fertilizing potential of volcanic ash in ocean surface water the fertilization potential of newly erupted and well preserved ash from the 2000 hekla eruption in iceland was measured for the first time by flow through experiments as previously shown 1 the north atlantic ocean including the subarctic seas surrounding iceland is the largest net sink of the world s oceans for atmospheric co 2 owing to biological drawdown during summer 2 almost complete consumption of phosphate in chlorophyll rich areas of the north atlantic ocean might limit primary production and 3 in the southern pacific ocean and parts of the equatorial pacific ocean iron might limit primary production we found through laboratory experiments that volcanic ash exposed to seawater initially releases large amounts of adsorbed phosphate 1 7 mmol g 21 h 21 iron 37 0 mmol g 21 h 21 silica 49 5 mmol g 21 h 21 and manganese 1 7 mmol g 21 h 21 dissolution of acid aerosols adsorbed to the surface of the ash caused the high initial release of major and trace elements because of the instantaneous dissolution of adsorbed components when newly erupted volcanic ash comes in contact with the ocean surface water macronutrients and bioactive trace metals are released fast enough to become available to support primary production

the posidonia shale lower toarcian of sw germany an oxygen depleted ecosystem controlled by sea level and palaeoclimate abstract the lower toarcian posidonia shale is famous for its excellently preserved fossils and its high amount of organic matter up to 16 both quality of preservation and accumulation of organic matter have been explained by permanent anoxic bottom water conditions high resolution geochemical sedimentological and palaeoecological investigations of various sections of the posidonia shale in sw germany however indicate that oxygen availability was variable and ranged from short oxygenated periods to longer term anoxia the benthic macrofauna consists of nine fossil communities and was used in combination with geochemical data to reconstruct a time averaged oxygen curve anoxic conditions prevailed during the deposition of the toarcian black shales they were however punctuated by various short periods weeks to years with oxygenated bottom water conditions sedimentological e g distinctiveness of microlamination siliciclastic content and geochemical parameters e g organic matter content isotopic signatures 18o and 13c molecular redox parameters pristane phytane ratio arylisoprenoids exhibit a remarkable covariation and seem to be controlled by sea level fluctuations maximum oxygen depletion and an extreme negative shift of 13corg values 34 occurred during the early falciferum zone this is explained by the recycling of 12c enriched carbon derived from remineralization of organic matter on and within the substrate during low sea level stand and a highly elevated redox boundary including photic zone anoxia the subsequent transgression permitted enhanced water exchange with the tethyan ocean and caused improvement of living conditions at the end of the falciferum zone other important factors controlling the depositional environment are the overall palaeogeographic situation and climate the early jurassic is the latest period before break up of pangaea and probably was ruled by a strong meridional atmospheric circulation system with pronounced seasonal changes of prevailing trade and monsoon wind systems an estuarine circulation with a positive water balance and surface water with slightly reduced salinity in the summer alternated with an anti estuarine circulation and a negative water balance in the winter during the summer months a stratified water column with anoxic conditions below the halocline developed 18o data indicate low salinity in the surface water during the monsoon influenced summer high productivity was then located in the photic zone and the corresponding isotopically light 18o signal was fixed in the calcareous nannoplankton during the winter months a saline circulation system brought oxygen to the benthic environment favouring temporary benthic colonization especially during times of relative sea level high stand

quantitative conodont based approaches for correlation of the late devonian kellwasser anoxic events we present the trends of absolute conodont abundance relative genera abundance and conodont morphometrics across the late devonian kellwasser horizons at three northern gondwanan epicontinental seaway locations at three contrasting depositional settings the kellwasser events are characterized by a decrease in conodont abundance high percentage of the conodont genus icriodus and morphological change of the conodont genus palmatolepis these changes can be identified in sections where the events are expressed as interbedded anoxic and oxic deposits as well as in settings characterized by continuous anoxic sediment accumulation hence these changes are interpreted as global and synchronous and can be thus used for event correlation the paradox of these results is that despite quite similar isotopic signals faunal change during the lower kellwasser event was less than during the upper kellwasser event we interpret that this discrepancy is due to an unconformity including topmost frasnian to earliest famennian at several f f sections which removed the record of peak paleoenvironmental change

carbonate periplatform sedimentation by density flows a mechanism for rapid off bank and vertical transport of shallow water fines existing theories of off bank sediment transport cannot account for rapid rates of sedimentation observed in bahama bank and florida shelf periplatform environments analysis of the physical processes operating during winter cold fronts suggests that accelerated off bank transport of shallow water mud may be achieved by sinking off bank flows of sediment charged hyperpycnal super dense platform waters

middle and late jurassic radiolarian palaeoecology versus carbon isotope stratigraphy abstract jurassic radiolarians are sensitive to palaeoclimatic palaeoceanographic changes recorded by the stable carbon isotope curve carbon isotopic variations have been linked to changes in ocean structure productivity and concentrations of greenhouse gases in the atmosphere in the middle upper jurassic terminilletto section of the umbria marche sabina apennines central italy well preserved radiolarians are present in a sequence of cherty limestones interbedded with platform derived carbonates the 13 c curve in the aalenian kimmeridgian interval indicates three main positive 13 c events in the lower bajocian late bathonian lower callovian and middle oxfordian the positive 13 c shifts are correlated to increases in visible chert in the outcrop and may represent periods of increased biological productivity of surface sea water spumellaria nassellaria ratios and the fluctuations of relative abundance of selected genera tend to correlate with 13 c and chert abundance values and seem to be related to episodes of high nutrient mobilisation from the base of the bajocian the radiolarian associations show a slight tendency towards diversification coincident with increasing 13 c values in the upper part of the middle bajocian last appearances prevail over first appearances associated with the peak of the 13 c event this may indicate maximum eutrophic conditions coincident with the late bathonian early callovian positive 13 c shift the radiolarian associations record a different trend with respect to the bajocian event when the 13 c values are increasing to a maximum radiolarian associations tend to be reduced in species diversity followed by a small diversification trend when the 13 c values are decreasing we speculate that during the callovian a more stressful palaeoenvironment due to high level of eutrophication is indicated by the combination of high productivity of biogenic silica and low carbonate input although varying preservational conditions may have influenced the observed trends in the radiolarian associations the good correlation between changes of sedimentation patterns radiolarian assemblages and 13 c positive anomalies open interesting avenues for further investigations concerning the palaeoecology of mesozoic radiolarians

frasnian famennian biotic crisis undervalued tectonic control the prime cause of the late devonian kellwasser crisis culminating in a mass extinction event near the frasnian famennian f f boundary remains conjectural nevertheless rapid sea level fluctuations of uncertain origin during tectono eustatic highstand paired with repeated oceanic anoxia and climatic changes are usually thought at present to be one of the main immediate triggers the cathles hallam model of stress induced changes in plate density accompanying rapid rift formation furnishes an alternative for understanding the enigmatic sudden eustatic variations in the non glacial time late devonian tectonic extension causing rifting and volcanicity appears to be strongly marked in several regions of eurasia particularly in kazakhstan and eastern laurussia all larger devonian continents were more or less tectonically affected a subtle record of this tectonic rearrangement is implied even for distant and apparently quiet carbonate platforms in local extensional block faulting and tilting hydrothermal mineralisation geochemical anomalies and localized blooms of siliceous biota interpreting the late frasnian regressive transgressive pattern in terms of the cathles hallam tectono eustatic model two major rifting events are hypothesized one at about the beginning of the rhenana zone and a second principal pulse in the late linguiformis zone that encompassed the f f transition developing the veimarn milanovsky scenario of the global extensional pulse it is assumed that the key endogenous factors were related to episodic super plume activity the tectonically triggered changes climaxed in thermal and nutrient pulses and induced the stepdown ecosystem destabilization observed in the f f bio crisis minor cometary strike s might have eventually participated in this prolonged multicausal environmental stress mainly due to additional thermal shocks but perhaps effective on a regional scale only

mercury spikes at the devonian carboniferous boundary in the eastern part of the rhenohercynian zone central europe and in the south china block abstract mercury hg chemostratigraphy is an efficient tool for tracing distal volcanism as suggested in many recent studies in our research we focused on hg and other trace element contents in two devonian carboniferous boundary sections from two different and spatially distant areas the lesni lom section czech republic was located in the south eastern part of the laurussia plate and the duli guangxi china section in the south china plate in both studied sections the highest hg hg fexs or hg al values occurred at the devonian carboniferous boundary in lesni lom organic matter remineralization was connected with origin of pyrite which sequestered a part of the hg content the decoupling of hg and toc within the duli section strata and the significant correlation with al and fe may suggest that hg is hosted primarily by clay particles derived from the landmass into the marine realm mercury was also incorporated into pyrites but the poor correlation between hg and ts total sulfur indicates a possible loss of s during oxygenation events in the lesni lom section and partly in the duli section fe and mn redox cycling may have played an important role in sediment hg content both sections were influenced by widespread hydrothermal and volcanic activity indicated by positive eu anomalies msi fe ti zr al2o3 and ti al2o3 values it remains to be clarified whether besides the interplay of local magmatic activity and redox oscillations there may have been some additional influence of the multi phase viluy large igneous province although its younger phase 364 4 1 7 ma slightly precedes the hg anomalies obtained

influence of palaeoweathering on trace metal concentrations and environmental proxies in black shales the mineralogical and chemical compositions of lower carboniferous tournaisian marine black shale from the kowala quarry the holy cross mountains poland were investigated this study focuses on disturbances in palaeoenvironmental proxies caused by palaeoweathering which progressively changed the major and trace element abundances palaeomagnetic investigations reveal that the devonian carboniferous succession was weathered during the permian triassic by the infiltration of oxidizing fluids related to karstification following post variscan exhumation the weathering process led to vermiculitization of chlorite partial dissolution of calcite and replacement of pyrite by hematite and goethite moreover the concentrations of some trace metals including co cu pb mo ni as and u significantly decreased consequently some elemental abundance ratios that are used as environmental proxies including u th ni co and v cr were altered elements that are bound to iron sulphides e g mo appear to be especially prone to mobilization by even a lightly weathered black shale the documented weathering including changes in elemental concentrations can potentially create misinterpretations of the original palaeoenvironmental conditions in addition the palaeoweathering of the studied samples appears to have substantially changed the carbon oxygen nitrogen and molybdenum stable isotope values the nitrogen and molybdenum stable isotope ratios in particular appear to be most sensitive to the effects of weathering and therefore are good indicators of palaeo weathering processes the major cause of these changes is the decay of organic matter and pyrite for the organic carbon stable isotopes ratios the main factor that controlls this process appears to be the preferential degradation of labile organic matter a combination of the total organic carbon toc total sulphur ts content mo concentration and stable isotope compositions seems to be the most useful for identify palaeo weathering our results suggest that reductions in ts and mo in tandem with diminished mo stable isotope values in the absence of obvious changes to the toc content provide the most compelling evidence of palaeo weathering

geochemical evidence for euxinia during the late devonian extinction events in the michigan basin u s a abstract several mass extinction events occurred in the late devonian but the trigger for these events remains elusive in this study geochemical evidence in the late devonian antrim shale michigan basin u s a records episodic euxinia contemporaneous with these extinction events diagnostic changes in iron proxy data and elevated trace metal enrichments correspond to the kellwasser crisis in this study carbon sulfur iron and trace metal geochemistry preserved in the antrim formation validates the establishment and expansion of euxinic conditions associated with the kellwasser crisis and the frasnian famennian boundary the strength of the sequential extraction iron mineral data presented here in concert with trace metal and sulfur isotope proxies provides definitive signatures of euxinia when other data may be more ambiguous in regard to paleoredox conditions during the time of the frasnian famennian boundary extensive sulfide oxidation at the chemocline the result of fe limiting conditions within the basin provides an alternative explanation for the oceanic decline in 34 s so 4 during and following the frasnian famennian event our geochemical evidence indicating the presence of anoxia in the michigan basin is consistent with data from other globally distributed locations euxinia should be considered a key driver for these global extinction events and possibly others such as the hangenberg event in the late devonian

eutrophication by decoupling of the marine biogeochemical cycles of c n and p a mechanism for the late devonian mass extinction the late devonian mass extinction was unusually protracted and ecologically selective with preferential diversity losses among reefbuilding organisms and tropical shallow water faunas in general we have investigated the link between the extinction s unique characteristics and changes in biogeochemical cycling through analyses of the 13 c and c n p atomic ratios of organic matter buried across the kellwasser horizons in western new york state each horizon is characterized by 1 a long term 4 5 excursion in 13 c 3 of which occurs within the horizon and 2 a dramatic increase in the burial ratios of c n p from values of 100 15 1 to an average of 5000 170 1 on the basis of these results we propose that 1 increased efficiency of biolimiting nutrient recycling resulting from cyclic water column stratification and mixing promoted eutrophication during kellwasser deposition in new york and 2 the isotope excursions represent the composite effect of long term global organic c burial and local changes in photosynthetic c isotope fractionation related to nutrient availability this eutrophication model forges a mechanistic link between proposed late devonian climatic cooling and the selective demise of taxa likely to have been narrowly adapted to oligotrophic conditions

silica secreting biota and mass extinctions survival patterns and processes abstract high survival and at least regional blooms of siliceous marine groups with coeval retreat of calcareous organisms is known from the frasnian famennian radiolarians silicisponges and end cretaceous diatoms radiolarians mass extinctions a strictly actualistic approach to the palaeoecology of silica secreting biota is of limited significance especially for silica enriched and oligotrophic palaeozoic epeiric seas and in particular during biotic turnovers adaptation among silica secreting marine plankton has led toward more efficient utilization of shrinking dissolved silica resources within surface waters of cenozoic oceans as shown by both radiolarians and diatoms this biosiliceous signal during the major biotic crises is mostly explained by a large scale increase in volcano hydrothermal activity during major plate boundary re arrangements triggering global ecosystem perturbations the cumulative stimulus favoured siliceous versus calcareous biota growth deposition and preservation because of 1 a higher rate of input of silica and other nutrients promoting eutrophication pulses 2 a punctuated or reversed greenhouse climatic effect episodically coupled with 3 vigorous oceanic circulation due to a variety of volcanogenic upwellings and turnovers siliceous communities adapted to more eutrophic conditions have thrived in the stressed niches on the other hand expanding anoxia and nutrification may lead to a stepwise loss of deep water niches and consequent selective decline of more specialized oligotrophic radiolarians and other pelagic biota by contrast siliceous faunas experienced severe non selective losses during the end permian mass extinction recorded as a chert gap thus the greatest environmental disaster of the phanerozoic was driven by a unique set of killing factors extremely effective for radiolarian productivity e g due to the combination of a drastic volcanic winter with expanding superanoxia

earliest oligocene increase in south atlantic productivity as interpreted from rock magnetics at deep sea drilling project site 522 the magnetic properties of the sediments rock magnetics at dsdp site 522 in the south atlantic exhibit clear differences between the latest eocene and earliest oligocene based on low temperature behavior of saturation remanence and hysteresis loops we attribute the difference to a slightly greater proportion of the finest grained so called superparamagnetic magnetite in the eocene sediments we believe that the lower proportion of very fine grained magnetite in the oligocene sediments is a result of incipient reduction diagenesis caused by increased productivity and hence increased labile organic carbon transport to the sediments due to an early oligocene increase in thermohaline circulation the eocene to oligocene transition at site 522 is also expressed by changes in microfossil assemblages increased carbonate content decreased insoluble residue and decreased foraminiferal shell fragmentation the increase in carbonate is synchronous with and parallels a change in the ratio of two of the rock magnetic parameters a ratio that tracks the decrease in the very fine grained magnetite component also parallel to these is a trend toward heavier 13c values in foraminiferal tests the increase in organic carbon transport to the sediments led to chemical dissolution of the finest grain size fraction of magnetite in the oligocene sediments hence a reduction in the superparamagnetic component and the change in the rock magnetic ratio in this way rock magnetics can be sensitive indicators of environmental changes such as fluctuations in organic carbon transport which may leave little other trace in the sedimentary record

microbial carbonate production in a starved basin the crenistria limestone of the upper visean german kulm facies abstract the crenistria limestone is a set of three autochthonous massive limestone beds occurring with great lithological persistence in the kulm facies cd iii upper visean of the eastern rheinisches schiefergebirge microfacies analysis reveals mainly minipeloidal fabrics and homogeneous micrite uncrushed sediment filled conchs of goniatites represent loci of sheltered preservation of primary carbonate textures calcified radiolarians are abundant forming between 20 and 80 of total rock volume the alleged algal genus rectangulina is common in the crenistria limestone it is reinterpreted to represent the faeces of goniatites for the first time the presence of in situ preserved sponges is reported they can be recognized as delicate networks of microsparitic needles embedded in peloidal fabrics hexactinellids with primary spicule arrangements can be found embedded in homogeneous micrite the carbonate forming the limestone beds was produced microbially during decomposition of soft tissue of the radiolarians and sponges during the cd iii anoxia in the bottom waters of the kulm basin persisted for long periods due to stable density stratification of the water column under humid climatic conditions oxic conditions in the bottom waters during formation of the limestone are indicated by bioturbation the presence of sponges and the high mn contents of the carbonate the latter derived from reduction of mn oxides during microbial carbonate formation

the early toarcian early jurassic and the cenomanian turonian late cretaceous mass extinctions similarities and contrasts abstract the early toarcian eto and cenomanian turonian c t mass extinctions are comparable from a wide range of scales and perspectives from a broad standpoint their similarities include virtually identical extinction intensity at the familial and generic levels widespread basinal facies deposited during sea level highstands an overall greenhouse climate and anoxia as an important causal mechanism the high resolution macroinvertebrate data analyzed here consisting of stratigraphic ranges diversity and abundance point to smaller scale similarities the two events resulted in significant ecological disruption and in both cases the biotic responses were very similar taxa inhabiting the upper water column were unaffected by anoxia and included ammonites and in the eto belemnites in addition epifaunal taxa adapted to low oxygen conditions such as the buchiids posidoniids and inoceramids flourished in the post extinction environment during the survival interval as conditions ameliorated the biota became more diverse and gradually began to resemble pre extinction biotas furthermore the 13c curves predict the end of the survival interval and suggest that the period characterized by carbon isotope excursions represent disrupted environmental conditions this points to the potential application of 13c as a tool for determining the repopulation modes and timing for other mass extinctions

the famennian brachiopod zilimia polonica gurich and its palaeoenvironmental significance abstract the rhynchonellid brachiopod zilimia polonica gurich 1896 is described based on new topotypic material the neotype of the species comes from the lower famennian upper crepida zone the crinoidal marls containing z polonica and an associated brachiopod assemblage are regarded as cohesive debris flow material redeposited from shallow water into an adjacent intrashelf basin the distribution of z polonica suggests that it populated open marine moderately shallow environments within the swell and basin topography developed along the margins of the east european and the eastern cratons

new u pb zircon ages and the duration and division of devonian time newly determined u pb zircon ages of volcanic ashes closely tied to biostratigraphic zones are used to revise the devonian time scale they are 1 417 6 1 0 ma for an ash within the conodont zone of icriodus woschmidti i w hesperius early lochkovian 2 408 3 1 9 ma for an ash of early emsian age correlated with the conodont zones of po dehiscens lower po inversus 3 391 4 1 8 ma for an ash within the po c costatus zone and probably within the upper half of the zone eifelian and 4 381 1 1 3 ma for an ash within the range of the frasnian conodont palmatolepis punctata pa punctata zone to upper pa hassi zone u pb zircon ages for two rhyolites bracketing a palyniferous bed of the pusillites lepidophyta spore zone are dated at 363 8 2 2 ma and 363 4 1 8 ma respectively suggesting an age of363 ma for a level within the late famennian pa g expansa zone these data together with other published zircon ages suggest that the base and top of the devonian lie close to 418 ma and 362 ma respectively thus lengthening the period by20 over current estimates we suggest that the duration of the middle devonian eifelian and givetian is rather brief perhaps no longer than 11 5 myr 394 ma 382 5 ma and that the emsian and famennian are the longest stages in the period with estimated durations of15 5 myr and 14 5 myr respectively 1998 elsevier science b v all rights reserved

global events of the late paleozoic early devonian to middle permian a review abstract the late paleozoic early devonian to middle permian was an interval of profound changes in earth surface systems reflected in dynamic interplay among the biosphere hydrosphere atmosphere and geosphere major events transpired including the colonization of landmasses by vascular plants the assembly of the supercontinent pangea two first order mass extinctions the frasnian famennian and devonian carboniferous boundary events and the most severe icehouse climate mode of the phanerozoic the late paleozoic ice age lpia the goals of the present review are 1 to summarize major global developments in climate oceanography and paleobiology during the late paleozoic 2 to examine the roles of land plant evolution global tectonics and large igneous province magmatism in driving these developments and 3 to serve as an introduction to the 23 contributions to this special issue of palaeogeography palaeoclimatology palaeoecology indicating how they advance our knowledge of various scientific issues related to these developments

microfacies sequence stratigraphy and clay mineralogy of a condensed deep water section around the frasnian famennian boundary steinbruch schmidt germany abstract a multidisciplinary analysis microfacies sequential stratigraphy and clay mineralogy was made on frasnian famennian f f boundary strata of the steinbruch schmidt section in western germany three major microfacies are recognised their succession records a shallowing upward evolution from deep quiet and poorly oxygenated environments below the storm wave base to environments influenced by current activities close to the storm wave base the kellwasser horizons correspond to the deepest microfacies the shallowest microfacies correspond to fine grained calcareous tempestites or turbidites coming from a distant shelf of northwest germany the sequential pattern through the f f boundary shows the succession of seven systems tracts two sequence boundaries are located just above the lower kellwasser horizon and at the f f boundary itself these are underlined by hardgrounds suggesting time gaps the kellwasser horizons correspond to sea level highstands and the overlying beds record a transition from lowstand to transgressive systems tracts illite and kaolinite are the dominant clay minerals associated with mixed layers and traces of chlorite illite abundance is maximal during kellwasser horizons illite and kaolinite were probably inherited from a highly weathered source area although part of the illite is diagenetic kaolinite is the second most abundant clay mineral and is particularly well represented up to 50 between the kellwasser horizons an unusual clay assemblage of illite and mixed layers is associated with a bentonite layer kaolinite increases during times when thin tempestites or turbiditic microbioclastic layers come from a distant shelf during sea level falls the kaolinite percentage reaches its maximum at the top of the lowstand systems tract the high percentage of kaolinite suggests a hot wet climate and could be related to global warming

concentrations of silicified cephalopods within upper frasnian carbonate concretions from the holy cross mountains poland abstract concentrations of silicified juvenile cephalopods from upper frasnian carbonate nodules from the ja wica quarry in the holy cross mountains are described here for the first time using conodonts the age of the investigated cephalopod rich nodules has been determined as the linguiformis conodont zone and may correspond to the upper kellwasser event the concentrations of silicified juvenile ammonoids described here resulted from a combination of biological and physical factors related to environmentally driven mass mortality induced by storms and perhaps additionally by anoxia following mass spawning and post mortem transport with the aid of bottom currents which enabled them to drift to small depressions on the sea floor rapid silification led to excellent preservation of the fossil assemblage

water column anoxia enhanced productivity and concomitant changes in δ13c and δ34s across the frasnian famennian boundary kowala holy cross mountains poland the investigation of the trace element and organic geochemistry of the frasnian famennian boundary section at kowala holy cross mountains poland shows that the lower water column was oxygen deficient during late frasnian and early famennian times the abundance and carbon isotopic composition of diaryl isoprenoids biomarkers indicative for green sulfur bacteria prove that euxinic waters reached into the photic zone at least episodically total organic carbon toc contents show two maxima that are time equivalent to the kellwasser horizons deposited in shallower water settings enhanced toc concentrations are explained by a higher primary productivity presumably as a consequence of an enhanced nutrient supply from the continent the increase in the abundance of hopanes and bituminite suggests that the bacterial contribution to toc increased at the frasnian famennian transition the sulfur isotopic composition of pyritic and organically bound sulfur shows a 27 excursion across the boundary the observation that the 34s values of organic bound sulfur closely resemble that of pyrite sulfur indicates a common sulfur source likely early diagenetic sulfide a change in the 13c of total dissolved inorganic carbon as a consequence of an enhanced burial of 12c enriched organic carbon is indicated by a 3 excursion measured for toc as well as for individual n alkanes and isoprenoids the burial of large amounts of organic carbon is expected to result in a decrease in pco2 and should affect the photosynthetic carbon isotope fractionation ep the fact that we observe no change in ep can be explained by the circumstance that ep was most probably at maximum values as a consequence of high atmospheric and oceanic dissolved co2 concentrations during the devonian

barium sio2 excess and p2o5 as proxies of biological productivity in the middle east during the palaeocene and the latest palaeocene benthic extinction event the distribution of barium and other elements related to biological productivity has been studied in two palaeocene sections from the middle east in the bathyal ben gurion section israel ba ba al2o3 15 concentrations are low in the range 0 04 to 0 3 in the lower palaeocene and very high 1 to 2 throughout most of the upper palaeocene in the neritic gebel aweina section in egypt ba values are low 0 1 throughout the entire palaeocene the ba enrichments at ben gurion and their correlations with increases in p2o5 and opaline silica and local and global 13c maxima indicate that upwelling and high productivity were important in this region during the late palaeocene the absence of ba enrichments in the shallower gebel aweina section probably reflects the strong depth dependence of biobarium deposition in the uppermost palaeocene at the level where the global benthic extinction event is registered ba concentrations in the ben gurion section increase to anomalous 6 which suggests that upwelling and possibly wind strengths intensified during this event the results speak against deep water formation in this region since downwelling and not upwelling is required

a role for organic petrology in integrated studies of mudrocks examples from devonian black shales of the eastern us abstract over the years the study of mudrocks has lagged far behind that of other lithologies a circumstance that is in part due to their fine grained nature and in part due to economic realities yet within petroleum systems mudstones are usually the main source of hydrocarbons and typically are also important as hydrocarbon seals recent work on late devonian mudstones from the eastern us shows that much progress can be made through an integration of outcrop study macro and micropaleontology ichnofossils gamma ray spectroscopy microscopic examination of thin sections in transmitted and reflected light electron microscopy sem bse electron microprobe carbon and sulfur isotopes and organic geochemistry erosion surfaces within this black shale succession have been traced over large distances and provide the foundation for a sequence stratigraphic re interpretation of these rocks evidence of storm wave reworking of the seabed as well as the realization that benthic colonization was much more widespread than previously believed suggest that anoxic conditions in the water column were not a controlling factor in the accumulation of the large quantities of organic matter found in these shales these distal devonian shales accumulated slowly and allowed accumulation of large proportions of organic matter in modern settings of abundant organic matter accumulation the original material is broken down by bacteria within a matter of months into a mass of largely unidentifiable organic particles and extracellular bacterial slime although one can still find identifiable material within this mass slime and amorphous material strongly dominate after burial and maturation this material turns into the various organic macerals that organic petrologists are accustomed to describe one might wonder in this context how much information about the origin of a given mudstone unit can we hope to extract through organic petrology in order to illustrate how organic petrology of mudrocks can contribute to their better understanding late devonian black shales of the eastern us will be examined from a sedimentological perspective combining sedimentologic and geochemical data with basic observations on organic petrology illustrates how the latter can contribute to more realistic scenarios of black shale genesis

the frasnian famennian boundary interval in the south polish moravian shelf basins integrated event stratigraphical approach abstract the late devonian mass extinction event near the frasnian famennian f f boundary has been analysed using conodont biostratigraphy and biofacies sedimentology magnetic susceptibility and geochemistry in reference sections of the south polish moravian shelf holy cross mountains cracow and brno areas high resolution biostratigraphic study revealed difficulties in the precise recognition of this natural stage boundary but confirmed the occurrence of a major third order sequence boundary in the f f transition in an active synsedimentary tectonic setting marked by erosional discontinuities hardgrounds and brecciation or omission surfaces conclusive evidence of an extraterrestrial impact has not been found among earth bound factors the main devastating role in the shelf habitats is ascribed to fluctuating anoxia and or nutrient dynamics in a disturbed greenhouse climatic setting the long term facies changes were determined by a conspicuous break in carbonate production accompanied by replacement of mature stromatoporoid coral reefs by pioneer shelly crinoid banks microbial mounds and localised oolitic bars the key f f passage interval was marked by intermittent but generally accelerated periplatform ooze debris input and severe storm events as well as by probably highly fluctuating oxygenation and biological overproduction best manifested in radiolarian silicisponge and cephalopod acmes eutrophication phenomena at least partly stimulated by various hydrothermal and volcanic processes were one of the major biogeochemical processes during this climax of the late devonian biotic crisis however significant oceanographic perturbations were also linked with the onset of the transgressive hypoxic upper kellwasser event still within the latest frasnian linguiformis zone i e well before the f f conodont collapse implied variations in the redox state of seawater through the kellwasser timespan probably in regionally highly variable temporal scales are in agreement with recent palaeoecological and biogeochemical inferences in particular suggesting recovering oxygenation just prior to the f f boundary in the other laurussian intrashelf basins all the data support a long time multicausal earth bound crisis instead a worldwide cosmic catastrophe

palaeozoic terranes and their lithospheric boundaries within the trans european suture zone tesz a review the trans european suture zone tesz is a broad and complex zone of terrane accretion separating ancient lithosphere of the baltic shield and east european craton eec from the younger lithosphere of western and southern europe there is debate about the number of terranes involved and their origins the most significant terrane boundaries originally oceanic sutures are poorly exposed and are defined using faunal provinciality prominent geophysical lineaments may represent sub terrane boundaries within composite terranes the avalonia composite terrane was amalgamated to baltica in latest ician time the provenance of the malopolska and moravo silesian terranes whose neoproterozoic basement is suspect with respect to baltica but with which they nonetheless share faunal affinities is still debated the extent of the variscide rhenohercynian zone defines the southern limit of the early palaeozoic accreted terranes terranes within the bohemian massif exhibit hp metamorphism recording subduction driven collision prior to incorporation in the tesz collage itself associated with a hp event in romania the saxothuringian zone and rheic suture are directly juxtaposed with the eec and the crustal structure of the tesz has been much modified by post palaeozoic tectonism deep seismic reflection data where available show that the oceanic sutures are frequently associated with inclined reflectivity zones irz in the lithospheric mantle here inferred to mark relict subduction zones interpreting the age of subduction is complicated by offset of originally coplanar mantle and crustal segments of the irz resulting from early orogenic lithospheric delamination at the moho interface and or post orogenic reordering processes the mantle irz appear to indicate a n directed polarity for early palaeozoic subduction apparently incompatible with the geological evidence which indicates subduction of the tornquist sea beneath avalonia and a large amount of underthrusting of avalonia by baltica possible explanations for these apparently incompatible observations are evaluated

chitinozoan bio event in the frasnian famennian boundary beds at la serre montagne noire southern france abstract chitinozoans and other palynomorphs have been investigated in frasnian famennian boundary beds from trench c at la serre montagne noire southern france this section is located some 30 km from the coumiac quarry containing the global stratotype section and point gssp for the base of the famennian at la serre the frasnian famennian f f boundary falls within interbedded anoxic dark shales and limestones this lithology proves to be more suitable for palynological investigations than the reddish nodular limestones of the f f stratotype in the coumiac section which are virtually devoid of organic matter at la serre the uppermost meter of frasnian deposits corresponding to the upper kellwasser event level contains only a few chitinozoans but other palynomorphs especially tasmanaceans maranhites proliferate in some horizons conversely the most basal famennian bed yields an exceptional number of chitinozoans up to 19 000 specimens per gram of rock a few tracheids but virtually no tasmanaceans the absence or the extremely low numbers of miospores and acritarchs in these f f boundary beds seems related to the distal position of the deposition site we have compared the fluctuation of the chitinozoan abundance both with the abundance of the other palynomorphs and with that of the conodonts present in the same samples these data collated with sedimentological and palaeoecological information document the relationships between the anomalous abundance of the chitinozoans and the latest frasnian earliest famennian mass extinction it is concluded that the exceptional chitinozoan concentration in the most basal famennian bed at la serre is not related to a sorting process generated by turbidity currents or by a temporary increase in the hydrodynamic energy at the water sediment interface it corresponds to the conjunction of a high production of chitinozoans a very low rate of destruction of the vesicles and minimal dilution of the deposit by terrestrial mineral input the environmental factors leading to such an exceptionally high record of chitinozoans are discussed with a particular attention to consequences of the late frasnian mass extinction

event stratigraphic markers within the kellwasser crisis near the frasnian famennian boundary upper devonian in germany abstract short time intervals of anomalous conditions often referred to as global events yield excellent tools for detailed stratigraphic correlations in addition to pronounced effects minor features may be applied for fine scale comparisons of rock sequences these include alternations within a given portion of rock or distinct layers at exactly the same position such marker horizons are often traceable over long distances recognition of these specific markers allows for a more detailed search for possible causes of anomalous events

ichnofabrics and chemostratigraphy argue against persistent anoxia during the upper kellwasser event in new york state abstract organic rich strata coeval with bioevents of varying magnitudes characterize global devonian sedimentary successions the upper kellwasser ukw black shale depositional event is coincident with the largest pulse of diversity loss within the marine late devonian mass extinction and has been shown to be an ecologically critical turnover for shallow water species marine anoxia euxinia is widely thought to be an important and ubiquitous driver of this biotic crisis though the duration intensity and global extent of these environmental conditions during the ukw event are not well constrained we characterized redox conditions during deposition of the ukw in the northern appalachian basin to constrain local variability and relative magnitude of dissolved oxygen fluctuations we used a combination of proxies relating to the bottom waters water column and photic zone to compile an integrated picture of basinal oxygen dynamics our multi faceted approach combines trace fossil evidence for faunal activity at the sediment water interface with inorganic and organic geochemical proxies for redox conditions within the water column minor biological disruptions to laminated sedimentary fabric indicate at least intermittent oxygenation of the bottom waters during deposition of the ukw albeit in a low dissolved oxygen seafloor setting trace metal proxies mo mn u and v and fe mineral speciation provide compelling evidence for a water column experiencing intermittent rather than persistent anoxic euxinic conditions lipid biomarkers reinforce the interpretation of variable dissolved oxygen conditions with very low concentrations of chlorobi carotenoid biomarkers pointing to seasonal rare episodes of photic zone euxinia this integrated dataset provides evidence for local redox variability in ukw deposition and supports the likelihood that marine anoxia and euxinia were not globally persistent at the frasnian famennian boundary

anoxia pre dates frasnian famennian boundary mass extinction horizon in the great basin usa abstract major and trace metal results from three great basin stratigraphic sections with strong conodont biostratigraphy identify a distinct anoxic interval that precedes but ends approximately 100 kyr before the frasnian famennian f f mid late devonian boundary mass extinction horizon this horizon corresponds to the final and most severe step of a more protracted extinction period these results are inconsistent with data reported by others from the upper kellwasser horizon in europe which show anoxia persisting up to the f f boundary in most sections conditions returned to fully oxygenated prior to the f f boundary in the study area these data indicate that the worst part of the f f extinction was not related directly to oceanic anoxia in this region and potentially globally

new aspects on the formation of hydrocarbon source rocks episodic volcanism favors as shown by examples from europe the usa and brazil the formation of organic rich sediments hydrocarbon source rocks the examples examined from europe comprise the lower carboniferous oil shale group scotland upper carboniferous coal measures western germany upper jurassic kimmeridge shale north sea area lower cretaceous blattertonstein northwest germany and eocene messel oil shale rheingraben examples from the usa are devonian mississippian gas shales permian phosphoria shale middle cretaceous mowry shale eocene green river shale and miocene monterey shale examples from brazil are permian irati oil shale and oligocene paraiba valley oil shale volcanism is reflected during sedimentation 1 by exhalation of so2 and or co2 2 volcanic ashfalls 3 by generation of anoxia and preservation of organic matter and 4 by halmyrolytic alteration of volcanic ashes into highly surface active clay minerals montmorillonite

the drowning of a carbonate platform an example from the devonian carboniferous of the southwestern holy cross mountains poland the broad middle devonian carbonate platform of the holy cross mountains was fragmented during the frasnian and afterwards submerged as isolated blocks and transformed into a topographic depression the section exposed in the ostrowka quarry illustrates a well documented drowning of the last small fragment seamount of this carbonate platform which submerged during late devonian and early carboniferous times the recognized facies succession reflects a progressive stepwise lowering of the sediment surface through time from a peritidal lagoonal environment to a deep water anoxic basin the frasnian shallow water carbonate platform is represented by lagoonal facies with peritidal sediments small scale deepening upward cycles punctuated with emersion surfaces are a feature of this stage they resulted from a combination and continuous balance between carbonate production subsidence and low order eustatic sea level fluctuations the carbonate platform aggraded at rates around 100 125 m ma the shallow water peritidal carbonates are separated from the post platform deposits by an unconformity surface developed during subaerial exposure the flooding of the faulted block of galezice in the pre late marginifera time and the subsequent initial drowning resulted primarily from a rapid sea level rise small dimension of the seamount and its cemented upper surface were the most important factors that facilitated the sediment removal and thus suppressed the sediment accumulation a condensed section was deposited on the top of the seamount its stratigraphic succession and rare cephalopod storm beds account for a model of redistribution of sediment over the swell disintegrated by small scale faulting during drowning the seamount traversed down through the photic zone at an average rate not higher than 20 25 m ma transformation of the swell into a basin accelerated in the late tournaisian anchoralis zone it is manifested by an increase of deposition rate and by a lithology of alternating limestones and clays with participation of fine grained calciturbidites the associated tephra deposits and syndepositional ferruginous hydrothermal mineralization were the result of extensional tectonics on the facies evolution the drowning was completed in the visean with deposition of black siliceous shales in the starved basin the death of the devonian carbonate platform in the galezice area illustrates well the famed paradox of drowned platforms as the subsidence rate was much slower during the drowning than during the phase of the platform aggradation

variations in ce anomalies of conodonts through the frasnian famennian boundary of poland kowala holy cross mountains implications for the redox state of seawater and biodiversity abstract rare earth element ree concentrations on upper devonian conodonts distinguished by very low color alteration index were measured by inductively coupled plasma mass spectrometry from a stratigraphic section across the frasnian famennian f f boundary in the holy cross mountains poland the present data show a hat shaped pattern of the ree spectra similarly to other devonian conodont spectra already documented however our sample composition suggests little to moderate alteration of the original oceanic pattern through the adsorption mechanism in a context of weak or early diagenesis all along the section the magnitude of the ce anomaly is always negative and there is an inverse correlation between the ce anomaly and the la sm sn ratio this has been interpreted as an la enrichment due to a terrestrial input a mathematical procedure was used in order to restore the original ce anomalies that would reflect the seawater environment not contaminated by terrestrial inputs no noticeable change is observed in the frasnian with homogeneous values of ce model but a sharp increase is initiated just below the f f boundary with maximum values in the lowermost famennian the measured la sm sn ratios co vary with the ce model in agreement with the hypothesis of a terrigenous input finally the inverse correlation between the values of ce model and the relative abundance of palmatolepis during the famennian constitutes the first evidence known of a redox control on the presence of a conodont genus that is an indicator of deep water environment

mass extinctions and sea level changes abstract review of sea level changes during the big five mass extinctions and several lesser extinction events reveals that the majority coincide with large eustatic inflexions the degree of certainty with which these eustatic oscillations are known varies considerably thus the late ordovician and end cretaceous extinctions are associated with unequivocal major regressions demonstrated from numerous widespread regions in contrast the multiple high frequency sea level changes reported for the frasnian famennian crisis based on the supposed depth preferences of conodont taxa have little support from sequence stratigraphic analyses which reveals the interval to be one of highstand the end permian mass extinction has long been related to a severe first order lowstand of sea level newell n d 1967 revolutions in the history of life geol soc am spec pap 89 63 91 based primarily on the widespread absence of latest permian ammonoid markers but field evidence reveals that the interval coincides with a major transgression newell s hypothesis that marine extinctions are related to shelf habitat loss during severe regression remains tenable for the end guadalupian and end triassic extinction events but not for other crises rapid high amplitude regressive transgressive couplets are the most frequently observed eustatic changes at times of mass extinction with the majority of extinctions occurring during the transgressive pulse when anoxic bottom waters often became extensive the ultimate cause of the sea level changes is generally unclear a glacioeustatic driving mechanism can only be convincingly demonstrated for the end ordovician and end devonian events at other times it is speculated that they may relate to the widespread regional doming and subsequent collapse caused by the impingement of superplumes and ultimate eruption on the base of the lithosphere

palaeokarst and its implication for the extinction event at the frasnian famennian boundary guilin south china a prominent palaeokarst within cyclic peritidal strata reported here at the frasnian famennian boundary in guilin southern china displays karren scalloped surfaces dissolution pits and pipes the last contain residual soil terra rossa and are then filled with marine sediment of the overlying strata the features of the palaeokarst depth of pipes and amount of missing strata indicate a significant and long lasting c 50 ka fall of sea level at the end of the frasnian the coincidence of the significant sea level fall with the first stage of the frasnian famennian mass extinction which mostly affected shallow marine and reef dwelling fauna and of the subsequent rapid sea level rise with the second stage of the extinction which mostly affected deeper water organisms reinforces the importance of sea level change in this mass extinction

does large igneous province volcanism always perturb the mercury cycle comparing the records of oceanic anoxic event 2 and the end cretaceous to other mesozoic events mercury hg is increasingly being used as a sedimentary tracer of large igneous province lip volcanism and supports hypotheses of a coincidence between the formation of several lips and episodes of mass extinction and major environmental perturbation however numerous important questions remain to be answered before hg can be claimed as an unequivocal fingerprint of lip volcanism as well as an understanding of why some sedimentary records document clear hg enrichment signals whilst others do not of particular importance is evaluating the impact of different volcanic styles on the global mercury cycle as well as the role played by depositional processes in recording global hg cycle perturbations here new mercury records of cretaceous oceanic anoxic event 2 oae 2 94 ma and the latest cretaceous 67 66 0 ma are presented oae 2 is associated with the emplacement of multiple predominantly submarine lips the latest cretaceous with subaerial volcanism of the deccan traps both of these connections are strongly supported by previously published trends towards unradiogenic osmium os isotope values in globally distributed sedimentary records hg data from both events show considerable variation between different locations attributed to the effectiveness of different sediment types in registering the hg signal with lithologically homogeneous records documenting more clear hg enrichments than sections with major changes in lithology such as limestones to claystones or organic rich shales crucially there is no geographically consistent signal of sedimentary hg enrichment in stratigraphic records of either oae 2 or the latest cretaceous that matches os isotope evidence for lip emplacement indicating that volcanism did not cause a global hg perturbation throughout the entire eruptive history of the lips formed at those times it is suggested that the discrepancy between os isotope and hg trends in records of oae 2 is caused by the limited dispersal range of hg emitted from submarine volcanoes compared to the global scale distribution of os a similar lack of correlation between these two proxies in uppermost cretaceous strata indicates that although subaerial volcanism can perturb the global hg cycle not all subaerial eruptions will do so these results highlight the variable impact of different volcanogenic processes on the efficiency of hg dispersal across the globe factors that could influence the impact of lip eruptions on the global mercury cycle include submarine versus subaerial volcanism volcanic intensity or explosivity and the potential contribution of thermogenic mercury from reactions between ascending magma and surrounding organic rich sediments

mercury enrichments and the frasnian famennian biotic crisis a volcanic trigger proved the frasnian famennian f f global event one of the five largest biotic crises of the phanerozoic has been inconclusively linked to rapid climatic perturbations promoted in turn by volcanic cataclysm especially in the viluy large igneous province lip of siberia conversely the triggers of four other phanerozoic mass extinction intervals have decisively been linked to lips owing to documented mercury anomalies shown as the diagnostic proxy here we report multiple hg enrichments in the two step late frasnian kellwasser crisis interval from paleogeographically distant successions in morocco germany and northern russia the distinguishing signal 1 ppm hg in the domain of closing rheic ocean was identified in different lithologies immediately below the f f boundary and approximately correlated with the onset of the main extinction pulse this key hg anomaly comparable only with an extreme spike known from the end ordovician extinction was not controlled by increased bioproductivity in an anoxic setting we suggest therefore that the global chemostratigraphic pattern near the f f boundary records a greatly increased worldwide hg input controlled by the center hill eruptive pulse of the eovariscan volcanic acme but likely not manifested exclusively by lip s consequently all five major biotic crises of the phanerozoic have now been more reliably linked to volcanic cataclysms

the late devonian frasnian famennian event in south china patterns and causes of extinctions sea level changes and isotope variations abstract the frasnian famennian f f event may be recognized in various facies areas in south china in the pelagic cherty basin facies both lower and upper kellwasser events can seemingly be recognized in the deeper water carbonate facies the f f event level is well controlled in light of conodont biostratigraphy in the shallow water carbonate and mixed carbonate shale facies the f f boundary may be defined by clear taxonomic distinction in benthic fossils articulate brachiopods and corals as well as evidence from minor pelagic fossils post extinction recovery rate of benthic organisms differs in different facies settings and different taxonomic groups in open shallow water platform to inter platform depression areas brachiopods seem to recover quickly probably in the middle pa triangularis zone benthic ostracodes seem to recover at a later stage recovery of rugose corals did not happen until the uppermost famennian three steps of the f f mass extinction are postulated 1 extinction of diverse brachiopods including most atrypids 2 extinction of pelagic conodonts 3 extinction of both benthic faunas very abundant and diverse rugose corals and ostracodes and pelagic conodonts evidence of an end frasnian regression in south china is clear particularly in shallow water settings however in deeper water settings the picture is complicated with evidence of both sea level rise and fall in the latest frasnian it may be assumed from overall data so far known that crustal evolution itself and associated multiple volcanic hydrothermal activities may have mainly caused frequent and rapid climatically warming cooling alterations and sea level changes as well as marine ecologic collapse eutrophication microbial blooming seawater acidification and anoxia which may explain the f f extinction pattern in south china

geochemistry of recent toc rich sediments from the gulf of california and the black sea major and minor elements incl ag as ba cd co cr cu mn mo ni pb sr v zn have been determined in recent sediments from the gulf of california upwelling area and black sea sapropels in order to reinterpret their chemical composition in view of reliable seawater and plankton data the chemistry of the gulf of california sediments reflects regeneration processes which occur in the water column i e only a small fraction 10 of elements like cd which in seawater are coupled to the labile nutrients c n p is buried in the sedimentary column in contrast elements like the more resistant nutrients si undergo a deeper regeneration cycle ba several trace metals which are present in comparatively higher concentrations in seawater as mo u v and at the same time are reactive under reducing conditions and or are able to form stable sulfides are fixed in the sediments during early diagenesis the early diagenetic behavior of ba is closely related to bacterial sulfate reduction the formation of barite concretions is discussed anoxic conditions in the water column act as ideal traps for a number of redox sensitive and or stable sulfide forming elements a simple trace metal balance calculation shows that the chemical composition of black sea sapropels is controlled by fluvial and mediterranean seawater element input and the accumulation rate of terrigenous detrital material

a revised classification of limestones abstract the most widely used classifications of limestones are now thirty years old and our appreciation of the diagenetic effects on limestone textures is now much greater a revision of the classifications of dunham 1962 and embry and klovan 1971 is offered and new diagenetic categories are proposed the confusing term lime mudstone is replaced by calcimudstone two categories of diagenetic textures are recognized non obliterative and obliterative the former contains limestones which are almost wholly composed of diagenetic cement cementstones and those whose fabric is the result of intergranular pressure solution condensed and fitted grainstones obliterative categories include limestones and dolomites whose original fabric has been destroyed sub categories include sparstones or dolosparstones crystals 10 m in size and microsparstones dolomicrosparstones crystals 4 10 m in size and dolomicrostones crystals m in size many diagenetic processes can produce fabrics which mimic depositional ones and these are reviewed

magnetostratigraphy susceptibility of the frasnian famennian boundary magnetosusceptibility event and cyclostratigraphy msec is used to establish a non polarity based magnetostratigraphy susceptibility mss between the stratotype region for the frasnian famennian f f boundary sequence in the montagne noire of southern france the eastern rheinisches schiefergebirge of germany belgium the eastern anti atlas of morocco and the arbuckle mountains of southern oklahoma usa despite differences of depositional environment the mss is remarkably consistent and can be described in the context of a hierarchy of magnetozones that allow the extension of correlation away from the montagne noire reference section the nature of the controls on the influx of iron into the marine system produces a natural hierarchy of at least seven orders or magnetozones designated msz1 msz2 msz3 msz4 msz5 msz6 and msz7 these are characterized in terms of the magnitude of their duration the mss reference section of choice for the f f boundary is the well known trench c at la serre lsc in the northeastern montagne noire of southern france the f f boundary is located at the lower boundary of magnetozone la serre i 3b at la serre as well as in all other sections studied msz4 and msz5 magnetozones are used to establish intra and inter regional correlation between the reference sequence and the other regions the base of the upper kellwasser event is as variable within the mss zonation as it is within the biostratigraphic zonation as is the position of the lower kellwasser event

tectonically controlled sedimentation impact on sediment supply and basin evolution of the kashafrud formation middle jurassic kopeh dagh basin northeast iran the kashafrud formation was deposited in the extensional kopeh dagh basin during the late bajocian to bathonian middle jurassic and is potentially the most important siliciclastic unit from ne iran for petroleum geology this extensional setting allowed the accumulation of about 1 700 m of siliciclastic sediments during a limited period of time upper bajocian bathonian here we present a detailed facies analysis combined with magnetic susceptibility ms results focusing on the exceptional record of the pol e gazi section in the southeastern part of the basin ms is classically interpreted as related to the amount of detrital input the amount of these detrital inputs and then the ms being classically influenced by sea level changes climate changes and tectonic activity facies analysis reveals that the studied rocks were deposited in shallow marine slope to pro delta settings a major transgressive regressive cycle is recorded in this formation including fluvial dominated delta to turbiditic pro delta settings transgressive phase followed by siliciclastic to mixed siliciclastic and carbonate shoreface rocks regressive phase during the transgressive phase hyperpycnal currents were feeding the basin these hyperpycnal currents are interpreted as related to important tectonic variations in relation to significant uplift of the hinterland during opening of the basin this tectonic activity was responsible for stronger erosion providing a higher amount of siliciclastic input into the basin leading to a high ms signal during the regressive phase the tectonic activity strongly decreased furthermore the depositional setting changed to a wave to tide dominated mixed carbonate siliciclastic setting because of the absence of strong tectonic variations bulk ms was controlled by other factors such as sea level and climatic changes fluctuations in carbonate production possibly related to sea level variations influenced the ms of the siliciclastic carbonate cycles carbonate intervals are characterized by a strong decrease of ms values indicates a gradual reduction of detrital influx therefore the intensity of tectonic movement is thought to be the dominant factor in controlling sediment supply changes in accommodation space and modes of deposition throughout the middle jurassic sedimentary succession in the pol e gazi section and possibly in the kopeh dagh basin in general

variscan tectonics in the holy cross mountains poland and the role of structural inheritance during alpine tectonics abstract the present study was carried out in the holy cross mountains hcm of south central poland and includes computation of palaeostresses following angelier s method and field structural analysis the palaeozoic basement of the hcm comprises two tectonic units separated by the major wnw ese striking holy cross fault hcf fold analysis indicates a n s to nne ssw direction of variscan shortening micro structures and fold analysis from upper devonian rocks further reveal 1 a brittle tectonic event due to a nw se compression preceding folding that could be related to pre late carboniferous tectonics due to block transport within the tornquist teisseyre zone ttz and 2 polyphase variscan folding comprising a an early stage of n s shortening marked by north verging ramps b a main folding event and axial cleavage formation involving n s to nne ssw shortening and c a late stage of shortening deforming older folds and cleavage a mainly extensional tectonic regime dominated from the permian until the cretaceous during which time the hcf was reactivated as a normal fault large nw se faults bordering the mid polish trough mpt developed subsequent tectonic inversion of the mpt resulted in basin uplift mid polish swell mps palaeostress computations from mesozoic strata suggest a ne sw direction for the main maastrichtian paleocene shortening phase in addition to two minor brittle events resulting from n s and e w compression analysis of local folds in the mesozoic cover indicates a causal relationship with the maastrichtian paleocene reactivation of older faults in particular en echelon folds in the radomsko elevation suggest a sinistral reactivation of the palaeozoic hcf folds in the southwestern part of the hcm argue for reactivation in the reverse mode of a nw se trending fault bordering the mps that originated in the mesozoic in palaeozoic strata post variscan brittle deformation and micro fault reactivation are attributed to the tectonic events of maastrichtian paleocene age reactivation of n s fractures is demonstrated in the rzepka quarry where fractures in devonian dolomites are filled by calcite probably formed during a late variscan event and by younger late permian early triassic sediments they were subsequently reactivated as dextral strike slip faults during the ne sw maastrichtian paleocene compression

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

the role of sea level change and marine anoxia in the frasnian famennian late devonian mass extinction johnson et al johnson j g klapper g sandberg c a 1985 devonian eustatic fluctuations in euramerica geological society of america bulletin 96 567 587 proposed one of the first explicit links between marine anoxia transgression and mass extinction for the frasnian famennian f f late devonian mass extinction this cause and effect nexus has been accepted by many but others prefer sea level fall and cooling as an extinction mechanism new facies analysis of sections in the usa and europe france germany poland and comparison with sections known from the literature in canada australia and china reveal several high frequency relative sea level changes in the late frasnian to earliest famennian extinction interval a clear signal of major transgression is seen within the early rhenana zone e g drowning of the carbonate platform in the western united states this is the base of transgressive regressive cycle iid of the johnson et al johnson j g klapper g sandberg c a 1985 devonian eustatic fluctuations in euramerica geological society of america bulletin 96 567 587 eustatic curve this was curtailed by regression and sequence boundary generation within the early linguiformis zone recorded by hardground and karstification surfaces in sections from canada to australia this major eustatic fall probably terminated platform carbonate deposition over wide areas especially in western north america the subsequent transgression in the later linguiformis zone recorded by the widespread development of organic rich shale facies is also significant because it is associated with the expansion of anoxic deposition known as the upper kellwasser event johnson et al s johnson j g klapper g sandberg c a 1985 devonian eustatic fluctuations in euramerica geological society of america bulletin 96 567 587 original transgression anoxia extinction link is thus supported although some extinction losses of platform carbonate biota during the preceeding regression cannot be ruled out conodont faunas suffered major losses during the upper kellwasser event with deep water taxa notably affected this renders unreliable any eustatic analyses utilising changes in conodont biofacies claims for a latest frasnian regression are not supported and probably reflect poor biostratigraphic dating of the early linguiformis zone sequence boundary

geochemical analysis and paleoecological implications of phosphatic microspherules otoliths from frasnian famennian boundary strata in the great basin usa phosphatic microspherules 1 mm diameter recovered from the upper devonian uppermost frasnian guilmette limestone in eastern nevada are interpreted here to be fish otoliths and thus provide insight into ocean water chemistry just prior to the frasnian famennian mass extinction boundary analysis by scanning electron microscope sem and electron microprobe indicates that they are apatite francolite and consist of radially aligned concentrically banded crystals around a central nucleus this type of microspherule previously interpreted to be conodont pearls has compositions more similar to fish teeth derived from the same unit than to conodonts microspherules and fish teeth have consistently lower concentrations in wt of p2o5 31 88 36 32 f 3 05 5 12 sro 0 15 0 34 and analysis totals indicating higher concentrations of oh and or co3 90 66 96 09 and higher cao 51 67 55 15 so2 0 50 0 90 mgo 0 09 0 15 and fe2o3 0 11 0 21 than the associated conodonts p2o5 37 32 40 01 f 4 99 6 89 sro 0 32 1 79 totals 96 07 100 55 cao 52 32 53 06 so2 0 05 0 21 mgo 0 01 0 05 fe2o3 0 02 0 11 these differences in composition are consistent from core to rim in all microfossils analyzed and reflect primary biogenic compositions rather than diagenetic or metamorphic signatures we interpret the apatite microspherules to be genetically related to the fish teeth rather than to the conodonts based on the geochemical analysis the microspherules are morphologically similar to modern teleost fish otoliths the fish teeth found associated with the microspherules are from acanthodian or actinopterygian fish which possessed otoliths in the devonian and are the distant ancestors to modern teleost fish modern fish otoliths normally have a calcium carbonate composition but their trace element composition is highly sensitive to ambient water temperature and chemistry we speculate that the stratigraphically restricted range and phosphatic composition of the devonian otoliths reflects secretion by fish under conditions of excess dissolved reactive phosphorus in the water column that was most likely associated with upwelling and cooler water conditions on the shelf during maximum transgression

molecular and petrographic indicators of redox conditions and bacterial communities after the f f mass extinction kowala holy cross mountains poland abstract pyrite framboid diameter analysis and organic geochemistry of the triangularis crepida boundary section at kowala holy cross mountains poland imply suboxic to oxic and sporadically euxinic bottom waters during the lower famennian in addition morphological web like structures typical for microbial mats as well as the recognition of 2 methylhopanes and monomethyl alkane cyanobacteria biomarkers is evidenced of microbial activity after the global frasnian famennian f f extinction event the presence of cyanobacterial mats also suggests suboxic to oxic environments and at the same time photic bottom water conditions however isorenieratane and its derivatives were detected in almost all samples the presence of this well known biomarker of green sulfur bacteria implies that euxinic conditions were present in the upper part of the water column at least intermittently or that temporal euxinia occurred in the water column presence of euxinic conditions is confirmed by the occurrence of small sized pyrite framboids which were particularly dominant in the lower part of the section the shift towards low 13 c values in both micritic limestones and in sedimentary organic matter seen at the beginning of the period of diminished photic zone might reflect an influx of newly respired co 2 to surface waters caused by enhanced respiration at depth after the f f transition in the checiny zbrza basin

diagenetic origin of quartz silt in mudstones and implications for silica cycling mudstone the most abundant sedimentary rock type1 composed primarily of clay or silt sized particles contains most of the quartz found in sedimentary rocks2 these quartz grains which are chemically and mechanically resistant and therefore preserve their characteristics well have long been considered to be derived from the continental crust1 here we analyse quartz silt from black shales in the eastern usa dating back to the late devonian period about 370 million years ago using backscattered electron and cathodoluminescence imaging and measure oxygen isotopes with an ion probe our results indicate that up to 100 of the quartz silt in our samples does not originate from the continental crust instead it appears to have precipitated early in diagenesis in algal cysts and other pore spaces3 with silica derived from the dissolution of opaline skeletons of planktonic organisms such as radiolaria and diatoms transformation of early diatoms into in situ quartz silt might explain the time gap between the earliest fossil occurrences of diatoms about 120 myr ago4 and molecular evidence for a much earlier appearance between 266 or even 500 myr ago5 6 moreover if many other mudstone successions show similarly high proportions of in situ precipitated rather than detrital quartz silt the sedimentary record in mudstones may have been misinterpreted in the past with consequences for our estimates of palaeoproductivity as well as our perceptions of the dynamics and magnitude of global biogeochemical cycling of silica

suboxic trace metal geochemistry in the eastern tropical north pacific abstract we analyzed al ti fe mn cu ba cd u mo v and re in water column settling particulate and sediment 0 to 22 cm samples from the intense oxygen minimum zone omz of the eastern tropical north pacific near mazatlan mexico the goal was to determine how the geochemistry of these elements was influenced by suboxic water column conditions and whether the sediments have a unique suboxic geochemical signature the water column was characterized by a mn maximum reaching 8 nmol kg 1 at 400 m concentrations of cu ba cd mo re u and v were unaffected by the low o2 conditions and were comparable to those of the open ocean sinking particles were composed of lithogenic particles of detrital origin and nonlithogenic particles of biogenic origin al ti and fe were mostly at least 79 lithogenic about 75 of the mn was nonlithogenic significant amounts at least 58 of cu ba cd and mo were nonlithogenic sediment geochemistry varied across the continental shelf and slope cadmium u and re have prominent maxima centered at 310 m with 12 3 ppm 10 9 ppm and 68 3 ppb respectively at the core top high values of mo averaging 6 8 ppm and v averaging 90 ppm are seen in omz surface sediment additional down core enrichment occurs for all redox sensitive elements in the top 10 cm for u mo v and re surface sediments are a poor indicator of metal enrichment comparison of the nonlithogenic composition of sediments with sinking particles suggests that direct input of plankton material enriched in metals makes a significant contribution to the total composition especially for cd u and mo we evaluated re mo and cd u ratios as tracers for redox environments rhenium and mo concentrations and re mo ratios do not lead to consistent conclusions concurrent enrichments of re and mo are an indicator of an anoxic depositional environment in contrast high re mo ratios are an indicator of suboxic conditions cadmium is enriched in surface sediments while u has considerable down core enrichment the concentrations of cd and u and the cd u ratio do not follow patterns predicted from thermodynamics though the water column is suboxic these four redox sensitive elements indicate that the sediments are anoxic the implication for paleostudies is that a trace metal sediment signature that indicates anoxic conditions is not necessarily attributable to an anoxic water column

orbitally induced limestone marlstone rhythms in the albian cenomanian cismon section venetian region northern italy sedimentology calcareous and siliceous plankton distribution elemental and isotope geochemistry abstract a multidisciplinary study of the upper albian cenomanian portion of the cismon section venetian region northern italy was undertaken in order to characterize the cyclic alternations of carbonate rich and carbonate poor layers and to investigate their possible origin and cyclic patterns limestone semicouplets are characterized by abundant radiolarians and micarbs micron sized calcitic fragments common planktonic foraminifera strong bioturbation good oxygenation as expressed by the mn and v v ni parameters high si al ratio low k al in the absence of pyrite and organic matter the marlstone semicouplets are on the contrary frequently laminated rich in pyrite and organic matter with common fish remains in the absence of radiolarians the mn and v v ni parameters indicate that the marlstone deposition occurred in dysoxic to anoxic conditions which allowed the preservation of organic matter the low si al ratio and high k al ratio the latter related to abundant feldspars indicate that marlstones received a substantial contribution from a terrigenous source the abundance of biogenic silica suggests that during limestone deposition surface waters were rather fertile due to an efficient recycling of nutrients from deeper waters the enhanced fertility was coupled with an efficient current system at the welloxygenated sea floor which prevented the organic matter from accumulating during marlstone deposition surface waters were less fertile than in the limestone semicouplets but still within the mesotrophic spectrum as indicated by the presence of fertility index species among calcareous nannofossils whereas the bottom waters were oxygen depleted to accommodate fertility at the surface with stagnation at the bottom the scenario implies an enhanced stratification caused by an increase in freshwater runoff monitored by 18o depleted values in the meantime the water discharge supplied the nutrients to the surface waters necessary for the calcareous nannofossils to proliferate the cyclic organization of limestone marlstone couplets as revealed by power spectral analysis seems to represent climatic cycles the alternating conditions are 1 efficient mixing highly fertile surface and near surface waters and a well oxygenated seafloor to 2 enhanced water runoff or decreased evaporation or both and oxygen depleted bottom waters we suggest that this deterministic sedimentary cyclicity could be explained by periodic orbital climatic cycles in tune with the milankovitch cycles within this scenario the latest cenomanian bonarelli level is an exceptional event marked by a large positive 13c spike it is characterized by high to very high fertility conditions in surface waters caused by increased upwelling that engendered high nutrient levels in near surface waters the enhanced production of organic matter was in excess for the oxygen available at the bottom floor thus allowing the organic matter to accumulate in the sediments

the baltica gondwana suture in central europe evidence from k ar ages of detrital muscovites and biogeographical data

the frasnian famennian boundary in central and eastern united states abstract the frasnian famennian f f boundary in the northern appalachian basin is found in the hanover shale and equivalent strata where it is locally associated with a black shale interval equivalent to the upper kellwasser interval in europe the boundary is immediately below the dunkirk huron black shale that represents the iie t r cycle transgression in the southern appalachian basin the southern edge of the cincinnati arch and the southeastern illinois basin the f f boundary is at or near the base of the gassaway member of the chattanooga shale or the morgan trail member of the new albany shale or was eroded during the iie t r cycle beginning in the middle triangularis zone in the western illinois basin grassy creek shale michigan basin lachine member of antrim shale and southern continental margin woodford shale the f f boundary is within black shale strata indicative of an earlier development of the iie t r transgression inboard of the appalachian basin or the juxtaposition of the iie t r transgression over the upper kellwasser black shale interval without significant or recognizable lithologic change

palynofacies around the frasnian famennian boundary in the holy cross mountains southern poland abstract palynofacies have been analysed in two representative frasnian famennian f f localities kowala quarry and agow plucki trench in the holy cross mountains poland with the aim of reconstructing sedimentary conditions and palynofloral history over the extinction boundary interval leiospheres are the most common palynomorphs taxonomically impoverished acritarch assemblages and a low proportion of land derived material indicate offshore sedimentation in a mid shelf environment with some evidence of an earliest famennian regression increased productivity of phytoplankton near the f f boundary was possibly related to eutrophication of the epeiric seas thus causing anoxic conditions close to and on the seafloor no significant changes in palynofacies have been observed through the f f boundary deposits in these laurussian shelf basins in agreement with data from other parts of the devonian world

soil creep and convex upward velocity profiles theoretical and experimental investigation of disturbance driven sediment transport on hillslopes the movement of unconsolidated materials near the earth s surface is often driven by disturbances that occur at a range of spatial and temporal scales the nature of these disturbances ranges from highly variable such as tree turnover to periodic and predictable such as frost heave or creep to explore the effect of probabilistic disturbances on surface processes we formulated a granular creep model with analogy to rate process theory rpt used for chemical reactions according to the theory individual particles must be energized to a height greater than adjacent particles in order for grain dilation and transport to occur the height of neighbouring particles which is akin to activation energy in chemical reactions varies with slope angle such that energy barriers get smaller in the downslope direction as slopes steepen when slopes approach the friction limited angle of repose the height of energy barriers approaches zero and grains ow in the absence of disturbance an exponential function is used to describe the probability distribution of particle excitation height although alternative distributions are possible we tested model predictions of granular dynamics in an experimental sandpile in the sandpile acoustic energy serves as the disturbance agent such that grains dilate and shear in response particle velocities are controlled by the frequency of energy pulses that result in grain displacement using tracer particles we observed a convex upward velocity pro le near the surface of the sandpile consistent with predictions of our rpt based velocity model in addition we depth integrated the velocity model to predict how ux rates vary with inclination of the sandpile and observed non linear ux gradient curves consistent with model predictions by varying the acoustic energy level in the experimental sandpile we documented changes in the rate of grain movement similar changes in modelled velocities were achieved by varying the exponent of the particle excitation probability distribution the general agreement between observed and modelled granular behaviour in our simple laboratory sandpile supports the utility of rpt based methods for modelling transport processes e g soil creep frost heave and till deformation thus enabling us to account for the probabilistic nature of disturbances that liberate sediment in natural landscapes copyright 2004 john wiley sons ltd

high productivity in the earliest triassic ocean black shales southwest japan abstract bedded cherts containing the permian triassic p t boundary exposed in the tanba and chichibu belts southwest japan contain interbedded organic rich black shales the organic carbon concentration of black shales before thermal maturation was evaluated to be about 3 average considering their maturity levels kerogens do not contain any debris of higher plant origins but are mostly composed of structureless amorphous kerogen black shales comprise organic matter derived mainly from plankton with additional organic matter derived from bacterial activity showing that the high primary production took place intermittently in the earliest triassic a stratified ocean with a well developed oxygen minimum layer rich in nutrients was intermittently disturbed due to tectonically and or climatically induced active ocean current systems in the earliest triassic resulting in upwelling causing remarkably high primary production to form organic rich black shales

geophysical records of dispersed weathering products on the frasnian carbonate platform and early famennian ramps in moravia czech republic proxies for eustasy and palaeoclimate abstract an exceptionally high sea level in frasnian times early late devonian changed many peneplained cratonised and tectonically undisturbed continental margins of tropical belts into carbonate platforms which became covered by thick banks of limestone the stages marked by very pure carbonates developed during partial sea level highstands since when the flooding reached its maximum the shoreline was distant and conditions for reef growth were good an increased extension of emerged flat coastal areas was coupled with an opposite situation when oscillating sea level fell to its momentary minimum and the accommodation space available for accumulation of carbonate material was low subaerially exposed surfaces were subject to weathering and the products were dispersed by aeolian or aquatic means to form layers when these weathering materials were trapped in carbonates this overall scenario relating to the trapping of weathering products in pure carbonates was tested at geographically isolated platform with a stable and only slowly subsiding basement eastern moravia czech republic the amounts of weathering products dispersed in limestone were documented using the combined methods of ray logging ray spectrometry and magnetic susceptibility measuring i e according to their radioactivity k th and u and magnetism fe six third order frasnian eustatic cycles have been inferred from the data with an estimated period of 1 ma the late frasnian and especially the frasnian famennian f f transition brought the total destruction or at least a strong overlay on this hypothetical background setting the record of strong sea level fluctuations in the f f interval is shown in strong oscillations and offsets related to pronounced hiatuses and flooding surfaces such rapid sea level fluctuation is typical for glacioeustatic control although the present estimates of the maximum amplitudes are larger than realisable by glaciation events and may be explained in combination with tectonoeustatic models comparison of sections between the centre and periphery of the platform substantiates the concept that oscillating late frasnian shorelines were rapidly prograding very low sea level stages of early famennian times changed the depositionary systems from extensive platforms to narrow carbonate ramps which were positioned out and down on the extinct reef bank slopes the central parts of the eastern moravian and also other frasnian platforms in the world were not normally covered by f f sediments the transgressive onlaps above any crystalline highs were not observed and therefore the drowned frasnian reefs on their periphery although emphasised by many geologists may reflect sliding or tectonic subsidence on the margins of platform blocks rather than eustatic rise of sea level

bypass margins basin restricted wedges and platform to basin correlation upper devonian canadian rocky mountains implications for sequence stratigraphy of carbonate platform systems abstract carbonate platforms can commonly keep up with relative sea level rise because of high rates of sediment accumulation and platform aggradation surrounding basinal environments are commonly starved but can receive variable extrabasinal siliciclastic input and episodically deposited carbonate sediment if accumulation rates in basinal settings lag behind those of the platform a bypass or erosional margin can develop under these circumstances platform and basin depositional sequences become physically detached and direct correlation of basinal and platform sequences is hindered we report here the results of high resolution stratigraphic analyses of two upper devonian isolated carbonate platforms in western alberta that provide insight into the sequence stratigraphy of bypass margins and criteria for accurate correlation of platform and basinal sequences the slope and basin sequences surrounding the miette and ancient wall platforms consist of basin restricted onlapping wedges of fine grained background sediment deposited dominantly from suspension and coarse grained platform derived sediment redeposited by a variety of gravity flow mechanisms sequence boundaries are identified within the redeposited carbonate intervals identification of sequence boundaries and differentiation of highstand and lowstand slope and basinal facies was based on the geometry mineralogy and clast content of redeposited carbonate units highstand carbonates contain sheet like debris flows and turbidites with abundant slope derived clasts and background facies with high total carbonate content lowstand carbonates contain sheet like and channelized debris flows and turbidites with abundant platform derived clasts and background facies with low carbonate content and locally high amounts of organic carbon transgressive facies are dominated by initially carbonate poor and organic rich background sediments that display a progressive increase in carbonate content and decrease in organic carbon content these patterns are interpreted to record abundant background carbonate sedimentation during late transgression and highstand when the carbonate factory was robust highstand redeposited carbonates record slope erosion due to oversteepening and slope readjustment processes lowstand redeposited carbonates indicate platform and platform margin erosion and low background carbonate sedimentation when the platform was either exposed or under very shallow peritidal conditions high siliciclastic and organic contents during lowstand and early transgression may partly be the result of reciprocal sedimentation but alternatively may represent continuous siliciclastic supply during times with little dilution by fine grained carbonate sediment successive stages of platform development at miette and ancient wall were controlled by accommodation changes driven by relative sea level fluctuations backstripping analyses of strata from both platforms confirm that significant differential subsidence was a major control on variations in platform thickness and patterns of slope development greater subsidence at ancient wall fostered the development of a steeper bypass margin and different slope evolution compared to miette slope oversteepening also initiated a process of slope readjustment that eventually reduced the platform to basin gradient and facilitated regressive platform progradation in conventional siliciclastic sequence stratigraphy basin restricted wedges are interpreted as lowstand deposits on the basis of their geometry and position relative to an updip margin wedge shaped basinal units along the miette and ancient wall bypass margins contain both highstand and lowstand facies that straddle sequence boundaries the results of this study provide objective criteria for differentiating systems tracts in carbonate slope and basin environments through mineralogic and compositional analyses providing more accurate correlation of detached platform and basin sequences interpretation of carbonate basin restricted wedges as purely highstand or lowstand deposits may lead to erroneous conclusions regarding sequence stratigraphy platform to basin correlation and the volumetric partitioning of sediments deposited in different systems tracts

facies patterns and depositional environments of palaeozoic cephalopod limestones abstract in the eastern anti atlas morocco a platform and basin topography was established during the late devonian probably as a result of early variscan tensional tectonics cephalopod limestones were deposited on shallow pelagic platforms platform slopes and shallow slowly subsiding basins on the platform a transition from land areas into nearshore quartzose brachiopod coquinas crinoidal limestones condensed cephalopod limestones and finally into nodular limestones is observed the latter often become disintegrated into incipient debris flows which pass into nodular limestone marl alternations of a shallow basin deeper basins with shale sedimentation lack cephalopod limestones similar facies types also occur in the late devonian of the montagne noire france rheinisches schiefergebirge west germany moravian karst czechoslovakia holy cross mountains poland and in the early carboniferous of the cantabrian mountains spain due to strong late variscan compressional tectonics and limited outcrops detailed facies patterns could not be mapped in these regions but the same facies types as in the eastern anti atlas suggest similar coast platform slope and shallow basin topographies during cephalopod limestone deposition water depth on the platforms was in the order of several tens to about one hundred metres as is inferred from repeated subaerial exposures and distinctive depositional and faunal floral features water depth in the adjacent shallow basins might have reached several hundreds of metres cephalopod limestones represent a typical stage in the evolution of geosynclines characterized by extremely low sedimentation rates 1 5 m m y 1 this stage is preceded by deposition of thick neritic clastics and or carbonates and is succeeded by deposition of deep water clastics or flysch

biomarkers as environmental indicators in a carbonate complex example from the middle to upper devonian holy cross mountains poland abstract autochthonous biomarker distributions were studied in an array of different subfacies of a devonian carbonate complex represented in platform reef and off platform shelf basinal systems it revealed that biomarkers are sensitive indicators of depositional environments and may serve to refine palaeoenvironmental interpretations of carbonate complexes based on classical sedimentological facies analyses the contrasting biomarker composition of the carbonate platform and reef complex versus shelf basin deposits is here interpreted as the effect of both more diverse biotic sources of a primary organic matter in the former environments highly scattered results of sterane distribution and contrasting styles of decay and bacterial reworking of the primary biomass peritidal dolostones deposited under anoxic to suboxic conditions and with scarce sedimentological evidence of elevated salinity reveal the highest potential of organic matter preservation among other platform reefal facies their biomarker composition includes several compounds indicating hypersaline conditions and anoxia whereas others in particular gammacerane indicate that the water column was stratified during sedimentation this observation constrains environmental interpretation of these deposits pointing to shallow subtidal lagoons with elevated salinity and low oxygen near bottom waters most probably originating from a salinity controlled stratification of the water column biomarkers diagnostic of green sulphur bacteria were found in both peritidal lagoonal dolostones and shelf basinal facies this indicates the existence of photic zone anoxia in the latter environment thus suggesting a shallow position of the redoxcline the frasnian famennian mass extinction event s apparently had no impact on the biomarker distribution in the shelf basinal system continuous across the stage boundary

biological depositional microspherule and geochemical records of the frasnian famennian boundary beds south china abstract the investigation of shallow subtidal inter reef depression and inter reef platform sections from central hunan of china shows that a transgression regression cycle occurred in the late frasnian linguiformis zone the lowest triangularis zone to middle triangularis zone deposits are either very thin or variously missing in some shallow water sections of hunan the uppermost frasnian upper linguiformis zone black shale interval including black shale and carbonates was not ubiquitously developed and probably formed in a regressive shallower water and anoxic to dysoxic conditions suggested from higher ce la ratios penecontemporaneous dolomitization of carbonates and low faunal diversity two steps of the frasnian famennian f f mass extinction are postulated the first is the extinction of the benthos near the end of the frasnian which was probably caused by the sudden onset of anoxic environments shallow water rugose corals and ostracods experienced sudden biomass loss right at the deposition of the black shale the second is the extinction of pelagic fauna at the end of the frasnian microspherules of probable impact origin are found in several layers in the xikuangshan f f boundary section including two major peaks respectively at the upper rhenana zone and upper linguiformis zone and two minor peaks respectively near the top of the linguiformis zone and lower triangularis zone the microtektites are white or brownish in color characterized by high contents of si al and intermediate cao mno and feo and minor k2o and na2o occurrences of these microtektites do not seem to be directly related to the f f mass extinction from the lower rhenana zone through the upper crepida zone there are four elemental anomalous layers these elemental anomalies are interpreted to have resulted from the contemporaneous active rifting process and hydrothermal activities in south china

dynamics of cyclic carbonate deposition and biotic recovery on platforms during the famennian of late devonian in guangxi south china constraints from high resolution cycle and sequence stratigraphy to better understand the dynamics of platform carbonate deposition evolution and biotic recovery during the famennian high resolution cycle and sequence stratigraphic analyses were carried out upon three platform sections one in ramp and two in rimmed platforms along with a biostratigraphically well constrained basinal section in guangxi south china four main facies and fourteen lithofacies are identified in the three isolated platforms these are vertically arranged into decimetre to metre scale shallowing upward peritidal and subtidal cycles or parasequces in which the peritidal cycles predominate over the lower middle famennian six third order sequences s1 to s6 are identified based on the cycle stacking patterns as illustrated by fischer plots and vertical facies changes these sequences are temporally calibrated through correlation with basinal sequences constrained with conodont zonation and match well the six main famennian transgressive regressive cycles t1 to t6 in euramerica and elsewhere indicating a eustatic control however an opposite longer term trend in accommodation change s3 to s4 between platform interior and deeper open shelf to basin settings during the middle famennian suggests a differential subsidence across the platform basin section likely driven by block tilting thus both eustatic fluctuations and local tectonism had played an important role in platform development and evolution after the frasnian famennian biotic crisis main marine benthos preferentially recovered in the normal marine niches on the nearshore open shelves and radiated gradually into offshore restricted platforms brachiopods notably rhychonellides were the taxa recovering the earliest s1 in the normal or near normal marine conditions then echinoderms s3 stromatoporoids upper s3 and corals s5 stepped in episodically however these benthos generally appeared later in the restricted platform interiors only as if the ecological conditions were improved well enough for their colonization therefore the biotic recovery processes were diachronous both taxonomically and ecologically specified

tracing paleoredox conditions across the devonian carboniferous boundary event a case study from carbonate dominated settings of belgium the czech republic and northern france the devonian carboniferous boundary was coeval with the hangenberg crisis which is regarded as a first order mass extinction event related with large sea level changes and widespread anoxia this study aims to trace the geochemical paleoproductivity and paleoredox proxies across the devonian carboniferous carbonate dominated successions of the namur dinant basin belgium northern france and the moravo silesian basin czech republic located in the variscan rhenohercynian zone the research was focused on the distribution of oxides sio2 al2o3 fe2o3 cao na2o k2o tio2 mno and trace elements th u v zr mo zn pb ni cu measured by icp oes and icp ms respectively the enrichment factors of mo and u and their ratios were used as the main paleoredox proxies whereas the enrichment factors of zn cu pb and ni were employed to trace the paleoproductivity changes high values of zr al2o3 0 001 tio2 al2o3 0 06 and fe ti 20 and low values of al al fe mn 035 coinciding with an increase of paleoredox proxies suggest a possible volcanic and hydrothermal source of nutrients related to late devonian and early carboniferous extensional magmatism in the rhenohercynian domain although a relationship between higher paleoproductivity and enhanced continental runoff of volcanic material cannot be excluded the studied devonian carboniferous boundary sections from the namur dinant basin gendron celles ardennes quarry reveal three levels with similar vectors of mo and u enrichments the pre crisis famennian pattern is typical for weakly restricted basins with fe mn redox cycling accompanying vertical fluctuations of the oxic anoxic chemocline close to the sediment water interface with the influence of particulate shuttle the mo ef and u ef patterns corresponding to the unrestricted or weakly restricted basin with alternating suboxic to anoxic conditions are considered to represent the transgressive hangenberg black shale event the lower tournaisian mo ef and u ef patterns fall along a vector in the direction of the strongly restricted marine conditions with prevailing suboxic conditions in the moravo silesian basin lesni lom section the pre crisis famennian mo ef and u ef vector indicates an unrestricted marine trend which converges with that of restricted systems redox conditions range from suboxic to euxinic in the tournaisian mo ef and u ef oscillate between oxic and anoxic conditions and fall along a vector of strongly restricted marine conditions increased isolation of both studied basins in the early tournaisian is regarded as a reflection of a significant eustatic fall during the hangenberg crisis linked to a severe episode of the gondwana glaciation these paleohydrographic patterns have correlative potential that should be considered for a revised devonian carboniferous boundary definition

carbon isotopic evidence for the associations of decreasing atmospheric co2level with the frasnian famennian mass extinction 1 a perturbation of the global carbon cycle has often been used for interpreting the frasnian famennian f f mass extinction however the changes of atmospheric co2 level pco2 during this interval are much debatable to illustrate the carbon cycle during f f transition paired inorganic 13ccarb and organic 13corg carbon isotope analyses were carried out on two late devonian carbonate sequences dongcun and yangdi from south china the larger amplitude shift of 13corg compared to 13ccarb and its resultant 13c 13c 13ccarb 13corg decrease indicate decreased atmospheric co2level around the f f boundary the onset ofpco2 level decrease predates that of marine regressions which coincide with the beginning of conodont extinctions suggesting that temperature decrease induced by decreased greenhouse effect of atmospheric co2might have contributed to the f f mass extinction

neomorphism and cementation in ancient deep water limestones cow head group cambro ordovician western newfoundland canada abstract lithification of thinly bedded lime mudstones and grainstones in the cow head group resulted mainly from precipitation of calcite cement and neomorphic spar at shallow burial depths below the sea floor these crystals are predominantly non ferroan although the iron content and the size of neomorphic spar commonly increase near the margins of nodular and continuous beds of lime mudstone displacive fringes of ferroan fibrous calcite represent the last stage of carbonate precipitation in some limestones most calcite 13c values range between 0 and 3 pdb but 13c values as negative as 15 indicate that bacterial degradation of orgnaic matter variably influenced pore water composition serial analyses from the centres to the margins of nodular and continuously bedded lime mudstones suggest that many of the limestones in this sequence were lithified prior to the precipitation of calcite having the prominent negative 13c values typical of concretionary carbonate calcite 18o values range from 5 to 8 pdb indicating precipitation from 18o depleted pore waters of uncertian origin cathodoluminescence shows that aggrading neomorphism in the lime mudstones did not take place by porphyroid or coalescive consumption of a more finely crystalline mosaic to yield a more coarsely crystalline mosaic instead scattered crystals enlarged by precipitation of progressively younger and eventually ferroan calcite especially at the margins of nodular and continuous limestone beds the cathodoluminescence zoning in calcite crystals is similar to that observed in meteorically altered limestones where pore waters were initially oxidizing but became progressively more reducing with time the preservation of trace element zoning crystal growth microfabrics and 13c values in authigenic calcite suggest collectively that recrystallization did not occur during subsequent burial

the magneto susceptibility event and cyclostratigraphy msec method used in geological correlation of devonian rocks from anti atlas morocco magneto susceptibility event and cyclostratigraphy msec is used here as a means of establishing sensitive chronostratigraphic markers and chronohorizons useful for high resolution correlation msec is a composite of the magnetic susceptibility ms record of marine strata and the coeval biostratigraphic record and similar to chronozones zones based on msec data have boundaries that are isochronous ms a measure of the concentration of magnetic grains in sediments proxies for the ratio of lithogenic to biogenic components controls on the detrital input of lithogenic material include eustasy and climate however induced and sea floor basin subsidence the development of an initial msec composite reference curve for the middle upper devonian of the anti atlas region of southern morocco is presented and discussed in the context of global sea level transgressive and regressive cycles msec trends composed of increasing ms magnitudes correlate well with episodes of regression whereas trends of decreasing ms magnitudes correlate with episodes of transgression