e i corrected paleolatitudes for the sedimentary rocks of the baja british columbia hypothesis paleomagnetic inclinations from sediments of the western terranes of canada are consistently too shallow for their reconstructed paleogeographic positions two contradicting explanations for these discrepancies are 1 terranes have been displaced northward with respect to the stable american craton by several thousands of kilometres between the late cretaceous 75 ma and the eocene 50 ma and 2 sedimentary inclination error has caused a shallow bias in the paleomagnetic directions here we apply the elongation inclination e i method to paleomagnetic data sets from sedimentary rocks of supposedly allochtonous terranes of western north america to correct for inclination flattening our results indicate that the paleomagnetic directions from the continental silverquick sediments 95 92 ma of southern british colombia are not seriously affected by inclination error because the magnetic signal most likely concerns a chemical remanent magnetisation crm in contrast the marine sediments of the nanaimo group 84 72 ma of vancouver island region appear seriously affected by inclination flattening f 0 7 and the e i corrected mean inclinations are about 98 steeper than the original data we arrive at corrected inclinations paleolatitudes of i 578 k 388n for the silverquick and i 558 k 368n for the nanaimo sediments our corrected paleolatitudes indicate that the canadian terranes were indeed located adjacent to the baja californian margin during the late cretaceous thus supporting the baja bc hypothesis d 2005 elsevier b v all rights reserved

petrography palynology and depositional environments of the early miocene oberdorf lignite seam styrian basin austria abstract an early miocene ottnangian lignite seam up to 36 m thick occurs in the oberdorf trough at the northwestern margin of the styrian basin it forms part of the fluvial koflach voitsberg formation petrographic and palynologic data together with ash yield and sulphur content of samples from two boreholes and two surface profiles have been used to study vertical and horizontal coal facies variations numerous partings and a high ash yield show that the lignite originated in a topogenous mire petrographic indices and palynological data suggest a wet forest swamp paleo environment a fluvial main parting with channel sediments at the eastern margin of the oberdorf trough and overbank sediments in its central part splits the lignite into a lower and an upper seam the lower seam consists of a lower high ash part with frequent splittings and a higher low ash part the upward decrease in number and thickness of silty clayey partings interpreted as crevasse splay deposits reflects the withdrawal of the fluvial sediment source coal composition is characterized by an upward increase in detro xylitic coal and in tissue preservation a good correlation between tissue preservation and percentages of taxodiaceae cupressaceae pollen suggests that this is mainly a result of an increasing contribution of decay resistant gymnosperms conifers the upper seam is also ash rich abundant inertinite at the eastern margin of the oberdorf trough is related to fire episodes inside or outside the mire main features of the upper seam in the central basin are an upward increase in tissue preservation and in percentages of taxodiaceae cupressaceae pollen high sulphur contents in the fresh water lignite are a result of a concentration of sulphate rich waters above the impermeable floors of the lower and upper seams carbonate rich surface waters from the graz palaeozoic and raasberg sequence raised the ph value and controlled sulphur and ash contents in those parts of the lower seam which are uninfluenced by the basal sulphur enrichment palynomorph spectra are dominated by taxodiaceae cupressaceae pollen and pollen from plants living in a mixed mesophytic forest pollen from aquatic and reed plants are rare the ratio between arctotertiary and paleotropic pollen is close to one and supports the early miocene age of the lignite the detected pollen spectra point to warm temperate subtropic and humid conditions

discordant paleomagnetic data for middle cretaceous intrusive rocks from northern baja california latitude displacement tilt or vertical axis rotation 1 paleomagnetic results and u pb zircon dating from the san marcos dike swarm and the el testerazo pluton in the cretaceous peninsular ranges batholith of northern baja california are used to evaluate alternative pre neogene paleogeographic reconstructions of the baja california peninsula the san marcos dike swarm is a dense northwest striking regional dike swarm that is exposed over an 100 km long segment of the batholith and has yielded a u pb zircon crystallization age of 120 1 ma dike attitudes from the swarm suggest a regionally consistent average 320 e strike and 79 ne dip the el testerazo pluton is a younger tonalite intrusion that truncates the northern end of the dike swarm all but one of 36 sites sampled in this study show remanence of normal polarity paleopoles for the san marcos dike swarm and el testerazo pluton are indistinguishable and were combined into a paleopole at 248 1 e 86 6 n a95 4 8 which is displaced with respect to the 122 ma reference pole for stable north america at 198 2 e 72 3 n a95 3 3 the displacement may be described by an apparent clockwise rotation of 18 6 and an apparent northward shift of 8 5 restoring a northward shift of about 3 related to the separation of baja california from north america since 10 ma only a marginal northward displacement of 5 5 is left the clockwise rotation may be the result of crustal block rotations within the right lateral shear systems in northern baja california although there is no geological evidence that supports this possibility alternatively the difference between paleopole and reference pole may be due to tilting of the study area restoring a northeastward tilt of 11 based on the mean dip measured for the san marcos dike swarm in the study area yields a paleopole at 187 6 e 70 8 n a95 5 6 which is indistinguishable from the 122 ma north american reference pole the tilting hypothesis suggested previously as a potential explanation for low inclination of paleomagnetic data from baja california therefore seems to be viable for the discordant paleopoles from this segment of the batholith data obtained previously about 150 km further south and along the western edge of the batholith defined a concordant paleopole without any tilt correction indicating that regional tilting may not be valid for all of baja california

the sandstone derived provenance record of the gualala basin northern california u s a abstract detrital zircon u pb ages and pb isotope compositions of detrital feldspars from the late cretaceous eocene gualala basin in northern california indicate that the basin received sediments from the southern sierra nevada the mojave block and the salinian block mesozoic detrital zircon age components and pb isotope compositions of detrital feldspars from the basin are similar to u pb zircon ages and pb isotope compositions from previously studied coeval conglomerate clasts the detrital zircons and feldspars however also include additional age and pb isotope components that are unobserved or poorly represented in the conglomerate based provenance record these new data suggest a more complex provenance history than that inferred from previously studied conglomerate clasts and strongly imply a connection to the mojave desert provenance evolution of the sediments in the basin indicates that significant contribution of sediment from the mojave desert began during the paleocene when it is inferred that the drainage network expanded eastward from its previous extent the presence of mojave derived late permian zircons as well as feldspars that have high 208pb 204pb ratios in the eocene age german rancho formation indicates that the basin remained in the vicinity of the mojave desert until the eocene this result demonstrates that the gualala basin had undergone very little northward motion at that time and consequently requires that no significant northward translation took place prior to 50 ma the results of this study highlight the value of additional provenance constraints combined with age distributions when identifying sediment source terranes

origin of perylene in ancient sediments and its geological significance the distributions of polycyclic aromatic hydrocarbons pahs in sediments of three upper triassic to middle jurassic sedimentary sequences from the northern carnarvon basin australia have been investigated perylene was found to be a major pah component in the top lower to base middle jurassic sediments that are immature or at low maturity its depth age profiles are not related to the combustion derived pahs that have been believed to be produced during ancient vegetation fires before deposition this suggests a diagenetic origin for perylene the concentration of perylene in the sediments is proportional to the amount of terrestrial input decreasing with distance from the source of land sediments its carbon isotope composition is slightly heavier than higher plant derived pahs but still in the range of the terrestrially sourced pahs including higher plant pahs and combustion derived pahs as suggested previously fungi are proposed to be the major precursor carriers for perylene in sediments based on the facts that 1 perylenequinone structures have been previously suggested to be the natural precursors for perylene 2 perylenequinone pigments exist in many fungal bodies 3 fungi have played an important role during geological processes

compaction corrected inclinations from southern california cretaceous marine sedimentary rocks indicate no paleolatitudinal offset for the peninsular ranges terrane paleomagnetic data have been used extensively to delineate the terrane displacement and accretion history of the western margin of north america however the anomalously shallow paleomagnetic inclinations used to indicate large scale northward translation might be alternatively interpreted as due to postmagnetization tilting of batholithic rocks and compaction of marine sediments to understand the magnitude of burial compaction effects on the post cretaceous motion history of the peninsular ranges baja borderlands terrane a rock magnetic compaction and paleomagnetic study of the ladd formation and the point loma formation from southern california was conducted the anhysteretic anisotropy of remanence of the characteristic remanence carrying grains and individual magnetic grain anisotropy were used to correct the inclinations of each formation individual magnetic grain anisotropy was determined by both compaction experiments and redeposition of a magnetic separate in a dc magnetic field standard paleomagnetic studies of the units indicated that previous ladd formation results could be reproduced and a correction was made at the sample level we were unable to adequately reproduce earlier results of the point loma formation so the average remanence anisotropy was used to correct the previously reported mean direction the mean inclination of the ladd formation was conected from 46 95 8 to 58 95 4 and the mean inclination of the point loma formation was conected from 39 5 5 4 normal and 36 4 16 6 reversed to 56 0 5 1 normal and 53 0 16 7 reversed these results suggest that the peninsular ranges baja borderland terrane has been part of the western north america since the late cretaceous and that clay containing sedimentary rocks may typically experience from 10 to 15 of inclination shallowing due to burial compaction

a hypothesis for the origin of perylene based on its low abundance in sediments of green bay wisconsin abstract perylene a polycyclic aromatic hydrocarbon pah that is common in sediments is believed to originate principally from anaerobic diagenesis of organic matter but its precursor material remains enigmatic we have investigated the formation of perylene in a dated sediment core from green bay wi comparisons of sedimentary profiles of perylene anthropogenic pahs land plant derived hydrocarbons and aquatic contributions of organic matter rule out a specific industrial terrigenous or aquatic precursor for perylene instead perylene seems to be formed from any kind of organic matter as a consequence of a specific type of microbial activity in sub bottom sediments despite an abundance of organic matter the amount of perylene is low in green bay and in other organic carbon rich lake sediments the abundant availability of organic matter that stimulates microbial activity in green bay sediments would seem to favor perylene formation in such sediments we therefore hypothesize that the microorganisms responsible for perylene formation do not compete successfully with those that flourish in sediments rich in organic matter perylene formation consequently does not become significant until deeper in sediments after the more reactive types of organic matter have been consumed

a method for evaluating basement exhumation histories from closure age distributions of detrital minerals we have developed a two dimensional thermokinetic model that predicts the closure age distributions of detrital minerals from pervasively intruded and differentially exhumed basement using this model we outline a method to determine the denudation history of orogenic regions on the basis of closure age distributions in synorogenic to postorogenic forearc strata at relatively high mean denudation rates of 0 5 km m y 1 sustained over millions of years magmatic heating events have minimal influence upon the age distributions of detrital minerals such as k feldspar that are moderately retentive of radiogenic ar at lower rates however the effects of batholith emplacement may be substantial we have applied the approach to detrital k feldspars from forearc strata derived from the deeply denuded peninsular ranges batholith prb agreement of the denudation history deduced from the detrital k feldspar data with thermochronologic constraints from exposed prb basement lead us to conclude that exhumation histories of magmatic arcs should be decipherable solely from closure age distributions of detrital minerals whose depositional age is known c 1999 american geophysical union

bacterial and algal hydrocarbons in sediments from a saline antarctic lake ace lake capillary gas chromatography mass spectrometry c gc ms and iatroscan thin layer chromatography flame ionisation detection tlc fid were used to study hydrocarbon distributions in a sediment core from ace lake a saline meromictic lake in the vestfold hills of antarctica hydrocarbons were abundant in most core sections up to 125 g g dry wt particularly in near surface samples and the distributions were very complex major constituents were identified as phytane 2 6 10 15 19 pentamethyleicosane tetrahydrosqualene a mixture of phytenes cholesta 3 5 diene and fern 7 ene smaller amounts of sterenes and hopenes were also present the predominance of the first 3 acyclic isoprenoids in sediments buried less than 30 cm is consistent with high populations of methanogenic bacteria known to be present phytenes were abundant in all core sections and there was no relationship between their abundance and that of phytane which suggests that they were not derived from methanogenic bacteria phytadienes were minor constituents at all depths studied an unusual feature of some distributions was the high concentrations of fern 7 ene which was the major hydrocarbon in the 20 25 cm core section this alkene was only abundant in sediments which contained high concentrations of methanogen markers suggesting that it may also be indicative of anoxic depositional environments a possible source might be from purple non sulphur bacteria high concentrations of straight chain c29 and c34 alkenes were also found in these sediments but their origin has not been determined major changes in the hydrocarbon distributions with depth indicate that the depositional environment in the lake has altered dramatically since the lake was formed less than 8000 years ago the present condition of permanent anoxic bottom waters probably developed only in the last 1000 years

a possible terrigenous origin for perylene based on a sedimentary record of a pond lorraine france abstract the origin of perylene a five ring polycyclic aromatic hydrocarbon pah in sediments has been a matter of constant debate and its formation mechanisms remain unclear a perylene record in sediment was described and could support a clear link between perylene and terrigenous organic matter om input the distributions of pahs the variations of organic proxies such as the ratio of terrigenous to aquatic n alkanes tar hc and 5 h stanols 5 sterols ratio in sediments have been investigated sediments were sampled from a pond artificially created during the middle ages from a swampy area in the period prior to the pond creation for which high contributions of terrigenous om were evidenced perylene was found to be the predominant pah furthermore perylene content was shown to increase in response to the establishment of more reducing conditions this result supports the common idea that the main source of perylene is natural and derives from biogenic precursors under reducing conditions the creation of the pond in this wetland is marked by the deposition of a wood rich level characterized both by more oxygenated conditions and higher concentrations of perylene these high concentrations could result from the introduction of high concentrations of biogenic precursors of perylene under oxidative conditions subsequently the progressive burial of the woody level could have allowed the establishment of oxygen depleted conditions and the formation of perylene these results validate the use of perylene as a paleoenvironmental marker of terrigenous sources but it must be carefully used as a marker for syn or post depositional oxygen depleted conditions in lacustrine environments

paleomagnetism of the mid cretaceous gem bearing pegmatite dikes of san diego county california usa pegmatite dikes in the peninsular ranges batholith of southwestern california have produced spectacular crystals of semiprecious and precious minerals for over a century aside from their economic importance these dikes straddle a major tectonic boundary and were used to test hypotheses related to the timing and development of this composite batholith paleomagnetic analysis of 252 specimens from 20 sites 12 and 8 sites in the western and eastern zones of the batholith respectively from 11 mines in five dike districts isolated a stable characteristic remanent magnetization direction at 19 sites the site mean directions for the western and eastern zones are statistically indistinguishable at 95 confidence supporting petrologic and geochemical arguments that the dikes of the two zones are coeval and cogenetic after correction for the neogene opening of the gulf of california the paleopole for all 19 site mean directions is indistinguishable from the 94 ma reference paleopole for north america and

mineralogy petrography and organic geochemistry of miocene coal seams in the kinik coalfield soma basin western turkey insights into depositional environment and palaeovegetation abstract the kinik coalfield is located in the south westernmost part of the soma basin in western turkey and hosts all three miocene coal seams from bottom to top km2 km3 and kp1 this study presents the coal petrographical mineralogical and organic geochemical features of samples collected from two deep cores samples from seam km2 generally display low ash yields and high toc content whereas the km3 and kp1 seams are characterized by relatively high ash yields and low toc values furthermore total s content of the kp1 is very high up to 7 0 on dry basis the maceral composition the coal facies diagrams and the distributions of n alkanes and diterpenoids indicate changes of depositional conditions and vegetation in the palaeomires of the km2 seam during early miocene the precursor peat of km2 seam started accumulating under limnotelmatic conditions followed by pure telmatic ones consequently initial mixed vegetation was replaced by a conifer dominant assemblage in the palaeomires in the upper parts of the km2 seam the coal facies indices and high concentrations of n alkanes along with the relatively low di di tri terpenoid ratios are indicators of the higher contribution of herbaceous species and minor abundance of conifers in the palaeomires of km3 and kp1 seams nevertheless the mineralogical composition of the km3 and kp1 seams indicate increased clastic input and alkalinity in the palaeomires that could reduce preservation of organic matter thus high ash yields and low toc were obtained from these seams in addition sulphate rich water supply along with synchronous pyroclastic air borne input into the palaeomires caused elevated total s content of the kp1 seam

late mesozoic and cenozoic thermotectonic history of the mexican pacific margin 18 to 25 n new insight from apatite and zircon fission track analysis of coastal and offshore plutonic rocks abstract apatite and zircon fission track dating was used to constrain cooling histories on granitic samples taken from the offshore acapulco trench batholith and onshore manzanillo and puerto vallarta batholiths located along the southwestern active margin of mexico and from the la paz batholith of southern baja california the apatite data indicate that many of the samples in the manzanillo acapulco trench batholiths cooled rapidly below 60 c shortly after emplacement between 70 and 55 ma the la paz batholith and the sample nm 20 08 of the acapulco trench batholith experienced an older and slower cooling across the apatite partial annealing zone the zircon fission track ages obtained from two samples of the puerto vallarta batholith indicate a rapid cooling from 250 to 110 c between 54 and 50 ma this non coeval cooling of batholiths at two different depths is probably due to uplift and erosion associated with the laramide event in southwestern mexico the three samples from the puerto vallarta batholith suggest a younger evolution across low temperatures with two flat stages located near the base of the apatite partial annealing zone and above it the first flat stage suggests that the denudation or rock uplift rate was reduced at a depth corresponding to the base of the apatite partial annealing zone the younger single apatite ages of the puerto vallarta batholith and the last common cooling of the other batholiths indicate the mild thermal influences of both the plio pleistocene trans mexican volcanic belt and the opening of the gulf of california

new interpretations of the facies of the rhenish brown coal of west germany abstract new ideas concerning the understanding of the facies of the rhenish brown coal of west germany are discussed these new interpretations are based on a significantly larger number of samples and refined procedures for analysis within the field of paleobotany palynology coal petrology and organic geochemistry than were available to p w thomson and m teichmuller the light and dark bands in the coal are mainly the result of different degrees of plant decomposition the influence of the peat forming plant communities plays a subordinate role in the petrographical composition of these particular strata of the rhenish brown coal

magnetostratigraphy of tertiary sediments from the hoh xil basin implications for the cenozoic tectonic history of the tibetan plateau summary we conducted an integrated palaeomagnetic and stratigraphic study on a 5452 8 m thick sedimentary sequence of the hoh xil basin in northern qinghai tibet plateau to obtain a chronostratigraphic framework for these sediments a total of 966 individual oriented palaeomagnetic samples spaced at stratigraphic intervals were collected from six measured sections in the hoh xil basin magnetic directions in these samples were obtained by progressive thermal mainly and alternating field demagnetization experiments most samples exhibit two components of magnetization the lower unblocking temperature component is an overprint resembling the present day geocentric axial dipole field direction at the sampling locality the most stable characteristic remanence chrm appears to be an early chemical remanent magnetization residing mainly in haematite the positive results of fold and reversal tests indicate that the chrm is a record of the palaeomagnetic field close to the time of formation of these sediments further evidence for the magnetization of these sediments acquired close to their time of deposition is the fact that patterns of magnetic reversals can be matched with the established polarity timescale on the basis of the distinct interval of magnetic reversal zones and biostratigraphic datums 13 magnetozones can be recognized at the hoh xil basin that range from chrons c11 to c23 30 1 51 0 ma the age of the fenghuoshan group is palaeomagnetically dated as 51 31 ma early eocene middle early oligocene and the age of the yaxicuo group is between 31 and 30 ma middle early oligocene late early oligocene the new palaeomagnetic data from the fenghuoshan group suggest that it has undergone no significant rotation since the oligocene in contrast declination data from the yaxicuo group in wudaoliang area imply a vertical axis clockwise rotation 29 1 8 5 since the late oligocene the tertiary palaeomagnetic pole position of the hoh xil basin implies a significant northward convergence of the hoh xil basin 1600 km with respect to eurasia siberia since early eocene late oligocene time our results are consistent with the pattern of disturbingly low palaeolatitudes derived from a large number of high quality palaeomagnetic studies of tertiary rocks from sites that reach all the way from eastern china to kyrgyzstan future work is needed to separate the influences of sedimentary inclination shallowing and tectonic shortening

algal and bacterial hydrocarbons in particulate matter and interfacial sediment of the cariaco trench particulate matter samples 53 m size fractions and sediment from the sediment water interface were collected in the cariaco trench an anoxic marine basin on the continental shelf of venezuela and analyzed for hydrocarbons concentrations of hydrocarbons were highest 10 20 ng 1 in oxic surface waters 0 150 m and at the top of the anoxic zone 350 600 m and were low 3 4 ng l in the low oxygen zone above the oxic anoxic interface 150 250 m and anoxic bottom waters 600 1150 m branched c25 trienes and tetraenes dominated the hydrocarbon distributions in 53 m particles particle size and depth distributions of the hydrocarbons demonstrate the importance of algal hydrocarbons in surface waters coupled with increased abundances of bacterial hydrocarbons especially in the 53 m particles in the anoxic zone these observations illustrate the importance of oxic anoxic interfaces even in the oceanic water column as zones of intense microbial alteration of organic matter and as sources of some of the organic compounds found in sediments

clockwise rotation and implications for northward drift of the western transverse ranges from paleomagnetism of the piuma member sespe formation near malibu california 1 new paleomagnetic results from mid tertiary sedimentary beds in the santa monica mountains reinforce the evidence for large scale rotation of the western transverse ranges and anisotropy measurements indicate that compaction induced inclination flattening may resolve a long standing controversy regarding the original paleolatitude of the rotated block previously published paleomagnetic data indicate that post oligocene rotation amounts to 70 110 clockwise affecting the channel islands santa monica mountains and santa ynez mountains the sespe formation near malibu consists of a lower member dominated by nonmarine sandstone and conglomerate and an upper section the piuma member which consists of gray red sandstone and mudstone interbedded with minor tuff and limestone beds the piuma member has a paleomagnetic pole at 36 6 n 326 7 e a95min 5 0 a95max 9 6 obtained by thermal demagnetization of 34 oriented cores from oligocene and early miocene beds after correcting for plunge of the geologic structure the data are consistent with significant clockwise rotation 77 7 of the region relative to stable north america rotation of the western transverse ranges is generally viewed as a consequence of pacific north american plate interactions after 28 ma when east west subduction gave way to northwest transform motion in southern california inclinations from the piuma study indicate a paleolatitude anomaly of 11 7 and are consistent with a mean northward drift that exceeds generally accepted san andreas fault displacement by a factor of 3 however sedimentary inclination error may accentuate the anomaly anisotropy of isothermal remanent magnetization indicates inclination flattening of approximately 8 and correction for the effect reduces the paleolatitude anomaly to 5 3 5 8 compaction may explain the inclination flattening in these sedimentary rocks but the process does not adequately explain lower than expected inclinations found in previous studies of miocene volcanic rocks of the western transverse ranges

organic geochemistry of the lower miocene oberdorf lignite styrian basin austria its relation to petrography palynology and the palaeoenvironment abstract in the oberdorf trough at the northwestern margin of the styrian basin austria an up to 36 m thick lower miocene ottnangian lignite seam occurs within the fluvial koflach voitsberg formation previous results indicate that the lignite originated in a topogenous mire within a wet forest swamp palaeoenvironment differences in soluble organic matter som yield of borehole samples from the lignite seam are related to free lipids present in plant waxes or resins and the presence of thermally labile polymers indicated by the contents of liptinite macerals i e resinite suberinite and liptodetrinite the n alkane distribution patterns are dominated by high molecular weight lipids with marked odd over even predominance originating from plant waxes a contribution of algae to the even numbered short chain lipids observed in considerable amounts in the footwall sediments is proposed terpenoid biomarkers characteristic for conifers and angiosperms were detected consistent with palynomorphic spectra which are dominated by forest swamp pollen taxodiaceae cupressaceae and pollen from plants living in a mixed mesophytic forest excellent relationships between higher plant biomarker composition and palynologic data indicate that the organic geochemical results reflect the varying inputs of coniferales vs angiosperms the data further imply that cuparene may be used for taxonomical differentiation of coniferales families organic geochemical data provide evidence that the content of land plant derived biomarkers is controlled by the input of resin rich conifers concentrations of hopanoids dominated by hop 17 21 ene generally increase towards the top of the lignite a section characterised by high extents of aromatisation of triterpenoid biomarkers the results suggest that the aromatisation of angiosperm derived biomarkers may be governed by the activity of anaerobic rather than by aerobic bacteria however changes in the depositional environment and palynologic facies during peat formation probably influenced the origin and fate of angiosperm derived triterpenoids the results indicate how biomarker composition may contribute to the evaluation of environmental changes cross correlations of organic geochemical parameters with palynological data and petrography based facies indicators will provide further insights in the peat forming vegetation and biogeochemical activities in the mire

paleomagnetism and tectonic significance of albian and cenomanian turbidites ochoco basin mitchell inlier central oregon 1 understanding continental growth and convergent margin dynamics associated with terrane accretion and modification of the cordilleran margin of north america is prevented by conflicts in paleogeographic models for major terranes oceanic plates and the north american margin we present new paleomagnetic data suggesting that the blue mountains superterrane located at an inboard portion of the cordilleran margin has undergone substantial northward translation and clockwise rotation relative to north america since mid cretaceous time positive baked contact conglomerate and fold tests provide evidence that the magnetization of these rocks dates from their deposition these results yield a mean direction of d 10 8 i 58 5 k 127 95 4 1 and n 11 comparison of magnetic inclinations and magnetic fabrics shows no evidence for inclination error a paleolatitude of 39 2 4 8 4 3 n is obtained indicating a paleolatitude anomaly of 15 9 4 1 northward translation of 1760 460 km and cw rotation of 37 7 3 with respect to north america since circa 93 ma application of an ad hoc 5 inclination error yields translation of 1200 460 km through comparison with other units in the western cordillera we infer that the mitchell inlier was located adjacent to the sierra nevada arc during mid cretaceous time and that the blue mountains province may correlate with the intermontane superterrane in british columbia other interpretations such as large inclination errors or an independent displacement history for the mitchell inlier are possible but unlikely more work is needed to fully test these hypotheses and resolve major questions of cordilleran tectonics

carbon isotope behaviour in wood and cellulose during artificial aging abstract modern wood was subjected to an artificial decay process to investigate its behaviour with respect to the stable carbon isotope composition of wood and the corresponding cellulose four different woods were used namely oak quercus robur beech fagus sylvatica pine pinus sylvestris sequoia sequoiadendron giganteum and pure spruce cellulose the process of decay was simulated by heating samples in water at 180 c from minutes to months during the decay period the carbon content of wood increased to almost 70 while the cellulose content decreased gradually to zero the degradation proceeds according to a two stage process an initial very fast break down is followed by a rather slow degradation after a strong discrimination against 13 c during the initial phase the 13c 12c ratio increases again mostly up to its initial value the carbon isotope trend for cellulose shows a similar pattern though it is less pronounced maximum discrimination was 1 relative to the untreated wood 13c values of cellulose decreased by up to 0 3 the 13 c depletion is presumably a consequence of the preferential decomposition of cellulose as compared to lignin data on fossil trees are compared with the results obtained from this treatment of aging the 13 c decrease is in line with observations from these fossil woods but the ensuing 13 c enrichment is at most weakly to be seen

a compaction correction for the paleomagnetism of the nanaimo group sedimentary rocks implications for the baja british columbia hypothesis 1 a paleomagnetic and magnetic anisotropy study of the late cretaceous northumberland formation on hornby island british columbia was conducted to determine if burial compaction could have caused its anomalously shallow inclinations the shallow nanaimo group inclinations have been used to support the baja british columbia baja bc model of continental dynamics in which superterranes were transported thousands of kilometers northward along the active north american continental margin in the cretaceous a mean of the site means from the northumberland formation is d 5 8 i 50 9 95 7 9 n 8 anisotropy of magnetic susceptibility ams and anisotropy of anhysteretic remanence aar were measured to identify and correct for any inclination shallowing caused by depositional compactional processes both concretion and fine grained rock samples had typical depositional compactional ams and aar fabrics with bedding perpendicular minimum principal axes a revised correction equation was used to account for the effects of either triaxial magnetic fabrics or small angular deviations of principal axes from the bedding plane the average inclination was increased by 9 6 after the compaction correction d 6 1 i 60 5 95 7 1 n 8 and the mean inclination of concretion and fine grained rock sites was significantly steeper than ward et al s 1997 result i 42 5 placing hornby island and the insular superterrane at a paleolatitude of 41 n in the late cretaceous this paleolatitude indicates that baja bc did translate northward since the late cretaceous by about 1600 km but not by the 3500 km previously indicated

evaluation of the baja controversy using paleomagnetic and faunal data plume magmatism and piercing points abstract the controversy over late cretaceous locations of baja alaska baja bc stikinia and western quesnellia centres around whether a they were within 1000 km of their present positions or b located 1000 5000 km south along the western coast of laurentia to be transported northwards by the kula plate during the late cretaceous and cenozoic the latter is supported by paleomagnetic data including data that pass a fold contact or reversal test whereas the former is based upon correlation of strata across faults although various critical tests have been proposed and tried interpretations are equivocal e g alternative interpretations for the source of detrital zircons in baja bc we propose that the presence of plume magmatism provides unique vertical piercing points thus correlation of the 70 ma plume magmatism in northern stikinia with the yellowstone hotspot locates stikinia 2000 km to the south and 1000 km off the western coast of laurentia on the other hand the absence of 90 70 ma yellowstone plume magmatism in the presently adjacent baja bc but the presence of 60 47 ma yellowstone plume spreading ridge magmatism in southern baja bc southern vancouver island and coast ranges of washington and oregon implies that it moved at least 1200 km northwards between 70 and 60 ma i e a rate of 12 cm year the spreading ridge may be correlated with the kula farallon ridge furthermore the presence of middle late triassic plume magmatism in wrangellia and the peninsula and alexander terranes suggests 2000 km of relative dextral movement between baja alaska and baja bc applying these conclusions to pre 90 ma paths of baja alaska bc across the pacific ocean suggests that it had three components 1 northeasterly between 230 and 180 ma 2 eastsoutheasterly between 180 and 140 ma and 3 northeasterly between 140 and 90 ma whereas the latter component is consistent with published terrane tracks the 180 140 ma component is at odds suggesting that this latter segment be reassessed the weight of evidence in favour of correlating geological piercing points across the gulf of california appears to outweigh paleomagnetic evidence for 1000 2500 km of apparent northward displacement of baja california in the cretaceous and early tertiary which may be explained by 15 20 tilting of fault blocks recorded by 40 ar 39 ar cooling ages thus we conclude that whereas baja alaska baja bc stikina and western quesnellia were transported between 1000 and 5000 km northwards along the western margin of laurentia during the late cretaceous and cenozoic baja california has not moved more than that required to open the gulf of california

coastal and baja california paleomagnetism reconsidered systematic reappraisal of paleomagnetic data from upper mesozoic and lower cenozoic sedimentary rocks and igneous rocks of late mesozoic age in coastal and baja california indicates that pluton tilt and shallowing of paleomagnetic directions by sedimentary compaction resolve observed discordances with the north american apparent polar wander apw path when the best available reference paleopoles are used for comparison the hypothesis of major tectonic transport in excess of distances inherent in current models for evolution of the san andreas transform system is unnecessary and in conflict with geologic observations fresh insights derived from recent data sets and improved analysis include the following 1 the limited paleomagnetic data recording primary remanence for upper jurassic and lower cretaceous volcanic rocks in coastal california are concordant with the north american apw path 2 the tilt of the peninsular ranges batholith inferred from paleobarometric data eliminates its declination discordance and reduces its inclination discordance to a level where ovals of confidence for observed and expected paleomagnetic directions overlap 3 key cretaceous and paleogene red bed successions on the salinian block of coastal california and in baja california have yielded concordant paleolatitudes 4 the discordances of different apparent paleolatitudes inferred from cretaceous and paleogene marine sedimentary strata lie within a range that can be attributed to compaction shallowing on the basis of both experimental information and observations from elsewhere 5 turbidites are more susceptible to compaction shallowing than shelf and deltaic strata 6 the uniform rotation of paleomagnetic directions inferred previously for peninsular california is not supported by the full array of data now available from multiple localities 7 basement ties of the salinian block in california and of the baja california peninsula to the continental interior preclude any hypothesis for tectonic transport much in excess of san andreas transform slip

compaction corrected paleomagnetic paleolatitudes for late cretaceous rudists along the cretaceous california margin evidence for less than 1500 km of post late cretaceous offset for baja british columbia the paleolatitudinal distribution of bivalve rudists has important significance for the baja british columbia baja bc hypothesis that western canadian superterranes from british columbia have been displaced 3000 km since cretaceous time rudists are not observed in baja bc sedimentary rocks yet they are common in late cretaceous strata in california and baja california which have the same paleomagnetically determined paleolatitudes approximately 25 n as baja bc rocks of late cretaceous age in order to resolve this contradiction and to delimit more exactly the southern paleolatitudes of baja bc paleomagnetic inclinations corrected for the effects of burial compaction were used to determine the paleolatitudinal distribution of rudists along the california margin compaction corrected paleomagnetic data from the peninsular ranges and salinia terranes indicate that rudists were restricted to paleolatitudes between 34 and 40 n evidence of coastal upwelling in the latest cretaceous marca shale may explain the northern limit of the rudist distribution these data suggest that baja bc was no farther south than 40 n in the late cretaceous thus limiting its post cretaceous displacement to less than 1500 km and that burial compaction has also affected the paleomagnetism of nanaimo group sedimentary rocks from vancouver island this result also helps resolve the conflict between paleomagnetic results which show 1500 km of post late cretaceous offset between the insular coast plutonic complex superterrane and the intermontane superterrane and geologic observations which can allow only tens of kilometers of offset between these terranes in the methow tyaughton basin

palaeohistological studies on miocene brown coals of central europe abstract the texture of peat forming plants is often excellently preserved in the miocene seam layers of the central european depression as the micropetrographic categories maceral and microlithotype are primarily based only on the optical properties and degree of coalification of the cell wall the additional consideration of histological characteristics is expected to bring about a considerable gain in knowledge regarding the petrographic description and facies interpretation of seam layers in the micropetrographic characterisation of some brown coal seams in germany the microlithotype group textite was used for textural descriptions the microlithotypes included in textite are defined by histological features and are comparable to phyterals the microlithotypes are 1 xylo textite tissue with histological characteristics of wood 2 marcoduria textite tissue of primary roots of conifer 3 peridermo textite cork tissue and bark parenchyme 4 phyllo textite leaf tissue in particular of conifers the various microlithotype proportions were determined by point counting a micropetrographic identification of the types of facies in the 2nd lusatian seam horizon was successful the facies types show a vertical recurrent succession the distribution of histological microlithotypes in seam profiles reveals asymmetric changes in contents of peridermo textite and marcoduria textite which correspond to facies successions the micropetrographic composition of facies successions both in the 2nd lusatian seam horizon and in the frimmersdorf seam of lower rhenish basin is similar

thermal evolution of monte blanco dome low angle normal faulting during gulf of california rifting and late eocene denudation of the eastern peninsular ranges footwall rocks of the canada david detachment fault northeastern baja california record late eocene earliest oligocene and late neogene cooling events previously unrecognized in the region biotite 40 ar 39 ar ages of 65 ma reflect slow cooling through 350 c 5 to 10 m y later than is typical in the region multiple diffusion domain modeling of k feldspar 40 ar 39 ar release spectra shows very slow cooling 1 c m y from 65 to 45 ma accelerated cooling from 315 c to 215 c between 45 and 33 ma records at least 3 4 km of denudation that we relate to east side up reactivation of late cretaceous structures that generally follow the oceanic continental suture previously established rivers flowing west from mainland mexico apparently became further entrenched during this uplift and continued to supply distinctive rhyolitic detritus to the coast ultimately surface uplift disrupted and rerouted the extraregional rivers some 2 to 6 m y before the cooling event ended footwall rocks remained nearly isothermal from 30 to 15 10 ma when renewed rapid cooling 33 17 c m y began in response to footwall exhumation by top to the west low angle normal faulting that accommodated rift related extension in what finally became the gulf of california apatite fission track and u th he ages of 5 ma and 4 ma respectively record final detachment related cooling through 110 c to 70 c thermal kinematic modeling suggests that 5 7 km of late neogene tectonic denudation and 10 12 km of horizontal extension were necessary in order to unroof the samples by 2 ma additional extension of unknown magnitude has probably occurred subsequently geodetically measured horizontal extension rates are considerably higher than the long term extension rate that can be attributed to detachment faulting

perylene an indicator of alteration processes or precursor materials abstract perylene is a polycyclic aromatic hydrocarbon pah that is found pervasively in both marine and freshwater sediments yet its origin remains obscure we have explored relationships between perylene and possible precursor materials in two 210 pb dated sediment cores from lake ontario in which contributions of aquatic and land plant organic matter and concentrations of anthropogenic pahs have been measured no significant correlations were identified between perylene occurrence and indicators of terrigenous or aquatic sources of organic matter distinct differences between perylene and anthropogenic pah sedimentary profiles rule out an industrial source for perylene at these locations the general pattern of low to absent perylene concentrations in upper oxic sediments and increasing concentrations with depth indicates that in situ diagenesis under anoxic conditions produces perylene and that its formation is kinetically controlled the results of our study suggest that perylene is formed from non specific precursor materials by biotic or abiotic transformation processes if this scenario accurately describes its formation then perylene is an indicator of depositional conditions rather than the source of organic matter

a paleomagnetic transect of the mid cretaceous peninsular ranges batholith baja california mexico we report structural paleomagnetic and magnetic fabric data for midcretaceous plutons of the peninsular ranges batholith along a transect at 30 n latitude four plutons in the western sector are characterized by characteristic magnetizations residing in magnetite in this sector el milagro aguaje del burro la zarza and san telmo plutons yield a combined paleopole at 82 1 n 169 7 e k 137 6 a 95 7 9 n 4 38 sites which rotated for closure of the gulf of california falls at 79 3 n 179 5 e and it is concordant with the north america reference pole plutons in the transition zone between the eastern and western sectors of the peninsular ranges have magnetizations residing in hematite el potrero and san jose plutons yield highly discordant paleopoles indicating apparent clockwise rotation r and fl attening f of 33 0 5 1 and 27 6 6 1 respectively san jose and 46 1 5 9 and 31 0 7 0 el potrero the discordance is best explained by west down tilt of the crustal block between the main martir thrust and the rosarito fault which are major compressional structures parallel to the trend of the peninsular ranges the san pedro martir pluton a large la posta type pluton on the eastern sector of the transect has magnetizations that reside primarily in hematite the mean

biomarker and stable carbon isotope systematics of fossil wood from the second lusatian lignite seam of the lubstow deposit poland abstract decay of fossil wood gelification collected from the middle miocene 2nd lusatian lignite seam at the lubstow open cast mine poland is characterised by its maceral variety fluorescence intensity and cellulose content cellulose decomposition leads to lower molar h c ratio values of the organic matter as indicated by higher total organic carbon toc content of samples characterised by low cellulose content biochemical formation of hydrocarbons in the wood due to enhanced microbial activity is evidenced by higher hydrocarbon content in the extracts higher relative proportions of n alkanes and hopanoids are observed in the hydrocarbon fractions of wood remains characterised by low cellulose yield the results provide evidence for the formation of these compounds during biogeochemical transformation of organic matter hopanoid contents are considered to reflect the activity of aerobic bacteria and or fungi because of enhanced perylene content in the hydrocarbon fractions from gelified wood samples fungi are considered as the major precursor carriers of this polycyclic aromatic hydrocarbon the results provide evidence that biomarker composition of fossil wood can be used to trace biochemical transformation processes chemotaxonomical classification of fossil wood fragments as gymnosperms most probably species of the coniferales families taxodiaceae cupressaceae are based on the molecular composition of terpenoid hydrocarbons and a mean 13 c value of 24 5 depletion of gelified samples in 13 c as compared to ungelified wood is caused by the effect of progressive decomposition of cellulose the data indicate that cellulose 13 c data mean 13 c 20 8 are also affected by wood decomposition and so only samples with comparable cellulose content should be used for the reconstruction of environmental changes inter species as well as intra plant variation in carbon isotope differences and of decay resistance between cellulose and lignin have to be taken into account

new paleomagnetic rock magnetic and petrographic results from the valle group baja california mexico exploring the causes of anomalously shallow paleomagnetic inclinations 1 a detailed paleomagnetic rock magnetic and sedimentologic study was conducted on cenomanian age strata of the valle group at el campito baja california to examine the burial compaction effects on the paleomagnetic inclination of marine sedimentary rocks alternating field and thermal demagnetization isolated a characteristic remanence at 16 of 18 sites with a mean of dec 342 6 inc 19 1 and 95 3 4 the inclination is 38 7 shallower than that predicted by the reference paleopole for north america laboratory experiments indicate that compaction could account for only 7 5 of the inclination shallowing fold tests at different scales yield both positive and negative results making a tight constraint on the remanence s age impossible a primary postdepositional remanence is supported by bedding parallel foliations in the anisotropy of anhysteretic remanence fabric although primary anomalously shallow inclinations could indicate significant southerly then northerly paleolatitudinal offset a more likely scenario is a late cenozoic low temperature remagnetization which is suggested by alteration along the edges of some detrital silicate grains and a bimodal magnetic grain size distribution revealed by isothermal remanence data the synthesis of the data indicates that the vizcaino terrane was contiguous with the cordillera margin during remagnetization and underwent a subsequent 13 5 5 4 clockwise rotation we tentatively interpret that the remagnetization resulted from burial and or miocene volcanism which caused an acquisition of thermochemical remanent magnetization tcrm this study reveals a complicated remanence that resists easy interpretation and suggests caution in studies of similar rocks

acquisition of detrital magnetization in four turbidites turbiditic events are mostly avoided in paleomagnetic studies and therefore their remanence and magnetic properties are poorly described turbidites are exempt of bioturbation and potentially provide pertinent information about depositional remanence we studied four quaternary turbidites of different origins in marine sediment cores upward fining of both magnetic and sedimentary fractions indicates that coarser grains reached the bottom first we observe a progressive shallowing of the magnetic inclinations between the upper and bottom layers of the turbidites that increases with the size of the events and obeys a simple linear scaling law measurements of magnetic anisotropy suggest that hydrodynamic conditions prevailing during deposition seem to be dominant for the alignment of the magnetic grains we suggest that small spherical grains are randomly oriented with zero resultant magnetization in presence of strong turbulent conditions while the alignment of elongated grains is constrained by the competition between gravity and magnetic forces a possible scenario is that under turbulent conditions they tend to rest at the bottom with their long axes parallel to the sediment surface and therefore with shallow inclinations whereas weakly turbulent conditions like during the smallest 26 cm thick event do not disturb the magnetic alignment and therefore do not generate inclination shallowing this article is protected by copyright all rights reserved

paleomagnetism of the duke island alaska ultramafic complex revisited the duke island ultramafic intrusion was emplaced into the alexander terrane immediately preceding development of a regional mid cretaceous thrust belt paleomagnetic samples were collected from exposures of ultramafic rock with cumulate layering northwest of judd harbor and northwest of hall cove thermal demagnetization results were analyzed using principal component analysis to isolate the characteristic remanent magnetization site mean characteristic directions determined from 16 sites fail the fold test at 95 confidence indicating that cumulate layering attitudes were highly contorted at the time of magnetization at least on a scale of tens of meters variations in cumulate layering attitudes probably resulted from the combined effects of thermal convection phenomena during crystallization and deformation following crystallization but prior to magnetization analysis of cumulate layering over larger structural domains indicates that kilometer scale deformation produced southwest plunging folds within the hall cove and judd harbor bodies bogue et al 1995 proposed that a compound structural correction involving unplunging of fold axes followed by unfolding of average cumulate layering could restore cumulate layering to horizontal however using the full set of 21 site mean paleomagnetic directions from duke island 16 from the current study and 5 from bogue et al 1995 the compound structural correction yields mean paleomagnetic directions from the judd harbor and hall cove areas that are statistically distinguishable at 99 confidence this result indicates that even on the kilometer scale cumulate layering within the duke island ultramafic intrusion was neither coplanar nor horizontal at the time of magnetization observations of cumulate layering in other ultramafic intrusive rocks indicate that this layering can significantly depart from horizontal by 10 20 even on the kilometer scale therefore use of cumulate layering of ultramafic rocks as a proxy for paleohorizontal is not justified and paleomagnetic directions from the duke island ultramafic intrusion cannot be used to infer the cretaceous paleolatitude of the insular superterrane

polar aromatic biomarkers in the miocene maritza east lignite bulgaria aromatic and polar compounds of lignite lithotype bitumens maritza east were analyzed diterpenoid phenols and ketophenols i e mainly ferruginol sugiol hinokione and products of their diagenetic transformations were identified as the dominant biomarkers a variety of sesquiterpenoids was present as well these compounds provided evidence for the assumption that members of the cupressaceae s 1 are the coal precursors polar triterpenoids i e lupeol lupenone adiantone and hopanones were present in subordinate quantities in the humoclarain sample these biomarkers support an input of deciduous angiosperm vegetation to the peat swamp source matter three diagenetic transformation schemes for the diterpenoid phenols ketophenols are proposed 1 ferruginol and or sugiol alteration through dehydrogenation demethylation and ring b cleavage 2 hinokione aromatization to simonellite and 3 7 ketototarol change through 7 ketototar 5 enol to 20 nor 3 oxo totara 5 10 6 dienol the identified diterpenoids demonstrated the presence of gymnospermae in the coal forming community furthermore the phenolic diterpenoids indicated a specific input of organic matter from conifers of the cupressaceae taxodiaceae or podocarpaceae as the most abundant trees in the coal forming swamp

bedrock geology of the san francisco bay area a local sediment source for bay and coastal systems abstract local watersheds may contribute over half of the sediment load coming into san francisco bay today the bedrock underlying these watersheds is the ultimate source for most of this sediment this paper outlines the geologic history of this bedrock which records the complex tectonic history of the san francisco bay area over the last 200 ma the jurassic to eocene franciscan complex in the bay area is the most widespread bedrock the local franciscan can be broken into nine tectonic terranes that represent pieces of seafloor that were accreted to the north american margin in over a 100 myr period of subduction each terrane has a unique age range sequence of seafloor rocks and metamorphic history the franciscan rocks were thrust eastward under the great valley complex the great valley complex reflects a forearc basin comprised of jurassic ocean crust the coast range ophiolite and overlying jurassic and cretaceous turbidite dominated sedimentary rocks of the great valley group by the beginning of the cenozoic era shallowing of the angle of subduction along the continental margin led to uplift and infilling of the forearc basin to shelf depth recorded at this time are sedimentary sequences governed by eustatic sealevel changes and evidence of the first unroofing of franciscan rocks marine sedimentary rocks dominate the region through the miocene and unconformities within the early tertiary sedimentary record reflect periods of tectonic activity and uplift middle to late miocene sedimentary rocks are extensively deposited throughout the bay area in the late miocene the mendocino triple junction passed northward through the area and transform tectonism commenced a slab window developed behind the triple junction resulted in volcanic activity that produced the sonoma volcanics in the north bay and volcanics of the east bay hills by pliocene time terrestrial sedimentary rocks were being deposited in many parts of the bay area faulting associated with the san andreas system led to the development of small basins the displacement of local bedrock blocks and the transport of the salinian complex from the southern sierra to the western margin of the bay area the modern topography of the region started emerging by about 6 ma to 4 ma when compression across the san andreas system increased and uplift of the coast ranges began the first estuarine influence in san francisco bay is recorded in 600 ka rocks about the same time as the modern sacramento river system started flowing through the san francisco estuary valley today s local san francisco bay watershed is comprised of numerous small stream systems around the bay with headwaters in the surrounding hills and mountains active tectonism produces relief in these watersheds of typically 500 m or more with the ridgelines typically supported by more resistant bedrock units steep topography leads to rapid bedrock erosion particularly of the finer grained sedimentary rocks landslides provide a significant portion of the sediment carried by the streams and several of the bedrock units are more prone to landslides particularly the central and novato quarry terranes of the franciscan complex and finer grained units of both the great valley group and tertiary rocks many of the larger streams have dammed reservoirs that trap much of their sediment load before it can reach the bay

palaeomagnetism of the west sakhalin basin evidence for northward displacement during the cretaceous summary a significant margin parallel translation of terranes is postulated by all models for tectonic evolution of the east asian continental margin although the timing and magnitude of displacements of individual elements are poorly constrained as yet the west sakhalin basin a forearc basin associated with the cretaceous volcanic arcs is one of the displaced tectonic elements our palaeomagnetic study of the basin rocks provides the first quantitative constraints on its cretaceous history we identified a characteristic magnetization in the berriasian valanginian basalt representing the oceanic basement of the basin and four characteristic magnetizations in a continuous sequence of the albian to maastrichtian siliciclastic fill of the basin a combination of the positive fold conglomerate and reversals tests supports the primary origin of the remanence in the sediments palaeomagnetic data indicate a gradual shift of the west sakhalin basin from subequatorial latitudes during the early cretaceous to about 40on by the late cretaceous the main phase of the margin parallel migration took place during the early cretaceous and ended by the cenomanian the continuous sedimentary sequence records 50 degrees of progressive clockwise rotation during the late cretaceous

revisiting the baranof leech river hypothesis for early tertiary coastwise transport of the chugach prince william terrane abstract according to the baranof leech river hypothesis originally proposed in 1982 1 schists on southern baranof island in southeastern alaska were contiguous with the leech river schist on southern vancouver island until 40 ma and 2 both rock units were part of the 2200 km long chugach prince william terrane which was displaced northward about 1100 km after 40 ma isotopic data obtained since 1982 show that the syn magmatic metamorphism that produced the baranof and leech river schists occurred at 50 ma not at 40 ma large magnitude coastwise slip of the terrane is therefore post 50 ma igneous rocks in the baranof and leech river units are part of the sanak baranof magmatic belt of forearc magmatism which has been ascribed to the early tertiary subduction of an oceanic ridge the slab window also gave rise to early eocene near trench plutonic and volcanic rocks on north american basement in the north cascades of washington state and probably to coeval igneous rocks on the western coast of vancouver island these igneous suites in the forearc fix the location of the intersection of the ridge with the continental margin 50 myr ago at latitude ca 48 49 n present day coordinates paleomagnetic data obtained since 1982 imply that before 50 ma the parts of the chugach prince william terrane that were to become the baranof and leech river schists were south of 48 49 n from 61 to 50 ma the northward movement of the terrane relative to north america can be reconciled with the southward migration of forearc magmatism in the chugach prince william terrane if the ridge trench intersection was fixed at 48 n present day coordinates the border ranges fault system is the on land structure that most likely accommodated hundreds of kilometers of post early eocene displacement

paleoenvironmental implications from biomarker and stable isotope investigations on the pliocene velenje lignite seam slovenia a pliocene lignite seam up to 160 m thick occurs in the velenje basin slovenia the seam originated in a topogenous mire and evolved within a non marine transgressive setting differences in soluble organic matter yield and hydrocarbon content of borehole samples from the lignite are related to differences in the composition of free lipids of microbial origin and or hydrocarbons derived from the biogeochemical degradation of plant tissue variations of the redox conditions within the mire are reflected by pristane phytane ratios the abundance of terpenoid biomarkers indicates the predominance of gymnosperms over angiosperms which is consistent with palynomorphic spectra dominated by pollen of the sequoia taxodium metasequoia plant community rather than by angiosperms evidence is also provided that the content of land plant derived biomarkers and the preservation of plant tissue is controlled by the input of resin rich decay resistant conifers sections of the seam characterized by a high degree of gelification of humotelinite gelification index show high contents of hop 17 21 ene but low hopane concentrations the results suggest that the gelification of plant tissue may be governed by the activity of anaerobic rather than aerobic bacteria despite the minor variation in the proportions of gymnosperms versus angiosperms in the peat forming vegetation a general influence of the floral assemblage on carbon isotopic composition of the coals 13c 25 3 to 27 0 is proposed carbon cycling during biogeochemical decomposition of plant tissue by bacteria is assumed to affect the 13c value of the lignite petrographic and geochemical data of gelified and ungelified fossil wood provide evidence that gelification may be governed by microorganisms e g anaerobic bacteria different from those responsible for decreasing cellulose contents during early diagenetic aerobic degradation of wood based on the molecular composition of terpenoid biomarkers the wood fragments are identified as derived from gymnosperms the relative proportions of saturated versus aromatic hydrocarbon fractions of fossil gymnosperms display a general tendency towards lower values in gelified wood remains this indicates that bacteria involved in gelification of plant tissue may also be involved in aromatisation of diterpenoid hydrocarbons the chemotaxonomical classification of the macrofossils as gymnosperms is corroborated by the mean carbon isotopic compositions of the macrofossils 13c 24 5 and the extracted cellulose 13c 22 0 the higher isotopic difference of about 2 5 between cellulose and fossil wood compared to that found in modern trees can most probably be explained by the smaller effect of 13c discrimination for cellulose when compared with wood during decomposition chem geol 158 1999 121 compared with the coals the 13c values of wood and extracted cellulose are affected to a minor extent by microbial activity

synkinematic emplacement of lassiter coast intrusive suite plutons during the palmer land event evidence for mid cretaceous sinistral transpression at the beaumont glacier in eastern palmer land new structural and geochronological data from the eastern palmer land shear zone in the vicinity of beaumont glacier provide the first evidence of dated structural control on emplacement of the 119 95 ma 13000 km 2 cretaceous lassiter coast intrusive suite during the accretionary mid cretaceous palmer land event orogeny a previously undated 100 m thick dyke like quartz tonalite intrusion was emplaced at 116 5 1 5 ma ar ar biotite cooling age along a nw se axis coeval with nw se compressional deformation and possibly controlled by sinistral transpression along the beaumont glacier shear zone the quartz tonalite preserves two styles of deformation and was probably progressively deformed by normal sinistral shearing during magmatic cooling with initial deformation of mafic enclaves in the dyke interior and final formation of proto mylonite to mylonite on the dyke margin the quartz tonalite cuts folding associated with phase 1 of the palmer land event indicating that this folding is older than 116 ma extending the onset of phase 1 back in time mylonite on the quartz tonalite sheet margin was subsequently thermally reset at c 107 ma ar ar biotite method during a peak in lassiter coast intrusive suite magmatism supplementary material country rock lithological data petrographic description of tonalite and ar ar geochronology data are available at www geolsoc org uk sup18552

neogene tilting of crustal panels near wrangell alaska a late oligocene miocene igneous complex south and west of wrangell alaska contains mafic dikes that yield a discordant paleomagnetic direction inclination i 70 4 declination d 39 3 95 4 8 n 72 sites combined with local and regional geobarometric metamorphic and structural observations the discordant paleomagnetic direction indicates east side up tilt by 16 about a tilt axis with azimuth 8 neogene tilt of crustal blocks in the insular superterrane accounts for much of the paleomagnetic discordance in cretaceous plutons without the coastwise translation of 1000 km as suggested by the baja british columbia hypothesis

tectonic and magmatic development of the salinian coast ridge belt california 1 we present new field structural petrographic and geochronologic data on a rare midcrustal 25 km exposure of a cordilleran arc the coast ridge belt located in the santa lucia mountains of central california the study area is composed primarily of a deformed suite of upper amphibolite to granulite facies rocks the sur series which is dominated by metaigneous tonalites diorites and gabbros with subordinate metasedimentary quartzite and marble inherited zircons in magmatic rocks suggest that the provenance of framework rocks is drawn heavily from miogeoclinal formations and that sedimentation occurred in the late paleozoic or later minor magmatism in the coast ridge belt began in the early or middle cretaceous but magmatic activity was most intense during a short period time from 93 to 81 ma based on u pb zircon ages of a felsic gneiss and two less deformed diorites the time period 93 81 ma also brackets a period of extensive thickening and high temperature ductile deformation while a thrusting cause for ductile deformation cannot be ruled out we favor the hypothesis that the exposed rocks correspond to a zone of return flow of supracrustal rocks locally displaced by granitoid plutons in the shallower crust magmatism ended throughout salinia between81and76ma coincidentwiththeattainmentof peak pressure and temperature conditions of 0 75 gpa and 800 c exhumation followed immediately bringing the coast ridge belt to the surface within 8 my at a rate of at least 2 3 mm yr exhumation was coincident with an episode of extensional collapse that has been documented elsewhere in the southern california arc during the early laramide orogeny and that may be related to underthrusting of the forearc at that time index terms 8102 tectonophysics continental contractional orogenic belts 8035 structural geology pluton emplacement 3640 mineralogy and petrology igneous petrology 8030 structural geology microstructures 8124 tectonophysics earth s interior composition and state 1212

constraining the travels of a suspect terrane paleomagnetism and geobarometry of two early cretaceous igneous complexes in the peninsular ranges batholith california paleomagnetic and rock magnetic measurements for 27 sites in the tonalitic ca 108 ma alpine and ca 100 ma ramona complexes in the suspect yuma terrane or western zone of the peninsular ranges batholith near san diego show that single and pseudosingle domain magnetite carries their characteristic remanence the alpine and ramona paleopoles agree with six published paleopoles from cretaceous igneous rocks in the yuma terrane but all eight paleopoles are discordant for north america al in hornblende geothermobarometric depth determinations at 16 sites plus published mapping and depth determinations suggest that the batholith is divided into blocks by orogen parallel faults or by orthogonal fault sets with large vertical displacements the paleomagnetic data show that the fault blocks in the terrane underwent on average ene side up tilting of 10 3 about an orogen parallel axis between ca 125 ma and ca 89 7 ma but they have not been translated northward as a suspect terrane by 500 km excluding neogene opening of the gulf of california the tilting is attributed to torque from ene shallow underthrusting of the farallon plate beneath the wsw overthrusting north american plate where subsequent extension has caused differential uplift of the fault blocks nonsignificant dextral displacement of 4 1 440 110 km between the eastern and western zones of the batholith suggests that this boundary represents an intraarc fault the large paleopole discordance found in younger sedimentary strata of baja california is attributed mainly to compaction shallowing of the remanence and or postdepositional remagnetization

stable carbon isotopes of wood a clue to palaeoclimate abstract detailed stable carbon isotope and molecular investigations were undertaken on a number of archaeological and fossil wood specimens to provide insights into their use as rigorous independent palaeoclimatic and palaeoenvironmental parameters the isotope data revealed large differences amongst the material with the oldest specimens being least depleted in 13 c although natural variation could account for some of the observed differences the isotope values of the archaeological and tertiary specimens are most probably related to the absolute abundance of polysaccharides present and the degree of lignin alteration the molecular data based on pyrolysis of the antarctic cretaceous conifer specimens revealed only transformed lignin with virtually no intact lignin building blocks 2 methoxyphenols preserved and no evidence of polysaccharides this degree of chemical alteration is suggested here to be one of the main causes for the 13 c enriched values of these conifer specimens these results show the importance of combining detailed molecular information on individual wood components with stable carbon isotope data for palaeoclimatic and palaeoenvironmental studies

where are the missing faults in translated terranes abstract a central dilemma in understanding terranes that have translated long distances is that modern plate tectonics and paleomagnetic studies indicate translations of thousands of kilometers while the faults along which the terranes moved these great distances are not found relations long known from geology and from recent studies of modern transform plate boundaries suggest that preserving strike slip faults that record 1000 km scale translations is unlikely and therefore in many cases paleomagnetism may be our only reliable indicator of how far terranes translated four reasons are explored here for why large offset strike slip faults are likely to be missing in translated terranes 1 strike slip faults in continents commonly are partially or wholly destroyed or reactivated only 400 500 km of over 1000 km of offset on cretaceous early tertiary strike slip faults in northern british columbia are accounted for in southern british columbia the missing strike slip faults probably continued south into the hinterland of the rocky mountain thrust belt as oblique thrust faults much like the modern alpine marlborough fault system of new zealand the major strike slip faults in southeastern british columbia were obliterated by eocene extensional faulting uplift and erosion 2 offsets of 1000 km scale are likely to occur on many anastomosing faults with offsets of 100 km scale many of which are left behind and not found in the translated terrane the greater san andreas plate boundary has accumulated 1200 km of transform motion that is distributed on numerous faults from the offshore borderland to eastern california there is a narrow terrane in the offshore borderland of california that has moved 1200 km relative to north america but no single fault has nearly that much offset 3 major faults in narrow oceans formed by oblique divergent plate boundaries have a low potential for preservation for example the deep dense oceanic crust of the gulf of california where the major transform faults of the oblique rift lie has a low potential for preservation in contrast baja california is currently a continental terrane that has translated 300 km relative to north america along the plate boundary in the gulf of california because of the relative buoyancy of continental crust baja california is likely to be preserved in any future accretion event 4 faults in the margins of oblique divergent plate boundaries are dominantly normal faults and not strike slip faults there is little strike slip faulting in central baja california even though the plate boundary has a rift angle of only 20 recent field data and modeling show that at 0 20 strike slip faults will dominate the secondary faults surprisingly at 20 to 35 there are both strike slip and normal faults and at 35 45 there are few or no strike slip faults even though the relative motion of these types of oblique rifts is dominated by transcurrent motion over extensional motion

a revised kinematic model for the relative motion between pacific oceanic plates and north america since the late cretaceous 1 the convergence between the pacific farallon and kula oceanic plates and the north american plate has provided a driving force for tectonic processes that have shaped the western margin of north america yet reconstructions of plate motion in the pacific basin have traditionally relied on the assumption of fixed hot spots in the last decade substantial cretaceous to paleogene motion between the pacific and atlantic hot spots has been recognized providing motivation to reevaluate the history of relative motion between pacific oceanic plates and north america by means of plate circuit reconstructions this paper presents new kinematic models based on two alternative plate circuits linking the pacific plate to north america since late cretaceous time when compared to models relying on fixity of pacific and indo atlantic hot spots our reconstructions suggest that the pacific kula and pacific farallon ridges were 600 1000 km closer to the western margin of north america and hence that the farallon and kula plates were smaller in late cretaceous to middle eocene time these findings cast significant doubt on the viability of a configuration of the farallon kula ridge that juxtaposes the kula plate with the southern part of the paleo north american margin during this time interval the results of our new reconstructions also suggest more oblique convergence between the farallon or kula plate and north america from the late cretaceous to the middle eocene related to the combination of dominantly northwest motion of the pacific plate and steady southwest motion of north america this provides an efficient mechanism for the coast parallel translation of some accreted terranes of north america it may also explain the structure of geological units in western north america such as the central belt of the franciscan complex which show a dominant coast parallel fabric formed during an interval coeval with the episode of oblique convergence

syntectonic remagnetization in the southern methow block resolving large displacements in the southern canadian cordillera 1 the upper cretaceous ventura member of the goat wall unit in the southern methow block of southern british columbia and northern washington state holds a syntectonic magnetization eight new sites from manning park in british columbia give a mean direction of d 27 5 i 60 1 k 304 7 95 3 2 after optimal partial tilt correction of five groups of bedded sites from farther south in the basin reported by bazard et al 1990 four have a syntectonic remanence with a direction similar to what we observe the exception is one group which has optimal concentration of remanence directions on 100 untilting and an abherent direction which must be rejected combining the accepted sites the optimal differential syntilting direction is d 11 8 i 61 5 k 39 3 95 3 4 n 47 giving a mean pole of 79 8 n 359 2 e k 19 5 and a95 4 8 the age of the remagnetization is constrained to be between 88 and 80 ma compared to cratonic north america this result indicates that the southern methow block was displaced from the south by 1800 500 km meaning it lay south of the sierra nevada subduction zone but well north of other paleomagnetically constrained cretaceous rock units from the insular superterrane including correlative strata of the mount tatlow area in the northern methow block among several possibilities to reconcile this discrepancy the most plausible has the whole methow block translated coherently but with the southern methow block strata remagnetized during transit

correction of inclination shallowing and its tectonic implications the cretaceous perforada formation baja california abstract a paleomagnetic and magnetic fabric study of the aptian to albian perforada formation the oldest sedimentary unit of the cretaceous valle group was conducted to determine whether the perforada inclination had been shallowed by burial compaction and to correct the inclination for any shallowing the perforada formation is located on the vizcaino terrane of the vizcaino peninsula of west central baja california an accurate paleolatitude will indicate whether the vizcaino terrane is far travelled eighty eight specimens from 43 independently oriented hand samples and cores were collected from 11 sites a small 10 m fold was sampled in order to constrain the age of the magnetization with a fold test thermal and alternating field demagnetization was able to isolate characteristic magnetizations for most samples maximum unblocking temperatures near 580 c indicate that magnetite is the magnetic carrier the characteristic magnetization passes the fold test at the 99 confidence level anisotropy of anhysteretic remanence aar and anisotropy of magnetic susceptibility ams measurements show that five sites had well developed bedding parallel foliations while four sites had poorly developed aar fabrics but foliated ams fabrics the remaining two sites had poorly developed foliations for both ams and aar the mean inclination i 35 6 of the five sites with well developed aar foliations is 13 7 shallower than the mean inclination i 49 3 of the two sites with poorly developed aar and ams fabrics when the inclinations of the sites with well developed aar foliations are corrected using an individual particle anisotropy of 1 5 determined from magnetic extract epoxy samples dried in 30 50 mt dc magnetic fields the corrected mean inclination i 50 1 is indistinguishable from the mean inclination of the sites with poorly developed aar fabrics a corrected formation mean direction for the perforada formation d 311 8 i 47 0 95 9 3 indicates a 33 5 11 1 counterclockwise rotation and 5 6 7 7 of post cretaceous northward motion after 3 of neogene fault motion has been removed these results indicate that the vizcaino terrane has moved little with respect to the peninsular ranges terrane and cratonic north america since the cretaceous

three dimensional reconstruction of an in situ miocene peat forest from the lower rhine embayment northwestern germany new methods in palaeovegetation analysis palaeovegetation reconstructions particularly of fossil forests are generally restricted to scant information on the taxonomic composition relative abundance of individual taxa or on tree density we have developed new techniques for the analysis of stump horizons that result in a relatively detailed three dimensional reconstruction of ancient forests in addition a rough estimate of their above ground standing biomass can be calculated these techniques are applied to an in situ miocene peat forest preserved in the lower rhine embayment northwestern germany in a study area of 2500 m2 476 stumps were mapped and used in the forest reconstruction additionally pollen samples and leaf remains have been analysed the peat forest consists primarily of conifers in particular taxodiaceae and pinaceae with sciadopitys being the most common genus the only angiosperms in the wood flora were palms but in the pollen flora evidence for the myricaceae mastixiaceae ericaceae and a few other angiosperms is also present the forest was relatively dense with 1904 trees ha and a basal area of 164 m2 mean trunk diameter was 28 cm while mean tree height is calculated to have been 9 9 m height diameter and density distribution are illustrated using contour and three dimensional surface plots estimated above ground biomass is 750 t ha but this value also includes dead or partly dead trees this peat forest does not closely compare with previous reconstructions of miocene peat forests its three dimensional structure and biomass differ from those of modern bald cypress swamps

rotation of porphyroblasts in non coaxial deformation insights from computer simulations porphyroblast inclusion trails have the potential to provide critical information about tectonometamorphic events recently however traditional interpretations of inclusion trails have been called into question by the suggestions that porphyroblasts do not rotate during non coaxial deformation and that apparent spiral inclusion trails can be generated in coaxial deformation we present a new computer model that simulates inclusion trail development model results suggest 1 that the extent of porphyroblast rotation is controlled by conditions at the porphyroblast matrix boundary 2 that curved inclusion trails may develop in unrotated porphyroblasts 3 that classic snowball inclusion trails are most simply explained by rotational growth histories and 4 that some of the observations used to support the view that porphyroblasts do not rotate e g weakly sigmoidal inclusion trails apparent truncations of inclusion trails can be accounted for by variations in the growth rate of rotating porphyroblasts

environmental history of the german lower rhine embayment during the middle miocene as reflected by carbon isotopes in brown coal stable carbon isotope investigations have been carried out on miocene brown coal from the garzweiler seam of the german lower rhine embayment material studied included fossil wood from seven different taxa and brown coal matrix isotope results from macrofossil analysis show variations of more than 6 within individual samples and reveal a general isotopic difference between angiosperm and gymnosperm wood specimens according to mean carbon isotope values found for gymnosperms angiosperms and brown coal matrix 23 3 26 0 and 25 8 the peat forming vegetation of the garzweiler seam was dominated by angiosperm taxa results from brown coal matrix establish a continuous high resolution depth profile of carbon isotope variations during the late middle miocene they show a significant and characteristic isotope pattern with distinct medium and short term cycles high frequency variations in the two main units of garzweiler seam locally split into three units the medium term 13c variations are most likely caused by varying proportions of gymnosperms within the peat forming vegetation while high frequency oscillations seem to be a direct signal of environmental changes a long term decline of carbon isotope values observed within the complete garzweiler seam from base to top is presumably due to a cooling trend in the miocene

parameters determining the carbon isotopic composition of coal and fossil wood in the early miocene oberdorf lignite seam styrian basin austria abstract petrographical and geochemical data of gelified and ungelified fossil wood from the early miocene oberdorf lignite seam styrian basin austria provide evidence that the early diagenetic aerobic degradation of wood by fungi may be followed by further decomposition under reducing conditions by the activity of anaerobic bacteria based on the molecular compositions of terpenoid hydrocarbons the wood fragments in the lignite are identified as gymnosperms this result is corroborated by the mean isotopic composition 13c 24 2 of the macrofossils the isotopic difference between fossil wood and extracted cellulose of most samples 3 9 2 5 is higher than in modern trees which can be explained by the smaller effect of 13c discrimination during decomposition of cellulose when compared with wood the mean carbon isotope values found for gymnosperms and coals 24 2 and 24 7 respectively confirm the results from biomarker analyses indicating that the peat forming vegetation of the oberdorf seam was dominated by gymnosperm taxa minor variation in the relative contributions of gymnosperms and angiosperms to coal deposition is of negligible influence on the isotopic composition of the coals cross correlations between 13c of the coals soluble organic matter yield and the proportions of liptinite macerals of higher plant origin imply that the carbon isotopic composition may be affected by the contents of plant lipids because of their 13c values ranging from 5 to 10 less than whole plant tissue values an isotopic shift of the coals towards more negative values due to the activity of prokaryotes i e anaerobic bacteria in organic matter degradation is proposed the results obtained from the early miocene oberdorf lignite indicate that the carbon isotope ratios of the coals are primarily affected by varying contributions of different parts of whole plant tissue due to their different isotopic and molecular compositions e g epicuticular leaf waxes resins wood and their different decay resistance against the early diagenetic changes involved in organic matter decomposition carbon cycling during anoxic decomposition of plant derived organic matter is assumed to affect the 13c values of coal 13c values of wood and extracted cellulose are affected only to a minor extent

pre miocene palaeogeography of the los cabos block baja california sur geochronological and palaeomagnetic constraints the los cabos block lcb is located at the southern end of the baja california peninsula and is composed mainly of intrusive rocks that were emplaced into pre cretaceous heterogeneous metasediments and are partly covered by miocene volcanic and volcaniclastic rocks field observations provide evidence that the undeformed homogeneous gabbronorite of the sierra el novillo in the ne part of the lcb is the oldest crystalline unit which is intruded by undeformed to slightly deformed tonalitic quartz dioritic granitoids for these rocks an rb sr intrusion age of 129 15 ma and a biotite whole rock cooling age of 116 2 ma were obtained low initial 87sr 86sr and high e nd values of about 0 7036 and 5t o 6 respectively characterise the intrusives as primitive mantle derived granites further to the southeast and south granitoids are more silicic with abundant deformed sequences orthogneisses diatexites and migmatites among others from the southern part of the lcb an rb sr intrusion age for the undeformed granites of 115 4 ma and a biotite cooling age of 90 2 ma were determined initial 87sr 86sr was determined to be 0 7054 and e nd values fall between 2 and 0 the isotopic data do not clearly allow us to characterise the deformed granitoids of the lcb as being intruded by the undeformed unit deformation could have been partly due to syn intrusive tectonics palaeomagnetic data suggest minor if any northward displacement of the lcb with respect to continental mexico corresponding to the rifting in the gulf of california since the late miocene and significant 35 45 clockwise rotations possible tilting evects which may have occurred given the dip of tertiary volcanics on top of the intrusives would modify these values for rotation and to a lesser degree of northward displacement geochemical isotopic and palaeomagnetic results and the cooling history of the lcb are similar to those from the puerto vallarta batholith whereas other mexican continental margin plutons further to the se display lower intrusion ages more rapid cooling rates and generally more primitive magma compositions in the light of the data presented a common magmatic evolution of the lcb and the puerto vallarta batholith is strongly suggested 2000 elsevier science b v all rights reserved

petrographic composition and depositional environments of the pliocene velenje lignite seam slovenia abstract a pliocene lignite seam up to 160 m thick occurs in the velenje depression in northern slovenia it forms part of a non marine transgressive sequence petrographic data together with ash and sulphur content of samples from two boreholes one located in the central and the other in the marginal part of the seam have been used to study vertical and lateral coal facies variations in the central part the lignite seam overlies fluvial sediments facies critical macerals and petrographic indices suggest that the lower ash rich part of the seam unit i accumulated in a wet forest swamp in an alluvial plain setting later this environment was replaced by a dry telmatic forest swamp unit iia according to our interpretation a decrease in tree density in units iib and iic reflects a change to a bush moor the transition from unit ii to unit iii is characterized by a rapid water table rise which resulted in the establishment of a wet limnotelmatic forest swamp within unit iii the tree density decreases and the degree of gelification increases towards the top of the seam suggesting a transition to a fen type environment another rapid water table rise ended peat formation in the eutrophic topogenous mire and established open lacustrine conditions a calcium rich environment resulted in high ph values and is responsible for high sulphur lignites up to 4 on a dry basis in the upper part of the seam the ph values were controlled by the amount of the inflowing lacustrine water only thin ash rich topotelmites accumulated along the northern margin of the mire there the seam originated in a wet forest swamp and was separated by limnic and fluvial sediments from other organic rich horizons due to its closer vicinity to the pre tertiary carbonates the depositional environment was probably even more alkaline therefore the lignite shows a higher degree of gelification and is even more sulphur rich up to 5 5 on a dry basis

petrographical and organic geochemical investigation of the oberpfalz brown coal deposit west germany abstract a detailed macro and micropetrographical investigation coupled with gc and gc ms analysis of the alkane fraction of tertiary brown coal samples from the oberpfalz region of bavaria west germany was undertaken distinctive petrographical and organic geochemical facies differences were evident in the coal seams investigated which came from two neighbouring open cast mines the lower seam was of a limnic nature while the upper seam in the neighbouring mine showed the more typical characteristics of terrestrial depositon both seams were generally characterized by high ash contents and extract yields microlayering and framboidal pyrite the predominance of texto ulminite a combined with relatively high resinite contents suggested that gymnosperms were the main peat forming plants additionally the coal extracts were characterized by the presence of the diterpane phyllocladane which made up to 60 of the alkane fraction in some samples bacterial activity in the coal swamp was marked by the presence of hopanes mainly 17a h 21 h homohopane and biodegradation of the n alkanes