioavailability of coal carbon the presence of a microbial community to convert coal carbon to methane and an environment supporting microbial growth and methanogenesis a set of treatments and controls was developed to bioassay the bioavailability of coal for conversion to methane under defined laboratory conditions treatments included adding a well characterized consortium of bacteria and methanogens enriched from modern wetland sediments and providing conditions to support endemic microbial activity the contribution of desorbed methane in the bioassays was determined in treatments with bromoethane sulfonic acid an inhibitor of microbial methanogenesis the bioassay compared 16 subbituminous coal samples collected from beds in texas tx wyoming wy and alaska ak and two bituminous coal samples from pennsylvania pa new biogenic methane was observed in several samples of subbituminous coal with the microbial consortium added but endemic activity was less commonly observed the highest methane generation 80 mol methane g coal 56 scf ton or 1 75 cm 3 g was from a south tx coal sample that was collected from a non gas producing well subbituminous coals from the powder river basin wy and north slope borough ak contained more sorbed original methane than the tx coal sample and generated 0 23 mol g up to 16 scf ton or 0 5 cm 3 g new biogenic methane in the bioassay standard indicators of thermal maturity such as burial depth nitrogen content and calorific value did not explain differences in biogenic methane among subbituminous coal samples no original methane was observed in two bituminous samples from pa nor was any new methane generated in bioassays of these samples the bioassay offers a new tool for assessing the potential of coal for biogenic methane generation and provides a platform for studying the mechanisms involved in this economically important activity

seismic structure across the active subduction zone of western canada the vancouver island seismic project was conducted in 1980 to study the structure of the subducting oceanic juan de fuca plate and the overriding continental america plate the principal seismic refraction line line i was a 350 km onshore offshore profile perpendicular to the continental margin an array of 32 receivers was located on the america plate on the mainland and across vancouver island and extended offshore with three ocean bottom seismometers obs s two shots were fired at the eastern end of the line and 17 shots were located along the westernmost 100 km of the profile control for the interpretation of the onshore offshore profile was provided by a reversed refraction profile along the length of vancouver island and by a marine refraction profile recorded on the obs s modeling of the seismic structure of this complex region utilized an iterative inversion method for travel times from explosions in which shots at several locations are recorded on the same set of receivers and utilized an algorithim based on asymptotic ray theory for the calculation of synthetic seismograms through two dimensional media the major features of the refraction structural model are that 1 the oceanic lithosphere dips at 3 or less beneath the continental slope so the bend in the subducting slab occurs landward of the foot of the slope 2 the oceanic lithosphere dips at 14 16 beneath the continental shelf until it passes beneath the continental moho at 37 km depth below western vancouver island 3 an upper mantle reflector may correspond to the base of the subducting lithosphere and 4 a segment of high velocity material above the downgoing crust with velocity 7 7 km s and depth range 20 25 km may represent a remnant of subducted lithosphere perhaps detached when the subduction zone jumped westward to its present position

crustal structure of the cascadia subduction zone southwestern british columbia from potential field and seismic studies the northern cascadia subduction zone is a region of convergence between the oceanic explorer and northern juan de fuca plates and the continental north american plate potential field and new seismic reflection data coupled with previous seismic results and geology enable derivation of a series of density magnetic susceptibility cross sections and a block density model from the ocean basin to the volcanic arc from 2 5 and 3 dimensional interpretations the lateral extent and thickness of the accreted wedge vary significantly along the zone the narrow metasedimentary pacific rim terrane lies immediately west of wrangellia and extends the length of vancouver island consistent with its emplacement by strike slip faulting following the accretion of wrangellia the ophiolitic crescent terrane is a narrow slice lying seaward of the pacific rim terrane but not extending northward beyond the juan de fuca plate in this region the crescent terrane was emplaced in a strike slip or obliquely convergent style

upper crustal velocity structure of the southwestern canadian cordillera from explosion recordings on the wctn earthquake seismic net the digital seismic network used to monitor earthquakes in southwestern british columbia recorded explosions from lithoprobe s southern cordillera refraction experiment score in 1989 and 1990 and from the usgs pacific northwest refraction survey in 1991 both p and s waves were recorded the geographical distribution of the shots and receiver stations enabled a large three dimensional area to be sampled for ray paths considered to be in the top 10 km of the crust we used a tomographic inversion procedure to estimate the 2 d distribution of upper crustal p and s wave velocities within blocks of a refracting velocity grid located beneath a near surface velocity layer of uniform thickness the p wave velocity distribution mapped the subsurface location of several terranes in the southwest cordillera volcanic rocks of wrangellia terrane which is the principal component of the insular belt were characterized by upper crustal velocities 6 3 km s 1 whereas plutonic rocks of the coast belt had velocities 6 3 km s 1 east of southern vancouver island the velocity distribution indicated that wrangellia extends in the subsurface beneath the coast belt for about 130 km eastward of the surface location of the insular coast belt boundary a portion of the southern boundary of wrangellia was also delineated by the p velocity map which suggested that metamorphic rocks of the northwest cascades thrust system may extend beneath sedimentary cover as far west as south central georgia strait inverted s wave velocities were typically 3 6 3 7 km s 1 corresponding values of poisson s ratio were 0 27 0 28 over vancouver island and 0 20 0 24 in the coast belt the higher values for vancouver island likely reflect the high mafic content of wrangellia volcanics compared to the high quartz content of the coast belt plutonics

a new evaluation of palaeo heat flows and eroded thicknesses for the carboniferous ruhr basin western germany palaeo heat flows and thicknesses of eroded carboniferous overburden in the coal bearing ruhr basin western germany were estimated using one dimensional basin modelling techniques thermal and burial histories for 11 localities were calibrated by comparing measured and calculated vitrinite reflectance data based on the assumption of pre tectonic maturation in contrast to former studies the kinetic easy r0 approach applied for the calculation of vitrinite reflectance lopatin s tti algorithm was used in addition for one well in order to demonstrate the impact of the selection of the algorithm for vitrinite reflectance calculation on the simulation results simulated palaeo heat flows for the time of maximum burial most probably in the stephanian range from 64 to 83 mw m2 and decrease towards the south these heat flows are lower than values computed during earlier studies but are still relatively high in comparison to recent foreland basins the regional distribution of palaeo heat flows indicates that the crust beneath the ruhr basin was relatively thin and thickened towards the south at the end of the carboniferous after the stephanian 2200 3500 m of carboniferous overburden were eroded an observed southward increase in eroded thicknesses is caused by an uplift of the area studied which decreased towards the north at the end of the variscan folding large thicknesses of deposited and later eroded carboniferous sediments have to be postulated to explain the maturity data even along the present southern margin of the ruhr basin this indicates that the late carboniferous sediments originally extended far to the south geological arguments suggest that the deposition of carboniferous sediments in the entire ruhr basin continued until the stephanian

thermogenic and secondary biogenic gases san juan basin colorado and new mexico implications for coalbed gas producibility the san juan basin is the most prolific coalbed gas basin in the world with 1992 production exceeding 440 gcf footnote 12 4 billion m3 resources of approximately 50 tcf 1 4 trillion m3 and proved reserves of over 6 tcf 170 billion m3 coalbed gas wells with the highest production initial potential greater than 10 mcf day or 0 28 million m3 day occur in the overpressured north central part of the basin hydrologic analysis indicates that overpressure in the fruitland formation is artesian in origin and represents repressuring that developed during the middle pliocene highly permeable laterally continuous coal beds override abandoned shoreline pictured cliffs sandstones and extend to the elevated recharge area in he northern basin to form a dynamic regionally interconnected aquifer system coal rank and basin hydrodynamics control the composition of fruitland coalbed gases which varies significantly across the basin chemically dry gases in the north central part of the basin coincide with meteoric recharge and regional overpressure the consistency of methane dgr13c values across the basin the presence of isotopically heavy carbon dioxide in coalbed gases and bicarbonate in formation waters and biodegraded n alkane distributions of some coal extracts indicate that coalbed gases in the north central basin are a mixture of thermogenic 25 50 secondary biogenic 15 30 and migrated thermogenic 12 60 gases migrated conventionally and hydrodynamically trapped gases in situ generated secondary biogenic gases and solution gases result in gas content that plot on or above the coal sorption isotherm bacteria transported basinward in groundwater flowing from the elevated northern basin margins metabolized wet gas components n alkanes and organic compounds in the coal and generated secondary biogenic methane and carbon dioxide subsequent to coalification uplift erosion and cooling these gases may be limited to basin margins where shallow depths and structural deformation result in higher permeability or may extend more than 35 mi 56 km basinward from the recharge zone the presence of appreciable secondary biogenic gas indicates an active dynamic flow system with overall permeability sufficient for high productivity basin hydrogeology reservoir heterogeneity location of permeability barriers no flow boundaries and the timing of biogenic gas generation and trap devel pment are critical for exploration and development of unconventional gas resources in organic rich rocks

electromagnetic images of regional structure in the southern canadian cordillera as part of lithoprobe s southern cordilleran transect investigations magnetotelluric mt soundings were made at 160 sites providing unprecedented coverage from the rockies to the west coast striking lateral variation which spatially correlates with the morphogeological belt boundaries is apparent at periods sensing the lower crust 10 s for the rockies mt phases are around 35 indicative of a moderately resistive 100 s 1000 s m north american basement foreland belt phases are transitional and increase from 60 in the east to 70 in the west omineca and coast belt phases are high 75 implying a conductive 10 30 m lower crust whereas intermontane belt phases are more than 10 lower equivalent to 150 m the regional variation in conductivity correlates to first order with surface heat flow changes along the profile and is also correlative with coincident seismic reflection sections in some aspects

distribution of thermogenic methane in carboniferous coal seams of the donets basin ukraine applications to exploitation of methane and forecast of mining hazards abstract the main purpose of this contribution is to estimate methane production and to define its migration paths and storage in the donets basin formations for exploitation of methane and forecast of mining hazards in order to study methane migration and storage maps of production calculated by 2d modelling adsorption capacity of methane in coal and present day methane contents were constructed for an altitude of 300 m close to 500 m depth in this basin the results show that three principal factors influenced the methane migration and accumulation in donets basin 1 faults that acted as migration pathways 2 a replacement of thermogenic methane by endogenic co 2 in the central and se parts and 3 the occurrence of magmatic events in some areas in this basin finally in donbas the areas with the highest methane potential and the maximum risk of outburst are not the areas with anthracite that produce the highest volume of methane but areas with volatile bituminous coals where an impermeable cover preserved the accumulated gas until the cenozoic and where dextral shear belts facilitated its migration

broadside wide angle seismic studies and three dimensional structure of the crust in the southeast canadian cordillera broadside or fan recordings of a lithoprobe seismic refraction wide angle reflection experiment in the southeastern canadian cordillera show several features further illuminating the crustal structure beyond that previously derived from score 90 southern cordillera refraction experiment of 1990 in line data analysis of a nearly in line profile centred on castlegar british columbia shows lower velocities in the upper crust associated with the purcell anticlinorium as well as velocity variations that may have some association with the purcell fault zone the depth to moho is almost 38 km somewhat deeper and on trend with the structure that has been established farther north the broadside records show high signal to noise ratio pmp arrivals i e reflections from the bottom of the crust these pmp fan picks were analysed in regions away from in line profiles providing further measurements of the depth to moho in the southeastern cordillera the analysis of the broadside records combined with t

sources and mechanisms of formation of gaseous hydrocarbons in sedimentary rocks abstract accepted concepts of principal stages of hydrocarbon formation fail to satisfactorily explain the accumulation of supergiant gasfields in west siberia u s s r such as for example urengoy which comprise 30 of the proven gas reserves of the world a new mathematical model has been developed which applies the concept of activation energy distribution to the formation of gases characteristic differences in the molecular structure of humic and sapropelic source organic matter are expressed in different activation energy distributions the model allows the calculation of isotope values for different types of organic matter and their dependence on maturity application of the model to west siberia suggests that the supergiant gas accumulations in urengoy are more likely formed from terrestrial organic matter through thermochemical reactions at moderate depths and are not the result of either deep overmature or bacteriogenic processes the new mathematical model suggests that humic organic matter in general has a high methane generating capacity at comparably low maturities of organic matter equivalent to 0 5 0 7 on the vitrinite reflectance scale

an isotopic study of hydrocarbon generation processes abstract the sources of reservoired liquid hydrocarbons in australia differ substantially from their northern hemisphere counterparts not only are australian source rocks largely of terrigenous origin but the concepts accepted as defining the hydrocarbon potential of source rocks have recently been challenged although isotopic measurements on australian source rocks and liquid hydrocarbon products closely parallel those published from elsewhere new interpretations of these data have been made particularly with regard to d h ratios in coals as interesting as such results may be the most important findings relate to the origins and histories of methane the higher gaseous hydrocarbons and carbon dioxide and the interpretation of these data in terms of hydrocarbon genesis simple northern hemisphere concepts which characterize gases as being biogenic oil associated etc on the bases of their isotopic and chemical compositions are clearly not applicable to the australian scene indeed justification of such precise classifications in the northern hemisphere on the available evidence is also questioned isotopic and compositional data from gases from the cooper bowen sydney and gippsland basins and from the north west shelf australia are reviewed and assessed in terms of generation pathways

electromagnetic images of crustal structures in southern and central canadian cordillera data from more than 400 magnetotelluric soundings made since the early 1980 s in the canadian cordillera over a 300 000 km2 area between 49 and 53 5 n are used to image qualitatively regional three dimensional crustal variation in electrical conductivity by means of phase maps phase frequency sections and maps of resistivity at depth two hundred of the soundings were acquired as part of lithoprobe southern canadian cordillera transect activities and their locations were coordinated with the seismic reflection and refraction experiments the lower crust has a generally pervasive low resistivity 1 100 m throughout the cordillera west of the foreland belt within this canadian cordilleran regional conductor the magnetotelluric data reveal both two dimensional structures with highest conductivities along the coast belt and omineca belt and three dimensional variation along geological strike this conductor mapped over a volume in excess of 106 km3 is most probably caused by fluids saline wat

crustal velocity structure in the eastern insular and southernmost coast belts canadian cordillera seismic refraction data recorded along a 330 km cross strike profile through the eastern insular and southernmost coast belts of the canadian cordillera are interpreted using an iterative combination of traveltime inversion and amplitude forward modelling the resultant model is characterized by large lateral variations in velocity the most significant of these variations is a decrease in upper and middle crustal velocities to the east of the surface trace of the harrison fault which likely represents the transition from crust of the insular superterrane to that of the intermontane superterrane this interpretation is consistent with some present geological models that place the possible probable location of the suture between the two superterranes less than 20 km east of the harrison fault velocities at the base of the upper crust average 6 4 and 6 2 km s west and east of the fault respectively mid crustal velocities average 6 6 6 9 km s to the west and 6 35 6 45 km s to the east of the fault low

lithoprobe crustal reflection structure of the southern canadian cordillera 2 coast mountains transect the lithoprobe seismic reflection transect across the southern coast mountains of the canadian cordillera images fundamental crustal structures presumably related to collision of the intermontane and insular composite terranes and deep levels in the upper plate of the offshore cascadia subduction belt the eastern part of the coast mountains are characterized by east dipping upper crustal reflectors that project to exposed faults and east dipping lower crustal reflectors they are truncated by subhorizontal to west dipping middle and upper crustal reflectors these geometric relationships are interpreted to have formed during an early phase of primarily west directed contraction that created the east dipping structures of the upper and lower crust and a later phase of east directed shortening caused by wedging of the intermontane belt into the lower and middle crust of the tectonic stack subsequently the coast belt may have been displaced eastward on contractional faults that ascend from the lower crust beneath the intermontane belt and surface in the omineca and foreland belts extensional faults bounding the east flank of the coast mountains and west flank of the central nicola horst in the intermontane belt flatten into the middle and lower crust of the intervening region and geometrically outline crustal boudinage within the western coast mountains east dipping reflections spanning the middle crust to upper mantle are traced updip to vancouver island and the underlying cascadia subduction zone the c reflector on vancouver island is believed to separate wrangellia from underlying accreted terranes and is correlated to the mainland where it forms the upper boundary of a reflective lower crustal wedge that flattens into the moho if the moho is not a young feature then some accreted material appears to have wedged into the continental framework above the crust mantle boundary possibly causing shortening in the overlying crust and creating midcrustal ramps observed on the reflection data the structurally lower e reflections interpreted as shear zones originate at the subduction contact offshore and project landward into sub moho reflections within the upper plate on the mainland the region between the e reflector and the descending oceanic plate is interpreted to be subducted lower continental crust and mantle

inversion of three dimensional wide angle seismic data from the southwestern canadian cordillera seismic refraction wide angle reflection data were recorded on a triangular array in southwestern british columbia centered on the boundary between the coast belt to the southwest and the intermontane belt to the northeast the experiment part of the lithoprobe southern cordillera transect enabled determination of the three dimensional 3 d velocity structure of the crust and upper mantle an algorithm for the inversion of wide angle seismic data to determine 3 d velocity structure and depth to reflecting interfaces is developed the algorithm is based on existing procedures for the inversion and forward modeling of first arrival travel times and forward modeling of reflection travel times including 1 forward modeling using a 3 d finite difference algorithm and 2 a simple velocity model parameterization for the inversion which eliminates the need to solve a large system of equations the existing procedure is extended to allow 1 the inversion of reflection times to solve for depth to a reflecting interface and or velocity structure 2 the inversion of first arrival travel times to solve for depth to a refracting interface and 3 layer stripping application of the algorithm to southern cordillera data uses pg to constrain upper crustal velocity structure pmp to constrain lower crustal velocity structure and depth to moho and pn to constrain upper mantle velocities and depth to moho the 3 d velocity model for the southwestern canadian cordillera is characterized by 1 significant lateral velocity variations at all depths that do not in general correlate with surface geological features or gravity data 2 a relatively high velocity middle and lower crust in the southwestern part of the study area which correlates with a strong relative gravity high and outlines the eastern extent of lower wrangellia an accreted terrane forming the insular belt to the west 3 a narrow zone of slower velocity in the lower crust and change in crustal thickness associated with the fraser fault system lending additional support to the view that it is a crustal penetrating fault 4 an average upper mantle velocity of 7 85 km s and 5 a depth to moho of 33 36 km in the intermontane belt and 36 38 km throughout most of the coast belt decreasing in the west to 33 km near the insular coast contact horizontal velocity structure slices and an interpreted cross section based on these and other results show the complexity of crustal structure in the region

stable isotope geochemistry of coals humic kerogens and related natural gases isotope systematics are well defined for conventional sapropelic type i ii kerogens and their associated bacterial and thermogenic natural gas products these geochemical tools are used to estimate source type maturity and depositional environment and as a correlation technique in many cases the natural gas signatures in near surface samples and drill cuttings can be used to classify or predict a deeper lying source rock or reservoir corresponding interpretative schemes for coals type iii kerogens and their associated hydrocarbons are progressing quickly the shift in attention to humic sources is driven primarily by depletion of conventional oil and gas resources and the economic and societal requirements of coal and coal bed methane carbon hydrogen and nitrogen stable isotope variations can be large between different coals and humic kerogens these differences can often be recognized in their bulk 13corg dorg and 15norg values isotope signatures of coals can be diagnostic of several factors including deposit age type geographic location maturity and generation history however these characteristic isotopic variations are substantially better defined by the c h and n isotope ratios of the separate maceral groups such as vitrinite exinite and inertinite this new application of stable isotopes at the maceral and compound levels have great potential to improve the interpretative precision over conventional whole coal or bulk techniques hydrocarbon gases including coal gases derived from coals and humic kerogens can be distinguished from type i ii sources based on their molecular rations i e c1 c2 c3 and by comparing their stable isotope compositions especially 13cch4 and dch4 the 13cc2h6 can also be valuable but ethane is generally present in small amount 1 vol and requires

microbial origin of australian coalbed methane bituminous coal seam gases from the permian sydney and bowen basins australia are characterized by 1 methane ethane ratios greater than or equal to 1000 2 dgr13c and dgrd values for methane of 60 10 pmil pdb and 217 17 pmil smow respectively 3 carbon dioxide contents of less than 5 and 4 dgr13c co 2 ch4 values of 55 10 pmil pdb these data suggest that microbial reduction of co2 rather than traditional thermogenic reactions is mainly responsible for gas composition invasions by co2 of deep seated external origins are readily recognized by their isotopic compositions 7 2 pmil pdb

multiple origins of methane in the earth methane occurrences in the earth s crust are predominantly of biogenic origin i e their ultimate source is biologically formed organic matter methane can also form through inorganic reactions and is consequently termed abiogenic biogenic methanes can either form through bacterial or thermogenic processes bacterial processes follow a co2 reduction and or fermentation pathway the fermentation processes are quantitatively more important in recent fresh sediments and swamps methane formed by co2 reduction however is most common in older sediments and commercial gasfields temperature organic substrate and age may be the major factors controlling the relative importance of the two pathways stable isotope concentrations in thermogenic methanes seem to be controlled by the extent of conversion of organic matter the timing of gas expulsion and trapping the different character of methane in individual sedimentary basins may be a result of the geologic history geothermal methanes are most likely derived from pyrolysis of organic matter abiogenic methane occurs in hydrothermal vents and ophiolite complexes inorganic reactions either surficial or deep seated are the likely source of such methanes a uniform mantle origin of methane is not supported by the observed isotope variations in naturally occurring methanes

isotopic geochemistry and habitat of the natural gases from the upper carboniferous žacleř coal bearing formation in the nowa ruda coal district lower silesia poland the nowa ruda coal district is located in the se part of the lower silesian coal basin the analysed coals have vitrinite reflectance from 1 12 to 1 56 and 13c values from 24 6 to 23 2 natural gases accumulated in coal seams reveal considerable variability of molecular and isotopic compositions geochemical indices and stable isotope ratios vary in the following ranges c2 wet gas index from 0 6 to 40 7 carbon dioxide methane index cdmi from 1 9 to 99 9 13c methane from 66 1 to 28 6 d methane from 256 to 211 13c carbon dioxide from 24 4 to 7 0 and 13c ethane from 27 8 to 25 5 stable isotope studies allow distinction between thermogenic endogenic magmatic and or upper mantle derived and probably even bacterial gases the intensity of migration mixing and accumulation of the natural gases of various origins appear to be variable in time and space the variability of both the molecular and the isotopic compositions of the analysed gases probably results from the specific primary reactions active during the generation of the thermogenic gases in coal seams decomposition of coal seam matrix and or cracking of n alkanes and or in humic dispersed organic matter of coaly mudstones an isotopic fractionation may also develop during the migration of the natural gases through the ultra fine pores of coals the results of this paper suggest that in the case of gases connected with coal seams the existing gas classifications cannot be directly applied to their genetic interpretation

methane exchange between coal bearing basins and the atmosphere the ruhr basin and the lower rhine embayment germany a precise knowledge of methane exchange processes is required to fully understand the recent rise of atmospheric methane concentration three of these processes take place at the lithosphere atmosphere boundary bacterial consumption of methane and emission of bacterial or thermogenic methane this study was initiated to quantify these processes on a regional scale in the ruhr basin and the lower rhine embayment since these areas are subject to bituminous coal and lignite mining natural and anthropogenically induced methane exchange processes could be studied the methane emission and consumption rates and their carbon isotope signal were measured at the lithosphere atmosphere boundary using flux chambers on most of the soils studied methane consumption by bacteria was identified thermogenic methane was released only at some of the natural faults examined in active and abandoned bituminous coal mining areas methane emissions were restricted to small areas where high emission rates were measured the carbon isotope composition of methane at natural faults and in mining subsidence troughs was typical of thermogenic methane 45 to 32 d 13 c methane exchange balancing revealed that natural methane emissions from these two basins represent no source of atmospheric importance however methane release by upcast mining shafts dominates the methane exchange processes and is by about two orders of magnitude greater than methane consumption by bacterial oxidation in the soils 2000 elsevier science ltd all rights reserved

petrology and genesis of upper carboniferous seams from the ruhr region west germany abstract the petrology of 21 seam profiles of upper carboniferous age westphalian c and b has been studied in order to determine their depositional environments and diagenetic history the youngest profile was drilled at a depth of 790 m and is mainly overlain by cretaceous sediments the oldest seam was reached at a depth of 1470 m the seam thicknesses vary from 0 4 to 2 5 m the main petrographic compounds are vitrinite intertinite liptinite and minerals the last group occurs as clay bands with illite kaolinite minor chlorite and minor quartz contents or as crack or pore filling calcite fe dolomite siderite pyrite or marcasite or as syngenetic siderite concretions and pyrite crystals the percentages of the different macerals and minerals vary mainly because of different depositional environments diagenetic loss or genesis of compounds is a less important factor in their distribution three types of profiles are distinguished by their different petrologies type i is most abundant and contains much vitrinite many clay bands and syngenetic iron sulfides whereas type iii is rich in inertinite and certain characteristic spores type ii is intermediate but generally contains only low percentages of minerals generally this type is vitrinite rich in the lower and inertinite rich in the central and upper parts of the profiles spores and other liptinites are much better preserved in all the seams than in clay partings or in siltstones and sandstones above and below the seams the seams are interpreted to be former autochthonous peats type i profiles are probably derived from swamps which were sometimes inundated and covered by overbank deposits type ii and iii seams represent former peats which were not inundated by rivers and partly grew under the influence of more oxidizing conditions therefore they contain more inertinite and less sulfide and clay bands they can be interpreted as former raised bogs diagenetic changes are expressed as increases of vitrinite reflectances from 0 65 to 1 0 and of liptinite reflectances a red shift of fluorescence of liptinites was found increasing amounts of exudatinite and micrinite and decreasing amounts of fluorinite and resinite were found minerals seem to be less affected by diagenesis illite crystallinity for example remains poor

coalbed methane in the ruhr basin germany a renewable energy resource abstract around the globe underground hard coal mining leads to a release of methane into the atmosphere about 7 of the global annual methane emissions originate from coal mining in the year 2002 16 countries used coal gas to generate heat and electricity in many cases the exact size of coalbed methane reservoirs is not identified the possibility of a long term gas production and its profitability at single sites are unknown to clarify these points the processes of gas generation as well as the gas in place volume have to be determined both issues are tackled here for the ruhr basin within this basin coal gas samples were taken at 13 gas production sites spread over three samplings within 14 months there were virtually no changes in the concentrations of gas components at single sites within this period the isotope composition of methane 13c methane 40 0 to 57 3 vs pdb revealed that the produced methane is a mixture of gases of thermogenic and microbial origin the microbial contribution of methane seems to be more pronounced at sites of active and especially abandoned coal mining than at unmined places ethane and propane are of thermogenic origin with ethane s isotopic composition tending to heavier values richer in 13c with time this time dependent phenomenon is interpreted as being caused by desorption in addition living methanogenic archaea were detected in mine water samples from depths down to 1200 m

the behaviour of major and trace elements in complete vertical peat profiles from three sphagnum bogs the distribution of major elements al ca k mg na in peat profiles from two contrasting ombrotrophic sphagnum bogs is interpreted in respect to the abundance and mineralogical composition of ash atmospheric deposition plant bioaccumulation and leaching high concentrations of ca are found in the minerotrophic peats from a continental bog underlain by calcareous sediments luther bog ontario aluminum is more abundant in the minerotrophic peats from a coastal bog in a siliceous terrain barrington bog nova scotia the peats at the coastal site contain an average of 3 times as much na and mg as the peats from the continental bog because of sea spray potassium is highly enriched in the surface peats at both sites because of plant bioaccumulation the behaviour of trace metals cr cu fe mn ni pb u v zn in peat profiles is explained in terms of the abundance and distribution of mineral matter plant bioaccumulation the response of metals to acidic anaerobic conditions and anthropogenic atmospheric deposition the distribution of ni v and cr in the peats from a third bog galbraith bog ontario follows that of mineral matter content and the metals are highly correlated with ash relative to the mean composition of the underlying mineral sediments clays collected at 30 other sites the peats are neither significantly 2 times enriched nor depleted in ni v and cr manganese is strongly enriched in surface and near surface peat layers because of plant bioaccumulation in contrast fe and mn are relatively depleted in subsurface peats due to their enhanced solubilities in acidic anaerobic waters the opposite is true for cu and u which accumulate in peats because of their diminished solubilities in anaerobic environments enrichments of zn and pb also occur but these are restricted to surface peats and are due to anthropogenic metal deposition

human impact on the vegetation of south wales during late historical times palynological and palaeoenvironmental results from crymlyn bog nnr west glamorgan wales uk palynological and palaeoenvironmental analyses of crymlyn bog a lowland fen in south wales reveal insights into the effects of documented industrial activity on the landscape during the last c 500 years the pollen and palaeoenvironmental profiles suggest that a predominantly wooded landscape in which some agriculture but little industrial activity took place occurred between the sixteenth and early eighteenth centuries significant increases in heavy metals spheroidal carbonaceous particles and sirm are coincident with rapid and substantial industrialization of the lower swansea valley from the mid eighteenth to early nineteenth centuries although the pollen evidence suggests that the vegetation of the area was dominated by birch hazel woodland the pollen profile suggests that large scale woodland clearance that was perhaps caused by increased land use pressure adjacent to the mire occurred in the late nineteenth and early twentieth centuries at the same time decreases in the profiles of coppe

radiometric dating 210pb 137cs 241am of recent ombrotrophic peat accumulation and evidence for changes in mass balance the paper summarizes and evaluates the results of 210pb 137cs and 241am analysis on 37 recent ombrotrophic peat profiles from these and previously published data it is concluded that radiometric measurements alone cannot be relied on to give an accurate chronology of peat accumulation where constrained by profiles of 241am activity in the upper part and one or more pollen dated horizons below this 210pb can provide good chronologies of peat accumulation provided the constraint does not displace the calculated 210pb dates by more than c 10 profiles of 137cs activity in most cases fail to contribute significantly to dating recent peat at somewhat degraded sites the residual dry mass of peat representing the last c 150 years is reduced further analysis of well dated profiles suggests that this may reflect loss of catolelm peat newly exposed to aerobic decomposition processes after a fall in water table several mechanisms are proposed for the displacement and net loss of lead including 210pb

coincident seismic reflection refraction studies of the continental lithosphere a global review nearly 50 coincident seismic reflection refraction studies to depths of at least the moho provide an improved understanding of the continental lithosphere some conclusions include the following 1 a transparent upper crust a common observation on vertical reflection profiles cannot generally be correlated with velocity gradients or low velocity zones rather a commonly transparent upper crust may be explained by short wavelength steeply dipping features in the brittle upper crust and to a lesser degree by signal contamination from source generated noise 2 the reflective lower crust in extensional terranes appears to be characterized by a high average seismic velocity 6 6 7 3 km s and to consist of laminated high and low velocity layers with typical thicknesses of 100 200 m 3 landward dipping reflectors observed in the middle to lower crusts of convergent zones have been identified as paired high and low velocity slabs which represent oceanic crust and mantle accreted via underplating to the continental margin 4 the crust mantle boundary may differ sufficiently when imaged with vertical incidence and wide angle data to justify the retention for the present of the concept of separate reflection and refraction mohos while there is good evidence that these features are coincident within measurement uncertainties in most regions recently recorded data from the basin and range admit the possibility for noncoincidence in that area 5 upper mantle reflections which cannot be migrated into the lower crust remain rare despite isolated unequivocal examples thus the upper mantle appears to be relatively homogeneous at seismic reflection wavelengths and to lack the laminations inferred for the lower crust the wide angle method will likely provide the most reliable information on the velocity structure and physical state of this portion of the lithosphere for some years to come 6 there appear to be clear and consistent basic differences between convergent and extensional terranes which have been identified from coincident experiments these differences may be sufficiently universal to infer the tectonic history of poorly exposed terranes 7 no truly three dimensional coincident experiment i e including three dimensional migration has been conducted but some three dimensional data have been collected using both methods measurements of attenuation poisson s ratio and anisotropy within the crust using coincident data sets remain frontiers

origin of brines in the upper silesian coal basin poland inferred from stable isotope and chemical data brines in the miocene formations of the upper silesian coal basin have isotopic composition close to smow which identifies them as the connate marine water however controversies exist on the origin of brines in the carboniferous formations isotopic and hydrochemical data exclude any relationship to marine water and enrichment by evaporation the most common brine which occurs at great depths can be identified as the oldest infiltration in a very hot climate 18o 2 d 20 cl content 34 to 140 g l this brine is free of so42 and u and rich in ba2 and226ra its salinity is probably related to the leaching of evaporites and intensive weathering of rocks during the rotliegendes other brines are difficult to identify because their isotopic contents are within the range of mixing between the oldest brine and the quaternary waters 18o 10 d 70 isotopic and hydrochemical data allow identification of several occurrences of brine formed by meteoric water of a warm tertiary climate after the last marine transgression in the tortonian that brine is rich in so42 and contains moderate contents of226ra and u its salinity is thought to result from leaching of miocene evaporites two other identified types of brines can be related to some infiltration periods before the last marine transgression the sources in salinity of these 2 types remain unknown mining activity results in a common occurrence of mixed brines when the quaternary component dominates its identification is easy from the isotopic composition whereas the end brine component can ususally be identified by chosen ion ratios and the presence or lack of sulphates

a middle jurassic to early tertiary andean sierran arc model for the coast belt of british columbia regional tectonic features of the western canadian cordillera can be interpreted in terms of middle jurassic accretion of a single composite superterrane stikinia wrangellia alexander to ancestral north america closure of the intervening cache creek bridge river ocean moved the continental edge to a new position west of the accreted superterrane the coast belt is primarily a succession of superimposed middle jurassic to early tertiary magmatic arcs related to prolonged subduction of pacific ocean lithosphere beneath the new north american margin discrete magmatic pulses separated by lulls or periods of relative quiescence successively overprinted the new margin the insular and intermontane superterranes previously viewed as widely separate entities prior to mid cretaceous time were already amalgamated before an initial middle jurassic overprint produced an ancestral coast belt late jurassic to early cretaceous rift related marine basins mid to late cretaceous compressional structures and early tertiary extensional features coincident with the coast belt are subsidiary intraplate attributes that reflect external adjustments in plate motions within a primary subduction related andean magmatic arc

human influence upon sedimentation in llangorse lake wales palaeolimnological studies at llangorse lake wales constitute part of the british contribution to igcp project 158 the palaeohydrology of the temperate zone in the last 15000 years the lake has been adopted as the reference site for the south wales region under subproject 158b lake and mire environments and is located in the reference area for britain the severn basin results of biological physical and multielement chemical analyses on a 12 35 m livingstone core are presented and compared with previous analyses on short mackereth cores taken from two troughs in the lake basin human impact upon post glacial sedimentation is assessed with reference to sediment chemistry physical properties and sedimentation rates based on relative pollen 14c and 210pb dating vegetational history of the catchment is inferred from a pollen diagram for a section of the core from c 8 to 6 75 m depth in which evidence for human impact is first apparent water content loss on ignition and carbonate content are presented for the whole core density water content loss on ignition carbonates and elemental analyses of p ca mg k ti al fe and mn for the interval 6 75 and 8 25 m depth sedimentation rates were low during boreal and atlantic times c 9000 5000 bp rose significantly from the time of the elm decline estimated at 5000 bp and increased further at c 1800 bp when nekron muds were succeeded by deposition of silty clay inferred rates of erosion of soils from the catchment are discussed and related to sediment chemistry

composition and origin of coalbed gases in the upper silesian and lublin basins poland abstract coalbed gases in the upper silesian coal basin uscb are highly variable in molecular and stable isotope composition geochemical indices and stable isotope ratios for coalbed gases from uscb vary within the following ranges ch4 c2h6 c3h8 hydrocarbon index from 122 to more than 10 000 cdmi carbon dioxide methane index cdmi co2 co2 ch4 100 from 0 0 to 21 0 13c ch4 from 79 9 to 44 5 d ch4 from 202 to 153 13c c2h6 from 24 6 to 22 3 13c c3h8 24 7 one sample and 13c co2 from 27 2 to 2 8 only two coalbed gases were collected from the lublin coal basin lcb geochemical indices and stable isotope ratios for these samples show the following values hydrocarbon index more than 10 000 cdmi 4 3 and 34 6 13c ch4 67 3 and 52 5 d ch4 201 one sample and 13c co2 13 7 and 11 9 methane higher gaseous hydrocarbons c2 to c5 and carbon dioxide occurring in the coalbed gases in both the uscb and the lcb were generated during the bituminous stage of the coalification process and probably during microbial reduction of carbon dioxide however depth related isotopic fractionation which has resulted from physical e g diffusion and adsorption desorption processes during gas migration cannot be neglected in both basins the coalification process lasted no longer than several ma and was completed at the end of the variscan orogeny at the turn of carboniferous and permian

crustal velocity structure in the southern coast belt british columbia we applied an iterative combination of two dimensional traveltime inversion and amplitude forward modelling to seismic refraction data along a 350 km along strike profile in the coast belt of the southern canadian cordillera to determine crust and upper mantle p wave velocity structure the crustal model features a thin 0 5 3 0 km near surface layer with an average velocity of 4 4 km s and upper middle and lower crustal strata which are each approximately 10 km thick and have velocities ranging from 6 2 to 6 7 km s the moho appears as a 2 km thick transitional layer with an average depth of 35 km and overlies an upper mantle with a poorly constrained velocity of over 8 km s other interpretations indicate that this profile lies within a collision zone between the insular superterrane and the ancient north american margin and propose two collision zone models i crustal delamination whereby the insular superterrane was displaced along east vergent faults over the terranes below and ii crustal

topogenous peat development and late flandrian vegetation history at a site in upland south wales three radiocarbon dated pollen diagrams were made from progressively shallower depths on a transect through an upland stream valley bog in south wales the peat ranges in age from approximately 400

mantle heterogeneities and their significance results from lithoprobe seismic reflection and refraction wide angle reflection studiesthis article is one of a series of papers published in this special issue on the theme lithoprobe parameters processes and the evolution of a continent lithoprobe contribution 1486 within lithoprobe s 10 transects data from more than 20 000 km of multichannel seismic mcs reflection profiling and 12 refraction wide angle reflection r war surveys were acquired while the

crust and upper mantle velocity structure of the intermontane belt southern canadian cordillera as part of the lithoprobe southern cordillera transect seismic refraction data were recorded along a 330 km long strike profile in the intermontane belt an iterative combination of two dimensional traveltime inversion and amplitude forward modelling was used to interpret crust and upper mantle p wave velocity structure this region is characterized by i a thin near surface layer with large variations in velocity between 2 8 and 5 4 km s and low velocity regions that correlate well with surface expressions of tertiary sedimentary and volcanic rocks ii an upper and middle crust with low average velocity gradient possibly a weak low velocity zone and lateral velocity variations between 6 0 and 6 4 km s iii a distinctive lower crust characterized by significantly higher average velocities relative to midcrustal values beginning at 23 km depth approximately 8 km thick with average velocities of 6 5 and 6 7 km s at top and base iv a depth to moho as defined by wide angle reflections that aver

characterization of the origin of coalbed gases in southeastern illinois basin by compound specific carbon and hydrogen stable isotope ratios abstract coalbed gases and waters from exploratory and production gas wells in the southeastern illinois basin were sampled to assess geochemically the origin of coalbed gases with an emphasis on the springfield and seelyville coal members that are commercially targeted for coalbed methane production in indiana on line analyses of hydrocarbon gases methane to butanes c 1 c 2 c 3 n c 4 i c 4 and co 2 yielded gas concentrations plus d and 13 c values the low thermal maturity of indiana coals with vitrinite reflectance r 0 0 6 is in agreement with an overwhelmingly biogenic isotopic signature of coalbed gases containing 96 methane generated via bacterial co 2 reduction in contrast thermogenic gas was generated in the stratigraphically equivalent coal beds in western kentucky s rough creek graben zone where higher maturities of up to r 0 0 8 were reached owing to tectonic and hydrothermal activity no secondary biogenic methane was observed in more mature western kentucky coal beds where greater burial depth limits the recharge of meteoric water biogenic and thermogenic coalbed gases represent two end members that are compositionally and isotopically distinct microbial biodegradation of thermogenic c 2 hydrocarbon gases in indiana coal beds preferentially targets c 3 and introduces isotope fractionation whereby remaining c 3 is enriched in deuterium and 13 c

pollen representation source area and basin size toward a unified theory of pollen analysis abstract the concepts of pollen source area and of production and dispersal biases in pollen representation are quantified by means of a simple theoretical model source areas and relative pollen representation are shown to depend on basin size according to functions that describe the amount of pollen remaining airborne at increasing distances from single pollen sources the form of these functions is determined by physical processes standard formulas for elevated sources do not apply but the integrated form of sutton s equation for particle dispersal from a ground level source gives useful approximations applicable to pollen transport over a forest canopy simulations using this equation yielded source areas that increased realistically with basin size showed substantial differences between source areas for pollen grains with different deposition velocities and predicted that lighter pollen grains should become better represented with increasing basin size all of these predictions are qualitatively consistent with present knowledge of the characteristics of pollen assemblages in different depositional environments the model further allows parameters that can be estimated by statistical calibration methods to be predicted from underlying physical quantities this extension suggests procedures for testing the theory with quantitative data on surface pollen and forest composition preliminary results showed reasonable agreement between estimated and predicted values of dispersal indices for the most abundant taxa in pollen spectra from the northern midwestern united states

transition from oceanic to continental crustal structure seismic and gravity models at the queen charlotte transform margin seismic refraction data have been interpreted along a line crossing the queen charlotte transform just north of the triple junction where the explorer ridge intersects the continental margin these data observed at three onshore sites help to define the structure of the continental crust beneath the queen charlotte sedimentary basin sediment thicknesses of up to 4 km were determined from a coincident multichannel reflection line beneath the sediments velocities increase from about 5 5 to 6 3 km s 1 at 8 km depth then increase from 6 5 to 6 7 km s 1 at 18 km depth below this depth the lower crust is partly constrained by moho wide angle reflections at the three receiving sites which indicate a lower crust velocity of 6 8 6 9 km s 1 and a moho depth of 26 28 km the crustal velocity structure is generally similar to that in southern queen charlotte sound it is in contrast to the velocity structure across hecate strait to the north where a prominent mid crust interface at 15 km depth was observe

basalts water or shear zones in the lower continental crust abstract bright sub horizontal laterally extensive multi cyclic layered reflections have now been recorded in the lower continental crust from many areas in contrast this reflection signature is rare in the continental upper crystalline crust and upper mantle and in the oceanic lithosphere with the present state of knowledge it is sensible to seek a single quantitative explanation for all such layering qualitative explanations for lower crustal layering abound and include igneous metamorphic structural and fluid related models measurements of reflection coefficients from the lower crust place strong quantitative constraints on possible models structurally induced anisotropy metamorphic layering or free fluids cannot realistically produce sufficiently bright reflections igneous layering or the juxtaposition of pre existing heterogeneities by shear zones can produce strong reflections results from crustal xenoliths helium isotope ratios palaeo geothermal gradients and chemistry of flood basalts together with numerical modelling of lithospheric extension and asthenospheric melting suggest that underplating and intrusion of the lower crust with mantle derived mafic igneous rocks is common the apparent spatial relationship between lower crustal layering and continental extension and the strength and continuity of the reflections suggest that underplating related to extension and or elevated mantle temperatures is a good explanation for lower crustal layering

the stable isotope geochemistry of australian coals abstract d h 13 c 12 c 18 o 16 o and 34 s 32 s ratios in the organic matrix and organic solvent extracts of australian coals and in the fluids and minerals associated with these coals are reported and reviewed against similar isotopic data for coals from other regions where coals are immature original isotopic differences between macrolithotypes and between solvent extracts lipid concentrates and insoluble residues are largely preserved however with increasing maturity these characteristic differences particularly those between macrolithotypes are rapidly erased conversely where as indicated by low total sulfur contents coals of cretaceous to permian age were deposited under essentially freshwater conditions 34 s values for the organically bound sulfur remain remarkably constant at 4 3 relative to meteoritic sulfur in similar younger tertiary coals the organic sulfur is markedly enriched in 34 s five distinctive isotopic patterns which may be interpreted in terms of the environment of sulfate reduction can be recognized from 34 s 32 s ratio measurements on the various forms of sulfur in australian coals isotopic studies of seam gas hydrocarbons collected in situ show these to be unexpectedly strongly depleted in the heavier isotopes of hydrogen and carbon relative to natural gases from proposed humic sources furthermore no pronounced increase in the 13 c content in methane with increase in rank of the parent coal was observed in addition several sources of associated carbon dioxide have been delineated including normal maturation processes invasion of the seams by magnetic carbon dioxide and interaction of the coal with intrusive magma isotopic exchange between free seam gases is not accepted as an explanation for some unusual isotopic fractionations seen rather the data suggest that these gases may be formed in a state approaching isotopic equilibrium this argument also satisfactorily explains the isotopic compositions of primary siderite and secondary calcite associated with bituminous coal seams however where seams are invaded and permeated with externally derived carbon dioxide usually of magnetic origin carbonates are frequently absent presumably as a result of the action of carbonic acid

lithospheric structure in the southern canadian cordillera from a network of seismic refraction lines lithospheric velocity structure and its relationship to regional tectonics and development of the southern canadian cordillera are derived from a synthesis of interpretations from nine in line seismic refraction wide angle reflection profiles and broadside data recorded during the lithoprobe southern cordillera refraction experiment score and other refraction experiments across southern british columbia and one profile in northwestern washington consistency of the score two dimensional models at their intersection positions is achieved through application of a simultaneous inversion of all relevant traveltime data the cross sectional and map presentations demonstrate the strong degree of three dimensional heterogeneity within the crust and upper mantle a first order characteristic is the continuous increase in crustal velocities westward from the foreland belt to the insular belt the variations do not correlate with the morphogeological belts they do correspond with large scale geological and or

dating of recent lake sediments in the united kingdom and ireland using spheroidal carbonaceous particle scp concentration profiles spheroidal carbonaceous particles scps produced from fossil fuel combustion are found in lake sediments and provide a historical record of atmospheric pollutant deposition the sediment record of these particles is remarkably consistent and the main features are now seen throughout europe and beyond once the scp record from a region has been established using accurately dated cores scp profiles can be used to determine dates at other sites in the region this technique was developed in sweden brit until recently has had limited use in the uk and ireland as the most useful dating feature the subsurface peak was not present in all cores in recent cores this can now almost always be observed dating features for uk and irish cores are found to differ slightly between regions the potential exists for extra dates to be allocated to a profile by using characterisation of scp surfaces to determine changes in fuel type use dates could then be allocated to these changes using documentary sources to derive combustion histories in future years scp dating will become increasingly valuable especially for mid to late nineteenth century sediments as continual decay renders 210 pb progressively less useful for this time interval

geochemistry of coalbed gas a review coals are both sources and reservoirs of large amounts of gas that has received increasing attention in recent years as a largely untapped potential energy resource coal mining operations such as ventilation of coalbed gas from underground mines release coalbed ch4 into the atmosphere an important greenhouse gas whose concentration in the atmosphere is increasing because of these energy and environmental issues increased research attention has been focused on the geochemistry of coalbed gas in recent years this paper presents a summary review of the main aspects of coalbed gas geochemistry and current research advances

iron age to medieval entomogamous vegetation and rhinolophus hipposideros roost in south eastern wales uk abstract karst cave systems are well developed in wales uk and in some instances constitute important bat roosts ogof draenen near blaenavon in south east wales is the most recent major cave discovery 1994 with already 70 km of passages explored spanning a vertical range of 148 m with the exception of one small chamber siambre ddu located directly above the main ogof draenen system very few bats have been noticed inside extensive accumulations of guano attributable to rhinolophus hipposideros are however found in parts of the ogof draenen system in places covering many square metres and sometimes building heaps 0 5 m thick these represent volumes not yet found in any other cave system in the british isles although the date of the abandonment of the main ogof draenen system as a bat roost remains unknown six radiocarbon dates on guano from ogof draenen place the occupation in the iron age to medieval period at least palynological analysis was undertaken on ten samples distributed through the cave comparisons were made with a moss polster and a lake mud sample from the area to provide a first approximation of the regional modern pollen rain and with two modern guano samples one from siambre ddu and one from agen allwedd cave 5 km to the north west to provide a temporal comparison with the fossil guano agen allwedd cave currently is one of the largest active roosts for lesser horseshoe bats in britain and lies close to the present northern limit of this endangered species in europe the main results are that 1 the cave appears to have been used both as a summer and a winter roost 2 most of the ogof draenen guano is formed within c 1600 14 c years and if the largest heap is continuous it has accumulated within 750 14 c years i e 0 16 mm yr 1 3 the fossil guano samples reflect a relatively closed oak forest with more abundant ivy hedera and holly ilex than at present 4 insect pollinated plants such as ilex acer hedera and impatiens glandulifera are over represented in the guano samples 5 in addition to the usual causes of bat roost decline pesticides pollution in the case of ogof draenen we may add entrance blocked by rock collapse and decline of the local forest cover as well as change in its composition

genetic characterization of natural gases natural gases can be characterized genetically using four properties c2 concentration carbon and hydrogen isotope variations in methane and carbon isotope variation in ethane three diagrams for genetic characterization of gases have been designed in which the carbon isotopic composition of methane is correlated with the other parameters in these diagrams compositional fields have been defined for primary gases biogenic thermogenic associated and thermogenic nonassociated and for gases which result from mixing of these gases these fields are strictly empirical and comprise compositional variations found in about 500 natural gases the isotopic and compositional variations in natural gases can be described in terms of 1 processes during formation of the gases such as bacterial fermentation or maturation of organic matter and 2 processes during secondary migration mixing of primary gases is an important and common process migration of gases predominantly affects the c2 concentration whereas the isotopic properties of gaseous hydrocarbons primarily remain unchanged allowing an assessment of the origin of migrated gases and properties of their source rocks the formation of gas from humic organic matter and coals is not yet clear from published data the diagrams use data from various basins and areas interstitial gases from the gulf of california are entirely of bacterial origin traces of thermogenic gases are formed only in the vicinity of dolerite sills gases in the south german molasse basin and in the vienna basin are of bacterial mixed and thermogenic origins data from the north italian po basin provide examples for genetic characterization of migrated gases

assessment of hydrocarbon source rock potential of polish bituminous coals and carbonaceous shales abstract we analyzed 40 coal samples and 45 carbonaceous shale samples of varying thermal maturity vitrinite reflectance 0 59 to 4 28 from the upper carboniferous coal bearing strata of the upper silesian lower silesian and lublin basins poland to evaluate their potential for generation and expulsion of gaseous and liquid hydrocarbons we evaluated source rock potential based on rock eval pyrolysis yield elemental composition atomic h c and o c and solvent extraction yields of bitumen an attempt was made to relate maceral composition to these source rock parameters and to composition of the organic matter and likely biological precursors a few carbonaceous shale samples contain sufficient generation potential pyrolysis assay and elemental composition to be considered potential source rocks although the extractable hydrocarbon and bitumen yields are lower than those reported in previous studies for effective type iii source rocks most samples analysed contain insufficient capacity for generation of hydrocarbons to reach thresholds required for expulsion primary migration to occur in view of these findings it is improbable that any of the coals or carbonaceous shales at the sites sampled in our study would be capable of expelling commercial amounts of oil inasmuch as a few samples contained sufficient generation capacity to be considered potential source rocks it is possible that some locations or stratigraphic zones within the coals and shales could have favourable potential but could not be clearly delimited with the number of samples analysed in our study because of their high heteroatomic content and high amount of asphaltenes the bitumens contained in the coals are less capable of generating hydrocarbons even under optimal thermal conditions than their counterpart bitumens in the shales which have a lower heteroatomic content

crustal velocity structure of the omineca and intermontane belts southeastern canadian cordillera we provide information on the physical properties across two important morphogeological regions of the southeastern canadian cordillera the omineca and intermontane belts and tie together two previously interpreted wide angle seismic lines which have separately probed each zone along strike the data analyzed here line 7 of lithoprobe s 1990 southern cordillera refraction experiment in southern british columbia is along a 410 km profile from the fraser river to radium hot springs near the rocky mountain trench iterative forward and inverse modeling of the seismic travel times constrained by seismic amplitude characteristics and earlier cross line interpretations defines a thin crust with relatively low velocities the upper crust has an average thickness of 15 3 km and an average p wave velocity of less than 6 1 km s 1 with velocities at the bottom reaching 6 2 6 3 km s 1 it is further characterized by velocity gradients which decrease markedly with depth and by low velocity trends which correlate with the traces of crustal scale shear zones a high velocity region at the west end of the profile is coincident with a major uplift structure the midcrust has an average thickness of 9 2 km with velocities below 6 1 km s 1 except for the extreme west end of the profile this defines a midcrustal low velocity zone lvz in the omineca belt and partly in the intermontane belt the lower crust from 24 km to 34 km depth has velocities averaging 6 6 6 7 km s 1 higher velocities in the deep crust may mark the westward extent of north american cratonic rocks at the okanagan valley the upper mantle velocity has an average 8 0 km 5 increasing to 8 2 km s 1 at the maximum depth of ray penetration at 48 km the model presented here compliments well the earlier interpretations of vertical incidence seismic reflection profiles the velocity structure of the crust especially the lvz closely correlates with the regional isotherms while there seems to be no well defined velocity boundary between the intermontane and omineca belts there are distinct velocity differences between the intermontane and neighboring coast plutonic complex to the west the low velocity characteristics of the omineca and much of the intermontane belts may be a consequence of temperature control of the physical parameters of the crust the lithosphere in the southeastern canadian cordillera is clearly anomalous with respect to much of northwest north america and in terms of crustal thickness and velocity structure it is similar only to the basin and range province of the united states

crustal structure of the northwestern basin and range province from the 1986 program for array seismic studies of the continental lithosphere seismic experiment the basin and range province of the western united states is characterized by active east west extension at strain rates of 1 cm yr 1 high regional heat flow of 90 mw m 2 and widespread late cenozoic bimodal rhyolitic basaltic magmatism the 1986 program for array seismic studies of the continental lithosphere basin and range seismic experiment imaged a portion of northwestern nevada to determine the crustal structure and to assess reported differences between refraction versus reflection determinations of moho depth and how the crustal composition and structure has been influenced by volcanic and extension mechanisms our interpretation of the refraction wide angle reflection data suggests that the crust is fairly uniform in thickness and varies by less than 5 km over the 280 km east west profile and 3 km over its 220 km north south length we characterize the velocity structure by five layers 1 an upper most crust composed of sedimentary rocks and basement that has an average velocity of 5 7 km s i 2 a middle crust that extends to a depth of 18 22 with an average velocity of 6 1 km s 1 3 a 10 12 km thick lower crust with an average velocity of 6 6 km s 1 4 a 2 5 km thick transitional crust mantle boundary defined by a 7 6 km s l velocity and 5 an upper mantle with an average pn velocity of 7 9 8 0 km s 1 these data show a uniformily thick crust of 28 km 5 km beneath northwestern nevada and a lack of evidence for significant low velocity crustal layers in general the entire crustal column exhibits uniform positive velocity gradients of 0 02 0 04 s the midcrustal discontinuity is interpreted as a small velocity increase of 0 2 km s l at 18 km depth the absence of a significant midcrustal reflection and the presence of large velocity gradients throughout the crust arises either from 1 a systematic increase in mafic composition with depth or 2 possibly high lower crustal pore pressure that acts to decrease the velocity contrast across the midcrustal boundary our interpreted seismic velocity structure is consistent with a broad range of bulk compositions for the crust upper crustal velocities are consistent with bulk compositions that range from metasediments and granites at shallow depth to diorites at midcrustal levels while lower crustal velocities suggest bulk compositions that range from diorites and amphibolities at midcrustal depths to mafic granulites and gabbros at the base of the crust the uniform crustal thickness of 30 34 km in northwestern nevada is close to the crustal average for the basin and range province but is thin when compared to surrounding regions such as the sierra nevada and colorado plateau where crustal thickness is greater than 40 kin similarily northwestern nevada pn velocities of 7 9 8 0 km s 1 are near the province wide average of 7 9 km s l temperature corrected pn velocities from a 90 mw m 2 geotherm for the basin and range to 60 mw m 2 for the stable interior of the united states are within one standard deviation of the continental average of 8 05 km s i and suggest a uniform upper mantle composition across the basin and range in addition to these observations the homogeneity of the velocity structure beneath the western basin and range argues for a youthful moho and crust that has been reworked by province wide late cenozoic extension episodic magmatism and underplating

the northern limit of the subducted juan de fuca plate system analysis of data recorded at an array of three component broadband seismograph stations deployed on northern vancouver island and the adjacent british columbia mainland at the northern end of the cascadia subduction zone provides the first constraints on the s wave velocity structure of this region and permits us to define the northern limit of the subducted juan de fuca plate system during a 2 year period more than 80 teleseisms were recorded at our five stations the method of receiver function analysis was used to constrain the s velocity structure to upper mantle depths beneath the northern three stations a relatively simple continental crust is interpreted with a well defined moho near 37 39 km depth an upper crustal s velocity discontinuity at these stations is interpreted as the top of the high velocity rocks of the wrangellia terrane in contrast more complicated structure dominated by pronounced low velocity zones dipping to the ne are interpreted beneath our southern two stations the shallower low velocity zone is 6 8 km thick has an s velocity contrast of 0 6 1 1 km s and lies within the continental crust this feature is similar to a pronounced low velocity layer the e zone imaged beneath southern vancouver island the deeper low velocity zone is interpreted as the subducted oceanic crust we interpret the pronounced change in s velocity structure that we observe as the northern limit of the subducted oceanic plate beneath vancouver island this change coincides with significant changes in topography heat flow gravity and geochemistry

crustal seismic velocity and density structure of the intermontane and coast belts southwestern cordillera seismic refraction wide angle reflection data were recorded along a 450 km profile across the intermontane coast and insular belts of the canadian cordillera crust and upper mantle structure was interpreted from traveltime inversion and forward amplitude modelling and the resultant seismic velocities were used to constrain modelling of the bouguer gravity data along the profile a high velocity high density block in the upper 8 km of crust was interpreted as the subsurface extension of harrison terrane the harrison fault at its eastern boundary may extend to at least 8 km depth and perhaps 20 km throughout the crust both seismic velocities and densities are in general high beneath the insular belt low beneath the coast and western intermontane belts and intermediate beneath the eastern intermontane belt however densities are unusually low in the lower crust beneath the coast belt 2800 kg m3 relative to velocities 6 6 6 8 km s this indicates that coast belt plutonic material is present

evidence for the dissolution of magnetite in recent scottish peats abstract magnetic hydrological and geochemical data for 11 scottish peat cores confirm previous reports that anthropogenic pollutants constitute the principal source of ferrimagnets to such environments but indicate that postdepositional fe3o4 persistence may be more limited than formerly envisaged in all cores the lower stratigraphic limit of magnetic enrichment coincides with the water table below which negative mv values and enhanced ratios of fe mn and cu zn depict an abrupt transition to a strongly anoxic regime dissolution of fe3o4 in the reducing inundated zone is also signified by the more rapid down core loss of magnetic properties in cores from topographically depressed sphagnum lawns than in those from more elevated calluna hummocks as a consequence the peak and cumulative sirm values for cores from the former settings appear disproportionately low and the magnetostratigraphic records from adjacent but topographically variant sites are frequently asynchronous in contrast to most marine and lacustrine sediments dissolution of fe3o4 in peat induces a refinement of magnetic mineral assemblages highlighted by declining sirm arm ratios with depth and a hardening of remanence near the base of the magnetically enhanced strata sem micrographs of magnetic extracts from one scottish core indicate that this refinement results from preferential dissolution along crystallographic weaknesses within multidomain phases ultimately causing their disintegration and the adoption of single domain type magnetic behavior rates of dissolution are considerably greater than those reported for marine sediments probably due to the unusually high dissolved sulfide concentrations in mire waters

an early holocene pollen mollusc and ostracod sequence from lake marl at llangorse lake south wales uk an integrated analysis of molluscs ostracods and pollen is presented from early holocene lake marl at llangorse lake powys south wales the mollusc and ostracod records reflect a littoral enviro

natural and antropogenic enrichments of trace metals in peat profiles abstract samples of mosses peats lake sediments and clays were collected from 35 canadian peatlands and analyzed for cr cu fe mn ni pb u v and zn the average composition of the analyzed peats is significantly depleted in fe and mn and enriched in cu u zn and pb compared to typical crustal abundance in contrast ni v and cr are neither significantly enriched nor depleted relative to typical crustal abundance the compositions of the peats vary widely depending on their botanical composition and degree of decomposition the amount of mineral matter present and depth in the peatland to summarize the voluminous trace metal chemistry data a composite sphagnum bog profile was constructed for each metal from the individual profiles using the peat stratigraphy typical of sphagnum bogs in eastern canada to do this the trace metal concentrations of samples of the same botanical composition and similar degree of decomposition were averaged after taking into account the differences in mineral matter contents of the sediments enrichments and depletions through the composite bog profile have been calculated for each stratigraphic layer relative to the average composition of the underlying mineral sediments clays these calculations emphasize the dynamic behaviour of cu u zn and pb and the conservative behaviour of ni v and cr through the composite peat profile cu zn and pb are enriched in ombrotrophic surface peat layers because of significant anthropogenic atmospheric inputs cu and u are enriched in minerotrophic basal peat layers because of natural geochemical processes ni v and cr are neither significantly enriched nor depleted we present a summary of the pore water chemistry ph so42 ch4 of a representative sphagnum bog which shows that these sediments typically range from being acidic ph approximately 4 and oxidizing at the surface above the water table to neutral ph approximately 7 and strongly reducing in the subsurface layers predominance area diagrams log po2 ph based upon equilibrium chemical thermodynamics were constructed and are presented for cr cu fe mn pb u and zn using the predominance area diagrams the behaviour of the dynamic metals in peatland environments is explained in terms of the influence of ph and redox potential on the relative stabilities of solid and aqueous species

a palaeoenvironmental investigation of sediments from the prehistoric mine of copa hill cwmystwyth mid wales this paper investigates the use of mine sediments to reconstruct the vegetational changes and atmospheric pollution history associated with prehistoric and mediaeval metal mining in the ystwyth valley dyfed mid wales pollen charcoal plant macrofossils fossil insects and chemical analyses are presented from radiocarbon dated sediments contained within a prehistoric mine situated on the upper slope of copa hill close to the village of cwmystwyth the results provide additional support to the hypothesis that prehistoric mining had a negligible impact on woodland and that deforestation took place after bronze age mining ceased although high concentrations of cu pb and zn were determined from sediments of prehistoric and roman age the patterns bear little resemblance to off site atmospheric pollution records and to the archaeological evidence for metal mining interpreting geochemical data from mine contexts is problematic as numerous factors influence the distribution and concentration of metals however an on site and off site approach to investigate human environment interactions caused by metal mining is advocated

isotopic and molecular composition of coal bed gas in the amasra region zonguldak basin western black sea previous studies on the coal bed methane potential of the zonguldak basin have indicated that the gases are thermogenic and sourced by the coal bearing carboniferous units in this earlier work the origin of coal bed gas was only defined according to the molecular composition of gases and to organic geochemical properties of the respective source rocks since data on isotopic composition of gases were not available furthermore in the western black sea region there also exist other source rocks which may have contributed to the coal bed gas accumulations the aim of this study is to determine the origin of coal bed gas and to try a gas source rock correlation for this purpose the molecular and isotopic compositions of 13 headspace gases from coals and adjacent sediments of two wells in the amasra region have been analyzed total organic carbon toc measurements and rock eval pyrolysis were performed in order to characterize the respective source rocks coals and sediments are bearing humic type organic matter which have hydrogen indices hi of up to 300 mghc gtoc indicating a certain content of liptinitic material the stable carbon isotope ratios 13 c of the kerogen vary from 23 1 to 27 7 o air free calculated gases contain hydrocarbons up to c 5 carbon dioxide 98 the stable carbon isotope ratios of methane ethane and propane are defined as 13 c 1 51 1 to 48 3 13 c 2 37 9 to 25 3 13 c 3 26 0 to 19 2 respectively the d 1 values of methane range from 190 to 178 according to its isotopic composition methane is a mixture partly generated bacterially partly thermogenic molecular and isotopic composition of the gases and organic geochemical properties of possible source rocks indicate that the thermogenic gas generation took place in coals and organic rich shales of the westphalian a kozlu formation the bacterial input can be related to a primary bacterial methane generation during carboniferous and or to a recent secondary bacterial methane generation however some peculiarities of respective isotope values of headspace gases can also be related to the desorption process which took place by sampling

a model of pollen source area for an entire lake surface a model of pollen deposition on the surface of an entire basin is developed to estimate pollen source area and results are compared with those for a point at the center of a basin i c prentice 1985 quaternary research 23 76 86 1988 vegetation history pp 17 42 kluwer academic this model is more appropriate for approximating the source area of pollen in lake sediment since mixing in lake water and focusing of sediment redistribute pollen originally deposited over the entire surface in general the pollen source radius for the entire basin surface is 10 30 smaller than the source radius for a point at the center the difference in the source radius is more profound for heavier pollen types such as spruce and sugar maple than for lighter types such as oak and ragweed the average pollen input to the entire surface is more strongly influenced by nearby pollen sources than pollen deposition at the center the pollen record from a lake may therefore provide different spatial resolution than the record from a bog of similar radius

review receiver function studies in the southern canadian cordillera receiver function analysis has proven to be a powerful yet inexpensive tool for estimating the s wave velocity structure of the crust and upper mantle beneath three component seismograph stations in the southern canadian cordillera receiver function studies using a portable broadband seismograph array across southwestern british columbia provided site specific estimates for the location of the subducting juan de fuca plate the oceanic crust was imaged at 47 53 km beneath central vancouver island and 60 65 km beneath the strait of georgia further these studies revealed a prominent low velocity zone vs 1 0 km s that coincides with the e reflectors imaged 5 10 km above the subducting plate on lithoprobe reflection lines the e low velocity zone was shown to extend into the upper mantle beneath the strait of georgia and the british columbia mainland to depths of 50 60 km combining the receiver function and refraction models revealed a high poisson s ratio 0 27 0 38 for this feature the contin

the southern coast mountains british columbia new interpretations from geological seismic reflection and gravity data the southern coast mountains of british columbia are characterized by voluminous plutonic and gneissic rocks of mainly middle jurassic to eocene age the coast plutonic complex as well as metamorphic rocks folds and thrust and reverse faults that mostly diverge eastward and westward from an axis within the present mountains and by more localized eocene and younger normal faults in the southeastern coast mountains mid cretaceous and younger plutons intrude bridge river cadwallader and methow terranes and overlap middle jurassic through early cretaceous marine clastic rocks of the tyaughton methow basin the combination of geological data with new or reanalyzed geophysical data originating from lithoprobe and related studies enables revised structural interpretations to be made to 20 km depth five seismic profiles show very cut up and chaotic reflectivity that probably represents slices and segments of different deformed and rearranged rock assemblages surface geology seismic interpretations ph

the ruhr coal basin germany structural evolution of an autochthonous foreland basin abstract the ruhr coal basin is part of the external fold and thrust belt of the variscan orogen in central europe information from extensive coal mining outcrops in the south of the ruhr district reflection seismic surveys and about 800 exploration boreholes in the north support the interpretation of a mostly molasse type sequence more than 6000 m thick of namurian and westphalian age both the southwest northeast trending sedimentary basin structures and the fold structures of the ruhr carboniferous were caused by the compressive regime of the variscan folding in its hinterland but there is no direct relationship between sedimentary basin structures and the later folding structures coal formation started in the namurian c reached its maximum during the westphalian a and b and ended during the westphalian d in total about 250 coal seams were formed but only 50 of them are of economic importance at present strata thicknesses and coal content are generally greater in the southeast of the ruhr coalfield than in the northwest an important exception can be observed in the lower part of the westphalian a where in contrast strata thicknesses are greatest in the northwest in the munsterland region although the coal content remains the greatest in the southeast detailed isopach maps covering 100 200 m thick stratigraphic intervals reveal the existence of a southwest northeast trending zone of reduced subsidence in the ruhr coalfield that moved from southwest northeast during the westphalian this structure can be interpreted as a peripheral bulge coal seems are purer and thicker in the area of this structure which therefore must have been a paleogeographic element within the ruhr basin the general effect of a general decrease in the coal content of the upper carboniferous towards the northwest is superimposed on the migration of the coal content maxima of individual formations towards the northwest during the namurian c and westphalian a the coal content maxima were situated in the area of the river ruhr and during the westphalian b and c in the area of the river lippe the deformation of the ruhr coal basin is of post westphalian age as demonstrated by the concordant folding of the devonian and carboniferous strata the tectonic structure is mainly characterised by the following elements stockwerk tectonics axial elevations and a succession of compressional and extensional tectonics due to the general dip of the ruhr coal basin towards the north different structural levels stockwerks can be observed the southern area displays the lowermost stockwerk with many minor folds of about constant wavelength and low amplitudes thrusts are mainly small and some of them show increasing displacement upwards the central part of the mining area displays the intermediate stockwerk with large tight anticlinoria with minor folds separated by open synclines these are accompanied by folded northwest and southeast vergent thrusts in the northern ruhr district high anticlines and broad trough shaped synclinoria with only few thrusts represent the uppermost stockwerk large fold controlled thrusts die out at this level axial culminations and depressions have strongly influenced the structural style of the folding as well according to this model of stockwerk tectonics excess volume created by disharmonic folding is redistributed by thrusts thrusts dying out downwards at different stratigraphic and structural levels give evidence that there is no regional basal detachment below the ruhr coal basin this interpretation fits very well to new results achieved by the deep seismic reflection profile dekorp 2 n the section clearly shows thick skinned tectonics in the rhenish massif with a shortening of the whole thickness of crust the ruhr coal basin can therefore be interpreted in terms of an autochthonous foreland basin in front of a buried thrust front to the south investigations on the post carboniferous strata of the ruhr basin indicate different periods of active faulting cross and diagonal faults were formed partly at the end of the variscan folding and partly before and during deposition of the zechstein strata a further important period of tectonic movements occurred during the early kimmerian phase in the late triassic furthermore earlier extensional faults in the ruhr basin have been affected by late cretaceous transpression