geochemistry and provenance of the middle ordovician austin glen member normanskill formation and the taconian orogeny in new england the austin glen member of the upper middle ordovician normanskill formation is a sandstone shale ysch succession deposited in the foreland of the taconian orogen petrographic major and trace element and nd pb isotopic data provide substantial constraints on its provenance lack of k feldspar and paucity of plagioclase in addition to the dominance of sedimentary rock fragments indicate that the source was dominated by recycled sedimentary components major and trace element data support this conclusion and indicate that the provenance of both shales and sandstones was the same no evidence of an ophiolitic or volcanic component was observed interpretation of nd isotopic characteristics are complicated by a partial resetting of the nd isotope system at about the time of sedimentation but indicate that the provenance of the austin glen member had a long term history of light rare earth element lree enrichment average tdm 1a8 ga furthermore nd isotopic compositions are extremely homogeneous end 8a1 0a6 1 s d n 23 at 450 ma the approximate depositional age indicating either a single source or very well mixed sources 207pb 204pb ratios are variable but within the range of pb isotopic compositions typically described as grenvillian the range of 207pb 204pb is greater than expected for the range of 206pb 204pb and suggests an additional component of pb possibly introduced during diagenesis the immediate source of the austin glen member may have been the accretionary prism that developed as older sediments of the laurentian margin were scraped off the basin oor incorporated within the accretionary prism and shed into the basin no evidence indicating the arrival of an undifferentiated island arc or continental fragment during the taconian orogeny has been found the data acquired during this study can be explained almost exclusively by grenville province source components but with possible additional contributions from older laurentian terranes and late proterozoic rift volcanics that are not readily quanti ed but likely to have been minor accordingly we conclude that the taconian orogeny in new england involved either 1 a continental arc that involved exclusively laurentia 2 collision of a continental block with identical geochemical characteristics as laurentia or 3 essentially no detritus from any exotic colliding block island arc or continental fragment reached the foreland basin at the time of austin glen deposition

cenomanian turonian carbon isotope events recorded in terrestrial organic matter from northern japan carbon isotopic fluctuations recorded in terrestrial organic matter from the upper cretaceous cenomanian turonian succession of hokkaido japan show a remarkably similar pattern to isotopic fluctuation in carbonate carbon reported from southern england and the italian apennines chronological correlation for the cenomanian turonian section of japan is based on planktonic foraminiferal biostratigraphy with some additional data from macrofossils allowing a detailed comparison of isotope stratigraphies for japan and europe three distinct features of the isotope profile namely a positive spike near the cenomanian turonian boundary a shoulder in the lower middle turonian and a level segment in the middle upper turonian are observed in japan these features are biostratigraphically comparable and correlative with isotope profiles reported from europe the single factor influencing isotopic composition of both terrestrial organic carbon and marine carbonate carbon is isotopic change in the global co2 reservoir of the ocean atmosphere system if these three carbon isotope features are synchronous they may be inferred as having been caused by global phenomena and as providing global high resolution chemo stratigraphic markers carbon isotope stratigraphy could be an important bridge between terrestrial inland sequences and marine sequences

δ13c and stomatal number variability in the cretaceous conifer frenelopsis abstract the 13 c 12 c ratios of leaves of the conifer morphotype frenelopsis were measured to decipher the influences of water and salt stress on stomatal density sd epidermal cell density ecd and stomatal index si three morphospecies were analyzed f ugnaensis from freshwater fluvio lacustrine deposits upper barremian f turolensis and alata from coastal deposits lower middle albian and upper albian respectively the cuticle 13 c values show a large variation from 28 to 21 comparison with previously published marine carbonate 13 c records indicate that the difference in cuticle 13 c between the different deposits are mainly due to difference in co 2 plant isotope fractionation rather than to change in isotopic composition of inorganic carbon in the atmosphere and ocean the less negative 13 c and wide range in 13 c of f turolensis and alata 27 5 to 21 compared to f ugnaensis 28 to 25 are interpreted as a result of salt and or water stress the data as a whole yield a good relationship between the 13 c 12 c ratio and sd r 0 67 n 42 p r 0 53 n 41 p f ugnaensis decreases with increasing 13 c value r 0 57 n 15 p 0 026 as well as a decrease of si r 0 62 n 15 p 0 013 possibly reflecting warmer and drier conditions average si of f alata does not significantly change with 13 c and inferred soil salinity in contrast to sd p

residence of ree y th and u in granites and crustal protoliths implications for the chemistry of crustal melts a systematic study with laser ablation icp ms scanning electron microscopy and electron microprobe revealed that 70 95 wt of ree except eu y th and u in granite rocks and crustal protoliths reside within reeythu rich accessories whose nature composition and associations change with the rock aluminosity the accessory assemblage of peraluminous granites migmatites and high grade rocks is composed of monazite xenotime in low ca varieties apatite zircon thorthosilicate uraninite and betafite pyrochlore metaluminous granites have allanite sphene apatite zircon monazite and thorthosilicaie peralkaline granites have aeschinite fergusonite samarskite bastnaesite fluocerite allanite sphene zircon monazite xenotime and th orthosilicate granulite grade garnets are enriched in nd and sm by no less than one order of magnitude with respect to amphibolite grade garnets granulitegrade feldspars are also enriched in lree with respect to amphibolite grade feldspars accessories cause non henrian behaviour of ree y th and u during melt solid partitioning because elevated fractions of monazite xenotime and zircon in common migmatites are included within major minerals their behaviour during anatexis is controlled by that of their host settling curves calculated for a convecting magma show that accessories are too small to settle appreciably being separated from the melt as inclusions within larger minerals biotite has the greatest tendency to include accessories thereby indirectly controlling the geochemistry of ree y th and u we conclude that ree y th and u are unsuitable for petrogenetical modelling of granitoids through equilibrium based trace element fractionation equations

analytical techniques for the separation and sem identification of heavy minerals in mudrocks heavy mineral investigations must be preceded by effective heavy mineral separation identification and determination of mineral compositions provenance determinations by heavy mineral variations and direct measurement of the control of trace elements by heavy minerals in mudrocks has not been possible because of the difficulties in separating heavy minerals from the obscuring mass of the clay matrix the technique to separate identify and determine the variability of heavy minerals in mudrocks presented here is nondestructive and works well with mudrocks of variable induration and maturation from mudstones to shales this methodology uses lithium metatungstate for heavy liquid separations of bulk samples and a combination of optical and scanning electron microscopy sem for identification and quantification of heavy mineral proportions

tectonically buried continent ocean boundary ouachita mountains arkansas a seismic reflection sequence observed at depth beneath the south flank of the benton uplift in arkansas is interpreted to mark the early paleozoic continent ocean boundary the sequence is similar in both external and internal geometry to wedge shaped features commonly observed in the narrow zone separating continental from oceanic basement on modern passive margins and interpreted as layered volcanic sequences it is suggested that slope and rise sediments now exposed in the benton uplift were thrust in a thin skinned fashion over the edge of the north american continent during initial stages of the carboniferous ouachita orogeny but that later uplift and slight northward translation of the continental margin basement occurred in a more thick skinned fashion preserving the boundary wedge intact beneath the earlier thrust sheets

relationships among vitrinite reflectance illite crystallinity and organic geochemistry in carboniferous strata ouachita mountains oklahoma and arkansas the ouachita mountains contain a thick section of carboniferous strata that display an extreme range in thermal maturity as determined by vitrinite reflectance clay mineralogy illite crystallinity and organic geochemistry of shales from those strata are systematically related to thermal maturity shales of the stanley jackfork and atoka formations are predominantly composed of illite and chlorite with minor occurrences of mixed layer clays restricted to samples characterized by mean vitrinite reflectance less than 1 5 and pyrophyllite restricted to samples characterized by mean vitrinite reflectance greater than 2 7 illite crystallinity is significantly related to vitrinite reflectance ro weaver s illite sharpness ratio sr increases with increasing ro log sr 0 28 0 08 ro whereas kubler s illite crystallinity index ci decreases with increasing ro log ci 1 01 0 07 ro plots of bitumen ratio bitumen total organic carbon vs vitrinite reflectance weaver s illite sharpness ratio and kubler s crystallinity index all reveal hydrocarbon generation preservation curves that define submature mature and supermature zones with regard to a liquid hydrocarbon window these results suggest that in the absence of vitrinite illite crystallinity can be used quantitatively to estimate levels of thermal maturity and cautiously to approximate hydrocarbon generation preservation stages of potential source rocks

mudstone petrology of the mesoproterozoic unkar group grand canyon u s a provenance weathering and sediment transport on intracratonic rodinia abstract the synthesis of mudstone petrology and interbedded sandstone detrital zircon geochronology provides insights into the provenance weathering regime hydrodynamic effects and diagenesis of the mesoproterozoic unkar group unkar mudstones were derived largely from the grenville orogen go of southwest texas and the adjacent yavapai mazatzal ym and southern granite rhyolite sgr terranes detrital zircon data indicate distinct pulses of go derived sediment during hakatai and dox formation deposition whereas shinumo sediment contains a larger component of ym and sgr material an increase in plagioclase and biotite abundances in the dox further suggest an orogenic pulse bulk chemistry including elevated cr and ni abundances and ree systematics implicate a heterogeneous provenance for unkar sediment best approximated by a mix of granite or granodiorite with some basalt weathering of unkar sediment as determined from mudstone and crystalline source bulk chemical trends is characterized as moderate cia values between 55 and 70 indicative of a temperate climate in an orogenic setting small less than 10 wt amounts of detrital kaolinite and chlorite are consistent with a moderate temperate weathering regime illite the dominant clay mineral in the unkar group is largely the 2m1 polytype and detrital in origin however it is estimated that 7 of the k in the escalante creek member results from k metasomatism and may form up to 15 wt authigenic 1m or 1md illite the clay size fraction and zircon are the chief contributors to the ree budget in unkar mudstones lithostratigraphic variations in the hree distributions can be attributed partially to variable zircon abundance in the silt size fraction a likely function of hydrodynamic sorting age constraints on the duration of unkar group sedimentation range from 30 to 100 my for the 1100 m conformable shinumo dox succession and result in compacted sedimentation rates of between 1 0 and 3 6 cm 103 yr these rates are comparable to mesozoic foreland basin settings

ecological distribution of cenomanian terrestrial plants based on 13c 12c ratios the cenomanian lagoonal member of the argiles du baugeois anjou france yielded a rich and exceptionally well preserved fossil leaf flora stable carbon isotope ratios of fossil plants were measured in order to investigate the presence of a palaeoenvironmental signal the small intraspecies variations of 13c values observed for most of the fossil leaves suggested that the isotopic signal had not been significantly altered hence an isotopic approach was used as an attempt to assist in reconstructing the ecological distribution of the flora the 13c enrichment of the fossil leaves suggested that the plants underwent water or salt stress the occurrence of the conifer frenelopsis suggested at least locally a saline environment such as a lagoon according to their decreasing 13c values all the plants collected could have been distributed along a decreasing salinity transect from the lagoon to a flood plain the predominant species eretmophyllum andegavense a fossil ginkgo exhibited a wide range of 13c values this could indicate that this taxon grew in a wide range of habitats with varying salinities the origin of the organic matter appeared to be terrestrial with a major contribution from water stressed plants such as frenelopsis as suggested by the similarity between 13c values of the conifer and the sedimentary organic matter 13c values of the sediment indicated stable palaeoenvironmental conditions during the deposition of the argiles du baugeois member hence while detailed palaeovegetation reconstructions are generally limited to the few deposits which present in situ palaeoflora the contribution of isotope geochemistry could allow reconstructions for a wider range of fossil plant deposits

loss of provenance information through subsurface diagenesis in plio pleistocene sandstones northern gulf of mexico abstract subsurface alteration of plagioclase potassium feldspar and a variety of nonopaque heavy minerals has substantially modified the detrital composition of plio pleistocene sediments in the northern gulf of mexico albitization of plagioclase and dissolution of unstable grains are the two principal mechanisms of grain alteration grain alteration increases progressively with depth and has taken place without the influence of significant amounts of meteoric fluids the degree to which strictly subsurface grain alteration has affected these young sediments suggests that grain assemblages in older rocks should be viewed most skeptically with regard to their state of preservation

paleoclimatic significance of δd and δ13c values in pinon pine needles from packrat middens spanning the last 40 000 years we compared two approaches to interpreting dd of cellulose nitrate in pinon pine needles pinus edulis preserved in packrat middens from central new mexico usa one approach was based on linear regression between modern dd values and climate parameters and the other on a deterministic isotope model modified from craig and gordon s terminal lake evaporation model that assumes steady state conditions and constant isotope effects one such effect the net biochemical fractionation factor was determined for a new species pinon pine regressions showed thatdd values in cellulose nitrate from annual cohorts of needles 1989 1996 were strongly correlated with growing season may august precipitation amount and d 13 c values in the same samples were correlated with june relative humidity the deterministic model reconstructed dd values of meteoric water used by plants after constraining relative humidity effects with d 13 c values growing season temperatures were estimated via modern correlations with dd values of meteoric water variations of this modeling approach have been applied to tree ring cellulose before but not to macrofossil cellulose and comparisons to empirical relationships have not been provided results from fossil pinon needles spanning the last40 000 years showed no significant trend in dd values of cellulose nitrate suggesting either no change in the amount of summer precipitation based on the transfer function or dd values of meteoric water or temperature based on the deterministic model however there were significant differences in d 13 c values and therefore relative humidity between pleistocene and holocene published by elsevier science b v

the permian to cretaceous structural evolution of the western approaches basin melville sub basin uk summary the tectonic sedimentary evolution of the western part of the western approaches basin melville sub basin was initiated during early permian times when synrift clastic sedimentation and volcanism commenced within an ene trending half graben this sequence thickened to the south and onlapped a high to the north during the permian an early nnw sse basin extension was accommodated on an array of ene wsw trending normal faults linked by nnw sse orientated transfer faults this was followed by a period of ene wsw extension along the basin axis when the normal and transfer faults of the previous faulting episode swapped roles this was possibly related to early rifting in the bay of biscay both sets of faults appear to be controlled to some extent by variscan thrusts and strike slip faults within the basement during the upper triassic the ridge in the north subsided allowing a thick sequence of salt to be deposited where there had previously been a topographic high during jurassic times sedimentation extended across the permian triassic half graben into the french sector this was followed by an episode of rifting and wrench deformation and inversion during which the permian to jurassic basin was domed and uplifted the cretaceous to tertiary sedimentation which followed probably resulted from postrift thermal subsidence related to cooling of the continental platform adjacent to the opening atlantic ocean steep normal and or strike slip faults data from the earliest part of this postrifting stage

do stable carbon isotopes of brown coal woods record changes in lower miocene palaeoecology stable carbon isotope ratios of fossil wood from the miocene brown coal deposits in former east germany are compared with palaeobotanical and sedimentological data to test the use of stable isotopes in determining palaeoenvironment significant differences in the chemical composition of samples from different horizons were observed those specimens preserved under the most bio degrading conditions yielded stable carbon isotope values least representative of original wood specimens overall the chemical preservation of the wood was seen to affect the stable isotope signal but deconvolving the preservational bias using a molecular approach enabled estimations of 13cbiomass and 13cpalaeoatmosphere that were then used to interpret more fully the palaeoenvironment

alterations in the non clay mineral fraction of pelitic rocks across the diagenetic to low grade metamorphic transition ouachita mountains oklahoma and arkansas abstract the transformation of smectite to illite has been cited by many authors as a source of silica during diagenesis of mudrocks illites themselves however undergo chemical changes as they recrystallize into micas during high grade diagenesis low grade metamorphism average compositions of phyllosilicates from the literature suggest that an equivalent amount of silica is available from transformation of illite to muscovite as from illitization of smectites the fate of silica released by this process has not been reported but could be a major contributor to the silt size quartz population the quartz and feldspar fraction of pelites from the stanley shale mississippian in the ouachita mountains of oklahoma and arkansas was separated using sodium bisulfate fusions the mineralogy and the grainsize distribution of this fraction were determined using standard petrographic and x ray diffraction xrd techniques bulk rock samples were analyzed using x ray fluorescence xrf and instrumental neutron activation analysis inaa methods the data obtained were related to illite crystallinity and vitrinite reflectance as reported by guthrie et al 1986 and houseknecht and matthews 1985 both the percentage of quartz and the mean grain size of the quartz and feldspar fraction increase with greater illite crystallinity values the growth in quartz is especially apparent in the finest size fractions a corresponding decrease in the silica content of the clay mineral fraction is also observed development of quartz polycrystallinity occurs across the same interval whole rock chemical abundances show no statistical correlation with thermal maturity relative to titanium both the major element and the trace element concentrations show little variation rare earth element ratios do not correlate with thermal maturity and remain essentially constant our results are consistent with reported differences between quartz in schists and their shale precursors and suggest that release of silica during diagenesis of phyllosilicates continues after the smectite illite transformation this silica precipitates as quartz within the pelite consistent with the suggestion by blatt 1987 that metapelites are the source of abundant silt size quartz the lack of whole rock chemical variation with thermal maturity implies closed system behavior across much of the pelite to metapelite transition

sandstone provenance of north western sectors of the intracontinental cenozoic qaidam basin western china tectonic vs climatic control abstract sandstone samples from all cenozoic formations of the nonmarine internally drained qaidam basin have been collected for provenance analysis to monitor possible changes in sandstone composition driven either by tectonics or climate provided an appropriate hinterland biotite contents may be a reasonable indicator for aridity moderately sorted sandstones with subangular to subrounded grains from the northwestern part of the qaidam basin are immature indicated by a high proportion of feldspars and lithic fragments nevertheless they have relatively high quartz contents of 29 65 averaging between 40 and 45 the average framework compositions of the formations show only a slight variation over time limited to the oldest and youngest cenozoic formations contents of white mica and biotite are significantly higher in upper portions of the section white mica contents increases from 1 0 to 3 7 and biotite from 0 1 to 1 6 respectively this change can be explained by increasing aridity during neogene and surface uplift of altyn mountains and qimantagh which led to higher relief when plotted on basic variation diagrams total quartz feldspar lithic fragments there is a slight shift from continental block field to orogenic field which might reflect the motion of the altyn tagh fault since oligocene times although climate changed during the cenozoic from arid over semiarid back to arid we could not find any distinct changes in the framework mineral compositions over time that could be related to climatic events few selected mudstones from eocene to lower miocene formations have been geochemically analysed by icp ms all samples display uniform high enrichment in light rees in chondrite normalized diagrams with one exception the ree concentrations are decreasing in a stepwise manner although insignificantly from formation to formation with time due to a diluting effect by carbonate

ree distribution in the clay fraction of pelites from the southern apennines italy abstract in order to evaluate whether clay minerals or accessory phases control the ree pattern of the only illite is correlated with ree while a smectite rich sample is characterized by the lowest content in ree strong correlations exist between ree and tio2 nb zr and a less significant one with sr no correlations exist between these elements and y r mode factor analysis indicated that three factors account for 87 of the total variance the first factor var 43 2 seems to express mainly the tendency of some resistate minerals to concentrate ree in the fine fraction the second factor var 30 0 may be related to the effect of circulating fluids responsible for dickite genesis the third factor may be linked to the weathering of micaceous phases the ree do not have a significant weight in the second and third factors resistate minerals appear dominant in controlling at least the lree and nb it is proposed that in the studied samples illite likely conveyed ree via the included minerals

late aptian palaeoclimatic turnovers and volcanism insights from a shallow marine and continental succession of the apennine carbonate platform southern italy abstract this study reports an integrated facies analysis carried out on a new section from the upper aptian of the se matese mts civitella licinio northern campania s italy which includes several decimeter to meter scale lacustrine intervals straddling a meter scale plant rich plattenkalk these intervals are assigned to the late gargasian early clansayesian by their stratigraphic relationship with the upper salpingoporella dinarica acme as well as lithologic and biostratigraphic supra regional key markers found in the apennine carbonate platform apcp including the orbitolina level we infer that the monogeneric parautochthonous plant remains frenelopsis sp were deposited in a supratidal to paralic coastal mudflat close to a restricted shallow marine lagoon at the verge of an arid semiarid climatic phase the plattenkalk was rapidly replaced by persistent lacustrine lithofacies at the onset of a major climatic turnover glacial trigger the overlying shallow marine deposits are capped by a deeply incised palaeokarstic surface and in turn by unconformable middle clansayesian transgressive shallow marine deposits interlayering of reliable lithologic indicators of palaeoclimate and high resolution event stratigraphic hires correlation of the civitella licinio succession with the astrochronologically tuned mt faito reference section of the apcp bring evidence of rapidly fluctuating hydroclimatic conditions wet and arid phases in the short 100 ky and long 400 ky eccentricity time band hires and astrochronological age assignment to crucial key markers and humid arid phases at civitella licinio permit to further refine the detailed stratigraphy of the mt faito reference section and to assign the upper s dinarica acme of the apcp to a numerical age of 118 55 118 50 my sem and eds analyses document common to abundant windblown volcanic particles glass shards and sanidine crystals throughout the frenelopsis rich plattenkalk 118 3 to 118 2 my and the encasing units especially in the overlying brackish lacustrine deposits palaeogeographic and palaeoclimatic reconstructions suggest that the pyroclastic material was probably transported by northeasterly trade winds from orogenic volcanic centers located within the dinaridic carpatho balkan arc trench system and have been supplied to the apcp for a time span of 3 my during the late aptian a preliminary tephrostratigraphic correlation of the upper aptian volcaniclastic levels of the apcp with the bentonite levels of the vocontian basin is proposed

gas bubbles in fossil amber as possible indicators of the major gas composition of ancient air gases trapped in miocene to upper cretaceous amber were released by gently crushing the amber under vacuum and were analyzed by quadrupole mass spectrometry after discounting the possibility that the major gases n2 o2 and co2 underwent appreciable diffusion and diagenetic exchange with their surroundings or reaction with the amber it has been concluded that in primary bubbles gas released during initial breakage these gases represent mainly original ancient air modified by the aerobic respiration of microorganisms values of n2 co2 o2 for each time period give consistent results despite varying o2 co2 ratios that presumably were due to varying degrees of respiration this allows calculation of original oxygen concentrations which on the basis of these preliminary results appear to have changed from greater than 30 percent o2 during one part of the late cretaceous between 75 and 95 million years ago to 21 percent during the eocene oligocene and for present day samples with possibly lower values during the oligocene early miocene variable o2 levels over time in general confirm theoretical isotope mass balance calculations and suggest that the atmosphere has evolved over phanerozoic time

trace elements in shale as indicators of crustal provenance and terrane accretion in the southern canadian cordillera in this study the trace element geochemistry of shale is used to infer the nature of adjacent crustal blocks during terrane amalgamation and accretion in southern british columbia the geochemistry of about fifty shale samples from one of the best dated stratigraphic sections in the north america cordillera is used to 1 infer proximity to source regions characterized by juvenile ocean arcs continental arcs and ophiolites and 2 address a controversy concerning the timing of terrane amalgamation and accretion this study includes analyses of shale from the entire mesozoic stratigraphic section of the cadwallader terrane and overlying tyaughton basin as well as argillites from the structurally adjacent bridge river complex the mid cretaceous albian strata of the upper taylor creek group show light rare earth lree enrichment la n sm n of 3 0 and anomalously high cr and ni older units upper triassic lower cretaceous that stratigraphically underlie the upper taylor creek group have less lree enrichment high ba n la n ratios and no cr or ni anomaly the mid cretaceous strata were probably derived from a continental arc during a period of uplift and erosion of ultramafic rocks probably ophiolites and the co extensive nature of these sediments suggests accretion of many basement terranes to the edge of a continent the trace element geochemistry of the older strata is similar to that of sediment derived from an oceanic arc however lower cretaceous strata of the relay mountain group may record the incipient collision and progressive closure of this ocean basin the bridge river complex which is dominated by oceanic rocks and is interpreted to be an accretionary complex contains two suites of argillites one of which shows significant lree enrichment and isotopic data suggest a jurassic cretaceous age for these argillites that compose the matrix in this complex leitch et al 1991 we suggest that the bridge river complex was a jurassic cretaceous accretionary complex that formed outboard of the methow section of rocks and was not juxtaposed with the cadwallader terrane and tyaughton basin until the albian when these terranes were accreted to north america paleomagnetic data from these rocks maxson et al 1993 indicate that accretion took place at the latitude of central mexico and that subsequent strike slip faulting brought these terranes to their present position by eocene time

testing provenance diagrams lessons from the well constrained cariaco basin abstract the fine grained sediments of the cariaco basin venezuela of the last 130 ky whose deposition history is well characterized were analyzed geochemically in order to test the validity of sediment bulk geochemistry as an indicator of detrital provenance several binary and ternary diagrams as well as the chemical index of alteration cia were tested for their capacity to discriminate the poorly contrasted detrital sources to the cariaco basin and to describe the temporal evolution of the contributions of these different sources most of the diagrams tested did not allow a good discrimination of sources or when sources were well discriminated did not allow an interpretation of the temporal variations consistent with the known history a relatively good discrimination of sources and a consistent interpretation of temporal variations were however obtained using hf vs th and la yb vs gd yb binary diagrams as well as ti zr th ti zr la and lu hf th ternary diagrams compared to the previous studies of the detrital content of the cariaco basin sediments the geochemical approach permitted the recognition of a sediment contribution eroded from the unare platform and gulf of cariaco during rapid sea level oscillations and the contribution of saharan eolian particles during the younger dryas preboreal and mis6 5 transition the choice of plotted elements was determined after considering carrier minerals so that different elements may be informative in different sedimentary contexts overall mineral sorting during transport appears as a major limit to quantitative estimation of the different contributions in particular mineral sorting leads to the selective enrichment of elements associated with clays al rb th and lree in sediments deposited in the basin unless the geochemical effect of mineral sorting can be measured it appears that quantitative provenance analysis should be performed on fractions of similar grain size instead of bulk sediment

response to high frequency sea level change in a fluvial to estuarine succession cenomanian palaeovalley fill bohemian cretaceous basin

relationships between environmental conditions and the diagenetic evolution of organic matter derived from higher plants in a modern mangrove swamp system guadeloupe french west indies abstract the sedimentary organic matter content of a series of 2 m deep cores was investigated along a sea land transect at five sites representing five species of mangrove and salt marsh vegetation the vegetation was settled at the same place for at least 1000 years and therefore sedimentary organic matter deriving from the decay of higher plants has accumulated in large amounts the global morphological and chemical preservation of the organic matter attested by various sedimentary parameters including the proportions of cellulose bearing tissues the toc contents the c n ratios the total sulphur contents and the 13 c compositions reveals that the sedimentary organic matter is less degraded when it has been under the influence of the marine water table for a long time this is indicated by a good correlation between the salinities of interstitial waters the redox potentials measured in the wet sediments and the chemical composition of the organic matter moreover the concentration of organic sulphur shows a positive correlation with the hydrogen index hi only under the marine water table influence suggesting the very local presence of sulphur hc compounds

diagenetic modification of sm nd model ages in tertiary sandstones and shales texas gulf coast sm nd model ages of sandstones and shales from the oligocene frio formation of south texas and the paleocene eocene wilcox group of south central texas increase with increasing depth of burial depleted mantle model ages tdm of frio shales increase from ca 800 ma at 1 km of burial to ca 1000 ma at 4km in frio sandstones tdm increases from ca 750 ma at 1 km to over 1200 ma at 4 km of burial in wilcox shales tdm increases from ca 1300 ma to ca 1500 ma over a burial depth of 1 5 to 4 5 km tdm of wilcox sandstones increases from ca 1450 ma at 2 5 km of burial to as much as ca 2000 ma at 4 0 km the sampling scheme employed minimizes but does not eliminate the possibility that these trends in tdm are due to detrital variability close correlation of these trends with diagenetic changes in the rock and evidence of rare earth element mobility preserved in the diagenetic products suggests that diagenesis has modified tdm diagenetic modification of tdm in frio sandstone and wilcox shale is due primarily to loss of radiogenic nd whereas increased 147sm 144nd produces elevated tdm in deeper wilcox sandstones the tdm of frio shales does not change appreciably with depth owing to the opposite effects on tdm of decreased 147sm 144nd and decreased nd 0 loss of radiogenic nd is due primarily to reactions involving unstable volcanic detritus which is more abundant in the frio than in the wilcox decreased 147sm 144nd in authigenic illite and consequent increased 147sm 144nd in pore fluids results in elevated tdm in wilcox and frio sandstones containing late diagenetic cement and in decreased 147sm 144nd in deeper frio shale the similar tdm trends observed in both units which have different detrital characteristics suggest that modification of sm nd model ages in siliciclastic rocks may be commonplace during burial diagenesis

burial diagenesis of argillaceous sediment south texas gulf of mexico sedimentary basin a reexamination cuttings from a well through a thick section of miocene oligocene mudrocks from kenedy county texas spanning a depth range of 2130 to 5490 m 7000 to 18 000 ft have been studied petrographically and geochemically on the basis of whole rock chemical analyses the deepest samples have lost 18 wt and approximately vol mostly as caco3 mineral bound h2o and sio2 but including additional ca as well as sr light rare earth elements ree la ce nd sm fe and li k2o and rb have been added to the deeper rocks the large chemical changes are accompanied mineralogically by loss of detrital calcite kaolinite k feldspar ca plagioclase and muscovite gain of chlorite and albite and continued reaction of smectitic illite smectite i s to more illitic and k rich compositions throughout the entire depth interval of the well the large chemical changes in this thick mud rich interval almost certainly require advection of water free convection to accomplish the mass transfer initial variation in sediment composition is ruled out as a cause of the observed compositional changes with increasing depth because 1 a variety of immobile elements al2o3 tio2 zr hf heavy ree er yb th and sc remain constant relative to each other despite their uneven distribution across various particle size fractions in the sediments 2 deep frio shales are unlike quaternary gulf of mexico sediments or average shales and 3 unreasonable primary mineralogic compositions would be necessary to explain the chemical composition of the deep samples these results indicate that burial diagenesis of argillaceous sediment can be a considerably more open chemical process than is conventionally assumed that it can account for the two major chemical cements calcite and quartz in associated sandstones and that it mirrors secular changes in shales throughout geologic time

effects of chemical weathering and sorting on the petrogenesis of siliciclastic sediments with implications for provenance studies the bulk chemical compositions mineralogy and mineral proportions of sands and muds of the mallacoota basin in southeastern australia reflect the composition of weathering profiles mantling source rocks rather than bedrock muds contain abundant clay minerals that are virtually absent from the source rocks but abundant in the weathering profiles sands are strongly enriched in quartz relative to source rocks even in the headwaters of the fluvial system demonstrating that feldspar destruction occurs by in situ chemical weathering within profiles and before detritus enters the fluvial system k feldspar is proportionally more abundant in fluvial sands than in source rocks because plagioclase is more rapidly destroyed than either quartz or k feldspar in weathering profiles subsequent erosion and sorting produce sands enriched in quartz with high k feldspar plagioclase ratios relative to source rocks the composition of plagioclase incorporated into the fluvial sands is also controlled by chemical weat

constraints on the accumulation of organic matter in upper ordovician lower silurian black shales from the lower yangtze region south china abstract the late ordovician to early silurian o s was an important period in which many significant geological events occurred during the o s transition organic rich black shales were widely deposited and became important unconventional energy sources paleoproductivity detrital input and redox conditions are the three major factors controlling organic matter om accumulation although the effect of each factor is relatively clear the complex influences of these factors remain poorly understood specifically the evolution of these factors and the corresponding influence on the accumulation of om during the o s transition has not yet been systematically investigated this paper investigates the constraints on om accumulation in o s transition black shales from the lower yangtze region based on graptolite fossil identification zircon u pb dating and geochemical analyses of a well sequenced drilling profile the results show that i the sy 1 core sequence was well constrained from graptolite zones wf2 447 62 ma to lm5 441 57 ma across the o s boundary with decreasing sedimentation rates srs in the upper katian wf2 to wf3 and increasing srs in the lower rhuddanian ii complementary volcanic inputs katian and rhuddanian and upwelling events hirnantian exerted strong control over paleoproductivity iii orogenic processes in south china controlled detrital inputs and redox conditions iv om accumulation in the lower yangtze area across the o s transition occurred in three stages in stage 1 wf2 wf3 strong volcanism boosted productivity whereas om preservation was not favored in the oxic environment in stage 2 wf4 lm3 upwelling and volcanism resulted in high productivity and provided the optimal configurations for om enrichment in stage 3 lm4 and later rare om was preserved due to terrestrial dilution and unfavorable preservation conditions eventually wf4 lm3 became the prominent om rich biozones due to the effective coordination of the controlling factors namely upwelling volcanism and redox conditions

detrital chromian spinel compositions used to reconstruct the tectonic setting of provenance implications for orogeny in the canadian cordillera abstract detrital chromian spinel is an important accessory mineral in chert and volcanic lithic sandstones from the northern bowser basin microprobe analyses show that bowser basin detrital chromian spinels have cr cr al between 0 21 and 0 89 mg mg fe2 between 0 24 and 0 70 and fe3 fe3 al cr values below 0 12 comparison with spinels from literature on ultramafic rocks indicates that the compositional range of the detrital spinels closely matches that of spinels from alpine type peridotites emplaced by obduction of marginal basin crust and island arc complexes furthermore bowser basin spinels are compositionally distinct from spinels derived from either mid ocean ridge stratiform ultramafic complex or alaskan type peridotite the composition of the detrital spinel demonstrates that the source for bowser basin sediments included extensive alpine type peridotite which probably originated as marginal sea lithosphere in addition there is no evidence for material derived from mid ocean ridge alaskan type peridotites or stratiform complexes this provenance interpretation is in agreement with earlier interpretations that related chert pebbles in the bowser basin to chert rich strata of the cache creek terrane and is consistent with the detrital modal analysis of sandstones which calls for a source terrane consisting of obducted oceanic crust and island arc the chemistry of the detrital spinels further suggests the source area was eroded prior to emplacement of alaskan type peridotites or any regional gree schist or higher grade metamorphic events thus microprobe compositional analysis of detrital spinels adds important detail to the provenance interpretation that is not available through analysis of detrital modes alone the inference that marginal basin lithosphere rather than material derived from mid ocean ridges was the sediment source suggests that the obducted source terranes were closely associated with north america

a petrographic approach for evaluating trace element mobility in a black shale abstract at the time of deposition black shales record geochemical information related to the provenance and conditions of deposition for that rock these initial geochemical conditions are susceptible to alteration and overprinting by the aggressive processes of black shale diagenesis in this study we evaluate a sequence of ordovician black shales from the southern welsh basin for the presence of such a diagenetic overprint through use of cathodoluminescence backscattered electron imaging reflected light microscopy fission tracks and microprobe elemental mapping we can discern textural relationships with in the welsh black shales the relationships observed constrain a paragenetic sequence and overall diagenetic history including the early diagenetic formation of pyrite apatite rare earth element ree rich and carbonate and later formation of diagenetic monazite ree u rich and late stage carbonate the chemical reactions necessary to produce this mineral sequence require postdepositional redistribution of ree including changing cerium anomalies ce ce and uranium as a result ree u and their associated isotopic systems sm nd and u pb can reflect a diagenetic overprint rather than the source area and depositional conditions the paragenetic sequence described in this study records several postdepositional changes in the whole rock mineralogy among these changes are the formation of ree rich apatite and ree and u rich monazite the formation of these phases requires that ree and u are being redistributed on at least a mineral scale and that the initial depositional and provenance information recorded by the whole rock has been disturbed therefore the approach used in this study to carefully characterize the paragenetic sequence from the llandeilo caradoc black shales should be considered necessary in order to fully evaluate the usefulness of trace element proxies susceptible to diagenetic redistribution

geochemical identification of clastic sediment provenance from known sources of similar geology the cretaceous scotian basin canada abstract this study tests the effectiveness of a geochemical approach in identifying provenance in a basin where different sources do not show strongly contrasting geology petrological studies indicate that at least three distinct rivers draining reactivated horsts of the appalachian orogen supplied sediment to the lower cretaceous deltaic sandstones and mudrocks in the offshore scotian basin ninety five samples mostly from conventional core were analyzed for 44 major and trace elements the data were first screened for variability unrelated to provenance including changes in elemental abundance due to weathering and diagenesis and the effects of grain size and sorting on element variation the effect of hydraulic sorting was distinguished from the effects of concentration of ultrastable heavy minerals from polycyclic sources multivariate statistical analysis by principal component analysis pca was used to test the hypothesis of three discrete sources suggested by the petrologic model major element pca on sandstones discriminated the sources but results from trace element pca required further investigation using element biplots to understand their significance only a few elements were found to be diagnostic of different sources namely k rb sr u th nb and ti with the latter two of value only for sandstones all of these are elements that are abundant in the granites of the appalachians most published geochemical discrimination diagrams did a poor job of distinguishing the three petrographically recognized sources in other basins with quite different hinterland geology other elements are known to be of value in discriminating provenance thus it is unlikely that a globally applicable set of elemental discriminants can identify terrigenous sediment sources rather systematic investigation is needed that evaluates processes such as diagenesis and sorting and then tests geographic and stratigraphic variability in bulk geochemistry informed by at least semiquantitative petrographic data

thin skinned tectonics in the northern rhenish massif germany a network of profiles in the hercynian mountain system geo traverse rhenoherzynikum is needed to determine details of the geological structure and find the reasons for tectonic movements outstanding features within the mountain system such as the large fault zone along the southern boundary of the hunsruck1 and the left flank of the rhinegraben have already been investigated by reflection seismology2 3 we describe here a new reflection refraction experiment carried out in 1978 in the most northern part of the rhenish massif across the stavelot venn massif near aachen fig 1 while layers in the lower crust dip to the nnw a strong upper reflector at 3 4 km depth shows a slight dip to the sse and indicates a prominent fault zone near aachen known in belgium as the faille du midi here a comparable and apparently identical reflector was found some 100 and 175 km to the west of our profile we interpreted this reflector as a prominent and well lubricated thrust fault along which a huge horizontal nappe displacement took place during the last stages of the variscan orogeny

late ordovician early silurian continental collisional orogeny in southern mexico and its bearing on gondwana laurentia connections new zircon and monazite u pb data tectonic mapping and petrologic studies in key units of the acatlan complex show a previously undocumented phase of continental collision orogeny of late ordovician early silurian age in southern mexico the event involved the partial eclogitization of oceanic lithosphere and continental crust which traveled westward more than 200 km over siliciclastic metasedimentary rocks of the trench forearc of an opposing continental margin the overriding eastern margin was the oaxaquia microplate attached to gondwana and the western overridden margin is considered to have been the eastern margin of laurentia this event which we name the acatecan orogeny was roughly synchronous with the possible closure of iapetus along the appalachian margin which involved according to current models either the docking of peri gondwanan terranes such as avalonia and carolina or the direct collision between gondwana and laurentia the permanence of oaxaquia in northwestern gondwana until the end of the silurian as suggested by tremadocian to silurian marine faunas in the cover of oaxaquia is more consistent with the direct collision of gondwana and laurentia at the end of the ordovician forming the acatlan complex between

variations in the carbon isotope composition of late holocene plant macrofossils a comparison of whole leaf and cellulose trends stable carbon isotope measurements 13c made on quaternary sequences of terrestrial plant subfos sils are frequently used to infer palaeoclimatic trends however differential decomposition of individual con stituents during incorporation of plant material into lake sediments could influence these interpretations there fore we investigated down core variations in the carbon isotope composition 13c of subfossil leaves of salixherbacea l and their holocellulose component from a late holocene c 0 3300 years ago site in northern sweden locally weighted regression curves fitted to both 13c data sets showed similar but conserved temporal patterns of change and there was no evidence for systematic shifts in the holocellulose yields or c n ratios of leaves with age small d13c variations over the past 3300 years probably reflect natural variations in microclimate within the lake catchment area this interpretation is quantitatively consistent with the variability determ ined from measurements made

tertiary volcanic rocks and the potassium content of gulf coast shales the smoking gun the majority of tertiary volcanic rocks of the western united states and mexico are alkaline in composition and may contain as much as 50 wt equivalent k feldspar emplacement of these volcanic strata is coeval with tertiary shale deposition in the texas gulf coast and they previously have been identified as likely sources of sediment for gulf coast shales evaluation of chemical trends in gulf coast shales particularly k 2 o indicates changes in sediment composition in the lower eocene oligocene and near the oligocene miocene boundary in particular there is a 250 increase in k 2 o content from 2 wt to 5 wt from the late eocene to the early oligocene gulf coast shale bulk rock compositions are consistent with a tertiary volcanic source estimates of erosion and mass balance calculations suggest that in the south texas gulf coast the oligocene frio formation may contain between 60 and 85 volcanic detritus and coeval frio shales to the north contain 25 vertical and lateral compositional variations highlight variable abundances of source detritus and the effects of weathering and depositional processes on gulf coast shale composition trends of increasing k 2 o content with depth in gulf coast shales previously have been interpreted to result from open system diagenesis and k metasomatism at depth the data presented herein suggest instead that these trends result from variable provenance and the influx of large volumes of tertiary alkaline volcanic material therefore diagenetic models that invoke a homogeneous initial shale composition and open system behavior may be invalid

beyond whole rock geochemistry of shales the importance of assessing mineralogic controls for revealing tectonic discriminants of multiple sediment sources for the ouachita mountain flysch deposits the origin of the ouachita mountains has been the focus of significant debate for decades considerable confusion also exists concerning the provenance of the carboniferous flysch of the ouachitas trace element geochemistry of shales from the stanley group delineates the provenance of the sediments and provides clues to the plate tectonic evolution of the southern continental margin during mississippian time th sc and cr th ratios indicate a cratonic source for the majority of the stanley group sedimentary rocks however in several samples low th sc ratios and high cr th ratios suggest a contribution from a mafic source using element ratio diagrams all of the samples plot along a curve consistent with a two component mixing model consisting of a dominant felsic and a subordinate mafic source the heavy mineral fraction of these shales sequester many of the trace elements used in whole rock studies monazite is ubiquitous in trace amounts and is the probable site for much of the rare earth elements in the whole rock the occurrence of monazite almost exclusively in sialic igneous rocks implies that sm nd isotopic signatures are not sensitive to sediment input from more mafic sources in some stanley shale samples chromite and mn oxides were identified and positively identify an oceanic crustal component as a source of stanley group sediment the results of this study emphasize the importance of determining the mineralogic sites of trace elements and realization of specific mineralogic contributions from mafic or sialic tectonic provenances

the effect of maturation on the isotopic composition of fossil fuels abstract few measurements of the d h ratios in liquid and solid fossil fuels have been made additional isotopic data are reported here in the form of d h and 13 c 12 c ratios for crude oils and brown coals which occur together in the bass strait region of australia studies of petrographic fractions of these coals and of the changes in the isotopic composition of coals and coal extracts with increasing maturity show that the original d h ratios characteristic of contributing plant materials are more readily erased and homogenized during early diagenesis than the corresponding 13 c 12 c ratios

zircon typology combined with smnd whole rock isotope analysis to study brioverian sediments from the armorican massif the identification of source materials contributing to mature terrigenous clastic deposits is made difficult due to a lack of useful discriminant criteria sm nd isotope analysis can provide some indication of the present of mantle derived constituents in clastic rocks however since this method is based on whole rock samples it is only possible to obtain the averaged composition of the different source materials involved moreover sm nd isotope systematics can be strongly influenced by the presence of heavy minerals rich in rare earth elements and or displaying isotopic ratios very different to the sedimentary host in this manner 0 1 of zircon or 0 01 of monazite from an extraneous source is sufficient to modify significatively the sm nd signature of the whole rock the typological study of zircon populations is an extremely valuable tool especially since this mineral is highly resistant and exhibits a morphology controlled by the physical and chemical conditions under which it crystallized zircons that have been reworked in a sedimentary deposit display typologies that make it possible to identify the different igneous rock types present in the source region moreover the typological study can be associated with a single grain pb pb dating this twofold approach was applied to brioverian sedimentary rocks neoproterozoic iii to early palaeozoic in age from the central brittany domain armorican massif nw france it is proposed that these deposits inherited a major component from juvenile crustal materials end 540 1 4 to 6 3 reflecting the presence of igneous precursors with a dominantly mantle derived origin zircon sub types s19 s20 s24 s25 etc to which was added another component of crustal anatectic affinity zircon sub types s2 s6 s7 etc two igneous source regions are identified on the basis of the present study the anatectic granitic massifs of the mancellian batholith 540 ma along with a coeval ignimbritic suite of end proterozoic eocambrian age and the syn and post tectonic dioritic massifs 590 to 530 ma apart from these main sources of clastic supply it is very likely that sporadic contributions arose from basic to intermediate volcanic activity of mantle origin linked to the cadomian orogeny and from the icartian basement

40ar 39ar phlogopite geochronology of lamprophyre dykes in cornwall uk new age constraints on early permian post collisional magmatism in the rhenohercynian zone sw england the spatial and temporal association of post collisional granites and lamprophyre dykes is a common but enigmatic relationship in many orogenic belts including the variscan orogenic belt of sw england the geology of sw england has long been interpreted to reflect orogenic processes associated with the closure of the rheic ocean and the formation of pangaea the sw england peninsula is composed largely of early devonian to carboniferous volcano sedimentary successions deposited in synrift and subsequent syncollisional basins that underwent deformation and low grade regional metamorphism during the variscan orogeny voluminous early permian granitic magmatism cornubian batholith is considered to be broadly coeval with the emplacement of lamprophyric dykes and lamprophyric and basaltic lava flows largely on the basis of geochronological data from lamprophyric lavas in devon although published geochronological data for cornish lamprophyre dykes are consistent with this interpretation these data are limited largely to imprecise k ar whole rock and biotite analyses hindering the understanding of the processes responsible for their genesis and their relationship to granitic magmatism and regional variscan tectonics 40 ar 39 ar geochronological data for four previously undated lamprophyre dykes from cornwall combined with published data suggest that lamprophyre magmatism occurred between c 293 6 and c 285 4 ma supporting previous inferences that their emplacement was coeval with the cornubian batholith these data provide insights into 1 the relative timing between the lamprophyres and basalts the cornubian batholith and post collisional magmatism elsewhere in the european variscides and 2 the post collisional processes responsible for the generation and emplacement of lamprophyres basalts and granitoids supplementary data complete datasets photomicrographs and photographs of sample locations are available online at http www geolsoc org uk sup18838

plant taphonomy and palaeoecology in the lacustrine una delta late barremian iberian ranges spain abstract plant cuticle compressions and sporomorphs were studied in coaly clays belonging to the upper barremian la huerguina formation in una south western iberian ranges cuenca spain cuticle assemblages are extremely monotonous and formed by the genera frenelopsis schenk emend watson classostrobus alvin et al and glenrosa watson and fisher sporomorphs are dominated by classopollis pflug emend srivastava the genus glenrosa is described for the first time in europe sedimentological and taphonomical analyses show that these assemblages originated by fragmentation and size selection during residence in the leaf litter and by fluvial transport final deposition occurred in crevasse splay deltaic front and pro deltaic environments our results indicate that the una delta was fed almost exclusively by remains of cheirolepidiaceous conifers living in the upper deltaic plain of a lacustrine delta a comparison with the flora found in the open lacustrine facies of las hoyas which is laterally equivalent of the beds studied shows that land plant assemblages of las hoyas are more diverse the parautochthonous matoniaceous tree fern weichselia reticulata dominated the lakeshore vegetation of las hoyas in contrast to the vegetation of the upper delta plain of una which was dominated by frenelopsis the habitats of frenelopsis and glenrosa from the upper barremian oligohaline basin of una las hoyas contrast with the habitats commonly hypothesized for both taxa in coastal marine environments or on saline edaphic profiles in conclusion frenelopsis appears to have a wider tolerance to salinities than previously thought and their adaptations to saline edaphic conditions should be considered species specific rather than genus specific

nd isotopic constraints on sediment sources of the ouachita marathon fold belt nd isotopes for the overthrust deep marine ouachita marathon sedimentary assemblage of arkansas oklahoma and west texas and associated paleozoic shelf and foreland deposits resolve into three distinct populations 1 lower to middle ordovician nd 13 to 16 average t dm 2 0 ga 2 upper ordovician to pennsylvanian nd 6 to 10 average t dm 1 6 ga and 3 mississippian tuffs nd 1 to 3 average t dm 1 1 ga a rapid shift in nd from 15 passive margin shales to 7 orogenic turbidites in the ouachita assemblage at ca 450 ma implies termination of craton dominated sources and the emergence of the appalachian orogen as the primary source of sediment for sea floor lying south of north america this connection is reinforced by nd isotopes in ordovician silurian turbidites from both the ouachita assemblage and the southern appalachian sevier martinsburg taconic foredeep which are identical nd 7 to 9 the post 450 ma ouachita assemblage falls along a single nd isotopic trend that significantly is not deflected by onset of carboniferous flysch nd 7 to 10 sedimentation nor by associated regional volcanism the less negative nd 2 of mississippian ash flow tuffs that erupted from arc s to the south probably resulted from isotopic mixing of old precambrian crust with young mantle derived components within a continental margin arc there is little isotopic trace element or petrographic evidence for any significant volcaniclastic detritus in the carboniferous turbidites indicating that volcanic arc sources were minimal nd isotopes in fluvio deltaic strata of the ouachita appalachian foreland and continental interior that is arkoma illinois and black warrior basins nd 7 to 10 imply that continental margin pathways and interior basins received the same detritus as the ouachita trough by pennsylvanian time these data are consistent with a composite carboniferous ouachita submarine fan complex built down the axis of a remnant ocean basin from varied mature immature delivery systems tapping dominantly appalachian fold thrust belt sources to the east graham et al 1975 carboniferous turbidites from the marathon fold belt west texas which are isotopically similar nd 8 to 11 to ouachita turbidites may have been ultimately derived from similar sources however they probably do not represent merely distal turbidites of a ouachita fan complex it is suggested that dominantly appalachian derived detritus augmented by uplifted plutonic and fold thrust belt sources south of the marathon basin was swept up into subduction complexes on the north side of the approaching arc and recycled along the collision zone

an interpretation of the variscan structures in sw england the variscan structures in sw england apart from the high level structures in the culm synclinorium of n devon are recumbent with an overall gentle southward dip of cleavages thrusts and recumbent folds translation was towards the nnw the structures are interpreted on a thin skinned model with a basal decollement dipping gently s related to a s dipping subduction zone s of the lizard the granites are thought to have been generated to the s of their present position and injected northwards above the decollement zone

another look at rare earth elements in shales linear correlation and mass balance considerations indicate that clays are more important than zircon or other heavy minerals in hosting both light and heavy ree in cratonic shales considering the uniformity of the eu anomaly and ree distributions in cratonic shales it seems likely that detritus is thoroughly mixed during weathering and sediment transport and that the ree patterns in shales reflect the average ree pattern of the sources regardless of the ratio of clays to heavy minerals in the shales shales suspended river loads and near shore marine sediments all have broadly similar ree patterns and reported hree depletions in the latter two groups may reflect incomplete dissolution of heavy minerals during sample preparation ree distributions in shales and suspended river loads determined by inna are similar to those in average upper continent crust and ree distributions in shale averages nasc and paas seem to be reasonably representative of the average composition of post archean upper continental crust

a new terrestrial plant rich fossil lagerstatte from the middle cenomanian late cretaceous of the apennine carbonate platform magliano vetere southern italy depositional and palaeoenvironmental settings abstract we describe a new terrestrial plant rich fossil lagerstatte discovered at magliano vetere campania region s italy in the middle cenomanian of the apennine carbonate platform the deposit 1 42 m thick is made up of a thin bedded interlayering of evenly laminated dolomicrites lenticular dolorudites and carbonaceous seams which contain well preserved remains of terrestrial plants yielding cuticles and minor fishes this study focuses on plant remains to provide systematical taphonomical and palaeoenvironmental considerations nevertheless a preliminary analysis carried out on fossil fishes has led to the identification of pycnodontids and teleosts the fossil lagerstatte retains sterile foliage bearing shoots with epidermal features belonging to the genus frenelopsis of the extinct conifer family of the cheirolepidiaceae plant remains possibly represent a stable biotope as floral composition displays no variation along the deposit nevertheless episodes of harsh environmental conditions occurred as demonstrated by a fish mortality event and ca sulphate evaporite precipitation taphonomical considerations and sedimentological evidence from the encasing sediments suggest a parautochthonous deposition of fossil plants in a supratidal intertidal mudflat including a salt marsh that was characterised by a restricted sea water circulation deposition of primary dolomite and episodical wildfires the presence of xeromorphic features in frenelopsis from magliano vetere could represent an adaptation to haline environment which was subjected to microtephra supply from a distant orogenic volcanism the facies evolution of the studied fossil lagerstatte records a rapid regressive and a following slower transgressive trend and constitutes the lowermost portion of a 20 m thick interval characterised by several dolomitic plattenkalk up to 1 50 m thick which are separated by cyclically stacked peritidal limestones we infer that 1 the 20 m thick plattenkalk bearing interval represents a sequence boundary zone in the stratigraphical record of the middle cenomanian apcp 2 frenelopsis thrived at the verge of an arid semiarid climatical phase during a major pulse of relative sea level fall

the cr th ratio in precambrian pelites from the kaapvaal craton as an index of craton evolution the cr th ratio in precambrian pelites from the kaapvaal craton in southern africa correlates with pelite th sc and co th ratios and appears to monitor changes in source composition it is a more sensitive indicator of provenance than other commonly used ratios including eu eu la yb and th u pelite cr th ratios are controlled most strongly by the effects of local provenance and local tectonics secular decreases in this ratio the most prominent of which occurred at 2 4 2 3 ga in pelites of the kaapvaal craton record rapid uplift exposing granite decreases in the ratio reflect increases in the abundance of komatiite basalt in sediment sources in response to arc collisions rift hotspot volcanism or intracratonic uplift of older greenstones relatively constant cr th ratios appear to require widespread uplift or and efficient sediment mixing during tectonic stability changes in cr th ratio of kaapvaal pelites reflect a complex tectonic history of the craton from about 3 3 ga to 1 8 ga and do not favor single stage cratonization in the late archean

evolution and hydrocarbon prospectivity of the brittany basin western approaches trough offshore north west france abstract the faulted preservation of a complete jurassic cretaceous succession in the brittany basin is primarily the result of early cretaceous rifting throughout the western approaches trough jurassic and cenozoic strike slip deformation has also contributed to the distribution of sedimentary successions now observed consequently the brittany basin has a different burial uplift history to the adjacent basins of the western approaches making the lias lower jurassic a mature source rock reservoir rocks are present but the unique deformation history has resulted in the late formation and possible breaching of structural traps the sedimentary record from the brittany basin allows us to observe the depositional effects of tectonic events occurring elsewhere in the western approaches trough these suggest middle jurassic early cretaceous late cretaceous and cenozoic uplift events each have different structural effects the origin of the most prominent intra mesozoic unconformity throughout the western approaches trough the early mid cretaceous is discussed with reference to causes of juxtaposed uplift and renewed rifting

a record of glacial aridity and milankovitch scale fluctuations in atmospheric dust from the pennsylvanian tropics abstract atmospheric dust is an important climatic agent as well as a valuable climatic archive this study documents systematic variations in a single upper pennsylvanian shallow water carbonate buildup of the midland basin west texas that was isolated from fluvio deltaic input and consists almost entirely of carbonate bounded by sequence boundaries thin 0 02 to 1 m intervals of dark pyritic siliciclastic mudrock with subtle pedogenic features occur commonly at the sequence boundaries and are interpreted as loessite deposited during lowstands primarily on the basis of paleogeographic isolation of the buildup the silicate mineral fraction smf extracted from the underlying carbonate which includes quartz clay and trace feldspars and heavy minerals varies in concentration weight from 0 015 to 6 69 in the carbonate this smf contains both fine grained detrital and authigenic silica interpreted to be eolian on the basis of geochemical petrographic and grain size characteristics as well as paleogeography hence the smf is considered a proxy for atmospheric dust whole rock geochemistry suggests that the dust was at least partly derived from uplifts of the ancestral rocky mountains with a possible minor contribution from active volcanic centers located to the present day south and southwest the estimated mean accumulation rate mar of dust in highstand carbonate facies full interglacial relative to carbonate facies that formed during relative fall in sea level suggest that dust flux increased 4 to 10 times accompanying the transition to glacial conditions mars in the siliciclastic mudrock which accumulated at lowstand full glacial to incipient transgression suggest glacial phase increases in dust flux of nearly 400 to 4000 times relative to full interglacial conditions spectral analyses of dust abundance through the study section show variations consistent with milankovitch forcing

ophiolitic source rocks for taconic age flysch trace element evidence flysch generated along the appalachian orogen during the ordovician taconic orogeny ranges in age from late arenig to early caradoc allochthonous flysch and from late llanvirn to ashgill autochthonous flysch sandstones in these units are dominantly lithic arenites with a heavy mineral suite containing common to abundant mg rich chromite north of the canada united states border the only reasonable sources for the chromite were the lower ultramafic units of obducted ophiolites trace element analyses cr ni v cu ti zr y of flysch sandstones indicate a striking increase in cr and ni concentrations from the united states appalachians to the canadian appalachians in the united states units cr is in the range of 10 to 50 ppm canadian flysch units average an order of magnitude more cr these results suggest that ophiolite obduction either did not occur or was of minor importance during the taconic orogeny in the united states appalachians the difference in ophiolite abundance between the canadian and united states appalachians suggests a fundamental difference in tectonic style along the orogen a feature that must be accommodated by plate tectonic models new models will probably need to consider both obliquity of subduction and geological complexity of the ordovician collision zone in order to explain the spatial distribution of obducted ophiolite sheets

inorganic geochemistry of the type caradoc series sandbian to middle katian upper ordovician onny valley shropshire uk the geochemistry and petrology of the type section of the caradoc series in the onny valley indicate that it was deposited on a marginal basin continental shelf similar to the western side of the present sea of japan the lower beds form a transgressive regressive sequence in which the rocks become less mature upwards all the coarser sediments above the basal quartzites and conglomerates are greywackes in which the apparent muddy and ferrous matrix is due to the breakdown of unstable minerals and particles higher values of na 2 o and na k ratios are found in the coarser shallow water sandstones of the horderley sandstone formation and decrease markedly in the succeeding beds accompanied by an increase in k 2 o higher values of carbonate corrected and hence related other major and minor elements like sio 2 cao p 2 o 5 mno and most trace elements correlate with the transgressive systems and maximum flooding surfaces of the three sequences recognized where they are related to condensation at those horizons chemical indices of alteration cia suggest that the horderley sandstone formation underwent greater predepositional physical weathering than lower and higher beds which is compatible with the petrography and were deposited during a cool phase within overall warm sandbian katian times trace element ratios suggest an oxic to suboxic depositional environment

geochemistry of mississippian tuffs from the ouachita mountains and implications for the tectonics of the ouachita orogen oklahoma and arkansas the ouachita orogeny was the result of plate convergence at the southern margin of the north american continent although the nature of the converging southern plate and the direction of subduction remain uncertain the presence of areally extensive tuff layers interbedded with shale in the mississippian stanley group of the ouachita mountains oklahoma and arkansas provides the potential to define the tectonic environment of volcanism from the geochemistry of the tuffs and thereby delimit the subduction configuration the tuffs contain relic primary magmatic quartz plagioclase and alkali feldspar and range from crystal to vitric rich mineralogical sorting and diagenetic effects have caused chemical variability within individual tuff units but overall the tuffs have retained their primary igneous geochemical characteristics the beavers bend and hatton tuffs are geochemically very similar and are more evolved higher sio2 rb th ree lower sr ba than the mud creek tuff the stratigraphically equivalent sabine rhyolite is geochemically distinct from the tuffs having less fractionated rare earth element ree patterns and different trace element ratios both the ouachita tuffs and sabine rhyolite have the geochemical characteristics of subduction related magmas for example strong depletion of nb and ta relative to other incompatible trace elements consideration of trace element systematics in the tuffs compared to those of modern high silica volcanic rocks from different subduction related tectonic settings suggests a continental arc origin and implies southward subduction beneath a southern continent during carboniferous ocean basin closure

the post variscan development of the british isles within a regional transfer zone influenced by orogenesis abstract the break up of pangaea after the variscan orogeny included rifting extending southwards from the barents sea via the norwegian greenland rift and into the north sea and northwards from the central atlantic these two major rift systems interacted to form an approximately 1200 km wide transfer zone across the british isles where a complex network of basins developed during the mesozoic fault patterns were commonly controlled by reactivation of precambrian caledonian and variscan structures the two main rift systems were unable to breach this regional transfer zone where the crust had been thickened by the caledonian and variscan orogenies until the eocene breaching did not occur down the north sea and through the english channel because of alpine contraction in nw europe instead breaching occurred around the west of ireland and nw scotland so the british isles remained connected to europe rather than to the north american plate

latest proterozoic stratigraphy and earth history the end of the proterozoic eon was a time of pronounced biological biogeochemical climatic and tectonic change new bio and chemostratigraphic data provide an improved framework for stratigraphic correlation making possible a deeper understanding of latest proterozoic earth history and providing tools for a chronostratigraphic division of late proterozoic time

late carboniferous to triassic reactivation of variscan basement in the western english channel evidence from onshore exposures in south cornwall south cornwall represents the westernmost part of the variscan basement massif in sw england field based investigations into the distribution geometry kinematics and relative chronology of post variscan deformation have been accompanied by preliminary palaeostress analyses these indicate three episodes of basement reactivation 1 stephanian to early permian nnw sse extension 2 early to late permian strike slip deformation and 3 late permian to triassic ene wsw extension these data have been used to test and refine previously published models based upon seismic and well data of late carboniferous to triassic basement reactivation and sedimentary basin development within the western approaches trough we confirm that nnw sse regional extension and reactivation of ene striking variscan thrusts had initiated by the latest carboniferous and that ene wsw regional extension and dip slip reactivation of nnw striking high angle faults occurred during the triassic permian strike slip deformation recognized onshore may have contributed to the development of widespread unconformities within the ovshore basins

elemental mobility in phosphatic shales during concretion growth and implications for provenance analysis shale normalized rare earth element ree patterns record variable redox conditions in coprolitic phosphorite concretions and their host shales from the pennsylvanian age cyclothems in the u s midwestern states of oklahoma kansas nebraska iowa and ohio as well as the mississippian age fayetteville shale of arkansas shale normalized enrichments in middle ree mree developed as the phosphatic concretions lithified under reducing conditions in pore waters of organic rich muds depletions in mree sm ho in host shales correspond to the mree enrichments in some nearby concretions rare and weak negative cerium depletions in both reworked and unreworked phosphorite concretions suggest exposure to oxygenated waters positive europium anomalies in thick phosphorite coatings on coprolitic phosphorite concretion cores suggest extreme reduction during lithification of the phosphorite coating flat ree patterns in both host shales and phosphorite concretions probably reflect detrital influence phosphate diagenesis can affect the trace element chemistry of black shale enough to alter provenance signals overall enrichment in ree in phosphorite relative to host shale suggests movement of ree as does the mree enriched phosphorite near the mree depleted host shale diagenetically mobile ree can affect la th sc relationships used in provenance analysis the extent of the diagenetic modification of la th sc distribution is related to the amount of p2o5 present typical la th sc distribution in host shale results when p2o5 values are below 0 5 high la abundance substantially skews la th sc distribution when p2o5 is above 5 0 but when p2o5 is between 0 5 and 5 0 the extent of the effect is unclear oxides of aluminum and other major elements may be useful in recording detrital influence and proximity to the shoreline in phosphorite concretions most of the concretions nearest to shoreline sources of detrital input have both flat ree patterns and elevated values of al2o3 al2o3 fe2o3

comparison of isotopic and petrographic provenance indicators in sediments from tertiary continental basins of new mexico abstract isotopic variations of nd in sedimentary rocks provide a new tool for provenance determination we have compared the isotopic technique with classic petrographic indicators of provenance in sediments from two tertiary basins of the rio grande rift north central new mexico the siliciclastic sediments in these basins were derived from varying proportions of precambrian basement and oligocene volcanic rocks which are isotopically and petrographically distinct in the analyzed sediments a good correspondence exists between petrographic and isotopic provenance indicators the data also suggest that the isotopic tracer is more sensitive to minor detrital input from a second source than is the framework petrology the similar sm nd ratios for all analyzed sediments and the identical isot pic values of interlayered mudstone and sandstone indicate that no significant fractionation of sm and nd occurs during the formation of the sediments thus the nd model ages of the sediments preserve the crust formation age of the source the sr isotopic and concentration data show trends generally similar to the nd data but they do not indicate the sedimentary provenance as clearly this ambiguity is a consequence of strong rb sr source heterogeneities and rb sr fractionation during the sedimentary cycle

rare earth element distributions among minerals in a granodiorite and their petrogenetic implications a study of the distribution of lanthanide rare earths in a granodiorite from the eastern peninsular ranges batholith southern california reveals that a large fraction of the ree in this rock resides in the accessory phases sphene and allanite the minerals plagioclase alkali feldspar biotite epidote and apatite each contribute approximately 1 or less of each ree to the whole rock with the exception of eu for which plagioclase contributes 7 sphene and allanite together contain 80 to 95 of each ree each of these phases is zoned in ree concentration with substantial decreases from core to margin textural observations argue for relatively early saturation and precipitation of sphene and allanite in the magma ree zoning trends in sphene and allanite and unexpectedly low ree concentrations in largely later crystallizing minerals such as feldspar indicate that the precipitation of sphene and allanite significantly reduced ree concentrations in residual melts these results illustrate the potential that sphene and allanite have for controlling the behavior of ree in granitic magmas available information collectively suggest that the sampled granodiorite existed as a complete melt that the ree contained in the assemblage of phases were derived by direct crystallization from the melt and that the melt behaved essentially as a closed system once crystallization of the phases now present began close correspondences between the major and trace element chemistries of the granodiorite and phenocryst poor lavas from similar tectonic settings support these conclusions the ree pattern of the granodiorite melt appears to have originated at depth and is characteristic of its source regions and derivation mechanism the high liquidus temperature of a granodiorite melt 1000 c indicates the importance of mantle derived components within the sources of batholithic magmas in the peninsular ranges

effects of chemical preparation protocols on δ13c values of plant fossil samples abstract for over a half century studies of the stable carbon isotope compositions of plant fossils have provided noteworthy conclusions about the evolution of earth climate however different preparation protocols were used prior to carbon isotope analysis of plant fossils and the accuracy of measured 13c 12c ratios may strongly depend on them we have applied the most frequently used chemical preparation protocols to frenelopsis leaves from four cretaceous localities of western europe our results indicate that procedures to extract plant fossils from sediments are not adequate to retrieve the original plant 13c values the use of schulze s reagent to bleach cuticles in paleobotany allows misleading 13c values of specimens from a same locality with positive shifts of up to 13 6 and increases intra specimen and inter specimen variances sample treatment involving hcl or hcl hf gives consistent 13c mean values for a same leaf and for leaves from a same sedimentary bed however although hf does not provide any advantage in removing potential contamination sources it alters plant fossil tissues slightly increasing the intra and inter leaf variances of 13c values our results indicate that processing plant fossils with hcl only is the most accurate and conservative way to retrieve original 13c values

the land plant δ13c record and plant evolution in the late palaeozoic abstract based on the evaluation of 1323 carbon isotope values for silurian to permian terrestrial organic carbon measured on plant fossils cuticules humic coals and bulk terrestrial organic matter tom we conclude that the temporal trend in 13ctom records variations in the global carbon cycle notably an increase in the fractional burial of light terrestrial organic matter in late palaeozoic sediments 13ctom values suggest that the late palaeozoic po2 peak could have been restricted to a time frame of 40 ma carbon isotope data from four taxonomic groups reveal small differences that could be a consequence of habitat conditions no significant differences in organic carbon isotopic composition in relation to variable climatic conditions are discernible the carbon isotopic composition solely reflects c3 plant metabolism

alteration of 15n14n and 13c12c ratios of plant matter during the initial stages of diagenesis studies utilizing archaeological specimens from peru abstract the stable carbon and nitrogen isotope ratios of plants extracted from peruvian archaeological sites ranging in age from 400 to 4000 years b p have been measured the 13 c and 15 n values of prehistoric plants that were carbonized prior to deposition are similar to those of modern plants which have the same carbon dioxide fixation or nitrogen assimilation mechanisms in contrast the 15 n values of prehistoric plants that were not carbonized are generally 10 20 and as much as 35 more positive than those of their modern counterparts the 13 c and 15 n values of different parts of prehistoric uncarbonized plants differ by as much as 8 and 21 respectively whereas the same parts of modern plants have 13 c or 15 n values that lie within 2 of one another sem analysis etiminated the possibility that diagenetic alteration of the isotope ratios of the prehistoric uncarbonized plants was caused by the adsorption of particulate soil matter isotopic analysis of the organic residues that remained after the prehistoric uncarbonized plants were treated to remove fractions that might have been added in the depositional environment indicated that the alteration of the 13 c values resulted from the adsorption of humic and fulvic acids whereas the diagenetic shifts of the nitrogen isotope ratios were not caused by adsorption of 15 n enriched organic or inorganic forms of nitrogen from the soil our observations do not permit us to speculate on a mechanism that accounts for the 13 n enrichment of the prehistoric uncarbonized plant remains although the excellent state of preservation of these samples suggests that isotopic fractionation during microbial decomposition was not the cause the observation that the isotope ratios of the prehistoric carbonized plants are similar to those of their modern counterparts indicates that it will be possible to separate carbonized plants residues into three groups legumes non leguminous c 3 plants or c 4 and cam plants based on their 13 c and 15 n values this method should provide useful information to archaeologists working in environments in which carbonized plant remains often burned beyond morphological recognition are the only archaeobotanical remains which are recovered

a warm equable cretaceous the nature of the problem abstract the nature of the problem of warm equable paleoclimates is defined by investigating the mid cretaceous period the problem consists of three components 1 defining precisely the climatic state during any specified interval of geologic time 2 specifying the external climatic forcing factors which may have been important and 3 understanding the climatic response to any specific modifying influence these components are characterized by limitations of critical importance in understanding paleoclimates the nature of the problem of a warm cretaceous is defined both qualitatively and quantitatively within these limits

comparative geochemistry of pleistocene and paleoproterozoic huronian glaciogenic laminated deposits relevance to crustal and atmospheric composition in the last 2 3 ga abstract comparison of the major and trace element geochemistry of glaciogenic laminated deposits of pleistocene and paleoproterozoic age from an area north of lake huron ontario has revealed differences and similarities that may provide insight into the erosional history of part of the archean superior province of the canadian shield during the last 2 ga and some aspects of the evolution of the earth s atmosphere both the major element and trace element compositions of the ancient and recent glacial deposits are very similar the paleoproterozoic mudstones are however enriched in fe and u characteristics that may reflect the oxygen content of the archean early paleoproterozoic atmosphere hydrosphere system strong ca depletion is exhibited by the paleoproterozoic glaciogenic argillites but is absent from the pleistocene samples the proterozoic argillites have slightly higher values for a chemical index of alteration than those of pleistocene muds these characteristics may reflect the acid natur

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

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

isotope reconstruction of plant palaeoecology case study of cenomanian floras from bohemia palaeoenvironments inferred from stable carbon isotope ratios of fossil plants collected from various environments of the cenomanian of bohemia were compared with palaeobotanical and sedimentological data to test the use of isotope ratios as a record of local palaeoenvironments and fossil plant ecology a number of isotope and biogeochemical patterns suggested that stable carbon isotope ratios in the cenomanian plants from bohemia have not been significantly affected by diagenesis stable carbon isotope ratios of the palaeoflora from one of the sections studied were used as a reference for a non stressed habitat since both sedimentological and palaeobotanical evidence suggested that the fossil flora underwent no environmental stresses that could have influenced its 13c values comparisons of 13c values of the other palaeofloras with that of the reference section allowed inference of the palaeoenvironmental stresses undergone by fossil plants these palaeoenvironmental patterns deduced from 13c 12c ratios are in agreement with the palaeoenvironments previously reconstructed by sedimentological and palaeobotanical studies combining evidence from those studies with isotope data provided detailed insights into the palaeoecology of the plants studied finally stable carbon isotope ratios allowed precise characterisation of the ecology of the best represented species of the deposits studied the ginkgoalean plant eretmophyllum obtusum and the conifer frenelopsis alata which were quite common in the salt marsh environments in europe during the cenomanian hence stable carbon isotope ratios can help in evaluating the environmental stresses undergone by fossil plants and the combination of these results with palaeobotanical and sedimentological data can provide detailed insights into fossil plant ecology

the paleozoic to mesozoic carbon cycle revisited the carbon isotopic composition of terrestrial organic matter 1 two thousand one hundred forty eight carbon isotope values for terrestrial organic matter plant fossils coal bulk terrestrial organic matter provide a proxy record for temporal changes in the global carbon cycle 13ctom 13ccarb and 13cco2 allow a full evaluation of carbon transfer in the atmosphere ocean system as well as between the marine and the terrestrial realm the temporal evolution of 13ctom parallels respective data sets from marine carbonate carbon thus reflecting the linkage between both reservoirs via atmospheric carbon dioxide on the basis of a comparison between measured and predicted isotope records for 13ctom changes in the carbon isotopic fractionation associated with plant metabolism are discernible this contradicts the notion of an invariable carbon isotopic fractionation associated with c3 plant metabolism in light of results from current plant growth experiments these changes are viewed as dependent on the atmospheric o2 co2 hence 13ctom might serve as a proxy signal for atmospheric composition

thermal maturity of carboniferous strata ouachita mountains the ouachita mountains a relatively untested potential hydrocarbon province contain a thick paleozoic section of apparently favorable source beds reservoir beds and trap configurations to estimate the thermal maturity of these strata vitrinite reflectance was measured on 89 samples collected mostly from carboniferous rocks from throughout the ouachita outcrop area thermal maturity contours generally parallel structural grain in the western two thirds of the ouachitas reflectance values in oil range from 3 0 in the core area in oklahoma and from about 1 0 to 3 0 in analogous positions in arkansas older strata on upthrown sides of thrust faults are more thermally mature than younger strata on downthrown sides in the eastern one third of the outcrop belt thermal maturities are significantly higher 2 0 5 0 ro and thermal maturity contours cut obliquely across structural grain strata on either side of thrust faults display identical levels of maturity in the western two thirds of the ouachitas sedimentary and tectonic burial have been the major influences of thermal maturation although a mesozoic thermal overprint has increased levels of maturity in arkansas throughout this area strata are within the oil and wet gas windows the anomalous levels and patterns of thermal maturity in the eastern third of the ouachitas are probably the result of a thermal overprint related to mesozoic rifting and intrusive activity in the mississippi embayment this thermal overprint has elevated the maturity of strata in most of this area above the level of hydrocarbon preservation although maturities within the dry gas window are retained locally

southern provenance of upper jackfork sandstone southern ouachita mountains cathodoluminescence petrology the source urea of the upper jackfork sandstone of the southern ouachita mountains of arkansas has been located by means of cathodoluminescence cl of quartz in conjunction with standard petrography comparison of frequency distributions of quartz cl colors between the jackfork and approximately coeval sandstones of the black warrior basin detected genetically based affinities which were not apparent by inspection of gross petrology the upper jackfork was derived from the same source area as the parkwood formation of the black warrior basin of alabama the parkwood is known to have come from the south and so the jackfork did also the jackfork represents a deep water lithologic equivalent of the deltaic and nearshore marine parkwood deposited as turbidites in the deeper water of the ouachita trough

diachronous variscan late orogenic collapse as a response to multiple detachments a view from the internides in france to the foreland in the irish sea